Nanoparticle-Imprinted Silica Gel for the Size-Selective Capture of Silver Ultrafine Nanoparticles from Water.

A synthetic approach has been developed to prepare silica gel monoliths that embed well separated silver or gold spherical nanoparticles (NP), with diameters of 8, 18 and 115 nm. Fe3+, O2/cysteine and HNO3 were all successfully used to oxidize and remove silver NP from silica, while aqua regia was necessary for gold NP. In all cases, NP-imprinted silica gel materials were obtained, with spherical voids of the same dimensions of the dissolved particles. By grinding the monoliths, we prepared NP-imprinted silica powders that were able to efficiently reuptake silver ultrafine NP (Ag-ufNP, d = 8 nm) from aqueous solutions. Moreover, the NP-imprinted silica powders showed a remarkable size selectivity, based on the best match between NP radius and the curvature radius of the cavities, driven by the optimization of attractive Van der Waals forces between SiO2 and NP. Ag-ufNP are increasingly used in products, goods, medical devices, disinfectants, and their consequent diffusion in the environment is of rising concern. Although limited here to a proof-of-concept level, the materials and methods described in this paper may be an efficient solution for capturing Ag-ufNP from environmental waters and to safely dispose them.

Layered silver nanoparticles embedded in a BaF(2) matrix: optical characterization.

Multilayer stacks of silver and BaF(2) alternate layers have been deposited by thermal evaporation on a silica substrate with the aim to obtain Ag clusters dispersed in a BaF(2) insulator matrix. The Ag layer thickness was approximately 1.2 nm; the thickness of the BaF(2) layer was approximately 25 nm. The samples were thermally treated for a 1 h thermal annealing process at 500 degrees C. These kinds of multilayer device also have several applications in the field of optics for the realization of antireflection coatings. However, optical characterization of dielectric matrices that contain layered metallic nanoparticles still remains an unsolved problem in the field of nanostructured optical coatings. Therefore, the surface plasmon resonance peak that appears in the optical absorption spectra because of the formation of Ag nanoclusters inside the BaF(2) insulator matrix has been monitored and fitted by numerical codes. In particular, a previously published theoretical model, based on the Maxwell-Garnett effective medium theory, modified to take into account the effects that are due to the particle shapes and the spatial arrangement of the clusters, has been employed to fit the optical absorption spectra.

Surface plasmon resonance of metal nanoparticles sandwiched between dielectric layers: theoretical modelling.

Composite films consisting of a ceramic matrix with embedded metal nanoparticles have received increased interest due to their numerous potential applications in the field of optics and optoelectronics. Numerous studies have been dedicated to the fabrication of these composite materials and it has been shown that nanocermet films can be obtained by successive deposition of alternate dielectric and metal films of thicknesses opportunely chosen. In this case, stacks of dielectric layers alternated with layers of metal nanoclusters (NCs) are obtained. However, until now, optical characterization of these kinds of multilayer stack has been used to retrieve mainly qualitative information on the dimension, shape, and geometric distribution of nanoparticles inside the dielectric matrix. An easy-to-handle model that quantitatively links the optical properties to the main features of the NCs embedded in the matrix is presented. This model can be applied to multilayer stacks of dielectric layers alternated with metal NC layers and is shown to be a valid alternative to a recently published model [Nanotechnology 19, 125709 (2008)NNOTER0957-448410.1088/0957-4484/19/22/225302] that was applied to the case of a three-layer structure (dielectric/metal:dielectric/dielectric).