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）电子结构与分层的钙钛矿触觉的光催化特性的相关性，rblnta_2o_7（ln = la，pr，nd，nd和sm），其中包含部分置置的ln4f-shell，通过基于价值（xps）测量的型结构来研究，以全率结构为基础上，该结构是在整个频段（xps）测量中计算。增强平面波（FLAPW）方法。没有占用的LA4F水平，有人建议未占用和占用的4F轨道并非完全定位，而是部分促进了与O2P和TA5D轨道的杂交。当前对整体水分裂的不同光催化活性与Ln-O-的程度密切相关，更多的杂交程度不仅会影响传统带和价带边缘的位置，而且还影响了两个频段中的状态（DOS）分布的密度（2）在两个频段中的分布。与LN4F水平对电子结构的影响有关的水分裂是研究的。价带XP，UV-VIS和第一原则电子计算表明，LN4F水平的位置在整个LN系列中单调降低。预计空的LA4F水平将高于导带边缘，而填充的4F水平为ND和SM化合物，位于价频段中。对于LN = CE和PR，与其他差距相比，占据的4F级别导致较低的频带差距（E_G）。最高的光催化活性是由LATAO_4附着的，该活性完全可以将水分解为化学计量的H_2/O_2混合物。这在很大程度上是由于TA5D和O2P轨道之间的重叠，该轨道在传导带中产生了较大的状态（DOS）分布。另一方面，包含一个（Ce^<3+>）到五个（SM^<3+>）4F电子的触觉较少，因为位于传导带边缘或下方的未占用的4F级别将作为光散发电子电子设备的捕获中心播放。在紫外线照射下产生的空的LN4F水平和载体之间的相互作用是LN依赖性光催化活性的可能原因。较少的

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。