Core-shell type nanostructures (metal nanoparticles decorated dielectric spheres) are of particular interest based on their application potentials ranging from catalysis, bio-sensing to optical devices because of their inherent characteristic physico-chemical properties. Herein, we utilized silica (SiO2) as the dielectric cores and Ag as the metal shell nanostructures. In this study, we carefully modified the conventional Stöber process for the in-situ one step synthesis as well as functionalization of large and highly uniform silica particles with the universally soluble homogenous polymer PVP (polyvinyl pyrrolidone). This facilitates cohesive control of uniform mass transfer of Ag+ metal ions onto the silica surface, thereby enabling their sequential reduction to zerovalent Ag atoms (in the presence of slightly excess NaOH), as confirmed from the detailed spectroscopic and microscopic measurements. The precise role of PVP in the stabilization as well as sequential reduction of the Ag nanoparticles onto the dielectric silica surface is prudently demonstrated through FTIR data analysis. The nonlinear dependence of the plasmonic peak wavelength on the refractive index (RI) describes the intriguing light-matter interaction of core-shell type nanostructures, disentangling the surface plasmon contribution at the dielectric-metal interfaces in a rigorous manner, quantifying the plasmonic ultra-sensitivity and figure of merit of our as-prepared optical metamaterials. 

Modified Stöber synthesis of SiO2@Ag nanocomposites and their enhanced refractive index sensing applications

Incorporation of g-C3N4 nanosheets and CuO nanoparticles on polyester fabric for the dip-catalytic reduction of 4 nitrophenol.

Fe3O4@CMC-Cu magnetic nanocomposite as an efficient catalyst for reduction of toxic pollutants in water

Fruits are safe, toxin-free, and biomolecule-rich raw materials that may be utilized to decrease metal ions and stabilize nanoparticles. Here, we demonstrate the green synthesis of magnetite nanoparticles which were first capped with a layer of silica, followed by the decoration of silver nanoparticles, termed Ag@SiO2@Fe3O4, by using lemon fruit extract as the reducing agent in a size range of ∼90 nm. The effect of the green stabilizer on the characteristics of nanoparticles was examined via different spectroscopy techniques, and the elemental composition of the multilayer-coated structures was verified. The saturation magnetization of bare Fe3O4 nanoparticles at room temperature was recorded as 78.5 emu/g, whereas it decreased to 56.4 and 43.8 emu/g for silica coating and subsequent decoration with silver nanoparticles. All nanoparticles displayed superparamagnetic behavior with almost zero coercivity. While magnetization decreased with further coating processes, the specific surface area increased with silica coating from 67 to 180 m2 g–1 and decreased after the addition of silver and reached 98 m2 g–1, which can be explained by the organization of silver nanoparticles in an island-like model. Zeta potential values also decreased from −18 to −34 mV with coating, indicating an enhanced stabilization effect of the addition of silica and silver. The antibacterial tests against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) revealed that the bare Fe3O4 and SiO2@Fe3O4 did not show sufficient effect, while Ag@SiO2@Fe3O4, even at low concentrations (≤ 200 μg/mL), displayed high antibacterial activity due to the existence of silver atoms on the surface of nanoparticles. Furthermore, the in vitro cytotoxicity assay revealed that Ag@SiO2@Fe3O4 nanoparticles were not toxic to HSF-1184 cells at 200 μg/mL concentration. Antibacterial activity during consecutive magnetic separation and recycling steps was also investigated, and nanoparticles offered a high antibacterial effect for more than 10 cycles of recycling, making them potentially useful in biomedical fields.

https://pubs.acs.org/doi/pdf/10.1021/acsabm.3c00122

Silver-Decorated and Silica-Capped Magnetite Nanoparticles with Effective Antibacterial Activity and Reusability

Ag-decorated PP nonwoven for excellent catalytic reduction of 4-nitrophenol and antibacterial study

Fabrication of Ag nanoparticles supported on amino-functionalized peeled-watermelon structured silica-coated nano-Fe3O4 with enhanced catalytic activity for reduction of 4-nitrophenol

Wending Zhou

Papers

Fabrication of Ag nanoparticles supported on amino-functionalized peeled-watermelon structured silica-coated nano-Fe3O4 with enhanced catalytic activity for reduction of 4-nitrophenol