Modificação química de quitosana com etoximetilenos: otimização reacional, caracterização e aplicação na adsorção de cristal violeta e diclofenaco

Abstract

The increasing presence of organic contaminants in aquatic environments has stimulated significant interest in the development of new adsorbent materials capable of efficiently removing these compounds from water. Among the materials investigated for this purpose, chitosan stands out as a promising biopolymer due to its abundance, biodegradability, and the presence of reactive functional groups along its polymeric backbone. However, the adsorption performance of chitosan can be significantly enhanced through chemical modifications that alter its structure and surface properties. In this context, the aim of this project was to develop functionalized chitosan derivatives through nucleophilic vinylic substitution reactions using alkoxymethylene derivatives bearing different substituent groups, and to investigate how the electronic nature and density of these functional groups influence the adsorption performance of the material. Initially, chitosan was modified using (Ethoxymethylene)malononitrile, allowing the establishment of suitable reaction conditions for polymer functionalization through the formation of conjugated enamine structures, achieving a degree of substitution of up to 0.91. Subsequently, new chitosan derivatives were synthesized using Diethylethoxymethylenemalonate and Ethyl 2-cyano-3-ethoxyacrylate (Ethyl (ethoxymethylene)cyanoacetate), introducing diester and ester–nitrile groups, respectively. For these systems, reaction conditions were optimized using a design of experiments approach in order to maximize the degree of polymer functionalization. The obtained materials were characterized by different analytical techniques to evaluate the structural and physicochemical modifications resulting from the introduction of these functional groups. The adsorption performance of the synthesized derivatives was evaluated for the removal of model organic contaminants from aqueous solutions, including the dye crystal violet and the pharmaceutical compound diclofenac. The results demonstrated that chemical modification of chitosan significantly altered the surface properties of the material, directly influencing its adsorption capacity. An increase in the density of functional groups along the polymer chain led to enhanced affinity between the adsorbent material and the investigated contaminants, reaching a maximum adsorption capacity on the order of 219 mg.g-1 for diclofenac and 383 mg.g-1 for violet crystal. Overall, the results obtained in this thesis demonstrate that the chemical modification of chitosan through nucleophilic vinylic substitution reactions represents an efficient strategy for the development of new biopolymer-based adsorbent materials. In addition to improving the adsorption performance of chitosan, this synthetic approach also opens new perspectives for the development of functional polymeric materials with tunable properties for environmental applications.