Sol-gel Matrix Research Articles

Glass-ceramic materials: influence of fluoride nanocrystals on emission properties of lanthanide ions

In this work, the oxyfluoride glass-ceramic materials containing LaF3 nanocrystals, prepared by using the sol-gel method, were described. The influence of fluoride nanocrystals on the photoluminescence properties of selected lanthanide ions was determined. The experimental results obtained for nano-glass-ceramics were compared to the precursor xerogels. Those Ln3+-doped sol-gel materials with dispersed LaF3 nanocrystals exhibit several visible emission bands. It was observed that heat-treatment process caused the elongation of the lifetimes of the 5D0 state from τ = 0.22 ms to τ1 = 0.79 ms, τ2 = 9.76 ms (for Eu3+-doped materials) and of the 4F9/2 state from τ = 0.027 ms to τ1 = 0.034 ms, τ2 = 1.731 ms (for Dy3+‑doped materials). The performed studies clearly revealed that luminescence behaviour also depends on an activator concentration and a distribution of energy levels of lanthanide ions.

Selectivity of a Bioreceptor Element of the Sensor Based on an Organosilicon Material and Microorganism Cells

The yeast cells from Ogataea polymorpha, Blastobotrys adeninivorans, and Debaryomyces hansenii were immobilized on an organosilicon material by the sol-gel method, resulting in a hybrid biocatalyst. The catalytic activity of the immobilized mixture of microorganisms was evaluated using it as a bioreceptor element in a biosensor. The proposed biohybrid material, consisting of the yeast association immobilized on the organosilicate sol-gel matrix, exhibited broad substrate specificity. Thus, the immobilization of multiple yeast strains provides a heterogeneous catalyst able to biologically oxidize a wide range of organic compounds commonly found in wastewater and surface water.

Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems

The results are summarised of the Seventh International Conference of CIS countries “Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems “Sol-gel 2023”, the key reports are discussed within the scientific sections: Theoretical aspects of sol-gel process; Films, coatings and membranes obtained using sol-gel technology; Hybrid organic-inorganic sol-gel materials; Xerogels, glasses and bulk ceramic materials synthesized by sol-gel method; Nano- and microstructured materials, nanotechnology; Methods of research of structure and properties of materials obtained using sol-gel synthesis.

Hybrid Activity of P–Si–N Moieties for Improved Fire Retardancy of Cotton Fabric Coated Using Sol-Gel Process

A sol-gel matrix was generated from S– and P-based acids to prepare a fire-retardant solution system for coating natural cotton fibers. The physical properties, surface morphology, and elemental composition of the coated samples were assessed using optical scanning electron microscopy. The thermal behavior of the coated samples was documented using TGA and VFT tests, which confirmed higher thermal stability of the phosphate-based coatings. High char residue formation (~44.5%) and self-extinguishing properties were observed for the phosphate-based coating under non-curing conditions. The superior properties of phosphate-based coatings P5-4h could be ascribed to the collaborative effect of P–Si–N—i.e., the combined activity during the combustion process and pyrolysis of the coated sample.

Cellular Automata Coupled with Two‐Phase Lattice Boltzmann Model for Modeling of Kinetics of Formation and Structure of Silica‐Based Sol–Gel Materials

A numerical model describing the sol–gel process on a mesoscopic scale is presented. The model is implemented as a cellular automaton‐based system, specifically reaction‐limited aggregation merged with two‐phase lattice Boltzmann method, which allows to describe the sol–gel process together with microscopic phase separation occurring during this process. The influence of model parameters on the structural properties of the resulting gel porosity, mesoporosity, and specific surface area, as well as on the kinetics of the gelation process: the shape of the kinetics curve and the structure formation time, is examined. It is proposed to combine the model parameters with the composition of the reaction mixture (the content of individual reagents and catalysts) and the process conditions.

Fabrication of luminescent disc-shaped microstructures via wet-chemical etching of hybrid sol–gel layers for potential photonic applications

Sol–gel materials based on SiO2 and TiO2 precursors are attractive as a new platform for planar photonics. Particularly interesting are those based on organically modified silica (ORMOSIL), which may improve the luminescent properties of organic dyes. However, their microstructurization remains a challenge as it requires optimization of various technological stages. Here, we report the structurization of thin layers based on ORMOSIL precursor and titanium(IV) ethoxide (TET) containing luminescent rhodamine B (RhB) dye. Films were fabricated using sol–gel synthesis and dip-coating method. Depending on the time of annealing performed at 200 °C, layers with different thicknesses (300–760 nm) and refractive indices (RI) (1.51–1.68) were obtained. Combining photolithography and wet-chemical etching processes made it possible to fabricate well-separated sol–gel waveguides and discs of different diameters. The etching time in buffered hydrofluoric acid (BHF) affected the depth of the etched luminescent microstructures. Additionally, it was found that a longer layer’s annealing time increased the etching selectivity of the substrate over the sol–gel layer. This enabled the obtaining of under-etched sol–gel goblet microstructures. Selected samples were investigated using scanning electron microscopy (SEM). UV–Vis photoluminescence measurements showed that long heat treatment also influenced the emission spectrum’s shape. The stability of the films under ambient conditions was established using spectroscopic ellipsometry. It was proven that films heat-treated at 200 °C did not change their properties during storage time of around 2 months. Relatively high RI, luminescent properties, and structurization potential make these microstructures interesting for application in integrated photonic devices, e.g., light amplifiers or sensing systems.

Development of a Paper-Based Sol–Gel Vapochromic Sensor for the Detection of Vapor Cross-Contamination within a Closed Container

Contamination of trace levels of volatile organic compounds (VOCs) in enclosed spaces is not usually a significant cause for concern; however, it can be relevant in the case of canine scent detection training as a canine’s superior sense of smell makes them highly likely to detect low levels of contamination, contributing to inefficient training. Thus, herein, we address the need for a simple, low-cost, robust, vapochromic sensor to determine the cross-contamination of VOCs within closed containers, such as canine training aid kits. This study focuses on the development of a vapor sensor, which produces a rapid colorimetric change when a target chemical vapor is present. A pH indicator is used as the colorimetric dye and its incorporation into a sol–gel matrix on a paper substrate is confirmed via SEM characterization. The sensor’s stability and performance is tested against exposure to various levels of sunlight and temperature. The design allows the sensor to present a clear and unambiguous visible response to the release of the volatile target within a closed container. It can be readily incorporated into existing training kits and functions as a straightforward reminder of when training aids need to be changed or a new containment system should be considered.

The photoluminescence studies of Gd3+/Tb3+ co-doped xerogels and nano-glass-ceramics dedicated for green-emitting devices

In this work, we reported the results of photoluminescent and structural investigations of Gd3+/Tb3+ co-doped silicate xerogels as well as derivative SiO2-LaF3 nano-glass-ceramics. The molar ratio of appropriate acetates used during the synthesis, i.e., La(AcO)3:Gd(AcO)3:Tb(AcO)3 was fixed to x:(0.95-x):0.05. Based on XRD measurements, the crystallization of hexagonal LaF3 nanophase was verified without any admixture of GdF3 phase, even for samples with La3+:Gd3+ molar ratio ≤1. The optical characterization of fabricated Gd3+/Tb3+ co-doped sol-gel materials involved the registration and analysis of photoluminescence excitation (PLE) and emission spectra (PL), as well as the decay curves for the 6P7/2 (Gd3+) and the 5D4 (Tb3+) excited levels. Upon excitation at λex = 275 nm wavelength, the fabricated sol-gel samples revealed the series of emission lines assigned to the electronic transitions from both dopants, i.e., Gd3+ and Tb3+, indicating apparently the occurrence of Gd3+/Tb3+ energy transfer process (ET). The photoluminescence measurements comprehensibly proved the competitiveness between Gd3+ and Tb3+ ions to be entered into LaF3 fluoride nanocrystal lattice, formed during annealing of as-prepared xerogels. Based on the recorded PL spectra for fabricated sol-gel samples, some chromatic parameters were calculated, i.e., chromaticity coordinates (CIE), correlated color temperatures (CCT), and color purities (CP). The prepared Gd3+,Tb3+ co-doped samples are able to emit green light with CCT values in a range from 5967 K to 6291 K, and high CP reached 70 %, which predispose them for use as efficient constituents for developing green-emitting devices.

Spectroscopic Analyses and the Influence of Concentration on the Photoluminescence Characteristics of Sm+3-Doped Silica Sol-Gel matrix

Spectroscopic Analyses and the Influence of Concentration on the Photoluminescence Characteristics of Sm+3-Doped Silica Sol-Gel matrix

Chiral Nanostructured Glycerohydrogel Sol-Gel Plates of Chitosan L- and D-Aspartate: Supramolecular Ordering and Optical Properties.

A comprehensive study was performed on the supramolecular ordering and optical properties of thin nanostructured glycerohydrogel sol-gel plates based on chitosan L- and D-aspartate and their individual components in the X-ray, UV, visible, and IR ranges. Our comparative analysis of chiroptical characteristics, optical collimated transmittance, the average cosine of the scattering angle, microrelief and surface asymmetry, and the level of structuring shows a significant influence of the wavelength range of electromagnetic radiation and the enantiomeric form of aspartic acid on the functional characteristics of the sol-gel materials. At the macrolevel of the supramolecular organization, a complex topography of the surface layer and a dense amorphous-crystalline ordering of polymeric substances were revealed, while at the nanolevel, there were two forms of voluminous scattering domains: nanospheres with diameters of 60-120 nm (L-) and 45-55 nm (D-), anisometric particles of lengths within ~100-160 (L-) and ~85-125 nm (D-), and widths within ~10-20 (L-) and ~20-30 nm (D-). The effect of optical clearing on glass coated with a thin layer of chitosan L-(D-)aspartate in the near-UV region was discovered (observed for the first time for chitosan-based materials). The resulting nanocomposite shape-stable glycerohydrogels seem promising for sensorics and photonics.

Eu-substituted hydroxyapatite/silica sol-gel treatment for corrosion protection of AZ31 magnesium alloy

Europium-hydroxyapatite (Eu-HA) nanocomposite was developed via continuous hydrothermal synthesis. Eu+3 ions partially replaced the Ca+2 ions within hydroxyapatite molecular structure. High quality Eu-HA nanorods of 20 nm width and 6 μm lengths were verified via TEM micrographs. Eu-HA maintained the crystalline structure of HA with minimum change; material studio software confirmed the partial replacement of Ca+2 by Eu+3. XPS analysis demonstrated Eu+3 content of 6.91 atom %. Ca/P ratio was found to be 1.405 and 0.118 for virgin HA and Eu-HA respectively; this was ascribed to the partial replacement of Ca+2 with Eu +3. The EDAX mapping verified the uniform dispersion of Eu ions within Eu-HA structure. Eu-HA nanocomposite was uniformly distributed in silica sol-gel matrix; subsequently it was applied on AZ31 magnesium alloy. The corrosion performance of Eu-HA sol-gel coating nanocomposite (Eu–S) was evaluated using different electrochemical techniques including Potentiodynamic Polarization (PDP), Electrochemical Impedance Spectroscope (EIS), and Electrochemical Noise (EN) in aerated 0.1 M NaCl solution. Corrosion protection was assessed to that of neat silica sol-gel coating (NSG). Pitting was detected over the whole NSG coated sample, after few hours of immersion in the corrosive solution. EuS coated AZ31 withstand up to 144 h without any sign of corrosion or delamination. EIS analysis with PDP parameters suggested the formation of protective layer; that is responsible for the corrosion resistance. Europium has unique ability to form a protective oxide layer acting as a barrier layer that could prevent the penetration of corrosive electrolyte to the underlying metal substrate.

Determination of hazardous vapors from the thermal decomposition of organochlorinated silica xerogels with adsorptive properties

The incorporation of organic groups into sol-gel silica materials is known to have a noticeable impact on the properties and structure of the resulting xerogels due to the combination of the properties inherent to the organic fragments (functionality and flexibility) with the mechanical and structural stability of the inorganic matrix. However, the reduction of the inorganic content in the materials could be detrimental to their thermal stability properties, limiting the range of their potential applications. Therefore, this work aims to evaluate the thermal stability of hybrid inorganic-organic silica xerogels prepared from mixtures of tetraethoxysilane and organochlorinated triethoxysilane precursors. To this end, a series of four materials with a molar percentage of organochlorinated precursor fixed at 10%, but differing in the type of organic group (chloroalkyls varying in the alkyl-chain length and chlorophenyl), has been selected as model case study. The gases and vapors released during the thermal decomposition of the samples under N2 atmosphere have been analyzed and their components determined and quantified using a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrophotometer and to a gas chromatography-mass spectrometry unit. These analyses have allowed to identify up to three different thermal events for the pyrolysis of the organochlorinated xerogel materials and to elucidate the reaction pathways associated with such processes. These mechanisms have been found to be strongly dependent on the specific nature of the organic group.

Holographic multiplexing in a photopolymerisable hybrid sol-gel

Holographic multiplexing techniques enhance functionality and information storage by leveraging the inherent selectivity of holograms. This is crucial for advancing holographic sensors, which excel in simultaneously detecting multiple parameters from a single input signal. This study explores the potential of the recent photopolymerisable hybrid sol-gel (PHSG) material for application in Space sensing systems through the investigation of its holographic angular multiplexing capabilities. For the first time, to the best of our knowledge, we report the successful recording of up to five angularly multiplexed gratings with diffraction efficiencies (DE) ≥ 15% in 187 ± 18 µm PHSG layers. A 3 mW/cm2 laser beam was used to record gratings (0–20° angular separation) with a spatial frequency of 800 ± 20 lines/mm utilising different exposure times. The study revealed that each successive multiplexing in the single-layer region resulted in a decrease in the material's recording sensitivity. Holographic recording sensitivity and DE growth during the grating formation period depend on the number of gratings multiplexed in the layer. The seven-month-old, multiplexed gratings demonstrate consistent DE, stable angular selectivity and diffraction angle. This study positions the PHSG material as a promising candidate for developing reliable multiplexed devices.

Investigations on the Impact of a Series of Alkoxysilane Precursors on the Structure, Morphology and Wettability of an Established Zirconium-Modified Hybrid Anticorrosion Sol-Gel Coating.

The current study reports on the impact of a series of functional alkoxysilanes on the wettability and structure of a well-established silicon/zirconium hybrid anticorrosion sol-gel coating. The selected functional alkoxysilanes comprise tetra ethylorthosilicate (TEOS), 3-glycidyloxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES) and vinyltriethoxysilane (VTES) and are incorporated at various concentrations (1, 5, 10 and 20%) within the silicon/zirconium sol-gel material. The prepared materials are successfully processed as coatings and cured at different temperatures in the range of 100-150 °C. The characterisation of the structures and surfaces is performed by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), silicon nuclear magnetic resonance spectroscopy (29Si-NMR), atomic force microscopy (AFM) and static water contact angle (WCA). Structural characterisations (DLS, FTIR,29Si-NMR) show that the functional alkoxysilanes effectively bind at the surface of the reference sol-gel material, resulting in the formation of functional core-shell nanoparticles. WCA results show that the hydrophobic properties of all materials decrease with curing temperature, and AFM analysis demonstrated that this behaviour is associated with a decrease in roughness. The physico-chemical processes taking place are critically assigned and discussed.

BaHf0.05Ti0.95O3 Ceramics from Sol-Gel and Solid-State Processes: Application to the Modelling of Piezoelectric Energy Harvesters.

A typical piezoelectric energy harvester is a bimorph cantilever with two layers of piezoelectric material on both sides of a flexible substrate. Piezoelectric layers of lead-based materials, typically lead zirconate titanate, have been mainly used due to their outstanding piezoelectric properties. However, due to lead toxicity and environmental problems, there is a need to replace them with environmentally benign materials. Here, our main efforts were focused on the preparation of hafnium-doped barium titanate (BaHfxTi1-xO3; BHT) sol-gel materials. The original process developed makes it possible to obtain a highly concentrated sol without strong organic complexing agents. Sol aging and concentration can be controlled to obtain a time-stable sol for a few months at room temperature, with desired viscosity and colloidal sizes. Densified bulk materials obtained from this optimized sol are compared with a solid-state synthesis, and both show good electromechanical properties: their thickness coupling factor kt values are around 53% and 47%, respectively, and their converse piezoelectric coefficient d33∗ values are around 420 and 330 pm/V, respectively. According to the electromechanical properties, the theoretical behavior in a bimorph configuration can be simulated to predict the resonance and anti-resonance frequencies and the corresponding output power values to help to design the final device. In the present case, the bimorph configuration based on BHT sol-gel material is designed to harvest ambient vibrations at low frequency (<200 Hz). It gives a maximum normalized volumetric power density of 0.03 µW/mm3/Hz/g2 at 154 Hz under an acceleration of 0.05 m/s2.

Synthesis and Optical Properties of Erbium-Doped Sodium Silicate in Sol-Gel Matrix

In this study, we investigated how the concentration of erbium (0.0, 1, 2 mol% Er) affects the structural and optical properties of thin films made from sol-gel sodium silicate doped with erbium nitrate, thermally treated at 250 °C. Through systematic investigation, we explore the structural evolution and optical behavior of the thin films across varying Er3+ concentrations. The sol-gel demonstrated effective capabilities for substantial concentrations of Er3+ oxides through doping at lower calcination temperatures. The spectroscopic characteristics were studied using visible-near infrared spectroscopy (UV–vis–NIR), transmission electron microscopy, and Fourier transform infrared spectroscopy. Increasing the Er ratio decreased both the transmission and the energy band gap (3.6–3.34 eV) of the films while the absorption peak increased. The obtained results suggest that Er3+ activators demonstrate advantageous optical properties in the evaluated sodium silicate glass matrix. With the introduction of Er, optical transmittance ranges from 85 to 55% in the visible and near-infrared (NIR) regions, highlighting their advantageous characteristics. This research contributes to advancing the understanding of erbium-doped thin films for potential applications in optoelectronic devices and photonics.

Кислородный биокатод на основе laccase Pleurotus ostreatus HK-35 для биотопливного элемента

The main reasons that make mankind look for new sources of energy are decreasing dependence on fossil fuels and reducing pollution. Wastewater treatment with the help of microbial fuel cells is an area where these two goals can be combined. Microbial fuel cells, in which microorganisms catalyze the oxidation of organic substances, represent a new and promising alternative for electricity generation. The creation of an efficient cathode in such systems is the important problem. It is evident that in these applications an oxygen (air) electrode is a promising cathode. In this study, the oxygen biocathode based on the laccase enzyme Pleurotus ostreatus HK-35 was developed and its electrochemical properties were studied depending on the immobilization method of the enzyme on the surface of a carbon-graphite electrode and the type of the electrolyte. It was experimentally established that laccase injection using a sol-gel matrix was the effective method for immobilizing laccase on the surface of a carbon-graphite electrode. It was shown that the more efficient operation of the laccase-based biocathode was observed in a phosphate-citrate (pH 4.0) buffer solution, i.e., in an acidic environment.

Effectiveness of Thymol Blue and Phenolphthalein in Sol-Gel Coatings for Sensing and Inhibiting Corrosion on Mild Steel.

Development of smart coatings incorporated with corrosion indicators that can warn of corrosion through signaling the alteration of pH or metal-ion concentration at the corrosion site, and simultaneously mitigate further corrosion, stands out as a highly efficient and economical approach to address corrosion issues. In this context, the present work provides a comprehensive comparison on the effectiveness of thymol blue (TB) and phenolphthalein (PhPh) in both sensing and inhibiting corrosion on mild steel. While most of the works primarily focused on independently investigating the corrosion indication behavior of different active agents, our study intends to offer valuable insights through the comparative analysis of TB and PhPh in making well-informed decisions when selecting the most effective indicator for a given set of application scenarios. Initially, TB and PhPh were dissolved in a 3.5% NaCl solution, and their ability to indicate and inhibit corrosion on mild steel was verified through a drop test and an electrochemical study, respectively. An electrochemical study and a salt spray test were carried out to evaluate the corrosion sensing and inhibiting capabilities of the coating produced on a mild steel substrate by integrating TB and PhPh in the sol-gel matrix. The synergistic effect of TB and PhPh in sensing and inhibiting corrosion was also studied by combining TB and PhPh in the sol-gel matrix. It was found that TB-based coatings showed approximately 8 times better inhibiting performance (in terms of charge transfer resistance) when compared to PhPh-based coatings, while the PhPh-based coating was around 16 times more sensitive (with respect to concentration and time) in indicating corrosion when compared to TB-based coatings on a mild steel substrate. Nevertheless, the combination of TB and PhPh in a 1:3 ratio incorporated into the sol-gel coating exhibited increased sensitivity in detecting corrosion and showed improved corrosion inhibition on mild steel.

Numerical computation of magnetic field with melting heat and homogeneous-heterogeneous chemical reaction effects on oblique stagnation flow of variable viscosity micropolar Fe3O4 nanofluids

The complex micro-structural characteristics of electro-conductive sol gel materials require simultaneous consideration of magneto-hydrodynamics, micro-rheology and also physico-chemical phenomena. In this editorial, a mathematical model is therefore developed to simulate the steady-state, oblique (non-orthogonal) stagnation flow of electro-conductive micropolar magneto-nano-liquid flow impacting on an extending horizontal plane under the impact of transverse magnetic field. To capture the sophisticated physico-chemistry, the simultaneous presence of homogeneous and heterogeneous chemical reactions is considered. Viscosity depending upon temperature is taken into consideration with Reynolds’ exponential model. Tiwari-Das and Maxwell-Garnett nano-liquid models are deployed which modifies density, thermal conductivity and electrical conductivity with volume fraction of nano-sized particles.

Investigating sol–gel matrix loading capacity toward producing surrogate nuclear explosive debris with realistic composition

Investigating sol–gel matrix loading capacity toward producing surrogate nuclear explosive debris with realistic composition