Water-based Sol Gel Method Research Articles

Band Gap Engineering and Lattice Distortion for Synergetic Tuning Optical Properties of NaNbO3 toward Enhanced Piezo-photocatalytic Activity.

Piezo-photocatalytic efficiency is severely constrained by the wide band gap and bad piezoelectric properties. Herein, La(Mn0.5Ni0.5)O3 was successfully introduced into NaNbO3 lattices (referred to as 0LMN, 0.05LMN, 0.10LMN, and 0.15LMN) through a water-based sol-gel method. The piezo-photocatalytic degradation ratio for Rhodamine B (RhB) is enhanced from 59.7% (0LMN) to 89.7% (0.10LMN) within 100 min, and the kinetic rate constant (k) is increased from 0.009 to 0.022 min-1. The enhanced performance is attributed to (i) the narrowed band gap (from 3.40 to 2.84 eV), which is conducive to the generation of photogenerated electrons and holes, and (ii) the enhanced piezoelectric properties, which can strengthen the piezoelectric polarization, thereby accelerating the separation of the photogenerated electrons and holes. And we also found that the synergetic effect of photocatalysis and piezocatalysis was superior to that of photocatalysis and piezocatalysis alone. This study could provide new perspectives for the reasonable construction of an efficient catalyst in the piezo-photocatalytic field.

Low-content barium doping induces two-phase coexistence in NaNbO3 to enhance the piezo–photocatalytic activity

Piezo–photocatalysis induced by ultrasound vibration and light irradiation is an emerging strategy to decelerate the rapid recombination of photoinduced charges in the catalytic process. Element doping-induced structural phase transition is an effective approach to improve catalytic performance. Herein, barium (Ba) doped sodium niobate (abbreviated as Na1-2xBaxNbO3, x = 0, 0.005, 0.010, 0.015, and 0.020) nanomaterials were successfully prepared by a water-based sol-gel method. With the increase of Ba content, the morphology changes from sphere to cubic, and the orthorhombic NaNbO3 transforms to an orthorhombic–cubic mixed phase. Compared with the single orthorhombic phase NaNbO3, the piezo–photocatalytic degradation ratio of mixed-phase Na0.97Ba0.015NbO3 is enhanced by 16% in the decomposing of Rhodamine B (RhB), and the kinetic rate constant is up to 0.0114 min−1, which is 1.65 times higher than that of the orthorhombic NaNbO3. The improved piezo–photocatalytic activity is attributed to the two-phase coexistence and optimum amount of oxygen vacancies. In addition, the photocatalytic, piezocatalytic, and piezo−photocatalytic performances and mechanisms of the Na0.97Ba0.015NbO3 sample were also investigated. This work provides a reference for the construction of structural phase and the practical application of the piezo–photocatalysis in the environmental field.

Sol-Gel Finishing for Protective Fabrics

Sol-gel method has been used since the early 1960s in various applications. There has been a growing interest in this method in recent decades, its materials, and its functionality. The sol-gel reaction consists of a series of simple hydrolysis and condensation reactions, and they are easy to perform and do not require special conditions or high temperatures. This reaction can be influenced by several factors: water-to-precursor molar ratio, types of catalyst, pH, modifier, reaction, aging temperature, and varying solvent. Scientific databases, namely Scopus and ScienceDirect, mainly address the organic solvent-based sol-gel method. Since 1996, the water-based sol-gel method has attracted much attention to simplify the procedure further and reduce cost and environmental damages. This is a review of water-based and typical solvent-based sol-gel methods, focusing on protective fabric coatings. It discusses the most relevant and recent findings related to the sol-gel method, including its applications, advantages and limitation, and future potential. It describes the effects of using water to replace organic solvents that can influence the characteristics and properties of sol-gel materials. Water-based sol-gel preparation methods are relatively advanced, and some products are currently on the market. However, many difficulties related to their water-precursor compatibility prevail. Therefore, chemistry and physics are areas that need to be exploited to create new materials that meet the protective fabric criteria.

Structural, thermal and in-vitro analysis of sol-gel derived zinc and fluorine co-substituted nanodimensional hydroxyapatite for biomedical applications

Hydroxyapatite (HA) is widely used as a bone and dental substitute material due to its biocompatible and bioactive nature. Improvements in HA can be achieved by substituting various ions that are present in the bone. The present study of co-substitution of Zinc and Fluorine in HA was intended to investigate the influence of substituent ions on the structural, thermal, and bioactive behavior of HA. The co-substituted hydroxyapatite nanopowder was synthesized by water-based sol-gel method. Characterization studies from XRD, FTIR and TEM confirmed the substitution of Zn and F ions in HA and the formation of nanorods. The thermal stability of as-synthesized nanopowder was assessed by calcining it at three different temperatures i.e. 800 °C, 1000 °C and 1200 °C. The bioactivity of as-synthesized and calcined nanopowders was assessed by measuring the change in pH of simulated body fluid (SBF) and FTIR spectra after immersion in SBF for 30 days. The results revealed the bioactive behavior of as-synthesized and calcined nanopowders.

Photocatalytic degradation of NOx and ethanol in the gas phase by spray dried Ce-TiO2

We synthesized Ce doped TiO2 (Cex-T) and tested it in the photocatalytic degradation of NOx and ethanol under visible light. Pristine TiO2 (T) and different dopant ratios of Ce-TiO2 (Cex-T; x = 0–1.0 wt%) were prepared by a water-based sol-gel method followed by spray drying. The successful doping of Ce in the lattice structure of TiO2 was confirmed by several characterizations such as X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), and Raman spectroscopy. All the prepared catalysts grew as spherical grains with a polycrystalline anatase phase. Ce0.8T revealed the lowest bandgap among all the prepared catalysts (2.8 eV) compared to 3.2 eV for T. The highest degradation of NOx and ethanol was attained by Ce0.8T (26 ± 1% and 23 ± 1%), which was 2.8 and 1.5 times the degradation by T, Furthermore, we proposed the photocatalytic degradation mechanism by the reactive oxidant species (ROS).

Synthesis of Water-Repellent Coating for Polyester Fabric

A new hydrophobic hexyltrimethoxysilane (HTMS) coating for polyester fabric was successfully synthesized via a one-step water-based sol-gel method under acidic condition. Five different molar ratios of HTMS: water (1;40, 1:30, 1:20, 1:12 and 1:3) were prepared and the solution was deposited onto the polyester fabric by a simple dip-pad-cure process. The effect of water content on hydrophobicity was evaluated by manual testing on the treated polyester fabric samples. The effectiveness of hydrophobicity properties was further characterized using water contact angle (WCA) measurement. The optimized molar ratio of 1:3 was found to obtain the best hydrophobic property of 136.2° with particle size 115.3 µm measured using Particle Size Analyzer (PSA). Fourier transform infrared spectroscopy (FTIR) analysis confirmed the success of sol gel process with the presence of Si-O-Si band, which was also determined using energy dispersive X-ray spectroscopy (EDX). The Scanning Electron Microscopy (SEM) images revealed a good surface morphology of the homogenous thin xerogel coating with no visible cracks. Using HTMS without combinations of other precursors resulted in rough surface structure due to the low surface energy caused by long-chain alkyl silane in the HTMS coating and this provided the treated polyester fabric with good hydrophobicity. Doi: 10.28991/esj-2021-01309 Full Text: PDF

Silicon Substituted Lithium Stannum Phosphate Ceramic Electrolytes: Structural, Electrical and Electrochemical Properties

Structural, electrical and electrochemical properties of silicon (Si) substituted NASICON-structured lithium stannum phosphate, Li1+ySn2P3-ySiyO12 with 0 < y < 1 that was prepared by the low-temperature water-based sol-gel method has been investigated. From the structural analysis, all samples in the system displayed rhombohedral symmetry. The total ionic conductivity, σt, and ionic mobility, µ was increased with the increase of silicon content, y. A high ionic conductivity value of 6.05 × 10-5 S cm-1 exhibited at y = 0.5 with a temperature of 500 °C. Linear sweep voltammetry analysis showed that the sample was electrochemically stable up to 5.1 V. Meanwhile, the ionic transference number value of the sample was 0.99, suggesting that the majority of mobile charge carriers were predominantly due to ions. Thus, from these results, it indicated that silicon substitution in LiSn2P3O12 ceramic electrolytes is significantly enhanced the electrical and electrochemical properties.

Thick Transparent Nanoparticle-Based Mesoporous Silica Monolithic Slabs for Thermally Insulating Window Materials

This paper presents a novel template-free water-based sol–gel method to synthesize thick transparent and thermally insulating mesoporous silica monolithic slabs by gelation and drying of a colloida...

Sol-gel auto-combustion synthesis of Ca2Fe2O5 brownmillerite nanopowders and thin films for advanced oxidation photoelectrochemical water treatment in visible light

This study describes a straightforward Ca2Fe2O5 brownmillerite nanopowder and thin film synthesis by the water-based sol-gel auto-combustion method. The material characterization results confirmed the phase pure narrow bandgap Ca2Fe2O5 nanoparticle formation. The surface area of synthesized nanopowder was 13.55 m2/g. Powders at loading 1 g/l exhibit high visible light photocatalytic activity by degrading 10 mg/l methylene blue in water in 120 min confirmed by total organic carbon studies. The high visible light photocatalytic activity is related to Ca2Fe2O5 narrow band gap and high reduction potential of its conduction band which triggers the formation of superoxide radical ∙O2-. The limited chemical stability for Ca2Fe2O5 nanopowders was observed due to self-reduction under photocatalytic conditions. The degradation rate constant decreased almost five times already in the second photocatalysis cycle. Further, we are demonstrating the application of Ca2Fe2O5 films in the photoelectrochemical water treatment (PECWT) process. We show that brownmillerite films are becoming stable against photo-corrosion under positive bias in PECWT and could be suitable for dye degradation in water. In the PECWT process, the Ca2Fe2O5 is protected from self-reduction since the photoinduced electron under positive bias is moved away to the Pt electrode. Under short circuit or biased (0.5 V) conditions the rate constant for MB degradation is decreased only for approximately 15% in 6 cycles.

Water-Based Sol–Gel Synthesis of Ce-Doped TiO2 Nanoparticles

Pure titanium dioxide (TiO2) and Ce-doped TiO2 nanoparticles (NPs) were synthesized with the different dopant percentages of 2%, 4%, 6%, 8%, and 10% by using titanium tetrachloride (TiCl4) and cerium chloride (CeCl3) precursors, pure water as a solvent, and hydrochloric acid (HCl) as the hydrolysis reactor in the presence of ethylene glycol (C4H10O3) stabilizer through the sol–gel method. The morphological, structural, optical and electronic properties of the NPs were investigated via x-ray diffraction (XRD) analysis, field emission scanning electron microscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). From the XRD analysis, it was found that the structure of the Ce-TiO2 NPs remained unchanged in the tetragonal state and anatase phase by increasing dopant, while the size of the nanocrystals (29 nm) in the pure state decreased down to 25 nm by increasing dopant up to 6%. The apparent pseudo-spherical shape and diameter of about 26 nm were obtained for the impure NPs through TEM. The UV-DRS analysis indicated the wide-band gap formation of the NPs through the water-based sol–gel method. As Ce increased, the band gap was enhanced from 5.02 eV for the pure TiO2 NPs up to 5.46 eV for the NPs of 10% dopant. The wide band gap created in these NPs allowed them to be used with an optimum absorption in the ultraviolet (UV) light applications. The results of FTIR analysis showed that the absorption peak of 508 cm−1 was related to the vibrational bond of Ti-O-Ce in the pure state, which changed towards the frequencies of 498 cm−1, 513 cm−1, 490 cm−1, 492 cm−1 and 469 cm−1 for the Ce dopant concentrations of 2%, 4%, 6%, 8%, and 10% entering into the TiO2 matrix, respectively. Finally, the results of the PL analysis revealed that the maximum energy-band interaction of TiO2 with Ce was created at 426 nm with a dopant of 6%.

An Eco-Friendly Method of BaTiO3 Nanoparticle Synthesis Using Coconut Water

BaTiO3 nanoparticles were successfully synthesized by a new coconut water-based sol–gel method using Ba(CH3COO)2 and TiCl3 as the starting salts. The influence of the amount of coconut water and calcination conditions on the barium titanate crystallization was investigated. The resulting nanoparticles were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and Raman and Fourier transform infrared (FTIR) spectroscopies. The ferroelectric tetragonal single phase of BaTiO3 was obtained in samples prepared with a ratio of coconut water volume (mL)/BaTiO3 mass (g) of 25 : 2 and 30 : 2, calcined at 1100°C, which was confirmed by XRD measurements. Crystallites with an average size of about 31 nm for both samples were obtained, and microscopy images revealed the presence of particles in the range of 40 to 60 nm. Raman and FTIR spectra confirmed the dominant tetragonal phase of BaTiO3, meanwhile traces of BaCO3 were identified in FTIR spectra.

Large piezoelectric properties of (1 − x)Na0.5Bi0.5TiO3–xBaTiO3 thin films prepared by sol–gel method

(1 − x)Na0.5Bi0.5TiO3–xBaTiO3 (BNT–xBT) thin films with x = 0, 0.04, 0.06, 0.08 were prepared on Pt(111)/Ti/SiO2/Si substrates via water-based sol–gel method. A new crystallization process called stepwise crystallization was used to obtain pure perovskite phase observed by XRD. Piezoelectric property and ferroelectric property of BNT–xBT thin films are investigated, and BNT–BT0.06 shows best piezoelectric and ferroelectric properties among the different compositions. The maximum strain value of 1.4–1.8 % and d 33 of 83 pm/V are observed for BNT–BT0.06 thin films. AFM and PFM images reveal the dense morphology and large piezoresponse of BNT–BT thin films without orientation.

Effect of water-based sol gel method on structural, thermal and conductivity properties of LiNO3–Al2O3 composite solid electrolytes

Composite solid electrolytes in the system (1−x)LiNO3–xAl2O3, with x=0.0–0.5 were prepared by sol gel method. No organic solvents but water was used as medium for the sol preparation. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy and impedance spectroscopy. Structural analysis evidenced amorphous phase of LiNO3 in all composite samples. Traces of crystalline LiAl5O8 and LiAlO2 were also present in the composite samples with x=0.3–0.5, as indicated by the X-ray diffractograms. The thermal analysis showed that the samples were in a stable phase between ∼48°C – ∼100°C and ∼120°C – ∼220°C. The conductivity values of the composites were in the range of 10−3Scm−1 at room temperature to 180°C. Our study demonstrates that water is suitable for the preparation of the composite solid electrolytes.

Large piezoresponse of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 thin films prepared via water-based sol–gel method

(Na0.85K0.15)0.5Bi0.5TiO3 (abbreviated as NKBT) thin films were fabricated via an economical aqueous sol–gel method on Pt(111)/Ti/SiO2/Si substrates. Overdoping of volatile cations in the precursor solutions was necessary to achieve pure perovskite structure due to compensation of cations loss that occurred during heat treatment. Different annealing temperature was investigated to get the films with single perovskite phase detected by XRD patterns. Thin films of 250nm thickness exhibited a dielectric constant and a loss tangent at 100kHz of 519 and 0.058, respectively. A high effective piezoelectric coefficient (d33) of approximately 76pm/V was obtained via PFM.

Synthesis of High Quality LaCoO3 Crystals Using Water Based Sol-Gel Method

Lanthanum cobaltite (LaCoO3) crystalline material is a promising material for its interesting electrical, magnetic, catalytic and thermoelectric properties. In this study, LaCoO3 powders were synthesized by water based sol-gel method using metal nitrates as precursors and citric acid as the chelating agent at room temperature. The dried powders were amorphous and their thermal decomposition occurs stepwise upon heating to 400 °C. Pure perovskite-type single phase LaCoO3 polycrystals are formed after heating at 600 °C. The pallets prepared from calcined powers were sintered at 1200 °C and crystalline pallets were characterized for investigation of electrical, optical and thermoelectric properties. The obtained results revealed that the prepared samples were highly crystalline with large cation ordering. The sol-gel method found to be efficient for much production of a lot of crystalline transition metal oxides at low cost.

Low-Temperature Sintering and Enhanced Piezoelectric Properties in KNN-LTS Nanopowder Prepared via a Low-Cost Water-Based Sol-Gel Method

nanoscale lead-free perovskite powders with a composition of (Na0.52K0.4425Li0.0375)(Nb0.9125Ta0.0375Sb0.05)O3 (KNN-LTS) have been synthesized via a low-cost water-based sol-gel method, to reduce the sintering temperature and enhance the electrical properties. KNN-LTS nanopowders with average particle size of about 20 nm are obtained by citrate precursor sol-gel process, where Nb (OH)5 and Sb2O3 are used to replace the costly mental alkoxides. The sol-gel derived nanopowders can be densified at lower temperature of 940 °C and exhibited excellent electrical properties after sintering at 1020 °C (d33 = 396 pC/N, kp = 50.1% = 1882 and tanδ = 0.02), providing a tremendous potential method for high-performance lead-free ceramics preparation.

Low Sintering Temperature for Li-, Sb-, and Ta- Modified (K,Na)NbO<sub>3</sub>-Based Ceramics from Nanopowders

In this paper, (Na0.52K0.44Li0.04)(Nb0.86Ta0.06Sb0.08)O3 (LTS-KNN) ultrafine-grained ceramic were fabricated over a low and wide temperature range, by using the nanopowder prepared from a water-based sol-gel method. nanopowders are demonstrated to be suitable for preparing fine-grained potassium-sodium niobate ceramics with desirable properties.

Transformation of hydrophilic cotton fabrics into superhydrophobic surfaces for oil/water separation

In the present study, silica hydrosols were firstly prepared by water-based sol-gel method with the surfactant emulsification, using tetraethoxysilane as the precursor and ammonium hydroxide as the catalyst. Then, the silica hydrosols were applied to the cotton fabrics by dipping process, followed by the modification with (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane and heat treatment to prepare superhydrophobic cotton fabrics. The process resulted in SiO2 nanoparticles covalently attached to the cellulose surface and fluorine-containing siloxane coupling agent which brought about an inherent microscale roughness and the superhydrophobic character. The investigation of oil/water mixture has been carried out using the as-prepared superhydrophobic cellulose fabric-based materials.

Enhanced density of sol–gel derived La0.8S0.2MnO3 thin film with an electric field assisted deposition

A uniform and dense (relative density 89%) La0.8Sr0.2MnO3−δ (LSM) thin film (84nm thick) has been prepared on La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) substrate using a water-based sol–gel method, in order to improve the operating stability of intermediate temperature cathode. An in situ static electric field was applied in the deposition/drying process, and found to obviously affect phase formation and thickness of the final LSM film. It was proposed that the orientation of macromolecules (such as chelating agents and surfactants) and the packing density of metal cations may be influenced by electric field during the deposition process.

Low-temperature formation of Ln silicate oxyapatite (Ln = La and Nd) by the water-based sol–gel method

Low-temperature formation routes of lanthanum silicate and neodymium silicate oxyapatites were analyzed by a combination of powder X-ray diffraction and thermogravimetric/differential thermal analysis by using precursors prepared from the water-based sol–gel method. Oxyapatite phase was found to form at about 1073 K in the case of lanthanum silicate and at about 1273 K in the case of neodymium silicate — temperatures much lower than those for a conventional solid-state reaction method. In each system, the oxyapatite phase was formed after decomposition of the lanthanoid oxycarbonate or metastable lanthanoid oxide. In particular, decomposition of lanthanum oxycarbonate was found to play an important role in lanthanum silicate oxyapatite formation. In addition to proposing a crystal structure for the lanthanoid oxycarbonate, we hypothesize an in-situ chemical pulverization process due to the delamination of lanthanoid oxide by carbon dioxide dissociation.