光降解刚果红的S型硫掺杂g-C3N4/TiO2异质结光催化剂

doi:10.1016/S1872-2067(20)63634-8

催化学报 ›› 2021, Vol. 42 ›› Issue (1): 56-68.DOI: 10.1016/S1872-2067(20)63634-8

光降解刚果红的S型硫掺杂g-C₃N₄/TiO₂异质结光催化剂

王娟^a, 王国宏^a^,^*(), 程蓓^b^,^#(), 余家国^b, 范佳杰^c

^a湖北师范大学化学化工学院, 湖北师范大学先进材料研究院, 污染物分析与资源化技术湖北省重点实验室, 湖北黄石435002
^b武汉理工大学材料复合新技术国家重点实验室, 湖北武汉430070
^c郑州大学材料科学与工程学院, 河南郑州450001

收稿日期:2020-03-17 接受日期:2020-04-26 出版日期:2021-01-18 发布日期:2021-01-18
通讯作者: 王国宏,程蓓
基金资助:
国家自然科学基金(51872220);国家自然科学基金(51932007);国家自然科学基金(51961135303);国家自然科学基金(21871217);国家自然科学基金(U1905215);国家自然科学基金(U1705251);国家重点研发计划项目(2018YFB1502001);中央高校基本科研基金(WUT:2019IVB050)

Sulfur-doped g-C₃N₄/TiO₂ S-scheme heterojunction photocatalyst for Congo Red photodegradation

Juan Wang^a, Guohong Wang^a^,^*(), Bei Cheng^b^,^#(), Jiaguo Yu^b, Jiajie Fan^c

^aHubei Key Laboratory of Pollutant Analysis and Reuse Technology, College of Chemistry and Chemical Engineering, Institute for Advanced Materials, Hubei Normal University, Huangshi 435002, Hubei, China
^bState Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, Hubei, China
^cMaterial Science and Engineering School, Zhengzhou University, Zhengzhou 450001, Henan, China

Received:2020-03-17 Accepted:2020-04-26 Online:2021-01-18 Published:2021-01-18
Contact: Guohong Wang,Bei Cheng
About author:^#Tel/Fax: +86-27-87871029; E-mail: chengbei2013@whut.edu.cn
^*Tel/Fax: +86-714-6515602; E-mail: wanggh2003@163.com;
Supported by:
National Natural Science Foundation of China(51872220);National Natural Science Foundation of China(51932007);National Natural Science Foundation of China(51961135303);National Natural Science Foundation of China(21871217);National Natural Science Foundation of China(U1905215);National Natural Science Foundation of China(U1705251);National Key Research and Development Program of China(2018YFB1502001);Fundamental Research Funds for the Central Universities(WUT:2019IVB050)

摘要/Abstract

摘要：

含有机物工业废水的处理仍然是人类实现可持续发展的重大挑战. 而光催化作为一种先进的氧化环保技术, 以其反应条件温和、能耗相对较低的优点在有机废水处理中受到越来越多的关注. 近年来, 人们设计和合成了许多不同结构和形状的光催化剂. 特别是金属氧化物半导体以其适宜的能带结构、稳定的物化性质、无毒性等特点已成为光催化降解有机废水的研究热点. 此外, 一维纳米结构(1D)已被证实有利于光催化降解过程, 其优势在于比表面积大, 离子的迁移路径短, 以及独特的一维电子转移轨道. 尤其是TiO₂纳米纤维由于其亲水性、特殊的形貌和合适的能带位置, 在污染物水溶液的处理中表现出优异的光催化性能. 然而, TiO₂(~3.2 eV)的宽禁带、光生载流子的易复合等缺陷导致其光利用率较低, 限制了其实际应用. 因此, 人们提出了许多提高光催化活性的策略, 如掺杂金属或非金属元素、负载贵金属、构建异质结等.
构建梯形(S型)异质结已被证实是提高复合材料光催化活性的一种有前途的策略. S型异质结不仅能有效地分离光生电子和空穴, 而且还原能力低的半导体CB上的电子和氧化能力低的半导体VB上的空穴复合, 而氧化还原能力较强的空穴和电子分别被保留. 因此, 这一电子转移过程赋予了复合物最大的氧化还原能力. 同时, 在g-C₃N₄中引入硫元素可以拓宽其光吸收范围, 从而产生更多的光生载流子. 此外, 额外的表面杂质将有助于e^--h⁺对的分离, 其光催化活性明显高于单纯的g-C₃N₄.
综合一维纳米结构、硫掺杂和S型异质结的优势, 本文采用静电纺丝和煅烧法制备了一系列硫掺杂的g-C₃N₄ (SCN)/TiO₂ S型光催化剂. 制备的SCN/TiO₂复合材料在光催化降解刚果红(CR)水溶液中表现出比纯TiO₂和SCN更优越的光催化性能. 光催化活性的显著增强是由于一维分布的纳米结构和S型异质结. 此外, XPS分析和DFT计算表明, 电子从SCN通过SCN/TiO₂复合材料的界面转移到TiO₂. 在模拟太阳光照射下, 界面内建电场、带边缘弯曲和库仑相互作用协同促进了复合物相对无用的电子和空穴的复合. 因此, 剩余的电子和空穴具有较高的还原性和氧化性, 使复合材料具有最高的氧化还原能力. 这些结果通过自由基捕获实验、ESR实验和XPS原位分析得到了充分的验证, 说明光催化剂中的电子迁移遵循S型异质结机理. 本文不仅可以丰富了新型S型异质结光催化剂的设计和制备方面的知识, 并为未来解决环境污染问题提供一个有前景的策略.

关键词: TiO₂纳米纤维, 硫掺杂g-C₃N₄, 梯形异质结光催化剂, 原位XPS, S型机理

Abstract:

Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C₃N₄ (SCN)/TiO₂ S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO₂ composites showed superior photocatalytic performance than pure TiO₂ and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO₂ across the interface of the SCN/TiO₂ composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future.

Key words: TiO₂ nanofiber, Sulfur-doped g-C₃N₄, Step-scheme heterojunction, photocatalysis, In situ XPS, S-scheme mechanism

王娟, 王国宏, 程蓓, 余家国, 范佳杰. 光降解刚果红的S型硫掺杂g-C₃N₄/TiO₂异质结光催化剂[J]. 催化学报, 2021, 42(1): 56-68.

Juan Wang, Guohong Wang, Bei Cheng, Jiaguo Yu, Jiajie Fan. Sulfur-doped g-C₃N₄/TiO₂ S-scheme heterojunction photocatalyst for Congo Red photodegradation[J]. Chinese Journal of Catalysis, 2021, 42(1): 56-68.

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图/表 10

Fig. 1. Schematic for the preparation of SCN/TiO2 hybrid nanofibers.

Fig. 2. (a) XRD patterns of g-C3N4, SCN, TiO2, and SCN/TiO2 composites; (b) FT-IR spectra of SCN, TiO2, and SCN/TiO2 composites; (c) Nitrogen adsorption-desorption isotherms and pore size distribution curves (inset) of SCN, TiO2, and SCN/TiO2 composites; (d) TG curves for SCN, TiO2, and SCN/TiO2 composites.

Table 1 Porosity and surface properties of the prepared samples.

Samples	S_BET (m²/g)	Pore volume (cm³/g)	Pore size (nm)
TiO₂	16	0.08	19.4
SCNT5	29	0.10	14.1
SCNT6	51	0.17	13.2
SCNT7	33	0.10	12.3
SCNT8	28	0.11	15.2
SCN	20	0.05	10.2

Fig. 3. (a) XPS survey spectra of TiO2, SCN, and SCNT6 samples; High-resolution XPS spectra of Ti 2p (b), O 1s (c) in TiO2 and SCNT6, C 1s (d), N 1s (e), and S 2p (f) in SCN and SCNT6.

Fig. 4. FESEM images of TiO2 (a) and SCNT6 (b); insets on left bottom are the corresponding low-magnification SEM images; TEM (c) and HRTEM (d) images of SCNT6; (e) EDX elemental mappings of O, Ti, N, C and S.

Fig. 5. (a) UV-vis diffused reflectance of SCN, g-C3N4, TiO2, and SCN/TiO2 composites; (b) Tauc plots of SCN, g-C3N4, and TiO2.

Fig. 6. (a) Photocatalytic activity curves of SCN, TiO2, and SCN/TiO2 composites for the degradation of CR aqueous solution under xenon lamp irradiation; (b) Comparison of the apparent rate constants k (10-3 min-1) of the SCN, TiO2, and SCN/TiO2 composites of the degradation of CR under xenon lamp irradiation; (c) Adsorption peaks of CR aqueous solution in the presence of the SCNT6 sample with increasing irradiation time under xenon lamp irradiation; (d) Circulating runs in the decomposition of CR for the SCNT6 sample under xenon lamp irradiation; (e) FT-IR patterns of the SCNT6 sample before and after 5 circulating runs.

Fig. 7. (a) PL spectra of TiO2, SCN, and SCNT6 under 320 nm excitation; (b) Time-resolved transient PL decay of SCN and SCNT6; (c) Transient photocurrent responses of TiO2, SCN, and SCNT6 under xenon lamp irradiation; (d) EIS spectra of TiO2, SCN, and SCNT6 under xenon lamp irradiation; (e) MS plots for TiO2 and SCN; (f) MS plot for g-C3N4.

Fig. 8. (a) Photocatalytic activities of the SCNT6 sample for CR degradation with disparate scavengers; ESR spectra of SCNT6 under dark and simulated solar light: DMPO ?O2- (b) in methanol dispersions and DMPO ?OH (c) in aqueous dispersions.

Fig. 9. (a) Calculated electrostatic potentials for the (101) face of TiO2 and (b) SCN. The blue and red dashed lines denote the Fermi level and vacuum energy level, respectively. In the geometric structures of TiO2 and SCN, the cyan, red, blue, orange, and yellow spheres stand for Ti, O, C, N, and S atoms, respectively. (c) Proposed step-scheme heterojunction photocatalytic mechanism for SCN/TiO2.

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光降解刚果红的S型硫掺杂g-C₃N₄/TiO₂异质结光催化剂

Sulfur-doped g-C₃N₄/TiO₂ S-scheme heterojunction photocatalyst for Congo Red photodegradation

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[2]	陆亚超, 欧小雨, 王文广, 范佳杰, 吕康乐. 静电纺丝-碱热法制备高活性由纳米片组装的TiO₂纳米纤维[J]. 催化学报, 2020, 41(1): 209-218.