Synthesis and Characterization of Novel Uracil-Modified Chitosan as a Promising Adsorbent for Efficient Removal of Congo Red Dye

Novel Uracil-modified chitosan (UCs) adsorbent has successfully been synthesized through a four-step method during which the amino groups of chitosan have been protected, then epoxy nuclei have been incorporated, afterwards the latter have been opened using 6-amino-1,3-dimethyl uracil, and finally the amino groups have been regained via removing the protection. Its structure was checked using FTIR, XRD and SEM techniques. The adsorption capacity of UCs for anionic Congo Red (CR) dye was studied under various conditions. It decreased significantly with increasing the solution pH value and dye concentration, while increased with increasing temperature. The adsorption of UCs for CR dye at different temperatures, solution pH and dye concentrations fitted to the kinetic model of pseudo-second order and Elovich model. The intraparticle diffusion model showed that the adsorption process involves multi-step process. The isotherm of CR dye adsorption by UCs conforms to the Langmuir isotherm model indicating the monolayer nature of adsorption. The maximum monolayer coverage capacity, q(max), was 434.78 mg g(-1). Studying the thermodynamic showed that the adsorption of CR dye onto UCs was endothermic as illustrated from the positive value of enthalpy (21.37 kJ mol(-1)). According to the values of Delta G degrees, the adsorption process was spontaneous at all selected temperatures. The value of Delta S degrees showed an increase in randomness for the adsorption of CR dye by UCs. The value of activation energy was 18.40 kJ mol(-1).

Automated summary

A novel uracil-modified chitosan (UCs) adsorbent has been successfully synthesized and its structure and adsorption performance have been studied. The results show that the adsorption capacity of UCs for anionic Congo Red dye is related to factors such as solution pH, dye concentration, and temperature. The adsorption process follows pseudo-second order and Elovich models, and involves multiple steps. The isotherm analysis indicates that the adsorption of CR dye by UCs follows the Langmuir model, suggesting monolayer adsorption. Thermodynamic analysis shows that the adsorption process is endothermic and leads to increased randomness in the system.