Heavy Metal Remediation Using Functionalized Mesoporous Silicas with Controlled Macrostructure

Abstract

A synthesis procedure is described for making functionalized mesoporous silica macrostructures that can serve as self-supporting adsorbents for environmental remediation and other separations applications. The material, whose mesopores were functionalized with 3-mercaptopropyltrimethoxysilane ligands, can be made into spheres, irregular particles, and truncated cones having diameters from 1 to 15 mm through a one-step emulsion synthesis procedure. Other shapes such as pellets can be formed by molding the precursor gel. The macro- and mesomorphology of the materials were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and 29Si MAS NMR. Physisorption properties were investigated using nitrogen adsorption measurements. The surface area of these materials determined via the BET method ranged from 864 to 1184 m2 g-1. The materials are extremely effective in the removal of mercury and silver ions from aqueous solutions. The amount of mercury adsorbed ranged from 0.24 to 1.26 mmol g-1, depending on the degree of functionalization. Silver is less strongly adsorbed than mercury, with a maximum loading of 0.89 mmol g-1. In binary adsorption of mercury and silver ion mixtures, the selectivity for mercury ranged from 1.39 to 2.24. The adsorption capacity of the functionalized materials for nitrogen is comparable to that of unfunctionalized materials.