Engineered SBA-15 with amino and thiol groups: A powerful platform for Cr(VI) to Cr(III) reduction in water

Abstract

A mesoporous SBA-15 system was synthesized via the sol-gel process, followed by removal of the template through calcination. Using N- or S-based silanes as post-grafting agents, functional groups were sequentially grafted to obtain two distinct ordered mesoporous platforms: one amino-functionalized and the other featuring amino and thiol surface groups. The resulting materials were characterized and evaluated to determine their ability to adsorb hexavalent chromium (Cr(VI)) from aqueous solution and reduce it to its trivalent form (Cr(III)). Xray diffraction patterns and nitrogen adsorption–desorption isotherms confirmed the formation of well-ordered mesoporous structures with long-range pore arrangements with pore diameters in the range of 4.9–5.4 nm. According to the Langmuir isotherm model, the amino-thiol functionalized SBA-15 exhibited a higher Cr(VI) adsorption capacity than the amino-functionalized counterpart, with maximum adsorption capacities of 180.9 mg/g and 150.1 mg/g, respectively. Chromium speciation analysis after 24 h of contact revealed Cr(III)/Cr(VI) ratiosof 1.2 and 0.7 for the amino-thiol/SBA-15 and amino/SBA-15 systems, indicating Cr(VI) reduction efficiencies of54 % and 40 %. The enhanced performance of the bifunctionalized mesoporous platform is attributed to the presenceof sulfur-containing groups jointly with amino, which not only facilitate Cr(VI) adsorption but also promoteits reduction. Notably, this improvement is maintained in the presence of Zn(II) ions, which, in contrast, suppressthe reductive capability of the amino-functionalized system. These findings highlight the amino and thiol-basedsystem as a promising candidate for the treatment of Cr(VI)-contaminated water effluents, given that trivalentchromium is significantly less toxic than the hexavalent form to living organisms.