Epoxide assisted sol-gel synthesis of rutile NixTi1-3xSb2xO2 solid solution nanoparticles

Rutile Ni _x Ti_1-3x Sb_2x O₂ solid solution nanoparticles were synthesized by a sol-gel route using propylene oxide as a gelation agent. Titanium oxide nanopowder and 12% TiCl₃ solution were used as the source for titanium to investigate the influence of the titanium precursors on the formation of the target materials. It was found that the nanoparticles prepared using 12% TiCl₃ solution showed a much lower phase formation temperature (700°C) as compared to those prepared from TiO₂ nanoparticles (1000°C). This lower phase formation temperature allowed a substantial reduction of the aggregation of the particles during calcination leading to the formation of nearly mono-dispersed nanoparticles of about 20 nm. The results of this work show that the epoxide assisted sol-gel method is capable to produce titanium-based ternary oxide solid solution nanoparticles, owing to the formation of a highly homogeneous precursor gel intermediate.     

Photostability of a photochromic naphthopyran dye in different sol-gel prepared ormosil coatings

A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores, affecting the stability of the molecules upon prolonged exposition to UV light. The photostability of the molecules was increased in matrices functionalized with larger organic groups, or with larger amount of modifying groups. In this way the photodegradation of the photochromic molecules could be reduced by a factor of 5, as compared with the photodegradation of the molecules in unfunctionalized silica matrix.     

Effect of HCl on the PPO assisted sol-gel synthesis of olivine-type Co2SiO4 ultrafine particles

Olivine-type Co₂SiO₄ ultrafine particles were synthesized by a sol-gel method using propylene oxide as a gelation agent. Owing to the high homogeneity of the intermediate gel precursor, the usage of this epoxide method results in a substantial reduction of calcination temperature and time as compared with the solid-state route, and a great reduction of calcination time as compared with other wet-chemistry routes. This high homogeneity is obtained by the usage of an appropriate amount of HCl, as a catalyst that matches the rate of hydrolysis of TEOS and the metal ions, allowing the formation of Si–O–Co bonds.     

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

Photochromic naphthopyran derivatives have been embedded in sol-gel prepared organically modified thin films. The introduction of organic functional groups into a silica matrix allows tailoring the surface of its pores and the polarity of the environment of the embedded host molecules. The photochromic properties of the naphthopyran molecules, such as the spectral properties of the coloured forms and the kinetics of the thermal bleaching, depend strongly on the polarity of the pores where the molecules are located and, hence, on the nature and loading of organic functional groups in the composition of the ormosil matrix. Important changes in the photochromic properties of the films have also been induced by modifications in the sol-gel preparation and processing parameters. The photostability of the photochromic molecules upon prolonged exposition to UV light is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix, where the dye molecules will be located, affects the stability of the molecules, in terms of the effectiveness of the interaction between the photochromic molecules and the pore surface.     

Surface Area Study of High Area Cobalt Aluminate Particles Prepared by the Sol-Gel Method

Cobalt aluminate particles were prepared by the sol-gel method, starting from aluminum sec-butoxide and cobalt salts with a Co:Al ratio of 1:3. Samples with the same composition were also prepared by the citrate-gel method from cobalt and aluminum nitrates and citric acid. The particles were calcined to temperatures between 400 and 1000°C, for the formation of the mixed oxide having spinel structure. The surface properties of the different samples (BET surface area and pore size distribution) were measured. The highest BET surface area obtained (about 339 m²/g) corresponds to a sample prepared by cobalt acetate and aluminum sec-butoxide, calcined at 400°C. The surface area of the sample is reduced progressively as the sample is calcined to higher temperatures (to about 65 m²/g at 1000°C). Narrow pore size distributions were observed with average pore radius ranging from 17–20 Å, for samples heated to 400°C, to about 55–65 Å, for samples heated to 1000°C. The different surface areas and porosities obtained for particles prepared by different methods, different precursors or calcination temperatures, are discussed.     

Gasochromic Effect in Platinum-Doped Tungsten Trioxide Films Prepared by the Sol-Gel Method

Tungsten oxide doped by a complex of platinum exhibits a gasochromic effect. A reversible coloration is observed on successive exposure to hydrogen and air. The films were prepared by the sol-gel method at room temperature. They showed strong darkening (blue color) on exposure to hydrogen and were bleached completely when exposed to air. The proccess has been reproduced completely hundreds of times without any losses. The cycling of the coloration was obtained from UV-Vis spectra and the mechanism deduced from both visible and Fourier transform infrared (FTIR) spectra. Colorimetric properties of the gasochromic films were expressed in color space chromaticity diagram.     

Sol-Gel Synthesis of Nanoscaled Spinels Using Propylene Oxide as a Gelation Agent

Spinel nanoparticles of CoAl₂O₄ (blue), CoCr₂O₄ (bluish green), ZnFe₂O₄ (brown) and CuCr₂O₄ (black) were synthesized by a sol-gel route with propylene oxide as a gelation agent. This method has proven to be an effective route to synthesize mixed oxide nanoparticles, especially for that with one of metal ion having a formal charge of less than +3. Transmission electron micrographs show the small particle size (less than 60 nm) of the four pigments and their narrow particle size distributions.     

Preventing UV-light damage of light sensitive materials using a highly protective UV-absorbing coating

One of the most important drawbacks of classical and new advanced functional materials for applications outdoors, or in environments with high UV irradiation, is the light induced damage that reduces drastically their effective operation lifetime or durability. This makes protecting light sensitive materials against UV irradiation a nowadays important technological demand in almost every industrial field. This tutorial review incorporates the main aspects of UV damage to materials and describes the recently developed highly effective thin UV-protective coatings, based on UV-absorber molecules entrapped in a Sol-Gel derived ormosil matrix.     

Inexpensive and robust iron-based electrode substrates for water electrolysis and energy storage

The instability of iron under anodic conditions makes iron-based electrode substrates unsuitable for alkaline electrolyzers and rechargeable alkaline batteries. Therefore, significantly more expensive substrates such as nickel foam or sintered nickel are used. Nickel adds a significant cost to electrolysis and energy storage systems. We show that iron substrates can be stabilized using a unique protective thermal coating. These coatings can also yield some of the most electrocatalytically active electrodes in addition to showing no notable change in performance even after 1500 h of anodic polarization. Besides sintered iron, low-carbon steel mesh can be stabilized similarly. Low-carbon steel protected by a thin layer of lithium-doped cobalt spinel was found to be an excellent current collector for positive nickel hydroxide electrodes in alkaline batteries. Thus, surface-modified iron substrates, 40 times less expensive than nickel, are promising for lowering the material costs of alkaline water electrolyzers and rechargeable alkaline batteries.     

In-Situ Formation of AgCl Nanocrystallites in Films Prepared by the Sol-Gel and Silver Nanoparticles in Silica Glass Films

We are reporting on a novel preparation of silver chloride in sol-gel silica films as a precursor for nanoparticles of silver. The precipitation of silver chloride particles in-situ was achieved by the reaction of silver nitrate with trichloroacetic acid. The reaction leads to a slow release of chloride leading to a controlled precipitation of AgCl. The existence of an isotropic crystalline AgCl phase in the glass films was demonstrated by X-rays Diffraction Analysis (XRD) and Scanning Electron Microscope and Energy Dispersive Analysis of X-rays (SEM-EDAX). The resulting films are of good optical quality and exhibit a strong coloration upon irradiation with sunlight or heating to 600°C, due to the reduction of AgCl to silver nanoparticles. The absorption spectra of the films before and after irradiation are shown.