COFs-Ph@CdS S-scheme heterojunctions with photocatalytic hydrogen evolution and efficient degradation properties

Abstract

Combining the advantages of inorganic semiconductor and organic semiconductor is an effective way to construct heterojunction to improve the photocatalytic activity of materials. In this work, two covalent triazine framework (COFs-Ph)-based heterojunctions, which named hollow COFs-Ph@CdS and solid COFs-Ph@CdS, were synthesized by a facile hydrothermal method. And they were developed for the photocatalytic hydrogen evolution and efficient degradation for tetracycline (TC), 2,4-dichlorophenol (2,4-DCP), rhodamine B (RhB) under sunlight irradiation for the first time. Compared with solid COFs-Ph@CdS, hollow COFs-Ph@CdS catalysts exhibited a significantly enhanced activity for the photodegradation of various pollutants and photocatalytic hydrogen evolution. Under the simulated sunlight, the degradation rate of TC, 2,4-DCP, RhB by hollow COFs-Ph@CdS-3 was 87.2 %, 95.4 %, 82.6 %, respectively. The hydrogen production rate of hollow COFs-Ph@CdS-4 was 726 μmol·h−1·g−1. Based on the experimental results, it found that the interactions between CdS nanospheres and COFs-Ph could enhance the sunlight harvesting and created a new pathway to extend the service life of photogenerated charge carriers via facilitating the electron transfer through the loaded CdS nanospheres. Furthermore, the results verified that the matched band structure between COFs-Ph and hollow CdS could induce a superfast S-scheme interfacial charge transfer path. Therefore, a reasonable S-scheme charge transfer mechanism was proposed based on the active species trapping experiments and the results of electron spin resonance (ESR). More importantly, hollow COFs-Ph@CdS-3 possessed a good stability and reusability after recycling five times, that showed application prospect for solar-to-chemical energy conversion.