Two-dimensional (2D) semiconductor nanomaterials hold great promises for future electronics and optics. In this paper, a 2D nanosheets of ultrathin GaSe has been prepared by using mechanical cleavage ...and solvent exfoliation method. Single- and few-layer GaSe nanosheets are exfoliated on an SiO2/Si substrate and characterized by atomic force microscopy and Raman spectroscopy. Ultrathin GaSe-based photodetector shows a fast response of 0.02 s, high responsivity of 2.8 AW–1 and high external quantum efficiency of 1367% at 254 nm, indicating that the two-dimensional nanostructure of GaSe is a new promising material for high performance photodetectors.
The first GaS nanosheet-based photodetectors are demonstrated on both mechanically rigid and flexible substrates. Highly crystalline, exfoliated GaS nanosheets are promising for optoelectronics due ...to strong absorption in the UV–visible wavelength region. Photocurrent measurements of GaS nanosheet photodetectors made on SiO2/Si substrates and flexible polyethylene terephthalate (PET) substrates exhibit a photoresponsivity at 254 nm up to 4.2 AW–1 and 19.2 AW–1, respectively, which exceeds that of graphene, MoS2, or other 2D material-based devices. Additionally, the linear dynamic range of the devices on SiO2/Si and PET substrates are 97.7 dB and 78.73 dB, respectively. Both surpass that of currently exploited InGaAs photodetectors (66 dB). Theoretical modeling of the electronic structures indicates that the reduction of the effective mass at the valence band maximum (VBM) with decreasing sheet thickness enhances the carrier mobility of the GaS nanosheets, contributing to the high photocurrents. Double-peak VBMs are theoretically predicted for ultrathin GaS nanosheets (thickness less than five monolayers), which is found to promote photon absorption. These theoretical and experimental results show that GaS nanosheets are promising materials for high-performance photodetectors on both conventional silicon and flexible substrates.
Mixed oxides of TiO₂-MgO obtained by the sol-gel method were used to convert waste cooking oil into biodiesel. Titanium improved the stability of the catalyst because of the defects induced by the ...substitution of Ti ions for Mg ions in the magnesia lattice. The best catalyst was determined to be MT-1-923, which is comprised of an Mg/Ti molar ratio of 1 and calcined at 923K, based on an assessment of the activity and stability of the catalyst. The main reaction parameters, including methanol/oil molar ratio, catalyst amount, and temperature, were investigated. The catalytic activity of MT-1-923 decreased slowly in the reuse process. After regeneration, the activity of MT-1-923 slightly increased compared with that of the fresh catalyst due to an increase in the specific surface area and average pore diameter. The mixed oxides catalyst, TiO₂-MgO, showed good potential in large-scale biodiesel production from waste cooking oil.
This study investigates the use of CaO-CeO2 mixed oxides as solid base catalysts for the transesterification of Pistacia chinensis oil with methanol to produce biodiesel. These CaO-CeO2 mixed-oxide ...catalysts were prepared by an incipient wetness impregnation method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The cerium improved the heterogeneous catalytic stability remarkably due to the defects induced by the substitution of Ca ions for Ce ions on the surface. The best catalyst was determined to be C0.15-973 (with a Ce/Ca molar ratio of 0.15 and having been calcined at 973 K), considering its catalytic and anti-leaching abilities. The effects of reaction parameters such as the methanol/oil molar ratio, the amount of catalyst amount and the reaction temperature were also investigated. For the C0.15-973 regenerated after five reuses, the biodiesel yield was 91%, which is slightly less than that of the fresh sample. The test results revealed that the CaO-CeO2 mixed oxides have good potential for use in the large-scale biodiesel production.
The preparation of a Li-doped MgO for biodiesel synthesis has been investigated by optimizing the catalyst composition and calcination temperatures. The results show that the formation of strong base ...sites is particularly promoted by the addition of Li, thus resulting in an increase of the biodiesel synthesis. The catalyst with the Li/Mg molar ratio of 0.08 and calcination temperature of 823
K exhibits the best performance. The biodiesel conversion decreases with further increasing Li/Mg molar ratio above 0.08, which is most likely attributed to the separated lithium hydroxide formed by excess Li ions and a concomitant decrease of BET values. In addition, the effects of methanol/oil molar ratio, reaction time, catalyst amount, and catalyst stability were also investigated for the optimized Li-doped MgO. The metal leaching from the Li-doped MgO catalysts was detected, indicating more studies are needed to stabilize the catalysts for its application in the large-scale biodiesel production facilities.
Zigzag micro-channel reactors have been fabricated and used for continuous alkali-catalyzed biodiesel synthesis. The influences of the main geometric parameters on the performance of the ...micro-channel reactors were experimentally studied. It has been found that the zigzag micro-channel reactor with smaller channel size and more turns produces smaller droplets which result in higher efficiency of biodiesel synthesis. Compared to conventional stirred reactors, the time for high methyl ester conversion can be shortened significantly with the methyl ester yield of 99.5% at the residence time of only 28
s by using the optimized zigzag micro-channel reactor, which also exhibits less energy consumption for the same amount of biodiesel during biodiesel synthesis. The results indicate that zigzag micro-channel reactors can be designed as compact and mini-fuel processing plant for distributive applications.
Two kinds of new conductive lubricating greases were synthesized using 1-octyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium tetrafluoroborate as base oil and the ...polytetrafluoroethylene as thickener. The conductivities of the new conductive lubricating greases are higher than the traditional conductive lubricating greases which contains conductive stuffing. In addition, the physical and tribological properties of the new lubricating greases were investigated in detail. The results show that the new lubricating grease show better friction reducing and anti-wear properties than the lubricating grease based on PAO10 at room temperature and 150 °C. The worn surfaces were observed and analyzed by scanning electron microscope and X-ray photoelectron spectroscope. Also, the possible friction mechanisms for the new lubricating greases are proposed.
Detection of proteins is powerfully assayed in the diagnosis of diseases. A strategy for the development of an ultrahigh sensitivity biosensor based on a network single-walled carbon nanotube (SWNT) ...field-effect transistor (FET) has been demonstrated. Metallic SWNTs (m-SWNTs) in the network nanotube FET were selectively removed or cut via a carefully controlled procedure of electrical break-down (BD), and left non-conducting m-SWNTs which magnified the Schottky barrier (SB) area. This nanotube FET exhibited ultrahigh sensitivity and fast response to biomolecules. The lowest detection limit of 0.5 pM was achieved by exploiting streptavidin (SA) or a biotin/SA pair as the research model, and BD-treated nanotube biosensors had a 2 × 10(4)-fold lower minimum detectable concentration than the device without BD treatment. The response time is in the range of 0.3-3 min.
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•A facile birch templated method for catalyst preparation was presented.•The birch templated catalysts had good basic properties.•Comparison of catalysts prepared by different methods ...was discussed.•Reaction parameters of transesterification process were optimized.
Ca/Zr mixed oxide catalysts were prepared using three different methods and were employed in the transesterification of rapeseed oil with methanol for biodiesel production. To elucidate their composition, morphology and basic properties, the resulting materials were characterized using: thermogravimetric analysis, N2-adsorption, X-ray diffraction, scanning electron microscopy, temperature programmed desorption of CO2 and X-ray photoelectron spectroscopy. A birch template method was found to improve the pore structure and dispersion of basic sites. The highest biodiesel yield reached 92.6% over CaO/ZrO2 catalyst prepared by template method with a Ca-to-Zr molar ratio of 0.3 under the optimal reaction conditions: catalyst mass fraction 8%, 72:1M ratio of methanol to rapeseed oil, reaction temperature 120°C and a reaction time of 6h.
