Preparation And The Visible Light Photocatalytic Activity Of TiO₂Modified By Palladium And Co-modiifed By Palladium（Zirconium） And Nitrogen

TiO₂modified by metal ions can inhibit the recombination of photo-generated electrons and holeseffectively, because the metal ions can effectively capture the photo-generated electrons, thus prolongingthe life of photo-generated carriers, to promote the improvement of the TiO₂photocatalytic activity. It hasbeen shown that non-metal N-doped can expand the spectral absorption of TiO₂to visible region, andachieve the visible light photocatalytic activity. Based on this, metal and non-metal co-modified TiO₂photocatalysts, which combined the advantages of metal modified and non-metallic doped, were synthesedin this paper with titanate nanotubes （denoted as NTA） as precursor of TiO₂.Firstly, Pd-modified TiO₂catalysts were prepared. The effect of heat treatment atmosphere andtemperature on crystal structure, morphology, form of Pd, visible light absorption and photocatalyticactivity of catalysts were investigated. ESR results showed that the Pd-modified TiO₂samples calcined innitrogen atmosphere generated more single-electron-tropped oxygen vacancies （denoted as SETOVs） thanthose calcined in air. We found that there was a linear relationship between the concentration of oxygenvacancies and catalytic activity, indicating that the concentration of oxygen vacancy played an importantrole on photocatalytic activity. A mechanism for visible light photocatalytic degradation of propylene onPd-modified TiO₂photocatalyst was proposed, in which Pd species as well as SETOVs were the origin ofvisible light response. At the same time, Pd species played a role of separation of photogeneration electronand hole, thus improving the photocatalytic activity.Pd/N co-modified TiO₂photocatalysts were prepared by the same method. Similarly, calcinationatmosphere and temperature were investigated. When calcined in nitrogen, NTA reacted with urea togenerate intermediates ammonium titanate, thus suppressing the formation of anatase phase. The SETOVswere detected in Pd/N co-modified TiO₂catalysts regardless calcined in nitrogen or in air. Also, SETOVs were demonstrated to promote the improvement of photocatalytic activity. In addition, the main activespecies for the resultant samples catalytic oxidation of propylene was hydroxyl radical.The precious metal modified TiO₂is costly, which greatly limits its application. Therefore, low-costtransition metal instead of precious metal to synthetize visible light active photocatalysts is promising. Zrand N co-modified TiO₂photocatalyst with different Zr concentrations were prepared in this paper. Withdoping of Zr, phase transformation temperature from amorphous-to-anatase rised in comparison withundoped TiO₂. The visible light sensitivity caused by the N-doping largely relevant to the existence of theinterstitial N-doped in the TiO₂. Doping of Zr contributed to keep the tubular morphology, and suppressedthe grain growth. Samples with0.6%Zr calcined at different temperatures were prepared and found thatsample calcined at500℃possessed the highest photocatalytic activity, which can be attributed to a bettercrystal structure and smaller grain size. We investigated the effect of precursor on the photocatalytic activity.With P25as precursor, co-doped samples had rare visible light response, correspondingly, photocatalyticactivity were negligible. On the contrary, visible light absorption and photocatalytic activity improvedsignificantly for samples with NTA as precursor. The larger specific surface area and dehydration of NTAduring calcination in favor of the doping of the N and Zr into TiO₂lattice along with transition from theorthorhombic phase to the anatase. Therefore, NTA has tremendous potential for the preparation of highlyactive photocatalyst.