Efficient removal of Pb(II) from water using silica gel functionalized with thiosalicylic acid: Response surface methodology for optimization

Abstract

The adsorption of Pb(II) onto silica gel functionalized with thiosalicylic acid (TSA@)amine modified SiO2) was studied at 300, 305, 310 and 315 K. The effects of independent variables (pH, adsorbent dose and initial concentration of Pb(II)) on the removal of Pb(II) from water were evaluated and response surface methodology was applied to optimize them. Under the optimized conditions (pH: 6; adsorbent dose, 0.20 g/20 mL and initial concentration: 50 mg/L), removal efficiency of Pb(II) was 98.78%. The adsorption equilibrium data obtained from batch experiments were examined by various isotherm models. Freundlich isotherm model fitted well to the experimental data and indicating the multilayer coverage of Pb(II) on the heterogeneous surface of TSA@)amine modified SiO2. Adsorption kinetic data were investigated by surface and diffusion based kinetic models. Kinetic data fitted well to pseudo-second order model with R2 > 0.999. Elovich model with R2 > 0.999 revealed the occurrence of chemical reaction between Pb(II) and active sites of TSA@)amine modified SiO2. Thermodynamic parameters suggested the spontaneous and endothermic nature of Pb(II) adsorption onto TSA@)amine modified SiO2.