Gas Sensing Properties of ZnO Tetrapod-Like Whiskers Prepared by Hydrothermal Process

ZnO tetrapod-like whiskers were prepared through a hydrothermal process using zinc powder as raw material.Its microstructure and morphology were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results showed that the crystal structure of as-obtained sample can be indexed to hexagonal wurtzite ZnO.TEM results revealed that the ZnO sample took on tetrapod-like whisker shape.The gas sensors were prepared with the traditional sintering process and their gas sensitivities were detected.The test results of gas sensitivity showed that the sensors based on ZnO tetrapod-like whiskers are very sensitive to dilute ethanol vapor and H_2S.The relatively high sensitivity and selectivity of these sensors made from ZnO tetrapod-like whiskers demonstrated the potential for developing a new class of selective ethanol sensors.

Self-assembly of hierarchical ZnSnO_3-SnO_2 nanoflakes and their gas sensing properties

A new type of hierarchical ZnSnO3-SnO2 flower-shaped nanostructure composed of thin nanoflakes as secondary units is successfully prepared through a simple hydrothermal process. The polyhedral ZnSnO3 core acts as a sacrificed template for the growth of hierarchical SnO2 nanoflakes, and the average thickness of SnO2 nanoflakes is around 25 nm. The time-dependent morphology evolution of ZnSnO3-SnO2 samples was investigated, and a possible formation mechanism of these hierarchical structures is discussed. The gas sensor based on these novel ZnSnO3-SnO2 nanostructures exhibits high response and quick response- recovery traits to ethanol （C2H5OH）. It is found that ZnSnO3-SnO2 nanoflakes have a response of 27.8 to 50×10-6 C2H5OH at the optimal operating temperature of 270 °C, and the response and recovery time are within 1.0 and 1.8 s, respectively.

Gasoline Sensor Based on Flower-Like ZnO

<正>Flower-like ZnO was prepared through a hydrothermal process using zinc sulfate as raw material.The microstructure and morphology of the samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).XRD results showed that the as-obtained sample could be indexed to hexagonal wurtzite ZnO.TEM results revealed that the ZnO sample presented flower-like shape.The gas sensors were prepared with the traditional sintering process and their gas sensitivities were detected.The gas sensitivity results showed that the sensors based on flower-like ZnO were very sensitive to dilute 90~# gasoline.The relatively high sensitivity and selectivity of these sensors made from flower-like ZnO demonstrated the potential for developing a new class of selective gasoline sensors.

Hydrothermal Synthesis of SnO_2 Nanoparticles

SnO_2 nanoparticles with the average size of 3.7 nm have been successfully synthesized by hydrothermal method. The particles were characterized by XRD,SEM and TEM.The XRD results show that the products are all at nanometer scale, and the crystallite size increases with increasing of the heat-treatment temperature.The SEM and TEM photographs indicate that the particles are all monodispersed with narrow size distribution.

Chemical synthesis of zinc oxide nanorods for enhanced hydrogen gas sensing

Zinc oxide （ZnO） nanorods are prepared using equimolar solution of zinc nitrate （（Zn（NO3）2） and hexamethylenete- tramine （C6HleN4） by the hydrothermal technique at 80 ~C for 12 h. Epitaxial growth is explored by X-ray diffraction （XRD） patterns, revealing that the ZnO nanorods have a hexagonal （wurtzite） structure. Absorption spectra of ZnO are measured by UV-visible spectrometer. The surface morphology is investigated by field emission scanning electron mi- croscopy （FESEM）. The synthesized ZnO nanorods are used for detecting the 150 ~C hydrogen gas with a concentration over 1000 ppm. The obtained results show a reversible response. The influence of operating temperature on hydrogen gas detecting characteristic of ZnO nanorods is also investigated.

Morphology-controlled preparation of tungsten oxide nanostructures for gas-sensing application

A novel three-dimensional（3D） hierarchical structure and a roughly oriented one-dimensional（1D） nanowire of WO3 are selectively prepared on an alumina substrate by an induced hydrothermal growth method.Each hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO3 nanowire arrays from a nanosheet preformed on the substrate.Only roughly oriented 1D WO3 nanowire can be obtained from a spherical induction layer.The analyses show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO3,respectively.The gas-sensing properties of the nanowires and the hierarchical structure of WO_3,which include the variations of their resistances and response times when exposed to NO2,are investigated at temperatures ranging from room temperature（20 ℃） to 250 ℃ over 0.015 ppm-5 ppm NO2.The hierarchical WO3 behaves as a p-type semiconductor at room temperature,and shows p-to-n response characteristic reversal with the increase of temperature.Meanwhile,unlike the1 D nanowire,the hierarchical WO3 exhibits an excellent response characteristic and very good reversibility and selectivity to NO2 gas at room temperature due to its unique microstructure.Especially,it is found that the hierarchical VO3-based sensor is capable of detecting NO2 at a ppb level with ultrashort response time shorter than 5 s,indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption.

Pure SnO₂Gas Sensor with High Sensitivity and Selectivity towards C₂H₅OH

To observation, poisonous gases in the environment, Sensors with high selectivity, high response and low operating temperature are required. In this work, pure SnO2 nanoparticles was prepared by using a simple and inexpensive technique (hydrothermal method) without a template. Various confirmatory tests were performed to characterize SnO2 nanoparticles such as energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM), during the detection of the gas, we found that pure SnO2 nanoparticles has a high selectivity for ethanol to 100 ppm at a low temperature (180°C) and a high response (about 27 s) and a low detection limit of 5 ppm, also it have response/recovery times about (4 s, 2 s) respectively. The distinctive sensing properties of SnO2 sensor make it a promising candidate for ethanol detection. Furthermore, the gas-sensing mechanism have been examined.

Synthesis and Characterization of SnO<SUB>2</SUB>Flower-Shaped by Hydrothermal Route for Formaldehyde Sensing Properties

In this work, we’ve made SnO2 flower formed with the aid of using easy test steps, and without cost, which is the hydrothermal approach and without a template. We have used a variety of techniques to characterize SnO2 flower-shaped by (SEM, TEM, XRD, BET and XPS) instruments. Confirmatory tests carried out have proven that the surface of the tetragonal structure of SnO2 has a rough surface which makes it excellent for its gas-sensing properties. The gas detection test of SnO2 flower-shaped proved that it possesses the selectivity of formaldehyde gas (about 30), the optimum operating temperature of the sensor is 220°C, and also the sensor has a high response time and recovery time is (5 s and 22 s) to 100 ppm, respectively. Particularly, the sensor has an obvious response value (2) when exposed to 5 ppm formaldehyde. As well, the mechanism of gas-sensing was also discussed.

水热处理对SnO_2厚膜气敏传感器性能的影响

研究了水热处理对于SnO2厚膜气敏传感器性能的影响。为了便于作对比,首先把SnO2纳米粉(平均粒径约200nm)平均分为两份:一份不经处理,直接用传统的厚膜传感器制备工艺制成气敏传感器(称为“原粉传感器”);另一份经过200℃水热处理后,用同样的工艺制备成厚膜气敏传感器(称为“预处理粉传感器”)。利用乙醇、丙酮、CH4、H2和CO气体对这两种气敏传感器的性能进行了测试,结果表明预处理粉传感器的灵敏度和选择性明显优于原粉传感器。为了分析出现这种差异的原因,我们对这两种传感器的显微结构进行了分析,并在此基础上对实验现象进行了讨论。

Microwave-assisted hydrothermal synthesis of Pt/SnO2 gas sensor for CO detection

In this paper,the Pt/SnO2 nanostructures were prepared via a facile one-step microwave assisted hydrothermal route.The structure of the introduced Pt/SnO2 and its gas-sensing properties toward CO were investigated.The results from the TEM test reveal that Pt grows on the SnO2 nanostructure,which was not found for bulk in this situ method,constructing Pt/SnO2.The results indicated that the sensor using 3.0 wt%Pt/SnO2 to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt%and 4.5 wt%Pt/SnO2 at 225℃.The response time of 3.0 wt%sensor is 16 s to 100 ppm CO at225℃.Such enhanced gas sensing performances could be attributed to the chemical and electrical factors.In view of chemical factors,the presence of Pt facilitates the surface reaction,which will improve the gas sensing properties.With respect to the electrical factors,the Pt/SnO2 plays roles in increasing the sensor’s response due to its characteristic configuration.In addition,the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.

Room-temperature chlorine gas sensor based on CdSnO_(3) synthesized by hydrothermal process

The perovskite-structure CdSnO_(3) was obtained by calcinating CdSnO_(3)·3H_(2)O precursor at 550℃,which was synthesized by hydrothermal process at 170℃for 16 h.The phase and microstructure of the obtained CdSnO_(3) powders were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The CdSnO_(3) powders exhibit uniformly cubic structure with side length of about 100 nm.The effects of working temperature and concentration of detected gas on the gas response were studied.The selectivity of chlorine gas against other gases and response-recovery time of the sensor were also investigated.The results reveal that the CdSnO_(3) gas sensor has enhanced sensing properties to 1-10 ppm chlorine gas at room temperature;the value of gas response can reach 1338.9 to 5 ppm chlorine gas.Moreover,the sensor shows good selectivity and quick response behavior(23 s)to chlorine gas,indicating its application in detecting chlorine gas at room temperature in the future.

Hydrogen Sensing Characteristics of ZnSnO_3 Micro-Particles Doped with Noble Metal Pd

Perovskite-type oxide ZnSnO_3 doped with 0.5 wt% Pd was prepared directly by a hydrothermal process,its crystal structure and ceramic microstructure were characterized by XRD and TEM,and the gas sensing properties were tested in static state.It is found that the sensors based on ZnSnO_3 micro-particles have good sensitivity and selectivity to H_2.Its sensitivity can be changed with working temperature;the sensitivity of the sensors to H_2 could arrive 21 times when the working temperature is 332℃.

Room temperature NO2-sensing properties of hexagonal tungsten oxide nanorods

Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope（SEM）, transmission electron microscope（TEM）, energy dispersive spectroscopy（EDS）, and x-ray diffraction（XRD）. The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor（400-℃-annealed WO_3 nanorods） showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.

纳米结构形貌二氧化钛的制备及其气敏响应

为获得高灵敏度的纳米结构感知元件，对二氧化钛的形貌调控进行了研究．结果表明，TiO2粉体经适当的水热处理可获得高比表面积的纳米TiO2形貌．SEM和XRD结果显示处理效果明显．将该形貌的纳米TiO2用于传感器原理型器件的制备，室温下对有机挥发性气氛显示出快速响应．这为高灵敏度化学传感器及其阵列的研发提供了一简便的材料制备途径。

Effect of varying hydrothermal temperature,time,and sludge pH on sludge solubilisation

In recent years,hydrothermal treatment has been considered as among the most promising option for sludge solubilisation and carbon recovery in terms of sludge management.In this study,the effect of different individual hydrothermal operating conditions like temperature(110-250℃),sludge pH(6-13)and reaction time(0.5-3 h)were varied to understand their influence on sludge solubilisation.The most effective hydrothermal conditions(severity factor of 9.7)were found to be at 200℃,sludge pH of 12 and reaction time of 1 h which solubilised about 1743 mg/g and 131 mg/g of COD and carbohydrates respectively into the aqueous phase.Also,gas chromatography-mass spectrometry(GC-MS)analysis was done that identified the organic compounds in the treated liquid phase to be mainly carboxylic acids,phenols,esters,and their derivatives.Although further studies are required to efficiently separate and recover the different organic compounds present,this work provides more insights for future valorisation of the organic rich hydrothermally treated liquid phase.

Micro-interfaces modulation by UV-ozone substrate treatment for MPEA vapor fluorescence detection

Drug abuse directly endangers human health and social security,hence its sensitive and rapid detection is vitally important.In recent years,organic film-based fluorescent sensing technology has attracted more and more attention in the detection of drugs and explosives due to its advantages of simple operation and rapid detection.For film-based fluorescent sensors,in addition to sensitive materials,the surface morphology of the film is also an important factor affecting the performance.In previous studies,the regulation of surface morphology mainly depends on concentration changes or complex templates.Here,a novel fluorescent polymer probe was designed and synthesized,and a simple and efficient ultraviolet(UV)-ozone substrate treatment method is used to adjust their surface morphology.The results show that film has an excellent fluorescence enhancement effect upon exposure to methylphenethylamine(MPEA,a simulant of methamphetamine)vapor.The sensing effect of the film is significantly improved after UV-ozone substrate treatment,and the limit of detection was decreased by 10.4 times from 2.59 to 0.25 ppm.Further experiments show that the sensing performance of other fluorescent probe can also be improved by the UV-ozone substrate treatment.This convenient and general method may become a very effective approach to improve the performance of film-based fluorescent sensors.

Facile synthesis of Ni-doped SnO_(2) nanorods and their high gas sensitivity to isopropanol

In this work,pure SnO_(2) and Ni-doped SnO_(2) nanorods were synthesized through a one-step template-free hydrothermal method and then used to detect isopropanol.Sensors fabricated with the Ni-doped SnO_(2) nanocomposites showed the best gas sensing performance when the Ni doping amount was 1.5 mol.%.The response reached 250 at 225℃,which was approximately 8.3 times higher than that of the pure SnO_(2) nanorods.The limit of detection for isopropanol was as low as 10 ppb at the optimum working temperature.In addition,it also displayed good selectivity and excellent reproducibility.It is believed that the enhanced isopropanol sensing behavior benefit from the increased oxygen defects and larger specific surface area by Ni doping.

Hydrothermal synthesis of hierarchical SnO_(2)nanomaterials for high-efficiency detection of pesticide residue

Acephate pesticide contamination in agricultural production has caused serious human health problems.Metal oxide semiconductor(MOS)gas sensor can be used as a portable and promising alternative tool for efficiently detection of acephate.In this study,hierarchical assembled SnO_(2)nanosphere,SnO_(2)hollow nanosphere and SnO_2 nanoflower were synthesized respectively as high efficiency sensing materials to build rapid and selective acephate pesticide residues sensors.The morphologies of different SnO_(2)3 D nanostructures were characterized by various material characterization technology.The sensitive performance test results of the 3 D SnO_(2)nanomaterials towards acephate show that hollow nanosphere SnO_(2)based sensor displayed preferable sensitivity,selectivity,and rapid response(9 s)properties toward acephate at the optimal working temperature(300℃).This SnO_(2)hollow nanosphere based gas sensor represents a useful tool for simple and highly effective monitoring of acephate pesticide residues in food and environment.According to the characterization results,particularly Brunauer-Emmett-Teller(BET)and Ultraviolet-Visible Spectroscopy(UV-vis),the obvious and fast response can be attributed to the mesoporous hollow nanosphere structure and appropriate band gap of SnO_2 hollow nanosphere.

利用纳米ZnO粉制备厚膜气敏传感器的研究

以ZnO纳米粉(平均粒径30nm)为原料,利用水热热压方法制备了ZnO多孔纳米固体,同时用通常的水热法对ZnO纳米粉进行了预处理(预处理ZnO纳米粉)。然后,分别以ZnO多孔纳米固体和预处理ZnO纳米粉为原料,制备了厚膜气敏传感器。本征电阻的测试结果表明,这两种厚膜气敏传感器的本征电阻比用未经处理的ZnO纳米粉(以下简称“原料ZnO纳米粉”)制备的厚膜气敏传感器大大降低并很快达到稳定状态。有效地改善了器件工作的稳定性。结合对三种传感器的显微结构分析,对出现上述差异的原因进行了讨论。

TiO_2 nanotubes as solid-phase extraction adsorbent for the determination of polycyclic aromatic hydrocarbons in environmental water samples

An analytical method based on TiO2 nanotubes solid-phase extraction （SPE） combined with gas chromatography （GC） was established for the analysis of seven polycyclic aromatic hydrocarbons （PAHs）： acenaphtylene, acenaphthene, anthracene, fluorene, phenanthrene, fluoranthene and pyrene. Factors affecting the extraction efficiency including the eluent type and its volume, adsorbent amount, sample volume, sample pH and sample flow rate were optimized. The characteristic data of analytical performance were determined to investigate the sensitivity and precision of the method. Under the optimized extraction conditions, the method showed good linearity in the range of 0.01-0.8 μg/mL, repeatability of the extraction （RSD were between 6.7% and 13.5%, n = 5） and satisfactory detection limits （0.017-0.059 μg/mL）. The developed method was successfully applied to the analysis of surface water （tap, river and dam） samples. The recoveries of PAHs spiked in environmental water samples ranged from 90% to 100%. All the results indicated the potential application of titanate nanotubes as solid-phase extraction adsorbents to pre-treat water samples.