Silver Nanoshells with Optimized Infrared Optical Response: Synthesis for Thin-Shell Formation, and Optical/Thermal Properties after Embedding in Polymeric Films

Abstract

We describe a new approach to making ultrathin Ag nanoshells with a higher level of extinction in the infrared than in the visible. The combination of near-infrared active ultrathin nanoshells with their isotropic optical properties is of interest for energy-saving applications. For such applications, the morphology must be precisely controlled, since the optical response is sensitive to nanometer-scale variations. To achieve this precision, we use a multi-step, reproducible, colloidal chemical synthesis. It includes the reduction of Tollens’ reactant onto Sn2+-sensitized silica particles, followed by silver-nitrate reduction by formaldehyde and ammonia. The smooth shells are about 10 nm thick, on average, and have different morphologies: continuous, percolated, and patchy, depending on the quantity of the silver nitrate used. The shell-formation mechanism, studied by optical spectroscopy and high-resolution microscopy, seems to consist of two steps: the formation of very thin and flat patches, followed by their guided regrowth around the silica particle, which is favored by a high reaction rate. The optical and thermal properties of the core-shell particles, embedded in a transparent poly(vinylpyrrolidone) film on a glass substrate, were also investigated. We found that the Ag-nanoshell films can convert 30% of the power of incident near-infrared light into heat, making them very suitable in window glazing for radiative screening from solar light.

Gold Nanoparticle-Loaded Silica Nanospheres for Sensitive and Selective Electrochemical Detection of Bisphenol A

“…Note that the nanospheres formed were hollow and the Au nanoparticles were dispersed in the materials. A core–shell, with a thin shell, is observed over silica which can be due to the coating of gold shells …”

“…The mean crystallite size of Au was calculated from the half-height width of the Au (111) diffraction peak (fwhm), using the Scherrer equation (eq ). , D = K λ / β .25em cos nobreak0em0.25em⁡ θ where D is the crystallite diameter, K is proportionality constant, K = 0.9 for spherical particles, λ is the incident wavelength of Cu-kα, 1,5405 Å, β is the half-height width of the peak, and θ is the diffraction angle. The values obtained for the nanoparticles of AuSiO 2 300 and AuSiO 2 700, were 25 and 27 nm, respectively (Table ).…”

“…A core−shell, with a thin shell, is observed over silica which can be due to the coating of gold shells. 36 To evaluate the changes in the crystallinity and the mean diameter of the crystallite, X-ray diffraction measurements of the materials containing Au nanoparticles were carried out. According to the pattern described, it is in the range of 5−50°t hat the first two gold diffraction peaks are observed [Joint Committee on Powder Diffraction Standart (JCPDS) 04-0784].…”

“…The mean crystallite size of Au was calculated from the half-height width of the Au (111) diffraction peak (fwhm), using the Scherrer equation (eq 1). 36,39 = D K / cos…”

Insights into the Synthesis and Kinetics of Silver-on-Silica Core–Shell Particles

“…The negatively charged surface silanol groups on the silica core will attract the positively charged diammine silver through electrostatic interactions and are reduced by either formaldehyde or glucose. Very recently, Lermusiaux et al 29 developed a procedure to deposit ultrathin silver nanoshells on silica cores. The particles were embedded in a transparent polymer matrix and exhibited stronger extinction in the IR region, making them suitable for window glazing.…”