Recovery and reuse of chromium (III) using a highly efficient adsorbent composed of poly(acrylamide/sodium acrylate) hydrogel

This work deals with the preparation of poly(acrylamide/sodium acrylate) hydrogels through free radical crosslinking polymerization using different molar ratios of AAm and SA monomers. N , N ′-methylenebisacrylamide (MBA) was used as the crosslinking agent and ammonium persulfate (APS) as the initiator. The prepared poly(AAm/SA) hydrogels were subjected to adsorption–desorption studies with respect to Cr(III) ions to give Cr-poly(AAm/SA) complexes. The hydrogels were obtained with a high capacity for the adsorption of Cr(III) ions. Notably, the efficiency of capturing Cr(III) ions still had a strong dependence on the composition of sodium acrylate in the monomer blend. Desorption studies resulted in a high percentage recovery, almost 100 wt%, hence showing their potential reuse in environmental applications. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) were used for the characterization of poly(AAm/SA) and Cr-poly(AAm/SA) hydrogels and X-ray diffraction (XRD). The swelling ratio of hydrogels was very high and attained a value as high as 13.563.4%. Studies on the influence of time and initial Cr(III) ion concentration revealed that the maximum adsorption capacity by hydrogels for Cr(III) ions was 206.3 mg/g dry gel. The Freundlich isotherm is consistent with their adsorption behavior, and their adsorption kinetics were investigated and found to be consistent with the pseudo-second-order model. These results justify that the prepared hydrogels hold great promise in wastewater treatment applications, especially for the effective removal and recovery of heavy-metal ions, and hence offer possible contributions toward cleaner water sources and greener industrial processes. Graphical abstract Representative diagram of chromium(III) recovery via adsorption and hydrogel reusability