Efficient removal of Cr(VI) by chitosan cross-linked bentonite loaded nano-zero-valent iron composite: performance and mechanism

A nano-zero-valent iron loaded with 2-aminoterephthalic acid cross-linked chitosan/bentonite (2ACB@nZVI) was developed to remove Cr(VI) from aqueous solution through adsorption-reduction. It was characterized by FTIR, XRD, TGA, BET, SEM, EDS, electrochemistry and XPS. This analysis showed that chitosan cross-linked bentonite not only enhanced the adsorption effect of chitosan and its chemical stability, but also provided a good carrier for loading nZVI and effectively improves its reaction activity. The optimal mass ratios of chitosan: bentonite and 2ACB:nZVI for synthesizing the 2ACB@nZVI composite were 3:1 and 1:4, respectively. The pH value had a great influence on the removal rate of Cr(VI), and its optimal value was 2.0. This is because nZVI was more susceptible to corrosion under acidic conditions, and a large amount of Fe(II) was leached to reduce the adsorbed Cr(VI) on the surface of 2ACB@nZVI. The Cr(VI) removal by 2ACB@nZVI constituted a spontaneous endothermic reaction, aligning with both the pseudo-second-order kinetic model and the Langmuir adsorption isotherm, with a maximum adsorption capacity reached 406.36 mg g