富含碳-氧、碳-金属键的铈基复合氧化物@C设计合成及其光催化性能研究

Photocatalytic technology plays an important role in environmental protection and energy chemical industry and has a broad application prospect. Effective separation of photogenerated electrons and holes is the bottleneck of photocatalytic efficiency. Based on this problem, this project will build C-O and C-Ce (M) chemical bonds in Ce-M-O@C (M= Pr, Fe, Ti), which will benefit for the transportation of photogenerated electrons and improve the separation efficiency of photogenerated electrons and holes, resulting in a highly photocatalytic efficiency. Ce-M-OH@dye will be prepared by adsorption of acid dyes on Ce-M-OH with high loading of hydroxyl groups, and then will be changed to Ce-M-O@C composite via calcination to thoroughly degradate the related dyes in wastewater under the irradiation of visible light. Effects of related experimental factors such as reactant ratio, reaction pH value and temperature on the properties of Ce-M-OH will be investigated to reveal the binding law between Ce-M-OH and acid dyes, providing basis for the formation of C-O and C-Ce (M) chemical bonds. Effects of Ce-M-OH structure, carbonization condition such as carbonization temperature and time and heating rate, dye adsorption, M doping method and doping amount on C-O and C-Ce (M) bonds formation and photoinduced electron transportation will be studied to elaborate the mechanism of photocatalytic degradation of dye from the effect of C-O and C-Ce (M) bond formation on the photocatalytic efficiency, which will provide scientific basis for the application of photocatalysis in other fields.

光催化在环境保护及能源化工方面具有重要作用，且应用前景广阔。光生电子与空穴有效分离是影响光催化效率的瓶颈。基于此问题，本项目将在Ce-M-O@C(M= Pr, Fe, Ti)内构筑C-O, C-Ce(M)化学键，利于光生电子传输，使之与空穴高效分离，从而提高光催化效率。以富含羟基的Ce-M-OH为吸附剂，吸附废水中酸性染料，形成Ce-M-OH@dye，经煅烧转化为Ce-M-O@C复合材料，利用可见光彻底催化降解废水中相关染料。拟研究影响Ce-M-OH性能相关实验因素，揭示Ce-M-OH与酸性染料结合规律，为C-O和C-Ce(M)键形成奠定基础；考察Ce-M-OH结构、碳化条件(如碳化温度与时间、升温速率)、染料吸附量、M掺杂方式及掺杂量等对相关碳键形成及光生电子传输的影响，从C-O, C-Ce(M)键形成对光催化效率影响角度阐述染料光催化降解机理，为光催化在其它领域中的应用提供科学依据。

基于CeO2@C光催化过程中存在以下问题：1，碳与基体CeO2间界面作用力弱；2，光生电子与空穴产率低。本项目利用氨水与相关铈盐(如Ce(NO3)3, CeCl3)，Pr、Fe盐(如Pr(NO3)3, Fe(NO3)3)，反应制备富含羟基的Ce-M-O (M=Pr, Fe)前驱物(Ce-M-OH)，以该前驱物为吸附剂对模拟废水中酸性红14和酸性橙7进行吸附；然后在氮气中煅烧已吸附酸性染料的前驱物，使前驱物转化为氧化物，酸性染料变成碳，最终形成Ce-M-O@C材料。利用酸性染料转化的碳提高光催化剂对有机污染物的吸附能力，通过碳与催化剂间形成的碳键提高光生电子与空穴分离效率，从而提高光催化效率。研究发现，用氨水作沉淀剂时，在产物中会产生大量铵根(NH )，利于前驱物与酸性染料中磺酸基(SO )结合；在pH=8.5，温度为25 ℃，陈化6小时的条件下合成的CeO2@xH2O对酸性染料吸附效率较好。此外，当引入其它金属元素(如Pr, Fe)时，在上述条件下合成的铈基氧化物前驱体对酸性染料吸附效率也较好。通过热解吸附的酸性染料获得的碳原子2p轨道上电子活性较大，容易与氧和/或碳原子2p轨道中的电子结合形成σ和π键，所以在合成产物(CeO2@C和Pr6O11@C)中检测到多种碳键，利于光生电子与空穴分离，且可使碳与光催化剂牢固结合。Pr掺杂CeO2@C时，可以提高产物中3价稀土离子(Pr3+, Ce3+)含量，从而提高稀土与碳的成键率；因为3价稀土离子含量增加，所以氧空位(由Pr3+, Ce3+取代Ce4+而形成)浓度提高，利于捕捉光生电子，使光生电子与空穴分离效率进一步提高。当以适量Fe3+掺杂CeO2@C时，也可提高碳键成键率，且合成产物中羟基数量大幅提升，利于有机污染物吸附，从而提高光催化效率。以少量Pr3+和Fe3+同时掺杂CeO2@C时，可以提高产物中金属与碳之间的成键率，且其它碳键数量也相应增多，还可以提高产物中羟基数量，所以合成产物的光催化效率提高。碳键成键率与碳键数量是提高光生电子与空穴分离效率的关键，合成产物中铵根和羟基有利于有机污染物的吸附，两者皆可使光催化效率提高。本项目研究成果可为相关光催化剂构筑及光催化机理深入理解奠定坚实基础。