Fabrication of Porous Metal Oxide Semiconductor Films by a Self-Template Method Using Layered Hydroxide Metal Acetates

Porous metal oxide (Co₃O₄, NiO, or ZnO) films were fabricated by a self-template method using layered hydroxide metal acetates (LHMA; metal = Co, Ni, or Zn) as templates. LHMAs were initially grown on glass substrates through a chemical bath deposition in methanolic-aqueous solutions of metal acetates at 60°C. The template films had a unique, nest-like morphology consisting of interlaced flake-like particles as a result of two-dimensional crystal growth of LHMAs in supersaturated solutions. The templates were successfully converted into porous Co₃O₄, NiO, or ZnO films by heating at 500°C for 10 min in air without microstructural deformation.     

Evolution of Structure of the Precursor During Sol-Gel Processing of ZnO and Low Temperature Formation of Thin Films

ZnO thin films were prepared on silicon substrate with Pt electrode by the sol-gel processing using Zn alkoxide solution prepared from Zn(NO₃)₂·6H₂O and 2-methoxyethanol. FT-IR spectroscopy showed the presence of Zn species in the alkoxide, with methoxyethoxide and nitrato groups as coordination ligands, indicating formation of Zn(NO₃)(OCH₂CH₂OCH₃). Smooth and homogeneous thin films were obtained by heat treating coating gel films in the temperature range from 250 to 500°C. The ZnO thin films exhibited a preferred growth of crystals with c-axis perpendicular to the Si substrate surface when fired at 250°C. It was discussed that the presence of nitrogen atoms in precursors had affected the phase development of crystals and was the basis of the structural relaxation for crystallization at low temperature.     

Facile Fabrication of Porous ZnS and ZnO Films by Coaxial Electrospinning for Highly Efficient Photodegradation of Organic Dyes

Porous ZnS and ZnO nano‐crystal films were fabricated via a three‐step procedure. First, Zn(CH₃COO)₂/Silk Fibroin nanofiber mats were prepared by coaxial electrospinning. Second, Zn(CH₃COO)₂/Silk Fibroin mats were immersed in NaS solution to react with S²⁻ to obtain ZnS/Silk Fibroin nanofiber mats. Finally, ZnO porous films were prepared by calcination of ZnS/Silk Fibroin composite mat at 600°C in air atmosphere. When ZnS/Silk Fibroin mats were calcinated in nitrogen, ZnS/Carbon composite mats were obtained accordingly. The resulting porous films were fully characterized. The ZnO porous films were the aggregation of ZnO nano‐crystal with hexagonal wurtzite structure. The seize of ZnO was estimated in the range of 10–20 nm. Both of the ZnS and ZnO nano‐crystal films exhibited high photocatalytic activities for the photodegradation of Methylene blue and Rhodamine B. It was also found that ZnO porous films are better than ZnS/Carbon nanofiber mats. In addition, photocatalysis of a real wastewater sample from a printing and dyeing company was conducted. The ZnO porous films exhibited excellent performance to treat the real samples. Moreover, the porous ZnO nano‐crystal photocatalyst could easily be recycled without notable loss of catalysis ability.     

p-Type behaviour of electrodeposited ZnO:Cu films

Cu-doped ZnO (ZnO:Cu) thin films and ZnO/ZnO:Cu homojunction devices were electrodeposited on conductive glass substrates in a non-aqueous electrolyte containing Cu and Zn salts. The Cu content of the films is proportional to the Cu/Zn precursor ratio in the deposition electrolyte. ZnO:Cu was found to be of a hexagonal wurtzite structure with (002) preferred orientation. A transition from n-type to p-type was observed for ZnO:Cu films with a Cu/Zn ratio higher than 2% as inferred from the change in the direction of the photocurrent. The rectifying characteristics shown by homojunction devices further confirm the p-type conductivity of ZnO:Cu layers.     

Electrochemical deposition of nano-structured ZnO on the nanocrystalline TiO2 film and its characterization

One-dimensional structure of ZnO nanorod arrays on nanocrystalline TiO₂/ITO conductive glass substrates has been fabricated by cathodic reduction electrochemical deposition methods in the three-electrode system, with zinc nitrate aqueous solution as the electrolyte, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence (PL) spectra. The effects of film substrates, electrolyte concentration, deposition time, and methenamine (HMT) addition on ZnO deposition and its luminescent property were investigated in detail. The results show that, compared with on the ITO glass substrate, ZnO is much easily achieved by electrochemical deposition on the TiO₂ nanoparticle thin films. ZnO is hexagonally structured wurtzite with the c-axis preferred growth, and further forms nanorod arrays vertically on the substrates. It is favorable to the growth of ZnO to extend the deposition time, to increase the electrolyte concentration, and to add a certain amount of HMT in the system, consequently improving the crystallinity and orientation of ZnO arrays. It is demonstrated that the obtained ZnO arrays with high crystallinity and good orientation display strong band-edge UV (375 nm) and weak surface-state-related green (520 nm) emission peaks.     

Enhanced zinc ion transport in gel polymer electrolyte: effect of nano-sized ZnO dispersion

The effect of the dispersion of zinc oxide (ZnO) nanoparticles in the zinc ion conducting gel polymer electrolyte is studied. Changes in the morphology/structure of the gel polymer electrolyte with the introduction of ZnO particles are distinctly observed using X-ray diffraction and scanning electron microscopy. The nanocomposites offer ionic conductivity values of >10^?3 S cm^?1 with good thermal and electrochemical stabilities. The variation of ionic conductivity with temperature follows the Vogel–Tamman–Fulcher behavior. AC impedance spectroscopy, cyclic voltammetry, and transport number measurements have confirmed Zn²⁺ ion conduction in the gel nanocomposites. An electrochemical stability window from ?2.25 to 2.25 V was obtained from voltammetric studies of nanocomposite films. The cationic (i.e., Zn²⁺ ion) transport number (t ₊) has been found to be significantly enhanced up to a maximum of 0.55 for the dispersion of 10 wt.% ZnO nanoparticles, indicating substantial enhancement in Zn²⁺ ion conductivity. The gel polymer electrolyte nanocomposite films with enhanced Zn²⁺ ion conductivity are useful as separators and electrolytes in Zn rechargeable batteries and other electrochemical applications.     

Hydrothermal synthesis of 2D ordered macroporous ZnO films

The ZnO films with two-dimensional ordered macroporous structure were successfully fabricated through hydrothermal crystal growth of ZnO on the ZnO substrate covered with a monolayer of polystyrene (PS) spheres as template. The precursor solution of hydrothermal crystal growth of ZnO were prepared by equimolar solution of Zn(NO₃)₂·6H₂O and hexamethylenetramine (HMT). The confinement effect of the PS spheres template on the growth of ZnO nanorods and the influence of sodium citrate on the crystal growth of ZnO had been studied. The film surface morphology and the preferential growth of ZnO crystal were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Also, the photoluminescence spectrum of ZnO films had been measured, and the corresponding mechanism was discussed. __________ Translated from Chemistry, 2007, 70 (8): 587–592 [译自: 化学通报]     

Synthesis and Optical Properties of ZnO Nanoparticles in Submicron PS Hollow Reactors

ZnO nanoparticles were first encapsulated in submicron PS hollow microspheres through two-step swelling process of core-shell structured PMMA/PS (PMMA: polymethyl methao-rylate) microspheres in acid-alkali solution, and the ZnO precursors, i.e. the ethanol solu-tions of (CH₃COO)₂Zn and LiOH. The transmission electron microscope, X-ray diffraction, and thermogravimetric analysis results show that the feeding order of ethanol solutions of (CH₃COO)₂Zn and LiOH in the second swelling step has great influence on the loading efficiency and the size of ZnO nanoparticles, but little on their crystal form. The photolumi-nescence and UV-Vis absorption behavior of ZnO/PS microspheres show that the PS shell can effectively avoid the fluorescence quenching effect.     

TiO2纳米管阵列负载不同形貌Cu2O薄膜的制备及光电性能研究

本论文采用阳极氧化法在金属钛基底上制备高度有序的TiO2纳米管阵列薄膜,然后采用脉冲电流法在TiO2纳米管阵列上沉积Cu2O,从而制备出Cu2O-TiO2纳米管阵列异质结复合薄膜。借助X射线衍射仪(XRD),场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)等表征手段,详细探讨了Cu2O沉积过程中电解液的不同扰动方式(静止、磁力搅拌和超声搅拌)对复合薄膜物相和形貌的影响。实验结果表明电解液的扰动方式会影响Cu2O沉积过程中的离子扩散和微区化学环境,从而影响Cu2O的形貌。通过漫反射紫外-可见吸收光谱(UV-Vis)和光电流性能测试可知所制备的负载Cu2O型TiO2纳米管阵列薄膜具有显著的可见光响应效应。     

Synthesis of layered zinc hydroxide chlorides in the presence of Al(III)

Zinc hydroxide chloride particles were synthesized by hydrolysis of ZnCl₂ solutions dissolving AlCl₃ at different atomic Al/Zn ratios from 0 to 1.0 and characterized by various techniques. Increasing Al/Zn ratio changed the crystal phases of the products as ZnO→ZnO+ZHC (Zn₅(OH)₈Cl₂·H₂O)→ZHC→LDH (layered double hydroxides, Zn-Al-Cl) and the particle morphology as agglomerates (ZnO)→fine particles (ZnO)→plates (ZHC)+rods (ZnO)→plates (ZHC)→plates (LDH). The atomic Cl/Zn ratios of LDH particles formed at Al/Zn?0.3 were ca. 0.3 despite the increase of Al/Zn ratio, being due to the intercalation of CO₃²⁻ into the LDH crystal. The OH⁻ content of LDH estimated by TG was reduced by the deprotonation of OH⁻ to counteract the excess positive charge produced by replacing Zn(II) with Al(III). ZHC exhibited a high adsorption selectivity of H₂O.     

Preparation and Studies of ZnO:Al Films and Powders

ZnO:Al (0–10 at% Al) films and powders were produced using acac-modified methoxy-ethoxide precursors, obtained from Zn(C₂H₅)₂ and Al₄(OPr ⁱ )₁₂. The conversion to oxide powders was monitored with TGA and DSC, and the phase development was investigated with XRD, FT-IR spectroscopy, and TEM-EDS. The gels obtained by air-hydrolysis contained ca 0.5 acac/(Zn + Al) and a small amount of water and hydroxyls. All residual groups were removed to yield ZnO:Al by heating to ca 400°C. The powders obtained at 400 and 500°C were elementally homogeneous, and consisted of hex-ZnO:Al as ca 3–5 (10 at% Al) or 20–30 (3 at% Al) nm sized crystalline particles. Spin-coating on quartz, Si/SiO₂, and window glass, followed by heating to 500°C resulted in 150–200 nm thick films of hex-ZnO:Al. 500 nm thick films were obtained by repeating the deposition and heat-treatment twice. The films were visually very clear and the measured transmittance high over the 400–800 nm range (91–93% at 800 nm) for ca 300 nm thick films.     

Influence of Rare Earth Ho3+ Doping on Structural,Microstructure and Magnetic Properties of ZnO Bulk and Thin Film Systems

We have investigated the doping behavior of rare earth element holmium (Ho³⁺) in ZnO semiconductor. The structural, microstructure, and magnetic properties of Zn_1-xHo_xO (x=0.0, 0.04, and 0.05) thin films deposited on Si(100) substrate by thermal evaporation technique were studied. The ceramic targets were prepared by conventional solid state ceramic technique. The pallets used as target were final sintered at 900 oC in the presence of N2 atmosphere. The experimental results of X-ray diffraction (XRD) spectra, surface morphology, and magnetic properties show that the Ho³⁺ doped ZnO thin films has a strong influence on the materials properties. The higher angle shift in peak position and most preferred (101) orientation were observed in XRD pattern. These spectra confirmed the substitution of Ho3+ in ZnO lattice. The surface morphology and stoichiometry for both bulk and thin films were analyzed by scanning electron microscopy and energy dispersive spectroscopy. It was observed that grain size decreases with the increase of Ho³⁺. Room temperature ferromagnetism was observed for Zn_0.95Ho_0.05O films. The ferromagnetism might be attributed to the substitution of Ho ions for Zn²⁺ in ZnO lattices.     

Zinc Oxide/Zinc Hexacyanoferrate Hybrid Film‐Modified Electrodes for Guanine Detection

An electroactive polynuclear hybrid films of zinc oxide and zinc hexacyanoferrate (ZnO/ZnHCF) have been deposited on electrode surfaces from H₂SO₄ solution containing Zn(NO₃)₂ and K₃[Fe(CN)₆] by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements demonstrate the steady growth of hybrid film. There are two redox couples present in the voltammograms of hybrid film and it is obvious in the case of pH 2. Surface morphology of hybrid film was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Energy dispersive spectrometer (EDS) data confirm existence of zinc oxide in the hybrid film. The effect of type of monovalent cations on the redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The electrocatalytic activity of ZnO/ZnHCF hybrid film was investigated towards guanine using cyclic voltammetry and rotating disc electrode (RDE) techniques. Finally, feasibility of using ZnO/ZnHCF hybrid film‐coated electrodes for guanine estimation in flow injection analysis (FIA) was also investigated.     

TiO2/ZnO composite nanodots films and their cellular responses

In the present study, TiO₂/ZnO composite nanodot films were prepared and the effects of Zn incorporation on light-induced cell detachment were investigated. The nanodots films, which were successfully synthesized by phase-separation-induced self-assembly method, were characterized on the morphology, composition, microstructure, and other properties, and evaluated on cell compatibility and cell detachment performances as well. Live-dead staining was used to study the viability of cell sheet detached by light illumination. Results shows that with the increasing of introduced Zn, the band gap widened and the absorbance in UV region increased, while the crystallinity and performance of light-induced hydrophilicity weakened. All the nanodots films showed good cell compatibility and cell detachment performance induced by light. The nanodots film which had a Zn/Ti molar ratio of 0.03 showed the highest detachment ratio of 91.0% after 20?min ultraviolet illumination. The prepared TiO₂/ZnO composite nanodots films could be helpful in optimizing light-induced cell detachment behavior.

     

Effect of continuous magnetic field on the growth mechanism of nanoporous anodic alumina films on different substrates

The effects induced by an external homogeneous magnetic field on the oxide film growth on aluminum in aqueous solutions of oxalic and sulfuric acid and on surface morphology of the alumina films were studied. Aluminum films of 100 nm thickness were prepared by thermal evaporation on SiO₂/Si and glass-ceramic substrates. The pore diameter for oxalic acid alumina films on the SiO₂/Si substrate decreased by 0.8 nm, the interpore distance by 5.9 nm, and cell diameter by 6.9 nm if a magnetic field of 0.5 T was applied. When aluminum was anodized in sulfuric acid on the same substrate, the significant changes in parameters of porous structure of alumina, which were similar to the ones in oxalic acid, are firstly observed in stronger magnetic fields (of 0.7 T). On the basis of data obtained in this study and of previous investigation on the negative space charge and thermally activated defects in anodic alumina, we concluded that the intensity of the magnetic field is associated with energy of electron traps and that the changes of cell diameter characterize the trap concentration. The energy of electron traps in oxalic acid alumina films was proved to be smaller than the one in films formed in sulfuric acid, but the concentration of traps was of the same order of magnitude. When the substrate was replaced with the glass-ceramic one, the pore diameter in oxalic acid alumina films increased to ca. 17.6 nm.     

Nanostructured metal sulfide surfaces by ion exchange processes

A scalable preparation procedure for structured semiconducting sulfide films from zinc oxide by means of subsequent anion and cation exchange processes is described, which is low in cost and waste production. The starting material was columnar ZnO films, which were grown in electrodeposition by O₂ reduction. Here, their detailed morphology depends on the substrate and the process parameters. These films were converted to ZnS by reaction with H₂S gas or sulfur vapour at temperatures around 450 °C. In this process the columnar morphology of the ZnO is preserved. A partial conversion is also possible and leads to tubular ZnS films. Then the ZnS films were reacted in metal salt solutions to convert them further to Ag₂S, Cu₂S, Bi₂S₃ and Sb₂S₃ films. Here the columnar or tubular morphology was, in general, also reproduced, but its outer quality depends on the interaction of the involved processes, namely dissolution, precipitation and exchange inside the solid. This was further examined by a series of Ag₂S films from modified solutions.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

氧化锌纳米棒微结构光电极的制备

通过两步法,即首先热分解醋酸锌制备氧化锌晶种层,在晶种的诱导下,再采用低温水热法在氟掺杂的SnO₂导电玻璃(fluorine-doped tin oxide, FTO)基底导电面上成功制备出高取向性的氧化锌纳米棒阵列光电极。系统研究了前驱液浓度、溶液pH值、反应时间等实验条件对光电极微结构的影响。实验结果表明在一定变化范围内,随着前驱液浓度和溶液pH值的增大,纳米棒的直径增大;随着反应时间的延长,纳米棒的长度增长。将氧化锌纳米棒阵列薄膜制作成染料敏化太阳电池(dye-sensitized solar cell, DSSC)的光电极,并对电池的I-V特性进行了表征。     

Cr2O3-modified ZnO thick film resistors as LPG sensors

Thick films of pure ZnO were obtained by screen-printing technique. Surface functionalized ZnO thick films by Cr₂O₃ were obtained by dipping pure ZnO thick films into 0.01 M aqueous solution of chromium trioxide (CrO₃). The dipped films were fired at 500 °C for 30 min. Upon firing, the CrO₃ would reduce to Cr₂O₃. Cr₂O₃-activated (0.47 mass%) ZnO thick films resulted in LPG sensor. Upon exposure to 100 ppm LPG, the barrier height between Cr₂O₃ and ZnO grains decreases markedly, leading to a drastic decrease in resistance. The sensor was found to sense LPG at 350 °C and no cross sensitivity was observed to other hazardous, polluting and inflammable gases. The quick response (∼18 s) and fast recovery (∼42 s) are the main features of this sensor. The effects of microstructures and dopant concentrations on the gas sensing performance of the sensor were studied and discussed.     

Photocatalytic activities of multilayered ZnO-based thin films prepared by sol–gel route: effect of SnO2 heterojunction layer

In present study, ZnO/SnO₂/ZnO/SnO₂/ZnO multi–layer, ZnO/SnO₂/ZnO triple layer and ZnO single layer films have been deposited on glass substrate by sol–gel dip–coating technique. The structural and optical properties of thin films have been investigated by X-ray diffractometer, UV–visible, photoluminescence spectroscopies and scanning electron microscopy. The structural analysis reveals structural inhomogeneities and different crystallite growth processes as function of number of deposited layers. A comparison between photocatalytic activity of zinc oxide samples toward photodegradation of phenol, 4-aminophenol and 4-nitrophenol has been performed under UV light irradiation. Experiments were conducted to study the effects of operational parameters on the degradation rate. Pseudo-first-order photodegradation kinetics was observed on all films and the reaction constants were determined. The results showed that the photocatalytic activity of ZnO multi–layer film was superior to that of the ZnO single- and triple-layer films. Differences in film efficiencies can be attributed to differences in crystallinity, surface morphology, defect concentration of oxygen vacancy and to presence of SnO₂ sublayer that may act as trap for electrons generated in the ZnO layer thus preventing electron–hole recombination. The results reveal that SnO₂ hetrojunction layers improve crystalline quality, optical and photocatalytic properties of ZnO multilayered films.     

Automated electrochemical synthesis and photoelectrochemical characterization of Zn1-xCo(x)O thin films for solar hydrogen production

High-throughput electrochemical methods have been developed for the investigation of Zn1-xCo(x)O films for photoelectrochemical hydrogen production from water. A library of 120 samples containing 27 different compositions (0 相似文献