Synthesis and characterization of chitosan bearing indole linked N-arylacetamide moiety for effective removal of...

The most secure method for the ecosystem is the chemical disposal of radioactive waste through sorption, as uranium is a radioactive and hazardous environmental material that requires safe disposal. Herein, three new chitosan Schiff bases containing N-substituted phenyl acetamide and indole groups were synthesized through condensation reaction of chitosan with 2-(3-formyl-1H-indol-1-yl)-N-phenylacetamide (DP), 2-(3-formyl-1H-indol-1-yl)-N-(4-methoxyphenyl)acetamide (DO), and N-(4-bromophenyl)-2-(3-formyl-1H-indol-1-yl)acetamide (DB). The obtained Schiff base derivatives were coded as C-D-P, C-D-O, and C-D-B, respectively, and used as sorbents for U(VI) removal. The prepared chitosan Schiff bases were characterized by FTIR, ¹H NMR, XRD, BET, zeta-potential, and SEM. At the optimum pH = 4.0, the maximum sorption capacity could be ranked according to the series: C-D-O (272.8 mg U g^-1) > C-D-P (214.2 mg U g^-1) > C-D-B (174.7 mg U g^-1); besides, U(VI) can be desorbed effectively by hydrochloric acid solution (0.5 M). Reusing the sorbents for at least 5 or 6 cycles results in little degradation of their effectiveness. The Langmuir model accurately represented the isotherm of adsorption. Uranium sorption occurs rapidly under specific experimental conditions, achieving equilibrium within 60 min of contact. The U(VI) uptake is an exothermic reaction and is spontaneous. These findings suggest that the used sorbents were successful and efficient for U (VI) removal from a waste aqueous solution.