Removal of uranium (VI) from aqueous solutions by adsorption using a novel electrospun PVA/TEOS/APTES hybrid nanofiber membrane: comparison with casting PVA/TEOS/APTES hybrid membrane

Abstract

Polyvinyl alcohol/tetraethyl orthosilicate/aminopropyltriethoxysilane (PVA/TEOS/APTES) nanofiber membrane was prepared by the sol–gel/electrospinning method and its application for adsorption of uranium from aqueous solutions was compared with PVA/TEOS/APTES membrane prepared by sol–gel/casting method. The prepared membranes were characterized by Fourier transform infrared, scanning electron microscope and Brunauer–Emmert–Teller analysis. The surface area of electrospun and casting hybrid membranes obtained were 153 and 282 m2 g−1, respectively. Experiments were carried out to investigate the influence of different sorption parameters, such as pH, contact time, initial concentration and temperature in a batch system. Results indicated that the pH of 4.5 and high temperature (45 °C at studied condition) proceeded earlier than the adsorption of uranium ions onto the both of prepared membranes. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to describe the equilibrium data of uranium to the prepared membranes at different temperatures (25–45 °C) and the kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The maximum adsorption capacity of uranium ions onto the PVA/TEOS/APTES hybrid nanofiber membrane was found to be 168.1 mg g−1 with the optimum pH of 4.5 and at the optimum temperature of 45 °C which is more than five-fold greater to that of uranium sorption onto the PVA/TEOS/APTES hybrid membrane (33.61 mg g−1 with pH of 4.5 and at a temperature of 45 °C). Thermodynamic parameters were evaluated to understand the nature of adsorption process for uranium ions. The negative values of Gibbs free energy change (∆G°) and positive value of enthalpy change (∆H°) showed that the adsorption of uranium onto both of the electrospun and casting hybrid membranes was feasible, spontaneous and endothermic in studied conditions. The reusability of hybrid membranes was determined after five sorption–desorption cycles and the results showed that these membranes can be utilized extensively in industrial activities.