Aminofunctionalized silica monolith for Pb2+ removal: synthesis and adsorption experiments

Lead(II) removal from aqueous solutions by adsorption on APTMS-functionalized silica monolith (APTMS-Monosil) was investigated. Functionalized silica monolith was selected as adsorbent due to its ease of synthesis and versatility. Adsorption experiments were performed in a batch system, and the effects of various operating parameters, such as solution pH, initial concentration and solid to liquid ratio were evaluated. According to the Response Surface Methodology results, the optimum operating conditions for Pb2+ removal by APTMS-Monosil were pH = 6.24, initial Pb2+ concentration of 89.5 mg L–1 and solid to liquid ratio of 1.84 g·L–1. The kinetic data suggested that chemical adsorption, rather than mass transfer, was the controlling step for lead capture. Equilibrium isotherms were analyzed using different models, and data were well fitted to the Langmuir isotherm. The thermodynamic parameters of the adsorption process (ΔH° = 30.9 kJ·mol–1, DS° = 0.187 kJ·mol–1 K–1, and ΔG° = –24.826 kJ·mol–1 at T = 298 K), calculated from three isotherms at T = 30– 60°C, revealed a spontaneous, endothermic process, with a strong chemical nature. The maximum adsorption capacity of APTMS-Monosil for lead was 450 mg·g–1, which is a high value if compared with other materials presented in the literature.