Facile synthesis of thiosalicylic acid functionalized silica gel for effective removal of Cr(III): Equilibrium modeling, kinetic and thermodynamic studies

Abstract

Thiosalicylic acid functionalized silica gel (SiO2-APS-TSA) was prepared after modification of silica with 3-aminopropyltrimethoxysilane. The adsorption of Cr (III) onto SiO2-APS-TSA was carried out in batch experiments and result shows high removal efficiency (99.90 %) of Cr (III). The characterization of SiO2-APS-TSA was done using FTIR, TGA, DTA, and SEM with EDX. The adsorption of Cr (III) onto SiO2-APS-TSA was optimized by response surface methodology. Central composite design of three factors was undertaken to examine the process parameters, namely pH (0.64–7.36), adsorbent dose (15.0–385.0 mg) and contact time (9.55–110.45 min). The goodness of fit of the experimental data to the second-order polynomial model was revealed with R2 of 0.9999. The results showed that 0.2 g of SiO2-APS-TSA was sufficient to remove 99.90 % Cr (III) from aqueous solution (20 mL; 20 mg L−1) at pH 4.0 in 60 min. Linear and nonlinear fitting of Freundlich isotherm model to adsorption data revealed the multilayer coverage of Cr (III) onto SiO2-APS-TSA. Pseudo second order kinetic model fitted well to the kinetic data. Negative values of ΔG° suggested the spontaneity of the adsorption of Cr (III). The sorption/desorption study demonstrated the potential of SiO2-APS-TSA as an adsorbent to remove Cr (III) from wastewater.