Stability and fate of hollow mesoporous silica nanoparticles in aqueous environment: Effects of pH and electrolyte

Hollow mesoporous silica nanoparticles (HMSNs) and their carboxyl-functionalized counterparts (C-HMSNs) are promising materials for environmental applications, but their stability in aquatic environments remains poorly understood. This study investigated the aggregation behavior of HMSNs and C-HMSNs under varying pH and electrolyte conditions. Experimental results showed that HMSNs had critical aggragation concentrations (CCC) of 35 mM in NaCl and 2 mM in CaCl 2 , while C-HMSNs exhibited higher CCCs of 52 mM and 3 mM, respectively, indicating greater stability. High concentrations of NaCl and CaCl 2 promoted rapid aggregation of HMSNs and C-HMSNs, with CaCl 2 being more efficient in promoting aggregation. Both HMSNs and C-HMSNs aggregated extensively in acidic environments, while remaining stable in neutral and alkaline environments. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and molecular dynamics (MD) simulations revealed weakened electrostatic repulsion and reduced total system energy in high ionic strength solutions supporting irreversible aggregation. Simulated environmental conditions showed that HMSNs and C-HMSNs remained stable in rivers, aggregated slightly in groundwater, and aggregated extensively in seawater. These findings provide critical insights into the environmental fate and potential ecological risks of silica nanoparticles, informing future studies on their transport and bioavailability in natural waters.