Removal of Hexavalent Chromium by Cross-Linking Chitosan and N,N’-Methylene Bis-Acrylamide

Abstract

The present work aims to make a novel chemical modification of chitosan to improve its ability in removing hexavalent chromium from its aqueous solution. Therefore, the use of N,N/−methylene bis-acrylamide as a cross linker for chitosan has been studied using simple method via nucleophilic addition, in the presence of FeCl3.6H2O as a Lewis acid catalyst. The obtained product (CMBA) was tested as an adsorbent for removal of Cr6+ ions from its aqueous solution. The CMBA was characterized using instrumental techniques such as FTIR, SEM, EDX, and TGA analyses. The FTIR analysis showed the presence of a peak at 3297–3355 cm−1 due to the stretching vibration mode of –OH and –NH2 groups, and a peak at 1745 cm−1 due to the C=O stretching in carboxylic group. The equilibrium data were studied using Langmuir, Freundlich and Tempkin isotherm models. The maximum monolayer adsorption capacity (Qm) calculated from Langmuir isotherm was 149 mg/g, which showed a 3-fold greater uptake for CMBA over non-modified chitosan. The pseudo-second-order kinetic model was the best model representing the adsorption data with correlation coefficient close to one, indicating that chemisorption is dominating the adsorption process. The intraparticle diffusion study proved that the adsorption process was performed under the control of more than one mechanisms. The present study proved that the novel cross-linked chitosan CMBA is a helpful material for the adsorption of Cr6+ ions from its water solution.