Latest ArticlesIn 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 at 225 ℃. 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.
Acetone is an important industrial raw material as well as biomarker in medical diagnosis. The detection of acetone has great significance for safety and health. However, high selectivity and low concentration (ppb level) detection remain challenges for semiconductor gas sensor. Herein, we present a novel sensitive material with bimetallic PtCu nanocrystal modified on WO3·H2O hollow spheres (HS), which shows high sensitivity, excellent selectivity, fast response/recovery speed and low limit of detection (LOD) to acetone detection. Noteworthy, the response (Ra/Rg) of WO3·H2O HS sensor increased by 9.5 times after modification with 0.02% bimetallic PtCu nanocrystals. The response of PtCu/WO3·H2O HS to 50 ppm acetone is as high as 204.9 with short response/recovery times (3.4 s/7.5 s). Finally, the gassensitivity mechanism was discussed based on gas sensitivity test results. This research will offer a new route for high efficient acetone detection.
To develop a novel food preservation technology for efficiently enhance bactericidal activity in a long term, hollow mesoporous silica spheres (HMSS) with regular nanostructures were applied to encapsulate natural organic antimicrobial agents. The chemical structures, morphologies and thermal stabilities of linalool, HMSS and linalool-functionalized hollow mesoporous silica spheres (L-HMSS) nanoparticles were evaluated by polarimeter, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), fourier transform infrared (FT-IR), thermal gravimetric analyzer (TGA), nitrogen adsorption-desorption, zeta potential and small angle X-ray diffraction (SXRD). The results show that the linalool was successfully introduced into the cavities of HMSS, and the inorganic host exhibited a high loading capacity of about 1500 mg/g. In addition, after 48 h of incubation, the minimum bactericidal concentrations (MBC) of L-HMSS against Escherichia coli (E. coli), Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes) were decreased to be 4 (< 5) mg/mL and 8 (< 10) mg/mL, respectively. These results revealed linaloolfunctionalized hollow mesoporous spheres could efficiently improve the bactericidal activities of the organic component. Furthermore, SEM images clearly showed that L-HMSS indeed had an extremely inhibitory effect against gram-negative (E. coli) and gram-positive (S. aureus) by breaking the structure of the cell membrane. This research is of great significance in the application of linalool in nano-delivery system as well as food industry.
Graphene quantum dots (GQDs) have both the properties of graphene and semiconductor quantum dots, and exhibit stronger quantum confinement effect and boundary effect than graphene. In addition, the band gap of GQDs will transform to non-zero from 0 eV of graphene by surface functionalization, which can be dispersed in common solvents and compounded with solid materials. In this work, the SnO2 nanosheets were prepared by hydrothermal method. As the sensitizer, nitrogen-doped graphene quantum dots (N-GQDs) were prepared and composited with SnO2 nanosheets. Sensing performance of pristine SnO2 and N-GQDs/SnO2 were investigated with HCHO as the target gas. The response (Ra/Rg) of 0.1% N-GQDs/SnO2 was 256 for 100 ppm HCHO at 60 ℃, which was about 2.2 times higher than pristine SnO2 nanosheet. In addition, the material also had excellent selectivity and low operation temperature. The high sensitivity of N-GQDs/SnO2 was attributed to the increase of active sites on materials surface and the electrical regulation of N-GQDs. This research is helpful to develop new HCHO gas sensor and expand the application field of GQDs.
Organic amines are important solvent and raw material in laboratory and industry, as well as releasing from cigarette smoke. It is significant to detect low-concentration amines for environment and public health. Here we reported that as-synthesized zinc oxide is an effective electrode material of electrochemical sensor for the detection of amines. The characterization results reveal that the ZnO morphologies experienced a change from hexagonal bowl-like microparticles, cones, prisms to nanoparticles by adjusting the reaction time, temperature, solvents and additives. Interestingly, ZnO material possessing hexagonal shapes and different sizes exhibits distinct electrochemical response in various amines solution, suggesting that there is a better dependent relationship between different morphological ZnO and amines detection. Particularly, regular hexagonal ZnO nanotablets exhibit a detectable electrochemical response and selectivity to ammonia, implying it can be serve as electrode material for highly effective detection of organic amines.
In the work, rGO nanosheet is synthesized using the typical Hummer's method, then Cu12Sb4S13 quantum dots@rGO composites are prepared by solvent thermal method, and Cu12Sb4S13 quantum dots with the average size of 5 nm are densely distributed on the surface of rGO sheet. NH3 gas response of Cu12Sb4S13 quantum dots@rGO nanosheet composites at room temperature of 25 ℃ is enhanced compared with the pure Cu12Sb4S13 quantum dots and rGO nanosheet, and the composites possess an excellent stability during the humidity range of 45%-80% with a low detection limit of 1 ppm, which is related with the intrinsic hydrophobicity characteristic of Cu12Sb4S13 quantum dots. It also proves that Cu12Sb4S13 quantum dots@rGO nanosheet composites have a quite high selectivity towards ammonia compared with ethanol, methanol, acetone, toluene, hydrogen sulfide and nitrogen dioxide at room temperature. The gas sensing mechanism of the composites is discussed primarily.
Ag- and Pt-doped WO3·0.33H2O nanorods with high response and selectivity to NH3 were synthesized from a tungsten-containing mineral of scheelite concentrate by a simple combined process, namely by a high pressure leaching method to obtain tungstate ions-containing leaching solution and followed by a hydrothermal method to prepare corresponding nanorods. The microstructure and NH3 sensing performance of the final products were investigated systematically. The microstructure characterization showed that the as-prepared WO3·0.33H2O nanorods had a hexagonal crystal structure, and Ag and Pt nanoparticles were uniformly distributed in the WO3·0.33H2O nanorods. Gas sensing measurements indicated that Ag and Pt nanoparticles not only could obviously enhance NH3 sensing properties in terms of response, selectivity as well as response/recovery time, but also could reduce the optimal operating temperature at which the highest response was achieved. The highest responses of 22.4 and 47.6 for Ag- and Pt-doped WO3·0.33H2O nanorods to 1000 ppm NH3 were obtained at 225 and 175 ℃, respectively, which were about four and eight folds higher than that of pure one at 250 ℃. The superior NH3 sensing properties are mainly ascribed to the catalytic activities of noble metals and the different work functions between noble metals and WO3·0.33H2O.
Due to the "trade-off" effect between the high water adsorption and low stability under high Relative Humidity of polymer matrix, fabrication of resistive-type polymer-based humidity sensors with a wide impedance response and excellent stability in high relative humidity remains a great challenge. Aim at solving that, a novel polymeric humidity sensing matrix, specifically a tadpole-shaped, polyhedral oligomeric silsesquioxane (POSS) containing block copolymers (BCPs) of POSS-poly(methyl methacrylate)-polystyrene (POSS-PMMA-SPS) were proposed. This novel BCP was synthesized using atom transfer radical polymerization (ATRP) employing a two-step approach, and following post sulfonation, a series of sulfonated BCPs (POSS-PMMA-SPS) with different sulfonation degree was obtained. The subject humidity sensors were produced using different sulfonated BCPs employing a dip-coating technique, and three wide-impedance response humidity sensors were produced. Each of these sensors exhibited an excellent humidity-sensing response of more than 104 within the humidity range from 11% to 95% RH. In particular, the humidity sensor S-6 that had a proper degree of sulfonation presented a relatively fast response (t90% of 11 s and 80 s in both the water adsorption and desorption processes), and superior repeatability for more than 30 days.
Noble metal is usually used to improve the gas sensing performance of metal oxide semiconductor (MOS) due to its better catalytic properties. In this work, we reported a synthesis of Pd/ZnO nanocomposite by an in situ reduction with ascorbic acid (AA). It was found that Pd/ZnO sensor has excellent selectivity to CO and the response of the Pd/ZnO sensor towards 100 ppm CO was as high as 15 (Ra/Rg), obviously higher than that of the pristine ZnO sensor (1.4) when the working temperature is 220 ℃. Moreover, the pure ZnO sensor almost has no selectivity to CO, but the Pd/ZnO sensor has excellent selectivity to CO, which may be ascribed to the electronic sensitization of Pd. Our present results demonstrate that the Pd can significantly improve the gas-sensing performance of metal oxide semiconductor and the obtained sensor has great potential in monitoring coal mine gas.
Nonaqueous Li-O2 batteries attract attention for their theoretical specific energy density. However, due to the difficulty of decomposition of Li2O2, Li-O2 batteries have high charge overpotential and poor cycling life. So all kinds of catalysts have been studied on the cathode. Compared to heterogeneous solid catalysts, soluble catalysts achieve faster and more effective transport of electrons by reversible redox pairs. Here, we first report ruthenocene (Ruc) as a mobile redox mediator in a Li-O2 battery. 0.01 mol/L Ruc in the electrolyte effectively reduces the charging voltage by 610 mV. Additionally, Ruc greatly increases the cycling life by four-fold (up to 83 cycles) with a simple ketjen black (KB) cathode. The results of SEM, XPS and XRD confirm that less discharge product residue accumulated after recharge. To verify the reaction mechanisms of the mediator, free energy profiles of the possible reaction pathways based on DFT are provided.
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