Tungsten Trioxide Nanorod Array from Ammonium Paratungstate for Photocatalytic Application

The ever-increasing energy demand in the world and the negative environmental impact of fossil fuels has made the development of renewable fuels a priority in science and engineering research. Photoelectrochemical (PEC) water splitting is considered a promising method to produce hydrogen using water as raw material.

Tungsten trioxide (WO3) is a promising semi-metal material with a band gap within 2.6 eV. It is believed to be an excellent material for hydrogen production through PEC. Moreover, WO3 only absorbs about 12% of the solar spectrum and it presents a relatively low stability in neutral solutions. Hence, a nanosized tungsten trioxide nanorod array film has been fabricated using ammonium paratungstate (APT), which has potential application in photoelectrochemical water splitting.

Synthesis method of the tungsten trioxide nanorod array film is as below:

1 g of ammonium paratungstate (APT, H40N10O41W12·xH2O) was heated in the necessary volume of lactic acid until complete dissolution, resulting in a final concentration of 10 wt%. Then, 1 ml of the solution was diluted by a factor 10 with ethanol to obtain the seed layer precursor solution. Prior to deposition, the fluorine-doped tin oxide (FTO) coated glass substrates were cleaned by consecutive ultrasonication for 30 min in acetone, ethanol and deionized water, and then dried under N2 flow at room temperature. The precursor solution was deposited on the substrate via spin-coating at 3000 rpm for 15 s. The coated substrates were annealed at 500 °C for 3 h in a furnace to obtain the WO3 seed layer.

Then, the substrates with the seed layer were placed into a Teflon-lined hydrothermal reactor filled with a solution prepared by mixing 1.25 g of an ammonium paratungstate solution (10 wt%) with 8.75 g lactic acid in 20 g ethanol containing 0.1383 g reduced l-glutathione (C10H17N3O6S). The reactor was placed into a stainless-steel autoclave and heated at 200 °C for 4 h. The obtained films were rinsed with ethanol and annealed in air at 550 °C for 1 h.

In conclusion, a nanosized tungsten trioxide nanorod array film fabricated using ammonium paratungstate (APT) that has potential application in photoelectrochemical water splitting. The thickness of the film is 960 nm and has uniform distribution. It is a promising material with excellent photoactivity.

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