Low Temperature Sol-gel Research Articles

Fabrication of CuO NP for NO2 Gas Sensing

NO2 is a very dangerous gas that is mainly emitted from fossil fuels and is a major cause of air pollution. It has environmental problems cause by acid rain and has a bad effect on human health. In this study, mesoporous CuOx nanoparticles (NPs) were successfully synthesized using a low-temperature sol–gel method. Subsequently, the synthesized NPs were annealed at temperatures of 250, 350, and 450 °C. The Properties of the synthesized samples showed that the size of NPs increased with increasing annealing treatment, while the surface area decreased. The samples annealed at 250°C/2h exhibited significantly higher surface area compared to the samples annealed at 350°C and 450°C, thanks to their finer particle size and mesoporous properties. Resistive gas sensors incorporating these samples were successfully fabricated and tested for sensitivity towards both NO2 (oxidizing gas) and H2S (reducing gas) at 200 °C. The sensor with the mesoporous CuOx NPs annealed at the lowest temperature (250 °C) exhibited an enhanced response to NO2 gas but no response to H2S. The strong response to NO2 gas is considered to be due to the high surface area of the sensing layer which provides plenty of adsorption sites for gas molecules and the oxidizing nature of NO2 gas with high affinity to electrons. These findings highlight the effectiveness of the sol–gel method in synthesizing CuO NPs for gas sensing, as well as the need for optimizing the annealing temperature to maximize the sensor response.

Transition Metal-Doped Layered Iron Vanadate (FeV3-xMxO9.2.6H2O, M = Co, Mn, Ni, and Zn) for Enhanced Energy Storage Properties.

With its distinctive multiple electrochemical reaction, iron vanadate (FeV3O9.2.6H2O) is considered as a promising electrode material for energy storage. However, it has a relatively low practical specific capacitance. Therefore, using the low temperature sol-gel synthesis process, transition metal doping was used to enhance the electrochemical performance of layered structured FeV3O9.2.6H2O (FVO). According to this study, FVO doped with transition metals with larger interlayer spacing exhibited superior electrochemical performance than undoped FVO. The Mn-doped FVO electrode showed the highest specific capacitance and retention of 143 Fg-1 and 87%, respectively, while the undoped FVO showed 78 Fg-1 and 54%.

Ce-TiO2 nanoparticles with surface-confined Ce3+/Ce4+ redox pairs for rapid sunlight-driven elimination of organic contaminants from water

Ce-TiO2 nanoparticles with surface-confined Ce3+/Ce4+ redox pairs for rapid sunlight-driven elimination of organic contaminants from water

Structural analysis and dielectric behavior of low-temperature synthesized nickel cobaltite

Structural analysis and dielectric behavior of low-temperature synthesized nickel cobaltite

A novel structure of cellulose-TiO2 nanocomposite for ultra-fast and recyclable organic dyes degradation in wastewater

A novel structure of cellulose-TiO2 nanocomposite for ultra-fast and recyclable organic dyes degradation in wastewater

Low temperature sol-gel synthesis of copper zinc ferrite for hydrogen catalytic hydrolysis of sodium borohydride

Low temperature sol-gel synthesis of copper zinc ferrite for hydrogen catalytic hydrolysis of sodium borohydride

Analysis and characterization of opto-electronic properties of iron oxide (Fe2O3) with transition metals (Co, Ni) for the use in the photodetector application

Analysis and characterization of opto-electronic properties of iron oxide (Fe2O3) with transition metals (Co, Ni) for the use in the photodetector application

Low-temperature sol–gel methods for the integration of crystalline metal oxide thin films in flexible electronics

The development of low-temperature sol–gel (solution) processes for the fabrication of crystalline metal oxide thin films has become a key objective in the emerging Flexible Electronics. To achieve this target, crystalline oxide films need to be deposited on flexible substrates, which have degradation temperatures below 350 °C (e.g., polymers or textile). This achievement would be a step towards improving the performance of the flexible device, making feasible applications now restrained (e.g. smart-skin, flexible-displays or solar-cells) and whose performance is associated to the functional properties of the crystalline oxide (e.g., ferroelectricity, pyroelectricity or piezoelectricity). However, this is a challenge because the crystallization of these oxides usually occurs at high temperatures, over 600 °C. This paper shows an overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites (e.g., BiFeO3, PbTiO3 or Pb(Zr,Ti)O3). We have made use of UV-light as an alternative energy source to the thermal energy conventionally used to obtain the crystalline oxide. High photosensitive sol–gel solutions have been synthesized and the solution-deposited layers irradiated with UV-excimer lamps. A precise control of the photoreactions occurring during the irradiation of these layers has been carried out with the aim of advancing the formation of a high-densified, defect-free amorphous metal oxide film that easily can be converted into crystalline at temperatures compatible with the use of polymer substrates.Graphical An overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites, is shown in this article. UV-light is used as an alternative energy source to the conventional thermal energy used to obtain crystalline oxide thin films. These solution strategies are based in the synthesis of high photosensitive sol–gel solutions and the irradiation of the solution-deposited layers with UV-excimer lamps under controlled irradiation atmospheres. A precise control of the photoreactions occurring in the system during the irradiation process has been carried out, with the aim of advancing the formation of high-densified, defect-free amorphous metal oxide films able to be converted into crystalline at temperatures compatible with the use of polymer substrates. This makes possible the integration of these advanced materials in the emerging Flexible Electronics.

The Low-Temperature Sol-Gel Synthesis of Metal-Oxide Films on Polymer Substrates and the Determination of Their Optical and Dielectric Properties.

Photoactive, optically transparent heterostructures from silver nanowires and titanium dioxide were obtained by the sol-gel method on the surface of a polyethylene terephthalate film. The characteristics of optical transmission on the wavelength and those of dielectric permittivity, conductivity and dissipation on frequency in the range of 25-1,000,000 Hz were investigated.

FeCoNi Ternary Nano-Alloys Embedded in a Nitrogen-Doped Porous Carbon Matrix with Enhanced Electrocatalysis for Stable Lithium-Sulfur Batteries.

The application of composite materials that combine the advantages of carbonaceous material and metal alloy proves to be a valid method for improving the performance of lithium-sulfur batteries (LSBs). Herein iron-cobalt-nickel (FeCoNi) ternary alloy nanoparticles (FNC) that spread on nitrogen-doped carbon (NC) are obtained by a strategy of low-temperature sol-gel followed by annealing at 800 °C under an argon/hydrogen atmosphere. Benefiting from the synergistic effect of different components of FNC and the conductive network provided by the NC, not only can the "shuttle effect" of lithium polysulfides (LiPS) be suppressed, but also the conversion of LiPS, the diffusion of Li+, and the deposition of Li2S can be accelerated. Taking advantage of those merits, the batteries assembled with an FNC@NC-modified polypropylene (PP) separator (FNC@NC//PP) can deliver a high reversible specific capacity of 1325 mAh g-1 at 0.2 C and maintain 950 mAh g-1 after 200 cycles, and they can also achieve a low capacity fading rate of 0.06% per cycle over 500 cycles at 1 C. More impressively, even under harsh test conditions (the ratio of electrolyte to sulfur (E/S) = 6 μL mg-1 and sulfur loading = 4.7 mg cm-2 and E/S = 10 μL mg-1 and sulfur loading = 5.9 mg cm-2), the area capacity of batteries is still much higher than 4 mAh cm-2.

Low-temperature sol–gel synthesis of magnetite superparamagnetic nanoparticles: Influence of heat treatment and citrate–nitrate equivalence ratio

Spinel ferrite nanoparticles are a remarkably versatile group of metal oxides with unique magnetic and electronic properties, making them promising candidates for certain electronic, biomedical, and environmental applications. Magnetite nanoparticles are obtained using complex synthesis methodologies that require inert atmospheres, additives to induce pH changes, expensive or toxic reagents, or complex equipment. In this work, a new approach to obtain superparamagnetic magnetite nanoparticles using citrate–nitrate sol–gel synthesis followed by heat treatment is presented. Iron nitrate and citric acid were added in different equivalence ratios (χ) (citrate/nitrate = 0.30, 0.85, and 1.40). The thermal behaviour of the xerogels was evaluated using thermal analysis techniques, and the results indicated that decreasing the equivalence ratio decreased the temperature required for magnetite formation, and the different release rates of reducing gases influenced the properties of the final material formed. The heat-treatment temperatures for the synthesis with the optimal χ were 130, 150, and 170 °C for 2, 4, and 8 h. Each condition was characterised in terms of the structure and magnetic properties of the product. The results showed that the prepared iron oxide nanoparticles were in the magnetite phase (Fe 3 O 4 ) and possessed a crystallite size of 4.5–6.0 nm and average particle size of <10 nm. The magnetite nanoparticles displayed superparamagnetic behaviour, with a saturation magnetisation of up to 26.24 emu/g and remanent magnetisation of almost zero. Therefore, these superparamagnetic magnetite nanoparticles have excellent potential for biomedical and environmental applications.

Study of low-temperature sol–gel processed In-doped ZnO for organic photovoltaics

This article studies low-temperature sol–gel processed indium (In)-doped ZnO (IZO) for highly efficient organic photovoltaics (OPVs). Contrary to the prior research trends adopting doped sol–gel processed ZnO with an annealing temperature of over 400 °C for the hydrolysis reaction, IZO with an annealing temperature of 200 °C is studied. Similar to the high-temperature solvent system, it is elucidated that low-temperature sol–gel processed IZO effectively improves the performance of OPVs, increasing the power conversion efficiency from 6.80% to 7.35%. For further analyses, the current–voltage (J–V) characteristics and ideality factors (n) are examined as a function of In doping ratios, which revealed that In doping on ZnO effectively reduces trap-assisted recombination within devices.

A novel method for the formation of bioceramic nano-calcium hydroxyapatite coatings using sol-gel and dissolution-precipitation processing

The wet chemistry route has been developed to prepare calcium hydroxyapatite (Ca10(PO4)6(OH)2, (HA)) thin films on a silicon substrate using the novel low-temperature sol-gel and dissolution-precipitation approach. The calcium carbonate thin films on the silicon substrate were obtained by spin-coating technique when substrates were repeatedly coated with 10, 20 and 30 layers of sol-gel solution. The composites formed of crystalline and amorphous CaCO3 were obtained by calcination of the coatings for different time at 600°C. A dissolution-precipitation procedure was used for the preparation of calcium hydroxyapatite thin films on silicon substrate at 80°C. The obtained synthesis products were characterised by X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM) and Raman spectroscopy.

Low Temperature Sol-Gel Processed Zirconium Oxide Based Transparent Resistive Random Access Memory Devices

In this work, solution-processed ZrO2-based resistive random-access memory (RRAM) device with ITO (Indium Tin Oxide) as a bottom electrode (BE) was fabricated at a low thermal budget by sol-gel spin coating technique. The grown devices (ZrO2/ITO) were found to be amorphous by XRD measurements and exhibit 80% transmittance in the visible region. The resistive switching characteristics of solution-processed ZrO2 thin films were investigated. The W/ZrO2/ITO device exhibits good cyclic endurance with an on-off ratio (~10) and reliable switching and good retention at room temperature. The conduction mechanism for the low resistance state is ohmic, whereas the conduction mechanism of the high resistance state is ohmic at low applied voltages, while a space charge limited conduction (SCLC) at the high applied voltages. The combined ohmic and space charge limited conduction mechanisms together indicate that the RS behavior in the ZrO2 layer is due to the formation and rupture of conducting filaments. Results suggest that solution-processed ZrO2 has great potential to develop transparent and flexible resistive random access memory devices.

Mild Sol–Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis

Solution processing of highly performing photonic crystals has been a towering ambition for making them technologically relevant in applications requiring mass and large-area production. It would indeed represent a paradigm changer for the fabrication of sensors and for light management nanostructures meant for photonics and advanced photocatalytic systems. On the other hand, solution-processed structures often suffer from low dielectric contrast and poor optical quality or require complex deposition procedures due to the intrinsic properties of components treatable from solution. This work reports on a low-temperature sol–gel route between the alkoxides of Si and Ti and poly(acrylic acid), leading to stable polymer–inorganic hybrid materials with tunable refractive index and, in the case of titania hybrid, photoactive properties. Alternating thin films of the two hybrids allows planar photonic crystals with high optical quality and dielectric contrast as large as 0.64. Moreover, low-temperature treatments also allow coupling the titania hybrids with several temperature-sensitive materials including dielectric and semiconducting polymers to fabricate photonic structures. These findings open new perspectives in several fields; preliminary results demonstrate that the hybrid structures are suitable for sensing and the enhancement of the catalytic activity of photoactive media and light emission control.

Effects of Bi doping on structural and magnetic properties of cobalt ferrite perovskite oxide LaCo0.5Fe0.5O3

Abstract Literature reports on magnetic transition of LaFe 0 . 5 Co 0 . 5 O 3 are highly ambiguous. The present study is an endeavour to address that particular issue of this ferrite perovskite. Here we report the low temperature sol-gel synthesis of pure and Bi-doped La 1-x Bi x Fe 0 . 5 Co 0 . 5 O 3 (x = 0, 0.1 & 0.2) perovskites. All the samples were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray (EDX) analysis and magnetization studies. LaFe 0 . 5 Co 0 . 5 O 3 crystallizes in a single phase rhombohedral (R -3c ) structure. Substitution of Bi at the A-site results in structural transition. La 0.9 Bi 0.1 Fe 0 . 5 Co 0 . 5 O 3 exhibits mixed rhombohedra (R -3c ) and orthorhombic (P bnm ) phases, whereas La 0.8 Bi 0.2 Fe 0 . 5 Co 0 . 5 O 3 is single phase orthorhombic (P bnm ). Favourable grain growth and good crystallinity observed in Bi doped samples are possibly due to the low melting temperature of Bi containing La 1-x Bi x Fe 0.5 Co 0.5 O 3 . EDX analysis confirms the chemical homogeneity of the samples. XPS studies and bond valence sum calculations confirm the nominal cationic oxidation states of the ions. Magnetization measurements reveal the weak ferromagnetic nature of La 1-x Bi x Fe 0 . 5 Co 0 . 5 O 3 (x = 0, 0.1 & 0.2) which is associated to the canted antiferromagnetic structure. The magnetically active subsystem of Fe 3+ ions are responsible for weak ferromagnetism which is explained by the antisymmetric Dzyaloshinskii–Moriya interaction, whereas the Co 3+ ions remain predominantly in the low spin state. The increase in magnetic transition and the lower magnetic moment with an increase in Bi content can be related to the weakening of Dzyaloshinskii–Moriya interaction due to structural modification and local lattice distortion associated to the stereochemically active 6s 2 lone pair electrons of the Bi 3+ ions. Our results confirm the high structure sensitivity of magnetic properties of cobalt ferrite perovskite.

Composite Li-ion battery cathodes formed via integration of carbon nanotubes or graphene nanoplatelets into chemical preintercalation synthesis of bilayered vanadium oxides

• Functionalization of CNTs and GNPs enabled integration with δ-LixV2O5· n H2O synthesis. • LVO/fCNT and LVO/fGNP nanocomposites for the first time cycled in Li-ion cells. • Capacity retention improved due to the oxide/carbon heterointerface stabilization. • Rate capability improved due to the increased electronic conductivity. • New strategy for the synthesis of multifunctional materials is demonstrated. Bilayered vanadium oxides are attractive cathode materials for rechargeable batteries. The expanded interlayer space and versatile chemistries of these oxides yield high specific capacities. However, capacity retention and rate performance are limited due to structural instability and low electronic conductivity of these materials. Assembling the oxides with one- and two-dimensional carbon nanoparticles may produce highly efficient heterointerfaces that would enhance electrochemical charge storage properties. Here, we synthesize for the first time bilayered vanadium oxide composites with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The nanostructured carbons were initially functionalized by flash oxidation in air to create polar groups on the carbon surface, producing fCNTs and fGNPs, and improve compatibility with an aqueous chemical preintercalation synthesis route. Lithium preintercalated bilayered vanadium oxide, LVO (LVO = δ-Li x V 2 O 5 · n H 2 O), was selected as a redox active oxide component to facilitate Li + ion diffusion through the interlayer region of δ-V 2 O 5 . A one-step process was developed to synthesize LVO/fCNT and LVO/fGNP composites by an in situ low temperature sol-gel method. We observed marked improvements in capacity retention and rate performance in the nanocomposites as compared to the pristine oxide, which were attributed to both improved electron transport and heterointerface stabilization effect enabled by integration with fCNTs and fGNPs. This work illustrates the ability to enhance material functionality through the in situ synthesis of nanocomposites with controllable heterointerface.

The use of the low-temperature sol–gel method for ZnO-TiO2 nanorods synthesis: structural analysis, morphology and photodegradation properties of methyl orange dye with benzoquinone scavenger

The use of the low-temperature sol–gel method for ZnO-TiO2 nanorods synthesis: structural analysis, morphology and photodegradation properties of methyl orange dye with benzoquinone scavenger

Comparison of microstructure and tensile behavior of hydroxyapatite-coated PEEK meshes and cellulose-based fabrics and mats

Polymeric biomaterials, such as polyether ether ketone (PEEK) and cellulose, have been explored as scaffolds for bone tissue engineering in the past decade. In this study, microstructure and mechanical behavior of uncoated and hydroxyapatite (HA)-coated polymeric meshes, fabrics, and mats were investigated. Commercially available monofilament PEEK meshes, and cellulose fabrics and mats were selected, then coated with a customized low temperature sol–gel method (≤ 150°C). Adhesive HA coating consisting of HA, β-TCP, and CaO with nanorod structure was derived. After HA coating, porosity of substrates (except filter-paper cellulose mats) decreased by up to 43%, indicating effective coating. Both uncoated and HA-coated substrates’ degradation rate in phosphate-buffered saline decreased after day 3. This is a result of ion precipitation or calcium compounds formation, indicating potential stability in biofluids for an extended period of time. Regarding tensile test results, highest tensile strength and elongation at break were obtained for PEEK meshes (approximately 80 MPa and 35%, respectively), as a result of the bulk material properties. HA coating did not significantly affect the tensile properties of the specimens, except for cellulose mats with an initial porosity of 77% (tensile modulus increased by 270% and strength by 210%). The increase in tensile properties could be attributed to increased rigidity, resulting from the adhesion between HA coating and cellulose fibers. Overall, HA-coated cellulose mats and PEEK meshes show promise as customizable, flexible scaffolds for implant applications and bone regeneration for future work.

Thermogravimetric analysis, Rietveld refinement, and atomic force micrography of cobalt ferrite nanoparticles exposed to 100 kGy Co60 γ-rays

• Rietveld refinement of sol–gel fabricated CoFe 2 O 4 nanoparticles. • TGA analysis for the thermal states CoFe 2 O 4 nanoparticles. • AFM and SEM images of CoFe 2 O 4 nanoparticles were used for topography. • Raman active modeshaves supported the structural data. • UV–Vis spectra and Tauc’s plot was reported the bandgap 3.82 eV. We have investigated the thermogravimetric temperature (TGA) of magnetic cobalt ferrite nanoparticles (CoFe 2 O 4 ) synthesized using a low-temperature sol–gel technique and a gamma irradiation dose of up to 100 kGy in a gamma chamber to create lattice defects inside the crystalline structure. The Rietveld refinement was performed with the help of advanced graphical tools which leads to the in-depth identification of Bragg’s reflections belonging to the space group Fd3m by evaluating the profile factor (R p ), weighted profile factor (R wp ), and the expected R-factor (R exp ) parameter. Eventually, the topographic qualities of the samples were investigated using atomic force micrography (AFM), which focused on metal ion dispersion and surface roughness and was aided by scanning electron micrography (SEM images). The Raman spectra have shown the active modes E g , 3T 2g , and A 1g near 250.53; 324.36; and 765.90 respectively. The UV–Vis spectroscopic absorption of CoFe 2 O 4 nanoparticles was reported at ∼ 208.2 Å, and the bandgap was reported to be 3.82 eV with the help of Tauc’s plot; Kubelka-Munk function F(R). The current study presents a complete X-ray diffraction pattern (XRD) analysis that may aid in the investigation of intra-atomic and molecular defects generated by 100 kGy gamma irradiation.