In-situ construction of Z-scheme silver phosphotungstate/polyimide photocatalysts and enhanced visible-light photocatalytic degradation of aflatoxin B1 in vegetable oil

Silver phosphotungstate/polyimide (MAPI) photocatalyst was successfully synthesized by a multi-step strategy combining the self-assembly and in-situ solid-phase thermal polycondensation. The construction of MAPI photocatalysts and their photocatalytic activity were investigated. The polyimide (PI) in MAPI photocatalysts obtains the weakened π-π stacking structure and more dendritic crystalline structure. However, the POMs-π interactions, charge-transfer form in conjugated organic ligands-modified polyoxometalate (POMs) materials, and the close contact between main components are beneficial to the charge transfer in MAPI photocatalysts. The coordination interactions of Keggin anions and organic ligands allow the Keggin units released during the thermal treatment process to act as shuttle redox mediators for Z-scheme heterojunction photocatalysts. The changes related to the physicochemical and interfacial interactions of the components enable the MAPI photocatalysts to exhibit the enhanced photocatalytic activity. Pristine PI shows little activity for photocatalytic degradation of Aflatoxin B1 (AFB1) under visible light (λ ≥ 420 nm) irradiation, but the rate constant k of 5-MAPI was 7.34 and 4.46 times than that of pristine AgPW and P25, respectively. The presence of H2O and the transfer behavior of AFB1 in the oil-H2O mixed system significantly promoted the photocatalytic degradation efficiency of AFB1 in peanut oil. Z-scheme charge transfer path and the photocatalytic degradation pathway of AFB1 were also proposed. Combined with the density functional theory (DFT) calculation results, AFB1 will be firstly degraded by the ·OH-induced cycloaddition reaction at the C19 = C20 of furan ring. Subsequently, methoxy (C23-O22), furan ring, lactone ring and carbonyl group (C9 = O10) are degraded in sequence. This work can provide some interesting insights into the construction of polymer/insoluble POMs photocatalysts and the photocatalytic degradation of exogenous harmful substances in vegetable oil.