Showing papers on "Sol-gel published in 2020"

Sol-Gel Synthesis of Spherical Mesoporous High-Entropy Oxides.

Abstract: High-entropy oxides (HEOs) have attracted increasing interest owing to their unique structures and fascinating physicochemical properties. Spherical mesoporous HEOs further inherit the advantages of spherical mesoporous materials including high surface area and tunable pore size. However, it is still a huge challenge to construct HEOs with uniform spheres and a mesoporous framework. Herein, a wet-chemistry sol-gel strategy is demonstrated for the synthesis of spherical mesoporous HEOs (e.g., Ni-Co-Cr-Fe-Mn oxide) with high specific surface area (42-143 m2/g), large pore size (5.5-8.3 nm), unique spherical morphology (∼55 nm), and spinel structure without any impure crystal phase using polyphenol as a polymerizable ligand. The metal/polyphenol-formaldehyde resin colloidal spheres are first synthesized via a sol-gel process. Because of their abundant catechol groups and strong chelating ability with different metal species, polyphenols can not only accommodate five different metal ions in their networks but also be well polymerized by formaldehyde to form colloidal spheres. After calcination, the metal species aggregate together to form HEOs, while the organic resin is fully decomposed to produce mesopores. Because of the open framework with accessible mesopores, they could be used as a peroxymonosulfate catalyst for degradation of organic pollutants and a nanoplatform for efficient detection of DNA. This work demonstrates a straightforward sol-gel strategy for design and synthesis of spherical mesoporous high-entropy materials, which would promote the exploration of new properties of high-entropy materials and extend their application.

Integrating sol-gel and carbon dots chemistry for the fabrication of fluorescent hybrid organic-inorganic films

Abstract: Highly fluorescent blue and green-emitting carbon dots have been designed to be integrated into sol-gel processing of hybrid organic-inorganic materials through surface modification with an organosilane, 3-(aminopropyl)triethoxysilane (APTES). The carbon dots have been synthesised using citric acid and urea as precursors; the intense fluorescence exhibited by the nanoparticles, among the highest reported in the scientific literature, has been stabilised against quenching by APTES. When the modification is carried out in an aqueous solution, it leads to the formation of silica around the C-dots and an increase of luminescence, but also to the formation of large clusters which do not allow the deposition of optically transparent films. On the contrary, when the C-dots are modified in ethanol, the APTES improves the stability in the precursor sol even if any passivating thin silica shell does not form. Hybrid films containing APTES-functionalized C-dots are transparent with no traces of C-dots aggregation and show an intense luminescence in the blue and green range.

Structural and Optical Properties of ZnO Thin Films Prepared by Molecular Precursor and Sol–Gel Methods

Abstract: Zinc oxide (ZnO) is a versatile and inexpensive semiconductor with a wide direct band gap that has applicability in several scientific and technological fields. In this work, we report the synthesis of ZnO thin films via two simple and low-cost synthesis routes, i.e., the molecular precursor method (MPM) and the sol–gel method, which were deposited successfully on microscope glass substrates. The films were characterized for their structural and optical properties. X-ray diffraction (XRD) characterization showed that the ZnO films were highly c-axis (0 0 2) oriented, which is of interest for piezoelectric applications. The surface roughness derived from atomic force microscopy (AFM) analysis indicates that films prepared via MPM were relatively rough with an average roughness (Ra) of 2.73 nm compared to those prepared via the sol–gel method (Ra = 1.55 nm). Thin films prepared via MPM were more transparent than those prepared via the sol–gel method. The optical band gap of ZnO thin films obtained via the sol–gel method was 3.25 eV, which falls within the range found by other authors. However, there was a broadening of the optical band gap (3.75 eV) in thin films derived from MPM.

Synthesis of high performance diesel oxidation catalyst using novel mesoporous AlLaZrTiOx mixed oxides by a modified sol-gel method

Abstract: High performance diesel oxidation catalyst (DOC) is achieved using novel Al2O3-LaAlO3-ZrO2-TiO2 (AlLaZrTiOx) mixed oxides and has been successfully fabricated by a modified sol-gel method. It is worth noting that novel AlLaZrTiOx mixed oxides own outstanding properties, such as mesoporous structure, high specific surface area, and thermal stability, which are confirmed by N2 adsorption-desorption, TEM, small-angle x-ray diffraction, and XRD spectrum. For these mixed oxides, temperature has a significant effect on their properties, for example, high specific surface area (206.5 m2/g) with a pore volume of 0.5 cc/g can be obtained by calcining at 700 °C for 4 h. Meanwhile, the possible synthesis mechanism of mesoporous AlLaZrTiOx mixed oxides was also discussed. Finally, the catalytic performances of Pt-Pd/AlLaZrTiOx catalyst and commercial catalyst were compared under the same simulated clean diesel combustion. Pt-Pd/AlLaZrTiOx catalyst demonstrated an excellent low temperature oxidation catalytic activity with the conversion of CO and total hydrocarbon (C3H6) reaching 90% at 196 °C and 200 °C, respectively. Specially, the conversion of NO reached 75% when the temperature was at around 200 °C.

Synthesis, structural and electrical properties of PVA/TiO 2 nanocomposite films with different TiO 2 phases prepared by sol–gel technique

Abstract: Titanium oxide (TiO2) nanoparticles were fabricated by using the sol–gel technique. By controlling the calcination temperature, the different structures of TiO2 (anatase and rutile) have been achieved which is considered a new technique for phase transformation. Moreover, PVA (polyvinyl alcohol)/TiO2 nanocomposite with various TiO2 phases was accomplished by room temperature casting method. The microstructure of TiO2 nanoparticles and its effect on the PVA amorphous phase was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The functional groups of PVA and TiO2 were inspected by Fourier transform infrared spectroscopy (FT-IR). SEM exhibits an agglomeration nature of TiO2 nanoparticles through the PVA matrix. In this study, the dc conductivity, as well as the transport properties such as activation energy, ions number in unit volume, hopping distance, and polaron's radius were discussed. In the light-temperature of the polaronic hopping conduction models, the electrical conductivity data were examined which is well-described by polaronic models. Besides, it is noted that the nonadiabatic small polaron hopping conduction is realized in this system. The density of state and the decay constant values are acceptable for the localized states.

A sol─gel synthesis to prepare size and shape-controlled mesoporous nanostructures of binary (II─VI) metal oxides

Abstract: A base-catalyzed sol–gel approach combined with a solvent-driven self-assembly process at low temperature is augmented to make manganese oxide (Mn3O4), copper oxide (CuO), and magnesium hydroxide (Mg(OH)2) nanostructures with size- and shape-controlled morphologies. Nanostructures of Mn3O4 with either hexagonal, irregular particle, or ribbon shape morphologies with an average diameter ranged from 100 to 200 nm have been prepared in four different solvent types. In all morphologies of Mn3O4, the experimental XRD patterns have indexed the nanocrystal unit cell structure to triclinic. The hexagonal nanoparticles of Mn3O4 exhibit high mesoporocity with a BET surface area of 91.68 m2 g−1 and BJH desorption average pore diameter of ∼28 nm. In the preparation of CuO nanostructures, highly nanoporous thin sheets have been produced in water and water/toluene solvent systems. The simulated XRD pattern matches the experimental XRD patterns of CuO nanostructures and indexes the nanocrystal unit cell structure to monoclinic. With the smallest desorption total pore volume of 0.09 cm3 g−1, CuO nanosheets have yielded the lowest BET surface area of 18.31 m2 g−1 and a BHJ desorption average pore diameter of ∼16 nm. The sol of magnesium hydroxide nanocrystals produces highly nanoporous hexagonal nanoplates in water and water/toluene solvent systems. The wide angle powder XRD patterns show well-defined Bragg's peaks, indexing to a hexagonal unit cell structure. The hexagonal plates show a significantly high BET surface area (72.31 m2 g−1), which is slightly lower than the surface area of Mn3O4 hexagonal nanoparticles. The non-template driven sol–gel synthesis process demonstrated herein provides a facile method to prepare highly mesoporous and nanoporous nanostructures of binary (II–IV) metal oxides and their hydroxide derivatives, enabling potential nanostructure platforms with high activities and selectivities for catalysis applications.

Novel approach of silica-PVA hybrid aerogel synthesis by simultaneous sol-gel process and phase separation

Abstract: In this study, a novel approach of silica-PVA hybrid aerogel synthesis is presented based on the simultaneous sol-gel reaction of the silica precursor tertramethoxysilane (TMOS) and thermally impacted non-solvent induced phase separation of polyvinyl alcohol (PVA). The method based on: (1) water from PVA solution is required for hydrolysis of TMOS; (2) methanol from TMOS solution, is a non-solvent for PVA. In the result of sol-gel reaction, phase separation and drying during extraction with supercritical CO2, the hybrid SiO2-PVA aerogels were obtained. Results indicated that, incorporation of the silica network into the PVA network caused an increase of the specific surface area up to 618 m2/g from 38.3–110 m2/g for pure PVA. The Young's modulus was associated with the bulk density. The obtained hybrid SiO2-PVA aerogels are a result of two phenomena – the chemical reaction of silica precursor (sol-gel process) and the physical transformation in PVA solution (phase separation).

Preparation and Characterization of Some Sol-Gel Modified Silica Coatings Deposited on Polyvinyl Chloride (PVC) Substrates

Abstract: Transparent and antireflective coatings were prepared by deposition of modified silica materials onto polyvinyl chloride (PVC) substrates. These materials were obtained by the sol-gel route in acidic medium, at room temperature (25 °C), using different alkoxysilanes with various functional groups (methyl, vinyl, octyl or hexadecyl). Physicochemical and microstructural properties of resulted silica materials and of thin coatings were investigated through Fourier Transforms Infrared Spectroscopy (FTIR), UV-Vis spectroscopy, Thermal Gravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA), Atomic Force Microscopy (AFM) and ellipsometric measurements. Wetting behaviors of the silica coatings were evaluated by measurement of static contact angle against water. FTIR spectra of materials confirmed the high degree of cross-linking that result from the formation of the inorganic backbone through the hydrolysis and polycondensation reactions together with the formation of the organic network. These sol-gel silica coatings showed a reduction in the reflectance (10%) compared with uncoated PVC substrate. AFM reveals that the films are uniform, and adherent to the substrate, but their morphology is strongly influenced by the chemical composition of the coating matrices. These silica coatings can be useful for potential electronic and optical devices.

Investigation of aluminum doping on structural and optical characteristics of sol–gel assisted spin-coated nano-structured zinc oxide thin films

Abstract: In this research, Al-doped (with 2, 4, 6, and 8 mol%) zinc oxide thin films deposited onto glass substrates using wet chemical spin coating technique were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and UV–Vis spectroscopic methods to realize the doping effect of Al on structural and optical properties of ZnO thin films. XRD analysis revealed that the Al-doped ZnO (AZO) thin films were polycrystalline in nature with hexagonal lattice structure, and crystallite growth along c-axis. SEM images on the film surface at lower Al content exhibited granular nanostructures. At higher Al content, the nanostructural features of ZnO thin films was observed to be diminished. The compositional analysis via EDS measurements indicated the presence of zinc, oxygen, and aluminium into the AZO thin films. AZO thin film containing 2 mol% Al exhibited higher transmittance of 97% and absorption edge at 385 nm in the visible region. Optical bandgaps of AZO thin films were varied within 3.30–3.37 eV. Noticeable variations on structural features, and optical parameters of AZO thin films were detected, and the changing trend showed was non-linear and non-monotonic in nature.

Microwave dielectric properties and optical transmittance of SrTiO3/ZnTiO3 heterolayer thin films fabricated by sol–gel processing

Abstract: SrTiO3/ZnTiO3 heterolayered thin films were fabricated by spin coating Sr–Ti and Zn–Ti sol–gel precursors on fused silica substrate. The SrTiO3 and ZnTiO3 were coated alternatively to form ABAB het...

Optical, electrical and electronic properties of SnS thin films deposited by sol gel spin coating technique for photovoltaic applications

Abstract: In the current study, thin films of tin sulfide (SnS) were grown by sol–gel spin-coating technique deposited on glass substrates. The obtained thin films were characterized using X-ray diffraction (XRD), photoluminescence (PL) and UV–Vis spectrometer and the four point technique, respectively. The effect of annealing temperature on the SnS properties has been studied. The XRD results reveal that the films annealed at 500 °C have good crystalline quality with orthorhombic phase. Fourier-transform infrared spectroscopy (FTIR) spectra shows the Sn–S bond. The photoluminescence spectra showed two categories of band emission. The optical parameters (α, e, n, k, Eg, and σop) were determined using UV–Vis spectroscopy. Moreover, the obtained results were compared to the theatricals results obtained with density functional theory (DFT) method using ab-initio approach. The optical and the electrical properties of the SnS Layers annealed at 400 °C and 500 °C offer the best possibility for their utilization in photovoltaic applications.

Precisely tailored synthesis of hexagonal hollow silica plate particles and their polymer nanocomposite films with low refractive index.

Abstract: Hollow silica particles are desirable for numerous applications, however, designing hollow silica materials with varying hollow structures and shapes remains a significant challenge. Herein, a strategy for the precisely controlled synthesis of hexagonal-shaped hollow silica plate (HHSP) particles was successfully prepared via a sol-gel method at room temperature, using tetraethyl orthosilicate (TEOS) as a silica precursor and zinc oxide (ZnO) particles as a colloidal template. The effect of reaction time was carried out to control the structure and morphology of HHSP particles, and the thickness of silica shell can be tuned in the range from 12.2 to 43.2 nm by adjusting the TEOS/ZnO molar ratios. In addition, the polymer/HHSP composite thin films were prepared using poly(methyl methacrylate) (PMMA) matrix and surface modified HHSP particles by grafting silane coupling agents. High transmittance values were observed (>95%) for the composite thin films (5 μm in thickness, 0.1–1.0 wt% HHSP) in the ultraviolet and visible regions. Furthermore, the refractive index of HHSP particles was observed to be 1.28, which is significantly lower than dense silica (n = 1.46). These results suggest that the approach adopted herein will open up opportunities for the development of a new generation of film materials with a low refractive index.

Sol-Gel-Derived Bioactive and Antibacterial Multi-Component Thin Films by the Spin-Coating Technique.

Abstract: Although metallic alloys commonly used as prosthetics are durable and mechanically strong, they are often bioinert and lack antibacterial properties. Implementing a bioactive glass material with antibacterial properties as a coating on a metallic substrate provides mechanical strength and bioactivity, as well as antibacterial properties. Many coating methods have been extensively investigated; however, most of them can be expensive, are difficult to scale up, or do not form thin films, which could prevent their translation to clinical practice. The formation of thin films by spin-coating multi-component solution-gelation (sol-gel)-derived glass with antibacterial and bioactive properties has not been achieved previously. For this study, stainless steel 316L substrates were spin-coated with a sol-gel-derived bioactive and antibacterial glass coating in SiO2 58.3-P2O5 7.1-CaO 25.6-Al2O5 5.4-Ag2O 2.1-Na2O 1.5 wt% system (Ag-BG). A sol-gel processing condition that avoids elemental separation upon spin-coating when sintering happens at below the calcination temperature (500 °C) has been developed. This work demonstrates that silver reduction occurs when the concentrations of other cations such as Ca2+ and Na+ in the solution increase. Increasing the stirring duration time prior to the increase of cations, Ag+ ions are stabilized by aluminum tetrahedra, and their reduction to metallic silver does not occur. This study also shows that large dilution ratios (water:tetraethyl orthosilicate) greater than 25:1, accompanied by long stirring durations, produce morphologically homogeneous coatings. Using this strategy, thin films were formed with antibacterial properties against methicillin-resistant Staphylococcus aureus (MRSA) biofilm and biological responses that promote eukaryotic cell adhesion and proliferation. In total, the improved synthesis strategy opens new avenues for the development of novel bioactive and antibacterial thin-film coatings, as it reveals the processing characteristics that control the physicochemical and morphological properties of the formed films.

Magnetic properties of (1 − x )Bi 0.5 Na 0.5 TiO 3 + x SrCoO 3 − δ solid-solution materials

Abstract: (1 − x)Bi0.5Na0.5TiO3 + xSrCoO3 − δ solid-solution system was synthesised through the simple sol–gel technique. X-ray diffraction and Raman scattering analyses were used to study the structure of (1 − x)Bi0.5Na0.5TiO3 + xSrCoO3 − δ system. Results showed that the SrCoO3 − δ materials dissolved well into the host Bi0.5Na0.5TiO3 crystal. The random incorporation of Sr and Co cations into the host Bi0.5Na0.5TiO3 crystal to form a solid solution resulted in reduced optical band-gap energy and induced the complex magnetic properties of host Bi0.5Na0.5TiO3 materials. The optical band-gap energy of pure Bi0.5Na0.5TiO3 materials was estimated to be approximately 3.09 eV, which decreased to 2.18 eV for 9 mol% SrCoO3 − δ solute incorporated into Bi0.5Na0.5TiO3 materials. The magnetic properties of Bi0.5Na0.5TiO3 materials were tuned as a function of SrCoO3 − δ concentration added into the host Bi0.5Na0.5TiO3 materials. The enhanced magnetic performance in SrCoO3 − δ-modified Bi0.5Na0.5TiO3 materials can be possibly applied in multifunction materials for electronic devices.