Performance And Mechanism Of Visible Photocatalytic Degradation Of Aflatoxin B1 By Carbon And Nitrogen Polymers/silver Phosphotungstate

Carbon-nitride（CN）-modified silver phosphotungstate photocatalysts（CN-Ag PW）were prepared by self-assembly and in situ solid-phase thermal transformation;polyimide（PI）-modified silver phosphotungstate photocatalysts（MAPI）were prepared by self-assembly and in situ solid-phase thermal polymerization.The effects of preparation temperature and precursor ratio on the chemical structure,crystal structure,light absorption and photogenerated carrier separation migration of the catalysts were investigated.The performance of the prepared composite catalyst for visible light-catalyzed degradation of aflatoxin B1（AFB1）was investigated,and the reasons for its enhanced performance in visible light-catalyzed degradation of AFB1 were analyzed in combination with the energy band structure of the composite photocatalyst,and the mechanism of its photocatalytic degradation of AFB1 was revealed.The composite photocatalyst 5-CN-Ag PW-2 was prepared with melamine（MA）,silver nitrate（Ag NO₃）and phospho tungstate（HPW）as precursors,the thermal conversion temperature was 390℃,and the molar ratio of MA:HPW:Ag⁺was 5:2:1.Under the illumination ofλ≥420 nm,the catalyst dosage was 0.40 g·L^-1.When the light time was 120min,the degradation rate of AFB1 in 5-CN-Ag PW-2 was 79.32%,and the rate constant k was 0.72 h^-1,which was 12.95 and 12.50 times that of CN-390 and Ag PW-390.The photocatalytic degradation of AFB1 in oil was tested under the same light condition.When the amount of catalyst was 5.0 g·kg^-1,the degradation rate of AFB1 was 92.65%,and the degradation rate constant k was 1.06 h^-1.The quality of oil did not change significantly before and after the photocatalytic reaction.Using MA,Ag NO₃,HPW and pyrophthalic dianhydride（PMDA）as precursors,the thermal conversion temperature is 325℃,MA:HPW:Ag⁺:When the molar ratio of PMDA was 5:1:2:5,the amount of catalyst was 0.1g·L^-1,underλ≥420 nm light for 100 min,the degradation rate of AFB1 in the system was75.80%,and the rate constant k was 0.68 h^-1,which was 7.34 times that of Ag PW-325.The photocatalytic degradation of AFB1 in oil was tested under the same light condition.When the amount of catalyst was 2.5 g·kg^-1,the degradation rate of AFB1 was 93.00%,and the degradation rate constant k was 1.05 h^-1.The quality of oil did not change significantly before and after the photocatalytic reaction.The characterization and degradation results of CN-Ag PW composite catalyst show that silver phosphotungstate is uniformly dispersed in the CN layer structure,which improves the difficulty of charge transfer between the CN layers.However,the high proportion of silver phosphotungstate will lead to the enhancement of the acidity of the composite catalyst,thus affecting the adsorption of substrate AFB1.At the same time,the participation of CN helps to improve the interface migration and separation of photogenerated charge carriers in the composite catalyst.In the PI structure,the existence of electron-absorbing groups enhances the formation of Type-Ⅱheterojunctions betweenπelectron delocalization Ag PW and PI,which is also beneficial to the separation of photogenerated charge carriers.The characterization and degradation results of MAPI composite catalyst show that POM-πinteraction and close contact between components are beneficial to enhance electron delocalization and charge transfer in the composite.The band structures of CN-Ag PW and MAPI series photocatalysts were analyzed by UV-Vis DRS and X-ray photoelectron valence band spectroscopy（VBXPS）.The main active substances in the photocatalytic degradation of AFB1 were detected by electron paramagnetic resonance（ESR）and free radical capture experiments.It is deduced that the electron transport form of carbon nitrogen polymer/silver phosphotungstate composite photocatalyst is Z-Scheme,and the main active substances of photocatalytic degradation of AFB1 are·O₂^-,·OH and h⁺.