Silica Gels Doped with Gold Nanoparticles: Preparation, Structure and Optical Properties

Abstract

A novel, one-pot sol–gel preparation scheme leading to reproducible incorporation of 20–40 nm sized gold nanoparticles (AuNPs) in SiO2 gels is developed based on in situ reduction during gelation using chloroauric acid and ascorbic acid. Variation in the preparation conditions affects the chemical composition, optical properties and size distribution of the AuNPs incorporated in the silica gels. Different organic dopants, i.e., oleic acid, acetic acid or dodecanethiol, are applied to modify the final composite material and to control the rate of reduction and growth of the AuNPs in the gels. The synthesized samples are characterized by UV/Vis/NIR spectroscopy, X-ray diffraction, transmission electron microscopy, thermal conductivity measurements and DTA/TG measurements. The optical properties of the obtained composites are explained using Mie theory. The incorporation of AuNPs leads to an increase in the thermal conductivity of the silica gels. The best process method in this contribution is the use of NaOH as a gelation catalyst and oleic acid as an organic modifier, leading to 20 nm AuNPs dispersed in the silica matrix.

One-pot synthesis of gold nanoparticles and aluminum hydroxide hydrogels-based composites with modulated optical properties

“…In this sense, numerous reports show that composite materials have both the intrinsic properties of each component and new features coming from the synergistic effect, mainly due to their interfaces with high surface areas. Thereby, catalytic [29,30], sensing [31][32][33], optical [34][35][36], and plasmonic [37,38] properties can be modulated, which would not be available from their individual components. In the case of metal hydroxide hydrogels, they can offer higher stability and can introduce sensing and/or catalytic properties to the final composite, different from those observed for organic hydrogels [39,40].…”

Functional Sol-Gel Composites: Preparation and Applications

“…This Special Issue, titled “Functional Sol-Gel Composites: Preparation and Applications”, aims to provide a collection of papers in the field of functional composites, with an emphasis on preparation strategies and applications in relation to materials. Sol-gel composites, based on a reproducible preparation strategy and complex characterization, allow for the development of materials with broad functionalities: thermal insulation, energy storage, tunable optical properties, metal nanoparticles embedded in oxides, biomaterials, and modern drug delivery systems [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ].…”

“…A special direction of research for sol-gel composites is the combination of spectroscopic and diffraction techniques, giving information about the microstructures and pore architectures of porous oxide materials. In advanced sol-gel composites, the shapes and dimensions of the pores starts to play an important role in the incorporation of optical, magnetic, or electrical active dopands, which is an advantage for IR spectroscopy when combined with texture investigations [ 5 , 6 , 7 , 8 ]. Another interesting direction of sol-gel composites is the use of highly luminescent hybrid nanoparticles for cell tracking purposes [ 6 ].…”

“…In recent years, scientific research in the field of sol-gel composites has focused on doped nanopowders, aerogels, thin films, and nanoparticles with different properties, all based on the possibilities of the sol-gel chemistry, including solution chemistry, gelation, aging, and drying [ 9 , 10 , 11 ]. Recently, a novel “in situ” sol-gel approach for the preparation of functional composites has been demonstrated for the preparation of silica composites containing nanosized Ln(phen) 2 (NO 3 ) 3 , Ln = Eu, Tb, or gold nanoparticles (AuNPs) [ 7 , 8 ]. In this way, materials with tunable optical properties and catalytic applications can be created using the pore architecture of the silica gels or aerogels.…”

“…Contributions 4 and 5 demonstrate the possibilities for the production of rare earth ion-doped materials by specific sol-gel formulations. Depending on the preparation conditions, solid solutions, doped thin films, or composites with desired properties can be designed [ 4 , 7 , 8 ]. Here, the physical properties of the materials obtained depend on the doping level and microstructure of the rare earth contamination, and can be controlled by the physico-chemical parameters of the sol-gel process.…”