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基氧化物中H_2O分解为H_2和O_2的抑制作用。结果表明，在KTaO_3的Ta位上掺杂Zr、Hf、La和Ga，可以有效地提高KTaO_3的光催化活性。从空穴效应的测量结果来看，KTaO_3是n型半导体，掺杂这些低价阳离子降低了电子电荷密度。光电动势测量也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荷密度是提高光催化分解H_2O活性的有效途径。在另一种化合物上也观察到类似的掺杂剂效应，SrTiO_3、Ba_2In_2O_5和<10.6>K_6Ta_O_3<30>。晶体结构的影响也进行了研究。采用醇盐法成功地制备了类焦绿石结构的K_2Ta_2O_6和钙钛矿结构的KTaO_3。K_2Ta_2O_6和KTaO_3虽然化学组成相同，但光解H_2O的活性却有很大差异。这表明，电子状态是由晶体结构中的原子排列和光催化分解水的活性的光催化剂的电子状态的影响很大。

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.