Highly selective ethanol In2O3-based gas sensor

The sensitive composite material was prepared by loading Pt and La₂O₃ into ultrafine In₂O₃ matric material (8 nm) synthesized by microemulsion method. A highly selective ethanol gas sensor was developed based on hot-wire type gas sensor, which was sintered in a bead (0.8 mm in diameter) to cover a platinum wire coil (0.4 mm in diameter). The gas sensor was operated by a bridge electric circuit. The influences of La₂O₃ and Pt additives on C₂H₅OH sensing properties of In₂O₃-based gas sensor were discussed. The addition of La₂O₃ resulted in a prominent selectivity for C₂H₅OH, and the addition of Pt improved the response rate to C₂H₅OH without affecting the sensitivity. The temperature and humidity characteristics of the sensor output were also investigated. The selective sensor had low power consumption, significantly minor humidity and temperature dependence, high selectivity and prominent long-term stability.     

In2O3 microcrystals obtained from rapid calcination in domestic microwave oven

The simple way to prepare In₂O₃ microcrystals is reported in this paper. The precursor, In(OH)₃ microstructures, were obtained using the Microwave-Assisted Hydrothermal (MAH) Method. By annealing as-prepared In(OH)₃ precursor at 500 °C for 5 min in a domestic microwave oven (MO), In₂O₃ microcrystals were prepared, inheriting the morphology of their precursor while still slightly distorted and collapsed due to the In(OH)₃ dehydration process which was studied by thermal analysis. The In(OH)₃ and In₂O₃ were characterized using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. These techniques confirm the chemical dehydration of In(OH)₃ and the formation of In₂O₃ powders. The domestic MO promotes a rapid structural organization as compared with a CF (conventional furnace). The MAH method and the subsequent annealing in a domestic MO were shown to be a low cost route for the production of In₂O₃, with the advantages of lower temperature and smaller time.     

In2O3 hollow spheres: One-step solvothermal synthesis and gas sensing properties

Hollow In₂O₃ spheres were prepared via a P123-assisted one-step solvothermal process for the first time. Ethanol medium played a key role in the direct cubic In₂O₃ phase formation whereas the triblock copolymer acted as a structure directing agent in the formation of the hollow spheres. The gas sensing properties of the as-prepared In₂O₃ hollow spheres were investigated. Compared to the products synthesized without P123, the In₂O₃ hollow spheres exhibited much faster response and higher sensitivity toward HCHO vapor.     

Preparation and visible-light-driven photoelectrocatalytic properties of boron-doped TiO2 nanotubes

In the present study, chemical vapour deposition (CVD) was applied to dope boron into TiO₂ nanotubes anodized Ti in C₂H₂O₄·2H₂O + NH₄F electrolyte with the goal of improving the photocatalytic (PC) activity under visible light. The undoped TiO₂ nanotubes had a highly self-organized structure. However, after doping through CVD, TiO₂ nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results confirmed that annealing temperature had an influence on the phase structure and boron impurities could retard anatase–rutile phase transition. Diffuse reflectance absorption spectra (DRS) analysis indicated that B-doped samples displayed stronger absorption in both UV and visible range. B-doped TiO₂ nanotubes electrode annealed at 700 °C through CVD showed higher photoelectrocatalytic (PEC) efficiency in methyl orange (MO) degradation than that annealed at 400 °C and 550 °C. MO degradation was substantially enhanced with the increasing applied bias potential. Moreover, there was a synergetic effect between the electrochemical and photocatalytic processes, and the synergetic factor R reached 1.45. B-doped TiO₂ nanotubes electrode showed good stability after 10 times by repeating photoelectrocatalysis of MO.     

Large-scale fabrication of H2(H2O)Nb2O6 and Nb2O5 hollow microspheres

Hollow micro-sized H₂(H₂O)Nb₂O₆ spheres constructed by nanocrystallites have been successfully synthesized via a bubble-template assisted hydrothermal process. In the reaction process, H₂O₂ acts as a bubble generator and plays a key role in the formation of the hollow structure. An in situ bubble-template mechanism has been proposed for the possible formation of the hollow structure. The spherelike assemblies of these H₂(H₂O)Nb₂O₆ nanoparticles have been transformed into their corresponding pseudohexagonal phase Nb₂O₅ through a moderate annealing dehydration process without destroying the hierarchical structure. Optical properties of the as-prepared hollow spheres were investigated. It is exciting that the absorption edge of the hollow Nb₂O₅ microspheres shifts about 18 nm to the violet compared with bulk powders in the UV/vis spectra, indicating its superior optical properties.     

Preparation of In2O3 octahedrons by heating InCl3 aqueous solution on the Si substrate

In₂O₃ octahedrons have been synthesized by heating InCl₃ aqueous solution on the Si substrate at 400-900 °C for 2 h. The average size of In₂O₃ octahedrons is decreased by increasing the heating temperature. The In₂O₃ octahedrons are single-crystalline with the body-centered cubic structure and have controllable sizes in the range of 0.7-1.0 μm. A possible mechanism was also proposed to account for the formation of In₂O₃ octahedrons. A strong photoluminescence with a peak at 458 nm was observed from the In₂O₃ octahedrons at room temperature. This emission can be attributed to oxygen vacancies and indium-oxygen vacancy centers.     

Deposition process of Si-B-C ceramics from CH3SiCl3/BCl3/H2 precursor

Si-B-C coatings have been prepared by chemical vapour deposition (CVD) from CH₃SiCl₃/BCl₃/H₂ precursor mixtures at low temperature (800-1050 °C) and reduced pressures (2, 5, 12 kPa). The kinetics (including apparent activation energy and reaction orders) related to the deposition process were determined within the regime controlled by chemical reactions. A wide range of coatings, prepared in various CVD conditions, were characterized in terms of morphology (scanning electron microscopy), structure (transmission electron microscopy, Raman spectroscopy) and elemental composition (Auger electron spectroscopy). On the basis of an in-situ gas phase analysis by Fourier transform infrared spectroscopy and in agreement with a previous study on the B-C system, the HBCl₂ species was identified as an effective precursor of the boron element. H_xSiCl_(4−x), SiCl₄ and CH₄, derived from CH₃SiCl₃, were also shown to be involved in the homogeneous and the heterogeneous reactions generating silicon and carbon in the coating. A correlation between the various experimental approaches has supported a discussion on the chemical steps involved in the deposition process.     

Photoluminescence properties of the In2O3 octahedrons synthesized by carbothermal reduction method

In₂O₃ octahedrons were synthesized by carbothermal reduction method. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction analysis (SAED) and room-temperature photoluminescence (PL) spectra. The results show that the products are single-crystalline In₂O₃ octahedrons with the arrises length in the range of 400-3000 nm. The PL spectra displays blue and green emission peaks which can be indexed to default and oxygen vacancies; blue-shift and intensity decrease was observed when excitation wavelength decreases from 380 nm to 325 nm. The growth mechanism of the In₂O₃ octahedrons is discussed.     

High sensitivity chlorine gas sensors using CdIn2O4 thick film prepared by co-precipitation method

Gas-sensing properties to dilute Cl₂ have been investigated for CdIn₂O₄ thick film sensors prepared by co-precipitation method. Cadmium nitrate and indium nitrate were mixed in de-ionized water. The 0.1 M NaOH was added to the mixed solution. The co-precipitate obtained was washed, filtered, dried, and calcined at 600-900 °C for 4 h. The CdIn₂O₄ sensor prepared using the powder calcined at 600 °C showed high sensitivity (S=R_g/R_a) to dilute Cl₂ at 250 °C. In particular, the CdIn₂O₄ sensor showed the sensitivity as high as 1200 even to 0.2 ppm Cl₂. The crystal structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.     

Influence of structural and preparation parameters of Fe2O3/Al2O3 catalysts on rate of production and quality of carbon nanotubes

The influence of catalytic and operational parameters on the rate of growth and quality of carbon nanotubes has been investigated. A series of Fe₂O₃/Al₂O₃ catalysts prepared by different methods were investigated under conditions of synthesis of CNTs via the process of CVD of ethylene. Deposition experiments were carried out in a thermogravimetric hot-wall reactor, which enables continuous monitoring of the evolution of carbon mass with time. Controlled explosive burning (CEB) of precursor compounds was found to be the most effective method of preparation of the catalyst with respect to rate of deposition and yield of CNTs. This result has been attributed to the presence of hematite particles of small diameter on the catalyst. The presence of hydrogen in the gas feed mixture, even at small concentration, proved to be beneficial for the rate of production of MWCNTs and to result in the synthesis of CNTs of narrower diameter distribution. Yield and quality of MWCNTs depend on the concentration of the carbon source (ethylene) in the feed mixture and on temperature of deposition. Under the present experimental conditions, the optimal reaction temperature was found to be 650 °C. The products of the deposition were characterized using scanning electron microscopy and Raman spectroscopy.     

Hydrothermal growth of V2O5 photoactive films at low temperatures

It is shown that the surface morphology and the photoactivity of hydrothermally grown V₂O₅ films at 95 °C are greatly affected by the deposition time. Well-defined phase of V₂O₅ films grown for a deposition period of 2 h were found to exhibit significant photocatalytic activity, degrading stearic acid by 57%. The films presented a relatively porous structure, appearing as a wall-like network. The correlation of deposition period with the structure, morphology and the photoinduced properties of the materials are discussed.     

A comparative study of the UV optical and structural properties of SiO2, Al2O3, and HfO2 single layers deposited by reactive evaporation, ion-assisted deposition and plasma ion-assisted deposition

Growing requirements for the optical and environmental stability, as well as the radiation resistance against high-power laser radiation, especially for optical interference coatings used in the ultraviolet spectral range, have to be met by new, optimised, thin-film deposition technologies. For applications in the UV spectral range, the number of useful oxide thin film materials is very limited due to the higher absorption at wavelengths near to the electronic bandgap of the materials. Applying ion-assisted processes offers the ability to grow dense and stable films, but in each case careful optimisation of the deposition process (evaporation rate, substrate temperature, bombarding gas, ion energy and ion current density) has to achieve a balance between densification of the layers and the absorption. High-quality coatings and multilayer interference systems with SiO₂ as the low-index material can be deposited by various physical vapour deposition technologies, including reactive e-beam evaporation, ion-assisted deposition and plasma ion-assisted deposition. In order to improve the degradation stability of dielectric mirrors for use in UV free-electron laser optical cavities, a comparative study of the properties of SiO₂, Al₂O₃ and HfO₂ single layers was performed, and was addressed to grow very dense films with minimum absorption in the spectral range from 200 to 300 nm. The films were deposited by low-loss reactive electron-beam evaporation, by ion-assisted deposition using a ‘Mark II’ ion source, and by plasma ion-assisted deposition using the advanced plasma source. Optical and structural properties of the samples were studied by spectral photometry, infrared spectroscopy, X-ray diffraction and reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energy values close to the bandgap was studied. For HfO₂ single layers, laser-induced damage thresholds at 248 nm were determined in the 1-on-1 and 1000-on-1 test modes as a function of the deposition technology and film thickness.     

Growth studies and characterization of In2S3 films prepared by hydrothermal method and their conversion to In2O3 films

For the first time, In₂S₃ films composed of nano-/microflakes were fabricated on fluorine-doped tin oxide (FTO) substrate using a simple and effective hydrothermal method. The structure, composition and morphology were examined by X-ray diffraction, energy-dispersive X-ray spectroscopy and field emission scanning electron microscopy. It was found that the reaction time, reaction temperature and the molar ratio of the reactants play key roles in controlling the final morphologies. The possible growth mechanism for the formation of In₂S₃ thin films was proposed. And the optical and photoelectrochemical properties were also investigated. In addition, In₂O₃ films were obtained by annealing the In₂S₃ precursor films in air at 500 °C.     

Synthesis and photoluminescence of In2O3 nanocrystals and submicron crystals from InCl3•4H2O and thiourea

Two routes have been proposed for the synthesis of In₂O₃ powders from InCl₃•4H₂O and thiourea. One route involved a two-step procedure (that is, firstly, In₂S₃ clusters constructed with mainly nanoflakes were synthesized by heating the mixture of InCl₃•4H₂O and thiourea in air from room temperature to 200 °C, coupled with a subsequent washing treatment; secondly, In₂O₃ was obtained by calcining the In₂S₃ clusters in air at 600 °C for 6 h), and the other route was a one-step procedure (that is, In₂O₃ was synthesized directly by calcining the mixture of InCl₃•4H₂O and thiourea in air at 600 °C for 6 h). The resultant products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electronic microscope and room temperature photoluminescence (RT-PL) spectra. It was observed that the In₂O₃ nanocrystals obtained via the two-step procedure exhibited PL peaks at about 453 and 471 nm, corresponding to the defeat-related emission; while the In₂O₃ submicron polyhedral crystals obtained via the one-step procedure and In₂O₃ pyramids obtained by calcining the only InCl₃•4H₂O in air at 600 °C for 6 h displayed a PL band centered at around 338 nm, corresponding to the band edge emission.     

Controlled synthesis and photocatalytic properties of porous hollow In2O3 microcubes with different sizes

Uniform single-crystalline In(OH)₃ hollow microcubes have been synthesized in large quantities via a hydrothermal reaction of InCl₃ with NaF and ethylene glycol (EG) at 140–220 °C for 12 h. Porous In₂O₃ hollow microcubes with a polycrystalline cubic structure can be obtained via calcining In(OH)₃ precursors at 400 °C for 2 h in air. Controlled Synthesis of In(OH)₃ and In₂O₃ hollow microcubes with the average edge lengths in the range of 2.0–4.7 μm can be achieved by changing the hydrothermal reaction temperature. The In(OH)₃ hollow microcubes were formed via an EG-assisted oriented attachment growth route using HF bubbles as the templates. Photocatalytic activities of the as-synthesized porous In₂O₃ hollow microcubes were studied at room temperature. The results indicated that the hollow In₂O₃ nanostructures display high photocatalytic activity in the photodegradation of rhodamine B and methyl orange.     

HCHO sensing properties of Ag-doped In2O3 nanofibers synthesized by electrospinning

Ag-doped In₂O₃ nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In₂O₃ nanofibers could be used to fabricate high performance HCHO sensors in practice.     

Low-temperature synthesis of LiV3O8 nanosheets as an anode material with high power density for aqueous lithium-ion batteries

Nanosheets of lithium vanadium oxide (LiV₃O₈) were successfully synthesized by a simple low temperature citrate sol–gel combustion route. Compact nanosheets of the active material were observed by scanning and transmission electron microscopies. X-ray diffraction measurements indicated that as-prepared nanosheets presented pure phase of monoclinic LiV₃O₈ with p2₁/m symmetry. Cyclic voltammetry (CV) was employed to investigate the electrochemical behavior of the nanosheets with special emphasis on the application potential as anodic material for aqueous rechargeable lithium batteries. CV studies demonstrated that the LiV₃O₈ nanosheets represent well-defined reversible peaks. The nanosheets showed a discharge capacity of 63 mAh/g in 1.0 M LiNO₃ solution at a 2C/5 rate.     

Synthesis and characterization of In2O3 nanocube via a solvothermal-calcination route

In₂O₃ nanocubes have been generated by a two-step process, a simple solvothermal technique for In(OH)₃ nanocubes and subsequent reaction with O₂ to form the In₂O₃ nanocubes, which exhibit morphologies identical to the original In(OH)₃ nanocube. The In(OH)₃ nanocubes and the In₂O₃ nanocubes are well-crystallized single-crystal nanostructure. Under optimal conversion conditions, the final geometry features of In₂O₃ are predetermined by the size and morphology of the In(OH)₃ nanocubes. The size of In(OH)₃ nanocubes is effected by pH value of solution.     

Preparation, characterization, and gas-sensing properties of Pd-doped In2O3 nanofibers

Pure and Pd-doped In₂O₃ nanofibers are synthesized via a simple electrospinning method and characterized by scanning electron microscopy and X-ray diffraction. Comparing with pure In₂O₃ nanofibers, Pd-doped In₂O₃ nanofibers exhibit much higher sensitivity to ethanol at 200 °C. The sensor fabricated from Pd-doped In₂O₃ nanofibers can detect ethanol down to 1 ppm (the corresponding sensitivity is 4) with good selectivity, and the response and recovery times are 1 and 10 s, respectively. The sensing mechanism and the effect of Pd doping are discussed. The results indicate that the Pd-doped In₂O₃ nanofibers can be used to fabricate high performance ethanol sensors.