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Abstract
One-dimensional MoO3 nanofibers doped with Ce (MoO3 : CeO2) are synthesized by a method combining a sol-gel process and an electrospinning technique. The resulting MoO3 : CeO2 is characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). The catalytic degradation of rhodamine B and safranin-T with MoO3 : CeO2 nanofiber catalyst is investigated in a continuous flowing mode using air (O2) as an oxidant. The results show that rhodamine B and safranin-T are degraded effectively and the removal efficiencies are 98.3%, and 98.5%, respectively. In addition, the organic dyes are totally mineralized to simple inorganic species such as CO3–, Cl– and NO3–.
... It is estimated that ca. 10% of the dye is lost during dyeing processes and released into wastewater which cause substantial threat to the environment [1]. For these reasons the decolorization/degradation of dye effluents has received a large attention recently [2][3][4]. ...
... For these reasons the decolorization/degradation of dye effluents has received a large attention recently [2][3][4]. Indeed, it is an essential need to develop novel treatment methods for converting these organic dyes to harmless compounds in terms of the increasing public concern and the stringent international environmental standards (e.g., ISO 14001) [1,5]. Many of the methods are available for the removable pollutants from water, the most important of the mare reverse osmosis, ion exchange, precipitation, adsorption, and advance oxidation process (AOP). ...
In this work, we report the results of the electrodeposition of MnO2 film on stainless steel (SS) electrode in aqueous MnSO4 solution which was used as photocatalyst to degrade the Rhodamine B (RhB). Different techniques such as field emission gun scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Braunauer Emett and Teller (BET), and UV-visible diffuse reflectance spectroscopy (UV-vis DRS) were used to characterize the deposited MnO2 film. It was found that MnO2 is electrodeposited as a γ-MnO2 nanoparticle film with a low rate of crystallinity and high specific surface area of about 140 m² g⁻¹. The particle size is less than 20 nm. In addition, the diffuse reflectance measurements show that the γ-MnO2 presents a direct band gap of about 1.41 eV. The Mott-Schottky plot confirms that γ-MnO2 is a n-type semiconductor with the flat band potential VFB = 0.016 V vs. Ag/AgCl and the electron concentration ND = 0.8 × 10²⁰ cm⁻³. The conduction and valence energy band values were estimated at Ec = 4.498 eV and Ev = 5.908 eV, respectively. It was shown also that these films exhibit good ability for the degradation of RhB especially under visible light irradiation. Indeed, degradation rates of about 90 and 55% were obtained after 60 min of visible and UV light irradiation, respectively. Finally, the degradation process mechanism of RhB is discussed.
Graphical abstractᅟ
... [9] Furthermore, the decrease of the COD has been related to the degree of mineralization. [43] The COD reduction ratio was determined for each sample and the results obtained are shown in Table 1. These indicate that the different solutions have undergone a major decrease in COD content, with subsequent considerable reduction in their toxicity. ...
... The use of nanostructures in the degradation of dyes has been widely reported [43,53,54] and the use of TiO 2 -doped particles has been extensively studied. [29,44,55] However, all these studies report the chemical synthesis of such structures. ...
This research was undertaken to determine the potential of biologically obtained ZnS-TiO2 nanocomposites to be used as catalysts in the photodegradation of organic pollutants, namely, Safranin-T. The photocatalysts were prepared by modifying the surface of commercial TiO2 particles with naturally produced ZnS, using sulfide species produced by sulfate-reducing bacteria and metal contaminated wastewaters. Comparative studies using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), prior and after photodegradation, were carried out in order to monitor possible structural and morphological changes on the particles. Adsorption properties and specific areas were determined by the Brunauer-Emmet-Teller (BET) method. The final solutions were characterized by UV-Vis and chemical oxygen demand (COD) content in order to determine Safranin-T concentration and toxicity. The influence of the catalyst amount, initial pH and dye concentration was also evaluated. Finally, the efficiency of the precipitates as catalysts in sunlight-mediated photodegradation was investigated, performing two scale experiments by using different volumes of dye-contaminated water (150 mL and 10 L). All tested composites showed potential to be used as photocatalysts for the degradation of Safranin-T, although the ZnS-TiO2_0.06 composite (0.06 g of TiO2 per 50 mL of the zinc solution) was the most effective. This substantiates the applicability of these biologically obtained materials as efficient photocatalysts for the degradation of organic pollutants, in laboratorial conditions and under direct sunlight.
... Using a powder diffractometer and Cu-K radiations with a 2-theta range of 10 • -80 • , it was captured. The phases of cerium oxide or yttrium oxide were found among all the recorded peaks from the XRD pattern, and it is evident that all the diffraction peaks are precisely coincident with the cubic phase of bi-nary metal oxide [12,13]. Additionally, it demonstrates the produced nanoparticles' excellent crystallinity and single phase of cubic fluorite crystal structure in the (Fm3m) space group. ...
... Therefore the reduced bandgap due to the midgap states generated by the addition of CeO 2 significantly increased the light-absorbing ability, and the presence of Ce]O]Mo bonds also improved the electron transfer, leading to an efficient separation of charges. During the catalytic reaction at room temperature (light off), MoO 3 and CeO 2 acted as oxidant and as oxygen storage and release reservoir (OSR), respectively [203,204]. The dye molecules firstly adsorbed on the surface of MoO 3 and were activated; then, they were oxidized into the intermediate species by Mo(VI), while Mo(VI) itself was reduced into Mo(V). ...
... Well known that the mixed systems based on cerium and molybdenum oxides are widely use as photocatalysts for organic dyes degradation [1][2][3], catalysts supports, and also effective catalysts for environment protection, namely oxidation CO [4], selective reduce of nitrogen oxides to ammonia [5,6], etc. The number of publications connected with the use of Ce/Mo-containing catalysts for acetaldehyde production from ethanol as an intermediate product for the synthesis of other chemicals such as acetic acid, acetic anhydride, ethyl acetate, butyl aldehyde, crotonaldehyde, pyridine, peracetic acid and vinyl acetate exist, also [7][8][9][10][11]. ...
... Based on the statement, it can be concluded that rhodamine 6 G was adsorbed by the CeO 2 -NPs and interacted with the functional groups present on their surface, giving rise to a new product (Fig. 9) that presented functional groups different to those characteristics of R6 G and of ceria ( Table 1). The IR spectra before and after the reaction also show that the final degradation products are inorganic ions [97]. One of the processes that may favor interaction between the CeO 2 -NPs and the molecules of rhodamine 6 G is the adsorption of the latter on the surface of the NPs. ...
In this work, the capacity to removal rhodamine 6 G (R6 G), in the absence of UV radiation, using cerium dioxide nanoparticles (CeO2-NP) was determined. The synthesized NPs were characterized by X-ray powder diffraction (XRD) and X-ray photoelectron (XPS), Raman and photoluminiscence spectroscopies. The results indicated that CeO2 powders had a crystallite size between ∼ 12 and ∼ 14 nm. The presence of the peroxide species (O2²⁻) η2, superoxide (O2-) η1, adsorbed species O2δ (0 < δ < 1) over the surface of the ceria nanoparticles was demonstrated in the Raman spectra. Additionally, the ability of the CeO2-NPs synthesized to interact with organic molecules was determined by evaluating the removal of the R6 G dye. The results of these tests showed substantial dye removal by the as-synthesized CeO2-NPs at pH∼9.1 (∼87 % within 120 min). The kinetic adsorption of the R6 G by these NPs was suitably described by a pseudo-second-order equation.
... Two-component compositions, which contain the molybdenum and cerium oxides, are promising materials used in modern electronics, adsorption, catalysis, and photocatalytic processes [1][2][3][4][5][6][7][8][9][10]. There are publications that show that the formation of nanodispersed materials in these compositions greatly improves their functional characteristics. ...
The influence of mechanochemical (MChT) and ultrasonic (UST) treatment on the properties of CeO2–MoO3 = 1:1 composition was studied. It was shown that in both processes changes in crystalline, porous structures, and morphology occurred. It was found that MChT and UST of samples affect the characteristics of hydrogen temperature-programmed reduction (H2-TPR). The results of the catalytic activity of activated samples in an ethanol oxidation reaction demonstrate the high yield of acetic aldehyde (95%) at 230 °C and the productivity of this product (0.9 mol/kgcat · h).
... The widespread applications of nanomaterials are primarily measured due to their grain shape, tiny size, high reactive surface to volume ratio, and high surface movement [16][17][18][19]. All these properties make nanomaterials attractive in numerous fields [20]. Among the rare earth metal oxides (REMO), ceria (CeO 2 ) is a mostly available noble metal oxide, because it has tendency to liberate and attract oxygen in the alternating redox reactions and becomes an exciting oxygen buffer source and its potent applications in the fields of green protection and in semiconductor industries [21]. ...
We report the new synthesis route of hierarchical yttria (Y2O3) nanosphere decorated ceria (CeO2) nanorods from the precursor cerium nitrate and yttrium nitrate under hydrothermal method (HM). Synthesized nanorods (NRs) were analyzed by different techniques to investigate their textural morphology, size and shape of nanorods and crystalline structures, morphology growth, optical activity and sizes of the samples. The luminescence blue peaks were observed in the range of 450–490 nm and green emission appeared at 533 nm at the room temperature (RT), the presence of oxygen vacancies was confirmed. The photodecomposition nature of the prepared nanosamples was investigated by using the industrial effluent Rhodamine-B (RhB) dye in aqueous medium by the illumination of solar light. The photocatalytic degradation efficiency showed 95.8% for RhB after 240 min. On illumination of visible light, the catalyst was found to tend to produce reactive oxygen species (ROS), which might account for the decay of dyes into small fractions. The enhanced photocatalytic effect of the synthesized NRs was primarily ascribed to the rising in the separation efficiency of electrons and holes. Keywords: Photocatalytic effect, Ceria, Yttria, Electron microscopy, Rhodamine-B (RhB)
... A C C E P T E D ACCEPTED MANUSCRIPT 25 processes hydroxyl radicals and superoxide radical anions are the major oxidizing species. ...
A low energy bandgap between Ce³⁺ and Ce⁴⁺ states in cerium oxides, high oxygen mobility and high oxygen storage capacity are the properties that qualify them to be the most widely used heterogeneous catalysts. This present work is an account of studies that were carried out on the synthesis and catalytic properties of pure CeO2, CeO2/La2O3 based binary metal oxide nanostructures prepared by the hydrothermal method. Our results revealed that the synthesis temperature and pressure during hydrothermal reactions played a critical role in controlling the shape, size, oxygen vacancy, and low temperature reducibility in CeO2 based nanostructures. In addition, OH⁻ ion concentration was found to play an important role in engineering the lattice constants and oxygen vacancy defects. The present report demonstrated that the hydrothermal synthesis is a facile one step approach for the preparation of compositionally homogeneous cerium based binary metal oxide nanostructures, in which CeO2/La2O3 mixed oxides have a superior low-temperature oxygen release capability compared to pure CeO2. We have also demonstrated that the nanomaterials are proved to have higher catalytic performance at low temperatures as compared to pure ceria nanoparticles.
... Molybdenum trioxide (MoO 3 ) has garnered much research attention recently due to this material offering prom- ising applications, coupled with its non-toxic nature, low cost and outstanding catalytic properties [1][2][3][4][5][6][7] . Further, MoO 3 is found to be one of the most important metal oxides used as the electron-injection layers and the elec- trode material in the fast-growing field of photovoltaics and solar-cell devices. ...
First-principles calculations were carried out to understand how anionic isovalent-atom doping affects the electronic structures and optical properties of α-MoO3. The effects of the sulphur and selenium doping at the three unique oxygen sites (Ot, Oa, and Ot) of α-MoO3 were examined. We found that the valence p orbitals of Sulphur/Selenium dopant atoms give rise to impurity bands above the valence band maximum in the band structure of α-MoO3. The number of impurity bands in the doped material depends on the specific doping sites and the local chemical environment of the dopants in MoO3. The impurity bands give rise to the enhanced optical absorptions of the S- and Se-doped MoO3 in the visible and infrared regions. At low local doping concentration, the effects of the dopant sites on the electronic structure of the material are additive, so increasing the doping concentration will enhance the optical absorption properties of the material in the visible and infrared regions. Further increasing the doping concentration will result in a larger gap between the maximum edge of impurity bands and the conduction band minimum, and will undermine the optical absorption in the visible and infrared region. Such effects are caused by the local geometry change at the high local doping concentration with the dopants displaced from the original O sites, so the resulting impurity bands are no long the superpositions of the impurity bands of each individual on-site dopant atom. Switching from S-doping to Se-doping decreases the gap between the maximum edge of the impurity bands and conduction band minimum, and leads to the optical absorption edge red-shifting further into the visible and infrared regions.
... It is recorded by using powder diffractometer employing Cu-Kα radiations in the 2-theta range 10°-80°. Among all the observed peaks from XRD pattern, the phases of cerium oxide or yttrium oxide phases were detected and it is clearly seen that all the diffraction peaks are perfectly coincident with the cubic phase of binary metal oxide [25,26] and confirms the absence of impurities. It also illustrates that the obtained nanoparticles have good crystallinity. ...
... Molybdenum trioxide is one of the most interesting transition metal oxides due to its outstanding catalytic properties in methanol selective oxidation [1][2][3], hydrocarbon selective oxidation [4] or photocatalyst [5][6][7]. Therefore it is the major component of many industrial catalysts such as iron molybdates based catalyst which are widely used for the industrial production of formaldehyde from methanol. Although Fe 2 (MoO 4 ) 3 is found to be more active than MoO 3 for formaldehyde formation due to the larger density of exposed catalytic active sites of isotropic Fe 2 (MoO 4 ) 3 than that of anisotropic MoO 3 [8,9], the commercial catalysts always have a large excess of molybdenum [10]. ...
β-MoO3 was successfully synthesized from all commercial materials using a fast, effective and simple method and characterized by differential scanning calorimetry, X-ray powder diffraction, field emission scanning electron microscopy, infrared and Raman spectroscopy. The prepared sample was highly active and selective to formaldehyde formation from methanol over a wide range of reaction temperatures. β-MoO3 catalyst also exhibited stable methanol conversion and formaldehyde selectivity at around 84% and over 95% respectively for over 15 operating hours at 320 °C. However, it may be deactivated at elevated reaction temperature due to transformation of metastable to stable phase. It was revealed that the prepared catalyst maintains its high selectivity to formaldehyde during deactivation. This can be considered as an advantage of the prepared MoO3 catalyst in comparison with the industrial one.
... Polyoxometalates (POMs) are oxo-clusters of early transition metals such as Mo (VI), W (VI), or V (V) in their highest oxidation states. They represent an increasingly important class of environmentally benign catalysts (Neumann and Khenkin, 2006;Ressler et al., 2005;Zhao et al., 2010). Compared to the quickly development of POM photocatalysts for pollutants' removal (Guo and Hu, 2007), there are only few studies on POMs applied for catalytic wet air oxidation (CWAO) of organic pollutants (Chai et al., 2008;Arslan-Alaton and Ferry, 2002) Therefore, (Hill, 2007) suggested that POMs might well find catalytic application in air oxidation at low temperature and dark, especially in cleansing or purifying environments or decontaminate chemical warfare agents, as photocatalysts for pollutant removal in several riches. ...
The nanocatalysts were fabricated by reacting amphiphilic quaternary ammoniums with polyoxoperoxometalates (POPMs) K(n)[PW(12-)(x)Ti(x)O(40-)(x)(O(2))(x)](x=1, 2 and 3; n=5, 7 and 9). Fourier transform infrared spectroscopy (IR), transmission electron microscopy (TEM), and UV-vis-NIR spectrophotometer were used to characterize the resulting samples. This kind of nanocatalysts could provide a kind of nanoreactors to promote the degradation of NH(4)SCN into simple inorganic compounds such as SO(4)(2-), HCO(3)(-) and NO(3)(-) using oxygen as an oxidant under room conditions. The leaching test showed that the POPMs micellar catalyst had excellent stability and could be used as a heterogeneous one at least five times.
The highly crystalline mesoporous series of various percentages such as 1, 3 and 5% of CeO2-doped MoO3 nanocomposite were synthesized successfully by using ultrasonic wave-assisted sol–gel synthesis procedure and calcined at 873 K for 3 h. The synthesized CeO2-MoO3 nanocomposite material characterized by different techniques like XRD, Raman, FT-IR, FE-SEM, HR-TEM, BET, XPS and UV-DRS measurements to find crystallinity, surface morphology, surface area, structural and optical properties. Among these, 5% CeO2-MoO3 nanocomposite shows excellent photo-Fenton dye degradation activity of Rhodamine-B (Rh-B) dye in visible light irradiation using direct sunlight. Maximum degradation was observed (95.36% in 120 min) with optimum condition of pH, catalyst amount and H2O2 concentration. These nanocomposite material was recovered, recycle and its reusability also gives excellent results up to the 4th cycle. Similarly, turn over number, turn over frequency, kinetic study and scavenger study of photo-Fenton degradation reaction were also discussed.
Organic–inorganic nanocomposite fibers can avoid the agglomeration of single nanoparticles and reduce the cost (nanoparticles assembled on the surface of nanofibers), but also can produce new chemical, electrical, optical, and other properties, with a composite synergistic effect. Aromatic polyimide (PI) is a high-performance polymer with a rigid heterocyclic imide ring and an aromatic benzene ring in its macromolecular framework. Due to its excellent mechanical properties, thermal stability, and easy-to-adjust molecular structure, PI has been widely used in electronics, aerospace, automotive, and other industries related to many applications. Here, we report that TiO2 nanorods were grown on polyimide nanofibers by hydrothermal reaction, and MoS2 nanosheets were grown on TiO2 nanorods the same way. Based on theoretical analysis and experimental findings, the possible growth mechanism was determined in detail. Further experiments showed that MoS2 nanosheets were uniformly coated on the surface of TiO2 nanorods. The TiO2 nanorods have photocatalytic activity in the ultraviolet region, but the bandgap of organic/inorganic layered nanocomposites can redshift to visible light and improve their photocatalytic performance.
Ceramics are composed of both metallic and nonmetallic elements and commonly exist as compounds of oxides, nitrides, and carbides. Two decades back, the use of ceramics was limited to a handful of applications, as in household utilities and some industrial uses. In the era of nanotechnology, the definition and application of materials are altered, especially in the case of ceramics. By the development of various fabrication techniques of nanostructured ceramics, the scope of ceramic materials is radically transformed, making them the most beneficial among the materials ever designed for several critical applications. The fabrication of ceramic nanostructures is challenging from an industrial point of view since many fabrication techniques need sophisticated instrumentation, skilled personnel, purity of chemicals, specificity of the medium, controlled atmosphere, etc. and are anticipated for lab-scale production. The electrospinning process is an exception, which can address all the former problems associated with other fabrication techniques. This chapter covers the electrospun ceramic nanofibers such as oxides, carbides, nitrides, sulfides, etc. from various precursors and their application in the field of biomedical engineering, filtration, energy, electronics, sensor, catalysis, etc. and their peculiar properties, such as photoluminescence, thermoelectric, piezoelectric, and magnetic. Nevertheless, the application of ceramic nanofibers, far more than what is discussed here, and advanced studies are essential to explore the applications of ceramic nanofibers in numerous untouched areas where conventional materials can be replaced.
Catalytic wet air oxidation (CWAO), one of the best-known methods for water treatment, has been intensely investigated for dyes degradation. However, the extreme operation conditions as well as the recovery of suspended catalyst are economically unattractive. In the current work, a novel Mo-based nanocrystal decorated ceramic membrane (Mo/Al2O3) has been prepared and applied for organics degradation via CWAO at ambient conditions for the first time. The catalytic Mo/Al2O3 membranes were prepared by an in-situ hydrothermal followed by calcination method. Their physical and chemical properties were characterized by field emission scanning electron microscope (FESEM), X-rays diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of Mo/Al2O3 membranes were evaluated via organics (safranine O and humic acid) degradation under a home-made membrane filtration system. The effects of calcination temperature, catalyst loading amount, and trans-membrane pressure (TMP) were systematically investigated. The stability and durability of the catalytic Mo/Al2O3 membrane were examined in a long-term filtration system. Results showed that the performance of Mo/Al2O3 membrane would decrease with increasing of calcination temperature as well as TMP. However, the catalyst loading amount was not a major effect on the removal of organics in the system. For one-time loading membrane calcined at 300 °C (1x-Mo/Al2O3[email protected]), the removal efficiency could achieve higher than 90% in 40 min in a recycled filtration system with an initial safranine O concentration of 10 mg L⁻¹. The chemical quenching experiment as well as radical quantification verified the main reactive oxygen species were ¹O2 and •O2- in the system. The ROS generation mechanism was proposed via the characterization of the catalyst after reaction. The deliberate combination of CWAO and membrane separation represents a new strategy that offers exciting possibilities for water treatment under ambient conditions.
From the viewpoint of engineering application, it is highly desirable to develop a low-cost, fossil energy–saving degradation technology. In this work, hydrated molybdenum oxide (MoO3·0.55H2O) is prepared by a simple chemical method. It is interesting that under indoor natural ambient conditions, 79% of methylene blue is degraded by hydrated molybdenum oxide after 150 min, but under the same conditions, anhydrous molybdenum oxide does not have any degradation activity. It is found that the outstanding ambient activity of hydrated molybdenum oxide is mainly attributed to the photothermal synergistic effect caused by structure water. On one hand, the coordination of structure water with molybdenum brings about the Jahn–Teller distortion of MoO6 octahedron, giving rise to Lewis acid sites that promote the adsorption and activation of oxygen. O2–temperature-programmed desorption and H2–temperature-programmed reduction profiles show that compared with MoO3, MoO3·0.55H2O has a higher oxygen adsorption ability and a higher oxidation ability. Jahn–Teller effect is mainly responsible for the thermocatalytic activity. On the other hand, the ligand-to-metal charge transfer (LMCT) transfer from structure water to molybdenum obviously increases the light absorption, thus LMCT is mainly responsible for the photocatalytic activity The most important is that compared with conventional photocatalysis, no artificial light source equipment is required; compared with thermocatalysis, no extra heating equipment is needed. Thus, this mild degradation process is low-cost, energy-saving and space-saving, which is very promising for indoor or limited space cleaning.
It was shown that mechanochemical treatment of 1 : 1 MoO3–CeO2 oxide mixture leads to the formation of nanosized particles with core–shell type of structure with a layer of amorphous molybdenum oxide on a core of nanocrystalline cerium oxide. It was established that the synthesized nanocomposites are highly active and selective catalysts for the oxidation of ethanol to acetaldehyde at low temperatures (~200 °C).
The influence of ultrasonic treatment (UST) of oxide CeO2-MoO3 system with atomic ratio Ce/Mo = 15:85, 25:75, 50:50, and 75:25 on their properties was investigated. The prepared samples were characterized by means of XRD, ESR, N2 adsorption, FT-IR-spectroscopy, SEM, and TEM methods. The catalytic properties of the samples in selective ethanol oxidation to acetaldehyde and their adsorption capacity relation to dye removal from water solutions were studied. The decrease of oxides particles size with nanoparticles formation as result of CeO2 chaotic destruction and MoO3 anisotropic deformation was established. It was shown that UST leads to an increase of the composition-specific surface area, formation of structural defects, and strong interaction between oxides nanoparticles. The change of physicochemical properties of the compositions as result of their sonochemical treatment leads to increase their catalytic and adsorption properties. The samples obtained after UST demonstrate very promising results in oxidative dehydrogenation of ethanol to acetaldehyde, and the treated composition with ratio Ce/Mo = 50:50 permits to obtain the acetaldehyde yield equal to 96% at reaction temperature 200 °C. On the other hand, sample with Ce/Mo = 75:25 has high adsorption capacity in process of dye removal from water solution.
The MoO3 catalysts as a wet air oxidation catalyst have been synthesized by a simple hydrothermal method. During the synthetic process, a detailed orthogonal design on the preparation conditions was performed, aiming to optimize the parameters to produce MoO3 with the most prominent catalytic performance. The catalytic activities of the synthesized materials were evaluated via the decolorization of dye wastewater at room conditions. The effects of calcination temperature, catalyst dosage, and initial concentration of Rhodamine B (RhB) on the degradation efficiency were investigated, where it was found that the sample calcinated at 400 °C exhibited superior catalytic performance.
α-MoO3 thin sheets were successfully synthesized from all commercial materials using a fast, effective and simple method and characterized by X-ray diffractometer, scanning electron microscopy, IR and Raman spectroscopy. The prepared catalyst was highly active and selective to formaldehyde formation from methanol over a wide range of reaction temperatures comparing to the commercial one. We found that the high selectivity of formaldehyde over the prepared α-MoO3 was originated from its special morphology, which had abundant exposed edges comparing to the commercial α-MoO3. Additionally, the prepared α-MoO3 showed significant stability due to its stable nature.
Graphical Abstract
Metastable MoO3 was successfully synthesized by a chemical transformation of α-MoO3 and characterized by TG-DSC, BET, XRD and Raman spectroscopy. The prepared material was highly active and selective to formaldehyde formation from methanol over a wide range of reaction temperatures. The formaldehyde selectivity can reach up to 99 % at about 98 % methanol conversion. The stability of the prepared catalysts was also investigated.
An anionic triphenyl methane dye, methyl blue ((disodium;4-[4-[[4-(4-sulfonatoanilino)phenyl]-[4-(4-sulfonatophenyl)azaniumylidenecyclohexa-2,5-dien-1-ylidene]methyl]anilino]benzene sulfonate) was degraded photocatalytically with undoped micro-TiO2- and Ag(+)-doped micro TiO2 in a slurry-type batch reactor under UV irradiation and the efficiency was compared with that obtained using nano-TiO2- and Ag(+)-doped nano-TiO2. The influence of different parameters, i.e., photocatalyst loading, dye concentration, initial pH, temperature, depth of solution, interfering ions and electron acceptors on the dye degradation was investigated. The decolorization and mineralization efficiency was better for Ag(+)-doped micro-TiO2 than undoped micro-TiO2. Nano-TiO2 was more efficient than micro-TiO2, while Ag(+)-doped nano-TiO2 was the most efficient of all. Cost analysis showed degradation using micro-TiO2- and Ag(+)-doped micro-TiO2 are much cheaper than that using nano-TiO2 and Ag(+)-doped nano-TiO2. Therefore Ag(+)-doped micro-TiO2 was used for the detailed study. The degradation products formed were identified using GC-MS analysis after photocatalytic degradation for 180 min with Ag(+) -doped micro TiO2. Ion chromatography analysis was carried out for anions to identify the end products of degradation.
Herein, an efficient Ce-doped MoO3 catalyst is prepared by an impregnation method. Under visible light irradiation (≥ 420 nm) or light-off, Ce(5)-doped MoO3 shows a degradation activity of methylene blue (MB) dye 10 times higher than MoO3 due to the doped Ce. It is proposed that the light-off degradation is predominated by a Mo/Ce redox cycle, instead of a photocatalytic reaction; while the light-on degradation is via a synergetic effect of both photocatalytic oxidation and Mo/Ce redox cycle. This study offers a new concept for environmental cleaning from cost-saving and energy-saving viewpoints.
CaMn3O6 films with hierarchical nanostructures were deposited for the first time on unheated quartz glass substrates by the radio frequency (RF) magnetron sputtering technique using a polycrystalline CaMnO3 sample as sputtering target, and their photocatalytic activity was evaluated on the decolorization of Rhodamine 6G (Rh6G)
aqueous solutions. The films scanning electron microscope (SEM) images evidence a growth of nanorods (NRs) arrays with planar endings and a narrow size distribution centered at about 30 nm in diameter. The CaMn3O6
films surface is uniform and presents a high density of nanorods (116 nanorods per μm2). The high surface area combined with the tunnels crystallographic structure, evidenced by X-ray diffraction (XRD), results in an
effective photocatalyst for Rh6G degradation under visible light irradiation. Based on the photodegradation experiments, it is suggested that a process of dye self-sensitization can be one of the key factors of the superior photocatalytic performance of CaMn3O6 NRs. The kinetics of photocatalytic degradation of Rh6G follows a first-order reaction. Furthermore, XRD of the used films did not reveal additional phases indicating high
photochemical stability, and the diffuse reflection infrared Fourier transform spectrum (DRIFT) does not show adsorbed organic species on the CaMn3O6 NRs surface. This work provides a potential route to develop high-performance immobilized nanostructures, and the achievements open up many possibilities to tailor visible light active materials for environmental applications.
Extensive studies have been conducted on molybdenum oxide since it has outstanding properties as an insertion layer for efficient charge injection and extraction in organic semiconductor devices. Efficient charge transfer at semiconductor and electrode interface is one of the most crucial issues for the performance of organic electronic device. A lot of efforts have been spent to address this issue, but there are still many unclarified issues to understand the physical mechanisms. In this review, the authors summarize surface analytical investigations on the mechanisms that govern the effectiveness of the insertion layer. Measurement results on the electronic structure, composition, and morphology are presented. It is found that the high work function of MoOx is the dominant factor for the device performance improvement. Compromising environmental effects and methods to recover or prevent such effects are described. Finally, the criteria for MoOx insertion layer to be effective are provided by comparing the work function of MoOx and the ionization potential of organic semiconductors.
In order to efficiently degrade organic pollutants via an easily operated method, Ce-doped MoO3 (Ce(x)/MoO3) samples are synthesized by a simple impregnation method. The samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), nitrogen sorption isotherms and UV-vis diffused reflectance spectra (UV-DRS), total organic carbon (TOC), infrared spectroscopy (IR) and mass spectrometry (MS) analyses. Furthermore, we have mainly investigated the degradation of different dye pollutants by the Ce(x)/MoO3 samples, including cationic methylene blue (MB), anionic methyl orange (MO), neutral phenol, and a MB-MO mixture dye. For the single-component MB and MO dyes, the highest degradation efficiencies are achieved by Ce(5)/MoO3 and Ce(10)/MoO3 samples. For the MB-MO mixture dyes, the highest degradation efficiency for MB is achieved by a Ce(10)/MoO3 sample. It is surprising that the degradation efficiency of MB in the MB-MO mixture dye solution is higher than that in the single-component MB dye solution, which has been mainly ascribed to the promoting effect of MO. Moreover, a plausible degradation mechanism of the dyes has been proposed and discussed. It should be noted that the degradation reaction is carried out at room temperature and normal atmospheric pressure, and without light irradiation. As a result, this degradation reaction is obviously different from the conventional thermally activated heterogeneous catalysis (or photocatalysis), in which thermal energy (or light irradiation) is indispensable; also different from a sorption technology, in which the pollutants cannot be degraded, but only transformed from one phase to another one. Thus, the reported degradation reaction is a quite promising environmental cleaning technology, which could be widely practically applied.
Commercial ZnO, MnO2, and their acid-treated forms were used as catalysts for oxidative
degradation of Orange II dye in water. ZnO and MnO2 were treated with 0.5, 0.75,
or 1.0N aqueous H2SO4. The acid treated oxides were found to be highly effective in
bringing about degradation of Orange II in water. As much as 68.7% of the dye in an
aqueous solution of 1 mg/L concentration could be degraded with untreated ZnO as the
catalyst. The degradation increased to 79.5% with 1.0N acid treated ZnO as the catalyst
when the reaction was carried out at room temperature for 240 min. The catalytic
activity was slightly affected by the solution pH in the range of 2.0–8.0. With MnO2 as
the catalyst, there was only 12.7% degradation of the dye, but this increased up to 100%
when 0.5N acid treated MnO2 was used as the catalyst. It was found that a catalyst
loading of 5.0 g/L of raw and acid-treated ZnO and a loading of 0.5 g/L of raw and acidtreated
MnO2 could bring about almost 100% degradation of Orange II in water in an
interaction time of 240 min at room temperature.
A micellar polyoxometalate catalyst [C16H33N(CH3)(3)](7)[PW10Ti2O38(O-2)(2)] was prepared and used for catalytic wet air oxidation of thiocyanate (SCN-). The 97.6% removal efficiency was obtained with oxygen and under room conditions. And the oxidation of SCN- was achieved completely leading degradation products SO42-, HCO3-, NH4+ and NO3- within 150 min. The leaching test showed that the POM micellar catalyst had excellent stability and could be used as heterogeneous catalyst for about five times. (c) 2010 Elsevier B.V. All rights reserved.
The photocatalytic activity of combustion synthesized nanocrystalline CeAlO3 was determined for the degradation of four anionic and four cationic dyes. The perovskite oxide showed high-photocatalytic activity and a complete degradation of all the dyes was possible within 2 h. The photocatalytic activity of the compound was comparable with the activity of the commercial Degussa P-25 TiO2 catalyst. The degradation of dyes was found to follow first order kinetics and the first order degradation rate constants were determined.
A facile process to prepare polyoxometalate Zn1.5[PW12O40] nanotube is presented. The structure and morphology of this nanotube were characterized using IR, elemental analyses, X-ray powder diffraction, 31P MAS NMR and transmission electron microscopy. This nanotube material has a self-supporting tube structure that can be used as a heterogeneous catalyst for the degradation of safranine T (ST) using molecular oxygen (air) as oxidant and can be easily separated from the aqueous phase, thus enabling it to be used several times.
The epoxidation of olefins with H2O2 was performed with a tungsten-containing catalyst. This insoluble catalyst forms soluble active species by the action of H2O2, and when the H2O2 is used up, the catalyst precipitates for easy recycling. Thus, the advantages of both homogeneous and heterogeneous catalysts are combined in one system through reaction-controlled phase transfer of the catalyst. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H2O2 production, O-2 can be used for the epoxidation of propylene to propylene oxide with 85% yield based on 2-ethylanthrahydroquinone without any co-produds. This approach avoids the problematic co-products normally associated with the industrial production of propylene oxide.
This article reports a simple method for functionalizing the surface of TiO2 (both anatase and rutile) and ZrO2 nanofibremembranes with Pt, Pd, and Rhnanoparticles. The TiO2 membranes were prepared in the form of nonwoven mats by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air to generate anatase (at 510 °C) or rutile (at 800 °C). The ZrO2 membranes were fabricated with a solution of poly(vinyl pyrrolidone) and zirconium acetylacetonate, followed by calcination in air at 550 °C to yield the tetragonal phase. The fibre mats were then immersed in a polyol reduction bath to coat the surface of the nanofibres with Pt, Pd, or Rhnanoparticles of 2–5 nm in size. In addition, the ceramic fibres decorated with Ptnanoparticles could serve as a substrate to grow Ptnanowires7 nm in diameter with lengths up to 125 nm. We subsequently demonstrated the use of Pd-coated anatase fibre membranes as a catalytic system for cross-coupling reactions in a continuous flow reactor. Contrary to the conventional setup for an organic synthesis, a continuous flow system has advantages such as short reaction time and no need for separation. The membrane-based catalytic system can also be fully regenerated for reuse.
Titanium dioxide is one of the best semiconductor photocatalysts available for photocatalysis. In this paper, titanium dioxide nanofiber membranes are prepared by post-anneal-assisted electrospinning process. The obtained membrane is composed of anatase titanium dioxide continuous and porous nanofibers with diameters ranging from 65 to 115 nm. An optimized annealing scheme is determined. Photocatalytic measurements show that the photocatalytic efficiency of the anatase TiO2 nanofiber membrane is 72%, which is highly superior to that of the anatase TiO2 thin film (44%). It is believed that the large specific surface area intensively enhances the photocatalytic reactions and the good shape retention might be favorable for recuperability and practicality. The potential applications for environmental purification are discussed.
Thin films of various compositions in the system SiO2–TiO2 were prepared by the sol–gel method, with the effects of laser-densification and heat treatment being studied. The etch rate of the resultant coating films was found to change by a factor of almost 1000 for various heat treatment conditions in the temperature range 600∼800°C. By combining laser sintering of selected areas and chemical etching techniques, the large difference between the etch rates of densified and undensified coatings can be used to produce channel waveguide structures. The etched coatings were characterized by X-ray diffraction, Fourier transform infrared spectra and micro-Raman spectra with these studies indicating that crystallization occurs in the region of laser scanning with dimensions corresponding approximately to the width of the beam used.
MoO3 thin films were intercalated with Mg ions using a standard three-electrode configuration. The concentration of Mg ions was varied from x=0.05 to x=0.4, where x is the ratio of Mg ions and host Mo ions. IR studies were carried out on unintercalated, intercalated, deintercalated and aged films. The effect of ion concentration (x) on lattice distortion and reversibility has been investigated by monitoring systematically the number of resonance absorption peaks, their respective intensities and spectral locations. At low values of x (
The surface acidic and redox properties of CeO2, MoO3, mechanically mixed CeO2–MoO3 and co-precipitated Ce–Mo–O catalysts were characterized by using microcalorimetric adsorption of ammonia and isopropanol (IPA) probe reaction, and the surface properties of these catalysts were correlated with their selectivity for the oxidation of toluene to benzaldehyde and benzoic acid. With the presence of O2, IPA converted to propylene and diisopropyl ether on acidic sites while converted to acetone on redox sites. It was found that CeO2 exhibited mainly the redox property while MoO3 the surface acidity. The IPA probe reaction showed that the mechanically mixed CeO2–MoO3 exhibited the surface acidic property, similar to that of MoO3, indicating that the surface of CeO2 might be covered by MoO3 in the mixture upon the calcination at 773K. On the other hand, the co-precipitated Ce–Mo–O catalyst showed the equivalent acidic and redox properties, and thereby the selectivity to benzaldehyde was greatly enhanced on it as compared to the other catalysts studied in this work.
A novel photocatalyst, nanoporous anatase TiO2 crystalline particles coupled by homogeneously dispersed Keggin unit, H3PW12O40/TiO2, was prepared by a simple and rapid process, i.e., at a lower temperature (200°C) by combined sol–gel and programmed temperature hydrothermal methods. The resulting material was characterized by UV diffuse reflectant spectroscopy, XRD, 31P MAS NMR, TEM, and nitrogen adsorption. This new photocatalyst exhibited visible-light photocatalytic activity to decompose 10 various organic dyes in aqueous systems. It was attempted to determine the feasibility of such a degradation by varying the chemical structures, either azoic (Congo Red (CR), Methyl Orange (MO), Ponceau G (PG), Orange II (OII), and Eriochrome Blue Black B (EB)), or anthraquinonic (Alizarin S (AS)), or heteropolyaromatic (Methylene Blue (MB)), or fluorescent (Neutral Red (NR), Rhodamine B (RB)), or sulfonic (Fuchsin Acid (FA)). The intermediates and the final products of degradation were detected by electrospray mass spectrometer (ES-MS) and ion chromatography (IC). According to the experimental results, we proposed a possible mechanism of the photodegradation of dyes under visible-light irradiation in the aqueous system.
Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SOx reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.
The reduction of CuO dispersed on fluorite-type oxide catalysts, namely La-doped CeO2 and Y-doped ZrO2 was studied in this work. On both supports distinct copper species were identified as a function of copper content by temperature-programmed reduction (TPR) by H2 and CH4, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and scanning transmission electron microscopy/energy dispersive X-ray (STEM/EDX) analyses. At low copper loading (15 at%), in addition to clusters, larger CuO particles are present which are reduced at higher temperature close to the reduction temperature of bulk CuO. At copper loading lower than ca. 5 at%, copper is present as highly dispersed clusters or isolated Cu ions, which interact strongly with the fluorite-type oxide, thus requiring higher reduction temperature. However, the latter is still below the bulk CuO reduction temperature. Copper is more stabilized when dispersed in Ce(La)O2 than in Zr(Y)O2 matrix, so that reduction of copper oxide species requires lower temperatures on the Zr(Y)O2-based catalysts. The reducibility of the doped ceria is enhanced by the presence of copper in both H2- and CH4-TPR. On the other hand no such interaction is present in CuZr(Y)O2 system. The activity of various copper species for methane oxidation is discussed.
The influence of yttria used as a doping agent for catalyst support, on the dispersion and the resistance to sintering of MoO3, CeO2 and bi-oxide MoO3-CeO2 species in the TCC catalysts has been investigated. Characterization techniques used included N-2 adsorption, X-ray diffraction, Raman, thermogravimetric analysis, and iso-electric point (IEP). It was explicitly found that yttria-doped alumina aerogel is by far more capable of homogenously dispersing the active molybdenum species and significantly retarding their sintering at quite high-calcination temperature than conventional alumina and alumina aerogel. Characterization results of supported mono-oxide MoO3 catalysts have clearly indicated that the fraction of (surface) tetrahedral monomolybdate species increases in the detriment of crystalline MoO3 as we varied the support from conventional alumina to yttria-doped alumina aerogel with increasing amounts of the yttria loading. This can be attributed to the incorporation of yttria into alumina aerogel network, which led to a change in the support surface charge IEP) and subsequently the stability of surface molybdate species. The dispersion degree of ceria (substituted ceria) on supported monooxide CeO2 was improved as well, upon using yttria-doped alumina aerogel. Such improvement was attributed to the formation of stronger Ce-Y-O bond, and/or the formation of CeO2-Y2O3 solid solution. In the bi-oxide MoO3-CeO2, characterization results have indicated the presence of surface interaction between Mo and Ce, probably through the formation of surface "Mo-O-Ce" type phase between the dispersed ceria and the molybdate monolayer. This interaction, which was highly favourable over yttria-doped alumina surface, contributed significantly to the overall surface stability of Mo-Ce catalysts. (c) 2007 Elsevier B.V. All rights reserved.
Tungsten oxide (WO3) and molybdenum oxide (MoO3) nanowires were synthesized through utilizing sol gel and electrospinning methods. Mixtures of metal oxide sol gel and polyvinylpyrrolidone (PVP) in ethanol solution were electrospun and resulted in metal oxide composite nanofiber mats. Precise annealing process removed all organic material, and pure metal oxide single crystal nanowires remained. Both the as-spun nanocomposite mats and the heat-treated nanofiborous materials were characterized using Scanning and Transmission Electron Microscopes. The average diameter of the nanofibers was concluded to be proportional to the flow rate used and inversely proportional to the metal oxide concentration in the solution.
A new method of fabricating hierarchically ordered nanofibers by combining electrospinning and controlled polymer crystallization techniques was studied. Poly(ethylene oxide) (PEO), dimethylformamide (DMF), toluene, gold (III) chloride, tetrabutylammonium borohydride, and didodecyldimethylammonium bromide were used and synthesized. PEO nanofibers were electrospun onto the surface of a carbon-coated nickel TEM grid. Ruthenium tetraoxide (RuO 4) was used to stain some of the TEM samples. Electrospinning nanofibers of PEO, which were collected on the surface of glass slides or TEM grids, were incubated in a polymer solution for 60 minutes. The nanofibers were then taken out from the solution and washed with DMF to remove free polymers. Scanning electron microscopy (SEM) was carried out using an environmental SEM. It was concluded that this new technique can find wide applications in the field of sensors, catalyst support, nanoelectronics, and tissue engineering.
In the present study, cobalt(II) oxide (CoO), which is hard to synthesize because of the chemical activity of cobalt metal, and the popular cobalt(II, III) oxide (Co3O4) have been successfully produced in smooth and continuous nanofibrous form by using the electrospinning technique. An aqueous cobalt acetate tetrahydrate and poly(vinyl alcohol) mixture has been electrospun and vacuously dried at 80 °C. Pure, smooth and solid Co3O4 nanofibers were produced when the dried nanofiber mats were calcined in air atmosphere at 700 °C. Water gas has been prepared by a novel technique to produce pure CoO nanofibers from the original cobalt acetate/poly(vinyl alcohol) nanofiber mats. The nanofiber mats have been hydrothermally treated in the presence of carbon at 300 °C in an especially designed reactor. The invoked physiochemical analyses have affirmed formation of both oxides in nanofibrous shape. The optical properties of the obtained nanofibers have been studied. UV−visible absorbance spectra have indicated that the band gap energy differences for the Co3O4 and CoO nanofibers are 2.4 and 2.21 eV, respectively.
Wet air oxidation (WAO), involving oxidation at high temperature (125--320 C) and pressure (0.5--20 MPa) conditions, is useful for the treatment of hazardous, toxic, and nonbiodegradable waste streams. The process becomes self-sustaining when the feed chemical oxygen demand (COD) is about 20,000 mg/l and can be a net energy producer at sufficient higher feed COD's. All the published information on WAO has been analyzed and presented in a coherent manner. Wet air oxidation studies on pure compounds have been critically reviewed. Mechanism, kinetics, and structure-oxidizability correlation for WAO of carboxylic acids, phenols, cyanides, and nitriles have been described. The industrial applications discussed include municipal sewage sludge treatment, distillery waste treatment, black liquor treatment, cyanide and nitrile wastewater treatment, spent carbon regeneration, and energy and resource regeneration. Waste streams from other sources and some miscellaneous applications of WAO have also been included. Special emphasis is given to WAO under supercritical conditions (above the critical temperature of water) and oxydesulfurization of coal. In addition to the industrial applications, some other aspects (like various catalysts and oxidizing agents) of WAO have also been discussed. Recommendations and suggestions for further investigations have been made. 560 refs.
In order to develop a catalyst with high activity and stability for catalytic wet air oxidation of pollutant dyes at room condition, a new polyoxometalate Zn1.5PMo12O40 with nanotube structure was prepared using biological template. The structure and morphology were characterized using infrared (IR) spectra, UV–vis diffuse reflectance spectra (DR-UV–vis), elemental analyses, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). And the degradation of Safranin-T (ST), a hazardous textile dye, under air at room temperature and atmospheric pressure was studied as a model experiment to evaluate the catalytic activity of this polyoxomolybdate catalyst. The results show that the catalyst has an excellent catalytic activity in treatment of wastewater containing 10 mg/L ST, and 98% of color and 95% of chemical oxygen demand (COD) can be removed within 40 min. And the organic pollutant of ST was totally mineralized to simple inorganic species such as HCO3−, Cl− and NO3− during this time (total organic carbon (TOC) decreased 92%). The structure and morphology of the catalyst under different cycling runs show that the catalyst are stable under such operating conditions and the leaching tests show negligible leaching effect owning to the lesser dissolution. So this polyoxomolybdate nanotube is proved to be a heterogeneous catalyst in catalytic wet air oxidation of organic dye.
We have prepared polymer core-shell fibers containing salts of palladium, rhodium, and platinum. These salts were reduced within the core of the fibers by thermal decomposition at elevated temperatures and by using hydrogen as reduction medium. Monometal nanoparticles as well as mixed bimetal nanoparticles were produced in this way. The resulting fibers consisted either of a hollow core carrying the nanoparticles or a polymer core in which the nanoparticles were distributed. Both systems were successfully applied to specific hydrogenation reactions in which the shell served the purpose of immobilizing the catalyst nanoparticles, controlling the access to them, and allowing their recovery after the reaction whereas the core acted as the confined reaction site with an easy access of the reactants to the catalytic sites.
In this work, nanobelt mats consisting of three potential metal oxides have been produced using the electrospinning technique.
An aqueous solution of cobalt acetate tetra-hydrate, copper acetate mono-hydrate, and manganese acetate tetra-hydrate was
mixed with poly(vinyl alcohol) solution to prepare a sol–gel which was electrospun at 20 kV. The obtained nanofiber mats have
been vacuously dried at 80 °C for 24 h and then calcined in air atmosphere at different temperatures and soaking times. The
utilized physiochemical characterizations have affirmed that nanobelts composed of three oxides (Co3O4, CuO, and MnO2) can be prepared by calcination at a temperature of 600 °C for 1 h. High-resolution transmission electron microscope and
selected area electron pattern images revealed good crystallinity for the synthesized nanobelts.
All advanced oxidation processes (AOP) are characterised by a common chemical feature: the capability of exploiting the high reactivity of HO radicals in driving oxidation processes which are suitable for achieving the complete abatement and through mineralization of even less reactive pollutants. The different AOP are considered and critically presented according to their specific features with reference, whenever possible, to their real applications for water pollution abatement. The experimental apparatus and working procedures which can be adopted for carrying out waste water treatments by AOP application are examined. Some remarks upon treatment economics are provided on the basis of the main parameters affecting the AOP costs.
Many synthetic dyes in industrial wastewaters are resistant to degradation in conventional biological treatment process. Decolorization of eight synthetic dyes including azo, anthraquinone, metal complex and indigo were examined in white-rot fungal cultures and by fungal peroxidase-catalysed oxidation. The dyes were not decolorized by manganese-dependent peroxidase (MnP) while above 80% color was removed by ligninase-catalysed oxidation. Dye decolorization rate increased linearly with ligninase doses. Compared with fungal cultures in which ligninase was detected, partially purified ligninase showed a consistent and higher extent of dye decolorization with other essential components being provided such as veratryl alcohol, hydrogen peroxide and acidic pH (3.5–5). Veratryl alcohol had a critical concentration level above which no further effect on dye decolorization was observed. Depending on the influence of H2O2 on dye decolorization, the eight dyes can be divided into two groups; one had an optimum H2O2 concentration and the other showed increased decolorization with high H2O2 doses. Dye concentration had a negative effect on decolorization rate in general. The dye concentration above which the negative effect was observed varied from 10 to 125 mg/L, depending on individual dye structure. These results indicate that a highly efficient bioprocess using white-rot fungi to remove color from industrial effluents should produce ligninase, H2O2, veratryl alcohol continuously and coordinately under acidic condition and controlled back-mixing flow of wastewater.
Nowadays, due to the increasing presence of molecules, refractory to the microorganisms in the wastewater streams, the conventional biological methods cannot be used for complete treatment of the effluent and hence, introduction of newer technologies to degrade these refractory molecules into smaller molecules, which can be further oxidized by biological methods, has become imperative. The present work aims at highlighting five different oxidation processes operating at ambient conditions viz. cavitation, photocatalytic oxidation, Fenton's chemistry (belonging to the class of advanced oxidation processes) and ozonation, use of hydrogen peroxide (belonging to the class of chemical oxidation technologies). The work highlights the basics of these individual processes including the optimum operating parameters and the reactor design aspects with a complete overview of the various applications to wastewater treatment in the recent years. In the next article of this two article series on imperative technologies, hybrid methods (basically combination of the oxidation processes) will be discussed and the current work forms a useful foundation for the work focusing on hybrid technologies.
The photocatalytic degradation of aqueous solutions of Acid Orange 7 in TiO2 suspensions has been investigated with the use of a solar light simulating source. The photoreaction was followed by monitoring the degradation of the dye and the formation of intermediates and final products, as functions of time of irradiation, both in solution and on the photocatalyst surface. It has been found that the dye adsorbs on TiO2 and undergoes a series of oxidation steps, which lead to decolorization and formation of a number of intermediates, mainly aromatic and aliphatic acids. These molecules are further oxidized toward compounds of progressively lower molecular weight and, eventually, to CO2 and inorganic ions, such as sulfate, nitrate and ammonium ions. A TiO2-mediated photodegradation mechanism for Acid Orange 7 is proposed on the basis of quantitative and qualitative detection of intermediate compounds.
Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions, Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SOx reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.
The photocatalytic degradation of p-chlorophenoxyacetic acid has been investigated in oxygenated aqueous suspensions of lanthanide oxide-doped TiO2 photocatalysts. Complete mineralization was achieved. The enhanced degradation is attributed to the formation of Lewis acid-base complex between the lanthanide ion and the substrate.
The epoxidation of olefins with H2O2 was performed with a tungsten-containing catalyst. This insoluble catalyst forms soluble active species by the action of
H2O2, and when the H2O2 is used up, the catalyst precipitates for easy recycling. Thus, the advantages of both homogeneous and heterogeneous catalysts
are combined in one system through reaction-controlled phase transfer of the catalyst. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone
redox process for H2O2 production, O2 can be used for the epoxidation of propylene to propylene oxide with 85% yield based on 2-ethylanthrahydroquinone without
any co-products. This approach avoids the problematic co-products normally associated with the industrial production of propylene
oxide.
A novel microwave electrodeless lamp (MWL) rather than traditional electrode lamp (TEL) was used in a H(2)O(2)/MWL system as light source. This technique provided a new way to study the simultaneous effect of both UV-vis light and microwave irradiations. This study showed that H(2)O(2)/MWL process was 32% more effective than H(2)O(2)/TEL process in degrading azo dye Acid Orange 7 (AO7). Further study found that the degradation of AO7 by the H(2)O(2)/MWL process was initiated by the attack of HO* radicals generated by the photolysis of H(2)O(2). However, the direct photolysis of AO7 by MWL irradiation was not negligible. Effect of operation parameters, such as the initial concentrations of AO7 and H(2)O(2) and pH, were investigated. A kinetic model of degradation of AO7 by H(2)O(2)/MWL process was found, in which not only the HO* oxidation but also direct photolysis were considered. The kinetic model was consistent with the experiment results. The degradation of AO7 by H(2)O(2)/MWL corresponded to a pseudo-first order reaction. The apparent reaction constant (k(ap)) was a function of initial concentrations of H(2)O(2) and AO7 and pH of the solution.
The photocatalytic degradation of C.I. Acid Red 27 (AR27), an anionic monoazo dye of acid class, in aqueous solutions was investigated with immobilized ZnO catalyst on glass plates in a continuous-mode. In the slurry ZnO system the separation and recycling of the photocatalyst is practically difficult. Thus, ZnO was immobilized on solid supports to solve this problem. The removal percent increases with increasing the photoreactor volume and light intensity but it decreases when the flow rate is increased. With decreasing flow rate from 43 to 15mlmin(-1), the complete decolorization and degradation was obtained at around 748 and 1080cm(3) from photoreactor volume. The increase in the light intensity from 21.4 to 58.5Wm(-2) increases the decolorization from 23 to 57.6% and degradation from 17.5 to 37.8% for 374cm(3) of photoreactor volume. NH(4)(+), NO(3)(-), NO(2)(-) and SO(4)(2-) ions were analyzed as mineralization products of nitrogen and sulfur heteroatoms. Results showed that final concentration of SO(4)(2-) ions and N-containing mineralization products were less than the finally expected stoichiometric values. The positive slope of production of NH(4)(+), NO(3)(-) and NO(2)(-) shows that these compounds are initial products resulting directly from the initial attack on the nitrogen-to-nitrogen double bond (-NN-) of the azo dye.
This work focused on the degradation of toxic organic compounds such as trichloroethylene (TCE) in water, using a combined photocatalysis/microfiltration (MF) system. The performances of the hybrid system were investigated in terms of the removal efficiency of TCE and membrane permeability, in the presence or absence of background species, such as alkalinity and humic acids. The mass balancing of the fate of TCE during photocatalytic reactions was performed in order to evaluate the feasibility of the photocatalytic membrane reactor (PMR). Greater TCE degradation (>60%) was achieved with an increase in the TiO2 dosage (up to 1.5g/L) in PMR, but a substantially large TiO2 dosage brought about a decrease in TCE degradation efficiency. The photocatalytic decomposition of TCE appeared to be more effective in acidic pH conditions than with a neutral or alkaline pH. The addition of alkalinity and humic acid into the feedwater did not have a significant effect on TCE degradation, while humic acids (whose dose was 1mg/L as TOC) in the feedwater played a part in a decline of permeability by 60%. Membrane permeability in the PMR was also affected by tangential velocities. An improvement of 60% in flux was achieved when the tangential velocity increased from 0.19 to 1.45m/s. This is because flow regimes can govern the deposition of TiO2 particles on the membrane surface.
This paper reports a simple procedure for derivatizing the surface of anatase TiO2 nanofibers with Pt nanoparticles and then Pt nanowires. The nanofibers were prepared in the form of a nonwoven mat by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air at 510 degrees C. The fiber mat was then immersed in a polyol reduction bath to coat the surface of anatase fibers with Pt nanoparticles of 2-5 nm in size with controllable density of coverage. Furthermore, the coated fibers could serve as a three-dimensional scaffold upon which Pt nanowires of roughly 7 nm in diameter could be grown at a high density and with a length up to 125 nm. The fiber membranes functionalized with Pt nanoparticles and nanowires are interesting for a number of catalytic applications. It was found to show excellent catalytic activity for the hydrogenation of azo bonds in methyl red, which could be operated in a continuous mode by passing the dye solution through the membrane at a flow rate of 0.5 mL/s.
The Role of Molybdenum in Catalysis Climax Molybdenum Co
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Weinheim www.clean-journal.com Figure 7. Changes in the FT-IR spectra of (a) ST, and (b) RhB during degradation
- Wiley-Vch Co
- Kgaa
i 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Figure 7. Changes in the FT-IR spectra of (a) ST, and (b) RhB during degradation. S. Zhao et al. Clean – Soil, Air, Water 2010, 38 (3), 268 – 274
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[22] N. Al-Yassir, R. L. V. Mao, Catalysts for the Thermo-catalytic Cracking
(TCC) Process: Interactions between the Yttria in Yttria-doped Alumina Aerogel and the Mono-oxide MoO3, CeO2, and Bi-oxide MoO3 –
CeO2 Species, Appl. Catal., A 2007, 332, 273 – 288.
Polymer Core-shell Fibers with Metal Nanoparticles as a Nanoreactor for Catalysis, Macromolecules
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M. Graeser, E. Pippel, A. Greiner, J. Wendroff, Polymer Core-shell
Fibers with Metal Nanoparticles as a Nanoreactor for Catalysis, Macromolecules 2007, 40, 6032 -6039.
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K. M. Sawicka, M. Karadge, P.-I. Gouma, Molybdenum and Tungsten
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N. Al-Yassir, R. L. V. Mao, Catalysts for the Thermo-catalytic Cracking
(TCC) Process: Interactions between the Yttria in Yttria-doped Alumina Aerogel and the Mono-oxide MoO3, CeO2, and Bi-oxide MoO3 -CeO2 Species, Appl. Catal., A 2007, 332, 273 -288.