Preparation And Characterization Of Doped TiO₂ Nanoparticles For Production Of H₂ By Photocatalytic Splitting Water

Due to the depletion of fossil fuels and the serious environmental problems accompanying their combustion, human has been searching for a new form of energy that is clean, renewable and a viable alternative to fossil fuels. Overall water splitting for the production of hydrogen using a particulate photocatalyst, is one of the measures to solve this problem. Titanium dioxide has been broadly used as a photocatalyst because of its various merits, such as stable, non-toxic and low cost. However, because of the low photo-quantum efficiency and the absorption capability only for ultraviolet light, its applications is limited to some extent. In this work, TiO₂ was doped with various elements to improve the photoefficiency as well as the response into the visible part of the spectrum.In this paper, cerium and nitrogen codoped TiO₂ and copper doped TiO₂ photocatalysts are prepared by sol-gel method using Ti(OC₄H₉)₄ for raw materials. The prepared samples are characterized by thermogravimetry-differential thermal analysis(TG-DTA), X-ray diffraction(XRD), UV-vis absorption spectroscopy (UV-vis) and X-ray photoelectron spectroscopy(XPS), to investigate the effects of preparation conditions and various doped elements on structure and performance of photocatalysts. The photocatalytic activity of TiO₂ doped is researched by the experiment of water splitting for the production of hydrogen.The results show that Ce doped in TiO₂ can inhibit phase transition of anatase to rutile and the growth of crystallite. The N-Ti bond and the N-Ti-O bond, which narrow the energy gap, are formed in codoped titania(Ce-N-TiO₂). The synergistic effects of the Ce and N codoped in TiO₂ make the red shift more distinct, and the absorption edge is extended to the visible light. Cerium doped acts as hole traps to prohibit the recombination between active electrons and holes. The results demonstrate that the rate of hydrogen production is up to 120μmol·h^-1 under the conditions of the doping content of Ce for 0.6%(molar ratio), molar ratio of urea to tetrabutyl titanate for 1:1 and calcination temperature of photocatalyst preparation at 500℃.Cu doped in TiO₂ significantly inhibit the growth of crystallite, while Cu doping also prevent the transformation of anatase to rutile. Cu existing as Cu⁺ and Cu²⁺ can prohibit the recombination rate of photoinduced electron–hole pairs. Cu2O and CuO coexisting in/at TiO₂, can narrow the energy gap and further extend its photoresponse into the visible light regions.The rate of hydrogen production is up to 158μmol·h^-1 under the conditions of the doping content of Cu for 2% and calcination temperature at 500℃.