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Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide nanostructured catalyst
摘要： In this paper, we report an in-situ synthesis of silver supported on cobalt oxide (Ag/Co3O4) nanoparticles (NPs) and studied the catalytic activity of this material as an eco-friendly, simple, recyclable and efficient catalyst for one‐pot photocatalytic oxidation of aromatic alcohols. Ag nanoparticles with the sizes of 2–5 nm supported on spherical Co3O4 with the radius between 40 and 60 nm were synthesized by homogeneous chemical precipitation followed by hydrothermal heating. The as-synthesized catalyst was thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherm (BET) analysis. It was observed that the catalysts with 1 wt% of silver loading shows high activity and selectivity toward the target aldehyde product. The effects of different reaction parameters such as reaction time, oxidant and solvent were investigated and studied in detail. The synergistic effect between the surface Ag NPs and Co3O4 nanospheres plays a vital role toward very high catalytic activity.
关键词： Oxide materials,Chemical synthesis,Catalysis,X-ray diffraction
更新于2025-09-23 15:23:52
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Boosted thermoelectric properties of molybdenum oxide thin films deposited on Si substrates
摘要： MoO2+x has novel peculiarities and complexities due to multiple valence states of 4d molybdenum, but high carrier density impedes its thermoelectric (TE) application. Recent investigation has demonstrated that the TE performance of transition metal oxide films can be greatly enhanced by activating a parallel conduction channel in the perovskite substrates through reversible incorporation of oxygen. In this work, we report the TE properties of MoO2+x thin films deposited on single crystalline Si and quartz glass substrates by magnetron sputtering. The TE power factor (PF) in the former is above 40 times bigger than that in the latter. Such a large enhancement originates mainly from the significantly enhanced Seebeck coefficient, correlated with the contribution of the Si substrate. The highest PF value 1.78 mW/(m · K2) at 700 K in this MoO2+x/Si system is comparable to the state-of-the-art in other TE thin films. Based on the preceding research, our experimental results suggest a more economic and scalable route to explore high-performance TE thin films.
关键词： thermoelectric,thin films,microstructure,Oxide materials
更新于2025-09-23 15:22:29
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Structural investigation of oxygen stoichiometry during thermocycles in PMN-28PT
摘要： The current research focuses on the role of oxygen partial pressure on structure and phase transitions of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with x ? 0.28 (PMN-28PT). The changes in oxygen content have been traced through weight gain/loss during 160 cycles between 250 and 300 (cid:2)C. The structural phase transitions have been investigated by in-situ high temperature powder X-ray diffraction and high temperature Raman spectroscopy. The variations in oxygen content in PMN-28PT result in structural changes and have a signi?cant effect on electrical impedance. It is suggested that bonding between oxygen and Ti and Pb atoms in the perovskite structure of PMN-28PT can be controlled by low oxygen partial pressure heat treatment.
关键词： Crystal structure,Phase transitions,Oxide materials,Thermodynamic properties,Thermal analysis
更新于2025-09-23 15:22:29
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Structure and properties of layered perovskites Ba1-Ln Fe1-Co O3-δ (Ln = Pr, Sm, Gd)
摘要： A series of samples of overall composition Ba1-xLnxFe1-yCoyO3-δ (Ln = Pr, Sm, Gd) with x = 0.3-0.4; y = 0-0.5 were prepared by glycerin nitrate technique in air. The crystal structure of single-phase Ba1-xLnxFe1-yCoyO3-δ (Ln = Pr, Sm, Gd) determined by XRD was described as cubic (sp. gr. Pm3(cid:1)m). However, transmission electronic microscopy revealed that both Sm- and Gd-doped oxides possess tetragonal structure with 5-fold and 3-fold increased c parameter respectively. Oxygen content in the complex oxides has been determined in air over wide temperature range by means of thermogravimetry and iodometric titration. The change in oxygen content with temperature for the phases with five-layered ordering was significantly smaller than for the disordered phases.
关键词： oxygen nonstoichiometry,X-ray diffraction,oxide materials,transmission electron microscopy,crystal structure
更新于2025-09-23 15:22:29
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Facile microwave-assisted synthesis of Cr2O3 nanoparticles with high near-infrared reflection for roof-top cooling applications
摘要： Microwave-assisted solution synthesis was employed for the preparation of Cr2O3 nanoparticles using Cr(acac)3 and ethylene glycol. The optimum conditions for the completion of the reaction forming a green precipitate (yield-95%) were: irradiation for 40e60 min at 220 (cid:1)C solution temperature. The as-prepared sample was barely crystalline; annealing in air at above 300 (cid:1)C formed nanocrystalline Cr2O3, as shown by X-ray diffraction (XRD). High-resolution transmission electron microscopy (HRTEM) of the “700 (cid:1)C sample” con?rmed the well-crystallised Cr2O3 formation with ~37 nm average size. The as-prepared powder (bluish-green) showed high near-infrared (NIR) re?ectance, whereas the annealed samples showed bright-green re?ectance, whose International Commission on Illumination L*a*b* (CIE L*a*b*) values shifted towards the green region. The higher Dq/B value (3.76), suggested that Cr3t lies in a strong crystal ?eld. Stainless steel blocks covered with the as-prepared (intermediate) material reduced heating under sunlight by 5 (cid:1)C, indicating its suitability as an easily prepared tile coating for roof-top applications. The annealed samples are found suitable as an anti-dazzling coating for automobile windscreens and rear-view mirrors.
关键词： Chemical synthesis,Ceramics,Microwave-assisted synthesis,Oxide materials,Cr2O3 nanoparticles
更新于2025-09-19 17:15:36
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Lanthanum containing barium stannate nanoparticles synthesized by cetyltriammonium bromide assisted wet chemistry route for application in perovskite solar cell
摘要： In this paper, we report comparative photovoltaic performance of cetyltriammonium bromide assisted wet chemical route synthesized Ba0.94La 0.06SnO3 and sol-gel synthesized TiO2 nanoparticles using CH3NH3SnCl3 as absorber and NiO as hole transport layer. The X-ray diffraction patterns of Ba0.94La 0.06SnO3, TiO2 and NiO nanoparticles showed the formation of cubic, tetragonal and cubic phases, respectively with average crystallite size ~ 25 nm. The X-ray diffraction pattern of CH3NH3SnCl3 nanoparticles exhibited the formation of monoclinic phase, with average crystallite size ~ 5 nm. The band gap values of Ba0.94La 0.06SnO3, TiO2, NiO and CH3NH3SnCl3 nanoparticles are estimated as 3.6, 3.4, 3.5 and 2.8 eV, respectively. The silver contacts, which work as counter electrode, were thermally deposited, and device has been studied for power conversion efficiency under the illumination of ~ 100 mW cm2.
关键词： oxide materials,perovskite,Inorganic materials,barium stannate nanoparticles,wet chemistry
更新于2025-09-16 10:30:52
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Ordered langasites La3Ga5MO14:Eu3+ (M = Zr, Hf, Sn) as red-emitting LED phosphors
摘要： The temperature-dependent luminescence behavior of three ordered langasites La3Ga5ZrO14 (LGZr), La3Ga5HfO14 (LGHf) and La3Ga5SnO14 (LGSn) doped with up to 20% Eu3+ were investigated. Band gap energies of 4.32 eV (LGZr), 4.43 eV (LGHf), and 4.46 eV (LGSn) were determined by diffuse reflection measurements of the undoped compounds. The influence of the structural differences on the luminescence properties of the three langasites were investigated by means of excitation, emission (77-500 K) and luminescence lifetime measurements (77-300 K). The quenching temperatures of the three langasites do vary. They were attained using different excitation wavelengths in the charge transfer band (300 nm) and in the 4f levels (394 nm). LGSn:Eu 20% Eu3+ showed the best temperature performance with intensities at 500 K of 85% (300 nm) and 67% of the intensity measured at 77 K. At room temperature and with an excitation wavelength of 394 nm, maximum quantum efficiencies of 41% for LGZr:Eu 20% Eu3+, 58% for LGHf:Eu 20% Eu3+ and 68% for LGSn:Eu 20% Eu3+ were reached. The quenching behavior observed is explained by semi-quantitative configurational coordinate diagrams. Based on these results and the high red color purity, the langasites were built into LEDs with (In,Ga)N chips emitting at 394 nm, to test the applicability of the materials as red LED phosphors.
关键词： inorganic materials,optical properties,rare earth alloys and compounds,phosphors,oxide materials,luminescence
更新于2025-09-11 14:15:04
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Metal Oxide Nanostructures || Chromogenic applications
摘要： There exist several forms of chromism, but this chapter only describes the phenomena that involve metal oxide materials. Chromism refers to changes in visible optical properties in response to an external stimulus such as electrical, optical, thermal, or mechanical [1]. It includes changes in color or intensity. It can also refer to a transition from transparent to a scattering reflective state. The chromogenic family of materials has been ever expanding over the past few years, with the development of new materials and nanomaterials. A schematic of the evolution of chromogenic effect and materials is shown in Fig. 4.1.
关键词： metal oxide materials,photochromic,chromism,gasochromic,electrochromic,thermochromic,magnetochromic
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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Influence of the Anatase and Rutile phases on the luminescent properties of rare-earth-doped TiO2 films
摘要： For a long time, the development of new and more efficient light-emitting materials has been the driving force to investigate the presence of trivalent rare-earth (RE3+) ions into solid hosts. It happens because RE3+ ions provide efficient and well-defined optical transitions whose intensities are determined by phenomena regarding excitation-recombination mechanisms or, ultimately, by the RE3+ atomic surroundings. Motivated by these aspects, this paper presents a comprehensive study of the influence exerted by TiO2 (under the amorphous and crystalline forms) onto the light emission due to Sm3+ and Tm3+ ions. To this end, Sm-, Tm-, and SmTm-doped TiO2 films were prepared and their structural-electronic properties were investigated by optical spectroscopic techniques - following appropriate thermal annealing treatments. As a result of the deposition method and conditions, the as-deposited (stoichiometric) TiO2 films present an amorphous structure and single RE concentrations around 0.5 at.%. Also, whereas thermal annealing the films at increasing temperatures resulted in almost no changes in their elemental composition, extensive variations were observed in their atomic structure and RE3+-related light emission characteristics. Based on the experimental results, it became clear the role played by the amorphous or crystalline (Anatase or Rutile) structures of the TiO2 films onto the RE3+-related luminescence features, and the likely mechanisms behind the phenomenon are presented and discussed in detail.
关键词： Vapor deposition (IBAD),Optical spectroscopy,Optical properties,Oxide materials (TiO2)
更新于2025-09-10 09:29:36