Effects of operating parameters on cadmium removal for wastewater treatment using zeolitic imidazolate framework-L/graphene oxide composite

Abstract

Water pollution due to heavy metal contamination has become a critical environmental issue. Thus, effective treatment for polluted water, such as simple adsorption to remove heavy metals, is gaining importance. Towards this end, zeolitic imidazolate framework-L (ZIF-L) with graphene oxide (GO) was successfully incorporated in the synthesis of novel ZIF-L/GO 20 and ZIF-L/GO 50 adsorbents using 20% and 50% loading percentages of GO, respectively, with ultrapure water as the solvent. The morphologies of ZIF-L changed to a flower-like structure with the introduction of 20% GO and turned into smaller irregular shapes when 50% GO was added. These novel adsorbents have demonstrated high adsorption capacities for Cd(II) adsorption at 172.42 mg/g (ZIF-L/GO 20) and 188.68 mg/g (ZIF-L/GO 50), with the optimum dosage of 0.2 g/L of adsorbents. The adsorption isotherms fit Langmuir isotherm, which suggested that adsorption occurred through uniform and monolayer sorption on the surface sites. The electrostatic attraction between the cationic Cd(II) and negatively charged surface played a crucial role as the main pathway in Cd(II) adsorption. Based on the investigated kinetic models, Cd(II) adsorption had a better correlation with the pseudo-second-order kinetic model, which showed that chemisorption occurred during the Cd(II) removal process. The findings of this study revealed that ZIF-L/GO has the potential of becoming the perfect adsorbent for cadmium removal from aqueous solutions.