Optimization And Characterization Of A Pesticide Residue Adsorbent From Melon Peel

China and our region are the dominant melon producing areas.The rind is an important bio-waste from melon fruits,about 500,000 tonnes per year in our region alone,and its deepening development is beneficial to further extend the industrial chain and promote the development of the dominant industry.The team’s preliminary research found that melon rind has the potential to be used as a pesticide residue adsorbent.In this paper,the preparation process of pesticide residue adsorbents from melon rind was investigated by combining domestic and international research progress,and the adsorption conditions of 23 pesticide residues(common pesticide residues in fruits and vegetables)were optimised by combining the techniques of gas chromatography-mass spectrometry,ultra-high performance liquid chromatography tandem mass spectrometry,FTIR,SEM,TGA,BET and EDXS.The adsorption effects of the prepared materials on pesticide residues of four fruits(strawberry,hawthorn,grape and cherry,fruits with relatively high risk of pesticide residues)and the safety of their application were evaluated,and the main findings were as follows.(1)The optimized parameters for the preparation of melon rind pesticide residue adsorbent were:charring time of 2 h;zinc chloride concentration of 10%;soaking time of 24 h;adsorbent to zinc chloride ratio of 1:4;sieving mesh of 40 mesh.The adsorbents prepared by the above process conditions showed 100%adsorption of pyridaben,mevinphos-methyl,abamectin,carbofuran,dimethoate,bifenthrin and cyfluthrin;89.62%to 98.57%adsorption of imazam,chlorpyrifos,propanil,rotamox,mefenoxam,malathion,triadimefon,isoxaflutole and difenocarb;and 89%or less adsorption of other pesticides.(2)The microstructure of melon peel changed from smooth to rough before and after modification;the pore size increased;the O-H,C=O and C-O bonds were displaced and the amplitude changed,suggesting that functional groups such as phenols,carbonyls and ethers may be involved in the pesticide residue adsorption process.The above changes in the structure of the melon peel may be responsible for the good pesticide residue adsorption effect of the prepared material.In contrast,the close proximity of pore volume and specific surface area may not be responsible for the pesticide residue adsorption effect.(3)The optimum adsorption conditions for the adsorption of 23 pesticide residues were as follows:pH 5;the amount of adsorbent used was 1 g;the initial concentration was 1 μg/ml;temperature and time had little effect on the adsorption of pesticide residues,and the recommended temperature was room temperature and time was 30 min.The adsorption rates were 100%for avermectin,carbendazim,carbofuran,acetamiprid,dimethoate,profenofos,triadimefon,cyfluthrin and imidacloprid,and 97.23%～99.53%for malathion,mefenoxam,bifenthrin and rotamox.The kinetic and isothermal adsorption models followed by the different pesticide residues differed.The adsorption of six pesticide residues tended to follow the pseudo-secondary kinetic model;the adsorption of eight pesticide residues followed the Langmuir model;and the adsorption of 12 pesticide residues followed the Freundich model better.(4)The melon rind adsorbent showed better adsorption of acetamiprid,chlorothalonil,pyridaben and carbendazim residues in the four fruits than water,detergent and watermelon rind adsorbent.There is a risk of residues of pyridaben,mevinphos,bifenthrin,propamocarb,phenothrin,methomyl,carbofuran,methomyl,cypermethrin and dimethoate in the prepared material processing raw materials,but this risk does not increase the risk of pesticide residues in the treated fruit.There is no contamination of the prepared material with the common heavy metals Cd,Cr,Pb and As elements.This indicates that the use of the prepared materials does not increase the risk of heavy metal contamination in the treated fruit.