2.2.2. Propyl sulfonic acid functionalized SBA-15
For surface functionalization of SBA-15 with sulfonic groups, of SBA-15 was firstly dispersed in toluene, and of 3-mercaptopropyl- trimethoxysilane was added portion wise to the suspension (Wang, 2018). The suspension was then stirred at for 8 h in nitrogen atmosphere. Then, the mixture was filtered off and the surface modified SBA-15 with thiol (-SH) groups was washed three times with ethanol to remove the residual solvent and unreacted reagent. The obtained white solid was dried at under vacuum for 12 h and denoted as SBA-15-TH. The anchored thiol groups (SBA-15-TH) were oxidized with dilute H2O2 in methanol under argon atmosphere for 4h (Karimi, 2012). Then, the solution was filtered off and washed with ethanol/water solution. The wet material was suspended in 1M H2SO4 for 2h. Finally, the functionalized silica was washed several times with ethanol/water solution and dried at 60oC under vacuum overnight,Scheme 1.