实验法探究Type-II模型和全固态Z-Scheme结构模型在同种降解体系中的适配程度

引用本文: 黄喆奥, 赵硕, 余颖. 实验法探究Type-II模型和全固态Z-Scheme结构模型在同种降解体系中的适配程度[J]. 催化学报, 2020, 41(10): 1522-1534. doi: S1872-2067(19)63495-9 shu

Citation: Zheao Huang, Shuo Zhao, Ying Yu. Experimental method to explore the adaptation degree of type-II and all-solid-state Z-scheme heterojunction structures in the same degradation system[J]. Chinese Journal of Catalysis, 2020, 41(10): 1522-1534. doi: S1872-2067(19)63495-9 shu

实验法探究Type-II模型和全固态Z-Scheme结构模型在同种降解体系中的适配程度

华中师范大学物理科学与技术学院纳米科技研究所, 湖北武汉 430079
基金项目:
国家自然科学基金（21573085，51872108）；武汉市应用基础前沿项目（2018010401011294）；华中师范大学中央高校基本科研业务费专项资金（CCNU18TS034）.

摘要: 随着光催化研究的深入开展，人们对复合催化剂的内部电子空穴转移路径产生了浓厚的兴趣，并提出几种相对合理的载流子迁移路径猜想.其中包括异质结构型（包括Type-I型异质结与Type-II型异质结）和Z-Scheme构型（包括直接Z-Scheme型异质结和间接Z-Scheme型异质结），解释了部分活性提升的机理.我们选取了全固态Z-Scheme异质结结构作为模型，制备出TiO₂-C-C₃N₄三元复合催化剂.全固态Z-Scheme异质结结构是指在两个带隙匹配的半导体之间引入导电材料，半导体之间不直接接触.在太阳光的激发下，导电材料两侧的半导体被同时激发，电子分别从两者的价带跃迁至导带，并在价带上留下空穴.由于两者之间存在电子导体，处于中间位置的导带电子会沿电子导体运动，与处于中间位置价带的空穴复合，留下氧化还原能力较强的价带空穴和导带电子.整个反应路线形成"Z"字形状，模拟了光合作用的反应路径.我们对TiO₂-C-C₃N₄三元催化剂以及TiO₂与C₃N₄形成的Type-II异质结的TiO₂-C₃N₄二元催化剂进行了XRD、SEM、TEM、BET、XPS、光电流、紫外漫反射和PL光谱等表征测试，并根据光催化实验结果解释了两种不同复合材料催化机理上的差异，证明两种不同异质结结构可以影响光催化性能.
由TEM图可知，TiO₂-C-C₃N₄催化剂由于碳的引入，TiO₂纳米颗粒表面被碳层包裹，与未引入碳的TiO₂-C₃N₄的TEM图像有着明显区别.由C₃N₄和TiO₂的界面可以看出二者不是简单的物理混合，而是形成连接紧密的界面，这在光电流测试中也有体现.光催化测试中，用两种不同碳材料修饰TiO₂的样品TiO₂-5C₃N₄和TiO₂-C的性能都有提高，但提高程度不同.因为TiO₂-C在分离载流子时是转移并储存电子，其中TiO₂的价带空穴不发生移动，而TiO₂-C₃N₄是通过Type-II异质结的机理分离载流子，C₃N₄导带的电子向TiO₂的导带移动，TiO₂的价带空穴向C₃N₄的价带移动，所以空穴的氧化能力下降，而且催化性能十分依赖于空穴的氧化能力，这就导致了TiO₂-C₃N₄的性能弱于TiO₂-C.理论上看，TiO₂-C₃N₄与TiO₂-C两种催化剂性能优越，复合在一起的三元复合物形成Z-Scheme结构，有着氧化能力强的电子和还原能力强的空穴，其催化性能应该进一步提高，但是在光催化测试中TiO₂-C-C₃N₄三元催化剂性能却大幅度下降，远不如TiO₂-C₃N₄与TiO₂-C的性能.由于TiO₂-C具有较高的光催化和光电流性能，所以TiO₂-C-C₃N₄三元催化剂的性能下降并不是碳层的影响.原因可能是，虽然Z-Scheme异质结结构的核心是处于中间位置的导带电子和价带空穴相结合，牺牲一部分氧化还原能力较弱的载流子，以保留氧化还原能力强的电子和空穴，但在TiO₂和C₃N₄的莫特肖特基曲线测试中发现，两者的导带位置和价带位置都很接近，C₃N₄的价带虽然处于中间，还是具有2.12eV的价带位置，所以C₃N₄能产生羟基自由基（PL测试中已证明），这样C₃N₄的空穴仍然具有较好催化能力，这就导致Z-Scheme异质结结构牺牲C₃N₄价带的空穴会对催化有消极影响.另一方面，可能是理想的Z-Scheme异质结结构需要中间导带和价带的载流子能够1：1复合，但由于C₃N₄的光电响应能力远弱于TiO₂（光电流测试中已证明），导致Z-Scheme异质结结构中光生电子和空穴的比例不一致，因此TiO₂的电子没有被完全消耗掉，Z-Scheme异质结结构的传输路径中断，不能按照理想模型工作，使得TiO₂-C-C₃N₄表现出差的光催化性能.
根据以上研究结果，我们提出了一种以宏观实验结果为主、微观内部机理为辅的方法来判断催化机理，使得更容易区分两种载流子转移模型，并探究Type-II模型和全固态Z字结构模型在同种降解体系中的适配程度，可以针对不同需求和不同环境来设计适应某些特殊降解条件的高效光催化剂.

关键词:

English

Experimental method to explore the adaptation degree of type-II and all-solid-state Z-scheme heterojunction structures in the same degradation system

Institute of Nanoscience and Nanotechnology, College of Physical Science and Technology, Central China Normal University, Wuhan 430079, Hubei, China
Received Date: 23 February 2020
Revised Date: 27 March 2020
Fund Project:
This work was supported by the National Natural Science Foundation of China (21573085 and 51872108), the Wuhan Planning Project of Science and Technology (2018010401011294), and the self-determined research funds of Central China Normal University (CCNU) from the college's basic research and operation through the Chinese Ministry of Education (CCNU18TS034).

Abstract: TiO₂ nanoparticles were prepared using the hydrothermal method and modified with C₃N₄ to synthesize a Type-II heterojunction semiconductor photocatalyst, TiO₂-C₃N₄. In addition, a carbon layer was coated onto the TiO₂ nanoparticles and the obtained material was uniformly covered on the surface of C₃N₄ to form an all-solid-state Z-scheme semiconductor photocatalyst, TiO₂-C-C₃N₄. Through characterization by XRD, XPS, SEM, TEM, BET, photoelectrochemical experiments, UV-visible diffuse reflection, and PL spectroscopy, the charge transfer mechanism and band gap positions for the composite photocatalysts were analyzed. The Type-II and all-solid-state Z-scheme heterojunction structures were compared. By combining microscopic internal mechanisms with macroscopic experimental phenomena, the relationship between performance and structure was verified. Experimental methods were used to explore the adaptation degree of different photocatalytic mechanisms using the same degradation system. This study highlights effective photocatalyst design to meet the requirements for specific degradation conditions.

Key words:

TiO₂-C₃N₄
/ TiO₂-C-C₃N₄
/ Photodegradation
/ Type-II heterojunction semiconductor
/ Z-scheme heterojunction structure semiconductor

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实验法探究Type-II模型和全固态Z-Scheme结构模型在同种降解体系中的适配程度

English

Experimental method to explore the adaptation degree of type-II and all-solid-state Z-scheme heterojunction structures in the same degradation system

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通讯作者: 陈斌, bchen63@163.com

中国化学会秘书处

实验法探究Type-II模型和全固态Z-Scheme结构模型在同种降解体系中的适配程度

English

Experimental method to explore the adaptation degree of type-II and all-solid-state Z-scheme heterojunction structures in the same degradation system

CCS Chemistry：嵌段共聚物自组装成 “三明治”二维有机材料，实现纳米级压力传感功能

CCS Chemistry：颜徐州、鲍哲南： 你的皮肤可能是一片SPMs

CCS Chemistry：工作高效不疲劳，只须让催化剂动起来

CCS Chemistry：静电组装导向聚合- 聚电解质纳米凝胶量化制备新策略

CCS Chemistry：金黄色葡萄球菌醛基脱氢酶是如何识别特异性底物的？

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