Adsorption characteristics of phenolic and amino organic compounds on nano-structured silicas functionalized with phenyl groups

Phenyl-functionalized mesoporous silicas (Ph-MSs) were synthesized as adsorbents of bisphenol A (BPA) from aqueous solutions via co-condensation method. Ph-MSs with different compositions, which were prepared using 10%, 15%, 20%, and 30% of phenyltriethoxysilane (PhTES) in silica precursors, were used in the adsorption of BPA in order to investigate the effect of surface hydrophobicities on the uptake of hydrophobic organic compounds. Material characterizations were carried out including X-ray diffraction, N₂ adsorption/desorption measurement, elemental analysis, Fourier transform infrared spectroscopy, and measurement of point of zero charge. The higher composition of PhTES offered higher hydrophobicity to the prepared Ph-MSs, whereas decreasing their structural order and surface area. Adsorption capacity of Ph-MSs for BPA depended on the surface area rather than the surface hydrophobicity. However, the adsorption data at low concentrations showed that the adsorption affinities for BPA were in the order of Ph-MS30 > Ph-MS20 > Ph-MS15 > Ph-MS10, which were fully consistent with the order of their surface hydrophobicities. Among the prepared materials, Ph-MS20 was selected as a representative adsorbent, and used to investigate further adsorption characteristics. Several aromatic compounds including p-t-butylaniline, p-t-butylphenol, aniline, and phenol, which had the similar molecular structures with BPA, were also adopted as adsorbates for the adsorption onto Ph-MS20. The selective adsorption behavior of Ph-MS was discussed using the equilibrium isotherms of the adsorbates on Ph-MS20.