A facile cooling strategy for the preparation of silica nanoparticles with rough surface utilizing a modified Stöber system

The well-known Stöber method has been widely used to synthesize dense silica particles with smooth surface, however, the preparation of silica nanoparticles with rough surface (RS-SiO₂ NPs) based on Stöber system via a facile one-pot method has not been achieved. Herein, a modified Stöber system (i.e., a specific ternary tetraethyloxysilane (TEOS)/ethanol (EtOH)-water (H₂O) with a precise molar ratio of 1: 45.8: 124) is used to prepare the primary SiO₂ NPs with low-condensed silica shell (LCSS) and unreacted TEOS. Subsequently, via a simple one-step cooling treatment, the RS-SiO₂ NPs with spherical morphology (177 nm), large specific surface area (85 m² g⁻¹) and controllable density were successfully prepared. Various experimental conditions, such as pre-reaction time (reaction time of primary SiO₂ NPs at room temperature before cooling treatment), cooling temperature (cooling treatment temperature) and ammonia solution concentration were studied. The results show that the migration rate of the unreacted TEOS in the primary SiO₂ NPs plays an important role in the formation of RS-SiO₂ NPs. This paper also provides us with a new idea to further understand the formation mechanism of SiO₂ particles by the Stöber method. The RS-SiO₂ NPs loaded with gold nanoparticles can effectively reduce 4-nitrophenol to 4-aminophenol.