Synergistic Effects Of K And Hydrogenation On Photocatalytic Hydrogen Production Of TiO₂

Photocatalytic splitting of water to produce hydrogen is an ideal strategy to obtain clean energy sources.TiO₂ has been widely used as a benchmark photocatalyst due to its suitable energy structure and stable photochemical property.In this work,we synthesized a series of TiO₂-based semiconductor materials by combining K addition and hydrogenation and systematically investigated the correlations between the crystal structure and the photocatalytic activity,the results of the research are summarized as below:1.we prepared the TiO₂ samples modified with K addition through a sol-gel method and then all of the samples were hydrogenated at 700°C.The effects of K with different addition amount and hydrogenation on the crystal morphology,phase composition and defect states of the as-prepared samples were investigated in detail.In addition to the stabilization of anatase phase,K addition can enhance the hydrogen-induced disorder engineering and modulate the concentration of oxygen vacancy to improve the light absorption of the photocatalysts.Furthermore,moderate additive K can promote the formation of heterostructure between K_xTi₈O₁₆ and anatase phase on the surface of TiO₂ during the hydrogenation treatment.The hydrogenation-induced defects,especially the in situ formed anatase and K_xTi₈O₁₆（0≤x≤2）heterostructure,enhances the light absorption and facilitates the separation of photogenerated charge carriers.Accordingly,the modified TiO₂ catalysts show the enhanced photocatalytic performances,especially for the hydrogenated TiO₂ with 5%K amount,whose hydrogen production rate（18.5μmol/h）is¹1 times higher than the unmodified TiO₂.This work provides a promising methodology to modulate the band energy structure of semiconductors and construct heterostructure at the same time for design of highly efficient photocatalysts.2.The optimized K added TiO₂ was chosen to investigate the effects of hydrogenation temperature and atmosphere on the crystal structure and the photocatalytic activity.When the sample is mainly composed of anatase,the concentration of oxygen vacancy increases with the elevated hydrogenation temperature.At 700°C,the oxygen vacancy content decreases due to the obvious phase transformation from anatase to rutile and the formation of hydrogenation induced K_xTi₈O₁₆（0≤x≤2）.Meanwhile,the anatase and K_xTi₈O₁₆（0≤x≤2）heterostructure forms on the surface of the modified TiO₂,which is mainly responsible for its best photocatalytic activity.When the hydrogenation temperature rises to 800°C,anatase is totally transformed into rutile and the rutile and K_xTi₈O₁₆（0≤x≤2）heterostructure forms on the surface of the sample and the photocatalytic activity begins to decrease.The nitrogen atmosphere treatment just facilitates the phase transformation from anatase to rutile and enhances the crystallinity of the sample,which lead to its little improved photocatalytic performance.Moreover,the growth of Pt particle size can be suppressed under the hydrogenation treatment,which is favorable to increasing the active interface of Pt-TiO₂.However,the Pt particle obviously aggregates under the nitrogen thermal treatment and this is disadvantageous to improving the photocatalytic hydrogen production.