A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylarnine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the inorganic surface. The modified material contained 1.13 +/- 0.06 mmol of amine per gram of silica, exhibited a surface area of 831 +/- 29 m(2) g(-1) and a porous diameter of 1.95 nm. Infrared, Si-29 and C-13 NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. This ordered organic-inorganic hybrid presented a high capacity for the removal of the agrochemical 2,4-dichlorophenoxyacetic acid from water: the Delta and Delta G values for the interaction were determined to be - 110.61 and -9.37 kJ mol(-1),respectively. (c) 2005 Elsevier Inc. All rights reserved.