Xuechun Xiao

Combustion synthesis of porous Pt-functionalized SnO2 sheets for isopropanol gas detection with a significant enhancement in response

Pt-functionalized SnO2 sheets with Pt contents of 0, 0.5, 1, and 2 wt% were synthesized by a facile solution combustion synthesis, and their crystal structure, morphology, and chemistry have been thoroughly characterized. In the combustion process, the urea (CO(NH2)2) has been employed as a fuel. The obtained products appear as porous sheets formed by the interconnected and loosely packed SnO2 nanoparticles. Pt nanoparticles are assembled together with SnO2 nanoparticles in several up to tens of nanometer clusters. The as-synthesized products were used as sensing materials in the sensors to detect the isopropanol (IPA) gas. Gas sensing tests exhibited that the Pt-functionalized SnO2 are highly promising for gas sensor applications, as the operating temperature was lower than current IPA sensors and the response to IPA was significantly enhanced. The 2 wt% Pt–SnO2 sheet based gas sensor displayed a response value of 190.50 for 100 ppm IPA at an optimized operating temperature of 220 °C, whereas the pristine SnO2 based gas sensor only showed a response of 21.53 under the same conditions. The roles of Pt nanoparticles on electronic sensitization of SnO2, catalytic oxidation (spillover effect), and the increased quantities of oxygen species on the surface of SnO2 are plausible reasons to explain the significant enhancement in response to a Pt-functionalized SnO2 sheet based gas sensor.

Porous NiO nanosheets self-grown on alumina tube using a novel flash synthesis and their gas sensing properties

Porous NiO nanosheets were self-grown on an alumina tube with a pair of Au electrodes connected by platinum wires via a simple solution combustion synthesis. A cubic NiO phase was obtained by a mixed solution of an oxidizer of nickel nitrate and a fuel of ethylene glycol (EG) at 400 °C. The phases and the morphologies of the materials self-grown on an alumina tube were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the alumina tube was entirely covered by NiO nanosheets with several micrometers in thickness. The NiO nanosheets on the surface of the tube were assembled by a large number of nanoparticles of irregular shapes and pores with different sizes. The electronic and gas-sensing characteristics of the self-grown porous NiO nanosheets for volatile organic compound (VOC) vapours (ethanol, acetone, methanol, and formaldehyde) were investigated. The resistance of the sensor directly based on the self-grown NiO dramatically drops from 100–240 °C, and then slightly decreases with further increasing temperature to about 28 kΩ at 400 °C. The sensor based on the self-grown NiO exhibits low detection limit, fast response and recovery and wide dynamic range detection to VOC vapours, especially ethanol, at the respectively optimal operating temperatures.

A high-performance n-butanol gas sensor based on ZnO nanoparticles synthesized by a low-temperature solvothermal route

ZnO nanoparticles with high crystallinity and several nanometers in size were synthesized by a low-temperature solvothermal route from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), potassium hydroxide (KOH) and methanol (CH3OH). The structural and the morphological characterizations of the ZnO nanoparticles were performed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption isotherms. The obtained nanoparticles are highly crystalline wurtzite-type ZnO with a uniform near-spherical shape and an average particle size estimated to be 8.4 ± 1.3 nm. Such a small particle size and slight agglomeration are attributed to the use of methanol, which acts as both a solvent and an inhibitor of growth and agglomeration. The as-synthesized ZnO nanoparticles were directly used as a gas sensing material toward n-butanol gas. Such a designed sensor device exhibits several advantages such as a high and fast response, short recovery time, and good stability toward n-butanol gas. At the optimal operating temperature (320 °C), its gas response toward 500 ppm n-butanol is 805 and the response and recovery times are 22 and 6 seconds, respectively.

The xylene sensing performance of WO3 decorated anatase TiO2 nanoparticles as a sensing material for a gas sensor at a low operating temperature

Here, pristine and WO3 decorated TiO2 nanoparticles were synthesized by a one-step hydrothermal method without the use of a surfactant or template and used to fabricate gas sensors. Various techniques were employed for the characterization of the structure and morphology of the as-prepared products. The gas-sensing characteristics of the fabricated sensors were investigated for various concentrations of xylene at different temperatures. At a low operation temperature of 160 °C, the sensors possess an excellent gas response, selectivity, linear dependence, low detection limitation, and repeatability as well as long-term stability. In particular, for the high gas response of the 10.0 mol% WO3 decorated TiO2 nanoparticles based sensor, its response reaches 92.53 for 10 ppm xylene, which is much higher than that of the pristine TiO2 based sensor. And the detection limit is 1 ppm. Those values demonstrate the potential of using WO3 decorated TiO2 nanoparticles for xylene gas detection, particularly with low concentration xylene. Apart from this, the mechanism related to the advanced properties was also investigated and presented.

Preparation and electrochemical performances of carbon sphere@ZnO core-shell nanocomposites for supercapacitor applications

Carbon sphere (CS)@ZnO core-shell nanocomposites were successfully prepared through facile low-temperature water-bath method without annealing treatment. The morphology and the microstructure of samples were characterized by transition electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. ZnO nanoparticles with several nanometers in size decorated on the surface of the carbon sphere and formed a core-shell structure. Electrochemical performances of the CS@ZnO core-shell nanocomposites electrodes were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge (GDC). The CS@ZnO core-shell nanocomposite electrodes exhibit much larger specific capacitance and cycling stability is improved significantly compared with pure ZnO electrode. The CS@ZnO core-shell nanocomposite with mole ratio of 1:1 achieves a specific capacitance of 630 F g−1 at the current density of 2 A g−1. Present work might provide a new route for fabricating carbon sphere and transition metal oxides composite materials as electrodes for the application in supercapacitors.

Enhanced formaldehyde sensing properties of SnO2 nanorods coupled with Zn2SnO4

Ternary oxide Zn2SnO4 was introduced to a rod-like nanostructured SnO2 gas sensor for formaldehyde detection by a facile one-step hydrothermal synthesis. The effects of the Zn2SnO4 additive on the structure, morphology and gas-sensing property of SnO2 were investigated in this study. It was confirmed that control of the Zn amounts in the precursor solution was effective in realizing well-developed one- and two-dimensional coexisting structured SnO2–Zn2SnO4 (SnZn) nanocomposites. The gas sensing properties of the resulting SnZn composites to HCHO vapor were tested. The results showed that the presence of Zn2SnO4 species in SnO2 powders could effectively enhance electrical conductivity, reduce optimal operating temperature and improve the gas response of the sensors. The composite exhibited the highest response towards HCHO in the case of 35 at% Zn2SnO4 nanoplates coupling with hierarchical branched structures of SnO2 nanorods (SnZn35) at a relatively lower operating temperature of 162 °C. The good gas-sensing performance of the SnZn35 composite can be ascribed to the smaller particle size, the larger surface area and the more absorbed Ox− species, which all are favorable for gas diffusion and sensing reactions. This work renders great potential in the fabrication of gas sensors using a binary–ternary oxide composite, which can be further applied in indoor pollution detection.

Enhanced methanol sensing properties of SnO2 microspheres in a composite with Pt nanoparticles

SnO2 microspheres in a composite with Pt nanoparticles (0, 0.5, 1.5, 2.5, 5.0 mol% Pt loading) were synthesized by a solvothermal method. The crystal structure, morphology, and specific surface area were thoroughly characterized. It is found that the Pt–SnO2 nanocomposites consist of a large amount of small spheres with average diameters up to hundreds of nanometers, and every small sphere is composed of numerous primary nanocrystallites with an average size of about 8 nm. Compared with the pristine SnO2, the presence of Pt nanoparticles has no influence on the growth behavior of the SnO2 microspheres. The gas sensors based SnO2 microspheres in a composite with Pt nanoparticles not only show a lower operating temperature and immensely enhanced responses, but also exhibit a faster response and recovery speeds and remarkable stability to methanol, especially the 5.0 mol% Pt–SnO2 nanocomposite. The gas sensor based on the 5.0 mol% Pt–SnO2 nanocomposite exhibits a response value of 190.88 to 100 ppm methanol at a low operating temperature of 80 °C, while the gas sensor based on pristine SnO2 only displayed a response value of 19.38 at an operating temperature of 200 °C. The reasonable explanation of the gas-sensing performance enhancement for the gas sensors based on Pt–SnO2 nanocomposites is attributed to the strong spillover effect of the Pt nanoparticles and the electronic interaction between Pt nanoparticles and SnO2 microspheres, both of which promoted the low temperature gas-sensing performance.

Butane detection: W-doped TiO2 nanoparticles for a butane gas sensor with high sensitivity and fast response/recovery

This article describes a new option for butane detection: W-doped TiO2 nanoparticles with high sensitivity and fast response/recovery toward butane, which were obtained from a simple, non-aqueous sol–gel route. The structure, morphology, surface chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) and N2-sorption isotherm, respectively. The obtained products are anatase-type TiO2 with a small grain size (7.5 ± 1.4 nm) and a high specific surface area (181.15 m2 g−1). Tungsten element presents in the +6 oxidation state. The resistance–temperature measurements indicate that tungsten dopant leads to the decrease in resistance. The as-prepared pure and W-doped TiO2 nanoparticles were used to fabricate gas sensor devices. Gas response toward 3000 ppm butane is increased from 6 to 17.8 through the doping of 5% tungsten. Meanwhile, the response and recovery time toward 3000 ppm butane are as fast as 2 and 12 s, respectively. Moreover, the sensor also possesses low detection limit, good linear dependence, good repeatability and long-term stability, indicating the potential of using W-doped TiO2 nanoparticles for butane gas detection. In addition, a possible mechanism for the enhanced sensitivity of W-doped TiO2 nanoparticles toward butane is also offered.

Synthesis and characterisation of highly ordered mesoporous Fe2O3–SiO2 composite and its removal properties of azo dyes from aqueous solution

Abstract Highly ordered mesoporous material MCM-41 was synthesised from tetraethylorthosilicate as an Si source and cetyltrimethylammonium bromide as a template. Fe2O3 with 100 wt-% was introduced into the highly ordered mesoporous MCM-41 by chemical precipitation method to prepare the highly ordered mesoporous Fe2O3–SiO2 composite. The samples were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectrophotometry, and nitrogen adsorption–desorption measurement respectively. The results indicate that the synthesised Fe2O3–SiO2 composite has a highly ordered mesoporous structure with a specific surface area of 593 m2 g−1 and a pore volume of 0·322 cm3 g−1. The performance of Fe2O3–SiO2 composite as a remover was further demonstrated in the removal of methyl orange (MO), Congo red, methylene blue (MB), rhodaming B (RB) under visible light irradiation respectively. A good ability to remove MB, RB and MO can be obtained. In especially, the Fe2O3–SiO2 composite shows an excellent removal performance for MB under the room temperature in short time, making them to be promising candidates for wastewater treatment.

Facile synthesis of CuO micro-sheets over Cu foil in oxalic acid solution and their sensing properties towards n-butanol

Here, CuO micro-sheets were successfully synthesized from Cu foil using the annealing procedure. Cupric oxalate (CuC2O4·xH2O) micro-sheets were firstly peeled off by immersing Cu foil in oxalic acid solution at room temperature, and then they were converted into CuO with preserved configuration after thermal treatment at 350 °C. Various techniques were employed for the characterization of the structure and morphology of as-prepared products. Results revealed that the samples were composed of a large amount of porous CuO micro-sheets, which were constructed by plenty of nano-sized primary particles. A gas sensor was fabricated using as-prepared CuO micro-sheets and was systematically investigated for its ability to detect n-butanol. Due to the porous structure of CuO micro-sheets, the sensor based on CuO micro-sheets manifests a remarkably improved sensing performance, including high response, good selectivity, excellent reproducibility and stability, and limit of detection as low as 10 ppm at 160 °C, suggesting its greatly promising applications in gas sensing.