Synthesis of a graft-copolymer adsorbent through a green route and studies on its interactions with chromium(iii) through active functional groups: kinetics and improved adsorption supported by SEM-EDX and AFM

Abstract

Chromium(III), a heavy metal, contributes towards pollution load, potentially even more than the 2000 ppm level in the effluent of many industries. Managing chromium by means of process intensification tools is one of the ways for the sustainable development of society and industry. A novel graft copolymer adsorbent prepared from collagen hydrolyzate and polyvinyl alcohol (PVA), with a narrow particle size of 1366 nm has been employed to enhance the uptake of Cr(III) in the tanning process up to 94% using 6% copolymer due to the participation of free functional groups of the copolymer. Kinetic studies reveal the mechanism of the adsorption–diffusion–absorption phenomena confirming the Langmuir isotherm. Mathematical models augmented with RSM (supported by DOE) are developed to optimize the process. The mechanism of improved absorption has been confirmed by ¹HNMR and SEM images indicating a strong ligand interaction; and by SEM-EDX confirming an increase in the rate of adsorption. AFM images indicate a larger amount of chromium adsorbed with an increase in the concentration of the copolymer. The increase in intensities of the XRD spectra supports the improved absorption of chromium with enhanced interactions with functional groups of the collagen–copolymer–chromium complex. CD spectra revealed that the addition of the copolymer increases the ellipticity (mdeg value) of the collagen in the cases of 6% and 4% copolymer as compared to the control sample. Application of the copolymer in tanning resulted in improved color properties and comparable/analogous physical strength properties in the leather samples.