Aflatoxin B1(AFB1)is easily found in agricultural products,feed and food processing and storage,posing a serious threat to the safety of food and oil.Among many photodegradation techniques,photocatalysis has been widely studied because of its advantages such as easy to use process,no re-pollution,direct use of sunlight,complete degradation and low operating costs.Currently,this technology is widely used for the degradation and purification of pollutants and dyes in water and has great potential for application.Nucleic acid aptamer(Aptamer),However,Ti O2based photocatalysts have poor selectivity and specificity on their own and may cause alteration or destruction of organic components in oils and fats in complex oil systems.A new low-cost molecular recognition element,is known as an"artificial antibody"and one of the hot spots of research in recent years.Due to their three-dimensional structure,nucleic acid aptamers can specifically bind to a wide range of targets,such as metal ions,organic substances,proteins as well as cells.In order to achieve selective degradation of low concentrations of target pollutants,this project uses nucleic acid aptamer-mediated magnetic graphene oxide/titanium dioxide(MGO/Ti O2-aptamer)carbon-based composites to investigate the selective photocatalytic degradation performance of AFB1,the photocatalytic degradation of AFB1in peanut oil and its effect on oil quality,the degradation pathway and mechanism of photocatalytic degradation of AFB1,and the safety of photocatalytic degradation products.The specific research contents are as follows.1.MGO/Ti O2composites were successfully prepared by hydrothermal synthesis,and MGO/Ti O2-aptamer was prepared by covalently combining the amino group of nucleic acid aptamer with the carboxyl group of MGO/Ti O2,and MGO/Ti O2-aptamer was characterized by scanning electron microscopy,Fourier infrared and transmission electron microscopy,etc.The results showed that MGO/Ti O2-aptamer was successfully prepared.aptamer was successfully prepared.Due to the mediation of Aptamer,the MGO/Ti O2-aptamer composites have enhanced degradation effect on low concentration of AFB1and selective degradation ability of AFB1in the mixed system.Under UV-visible light irradiation,the degradation rate of AFB1by MGO/Ti O2-aptamer was 98.3%after the addition of 6 mg and 120 min of light exposure at p H=3,and the photocatalytic degradation process was in accordance with the quasi primary kinetic model.The degradation rate of AFB1solution was still around 80%after 4 repeated applications.The hydroxyl radicals(·OH)and valence band vacancies(h+)played a major role in the degradation of AFB1by MGO/Ti O2-aptamer.2.Using peanut oil as the reaction system,the peanut oil samples containing AFB1were treated with UV-visible light irradiation,and the results showed that the MGO/Ti O2-aptamer composites had an enhanced effect on the degradation of AFB1at low concentrations in peanut oil,and the addition of 8 mg of photocatalyst to peanut oil containing 40μg/kg of AFB1under UV-visible light irradiation resulted in a degradation rate of 77.3%at 120 min.The degradation rate was 77.3%and the toxin concentration was about 9.08μg/kg after degradation.During the photocatalytic process,though the acid value and peroxide value of peanut oil tended to a small extent increase and the iodine value decreased significantly after 60 min of light exposure,both of them were within the range of national limit standards.The fatty acid composition of peanut oil did not change significantly,while sterols and vitamin E content changed significantly with small fluctuations.3.Structural analysis of photocatalytic degradation products using HPLC-MS/MS,and the structural and molecular formulae of the three degradation products were inferred to be P1(C17H14O8),P2(C17H16O7)and P3(C16H12O7).The structure and physical properties of the composites were analysed by DFT theory to investigate the possible degradation pathways and mechanisms of the photocatalytic degradation process,where the natural bond orbital(NBO)indicated that the natural charge of C9(atom No.C31)of AFB1was-0.28901,with more negative charge than C8(atom No.C29,0.12138),and the frontline molecular orbital theory of the calculations for the photocatalytic materials,AFB1and hydroxyl radicals(·OH),showed that the photocatalyst modifications led to increasing activity,easier electron leap and easier excitation by UV-visible light,that the mediation of nucleic acid aptamers did not significantly affect the molecular activity of the MGO/Ti O2materials,and that the LOMO of AFB1and The interaction between the LUMO of AFB1and theβ-HOMO of-OH is the largest,with an energy gap as low as?E=0.047 e V,and the interaction between the leading orbitals of both is extremely strong.It is postulated that the addition reaction of·OH occurs preferentially at the C8=C9 double bond of AFB1,where·OH is most likely to interact with the C9 position.The energy analysis of the degradation products justified the structure of the presumed degradation products and also verified that·OH was most likely to interact with the C9 position.4.The toxicity analysis of the photocatalytic degradation of AFB1products was carried out by Ames experiment and zebrafish model experiment,and the results showed that the number of revertant mutations of the photocatalytic degradation of AFB1products on Salmonella typhimurium TA98 and TA100 in the methanol system and peanut oil system were both significantly smaller than that of the number of revertant colonies of the same dose of AFB1.There was almost no difference in the reversion mutation rate of degradation products in the methanol system compared with the negative control group,but the reversion mutation rate of degradation products in the peanut oil system was somewhat different compared with the negative control group,which might be caused by the incomplete degradation of AFB1due to the complex composition of peanut oil.The survival rate of the zebrafish chicks after induction of AFB1at 80 ng/m L up to 96 hpf was about 74%and showed signs of blackening of the liver and yolk sac,enlargement of the yolk sac due to poor uptake by the chicks,and curvature of the spine and tail,whereas the survival rate of the zebrafish chicks in the degradation product experimental group was 100%,with the liver and yolk sac in good condition and no curvature of the spine and tail.The results of the supernatant assay after homogenization showed that AFB1caused serious impairment of liver function in the zebrafish litter,with significant increases of lactate dehydrogenase,glutamate transaminase and glutamic oxalacetic transaminase levels in the litter,whereas the degradation products had little effect on the litter’s liver function.Overall,the photocatalytic degradation of AFB1resulted in a significant reduction in toxicity and a high safety level,but a small amount of toxicity was still retained due to incomplete degradation and other factors. |