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Abstract: Biomorphic porous ZnO nanostructures were successfully synthesized via an aqueous sol–gel soaking process using pieces of apple flesh and skin as templates and employed for glucose direct electrochemical biosensor. The structure and morphology of ZnO nanostructures were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). By modifying glassy carbon electrode with the biomorphic ZnO nanostructures and Nafion, two glucose biosensors were constructed and their direct electrochemistry of glucose oxidase (GOD) was successfully investigated by cyclic voltammetry (CV). The biomorphic porous ZnO nanostructures using apple skin template (S-ZnO) were more effective in facilitating the electron transfer of immobilized GOD than that of using flesh apple template (F-ZnO). This may be a result of the unique morphology and smaller average crystallite size of the S-ZnO nanostructure. GOD immobilized on Nafion-porous S-ZnO nanostructure composite display direct, reversible, and surface-controlled redox reaction with a detection limit of 10μM, a response time of 7s, high sensitivity of 23.4μA/mMcm2 and a fast heterogeneous electron transfer rate with a rate constant (k s) of 3.9s−1. It was found that S-ZnO significantly has improved the direct electron transfer between GOD and glassy carbon electrode with good stability and reproducibility. [Copyright &y& Elsevier]

Abstract: Nanostructured SnO2–ZnO as selective ethanol gas sensor materials with controlled grain size and morphology were successfully synthesized by a precipitation method. The structure, morphology, and gas sensing performance of calcined SnO2–ZnO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area analyzer (using BET method), and a continuous-flow gas sensing measurement system, respectively. The sensors responses depend on the composition, size and morphology of the samples. The sensor with 0.05:1.0 Zn2+:Sn2+ molar ratio was highly sensitive and selective for the detection of ethanol. The gas-sensing mechanism of the nanostructures was discussed. The different reductive–oxidative and acid–base heterostructures of SnO2 and ZnO were suggested as the main reasons for the selective detection of ethanol. [Copyright &y& Elsevier]

Abstract: Different structures and morphologies of SnO2 containing various amounts of ZnO were synthesized via a hydrothermal method (without any template), characterized by scanning electron microscopy and powder X-ray diffraction, and used for photocatalytic degradation of Congo red. The results revealed that using different ratios of Zn+2/Sn+2 affects the phase and morphology of the Zn2x Sn1−x O2 compounds. This type of tailoring the morphology of SnO2 nanoparticles, ZnO doped SnO2 porous structure, ZnSnO3 flower-like, and Zn2SnO4 octahedrals was possible, by varying the Zn+2/Sn+2 ratio of 0, 1/10, 1/5 and 1/1, respectively. The formation mechanism of these products was proposed. Zn2SnO4 with octahedral morphology exhibited a significant enhancement of photocatalytic activity toward degrading Congo red, as compared to other samples. This could be attributed to enhanced oxygen vacancies and crystallite defects formed by substitution of Zn+2 in the lattice of SnO2, revealed in photoluminescence measurements. [ABSTRACT FROM AUTHOR]

Abstract: SnO2 nanoparticles and nanorods are synthesized via a facile template-free hydrothermal method, using SnCl2·2H2O and deionized water without any alkaline solution. The influences of the hydrothermal reaction time in the range of 5–48h and temperatures of 130 and 160°C and also calcination temperature on the size and morphological and gas-sensing properties of SnO2 particles were investigated. The SnO2 samples were characterized by X-ray diffraction analysis (XRD), surface area analyzer (using BET method) and scanning electron microscopy. The response of the SnO2 nanostructures sensors to ethanol and various concentrations of CO were measured in an automated flow setup at different temperatures. As the hydrothermal synthesis temperature and time increases, the crystallite sizes enlarge nonlinearly and morphology of SnO2 nanostructures changes from nanoparticles to nanorods. The most SnO2 samples are thermally stable at calcination temperature of 350°C. SnO2 nanoparticles as small as 3.1nm with the highest specific surface area of 254m2/g are hydrothermally synthesized at 130°C in 5h. This sample shows the highest response of 30 and 2565 to 1000ppm CO and ethanol at 200 and 250°C, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured SnO2 with different morphologies of flower-like, sheet-like and granular have been successfully prepared via a solid-state reaction in the presence of NaBr, NaCl, and NaF, respectively. The added salts not only prevent a drastic increase in the size of the tin species but also provide suitable conditions for the oriented growth of primary nanoparticles. The formation mechanisms of these materials by solid-state reaction at ambient temperature are proposed. The gas sensitivity experiments have demonstrated that the as-synthesized SnO2 especially, flower-like morphology, exhibit high sensitivity to CO, which may offer potential applications in gas sensors. [Copyright &y& Elsevier]

LaFe x Co (1-x) O 3 nanoparticles were prepared via a coprecipitation method and the effects of Pd dopant along with the type of alkaline agent on the powder particle characteristics have been studied. The catalytic activities of the synthesized perovskites for the CO and CH 4 oxidation were also studied. X-ray diffraction (XRD) patterns confirmed the formation of a single-phase orthorhombic perovskite structure in the synthesized samples. Field emission scanning electron microscopy (FESEM) and BET analyses showed that using ammonia as the precipitant yields finer particles with higher specific surface areas for both un-doped and Pd-doped samples. FESEM micrographs also indicated that incorporation of Pd decreases the mean particle size of the perovskite powders. Raman spectroscopy results demonstrated that palladium occupies the B octahedral sites of the perovskite lattice. H 2 temperature programmed reduction (H 2 -TPR) and O 2 temperature programmed desorption (O 2 -TPD) results revealed that Pd-doping not only improves the reducibility of the iron and cobalt cations, but also boosts the number of mobile lattice oxygen species. Transmission electron microscopy (TEM) analysis confirmed formation of metallic Pd clusters having the size of 2–7 nm on the surface of Pd-doped perovskite under the reductive atmosphere. LaFe 0 . 57 Co 0 . 38 Pd 0 . 05 O 3 sample co-precipitated by NH 4 OH enjoys the highest catalytic activity for both CO and CH 4 oxidation. [ABSTRACT FROM AUTHOR]

SnO 2 decorated SiO 2 chemical sensors with different Sn/Si ratios were synthesized by micro-emulsion followed by ultrasonic-assisted deposition-precipitation method and used for highly sensitive and selective detection of ethanol and acetone. XRD, EDS, SEM, and TEM were used to characterize the samples. The results confirm deposition of small crystalline tin oxide particles on the surface of silica particles. Using these formed materials for detection of ethanol and acetone resulted in significant enhancement of the sensitivity and reducing temperature of maximum response in comparison to the pure SnO 2 . The selectivity of the sample with the highest sensitivity to ethanol and acetone, i.e. 80 wt% SnO 2 /SiO 2 , was examined by measuring its sensitivity to some interfering gases including carbon monoxide, methane, toluene, Trichloroethylene (TCE) and propane; the results showed very high selectivity of the sensor to ethanol and acetone, especially at low temperatures. The sensor responses to traces of acetone in the air with the concentration ranging from 0.5 to 5 ppm at different temperatures of 70, 170 and 270, and 370 °C were measured to evaluate the capability of the sensor for detection of acetone in the breath of human, which is helpful in the diabetes diagnosis. The sensor could effectively show high enough sensitivity even to these very low concentrations of acetone which reveals its high potential for being used in acetone detection devices. Finally, the effect of humidity on the sensitivity of sensor to acetone was investigated. Increasing the humidity of background air, caused the sensor response to decrease and the operating temperature of maximum response of the sensor to increase. [ABSTRACT FROM AUTHOR]

NO 2 gas sensing performance of bare and Pd-loaded SnO 2 thick film sensors were measured under UV-light irradiation, using a UV-LED of 365 nm wavelength and light intensities ranging from 0 to 137 mW cm −2 at room temperature (30 °C). Template free conventional and microwave-assisted hydrothermal methods were applied to synthesize SnO 2 powder with different specific surface areas and morphologies (rod-shape and nanoparticle). Two different Pd-loaded SnO 2 (0.03 and 0.1 wt%) powders were also prepared by a simple wet-impregnation method. XRD, FE-SEM/SEM, XPS, BET surface area and BJH pore size distribution measured with N 2 adsorption isotherms were utilized to characterize structural and morphological characteristics of all the samples. The results clearly confirmed that the presence of a low amount of Pd could effectively enhance the response value to 5 ppm NO 2 gas and shorten the recovery time under the UV-light irradiation so that the sensor loaded with 0.1 wt% Pd (0.1Pd_MH1_400 sensor) showed the largest improvement in response value (almost 11 times) and recovery time (around 27 s) compared with the bare SnO 2 sensor (MH1_400) at an UV-light intensity of 79 mW cm −2 . This enhancement is most likely due to the role of Pd in facilitating the sensing reactions via producing additional NO 2 adsorption sites on the SnO 2 surface. Moreover, in the present study, the SnO 2 sensor which was fabricated from as-synthesized, i.e. uncalcined, powder (MH1) showed the highest response (over 3000) compared with other sensors under an UV-light intensity of 7 mW cm −2 with a recovery time of about 48 s. The drastic decrease in the resistance in air of this sensor under the UV-light irradiation may be a possible reason for the highest response value. It was also revealed that high NO 2 response could be achieved only at the optimum conditions of both the number of the NO 2 adsorption sites (optimum specific surface area) and the electron density in the bulk under the UV-light irradiation. [ABSTRACT FROM AUTHOR]

Multiwall carbon nanotubes (MWCNTs)/SnO 2 nanocomposites containing 0.03–1.0 wt% MWCNTs were synthesized and used for the fabrication of gas sensors for ethanol, methane, CO and NO detection at low temperatures. Acid functionalized MWCNTs were dispersed in SnO 2 using ultrasonic-assisted deposition–precipitation method. The nanocomposites were characterized by BET surface area measurement, FE-SEM, and XRD. The sensors response to 100 ppm ethanol, CO and NO and 1% CH 4 were measured at a temperature range of 150–350 °C. The addition of carbon nanotubes causes up to 4.7 times decrease in SnO 2 nanoparticles sizes. Our results indicate that 0.05 wt% is the optimum amount of carbon nanotubes, which remarkably increases the response of the SnO 2 -based sensors to all the gases. The most considerable response of 0.05 wt% MWCNTs/SnO 2 nanocomposite sensor is related to CH 4 detection, which is dramatically enhanced by a factor of 45 at 200 °C, compared to SnO 2 . Moreover, this sensor operating temperature for ethanol, CO and methane decrease by about 50–100 °C, upon addition of carbon nanotubes. [ABSTRACT FROM AUTHOR]

The electro-catalytic behavior of Pt-CoO x /MWCNTs in methanol electro-oxidation reaction (MOR) is investigated and compared to that of Pt/MWCNTs. The electro-catalysts were synthesized by an impregnation method using NaBH 4 as the reducing agent. The morphological and physical characteristics of samples are examined by XRD, TEM, ICP and EDS techniques. In the presence of CoO x , Pt nanoparticles were highly distributed on the support with an average particle size of 2 nm, an obvious decrease from 5.1 nm for Pt/MWCNTs. Cyclic voltammetry, CO-stripping, Chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements are used to study the electrochemical behavior of the electro-catalysts. The results revealed a considerable enhancement in the oxidation kinetics of CO ads on Pt active sites by the participation of CoO x . Compared to Pt/MWCNTs, Pt-CoO x /MWCNTs sample has a larger electrochemical active surface area (ECSA) and higher electro-catalytic activity and stability toward methanol electro-oxidation. According to the results of cyclic voltammetry, the forward anodic peak current density enhances more than 89% at the optimum atomic ratio of Pt:Co = 2:1. Furthermore, inclusion of cobalt oxide species causes the onset potential of methanol electro-oxidation reaction to shift 84 mV to negative values compared to that on Pt/MWCNTs. Based on EIS data, dehydrogenation of methanol is the rate-determining step of MOR on both Pt/MWCNTs and Pt-CoO x /MWCNTs, at small overpotentials. However, at higher overpotentials, the oxidation of adsorbed oxygen-containing groups controls the total rate of MOR process. [ABSTRACT FROM AUTHOR]

Ruthenium promoted cobalt catalysts supported on γ-Al2O3 were prepared by stepwise and co-impregnation methods. The effects of impregnation order on activity and selectivity of the Fischer-Tropsch synthesis (FTS) were investigated using fixed bed microreactor. The catalysts were characterized by TPR, XRD and TEM. The selected Ru loading was 0.15 wt.% while that of Co was 15.0 wt.% in all of the prepared samples by different order of impregnation. The catalyst prepared by co-impregnation method shifted both steps of cobalt oxide reduction temperatures to lower temperatures by about 100 °C. However, temperature shift was lower for the catalyst prepared by stepwise impregnation method. The highest CO conversion and C5+ selectivity and the lowest methane selectivity were obtained for the catalyst synthesized by co-impregnation method. Two other catalysts with 0.3 and 0.6 wt.% of Ru loadings on 15.0 wt.% Co were synthesized by co-impregnation and its effect on the FTS was investigated. The prepared catalysts showed an increase in CO conversion with the increase of Ru from 0 to 0.30 wt.%. However, further increase in Ru led to lower CO conversion for a Ru loading of 0.6 wt.%. The effects of temperature and H2/CO ratio for all catalysts were examined and their performance modeled by a Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expression. [ABSTRACT FROM AUTHOR]