PHOTOCATALYTIC PROPERTY AND STRUCTURAL MODIFICATION OF LANTHANIDE TANTALATES CONTAINING PARTIALLY FILLED 4F ORBITAL

部分填充4F轨道的镧系钽酸盐的光催化性能及结构修饰

• 批准号: 12650780
• 负责人: MACHIDA Masato
• 金额: $ 2.3万
• 依托单位: University of Miyazaki
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650780/
• 关键词: PHOTOCATALYST; LANTHANIDE; LAYERED PEROVSKITE; BAND STRUCTURE; HYDROGEN; ION EXCHANGE; FLAPW; INTERCALATION; 4f電子; タンタル酸塩; 層状構造; 構造変換

1) The correlation of electronic structure with photocatalytic properties of layered perovskite tantalates, RbLnTa_2O_7 (Ln=La, Pr, Nd, and Sm), containing the partly-occupied Ln4f-shell is studied by means of valence band photoemission (XPS) measurement and first-principles calculations of the band structure based on the all-electron full-potential linear augmented plane-wave (FLAPW) method. The unoccupied La4f level is located on the bottom of the conduction band, whereas the partially occupied 4f levels become lowered with an increase of 4f electrons down to the position above the valence band edge (Ln=Pr) and finally fall into the valence band mainly comprised of O2p orbitals (Ln=Nd and Sm). It was suggested that unoccupied as well as occupied 4f orbitals are not completely localized but partly contribute to the hybridization with O2p and Ta5d orbitals. The different photocatalytic activity of the present for the overall water splitting is closely related to the degree of the Ln-O- … More Ta hybridization, which affects not only the positions of the conduction band and valence band edges, but also the density of states (DOS) distribution in both bands.2) Photocatalytic activity of lanthanide tantalates, LnTaO_4 (Ln=La, Ce, Pr, Nd, and Sm), for the water splitting was studied in connection to the effect of Ln4f levels on the electronic structure. Valence band XPS, UV-vis, and first-principle electronic calculations suggested that the position of Ln4f levels becomes lowered monotonously across the series of Ln. The empty La4f level is supposed to be higher than the conduction band edge, whereas the filled 4f levels of the Nd and Sm compounds lie in the valence band. For Ln=Ce and Pr, occupied 4f levels lying within the forbidden gap lead to the lower band gaps (E_g) compared to others. The highest photocatalytic activity was attained by LaTaO_4, which solely can decompose water into stoichiometric H_2/O_2 mixtures. This is largely due to the overlap between Ta5d and O2p orbitals, which produces a wide density-of-states (DOS) distribution in the conduction band. On the other hand, the tantalates containing from one (Ce^<3+>) to five (Sm^<3+>) 4f electrons were much less active, since unoccupied 4f levels lying on or below the conduction band edge would play as a trapping center for photoexcited electrons. The interactions between the empty and filled Ln4f levels and carriers generated under UV irradiation are possible reasons for the Ln-dependent photocatalytic activity. Less

1)利用价带光电子能谱（XPS）测量和基于全电子全势线性缀加平面波（FLAPW）方法的能带结构计算，研究了层状钙钛矿钽酸盐RbLnTa_2O_7（Ln=La，Pr，Nd，Sm）的电子结构与光催化性能的关系.未被占据的La 4f能级位于导带的底部，而部分被占据的4f能级随着4f电子的增加而降低到价带边缘（Ln=Pr）上方的位置，并最终落入主要由O2 p轨道组成的价带（Ln=Nd和Sm）。有人建议，未占用以及占用4f轨道不完全本地化，但部分有助于与O2 p和Ta 5d轨道的杂化。本发明的光催化剂对整体水裂解的不同活性与Ln-O- ...更多信息 Ta杂化不仅影响导带和价带边的位置，而且影响导带和价带边的态密度分布。2）研究了镧系钽酸盐LnTaO_4（Ln=La，Ce，Pr，Nd，Sm）光催化分解水的活性，并讨论了Ln 4f能级对电子结构的影响。价带XPS，UV-vis，和第一原理电子计算表明，Ln 4f能级的位置变得单调降低整个系列的Ln。空的La 4f能级应该高于导带边缘，而Nd和Sm化合物的填充的4f能级位于价带中。当Ln=Ce和Pr时，禁带中的4f能级导致了较低的带隙（E_g）。LaTaO_4的光催化活性最高，它能将水分解为化学计量比的H_2/O_2混合气体。这在很大程度上是由于Ta 5d和O2 p轨道之间的重叠，这在导带中产生了宽的态密度（DOS）分布。另一方面，含有1个（Ce^3+）到5个（Sm^3+）4f电子的钽酸盐的活性要低得多，因为位于导带边缘或导带边缘以下的未被占据的4f能级将作为光激发电子的捕获中心。空的和填充的Ln 4f能级和在紫外光照射下产生的载流子之间的相互作用是可能的原因的Ln依赖的光催化活性。少

项目成果

町田正人: "光触媒による水からの水素製造技術の最新動向(執筆分担-4.6 層状タンタル酸塩光触媒による水分解)」"シーエムシー出版(印刷中). (2003)

Masato Machida：“利用光催化剂从水中制氢技术的最新趋势（书面作业 - 4.6 使用层状钽酸盐光催化剂分解水）”CMC Publishing（目前正在印刷）。

M.Machida: "Intercalation and Pillaring of Layered Tantalate Photocatalysts"Molecular Crystals and Liquid Crystals. 341巻. 249-252 (2000)

M. Machida：“层状钽酸盐光催化剂的插层和柱化”，《分子晶体和液晶》，第 341 卷，249-252 (2000)。

M. Machida, S. Murakami, T. Kijima, S. Matsushima, M. Arai: "Photocatalytic Property and Electronic Structure of LnTao_4 (LN=LA, Ce, Pr, Nd, and Sm)"Journal of Physical Chemistry B. Vol.105, No.16. 3289-3294 (2001)

M. Machida、S. Murakami、T. Kijima、S. Matsushima、M. Arai：“LnTao_4 (LN=LA、Ce、Pr、Nd 和 Sm) 的光催化性能和电子结构”Journal of Physical Chemistry B. Vol

M.Machida, S.Nagasaki, T.Kijima: "Preparation of CuO_x-TiO_2 Nano-composites Photocatalysts from Intercalated Layered Structure"Studies in Surface Science and Catalysis. 143. 863-872 (2002)

M.Machida、S.Nagasaki、T.Kijima：“从插层结构制备CuO_x-TiO_2纳米复合材料光催化剂”表面科学与催化研究。

M. Machida, J. Yabunaka, T. Kijima: "Synthesis and Photocatalytic Property of Layered Perovskite Tantalates, RbNdTa_2O_7 (Ln=La, Pr, Nd, and Sm)"Chemistry of Materials. Vol.12, No.3. 812-817 (2000)

M. Machida、J. Yabunaka、T. Kijima：“层状钙钛矿钽酸盐 RbNdTa_2O_7（Ln=La、Pr、Nd 和 Sm）的合成和光催化性能”材料化学。