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Abstract In this work, CdO-Ag-ZnO nanocomposites with hierarchically porous structure and large surface area were successfully fabricated by solution combustion synthesis (SCS) method. Crystalline structure, morphology, surface chemical states and specific surface area were investigated by XRD, SEM, TEM, XPS and BET techniques, respectively. Sensors fabricated from CdO-Ag-ZnO nanocomposites were made based on indirect heating method, which showed superior sensing properties in detecting different concentration of volatile organic compounds (VOCs). In contrast with singular ZnO, gas-sensing experiment results reveal that the addition of CdO and Ag effectively decreases optimum working temperature, increases gas response value and shortens response and recovery time. What's more, other gas-sensing properties including repeatability, sensitivity and long-term stability are also discussed in this research. Particularly, gas sensor based on 10 mol% CdO-Ag-ZnO shows modest gas-sensing performance to VOCs at the operating temperature of 200 °C, and its gas response values are 198.63, 156.07, 53.04, 64.23, 183.65 towards 100 ppm formaldehyde, ethanol, acetone, methanol and isopropanol, respectively, indicating it a promising candidate in detecting VOCs. Superior sensing property is mainly ascribed to large specific surface area, special porous surface morphology, unique combination of nanocomposites and good catalytic ability of metallic Ag. [ABSTRACT FROM AUTHOR]

This paper reported the synthesis and gas-sensing properties of Pt nanoparticles modified Al-doped ZnO (AZO) macro-/mesoporous nanosheets, which were prepared via a solution combustion approach with a subsequent heat treatment at 400 °C for 50 min. The high performance in detecting butane were achieved for the well-adhered products with unique porous surface appearance on the sensors fabricated using indirect heating method, which demonstrated the superiority of solution combustion synthesis (SCS) in synthesizing complex oxides. The possible explanations of the high butane gas-sensing characteristics of these sensors were based on the results of BET and XPS. The large surface area could provide sufficient interface between the materials and butane gas, and the adsorbed oxygen species having strong oxidation activity could break the butane molecules into CO 2 and H 2 O. The gas-sensing properties of Pt-modified AZO were investigated by testing the gas responses towards butane. The maximum response of the 5% Pt-AZO based gas sensor reached 56.52–3000 ppm butane at 200 °C. What’s more, the sensor also exhibited good short- and long-term stability, repeatability and selectivity, which made it a potential candidate in the application of monitoring butane. In the end, the possible mechanisms of gas-sensing properties were discussed. [ABSTRACT FROM AUTHOR]

In this paper, a convenient solution combustion method to synthesis hierarchically porous Ag-loaded ZnO heterojunction nanocomposites with various Ag contents was reported. The analysis of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption were conducted to characterize the ingredients, microstructure and surface morphology. Ag and ZnO show separate phases due to the reduction of Ag + and the faster crystallization rate of ZnO. The as-synthesized powders were used as gas sensing materials to fabricate gas sensors. The gas-sensing performance was tested towards 100 ppm formaldehyde at an optimum operating temperature of 240 °C and Ag-loaded ZnO (with the different Ag atomic ratio) based gas sensors showed a superior gas-sensing performance comparing with pure ZnO. Especially 1 at% Ag-loaded ZnO has the highest gas response as 170.42. The possible gas-sensing mechanism was discussed in this paper. For example, the influence of surface area, the formation of heterostructure, Ag elements, adsorbed oxygen and so on. [ABSTRACT FROM AUTHOR]

Macro-/nanoporous Al-doping ZnO powders with enhanced gas sensing properties are prepared by a solution combustion method using Zn(CH 3 COO) 2 ·2H 2 O, Zn(NO 3 ) 2 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O, N 2 H 4 ·H 2 O and C 2 H 5 NO 2 as precursors. Characterization by TEM, SEM and BET techniques demonstrates that the Al-doping ZnO powders have a coral-like morphology with a hierarchically porous structure from macro pores, with the wall containing smaller mesopores. The gas-sensing characteristics of the ZnO samples with different Al-doping concentrations are investigated and the results indicate that the gas sensor prepared from 2.5 at% Al doping ZnO powders shows the highest gas sensitivity and selectivity towards n -butanol. A maximum gas response of 751.95 towards 100 ppm n -butanol is achieved at the operating temperature of 300 °C. The mechanisms of responses are also proposed considering the unique material structure. [ABSTRACT FROM AUTHOR]

Hollow CuO fibers were successfully fabricated using a facile solution combustion method by incorporating cotton fibers as biotemplate. XRD patterns along with Rietveld refinement confirm the formation of CuO with monoclinic phase. The length of the as-synthesized CuO fibers is at micrometer scale, and the average fiber diameter ranges from several nanometers up to order of micrometers. After combustion reaction, a large amount of coalescent particles left on the surface of the cotton fibers to form porous walls of CuO. By totally removing cotton body at 600 °C, hollow CuO fibers were obtained. A possible growth mechanism of hollow CuO fibers using cotton fibers as templates was given based on experimental data. When used as a sensing material in gas sensor, it exhibited a superior sensitivity and good selectivity toward low-ppm-level (1–100 ppm) n -propanol. Theses findings not only provide a novel approach to fabricate hollow CuO fibers via a solution combustion route, but also explore a promising gas sensor toward n -propanol. [ABSTRACT FROM AUTHOR]

Pd-functionalized one-dimensional (1D) SnO2 nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO2 composites were measured. All results indicate that the sensor based on 5 mol % Pd-functionalized SnO2 composites exhibited significantly enhanced gas-sensing performances toward butane. With regard to pure SnO2, enhanced levels of gas response and selectivity were observed. With 5 mol % Pd-functionalized SnO2 composites, detection limits as low as 10 ppm with responses of 1.38 ± 0.26 were attained. Additionally, the sensor exhibited rapid response/recovery times (3.20/6.28 s) at 3000 ppm butane, good repeatability and long-term stability, demonstrating their potential in practical applications. The excellent gas-sensing performances are attributed to the unique one-dimensional morphology and the large internal surface area of sensing materials afforded using bio-templates, which provide more active sites for the reaction between butane molecules and adsorbed oxygen ions. The catalysis and "spillover effect" of Pd nanoparticles also play an important role in the sensing of butane gas as further discussed in the paper. [ABSTRACT FROM AUTHOR]

This paper describes the preparation with a sol-gel method as well as formaldehyde (HCHO) gas sensing properties of CdIn 2 O 4 nanoporous thin film. CdIn 2 O 4 nanoporous thin film was prepared using poly(ethylene- co -butylene)- b -poly(ethylene oxide) diblock copolymers as template. The film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), and x-ray photoelectron spectroscopy (XPS), respectively. The analyzed results indicate that the obtained thin film is highly crystalline and has pore-solid architectures after removal of the polymer template by calcination. As-prepared CdIn 2 O 4 nanoporous thin film was used directly as sensing device to investigate the sensing properties in HCHO atmosphere. The home-built CdIn 2 O 4 nanoporous thin film gas-sensor shows high response, selectivity, and long-time stability toward HCHO gas at low operating temperature (100 °C), making the thin film not only interesting for sensor devices, but also for a number of related electrochemical applications. [ABSTRACT FROM AUTHOR]

ZnO hollow spheres with high crystallinity were prepared successfully via a simple template process using ZnCl 2 , carbamide and polystyrene spheres (PSS) as raw materials. The structural and morphological characterizations of the samples were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Indirect-heating sensor using ZnO hollow spheres as sensing materials was fabricated on an alumina tube with Au electrodes and Pt wires. The gas sensing properties of the as-synthesized ZnO hollow spheres for n -butanol were investigated. It is shown that the sensor exhibited good sensing performances, characterized by high response, very short response time, and stability to n -butanol gas at operating temperature of 385 °C. These results indicate that the ZnO hollow spheres are highly promising candidates for practical detectors for n -butanol. [ABSTRACT FROM AUTHOR]

As a new methanol sensing material, the composite of palladium-platinum-In 2 O 3 composited nanocrystalline SnO 2 was successfully obtained by a solid-phase reaction method. The phase composition and the unique structure of as-prepared SnO 2 -Pd-Pt-In 2 O 3 composite were comprehensively characterized using the techniques such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results of gas sensing properties indicate that the sensor based on the as-prepared SnO 2 -Pd-Pt-In 2 O 3 composite shows the ultra-high response to methanol at an optimal operating temperature of 160 °C when the mass ratio of SnO 2 , Pd, Pt and In 2 O 3 is 100:0.8:2:30. The gas response toward 100 ppm of methanol reaches as high as 320.73. The detection limit of the sensor is estimated to be 0.1 ppm. The sensor also exhibited good response-recovery properties, selectivity, remarkable repeatability and stability, suggesting its greatly promising application in gas sensing. This work could stimulate an effective means to fabricate methanol sensor with superior performance. At the same time, a possible sensing mechanism of the SnO 2 -Pd-Pt-In 2 O 3 composite is discussed. [ABSTRACT FROM AUTHOR]

The raspberry-like SnO 2 hollow nanostructure was synthesized by a simple hydrothermal method. The composition, microstructure, morphology, surface area and chemical states are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N 2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS), respectively. The characterization results show that the raspberry-like SnO 2 with a diameter of about 60 nm is composed of numerous SnO 2 nanoparticles with grain size about 8 nm. The raspberry-like SnO 2 was used as sensing material for gas sensor to detect n-butanol gas. The gas-sensing properties including gas response, selectivity, response-recovery time, repeatability, stability and dynamic response character were investigated carefully. It can be found that the response value of the sensor towards 100 ppm n-butanol gas was 303.49 at the low operating temperature of 160 °C. And the detection limit as low as 1 ppm. All results demonstrate the potential of using raspberry-like SnO 2 for n-butanol gas detection. At the same time, the possible formation mechanism and gas-sensing mechanism were also discussed. [ABSTRACT FROM AUTHOR]

SnO 2 -composite Pd nanoparticles (0, 2.5, 7.5, 10 mol% Pd loading) were synthesized via solvothermal method, followed by calcination. The structure, morphology, chemical state and specific surface area of the Pd-SnO 2 composite were analyzed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), N 2 physisorption, respectively. It is found that the composites consist of large amount of SnO 2 microspheres with average diameters up to hundreds of nanometers, and the microspheres are assembled by numerous nanoparticles with average sizes of about 8 nm. To demonstrate their potential application, gas sensors based on the as-synthesized Pd-SnO 2 composites were fabricated to test their sensing performances. The 10 mol% Pd-SnO 2 composite shows an excellent sensing response towards different concentrations of hydrogen at 200 °C. The highest sensing response is up to 315.34 for 3000 ppm hydrogen with a fast response-recovery time (4 s/10 s), which is over 8 times higher than that of pristine SnO 2 , and the lowest detection limit is down to 10 ppm. More significantly, it presents excellent selectivity and stability for hydrogen. The improved sensing response characteristics of the composite could be attributed to the chemical sensitization and electronic sensitization of Pd catalyst. [ABSTRACT FROM AUTHOR]

Tin oxide microspheres were successfully obtained through a facile hydrothermal method without any polymer templates or surfactant. The as-synthesized SnO 2 microspheres are composed of large amount of small spheres with average diameters of about 250 nm, and every small sphere consists of numerous primary nanocrystallites with average sizes of about 8 nm. The resultant product was used as sensing material for gas sensor to detect the formaldehyde (HCHO) gas. The gas response, response and recovery time, selectivity and stability were carefully studied. It was found that the response value of the sensor to 100 ppm HCHO was 38.3 at the operating temperature of 200 °C. The gas sensor based on SnO 2 microspheres has excellent gas response, good response-recovery properties, linear dependence, repeatability and selectivity, making it to be a promising candidate for practical detectors for HCHO. [ABSTRACT FROM AUTHOR]

Nanoporous titanium dioxide was synthesized by a hydrothermal method without using of surfactant or template. The structure, morphology, surface chemical states and specific surface area were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption-desorption isotherms, respectively. The as-synthesized products are anatase-TiO 2 with small grain size (about 12.27 nm) and high surface area (147.17 m 2 g −1 ). The as-synthesized porous TiO 2 powder was used to fabricate indirect-heating gas sensor whose gas-sensing characteristics toward acetone were investigated. At its optimal operation temperature, the sensor possesses a good sensitivity, selectivity, linear dependence, low detection limitation, and response/recovery, repeatability as well as long-term stability. Especially for the high sensitivity and fast response/recovery, its response reaches 25.97 for 500 ppm acetone, which is several times higher that of the reported TiO 2 -based sensors. The response and recovery times are only 13 and 8 s, respectively. Those values demonstrate the potential of using as-synthesized TiO 2 for acetone gas detection, particularly in the dynamic monitoring. Apart from these, the mechanism related to the advanced properties was also investigated and presented. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) structural Cd-doped SnO 2 are prepared using shaddock peels as bio-templates via a facile hydrothermal method. The as-synthesized materials are characterized by different techniques, including XRD, FESEM, TEM, XPS and N 2 adsorption-desorption. Interestingly, unique 1D fiber-like structures are observed and composed of numerous small nanoparticles. Moreover, the result shows that 5 mol% Cd-doped SnO 2 nanofibers possesses a larger specific surface area of 38.850 m2/g. At the same time, the gas-sensing properties of sensors based on as-prepared SnO 2 nanofibers are also investigated. The 5 mol% Cd-doped SnO 2 nanofibers based sensor shows the highest response towards formaldehyde at a lower operating temperature of 160 °C. The excellent gas-sensing properties of sensor towards formaldehyde may attribute to the unique 1D fiber-like structure, large specific surface area and the additive of Cd, which can provide more active sites for the reaction between adsorbed oxygen ions and formaldehyde molecules on the surface of sensing materials. In addition, based on the above experimental results, the possible sensing mechanism of sensor towards formaldehyde is discussed in detail. Gas sensor based on 5 mol% Cd-doped SnO 2 nanofibers prepared using shaddock peels as bio-templates via a facile hydrothermal method shows high gas response, low detection limit and fast response toward various formaldehyde gas at the relative low operating temperature of 160 °C. Image 1 • Cd-doped SnO 2 nanofibers were using shaddock peels as bio-templates at first time. • Cd-doped SnO 2 nanofibers based gas sensor shows a high response towards formaldehyde. • Sensor has good repeatability, stability, fast response and recovery towards formaldehyde. • 1D structure increases surface area and oxygen specie to promote oxidation of formaldehyde. [ABSTRACT FROM AUTHOR]