UV-enhanced room-temperature gas sensing of ZnGa2O4 nanowires functionalized with Au catalyst nanoparticles

ZnGa₂O₄ nanowires were synthesized using a thermal evaporation technique. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction revealed that the nanowires were single crystals 30–200 nm in diameter and ranged up to ～100 μm in length. The sensing properties of multiple networked ZnGa₂O₄ nanowire sensors functionalized with Au catalyst nanoparticles with diameters of a few nanometers toward NO₂ gas at room temperature under UV irradiation were examined. The sensors showed a remarkably enhanced response and far reduced response and recovery times toward NO₂ gas at room temperature under 254 nm-ultraviolet (UV) illumination. The response of ZnGa₂O₄ nanowires to NO₂ gas at room temperature increased from ～100 to ～861 % with increasing the UV intensity from 0 to 1.2 mW/cm². The significant improvement in the response of ZnGa₂O₄ nanowires to NO₂ gas by UV irradiation is attributed to the increased change in resistance due to the increase in the number of electrons participating in the reactions with NO₂ molecules by photo-generation of electron–hole pairs.     

Synthesis and physical properties of mixed Co3O4/CoO nanorods by microwave hydrothermal technique

A mixture of crystalline Co₃O₄/CoO nanorods with non-uniform dense distribution has been successfully synthesized by microwave hydrothermal technique. The synthesized nanorods have been characterized by several techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FT-IR). The results showed that the as synthesized specimens contained mixed crystalline Co₃O₄/CoO nanorods with an average length of around 80 nm and an average diameter of 42 nm. UV–Vis spectrum of the nanorods exhibited a strong UV emission. The band energy gap of the product was 1.79 eV which lies between the energy gap of CoO and that for Co₃O₄. The obtained carrier concentration is of the order 4.32 × 10²⁷ m⁻³ and the dielectric constant is found to be 4.89. The electrical conductivity increases with increasing temperature and behaves as a semiconducting material with an activation energy of a bout 0.26 eV. This makes the as synthesized mixed Co₃O₄/CoO nanorods very useful for supercapacitor devices application. Magnetic hysteresis loops at room temperature of the as synthesized mixed oxides (Co₃O₄/CoO) nanorods exhibit typical soft magnetic behavior.     

Facile synthesis of flower-like α-Fe2O3/ZnFe2O4 architectures with self-assembled core-shell nanorods for superior TEA detection

Uniform flower-like α-Fe₂O₃ architectures with self-assembled core-shell nanorods are constructed and successfully prepared via the facile process. The concentration of Fe salt plays a great significance for morphological evolution from nanorods to self-assembled microflowers. Flower-like α-Fe₂O₃/ZnFe₂O₄ consisting of α-Fe₂O₃ core and ZnFe₂O₄ shell nanorods are derived from FeOOH/ZIF-8 precursors. The detailed studies reveal that the tunable growth of ZIF-8 nanoparticles on three-dimensional FeOOH microflowers at room temperature and the availble calcination regulation are responsible for the formation of core-shell Fe₂O₃/ZnFe₂O₄ composites. The highest response value of flower-like α-Fe₂O₃/ZnFe₂O₄ architectures to 100 ppm triethylamine (TEA) has been improved to 141 at 280 °C, which is calculated to be 6.2 times compared with flower-like α-Fe₂O₃ architectures (22.7). The enhanced gas-sensing mechanism of α-Fe₂O₃/ZnFe₂O₄ composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe₂O₃ core and ZnFe₂O₄ shell, and the improved electron transfer process.     

The optimized preparation and electrochemical properties of LiMn1.95Co0.05O4 and Al2O3-coated LiMn1.95Co0.05O4

Cathode material LiMn_1.95Co_0.05O₄ for lithium ion battery was synthesized via solid state reaction, and calcination temperature and time were investigated, respectively. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The optimized calcination temperature and time are 850 °C and 15 h. The surface of LiMn_1.95Co_0.05O₄ cathode is coated using Al₂O₃ coating materials. The phase structures, surface morphologies, and element types of the prepared LiMn_1.95Co_0.05O₄ and Al₂O₃-coated LiMn_1.95 Co_0.05O₄ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy spectrum analysis (EDS). The 0.5 wt% Al₂O₃-coated compound exhibited better specific capacity and capacity retention than bare sample. The initial discharge capacity was 140.9 mAh/g and capacity retention was 96.7 % after 10 cycles at 0.1 C. Such enhancements are attributed to the presence of a stable Al₂O₃ layer which acts as the interfacial stabilizer on the surface of LiMn_1.95Co_0.05O₄.     

纳米结构CoxFe3-xO4多孔微球的磁性及交换偏置效应研究

用乙二醇为溶剂,用三氯化铁、二氯化钴和醋酸铵为起始反应试剂,通过溶剂热反应首次合成了纳米结构Co_xFe_3-xO₄多孔微球.用X射线衍射仪(XRD)、透射电子显微镜(TEM)和扫描电子显微镜(SEM)表征样品的结构和形貌,结果表明,所制备的单分散Co_xFe_3-xO₄多孔微球为立方多晶结构,其直径约300 nm,是由约30 关键词： xFe_3-xO₄')" href="#">Co_xFe_3-xO₄ 多孔微球 磁性 交换偏置效应     

The multiferroic properties of Bi(Fe0.95Co0.05)O3 films

Bi(Fe_0.95Co_0.05)O₃ films were prepared on conductive indium tin oxide (ITO)/glass substrates by chemical solution deposition. Well saturated polarization hysteresis loop has been observed with a remnant polarization value of about 22 μC/cm² at room temperature. Weak ferromagnetism with saturation magnetization of about 3 emu/cm³ was observed at room temperature. The clear observation of both room temperature ferroelectric and ferromagnetic properties suggests the potential multiferroic applications of Bi(Fe_0.95Co_0.05)O₃.     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.     

Magnetic resonance study of phases in FeVO4-Co3V2O8 system

Multicomponent vanadates Co_3+xFe_4−xV₆O₂₄ have been synthesized using the solid state reaction method from Co₃V₂O₈ and FeVO₄.oxides. The electron paramagnetic resonance/ferromagnetic resonance (EPR/FMR) spectra of 20 samples containing solid state phases formed in the FeVO₄-Co₃V₂O₈ system have been recorded at room temperature. The howardevansite structure (H-type phase) is produced, which corresponds to the Co_2.616Fe_4.256V₆O₂₄ formula while a homogeneity range of lyonsite (L-type phase) type structure could be described by the Co_3+1.5xFe_4−xV₆O₂₄ formula (0.476<x<1.667). Considering the values of g-factor and linewidth of each registered spectrum the existence of three types of magnetic centers was inferred and correlated with phases detected by XRD method.     

Liquid precipitation synthesis of Co3O4 for high-performance electrochemical capacitors

The amorphous Co₃O₄ nanostructure, which adopted sodium hexametaphosphate as structure-directing agent, has been successfully synthesized in large scale via two steps: preparation of the precursor and the calcination process. The results of X-ray diffraction indicate that the prepared materials are mainly composed of Co₃O₄; the formless Co₃O₄ nanoplate with loose structures is observed by scanning electron microscopy. Cyclic voltammetry, chronopotentiometry, and electrochemical impedance measurements are applied in a mild aqueous electrolyte (2 mol L^?1 KOH) to investigate the performance of the Co₃O₄, which show a high specific capacitance (SC) of 482.61 F g^?1 at 5 mA cm^?2. Besides, the SC degradation is only 10.05 % after 250 continuous charge–discharge cycles at 5 mA cm^?2, indicating an excellent electrochemical stability. The improved performance is reasonably ascribed to their irregular structure for ionic transport during the electrochemical reaction, which presents as promising candidates for supercapacitors.     

Suppression of structural degradation of LiNi0.9Co0.1O2 cathode at 90 °C by AlPO4-nanoparticle coating

This study examined the electrochemical and structural stability of ∼1.5 wt.% AlPO₄-coated LiNi_0.9Co_0.1O₂. The AlPO₄-coated LiNi_0.9Co_0.1O₂ retained ∼60% of the original capacity after 50 cycles, compared with the ∼30% capacity retention of the bare LiNi_0.9Co_0.1O₂. The discharge profiles and cyclic voltammograms from 4.5 V at 90 °C for 4 h showed enhanced structural stability. Scanning electron microscopy and X-ray diffraction revealed that the AlPO₄-coated LiNi_0.9Co_0.1O₂ had less degradation than the bare LiNi_0.9Co_0.1O₂.     

细菌纤维素模板法制备p-Co3O4/n-ZnO复合材料及气敏特性研究

本文利用细菌纤维素为模板制备了p型Co₃O₄修饰的n型ZnO纳米复合材料，通过XRD、SEM、HRTEM、EDS和XPS等手段对纳米复合材料的组成、形貌与元素分布进行了相应的表征. 相对于纯ZnO来说，p-Co₃O₄/n-ZnO复合材料对有机挥发性气体响应的灵敏度有明显提升，例如复合材料对100 ppm丙酮的灵敏度为63.7(最佳温度为180 °C)，是纯ZnO(最佳温度为240 °C，灵敏度为2.3)的26倍. 从材料表面氧空位(缺陷控制)、Co₃O₄的催化活性以及p-n异质结三个方面解释了复合材料对VOCs的高响应特性. 同时细菌纤维素可以作为模板设计功能化的异质结复合物用于VOCs的测试或者其他应用.     

Synthesis and magnetic properties of antiferromagnetic Co3O4 nanoparticles

Antiferromagnetic Co₃O₄ nanoparticles with diameter around 30 nm have been synthesized by a solution-based method. The phase identification by the wide-angle X-ray powder diffraction indicates that the Co₃O₄ nanoparticle has a cubic spinel structure with a lattice constant of 0.80843(2) nm. The image of field emission scanning electron microscope shows that the nanoparticles are assembled together to form nanorods. The magnetic properties of Co₃O₄ fine particles have been measured by a superconducting quantum interference device magnetometer. A deviation of the Néel temperature from the bulk is observed, which can be well described by the theory of finite-size scaling. An enhanced coercivity as well as a loop shift are observed in the field-cooled hysteresis loop. The exchange bias field decreases with increasing temperature and diminishes at the Néel temperature. The training effect and the opening of the loop reveal the existence of the spin-glass-like surface spins.     

氧化钨纳米线-单壁碳纳米管复合型气敏元件的室温NO2敏感性能与机理

利用溶剂热法合成了一维的氧化钨纳米线, 通过掺入适量单壁碳纳米管(SWNT)制备了基于氧化钨纳米线-SWNT 复合结构的室温气敏元件并评价了其对NO₂气体的室温敏感性能. 利用X射线与扫描电子显微镜表征了材料的微结构, 结果表明, 合成的氧化钨纳米线具有单斜的W₁₈O₄₉结构, 复合材料中SWNT被包埋在氧化钨纳米线中间. 气敏性能测试结果表明, 氧化钨纳米线-SWNT复合结构气敏元件在室温下对NO₂气体表现出了高的灵敏度和超快的响应特性; 较低的SWNT掺入量对获得好的气敏性能有利. 分析了基于复合结构材料气敏元件的可能的气敏机理, 认为元件良好的室温敏感性能与SWNT掺入在复合结构材料中引入大量的贯穿气孔和p-n异质结有关.     

Sensor Properties of Nanostructured Systems Based on Indium Oxide with Co<Subscript>3</Subscript>O<Subscript>4</Subscript> or ZrO<Subscript>2</Subscript> Additives

The effect of Co₃O₄ and ZrO₂ additives on the sensory response of In₂O₃-based nanostructured composites to H₂ and CO is studied. It is shown that the addition of small amounts of Co₃O₄ or ZrO₂ to In₂O₃ leads to a sharp increase in the sensory response to hydrogen. The maximum sensory response of the ZrO₂?In₂O₃ composite to 1100 ppm of hydrogen increases from 80 to 270 as the ZrO₂ content changes 0 to 20 wt %. The response to CO varies only slightly. For Co₃O₄?In₂O₃ composites, the maximum response to H₂ and CO increases with the Co₃O₄ content within 0?10 wt %. A further increase in the Co₃O₄ content leads to a significant decrease in the response, with composites containing ～60 wt % Co₃O₄ being characterized by a very low efficiency. In the Co₃O₄?In₂O₃ system with a content of up to 60 wt % Co₃O₄, electronic conduction is realized, which changes to hole conduction at Co₃O₄ within 80?100 wt %. In the ZrO₂?In₂O₃ system, electric current flows through In₂O₃ nanocrystals, i.e., n-type conduction takes place. Possible reasons for the observed effects are discussed.     

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.     

Facile synthesis and optical properties of Co3O4 nanostructures by the microwave route

Cobalt oxide (Co₃O₄) nanoplatelet shape like nanostructures have been successfully synthesized through a simple microwave route for the first time using cobalt acetate, NaOH and citric acid at 200 °C for 30 min. The structure and morphology of as-prepared Co₃O₄ nanoplatelets are characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), and scanning electron microscope (SEM). XRD measurements indicate that the product has a perfect crystalline cubic phase of Co₃O₄ with a lattice constant a=8.082 Å. The SEM images show that the obtained Co₃O₄ nanopowder consists of nanoplatelets with diameter 125 nm and thickness 20 nm. Energy-dispersive X-ray spectroscopy (EDS) show that the composition of Co₃O₄ is stoichiometric. Room temperature photoluminescence measurement is exhibited by a strong UV emission and a suppressed green emission, confirming the good optical properties for the as-prepared Co₃O₄ nanoplatelets.     

Synergistic effect of Cr2O3 and Co3O4 nanocomposite electrode for high performance supercapacitor applications

The fabrication of high performance supercapacitor electrodes has been greatly investigated for future high power storage applications. In this present work, chromium oxide-cobalt oxide based nanocomposite (Cr₂O₃–Co₃O₄ NC) was synthesized using the hydrothermal approach. Moreover, the cyclic voltammetry (CV) study reveals the Cr₂O₃–Co₃O₄ NC delivers a high specific capacitance of 619.4 F/g at 10 mV/s. The electrochemical impedance spectra (EIS) of Cr₂O₃–Co₃O₄ NC possess the solution resistance (R_s) and charge transfer resistance (R_ct) of 0.68 Ω and 0.03 Ω respectively. The Galvanostatic charge-discharge (GCD) analysis demonstrated the prolonged charge-discharge time and good rate capability of the Cr₂O₃–Co₃O₄ NC. The cyclic stability of Cr₂O₃–Co₃O₄ NC delivers superior capacitive retention of 83% even after 2000 cycles. The asymmetric supercapacitor (ASC) device based on Cr₂O₃–Co₃O₄//AC yielded an energy density of 4.3 Wh/kg at the corresponding power density of 200 W/kg. Furthermore, the ASC delivers superior cyclic stability of 74.8% even after 1000 consecutive charge-discharge cycles.     

Electrochemical performances of nano-Co3O4 with different morphologies as anode materials for Li-ion batteries

Three kinds of Co₃O₄ nanomaterials with different morphologies were synthesized controllably by a post-anneal-assisted hydrothermal method in this study. X-ray diffraction and scanning electron microscopy indicated that all three kinds of samples were pure cubic phase of Co₃O₄ with morphologies of nanorods, nanoclusters, and nanoplates. Moreover, the transmission electron microscopy (TEM) and high-resolution TEM showed that the Co₃O₄ nanorods were bamboo-like and highly crystalline structures. When these materials were applied to the lithium-ion batteries (LIBs) as anode materials, the Co₃O₄ of nanorods demonstrated the best performance. It has a stable reversible capacity of 954 mAh g^?1 as the anode of a LIB, much higher than the other two kinds of Co₃O₄ of rod-like nanoclusters and nanoplates, even after 35 cycles. All results showed that the morphology and microstructure take very important roles in the performance of Co₃O₄ as the anode materials in LIBs.     

Transition of hexagonal to square sheets of Co3O4 in a triple heterostructure of Co3O4/MnO2/GO for high performance supercapacitor electrode

Cobalt oxide and manganese oxides are promising electrode materials amongst the transition metal oxides (TMOs) for pseudocapacitors. The lack of reversibility and deterioration of capacitance at higher current densities is major flaw in Co₃O₄ as an electrode for supercapacitor while MnO₂ suffers from low electrical conductivity and poor cycling stability. It is inevitable to bridge the performance gap between these two TMOs to obtain a high performance supercapacitor based on environmental benign and earth abundant materials. Herein, we fabricated a hybrid triple heterostructure high-performing supercapacitor based on hexagonal sheets of Co₃O₄, MnO₂ nanowires and graphene oxide (GO) to form a composite structure of Co₃O₄/MnO₂/GO by all hydrothermal synthesis route. The Co₃O₄ square sheets serves as an excellent backbone with good mechanical adhesion with the current collector providing a rapid electronic transfer channel while the integrated nanostructure of MnO₂ NW/GO permits more electrolyte ions to penetrate capably into the hybrid structure and allows effective utilization of more active surface areas. A triple heterostructured device exhibits a high areal capacitance of 3087 mF cm⁻² at 10 mV s⁻¹ scan rate along with the exceptional rate capability and cycling stability having capacitance retention of ∼170% after 5000 charge/discharge cycles. The TMOs based pseudocapacitor with the conducting scaffolds anchoring based on graphene derivatives like this will pave an encouraging alternatives for next generation energy storage devices.