Mono- and quaternary-ammonium functionalized mesoporous silica materials for nitrate adsorptive removal from water and wastewaters

Mesostructured porous silica SBA-15 materials functionalized with either primary or quaternary ammonium groups have been prepared by co-condensation and post-synthesis grafting using either aminopropyltriethoxysilane or N-((trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride as functional groups precursors. The materials functionalized with aminopropyl groups were further treated in acid solutions to convert the amine groups into charged propyl-ammonium groups. The physicochemical characteristics of the resulting adsorbent materials have been investigated using various techniques and discussed with respect to the nature of organo-functional groups in the materials. The adsorption performances were evaluated from batch experiments for the removal of nitrate anions from aqueous solutions. Results showed that adsorption capacity was influenced by the organic functional group nature and the functionalization strategy. In the case of propyl-ammonium functional groups, the adsorption capacity reached 46 and 55 mg NO3−/g for the materials synthesized via co-condensation and grafting, respectively. Similar tendency was observed in the case of propyl-trimethyl-ammonium organic functional groups where the grafted material registered a remarkably high capacity of 63 mg NO3−/g under the experimental conditions investigated.