Amino functionalized zirconia as novel adsorbent for removal of Cr(VI) from aqueous solutions: kinetics, equilibrium, and thermodynamics studies

Abstract

An effective hybrid adsorbent based on zirconia (ZrO2) and 3-aminopropyltriethoxysilane (APTES) was prepared for the removal of Cr(VI) from aqueous solutions. Co-precipitation method was used to prepare nano-crystalline zirconia (ZrO2) while its functionalization with 3-aminopropyltriehoxysilane (APTES) was carried out by grafting method. The characterization of ZrO2 and functionalized zirconia (NH2–ZrO2) was performed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis, scanning electron microscopy (SEM), and thermogravimetric analysis. The presence of carbon (10.73%), nitrogen (2.07%), silicon (0.15%), and a rise in the percentage of oxygen (from 26.79% to 28.23%) in the energy dispersive X-ray spectra of NH2–ZrO2 supported by FTIR analysis, showed that ZrO2 has been successfully functionalized with APTES. The adsorption characteristics of NH2–ZrO2 for the removal of Cr(VI) were examined by the batch method. Adsorption was found to be highly dependent on solution pH, contact time, Cr(VI) initial concentration, and adsorbent dosage. Kinetic data was explained well by pseudo-second-order kinetic model, while the equilibrium data were best fitted the Langmuir model with a maximum adsorption capacity of 17.89 mg/g at 298 K. The thermodynamic parameters, that is, negative values of ∆H° and ∆G° confirmed the exothermic and spontaneous nature of adsorption process.