Removal of 2,4-D from aqueous solutions by adsorption processes using two biopolymers: chitin and chitosan and their optical properties

•The extraction of chitosan by deacetylation of chitin.•Preparation of the sample from chitin from crustacean shells.•Description of the adsorption by Langmuir-type isotherm and Freundlich-type isotherm.•Theoretical calculation of UV–Vis spectra and optical parameters.

Chitin, extracted primarily from exoskeleton shellfish, is one of the most abundant biopolymer in the world. It is estimated to be produced annually almost as much as cellulose.The development of fishing activities in Morocco (coastline of 3500 km on both the Atlantic and the Mediterranean) induced an important fish industry waste. The aim of this work is to recover chitin, extracted from shellfish waste, and chitosan, produced by deacetylation of chitin, in the adsorption of organic pesticide 2,4-dichlorophenoxyacetate (2,4-D). The chitosan samples were prepared from chitin from crustacean shells. The chitin deacetylation was carried out in aqueous sodium hydroxide. Characterization of chitin and chitosan was performed by infrared spectroscopy, nuclear magnetic resonance and theoretical calculation of UV–Vis spectra and optical parameters. Analysis of theoretical spectra shows a substantial sensitivity to the hydroxyl and amino groups. The presented hydroxyl group in chitin determines the conformation of the molecule and also the stereochemistry of chemical reactions and kinetics. The presence of functional groups causes the substantial changes of both absorption spectra as well as permanent dipole moment. The adsorption of 2,4-D by chitin and chitosan was performed at different pH values, the pesticide-adsorbent contact time and initial pesticide concentration. The adsorption is described by Langmuir-type isotherm and Freundlich-type isotherm. Recovery tests of 2,4-D confirm the initial interest in using chitin and chitosan as a depolluting agent.