Abstract
In this work we report to use a gas-phase approach to synthesize SiO2-Ag hybrid nanoparticles (NPs) with controlled properties in size, composition, and morphology. TEOS and colloidal silica were used as precursors for fabricating SiO2 core template, and AgNO3 was employed for the precursor of Ag deposits to the SiO2 template. Differential mobility analysis (DMA) was used to in-situ characterize particle size distributions and number concentrations of aerosolized NPs directly in gas phase. Transmission electron microscopy (TEM) with elemental-mapping energy dispersive spectroscopy was employed orthogonally to provide visual information and the elemental composition of these functional hybrid NPs with spatial resolution. Thermogravimetric analysis was chosen to provide the information of the required pyrolysis temperature, and the crystalline state of Ag in the hybrid NPs was confirmed using x-ray diffractometer. Prior to integration, we found T > 500°C was required for a complete pyrolysis of AgNO3 to be Ag, where the SiO2 cores were shown to be less sensitive to the heating temperature. The volume of Ag and the primary size of TEOS-formed SiO2 cores were shown to be proportional to the concentrations of precursors. Using silica colloids as the cores, we found the conformation of cores can be tuned from the finite sized SiO2 clusters to be mesoporous SiO2 sub-micron sized sphere. Results show Ag penetrate into the pore structure of SiO2 to form Ag cores in the SiO2 template, and the core size of Ag was increased with an increase of AgNO3 concentration above the melting point. After integration, we found a formation of Ag-core, SiO2 shell by choose TEOS-synthesized SiO2 as the core template. By choosing colloidal SiO2 as the precursor, the structure of hybrid NPs transferred to be Ag-core with surface decoration in the mesopores of SiO2 template. The related volume and composition were close to the designed value before integration. Our work provides a generic way to implement the design of nanomaterials through a well-controlled synthesis route for emerging biomedical (e.g., drug carriers, imaging agents) and energy applications (e.g., fuel additives, catalysts).