Preparation Of Lignin-based Biochar From Sesame Straw And Its Adsorption Capacity For Benzo(a)pyrene In Sesame Oil

Benzo（a）pyrene（BaP）is an internationally recognized chronic toxic and teratogenic,carcinogenic and mutagenic substance that poses a major threat to human health,and the special production process of sesame oil increases the risk of exceeding the BaP content significantly.Biochar prepared with agricultural and sideline products and other biomass raw materials has attracted attention because of its advantages of easy availability,low cost,large adsorption capacity and ecological friendliness.Lignin is abundant in biomass raw materials.Lignin is an ideal precursor for the preparation of biochar materials because of its high carbon content.Therefore,in this study,agricultural waste sesame straw was used as a raw material to extract its main biomass component lignin.Then,lignin was used as a precursor to prepare biochar to investigate the adsorption of BaP in sesame oil.The main works and conclusions are as follows:（1）The adsorption and removal of BaP in sesame oil by biochar prepared from sesame stalk lignin,cellulose and hemicellulose were investigated.Compared with the unmodified hemicellulose and lignin biochar,the unmodified cellulosic biochar had a more abundant pore structure（0.2145 cm³/g）,a larger specific surface area（387.8343 m²/g）and a higher removal rate of BaP（39.15%）.The modified biochars showed higher removal rate for BaP than unmodified biochars.The highest adsorption（95.79%）of BaP was achieved using the modified lignin biochar,which was therefore selected for evaluation of adsorptive capacity.The ability of the modified lignin biochar to adsorb BaP was consistent with the pseudo-second order kinetic equation indicating mainly chemisorption,and it fit the Freundlich isotherm（R²>0.999）,thereby revealing the occurrence of multilayer adsorption.The effect ofπ-πconjugation interaction and pore-filling together promoted the high adsorption performance of the modified lignin biochar.（2）The effects of lignin precursors（different raw materials and extraction methods）on the structure and BaP adsorption of biochar were investigated.The carbon content and aromatic index of lignin-based biochar were higher than that of precursor lignin.Biochar（BGS）prepared from acetic acid lignin from white sesame stalk had the highest specific surface area（1065.8187 m²/g）and the most abundant pore structure（0.8531 cm³/g）.In terms of raw materials,biochar prepared from lignin extracted from white sesame stalk and white sesame capsule has better BaP removal efficiency than black sesame stalk and black sesame capsule.In terms of extraction methods,the removal effect of BaP by biochar from lignin extracted by acid extraction was better than that by organic solvent and alkali extraction.The removal rates of BaP from sesame oil by biochar prepared from lignin extracted from different materials and methods were all higher than 72.05%.Among them,BGS had the highest removal rate of BaP in sesame oil,reaching 91.44%.（3）The effects of preparation methods（different activation methods and activators）on the structure and BaP adsorption of lignin-based biochar were investigated.The results showed that compared with the two-step activation method,the lignin-based biochar prepared by one-step activation method had rich pore structure and high specific surface area,and had better adsorption performance for BaP in sesame oil.In the one-step activation method,the biochar prepared with ZnCl₂ as activator had the highest carbon content and the lowest H/C,and had the best removal effect on BaP.（4）Graphene-like lignin-based biochar（FZBC）was prepared to investigate its adsorption performance on BaP in sesame oil.FZBC had a foamy,highly porous and graphene-like structure.FZBC showed a high adsorption capacity in adsorbing BaP from contaminated sesame oils because of its porous structure,high specific surface area and abundant surface functional groups.Using a 0.22%FZBC adsorbent dosage,a BaP removal efficiency of 91.73%was achieved when the initial BaP content was 21.25μg/kg.The kinetic and thermodynamic model fitting results showed that the adsorption of BaP in sesame oil by FZBC was a spontaneous heat absorption process,and the adsorption process was in accordance with the Freundlich isothermal adsorption model and the quasi-secondary kinetic model,indicating that the adsorption was multilayer adsorption.（5）The adsorption effect of biochar FZBC and BGSZ-1,commercially available activated carbon（Norit 8015 and YS-900）on BaP in sesame oil and the effect on the quality of sesame oil were investigated.The results showed that biochar was a better adsorbent for the removal of BaP in sesame oil.When the amount of adsorbent was 0.22%and the adsorption time was 35 min,the concentration of BaP in the sesame oil treated by FZBC was 1.76μg/kg,and the concentration of BaP in the sesame oil treated by Norit 8015,YS-900 and BGSZ-1were 2.62μg/kg,9.79μg/kg and 7.96μg/kg,respectively.The differences in fatty acid composition andγ-tocopherol of all adsorbed sesame oils were not significant compared to those of crude oil.After adsorption treatment,the sesame oil showed a decrease in sesamin,sesaminarin,fatty acid content,sterols and volatile components,and the yellow value of sesame oil decreased and the colour became lighter.In this study,agricultural waste sesame straw was used as raw material,and lignin was used as the starting point to extract lignin and prepare biochar to remove BaP in edible oil.It was found that lignin-based biochar has excellent adsorption performance for BaP in edible oil,which provided a new way to remove harmful substances in edible oil and had great significance for the resource utilization of agricultural waste.