Abstract
Double modifications of TiO2 by doping with WO3 and by dispersing on a SiO2 support were made by the one-pot sol-gel method. Doping with W shifts the TiO2 band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO2/SiO2 material was significantly increased, by approximately 3 times, in comparison to the bare TiO2. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO2/SiO2 catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals such as O2- and ⋅OH, together with W6+/W5+ couples and e-/h+ pairs in the catalysts in the p-nitrophenol photodegradation. The one-pot sol-gel synthesis method was proven to be effective to obtain W-TiO2/SiO2 catalyst with large surface area and high photocatalytic activity, and it can be also used for the preparation of other heterogeneous catalysts.
Highlights
Industrial development around the world has greatly increased the volume of contaminated residual water [1,2,3]
The one-pot sol-gel synthesis method reported was proven to be effective to obtain a W-TiO2/SiO2 catalyst with a large surface area and high photocatalytic activity, and it can be used for the preparation of other heterogeneous catalysts
The X-ray photoelectron spectroscopy (XPS) and UV-vis spectra show that after W doping, a slight displacement of the electromagnetic spectrum towards the visible region was observed for the W-TiO2 catalyst
Summary
Industrial development around the world has greatly increased the volume of contaminated residual water [1,2,3]. Nanotechnology for eliminating or reducing environmental pollutants has shown significance in the last decades, for water contaminant control [4]. Heterogeneous photocatalysis represents a part of the solution for addressing environmental concerns due to its significant benefits compared to traditional decontamination methods, allowing the complete mineralization of organic contaminants without producing dangerous intermediate residuals [1, 5]. Photocatalysis involves the use of solar or ultraviolet light and a semiconductor such as TiO2 [3]. TiO2 only absorbs light in the UV region due to its relatively large band gap energy (~3.2 eV), which is the main drawback for its application, since only 4~5% of the solar spectrum falls within this range [6]. Doping TiO2 with transition metal oxides is another effective way to overcome this problem and improve its photoactivity [9, 10]
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