Application Of Magnetic Biochar Composites In Pesticide Residues Detection And Investigation Of Adsorption Performance

The widespread use of pesticides in agriculture is conducive to controlling pests,thereby increasing crop yields to meet human demands.However,excessive use of pesticides can cause contamination of a large number of crops,posing a serious threat to the environment?water,soil and air pollution?and human health?teratogenic,carcinogenic,mutagenesis?.Therefore,it is essential to monitor the concentrations of pesticide residues.In order to accurately determine pesticide residues in vegetables,a fast,simple and reliable pretreatment method should be developed.QuEChERS pretreatment method has been widely used in the analysis of multiple pesticide residues in various samples since it was proposed by Anastassiades et al.in 2013.However,the adsorbent used in the traditional QuEChERS method(such as C₁₈,PSA)has a single adsorption performance and a complicated separation process.Therefore,it is urgent to develop a new type of environmentally-friendly,low-cost,excellent performance adsorbent.Biochar is a carbon-rich product produced by the pyrolysis of biomass?such as wood,fertilizer,or crop residues?under hypoxic conditions.Biochar is a stable solid with carbon containing aromatic ring structure.It has porous structure with a relatively high specific surface area and porosity,and can be used as a good adsorbent for pollutant management.Assembling a magnetic matrix on the surface of biochar will make the collection and the separation of biochar only by an external magnetic field without any additional centrifugation process,thereby achieving a faster and simpler phase separation process.In this paper,magnetic biochar composites were successfully prepared.A simple and effective method for the analysis and detection of various pesticide residues in vegetables was established.The structure and properties of biochar were further optimized and modified,which increased the specific surface area,porosity,and degree of aromatic ring of biochar.At the same time,the enhanced effect of modified biochar on the adsorption of other pollutants and the microscopic mechanism were discussed.Part?A three dimension magnetic bio-char composite-basedQuEChERS method for multi-pesticides analysis of vegetablesObjective:A three-dimensional?3D?Fe₃O₄-biochar composites from waste citrus peels was synthesized and used as adsorbent in QuEChERS pretreatment methods,combined with ultra performance liquid chromatography-tandem mass spectrometry?UHPLC-MS/MS?)for the detection of 49 trace pesticide residues in vegetables.Methods:The citrus peel powder was chemically activated and carbonized at high temperature to obtain biochar,and then co-precipitated with Fe₃O₄ to obtain Fe₃O₄-biochar.Multivariate approach was employed to optimize the extraction parameters including sample amount,solvent volume,NaCl amount,extraction time,anhydrous MgSO₄ amount,adsorbent amount and purification time.UHPLC-MS/MS was used as a detection method for 49trace pesticides in vegetables.Results:The extraction time and Fe₃O₄–biochar amount had significant influences on the recovery yield of pesticides and the 20 min extraction time and 13.9 mg Fe₃O₄–biochar are optimal conditions.Under the best conditions,the proposed extraction method exhibited good linearity with correlation coefficient greater than0.9902.The limits of quantitation?LOQs?were in the range of 0.03-0.67?g kg^-1.The average recoveries were between 81.3%and 117.3%with relative standard deviation?intra-day RSD=0.5-7.5%and inter-day RSD=0.6-6.9%?.Conclusion:Fe₃O₄-biochar composite can obtain excellent recoveries in the analysis of pesticide residues in vegetables containing complex pigments and has important application value and great potential.Part?Study on adsorption performance of the novel Fe₃O₄/graphene oxide/citrus peel-derived bio-char basednanocompositeObjective:The new magnetic bio-nanocomposites modified with graphene oxide?mGOCP?were prepared and the ciprofloxacin?CIP?and sparfloxacin?SPA?were selected as representatives to study their adsorption performance.Methods:mGOCP-X were synthesized by a simple one-pot pyrolysis method with the mixture of waste citrus peel,different radios of GO?-0.1%,-0.5%,-1%?and Fe₃O₄ nanoparticles.The synthesized materials were characterized by BET adsorption,SEM,EDS,VSM,Raman spectrum,FT-IR,XPS,and TGA.The kinetic and isothermal adsorption experiments were used to study its adsorption performance and mechanism.Results:As the ratio of GO increases,the surface characteristics of the materials become more excellent.The adsorption capacity of mGOCP-1%for CIP and SPA was 283.44 mg g^-1 and 502.37mg g^-1,respectively,showing outstanding adsorption capacity.The primary adsorption mechanisms for CIP and SPA included?-?electron donor-acceptor interaction,H-bonding,hydrophobic interaction and electrostatic interaction.Conclusion:The new magnetic bio-nanocomposites modified with graphene oxide?GO?have improved surface morphology and structure,enhanced adsorption capacity,and could be extended as an organic pollutant adsorbent to purify the natural environment.