Study On Prepationon Of Potocatalys Zn_xTiO_yN_z And Splitting The Water Into H₂ Under Visible Light

Nowadays, how to produce hydrogen by using solar energy to photolyze water is being paid high attention. And the key to use sunlight efficiently is to develop photocatalyst which could respond to visible light. Most transitional metal oxynitrides exhibit the feature of strong absorption in the visible region, with the potential for overall water splitting into H2 and O2. A new kind of photocatalyst ZnxTiOyNz with small band gap energy has been prepared, which is based on the theory of the catalysis of semi-conductor photocatalysts. In addition, its photocatalytic properties for water splitting into H2 and O2 under visible light have been studied.Using Zn(NO3)2·6H2O and Ti(OC4H9)4 as raw materials, ZnxTiOyNz was prepared by the sol-gel method and high-temperature nitridation technique. The catalyst samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy. The effects of the reaction temperature, time on the structure and composition of ZnxTiOyNz are investigated. The results indicated that the optimal nitridation temperature is 1073K and the ideal nitridation time is 5h; The XPS spectra of ZnxTiOyNz obtained by nitridation at 1073K for 5h shows that due to oxygen of sample replaced by nitrogen, the crystal ZnxTiOyNz has been formed. The composition of ZnxTiOyNz obtained by nitridation at 1073K for 5h was roughly estimated to be Zn0.8TiO1.69N0.74 by XPS. The XPS spectra of ZnxTiOyNz obtained by nitridation at 1123K for 5h shows that sample was not zinciferous. U-vis diffuse reflectance spectra of ZnxTiOyNz shows that the absorption edges of the samples were siginificantly shifted to the visible region with nitridation temperature increasing. The band gap energies of ZnxTiOyNz obtained by nitridation at 1073K for 5h were estimate to be 2.38eV. The XPS spectra of ZnxTiOyNz loading different noble metal shows that noble metal is mostly metal atom state on the surface of ZnxTiOyNz.In addition, ZnxTiOyNz was loaded noble metal by the method of formaldehyde deoxidizing or ultraviolet, and the effects of different methods of loading noble metal on photocatalytic activity were also investigated in the paper. The results indicated that the effect of formaldehyde deoxidizing was better than ultraviolet in loading noble metal on photocatalytic activity. ZnxTiOyNz loaded Pt,Ru and Rh by formaldehyde deoxidizing as well as the effect of the amount of noble metal on photocatalytic activity were also investigated. The results show that the Pt/ZnxTiOyNz on photocatalytic activity was the best ideal, the optimal amount of Pt was 1.8wt% (quality percentage). The finally results show that 0.3g Pt/ZnxTiOyNz be added into 350mL methanol solution of which the volume percentage was 5%. The methanol solution was adjusted to pH 3 by H2SO4. Under the irradiation of visible light (λ≥400nm), the rate of hydrogen evolution was 36.2μmol/h.