Preparation of ordered mesoporous Ag/WO3 and its highly efficient degradation of acetaldehyde under visible-light irradiation
Introduction
In recent years, numerous studies have been reported on semiconductor photocatalysis which can utilize solar energy to decompose harmful organic pollutants in air and aqueous systems [1], [2], [3], [4], [5]. Among the semiconductors employed, TiO2 is the most extensively studied photocatalyst because of its low cost, high efficiency and stability. However, TiO2 is only active in the ultraviolet (UV) light range due to its wide band gap. To obtain visible-light-driven photocatalysts so as to utilize visible light, doping or ion-implanting has been used to modify TiO2 [6], [7], [8], [9], but dopants usually act as recombination centers between the photogenerated electrons and holes, which greatly reduced the photocatalytic activities [10]. Thus researchers are devoted in searching for other candidates to solve this problem.
Tungsten trioxide (WO3), which possesses a small band gap of 2.4–2.8 eV, has many advantages for visible-light-driven photocatalysis such as strong adsorption within the solar spectrum, stable physicochemical properties, and resilience to photocorrosion effects [11], [12], [13], [14]. In addition to the visible-light absorption, there are many other factors influencing the photocatalytic activity, such as the potential levels of energy bands, the separations of photogenerated electron–hole pairs and the microstructures of photocatalysts, etc. Like other simple binary metal oxides, WO3 has a deep valence band which is mainly composed of O 2p orbitals. The deep valence band combined with the small band gap results in a low conduction band level, which limits the photocatalysts to react with electron acceptors [15], [16], [17] and then increases the recombination of photogenerated electron–hole pairs. This was one of the reasons limited the development of WO3 as a practical photocatalyst. Therefore, one of the principles to improve the photocatalytic performance of WO3 is to increase the efficiency of electron–hole separation. Loading noble metals on the photocatalyst has been proved as an effectual approach recently [18], [19], [20]. Among various noble metals, silver is of considerable interest not only because of the resultant enhanced electron–hole separation but also ascribed to the extension of visible-light absorption and enhanced photocatalytic activity from the surface plasmon resonance (SPR) effect of silver nanoparticles [21], [22].
As mentioned above, the microstructures of the photocatalyst also influence the photocatalytic activity significantly. Mesoporous structures exhibit the obvious advantages for the heterogeneous catalysis [23], [24]. Especially, ordered mesoporous structures have been proved to be excellent structures for photocatalysis due to their larger surface area and multiple scattering, enable more light to be harvested and also possess continuous pore channels that facilitate the transfer of reactant molecules [25]. Inspired by the above analysis, we conceive that mesoporous silver loaded WO3 (m-Ag/WO3) may exhibit high photocatalytic activity. However, the preparation and photocatalytic property of m-Ag/WO3 have not been reported up to the present.
In the present paper, photocatalytic active m-Ag/WO3 was synthesized by an ultrasound assisted insertion method. The photooxidation of a common air pollutant acetaldehyde was adopted to evaluate the photocatalytic performance of the as-prepared sample under visible-light irradiation. Comparative studies indicate that the photocatalytic activity of m-Ag/WO3 is much superior to that of pure mesoporous WO3 (m-WO3), silver loaded commercial WO3 (c-Ag/WO3) and nitrogen-doped TiO2 (N-TiO2) nanoparticles under the same conditions. Besides, the photocatalytic mechanism was investigated to understand the much enhanced photocatalytic activity.
Section snippets
Sample preparation
Mesoporous silica with cubic Ia3d symmetry (KIT-6) was prepared according to the reference using tri-block copolymer Pluronic P123 (EO20PO70EO20, MW = 5800, Aldrich) as template in an acidic aqueous solution [26].
Mesoporous WO3 was prepared by a hard template replicating technique. Typically, 1.2 g of 12-phosphotungstic acid (AR, Sinopharm) was dissolved in 10 mL of ethanol, and this solution was incorporated into 0.4 g of as-prepared KIT-6 template under stirring by the impregnation technique.
Structural characteristics
The crystalline phase and mesostructural ordering of the m-WO3 and m-Ag/WO3 samples were characterized by both wide-angle X-ray diffraction (WXRD) and low-angle X-ray diffraction (LXRD) measurements. As shown in Fig. 1a, WXRD demonstrates the m-WO3 sample was well crystallized in a single phase and all of the diffraction peaks can be indexed to monoclinic WO3 (JCPDS 72-0677). The WXRD of the m-Ag/WO3 sample was similar to that of m-WO3 except for the diffraction peak of Ag (1 1 1) at 2θ of 38.1°
Conclusion
Mesoporous silver loaded WO3 has been successfully synthesized by an ultrasound assisted insertion method. The as-prepared m-Ag/WO3 sample exhibits excellent photocatalytic decomposition of a common air pollutant of acetaldehyde under visible-light irradiation. Comparative studies indicated that the photocatalytic activity of the m-Ag/WO3 sample is much superior to that of m-WO3, c-Ag/WO3 and N-TiO2 under the same conditions. The photocatalytic mechanism was investigated to understand the much
Acknowledgements
This work is financially supported by the National Natural Science Foundation of China (Nos. 50732004 and 50672117) National Basic Research Program of China (973 Program, 2007CB613305) and Nanotechnology Programs of Science and Technology Commission of Shanghai Municipality (0852nm00500).
References (36)
- et al.
Photocatalytic decomposition of acetaldehyde and Escherichia coli using NiO/SrBi2O4 under visible light irradiation
Appl. Catal. B: Environ.
(2006) - et al.
Influence of TiO2 and ZnO photocatalysts on adsorption and degradation behaviour of Erythrosine
Dyes Pigments
(2007) - et al.
Photocatalytic oxidation of toluene at indoor air levels (ppbv): towards a better assessment of conversion, reaction intermediates and mineralization
Appl. Catal. B: Environ.
(2009) - et al.
Effect of calcination temperatures on microstructures and photocatalytic activity of tungsten trioxide hollow microspheres
J. Hazard. Mater.
(2008) - et al.
The visible light induced photocatalytic activity of tungsten trioxide powders
Appl. Catal. A
(2001) - et al.
Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity
Appl. Catal. B: Environ.
(2005) - et al.
Structural, electrical and optical properties of TiO2 doped WO3 thin films
Appl. Surf. Sci.
(2005) - et al.
Efficient degradation of toxic organic pollutants with Ni2O3/TiO2−xBx under visible irradiation
J. Am. Chem. Soc.
(2004) - et al.
Electron transport and recombination in dye-sensitized mesoporous TiO2 probed by photoinduced charge-conductivity modulation spectroscopy with monte carlo modeling
J. Am. Chem. Soc.
(2008) - et al.
The role of metal ion dopants in quantum-sized TiO2: correlation between photoreactivity and charge carrier recombination dynamics
J. Phys. Chem.
(1994)
Visible-light photocatalysis in nitrogen-doped titanium oxides
Science
Efficient photochemical water splitting by a chemically modified n-TiO2
Science
Daylight photocatalysis by carbon-modified titanium dioxide
Angew. Chem. Int. Ed.
Nonaqueous sol–gel synthesis of a nanocrystalline InNbO4 visible-light photocatalyst
Adv. Mater.
High photocatalytic capability of self-assembled nanoporous WO3 with preferential orientation of (0 0 2) planes
Environ. Sci. Technol.
Nanoporous-walled tungsten oxide nanotubes as highly active visible-light-driven photocatalysts
Angew. Chem. Int. Ed.
Photo-oxidation of water sensitized by WO3 powder
J. Chem. Soc., Faraday Trans.
Visible-light-induced O2 generation from aqueous dispersions of WO3
J. Phys. Chem.
Cited by (164)
Chitosan-based synthesis of silver-doped tungsten oxide nanoparticles and assessment of its cytotoxicity and photocatalytic performance
2024, Journal of Photochemistry and Photobiology A: ChemistryTNAs/g-C<inf>3</inf>N<inf>4</inf>/AuNPs heterojunction used as integrated device of photocatalytic degradation and SERS detection
2023, Chemical Engineering Journal AdvancesSynchronized surface oxygen states and electron-hole passage in microwave-assisted tungsten oxide for photocatalytic organic decomposition and antibacterial activity
2022, Journal of Environmental Chemical EngineeringMultifunctional SERS chip mediated by black phosphorus@gold-silver nanocomposites inserted in bilayer membrane for in-situ detection and degradation of hazardous materials
2022, Journal of Colloid and Interface ScienceEffect of incorporation of La into WO<inf>3</inf> nanorods for improving photocatalytic activity under visible light irradiation
2022, Journal of Physics and Chemistry of Solids