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Sol-gel synthesis and characterization of ZnAl2O4 powders for transparent ceramics
摘要： The sol-gel synthesis of ZnAl2O4 ceramic powders from alkoxide and acetate sources of metals, as well as the microstucture and the hardness of the hot-pressed ZnAl2O4 specimens were considered. ZnAl2O4 powders were prepared by the hydrolysis of an alcohol solution of aluminium isopropoxide using an aqueous solution of zinc acetate followed by heat treatment. The thermal evolution of the ZnAl2O4 precursor was investigated. The effect of calcination temperature on the morphology and the specific surface area of ZnAl2O4 powders were also studied. The sintering of the resultant powders to the high transparent ceramic using a hot pressing with 1 wt% ZnF2, as a sintering additive was successfully demonstrated. The in-line transmittance of ZnAl2O4 ceramics (1 mm thickness) achieved 80% in the visible region and 85 % at 5 μm; Vickers hardness was 11.6 GPa.
关键词： transparent ceramic,powders,sol-gel synthesis,ZnAl2O4
更新于2025-09-10 09:29:36
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Dry-co-grinding of doped TiO2 with nitrogen, silicon or selenium for enhanced photocatalytic activity under UV/visible and visible light irradiation for environmental applications
摘要： TiO2 doped with nitrogen (N), silicon (Si), or selenium (Se) (N-TiO2, Si-TiO2, and Se-TiO2) were obtained by the integrated sol-gel and solvothermal method with short time of crystallization and low temperature. The UV/visible and visible light absorption and photocatalytic activity of these doped TiO2 materials were improved by a dry-co-grinding process with a short grinding time and low rotational speed (30 min at 200 rpm) to obtain N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 catalysts. The materials were characterized by XRD, Raman, BET surface area and porosity, XRF, SEM, TEM, FTIR-ATR, and UV/vis-DRS analyses. The photocatalytic activity of these materials was evaluated by the degradation of phenol under UV/visible and visible light irradiation. The integrated sol-gel and solvothermal methods with short time of crystallization (2 h) and low temperature (225 °C), and the dry-co-grinding process during 30 min at 200 rpm led to materials (N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2) with higher specific surface area, a reduction in the band gap value, and an enhancement of the absorption in the visible light spectrum. Moreover, N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 exhibited higher photocatalytic activities for degradation of phenol under UV/visible and visible light irradiation than those obtained with the doped TiO2, synthesized TiO2 or TiO2 P25.
关键词： Doping TiO2,Titanium dioxide,Sol-gel,Co-grinding process,Solvothermal
更新于2025-09-10 09:29:36
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Sol-gel synthesis of Ag-loaded TiO2-ZnO thin films with enhanced photocatalytic activity
摘要： Ag-loaded TiO2-ZnO thin films, with low ZnO content, were synthesized by a one-step sol-gel process. The Ag content varied in the interval 0-4 mol% Ag. The films were deposited on glass substrates and post-annealed at 500 °C to induce crystallinity. By using the Tauc model, it was determined that the higher the Ag concentration the higher the optical band-gap energy of the films, a result attributed to the Burstein-Moss effect. Images obtained by scanning electron microscopy and transmission electron microscopy depicted aggregated particles with grain size close to 20 to 25 nm for the oxides with no Ag, whereas the particle size decreased with the addition of Ag. X-ray photoelectron spectroscopy measurements indicated the formation of the Ti4+ and Zn2+ oxidation states, while Ag was found in the metallic state. A depth profile analysis, performed by secondary ion mass spectrometry, confirmed the presence of Ti, Zn, and Ag in the films. X-ray diffraction patterns displayed the anatase phase of TiO2. For (TiO2)0.95-(ZnO)0.05 thin films, a BET analysis showed that the specific surface area increased from 4.56 up to 48.84 m2/g as a consequence of Ag doping. The photocatalytic degradation of the materials under UV irradiation was assessed by using methylene blue as a model pollutant. For (TiO2)1-x-(ZnO)x compounds with no Ag, the highest response corresponded to x = 0.05. In addition, the optimum photodegradation was found for (TiO2)0.95-(ZnO)0.05 thin films with 2 mol% Ag.
关键词： Optical spectroscopy,Catalysis,X-ray diffraction,Sol-gel process,Thin films,Oxide materials
更新于2025-09-10 09:29:36
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Mixing time between organometallic precursor and ligand: a key parameter controlling ZnO nanoparticle size and shape and processable hybrid materials
摘要： Since the advent of nanoscience, chemists’ grail is to perfectly and reproducibly elaborate nanoparticles (NPs) of fully defined size, shape, polydispersity, and surface state. It implies a total control of the experimental parameters impacting the synthesis. In the preparation of metal oxide nanoparticles using an organometallic approach, we evidenced that the mixing time between the precursor and the ligand is surprisingly a parameter of tremendous importance. Using NMR spectroscopy, Wide Angle X-ray Scattering and computational DFT studies, the formation of Zn-amido oligomers through an acid-base reaction between the organometallic zinc precursor and the amine ligand is demonstrated. Over time, this polymerization process plays a major role on the control of the size and shape of the ZnO nanoparticles formed through hydrolysis reaction. Hence, nanorods are obtained for short mixing time before hydrolysis while isotropic NPs are obtained for longer ones. Furthermore, it induces the formation of a gel with adjustable rheological properties thus opening new opportunities for the design of processable hybrid materials.
关键词： ZnO,gel formation,organometallic synthesis,nanoparticles,size and shape control
更新于2025-09-10 09:29:36
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Electrical Control of Electromagnetically Induced Transparency by Terahertz Metamaterial Funneling
摘要： Electromagnetically induced transparency (EIT) analogs using metamaterials have diverse applications, including nonlinear optics, telecommunications, and biochemical sensors. These EIT analogs can be actively controlled by embedding semiconducting materials into metamaterial structures, but most active EIT metamaterials require complex optical setups and complicated fabrication processes. Graphene-based EIT metamaterials are some of the most promising active EIT systems because of their simple controllability by electrical bias, but related researches have so far been limited to theoretical or numerical studies. Here, experimentally verified graphene EIT metamaterials are provided by controlling the terahertz funneling of the unique metaatom structures. The proposed active EIT metamaterials are fabricated on flexible and ultrathin polyimide films to acquire the lowest substrate insertion losses and achieve a 1 ps group delay change at the transmission peak of the EIT analog. Moreover, because the proposed metamaterials exhibit resonance properties that vary depending on the polarization direction, the phase delay can be controlled up to 80° from the proposed metamaterials by rotating the incident polarization to the orthogonal direction. Overall, by controlling the group and phase delay of incident waves in a single metamaterial device simultaneously, a multifunctional active tuning system can be realized in the terahertz range.
关键词： terahertz,field enhancement,graphene,ion-gel,active metamaterials
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP) - Hiroshima (2018.5.27-2018.6.1)] 2018 IEEE ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP) - Bi<inf>4</inf>Ti<inf>3</inf>O<inf>12</inf>/SrTiO<inf>3</inf>Sol-Gel Composite for Ultrasonic Transducers
摘要： In this study, lead-free new sol-gel composite, Bi4Ti3O12(BiT)/SrTiO3(ST) was developed. 100μm thick films were fabricated on 3mm thick titanium substrates by sol-gel spray technique. Polarization process was carried out at room temperature and 400°C. Samples were set onto a hot plate and ultrasonic response in pulse-echo mode was recorded by a digital oscilloscope from room temperature to 500°C. As a result, each samples showed reflected wave at 500°C. Therefore, BiT/ST sol-gel composite have high temperature endurance up to 500°C. In addition, BiT/ST films was able to polarize at room temperature.
关键词： ultrasonic transducer,high temperature,nondestructive testing,sol-gel composite
更新于2025-09-10 09:29:36
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Influence of TiO2 structure on its photocatalytic activity towards acetaldehyde decomposition
摘要： Sol-gel method was used for preparation of TiO2 having different structure and phase composition. Prepared titania samples were applied for acetaldehyde decomposition under UV light irradiation. The obtained results showed, that TiO2 consisted from mixed phases of anatase and brookite, which was prepared at neutral pH and calcined at 450 °C was the most active. Charge separation of free carriers was investigated by measurements of electron traps density. It was proved, that density of electron traps can be enhanced by nitrogen doping or by coexisting of two phases such as anatase and brookite. However nitrogen doping to TiO2 did not increase of its photocatalytic activity towards acetaldehyde decomposition. Therefore preparation of TiO2 having mixed phases of anatase and brookite appeared to be the most favourable towards elimination of acetaldehyde under UV at ambient conditions. Moreover, temperature of calcination such as 450 °C was the most optimal, because at that temperature total crystallisation of amorphous titnia occurrs and then interparticle contact increases, which facilitates the interfacial charge transfer between titania particles.
关键词： Density of electron traps,Acetaldehyde decomposition,TiO2,Sol-gel
更新于2025-09-10 09:29:36
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Preparation of core–shell nanostructured black nano-TiO <sub/>2</sub> by sol–gel method combined with Mg reduction
摘要： Black nano-TiO2 samples with core–shell nanostructure were successfully prepared by sol–gel method combined with Mg reduction using butyl titanate as titanium source and calcining at 500°C in air atmosphere and at 400–600°C in nitrogen atmosphere. The prepared black TiO2 samples were characterized by X-ray diffraction, high resolution transmission electron microscopy, Raman spectra, photoluminescence emission spectra, N2 adsorption–desorption, and ultraviolet–visible spectroscopy. The results show that the black TiO2 exhibits a crystalline core–disordered shell structure composed of disordered surface and oxygen vacancies, and the thickness of the disordered layer is about 2–3 nm. The optical absorption properties of black nano-TiO2 samples have been remarkably enhanced in visible light region. Compared with the white TiO2, the reduced black TiO2 samples exhibit enhanced photocatalytic hydrogen production under the full solar wavelength range of light, and the sample prepared with the Mg and TiO2 ratio of 9:1 calcined at 500 °C has the maximum hydrogen production rate.
关键词： core–shell nanostructure,Black nano-TiO2,photocatalytic hydrogen production,sol–gel method,Mg reduction
更新于2025-09-10 09:29:36
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Highly enhanced solar conversion efficiency of novel layer-by-layer PbS:Hg and CdS quantum dots-sensitized ZnO thin films prepared by sol–gel spin coating
摘要： Owing to superior optical properties, ZnO thin ?lms have immense potential in solar cell preparation. ZnO thin ?lms were prepared by sol–gel technology. However, this is prolonged technique and it necessitates a complex precursor solution. In the present work, ZnO thin ?lms are prepared by sol–gel spin coating with simple precursor, zinc acetate. A very remarkable feature of the method is that polycrystalline, non-abrasive and translucent ?lms were obtained. Additionally, novel PbS:Hg quantum dots (QDs) and CdS QDs are successfully synthesized. Moreover, both types of QDs are deposited layer-by-layer over pure ZnO and Ag:ZnO thin ?lms. The ?lms are characterized by X-ray diffraction, and crystallinity continuation is observed even after the addition of QDs layer. Presence of synthesized QDs over thin ?lms is also con?rmed. The ?lms were also characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. Uniform, dense and porous surface morphology is clearly revealed. Sensitized thin ?lms show a huge decline in band gap and large enhancement in ef?ciency. Superior current density (10.87 mA cm?2) is achieved with PbS:Hg/CdS/Ag:ZnO, which leads to enhancement in overall solar conversion ef?ciency by 6.34 times.
关键词： PbS:Hg quantum dots,sol–gel,Ag:ZnO ?lm,CdS quantum dots
更新于2025-09-10 09:29:36
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Microwave assisted sol–gel synthesis of titanium dioxide using hydrochloric and acetic acid as catalysts
摘要： Titanium dioxide (TiO2) was synthesized by microwave assisted sol–gel. The effect of the acid type used as catalyst on the phase transformation of TiO2 was investigated (hydrochloric or acetic acid). The samples obtained were characterized by scanning electron microscopy (SEM), this micrographs showed particles with irregular shapes. The results of Fourier transform-infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed present signals of O and Ti. When hydrochloric acid was used as catalyst, three titania polymorphs were detected by X-ray diffraction (XRD), anatase, rutile and brookite, where the crystallite size was in the range of 9 and 16 nm. On the other hand, a single anatase phase was formed when acetic acid was used after only 15 min of reaction time. The anatase average crystallite size was obtained between 11 and 22 nm.
关键词： Microwave-assisted sol–gel,Acetic acid,Hydrochloric acid,Titanium dioxide
更新于2025-09-10 09:29:36