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 30 mg/L of dissolved silica after 2 hours. In column experiments, more than 45% of an initial mass of 0.25 g 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.

Quantum-dots containing Fe/SBA-15 silica as “green” catalysts for the selective photocatalytic oxidation of alcohol (methanol, under visible light)

“…Fe/SBA-15 catalysts were used for selective oxidation reactions in the gas phase [6,7] as well as in the liquid phase for the transformation of phenol derivatives, such as catechol and hydroquinone [8] and also for water purification treatments (in particular by dyes decomposition [6,9,10]). To the best of our knowledge, interrogations remain about the nature of Fe-species responsible for the catalytic activity of Fe-SBA- 15 catalysts and also about their long-term stability since a silica dissolution associated with a photo-activated corrosion of Fe-species have been observed, at neutral pH and in basic aqueous solutions [11].…”

Evaluating the chemical stability of metal oxides in SO3 and applications of SiO2‐based membranes to O2/SO3 separation

“…10 However, amorphous SiO 2 membranes had network pores smaller than 0.35 nm, which made it difficult to obtain high permeance for O 2 (kinetic diameter 0.346 nm) and SO 2 (kinetic diameter 0.36 nm 11 ). In addition, the SiO 2 membrane was not suitable for the IS process because the water vapor that was produced by H 2 SO 4 decomposition damaged the network structure, 12 which resulted in a loss of gas-permeation performance. 13 Since SO 3 and SO 2 are similar in molecular size and both are strongly reactive molecules that actively participate in corrosion reactions, CMRs require a membrane with a welldefined pore size distribution for high levels of gas permeance and selectivity, as well as chemical and thermal stability under an O 2 /SO 3 atmosphere.…”

On the intracellular release mechanism of hydrophobic cargo and its relation to the biodegradation behavior of mesoporous silica nanocarriers

“…(Brinker and Scherer, 1990;Iler, 1979) Thus, a slower release in MES (pH 4.8) compared to HEPES (pH 7.2) is expectable, owing to a decreased dissolution rate of the silica matrix at lower pH. (Pham et al, 2012) The release is, however, also dependent on the solubility of the drug compounds at varying pH, which is reflected in their pK a values, and has to be taken into account. To investigate the impact of compound solubility, further investigations were performed in HEPES buffer solution containing 1 wt% Here, we note that, having previously determined that the presence of a PEI-coating can retard the release of hydrophobic drug molecules as compared to non-PEI-functionalized MSNs owing to a proposed "molecular gate" mechanism, (Niemelä et al, 2015;Rosenholm et al, 2009b) a detachment of this organic layer by hydrolytic degradation could potentially also enhance the release.…”