Preparation Of Modified Biochar And Its Application In The Analysis Of Pesticide Residues In Rice

Herbicides are used to prevent weeds from growing during crop growth.Triazine,a kind of selective pre-and post mergence herbicide,has stable properties and can persist in crops.Their residues will cause potential health threats.Therefore,the establishment of a new analytical method for determinnation of triazine herbicide residues in crops has become a hot spot in the field of food analysis.However,there are some problems in crops,such as complex sample matrix and low content of pesticide residues.It is necessary to carry out sample pretreatment for effective separation and high-efficiency enrichment of trace targets,and realize the detection of pesticide residues in complex matrix.The choice and design of adsorbent material is the core of sample pretreatment technology.Biochar is a highly aromatic solid product rich in carbon,which prepared by pyrolysis of waste biomass under anoxic or anaerobic conditions.With the characteristics of low cost,wide source,large specific surface area and strong adsorption capacity,biochar is a potential adsorption material.However,the adsorbent based on biochar is rarely used in sample pretreatment.In order to increase the application range and adsorption selectivity of biochar,in this paper,chitosan modified biochar(CS-PBC)was prepared by phosphoric acid activation with Zizyphus jujuba core shell as the raw material.The CS-PBC exhibited mixed adsorption mechanism.With the combination of high performance liquid chromatography,the analytical method of triazine herbicides from rice was successfully constructed.The research results are as follows:(1)CS-PBC was prepared by activating the core shell of Zizyphus jujuba with phosphoric acid and modifying with chitosan.The parameters and conditions in the preparation process were optimized and investigated.The results showed that when the concentration of phosphoric acid was 50%,the carbonization temperature was 400℃,and the mass ratio of CS to PBC was 1:1,the extraction recovery rate of four triazine hebicides was the best.The appearance,specific surface area,pore structure and surface functional groups of BC,PBC and CS-PBC were characterized by elemental analyzer,specific surface area analyzer,scanning electron microscope and fourier transform infrared spectrometer.The characterization exhibited that CS-PBC has large specific surface area and porous structure,and the surface functional groups were abundant,which increased the adsorption sites on the material surface.(2)The adsorption behavior of CS-PBC with four triazine herbicides in aqueous solution was investigated.The adsorption kinetics fitting results showed that the pseudo-second-order kinetic equation could describe the adsorption process well,indicating that chemical adsorption was dominant;The fitting results of intra-particle diffusion showed that the adsorption process also involved edge layer diffusion and intra-particle diffusion.The adsorption isotherm fitting results showed that the adsorption process of the four triazine herbicides conformed to Langmuir model,which indicated that the adsorption process was monolayer adsorption.The calculation results of thermodynamic parameters showed that the adsorption process of CS-PBC for four triazine herbicides was spontaneous and endothermic,and their affinity was high.(3)CS-PBC was used as the adsorbent of PT-SPE.The type and volume of extraction solvent,the adsorbent amount,the p H value of the sample solution,the type and volume of the elution solvent were optimized.Under the optimal condition,the method was evaluated by performance indexes such as linearity,detection limit,quantitative limit and precision.The results showed that the linear range of the method was wide,and the values of R~2were greater than 0.99.The LOD and LOQ ranged from 7.1 to 20.3 and 23.5 to 67.7 ng/g,respectively.The method was employed to detect the actual rice samples from different producing areas,and the result showed that this method has good applicability.The comparison with other commercial adsorbents implied that this adsorbent could be well applied in the extraction of triazine herbicides from complex substrates.Research on the adsorption mechanism indicated that,the main forces between CS-PBC and triazine herbicides included channel trapping interaction,electrostatic interaction,hydrogen bonding and hydrophobic interaction.Based on the above results,as an adsorbent of PT-SPE,CS-PBC can provide a variety of adsorption effects and has a good extraction effect of triazine herbicides from rice,which further indicates that plant biochar,represented by Zizyphus jujuba core shell biochar,has great application potential in food safety detection.