Construction of a PCN/Fe2O3/CdS double Z-type heterojunction photocatalyst and its application in the oxidative coupling reaction of benzylamine

Abstract

In this work, a PCN/Fe₂O₃/CdS ternary heterojuction photocatalyst was constructed by introducing an appropriate amount of ferric oxide (Fe₂O₃) and cadmium sulfide (CdS) onto porous carbon nitride (PCN), denoted as PCN/Fe₂O₃/CdS. In the presence of PCN/Fe₂O₃/CdS, the turnover frequency value and selectivity of the oxidative coupling reaction of benzylamine were 6740 μmol g⁻¹ h⁻¹ and 99.4%, respectively. The excellent catalytic performance of the PCN/Fe₂O₃/CdS photocatalyst is attributed to fully exposed active sites due to the porous structure of PCN, improved light utilization efficiency by introduction of Fe₂O₃ and CdS, and increased mobility of e⁻–h⁺ pairs by construction of a ternary heterostructure, and was proved by the analysis of its structural and optical properties. According to the substrate scope study and Hammett diagram analysis, the rate determining step of the benzylamine self-coupling reaction photocatalyzed by PCN/Fe₂O₃/CdS was the condensation of imine and benzylamine into N-benzylidenebenzylamine. The results of the free radical quenching experiment and electron spin resonance tests showed that h⁺ played a major role in the photoreaction process, followed by ˙O₂⁻ and ˙OH. After four photocatalytic reaction cycles, the catalytic performance of the PCN/Fe₂O₃/CdS heterojunction composite material remained good. Finally, combined with the free radical trapping experiment and energy band structure analysis, a possible double Z-type reaction mechanism was proposed.