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1.
The microscale structure and size are extremely important factors for gas sensing materials. In this study, hierarchical flower-like ZnO architectures were synthesized by a biomolecular mediated route. The influence of various experiment parameters including reaction time, pH value, and reaction temperature on the formation of ZnO architectures was studied. When used as sensing material, this material possesses a higher sensing response towards ethanol and formaldehyde. Towards 100 ppm of ethanol and formaldehyde, the ZnO sensor can display remarkable sensing responses (R a/R g) of 13.6 and 16.5, respectively. These values are higher than or comparable to most of reported ZnO-based gas sensors. In addition, the sensors can show obvious sensing response to 5 ppm of ethanol and formaldehyde, indicating the lower limit of detection. It is proposed that the unique hierarchical microstructure contributes to the enhanced sensing performance. 相似文献
2.
Self-assembled superstructure of SnO 2/ZnO composite was synthesized by using alcohol-assisted hydrothermal method gas sensing properties of the material were investigated by using a static test system. The structure and morphology of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The diameter of the SnO 2 nanorods was about 40 nm with a length of about 300 nm, SnO 2 nanorods and ZnO nanosheets interconnect each other to form a superstructure. The gas sensing properties of superstructure SnO 2/ZnO composite with different content of ZnO were investigated. Furthermore, the superstructure SnO 2/ZnO composite sensor is characterized at different operating temperatures and its long-term stability in response to ethanol vapor is tested over a period of 3 months. 相似文献
3.
Hematite solid spindles and hollow spindles have been selectively synthesized by a template-free, economical hydrothermal method, using FeCl 3·6H 2O as the starting materials and NaOH as the homogeneous precipitant. XRD analyses indicated that the products consisted of α-Fe 2O 3. SEM and TEM measurements showed that the morphologies of products were in the shape of solid spindles and hollow spindles, respectively. A possible formation process based on the nucleation-oriented aggregation-recrystallization mechanism is proposed. Moreover, the as-prepared hollow spindle-like α-Fe 2O 3 exhibits a good response and reversibility to some organic gas, such as 2-propanol and acetone. Compared with other hematite nanostructures, the porous hollow hematite spindles show outstanding performance in gas sensing due to their large surface area and porous hollow structure. Because of the unique porous hollow structures of the samples, the photocatalytic property of the spindle-like α-Fe 2O 3 was also investigated. 相似文献
4.
La-doped ZnO nanoparticles have been successfully synthesized by a simple solution combustion method via employing a mixture of ethanol and ethyleneglycol (v/v = 60/40) as the solvent. Zinc acetate and oxygen gas in the atmosphere were used as zinc and oxygen sources, and La(NO 3) 3 as the doping reagent. The as-obtained product was characterized by means of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. Experiments showed that La-doped ZnO nanoparticles exhibited the higher capacities for the removal of Pb 2+ and Cu 2+ ions in water resource than undoped ZnO nanoparticles. 相似文献
5.
The study reports H 2S gas sensing characteristics of platinum (Pt) coated porous alumina (PoAl) films. The porous alumina (PoAl) thick layers were formed in the dark on aluminum substrates using an electrochemical anodization method. Thin semitransparent platinum (Pt) films were deposited on PoAl samples using chemical bath deposition (CBD) method. The films were characterized using energy dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM). The thicknesses of coated and bare films were measured using ellipsometry. The sensing properties such as sensitivity factor (S.F.), response time, recovery time and repeatability were measured using a static gas sensing system for H 2S gas. The EDAX studies confirmed the purity of Pt–PoAl film and indicated the formation of pure platinum (Pt) phase. The ellipsometry studies revealed the thickness of PoAl layer of about 15–17 μm on aluminum substrates. The SEM studies demonstrated uniform distribution of spherical pores with a size between 0.250 and 0.500 μm for PoAl film and nearly spherical platinum particles with average particle size ∼100 nm for Pt–PoAl film. The gas-sensing properties of these samples were studied in a home-built static gas characterization system. The H 2S gas sensing properties of Pt–PoAl at 1000 ppm of H 2S gave maximum sensitivity factor (S.F.) = 1200. The response time and recovery time were found to be 2–3 min and ∼1 min respectively. Further, the measurement of H 2S gas sensing properties clearly indicated the repeatability of gas sensing response of Pt–PoAl film. The present study indicated the significant potential of Pt coated PoAl films for H 2S gas sensing applications in diverse areas. 相似文献
6.
A sea-urchin-like CuO/ZnO porous nanostructure is obtained via a simple solution method followed by a calcination process. There are abundant pores among the resulting nanowires due to the thermal decomposition of copper–zinc hydroxide carbonate. The specific surface area of the as-prepared CuO/ZnO sample is determined as 31.3 m 2·g −1. The gas-sensing performance of the sea-urchin-like CuO/ZnO sensor is studied by exposure to volatile organic compound (VOC) vapors. With contrast to a pure porous sea-urchin-like ZnO sensor, the sea-urchin-like CuO/ZnO sensor shows superior gas-sensing behavior for acetone, formaldehyde, methanol, toluene, isopropanol and ethanol. It exhibits a high response of 52.6–100 ppm acetone vapor, with short response/recovery time. This superior sensing behavior is mainly ascribed to the porous nanowire-assembled structure with abundant p–n heterojunctions. 相似文献
7.
Visible light sensitive photocatalysts of Fe 2O 3/ZnO nanocomposites were prepared by a simple solid-state reaction method, using zinc acetate, α-Fe 2O 3 and sodium hydroxide at room temperature. The products were characterized by scanning electron microscopy, powder X-ray diffraction, N 2 adsorption–desorption measurement, UV–vis absorption, and photoluminescence spectroscopy and used for photodecolorization of Congo red. The characterization results showed that the morphology, crystallite size, BET surface area and optical absorption of the samples varied significantly with the Fe 3+ to Zn 2+ ratios. The nanocomposites show two absorption edges at ultraviolet and visible region. The optical band gap values of these nanocomposites were calculated to be about 3.98–3.81 eV and 2.88–2.98 eV, which show a red shift from that of pure ZnO. These red shifts are related to the formation of Fe s-levels below the conductive band edge of ZnO and effectively extend the absorption edge into the visible region. The growth mechanisms of the samples are proposed. These nanocomposites showed high decolorization ability in visible light with wavelength up to about 400 nm. Among the samples, Fe 2O 3/ZnO nanoflower (molar ratio of Fe 3+ to Zn 2+ is 1:100) exhibited higher decolorization efficiency than the other nanocomposites. It could be considered as a promising photocatalyst for dyes treatment. 相似文献
8.
A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response ( S = Rair/ Ralcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R2 of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature. 相似文献
9.
An organic–inorganic hybrid zirconium phosphonate (noted as ZrNCP) with window type porous structure was synthesized by using β–alanine– N, N-dimethylidenephosphonic acid and zirconium dichloride oxide octahydrate. The sample possesses regular flake morphology, and these flakes have porous framework structure, which were characterized by SEM, HRTEM, N 2 sorption, XRD, TGA–DSC, elemental analysis, XPS, and FT-IR spectroscopy techniques. The as-prepared ZrNCP can be used as catalyst to oxidation of formaldehyde after Fe 3+ was intercalated and coordinated with nitrogen and carbonyl groups inside the porous walls of ZrNCP. 90.1% of oxidized efficiency was obtained when the catalyst was added into formaldehyde solution (40% water solution) at 80 °C. 相似文献
10.
An ethanol gas sensor was fabricated based on Ti doped ZnO nanotetrapods which were prepared by chemical vapor deposition (CVD) of ZnO nanotetrapods followed by co-annealing with TiO 2 powder. X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) were used to characterize the morphology and structure of the as-obtained sample and the ethanol-sensing characteristics of the device were investigated. ZnO:Ti sensors show higher gas response than ZnO counterparts towards 100 ppm ethanol gas at a temperature of 260 °C. The recovery times of the devices are 3.1 min for ZnO:Ti and 10.1 min for ZnO, respectively. The enhancement of sensing properties of ZnO:Ti tetrapods indicates the potential application for fabricating low power and highly sensitive gas sensors. 相似文献
11.
In this paper, a hydrothermal method was applied to synthesize the nanosheet-like pure ZnO and 0.5%, 1 and 3% Co-doped ZnO (Co-ZnO). The pristine and Co-doped ZnO flower-like particles were assembled by porous nanosheets, with the uniform diameter about 18 μm. The N2-BET test found that Co doping significantly increased the specific surface area of the material which was conducive to gas diffusion and adsorption. HRTEM presented that 1% Co-ZnO nanosheets were composed of coral-like nanoparticles. The lattice distances 0.259 nm and 0.276 nm correspond to (002) and (100) crystal plane of ZnO. The gas sensing properties reveal that the 1% Co-doped ZnO present an outstanding enhanced sensitive performance comparing with pure ZnO to ethanol. To 100 ppm target gas, the response increased from 103 to 279.8 and the optimal operating temperature decreased from 369 to 348 °C, and the recovery time decreased from 40 to 18 s. The increased surface carrier concentration which promoted oxygen adsorption by Co was considered to be the key factor to improve the performance. 相似文献
12.
In this study, pure ZnO microbullets, ZnO–ZnFe 2O 4 composite, and ZnO–Fe 2O 3–ZnFe 2O 4 composite with micron structured balloons, rods, and particles were prepared by a simple solvent thermal process using methanol
or ethanol as solvents. The influence of solvents on the composition and morphology of the products was studied, and their
gas-sensing properties were also investigated. The morphology of ZnO microbullets synthesized in ethanol is similar to but
more uniform than that of ZnO microbullets synthesized in methanol. The Fe-doped ZnO synthesized in ethanol contains many
micron particles homogeneously dispersing on the surface of the microbullets, which is composed of hexagonal wurtzite ZnO
and franklinite ZnFe 2O 4, while Fe-doped ZnO prepared in methanol consists of micron structured balloons, rods, and particles, which is composed of
hexagonal wurtzite ZnO, hematite Fe 2O 3, and franklinite ZnFe 2O 4. Compared with pure ZnO and ZnO–ZnFe 2O 4 composite, the ZnO–Fe 2O 3–ZnFe 2O 4 composite presented high response, rapid response/recovery characteristics, good selectivity, and excellent stability to
acetone at relatively low operating temperature of 190 °C. This sensor could detect acetone in wide range of 1–1000 ppm, which
was expected to be a promising gas sensor for detecting acetone. 相似文献
13.
Undoped and Ni doped zinc oxide (Ni–ZnO) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of anhydrous zinc acetate (Zn(CH 3COOH) 2 and hexahydrated nickel chloride (NiCl 2·6H 2O) as sources of zinc and nickel, respectively. The films were deposited onto the amorphous glass substrates kept at (450 °C). The effect of the [Ni]/[Zn] ratio on the structural, morphological, optical and electrical properties of Ni doped ZnO thin film was studied. It was found from X-ray diffraction (XRD) analysis that both the undoped and Ni doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The scanning electron microscopy (SEM) images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The optical transmittance in the visible region varied between 75 and 85%, depending on the dopant concentrations. The variation of the band gap versus the [Ni]/[Zn] ratio showed that the energy gap decreases from 2.95 to 2.72 eV as the [Ni]/[Zn] ratio increases from 0 to 0.02 and then increases to reach 3.22 eV for [Ni]/[Zn] = 0.04. The films obtained with the [Ni]/[Zn] ratio = 0.02 showed minimum resistivity of 2 × 10 −3 Ω cm at room temperature. 相似文献
14.
The porous WO 3 (pore size 2–5 nm) nanoparticles were synthesized using a high intensity ultrasound irradiation of commercially available WO 3 nanoparticles (80 nm) in ethanol. The high resolution transmission electron microscopic (HRTEM) and X-ray studies indicated that the 2–5 nm uniform pores have been created in commercially available WO 3 nanoparticles without much changing the initial WO 3 nanoparticles (80 nm) sizes. The nanocomposites of WO 3/SC-15 epoxy were prepared by infusion of 1 wt.%, 2 wt.% and 3 wt.% of porous WO 3 nanoparticles into SC-15 epoxy resin by using a non-contact (Thinky) mixing technique. Finally the neat epoxy and nanocomposites were cured at room temperature for about 24 h in a plastic rectangular mold. The cured epoxy samples were removed and precisely cut into required dimensions and tested for their thermal and mechanical properties. The HRTEM and SEM studies indicated that the sonochemically modified porous WO 3 nanoparticles dispersed more uniformly over the entire volume of the epoxy (without any settlement or agglomeration) as compared to the unmodified WO 3/epoxy nanocomposites. 相似文献
15.
The porous sphere-like ZnO inorganic-organic nanocomposites have been prepared by self-assembly at the present of CTAB (cetyltrimethylammonium bromide, CH 3(CH 2) 15N +(CH 3) 3Br −) surfactant on the titanium substrate. After high temperature oxidation, all the organic were removed and the porous sphere-like ZnO dendrite nanocrystals were obtained. The resultant products have been characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD pattern shows that the as-synthesized porous sphere-like is multilayered inorganic-organic nanocomposite, and the sample calcined at 500 °C for 2 h has a hexagonal wurtzite crystal structure. FE-SEM and TEM images demonstrate that porous sphere-like ZnO dendrite nanocrystals are formed. A possible formation mechanism is preliminary proposed for the formation of the novel nanostructure. 相似文献
16.
The nanocomposite oxide (0.2TiO 2-0.8SnO 2) doped with Cd 2+ powder have been prepared and characterized by XRD and their gas-sensing sensitivity were characterized using gas sensing measurement. Experimental results show that, bicomponent nano anatase TiO 2 and rutile SnO 2 particulate thick film doped with Cd 2+ behaves with good sensitivity to formaldehyde gas of 200 ppm in the air, and the optimum sensing temperature was reduced from 360 °C to 320 °C compared with the undoped Cd 2+ thick film. The gas sensing thick films doped with Cd 2+ also show good selectivity to formaldehyde among benzene, toluene, xylene and ammonia as disturbed gas and could be effectively used as an indoor formaldehyde sensor. 相似文献
17.
The zinc–barium–metaphosphate glasses (ZBP) with composition of (50 − x)BaO– xZnO–50P 2O 5; (0 ≤ x ≤ 50 mol %), have been successfully prepared. The influences of the amount of ZnO on the structure, physical and chemical properties, and crystallization behavior of the glasses were investigated using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction and energy dispersive X-ray techniques (XRD/EDX). The density and the glass transition temperature ( Tg) of glass were measured using Archimedes' method and differential thermal analysis (DTA). The FTIR analysis revealed a shortening of the phosphate chains by the shift of (P–O–P) as band to higher wave number owing to the substitution ZnO of BaO. The amount of ZnO was further increased, [ZnO4] tetrahedra were formed and ZnO acted as a glass network former, integrating the phosphate glass network. The density, chemical stability and the activation energy of crystallization of the glasses increased with the amount of ZnO, whereas the glass transition temperature decreased. The dc- and ac-conductivity were measured. The results obtained from ac-conductivity reveals that the values of σ( ω) increases on increasing frequency and it is also increases on increasing the ZnO content level. The dc-conductivity of all the glasses increases with an increase in temperature. The dielectric permittivity ( ?′) and loss factor ( ?″) were calculated in the frequency range of 50 Hz–1 MHz. The dipolar relaxation occurred between 10 5–10 6 Hz. Finally, the dielectric strength (Δ ?) and the relaxation time ( τ) were estimated. 相似文献
18.
ZnO nanorods with diameters in the 80-800 nm range are readily synthesized by the reaction of zinc acetate, ethanol and ethylenediamine under solvothermal conditions. The best products are obtained at 330 °C with a slow heating rate. Addition of the surfactant Triton ®-X 100 gave nanorods of uniform (300 nm) diameter. By adding a small amount of liquid NH 3 to the reaction mixture, N-doped ZnO nanorods, with distinct spectroscopic features are obtained. CdO nanorods of 80 nm diameter have been prepared under solvothermal conditions using a mixture of cadmium cupferronate, ethylenediamine and ethanol at 330 °C. Similarly, Zn 1−xCd xO nanorods of a 70 nm diameter are obtained under solvothermal conditions starting with a mixture of zinc acetate, cadmium cupferronate, ethanol and ethylenediamine. 相似文献
19.
A chemical route has been used to synthesize composite oxides of zinc and tin. An ammonia solution was added to equal amounts of zinc and tin chloride solutions of same molarities to obtain precipitates. Three portions of these precipitates were annealed at 400, 600 and 800 °C, respectively. Results of X-ray diffraction and transmission electron microscopy clearly depicted coexistence of phases of nano-sized SnO 2, ZnO, Zn 2SnO 4 and ZnSnO 3. The effect of annealing on structure, morphology and sensing has been observed as well. It has been observed that annealing promoted growth of Zn 2SnO 4 and ZnSnO 3 at the expense of zinc. The sensing response of fabricated sensors from these materials to 250 ppm LPG and ethanol has been investigated. The sensor fabricated from powder annealed at 400 °C responded better to LPG than ethanol. 相似文献
20.
Hierarchically porous intestine-like SnO 2 hollow nanostructures of different dimension were successfully synthesized via a facile, organic template free, H 2O 2-assisted method at room temperature. The morphology as well as texture (congregated solid sphere, intestine-like solid nanostructure, hollow core–shell one, and intestine-like hollow one) of SnO 2 materials can be controlled by varying H 2O 2 concentration and the size of intestine-like hollow SnO 2 can be tuned in the range of 20–120 nm by changing SnSO 4 concentration. The hierarchically porous intestine-like SnO 2 has high specific surface area (142 m 2 g −1). The gas-sensing behaviors of the intestine-like SnO 2 material to different gas probes such as ethanol, H 2, CO, methane, and butane have been investigated; among them a high selectivity to ethanol was achieved. 相似文献
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