Latest ArticlesMonodispersed ZnSnO3 microspheres are successfully prepared via a facile microwave-assisted method together with subsequently calcination treatment. Powder X-ray diffraction (PXRD) results indicate that the structure of the products shifted from crystalline to amorphous under high-temperature treatments. Field emission scanning electron microscope (FESEM) and the transmission electron microscope (TEM) observations demonstrate that the as-obtained products are composed of uniform microspheres with rough surfaces and the mean diameter is measured as ~700 nm. Moreover, the morphology of ZnSnO3 microspheres can be well controlled by adjusting the ratio of Zn2+ and Sn4+. The gas sensing properties of ZnSnO3 microspheres with different ratios of Zn2+/Sn4+ are investigated. Our results indicate that the ZnSnO3 microspheres exhibit good selectivity and high sensitivity towards ethanol at the optimum working temperature of 230 ℃. When the sensor is exposed 50 ppm ethanol, the value of response is 47 and the response/recovery times are 11 s and 12 s, respectively.
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.
It is known that exposed surface determines materialos performance. WO3 is widely used in gas sensing and its working surface is proposed to control its sensitivity. However, the working surface, or most exposed surface with detailed surface structure remain unclear. In this paper, DFT calculation confirmed that oxygen vacancy O-terminated surface is the most exposed hexagonal WO3 (001) surface, judging from competitive adsorption of CO and O2, working surface determination for CO sensing and comparison of oxygen vacancy formation energies on different h-WO3 (001) surfaces. It is found that DFT can be a useful alternate for exposed surface determination. Our results provide new perspectives and performance explanations for material research.
In this work, the two-dimensional MoS2 film was prepared by sulfuring the molybdenum atomic layer on SiO2/Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS2 film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 ℃/min, reaction temperature of 750 ℃, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS2 gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH3) and oxidizing gas (NO2) at room temperature. The sensitivity to 100 ppm of NO2 was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO2 sensors.
MoS2, acting as a promising gas sensing material, has shown huge potential in monitoring of toxic and harmful gases at room temperature. However, MoS2-based gas sensors still suffer from poor gas sensing performance such as poor sensitivity, long response time. Constructing the heterostructure is an effective approach to improve gas-sensing performance of MoS2. Herein, PbS@MoS2 composites synthesized by mechanical exfoliation combining with wet-chemical precipitation are used to investigate its performance in detecting NO2 at room temperature. The response value of PbS@MoS2 gas sensor against NO2 is significantly improved compared with the pure MoS2 gas sensor. At the same time, the modification with PbS also accelerates the response speed of MoS2, and the response time is almost reduced by two orders of magnitude, from hundreds of seconds to less than ten seconds. The enhanced response value and fast response time are mainly benefited from the modulation effect of NO2 to PbS@MoS2 heterostructure and the mechanically exfoliated MoS2 surface with few defects. This work can be expected to provide useful guidance for designing composite materials with excellent gas sensing properties.
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.
Dihydronicotinamide adenine dinucleotide (NADH) is an important enzyme in all living cells, which is found to be abnormally expressed in cancer cells. Since it is redox-active, an electrochemical detection method would be suitable for monitoring its concentration in biological fluids. Here we present a strategy for specific determination of NADH in real human serum by using RhIr@MoS2 nanohybrids based microsensor. To implement the protocol, RhIr nanocrysrals are in-situ grown onto MoS2 interlayers forming a nanohybrid structure (RhIr@MoS2). After being locally deposited on an electrochemical microsensor, it could be used for the analysis of NADH. The developed RhIr@MoS2 nanohybrids based microsensor possesses the ability for analyzing NADH at the applied potential of 0.07 V (much lower than most reported values). The detection limit is evaluated as low as 1 nmol/L even in bovine serum albumin (BSA) media. In addition, the sampling analysis of human serum from cancer patients and health controls shows that the microsensor displays good diagnostic sensitivity and specificity, illustrating that this developed detection technique is a relatively accurate method for measuring NADH in biological fluids. The proposed electrochemical microsensor assay also owns the benefits of convenience, disposable and easy processing, which make it a great possibility for future point-of-care cancer diagnosis.
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.
This work reports a superhydrophobic divinylbenzene polymer with hierarchical porous structure as sensing material to modify the quartz crystal microbalance (QCM) to detect benzene, toluene, ethylbenzene, and xylene (BTEX) vapor. Notably, sensing results toward toluene vapor in different relative humidities indicates that this superhydrophobic polymer has favorable toluene/water selective detection performance. Besides, the limit of detection toward toluene is lower than 1 ppm.
In order to improve the convenience and sensitivity of amphetamines drug testing and reduce the threat of drugs to humans, we have designed a QCM gas sensor to detect amine-containing drugs. The sensing material is designed based on the chemical nature of amine drugs. The sensing mechanism is derived from a reversible Schiff base interaction between the amino group of the drug and the carbonyl group of the novel calix[6]arene derivatives as well as the hydrogen bond interaction between amino group and hydroxyl. The new composite material was well characterized by different analytical techniques including 1H nuclear magnetic resonance (1H-NMR), fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), transmission electron microscope (TEM), Raman spectra, powder X-ray diffraction, etc. The sensing experiments were conducted by coating the composite onto quartz crystal microbalance (QCM) transducers. The experimental results indicated that the novel calixarene derivatives and their GO complexes based on the design have excellent selectivity, high sensitivity and repeatability to β-phenylethylamine.
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