Rational design of novel Ag-MoS2@COF ternary heterojunctions and their photocatalytic applications

Constructing semiconductor composites composed of multiphase heterojunctions has been considered as an effective strategy for designing promising photocatalyst systems. In this work, a novel ternary heterojunction photocatalyst was prepared by integrating MoS 2 semiconductor nanoflowers with silver doped covalent organic frameworks (COFs) and used for photocatalytic degradation of antibiotics. The regular pore structure and solid skeleton of COFs matrix optimize the distribution of constituent units, making Ag-MoS 2 nanoflower uniform and highly dispersed on the COFs material matrix. Moreover, the silver nanoparticles in the catalyst acted as an electron mediator, which inhibited the recombination of charge carriers, and effectively enhanced the photocatalytic activity of Ag-MoS 2 @COF. The as-prepared Ag-MoS 2 @COF ternary heterojunction photocatalyst exhibited high degradation efficiency for tetracycline (TC), reaching 90.1 % after 50 min of visible light irradiation, which was superior to most heterojunction photocatalysts. The Ag-MoS 2 @COF also demonstrated good reusability, almost maintaining the initial photocatalytic efficiency after 5 cycles. In addition, the plausible direct solid-state Z-scheme photocatalytic mechanism for TC degradation with Ag-MoS 2 @COF ternary catalyst under visible light irradiation was proposed according to LC-MS analysis, radicals trapping experiment and photoelectric chemical test. This work provides a new paradigm for the design and development of COF-based ternary heterojunction photocatalysts for environmental remediation.