Novel hierarchically dispersed mesoporous silica spheres: effective adsorbents for mercury from wastewater and a thermodynamic study

Abstract

Novel hierarchically dispersed spherical mesoporous silica (HSMS) was synthesized using a surfactant mixture of fluorocarbon (FC-4), cetyl-trimethyl ammonium bromide (CTAB), and block copolymer Pluronic F127 (PF127). To prepare the thiol-functionalized HSMS (T-HSMS), the synthesized HSMS was functionalized by a co-condensation method using 3-mercaptotrimethoxysilane (3-MPS) as a thiol reagent. The obtained HSMS and T-HSMS possess a cubic morphology with a lmm space group and a particle diameter of 75–200 nm. The HSMS and T-HSMS materials exhibit large free surface areas exceeding 844 and 663 m² g⁻¹ and pore radii of approximately 3.2 and 3.1 nm, respectively. The synthesized materials were characterized using small angle X-ray scattering, N₂-physisorption studies, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy studies. The efficacy of mercury adsorption by T-HSMS was studied at different temperatures, 283, 298, and 313 K. The obtained results were fitted with a Langmuir adsorption isothermal plot. The changes in the negative Gibbs free energy values for the spontaneity of the process were calculated. Mercury could be successfully desorbed using thiourea in a 2 M HCl solution, and the adsorbents could be subsequently reused without severe loss of their activity after repeated adsorption tests.