Facile one-pot synthesis of thiol-functionalized mesoporous silica submicrospheres for Tl(I) adsorption: Isotherm, kinetic and thermodynamic studies

For the first time, thiol-modified mesoporous silica submicrospheres (TMS-SMSs) have been applied to remove extremely high toxic Tl(I) ions from aqueous solution by an adsorption approach. TMS-SMSs as a silica-based material is basically environmentally benign, with combined advantages of porosity and functionality. XRD measurement and TEM images clearly exhibited a parallel arrangement of mesopores in TMS-SMSs with a combination of both semi-long-range ordering and wormhole-like motif structures. The batch adsorption of Tl(I) onto TMS-SMSs showed a typical Langmuir adsorption isotherm (among various non-linear isotherm models) with the maximum adsorption capacity of 452.8 mgg^-1. TMS-SMSs show a fast adsorption rate, and pseudo-second-order kinetic model provides the best correlation between experimental data. The thermodynamic constants indicated that the adsorption of Tl(I) ions was an endothermic (ΔH° = 24.80 kJ mol^-1), entropy driven (ΔS° = 0.161 kJ mol^-1K^-1), and spontaneous process (ΔG° = 23.15-27.95 kJ mol^-1). This study provides an exciting opportunity to advance our knowledge of functionalized-mesoporous silica submicrospheres as a promising adsorbent for the removal of toxic Tl(I) ions from aqueous solution using adsorption approach.