Tungstate / Tungsten Oxide Heterojunction Photocatalyst

Tungsten trioxide (WO₃) is a typical n-type semiconductor material, which has broad application prospects in electrochromic devices, gas sensors and photocatalysts. Particularly in the field of photocatalysis, WO₃ has a narrow band gap (2.4-2.8eV) compared with other semiconductors (such as titanium dioxide and Bi₂O₃), which can utilize solar energy more effectively.

However, the high photogenerated electron-hole recombination efficiency on the surface of tungsten trioxide semiconductor is one of the main factors affecting its photocatalytic performance, which limits the industrial application of WO₃ in the field of photocatalysis. The key to solve this problem is to improve the efficiency of electron-hole separation, so as to improve the utilization of solar energy.

Heterojunction structures are mainly used in semiconductor lasers, light-emitting devices, solar cells and other scientific fields. The application of heterojunction in gas sensing field is a potential direction. The method of hydrothermal synthesis to synthesize tungstate/tungsten oxide heterojunction photocatalyst in situ can produce stable and highly photocatalytic products. For example, cupric tungstate / tungsten oxide heterojunction photocatalysts:

(1)15g ammonium tungstate was dissolved in 150 mL deionized water and heated in water bath to dissolve it. After adding 250 mL nitric acid of 3 mol L-1 drop by drop, the ammonium tungstate was heated in water bath at 80 for 1 hour and aged for 12 hours. WO_3·H₂O was obtained by centrifugation, washing and drying at 80 degrees.

(2)For WO₃·(H₂O) obtained by step (1), 6h was roasted at 500 degrees centigrade, and WO₃ carrier was obtained.

(3)Preparing a series of concentration of copper (NO₃)₂ solution, immersing 1.0 gWO₃ carrier in the solution of copper (NO₃)₂ (mass ratio of metal element Cu to W is 0.2%, 0.5%, 1%, 3%, 5%, 7%, 10%) respectively, and stirring and drying in water bath at 90 ~℃ for 24 hours. In this process, copper nitrate and tungsten oxide are fully contacted and mixed evenly.

(4)CuWO₄/WO₃ heterojunction photocatalyst can be obtained by calcining the mixture of copper nitrate and tungsten oxide at 500 ℃ for 4 hours.

The photocatalytic activity of CuWO₄/WO₃ heterojunction photocatalyst was investigated using photocatalytic degradation of rhodamine B as a model reaction. After comparing the effects of copper tungstate, it can be found that the degradation rate of rhodamine B by 1wt% CuWO₄/WO₃ sample is 97% under 90 min illumination. The photocatalytic activity is not only much higher than that of CuWO₄, but also significantly higher than that of WO₃ carrier. It shows that CuWO₄/WO₃ heterojunction photocatalyst has excellent photocatalytic properties.

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