Sol–gel nanohybrid materials prepared via supramolecular organization

This article reports on recent progress in the synthesis of sol–gel nanohybrid materials based on the supramolecular organization. A variety of nanohybrid materials has been obtained by molecular design of the precursors and systematical control of synthetic processes. Organoalkoxysilanes with covalently attached hydrophobic tails are hydrolyzed to form amphiphilic molecules containing silanol groups, leading to the formation of vesicular structures. The obtained hybrid has analogous structures of both cell membrane and silica particle and was named “cerasome”. The cerasome can achieve the hierarchical three-dimensional organization of vesicular particles on the substrate. The nanohybrids are developed not only by the hydrophobic interaction of amphiphilic molecules but also by the electrostatic interaction. The layer-by-layer (LbL) assembly of the water-soluble titania precursor with polycation is adopted for nanohybrid coatings containing titania nanoparticles on the substrates. In addition, preparation of hybrid hollow capsules via LbL assembly and sol–gel method with colloid templating is also discussed.     

Sol–gel derived dye-bridged hybrid materials for white luminescence

Novel yellow and blue emissive dyes have been synthesized using 2,5-diamino-3,6-dicyanopyrazine and various alkoxysilanes and they are covalently bridged to cycloaliphatic epoxy functional oligosiloxane via non-hydrolytic sol–gel reaction. Dye-bridged hybrid materials (DBH) are fabricated by thermal curing the dye-bridged oligosiloxane. Structure and formation of dyes and siloxane network is studied using analysis method. Four components of red, yellow, green and blue emitting DBH cover entire visible range and white luminescence with high color rendering index is realized by controlling their combinations. We have ensured superior thermal stability DBH at 120 °C for 200 h caused by covalently bridged structure and robust siloxane matrix.     

Sol–gel synthesis of sodium and lithium based materials

Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol?Cgel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na_2/3CoO₂, Li(Ni_1/3Mn_1/3Co_1/3)O₂, and Li(Ni_1/2Co_1/2)O₂ powders are phase pure with grain sizes below 1???m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol?Cgel route at temperatures typically 100?C200?K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol?Cgel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations.     

Sol–gel synthesis and structure of silica hybrid materials

In this work the research results on the sol–gel synthesis and structure of silica nanocomposites, containing carrageenan and their application as carriers for cell immobilization were described. The samples were prepared at room temperature by replacing different quantity of the inorganic precursor with κ-carrageenan. For studying the structure of the synthesized hybrids the following methods were used: FT-IR, XRD, BET-Analysis, SEM, AFM and Roughness Analysis. The influence of the type of silicon precursors, nature and quantity of organic component on the structure, surface area, design and size of nanostructures was established. The possibility of application of the synthesized biocatalysts in an enzyme degradation process of the toxic, carcinogenic and mutagenic substances benzonitrile, fumaronitrile, o-, m-, and p-tolunitriles was investigated at batch experiments. A two-step biodegradation process in a column bioreactor of fumaronitrile was followed. After operation of the system for 8 h at a flow rate 45 mL h^?1 and at 60 °C, the overall conversion was 89%, showing a good stability of the developed process.     

Sol–gel derived organic–inorganic hybrid materials: synthesis,characterizations and applications

Organic/inorganic hybrid materials prepared by the sol–gel approach have rapidly become a fascinating new field of research in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental understanding of the sol–gel process and the development and applications of new organic/inorganic hybrid materials. Polymer-inorganic nanocomposite present an interesting approach to improve the separation properties of polymer material because they possess properties of both organic and inorganic such as good permeability, selectivity, mechanical strength, and thermal and chemical stability. Composite material derived by combining the sol–gel approach and organic polymers synthesis of hybrid material were the focus area of review It has also been demonstrated in this review that a more complete understanding of their structure–property behavior can be gained by employing many of the standard tools that are utilized for developing similar structure–property relationships of organic polymers. This review article is introductory in nature and gives introduction to composite materials/nanocomposite, their applications and the methods commonly employed for their synthesis and characterization. A brief literature survey on the polysaccharide templated and polysaccharide/protein dual templated synthesis of silica composite materials is also presented in this review article.     

Sol–gel composite coatings from methyltriethoxysilane and polymethylhydrosiloxane

New composite coatings were prepared by mixing pre-hydrolyzed methyltriethoxysilane (MTES) sol by an acidic catalyst dibutyltin dilaurate (DBTDL) and polymethylhydrosiloxane (PMHS) in gasoline at room temperature. The gel process was thoroughly investigated regarding the use of different basic catalyst [3-aminopropyltriethoxysilane (APTES) or triethylamine (TEA)], as well as the ratios of pre-hydrolyzed MTES sol and PMHS with various content of active H. It was revealed that the composite coating from 2:1 ratio (w/w) of pre-hydrolyzed MTES sol with equimolar amounts of water and PMHS_1.55 under the catalysis of APTES demonstrated high pencil hardness, and excellent resistance against contamination and corrosion. This composite coating (MTPM21-A) was further characterized by FTIR, ²⁹Si NMR, DSC and TGA.     

Sol–gel chemistry of an aqueous precursor solution for YBCO thin films

A water based YBa₂Cu₃O_7−x (YBCO) precursor using a triethanolamine (TEA)/acetic acid complexing method to obtain YBCO thin films is described in detail. The influence of complexation behavior in the formation of transparent and homogenous sols and gels after the combination of Y, Ba and Cu—acetates, acetic acid and TEA has been studied by potentiometric titration and the results are compared with analytical simulations. The decomposition of the gel was studied by IR (infrared) and Thermal Gravimetric Analysis/Differential Thermal Analysis (TGA/DTA). The results in sol-gel chemistry can be used to decide on the necessities in the preparation of stable sol–gel precursors with a minimum amount of organic compounds. The sol–gel system was also used for the deposition of high textured superconducting thin films on STO substrates by dip coating. The synthesized YBCO showed a superconducting transition temperature of 90.95 K with narrow ΔT (2 K) for thin films. The results from X-ray diffraction show that the single phase YBCO was obtained. SEM pictures also indicate that the properties of the surface thin films are good.     

Silica sol–gel chemistry: creating materials and architectures for energy generation and storage

There is widespread recognition that the use of energy in the twenty-first century must be sustainable. Because of its extraordinary flexibility, silica sol–gel chemistry offers the opportunity to create the novel materials and architectures which can lead to significant advances in renewable energy and energy storage technologies. In this paper, we review some of the significant contributions of silica sol–gel chemistry to these fields with particular emphasis on electrolytes and separators where sol–gel approaches to functionalization and encapsulation have been of central importance. Examples are presented in the areas of dye-sensitized solar cells, biofuel cells, proton exchange membrane fuel cells, redox flow batteries and electrochemical energy storage. Original work is also included for the sol–gel encapsulation of a room temperature ionic liquid to create a solid state electrolyte for electrochemical capacitors. In view of the critical importance of energy and the versatility of the sol–gel process, we expect the sol–gel field to play an increasingly important role in the development of sustainable energy generation and storage technologies.     

Sol–gel chemistry: evidence of redistributionat silicon atom induced by NaOH as catalystduring ageing

The influence of the ageing conditions on the properties of organic-inorganic hybrid solids obtained by sol–gel route using NaOH catalysis has been studied. The cases of 1,4-bis(trimethoxysilyl)benzene 1 (‘rigid’ precursor) and 1,4-bis(trimethoxysilylethyl)benzene 2 (‘more flexible’ one) have been investigated. The ²⁹Si CP MAS NMR spectra of the silsesquioxanes clearly reveal that Si–O–Si bond cleavage and redistribution reactions occur when the ageing time is increased or is performed at higher temperatures. This particular behaviour observed only with NaOH is of importance in the choice of the catalyst.     

Sol–gel synthesis of nanosilver embedded hybrid materials using combined organosilica precursors

A facile sol–gel route to the fabrication of size-controllable nanosilver embedded hybrid materials at room-temperature is presented. The preparation process involves using three kind of organosilica precursors, i.e. tetraethoxysilane, 3-mercaptopropyltrimethoxysilane and polymethylhydrosiloxane, which behaved as framework constructor, complexing agent toward metal ions and in situ reducing agent for Ag⁺ ions, respectively, under alcohol-rich synthesis conditions. The prepared hybrid materials were characterized by Ultraviolet–visible diffuse reflectance spectra, Fourier transform infrared, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption measurements. It was shown that well-dispersed silver nanoparticles (AgNPs) with small particle size were successfully embedded in the hybrid skeleton, and the mean particle size of AgNPs could be controlled at ca. 2–5 nm.     

Sol–gel synthesis and thermal behavior of bioactive ferrous citrate–silica hybrid materials

Journal of Thermal Analysis and Calorimetry - Imbalance of the iron level in the body causes several diseases. In particular, the low level of iron, during pregnancy, is responsible for the iron...     

Fast sol–gel technology: from fabrication to applications

A novel method to prepare crack-free sol–gel materials without shrinkage is reviewed. The method allows fabrication of a viscous sol–gel resin in a few minutes followed by either thermal-curing or UV-curing requiring several hours or several minutes, respectively. The method is distinguished by the short time required to achieve a solid monolith. The fast sol–gel method uses a combination of organically modified alkoxides with traditional alkoxides as precursors, to produce a final product which is an organic-inorganic hybrid with properties that vary from silicone rubbers to silica glass. Optical and physical properties, such as refractive index and thermal expansion, can be engineered by controlling the ratio between the precursors. This class of materials is a promising candidate for preparation of optical elements such as waveguides and submicron structured replicas and can also be used as an optical bonding material. This paper reviews the fast sol–gel technology, as well as methods to characterize the process and its final products. Various applications of fast sol–gel materials are presented.     

Sol–gel research in Italy

A short story of the research on sol–gel in Italy is given, and the evolution is presented and compared with the rest of the world in terms of number of publications, citations and patents. It is shown that both basic and applied research are active and effective in Italy.     

Click approaches in sol–gel chemistry

The combination of the copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction with sol–gel processing enables the versatile preparation of sol–gel materials under different shapes with targeted functionalities through a diversity-oriented approach. In this account, the development of the CuAAC reaction under anhydrous conditions for the synthesis of sol–gel precursors and for the assembling of magnetic nanoparticles on self-assembled monolayers is related, as well as the use of the classical CuAAC methodologies for the functionalization of mesoporous silica nanoparticles and microdots arrays. Coupling CuAAC and Sol–Gel will result in simplified preparations of multifunctional materials with controlled morphologies.     

Next generation pseudocapacitor materials from sol–gel derived transition metal oxides

Capacitive energy storage is distinguished from other types of electrochemical energy storage by short charging times and the ability to deliver significantly more power than batteries. A key limitation to this technology is its low energy density and for this reason there is considerable interest in exploring pseudocapacitive charge storage mechanisms which offer the prospect of increasing energy density without compromising the power density of electrochemical capacitors. In this paper we review our recent work on using sol–gel synthesis methods to prepare nanostructured transition metal oxides which exhibit increased levels of pseudocapacitance and enhanced energy storage properties. Our work with TiO₂ nanoparticles and mesoporous films of TiO₂ and CeO₂ is highlighted as we use these studies to understand the role of crystallite size, nanoscale porosity and understanding the differences between pseudocapacitance and intercalation processes.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Sol–gel combustion synthesis of BNBT powders

Ba-modified bismuth sodium titanate with composition 0.94[(Bi_0.5Na_0.5)TiO₃]-0.06BaTiO₃ (BNBT) was prepared by a citrate nitrate sol–gel combustion method. The sol was obtained using barium acetate, bismuth nitrate, sodium nitrate and a peroxo-citrate complex of titanium isopropoxide as starting precursors. Various molar ratios of citrate/nitrate (C/N) were considered for the sol production. The corresponding gels were fired at different temperatures (300, 400, 500 °C) in order to evaluate the conditions necessary to obtain the decomposition of the precursors and the formation of the pure BNBT perovskitic phase in a single step. The best conditions to obtain the desired phase are: (C/N) = 0.2, and combustion temperature of 500 °C. Ball milled powders were densified at a temperature 100 °C lower than the one generally used for powder produced with the conventional mixed oxide route. The electrical properties are comparable to those reported for conventionally prepared materials.     

Sol–gel derived near-UV and visible antireflection coatings from hybridized hollow silica nanospheres

This paper reports a facile means to gradually tailor refractive index from an ultra-low-n of 1.10–1.45 based on hollow silica nanospheres hybridized with acid-catalyzed silica. The influences of the hybridization on refractive index, thin-film uniformity, and roughness were systematically investigated. The single-layered antireflection (AR) coatings and the three-layered AR coatings were prepared using the hybridized thin films as building blocks. The former showed the near-perfect transmittance and reflectance, 99.16 and 0.42 %, respectively, at a single wavelength of 600 nm, while the average transmittance (T _ave) and reflectance (R _ave) from the near ultraviolet (UV) to the visible region (300–800 nm) were moderate; the latter demonstrated an excellent AR capability in broadband that T _ave reaches 97.29 %, much higher than that of the single-layered AR coating, 95.86 %. More interestingly, the three-layered AR coating showed an average transmittance of 97.94 % in the near-UV wavelength range from 345 to 400 nm and it was 6.77 % higher than that of bare glass. Moreover, the three-layered AR coatings had the less degradation in transmission and surface morphology after the highly-accelerated temperature and humidity stress tests, and the wet abrasion scrub tests. The findings imply that both good optical performance and durability are likely to be achieved using the sol–gel derived multilayered AR coatings.     

Formation and characterization of phosphate-modified silicate materials derived from sol–gel process

Phosphate-containing silicate materials prepared using sol–gel method from Si(OC₂H₅) were investigated at the variation of the amount of phosphate modifier from 5 to 50 wt% in term of P₂O₅. Chemical composition, textural and structural properties of these materials were characterized by FTIR-spectroscopy, TEM, X-ray diffraction and nitrogen adsorption. It was shown that the materials posse monomodal pore size distribution of 5–20 nm for the samples dried at 100 °C and 40–60 nm for the specimens calcined at 600 °C. The mean pore size and surface area depended on the amount of phosphoric acid. Before the stage of high temperature treatment phosphoric acid, introduced into the structure of the materials as a modifying agent, was uniformly distributed inside a porous space of the material and was not chemically bonded with silicate. After high temperature treatment both chemical interaction of silicate with phosphate, providing the formation of silicate-phosphate structures, as well as redistribution of free modifier from the bulk of granules to their surface took place. The polyphosphate layer is formed on the material surface closing the internal porous space. However, in this case a part of the phosphate modifier remains chemically unbound to SiO₂ structure.     

Sol–gel synthesis of iron oxide–silica composite microstructures

Spherical silica particles doped with iron oxide have been synthesized via base-catalyzed one-pot sol?Cgel process using tetraethoxysilane (TEOS) and iron(III) ethoxide (ITE) as co-precursors. In the modified St?ber process adopted, depending on the concentration of ITE in the starting composition, materials of various morphologies were observed under a scanning electron microscope and an atomic force microscope. The presence of ITE significantly affected the formation process of particulate silica; the spherical particles were formed accompanied by the co-presence of irregular-shaped finer aggregates. The fraction of the aggregates with rough surfaces increased with an increase of the ITE content in the reaction mixture. Both the spherical particles and irregular-shaped aggregates contained iron hydroxide and they exhibited paramagnetic behavior. The chemical composition and physicochemical properties of the materials were determined using various complementary spectroscopic methods.