Room temperature synthesis of Ce based UiO-66 and UiO-66-NH2 metal organic frameworks for arsenic adsorption from aqueous solution

The exploration of a suitable adsorbent for removal of toxic elements is a challenging task and in this context we have employed UiO-66 (Ce) based Metal Organic Frameworks (MOFs) synthesized by a room temperature method for the remediation of arsenic from aqueous solutions. The synthesized UiO-66 (Ce) and UiO-66 (Ce)-NH₂ MOFs were well characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Thermogravimetry (TG), Brunauer–Emmett–Teller (B.E.T.), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Octahedral morphology was observed for UiO-66 (Ce) whereas the morphology of UiO-66 (Ce)-NH₂ synthesized by this method was non-uniform. Bare MOF exhibited higher surface area and higher thermal stability in contrast to the amine functionalized MOF. We have studied the arsenic adsorption on both these MOFs in varying pH conditions. The adsorption isotherm studies revealed that bare MOF is much superior for adsorption of arsenic with adsorption capacity of ∼308 mg/g whereas the adsorption capacity of amine functionalized MOF was mere 70 mg/g. Adsorption kinetic studies demonstrated that MOFs follow Pseudo Second Order (PSO) model and elucidated that the adsorption process is predominantly chemisorption in nature. UiO-66 (Ce) could be successively used multiple times without much penalty in the adsorption capacity and the thermodynamics of adsorption suggested it to be spontaneous and favorable. Finally, an overview of the probable mechanism of adsorption is discussed by employing different experimental techniques like XRD, FT-IR and XPS.