Direct carboxylation of cellulose in deep eutectic solvent and its adsorption behavior of methylene blue

The surface of cellulose particles was carboxylated (2.44 mmol/g) in a deep eutectic solvent containing carboxylic acid. Based on the carboxyl content, the effects of key factors on cellulose carboxylation was systematically investigated. In addition, the reaction mechanism was studied by using liquid chromatography-mass spectrometry, and the influence of deep eutectic solvent containing carboxylic acid on the structure and physicochemical properties of cellulose during carboxylation was examined using different characterization techniques. The results showed that the type of carboxylic acid, cellulose particle size, and pretreatment methods significantly affect the carboxylation efficiency, degradation, and carbonization of cellulose. The internal crystal structure of cellulose did not change after the carboxylation reaction, while the surface crystal structure was destroyed by carboxylation, which greatly improved the dispersion and hydrophilicity properties of the product. The kinetics and thermodynamics of carboxyl cellulose adsorption were studied as well. Potential application of carboxyl cellulose in the adsorption of pollutants was demonstrated. This study provides a new method for the direct modification of cellulose in deep eutectic solvents, as well as a new sustainable strategy for modifying other materials.