Evaluation of different bridged organosilicas as efficient adsorbents for the herbicide S-metolachlor†
Abstract
Three groups of porous non-ordered bridged organosilicas and silicas have been synthesized using three different surfactants of the Tween family as porogens. One group consisted of silica materials while the other two were organosilicas, i.e., ethanesilicas and benzenesilicas, but differing within each group in their textural properties. The adsorption of the herbicide S-metolachlor from an aqueous solution was then compared on all solids. The composition of the walls, i.e., the bridging group, was the main factor governing the adsorption capacity. Broadly, the uptake of the herbicide follows the sequence: benzenesilica > ethanesilica > silica. However, pore volume also has a significant influence on adsorption. Thus, higher capacities result from materials with larger pore volumes and with a larger size of the mesopores. Moreover, surface area and pore size distributions also affect the adsorption behavior, even though their influence seems to be less pronounced. Finally, a comparison between the porous non-ordered (organo)silicas and the corresponding periodic mesoporous (organo)silicas has revealed some interesting features for the use of these materials as adsorbents. Benzenesilicas with a large pore volume and pores in the micropore and/or large mesopore regions seemed to be the best adsorbents for adsorption in a single step whereas periodic mesoporous benzenesilicas were more appropriate for repetitive adsorptions.
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