Exploring the potent hydrolytic activity of chitosan-cerium complex microspheres resin for organophosphorus pesticide degradation

Chitosan is a biocompatible, non-toxic and renewable natural basic polysaccharide that can be cross-linked and reacted with Ce(IV) to form a physiologically active chitosan-Ce(IV) complex. To investigate this novel complex and its potential to hydrolyze phosphate ester bonds, chitosan-cerium complex microspheres resin (CS-CCMR) was prepared from chitosan and ceric ammonium nitrate by reversed-phase suspension cross-linking polymerization. CS-CCMR was characterized, its ability to hydrolyze disodium p-nitrobenzene phosphate (PNPP2Na) and organophosphorus pesticides was investigated, and the hydrolytic mechanism was explored. CS-CCMR was composed of dark yellow microspheres with smooth surfaces and dense pores. It was found that CS-CCMR contained 4.507 mg/g Ce(IV), indicating that coordination polymerization between Ce(IV) and chitosan was successful. The presence of Ce(IV) in CS-CCMR was confirmed by multiple analytical methods and it was found that coordination of Ce(IV) by chitosan was mediated by the nitrogen atom of the amino group and the oxygen atom of the hydroxyl group of chitosan. It was shown that CS-CCMR efficiently hydrolyzed the phosphate ester bonds of PNPP2Na and five organophosphorus pesticides. Hydrolysis of PNPP2Na is potentially accomplished by charge neutralization and nucleophilic substitution. The mechanism of parathion degradation by CS-CCMR involves modification of the nitro group to give aminoparathion, followed by cleavage of the P–O bond to generate diazinphos. Consequently, the novel chitosan-Ce(IV) complex exhibits great efficiency for hydrolysis of phosphate ester bonds and CS-CCMR is expected to be developed as an agent to reduce the possibility of contamination of fruit and vegetable drinks by organophosphorus pesticides.