Use of hollow mesoporous silica spheres as vehicles for delivery of nanoscale zerovalent iron in porous media

The rapid aggregation and subsequent deposition of nanoscale zero-valent iron (nZVI) cause extremely low mobility in porous media. This study fabricated novel hollow mesoporous silica (HMS) supported nZVIs (HMS-nZVIs) by decorating spherical nZVI on HMS surfaces in a monolayer and examined the stability and transport of the HMS-nZVIs in porous media. Results show that the stability of the HMS-nZVIs was similar to that of HMSs, which was much greater than that of nZVIs due to increased electrostatic repulsion. The HMS-nZVIs showed greater mobility in porous media even than HMSs. This is because while decorating of nZVIs on the HMS surfaces reduced repulsive energy barrier, the nZVIs reduced the primary minimum depth and accordingly the adhesive force, causing less deposition of the HMS-nZVIs on the collector surfaces compared to HMSs. Increasing the loading concentration of nZVIs led to the aggregation of nZVIs on HMS surfaces, which increased the sizes of HMS-nZVIs and the retention of HMS-nZVIs in porous media through straining. The great mobility of the HMS-nZVIs revealed by this study shows the potential of using hollow particles as vehicles for delivery of nZVIs for in situ soil and groundwater remediation.