Development of New Tantalum Base Mixed Oxide for Photocatalytic Decomposition of H_2O into H_2 and O_2

研究了氧化物半导体的电子态对KTaO_3基氧化物光催化分解H_2O为H_2和O_2的影响。结果表明，在KTaO_3的Ta位上掺杂Zr、Hf、La和Ga能有效地提高其光催化分解H2O的活性。空穴效应测量表明，KTaO_3为n型半导体，掺杂这些低价阳离子后，电子电荷密度降低。光电动势测量还表明，低价阳离子的掺杂延长了空穴和电子的寿命。结果表明，控制光催化剂中的电子电荷密度是提高光催化分解H2O活性的有效方法。在另一种化合物，即SrTiO_3、Ba2In_2O_5和K_6Ta_&lt；10.6&gt；O_&lt；30&gt；上也观察到类似的掺杂效应。并考察了晶体结构对其性能的影响。采用醇盐法制备了类烧绿石结构的K_2Ta_2O_6和钙钛矿结构的KTaO_3。虽然化学组成相同，但K_2Ta_2O_6和KTaO_3对H2O的光解活性有很大的不同，这表明K2Ta_2O_6的电子态受晶体结构中原子排列的影响较大，光催化剂的电子态对水的光催化分解活性有很大影响。

Effects of electronic state of oxide semiconductor on photocatalysis of H_2O splitting into H_2 and O_2 were investigated on KTaO_3 based oxide. It was found that doping Zr, Hf, La and Ga to Ta site of KTaO_3 is highly effective for increasing the photocatalytic activity to H_2O decomposition. From the hole effects measurement, KTaO_3 is n-type semiconductor and electronic charge density decreases by doping these lower valence cations. Photo-electromotive force measurement also suggests that the life of existed hole and electron is prolonged by doping the lower valence cations. As a result, it becomes clear that the control of electronic charge density in photocatalyst is effective for increasing the photocatalytic activity to H_2O decomposition. Similar dopant effects were also observed on another compounds, i.e., SrTiO_3, Ba_2In_2O_5, and K_6Ta_<10.6>O_<30>. Effects of crystal structure was also investigated. K_2Ta_2O_6 with pyrochlore like structure and KTaO_3 with perovskite structure was successfully prepared by alkoxide method. Although the chemical composition is the same, the activity to photolysis of H2O is greatly different between K_2Ta_2O_6 and KTaO_3. This suggests that the electronic state is varied by the atomic arrangements in crystal structure and the activity to photocatalytic decomposition of water is highly affected by the electronic state of photocatalyst.