ZIF-67 loaded thio-groups modified chitosan hydrogel for high efficient Hg(II) removal from water

In the past few years, there has been an increasing worry about the pollution of water caused by the presence of heavy metals. To address this environmental issue, a highly effective adsorbent called ZIF-67/CS-SH was developed. This adsorbent was prepared by grafting thioglycolic acid and loading a metal-organic framework called ZIF-67 onto chitosan, to remove Hg(II) from water. Confirmation of the ZIF-67/CS-SH was achieved by employing a range of techniques including FTIR, XRD, TGA, SEM, EDS, BET, and XPS. Due to the presence of abundant active sites (-SH, O/N-containing functional groups) and ZIF-67, ZIF-67/CS-SH exhibited a high adsorption capacity (949 mg/g at 298 K) and rapid adsorption kinetics (20 min for 91 % removal). The optimal pH for the adsorption process was found to be 5. The adsorption process followed a pseudo-second-order kinetics and Langmuir isotherm, with chemisorption being the main adsorption mechanism. The adsorption process was determined to be spontaneous and endothermic. Additionally, ZIF-67/CS-SH demonstrated selective adsorption in the presence of other metal cations at concentrations of 100 mg/L. Furthermore, ZIF-67/CS-SH exhibited excellent regenerative properties, with only a 10 % decrease in adsorption capacity after ten cycles. The key adsorption sites were identified as the –SH groups, O/N-containing functional groups, and ZIF-67 in ZIF-67/CS-SH through FTIR, EDS, and XPS analyses. Considering its outstanding performance in removing Hg(II), ZIF-67/CS-SH shows promise for application in industrial wastewater treatment. The schematic diagram of adsorption mechanism. [Display omitted] •This adsorbent was prepared by thioglycolic acid and metal-organic framework.•ZIF-67/CS-SH exhibited a high adsorption capacity (965 mg/g at 308 K).•The key adsorption sites were –SH groups and O/N-containing functional groups.