Systematic study of the implications of calcination and solvent extraction of the surfactant in MCM-41-type mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSN) have been growing in recent years in a broad range of applications, such as nanomedicine, catalysis, and gas storage. For the preparation of MSN, especially in nanomedicine applications, the extraction of the surfactant template, generally 1-hexadecyltrimethylammonium bromide (CTAB), is required. Several methods to remove the surfactant from MNS have been reported in the literature, such as calcination, solvent extraction, and dialysis. Depending on the method employed, the materials obtained have different properties; however, a systematic study that compares the use of different surfactant extraction methods and their implications in the final characteristics of the MSN has not been reported. Hence, the aim of this work is to study the effect of surfactant removal on MSN by calcination at different temperatures (400 °C, 450 °C, 500 °C and 550 °C) or by extraction with HCl/ethanol or NH4NO3/ethanol. The final materials are fully characterised by different techniques. The study performed shows the removal efficiency when the different methods are used, and their effect on silica condensation degree, mesoporosity, cytotoxicity, and degradation rate. The results allow for obtaining a deeper knowledge of the surfactant removal processes.