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Scalable Surface Area Characterization by Electrokinetic Analysis of Complex Anion Adsorption
Abstract
By means of the in situ electrokinetic assessment of aqueous particles in conjunction with the addition of anionic adsorbates, we develop and examine a new approach to the scalable characterization of the specific accessible surface area of particles in water. For alumina powders of differing morphology in mildly acidic aqueous suspensions, the effective surface charge was modified by carboxylate anion adsorption through the incremental addition of oxalic and citric acids. The observed zeta potential variation as a function of the proportional reagent additive was found to exhibit inverse hyperbolic sine-type behavior predicted to arise from monolayer adsorption following the Grahame-Langmuir model. Through parameter optimization by inverse problem solving, the zeta potential shift with relative adsorbate addition revealed a nearly linear correlation of a defined surface-area-dependent parameter with the conventionally measured surface area values of the powders, demonstrating that the proposed analytical framework is applicable for the in situ surface area characterization of aqueous particulate matter. The investigated methods have advantages over some conventional surface analysis techniques owing to their direct applicability in aqueous environments at ambient temperature and the ability to modify analysis scales by variation of the adsorption cross section.
... Nitrogen is preferred in this study in order to prevent excess burn-off and also to reduce the formation of CO 2 . Activation is typically carried out at higher temperatures typically around 900 ℃ [28]. ...
... The aim of the BET test in this study is to explain the physical adsorption of gas molecules on the AC. Nitrogen is one of the most commonly used adsorbates in BET analysis for surface probing [28] and it is employed in this study. The general BET equation is as follows: ...
... where p and p o are the equilibrium pressure and saturation pressure of adsorbate at the adsorption temperature in bar, v is the quantity of adsorbed gas in m 3 , v m is the quantity of the adsorbed gas monolayer in m 3 , and c is the BET constant. Eq. (3.10) is an adsorption isotherm that can be plotted in the form of a straight line [28]. The value of the slope and the intercept of the line can be used to calculate the v m and c. ...
Gasification is one of the most efficient thermo-chemical conversion processes for transforming waste tyres into syngas and high-valued solid carbon products such as activated carbon (AC). This study evaluated the co-production of syngas and AC in three reactor configurations: fluidized bed, fixed bed, and rotary kiln at the systems level. A single-stage steam gasification and char activation process was simulated using Aspen Plus V10 software. The effects of gasification parameters such as equivalence ratio (ER) and steam-to-fuel ratio (SFR) were investigated and compared. The best conditions for the co-production of syngas and AC in the reactors were evaluated and compared. Brunauer-Emmett-Teller (BET) computational analysis was used to predict the surface area of the AC. The fluidized bed gasifier has the potential to produce syngas with a low heating value (LHV) of 6.67 MJ/Nm³, cold gas efficiency (CGE) of 82.4%LHV, AC with BET surface area of 698.63 m²/g and a carbon conversion ratio (CCR) of 92.5%, the fixed bed gasifier has a syngas LHV of 6.25 MJ/Nm³, CGE of 85.9%LHV, AC with BET surface area of 432.51 m²/g and CCR of 97.3% and the rotary kiln gasifier has a syngas LHV of 5.96 MJ/Nm³, CGE of 74%LHV, AC with BET surface area of 661.73 m²/g and CCR of 93%.
... BET analysis is used when mass transfer is surface driven, hence the need to evaluate the gas accessible surface area [19]. BET surface area (SBET) can be used to determine micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials [12]. ...
... Also it is unreliable when applied to ultra microporous molecules, which contains pores of molecular dimensions (e.g., molecular sieve carbon or zeolite) [49]. BET analysis is now being replaced by an anion adsorbate approach which can be applied directly to aqueous medium at ambient temperature and ease of modification of analysis scale by variation of adsorption cross-section [19]. ...
Rice husk-based biomaterial (RHBB) is a waste from the rice milling industry which can be effectively used as a low-cost material in treating textile wastewater. Textile industries are known for their significant water demand, as much as 200 L used per kg of dyestuff. This leads to the generation of a large amount of water which is contaminated majorly by dyestuff as well as heavy metals, complex salts, acids, etc. As expected, this will create pollution-related problems for the receiving water bodies. Several works reviewed showed that this challenge is been addressed through different techniques such as; ozonation, adsorption, coagulation, chemical oxidation, catalysis, membrane separation, advanced oxidation, etc. with inherent difficulty, ineffectiveness, and eco-unfriendliness observed in some of them. RHBB can be modified for better performance in the treatment of textile wastew-ater. Among the three approaches, chemical modification was recommended for 231 232 C. E. Onu et al. better result in the treatment of textile wastewater. RHBB can be used in conjunction with other processes to achieve concerted degradation of the target pollutants. The thermodynamics, kinetics, isotherms, optimization studies, and artificial intelligence approach were dwelled upon in this review. Therefore, RHBB is proposed as a granular, chemically stable, efficient, and cost-effective material for the treatment of textile wastewater.
... BET analysis is used when mass transfer is surface driven, hence the need to evaluate the gas accessible surface area [19]. BET surface area (SBET) can be used to determine micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials [12]. ...
... Also it is unreliable when applied to ultra microporous molecules, which contains pores of molecular dimensions (e.g., molecular sieve carbon or zeolite) [49]. BET analysis is now being replaced by an anion adsorbate approach which can be applied directly to aqueous medium at ambient temperature and ease of modification of analysis scale by variation of adsorption cross-section [19]. ...
Rice husk-based biomaterial (RHBB) is a waste from the rice milling industry which can be effectively used as a low-cost material in treating textile wastewater. Textile industries are known for their significant water demand, as much as 200 L used per kg of dyestuff. This leads to the generation of a large amount of water which is contaminated majorly by dyestuff as well as heavy metals, complex salts, acids, etc. As expected, this will create pollution-related problems for the receiving water bodies. Several works reviewed showed that this challenge is been addressed through different techniques such as; ozonation, adsorption, coagulation, chemical oxidation, catalysis, membrane separation, advanced oxidation, etc. with inherent difficulty, ineffectiveness, and eco-unfriendliness observed in some of them. RHBB can be modified for better performance in the treatment of textile wastewater. Among the three approaches, chemical modification was recommended for better result in the treatment of textile wastewater. RHBB can be used in conjunction with other processes to achieve concerted degradation of the target pollutants. The thermodynamics, kinetics, isotherms, optimization studies, and artificial intelligence approach were dwelled upon in this review. Therefore, RHBB is proposed as a granular, chemically stable, efficient, and cost-effective material for the treatment of textile wastewater.KeywordsRice husk-based biomaterialTextile effluentTreatmentDyesWastewaterPollutionModificationArtificial intelligenceRegenerationOptimization
... Debye screening length (λ D ) 35 is an existing challenge for field-effect sensor applications, as shown in eq 3: ...
... SPR experiments were conducted using a P4SPR (Affinity Instruments, Canada). The morphology results were obtained using a NanoWizard 4 (Bruker, Germany) in QI mode using an SLN-10 probe with a 2 nm tip radius and a spring constant of 0. 35 ...
With the rapid spread and multigeneration variation of coronavirus, rapid drug development has become imperative. A major obstacle to addressing this issue is adequately constructing the cell membrane at the molecular level, which enables in vitro observation of the cell response to virus and drug molecules quantitatively, shortening the drug experiment cycle. Herein, we propose a rapid and label-free supported lipid bilayer-based lab-on-a-chip biosensor for the screening of effective inhibition drugs. An extended gate electrode was prepared and functionalized by an angiotensin-converting enzyme II (ACE2) receptor-incorporated supported lipid bilayer (SLB). Such an integrated system can convert the interactions of targets and membrane receptors into real-time charge signals. The platform can simulate the cell membrane microenvironment in vitro and accurately capture the interaction signal between the target and the cell membrane with minimized interference, thus observing the drug action pathway quantitatively and realizing drug screening effectively. Due to these label-free, low-cost, convenient, and integrated advantages, it is a suitable candidate method for the rapid drug screening for the early treatment and prevention of worldwide spread of coronavirus.
... The aim of BET test in this study is to explain the physical adsorption of gas molecules on the activated carbon. Nitrogen is one of the most commonly used adsorbates in BET analysis for surface probing [185] and is employed in this study. The general BET equation is as follows: where A and I are the slope and intercept. ...
... and po are the are the equilibrium pressure and saturation pressure of adsorbate at the adsorption temperature, v is the quantity of adsorbed gas and vm is the quantity of the adsorbed gas monolayer and c is the BET constant. Equation 3.42 is an adsorption isotherm which can be plotted in the form of a straight-line equation[185]. The value of the slope and the intercept of the line can be used to calculate the vm and c. ...
The high level of waste tyres in stockpiles has contributed tremendously to environmental pollution and global warming on daily basis. These tyres have also been known to serve as breeding sites for mosquitoes and other disease-causing microbes. Gasification has been identified as one of the alternative pathways that can be used to recover energy from waste tyres. In addition to the gaseous products (syngas), high-value solid products like carbon black, activated carbon and carbon nanotubes can also be obtained from the gasification of waste tyres.
This study has evaluated the simultaneous production of syngas and solid carbon (activated carbon) in three different reactor configurations namely; fluidized bed, fixed bed, and rotary kiln. A single stage gasification and activation process was employed in the production process by using Aspen Plus® software. This study also evaluated the effects of gasification parameters like the equivalence ratio (ER), the steam-to-fuel ratio (SFR) and the gasifier temperature (GT) on the gasification products from the three reactor configurations. The ER was varied from 0.18 to 0.38, the SFR from 0.1 to 0.25 and the GT from 700 ℃ to 1000 ℃. BET analysis was used in the determination of the surface area of the activated carbon formed at the end of the char activation stage.
The optimum conditions for the co-production process in the fluidized bed gasifier occurred at ER of 0.3, SFR of 0.2 and GT of 800 ℃. At this condition, the fluidized bed gasifier has a syngas (CO + H2) composition of 50.2%, the gas yield of 4.81 Nm3/kg, gas LHV of 6.29 MJ/kg, cold gas efficiency of 84.8%, 89.2 kg (2.02% AC to carbon in feedstock ratio) with BET surface area of 2236 m2/g and carbon conversion ratio of 97.8%.
The optimum conditions for the co-production process in the fixed bed gasifier occurred at ER of 0.3, SFR of 0.25 and GT of 800 oC. At this condition, the fixed bed gasifier has a syngas (CO + H2) composition of 51.76%, gas yield of 4.92 Nm3/kg, gas LHV of 6.25 MJ/kg, cold gas efficiency of 85.9%, 0.53 kg (3.22% AC to carbon in feedstock ratio) with BET surface area of 822.25 m2/g and carbon conversion ratio of 96.8%.
The optimum conditions for the co-production process in the rotary kiln reactor occurred at ER of 0.3, SFR of 0.25 and GT of 800 ℃. At this condition, the rotary kiln gasifier has a syngas (CO + H2) composition of 48.8%, the gas yield of 4.91 Nm3/kg, gas LHV of 6.05 MJ/kg, cold gas efficiency of 83.1%, 0.91 kg (5.56% AC to carbon in feedstock ratio) with BET surface area of 664.94 m2/g and carbon conversion ratio of 94.4%.
A comparative analysis was also done for the three reactor configurations, from the results obtained, the fluidized bed reactor performed best for the waste tyre gasification production process of both syngas and value-added solid activated carbon product followed by the fixed bed. The rotary kiln reactor did not perform well as the others in the co-production process.
... The most commonly known types of NPs are the spherical ones, for example those based on metal oxides (silica, titania, etc) [7], the nanotubes, with the mostly used ones being the carbon nanotubes (CNT) [8] and the nanoplatelets (e.g., graphene, nano-clays) [9,10]. The PNCs' improved properties have been explained in terms of the quite large surface to volume ratio of the nano-as compared to macro-inclusions [11], whereas, from the dimensionality point view, there have been rationalized via the terms of 'aspect ratio (AR)' [12] and the 'specific surface area' [13,14]. As expected, the improved PNC's performance depends on the quality of filler dispersion in the matrix and, secondly, on the degree of polymer-filler interaction [15][16][17]. ...
A series of polymer nanocomposites (PNCs) based on the renewable poly(butylene-succinate) (PBSu) reinforced with 1 wt% of different nanoparticles (NP), namely, silica (SiO2), montmorillonite (MMT), graphene oxide (GO) and carbon nanotubes (CNT), were synthesized and studied herein. The investigation focuses on both the direct and indirect NP effects on the interfacial interactions, thermal transitions, crystallinity, electrical and thermal conductivity, mechanical properties and molecular dynamics. For that, a sum of complementary techniques was employed, regarding both the structure and performance. The clearly direct effect is related to the promotion of crystal nucleation at the presence of both particles, related to the fillers’ dimensionality (aspect ratio) and the non-worth noting interfacial interactions. The degree of crystallinity of PBSu mildly increases, whereas the semicrystalline morphology (sizes, numbers, distributions of the crystals) is systematically denser in the PNCs. In agreement with previous findings on PBSu, the polymer cannot be preserved amorphous, at least by conventional methods. Consequently, the macroscopic properties, namely, the thermal diffusivity/conductivity as well as the mechanical performance were found connected to crystallinity, in particular, to the semicrystalline morphology (indirect filler effect). PBSu/CNT was surprisingly found electrically conductive, despite the low CNT loading, whereas the rest of the samples are insulating. The molecular dynamics map was constructed here for the first time, obviously only for the semicrystalline state. The cooperativity of PBSu chains drops in the PNCs, most probably, affected by the dense semicrystalline structures that seem to impose an increase in the free volume of the amorphous polymer fraction. Overall, the PBSu PNCs were found to offer potentials for wide range manipulation of properties, via relatively mild processing (synthesis, thermal treatments).
... Металлические наночастицы Ag, Au, Zn, Cu широко применяются для эффективного удаления биологических загрязнений, таких как бактерии и грибки. Особенно наноразмерные наночастицы Cu проявляют высокое качество при химической и биологической переработке отходов, благодаря своей высокой реакционной способности [5]. Полиуретаны, включающие наночастицы Cu и Ag, обладают бактерицидными свойствами, которые проявляются в отношении грамположительных и грамотрицательных бактерий, а также дрожжеподобных грибов [6][7][8][9][10]. ...
... It can be defined the Langmuir adsorption through a physico-chemical interaction on the area of the homogeneous solid state that adsorb compounds without any interactions with each other making a monolayer of molecules on the surface of the solid state. The Langmuir adsorption equation is as the following [28]: ...
Progress of largely selective and sensitive compounds is essential for removing two toxic gases of hydrogen sulfide (H2S) and sulfur dioxide (SO2).The effect of Iron (Fe), Nickel (Ni), and Zinc (Zn) doping of graphene (Gr) nanosheet (NS) on their adsorption for both H2S and SO2 gases has been investigated in this work using first-principles density-functional theory (DFT) computations. In this research, it has been investigated the ability of transition metals of iron, nickel, and zinc doping of Gr@NS for adsorption toxic gas of Sulfur Dioxide and Hydrogen Sulfide Removal. The Langmuir adsorption model with a three-layered ONIOM used CAM-B3LYP functional accompanying LANL2DZ and 6–31 + G (d,p) basis sets due to Gaussian 16 revision C.01 program on the complexes of H2S and SO2 → TM(Fe, Ni, Zn) doping of Gr nanosheet. The changes of charge density have shown the values of ∆QFe-doped = − 0.566 >> ∆QZn-doped = + 0.387 >>> ∆QNi-doped = + 0.605 for H2S adsorption and ∆QFe-doped = − 0.336 >> ∆QZn-doped = + 0.376 >>> ∆QNi-doped = + 0.618 for SO2 adsorption. Based on these amount of changes of charge density, H2S and SO2 have exhibited a significant charge transfer for Fe doping of graphene nanosheet compared to Ni- and Zn-doped Gr@NS. Based on NMR spectroscopy, it has been illustrated that the sharp peaks in the adsorption site are due to the Fe, Ni, and Zn doping on the surface of graphene nanosheet through H2S and SO2 adsorption. However, it has represented some fluctuations in the chemical shielding of isotropic and anisotropy behaviors around Zn-doped on the H2S/ SO2 → Zn-doped/Gr@NS. Moreover, it has exhibited the fluctuation of occupancy of NBO for H2S/SO2 → Fe-doped, H2S/SO2 → Ni-doped, and H2S/SO2 → Zn-doped graphene nanosheet through the Langmuir adsorption process by indicating the active sulfur atom in hydrogen sulfide (H2S) and sulfur dioxide (SO2) becoming close to the nanosheet. The amounts of ΔGadso\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta {G}}_{\mathrm{ads}}^{\mathrm{o}}$$\end{document} through IR computations based on polarizability have exhibited that ΔGads,SO2→Fe-Co\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta {G}}_{\mathrm{ads},\mathrm{SO}2\to \mathrm{ Fe}-\mathrm{C}}^{\mathrm{o}}$$\end{document} and ΔGads,H2S→Fe-Co\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta {G}}_{\mathrm{ads},\mathrm{H}2\mathrm{S}\to \mathrm{ Fe}-\mathrm{C}}^{\mathrm{o}}$$\end{document} have exhibited the most energy gap because of charge density transfer from sulfur atom in hydrogen sulfide (H2S) and sulfur dioxide (SO2) to Fe doping of Gr@NS, although, ΔGH2S/SO2→Zn-C0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta {G}_{\mathrm{H}2\mathrm{S}/\mathrm{SO}2 \to \mathrm{ Zn}-\mathrm{C }}^{0}$$\end{document}> ΔGH2S/SO2→Ni-C0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta {G}_{\mathrm{H}2\mathrm{S}/\mathrm{SO}2 \to \mathrm{ Ni}-\mathrm{C }}^{0}$$\end{document}> ΔGH2S/SO2→Fe-C0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta {G}_{\mathrm{H}2\mathrm{S}/\mathrm{SO}2 \to \mathrm{ Fe}-\mathrm{C }}^{0}$$\end{document}. Frontier molecular orbitals of HOMO, LUMO, and band energy gap accompanying some chemical reactivity parameters have represented the attributes of molecular electrical transport of TM (Fe, Ni, Zn) doping of Gr nanosheet for adsorption of H2S and SO2 gases. Our results have provided a favorable understanding of the interaction between TM doping of Gr@NS nanosheet and H2S and SO2 molecules. A high performance of TM doping of Gr@NS as gas sensor is demonstrated by modeling the material’s transport characteristics by means of the Langmuir adsorption and three-layered ONIOM/DFT method. Furthermore, the results of partial electron density of states (PDOS) have confirmed an obvious charge accumulation between the graphene nanosheet and doped atoms of Fe, Ni, and Zn through adsorption of H2S and SO2 molecules on the surface due to the recognition of the conduction band region. Finally, this research can build up our knowledge about the electronic structure, relative stability, and surface bonding of various metal-doped graphene nanosheets, metal alloy surfaces, and other dependent mechanisms, like heterogeneous catalysis, friction lubrication, and biological systems.
... Further, the linear correlation coefficient (R 2 ) was high, so the adsorption isotherms fit well for the Langmuir model. This model indicates that the adsorbent surface was completely flat and homogeneous and that each surface site can only hold one molecule of the adsorbate, resulting in monolayer-type adsorption [55,56]. The metal-π interaction is one of the mechanisms reported in the literature for organic compounds in modified biochars with metallic oxides [57][58][59][60]. ...
Biochar is a carbonaceous and porous material with limited adsorption capacity, which increases by modifying its surface. Many of the biochars modified with magnetic nanoparticles reported previously were obtained in two steps: first, the biomass was pyrolyzed, and then the modification was performed. In this research, a biochar with Fe3O4 particles was obtained during the pyrolysis process. Corn cob residues were used to obtain the biochar (i.e., BCM) and the magnetic one (i.e., BCMFe). The BCMFe biochar was synthesized by a chemical coprecipitation technique prior to the pyrolysis process. The biochars obtained were characterized to determine their physicochemical, surface, and structural properties. The characterization revealed a porous surface with a 1013.52 m2/g area for BCM and 903.67 m2/g for BCMFe. The pores were uniformly distributed, as observed in SEM images. BCMFe showed Fe3O4 particles on the surface with a spherical shape and a uniform distribution. According to FTIR analysis, the functional groups formed on the surface were aliphatic and carbonyl functional groups. Ash content in the biochar was 4.0% in BCM and 8.0% in BCMFe; the difference corresponded to the presence of inorganic elements. The TGA showed that BCM lost 93.8 wt% while BCMFe was more thermally stable due to the inorganic species on the biochar surface, with a weight loss of 78.6%. Both biochars were tested as adsorbent materials for methylene blue. BCM and BCMFe obtained a maximum adsorption capacity (qm) of 23.17 mg/g and 39.66 mg/g, respectively. The obtained biochars are promising materials for the efficient removal of organic pollutants.
... The values of K f and n are illustrated in Table 2, where a value of (1 < n < 10) indicated a favorable adsorption of Cd(II) onto MG@HNTs [70]. The Langmuir isotherm, on the contrary, implies that adsorption occurs as a continuous monolayer of adsorbate molecules covering homogenous sites on the adsorbent's surface [71], implying that once an adsorbate occupies a site, no additional adsorption can occur at that occupied site. The Langmuir isotherm is expressed by Eq. 5 [72]: ...
Kaolinite is a widely available and inexpensive substance that has been successfully employed to decontaminate different hazardous contaminants from wastewater by adsorption. In this study, halloysite-like nanotubes (HNTs) were prepared via intercalation followed by ultrasonic rolling of the kaolinite layers. Then, maghemite nanoparticles were co-precipitated within the HNTs matrix to produce a maghemite/HNTs nanocomposite (MG@HNTs). XRD, SEM, TEM, FTIR, and a BET analyzer were used to characterize the MG@HNTs nanocomposite, which was then utilized to eliminate Cd(II) from aqueous solutions (water and wastewater). Using a batch methodology, the impact of various adsorption parameters on Cd(II) removal was explored. MG@HNTs nanocomposite exhibited a high adsorption capacity ( q e ) of 264.47 mg g ⁻¹ for Cd (II). The kinetic data well conformed to pseudo-2nd-order, while the adsorption isotherms conformed to the Langmuir model. The desorption study demonstrated that the MG@HNTs nanocomposite could be successfully regenerated and recycled five times, without losing its original removal efficiency. Furthermore, MG@HNTs exhibited effective implementation to remove cadmium from real water samples, including tap and industrial wastewater. This study confirmed the successful application of MG@HNTs as an efficient, eco-friendly, and sustainable adsorbent at a high level of feasibility for the uptake of hazardous contaminants from industrial wastewater.
... The Langmuir adsorption equation is the following [32]: ...
Carbon dioxide (CO2) adsorption on decorated graphene (GR) sheets with transition metals (TMs) including iron, nickel and zinc was investigated for removing this hazardous gas from the environment. TM-doped GR results in higher activity toward gas detecting than pristine graphene nanosheets. TM embedding restrains hydrogen evolution on the C sites, leaving more available sites for a CO2 decrease. The Langmuir adsorption model with ONIOM using CAM-B3LYP functional and LANL2DZ and 6-31+G (d,p) basis sets due to Gaussian 16 revision C.01 program on the complexes of CO2→(Fe, Ni, Zn) embedded on the GR was accomplished. The changes of charge density illustrated a more considerable charge transfer for Zn-embedded GR. The thermodynamic results from IR spectroscopy indicated that ΔGads,CO2→Zn@C−GRo has the notable gap of Gibbs free energy adsorption with a dipole moment which defines the alterations between the Gibbs free energy of the initial compounds (ΔGCO2 o and ΔGZn@C−GRo) and product compound (ΔGCO2→Zn@C−GRo) through polarizability. Frontier molecular orbital and band energy gaps accompanying some chemical reactivity parameters represented the behavior of molecular electrical transport of the (Fe, Ni, Zn) embedding of GR for the adsorption of CO2 gas molecules. Our results have provided a favorable understanding of the interaction between TM-embedded graphene nanosheets and CO2.
... To quantify TNF-a, Fig. 3B plots the C1 variation as a function of TNF-α absorption concentrations. Since this adsorption is monolayer adsorption, the Langmuir isotherm adsorption was studied to describe the formation of TNF-α monolayer over the surface of SPE/ PANI/ABs [58]. The excellent fitting to experimental results which was served as the starting point for our following sensor array calibration and automatic data collection and analysis in the wearable device. ...
Early osteoarthritis (OA) joint inflammation detection is crucial for effective diagnosis and treatment. Thus, regular screening of OA is highly recommended, especially for the higher-risk population. However, the current OA biomarker detection methods are based on laboratory testing, which is low efficiency and high cost, and there is no point of care (POC) method available. In this work, we synthesized a biocomposite thin film in which TNF-a antibody (Abs) was covalently crafted on the PANI conjugating skeleton to form the semiconductive Ab-PANI composites, as the TNF-a acceptor and also the signal amplifier. The PANI structure was altered during the adsorption with the UV–visible spectroscopy and also caused the electrochemical impedance spectroscopy (EIS) signal change by monitoring the TNF-a adsorption behavior. A complex EIS analysis quantified the concentration of TNF-a, and the detection method was trained in a wide concentration range of TNF-a of PBS buffer solution. This screen-printed PANI-Ab sensor (SPAS) was further evaluated with the mice serum samples showing compatible accuracy and precision in comparison to conventional enzyme-linked immunosorbent assay (ELISA). Finally, the parallel accuracy validations on SPAS arrays indicate no significant difference in both precision and accuracy of measurement, which is suitable for the future interchangeable application of long-term inflammation monitoring.
... At these conditions, the adsorbate's partial pressure is related to the volume of it adsorbed to the solid adsorbent. It is equivalent to the Hill equation [28]. The Temkin adsorption isotherm is a modification of the Langmuir adsorption isotherm. ...
Inhibition effect of Costus afer on mild steel in 0.5 M HCl was studied using gravimetric method at room temperature. It was found out that Costus afer inhibited the corrosion of mild steel in the acidic environment and that the efficiency of inhibition increased as the concentration of the inhibitor in the environment increased. The data was used to test different isotherms and it suited the Langmuir isotherm. A value of -15.995 kJmol ⁻¹ was gotten for the ∆G o ads . This value showed that the extracts of Costus afer inhibited the corrosion process through physiosorption mechanism. The high value of inhibition efficiency of the extract as the concentration increased in rationalized in terms of the increase in herteroatoms, saponnins and tannins which are present in the extract.
... This observation might arise from the Sips and Toth isotherms' capability to consider the surface heterogeneity [58]. In contrast, a continuous monolayer of adsorbate species covering a homogeneous flat solid surface is the conceptual basis for the Langmuir adsorption isotherm [59,60]. The predicted values of the surface affinity (b) for CO 2 were higher than those of CH 4 and N 2 , indicating the stronger interactions between the polarizable and electron-deficient CO 2 molecules and the electron-rich π-conjugated structure of the ETM-1 material with enhanced basicity [61,62]. ...
This study aims at developing a novel freestanding conjugated triazine-based membrane (ETM-1) with permanent porosity via a low-temperature superacid-promoted polymerization reaction. In this venue, we used the bifunctional 4-ethynylbenzonitrile (4-EBN) monomer featuring ethynyl (C-CH) and nitrile (C-N) functional-ities. At the same time, trifluoromethanesulfonic acid (CF 3 SO 3 H) served as both the catalyst and solvent. The cross-linked Polymer's physicochemical properties were systematically examined using TGA, BET, solid-state 13 C CP-MAS NMR, ATR-FT-IR, and XPS spectroscopy techniques. With conjugated s-triazine (as a result of cyclo-trimerization of nitrile) and C-CH (as a result of cationic polymerization of ethynyl), the microporous ETM-1 membrane displayed a superior CO 2 uptake capacity of up to 3.87 mmol g − 1 (170.3 mg g − 1) and enhanced ideal CO 2 /N 2 and CO 2 /CH 4 permselectivity values of 47 ± 2 and 21 ± 1 at 298 K and 1 bar, respectively. The notable selectivity of ETM-1 towards CO 2 can be stated in terms of the molecular sieving (i.e., kinetic selection) characteristic of the microporous membrane, its electron-rich π-conjugated skeleton, and enhanced basicity, suitable for interacting with CO 2 via dipole-quadrupole and acid-base interactions. Moreover, ETM-1 exhibited the isosteric heat of CO 2 adsorption ranging from 28.1 to 34.3 kJ mol − 1 , implying strong physisorption of CO2 upon the high-affinity adsorption sites of the membrane.
... Also, this equation is applicable for solute concentration that adsorbed onto solid surface and solute concentration of solute in liquid phase [27]. However, Langmuir adsorption model is designed to explain adsorption depending on assume adsorbate behaves as an ideal gas at isotherm conditions and adsorption with desorption in reversible relationship [28,29]. ...
Eriochrome Black T dye is an indicator of complex titration as water hardness, as an azo dye, blue in its deprotonated form, and turns red when it forms a complex with metal ions such as Ca, Mg, Cd . .etc. Water contamination is considered one of the most important problems that threaten human life on earth. An efficient method is done to remove EBT from wastewater via using cadmium sulfide Nanoparticles (CdS NPS) that was prepared by using an inexpensive and simple method (chemical precipitation) and was diagnosed this nanomaterial using an X-ray diffractometer (XRD), Transmission electron microscope (TEM), Scanning electron microscope (SEM) and Energy Dispersive X-Ray Analyzer (EDX). TEM characterization results for CdS nanoparticles illustrated that the nanoparticles have a pointy shape-like needles morphology and with miscellaneous sizes, the statistical calculation gives (32) nm as the rate particle size.
Through this study, the CdS nanomaterial proved that it has a high ability to adsorb Eriochrome Black-T (EBT) dye under certain conditions where we noticed that the maximum adsorption capacity of this dye by CdS nanoparticles was at Temperature (293) K, (pH = 6) and at a concentration (0.01 g) of the CdS nanomaterial with contact time up to (40) minutes and CdS. Also calculated the thermodynamic functions, (ΔS, ΔH, ΔG), we found that the process was spontaneous and exothermic under the specific condition through The thermodynamic parameters
... Not all points on the surface are available for interaction with the adsorbate; the points of interaction, binding sites, must fulfil some conditions related to electron density, acidity and even morphology depending on the chemical characteristics of the adsorbate. According to this, the commonest and simplest approach to adsorption is Langmuir's model that includes a number of assumptions: (1) the adsorption-desorption process approaches equilibrium, (2) the surface of the catalyst is homogeneous, (3) the different binding adsorption sites on the surface are energetically equivalent, (4) the adsorbent-adsorbate interaction takes place through the same kind of functional groups, (5) each binding site interacts with only one adsorbate species, (6) a single layer of adsorbate is formed on the surface, and (7) there is no lateral interaction between adsorbed species once on the surface [15][16][17]. Although these assumptions imply an oversimplification of the problem, they lead to the well-known Langmuir adsorption isotherm. ...
... The values of the calculated parameters along with ERRSQ and regression coefficients at different temperatures are accessible in Table 5. It seems that the Langmuir model perfectly fits the experimental data where the R 2 values approach one, indicating that the adsorption is limited to one molecular layer where no side interaction between adjacent adsorbed molecules when a single molecule occupies a single surface site [64]. The maximum adsorption capacities, Q m , for full monolayer coverage are found at 13.9, 12.7, and 9.9 mg/g for 311, 302, and 293 K adsorption temperatures, respectively. ...
Olive oil production generates solid and liquid wastes that cause various environmental problems due to their high phenols and polyphenols load. Although many treatment methods were investigated to manage these wastes, more research is still needed to identify simple and cost-effective approaches. In this study, activated carbon (AC) was prepared from olive cake waste and functionalized with Cu/Cu2O/CuO for efficient and selective removal of phenolic content from olive mill wastewater (OMW). AC media were characterized by scanning electron/dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, and Brunauer–Emmett–Teller (BET) surface area analysis. The optimum adsorption parameters were investigated, and the adsorption isotherms, thermodynamics, and kinetics were determined. The adsorption of phenols onto copper oxide AC was best described by the Langmuir adsorption with maximum adsorption capacity of 13.9, 12.7, and 9.9 mg/g at 311, 302, and 293 K, respectively. The adsorption reaction was found to be spontaneous and endothermic where ∆H° and ∆G° were found to be 30.104 kJ/mol and −1.765, −2.839, and −3.723 (kJ/mol) at 311, 302, and 293 K, respectively. In addition, the kinetics data were perfectly fit by the pseudo-second-order model. The activated product derived from recyclable olive cake and enriched with inorganic functionality can offer a cost-effective treatment solution for OMW; thus, reducing both the liquid and solid waste generated from the olive mill industry.
... To study the adsorption behavior between the BP adsorbent and the IC adsorbate, the linear form of the Langmuir and Freundlich models are given by the following equations, respectively [23]. ...
This study investigated the preparation method and adsorption efficiency of porous adsorbents prepared from banana peels (BP) waste. The BP waste was acquired from banana fried chip factories in Sukhothai province. Chemical activation by sulfuric acid was used to activate the raw material, followed by carbonization at 500 °C. The activated BP adsorbent has been characterized by energy dispersive X-ray spectrometer (EDXRF), N2 adsorption-desorption isotherms (BET), scanning electron microscopy (SEM), and zeta potential measurements. The analysis of chemical properties showed that it mainly contained 70.39 % K matter. The specific surface area of the BP sample reached 215.05 m2/g under acid activation and thermal treatment. The SEM images showed the morphologies of the BP adsorbent before and after activation. There was a significant change in the morphology and in the dried BP and activated BP. The pHPZC value of the activated BP obtained under optimal conditions was 4.13. Adsorption of indigo carmine (IC) onto porous activated BP at different initial IC concentrations (10 - 100 mg/L) and contact times (30 - 120 min) was investigated using batch experiments (0.1 g/50 mL). At an optimum contact time of 60 min, maximum adsorption capacity was determined at 56.18 mg/g. The Freundlich isotherm model with a high correlation coefficient was used to describe multilayer adsorption. The kinetic study fit well with a pseudo second-order kinetic model that represented chemisorption. The negative deltaG° value of –14.64 kJ/mol indicated that adsorption of IC onto the BP adsorbent was spontaneous in nature at 305.15 K. HIGHLIGHTS Increase the value of the biomass resources was produced form banana peels as high surface area adsorbent The qmaxfor indigo carmine (IC) adsorption was 56.18 mg/g under optimized conditions The adsorption of the IC follows the Freundlich model and pseudo-second order kinetic model Negative deltaG° value indicated the possibility of IC adsorption process GRAPHICAL ABSTRACT
... At these conditions, the adsorbate's partial pressure is related to the volume of it adsorbed to the solid adsorbent. It is equivalent to the Hill equation [28]. The Temkin adsorption isotherm is a modification of the Langmuir adsorption isotherm. ...
Inhibition effect of Costus afer on mild steel in 0.5 M HCl was studied using gravimetric method at room temperature. It was found out that Costus afer inhibited the corrosion of mild steel in the acidic environment and that the efficiency of inhibition increased as the concentration of the inhibitor in the environment increased. The data was used to test different isotherms and it suited the Langmuir isotherm. A value of -15.995 kJmol-1 was gotten for the ∆Goads. This value showed that the extracts of Costus afer inhibited the corrosion process through physiosorption mechanism. The high value of inhibition efficiency of the extract as the concentration increased in rationalized in terms of the increase in herteroatoms, saponnins and tannins which are present in the extract.
... These studies have generally been constructed on the basis of a single distribution of asperity heights with assumed spherical features. However, naturally occurring surfaces tend to exhibit asperities at multiple scales in a fractal geometry exhibiting statistical self-similarity [49][50][51][52] and thus in recent years the fractal nature of surfaces has become a significant aspect in the field of experimental and computational surface analysis and contact mechanics [53][54][55][56]. The importance of considering surface fractality in contact mechanics can be explained by the tendency of first order roughness descriptors to be dominated by highest level features, while second order descriptors, such as mean slope or kurtosis, are dominated by the finest scales of surface features. ...
Tribological phenomena are governed by combined effects of material properties, topology and surface-chemistry. We study the interplay of multiscale surface structures with molecular-scale interactions towards interpreting static frictional interactions at fractal interfaces. By spline-assisted-discretization we analyse asperity interactions in pairs of contacting fractal surface-profiles. For elastically deforming asperities, force analysis reveals greater friction at surfaces exhibiting higher fractality, with increasing molecular-scale friction amplifying this trend. Increasing adhesive strength yields higher overall friction at surfaces of lower fractality owing to greater true-contact-area. In systems where adhesive-type interactions play an important role, such as those where cold-welded junctions form, friction is minimised at an intermediate value of surface profile fractality found to be around 1.3 to 1.5. Results have implications for systems exhibiting evolving surface structures.
With the rise of wearable device applications, efficient energy storage devices with flexible properties have become an important research direction. Among these devices, supercapacitors with high stability and instantaneous high power output for energy storage systems have attracted research attention. In this study, we demonstrate the possibility of applying nitrogen-doped chromium (Cr:CrN) thin films to flexible electrostatic double-layer capacitor (EDLC) electrodes. Chromium (Cr) electrodes undergo nitriding through sputtering, imparting interstitial defect characteristics and a nanoporous structure to the Cr layers. The resulting Cr:CrN layer not only exhibits excellent electrical conductivity but also enhances the faradaic process due to its interstitial defect properties. Experimental findings demonstrate that EDLCs employing Cr:CrN thin film electrodes exhibit exceptional performance, including fast charging, high current density tolerance, and cost-effectiveness. On glass substrates, the device achieves a maximum specific capacitance value of 6.69 mF/cm2 and an energy density of 0.33 Wh/m2 at an operating voltage of 3 V. Meanwhile, the flexible device demonstrates a specific capacitance value of 0.90 mF/cm2 and an energy density of 0.02 Wh/m2 at an operating voltage of 2 V. These results underscore the significant potential of Cr:CrN films as electrodes for EDLCs, particularly in flexible applications.
Regarding two-dimensional (2D) nanomaterials as gas sensors, we have studied the adsorption of gas molecules (NH 3 , NO 2 , NO) on the graphitic GaN sheet (PL-GaN) using density functional theory calculations. “Langmuir” adsorption of gas molecules of NH 3 , NO 2 , and NO on the graphitic GaN sheet has been accomplished using density functional theory. The changes in charge density have shown a more important charge transfer on the hexagonal honeycomb nanosheet of gallium nitride (GaN) which acts as the electron acceptor while gas molecules act as the stronger electron donors through adsorption on the graphitic-like GaN surface. The adsorption of NH 3 , NO 2 , and NO, respectively, on GaN nanosheet has more contribution with high expansion curves of hydrogen, nitrogen and oxygen. The results extracted from PDOS curves after optimization show the electron transferring from nitrogen and oxygen of gas molecules (adsorbate/donor) towards gallium in the active site of GaN surface (adsorbent/acceptor). GaN nanosheet represents enough capability for adsorbing gases of NH 3 , NO 2 , and NO through charge transfer from nitrogen and oxygen atoms to the gallium atom regarding the intra-atomic and interatomic interactions. Concerning the change of physicochemical properties of the PL-GaN sheet before and after molecule adsorption, the PL-GaN nanosheet can be applied as an appropriate selective gas sensor for NH 3 , NO 2 and NO detection.
Purpose
The purpose of this paper is to investigate the ability of transition metals (TMs) of iron-, nickel- and zinc-doped graphene nanosheet for adsorption of toxic gas of nitric oxide (NO). The results of this paper have provided a favorable understanding of the interaction between TM-doped graphene nanosheet and NO molecule.
Design/methodology/approach
A high performance of TM-doped graphene nanosheet as a gas sensor is demonstrated by modeling the material’s transport characteristics by means of the Langmuir adsorption and three-layered ONIOM/ density functional theory method. The Langmuir adsorption model has been done with a three-layered ONIOM using CAM-B3LYP functional and LANL2DZ and 6–311G (d, p) basis sets by Gaussian 16 revision C.01 program towards the formation of of NO→TM(Mn, Co, Cu)-doped on the Gr nanosheet.
Findings
The changes of charge density for Langmuir adsorption of NO on Mn-, Co- and Cu-doped graphene nanosheet orderly have been achieved as: ΔQ Co-doped = +0.309 >> ΔQ Mn-doped = −0.074 > ΔQ Cu-doped = −0.051. Therefore, the number of changes of charge density have concluded a more remarkable charge transfer for Mn-doped graphene nanosheet. However, based on nuclear magnetic resonance spectroscopy, the sharp peaks around Cu doped on the surface of graphene nanosheet and C19 close to junction of N2 and Co17 have been observed. In addition, Cu-doped graphene sheet has a large effect on bond orbitals of C8–Cu 17, C15–Cu 17 and C16–Cu17 in the adsorption of NO on the Cu-doped/Gr which has shown the maximum occupancy. The amounts of Δ G ads , NO → Mn − C o through IR computations based on polarizability have exhibited that Δ G ads , NO → Mn − C o has indicated the most energy gap because of charge density transfer from the nitrogen atom in NO to Mn-doped graphene nanosheet, though Δ G ( N O → C u − C ) 0 > Δ G ( N O → C o − C ) 0 > Δ G ( N O → M n − C ) 0 .
Originality/value
This research aims to explore the adsorption of hazardous pollutant gas of “NO” by using carbon nanostructure doped by “TM” of iron, nickel and zinc to evaluate the effectiveness of adsorption parameters of various TM-doped graphene nanosheets.
Alkali-activated materials (AAMs) have been extensively studied for their superior performance and eco-friendliness. While previous researches have primarily focused on the hardened properties of AAMs, the assessment of their fresh properties has often been overlooked. The preparation process of AAMs involves key factors in mix design that significantly impact their workability. This study comprehensively evaluates the workability of different types of AAMs, analyzing a total of 402 mixtures extracted from 26 individual papers. The examination focuses on key factors in AAM mix design, specifically the precursors, alkali activator, and aggregate phases. Finally, a mathematical model for predicting the workability of AAMs was constructed based on the LightGBM (LGBM) algorithm. In this model, the reactivity of precursors, alkali activator, geopolymer paste volume, superplasticizer content, and aggregate were set as the inputs, and the flowability was set as the output. Additionally, the predictive efficiency of LGBM model was evaluated and compared to the multi-linear regression model. Meantime, a validation experiment for proving its accuracy was also conducted. This study largely advanced the understanding of the workability of AAMs by providing practical guidelines on AAM mix design with high workability and consistency.
Nowadays, the only economic and effective way to exploit shale reservoirs is multi-stage fracturing of horizontal wells. The backflow after fracturing affects the damage degree of a fracturing fluid to a formation and fracture conductivity, and directly influences a fracturing outcome. At present, the backflow control of the fracturing fluid mostly adopts empirical methods, lacking a reliable theoretical basis. Therefore, it is of positively practical significance to reasonably optimize a flowback process and control the flowback velocity and flowback process of a fracturing fluid. On the other hand, the previous research on the productivity of multi-stage fracturing horizontal wells after fracturing is limited, and an equation derivation process has been simplified and approximated to a certain extent, so its accuracy is significantly affected. Based on previous studies, this paper established a new mathematical model. This model optimizes the flowback velocity after fracturing by dynamically adjusting a choke size and analyzes and predicts the production performance after fracturing. To maximize fracture clean-up efficiency, this work builds the model for a dynamic adjustment of choke sizes as wellhead pressure changes over time. It uses a two-phase (gas and liquid) flow model along the horizontal, slanted and vertical sections. The forces acting on proppant particles, filtration loss of water, the compressibility of a fracturing fluid, wellbore friction, a gas slippage effect, water absorption and adsorption are simultaneously considered. With the theories of mass conservation, we build a mathematical model for predicting production performance from multi-fractured horizontal wells with a dynamic two-phase model considering dual-porosity, stress-sensitivity, wellbore friction, gas adsorption and desorption. In this model, the gas production mechanisms from stimulated reservoir volume and gas and water relative permeabilities are employed. Based on shale reservoir parameters, wellhead pressure, a choke size, a gas/liquid rate, cumulative gas/liquid production, cumulative filtration loss and a flowback rate are simulated. In the simulations, the influential factors, such as shut-in soak time of the fracturing fluid, forced flowback velocity, fracturing stages and fracture half-length after fracturing, are studied. It is found by comparison that in the block studied, when a well is shut in four days after fracturing, the dynamic choke size is adjusted with wellhead pressure changing over time, the fracturing stage is 11, and the fracture half-length is 350 meters, the fracture conductivity after flowback is the largest, and the productivity of the horizontal well is the highest.
Context:
In this research, CO2 and NO2 adsorption on doped nanographene (NG) sheets with transition metals (Fe, Ni, Zn) and (Mn, Co, Cu), respectively, have been applied for scavenging of these toxic gases as the environmental pollutants. The values of changes of atomic charge density have illustrated a more significant charge transfer for Ni-doped C-NG through CO2 adsorption and a more remarkable charge transfer for Co-doped C-NG through NO2 adsorption. The data of NMR spectroscopy has depicted several fluctuations around the graph of Zn-doped on the nanographene surface. The thermodynamic results from IR spectroscopy have indicated that [Formula: see text] values are almost similar for doped metal transitions of Mn, Co, and Cu on the C-NG nanosheet, while [Formula: see text] has the largest gap of Gibbs free energy adsorption with dipole moment.
Methods:
The Langmuir adsorption model with a three-layered ONIOM using CAM-B3LYP functional accompanying LANL2DZ, EPR-III and 6-31 + G (d,p) basis sets due to Gaussian 16 revision C.01 program on the complexes of CO2 → (Fe, Ni, Zn) and NO2 → (Mn, Co, Cu) doped on the C-NG has been accomplished. Then, NMR and IR spectroscopy, nuclear quadrupole resonance, and natural bond orbital analysis have been accomplished for evaluating chemical shielding tensors, thermodynamic properties, electric potential, and occupancy fluctuation through bond orbitals, respectively. In addition, frontier orbitals of LUMO, HOMO, and also a series of chemical reactivity parameters have been calculated. Finally, time-dependent-DFT method due to UV-VIS spectrums has been accomplished to discern the low-lying excited states of CO2 and NO2 adsorption on the (Fe, Ni, Zn) and (Mn, Co, Cu), respectively, doped C-NG sheet.
The high surface-to-volume ratio and flatness of mechanically exfoliated van der Waals (vdW) layered materials make them an ideal platform to investigate the Langmuir absorption model. In this work, we fabricated field effect transistor gas sensors, based on a variety of mechanically exfoliated vdW materials, and investigated their electrical field-dependent gas sensing properties. The good agreement between the experimentally extracted intrinsic parameters, such as equilibrium constant and adsorption energy, and theoretically predicted values suggests validity of the Langmuir absorption model for vdW materials. Moreover, we show that the device sensing behavior depends crucially on the availability of carriers, and giant sensitivities and strong selectivity can be achieved at the sensitivity singularity. Finally, we demonstrate that such features provide a fingerprint for different gases to quickly detect and differentiate between low concentrations of mixed hazardous gases using sensor arrays.
In this research, the ability of transition metals (TM)-doped graphene nanosheets to adsorb the toxic gas CO has been investigated. The Langmuir adsorption model was used, with a three-layered ONIOM, using the CAM-B3LYP functional accompanying the LANL2DZ and 6-31+G (d,p) basis sets, and using the Gaussian 16 revision C.01 program, on the complexes of CO adsorbed on (Fe, Ni, Zn)-doped graphene nanosheets. The order of the changes of charge density for the Langmuir adsorption of CO on Fe-doped, Ni-doped, and Zn-doped graphene nanosheets has been investigated. This shows the greatest change of charge density for the Ni-doped graphene nanosheet. However, based on NMR spectroscopy, sharp peaks around the Ni-doped area on the surface of the graphene nanosheet have been observed. In addition, the Ni-doped graphene nanosheet has a large effect on the bond orbitals of C-Ni in the adsorption of CO, having the maximum occupancy. The values of ΔGadso, calculated through IR, showed that ΔGads,CO→ Fe-doped GRo has the highest value, because of a charge density transfer from the oxygen atom in carbon monoxide to the Fe-doped graphene nanosheet. The frontier molecular orbitals, HOMO and LUMO, and the band energy gap accompanying some chemical reactivity parameters, have revealed the attributes of the molecular electrical transport of (Fe, Ni, Zn)-doped graphene nanosheets for the adsorption of CO. As a result, since a CO molecule interacts simultaneously with a Fe, Ni, or Zn atom and the C-C nanosheet, at first it might be separated, as in this state a CO atom constructs a physical bond with the Fe, Ni, or Zn atom, and then the other could be adsorbed chemically on the C-C nanosheet surface. Finally, our results have shown that a considerable amount of charge transfer occurs between CO molecules and TM-doped graphene nanosheets after adsorption, which suggests that TM-doped graphene is more sensitive and selective to the adsorption of CO than a pristine graphene surface.
Owing to its inexpensive, facile, and eco-friendly nature, adsorption process has enjoyed considerable attention in purification and separation industries. Its importance necessitates extraordinary endeavors in its modeling. This chapter discusses the widely used adsorption isotherms such as adsorption empirical isotherms, isotherms based on Polanyi's theory, chemical adsorption isotherms, physical adsorption isotherms, and ion exchange model, and their related definitions, along with examples of correlated work from the recent decade.
This chapter provides an introduction to adsorption technology and surface science. It also discusses the surface and interface science of adsorbents and nanoadsorbents. The chapter introduces the fundamental information of different types of mechanisms used in understanding the adsorption phenomena.
This paper presents technical and technological characteristics of pontoon bridges that are in operational use of
the Serbian Armed Forces, Armed Forces of the United States and the Russian Federation. A comparative analysis of the
technical and technological characteristics and pontoon bridges provides an overview of the state of pontoon bridges in the
Army of Serbia, but we also come to a conclusion about the desirable characteristics sets of pontoon bridges that the
engineering units of the Serbian Armed Forces should have. For the purposes of the comparative analysis, the pontoon
bridges, which are the most exploited in the armed forces of the said countries, were used.
Environmental pollution and public health is a serious concern posed by effluents from textile industries. The effluents from textile industries, which are primarily contaminated by dyes, are due to large use of dyes and water. The dye contaminants are primarily classified into anionic, cationic and non-ionic dyes. The anionic dyes are essentially composed of acid, direct and reactive dyes containing chromophore groups characteristic for azo, triarylmethane, phthalocyanine and anthraquinone. Therefore, the presence of the anionic dyes in textile effluents may cause a number of diseases to humans such as damages to the liver, kidney, intestines and highly mutagenic and carcinogenic. In the environment, the presence of these contaminants also obstructs the penetration of sunlight, thereby causing reduction in the rate of photosynthesis. Thus, these contaminants also decrease the amount of dissolved oxygen available to the ecosystem. In view of these, there is a great concern for appropriate treatment method to ensure effective removal of the dyes. We reviewed (1) textile dyes classification, (2) toxicity of dyes, (3) treatment technologies for dyes, (4) agricultural waste materials and (5) the removal of anionic dyes using agricultural waste. The removal of the anionic dyes by agricultural wastes were studied based on adsorption due to its advantages of ease of operation, simplicity, lack of chemical use and effectiveness of the process.
Textiles are among the basic needs for human. The manufacture of textile in various industries involves various operations. The large volumes of water used in the textile processing are later generated as wastewater, containing various dyes, heavy metals and other contaminants. This water pollutes soil and water sources if disposed without proper treatment. This chapter reviews the treatment of textile effluent to eliminate heavy metals and puts an emphasis on the adsorption process as a cheap and efficient alternative. Adsorbents made of inorganic and organic/bio-based materials as well as their composites are discussed. Bacteria, algae, fungi, chitin and, chitosan, cellulose and lignocellulosic materials are discussed as biosorbent. Inorganic adsorbents such as clay and zeolites are also reviewed. The interest of this chapter is on the use of composites of inorganic bio-based materials to eliminate heavy metals from textile wastewater by adsorption. Clay–cellulose, cellulose–zeolites and clay–chitosan composites are discussed as adsorbents. Combination of biosorbent with inorganic adsorbent is interesting as the important property of recyclability of a good adsorbent is achieved.KeywordsTextile wastewaterHeavy metalsAdsorptionInorganic bio-based adsorbent
Average Daily Traffic (ADT) data are mostly used in transportation engineering for the purpose of planning and designing roads, pavement capacity designing, prioritizing road maintenance investments, accident studies, etc. In conceptual planning stage, it is sufficient to use estimated ADTs obtained from a model, which saves time and cost. ADT estimation models have been developed using different methods such as regression analysis, and neural networks. This paper aims to make a comparison between three recently developed models to estimate the ADT at any location of the class-A road network in Sri Lanka. These models assume that the ADT at a specific location is contributed by local traffic, regional traffic, and inter-district traffic across the measurement location. The first model considered has been developed based on the travel distance and incorporated six input variables. The model parameters have calibrated through regression analysis. The second model considered is based on the travel time, and calibrated using the regression analysis method. It was identified that at some locations the estimated ADT is distorted because of the presence of expressways and important class-B links which facilitate inter-district traffic. Therefore, the model is further developed, incorporating important class-B road links, AB road links, and expressways to the link node system. A generalized cost function, representing the travel time, distance, and toll cost, is used instead of travel distance which has resulted in an improved Network Connectivity Factor through the revised link node system. The paper presents a comparison of the pros and cons of each ADT estimation model and recommends the most appropriate model for different conditions.
Keywords — ADT estimation, regression analysis, neural networks, origin-destination data, generalized cost function
Rapid and effective differentiation and quantification of a small molecule drug, such as fentanyl, in bodily fluids are major challenges for diagnosis and personal medication. However, the current toxicology methods used to measure drug concentration and metabolites require laboratory-based testing, which is not an efficient or cost-effective way to treat patients in a timely manner. Here, we show an assay for monitoring fentanyl levels by combining the intermolecular interaction-enabled small molecule recognition (iMSR) with differential impedance analysis of conjugated polymers. The differential interactions with the designed anchor interface were transduced through the perturbance of the electric status of the flexible conducting polymer. This assay showed excellent fentanyl selectivity against common interferences, as well as in variable body fluids through either testing strips or skin patches. Directly using the patient blood, the sensor provided 1%-5% of the average deviation compared to the "gold" standard method LC-MS results in the medically relevant fentanyl range of 20-90 nM. The superior sensing properties, in conjunction with mechanical flexibility and compatibility, enabled point-of-care detection and provided a promising avenue for applications beyond the scope of biomarker detection.
Diversifying energy sources by incorporating cleaner technologies i.e., renewable energy sources, are expected to play an important role to move from the current non-renewable dominated energy system. One of the promising energy carriers for renewable energy systems is hydrogen, and proton exchange membrane water electrolyzer (PEMWE) is one of the technologies known to produce highly pure H2. Regardless the promising performances, large-scale use of such device faces efficiency and cost issues, among which the anode catalyst material is one of the main contributors due to its composition (Ir-based materials) and high overpotential towards the oxygen evolution reaction (OER) (slow kinetic).This thesis work aimed to electrochemically study several Ir-based OER catalysts by different strategies since properties such as electrochemical surface area (ECSA), stability/degradation tests and catalytic processes are critical characteristics to describe, analyze and compare electrocatalysts. The mixed oxides derived from Ir1-xMoxO2 (x =0, 0.1, 0.3, 0.5, 0.7 and 1) were synthesized by the spray-drying process and calcined at different temperatures in the range 450 – 800 °C. The electrocatalysts were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The SEM study of these materials confirmed the amorphous - porous morphologies at lower calcination temperatures. XRD analysis showed that the crystallite size increases with temperature and decreases with molybdenum content. XPS spectra demonstrated that the main oxidation states present on the mixed oxides are Ir3+/Ir4+ or Ir4+. The electrochemical characterization using rotating disc electrode (RDE) technique consisted of cyclic voltammetry (CV) and chronoamperometry, as well as double layer capacitance (Cdl) and Hg underpotential deposition (Hg-UPD), which allowed to investigate their ECSA. The CV of all the mixed oxides allowed to compare and observed the influence of the sintering temperature on the performance towards OER. Three of the compounds of the series Ir1-xMoxO2 (x = 0.1, 0.3, 0.5) calcined at 450, 500 and 550 °C were studied for stability as anode materials. The Cdl method allowed to obtain a trend of the charging current behavior of the electrocatalyst as function of the sintering temperature, while the HgUPD method results prove its relevancy and applicability for ultraporous and Ir-mixed oxides when tested in RDE giving consistent ECSA values in agreement with BET measurements.
The removal of chemical oxygen demand (COD) from fish pond wastewater using waste alum sludge from water treatment plant was studied in a continuous flow system. Characterization of the sludge revealed the Braunuer–Emmett–Telller results with surface area of 139 cm² g⁻¹, pore volume of 0.126, and mesoporous pore radius of 5.228 nm. The Fourier-transform infrared spectroscopy analysis indicates -OH bonding to inorganic matter and for the loaded sludge around 2361 cm⁻¹ attributed to vibration of sulfur–hydrogen interaction (S–H) in the sludge matrix. The effects of varied bed height and influent flow rate on the shape and characteristics of breakthrough curves were determined. At a constant influent concentration of 72 mg L⁻¹, results confirmed that early bed saturation and breakthrough time occurred at higher flow rate and smaller bed depth. The optimum COD removal of 70.25% was obtained at flow rate of 3 mL min⁻¹ and 50 mm bed depth and the maximum adsorption capacity of 53.98 mg g⁻¹ was obtained at 7 mL min⁻¹ flow rate and 50 mm bed depth. The adsorption data were fitted into Thomas, Yoon–Nelson, Adams–Bohart, bed-depth service time, and Clark’s models. Based on regression and SS error analysis, Clark model best described the adsorption of COD by alum sludge at all conditions. It can be deduced from the results obtained that waste alum sludge is a suitable adsorbent for the treatment of fish pond wastewater.
A variety of instruments are available for measuring the particle size (PS), particle size distribution (PSD), and zeta potential with the requisite and available data statistics. These instruments work on various concepts such as laser light diffraction, moving particle tracking, morphological imaging, spatial filter velocimetry, resonant mass measurement, and Taylor dispersion. Small particles have a considerable variation in their shapes, and it is challenging to represent their size in terms of a single dimension. Several physicists and mathematicians have established different concepts to define PS in an equivalent dimension such as diameter equivalent, identical minimum length, identical maximum length, and identical surface area. The concept of dynamic light scattering (DLS) has been globally adopted by most manufacturers of PS analyzers. The scope of selected PS analyzers has been extended to measure the PS at subnanometer scale. This chapter will provide a comprehensive study of various popular techniques for PS measurement. Inflight PS and particle shape analysis, particle shape imaging technique, multiangle DLS, and electrophoretic light scattering are the latest versions of PS analysis techniques.
Textile industry is emerging as a primary source of wastewater that cause permanent
damage to the environment and human health. Textile effluents have high pollution
potential and require adequate pretreatment before their discharge into the atmosphere.
Several methods, including adsorption, have been explored for the remediation of
priority pollutants of textile wastewater. Adsorption serves as the most preferred
option because of its design simplicity, low operational cost, high efficiency and
negligible sludge production. So far, various adsorbents, including natural and
artificial materials have been explored.
Among the available adsorptive materials, the immobilization of priority pollutants
using phosphate minerals such as hydroxyapatite (Ca10(PO4)6(OH)2), is a promising,
recent, and effective strategy for wastewater remediation. Hydroxyapatite (HAP) is a
vital component of vertebrate bone minerals and can easily be extracted from natural
sources. However, its properties can further be enhanced using appropriate synthetic
procedures and suitable modifications. The primary advantage of using HAP is its
functionality, porosity and the crystal structure. Its promising adsorption behavior
helps in effectively removing the priority pollutants of textile waste water e.g.,
sulphates, oils, phenols, dyes and toxic heavy metals. The mechanism of adsorption
process of HAP is well explained by isothermal and thermodynamic studies and
Equilibrium Kinetic Modelling. Thus, its efficiency, cost-effectiveness and reusability
provide viable option to target textile waste pollutants.
Insoluble gas in water can remarkably affect the boiling heat transfer performance, which is of great practical importance for many applications. The effect of insoluble nitrogen gas on the boiling of water over copper surfaces with different temperature conditions is investigated through molecular dynamics simulations. Observations on the nanofilm boiling phenomena and insights into the fundamental mechanism are analyzed in terms of the temporal and spatial evolutions of temperature and the instantaneous heat flux curves. Results show that the nanofilm boiling processes change from normal evaporation to explosive boiling by increasing surface temperature owing to the conduction dominating the heat transfer mode. The nitrogen molecules are adsorbed on the copper substrate. This condition makes the explosive boiling of water containing nitrogen to occur easily due to its low substrate temperature and short onset time. Compared with the water boiling on nitrogen adsorption substrate, the boiling of pure water on bare substrate benefits the heat transfer in large superheat range because it has higher heat flux and the normal evaporation still works on a surface with relatively high temperature. This work may benefit the fundamental understanding and practices of boiling heat transfer in many industrial applications.
The scope of this chapter is to apprise the researchers about the applications of various metal nanoclusters such as palladium and its hybrid structures to be employed in hydrogen storage. Nanoclusters, the materials with a high surface-to-volume ratio, have the potential to behave as an excellent hydrogen storage device. This chapter discusses the details of nanoclusters and their formation using a nanocluster deposition system. We also discuss physisorption and chemisorption mechanisms for hydrogen storage and developments of magnesium and palladium film-based hybrid structures on hydrogen storage properties such as hydrogen-storage capacity and absorption/desorption temperature. Magnesium-based hybrid structures present a promising candidate for good hydrogen storage with large capacities but high absorption/desorption temperatures. So, the critical challenge is to decrease their desorption temperature, enhance the kinetics, and cycle life. These kinetics can be modified by using them in conjunction with Pd structures that have ambient condition hydrogenation and dehydrogenation properties. Guided by theoretical consideration that showed improved hydrogen storage properties in a nanocluster form, we propose that making hybrid Pd–Mg–Pd nanoclusters may well be the alternative for good hydrogen storage, making nanoclusters the system of choice for future practical use robust hydrogen storage system.
Tissue engineering has recently gained popularity as an alternative to autografts to stimulate bone tissue regeneration through structures called scaffolds. Most of the in vivo experiments on long-bony defects use internally-stabilized generic scaffolds. Despite the wide variety of computational methods, a standardized protocol is required to optimize ceramic scaffolds for load-bearing bony defects stabilized with flexible fixations. An optimization problem was defined for applications to sheep metatarsus defects. It covers biological parameters (porosity, pore size, and the specific surface area) and mechanical constraints based on in vivo and in vitro results reported in the literature. The optimized parameters (59.30% of porosity, 5768.91 m⁻¹ of specific surface area, and 360.80 μm of pore size) and the compressive strength of the selected structure were validated in vitro by means of tomographic images and compression tests of six 3D-printed samples. Divergences between the design and measured values of the optimized parameters, mainly due to manufacturing defects, are consistent with the previous studies. Using the mixed experimental-mathematical scaffold-design procedure described, they could be implanted in vivo with instrumented external fixators, therefore facilitating biomechanical monitoring of the regeneration process.
Shale gas is an important unconventional natural gas resource. Studying the microstructure of shale and the gas transport law is of great significance for the development of shale gas. This paper uses the field emission scanning electron microscope to observe shale samples of the BC shale gas reservoirs in southern China. It is found that there are three types of storage spaces on the micro–nano-scale of shale samples. The storage space can be distributed either in pure organic matter or pure inorganic matter or in both organic matter and inorganic matter. They are called organic storage space, inorganic storage space, and mixed storage space of organic matter and inorganic matter, respectively. According to these types of storage spaces, an ideal conceptual model that reflects various types of storage spaces has been researched and established on the micro–nano-scale. At the same time, the transport mechanisms of slip, diffusion, adsorption, and coupling have been considered, and shale mixed storage space has also been considered in particular. On this basis, a comprehensive equation that can simulate the transport of shale gas in various types of storage spaces is derived. The equation also introduces the proportional parameters of the organic part, fractal characteristics, and water film of the inorganic part in the mixed storage space. Researchers can adjust this parameter to simulate shale gas transportation in different types of storage spaces and then use the finite element method to solve it numerically. This paper analyzes the influence of shale reservoir space types on shale gas transport. The larger the proportion of organic components in the mixed pores, the better the gas transport. The rough fractal dimension of the pores also affects the gas transport. However, when the pore diameter is less than 300 nm, the rough fractal dimension of the pores has a negligible influence on gas transport. For the water film on the inorganic wall surface of mixed pores, the gas transport of the macropore is more sensitive to the change in water film thickness.
In order to investigate the effect of using different solid state forms and specific surface area (TBET) of active pharmaceutical ingredients on tabletability and dissolution performance, the mono- and dihydrated crystalline forms of chlorothiazide sodium and chlorothiazide potassium (CTZK) salts were compared to alternative anhydrous and amorphous forms, as well as to amorphous microparticles of chlorothiazide sodium and potassium which were produced by spray drying and had a large specific surface area. The tablet hardness and tensile strength, porosity and specific surface area of single-component, convex tablets prepared at different compression pressures were characterised. Results confirmed the complexity of the compressibility mechanisms. In general it may be concluded that factors such as solid-state form (crystalline vs. amorphous), type of hydration (presence of interstitial molecules of water, dehydrates) or specific surface area of the material have a direct impact on the tabletability of the powder. It was observed that, for powders of the same solid state form, those with a larger specific surface area compacted well, and better than powders of a lower surface area, even at relatively low compression pressures. Compacts prepared at lower compression pressures from high surface area porous microparticles presented the shortest times to dissolve, when compared with compacts made of equivalent materials, which had to be compressed at higher compression pressures in order to obtain satisfactory compacts. These results suggest that such processed materials may find applications as suitable solid-state forms of APIs in fast disintegrating or fast dissolving solid dosage forms.
The agglomeration, electrokinetic properties and electrophoretic deposition
behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were
studied in comparison with conventional pH adjustment. It was found that citric
acid imparted negative zeta-potential values and electrosteric stabilisation to
particles in suspensions at all pH levels. The examination of additions of
carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp
drop in zeta-potential at distinct addition levels, which correspond to surface
saturation of the particles with negatively charged carboxylate groups.
Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated
from these results, showing that both citric acid and EDTA coordinate to ZrO2
surfaces by two carboxylate groups while oxalic acid is coordinated by one
group. The use of carboxylic acids was shown to facilitate superior
electrophoretic deposition in comparison with zeta-potential modification by
conventional pH adjustment through improved suspension stability.
The dispersion of anatase phase TiO2 powder in aqueous suspensions was
investigated by zeta-potential and agglomerate size analysis. The iso-electric
point (IEP) of anatase was determined to be at pH 2.8 using monoprotic acids
for pH adjustment. In comparison, it was found that the use of carboxylic
acids, citric and oxalic, caused a decrease in zeta-potential through the
adsorption of negatively charged groups to the particle surfaces. The use of
these reagents was shown to enable effective anodic electrophoretic deposition
(EPD) of TiO2 onto graphite substrates at low pH levels with a decreased level
of bubble damage in comparison with anodic EPD from basic suspensions. The
results obtained demonstrate that the IEP of TiO2 varies with the type of
reagent used for pH adjustment. The low pH level of the IEP and the ability to
decrease the zeta-potential through the use of carboxylic acids suggest that
the anodic EPD of anatase is more readily facilitated than cathodic EPD.
The properties of the double layer capacity on rough electrodes are discussed in terms of the recently developed linear Poisson-Boltzmann theory [L.I. Daikhin, A.A. Kornyshev, M. Urbakh, Phys. Rev.E53, 6192 (1996)]. This theory offers a concept of a “Debye-length κ dependent roughness factor”, ie roughness function, which determines the deviation of capacitance from the Gouy-Chapman result for a flat interface. Analytical expression for the roughness function is available for the case of weak Euclidean roughness. The two parameters—mean square height and correlation length—appear there. The way how the result changes in the case of moderate and strong roughness is analyzed on the basis of a numerical solution obtained for a model roughness profile; an efficient interpolation formula which covers the limits of weak and strong roughness is suggested. The role of anisotropy of the roughness profile is investigated. The predicted effects could be screened by the crystallographic inhomogeneity of a rough surface not taken into account here. Tentatively ignoring such (often important) complications we discuss the results in the context of a possible method for in situ characterization of surface roughness of metal electrodes, based on the double layer capacity measurements in solutions of variable concentration.
The gap between theory and practice, in the field of adsorption, is closing. The development of new theoretical approached formulated on a molecular level, by means of computer simulation, has led to the progress of theoretical description of adsorption. New classes of solid absorbents, such as activated carbon fibers and carbon molecular sieves, fullerenes and heterofullerenes, microporous glasses and others, were developed in last 15 years. The sorption, catalytic, magnetic, optical and thermal properties of nanostructured solids has made them popular in science and technology.
We investigated the adsorption of bovine serum albumin (BSA) on colloidal Al2O3 particles in an aqueous environment. Changes in the zeta potential of the Al2O3 particles upon the adsorption of BSA were measured using an electro-acoustic technique. The mass of protein adsorbed was determined by using UV-vis spectroscopy. The change of the isoelectric point of the Al2O3 powder-protein suspension was found to be a function of adsorbed protein mass. It was shown that approximately one monolayer of BSA was needed to fully mask the surface and to compromise the charge of Al2O3. From titration experiments it follows that about 30-36% of the negatively charged groups of the protein form bonds with the protonated and charged Al2O3 surface. On the basis of our observations we introduced a new adsorption model for BSA on Al2O3 particles.
This book covers the development of both experiment and theory in natural surface particle chemistry. It emphasizes insights gained over the past few years, and concentrates on molecular spectroscopy, kinetics, and equilibrium as they apply to natural particle surface reactions in aqueous media. The discussion, divided among five chapters, is complemented by lengthy annotations, reading suggestions, and end-of-chapter problem sets that require a critical reading of important technical journal articles.
We report that fractal scaling laws relate the details of the complex reactive and non-reactive geometries of porous materials with a wide variety of chemical and physical molecule-surface interactions. These scaling laws relate the following property/scale pairs: physisorption monolayer value/particle size of the adsorbent; chemisorption capacity/particle size; catalytic activity of supported metal catalysts/dispersion or catalyst particle size; adsorbate surface reaction rate/particle size; monolayer value/physiorbed adsorbate size; monolayer of adsorbed polymer/the molecular weight of the polymer; the amount of derivatizing agent necessary for full surface grafting/size of the reverse-phasing reagent; In all these cases the property/scale relation has the form of a power-law in which the exponent is a simple function of the effective fractal dimension of the process. Well over one hundred case analyses show the generality and applicability of fractal scaling laws in heterogeneous chemistry. © 1988 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands.
This chapter discusses chemisorption of probe molecules. Standard methods for catalytic surface area determinations formally exist for several supported-metal catalysts. However, there is not general acceptance of such methods for supported-metal oxides (or sulfides). There are inherent difficulties in selecting any method as a standard for surface area measurements, because catalyst manufacturers throughout the world prepare their materials from different precursors and in different ways. These differences can cause marked variations in the procedure required to measure accurately the surface area of metal oxides. The chemisorption of suitable probe molecules is the method of choice for such purposes. It is also of great interest to combine the chemisorption measurements with appropriate surface spectroscopic techniques, in order to determine precisely the stoichiometry between the probe and the surface area of the supported active component and the number of sites responsible for a given reaction. One may not select a catalyst on the basis of a “standard test.” High surface area is, however, of such basic importance to any catalytic process that it should always be measured as a necessary, but not sufficient, characteristic of the system.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
This paper reports the performance of bacterial disinfection using 3D dendritic titanium dioxide with nanoribbon structures (3DD-TiO2), which is newly developed by the researchers. Characterization of 3DD-TiO2 using SEM and TEM shows that the diameter of nanoribbons is nearly 18 nm only, resulting in an aspect ratio of more than 50. The hierarchical porous structure of the 3DD-TiO2 would greatly favor the improvement of photocatalytic activity via enlarging the specific surface area. In comparison with the same-sized microspheres and commercial Degussa P25, which are both spherically structured, 3DD-TiO2 displays a consistently better performance under the tested environment. Without UV illumination, the removal efficiency of Escherichia coli by 3DD-TiO2 is 6.4% and 8.7% higher than that of microspheres and P25, respectively. Under UV radiation, the disinfection kinetic constant k of the disinfection reaction using 3DD-TiO2 is 23.2% and 33.9% higher than that of using microspheres and P25, respectively. A series of optimization studies have been carried out to identify the optimum operating parameters of a photocatalytic process using 3DD-TiO2. The results tend to suggest: (a) optimum catalyst concentration is around 100 mg/L; (b) the optimum temperature for bacteria inactivation ranges between 10 °C and 20 °C; (c) presence of humic acid and anions (SO42−) exhibits an inhibitory effect on water disinfection process; and (d) cations (Ca2+) enhance the disinfection rate. These optimum operating parameters could be directly referenced for full-scale applications in future.
Serving as a general introduction to surface and interface science, this
book focuses on essential concepts rather than specific details, on
intuitive understanding rather than learning facts. The text reflects
the fact that the physics and chemistry of surfaces is a diverse field
of research and shows this in its Interdisciplinary conceptual design.
Once the most important techniques and methods have been introduced,
readers will be able to apply simple models to their own scientific
problems. Furthermore, manifold high-end technological applications from
surface technology, biotechnology, or microelectronics illustrate the
basic scientific treatment. The authors address advanced students of
chemistry, physics, materials science, chemical engineering and related
subjects with a basic knowledge of natural sciences and mathematics,
since the mathematical calculations are thoroughly explained and made
comprehensible for the reader. As such, non-specialists in surface
science who want to learn more about this important subject will also
benefit from the book.
Graphene oxide (GO) forms persistent dispersions in aqueous solutions up to concentrations of 0.2 mg•mL-1. Addition of methylene blue (MB) to these aqueous dispersion of GO gives rise to the observation in optical spectroscopy of new absorption bands that are indicative of the formation of MB/GO conjugates. Four new absorption maxima have been characterized, their intensity varying depending on the relative concentration of MB with respect to GO. Two of these bands appearing at 677 and 757 nm correspond to individual MB molecules adsorbed on neutral or acid sites of GO, respectively. Two other bands at 615 and 580 nm are attributable to adsorbed MB molecules showing interaction with other neighbor dye molecules at incomplete (615 nm) or complete (580 nm) surface coverage. Complete coverage of GO surface by MB causes the formation of a precipitate and the separation of the MB/GO conjugate. EDS mapping of carbon and sulfur atoms of MB/GO conjugate indicates the homogeneous distribution of MB molecules coating GO sheets. A simple and reliable protocol for surface area measurement and determination of the level of aggregation for GO dispersions in water has been proposed by determining the amount of MB that leads to the maximum intensity of the 580 nm band and precipitation of the MB/GO conjugate. Specific surface area as high as 736.6 m2•g-1 in the range of the theoretical value for GO has been experimentally measured for diluted GO solutions, but aggregation levels of 15% were estimated for GO concentration of 50 μg•mL-1.
Adsorption of citrate by whewellite was examined with three different techniques: solution depletion, seeded crystal growth inhibition, and microelectrophoresis (zeta potential). Comparison of the results from the three techniques indicates that at the concentrations giving 50% coverage or 50% inhibition, there was reasonable agreement if the adsorbate was assumed to be trivalent citrate.
Adsorption of binary mixtures of chromate and oxalate onto [alpha]-FeOOH was quantified as a function of pH for a wide range of absorbate concentrations. Oxalate diminished the adsorption of chromate most effectively at low pH and when adsorbate concentrations were near surface-saturation levels. Chromate significantly inhibited oxalate adsorption over the entire pH range, reflecting the higher affinity of chromate for the [alpha]-FeOOH surface. The results indicate the adsorption of organic acids can enhance the mobility of chromate in acidic environments, while competitive adsorption of inorganic oxy anions may sharply diminish organic acid adsorption, thereby exerting an important control on mineral weathering rates. The ability of two surface complexation models to quantitatively predict the binary-solute data was evaluated using model constants that successfully described goethite surface hydrolysis and single-solute adsorption. Diffuse layer and triple-layer model simulations were highly similar and quantitatively accounted for binary-solute adsorption as a function of pH when surface concentrations of both coadsorbates were high. However, these models significantly underpredicted adsorption of minor species. 58 refs., 7 figs.
Various methods for solving the partial contact of surfaces with regularly periodic profiles - which might arise in analyses of asperity level contact, serrated surfaces or even curved structures - have previously been employed for elastic materials. A new approach based upon the summation of evenly spaced Flamant solutions is presented here to analyze periodic contact problems in plane elasticity. The advantage is that solutions are derived in a straightforward manner without requiring extensive experience with advanced mathematical theory, which, as it will be shown, allows for the evaluation of new and more complicated problems. Much like the contact of a single indenter, the formulation produces coupled Cauchy singular integral equations of the second kind upon transforming variables. The integral equations of contact along with both the boundary and equilibrium conditions provide the necessary tools for calculating the surface tractions, often found in closed-form for regularly periodic surfaces. Various loading conditions are considered, such as frictionless contact, sliding contact, complete stick, and partial slip. Solutions for both elastically similar and dissimilar materials of the mating surfaces are evaluated assuming Coulomb friction.
This study compares the Brunauer–Emmett–Teller (BET) and Langmuir equations when applied to N2 adsorption isotherms at 77 K on various carbon blacks and activated carbons. Adsorbent samples varied greatly in the degree of development of their surface area and porosity. The activated carbons were more microporous and less mesoporous than the carbon blacks. The equations were applied up to p/p0=0.20, 0.30, and 0.40. The values of the lineal correlation coefficient as a rule were above 0.990. From the derived BET (SBET) and Langmuir (SL) surface areas, the conversion factor (α) of SL to SBET was calculated. The α mean value (ᾱ) and the standard deviation coefficient (σ) were also obtained. The N2 isotherms fit better to the Langmuir equation for the activated carbons and to the BET equation for the carbon blacks. The factor α was markedly higher than the unit for all carbons. It increased significantly with increasing p/p0 range. The α values were closer for each series of carbons, and larger for the carbon blacks than for the activated carbons; in spite of the fact that the carbon blacks were more mesoporous. As shown by the ᾱ increments, the dependence of ᾱ on the p/p0 range was less strong for the activated carbons for the two narrowest p/p0 ranges. The σ values indicated that the influence of the type of carbon on ᾱ was greater for the carbon blacks when fitting up to p/p0=0.30 or 0.40.
The surface of the polyamidoamine (PAMAM) starburst dendrimers of Tomalia et al. is indeed fractal. Two independent analyses yielded as fractal dimension D 2.41 ± 0.04 and 2.42 ± 0.07. The fractal dimension of several enzymes lie in this region, so the starburst dendrimers will probably mimic biomolecules.
The problem of relating electrophoretic mobilities to surface charge densities of particles in suspension has been investigated mainly experimentally. The subject has been approached by comparing the surface potentials at an oil/water interface calculated for adsorbed films of ionic surface active agents, with the zeta potentials of oil droplets in similar surface-active agent solutions. When the bulk viscosity and dielectric constant were used in calculating the zeta potentials, the surface and zeta potentials converged towards low surface charge densities. At higher charge densities the zeta potentials fell well below the surface potentials. The reasons for this discrepancy have been investigated. Misapplication of the Gibbs equation, surface hydrolysis of adsorbed ions, specific interaction of adsorbed ions with counter-ions, surface conductivity, internal circulation in the liquid droplets and double-layer dielectric constants and viscosities were considered. By elimination it has been concluded that only enhanced values of the $\eta$/D ratio in the electrical double layer can account for the experimental observations. Independent evidence for this phenomenon has been briefly examined. The circumstances under which a reliable value of surface charge may be determined from electrophoretic measurements have been discussed.
A more complete understanding of the structural and mechanistic details of a catalyzed heterogeneous reaction leads both directly and indirectly to the development of new and better catalysts. For catalyst technology, the most sensitive probe of catalysts performance will continue to be the rate and selectivity of a chemical reaction. However, these macroscopic observations, adequate for determining how good a catalyst is, require supplementary microscopic information to remove ambiguity in the deduction of a catalytic mechanism. This information, almost down to the atomic level, concerning the structure and reactivity of the intermediates, the nature of adsorption sites (and sometimes the active sites) and their number, is the main objective of the science of catalysis. The most promising approach to this problem is the use of suitable probe molecules for the quantitative titration of site density and qualitative characterization of their nature by means of surface spectroscopies of the chemisorbed probe molecules [1, 21. This framework of action is schematically represented in Fig.1.
The concept of fractal dimension D of surfaces, advanced as natural measure of surface irregularity in part I of this series, is shown to apply to a remarkable variety of adsorbents: graphites, fume silica, faujasite, crushed glass, charcoals, and silica gel. The D values found for these examples vary from two to almost three (for smooth and very irregular surfaces, respectively), thus covering the whole possible range. They quantify the intuitive picture that surface inhomogeneities are minor, e.g., in graphites, but dominant, e.g., in charcoal. The analysis is based on adsorption data, with main focus on adsorbates of varying molecular cross section. They include N2, alkanes, polycyclic aromatics, a quaternary ammonium salt, and polymers. The straight‐line plots so obtained confirm also a number of reported on‐surface conformations of specific adsorbates. The converse method to get D from varying the size of adsorbent particles is exemplified for fume silica and crushed glass.
In this letter we report that, at the molecular-size range, the surfaces of most materials are fractals, that is, at this range, surface geometric irregularities and defects are characteristically self-similar upon variations of resolution. The whole range of fractal dimension1, 2D<3, is found in the many examples presented. Two representative examples, namely adsorption of polystyrene on alumina and adsorption of krypton on dolomite are discussed in some detail. Our findings suggest a simple solution to the problem of quantifying the degree of surface irregularity2,3 at a resolution which is of relevance to many aspects of surface science. The results provide a general explanation for phenomenological links between various surface parameters, and we derive a set of equations of use in predicting surface variables.
The activity in our laboratory and in collaboration with other laboratories in applying fractal geometry for the characterization of irregular surfaces and materials and for the analysis of molecular interactions with such objects are summarized in this report. Most of the studies were performed on the xerogel of silica. Various theories and experimental techniques have been employed for this purpose. They include adsorption studies, computerized image analyses in one (boundary lines), two (textures) and three (proteins) dimensions; non-radiative, Förster-type, one step electronic energy transfer (EET); small angle X-ray scattering; and analysis of chemical reactivity of fractal objects. The relation between porosity and fractal dimension has been studied by EET, by the photophysics of adsorbed pyrene and by monolayer adsorption studies. A direct method for the determination of adsorption conformations has been developed. Limitations of the fractal approach have been identified and outlined.
The adsorption of phosphate ions from aqueous solution onto thin films of colloidal TiO2 has been studied for the first time by in situ internal reflection infrared spectroscopy. Phosphate binds strongly to TiO2, as evidenced by the large changes in the PO stretching band structure in the infrared spectrum of the adsorbed species compared with the solution species. The Langmuir binding constant for phosphate onto TiO2 at pH = 2.3 is (3.8 ± 0.8) × 104 dm3 mol-1, which is similar to the binding constants onto TiO2 for bidentate ligand species such as oxalate and catechol. The strength of the binding is also apparent in the kinetics of adsorption, showing fast adsorption and much slower desorption, as expected for a strongly bound species. The kinetics data at pH = 8.3 have indicated coverage-dependent phosphate adsorption and desorption. Experiments with substituted phosphate species have confirmed the bidentate binding of phosphate to Ti(IV) ions at the TiO2 surface.
Sequential addition of anionic and cationic polyelectrolytes may lead to the formation of multilayers at a solid surface. The buildup of such multilayers is characterized by a stepwise increase of the adsorbed amount and layer thickness and by alternating highly positive and highly negative values for the ζ-potential. The prime variables which determine the stability of these structures are the polymer charge and the ionic strength. Very stable multilayers are formed when both polymers are highly charged and when the ionic strength is low. For weakly stable multilayers complexation at the surface may first occur, followed by desorption of the complexes. For strongly charged polyelectrolytes the charge stoichiometry, which is not always 1:1, seems to be unique for each pair of polyelectrolytes; no influence of the substrate, of the pH, or of the ionic strength could be observed.
Surface fractal dimensions, DS, of smooth and corrugated bovine serum albumin particles were obtained from N2 adsorption isotherms using modified Frenkel−Halsey−Hill (FHH) theory. It was found that for different particles, the correct DS values depended on the number of adsorbed layers, n. For corrugated particles, when 1 ≤ n ≤ 10, the value of DS is equal to 2.39, which agrees with the value obtained from light scattering (2.39 ± 0.05). Unlike the corrugated particles, the adsorption isotherm for the smooth particles generated the correct value of DS (2.12) only for 1.0 ± 0.5 ≤ n ≤ 2.0 ± 0.5 (i.e., around monolayer coverage). Determination of DS in the multilayer region (n > 2) produced a higher value than the one obtained from monolayer coverage. This was because the smooth particles were in closer contact with each other; at higher coverage the gas molecules probed the surface of the aggregates instead of the single particles. As there were fewer contact points between the corrugated particles compared to the smooth particles, this effect took place at higher coverage (pressure) causing deviation from the expected values. This finding is supported by the fact that for corrugated particles, the value of DS started to deviate at higher n and increased to 2.58 when n > 10. The use of modified FHH theory is thus limited by the number of adsorbed layers on the particles. The closer the particles come in contact, the thinner is the coverage region describing the correct DS. To ensure reliable determination of DS, it is therefore recommended to determine DS only around monolayer coverage.
A detailed analysis and calculation of the uncertainties associated with manometric gas-adsorption measurements are presented for experimental data for nitrogen adsorption at ≈77 K by a traceable standard carbon black material (004-16820-02). Equipment- and measurement-related uncertainty sources derive from the dosing and sampling volumes; temperature control of these volumes; dosing, equilibrium, and barometric-pressure measurements; liquid nitrogen level control; and sample-mass measurements. Data processing errors derive from ignoring thermal transpiration effects and nonideal gas behavior. Departure from ideal gas behavior contributions to the amount adsorbed was accounted for by considering the temperature relationship of the second virial coefficient of the virial equation of state. Variation in the liquid nitrogen level control is shown to have an enormous impact on the pressure-measurement precision and, hence, the amount adsorbed. Variation of the liquid nitrogen level by ±1 mm results in a variation of the equilibrium pressure from −0.42 to +0.52% and the volume of gaseous nitrogen adsorbed from −8.53 to +5.94% when compared with the results obtained during precise level control (within ±0.2 mm). In addition to these uncertainty sources, reproducibility in the sample-mass measurement is important; a decrease in the mass resolution from 5 × 10-5 to 5 × 10-4 g generates a relative combined standard uncertainty of the volume of nitrogen adsorbed by 10-fold varying from 2.78 to 9.86% over the relative pressure range from 0.0007 to 0.98. For a similar standard mass uncertainty applied to the Brunauer−Emmet−Teller specific surface area analysis, the final area relative combined uncertainty increases from 0.63 to 6.19%. The calculated cumulative relative combined uncertainty in the volume adsorbed increases continuously with each experimental point from 0.28 (for the first experimental point on the adsorption branch of the isotherm) to 9.54% (for the last experimental point on the desorption branch of the isotherm), with subsequent implications for mesopore modeling and analysis accuracy.
An electrical double-layer model is developed to predict electrosorption of ions from aqueous solutions by carbon aerogel electrodes. The carbon aerogel electrodes are treated as electrical double-layer capacitors, and electrosorption is modeled using classical electrical double-layer theory. Because of the porous characteristics of the electrodes, the total capacity of the system is obtained by summing the contributions of the individual pores. The pore size distribution of the carbon aerogel is measured by the physical adsorption of N2 and CO2 as well as by mercury intrusion porosimetry. When a pore has a width smaller than a specific value (cutoff pore width), it does not contribute to the total capacity because of the electrical double-layer overlapping effect. This effect greatly reduces the electrosorption capacity for electrodes with significant numbers of micropores, such as carbon aerogel; thus, it is considered in the electrical double-layer model. The model in this study focuses on the electrosorption of sodium fluoride, which exhibits minimal specific adsorption. Several equilibrium electrosorption experiments are performed under various conditions of ion solution concentration and applied voltage. When the overlapping effect is considered, modeling results agree well with experimental data obtained at voltages up to 1.2 V. Without the double-layer overlapping correction, the model greatly overestimates the electrosorption capacity. The cutoff pore width is found to decrease with increasing ion solution concentration and applied voltage. An approximate modeling approach is also presented in this work, which is more efficient than the exact solution in terms of numerical computations.
Imposing a pore size distribution of a fractal surface on the Dubinin approach for adsorption in porous materials yields the simple isotherm θ = K[ln (p0/p)]D-3 in which θ is the relative adsorption, p0 and p are the saturation and equilibrium pressures, respectively, K is a constant, and D is the fractal dimension of the surface accessible to adsorption. The isotherm has the form of the Frenkel-Halsey-Hill (FHH) equation, and the theoretical range of the exponent 3 - D (2 ≤ D < 3) indeed falls into the range of experimentally observed FHH exponents.
Adsorption of N2, Ar, Kr, and O2 at 76.6 K was investigated on Aerosil samples and three different categories of carbons: graphitized, ungraphitized, and activated graphitized substrates. With the BET equation, the appropriate ranges of relative pressure are defined and the corresponding experimental cross-sectional areas, σ (nm2/adsorbed species), are reported, based on σ(N2) = 0.162. Values of σ on the carbons were fitted to physical models illustrating possible arrangements of adsorbed species on the surface. With graphitized carbons, σ(O2) = 0.147 and σ(Ar) = 0.138. With ungraphitized or activated carbons, values of σ are 0.157 for Ar, 0.214 for Kr (at P/Po = 0.02-0.25), and 0.148 for O2. With Aerosils, however, the value of σ(Ar) = 0.186, obtained by the calibration, is high and could not be fitted to a model. An alternative approach has been considered. When comparing the present data with those reported in the literature, the recommended new values on Aerosils (and other silicas) are σ(N2) = 0.143, σ(O2) = 0.147 and σ(Ar) = 0.165 nm2/mol. The present results indicate that oxygen could be considered as the standard gas for adsorption on carbons and silicas, provided that it does not change the carbon structure or its surface characteristics when adsorbed at 77 K.
With a modified attenuated total reflection infrared absorption (ATR-IR) method, vibrational spectra and adsorption isotherms of sulfate, acetate, and oxalate on TiO2 (Degussa P-25, mostly anatase) were measured. For oxalate, the dependence of the spectral shape on the surface coverage is consistent with the formation of several surface complexes. The method uses a horizontal attenuated total reflection (HATR) element coated with a layer of highly dispersed solid material and allows quantitative in situ FTIR measurements of adsorption as a function of solution parameters (adsorbate concentration, pH, ionic strength, etc.). Sets of FTIR spectra obtained under varying conditions are analyzed using singular value decomposition (SVD) and global analysis with acid-base and various adsorption isotherm expressions. This allows for a separation of spectral contributions from dissolved and adsorbed species and of species with distinct structures and/or different adsorption equilibrium constants. The vibrational spectra of adsorbed oxalate suggest that several forms of inner spherically bound surface complexes are formed at lower pH values. This can be explained by the formation of protonated and unprotonated surface complexes and by the heterogeneity of the TiO2 used (Degussa P-25 anatase contains ca. 15-30% rutile). We compare the spectra of surface-bound oxalate species with those in aqueous solutions and discuss possible structural assignments.
The interaction between citric acid and alumina in aqueous solution is characterized. Adsorption isotherms of the dispersant on the alumina surface, electrophoretic mobility of the alumina particles as a function of the citric acid concentration, and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy of the citratealumina surface complex have been used. The adsorption behavior of citric acid is dependent on the pH of the suspension and the concentration of the citric acid. The maximum amount of citric acid adsorbed on the alumina surface, 2.17 μ.mol/m2 at pH 3, decreases to 1.17 μmol/m2 at pH 8. The adsorption of citrate causes a highly negatively charged powder surface and a shift of the isoelectric point (IEP) to lower pH values. The IEP of alumina can be fixed at any pH value between 9 and 3 by proper adjustment of the citric acid concentration. In situ ATR-FTIR spectroscopy of the citrate-alumina surface complex gives evidence for a direct interaction between the carboxylate groups of the citrate and the surface aluminum(III) atoms. The rheological properties of alumina suspensions are studied as a function of the citric acid concentration. The data obtained from the viscosity and dynamic electrophoretic measurements correlate well and allow the construction of a stability map of alumina suspensions stabilized with citric acid. The influence of citric acid on the viscosity is discussed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The interaction potential between the particles is determined by the citrate adsorbed on the surface, leading to a negative particle charge, and the citrate anions remaining in the solution, resulting in an increase of the ionic strength. The adsorption of citric acid also creates a steric barrier that inhibits the complete mutual approach of the individual alumina particles.
Data are presented for adsorption of methylene blue from aqueous solutions on two non-porous carbons and on a porous activated charcoal. From the specific surface areas of the non-porous carbons (determined by low-temperature adsorption of nitrogen) it is calculated that the adsorbed methylene blue occupies an area of between 102 and 108 sq. Å/molecule. These values are compared with those derived from a structural model and with those reported in the literature. It is concluded that this type of adsorption cannot yet be used for accurate determination of surface areas of carbons, nor can it give more than semi-quantitative information when used as a ‘molecular probe’ to investigate the pore structure of porous charcoals.
It is shown that the adsorption of phenol and 3-chlorophenol from aqueous solutions, by basic active carbons and at an equilibrium solution pH below that of dissociation of the phenols, can be described by an equation of the DRK type with exponent n) 4. The principle of temperature invariance is fulfilled between 283 and 313 K, which means that predictions can be made on the basis of a characteristic energy, Es, and of affinity coefficients, s, relative to phenol. This approach presents an advantage over the traditional Langmuir isotherm. Moreover, the comparison of the limiting amounts adsorbed by the different carbons suggests that phenol and 3-chlorophenol are adsorbed in a monolayer as observed for carbon blacks, except in the case of activated carbons with a low degree of activation in which molecular-sieve effects can take place. Similar conclusions are obtained from the enthalpies of immersion into the aqueous solutions and their comparison with graphitized carbon blacks.
A general expression is given for the electrophoretic mobility of a large charged colloidal particle coated with a layer of adsorbed charged polymers. A liquid flow within the polymer layer is taken into account. The potential distribution is calculated on the basis of the non-linear Poisson Boltzmann equation. Simple approximate analytic expressions for the electrophoretic mobility are derived for various cases.
The real objects found in nature have complex structures which Euclidean geometry can not characterize.
Problems, which may arise when low-temperature nitrogen adsorption is used for the characterisation of porous materials, are discussed in this review. Continuous or discontinuous manometric techniques can be employed for nitrogen adsorption measurements at 77 K. For pore structure analysis, the nitrogen adsorption–desorption isotherms should be determined over the widest possible range of relative pressure, while allowing for slow equilibration and other operational problems, particularly at very low pressures. In spite of its artificial nature, the Brunauer–Emmett–Teller (BET) method is still used for the determination of surface area. In principle, nitrogen isotherms of Types II and IV are amenable to BET analysis provided that pores of molecular dimensions are absent and that the BET plot is obtained over an appropriate range of the isotherm. An empirical method based on the application of standard adsorption data is useful for checking the validity of the BET-area. All the computational procedures for pore size analysis have limitations of one sort or another. The various assumptions include an ideal pore shape, rigidity of the structure and an oversimplified model (capillary condensation or micropore filling). The derived pore widths and pore volumes should be regarded as effective (or apparent) values with respect to the adsorption of nitrogen at 77 K.
Ionic diffusion towards a self-affine fractal electrode was investigated experimentally using both cyclic voltammetry and atomic force microscopy (AFM). For this purpose, three kinds of self-affine fractal Pt film electrodes were first prepared by dc sputtering of Pt on such substrate materials with different roughnesses as polished Al2O3, etched Ni and unpolished Al2O3. Then, the surface morphologies of the electrode specimens were examined by using AFM and cyclic voltammograms (CVs) were measured on the electrode specimens in a 30 wt.% glycerol+70 wt.% (0.01 M K4[Fe(CN)6]+0.5 M Na2SO4) solution at various scan rates. Finally, the fractal dimensions of the electrode surfaces were determined from analyses of AFM images and the power relation between peak current and scan rate in the CVs. All the fractal dimensions determined from the CVs were much smaller than the self-affine fractal dimensions determined by the perimeter–area method. Assuming that the self-affine fractal surface can have a self-similar scaling property, the apparent self-similar fractal dimensions of the self-affine fractal electrodes were determined by a triangulation method. These values agreed well with the fractal dimensions determined from the CVs. From the above results, it is concluded that ionic diffusion towards a self-affine fractal electrode should be described in terms of the apparent self-similar fractal dimension rather than the self-affine fractal dimension.
"...a blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) ...and the illustrations include many superb examples of computer graphics that are works of art in their own right." Nature
The origin, the classification and the effect on catalytic performance of pore texture of heterogeneous catalysts are briefly examined. The techniques and the methods suitable for the determination of related properties (surface area, pore volume and pore size distribution) are reviewed. Particular attention is paid to the most widely used ones: vapour adsorption at low temperature, mercury porosimetry, incipient wetness impregnation and picnometry. Advantages, disadvantages and applicability of each method to different pore textures are pointed out. The best choice of a group of methods, allowing a complete characterization of catalysts, is proposed.
Water-vapor adsorption on poorly crystalline boehmite (PCB) was studied using a gravimetric FTIR apparatus that measured FTIR spectra and water adsorption isotherms simultaneously. The intensity of the delta(HOH) band of adsorbed water changed linearly with water content and this linear relationship was used to determine the dry mass of the sample. Adsorption and desorption isotherms of PCB showed a Type IV isotherm. The BET(H2O) surface area of PCB was 514+/-36 m2/g. The mean crystallite dimensions of PCB were estimated to be 4.5 x 2.2 x 10.0 nm (dimensions along the a, b, and c axes, respectively) based on application of the Scherrer equation to powder diffraction data of PCB. A surface area value of 504+/-45 m2/g calculated using the mean crystallite dimensions was in good agreement with the BET(H2O) surface area. This work also demonstrated a method to determine surface areas for materials with minimal perturbation of their surface structure. In addition, the FTIR spectra of PCB were influenced by changes in water content. The delta(AlOH) band at 835 cm(-1) observed under dry conditions was assigned to the non-H-bonded surface OH groups. As the amount of adsorbed water increased, the intensity at 835 cm(-1) decreased and that at 890 and 965 cm(-1) increased. The 890- and 965-cm(-1) bands are assigned to surface OH groups H-bonded with adsorbed water.
The influence of the surface chemical groups of an activated carbon on the removal of different classes of dyes is evaluated. Starting from the same material (NORIT GAC 1240 PLUS), the following treatments were carried out in order to produce a series of samples with different surface chemical properties but with no major differences in their textural properties: oxidation in the liquid phase with 6M HNO(3) and 10 M H(2)O(2) (acid materials) and heat treatment at 700 degrees C in H(2) or N(2) flow (basic materials). The specific micropores volume and mesopores surface area of the materials were obtained from N(2) adsorption equilibrium isotherms at 77K. The surface chemistry was characterised by temperature programmed desorption, by the determination of the point of zero charge (pH(pzc)) and by the evaluation of the acidity/basicity of the samples. Elemental and proximate analyses were also carried out. Equilibrium isotherms of selected dyes (an acid, a basic and a reactive dye) on the mentioned samples were obtained and the results discussed in relation to their surface chemistry. In general, the Langmuir model provided the best fit for the adsorption data. It is shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H(2) flow at 700 degrees C is the best material for the adsorption of all the tested dyes.
The mode of adsorption of bovine serum albumin (BSA) on porous polyethylene (PE) membrane was studied as a function of time and concentration, which may contribute to the surface coverage. An improved physical model for adsorption is initiated based on the results of the adsorptional and desorptional measurements, FTIR analysis, and AFM observations as well as streaming potential measurements. The results obtained indicate that the adsorptional mode depend on both time and concentration. It is shown that a critical concentration (about 1000 ppm here) exists in the adsorptional process. Below this concentration, the adsorption seems to be conducted in a normal side-on way but time elapse gives rise to greater conformational change than concentration increase; above this concentration, the aggregation of protein molecular plays a decisive role and the adsorption is in an aggregation way, which is similar to end-on, but a relative large gap between the adsorbed molecules exists due to aggregation. This conclusion is general and can be expected to apply in other globular protein-hydrophobic porous surface systems.