Development Of Carbon Nanomaterials From Citrus Pomace And Application In Determination Of Pesticide Residues In Fruits And Vegetables

In recent years,the problem of food safety and environmental protection has attracted the attention of people all over the world.The problem of pesticide residues in the daily edible fruits and vegetables is a huge hidden danger in food safety.In the analysis of pesticide residues in fruits and vegetables,the sample pretreatment technology is the key step in the whole process of analysis.Due to the amount of pesticide residues in fruits and vegetables are generally low,target analyte separation and enrichment and reduce or eliminate the sample matrix interference has become the key to the whole analysis process.So,the establishment of sample pretreatment technology which is rapid,accurate and efficient in the process of detection of pesticide residues is very important.Carbon nanomaterials are widely used in various fields like environment,chemical industry,energy,biology and medicine because of their high specific surface area and unique optical,electrical and adsorption properties.However,the world is faced with the increasingly serious problem of non-renewable resource depletion and environmental pollution,the use of environmentally friendly and cheap renewable biomass resources as raw material for the synthesis of low cost and excellent adsorption performance of carbon nanometer materials has become the focus of attention in recent years.Citrus as the largest type of fruit in the world,a large number of citrus peel will be produced every year after the processing of citrus.The discarded citrus peel not only causes the waste of biomass resources,but also deepens the serious environmental pollution.Therefore,the scientific and efficient use of abundant and cheap citrus pomace to prepare new carbon nanometer materials,and used as adsorbents apply to determinate pesticide residues in fruits and vegetables.On the one hand,the comprehensive utilization of biological resources,the protection of environment and the conversion of waste into novel carbon materials,provide a reference for further development and use of carbon nanometer materials.On the other hand,the application of new carbon nanomaterials in determination of pesticide residues in fruits and vegetables has important practical value and significance.In this study,2 kinds of carbon nanometer materials based on citrus pomace by the simple,cheap and environmentally friendly activation method and one step hydrothermal method was prepared,named porous carbon nanoparticles（NPC）and carbon based Fe₃O₄ nanocomposites（C/Fe₃O₄ NCs）,respectively.And they used as new adsorbents apply to the sample pretreatment methods in order to detect pesticide residues in fruits and vegetables.The main research results were presented as follows:1,The porous carbon nanoparticles（NPC）was prepared by ZnCl₂ activation and carbonization using citrus pomace as carbon source.The characterization of NPC was performed by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Raman spectroscopy,FT-IR spectra,Brunauer,Emmett and Teller surface area（BET）.Those results showed that the NPC was an amorphous porous carbon material with a pore size in the range of 0-15 nm.Its specific surface area and pore volume is 1242.64 m² g^-11 and1.28 cm³ g^-1,respectively.2,A sample pretreatment method with porous carbon nanoparticles（NPC）as dispersive solid phase extraction（d-SPE）absorbent was established for the determination of organophosphorus pesticides in fruits and vegetables by gas chromatography.The analysis conditions,including the amount and clean up time of adsorbent,were optimized by analysis of 14 kinds of oranophosphorus pesticides in fruits and vegetables prior to gas chromatography-flame photometric determination.Moreover,the comparison for NPC with commercial materials of PSA,C18 and GCB was investigated in this study.The results indicated that the purification time was only 2min using 0.01 g NPC.And the purification efficiency of NPC was significantly higher than the three commercial materials mentioned above.Under the optimum conditions,the calibration curves of the 14 organophosphorus pesticides were linear in the range of0.02-1.0 mg/L with good correlation coefficients（R²>0.99）,and the detection limit（LOD）ranging from 0.63 to 5.30μg/kg.The recoveries of the pesticides at three spiked levels ranged from 71.3%to 114.7%with the relative standard deviations（RSDs）of0.9%-12.9%.The method is simple,rapid,sensitive,low cost,and can satisfy the requirements of detection of organophosphorus pesticide residues in fruits and vegetables,displaying a good application prospect.3,Carbon based Fe₃O₄ nanocomposites（C/Fe₃O₄ NCs）were synthesized by a simple one-step hydrothermal method using waste pomelo peels as the carbon precursors and characterized by SEM,transmission electron microscope（TEM）,XRD,Raman vibrating sample magnetometer（VSM）and FT-IR.Those results showed that the C/Fe₃O₄ NCs were approximately spherical carbon nanomaterials with the average size of about 50 nm.Moreover,they had superparamagnetic behavior with a high saturation magnetization of 45.9 emu g^-1 at room temperature.The surface of C/Fe₃O₄NCs existed oxygen containing groups such as carboxyl（-COOH）and hydroxyl（-OH）.4,A magnetic solid phase extraction method（MSPE）based on C/Fe₃O₄ NCs as absorbents was established for the determination of triazole fungicides in fruit samples by gas chromatography/mass spectrometry.Several parameters affecting extraction efficiency including the amount of adsorbents,extraction time,the type and volume of desorption solvent and desorption time were optimized.Under the optimized conditions,the good linearity with satisfactory correlation coefficients（R²>0.9916）was obtained in the range of 1-100μg/kg for 11 triazole fungicides.The limits of detection（LOD）and quantification（LOQ）of the method were obtained in the range of 0.12-0.55 ug/kg and0.39-1.85 ug/kg,respectively.The recoveries in the range of 82.1%to 109.9%with RSDs below 8.4%.Thus,the C/Fe₃O₄ NCs based MSPE method had a great potential for analysing trace level of triazole fungicides in real fruit samples.