Facile and controllable preparation of mesoporous silica nanoparticles with ultra-large mesopores enabled by an ammonium chloride–assisted hydrothermal process

This work reports the facile preparation of monodispersed ultra-large mesopore mesoporous silica nanoparticles (ULP-MSNs) with controllable mesopore sizes and particle sizes. The key design to such preparation lies in the application of ammonium chloride (NH4Cl) assisted-hydrothermal (AAH) process to as-prepared conventional MSNs, whose small mesopore sizes of about 2 nm can be effectively enlarged to over 16 nm. Based on the systematic study of the synthetic parameters, it was recognized that the initial ethanol added in the synthesis mixture (1st ethanol), NH4Cl, and the ethanol added in the mixture (2nd ethanol) during the hydrothermal (HT) process and HT conditions play synergistic roles in enlarging mesopores by AAH process. The mechanism of mesopore enlargement was also studied. By this method, ULP-MSNs with variable mesopore sizes in a range of 14 nm–26 nm, large synthesis domain, and controllable particle sizes ranging from 106 nm to 267 nm can be produced in a facile manner. This work, we believe, represents a new strategy for the preparation of ULP-MSNs and will promote their various applications.