Study On Photocatalytic Degradation Of Aflatoxin B₁ In Peanut Oil By Iron-iodine Co-doped Supported Nano-TiO₂ Thin Film

China is a big country in oil production and consumption.The output of edible oil can reach 27.22 million tons,and the domestic consumption of edible oil can reach 32.84million tons.Among them,peanut oil has an irreplaceable role in edible oil,and the annual output can reach 3 million tons.Peanut oil is very nutritious.It not only contains rich fatty acids,but also contains anti-aging ingredients,which can effectively delay the aging and degeneration of the brain.Moreover,peanut oil is an important zinc supplement for the public,and its zinc content is several times higher than that of soybean oil,salad oil and canola oil.However,peanut oil is highly susceptible to aflatoxins during processing,storage and transportation.Aflatoxins are a class of highly toxic substances,which are classified as I carcinogens by the cancer institute of The World Health Organization.The toxicity of aflatoxin was much higher than cyanide,arsenide and organic pesticide,aflatoxin B₁ is the most toxic of them.There are three traditional methods for removing aflatoxins,which are generally divided into physical,chemical,and biological methods.However,these methods have some problems,and it is impossible to safely and effectively remove aflatoxins,introduce new pollutants,and reduce the quality of peanut oil.Titanium dioxide(TiO₂)photocatalytic technology is a new catalytic degradation technology in recent years,which has been widely used in photoelectrochemistry,environmental protection,hydrolysis and other fields.TiO₂ can absorb energy greater than its band gap and make electrons on the valence band to transition,forming photogenerated electrons(e^-)and photogenerated holes(H⁺)with high catalytic activity.However,nano-semiconductor TiO₂ has a wide band gap and can only use 5%of the sunlight energy,which is low in utilization efficiency.Moreover,the photogenerated electron hole pairs are easy to compound,which lead to low photocatalytic activity of TiO₂.Therefore,TiO₂ must be doped to reduce the band gap width,inhibit the composite of photogenerated electron hole pairs,and improve the photocatalytic efficiency.Recently,some scholars have found that co-doping modification of TiO₂ can make different ions synergize and improve photocatalytic activity.In this study,TiO₂(P25,Degussa)was loaded onto quartz glass tube by dip coating and calcination.The effect of the light intensity,PVP-K30 addition,iron doping amount,iodine doping amount and iron-iodine co-doping amount on the AFB₁ degradation in pranut oil were investigated.FESEM,XRD,XPS and UV-Vis DRS were used to characterize the photocatalytic materials,and analyze the main factors of affecting the photocatalytic activity and the optimal conditions for preparation.(1)Supported nano-TiO₂ thin film(STF)was prepared by sol-gel method and impregnation calcination method.The test was carried out in a self-made reactor,and the initial concentration of AFB₁ was fixed at 80?g/kg,the peanut oil circulation rate was 500m L/min.When the light intensity was 240?w/cm² and the PVP-K30 was 15 wt%,the degradation rate was 60.67%.The pseudo first-order kinetic model has a good fitting effect(R²>0.95),and the maximum K'value was 0.00668 min^-1.(2)Iron doped supported nano-TiO₂ thin film(Fe-STF)was prepared by doping the STF with Fe(NO₃)₃ as the iron source.The results showed that the degradation rate of AFB₁increased first and then decreased with the increase of iron doping.When n(Ti):n(Fe)=3:1(Fe-STF-3),AFB₁ had the highest degradation rate of 69.73%.The pseudo first-order kinetic model has a good fitting effect for the results(R²>0.95),and the K'value of Fe-STF-3 was0.00921 min^-1,which was 37.87%higher than that of undoped STF.(3)Iodine doped supported nano-TiO₂ thin film(Fe-STF)was prepared by doping the STF with KIO₃ as the iron source.The results showed that with the increase of iodine doping,the degradation rate of AFB1 gradually increased.When n(Ti):n(I)=1:4(I-STF-4),the degradation rate of AFB₁ reached the maximum,which was 67.46%.After that,the degradation rate of AFB₁ began to decrease.The pseudo first-order kinetic model has a good fitting effect for the results(R²>0.95),and the K'value of I-STF-4 was 0.0091 min^-1,which was 36.23%higher than that of undoped STF.(4)Fe(NO₃)₃ was used as the iron source and KIO₃ was used as the iodine source.KIO₃and Fe(NO₃)₃ co-doped STF in different ratios to prepare iron-iodine co-doped supported TiO₂ thin films(Fe-I-STF).The results showed that the photocatalytic efficiency of Fe-I-STF-5 was the highest,and the degradation rate of AFB₁ reached 75.73%,which was 15.06%high than that of undoped STF.The pseudo first-order kinetic model has a good fitting effect for the results(R²>0.95),and the K'value of Fe-I-STF-5 was 0.01163 min^-1,which was70.76%%higher than that of undoped STF.The circulation experiments showed that Fe-I-STF had good repeatability,and the degradation efficiency did not decrease obviously when it was reused.AFB₁ content after degradation conforms to the national standard and has good stability.(5)The acid value(AV)and peroxide value(POV)of peanut oil showed a similar trend under different photocatalysts(STF,Fe-STF,I-STF,Fe-I-STF)after the photocatalytic degradation for 120min.AV showed no significant change and fluctuated around 0.7mg/g.POV increased slightly after photocatalytic degradation,and the POV was fitted with first-order exponential decay(Exp Dec1)to describe its changing trend.After a period of reaction,the POV will reach a similar equilibrium state and will no longer rise.After photocatalytic degradation for 120min,both AV and POV of peanut oil still meet the standards of first-class press peanut oil in China.(6)FESEM and EDS mapping characterization results:undoped STF photocatalyst is uniformly loaded on the surface of quartz glass tube,and has a small agglomeration phenomenon.After iron and iodine doping modification,the photocatalyst is densely loaded onto the surface of quartz glass tube.And gathered together to form a large three-dimensional structure,which expands the contact area and reaction site.(7)XPS characterization results:the eight different photocatalysts(STF,Fe-STF-3,Fe-STF-4,I-STF-2,I-STF-4,Fe-I-STF-1,Fe-I-STF-5,Fe-I-STF-9)were characterized by XPS,we found that the doping of iron and iodine help to increase the content of hydroxyl radicals·OH and Ti³⁺in titanium dioxide.Hydroxyl radicals·OH and Ti³⁺were important active materials for photocatalytic degradation.The increase of the ratio of·OH and Ti³⁺has beneficial to increase the photocatalytic activity of photocatalyst and improve the degradation efficiency.(8)XRD characterization results:STF,Fe-STF,I-STF and Fe-I-STF were characterized by XPS,it can be found that the doping of iron and iodine changes the titanium dioxide anatase phase and rutile to some extent,and mixed crystal effect could improve the activity of photocatalyst.(9)UV-Vis DRS characterization results:the band gap of pure P25 was about 3.2e V.After dip coating and calcination,the band gap of STF is reduced to 2.995e V;the band gap of Fe-STF and I-STF were 2.783 e V and 2.633 e V respectively.Doping modification reduced the band gap of TiO₂.The band gap of Fe-I-STF is 1.808e V,which is significantly lower than that of iron-doped or iodine-doped photocatalyst.The photocatalytic response range was extended to the visible light region,and the photocatalytic activity was improved.