Adsorptive removal of dihydrogenphosphate ion from aqueous solutions using mono, di- and tri-ammonium-functionalized SBA-15

Adsorption of monovalent phosphate anions from aqueous solutions on mono, di- and tri-ammonium-functionalized mesoporous SBA-15 silica was investigated. The adsorbent was prepared via a post-synthesis grafting method, using 3-aminopropyltrimethoxysilane (N-silane), [1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (NN-silane) and 1-[3-(trimethoxysilyl)-propyl]-diethylenetriamine (NNN-silane), followed by acidification in HCl solution to convert the attached surface amino groups to positively charged ammonium moieties. The loading of amino moieties on the SBA-15 surface was varied from 5% to 40% as organoalkoxysilane/silica molar ratio. The adsorption experiments were conducted batch-wise at room temperature. Results showed that adsorption capacity increased with increasing the concentration of functional groups on the SBA-15 adsorbent whatever the nature of the functional group. In the case of monoammonium functional groups, the adsorption capacity increased from 0.64 to 1.07 mmol H2PO4-/g when the molar ratio organoalkoxysilane/silica was varied from 5% to 40%, respectively. Similar tendency was observed in the case of diammonium and triammonium organic functional groups. Also, for the same organoalkoxysilane/silica molar ratio, the adsorption capacity increased markedly with the increase of the number of protonated amines in the functional groups. Therefore, maximum adsorption capacities of 1.07, 1.70 and 2.46 mmol H2PO4-/g adsorbent were obtained using mono-, di- and tri-ammonium-functionalized SBA-15, respectively. (C) 2009 Elsevier Inc. All rights reserved.