催化学报 ›› 2019, Vol. 40 ›› Issue (3): 424-433.DOI: 10.1016/S1872-2067(18)63183-3

• 论文 • 上一篇    下一篇

缺陷辅助表面修饰提高g-C3N4@C-TiO2直接Z型异质结的可见光光催化性能

李喜宝a, 熊杰a, 许英b, 冯志军a, 黄军同a   

  1. a 南昌航空大学材料科学与工程学院, 江西南昌 330063;
    b 湖南科技大学物理与电子科学学院, 湖南湘潭 411201
  • 收稿日期:2018-08-28 修回日期:2018-10-09 出版日期:2019-03-18 发布日期:2019-02-22
  • 通讯作者: 李喜宝
  • 基金资助:

    国家自然科学基金(51772140);江西省自然科学基金(20161BAB206111,20171ACB21033);江西省教育厅科技项目(GJJ170578).

Defect-assisted surface modification enhances the visible light photocatalytic performance of g-C3N4@C-TiO2 direct Z-scheme heterojunctions

Xibao Lia, Jie Xionga, Ying Xub, Zhijun Fenga, Juntong Huanga   

  1. a School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, Jiangxi, China;
    b School of Physics and Electronic Science, Hunan University of Science and Technology, Xiangtan 411201, Hunan, China
  • Received:2018-08-28 Revised:2018-10-09 Online:2019-03-18 Published:2019-02-22
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (51772140), the Natural Science Foundation of Jiangxi Province, China (20161BAB206111, 20171ACB21033) and the Scientific Research Foundation of Jiangxi Provincial Education Department, China (GJJ170578).

摘要:

光催化技术被认为是解决能源和环境问题的最有前途方法之一.较高光催化活性的石墨相氮化碳(g-C3N4)及碳掺杂TiO2(C-TiO2)的制备及性能一直是环境光催化研究的热点,然而,单一光催化剂存在光生电子空穴易复合及量子效率低等问题.
本课题组曾通过简单的水辅助煅烧法成功制备了纳米多孔g-C3N4,结果发现,多孔g-C3N4光催化活性较体相的明显提高,但光催化效率仍不够理想,原因是光生电子空穴复合较严重.传统的制备C-TiO2的方法亦存在一些不足,如需要添加碳源或碳组分聚集体.我们采用原位掺杂的方法合成了含有一定氧空位和活性位的纳米碳改性的C-TiO2,后辅以简单的化学气相沉积法构建了g-C3N4表面修饰的g-C3N4@C-TiO2.结果表明,相比纯g-C3N4,TiO2及C-TiO2,g-C3N4@C-TiO2具有更高的光催化活性;但其原因及碳掺杂态的影响尚不清楚.基于此,本文采用X射线光电子能谱技术(XPS)、透射电子显微镜(TEM)、电化学阻抗谱(EIS)、光致发光谱(PL)、电子顺磁共振技术(EPR)及理论计算等手段研究了g-C3N4@C-TiO2光催化活性提高的原因和机理.
XPS结果表明,随着碳含量的增加,间隙掺杂产生的O-C键的峰值强度先增大后趋于稳定,而晶格取代掺杂产生的Ti-C键的峰值强度逐渐增大.Ti-O峰的减少进一步证明了更多的碳取代了氧晶格的位置.随着碳掺杂量的增加,C-TiO2的带隙逐渐减小,因而吸收边红移;同时,g-C3N4@C-TiO2的光催化降解效率先升高后降低.g-C3N4@C-TiO2对RhB(苯酚)光降解的最大表观速率常数为0.036(0.039)min-1,分别是纯TiO2,10C-TiO2,g-C3N4和g-C3N4@TiO2的150(139),6.4(6.8),2.3(3)和1.7(2.1)倍.g-C3N4通过π-共轭和氢键与C-TiO2表面紧密结合,在催化剂中引入了新的非局域杂质能级和表面态,可以更有效地分离和转移光生电子,因而光催化活性增加.由此可见,碳掺杂状态和g-C3N4原位沉积表面改性对g-C3N4@C-TiO2复合光催化剂性能的影响很大.

关键词: 光催化剂, 异质结, 直接Z型, 掺杂, 修饰

Abstract:

To increase the number of active sites and defects in TiO2 and promote rapid and efficient transfer of photogenerated charges, a g-C3N4@C-TiO2 composite photocatalyst was prepared via in situ deposition of g-C3N4 on a carbon-doped anatase TiO2 surface. The effects of carbon doping state and surface modification of g-C3N4 on the performance of g-C3N4@C-TiO2 composite photocatalysts were studied by X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible diffuse-reflectance spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, photoluminescence, and electron paramagnetic resonance. With increasing carbon doping content, the carbon doping state in TiO2 gradually changed from gap to substitution doping. Although the number of oxygen vacancies gradually increased, the degradation efficiency of g-C3N4@C-TiO2 for RhB (phenol) initially increased and subsequently decreased with increasing carbon content. The g-C3N4@10C-TiO2 sample exhibited the highest apparent reaction rate constant of 0.036 min-1 (0.039 min-1) for RhB (phenol) degradation, which was 150 (139), 6.4 (6.8), 2.3 (3), and 1.7 (2.1) times higher than that of pure TiO2, 10C-TiO2, g-C3N4, and g-C3N4@TiO2, respectively. g-C3N4 was grown in situ on the surface of C-TiO2 by surface carbon hybridization and bonding. The resultant novel g-C3N4@C-TiO2 photocatalyst exhibited direct Z-scheme heterojunctions with non-local impurity levels. The high photocatalytic activity can be attributed to the synergistic effects of the improved visible light response ability, higher photogenerated electron transfer efficiency, and redox ability arising from Z-type heterojunctions.

Key words: Photocatalyst, Heterojunction, Direct Z-scheme, Doping, Modification