Enhanced photocatalytic performance of S-doped covalent triazine framework for organic pollutant degradation

Abstract

Photocatalysis using the abundant solar energy is an environmentally friendly and efficient way to degrade organic matter. Covalent triazine frameworks (CTFs), a new class of metal-free organic semiconductors responsive to visible light, are promising materials for water treatment. In this study, an original CTF, namely CTF-1, was modified by S-doping to form CTFS_x, which were used as metal-free catalysts for degradation of methyl orange (MO) and bisphenol A (BPA). The outcomes demonstrated that the photocatalytic degradation of MO and BPA by CTFS_x was superior to that by CTF-1, with better stability and reusability. Within 6 h, 53.2% MO and 84.7% BPA were degraded by CTFS₅, and the degradation rate constants were 0.145 h⁻¹ and 0.29 h⁻¹, respectively, which were 3.6 and 5.8 times higher than those of CTF-1. Further investigation revealed that enhanced visible light absorption, a reduced degree of free carrier recombination, rapid separation and transfer of photogenerated electrons and holes, and improved ·OH oxidation capacity were important factors contributing to the significantly enhanced photocatalytic activity. The S-doping method effectively improved the light absorption performance, electronic structure, and modulation band structure of CTF-1. This work highlights the potential application of low-cost metal-free catalysts driven by visible light for the removal of organic pollutants from wastewater.

Abstract

目的

随着工业化的快速发展，各种有机化合物会导致水质的恶化，进而对生态系统和人类健康构成巨大威胁。因此，有机废水的污染控制显得尤为重要。甲基橙（MO）和双酚A（BPA）作为典型的有机污染物，对环境和健康有不可忽视的影响。本文旨在构建可见光驱动去除废水中有机污染物的低成本无金属催化剂（CTFSx），探究其降解有机污染物的性能，并提供一种实用有效的去除水中有机污染物的方案，为基于CTF的光催化剂的设计和优化提供一种可行的方法。

创新点

针对MO和BPA污染物的性质和结构差异，考察了CTFSx的光催化能力和污染物分子中羟基官能团的影响，实现了水中有机污染物的高效去除和光催化剂的循环利用，并探明其光催化机制，不仅为解决水中低浓度有机污染物去除的难题提供了针对性策略，也为开发具有增强可见光收集和电荷分离的无金属催化剂的设计提供了可行有效的方案。

方法

1. 通过实验分析，以MO和BPA作为染料和药品及个人护理品（PPCPs）的代表性污染物探针，检测材料的光催化性能与污染物分子中羟基官能团的关系；2. 基于表征和性能实验从活性氧（ROS）和材料性质两方面得出催化剂性能提升的机制。

结论

1. CTFSx对MO和BPA的光催化降解效果优于CTF-1，具有较好的稳定性和可重用性；CTFS5具有最佳的光催化性能；在可见光催化反应的6 h内，53.2%的MO和84.7%的BPA被降解，且降解的拟一级速率常数可分别达到0.145 h−1和0.29 h−1，分别是CTF-1的3.6倍和5.8倍。2. 可见光吸收的增强、自由电荷复合程度的降低、光生电子和空穴的快速分离和转移以及·OH产生量的提高是导致光催化活性显著提高的重要因素。3. S掺杂方法有效地改进了CTF-1的光吸收性能、电子结构和调制能带结构。