Enhanced and selective adsorption of urea and creatinine on amine-functionalized mesoporous silica SBA-15 via hydrogen bonding

In this study, mesoporous silica SBA-15 particles were synthesized using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and tetraethoxysilane as the precursors and were subsequently modified with 3-aminopropyl triethoxysilane (APTES). The amine-functionalized particles were characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, N2 sorptiometry, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy, and thermogravimetric analysis. The prepared materials were subsequently used for the adsorption removal of small uremic toxins, namely urea, creatinine, and hippuric acid. The adsorption of these single toxins from synthetic serum samples on SBA-15–based adsorbents followed a pseudo-second-order kinetic model, and the adsorption was well described by the Langmuir isotherm. It was determined that the adsorption capacity of SBA-15 for urea and creatinine was increased after APTES functionalization. The highest adsorption capacities of SBA-15 modified with 0.2 mol/L APTES in toluene for urea and creatinine were 1644.7 and 181.7 mg/g, respectively, at 37 °C, whereas the highest adsorption capacity of pristine SBA-15 for hippuric acid was 111.7 mg/g. Preferential and competitive hydrogen bonding-promoted adsorption of urea over hippuric acid in binary mixtures occurred for the APTES-modified SBA-15 adsorbents, as demonstrated using the FTIR spectra of the adsorbents before and after adsorption. Mesoporous silica SBA-15 particles were synthesized using poly(ethylene glycol)-block-poly(propylene glycol)- block-poly(ethylene glycol) and tetraethoxysilane as the precursors. They were then modified by 3-aminepropyl triethoxysilane (APTES) to form SBA-15-APTES particles. The adsorption of urea and creatinine was enhanced on SBA-15-PES, compared to SAB-15. The formation of hydrogen bonds between N molecules contained in the amine groups on the modified SBA-15 surface and the H atoms in urea and creatinine molecules will be the dominant adsorption mechanism, which was supported by the FTIR spectra of SBA-15-APTES before and after urea adsorption. For hippuric acid, the adsorption decreased when SAB-15 was modified. Hippuic acid might have no affinity to the amine group, while it had a good affinity to the hydroxyl group on SBA-15. Therefore, such a decrease in adsorption ability could be attributed to the reduction of the affinity with silanols in mod