Benzoylthiourea-modified mesoporous silica for mercury(II) removal

Abstract

An incorporation of 1-benzoyl-3-propylthiourea groups into siliceous mesopores of MCM-41 afforded an ordered material with open porosity. This material was prepared via a two-step modification by attachment of an aminopropyl functionality and its subsequent conversion into a thiourea ligand. About 1.5 mmol/g of 1-benzoyl-3-propylthiourea groups was attached to the silica surface, which resulted in ca. 70% conversion of amino groups. Such material has a large surface area of 380 m(2)/g and accessible mesopores of 3.0 nm in diameter. The presence of several functional groups in the thiourea structure, able to coordinate metal ions, causes a significant enhancement of the maximum capacity of this material toward mercury ions. The maximum loading of mercury ions from aqueous solution for this material was ca. 1.0 g Hg2+/g or 5.0 mmol Hg2+/g, exceeding the capacity of the previously known samples by about twice. The fit of the mercury adsorption isotherm by a two-term Langmuir-Freundlich equation suggests a two-step adsorption process characterized by different adsorption constants. A relatively weak mercury interaction with 1-benzoyl-3-propylthiourea ligands made the adsorbent's regeneration possible under mild conditions via washing the mercury-loaded samples with slightly acidified aqueous thiourea solution. The regenerated material retained over 70% of the initial adsorption capacity.