Adsorption of aqueous Cr (VI) onto UiO66NH2 MOF: Isotherm, thermodynamics and mechanism studies

Abstract

As a member of the UiO-66 family, UiO66NH2 MOF (UNH) possessed enhanced stability, high surface area, increased pore size, and pore volume. Additionally, its amino groups offer spectacular affinity to capture Cr (VI). With these propitious features, UNH was fabricated by a facile solvothermal route in this study. It was then characterized by XRD and FTIR to confirm its successful formation. Its affinity towards efficacious capture of aqueous Cr (VI) was explored with the help of isotherm models and thermodynamic parameters. The Langmuir isotherm model fits best the experimental data, demonstrating monolayer Cr (VI) sorption on a homogenous UNH surface. The maximum adsorption capacity was determined as 51 mg/g. Negative ΔG° values suggested that the Cr (VI) uptake process is spontaneous and favorable, while the endothermic nature of the sorption was evident from positive values ΔH°. Thermodynamic parameters such as standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard Gibbs free energy change (ΔG°) were determined as 6.651 kJ mol−1, –3.216 kJ mol−1, and 33.76 KJ K−1.mol−1 respectively. FTIR and pH studies evidenced that the sequestration of Cr (VI) onto UNH proceeds through the electrostatic attraction mechanism, supported by the fitted isotherm model and thermodynamic parameters’ results.