Silica xerogels modified with amine groups: Influence of synthesis parameters on porous structure and sorption properties

Porous polysiloxane xerogels functionalized with amine groups were synthesized by a single-step sol-gel method. The influence of a range of synthesis conditions (including inter alia a type of amine co-monomer, its concentration and time of ageing) on the final porous structure was investigated. It was found that all of them affect the formation of porous structure of the silica network leading to highly porous materials in some cases, in others - to nonporous ones. Apart from nitrogen sorption measurements, the physicochemical properties of the obtained xerogels were investigated by SEM, TEM, FTIR, NMR and elemental analyses to get a detailed insight into their structure and surface chemistry. To reveal their potential application the selected xerogels were tested as sorbents of model drug, diclofenac, which is considered as a priority hazardous pharmaceutical. High uptakes of diclofenac reaching 457 mg g(-1) proved that some of the obtained xerogels are potential candidates for removal of drugs from waters and wastewaters, particularly when high concentrations of pharmaceutical have to be eliminated. Protonation of amine groups significantly increases the sorption capacity (up to a few times) due to the enhancement of electrostatic interactions with diclofenac anions, which was also shown by theoretical DFT studies. Protonation and sorption mechanisms were also proposed based on the calculations. The porous structure seems to have minor effect on the sorption capacity when compared with surface chemistry determined by the number of amine functional groups.