Environmental and industrial impacts of Cr(vi) in wastewater: high performance removal efficiency using novel ZIF-8 MOFs doped with cesium

Abstract

Chromium is a heavy element that is extremely hazardous to both humans and the environment and is present in industrial waste. In this work, novel ZIF-8 MOFs doped with various molar ratios of cesium were prepared for the first time. Cs-2@ZIF-8 MOF was employed as an adsorbent material for removing Cr(VI) ions from wastewater. Several methods, like XRD, SEM/EDX, FT-IR, TEM, TGA, PL, BET, and XPS, were employed to characterize the physico-chemical and structural characteristics of the produced MOFs. The specific surface area of the ZIF-8 MOF was significantly enhanced from 1019.57 to 1204.95 m² g⁻¹ when doped with Cs ions. SEM images revealed that the Cs-2@ZIF-8 MOF particles had a flower-like morphology. TEM images of the Cs-2@ZIF-8 MOF revealed a rhombic dodecahedron structure, with crystallite diameters between 20 to 30 nm. TGA investigation revealed that the thermal stability of the ZIF-8 MOF increased significantly after doping with cesium. The impact of key experimental factors on the removal of Cr(VI) ions using Cs-2@ZIF-8 was studied in a batch mode. The Cs-2@ZIF-8 MOF had an adsorption capacity of 61.05 mg g⁻¹ for Cr(VI) adsorption, and even after four cycles, it maintained its removal ability. The Cr(VI) adsorption process employing the Cs-2@ZIF-8 MOF was exothermic and spontaneous, and it was in good agreement with the Freundlich isotherm and pseudo-second-order kinetics. The high recovery rate of Cr(VI) from actual water samples highlighted the excellent efficiency of the Cs-2@ZIF-8 MOF in wastewater remediation.