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Synthesis and characterization of Ni-doped TiO2 activated carbon nanocomposite for the photocatalytic degradation of Anthracene
Abstract
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Nickel-doped titanium dioxide nanoparticles (NDT) deposited on pine cone activated carbon (PAC) have been successfully synthesized by a hydrothermal method. The as synthesized nanocomposite was characterized by X-ray diffraction pattern (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron (XPS), Fourier transform infrared (FT-IR), UV-visible diffuse reflectance spectra (UV-vis DRS), Photoluminescence (PL), BET surface area, and pHzpc. The characterization results of the prepared nanocomposite revealed that Ni-TiO2 was loaded on the surface of PAC, and had a higher surface area and narrower bandgap than TiO2 nanoparticles. The visible-light photocatalytic activity of the Ni-TiO2@C nanocomposite towards anthracene degradation was found to be 99.9% in 50 mins leading to end products of (1E, 3Z)-hexa-1,3,5-trien-1-ol (1a; m/z = 96), and (1E, 3E)-penta-1,3-dien-1-ol. The synthesized Ni-TiO2@C nanocomposite exhibited a better photocatalytic activity towards the photocatalytic degradation of anthracene as compared to the TiO2 nanomaterial (22.5%) and TiO2/activated carbon nanocomposite (31%) under similar conditions. The photodegradation of anthracene followed the pseudo first-order rate kinetics. The Ni-TiO2@C nanocomposite had excellent regeneration properties till the fifth cycle of use during which it degraded around 73% anthracene.
... The complete removal process is oen divided into two steps: initial adsorption of pollutants on nanocatalyst surfaces, and then photocatalytic disintegration by reactive oxygen species generated by the semiconducting characteristics of nanocatalysts. [50][51][52] The adsorption capacity of nanoparticles was increased by Cu doping due to the large surface area, which also allowed for the rapid transfer of ANT and NAP molecules to active sites. The valence (VB) and conduction (CB) band gap energies of photocatalysts are equivalent to or greater than that of the photons absorbed by the photocatalytic materials. ...
... The comparative decline in the removal efficacy of the real sample compared to the control is caused by two factors: (i) the number of active species is limited according to catalyst dose, which removes both PAHs simultaneously; and (ii) the sample may contains other pollutants (PAHs, heavy metals, and pesticides) despite the NAP and ANT, which further suggests the effectiveness of nanocatalysts. [51][52][53][54][55][56][57][58] Hence, the Cu@ZnO photocatalyst proved to be an efficient sunlight-active catalyst for real samples. ...
This research investigated the detection and removal of priority polycyclic aromatic hydrocarbons (PAHs) from metropolitan rainwater runoff through photocatalytic degradation. The ubiquitous distribution of PAHs in all environment matrices has gained scientific interest because of the risk for the security of drinking water which is a growing concern to the next generation worldwide. Anthracene and naphthalene are primarily used in the petrochemical, chemical, and food industries and are suspected to have carcinogenic and persistent properties and have been detected in rainwater runoff. Herein, a Cu doped ZnO nanocomposite is green synthesized via facile precipitation and used for photodegradation of NAP and ANT in simulated rainwater under natural light exposure. Sharp PXRD peaks confirmed that the spherical nanocomposite had great crystallinity and purity. XPS analysis, PXRD, and FE-SEM confirmed the effective doping of Cu with ZnO. Following this, under various reaction conditions (pollutant: 10–60 mg L⁻¹; catalyst: 2–12 mg; pH: 3–9, dark sunlight, humic acid, and chloride ion: 0.1–1 M), the Cu@ZnO nanocomposite was assessed for the efficient removal of NAP and ANT. Cu@ZnO displayed maximum degradation of NAP (96%) and ANT (94%) at 10 mg L⁻¹ conc. of each PAH with a 10 mg catalytic dose at neutral pH in the presence of direct sunlight. First-order kinetics followed by initial Langmuir adsorption constituted the degradation process. The efficiency of green fabricated Cu@ZnO for the removal of NAP and ANT in real rainwater samples was analyzed by HPLC. Predominant reactive species and safer metabolite formation in the photocatalysis process of PAHs were studied by scavenger and GC-MS analysis. The reusability of the nanocomposite up to nine cycles demonstrated the remarkable sustainability and cost-effectiveness of the nanocomposite. Thus, the Cu@ZnO nanocomposite has good catalytic properties for pollutant remediation, and industrial and other applications in laboratory control as well as real systems.
... They concluded that, among the proposed kinetic models, pseudo-second-order chemical seems to better in long run for treating heavy metals [19,21]. Baruah et al. have reported that titanium dioxide based nanocomposites were found to be more effective than indi- vidual titanium dioxide nanoparticles in photo catalytic degradation of anthracene, which follows pseudo-first-order kinetics [22]. In 2010, Afkhami et al. demonstrated the capability and usefulness of newly modified alumina nanoparticles -immobilized-2,4dinitrophenlhydrazine adsorbent for removal of heavy metal ions in wastewater. ...
... Based on the SEM-EDX analysis, Baruah and co-workers reported that nanocomposites have more area than do individual TiO 2 nanoparticles [22]. ...
Increasing urbanization and industrialization has led to a dramatic increase in demand for clean potable water. Nanotechnology is used in environmental applications to eliminate pollutants, pathogens, and other effluents from water. Nanomaterials have gained importance in sustainable development. Alumina (Al2O3) and its composites are generally used as nanomaterials because of high surface area, porous nature, large number of active sites, formation of meta-stable phase and hexagonal structure, which makes it a potential candidate for water treatment. The nano alumina can be coated on membranes and the composites can be used for purification of water, specifically for the removal of heavy metal ions, dyes and other microbes. The prime focus of the review paper is the treatment of water using alumina composites; the same can be extended to other applications like dye removal and desalination with some modifications.
... This was attributed to the formation of defects that can induce unwanted electron-hole recombination or segregation of metallic nickel without entering the TiO 2 crystal structure. In contrast, Saleem et al. [29] and Baruah et al. [30] reported the enhancement of photocatalytic activity for TiO 2 doped with nickel, in which the fraction of UV light can play an important role. ...
One of the most challenging goals in materials science is to shift the absorption band of TiO2 toward the visible region of the electromagnetic spectrum. This is a fundamental strategy to improve its photocatalytic performance. In this paper, we present a simple methodology based on the sol-gel method, which allows the displacement of the band edge of TiO2, accompanied by the appearance of additional absorption bands in the optical spectrum. In our methodology, TiO2 was synthesized and doped with 5% and 10% w/w nickel. The resulting material was dried at 100 °C and subjected to thermal treatment at 500 °C for 1 h each. The obtained material was characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, diffuse reflectance, X-ray diffraction, Raman spectroscopy, and XPS. Our results indicate that Ni doping of TiO2 was successfully carried out, while NiTiO3 appears from the first drying stage at 100 °C and undergoes the transition from the amorphous to the crystalline phase during the sintering process at 500 °C. Furthermore, all the materials studied showed high catalytic activity under UV irradiation. In particular, the nickel-doped thermally treated materials also exhibited good catalytic performance under visible light, even better than the amorphous phases obtained under UV irradiation.
Graphical Abstract
... This interaction sets off a cascade of reactions that ultimately result in the degradation of pollutants, particularly MO and MB dyes. [69] As the radicals react with the water molecules, they create a series of oxidizing events that lead to the cleavage of molecular bonds within the dye molecules. This breakdown process transforms the complex dye molecules into simpler and less harmful carbon dioxide compounds, ultimately promoting the effective remediation of water pollutants. ...
The alarming global issue of dye contamination in water poses a critical threat to both human health and aquatic ecosystems, exacerbated by the irresponsible discharge of colored pollutants from the textile industry. Amidst various remedies, photocatalysis utilizing Titanium dioxide (TiO2) stands out as a remarkably effective solution for combatting dye pollution. In an endeavor to elevate the efficiency of TiO2, this study dedicated its focus to the successful synthesis of anatase-phase coupled doped Zinc-Cobalt (Zn-Co) TiO2 nanoparticles (TDNPs), achieved through a dual approach involving chemical encapsulation with Polyvinylpyrrolidone (PVP) and green encapsulation with Tinospora Cordifolia (T. Cordifolia). The encapsulated Zn-Co TDNPs underwent meticulous analysis, unveiling a tetragonal crystal structure and presenting a visually appealing spherical morphology, with particle sizes ranging from 61 to 82 nm. The photocatalytic prowess of the encapsulated TDNPs proved to be nothing short of impressive, showcasing an outstanding degradation efficiency of up to 99 % for both methyl orange (MO) and methylene blue (MB) dyes under UV radiation. Beyond their exceptional dye remediation capabilities, these encapsulated TDNPs also exhibited noteworthy antioxidant activity, demonstrating an efficacy of up to 96 and 95 % in the DPPH (2,2-diphenyl-1-picrylhydrazyl) and hydrogen peroxide (HP) assay, respectively. This study not only addresses a critical environmental concern but also highlights the tantalizing potential of encapsulated Zn-Co TDNPs in paving the way for sustainable and effective water treatment solutions.
... Their strong oxidizing nature enables them to effectively break down contaminants into smaller carbon dioxide molecules through a mineralization process. These radicals readily bond with water molecules, resulting in the degradation toward MO and MB dyes [6,33]. ...
Dye contamination in water is a global concern due to its harmful impact on human health and aquatic ecosystems. Particularly, the textile industry contributes hazardous colored pollutants that often find their way untreated into nearby natural water bodies. Among various methods, photocatalysis stands out as the most effective solution for addressing dye pollution, with titanium dioxide (TiO2) being a leading photocatalyst due to its exceptional capability for dye removal from wastewater. To enhance the efficiency of dye degradation under UV light, extensive research has focused on augmenting TiO2 efficiency through doping and altering its morphology. In this study, the anatase phase of cobalt–nickel (Co–Ni)-doped TiO2 nanoparticles (TNPs) was synthesized using both chemical and green methods, employing a microwave-assisted technique. These methods incorporated polyvinylpyrrolidone (PVP) and Tinospora Cordifolia (T. Cordifolia) for chemical and green encapsulation, respectively. Various physicochemical attributes of the encapsulated Co–Ni-doped TNPs were analyzed through a range of characterization spectroscopy. The encapsulated NPs exhibited tetragonal crystal structure and spherical morphology with particle size ranging from 17 to 24 nm. During the evaluation of their photocatalytic performance toward methyl orange (MO) and methylene blue (MB), it was noted that as the dosage of NPs catalysts increased, the degradation rate also showed an augmentation when exposed to UV radiation. About 100% value for degradation was noted for MO and MB dyes'. Furthermore, encapsulated Co–Ni-doped NPs displayed significant antioxidant activity, with efficacy upto 93% for DPPH assay.
... In continuing the mechanism, species such as anthrone and anthraquinone can be produced by hydroxyl radical ( • OH) attack. Still, as these by-products are not fluorescent, no signal is observed[46,47]. The maximum degradation of NAP in the mixture or individual solution was 88% and 79% in 1 minute, respectively(Fig. ...
This study proposes a new approach for the efficient photodegradation of polycyclic aromatic hydrocarbons (PAH) and derivatives. PAH removal was achieved in just a few minutes using a microwave photochemical reactor capable of producing a high concentration of •OH (2.3 mmol L−1 h−1). Fluorescence excitation-emission matrix (EEM) spectroscopy coupled to parallel factor analysis (PARAFAC) was used for quantifying two PAH and one alkylated PAH at low concentrations (μg L−1). These results highlight the high potential of the photochemical degradation system coupled to EEM-PARAFAC as an alternative fast, inexpensive, and efficient approach for environmental remediation studies of PAH.
... Photocatalysts with incorporated carbon materials can be used to degrade volatile organic molecules (VOCs). Incorporating carbon materials with other photocatalysts can enhance photocatalytic oxidation (PCO) performance in a number of ways, including enhanced light absorption, effective charge separation, and high pollutant adsorption capacity (Baruah et al., 2022b). Therefore, a great range of carbon compounds, including porous carbon, graphitic carbon nitride, carbon nanotubes (CNT), AC, and graphene, could be employed as photocatalyst supports because of their specific properties (Pérez-Mayoral et al., 2020). ...
Nowadays, water contamination resulting from the disposal of industrial and urban waste poses a significant threat to marine life and human. Hence, providing an effective treatment approach to reduce the total cost and duration of the wastewater treatment process is crucial. Although the adsorption and photocatalysis methods show superb potential for removing hazardous pollutants from water, their combination through a suitable synthesis route is one of the most effective ways to overcome their limitations. Activated carbon (AC) significantly accelerates the rate of pollutant degradation for AC-based photocatalysts compared to bare photocatalysts because of its ability to increase the number of attachment sites, strengthen the interaction between pollutants and photocatalysts, and facilitate rapid electron transfer to prevent electron or hole recombination. This study aims to investigate four main objectives: 1) evaluating key parameters to enhance the surface characterization of AC-derived from lignocellulosic sources using physical and chemical techniques; 2) Surveying various approaches for synthesizing AC-based photocatalysts; 3) explaining the mechanism of photocatalytic degradation of pollutants and the operating parameters in the wastewater treatment process; and 4) providing an overview of the opportunities, challenges, suggestions, and potential future outlooks. Future studies should focus on understanding the structural properties of AC to design effective photocatalytic systems for degrading hazardous contaminants. Generally, AC-based nanocomposites reduce both process costs and duration and promote environmental sustainability by effectively eliminating pollutants.
... This leads to the tailoring of the bandgap and hence enhances the photo-and electrocatalytic performance of the nanocatalysts [43][44][45][46]. For instance, iron, cobalt, molybdenum, strontium, magnesium or noble metals (Ag, Pt, Au) and non-metal elements (C, N, S) have been exploited as dopants to improve the photocatalytic and electrocatalytic performance of pristine TiO2 [47][48][49][50]. Strontium is a significant alkaline earth metal extensively used in many research fields, electronics, the military industry, the chemical industry, optics, metallurgy, etc. ...
Pristine TiO2 and Sr-doped TiO2 (1%, 2.5% and 5%) nanoparticles were synthesized at low temperatures via an eco-friendly hydrothermal route for water-splitting applications. XRD, EDAX and Raman analysis were performed to analyze the crystallinity, purity and structure of the as-synthesized materials. TEM, SEM, BET and UV-DRS studies were carried out to elucidate the size, morphology, surface area and optoelectronic properties of the nanoparticles. High surface areas of 169, 182, 178 and 141.16 m2 g−1 for pristine TiO2 (12 ± 0.6 nm) and 1% (11.1 ± 0.6 nm), 2.5% (12.1 ± 0.6 nm) and 5% (13 ± 0.7 nm) Sr-doped TiO2 nanoparticles were obtained, respectively. One-percent Sr-doped TiO2 nanoparticles were found to be active photocatalysts, as they showed higher hydrogen production (26.30 mmol). Furthermore, electrocatalysis was investigated for HER and OER in 0.5 N H2SO4 and 0.1 N KOH electrolytic solutions using calomel as a reference electrode, revealing that 1% and 5% Sr-doped TiO2 showed maximum current density for both HER (≈10 mA/cm2) and OER (≈2.49 mA/cm2), with an onset potential of 0.96 V for HER and 1.55 V for OER, and Tafel slopes of 84.09 and 91.60 mV/dec, respectively.
Waste management is an essential issue in environmental management, as the majority of this waste is not reused or has an incorrect destination. In this way, the porongo (Langenatia siceraria) is a curcubitaceae known in the southern region of Brazil and used culturally to prepare the drink in the state of Rio Grande do Sul. However, during its processing, significant amounts of waste are generated becoming a socio-environmental problem. An alternative for the treatment and adequate disposal of this waste is the production of catalysts using Advanced Oxidative Processes (AOPs), highlighting the heterogeneous photocatalysis. The present work denoted ecotechnological strategies for reusing of residual porongo biomass, highlighting its application in heterogeneous photocatalysis to photodegrade organic pollutants.
Being chemically stable, low cost and made from abundant resources, titanium dioxide (TiO2) possesses the most desired advantages for photocatalytic applications. However, the intrinsic limits of high surface hydrogen adsorption energy, wide band gap, low separation rate and rapid recombination of the photogenerated charge carriers greatly hamper its utilization. To address these issues, the present work combines density functional theory (DFT) calculations with rational modifications of TiO2 with nickel doping and an ultra-thin shield of fluorinated carbon (FNT) for application in the photocatalytic hydrogen evolution reaction (HER). Comprehensive studies imply that the synergistic modifications not only optimize the surface H adsorption, but also facilitate the interfacial charge transfer and simultaneously prevent the photochemical and chemical corrosion of the catalysts. In good agreement with the theoretical predictions, the resulting FNT photocatalysts demonstrate an optimal HER efficiency of 13.0 mmol g-1 h-1, nearly 33-times and over three-times beyond that of the pristine TiO2 (0.4 mmol g-1 h-1) and the Ni-doped TiO2 (4.2 mmol g-1 h-1), respectively. Moreover, the composite also exhibits excellent stability with a well-reproducible HER performance over a 66-hour cyclic HER test of 15 cycles.
This paper describes the photocatalytic degradation of the organophosphorus insecticide chlorpyrifos in aqueous suspensions using Schima wallichii activated carbon/ZrO2-ZnO (SWAC/ZrO2-ZnO) nanocomposite in UV light. Analytical techniques such as XRD, FT-IR, TEM-SEAD, XPS, PL, and BET analyzer were used to characterize the SWAC/ZrO2-ZnO nanocomposite. The BET surface area of the photocatalyst was found to be 223.387 m2g−1, having a total pore volume of 0.1845 cm3g−1. The photocatalytic degradation of chlorpyrifos followed pseudo-first-order rate kinetics with a half-life period (t1/2) of 7.088 mins and Kap (apparent rate constant) of 0.09778 min−1. The mechanism of composite formation was explained using DFT investigations, which demonstrated a favorable immobilization of ZrO2-ZnO on SWAC. Chemical descriptors gained from DFT investigations, such as HOMO-LUMO energy, ionization energy, dipole moment, chemical softness, and chemical hardness, supported an understanding of the relative efficiency and reactivity of ZrO2-ZnO and SWAC/ZrO2-ZnO towards chlorpyrifos degradation.
In this research, we report a comparative study of trilayer TiO2(60 nm)/Cu/TiO2(60 nm) thin film as a function of different Cu interlayer thickness (20, 40 and 60 nm), fabricated by atomic layer deposition (ALD) and DC magnetron sputtering. The surface morphology, elemental information and optical properties, were tested as a function of Cu interlayer thickness by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX) and double beam spectrophotometer (UV–vis) respectively.The growth mechanism and the microstructural conversion were investigated. The absorption spectrum was mesured and used to calculate the energy band gap (Eg). The obtained results show that the increase of the Cu interlayer enhance the activity of photocatalysis by employing distinct modification strategies to decrease the indirect optical band gap energy from 2.85 to 1.86 eV, and conventionally making the photocatalyst efficient to absorb visible light range. The role of the optical energy band gap Eg as well as the average electronegativity (χ) as basic parameters of optical basicity (Å) and refractive index (n) has been emphasized. Values of electronegativity (χ), phase velocity (V) and transmission coefficient (TC) decreased, while the refractive index, optical basicity, electronic polarizability (αe), and reflection loss (RL) increased with increasing Cu interlayer thickness. A good agreement is observed among the selected parameters. The results demonstrate that the ALD and the DC magnetron sputtering are promising techniques for preparing TiO2/Cu/TiO2 thin films, with different thickness of copper (Cu), that can be used in low-cost mid-IR detection and can enhanced the properties of optoelectronic devices.
In this work, the synthesis, characterization, and photocatalytic activity of iron-doped titanium dioxide nanoparticles (FDT) supported on environmentally benign activated carbon (PAC) has been discussed. The photocatalytic activity of the nanocomposite was investigated for the degradation of Congo red (CR) dye from aqueous solution under visible light (520 nm), and it was observed that 100% degradation for 20 ppm CR solution took place within 60 mins. The experimental data of photodegradation of CR using the FDT/PAC nanocomposite had the highest correlation with Langmuir Hinshelwood model and pseudo-first-order rate kinetics with an apparent rate constant of 0.05341 min−1 and half-life period of 12.97 mins, respectively. The thermodynamics study revealed that the degradation process is exothermic and spontaneous. The effect of interfering ions on the degradation of CR solution was also examined. The photocatalytic antibacterial activity of the nanocomposite was tested against two bacteria pathogens, Escherichia coli and Staphylococcus aureus, and it was found that for the concentration of 105 CFU ml−1, 100% photocatalytic inactivation was achieved for both Escherichia coli in 120 mins and Staphylococcus aureus in 75 mins under visible light irradiation. The total electrical energy consumed and operating cost were measured and the total operating cost was 312.50, 236.74, and 166.67 INR (Indian rupee) for 20 ppm, 60 ppm, and 100 ppm CR dye removal using 0.06 g FDT/PAC nanocomposite, respectively.
Iron-doped titanium dioxide nanoparticles, with Fe/Ti atomic ratios from 0% to 10%, were synthesized by flame spray pyrolysis (FSP), employing a single-step method. Ferrocene, being nontoxic and readily soluble in liquid hydrocarbons, was used as the iron source, while titanium tetraisopropoxide (TTIP) was used as the precursor for TiO 2. The general particle characterization and phase description were examined using ICP-OES, XRD, BET, and Raman spectroscopy, whereas the XPS technique was used to study the surface chemistry of the synthesized particles. For particle morphology, HRTEM with EELS and EDS analyses were used. Optical and magnetic properties were examined using UV-vis and SQUID, respectively. Iron doping to TiO 2 nanoparticles promoted rutile phase formation, which was minor in the pure TiO 2 particles. Iron-doped nanoparticles exhibited a uniform iron distribution within the particles. XPS and UV-vis results revealed that Fe 2+ was dominant for lower iron content and Fe 3+ was common for higher iron content and the iron-containing particles had a contracted band gap of~1 eV lower than pure TiO 2 particles with higher visible light absorption. SQUID results showed that doping TiO 2 with Fe changed the material to be paramagnetic. The generated nanoparticles showed a catalytic effect for dye-degradation under visible light.
Along with industrialization and rapid urbanization, environmental remediation is globally a perpetual concept to deliver a sustainable environment. Various organic and inorganic wastes from industries and domestic homes are released into water systems. These wastes carry contaminants with detrimental effects on the environment. Consequently, there is an urgent need for an appropriate wastewater treatment technology for the effective decontamination of our water systems. One promising approach is employing nanoparticles of metal oxides as photocatalysts for the degradation of these water pollutants. Transition metal oxides and their composites exhibit excellent photocatalytic activities and along show favorable characteristics like non-toxicity and stability that also make them useful in a wide range of applications. This study discusses some characteristics of metal oxides and briefly outlined their various applications. It focuses on the metal oxides TiO2, ZnO, WO3, CuO, and Cu2O, which are the most common and recognized to be cost-effective, stable, efficient, and most of all, environmentally friendly for a sustainable approach for environmental remediation. Meanwhile, this study highlights the photocatalytic activities of these metal oxides, recent developments, challenges, and modifications made on these metal oxides to overcome their limitations and maximize their performance in the photodegradation of pollutants.
In this study, phthalocyanine (Pc)–TiO2 nanocomposites were prepared via in situ hydrothermal method. The metal-free, zinc(II), cobalt(II), nickel(II) and copper(II) Pc compounds were used for formation of nanocomposites. A total of 5 different Pc–TiO2 nanocomposites was successfully prepared by hydrothermal method. The prepared nanocomposites were also characterized by FT-IR, XRD, FEG-SEM, EDX, UV-DRS and BET techniques. All prepared nanocomposites were tested for their photocatalytic activity to be used as photocatalyst. For this purpose, photocatalytic activities of Pc–TiO2 nanocomposites were evaluated for the degradation efficiency of methylene blue (MB) under visible light irradiation by monitoring the UV–Vis absorption spectra. Based on the conducted studies, it was observed that Pc–TiO2 photocatalysts have significant photocatalytic activities on degradation of MB under visible light irradiation, resulting in complete degradation of MB in 100–130 min for full degradation (100%). Furthermore, the reusability studies revealed that photocatalysts show 76% activity even after 5 uses.
Graphic abstract
In this study, we prepared and characterized TiO2 nanocomposites using peripherally tetra-substituted metal-free, Zn(II), Co(II), Ni(II) and Cu(II) phthalocyanine complexes. The phthalocyanine–TiO2 nanocomposites showed significant photocatalytic activities for cleaning a common organic pollutant under the visible light irradiation.
In this work, the Ni-doped anatase TiO2 single crystals loaded on activated carbon (Ni-T/AC) were synthesized by a sol–gel method. The chemical compositions and physical properties of as-prepared materials were analyzed by XRD, TEM, BET, FTIR, XPS, and PL characterizations. The obtained results implied that all of samples presented anatase phase with a clear mesoporous structure. The photocatalytic properties of nanocomposites were evaluated through photodegradation of crystal violet (CV), basic fuchsine (BF), and malachite green (MG). The results revealed that the catalyst Ni-T/AC-loaded AC exhibited an excellent photocatalytic activity compared with the original TiO2, and the photodegradation efficiency for CV, BF, and MG is 99.00%, 94.85%, and 98.89% after 120 min of irradiation, respectively. This enhancement may be ascribed to the small crystallite size, large specific surface area, and pore volume of the photocatalysts. In addition, the possible degradation mechanism and pathway for triphenylmethane dyes (TPMs) were also well investigated. This work provides a new, low-cost, and effective route to improve the performance of TiO2 for effective removing TPMs.
The utilization of solar energy to produce hydrogen from water is showing increased importance and desirability in the field of artificial photosynthesis to produce clean and sustainable fuels. In a typical three‐component dye‐sensitized semiconductor system for photocatalysis, the dye sensitizer plays an essential role of energy antenna for harvesting visible light and promoting the reduction reaction to generate hydrogen. In recent decades, a lot of attention has focused on metal‐free organic sensitizers, which have the advantages of low cost, high molar extinction coefficient, good modifiability and, most importantly, ability to avoid the use of noble metal ions. This Review enumerates the design strategies, specific properties and photocatalytic performances of metal‐free sensitizers in the past 30 years and concludes their evolution process. The advantages of different types of metal‐free sensitizers are highlighted and the instructively enlightening experiences are systematic summarized.
Photocatalysts are highly applicable in treatment of the water pollution. However, most of the applied photocatalysts suffer from the inapplicability and non-recyclability which limited their application. Herein, applicable and recyclable effective photocatalyst composites of Ag2WO4@MIL-125-NH2@cotton and Ag3VO4@MIL-125-NH2@cotton successfully prepared by direct synthesis of MIL-125-NH2 and Ag2WO4 or Ag3VO4 within the cotton fabric as supported template, sequentially. Agglomerated rock structure of Ag2WO4@MIL-125-NH2 and smaller particles of Ag3VO4@MIL-125-NH2 formed onto the cotton. The prepared composites applied as photocatalysts in the degradation of Methylene Blue (MB) and Rhodamine B (RhB) dyes in the visible light. The highest photodegradtion of dyes observed for Ag2WO4@MIL-125-NH2@cotton and Ag3VO4@MIL-125-NH2@cotton composites because of their low optical band gaps (2.36 eV and 1.87 eV) and their quenching in luminescent spectrum which helped in the ease transfer of photoexcited electrons. The rate constant (k2) for the photodegradation of MB (RhB) dye reduced significantly from 1.78 × 10–3 (2.8 × 10–3) L/mg min to 0.43 × 10–3 (1.04 × 10–3) L/mg min and 0.29 × 10–3 (0.79 × 10–3) L/mg min, when Ag2WO4 and Ag3VO4 incorporated in MIL-125-NH2@cotton composite, respectively. After 4 recycling process, the photodegradation activity of the applied composites diminished from 86–92% (68–80%) to 58–65% (47–54%). The obtained results declared the topmost photocatalytic activity in daylight of the recyclable prepared tri-component composites, reflecting their promising potentials in environmental applications.
Graphic abstract
Photocatalysis is an alternative wastewater treatment method for the removal of toxic pollutants. The present work describes the hydrothermal synthesis of a new photocatalytic composite material involving activated carbon (PAC) and titanium dioxide nanoparticles (TiO2-NP) and its application for removal of Alizarin Red S (ARS) dye from wastewater. Characterization of the TiO2-NP/PAC composite was done by different analytical methods like SEM–EDX, XRD, FT-IR, photoluminescence, pHZPC and UV–visible diffuse reflectance spectroscopy. In order to evaluate the efficacy of the composite in the simultaneous adsorption and degradation of an anionic dye, ARS aqueous solution at varying TiO2-NP/PAC dosage, contact time, ARS concentrations and pH was evaluated. A composite dosage of 0.05 g shows 99.10% degradation of 20 mg l−1 ARS dye concentration in 80 min contact time at pH 2. It was observed that photocatalytic degradation of the dye followed pseudo-first-order rate kinetics and the adsorption isotherm was found to be best fitted with Freundlich isotherm model. The negative enthalpy and free energy indicated an exothermic and spontaneous process. DFT studies were used to explain the mechanism of formation of the composite, and results revealed a favourable immobilization of TiO2-NP on PAC via O-linkage of the O–Ti–O bond resulting in the formation of TiO2-NP/PAC composite. Chemical descriptors such as dipole moment, ionization energy, chemical softness and hardness and HOMO–LUMO energy obtained from DFT studies helped in understanding the comparative efficiency and reactivity of PAC and TiO2-NP/PAC towards ARS degradation.
Polycyclic hydrocarbons constitute an important source of very dangerous pollutants. Different materials have been used as adsorbent for their removal, but they present difficulties in the separation process. The use of a material based on metal-organic framework (MOF) with large pores and high surface area and magnetic nanoparticles with superparamagnetic properties is an interesting strategy. In this work a magnetic composite based on MOF (MIL-101) and Fe3O4 magnetic nanoparticles (Fe3O4/MIL-101) was obtained by a simple synthesis method and used as adsorbent for the removal of anthracene. The composite was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that kinetic data followed a first-order model and equilibrium data were well fitted by the Langmuir model. The maximum adsorption capacity was 12.7 mg/g at pH 6 in 60 min of exposure. The composite was applied for the adsorption of anthracene in water samples reaching more than 95% of anthracene removal in 1 h of contact. The composite material was effectively separated using an external magnet, and no further centrifugation or filtration processes were needed. This composite is a great alternative to remove polycyclic hydrocarbons from water samples and has potential to extend to the removal of other contaminants.
Three adsorbents based on the metal–organic frameworks (MOFs), viz.; MIL-88(Fe), NH2-MIL-88(Fe), and mixed-MIL-88(Fe) were synthesized using a microwave-assisted solvothermal technique. The as-synthesized MOFs were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The MOFs were shown to possess highly crystalline and porous structures with specific surface areas of 1240, 941, and 1025 m² g⁻¹ and pore volumes of 0.7, 0.6 and 0.6 m³ g⁻¹ for MIL-88(Fe), NH2-MIL-88(Fe) and mixed-MIL-88(Fe), respectively. Faster removal of a model polycyclic aromatic hydrocarbon, anthracene (ANT) within 25 minutes, was achieved when these MOFs were used as adsorbents in water. The removal efficiency was 98.3, 92.4 and 95.8% for MIL-88(Fe), NH2-MIL-88(Fe) and mixed-MIL-88(Fe), respectively. The kinetics and isotherms of the process were best statistically described by pseudo-second-order and Langmuir models, respectively, while the thermodynamic studies revealed the exothermic and spontaneous nature of the process. Docking simulations were found to be consistent with the experimental results with MIL-88(Fe) showing the best binding capacity with the ANT molecule.
Persistent organic pollutants (POPs) present in foods have been a major concern for food safety due to their persistence and toxic effects. To ensure food safety and protect human health from POPs, it is critical to achieve a better understanding of POP pathways into food and develop strategies to reduce human exposure. POPs could present in food in the raw stages, transferred from the environment or artificially introduced during food preparation steps. Exposure to these pollutants may cause various health problems such as endocrine disruption, cardiovascular diseases, cancers, diabetes, birth defects, and dysfunctional immune and reproductive systems. This review describes potential sources of POP food contamination, analytical approaches to measure POP levels in food and efforts to control food contamination with POPs.
This paper presents a comparative review of arsenite (As(III)), arsenate (As(V)), and fluoride (F ⁻ ) for a better understanding of the conditions and factors during their adsorption with focus on (i) the isotherm adsorption models, (ii) effects of pH, (iii) effects of ionic strength, and (iv) effects of coexisting substances such as anions, cations, and natural organics matter. It provides an in-depth analysis of various methods of arsenite (As(III)), arsenate (As(V)), and fluoride (F ⁻ ) removal by adsorption and the anions’ characteristics during the adsorption process. The surface area of the adsorbents does not contribute to the adsorption capacity of these anions but rather a combination of other physical and chemical properties. The adsorption capacity for the anions depends on the combination of all the factors: pH, ionic strength, coexisting substances, pore volume and particles size, surface modification, pretreatment of the adsorbents, and so forth. Extreme higher adsorption capacity can be obtained by the modification of the adsorbents. In general, pH has a greater influence on adsorption capacity at large, since it affects the ionic strength, coexisting anions such as bicarbonate, sulfate, and silica, the surface charges of the adsorbents, and the ionic species which can be present in the solution.
In this work, Ag doped nano TiO2 photocatalysts were synthesized in powder form by hydrothermal method at 180 ºC in 120 min using different reduction agents. The synthesized powders were characterized by powder X-ray diffraction (XRD), Energydispersive X-ray spectroscopy (EDS), Surface area measurements (BET), Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses. The effect of reduction agents on the morphological properties of Ag doped nano TiO2 has been studied. We have been observed that the use of different reduction agents affects the particle size and surface area. Ag doped nano TiO2 photocatalysts were coated to the ceramic pellets by dip coating technique for photocatalytic study. Photocatalytic properties of the synthesized powder were examined in a circulating aquarium filled with indigo blue (IB) solution under UV irradiation. Periodical UV spectrophotometric analysis showed that indigo blue (IB) has been degraded and its concentration has decreased under UV irradiation by time.
Photocatalysis with modified titania is a promising approach to improve both air and health quality. Modified titania with novel photocatalytic properties under indoor light irradiation leads to smart coatings, which are benchmark materials suitable for their indoor applications. It is generally accepted that the photocatalytic activity is affected by the light absorption, charge creation/recombination rate and surface reactivity. In this contribution we focus on modified TiO2 as catalyst in heterogeneous photo-catalytic processes and address the efficiency of TiO2 -based building and construction materials on the removal of environmental pollutants indoors and outdoors. We also present data on the presence of eventually formed, toxicologically relevant and harmful by-products as the result of the photo-induced degradation of pollutants in an effort for better evaluation of induced risks for human health from the application of TiO2 modified materials. Finally, we present recent results on the disinfection performance of these material and the inactivation of severe pathogens contained in water and indoor air environments.
Anthracene, a three ringed polycyclic aromatic hydrocarbon is a widely known hazardous ubiquitous environmental pollutant. The present study investigates the efficiency of activated carbon developed using banana peel as a precursor material. The influence of variation of shaking time, adsorbent dose, initial concentration, temperature and pH has been studied under a set of diverse conditions. The amount of anthracene in aqueous medium continuously decreases with the shaking time and acquire a constant value after 70 min. The adsorbent dose of 8 mg was found to be sufficient for the adsorption of anthracene in the present study. The maximum adsorption of anthracene was at pH 2 and it was reduced with the increase in solution pH. Among the studied temperature range, the removal of anthracene was higher at 50 °C, indicating endothermic nature of the adsorption. The data obtained were analysed with Langmuir and Freundlich adsorption isotherms and parameters corresponding to both isotherms were evaluated. The work provides an efficient method for the removal of priority pollutant anthracene from aqueous media.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants generated primarily during the incomplete combustion of organic materials (e.g. coal, oil, petrol, and wood). Emissions from anthropogenic activities predominate; nevertheless, some PAHs in the environment originate from natural sources such as open burning, natural losses or seepage of petroleum or coal deposits, and volcanic activities. Major anthropogenic sources of PAHs include residential heating, coal gasification and liquefying plants, carbon black, coal-tar pitch and asphalt production, coke and aluminum production, catalytic cracking towers and related activities in petroleum refineries as well as and motor vehicle exhaust. PAHs are found in the ambient air in gas-phase and as sorbet to aerosols. Atmospheric partitioning of PAH compounds between the particulate and the gaseous phases strongly influences their fate and transport in the atmosphere and the way they enter into the human body. The removal of PAHs from the atmosphere by dry and wet deposition processes are strongly influenced by their gas/particle partitioning. Atmospheric deposition is a major source for PAHs in soil.
Many PAHs have toxic, mutagenic and/or carcinogenic properties. PAHs are highly lipid soluble and thus readily absorbed from the gastrointestinal tract of mammals. They are rapidly distributed in a wide variety of tissues with a marked tendency for localization in body fat. Metabolism of PAHs occurs via the cytochrome P450-mediated mixed function oxidase system with oxidation or hydroxylation as the first step.
Several different remediation technologies have been tested in efforts to remove these environmental contaminants. Among them, bioremediation is showing particular promise as a safe and cost-effective option. In spite of their xenobiotic properties, a variety of genera of gram-positive and -negative bacteria, fungi and algae have been isolated and characterized for their ability to utilize PAHs.
The aim of this review is to discuss PAHs impact on the environmental and the magnitude of the human health risks posed by such substances. They also contain important information on concentrations, burdens and fate of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. The main anthropogenic sources of PAHs and their effect on the concentrations of these compounds in air are discussed. The fate of PAHs in the air, their persistence and the main mechanisms of their losses are presented. Health hazards associated with PAH air pollution are stressed.
Zinc oxide nanoparticles were prepared using corriandrum sativum leaf extract and zinc acetate dihydrate. It was utilized as a photocatalyst for the degradation of anthracene. The catalyst was characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, dynamic scattering light, Raman spectrometry and UV-vis spectrophotometry. The catalyst was used in a bench-scale design for degradation of anthracene. The factors affecting the photocatalytic degradation efficiency, including irradiation time, loading catalyst doses, and initial concentration of anthracene were investigated. The results obtained showed that the photocatalytic degradation efficiency was increased with both the decrease of the initial anthracene concentration and the increase of the photocatalyst doses. The optimum photocatalytic degradation was obtained at pH 7, irradiation time of 240 min and loading catalyst dose of 1000 μg L-1. Under these conditions, the photocatalytic degradation percentage of anthracene was 96%. The byproduct was the much less toxic (9, 10-anthraquinone) and a small amount of phthalic acid as confirmed by gas mass spectrometry and high-pressure liquid chromatography. The kinetic studies revealed that the photocatalytic degradation process obeyed the Langmuir-Hinshelwood model and followed a pseudo-firstorder rate expression.
The photocatalytic activity of methyl orange (MO) in aqueous solution was studied using the hydrothermal synthesis of activated carbon-loaded TiO2 at different weight ratios. The hydrothermal process was conducted at a temperature of 180°C for 12 h in order to obtain a high surface area and porosity for the purpose of degradation activity. The results indicated that TiO2-PEG-Ac (0.50%) exhibited better photocatalytic performance compared to other prepared photocatalysts. The photodegradation process was observed to be pH dependent, since almost 100% of MO removal was possible in an acidic medium. In contrast, the degradation activity seems to be diminished in basic media. The overall photocatalytic activity of TiO2 was enhanced due to the presence of porous activated carbon as co-catalyst and support.
This review is focused on studies related to the elimination of organic pollutants present in aqueous systems by titanium dioxide photocatalyst under visible light illumination. The titanium dioxide semi-conductor has emerged as a very promising technology for the oxidation and mineralization of aqueous organic pollutants because of its properties such as high stability, low cost and non-toxicity. This photocatalytic process has also been used for the oxidation of organic pollutants present in air and soil besides water, in addition to the production of electricity and hydrogen in photoelectrochemical cells fed with organic wastes which renders benefits to the environment. This work covers different approaches reported in the literature for the degradation of aqueous organic pollutants by heterogeneous titanium dioxide photocatalysis. With attention given to influencing parameters, such as catalyst preparation, modification, loading and phase, pH, annealing temperature, bias potential application and inorganic ions. Such parameters are paramount to the photoactivity of this semiconductor, particularly under visible light radiation; conditions of which are imperative for viable technological green application of the phenomena.
X-ray diffraction (XRD) is a powerful nondestructive technique for characterizing crystalline materials. It provides information on structures, phases, preferred crystal orientations (texture), and other structural parameters, such as average grain size, crystallinity, strain, and crystal defects. X-ray diffraction peaks are produced by constructive interference of a monochromatic beam of X-rays scattered at specific angles from each set of lattice planes in a sample. The peak intensities are determined by the distribution of atoms within the lattice. Consequently, the X-ray diffraction pattern is the fingerprint of periodic atomic arrangements in a given material. This review summarizes the scientific trends associated with the rapid development of the technique of X-ray diffraction over the past five years pertaining to the field of pharmaceutical industry, forensic science, geological applications, microelectronics and glass industry, as well as in corrosion analysis.
Polycyclic aromatic hydrocarbons (PAHs) represent a large class of persistent organic pollutants in an environment of special
concern because they have carcinogenic and mutagenic activity. In this paper, we focus on and discuss the effect of different
parameters, for instance, initial concentration of Anthracene, temperature, and light intensity, on the degradation rate. These
parameters were adjusted at pH 6.8 in the presence of the semiconductor materials (TiO2) as photocatalysts overUVlight.Themain
product of Anthracene photodegradation is 9,10-Anthraquinone which isidentified and compared with the standard compound by
GC-MS. Our results indicate that the optimum conditions for the best rate of degradation are 25 ppmconcentration of Anthracene,
regulating the reaction vessel at 308.15K and 2.5mW/cm2 of light intensity at 175mg/100mL of titanium dioxide (P25).
The development and investigation of environmentally-friendly photocatalysts remain a challenge for eco-system remediation concerns. Herein, an ultrasonically-driven, biogenic, green synthesis of titanium dioxide (TiO2) nanoparticles (NPs) utilizing the extract of Mentha Aquatica leaves is reported. The TiO2 nanoparticles were further functionalized with carbon (TiO2@Carbon). The product composition and structure were examined through Raman, BET, and XPS analysis. The XRD studies confirmed the anatase phase of TiO2 NPs. The [email protected] NPs displayed enhanced photocatalytic activity(doubled) compared to pristine TiO2 due to their increased surface area, a bathochromic shift in the optical absorption band, and effective charge separation. Significantly, greater than 90% RhB dye was decayed via photocatalytic oxidation method, which is validated via trapping active species experiment. Carbon is a powerful substrate for the TiO2 hybrid and can be reused over successive five catalytic cycles. The experimental results demonstrated the [email protected] as a potential candidate for highly-efficient, eco-friendly, reusable, cost-effective photocatalyst.
Photocatalytic studies are primarily focused on the low cost and sustainable materials possessing with suitable bandgap and higher surface area. The ultra-fast electron-hole pair recombination and limited light absorptions are affecting the photocatalysts in an adverse manner, which can be unravelled by choosing an efficient combination of photocatalysts and suitable co-catalyst/support materials. The present work explores the combination of low-cost and high potentials activated carbon and TiO2 as a nanocomposite, which was prepared through a one-pot hydrothermal process. The hydrogen production studies were carried out under natural solar light irradiation. The influence of the annealing temperature of the prepared Activated carbon/TiO2 catalysts on photocatalytic activity was discussed. Among the synthesized photocatalysts, calcined at 400 °C for 2h was found to be the best catalyst which was exhibited a 3.5 times higher hydrogen production rate than the pristine TiO2 while tested with purified water. Importantly, the same nanocomposite was also tested for hydrogen production from simulated seawater and it showed a hydrogen production rate is 20,383 μmol g⁻¹ h⁻¹, which is 2.4 times higher than the purified water. The enhanced hydrogen production rate is due to their narrowing bandgap of AC-TiO2 nanocomposite and these results offered more light absorption compared to the pristine TiO2. Moreover, these results were proved with the analysis of UV-DRS and valence band X–PS characterization techniques. The X-RD, Raman, TEM, and PL analysis were also examined to investigate the crystallinity, morphology, and recombination rates of synthesized catalysts.
This study reports the application of immobilized Ag/TiO2 onto coconut and sisal fibers to anthracene degradation via the UV-vis radiation. The fibers were previously treated with hot water and CTAB to clean their impurities surfaces. Immobilizations of Ag/TiO2 to the fibers were performed by anchorage of the catalysts via the post-synthesis method. The materials were characterized using AAS, TGA, XRD, UV-vis DRS, FTIR, STEM, EDS, and XPS analysis. FTIR and XPS results indicated the presence of hydroxyl groups and different silver species (Ago, Ag+, and Ag2+) on the catalyst surface. Immobilized Ag/TiO2 exhibited higher activity as compared to suspended Ag/TiO2 and TiO2. Ag/TiO2 immobilized on fibers treated with CTAB promoted the full anthracene photodegradation within 2h at 40 °C. The results demonstrated that sisal and coconut fibers could be used as a support for Ag/TiO2.
The aim of the present study was to synthesis Ni-doped TiO2 nanoparticles (NPs) in order to evaluate their effectiveness in photocatalytic degradation of formaldehyde in the aqueous phase. The Ni-doped TiO2 NPs were synthesised using a mild hydrothermal method. They were then immobilized on glass plates by the calcination method. Characterisation of Ni-doped TiO2 NPs was also carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The SEM images showed the uniform distribution of as-synthesised NPs on the surface of glass plates, with multidimensional crystalline structures. The results indicated that increasing the dopant weight ratio to 0.7% enhanced the photocatalytic degradation efficiency of formaldehyde; however, a further increase in the dopant weight ratio reduced the process efficacy. According to the results, increasing the initial pH from acidic and neutral to alkaline conditions decreased the efficacy of the process. Furthermore, the results showed that increasing the amount of nanocatalyst and decreasing the initial concentration of formaldehyde favoured the photocatalytic degradation of formaldehyde.
This paper reports the synthesis of pure ZnO, Gd and Nd co-doped ZnO nanorods based nanocomposites via simple hydrothermal method. Subsequently, the prepared photocatalysts were characterized using XRD, SEM/EDX, TEM, UV–visible and PL spectroscopy. The XRD results demonstrate that Gd and Nd ions were incorporated into ZnO lattice in the synthesized ZnO based nanocomposites and showed hexagonal wurtzite structure. The SEM and TEM results show that nanorods having nanoscale diameter and length were successfully synthesized by hydrothermal method. The UV–visible spectroscopy verified that the band gap of ZnO was reduced due to incorporation of Gd and Nd into ZnO photocatalyst. Similarly, Gd and Nd incorporation into ZnO was found effective to reduce the recombination of electrons and holes as confirmed by PL spectroscopy. Moreover, the prepared nanocomposites with various atomic ratios (0.5–2%) were tested for photocatalytic degradation of methylene blue (MB), under visible light irradiation. The highly efficient and optimized 1.5% Nd/ZnO nanocomposite demonstrated enhanced photocatalytic performance for the degradation of methylene blue compared to pure ZnO and other nanocomposites. Furthermore, the recycling results show that the 1.5% Nd/ZnO nanocomposites displayed good stability and long-term durability. These finding suggest that the ZnO based nanocomposite could be efficiently used in various energy and environmental applications.
TiO2 modified oxygen functionalized activated carbon ([email protected]) loaded nickel-based catalysts (Ni/[email protected]) were synthesized and applied in chloronitrobenzenes (CNB) hydrogenation to chloroanilines (CAN). The characterization results indicate that introduction of TiO2 restrains nickel nanoparticles sintering and improves the stability of the catalysts by strong metal-support interaction. Additionally, the XPS results suggest that the electron donating effect of Ti3+ produces electron-rich Ni (Niδ-), which inhibits C-Cl moiety adsorption. The formed Niδ- species might induce the electron-rich hydrogen (H-) generation which facilitates the nucleophilic attack on -NO2 rather than the electrophilic attack on C-Cl bond. Furthermore, the electron-donating ability of -NH2 could be reduced because of the interaction between the -OH in [email protected] and -NH2 in CAN. Hence, the dechlorination is inhibited and the selectivity to m-CAN is up to 99.0%. The catalytic performance of Ni/[email protected] could be maintained after fifth cycles.
Titanium dioxide remains a benchmark photocatalyst with high stability, low cost, and less toxicity, but it is active only under UV light; thus, in practical applications using visible light, its catalytic reactions are stalled. To enhance its catalytic activity under visible light, non-metal/codoped TiO2 structures are being studied. These structures improve the photocatalytic activity of TiO2 in visible light by reducing its energy bandgap. This might be useful in wastewater treatment for the photocatalytic degradation of organic contaminants under visible and UV light irradiation. In this intensive review, we describe recent developments in TiO2 nanostructured materials for visible-light driven photocatalysis, such as (i) mechanistic studies on photo-induced charge separation to understand the photocatalytic activity and (ii) synthesis of non-metal doped/codoped TiO2 and TiO2 nanostructured hybrid photocatalysts. Furthermore, the effects of various parameters on their photocatalytic efficiency, photodegradation of various organic contaminants present in wastewater, and photocatalytic disinfection are delineated.
Polycyclic aromatic hydrocarbons (PAHs) are causing environmental concerns due to their persistent nature and carcinogenicity. Hence, their removal through advanced nanomaterials with characteristics of low-cost and high efficiency is essential. In view of this, bimetallic oxides (BMOs) nanocomposites of NiO-ZnO, ZnCo2O4, MnCo2O4 and CoFe2O4 were synthesized via green route using leaf extract of Aegle marmelos. Subsequently, these BMOs were investigated for photocatalytic removal of selected PAHs like anthracene (ANTH) and phenanthrene (PHEN) from water. Nanospheres of NiO-ZnO, ZnCo2O4, and CoFe2O4 and nanosheets of MnCo2O4 with particle size range of 10-30 nm were confirmed by transmission electron microscopy. At neutral pH, nanocomposites showed excellent ability in degrading 2 mg L-1 of PAHs (ANTH: 98%; PHEN: 93%) within 12 h under the exposure of sunlight. Among the synthesized BMOs, NiO-ZnO was found best followed by ZnCo2O4, MnCo2O4 and CoFe2O4. This fact is attributed to the highest surface area (129 m2 g-1) and particles stability (zeta potential: -30 eV) of NiO-ZnO. Photodegradation of PAHs by nanocomposites followed first order kinetics and fitted in Langmuir model for adsorption. Higher degradation under sunlight and lower removal efficiency with scavenger confirmed the photodegradation activity of nanocomposites. Overall, reusable (n = 10) nanocomposites with no loss of activity have high photocatalytic potential in the removal of carcinogenic PAHs.
The activity and separation performance of nano-structure photocatalyst have always been the focus in the field of environmental pollutant removal. In this work, BiOCl/diatomite composites were successfully fabricated via a simple hydrolysis method, which could meet the above two requirements. The superior performance of composites was explained by using X-ray diffractometer (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that the tetragonal phase BiOCl and diatomite coexisted in the composites, producing the synergistic effect. The diatomite had the high adsorption and silicon hydroxyl groups while the BiOCl had the exposed (0 0 1) facets. Diatomite as a carrier was actually equivalent to a solid dispersant, which could immobilize BiOCl microspheres evenly on its surface and prevent their aggregation, guaranteeing more active sites of BiOCl be exposed and promoting the transfer and separation of photo-induced carriers. The prepared BiOCl/60%D presented 94% removal efficiency for ciprofloxacin (CIP) under simulated solar light within 10 min irradiation, and also presented a 42.9% of total organic carbon (TOC) removal after 240 min. Despite the mineralization of CIP was incomplete, toxicity assessment indicated effective elimination of CIP antibacterial property by BiOCl/60%D in a short time. Moreover, the BiOCl/60%D exhibited good stability and reusability. The formation mechanism of BiOCl/diatomite composites was speculated, meanwhile, the photocatalytic degradation mechanism and pathways of CIP were also deduced by using radicals trapping experiments, electron spin resonance (ESR), high performance liquid chromatography (HPLC) and mass spectrometry (MS). This study provided a simple method of building efficient BiOCl/diatomite composites for fast degradation of CIP in water, which had substantial attraction for application.
In this study, carboxylic acid terminated Zn(II), Cu(II), Co(II) and Ni(II) phthalocyanine dyes were synthesized using 3-(4-(3,4-dicyanophenoxy)-3-methoxyphenyl)acrylic acid. Phthalocyanine dyes were characterized by elemental analysis, FT-IR, UV–Vis, ¹H-NMR and MALDI-TOF MS techniques. The sensitizing abilities of these dye molecules in standard dye-sensitized solar cells (DSSCs) were also investigated as function of sensitizing time (the sensitizing time was varied from 12 to 72 h). Preliminary studies showed that the sensitization time of TiO2 photoelectrodes has a strong effect on the device performance parameters. Interesting results were obtained for ZnPc sensitized device under optimized conditions. 36 h sensitized ZnPc based device gave a short circuit current density of 18.8 mA cm⁻², an open circuit voltage of 751 mV, a fill factor of 0.46, corresponding to an overall conversion efficiency of 6.37%. Relatively low photovoltaic conversion efficiency for 36 h CoPc sensitized device was obtained which can be attributed to redox active nature of Co(II) metal ion.
Polycyclic aromatic hydrocarbons (PAHs), pervasive plus priority emerging pollutants have the potential to destruct the bionetwork. Therefore, photocatalytic decay of toxic 4- and 5-ring membered PAHs, namely benz[a]anthracene (BaA) and benzo[a]pyrene (BaP), was explored in water. The nanocomposite of zinc hexacyanoferrate encapsulated with zinc oxide (ZnHCF@ZnO) was synthesized by Azadirachta indica mediated co-precipitation under normal conditions. Sunlight exposure caused a quick downfall in the concentration of PAH with composite exposing its eminent photo-activity. Encapsulation resulted in enhanced surface area (113 m2g-1) and lesser band gap energy (2.2 eV) of nanocomposite owing to the synergism of semiconducting stuff of zinc oxide and intercalative properties of ZnHCF. At neutral pH, photo-degradation of PAHs (2 mg L-1) by optimum dose of catalyst followed first order kinetics and Langmuir isotherms (R2≥0.98; p≤ 0.05). Slightly lower elimination of BaP (90%) than BaA (93%) might be due to its higher molecular weight and conjugation. Mechanism exploration revealed the involvement of “cation- π” interaction effectively between nanocomposite and PAHs (Xm = 25.6 mg/g of BaA and 21.7 mg/g of BaP) than bared (ZnO and ZnHCF). Besides, it compacts the t1/2 value of BaA(0.35 h) and BaP (0.49 h) up to manifolds than its constituents (13-26 h). Smaller by-products like prop-2-en-1-ol, propionic acid and acrylic acid identified in GC–MS, clearly supported electron excitement from encapsulated nanocomposite followed by •OH (active species)based oxidation of PAHs. Particularly, the mineralization evaluation of PAHs through TOC analysis confirmed its conversion into H2O and CO2. Inclusive of the present study provides promising photo-catalyst with greater surface activity, low quantum yield with charge separation and reusable for ten cycles deprived of substantial loss of its action. Similar studies can be promoted to build up methods that can accurately predict the acceleration in the environment clean up strategies.
n-ZnO/p-MnO nanocomposites with different percentages of manganese (0.5%, 1.1%, and 2.25%) with a semiconducting junction were prepared. Changes in Flat band potential (Efb) for ZnO due the different amounts of MnO was observed, meanwhile same donor density (Nd) was held in all materials. From chronoamperometric experiments under on-off illuminated conditions a transient time constant (τ), related to the electron transport in the electrodes were calculated, where higher values are observed in materials with high amounts of MnO. Photodegradation studies of anthracene in an ethanol:water (1:1, pH 12) solution were performed, showing that anthraquinone is the main product with no photodegrading of ethanol. The results suggest that the junction n-ZnO/p-MnO and materials with high transient time constant (τ), enhance the photocatalytic degradation. The best photocatalytic performance for the photodegradation of anthracene was obtained with the nanocomposite n-ZnO /p-MnO(Mn=2.25%).
This study describes the synthesis of activated biocarbon from Pinus kesiya cone by ZnCl2 activation and it’s efficacy in the removal of Alizarin Red S (ARS) dye. The prepared biocarbon was characterized using Elemental analysis, Scanning Electron Microscopy (SEM), FT-IR spectroscopy, Brunauer-Emmett-Teller(BET) surface area analysis and zero point charge. BETsurface area and total pore volume of the synthesized carbon was found to be 878.07 m2g-1 and 0.412 cm3g-1 respectively. The impact of process parameters like adsorbent dosage, pH, initial concentration, and contact time were determined using batch experiments and an increase in adsorption capacity was observed with increase in the initial dye concentration, adsorbent dosage and contact time. The adsorption isotherm was well defined by Langmuir model with a maximum adsorption capacity of 118.06 mg g-1. Pseudo-second order kinetics gave the best correlation value (R2> 0.99) reflecting the chemical nature of the adsorption process. Thermodynamic studies showed that adsorption was spontaneous (negative ∆G°) and endothermic in nature (positive∆H°). Regeneration of spent carbon was also evaluated in order to assess the reusability which shows that the regenerated carbon can be used till the third cycle.
In this work, a simple sol-gel method was used to fabricate a ternary nanocomposite of Fe-doped TiO2 decorated on reduced graphene oxide (Fe-doped TiO2/rGO). XRD, Raman shift, FT-IR, BET, DRS, EIS, TEM, FESEM, EDX and EDS techniques were applied for characterization of the structural, optical, and surface morphological properties of the synthesized catalysts. The DRS results of the photocatalysts showed a narrowing band gap by the introduction of Fe ions to the titania framework. The photocatalytic performance of the prepared samples was determined through the decontamination of rhodamine B under solar illumination. The optimum content of iron and graphene oxide and the effect of operational factors including pH, catalyst dosage and the initial concentration of rhodamine B were studied. The findings revealed that a 0.6 g Fe-doped TiO2/rGO nanocomposite containing 3% Fe and 5% rGO, with an initial pH of 6 and rhodamine B concentration of 20 mg/L could achieve a removal of 91% after 120 min under solar illumination. TOC analyses were conducted to explore the rhodamine B mineralization rate; the data showed complete mineralization after 300 min. The effect of co-existing ions was examined and the results indicated that the degradation efficiency was significantly decreased by the addition of chloride and sulfate anions, although it slightly decreased in the presence of nitrate and phosphate anions. Furthermore, the addition of H2O2 as an enhancer was investigated and the data demonstrated that the addition of 8 mM H2O2 enhanced the photocatalytic efficacy to complete degradation. Finally, in the treatment of real textile wastewater, the concentrations of TOC and COD decreased from 930 mg/L and 1550 mg/L to 310 mg/L and 634 mg/L, respectively, after 390 min under similar operational conditions.
In this work, Fe-doped (1 wt%) TiO2 loaded on the activated carbon nano-composite was prepared using a sol-gel method. A prepared nano-composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), BET surface area, Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) spectroscopy and UV–Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the nano-composite was evaluated through degradation of synthetic textile wastewater, reactive red 198, under visible light irradiations. The XRD result indicated that the TiO2 nano-composite contained only anatase phase. The surface area of the TiO2 increased from 48 m²/g to 100 m²/g through the fabrication of the nano-composite. The FE-SEM results indicate that the TiO2 particles with an average particle size of 35–70 nm can be deposited homogeneously on the activated carbon surface. DRS showed that the Fe doping in the TiO2 -activated carbon nano-composite induced a significant red shift of the absorption edge and then the band gap energy decreased from 3.3 to 2.9 eV. Photocatalytic results indicated that the photocatalytic activity of the Fe doped TiO2 increased under visible light irradiation in the presence of the activated carbon.
Photoelectrochemical (PEC) water splitting hydrogen production provides a promising way for sustainable development. In this work, we prepared Ni-doped TiO2 (Ti–Ni–O) nanotubes through anodizing different Ti-Ni alloys and further annealing them at elevated temperatures, and reported their PEC water splitting performance. It was found that Ni doping could improve light absorption and facilitate separation of photo-excited electron-hole pair. The nanotubes fabricated on Ti-1 wt.% Ni alloy and annealed at 550 °C exhibited better PEC water splitting performance than those on Ti-10 wt.% Ni alloy. The photoconversion efficiency was 0.67%, which was 3.35 times the photoconversion efficiency of undoped TiO2. It demonstrated that it was feasible to fabricate high-performance Ti–Ni–O nanotubes on Ti-Ni alloys and used as photoanode for improving PEC water splitting.
NiFe2O4/polyaniline (PANI) magnetic composite was prepared by in situ chemical oxidative polymerization of aniline in the presence of NiFe2O4 particles, where the NiFe2O4 particles were synthesized by a facile hydrothermal method. The magnetic composite was characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area method and vibrating sample magnetometer (VSM) techniques. The adsorption characteristics of the NiFe2O4/PANI composite were assessed by using alizarin red S (ARS) as an adsorbate. The adsorption process was investigated as the function of ionic strength, temperature, solution pH, adsorbent dosage, contact time and initial ARS concentration. The equilibrium adsorption data fitted well to the Langmuir model and the maximum adsorption capacity was found to be 186 mg g⁻¹ at 303 K. The remarkable adsorption capacity of ARS onto NiFe2O4/PANI was attributed to stronger π-π interaction and weak electrostatic attraction between ARS and NiFe2O4/PANI.
Kinetic studies indicated that ARS adsorption followed the pseudo-second-order kinetic model. The whole adsorption process was jointly controlled by external mass transfer and intraparticle diffusion. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) revealed that the adsorption of ARS on the NiFe2O4/PANI composite was a spontaneous and endothermic process. Magnetic NiFe2O4/PANI with adsorbed ARS could be regenerated using basic ethanol solution and was separable from liquid media using a magnetic field.
In this study, novel 2-hydroxymethyl-1,4-benzodioxane substituted phthalonitrile ligand (1) and its non-peripherally tetra-substituted phthalocyanine derivatives with metal-free (2), zinc(II) (3), cobalt(II) (4), nickel(II) (5) and copper(II) (6) were synthesized. These compounds were characterized by several techniques including elemental analysis, FT-IR, UV–vis, ¹H-NMR, ¹³C-NMR, GC-MS and MALDI-TOF MS. The TiO2 nanocomposites of these phthalocyanines (Pcs) were synthesized via the hydrothermal method in the presence of titanium(IV) isopropoxide. These nanocomposites were also characterized by FT-IR, XRD, FEG-SEM, EDX, UV-DRS and BET techniques. By monitoring the UV–vis absorption spectra, we found all the nanocomposites to have significant photocatalytic activities on methylene blue (MB), a common organic pollutant, under visible light irradiation (250 W). All the phthalocyanine-TiO2 nanocomposites have similar activities within the range of 100–140 min for full degradation (100%). Furthermore, the reusability studies showed the maintaining of more than 76% of the activity even after 5 recycles.
Due to their unique physicochemical, optical and electrical properties, 2D semimetallic or semiconducting graphene has been extensively utilized to construct highly efficient heterojunction photocatalysts for driving a variety of redox reactions under proper light irradiation. In this review, we carefully addressed the fundamental mechanism of heterogeneous photocatalysis, fundamental properties and advantages of graphene in photocatalysis, and classification and comparison of graphene-based heterojunction photocatalysts. Subsequently, we thoroughly highlighted and discussed various graphene-based heterojunction photocatalysts, including Schottky junctions, Type-II heterojunctions, Z-scheme heterojunctions, Van der Waals heterostructures, in plane heterojunctions and multicomponent heterojunctions. Several important photocatalytic applications, such as photocatalytic water splitting (H2 evolution and overall water splitting), degradation of pollutants, carbon dioxide reduction and bacteria disinfection, are also summarized. Through reviewing the important advances on this topic, it may inspire some new ideas for exploiting highly effective graphene-based heterojunction photocatalysts for a number of applications in photocatlysis and other fields, such as photovoltaic, (photo)electrocatalysis, lithium battery, fuel cell, supercapacitor and adsorption separation.
Significance and impact of the study:
Polycyclic aromatic hydrocarbons (PAHs) are recognized as significant health risks and consequently listed as priority pollutants by environmental protection agencies across the globe. The aim of the present study was to degrade one of the important PAHs, anthracene, by a newly isolated Bacillus thuringiensis strain. This is the first report of anthracene degradation by B. thuringiensis. This is also the very first growth kinetic study of a bacteria in an anthracene-containing medium. Some diphenol metabolites were found for the first time as anthracene biodegradation by-products, which can be an indication towards a new pathway.
Luminescent Mn/Co/Ti LDH, synthesized by a single step hydrothermal route, has been found to
be optically responsive for utilization as a highly efficient photocatalyst in destruction of the
cationic dye Rhodamine B, in aqueous solution under visible light irradiation. The material has
been found to be better than the commercial catalysts like MnO, CoO, TiO2 and Degussa P25.
Multiple techniques like XRD, XPS, FT-IR, EIS, TG, UV-visible DRS, PL, TRES, N2-sorptiondesorption,
dynamic light scattering, TEM-EDS and AFM analyses were used to characterize the
LDH. The results indicated Mn/Co/Ti LDH to be having a multilayered crystalline structure with
hexagonal morphology that carries metal ions in mixed valences, oxygen vacancies, defect
states, thermal stability, narrow band gap, high surface area, and electrostatic surface charge
variation with pH. The photocatalytic activity of the LDH could be co-related with the structural
aspects such as oxidation states, narrow band gap, high surface area and existence of defects. The
active species responsible for photocatalysis have been evaluated with EPR, terephthalic acid
fluorescence probe and indirect radical-hole trapping experiments. The photodegradation
mechanism involves electron and hole hopping across the material and also by photosensitization
of the dye. Ex-situ 1H-NMR and GC-MS analyses of the colorless end products of Rhodamine B
destruction provides further insight into the reaction mechanism. The complete mineralization of
the decolorized end product of degradation was evaluated with TOC analysis. The results
indicate the potential for using multi metal incorporated
The photocatalytic degradation of organic pollutants in a real petroleum refinery wastewater (PRWW) by a heterogeneous photocatalytic process using synthesized nano-TiO2 supported on Fe-ZSM-5 zeolite as photocatalyst irradiated with UV light has been studied. The influence of various operational parameters such as photocatalyst concentration, pH and temperature was investigated. The degradation rates of the organic pollutants followed mainly a pseudo-first order kinetic model. Results showed that the maximum photodegradation efficiency was achieved at a photocatalyst concentration of 3 g/l, pH of 4 and temperature of 45 °C under UV irradiation time of 120 min. TiO2 loaded with the existence of oxo-iron ions in the framework of zeolite increased photocatalytic degradation of COD. The kinetics of photodegradation reaction was accelerated by an increase in temperature in the range of 15–45 °C. The activation energy for photocatalytic degradation of organic pollutants in PRWW was 18.76 kJ/mol. Thermodynamic parameters of activation were assessed in the photodegradation process. Kinetics computation using transition state theory (TST) showed that the temperature had a significant effect on the rate constants during the photocatalytic degradation process. Significant photodegradation efficiency of organic pollutants using the synthesized photocatalyst indicates a good potential for this technique as a treatment system for real PRWW.
Effect of different type of organic or inorganic additions (formic acid, AgNO3, NaCl) on the photocatalytic reduction of copper and photooxidation of cyanide with illuminated TiO2@yeast was studied in this work together with the impact of solution pH values and contact time. The results indicated that pH values exhibited a great effect on the adsorption and photocatalytic performance of cyanide and copper because the surface charge of the TiO2@yeast and the existence form of cyanide and copper are highly pH dependent. The optimal adsorption and photo-oxidation of cyanide was observed at pH 2.0 while the best adsorptive and photocatalytic efficiency for copper was achieved at pH 5.0 within the studied range. The addition of formic acid increased the photo-reduction rate of copper and inhibited the photo-oxidation of cyanide. AgNO3, as electron acceptor, restrained the Cu(II) reduction from 75.0 to 30.5 %, whereas accelerate the photo-oxidation of cyanide. Besides, the presence of chloride ions retarded the removal efficiency of both cyanide and copper. The first-order kinetic model well described the experimental data. One possible mechanism of the effect of additives on copper and cyanide degradation was discussed.
We synthesized different Fe/TiO2 catalysts and studied the influence of Fe on the structure and performance of Fe/TiO2 as a photocatalyst to remove gaseous NO in air under visible light. The electron paramagnetic resonance results revealed that Fe ions substituted the Ti ions of TiO2 prepared by co-precipitation and homogeneous precipitation method. More Fe ions were incorporated into the crystal lattice of TiO2 prepared by co-precipitation method than that prepared by homogeneous precipitation method. No Fe ions were incorporated into the crystal lattice of TiO2 prepared by conventional wet impregnation method. Furthermore, Fe doping influenced the UV–vis absorption and photoluminescence of TiO2. The higher photocatalytic activity of Fe/TiO2 prepared by co-precipitation method was attributed to the synergistic effects of more visible light absorption and minimum electron hole recombination caused by the Fe ions incorporated into the crystal lattice of TiO2. Density functional theory calculations further confirmed the role of Fe on the electronic structure of TiO2.
In this research, effect of pH on phase, morphologies and photocatalytic activities of Bi2WO6 synthesized in the precursor solution with the pH of 2-12 by the 180 °C and 20 h hydrothermal reaction is reported. The as-synthesized Bi2WO6 products were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectrophotometry, Brunauer-Emmett-Teller (BET) isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible spectroscopy. The photocatalytic activities of the as-synthesized Bi2WO6 products were evaluated via the photodegradation of rhodamine B (RhB) under visible-light radiation. The results showed that the precursor solution pH had an important influence on the photocatalytic activities of the Bi2WO6 nanocatalyst. When the precursor solution pH was 2, the RhB degradation exhibited the highest decolorization efficiency of 98% within 100 min.
TiO2 and Ni-doped TiO2 thin films have been prepared by sol-gel dip coating method. X-ray diffraction studies show that TiO2 and Ni-doped nanocrystalline TiO2 thin films are of anatase phase. The surface morphology of CdS quantum dot sensitized TiO2 thin film and CdS quantum dot sensitized Ni-doped TiO2 thin film were analysed by scanning electron microscopy. The absorption edge of TiO2 thin films shift towards longer wavelengths (i.e. red shifted) with Ni doping, which greatly enhances the light absorption of TiO2 in the visible region. The power conversion efficiency of CIS quantum dot sensitized Ni-doped TiO2 (CdS QDS-NT) based solar cell exhibited an efficiency of 1.33%, which is higher than that of CdS quantum dot sensitized TiO2 (CdS QDS-T) (0.98%) solar cells.
Transition metal oxides and mixed oxides are the largest group of materials for photocatalytic applications. Many highly active compounds are known from literature for environmental remediation, pollutant degradation and solar fuel generation. However, most of these oxides can only absorb UV light to perform photocatalytic reactions at their surface due to their large band gap. In this review, we present the recent progress in non-metal doping of transition metal oxides and mixed oxides, one of the major strategies to reduce the large band gap of semiconductor materials into the visible light range. We outline the advantages of this strategy compared to other band gap engineering methods, and especially stress the effect of efficient homogeneous non-metal doping on the optical, electronic and photocatalytic properties of photocatalysts, compared to surface doping and surface modification, including the effects of an open crystal structure on the efficiency of the doping process. We then present the highlights and breakthroughs of the last ten years in the research field and point out major improvements important for future applications, covering all the available non-metal doped transition metal oxides concerning photocatalytic reactions.