Influence of water on amine loading for ordered mesoporous silica

SBA-15, a mesoporous silica, was employed to systematically study the influence of water concentration during amine grafting and also on amine loading. It was found that water as opposed to alcohol was a more effective agent for influencing amine loading. The addition of alcohol did not result in higher amine loadings; however, the addition of water leads to higher amine loading. Under the reported synthesis conditions, further increase in water concentration resulted in further increase in amine loading without plateauing. Additionally, increasing the aminosilane content beyond 2 mL/g (SiO₂) during amine grafting did not yield higher amine loading. Moreover, the mere presence of water during grafting affects the grafting rate of the aminosilanes, resulting in complete grafting of amines to supports in 30 min. The stability of wet grafted materials and the universality of the studied effects for other aminosilanes and mesoporous silica supports (KIT-6 and MCM-48) were also demonstrated.