Adsorption of paraquat, diquat and methylene blue in aqueous solution onto the biopolymer chitin

Abstract

Today, fresh water resources are reached by pollution, in particular the organic pollutants. Recent studies reveal the presence of various toxic substances, such as pesticides and textile colorants, in surface or underground waters everywhere in the world. Among these products, we are interested in two pesticides, the paraquat (PQ) and diquat (DQ) as well as a textile colorant: methylene blue (BM). The treatment of these pollutants requires in addition to the usual treatments (coagulation-flocculation, decantation, filtration, oxidation…), a stage of refining by adsorption on activated carbon. These processes remain hard and expensive. In this respect, this actual work depends on the elimination of the PQ, the DQ and the BM, by adsorption on natural polymeric chitin, which is a principal structural constituent of the protective cuticles shellfish, insects and also of the cellular walls of certain mushrooms and micro-organisms. This material is chosen because of on one hand its great abundance in Morocco, and on the other hand, its structural and textural properties, allowing its use in the treatment of polluted water. Chitin were extracted primarily from Moroccan exoskeleton shellfish. Characterization of chitin was performed by infrared spectroscopy and nuclear magnetic resonance. The adsorption of PQ, DQ and BM by chitin was studied at different pH values, the pollutants-adsorbent contact time and initial pollutants concentration. The adsorption is described by both Langmuir-type isotherm and Freundlich-type isotherm.