Sol-gel Technology Research Articles

Materials for Solid-Phase Extraction of Organic Compounds

This review provides an overview of the most recent developments involving materials for solid-phase extraction applied to determine organic contaminants. It mainly concerns polymer-based sorbents that include high-capacity, as well as selective sorbents, inorganic-based sorbents that include those prepared using sol-gel technology along with structured porous materials based on inorganic species, and carbon nanomaterials, such as graphene and carbon nanotubes. Different types of magnetic nanoparticles coated with these materials are also reviewed. Such materials, together with their main morphological and chemical features, are described, as are some representative examples of their application as solid-phase extraction materials to extract organic compounds from different types of samples, including environmental water, biological fluids, and food.

NH3-Sensing Mechanism Using Surface Acoustic Wave Sensor with AlO(OH) Film.

In this study, AlO(OH) (boehmite) film was deposited onto a surface acoustic wave (SAW) resonator using a combined sol-gel and spin-coating technology, and prepared and used as a sensitive layer for a high-performance ammonia sensor. The prepared AlO(OH) film has a mesoporous structure and a good affinity to NH3 (ammonia gas) molecules, and thus can selectively adsorb and react with NH3. When exposed to ammonia gases, the SAW sensor shows an initial positive response of the frequency shift, and then a slight decrease of the frequency responses. The sensing mechanism of the NH3 sensor is based on the competition between mass-loading and elastic-loading effects. The sensor operated at room temperature shows a positive response of 1540 Hz to 10 ppm NH3, with excellent sensitivity, selectivity and stability.

Obtaining of NiO Nanosheets by a Combination of Sol–Gel Technology and Hydrothermal Treatment Using Nickel Acetylacetonate as a Precursor

Nickel oxide nanosheets were manufactured using sol–gel technology and hydrothermal treatment. The effect of hydrothermal treatment on the hierarchical organization character of the thus-manufactured oxide powder was shown. The microstructural parameters of the powder were studied by transmission (TEM) and scanning (SEM) electron microscopy; The homogeneity of the powder and the absence of impurities of another chemical composition were verified by energy dispersive elemental microanalysis (EDX).

Carbon Monoxide Hydrogenation over Gd(Fe/Mn)O3 Perovskite-Type Catalysts

Catalytic properties of GdFeO3 and GdMnO3 perovskite-type oxides in CO hydrogenation processes is conducted. Complex oxides Gd(Fe/Mn)O3 are synthesized by the sol–gel technology and characterized by X-ray diffraction, temperature-programmed reduction, and scanning electron microscopy. It is found that the iron-containing catalyst has fairly high catalytic characteristics; therefore, it provides lower temperatures of carbon monoxide hydrogenation. The presence of manganese in the catalyst leads to an increase in light olefin selectivity compared with the sample containing iron at the B-site. It is assumed that gadolinium cations are responsible for dissociative chemisorption, while iron and manganese cations are responsible for the formation of atomic hydrogen. The two catalysts exhibit resistance to carbon deposition.

Sol-Gel Technology Adaptation of Nanostructured Zinc Oxide for Flexible Electronics

The possibility of replacing classical sol-gel operation methods of high-temperature annealing by photo-annealing using ultraviolet-range radiation has been analyzed. A technique for synthesizing hierarchically organized zinc oxide films using sol-gel technology based on the parallel combination of low-temperature treatment and UV photo-annealing is proposed. Spectroscopic studies of the qualitative composition of the film-forming sol and nanomaterials based on it, obtained on various types of substrates, have been carried out before and after initiation of photochemical reactions.

Production improvement of aqueous solutions of nanosized silica

The article deals with the method for obtaining aqueous solutions of silica nanoparticles based on sol-gel technology, namely, products of hydrolysis of silicon alkoxides and their polycondensation in an alcohol medium. In order to prevent polymorphic changes and dehydration of SiOH-groups, preference was given to low-temperature and vacuum methods. To combat the excessive foaming ability of surfactants and replace the solvent (alcohol with water), a method of distillation was proposed for partial supply of dry steam with air and water. To separate aqueous surfactant solution (tween-80), a method of oil flotation with petroleum ether addition, characterized by its low solubility, both in water and in alcohol, was proposed. The specifications of obtained nanosilica of aqueous solutions can be estimated using optical spectrophotometry, for which the concentration and size coefficients of the Geller Equation for this system were determined. The optimum concentration of SiO2 in the system was also determined when no particles above 100 nm were formed. Methods for the reagents reuse of ethanol, petroleum ether and tween-80 were proposed.

КРЕМНІЙОРГАНІЧНІ ПОКРИТТЯ ДЛЯ ЗАХИСТУ ПАПЕРУ, ОТРИМАНІ З ЕЛЕМЕНТАМИ ЗОЛЬ-ГЕЛЬ ТЕХНОЛОГІЇ

Мета. Розробка двошарових кремнійорганічних покриттів для захисту паперу звикористанням золь-гель технології та оцінка ефективності їх застосування приексплуатації в умовах підвищеної вологи.Методика. Дослідження проведені з використанням стандартнихзагальноприйнятих методик та методу кількісної ІЧ-спектроскопії.Результати. Розроблено захисні двошарові покриття для паперу з небіленоїцелюлози із використанням елементів золь-гель технології на основі силоксанів, щомістять групи →Si – OK та →Si – OЕt у функціональному підшарі таполіетилгідридсилоксан – в поверхневому. Дана кількісна оцінка застосування такихпокриттів для захисту паперу у вологих умовах. Визначено найбільш ефективні захиснікремнійорганічні покриття та оцінено їх ефективність при експлуатації.Наукова новизна. Вперше обґрунтовано доцільність застосування технології звикористанням золь-гель елементів на стадіях гідролізу та конденсації, що дозволяєефективно використовувати силоксани з групами →Si – OK та →Si – OC2H5 в якостібазових для формування функціональних підшарів на поверхні целюлозовмісних матеріалів.Практична значимість. Досліджено особливості формування системисилоксанових покриттів для захисту паперу з небіленої целюлози із елементами золь-гельтехнології. Показана ефективність застосування двошарової системи, що включаєможливість зв’язування гідроксильних груп поверхні паперу та додаткового формуваннягідрофобного захисного шару шляхом застосування силоксанів з різнимиреакційноздатними групами біля атома кремнію (→Si – OK, →Si – OEt, →Si – OH, →Si –H). Обґрунтовано доцільність застосування технологій з використанням золь-гельелементів на стадіях гідролізу та конденсації. Запропоновано схему формування захиснихдвошарових покриттів для паперу з небіленої целюлози, досліджено її механізм, данакількісна оцінка та визначено найбільш ефективні системи захисних кремнійорганічнихпокриттів.
 Purpose. Development of two-layer silicon-organic coatings for paper protection using solgel technology and evaluation of their application efficiency in conditions of high humidity.Methodology. The researches were carried out using standard common methods andquantitative IR spectroscopy.Findings. Protective two-layer coatings for paper made from unbleached cellulose with theuse of sol-gel elements based on siloxane-based materials containing → Si-OK and → Si-OEt inthe functional sublayer and polyethylhydrisiloxane-in the surface are developed. This is aquantitative assessment of the application of such coatings to protect paper in wet conditions. Themost effective protective silicon organic coatings are determined and their efficiency duringoperation is estimated.Originality. For the first time, the feasibility of using the technology using sol-gel elementsat the stages of hydrolysis and condensation has been substantiated, which allows the effectiveuse of siloxanes with Si-OK and → Si-OC2H5 groups as the base for the formation of functionalsublayers on the surface of cellulosic materials.The practical value. Silicone coatings to protect the paper, obtained with elements of solgel technology. The features of the formation of a system of siloxane coatings to protect paperfrom unbleached pulp with elements of sol-gel technology are investigated. The feasibility andefficiency of using a two-ball scheme, which includes the possibility of binding hydroxyl groups ofthe paper surface and the additional formation of a hydrophobic protective ball by usingsiloxanes with different reactive groups near the silicon atom (→ Si-OK, → Si-OEt, → Si-OH, →Si - H). In addition, the feasibility of applying technologies using sol-gel elements in the stages ofhydrolysis and condensation has been substantiated. The scheme of formation of protective twolayer coatings for paper made of unbleached cellulose was proposed, the mechanism of itsformation was investigated, a quantitative assessment was made and the most effective schemes ofprotective silicon-organic coatings were determined.

The effect of the organosilane content on the barrier features of sol-gel anticorrosive coatings applied on carbon steel

The main objective of this work was to determinate the influence of the molar ratio of two compounds on the structure of the molecular net synthesized by sol-gel technology for the protection corrosion coating on carbon steel. Three different molar ratio were use to prepared the organic–inorganic hybrid materials by hydrolysis and condensation of (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and tetraethylorthosilane (TEOS) in an ethanol/water solution. The behavior of the three different syntheses was evaluated by chemical, physical, and electrochemical methods. The evolution of the synthesis was determinate by FT-IR and viscosity until the optimal moment prior to apply the sol to the metallic substrate. Chemical cross-linking of xerogel was determined by solid state of 29Si-NMR and the behavior on thermal stability is given by TGA analysis. Samples of carbon steel were coated by the synthesis and the coatings were characterized using scanning electrochemical microscopy (SEM) finding considerably differences between the three coatings. Potentiodynamic polarization and impedance measurements were carried out to study the effect of the corrosion resistance of the synthesis in 10 mM NaCl solution.

Characterization of Ceramics Coatings Processed by Sol-Gel for Cutting Tools

In order to obtain better cutting tool performance, the coatings appear as an alternative in the machining process. The goal of the coating is to improve tribological conditions in the chip-tool and tool-workpiece interfaces. On the other hand, the use of coated tools decreases the wear of the tools. This study discusses the ceramic coatings characterization deposited in WC tools. The Al2O3 and TiO2 films present properties such as thermal stability, chemical inertia, high hardness, and good mechanical properties. These coatings were prepared by sol-gel technology. The results indicated that the multilayer coating presents better adhesion on the substrate. Moreover, lower coefficients of friction were found for the coated tools. The analysis of variance (ANOVA) was used to evaluate the influence of the cutting parameters and tool coating on the cutting force. The lower cutting force was obtained using the multilayer-coated tool. Thus, the sol-gel method appears as a novel technique to deposit coating in the WC tools to improve their performance.

Determination of the fractal dimension of mesopores in metal-oxide structures obtained via sol-gel synthesis

The work is devoted to the development of a combined method of analyzing the porous structure of metal oxide materials. The method is based on a combination of fractal analysis from data obtained by the sorption method using a thermodynamic approach and fractal analysis of atomic force microscopy images. The objects under research are optically transparent materials of the SiO2 – SnO2 – ZnO system, obtained by the sol-gel technology.

Study of the influence of the ZnO:Al polycrystalline film morphology on the silver nanoparticles formation

The paper presents the results of the optical and structural properties studies of samples consisting of ZnO:Al (AZO) oxide films with an intermediate silver nanoparticles layer. Obtaining samples were carried out by the method of sol-gel technology using different types of composition, and the conditions for drying and final annealing of the samples were varied. The study of the samples optical properties consisted of the optical absorption spectra measurements, and their structural properties were determined by X-ray diffraction and small-angle X-ray scattering. Comparison of data obtained from measurements of optical and structural properties of samples confirmed the results obtained from modeling in the Comsol Multiphysics software. X-ray diffraction demonstrated that the AZO films have a polycrystalline structure and are highly textured in the [002] direction. Zinc oxide grains are 10-15 nm. Silver nanoparticles are the comparable with AZO grains and have dimensions of several tens of nanometers. An increase in the annealing temperature of the films leads to a redistribution of silver nanoparticles in the AZO film, the distance between the particles increases. Consequently, the effect of the plasmon eigenmodes of the nanoparticles prevails over the effect of the system of particles oscillations interacting with each other. The analysis of the coatings obtained by the method of small-angle X-ray scattering showed that nanoparticles in the AZO film form an ordered structure.

Physicochemical Processes of Fabricating Ceramic Materials Based on Nanopowders of Zirconium, Yttrium, Cerium, and Aluminum Oxides

When studying nanoceramics, it is necessary to constantly keep in mind the closest interrelation of their fabrication method, structure, and properties. Nanoceramic materials are used in various branches of technology as structural and functional materials. Nanoceramics are also widely used in medicine. They are harmless, stable, and have great affinity to living organisms. ZrO2-based nanoceramics have a lower elastic modulus than other oxide materials. The specificity of their application lies in their high rupture strength, thermal shock resistance, and chemical stability at high temperatures. However, it is necessary to solve the problem of increasing the fracture toughness of ZrO2-based ceramic materials. The complex alloying of ZrO2 with yttrium and cerium oxides and the use of the Al2O3 additive leads to an increase in the fracture toughness and lowering of the negative effect of materials in the biological medium. In this work, the physicochemical properties of ceramic powders and materials of the ZrO2–2Y2O3–4CeO2–Al2O3 system synthesized by the chemical deposition of inorganic precursors when applying the sol-gel technology are considered based on scientific data and experimental studies. Alloying pure zirconium oxide by stabilizing Y2O3 and CeO2 oxides and thermal hardening of Al2O3 ensure the conservation of the tetragonal structure at room temperature, which makes it possible to retard and control the crack resistance of the material under the load. Investigations into the influence of the sintering temperature and aluminum oxide content on the microstructure and grain size, as well as physicomechanical properties of ceramic materials of compositions ZrO2–2Y2O3–4CeO2 + 1 wt % Al2O3 and ZrO2–2Y2O3–4CeO2 + 3 wt % Al2O3, are carried out.

The effect of sol-gel process on the microstructure and particle size of ZrC–SiC composite powders

ZrC–SiC composite powders were successfully synthesized by the combination of sol-gel technology and carbothermal reduction. The characterization of these powders was conducted by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the important parameters of sol-gel process including the desiccant method, timing of introducing carbon source and heating-drying temperature on the final ZrC–SiC particle size and its distribution range were studied in details, and the mechanism of ZrC–SiC particles agglomeration and coalescence was also explored. The results show that the mean particle size increases with the heating-drying temperature rising, but introducing carbon source before gelation together with a freeze-drying treatment can produce the ultrafine ZrC–SiC composite powders having a minimum particle median diameter of 0.174 μm and the narrowest size distribution range.

Investigation of Gas-Sensitive Properties of Thin-Film Thermovoltaic Sensor Elements Based on Zinc Oxide

Systematic research on a new type of gas sensor devices based on the thermovoltaic effect in zinc oxide, inhomogeneously doped with impurities of variable valence, is presented in the article. The ZnO–ZnO–Me two-layer sandwich structure, in which the thermovoltaic effect is observed, is synthesized using sol–gel technology from sols by dissolving the inorganic zinc salt in alcohol and adding a surfactant, followed by the mixing and maturation of the sol. The lower layer of the nanostructure is formed from pure zinc oxide by immersing the substrate at ⅔ length in sol and drying. The upper layer of zinc oxide doped with copper or iron is formed by two or three immersions of the other end of the substrate by ⅔ length, followed by drying and annealing. It has been established that, based on the developed sensor device, it is possible to obtain an increased response to gas-analyzers (ethanol being an example).

The performance evaluation of nanostructured perovskite-type complex oxides GdBO3 (B = Fe, Co, Mn) for carbon monoxide hydrogenation

Nanostructured perovskite-type oxides GdBO3 (B = Fe, Co, Mn) synthesized by sol-gel technology, have been used as catalysts for the light olefins production by carbon monoxide hydrogenation. Perovskite materials were characterized using different techniques: XRD, SEM+EDX, BET, TG to study structure and morphology. Oxidation state of Fe and Mn was determined by XPS. The catalytic activity test was carried out in a continuous-flow mode with chromatographic analysis of the reaction mixture. It was found that the catalytic characteristics are determined by the nature of the metal in the B-site of perovskite. The specific catalytic activity increases in the series GdMnO3 <GdFeO3 <GdCoO3, and selectivity for olefins - in the reverse order.

Impact of high pressures during compaction of zirconia nanopowder on material structure formation

The study covers the effect of compaction pressure during semi-dry pressing of zirconia nanopowder partially stabilized with yttria in a steel mold on the phase composition and microstructure of compacts and samples sintered at 1400 °C for 2 hours. An aqueous solution of polyvinyl alcohol was used as a temporary process binder. According to X-ray fluorescence analysis, the content of yttria in the powder synthesized by sol-gel technology (precipitation with aqueous ammonia solution from water-ethanol solutions of the corresponding reagents with the agar-agar additive) was 3.2 mol.%. The paper provides the results obtained when studying compacts and sintered samples by Raman spectroscopy, optical and atomic force microscopy. It was found that the increase in their density is not a monotonous process. There is a critical compaction pressure interval of Р = 400÷450 MPa where a sharp change in the material porosity, pore shape and size, microstructure and phase composition occurs. A monoclinic phase was observed in compacted samples along with tetragonal zirconia. Its content varies with a variation in Р values. The grinding of material grains is associated with the agglomerate destruction process and actively occurs in the interval of Р = 350÷550 MPa. A similar effect was observed by other researchers during zirconia nanopowder compaction who suggested that the nanopowder system response to the effect of pressure is related to the influence on the water component (in this case, the temporary process binder) and is due to the transition of one water form to another at 10–25 °С and 400–700 MPa.

The Witten-Sander stochastic fractal approximation as the basis for a model of sensory response of multicomponent oxide nanomaterials to changes in environmental pressure

A model developed on the Witten-Sander fractal approximation of sensory response of vacuum sensors with sensitive elements, based on multicomponent oxide nanomaterials, is proposed. A key feature of the model is a mechanical contact of three-dimensional fractal aggregates consisting of conductive and non-conductive nanoparticles. It leads to the formation of a conductive channel, being a two-dimensional fractal. An agreement between the simulation results and experimental data for a two-component tin dioxide-silicon dioxide system with a labyrinthine structure, synthesized using the sol-gel technology, has been demonstrated in a wide range of pressures

Recent Applications of Molecularly Imprinted Sol-Gel Methodology in Sample Preparation.

Due to their selectivity and chemical stability, molecularly imprinted polymers have attracted great interest in sample preparation. Imprinted polymers have been applied for the extraction and the enrichment of different sorts of trace analytes in biological and environmental samples before their analysis. Additionally, MIPs are utilized in various sample preparation techniques such as SPE, SPME, SBSE and MEPS. Nevertheless, molecularly imprinted polymers suffer from thermal (stable only up to 150 °C) and mechanical stability issues, improper porosity and poor capacity. The sol-gel methodology as a promising alternative to address these limitations allowing the production of sorbents with controlled porosity and higher surface area. Thus the combination of molecularly imprinted technology and sol-gel technology can create influential materials with high selectivity, high capacity and high thermal stability. This work aims to present an overview of molecularly imprinted sol-gel polymerization methods and their applications in analytical and bioanalytical fields.

Directional Self-Assembly of Zinc Oxide Micro- and Nanowires

Approaches to the directional self-assembly of zinc oxide micro- and nanowires with the aid of centrifugal forces have been developed in the framework of a sol-gel technology. According to this, fibrous zinc oxide structures preliminarily formed in the sol are artificially ordered at the substrate periphery by means of high-rate centrifuging.

Synthesis of molecularly imprinted fluorescent probe based on biomass-derived carbon quantum dots for detection of mesotrione.

A novel fluorescent probe based on molecularly imprinted polymers (MIPs) coupled with carbon quantum dots (CQDs) was fabricated and successfully used for selective recognition of mesotrione. In this probe, the biomass-derived CQDs were prepared through a hydrothermal method using mango peels as carbon source, and the whole synthesis procedure was green without chemical reagents. The CQDs were encapsulated into MIPs by using sol-gel technology. After removal of the template molecule mesotrione, specific binding sites are formed and there is electrostatic attraction between the probe and the template molecule. The synthetic CQDs@MIPs were able to selectively capture the target mesotrione with fluorescence quenching via the specific interaction between mesotrione and the recognition cavities. The probe was used for determination of mesotrione in corn to verify the practicality of the proposed method. The detection limit of mesotrione was 4.7nmolL-1, and the linear range was 15nmolL-1 to 3000nmolL-1. Meanwhile, the recoveries of this method for mesotrione were 91.4-96.2%, and the relative standard deviations (RSDs) were 3.2-6.1%. This work provides a novel research method to synthesize CQDs@MIPs with high selectivity (imprinting factor = 5.6), and which can be used for convenient, rapid recognition and sensitive detection of trace compounds from complex matrices.