Facile synthesis of dual Z-scheme g-C3N4/Ag3PO4/AgI composite photocatalysts with enhanced performance for the degradation of a typical neonicotinoid pesticide

A dual Z-scheme photocatalyst AgI/Ag3PO4/g-C3N4 (AAC) is prepared by an in-situ ion exchange method from Z-scheme Ag3PO4/g-C3N4. This dual Z-scheme photocatalyst exhibits higher activity for the degradation of nitenpyram (NTP) than pure g-C3N4, Ag3PO4 and AgI and their binary composites. The apparent rate constant of NTP degradation for the optimal sample (0.76 min(-1)) is about 16.2, 2.4 and 2.9 times as that of g-C3N4, Ag3PO4 and AgI, respectively. The results of photoluminescence spectroscopy and transient photocurrent response show that the separation efficiency of photogenerated electrons and holes for AAC is significantly improved, which is beneficial to improve its photocatalytic activity. Active species capture experiments and electron spin resonance spectra show that superoxide radicals and holes are the main active substances for NTP degradation and prove the formation of Z-scheme structure. In addition, basing on the results of high-performance liquid chromatography mass spectrometry, a possible degradation pathway of NTP is deduced.