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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]

This work uses ZnO nanoparticles as the probe and a case, proving that the grey level can replace fluorescent intensity to realize a quantitative detection function of paper-based Cu 2+ sensor. Portable Cu 2+ test papers were obtained through dipping filter papers in as-prepared ZnO sol possessing the Cu 2+ quenching property. Based on grey level which is obtained through ordinary digital camera and computer, the detection function of the fabricated Cu 2+ test paper is extended from qualitative detection relied on naked eyes to quantitative detection whose detection range is calculated to be 10–1000 μM. The fabricated test papers also could resist the interruption of some competing ions and is a potential candidate for portable Cu 2+ detection device with quantitative function. Since the strategy of replacing fluorescence intensity by grey level is based on the map relationship between the fluorescence intensity and the digital signal (grey level), it is promising to be applied to other fluorescent test papers to gain quantitative test papers aimed at corresponding chemicals. At the same time, the mechanism of Cu 2+ -induced fluorescence quenching was also investigated by fluorescence lifetime, UV–vis spectra, and photoluminescence spectra. And a static quenching mechanism based on the non-fluorescence complex formed by Cu 2+ and O x − is brought up. [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]

Cobalt ion (Co 2+ ) is known to be harmful for human beings, and effectively portable sensor is one of the key for its prophylaxis and treatment. In this work, Zn(CH 3 COO) 2 ·2H 2 O, Na 2 S·9H 2 O and thioglycolic acid were used to prepare ZnS quantum dots through a facile water-bath method. The structure and morphology of the ZnS quantum dots were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Scanning electron microscope (SEM) was also used to observe the surface morphology of the test paper prepared by a simple dipping-drying process. The Co 2+ sensing properties of as-prepared test paper were investigated. And it was found that the color of as-fabricated test paper could change from white to brown within 1 min with addition of Co 2+ aqueous solution, which makes it possible for qualitative detection of Co 2+ through naked eyes. In this mode, a widely detectable range from 10 to 1000 mg L −1 is reached by the test paper. In addition, through measuring the grey level of the test paper by ordinary smart phone and laptop, a semi-quantitative function of the test paper is realized. Moreover, the as-fabricated paper sensor can resist the interference of a serious cations and anions, and suits for a wide pH surrounding from 1.08 to 9.65, which makes it a promising Co 2+ sensor for practical use. In addition, through X-ray diffraction and UV–vis spectra, the sensing properties of as-fabricated test paper are attributed to the chemical reaction between as-prepared ZnS quantum dots and Co 2+ ions. And the formation of CoS 2 should be responsible for the color change from white to brown. [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]