Thermoplasmonic Heat Generation Efficiency by Nonmonodisperse Core–Shell Ag⁰@SiO₂ Nanoparticle Ensemble

The plasmon-induced heat generation by core–shell Ag 0 @SiO 2 nanoparticle ensemble, i.e., Ag 0 nanoparticles coated with a nanometric, amorphous SiO 2 layer, has been studied for nanoparticles dispersed in liquid suspensions or deposited in film. Nonmonodispersed, fractal-like Ag 0 @SiO 2 ensembles were synthesized by flame spray pyrolysis, varying Ag 0 particle size distribution, and SiO 2 shell thickness, ranging from 1 nm up to 5 nm. The particles were characterized by TEM, XRD, XPS, and UV–vis, while the thermoplasmonic heat-generation efficiency was monitored in situ by measuring the temperature rise over the nanoparticle ensembles by an infrared thermal imager under UV–vis irradiation or ambient solar light. We have carried out a systematic investigation of parameters regarding (i) the particle characteristics, (ii) the surrounding medium, and (iii) the irradiation characteristics. The data reveal the determinant role played by the SiO 2 shell in the plasmonic heating by Ag 0 @SiO 2 . Thus, for the thinner SiO 2 coating tailored herein (∼1 nm), under focused solar light, Ag 0 @SiO 2 films were able to produce a significant temperature rise up to T max ∼ 400 °C. The data are analyzed quantitatively within the theoretical frame of Mie theory as extended by Baffou for multiple plasmonic nanoheaters, where we take into account the fractal dimension of the flame-made Ag 0 @SiO 2 ensemble and the occurring collective thermal effects in this geometry. In this context, we interpreted the observed phenomena in terms of the neighboring Ag 0 –Ag 0 coupling within each fractal and the dual role of SiO 2 as the dielectric shell medium around the metallic core, as well as the plasmonic separator. Accordingly, we provide a consistent theoretical frame which provides a quantitative hierarchy of the physicochemical parameters, which determine the photoinduced heat generation for realistic nonideal/nonmonodisperse Ag 0 ensembles.