Search Results (24)

The limited oxidation resistance of MoSi₂ between 400 °C and 600 °C restricts its aerospace applications. This study develops a silica-sol derived core-shell MoSi₂@SiO₂ composite to enhance the low-temperature oxidation resistance of MoSi₂. Acidic, neutral, and basic silica sols were systematically applied to coat MoSi₂ powders through sol-adsorption encapsulation. Two pathways were used, one was ethanol-mediated dispersion, and the other was direct dispersion of MoSi₂ particles in silica sol. Analysis demonstrated that ethanol-mediated dispersion significantly influenced the coating efficiency and oxidation resistance, exhibited significantly decreased coating weight gains (maximum 27%) and increased oxidation weight gains (10–20%) between 340 °C and 600 °C compared with direct dispersion of MoSi₂ particles with silica sol, ascribe to the kinetic inhibition of hydroxyl group condensation and steric hindrance of MoSi₂-silica sol interface interactions of ethanol. Systematic investigation of silica sol encapsulation of MoSi₂ revealed critical correlations between colloid properties and oxidation resistance of MoSi₂@SiO₂. Basic silica sol coated MoSi₂ (BS-MoSi₂) exhibits the lowest coating efficiency (coating weight gain of 7.74 ± 0.06%) as well as lowest oxidation weight gain (18.45%) between 340 °C and 600 °C compared with those of acid and neutral silica sol coated MoSi₂ (AS-MoSi₂ and NS-MoSi₂), arises from optimal gelation kinetics, enhanced surface coverage via reduced agglomeration, and suppressed premature nucleation through controlled charge interactions under alkaline conditions. Full article

Organic–inorganic hybrid dielectric nanomaterials are vital for OTFT applications due to their unique combination of organic dielectric and inorganic properties. Despite the challenges in preparing stable titania (TiO₂) nanoparticles, we successfully synthesized colloidally stable organic–inorganic (O-I) TiO₂ hybrid nanoparticles using an amphiphilic polymer as a stabilizer through a low-temperature sol–gel process. The resulting O-I TiO₂ hybrid sols exhibited long-term stability and formed a high-quality dielectric layer with a high dielectric constant (κ) and minimal leakage current density. We also addressed the effect of the ethylene oxide chain within the hydrophilic segment of the amphiphilic polymer on the dielectric properties of the coating film derived from O-I TiO₂ hybrid sols. Using the O-I TiO₂ hybrid dielectric layer with excellent insulating properties enhanced the electrical performance of the gate dielectrics, including superior field-effect mobility and stable operation in OTFT devices. We believe that this study provides a reliable method for the preparation of O-I hybrid TiO₂ dielectric materials designed to enhance the operational stability and electrical performance of OTFTs. Full article

The colloidal stability of silica O-I hybrid sols that have a high degree of condensation could result in the formation of a hard coating film on a substrate, which could depend on the properties of solvents used in the sol-gel reaction. In this study, the effect of the solvent type on the colloidal stability and degree of condensation of the silica sols was investigated by preparing various silica O-I hybrid sols using different solvent mixtures composed of various aprotic and protic solvents in the presence of amphiphilic urethane acrylate. Silica sols prepared using the appropriate aprotic-protic solvent mixture showed a higher degree of condensation and long-term colloidal stability, which was confirmed using ²⁹Si-NMR and DLS. Furthermore, the coating film formed from these silica sols showed a remarkable hardness of 0.97 GPa, with a thickness of 4.76 µm confirmed using nanoindentation measurements. Full article

Thin, flat textile roofing offers negligible heat insulation. In warm areas, such roofing membranes are therefore equipped with metallized surfaces to reflect solar heat radiation, thus reducing the warming inside a textile building. Heat reflection effects achieved by metallic coatings are always accompanied by shading effects as the metals are non-transparent for visible light (VIS). Transparent conductive oxides (TCOs) are transparent for VIS and are able to reflect heat radiation in the infrared. TCOs are, e.g., widely used in the display industry. To achieve the perfect coatings needed for electronic devices, these are commonly applied using costly vacuum processes at high temperatures. Vacuum processes, on account of the high costs involved and high processing temperatures, are obstructive for an application involving textiles. Accepting that heat-reflecting textile membranes demand less perfect coatings, a wet chemical approach has been followed here when producing transparent heat-reflecting coatings. Commercially available TCOs were employed as colloidal dispersions or nanopowders to prepare sol–gel-based coating systems. Such coatings were applied to textile membranes as used for architectural textiles using simple coating techniques and at moderate curing temperatures not exceeding 130 °C. The coatings achieved about 90% transmission in the VIS spectrum and reduced near-infrared transmission (at about 2.5 µm) to nearly zero while reflecting up to 25% of that radiation. Up to 35% reflection has been realized in the far infrared, and emissivity values down to ε = 0.5777 have been measured. Full article

Porous Nb₂O₅ films obtained by a modified hard-template method were studied and their optical and sensing properties were optimized in order to find applications in chemo-optical sensing. Porous films were prepared by following three steps: liquid mixing of niobium sol and SiO₂ colloids in different volume fractions, thermal annealing of spin-coated films for formation of a rigid niobia matrix, and selective removal of silica phase by wet etching thus generating free volume in the films. The morphology and structure of the films were studied using transmission electron microscopy and selected area electron diffraction, while their optical and sensing properties were estimated using UV-VIS-NIR reflectance measurements in different ambiences such as air, argon and acetone vapors and nonlinear curve fitting of the measured reflectance spectra. Bruggeman effective medium approximation was applied for determination of the volume fraction of silica and air in the films, thus revealing the formation of porosity inside the films. For further characterization of composite films, their water contact angles were measured and finally conclusions about the impact of initial chemical composition and etching duration on properties of the films were drawn. Full article

In this study, we developed a filtering material for facial masks, which is capable of trapping and subsequent inactivation of bacteria under white light emitting diodes (LED) or sunlight irradiation. Such a functionality is achieved via the modification of the composite membrane based on porous polymer with photocatalytic (TiO₂) and plasmonic (Ag) nanoparticles. The porous polymer is produced by means of a computer numerical control machine, which rolls a photoresist/thermoplastic mixture into a ~20-µm-thick membrane followed by its thermal/ultraviolet (UV) hardening and porosification. TiO₂ nanoparticles are prepared by hydrothermal and sol-gel techniques. Colloidal synthesis is utilized to fabricate Ag nanoparticles. The TiO₂ photocatalytic activity under UV excitation as well as a photothermal effect generated by plasmonic Ag nanoparticles subjected to LED irradiation are studied by the assessment of methylene blue (MB) decomposition. We demonstrate that, in contrast to the filter of the standard facial medical mask, the polymer membrane modified with spray-coated TiO₂ and Ag nanoparticles prevents the penetration of bacillus subtilis from its top to bottom side and significantly inhibits bacterial growth when exposed to LED or sunlight. Full article

In this current study, facile, one-pot synthesis of functionalised nanocomposite coating with simultaneous hydrophilic and oleophobic properties was successfully achieved via the sol–gel technique. The synthesis of this nanocomposite coating aims to develop a highly efficient, simultaneously oleophobic-hydrophilic coating intended for polymer membranes to spontaneously separate oil-in-water emulsions, therefore, mitigating the fouling issue posed by an unmodified polymer membrane. The simultaneous hydrophilicity-oleophobicity of the nanocoating can be applied onto an existing membrane to improve their capability to spontaneously separate oil-in-water substances in the treatment of oily wastewater using little to no energy and being environmentally friendly. The synthesis of hybrid chitosan–silica (CTS-Si)/halloysite nanotube (HNT) nanocomposite coating using the sol–gel method was presented, and the resultant coating was characterised using FTIR, XPS, XRD, NMR, BET, Zeta Potential, and TGA. The wettability of the nanocomposite coating was evaluated in terms of water and oil contact angle, in which it was coated onto a polymer substrate. The coating was optimised in terms of oil and water contact angle using Response Surface Modification (RSM) with Central Composite Design (CCD) theory. The XPS results revealed the successful grafting of organosilanes groups of HNT onto the CTS-Si denoted by a wide band between 102.6–103.7 eV at Si^2p. FTIR spectrum presented significant peaks at 3621 cm⁻¹; 1013 cm⁻¹ was attributed to chitosan, and 787 cm⁻¹ signified the stretching of Si-O-Si on HNT. ²⁹Si, ²⁷Al, and ¹³H NMR spectroscopy confirmed the extensive modification of the particle’s shells with chitosan–silica hybrid covalently linked to the halloysite nanotube domains. The morphological analysis via FESEM resulted in the surface morphology that indicates improved wettability of the nanocomposite. The resultant colloids have a high colloid stability of 19.3 mV and electrophoretic mobility of 0.1904 µmcm/Vs. The coating recorded high hydrophilicity with amplified oleophobic properties depicted by a low water contact angle (WCA) of 11° and high oil contact angle (OCA) of 171.3°. The optimisation results via RSM suggested that the optimised sol pH and nanoparticle loadings were pH 7.0 and 1.05 wt%, respectively, yielding 95% desirability for high oil contact angle and low water contact angle. Full article

To mitigate the damage of oil spills, a filter modified with a hydrophilic and oleophobic coating is proposed for affordable and efficient oil separation and recovery from water. The sol–gel method was chosen to produce a colloidal suspension of titanium dioxide particles for its ease of production and its versatility in application for many different substrates, including paper and cloth fabric. After immersing the substrates into a titanium-containing solution, three techniques were applied to increase the production of titanium dioxide—microwave-assisted, refrigeration, and ultra-sonication. Contact angle tests were done to investigate the change in the filter’s oleophobicity. The titanium dioxide present on the surface of the filter was amorphous, but all treatment methods showed an improvement in oleophobicity. All treated filters improved oil filtration performance by up to eighty percent. The filters isolated motor oil from a mixture while allowing water to pass through. The coated filters also displayed photocatalytic activity by degrading methylene blue on its surface when exposed to sunlight, demonstrating the filter’s self-cleaning ability. For real-world applications, the filter can be supported by a stainless mesh for enhanced strength and durability. While being dragged through the water, the filter collects the surface oil, allowing water to pass through via gravity. Full article

Zirconium oxide (ZrO₂) is a well-studied and promising material due to its remarkable chemical and physical properties. It is used, for example, in coatings for corrosion protection layer, wear and oxidation, in optical applications (mirror, filters), for decorative components, for anti-counterfeiting solutions and for medical applications. ZrO₂ can be obtained as a thin film using different deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). These techniques are mastered but they do not allow easy micro-nanostructuring of these coatings due to the intrinsic properties (high melting point, mechanical and chemical resistance). An alternative approach described in this paper is the sol-gel method, which allows direct micro-nanostructuring of the ZrO₂ layers without physical or chemical etching processes, using optical or nano-imprint lithography. In this paper, the authors present a complete and suitable ZrO₂ sol-gel method allowing to achieve complex micro-nanostructures by optical or nano-imprint lithography on substrates of different nature and shape (especially non-planar and foil-based substrates). The synthesis of the ZrO₂ sol-gel is presented as well as the micro-nanostructuring process by masking, colloidal lithography and nano-imprint lithography on glass and plastic substrates as well as on plane and curved substrates. Full article

In the frame of the nanoarchitectonic concept, the objective of this study was to develop simple and easy methods to ensure the preparation of polymorphic HfO₂ thin film materials (<200 nm) having the best balance of patterning potential, reproducibility and stability to be used in optical, sensing or electronic fields. The nanostructured HfO₂ thin films with micropatterns or continuous morphologies were synthesized by two different methods, i.e., the micropatterning of sol-gel solutions by deep ultraviolet (DUV) photolithography or the electrophoretic deposition (EPD) of HfO₂ nanoparticles (HfO_2-NPs). Amorphous and monoclinic HfO₂ micropatterned nanostructured thin films (HfO_2-DUV) were prepared by using a sol-gel solution precursor (HfO_2-SG) and spin-coating process following by DUV photolithography, whereas continuous and dense monoclinic HfO₂ nanostructured thin films (HfO_2-EPD) were prepared by the direct EPD of HfO_2-NPs. The HfO_2-NPs were prepared by a hydrothermal route and studied through the changing aging temperature, pH and reaction time parameters to produce nanocrystalline particles. Subsequently, based on the colloidal stability study, suspensions of the monoclinic HfO_2-NPs with morphologies near spherical, spindle- and rice-like shapes were used to prepare HfO_2-EPD thin films on conductive indium-tin oxide-coated glass substrates. Morphology, composition and crystallinity of the HfO_2-NPs and thin films were investigated by powder and grazing incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-visible spectrophotometry. The EPD and DUV photolithography performances were explored and, in this study, it was clearly demonstrated that these two complementary methods are suitable, simple and effective processes to prepare controllable and tunable HfO₂ nanostructures as with homogeneous, dense or micropatterned structures. Full article

This study presents the development of a method for the washcoating of Ni/boehmite gels, prepared by the sol–gel process, onto the surface of a commercial ceramic monolith. Indeed, a cordierite monolith in a honeycomb shape was used as the substrate for the Ni/Al₂O₃ deposition. An experimental assembly was made in order to apply the coating on the cordierite surface. Different suspensions were used with various viscosities, and multiple coating parameters were tested as the withdrawal speed, or the number of impregnations. It was observed that the simple deposition of the Ni/boehmite gel led to the formation of coating. Different morphologies were observed, and defects were highlighted as cracks, coating-free areas or aggregates. Among the various parameters studied, the pH of the sol appeared to play a role even more important than the viscosity. Indeed, the sol acidified with nitric acid showed a coating which was almost free of cracks or of large aggregates. Moreover, the use of a slurry mix of calcined alumina particles and colloidal boehmite appeared also as an interesting path. The beneficial influence of the slurry was attributed to a better resistance of the coating against the stresses induced during drying, and a deviation of the cracks in the gels by slurry grains. Full article

V-TiO₂ photocatalyst with 0 ≤ V ≤ 20 mol% was prepared via the sol–gel method based on mixed oxide titanium–vanadium nanoparticles with size and composition control. The mixed oxide vanadium–titanium oxo-alkoxy nanonoparticles were generated in a chemical micromixing reactor, coated on glass beads via liquid colloid deposition method and underwent to an appropriate thermal treatment forming crystallized nanocoatings. X-ray diffraction, Raman, thermogravimetric and differential thermal analyses confirmed anatase crystalline structure at vanadium content ≤ 10 mol%, with the cell parameters identical to those of pure TiO₂. At a higher vanadium content of ~20 mol%, the material segregation began and orthorhombic phase of V₂O₅ appeared. The crystallization onset temperature of V-TiO₂ smoothly changed with an increase in vanadium content. The best photocatalytic performance towards methylene blue decomposition in aqueous solutions under UVA and visible light illuminations was observed in V-TiO₂ nanocoatings with, respectively, 2 mol% and 10 mol% vanadium. Full article

The purpose of this study was to comparatively investigate the behavior of silicate and sol-silicate coatings non-modified or modified with an organosilane on wood and on wood pre-coated with silica-mineralized primers. Adhesion strength, morphology, and water permeability and related damages were studied to evaluate the possibility of utilizing such inorganic-based coating systems for durable protection of wood without or with relatively cheap and water-borne primers. Potassium silicate and potassium methylsiliconate aqueous solutions and a colloidal silica were used for the preparation of the coatings. The white coating paints were brushed on beech wood substrates at a rate of 220 g·m⁻². The coatings exhibited good coverage ability. The pull-off adhesion strength values appeared to be related to pH following a polynomial law. The adhesion strength for the silicate coatings were adequate (above 3 MPa and up to 5 MPa) for wood, whereas the values for the sol-silicates were too low for practical applications. The adhesion values were in general higher for the samples cured in a climate room (23 ± 3 °C and 75 ± 2% relative humidity) than the samples cured in the ambient atmosphere of the laboratory (23 ± 3 °C and 25 ± 5% relative humidity). The presence of microdefects (cracks, holes) was revealed in the coating layers by optical and scanning electron microscopy. The surface roughness parameters assessed by confocal scanning laser microscopy were dependent on the magnification applied for their measurement. The arithmetic average roughness S_a was between 5 µm and 10 µm at magnification 5× and between 2.5 μm and 10 µm at magnification 20×. The maximum peak-to-valley height S_z confirmed the presence of open pores emerging through the coatings. The open pores constitute free pathways for water ingress through the coatings, and could explain the high water absorption of the coatings including the methysiliconate-containing silicate coating and despite the relatively high water contact angle and low wettability exhibited by this sample. The post-application of a hydrophobizing solution containing hexadecyltrimethoxysilane and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride considerably reduced the water permeability, while application of nanosilica-containing organic primers increased the adhesion for the coatings. Silicate coatings with adhesion great enough and resistance against water damages can be generated on wood even without a primer using low silica-to-alkali ratio binders and an organosilane additive. The sol-silicate coatings appear to be applicable only with a primer. The improvement of the paint formulations to control the formation of microcracks and open pores could be useful to reduce the liquid water permeability and increase durability. Otherwise, the application of a hydrophobizing treatment can be used for this purpose. Full article

Nowadays, numerous researches are being performed to formulate nontoxic multifunctional magnetic materials possessing both high colloidal stability and magnetization, but there is a demand in the prediction of chemical and colloidal stability in water solutions. Herein, a series of silica-coated magnetite nanoparticles (MNPs) has been synthesized via the sol-gel method with and without establishing an inert atmosphere, and then it was tested in terms of humic acids (HA) loading applied as a multifunctional coating agent. The influence of ambient conditions on the microstructure, colloidal stability and HA loading of different silica-coated MNPs has been established. The XRD patterns show that the content of stoichiometric Fe₃O₄ decreases from 78.8% to 42.4% at inert and ambient atmosphere synthesis, respectively. The most striking observation was the shift of the MNPs isoelectric point from pH ~7 to 3, with an increasing HA reaching up to the reversal of the zeta potential sign as it was covered completely by HA molecules. The zeta potential data of MNPs can be used to predict the loading capacity for HA polyanions. The data help to understand the way for materials’ development with the complexation ability of humic acids and with the insolubility of silica gel to pave the way to develop a novel, efficient and magnetically separable adsorbent for contaminant removal. Full article

Conventional therapies to treat cancer often exhibit low specificity, reducing the efficiency of the treatment and promoting strong side effects. To overcome these drawbacks, new ways to fight cancer cells have been developed so far focusing on nanosystems. Different action mechanisms to fight cancer cells have been explored using nanomaterials, being their remote activation one of the most promising. Photo- and sonodynamic therapies are relatively new approaches that emerged following this idea. These therapies are based on the ability of specific agents to generate highly cytotoxic reactive oxygen species (ROS) by external stimulation with light or ultrasounds (US), respectively. Crystalline (TiO₂) and amorphous titania (a-TiO₂) nanoparticles (NPs) present a set of very interesting characteristics, such as their photo-reactivity, photo stability, and effective bactericidal properties. Their production is inexpensive and easily scalable; they are reusable and demonstrated already to be nontoxic. Therefore, these NPs have been increasingly studied as promising photo- or sonosensitizers to be applied in photodynamic/sonodynamic therapies in the future. However, they suffer from poor colloidal stability in aqueous and biological relevant media. Therefore, various organic and polymer-based coatings have been proposed. In this work, the role of a-TiO₂ based NPs synthesized through a novel, room-temperature, base-catalyzed, sol-gel protocol in the generation of ROS and as an enhancer of acoustic inertial cavitation was evaluated under ultrasound irradiation. A novel biomimetic coating based on double lipidic bilayer, self-assembled on the a-TiO₂-propylamine NPs, is proposed to better stabilize them in water media. The obtained results show that the biomimetic a-TiO₂-propylamine NPs are promising candidates to be US responding agents, since an improvement of the cavitation effect occurs in presence of the developed NPs. Further studies will show their efficacy against cancer cells. Full article