Gas sensing properties of nanostructured MoO3 thin films prepared by spray pyrolysis

Thin films of molybdenum trioxide (MoO₃) were deposited on common glass using the chemical spray pyrolysis technique. A (NH₄)₆Mo₇O₂₄4H₂0 solution 0.1 M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO₃ thin films was studied. MoO₃ can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO₃ and the metastable monoclinic β-MoO₃ phase. XRD-spectra showed a growth of α-MoO₃ phase percentage as substrate temperature increases from 420 K up to 670 K. Films deposited in the 500–600 K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO₃ thin films electrical resistance when films temperature varied from 100 K up to 500 K. The sensing property of these MoO₃ films was also studied. The sensitivity was investigated in the temperature range 160 and 360 K for H₂O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H₂O.     

Catalytic performance of Mn3O4 and Co3O4 nanocrystals prepared by sonochemical method in epoxidation of styrene and cyclooctene

A simple sonochemical method was developed to synthesis uniform sphere-like Co₃O₄ and Mn₃O₄ nanocrystals. Epoxidation of styrene and cyclooctene by anhydrous tert-butyl hydroperoxide over the prepared Co₃O₄ and Mn₃O₄ nanocatalysts was investigated. The results of conversion activity were compared with bulk Co₃O₄ and Mn₃O₄. Under optimized reaction conditions, the nanocatalysts showed a superior catalytic performance as compared to the bulk catalysts. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area, were used to characterize and investigate the nanocatalysts.     

Luminescence of ZnWO4 and CdWO4 thin films prepared by spray pyrolysis

Thin films of ZnWO₄ and CdWO₄ were prepared by spray pyrolysis and the structural, optical, and luminescence properties were investigated. Both ZnWO₄ and CdWO₄ thin films showed a broad blue-green emission band. The broad band of ZnWO₄ films was centered at 495 nm (2.51 eV) consisted of three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 540 nm (2.30 eV). The broad band of CdWO₄ films at 495 nm (2.51 eV) could be decomposed to three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 545 nm (2.28 eV). These results are consistent with emission from the WO₆⁶⁻ molecular complex. The luminance and efficiency for ZnWO₄ film at 5 kV and 57 μA/cm² were 48 cd/m² and 0.22 lm/w, respectively, and for CdWO₄ film the values were 420 cd/m² and 1.9 lm/w.     

A novel chemical synthesis and characterization of Mn3O4 thin films for supercapacitor application

Mn₃O₄ thin films have been prepared by novel chemical successive ionic layer adsorption and reaction (SILAR) method. Further these films were characterized for their structural, morphological and optical properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), field emission scanning electron microscopy (FESEM), wettability test and optical absorption studies. The XRD pattern showed that the Mn₃O₄ films exhibit tetragonal hausmannite structure. Formation of manganese oxide compound was confirmed from FTIR studies. The optical absorption showed existence of direct optical band gap of energy 2.30 eV. Mn₃O₄ film surface showed hydrophilic nature with water contact angle of 55°. The supercapacitive properties of Mn₃O₄ thin film investigated in 1 M Na₂SO₄ electrolyte showed maximum supercapacitance of 314 F g⁻¹ at scan rate 5 mV s⁻¹.     

Chemical bath deposition of hausmannite Mn3O4 thin films

A low-temperature chemical bath deposition (CBD) technique has been used for the preparation of Mn₃O₄ thin films onto glass substrates. The kinetic behavior and the formation mechanism of the solid thin films from the aqueous solution have been investigated. Structure (X-ray diffraction and Raman), morphological (atom force microscope), and optical (UV-vis-NIR) characterizations of the deposited films are presented. The results indicated that the deposited Mn₃O₄ thin films of smooth surface with nanosized grains were well crystalline and the optical bandgap of the film was estimated to be 2.54 eV.     

High temperature and low current density synthesis of Mn3O4 porous nano spheres: Characterization and electrochemical properties

Uniform and single-crystalline Mn₃O₄ nano-spheres were synthesized by cathodic electrodeposition at high temperature (80 °C) and low current density (0.25 mA cm⁻¹) on steel electrode. Further the annealed samples were characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) studies. TEM and SEM images showed that particles have spherical shapes and the average diameter size was about 50 nm. Formation of Mn₃O₄ compound was confirmed from FTIR studies. The XRD pattern showed that the Mn₃O₄ exhibit tetragonal hausmannite structure. The results of N₂ adsorption-desorption analysis indicated that Mn₃O₄ nano-sphere has BET surface area of about 177.6 m² g⁻¹ and average pore diameters of 3 and 4 nm. The possible formation mechanism of Mn₃O₄ nanostructures has been discussed. The supercapacitive properties of Mn₃O₄ sample in 0.5 M Na₂SO₄ electrolyte showed maximum supercapacitance of 235.4 Fg⁻¹ at scan rate 10 mV s⁻¹. Coulumbic efficiency could be kept about 90% during 1000 cycles at 10 mV s⁻¹.     

Cathodoluminescence characteristics of particles and film of (Y, Zn)2O3:Eu phosphor prepared by spray pyrolysis

Eu-doped Y₂O₃ particles with spherical shape and fine size were prepared by spray pyrolysis. The cathodoluminescence of Y₂O₃:Eu³⁺ powder was optimized by substituting small amount of zinc atoms in place of yttrium sites. As a result, the optimized (Y, Zn)₂O₃:Eu³⁺ phosphor showed 60% improved cathodoluminescence compared with Y₂O₃:Eu³⁺ particles. The prepared (Y, Zn)₂O₃:Eu³⁺ phosphor had spherical shape and 0.726 μm in mean size. Using these particles, the thickness of the phosphor film was controlled by varying the phosphor loading. The brightness and luminous efficiency of phosphor films prepared were monitored with varying the accelerating voltage ranges from 4 to 14 kV. The dependency of the luminous efficiency on the accelerating voltage was very sensitive to the phosphor loading. As increasing the accelerating voltage from 4 to 14 kV, the brightness of phosphor films prepared was monotonically increased from 200 to 1085 cd/cm²_, but the saturation in the luminous efficiency appeared at 10 kV. The highest efficiency was achieved when the number of phosphor-particles layer was about 3. More details about the luminous efficiency and brightness were discussed with changing the phosphor loading.     

Charge-discharge characteristics of nanocrystalline Co3O4 powders via aerosol flame synthesis

Nanocrystalline Co₃O₄ powders were synthesized by aerosol flame synthesis (AFS) method for the anode of lithium ion batteries and the basic electrochemical properties were investigated. The effects of synthesis conditions and heat-treatment temperature on the morphology, crystallite size and electrochemical properties were investigated. As-prepared soot contained Co₃O₄, CoO and Co(OH)₂, which were eventually converted into cubic spinel Co₃O₄ by post heat treatment. The as-prepared particle size was in the range of 10-30 nm and grew to 50-85 nm by the heat treatment. With growing particle size and improved crystallinity, charge-discharge capacity and cycle performance were improved and the discharge capacity of the powder heat-treated at 700 °C was 571 mAh/g after 30 cycles, which was better than Co₃O₄ powder reported in the previous literature.     

Fabrication of textured SnO2:F thin films by spray pyrolysis

Transparent conductive SnO₂:F thin films with textured surfaces were fabricated on soda-lime-silica glass substrates by spray pyrolysis. Structure, morphology, optical and electrical properties of the films were investigated. Results show that the film structure, morphology, haze, transmittance and sheet resistance are dependent on the substrate temperature and film thickness. An optimal 810 nm-thick SnO₂:F film with textured surface deposited at 520 °C exhibits polycrystalline rutile tetragonal structure with a (2 0 0) orientation. The sheet resistance, average transmittance in visible region, and haze of this film were 8 Ω/□, 80.04% and 11.07%, respectively, which are suitable for the electrode used in the hydrogenated amorphous silicon solar cells.     

Facile method to prepare stable superhydrophobic Co3O4 surface

A facile and novel method was developed to fabricate rough Co₃O₄ surface with hierarchical micro- and nanostructures by the combination of simple solid state reactions and coating process. After modification with stearic acid, a superhydrophobic surface with water contact angle of 155 ± 1.8° and sliding angle of 2° was obtained. The superhydrophobic Co₃O₄ surface remained superhydrophobic property in a wide pH range from 3 to 14. The superhydrophobic Co₃O₄ surface also showed excellent self-cleaning property and high stability in ambient environments.     

Synthesis of urchin-like Co3O4 hierarchical micro/nanostructures and their photocatalytic activity

Urchin-like Co₃O₄ hierarchical micro/nanostructures have been successfully synthesized by calcining urchin-like precursor CoCO₃, which are prepared by a facile hydrothermal route. The particle size of the urchin-like Co₃O₄ could be easily controlled by altering the calcination temperature. The morphology and structure of the as-prepared urchin-like products were characterized by XRD, FESEM and TEM. Photocatalytic measurement demonstrates that these urchin-like Co₃O₄ micro/nanostructures show good photocatalytic effect and their degradation efficiency is strongly dependent on their particle size. Furthermore, a plausible reaction mechanism is also proposed to illustrate the photocatalytic processes of Co₃O₄.     

三维海胆状Co3O4的微纳结构制备及锂电池性能

水热法制备的合成海胆状Co₃O₄前驱物在空气中退火得到三维海胆状Co₃O₄的微纳结构. 采用FESEM、TEM、HRTEM以及XRD对产物进行形貌和结构的表征. 结果表明,合成的海胆状结构Co₃O₄由许多粒径约为15 nm的颗粒串接形成. 锂电池测试性能表明,制备的海胆状Co₃O₄首次放电容量达到1.369 Ah/g,经过20次循环     

Physico-chemical, optical and electrochemical properties of iron oxide thin films prepared by spray pyrolysis

Iron oxide thin films were prepared by spray pyrolysis technique onto glass substrates from iron chloride solution. They were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and (UV-vis) spectroscopy. The films deposited at T_s ≤ 450 °C were amorphous; while those produced at T_sub = 500 °C were polycrystalline α-Fe₂O₃ with a preferential orientation along the (1 0 4) direction. By observing scanning electron microscopy (SEM), it was seen that iron oxide films were relatively homogeneous uniform and had a good adherence to the glass substrates. The grain size was found (by RX) between 19 and 25 nm. The composition of these films was examined by X-ray photoelectron spectroscopy and electron probe microanalysis (EPMA). These films exhibited also a transmittance value about 80% in the visible and infrared range. The cyclic voltammetry study showed that the films of Fe₂O₃ deposited on ITO pre-coated glass substrates were capable of charge insertion/extraction when immersed in an electrolyte of propylene carbonate (PC) with 0.5 M LiCLO₄.     

Neutron powder diffraction and magnetic studies of mesoporous Co3O4

Samples of mesoporous Co₃O₄, created by using mesoporous silicas KIT-6 and SBA-16 as hard templates to control the growth of Co₃O₄ have been investigated with SQUID magnetometry and neutron powder diffraction, to reveal the effects of high surface area on the magnetic and electronic properties. DC magnetic susceptibility measurements show lower Néel ordering temperatures and lower magnetic moments than in a “bulk” reference. A lower second transition temperature is also observed in the mesoporous samples, associated with the freezing of the surface (shell) magnetic moments. Measurements taken with increasing applied field at constant temperature show the materials to be antiferromagnetic as expected. Complementary parametric neutron powder diffraction studies show similar trends between the two mesoporous samples when looking at their Néel temperatures, and verify long range order within the samples.     

径向生长的具有分级结构的四氧化三钴微晶及其在气体传感上的应用

通过在水热合成后追加退火处理,制备了径向生长的具有分级结构的树枝状三维Co₃O₄晶体,并用X射线衍射仪、扫描电子显微镜和透射电子显微镜对其结构和形貌进行了表征. 在110 oC对其气体探测性能的研究表明这种Co₃O₄分级结构对氨气有较高的探测灵敏度和响应速度(10 s),性能稳定并具有可重复性. 同时,还在较低的探测温度下对酒精、丙酮和苯进行了气敏探测.     

Electrochromic and photoluminescence properties of cobalt oxide thin films prepared by spray pyrolysis

Cobalt oxide thin films were prepared by a facile spray pyrolysis technique, using a perfume atomizer with an aqueous solution of hydrated cobalt chloride salt with a molar concentration of 0.025?M as a source of cobalt. The films were deposited onto glass substrates at temperature of 350?°C. The structural, morphological, and electrochromic properties of the obtained films were studied. It was found from X-ray diffraction analysis that the films were polycrystalline in nature with spinel-type cubic structure and preferred orientation along [111] direction. The Scanning Electron Microscopy images revealed a porous structure with the average grain size around 200?nm. The cyclic voltammetry measurements revealed that Cobalt oxide thin film is an anodically coloring electrochromic material with a transmittance variation in the visible range of 31%, and a fast response time (about 2?seconds) and a good cycling stability. These electrochromic performances make cobalt oxide thin film an attractive material for using as an anodic electrochromic material in smart windows devices. The photoluminescence spectra exhibited a strong emission in the visible region confirming the good crystallinity properties of Co₃O₄ thin films.     

SrBi2Ta2O9/Bi4Ti3O12复合铁电薄膜的制备与特性研究

采用溶胶凝胶工艺在p-Si衬底上制备了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合铁电薄膜. 研究了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合薄膜的微观结构与生长行为、铁电性能和疲劳特性. 研究表明: Si衬底Bi₄Ti< 关键词： 2Ta₂O₉')" href="#">SrBi₂Ta₂O₉ 4Ti₃O₁₂')" href="#">Bi₄Ti₃O₁₂ 复合铁电薄膜 溶胶凝胶工艺     

调控氧空位实现高比表面积Co3O4纳米片上的产氧反应

Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we designed an efficient Co₃O₄ electrocatalyst using a pyrolysis strategy for oxygen evolution reaction (OER). Morphological characterization confirmed the ultra-thin structure of nanosheet. Further, the existence of oxygen vacancies was obviously evidenced by the X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. The increased surface area of Co₃O₄ ensures more exposed sites, whereas generated oxygen vacancies on Co₃O₄ surface create more active defects. The two scenarios were beneficial for accelerating the OER across the interface between the anode and electrolyte. As expected, the optimized Co₃O₄ nanosheets can catalyze the OER efficiently with a low overpotential of 310 mV at current density of 10 mA/cm² and remarkable long-term stability in 1.0 mol/L KOH.     

Bulk and surface properties of spinel Co3O4 by density functional calculations

DFT calculations are employed to bulk and surface properties of spinel oxide Co₃O₄. The bulk magnetic structure is calculated to be antiferromagnetic, with a Co²⁺ moment of 2.631 μ_B in the antiferromagnetic state. There are three predicted electron transitions O(2p) → Co²⁺(t_2g) of 2.2 eV, O(2p) → Co³⁺(e_g) of 2.9 eV and Co³⁺(t_2g) → Co²⁺(t_2g) of 3.3 eV, and the former two transitions are close to the corresponding experimental values 2.8 and 2.4 eV. The naturally occurring Co₃O₄ (1 1 0) and (1 1 1) surfaces were considered for surface calculations. For ideal Co₃O₄ (1 1 0) surfaces, the surface relaxations are not significant, while for ideal Co₃O₄ (1 1 1) surfaces the relaxation of Co²⁺ cations in the tetrahedral sites is drastic, which agrees with the experiment observation. The stability over different oxygen environments for possible ideal and defect surface terminations were explored.     

Non-equilibrium effects in the magnetic behavior of Co3O4 nanoparticles

We report detailed studies of the non-equilibrium magnetic behavior of antiferromagnetic Co₃O₄ nanoparticles. The temperature and field dependence of magnetization, wait time dependence of magnetic relaxation (aging), memory effects, and temperature dependence of specific heat have been investigated to understand the magnetic behavior of these particles. We find that the system shows some features that are characteristic of nanoparticle magnetism such as bifurcation of field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities and a slow relaxation of magnetization. However, strangely, the temperature at which the ZFC magnetization peaks coincides with the bifurcation temperature and does not shift on application of magnetic fields up to 1 kOe, unlike most other nanoparticle systems. Aging effects in these particles are negligible in both FC and ZFC protocols, and memory effects are present only in the FC protocol. We show that Co₃O₄ nanoparticles constitute a unique antiferromagnetic system which enters into a blocked state above the average Néel temperature.