Dissolution of mesoporous silica supports in aqueous solutions: Implications for mesoporous silica-based water treatment processes

Abstract

Under pH 7–10 conditions, the mesoporous silica supports proposed for use in water treatment are relatively unstable. In batch experiments conducted in pH 7 solutions, the commonly used support SBA-15 dissolved quickly, releasing approximately 30mg/L of dissolved silica after 2h. In column experiments, more than 45% of an initial mass of 0.25g SBA-15 dissolved within 2 days when a pH 8.5 solution flowed through the column. In a mixed iron oxide/SBA-15 system, the dissolution of SBA-15 changed the iron oxide reactivity toward H2O2 decomposition, because dissolved silica deposited on iron oxide surface and changed its catalytic active sites. As with SBA-15, other mesoporous silica materials including HMS, MCM-41, four types of functionalized SBA-15, and two types of metal oxide-containing SBA-15 also dissolved under circumneutral pH solutions. The dissolution of mesoporous silica materials raises questions about their use under neutral and alkaline pH in aqueous solutions, because silica dissolution might compromise the behavior of the material.