Understanding photocatalytic activity and mechanism of nickel-modified niobium mesoporous nanomaterials
TL;DR: In this article, mesoporous Niobium(V) oxides (n-type) with relatively high surface areas were synthesized by Evaporation Induced Self-Assemble method and modified with different amounts of NiO (p-type).
Abstract: To better understand the photocatalysis oxidation mechanism of different types of coupled semiconductors, mesoporous niobium(V) oxides (n-type) with relatively high surface areas (140 m2 g−1) were synthesized by Evaporation Induced Self-Assemble method and modified with different amounts of NiO (p-type). The materials are polycrystalline nanostructures, with mesoporous of approximately 12 nm and bandgap values in the UVA range of the spectrum (344–356 nm). The materials showed remarkable photocatalytic activity and the addition of nickel oxide increased the reducibility of the Nb5+ species and improved the charge transfer in the materials. Studies with indigo carmine dye have shown that the niobium-based materials are able to decolorize a 40 ppm solution in 20 and 60 min (1.0% NiO material) in photo-Fenton like reaction, and photocatalysis reactions, respectively, without the strong adsorption of the molecule to the material surface. In addition, in the presence of a radical scavenger the photocatalytic reactions half-life time showed an increase of up to 11 times, which indicates that the indirect oxidation mechanism, with the formation of radicals, is predominant. The formation of hydroxyl radicals during irradiation was confirmed by EPR analysis with the spin trapping method.
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TL;DR: The recent advances in the synthesis and application of Niobium pentoxide (Nb2O5)-based photocatalysts, including the pure Nb 2O5, doped nb 2 o5, metal species supported on Nb2 o5 and other composited Nb o5-based catalysts, are summarized in this article.
Abstract: Photocatalysis is one potential solution to the energy and environmental crisis and greatly relies on the development of the catalysts. Niobium pentoxide (Nb2O5), a typically nontoxic metal oxide, is eco-friendly and exhibits strong oxidation ability, and has attracted considerable attention from researchers. Furthermore, unique Lewis acid sites (LASs) and Bronsted acid sites (BASs) are observed on Nb2O5 prepared by different methods. Herein, the recent advances in the synthesis and application of Nb2O5-based photocatalysts, including the pure Nb2O5, doped Nb2O5, metal species supported on Nb2O5, and other composited Nb2O5 catalysts, are summarized. An overview is provided for the role of size and crystalline phase, unsaturated Nb sites and oxygen vacancies, LASs and BASs, dopants and surface metal species, and heterojunction structure on the Nb2O5-based catalysts in photocatalysis. Finally, the challenges are also presented, which are possibly overcome by integrating the synthetic methodology, developing novel photoelectric characterization techniques, and a profound understanding of the local structure of Nb2O5.
60 citations
TL;DR: In this paper, a review summarizes the special characteristics of Niobium-based catalysts, and the application of these catalysts on the catalytic conversion of biomass, including properties of Nb-based catalyst, including catalytic hydrolysis/dehydration for platform chemicals, catalytic pyrolysis for hydrocarbons, and catalytic esterification.
27 citations
TL;DR: In this article, the wet impregnation method was used to synthesize SnO2/MoO3 heterojunctions containing different amounts of Mo (5, 25 and 50) and their photocatalytic properties were evaluated in the photodegradation of methylene blue dye.
Abstract: The wet impregnation method was used to synthesize SnO2/MoO3 heterojunctions containing different amounts of Mo (5, 25 and 50 wt%). The materials obtained were characterized and their photocatalytic properties were evaluated in the photodegradation of methylene blue (MB) dye. The presence of superficial Lewis and Bronsted acid sites enhanced in photocatalytic efficiency of the materials. The order of photocatalytic activity in MB photodegradation was MoO3 > SnO2/MoO3-50 % > SnO2/MoO3-25 % > SnO2/MoO3-5% > SnO2, demonstrating that MoO3 acts as a modulator of acidity and this behavior directly influences the photocatalytic performance. In the photodegradation study, the physical mixture of SnO2+MoO3-25 % provided lower performance values than the heterojunction SnO2/MoO3-25 %, highlighting the importance of the appropriate synthesis of these materials.
18 citations
TL;DR: In this article, the effect caused by the presence of hydroxyl radicals (1-butanol and 2-propanol), positive holes (h+) (potassium iodide) and singlet oxygen (azide) was studied.
Abstract: This study is aimed at investigating the influence of different scavenger species of radicals that might possibly be involved in the TiO2/UVA photocatalytic degradation of Indigo Carmine dye. The effect caused by the presence of hydroxyl radicals (1-butanol and 2-propanol), positive holes (h+) (potassium iodide) and singlet oxygen (azide) was studied. Kinetics and optimal degradation conditions were evaluated using a factorial experiment design. The highest pseudo-first-order kinetics (k = 5.22 × 10−2 ± 0.002 and t1/2 = 13.25 ± 0.49 min) was achieved at pH 4.0, 6 mg L−1 of Indigo Carmine dye and 12 mg L−1 of TiO2. Mineralization was not achieved, and direct photolysis was not observed under the studied conditions. Indigo Carmine degradation occurs mainly due to oxidation in the positive hole (h+) followed by singlet oxygen action and on a smaller scale by hydroxyl radical. The use of the aforementioned radical scavengers made it possible to verify the mechanism and kinetics of Indigo Carmine dye through TiO2 heterogeneous photocatalysis.
15 citations
TL;DR: In this paper, the deposition of a small loading of Cu nanoparticles by DC-magnetron sputtering over niobium oxide (Nb2O5) increases its photocatalytic activity for the reduction of carbon dioxide (CO2) into methane (CH4), methanol (CH3OH), acetone(CH3COCH3), acetic acid (CH 3COOH), isopropanol(CH 3CH(OH)CH3) and formate (HCOO−).
Abstract: Herein we demonstrate that the deposition of a small loading of Cu nanoparticles (0.51 wt %) by DC-magnetron sputtering over niobium oxide (Nb2O5) increases its photocatalytic activity for the reduction of carbon dioxide (CO2) into methane (CH4), methanol (CH3OH), acetone (CH3COCH3), acetic acid (CH3COOH), isopropanol (CH3CH(OH)CH3) and formate (HCOO−). The improvement in the CO2 photoreduction of the Nb2O5/Cu can be attributed mainly to a reduction in the recombination rate of the electron-holes pairs photogenerated due to the electron trapping by Cu species as observed by the photoluminescence analysis, high dispersion of Cu, and high specific surface area of material even after addition Cu.
9 citations
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TL;DR: In this article, the authors present the presentation, nomenclature, and methodology associated with the application of physisorption for surface area assessment and pore size analysis.
Abstract: Gas adsorption is an important tool for the characterisation of porous solids and fine powders. Major advances in recent years have made it necessary to update the 1985 IUPAC manual on Reporting Physisorption Data for Gas/Solid Systems. The aims of the present document are to clarify and standardise the presentation, nomenclature and methodology associated with the application of physisorption for surface area assessment and pore size analysis and to draw attention to remaining problems in the interpretation of physisorption data.
11,019 citations
TL;DR: In this article, the authors focus on interfacial processes and summarize some of the operating principles of heterogeneous photocatalysis systems, including the electron transfer and energy transfer processes in photocatalytic reactions.
Abstract: In 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO{sub 2} electrodes. This event marked the beginning of a new era in heterogeneous photocatalysis. Since then, research efforts in understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO{sub 2} have come from extensive research performed by chemists, physicists, and chemical engineers. Such studies are often related to energy renewal and energy storage. In recent years, applications to environmental cleanup have been one of the most active areas in heterogeneous photocatalysis. This is inspired by the potential application of TiO{sub 2}-based photocatalysts for the total destruction of organic compounds in polluted air and wastewaters. There exists a vast body of literature dealing with the electron transfer and energy transfer processes in photocatalytic reactions. A detailed description of these processes is beyond the scope of this review. Here, the authors tend to focus on interfacial processes and to summarize some of the operating principles of heterogeneous photocatalysis. In section 2, the authors first look at the electronic excitation processes in a molecule and in a semiconductor substrate. The electronic interaction between the adsorbate molecule and the catalyst substrate is discussed in terms of the catalyzed ormore » sensitized photoreactions. In section 3, thermal and photocatalytic studies on TiO{sub 2} are summarized with emphasis on the common characteristics and fundamental principles of the TiO{sub 2}-based photocatalysis systems. In section 4, they address the research effort in the electronic modification of the semiconductor catalysts and its effect on the photocatalytic efficiency. Several representative examples will be presented including the Schottky barrier formation and modification at metal-semiconductor interfaces. Some concluding remarks and future research directions will be given in the final section. 160 refs.« less
10,719 citations
TL;DR: This paper presents a meta-analyses of the chiral stationary phase transition of Na6(CO3)(SO4)2, Na2SO4, and Na2CO3 of the Na2O/Na2O 2 mixture at the stationary phase and shows clear patterns in the response of these two materials to each other.
Abstract: Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China
4,353 citations
TL;DR: In this article, the TiO2/UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions, and it has been shown that the degradation pathway can be determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening.
Abstract: The TiO2/UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions. In addition to a prompt removal of the color, TiO2/UV-based photocatalysis was simultaneously able to oxidize the dye, with an almost complete mineralization of carbon and of nitrogen and sulfur heteroatoms into CO2 ,N H4 + ,N O3 − and SO4 2− , respectively. A detailed degradation pathway has been determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening. These results suggest that TiO2/UV photocatalysis may be envisaged as a method for treatment of diluted waste waters in textile industries. © 2001 Elsevier Science B.V. All rights reserved.
2,359 citations
TL;DR: In this article, a simple and versatile procedure for the synthesis of thermally stable, ordered, large-pore (up to 140 A) mesoporous metal oxides was described.
Abstract: Surfactants have been shown to organize silica into a variety of mesoporous forms, through the mediation of electrostatic, hydrogen-bonding, covalent and van der Waals interactions1,2,3,4,5,6,7,8. This approach to mesostructured materials has been extended, with sporadic success, to non-silica oxides5,6,7,8,9,10,11,12,13,14,15,16,17, which might promise applications involving electron transfer or magnetic interactions. Here we report a simple and versatile procedure for the synthesis of thermally stable, ordered, large-pore (up to 140 A) mesoporous metal oxides, including TiO2, ZrO2, Al2O3, Nb2O5, Ta2O5, WO3, HfO2, SnO2, and mixed oxides SiAlO3.5, SiTiO4, ZrTiO4, Al2TiO5 and ZrW2O8. We used amphiphilic poly(alkylene oxide) block copolymers as structure-directing agents in non-aqueous solutions for organizing the network-forming metal-oxide species, for which inorganic salts serve as precursors. Whereas the pore walls of surfactant-templated mesoporous silica1 are amorphous, our mesoporous oxides contain nanocrystalline domains within relatively thick amorphous walls. We believe that these materials are formed through a mechanism that combines block copolymer self-assembly with complexation of the inorganic species.
2,325 citations