Comparative study on PVA/silica membrane functionalized with mercapto and amine groups for adsorption of Cu(II) from aqueous solutions

Poly(vinyl alcohol)/silica (PVA/silica) membranes functionalized with 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltriethoxysilane (APTES) were prepared by solution-casting and their applications for adsorption of Cu(II) from aqueous solutions were investigated. The membranes were characterized by FTIR, BET, SEM and EDAX analyses. The adsorption capacities of the mercapto-functionalized PVA/silica membranes were greater than the amino-functionalized PVA/silica membranes in the whole range of MPTMS and APTES weight percent studied (5–20%). Experimental parameters affecting Cu(II) sorption onto the PVA/silica/MPTMS15% such as pH, contact time, initial concentration and temperature were studied. The kinetic data were analyzed by the pseudo-first-order, pseudo-second-order and intra-particle-diffusion kinetic models and consequently, the pseudo-second-order model best described the adsorption of Cu(II) ions. The equilibrium data were fitted to the three isotherm models: Freundlich, Langmuir and Dubinin–Radushkevich (D-R), and as a result the Freundlich model gave the best fit for the experimental data. Also, the calculation of adsorption free energy from the D-R model showed that the mechanism of Cu(II) adsorption onto the membrane was chemisorption. Thermodynamic parameters showed that the adsorption of Cu(II) onto the membrane was endothermic and spontaneous. The reusability of the membrane was also evaluated after five adsorption–desorption cycles.