Doping is commonly used to improve visible light responsive of transition metal oxide. A lot of researches show that metal ion like rare earth can promote the photocatalytic property of semiconductor material, however, metal doping may cause thermal stability of catalyst decreasing, it will introduce photo electron and recombination center of valance to lower its photoelectric property. Doping N can greatly improve the visible light absorption rate of semiconductor material.
Preparing of nanoporous tungsten oxide:
1) Treating method for tungsten foil: Firstly cut it into 10mm x 15mm pieces, using waterproof abrasive to polish it, then clean it with acetone, isopropanol, methyl alcohol and deionized water ultrasound cleaning for 15min, blow it with nitrogen gas.
2) Use tungsten foil as anode, Pt foil of 10 x 15mm as counter electrode, put them into electrobath, the distance between two electrodes is 25mm. Then put electrobath in water bath of constant temperature, adjust the bath temperature to control the reaction temperature. The reacting area is 0.88cm2. Adding a certain amount of ready-prepared 1mol/L（NH4）2SO4 solution electrolyte with different concentration of NH4F.
Put the prepared nanoporous WO3 in tube furnace, inject NH3/N2(1:2), heat to certain temperature by heat up rate 5℃/min, keep it for a while, then cool it down to room temperature. Purity of NH3 and N2 is 99.999%, flow rate is 120ml/min.