Understanding porous structure of SBA-15 upon pseudomorphic transformation into MCM-41: Non-direct investigation by carbon replication

Abstract A series of mesoporous silicas with bimodal porosity combining the features of broad-mesoporous SBA-15 and narrow-mesoporous MCM-41 was synthesized by the pseudomorphic transformation of SBA-15. The pore size of the MCM-41-like fraction was adjusted using different quaternary ammonium salts, while the degree of pseudomorphic transformation was tuned by the alkalinity of the mother-silica dissolving agent. The produced silicas were applied as hard templates for the synthesis of carbon replicas by nanocasting. The mechanism of pseudomorphic transformation of mesoporous silica was for the first time investigated non-directly, employing the strategy of inverse carbon nanoreplication followed by comprehensive study of the textural and structural parameters of replicas with regard to silica matrices. It was found that the conversion of SBA-15 into MCM-41 occurs simultaneously throughout the entire particle’s body according to the mechanism of homogeneous pseudomorphic transformation. It was evidenced that the strategy of inverse carbon replication could be successfully employed as an ingenious tool for non-direct investigation of suchlike silica transformations towards hierarchical porous systems. Furthermore, the unique bimodal mesoporosity of the carbons obtained from SBA-15 partially transformed into MCM-41 opens a possibility for their application in a variety of purposes, mainly in catalysis and adsorption.