Acid-catalyzed Sol-gel Method Research Articles

Superhydrophilic antireflection films with excellent optical and mechanical performance for perovskite solar cells

SiO2-based antireflection (AR) films can obviously improve the transmittance of the glass cover on the solar cells. Nevertheless, it’s still challenging to fabricate SiO2 films in a facile way with great antireflective properties, high hardness and good weather resistance to ensure their long-term use in outdoor environments. To solve this problem, a double-layer broadband SiO2 antireflective film with high transmittance increase and excellent mechanical properties was successfully prepared via an acid-catalyzed sol–gel method using polyethylene glycol (PEG) as pore-forming agent. The porous PEG2000-modified SiO2 films were selected as the outer layer for coating onto the pure SiO2 film to form double-layer SiO2 films with graded refractive index. When the mass ratio of PEG2000 to TEOS was 40 %, the obtained film showed the highest transmittance increase of 3.03 % in the wavelength range of 380–1100 nm and a high hardness of 3H. After applied to the perovskite solar cell, a significant enhancement of 1.19 % in photoelectric conversion efficiency (PCE) was achieved compared to the solar cell covered with bare substrate. Furthermore, the water contact angle (WCA) was also reduced to 6° while that of pure SiO2 film was 51.3°, endowing the double-layer SiO2 film superhydrophilic and anti-fogging performance. After the weather resistance test, the transmittance loss of the film was only 0.38 %. Therefore, this work demonstrated that the use of an appropriate amount of pore-forming agent PEG and the double-layer graded refractive index structure can enhance the transmittance of acid-catalyzed SiO₂ films, while maintaining high hardness and good weathering resistance for perovskite solar cells.

Effect of Synthetic Low-Odor Thiol-Based Hardeners Containing Hydroxyl and Methyl Groups on the Curing Behavior, Thermal, and Mechanical Properties of Epoxy Resins

A novel thiol-functionalized polysilsesqioxane containing hydroxyl and methyl groups was synthesized using a simple acid-catalyzed sol–gel method to develop an epoxy hardener with low odor, low volatile organic compound (VOC) emissions, and fast curing at low temperatures. The synthesized thiol-based hardeners were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis (TGA), and gel permeation chromatography and compared with commercially available hardeners in terms of odor intensity and VOC emissions using the air dilution olfaction method and VOC analysis. The curing behavior and thermal and mechanical properties of the epoxy compounds prepared with the synthesized thiol-based hardeners were also evaluated. The results showed that synthetic thiol-based hardeners containing methyl and hydroxyl groups initiated the curing reaction of epoxy compounds at 53 °C and 45 °C, respectively. In contrast, commercial thiol-based hardeners initiated the curing reaction at 67 °C. Additionally, epoxy compounds with methyl-containing synthetic thiol-based hardeners exhibited higher TGA at a 5% weight loss temperature (>50 °C) and lap shear strength (20%) than those of the epoxy compounds with commercial thiol-based hardeners.

Effect of Modified Silica Materials on Polyvinyl Chloride (PVC) Substrates to Obtain Transparent and Hydrophobic Hybrid Coatings

In this research, we report a simple and inexpensive way to prepare transparent and hydrophobic hybrid coatings through deposition of different silica materials on polyvinyl chloride (PVC) substrates. The silica materials were prepared using an acid-catalyzed sol–gel method at room temperature (25 ± 2 °C), using alkoxysilanes: tetraethoxysilane (TEOS), as the silica source, and ethoxydimethylvinylsilane (DMVES), triethoxyoctylsilane (OTES), and trimethoxyhexadecylsilane (HDTMES), as modifier agents. The obtained materials were characterized (either as powders or as thin films) by Fourier-transform infrared spectroscopy (FTIR), UV/Vis spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and water contact-angle measurements. UV/Vis spectra showed that the PVC substrate coated with the silica material containing TEOS/DMVES/OTES had a transmittance of about 90% in the wavelength range of 650–780 nm. The water contact angles increased from 83° for uncoated PVC substrate to ~94° for PVC substrates coated with the sol–gel silica materials. These PVC films with hybrid silica coatings can be used as the materials for outdoor applications, such as energy-generating solar panel window blinds or PVC clear Windmaster outdoor blinds.

Fabrication and Characteristics of Methyl-Modified TiO2-SiO2 Membrane by Sol-Gel Method: Effect of Titania Content

Titania-doped methyl-modified silica membrane was prepared via an acid-catalyzed sol-gel method using tetraethylorthosilicate and methyltriethoxysilane as the silicon source and tetraethylorthosilicate as the titanium source. The influence of titanium/silicon molar ratio (nTi ) on the properties of TiO2-SiO2 sol and microstructure of unsupported TiO2-SiO2 membrane was systematically studied. The gas permeance and vapor stability of TiO2-SiO2 membrane were also tested. The results showed that, as nTi increased, the density, viscosity, refractive index and viscous activation Gibbs free energy of TiO2-SiO2 sol gradually decreased, while the particle size increased. The existence of Si-CH3 and Ti-O-Si bonds in TiO2-SiO2 membrane proved that the hydrophobic modification was successful and that SiO2 was chemically bonded to TiO2, respectively. The titanium element exists in form of Ti-O-Si structure and anatase phase TiO2 in TiO2-SiO2 membrane. When operated at 150 °C and a pressure difference of 0.3 MPa, the H2 permeance and H2/CO2 permselectivity of TiO2-SiO2 membrane with nTi =0.1 is 6.84 × 10−6 mol·m −2·Pa−1·s −1 and 6.96, respectively. After aging in the moist circumstance for 9 d, the H2 permeance of TiO2-SiO2 membrane reduced by 6.86%, while the H2/CO2 permselectivity increased by 2.71%.

Trimodal attributes within acidic mesostructured bioactive glass nanoparticles

This study reports the synthesis of multicomponent 80SiO2-15CaO-5P2O5 bioactive glass having a spherical morphology with an ordered mesoporous structure comprising of uniformly grown nanocrystals of apatite embedded within it. These nanospheres were synthesized through a centrifugation-assisted two step acid-catalyzed sol–gel method and were found to have a size range of 200–250 nm. The bulk crystallographic analysis together with microstructural characterizations reveals that the inorganic amorphous glass matrix is composed of nanocrystalline apatite domains. These nanoapatite domains those are dispersed throughout the matrix are found to influence the textural properties since the crystal growth of apatite interrupts the mesoporous structuring. Alongside the mesoporous ordering is observed to have a short range order. These particles find its potential use in drug delivery since spherical and also due to the apatite nanocrystals that can act as temporary barrier to prevent rapid release of drugs.

Theoretical and experimental characterization of Cu-doped amorphous silicate glass

The coordinative environment of Cu2+ ions incorporated in oxide glasses has been intensively studied for glasses doped with copper ions by melting or ion exchange. Much less is known about their coordination in a sol-gel derived silicate glass. Mesoporous silicate glasses doped with copper (II) ions coming from four different salts were synthesized by the acid-catalyzed sol-gel method. The electronic and structural states of copper sites were probed by optical and X-ray spectroscopies. The experimental observations were confronted with the results of quantum-chemical calculations. The theoretical models consisted of four- and five-coordinated Cu2+-complexes, where water ligands were sequently replaced with the SiO44‒ tetrahedra. The best agreement between the experimental and theoretical electronic spectra has been reached for the four-coordinated Cu2+-complex with a water molecule and three or four SiO44‒ tetrahedra. The energy band gap intervals of 4.21–4.61 eV and 4.09–4.23 eV were estimated graphically by the TAUC plot method and from quantum-chemical modelling, respectively.

Antireflective coating based on TiO2 nanoparticles modified with coupling agents via acid-catalyzed sol-gel method

TiO2 – based materials were synthesized via acid-catalyzed sol-gel method using tetraethoxysilane (TEOS) and/or methyltriethoxysilane (MTES) - as silane coupling agents. The physical and chemical properties of the obtained TiO2 – based materials were characterized through FT-IR and UV–Vis spectroscopy, TGA, AFM analysis and contact angle measurements. FT-IR spectra demonstrated that the silane coupling agents react via a cross-link and covalently bond on the TiO2 surface. TGA analysis of samples was used to investigate the effect of addition of silane precursor into the TiO2 matrix. Diffuse reflectance spectra revealed that the addition of silane agents improved the antireflective properties of obtained thin films. Water contact angle of TiO2 - based materials showed that the wettability of the thin films was influenced by the addition of TEOS and/or MTES during the modification process. AFM images showed smooth surfaces (RMS roughness up to 3 nm) but with morphological peculiarities depending on the chemical modification, with TEOS, MTES or both, of the TiO2 parental matrix. Transparent and hydrophobic coatings were obtained with MTES addition in the modification process of TiO2 nanoparticles via acid-catalyzed sol-gel method.

Fixed-Quat: An Attractive Nonmetal Alternative to Copper Biocides against Plant Pathogens.

In this paper, we report a nonphytotoxic bactericide and fungicide formulation containing a composite of silica and quaternary ammonium compound (quat). The composite material was prepared using an acid-catalyzed sol-gel method. Positively charged quat was associated with a negatively charged silica-gel matrix, producing a stable suspension of fixed-quat gel (FQ-G). The morphology of FQ-G and the interaction of quat with silica were characterized using SEM and FTIR, respectively. Silica gel significantly reduced quat phytotoxicity when tested at 500 and 1000 μg/mL foliar-application rates. The in vitro antimicrobial efficacy of FQ-G was evaluated against Xanthomonas alfalfae, Pseudomonas syringae, and Clavibacter michiganensis, showing comparable efficacies to that of quat itself. In field conditions, its efficacy in controlling the bacterial and fungal diseases citrus canker, scab, and melanose on 'Ray Ruby' red grapefruit was evaluated. Foliar application rates at 100 and 200 μg/mL provided comparable disease control to those of several copper standards, demonstrating the potential for use as an alternative agricultural biocide.

Antireflective mesoporous silica coatings by optimization of water content in acid-catalyzed sol-gel method for application in glass covers of concentrated photovoltaic modules

Porous silica layers with outstanding antireflective properties have been prepared by acid-catalyzed sol-gel process in presence of organic phases as structure directing agents (SDA) and excess water, with the aim of offering a cost-competitive, easy up-scaling and high efficiency process that contributes to reduce current levelized cost of energy (LCOE) of concentrating photovoltaics (CPV). The process has been optimized by controlling the water/alkoxide ratio, which is an important structure-regulating tool, having a strong influence in the structural properties of sol-gel synthesized materials. Hydrolysis of the inorganic precursor has been accomplished in high water/alkoxide conditions and in the presence of SDAs. Evaporation induced self-assembly (EISA) during coating deposition and the scanning of four types of SDAs have permitted to select the coating that fulfilled specific thickness and refractive index values with, in parallel, excellent results on sol stability. The final optimization has produced mesoporous coatings with ∼9 nm mean pore size, leading to an enhancement in transmittance up to 7.4% over bare glass in the 300–1500 nm wavelength range. The transmittance spectra have been used as inputs for the theoretical calculation of the short-circuit current density of a commercially available multijunction solar cell for CPV applications.

Covalent immobilization of TiO2 within macroporous polymer monolith as a facilely recyclable photocatalyst for water decontamination

This study focused on the covalent immobilization of TiO2 on the surface of a porous polymer monolith by a two-step method. Firstly, porous polymeric monolith with trimethoxysilane anchor groups was fabricated by w/o emulsion templated copolymerization of vinyl acetate (VAc) and methacryloxypropyl-trimethoxysilane (MPS). Then, anatase TiO2 were covalently immobilized within the voids of poly(VAc-MPS) monolith via an acid-catalyzed co-condensation of the trimethoxysilane group with a TiO2 sol precursor at low temperate. Scanning electron microscopy images demonstrated that both poly(VAc-MPS) and Ti-P(VAc-MPS) possess dense honeycomb-like macroporous structures. The chemical structure analysis by Fourier transform infrared spectroscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy revealed that (i) acid-catalyzed sol-gel method in this case could fully convert the amorphous TiO2 sol to anatase TiO2 even at low temperature (70°); (ii) TiO2 particles were covalently immobilized within the voids of the polymer monolith via Si–O–Ti linkage; (iii) acid-catalyzed hydrolysis of the trimethoxysilane groups and VAc led to significant increase in the hydrophilicity of the obtained hybrid porous monolith, Ti-P(VAc-MPS), with a water contact angle of 19.6°. Exemplified by the photo-degradation of methyl orange (MO) in aqueous solution, Ti-P(VAc-MPs) exhibited good photocatalytic activity and excellent recyclability for water decontamination. The as-prepared Ti-P(VAc-MPS) monolith could be efficiently regenerated for cyclic runs without further energy-consuming separation process such as centrifugation and filtration. The present approach opens a green way for obtaining other porous inorganic-organic photocatalyst for water contaminant removal.

Broadband antireflective coating stack based on mesoporous silica by acid-catalyzed sol-gel method for concentrated photovoltaic application

Silica multi-layer stacks have been designed with the aim to provide broadband antireflective (AR) properties for glass components in concentrated photovoltaic (CPV) application. Silica porous coatings were grown by combining acid-catalyzed sol-gel route and evaporation induced self-assembly (EISA) method with four types of organic/inorganic systems. Sols were prepared using tetraethylorthosilicate (TEOS) as inorganic precursor assembled with two di-block copolymers, one tri-block copolymer and one cationic surfactant as organic templates. Optical properties were characterized by ellipsometry and spectrophotometry while the material structure was analyzed by environmental ellipsometric porosimetry (EEP) and atomic force microscopy (AFM). The concentration of inorganic and organic phases was optimized and a broadband AR bi-layer stack was obtained providing a 7.2% (under the reference AM1.5 solar spectral irradiance) increase in transmittance over bare glass in the wavelength range 300–2000 nm when coated on both sides.

Effects of PEG-TMS on the stability and antifouling performances of hydrocarbon-modified amphiphilic xerogel coatings

Amphiphilic xerogel films with slight swelling were prepared by the acid-catalysed sol-gel method starting from tetraethoxysilane (TEOS), triethoxyoctylsilane (C8Si), n-octadecyl trimethoxysilane (C18Si) and poly(ethylene glycol) siloxane (PEG-TMS). In these amphiphilic xerogel films, the presence of hydrophobic chains, especially C18Si facilitated the emigration of PEG chain to the coating/air interface during the film formation/curing process, and then the PEG chains enriched at the surface of coatings further slightly emigrated to form hydration layer underwater confirmed by energy dispersive X-ray spectroscopic (EDS) analysis, captive air-bubble contact angle (CA) and CA hysteresis. Furthermore, the amphiphilic xerogel films showed the optimal water absorption ratio lower than 1.0% due to the restraint of higher crosslinked density and little network aperture of the films on PEG chains. The antifouling performances of amphiphilic xerogel films included the protein resistance for FITC-BSA, antibacterial property for Escherichia coli and the resistance for diatom Navicula, were better than those of the elastic silicone-based coatings and xerogel film without hydrophilic PEG chains. In general, the amphiphilic xerogel films containing both PEG and proper levels of C8Si and C18Si possessed excellent fouling release properties and slight swelling due to the synergistic effects.

Facile Synthesis and Chiral Separation of Chiral Mesoporous Silica Microspheres.

Mesoporous silica microspheres were synthesized by an acid-catalyzed sol-gel method using tetraethoxysilane (TEOS) as a precursor. The hydrochloric acid was used as a catalyzer to induce the hydrolysis of TEOS, while the cyclohexane acted as a stabilizer of the sol. The addition of polyethylene glycol can introduce the uniform mesoporous structure into the microspheres by phase separation. The as-prepared mesoporous silica microspheres possess a narrow particle size distribution, a mesopore size of 5.0 nm and a Brunauer-Emmett-Teller specific surface area as high as 230 m2·g-1. The resultant silica microspheres were used for packing chiral high-performance liquid chromatography (HPLC) columns, after activated by hydrochloric acid and modified by amylose-tris(3,5-dimethylphenylcarbamate), respectively. The flurbiprofen axetil as a typical chiral drug with two stereocenters can be successfully separated by the as-obtained chiral HPLC columns using different mobile phases.

Photocatalytic decolorization of azo dyes on TiO2: Prediction of mechanism via conceptual DFT

The aim of this study is to develop a shortcut method to predict the intermediates and the mechanism of decolorization reactions of azo dyes. To this purpose, Reactive Red 195 (RR195) was chosen as the representative member of azo dyes and photocatalytic decolorization reaction of RR195 in the presence of TiO2 under UV-A light irradiation was investigated. TiO2 was synthesized by an acid-catalyzed sol-gel method from an alkoxide precursor and characterized by XRD, XPS, ESEM-EDX and BET measurements. The decolorization reaction was monitored by UV–vis, FTIR, GC–MS and ESEM-EDX techniques. Conceptual Density Functional Theory was applied to the degradation reaction of the target molecule and reactivity descriptors were calculated by means of DFT/B3LYP/6-31G* level of theory. Eventually, the reactive sites of the molecule for OH radical attack were determined and the reaction mechanism was predicted by combining the results of the DFT calculations with the experimental FTIR and GC–MS analyses. The predicted mechanism was confirmed by comparison with the experimental results on simple structures reported in the literature. The results of the study suggest that TiO2/UV photocatalysis may be used as a method for treatment of diluted wastewaters in textile industries, adsorption on TiO2 surface occurs through sulfo and carbonyl groups of the dye molecule, while decolorization by the breaking of the NN double bond of the chromophore group.

Preparation of sponge-like porous SiO2antireflective coatings with excellent environment-resistance by an acid-catalysed sol–gel method

Silica coatings with high-transmittance and excellent environment-resistance property were prepared by adding hexamethyldisilazane (HMDS) into acid-catalyzed through sol–gel method.

Graphene/nanoporous-silica heterostructure based hydrophobic antireflective coating

Highly transparent with hydrophobic noncorrosive antireflective (AR) coating of Graphene/Nanoporous-silica heterostructure is designed for advance solar devices. On a standard glass matrix, a thin layer of silica coating is prepared by acid-catalyzed sol–gel method and porosity is introduced with the controlled addition of polyethylene glycol (PEG) with different molecular weights to optimize wide angle and broadband transmittance. The test results of atomic force microscope and field emission scanning electron microscope show that the PEG significantly affects the porosity and surface morphology of the coating layer. The presence of groove-like porous structure within the film matrix effectively reduces the refractive index (1.46–1.41) of the silica coating and thereby enhancing the percent (%) transmission. This nanoporous silica thin film with PEG4000 shows the highest transmittance of 98.19% with an average pore size 1–3nm. The hydrophobicity is imparted by adopting a novel approach by depositing large area homogeneous graphene layer on top of the silica film. This heterostructure film demonstrates 6-fold enhancement of hydrophobicity due to graphene layers and is compromised with a loss of 1–2% transmittance. The hardness analysis of the graphene coated AR film by 100 times abrasion test shows the strong van der Waals interactions between the porous silica film and graphene layers. The prolong acid test for long term durability proves great sustainability of such hydrophobic coating against harsh weather conditions without altering its intrinsic properties of wide angle and broadband transmittance.

Sol–Gel Synthesis of Microporous Carbon Using Resorcinol and Formaldehyde

Microporous carbon materials were prepared by thermal decomposition of a xerogel. The xerogel was synthesised through polycondensation of resorcinol and formaldehyde using an acid-catalysed sol–gel method. Acetic acid (1 M) was used as a catalyst. The effect of the molar ratio of resorcinol/catalyst (10/3, 5, 10, 20) on the obtained hydrogel was studied. The temperature range 25–110 °C was used to convert the hydrogel into a solid resorcinol/formaldehyde xerogel. The optimum molar ratio of resorcinol/catalyst was found to be 10/3. The dried xerogels were pyrolysed under an argon atmosphere at 800 °C to obtain microporous carbon materials with a uniform structure consisting of hollow particles and a specific surface area of 650 m2 g−1.

Iron doped anatase for application in photocatalysis

Titanium dioxide nanopowders, doped with different amount of Fe3+ ions (0.3–5.0 mass%), were synthesized by acid-catalyzed sol–gel method in a non-aqueous medium. The obtained powders were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometry (EDX) and UV/vis spectroscopy. Degradation reaction of crystal violet (CV) azo dye is used to test the photocatalytic activity of iron doped titanium dioxide nanopowders. The results are correlated with previous investigations about the structure and physico-chemical characteristics of obtained nanopowders.

Phosphorylated cellulose triacetate–silica composite adsorbent for recovery of heavy metal ion

Phosphorylated cellulose triacetate (CTA)/silica composite adsorbent was prepared by acid catalyzed sol–gel method using an inorganic precursor (3-aminopropyl triethoxysilane (APTEOS)). Reported composite adsorbent showed comparatively high adsorption capacity for Ni(II) in compare with different heavy metal ions (Cu2+, Ni2+, Cd2+ and Pb2+). For Ni(II) adsorption, effect of time, temperature, pH, adsorbent dose and adsorbate concentration were investigated; different kinetic models were also evaluated. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also estimated and equilibrium adsorption obeyed Langmuir and Freundlich isotherms. Developed adsorbent exhibited about 78.8% Ni(II) adsorption at pH: 6 and a suitable candidate for the removal of Ni(II) ions from wastewater. Further, about 65.5% recovery of adsorbed Ni(II) using EDTA solution was demonstrated, which suggested effective recycling of the functionalized beads would enable it to be used in the treatment of contaminated water in industry.

Hydrophilic and photocatalytic activities of Nd-doped titanium dioxide thin films

The Nd-doped TiO2 thin films with higher hydrophilic and photocatalytic activities were prepared on glass slides by an acid-catalyzed sol–gel method. The effects of Nd doping on crystalline phase, surface composition and optical property were investigated by means of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), optical contact angle tester and UV-Vis spectroscopy. The results show that Nd doping obviously influences the hydrophilic and photocatalytic activities of TiO2 thin films. Nd doping could cause the TiO2 lattice distortion, inhibit phase transition from anatase to rutile, cause red shift of the absorption spectrum edge, produce hydroxyl radicals (·OH), and accelerate surface hydroxylation, which result in a significant improvement in the hydrophilicity and photoreactivity of Nd-doped TiO2 thin films. When the content of Nd is 0.1% (mass fraction), TiO2 thin films achieve the smallest grain size (about 15 nm), and the hydrophilic and photocatalytic activities of TiO2 thin film reach the maximum, the contact angle is only 8.1°, and 92% of methylene blue is finally degraded. Moreover, the modification mechanism of Nd doping was also discussed.