A copper‐catalyzed asymmetric radical oxytrifluoromethylation of alkenyl oxime and Togni's reagent has been successfully developed, thereby providing straightforward access to CF3‐containing ...isoxazolines bearing α‐tertiary stereocenters with excellent yield and enantioselectivity. The key to success is the rational design of cinchona‐alkaloid‐based sulfonamides as neutral/anionic hybrid ligands to effectively control the stereochemistry in copper‐catalyzed reactions involving free alkyl radical species. The utility of this method is illustrated by efficient transformation of the products into useful chiral CF3‐containing 1,3‐aminoalcohols.
Powerful hybrid ligand: Cinchona‐alkaloid‐based sulfonamides were designed as effective hybrid ligands for copper, which enabled catalytic asymmetric radical oxytrifluoromethylation of alkenyl oximes to give CF3‐containing isoxazolines bearing α‐tertiary stereocenters with excellent yield and enantioselectivity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Pure and Au-loaded SnO2 are synthesized by the method of sol-gel. XRD, SEM, XPS and electrochemical workstation are used to characterize the crystal structure, surface morphology, chemical ...composition and electrochemical property of the material, respectively. The effect of operating temperature and Au loading on n value is studied. It is shown that the response time of Au-loaded SnO2 sensor to 2000 ppm H2 is 43 s at 200 °C, which is much shorter than that of pure SnO2 sensor. It is found that the Au-loaded SnO2 sensor can detect H2 down to 1 ppm. Meanwhile, the Au-loaded SnO2 selectivity to H2 against CO is given. In conclusion, the Au-loaded SnO2 sensor is a good candidate for practical H2 sensors.
•The influence factor of n value in Equation (R=Ra/Rg=1+kCn) is presented.•The effect of Au loading on sensing properties is presented and explained.•Au-loaded SnO2 sensor can detect H2 down to 1 ppm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
First-principles calculations were used to explore the effect of various Y-doping levels on the electrical conductivity of SrTiO
3
. Herein, we prepared ((Y
0.07
Sr
0.93
Ti
0.6
Fe
0.4−
x
O
3−
δ
)/
x
.../3Co
3
O
4
(
x
= 0.1, 0.2, 0.3)) composites using a solid state reaction method. The properties of these sensing materials and the fabricated sensors including crystal phase composition, microstructures, oxygen ionic conductivity, total conductivity and sensor performance were investigated in detail. XRD demonstrates the formation of a highly cubic perovskite structure. The introduction of Co
3
O
4
promotes remarkably the electronic conductivity of the Y
0.07
Sr
0.93
Ti
0.6
Fe
0.4−
x
O
3−
δ
/
x
/3Co
3
O
4
composites due to the formation of n-type CoO and p-type Co
2
O
3
. A limiting current oxygen sensor based on (Y
0.07
Sr
0.93
Ti
0.6
Fe
0.4−
x
O
3−
δ
)/
x
/3Co
3
O
4
as a dense diffusion barrier shows excellent sensing performance. The recovery time is less than the response time, indicating that Co
2
O
3
promotes the gas desorption reaction which results in a shorter recovery time. The obtained results demonstrate a direct relationship between limiting current (
I
L
) and oxygen content.
First-principles calculations were used to explore the effect of various Y-doping levels on the electrical conductivity of SrTiO
3
.
Heterojunction fabrication is an effective way to improve the performance of gas sensors. In this work, NiO-modified ZnO nanoparticles and self-assembled nanosheets were prepared by a simple one-pot ...hydrothermal method. The morphological and structural characterizations demonstrated that the addition of NiO increased the surface area and provided more adsorption sites for the reaction. The results of gas sensing tests showed that the response of 1 % NiO-loaded ZnO to n-butanol reached 220 at 200 ℃. In addition, the sensor exhibited better selectivity (4.5 times that of n-butanol for other target gases), repeatability, and long-term (25 days) stability. The gas sensing performance is mainly enhanced by the formation of heterojunctions; the corresponding mechanism is also described.
●NiO-modified ZnO nanosheets were synthesized by a sample hydrothermal method.●The increased specific surface area provides more reaction sites.●1 % NiO-modified ZnO nanosheets showed great sensor performance to n-Butanol.●The enhanced sensing properties can be attributed to the heterojunctions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Undecorated and Pt-decorated SnO2 nanoparticles (NPs) were prepared using sol-gel and hydrothermal methods. The tin dioxide NPs, as sensing materials, were screen printed on alumina substrates with ...Pt test electrode to fabricate the gas sensors. The characteristics of these gas sensors in terms of composition, morphology, and sensing property were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and electrochemical workstation, respectively. The results elucidated that the response time of Pt-decorated SnO2 sensor to 100 ppm H2 is 29 s at 350 °C, which is almost half of that of pure SnO2 gas sensor. Meanwhile, the effect of operating temperature and Pt decorating on the sensing properties and the ‘n’ value is studied. Comparing with many fabricated H2 gas sensors, our as-prepared sensor exhibits not only a high response time but also detects H2 gas down to 0.08 ppm. To the author's best knowledge, the detection limit of 0.08 ppm is the best reported detection limit for the gas sensors based on tin oxide NPs so far. Moreover, there is a significant enhancement in the selectivity of Pt-decorated SnO2 sensor to the H2 gas against other investigated gases such as carbon monoxide (CO), methane (CH4), nitrogen dioxide (NO2), sulfur dioxide (SO2). Overall, the obtained results clearly demonstrate that the Pt-decorated SnO2 is an excellent sensing material for the fabrication of gas sensors and the detection of trace concentration of H2 down to 0.08 ppm. Furthermore, the results of statistical and fractal analysis on 2D microstructures of FESEM images showed a coefficient correlation of about 0.991 for all the samples.
•Pt-SnO2 was synthesized using sol-gel and hydrothermal techniques.•The influence of ‘n’ value on the sensing properties of the fabricated gas sensors is discussed in details.•Pt-SnO2 gas sensors demonstrated excellent sensing properties and can detect H2 down to 0.08 ppm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Saliency detection for images has been studied for many years, for which a lot of methods have been designed. In saliency detection, background priors, which are often regarded as pseudo-background, ...are effective clues to find salient objects in images. Although image boundary is commonly used as background priors, it does not work well for images of complex scenes and videos. In this paper, we explore how to identify the background priors for a video and propose a saliency-based method to detect the visual objects by using the background priors. For a video, we integrate multiple pairs of scale-invariant feature transform flows from long-range frames, and a bidirectional consistency propagation is conducted to obtain the accurate and sufficient temporal background priors, which are combined with spatial background priors to generate spatiotemporal background priors. Next, a novel dual-graph-based structure using spatiotemporal background priors is put forward in the computation of saliency maps, fully taking advantage of appearance and motion information in videos. Experimental results on different challenging data sets show that the proposed method robustly and accurately detects the video objects in both simple and complex scenes and achieves better performance compared with other the state-of-the-art video saliency models.
Due to the excellent properties, multi-dimensional p-n heterojunction materials are widely used in the field of gas sensing. In this work, In2O3-modified Mn2O3 nanorod was prepared by a hydrothermal ...method. The composites had excellent detection performance for triethylamine (TEA). The composites had rich 0D-1D multi-dimensional nanostructures. The sensing properties of composites with different In/Mn ratios were investigated by adjusting the proportion of Mn. The test results showed composite material had high response, excellent selectivity, ultra-high resistance stability and repeatability during repeated testing. High specific surface area, abundant active sites by the formation of multi-dimensional heterojunction, and Mn3+/Mn4+ fast redox cycling of compound material made the excellent sensing performance. This work provided a reference for designing multi-dimensional heterostructures and high performance gas sensors.
•In2O3/Mn2O3 materials were synthesized by a two-step hydrothermal method for the first time.•Highest sensitive and selective detection of triethylamine at 180 ℃ among the previous composite materials (p-n junction).•One-dimensional nanorod structure with high specific surface area.•The gas sensing performance was enhanced by constructing heterojunctions and fast redox reactions of Mn3+/Mn4+.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We demonstrated a novel long-period fiber grating (LPFG) written in a tri-hole fiber (THF). The LPFG was fabricated by periodically collapsed micro holes utilizing CO 2 laser irradiation integrated ...with pressure-assisted technology. The mode coupling between the fundamental mode and higher mode of the proposed grating is mainly caused by geometric deformation along the fiber axis. Compared with conventional LPFGs, such a grating has strong refractive index modulation due to periodic collapsed structure. We have established an approximate hypothesis to simulate the transmission spectrum of the grating. The measured spectrum is basically consistent with the simulated transmission spectrum at the resonant peak position. We investigated the sensing characteristics of the proposed LPFG, including axial strain, bending, torsion, and temperature. The sensitivity of bending, temperature and torsion are −9.56 nm/m −1 , 162.8 pm/(rad/m) in clockwise and −346.9 pm/(rad/m) in counterclockwise and 86.8 pm/°C, respectively. The experimental data shows that the fabricated LPFG has potential applications in the field of external high-sensitivity strain sensing with a sensitivity of −26 pm/μϵ.
Stable lithiophilic sites in 3D current collectors are the key to guiding the uniform Li deposition and thus suppressing the Li dendrite growth, but such sites created by the conventional surface ...decoration method are easy to be consumed along with cycling. In this work, carbon fiber (CF)‐based 3D porous networks with built‐in lithiophilic sites that are stable upon cycling are demonstrated. Such heterostructured architecture is constructed by the introduction of zeolitic imidazolate framework‐8‐based nanoparticles during the formation of the 3D fibrous carbonaceous network and the following annealing. The introduced Zn species are found to be re‐distributed along the entire individual CF in the 3D network, and function as lithiophilic sites that favor the homogenous lithium nucleation and growth. The 3D network also presents a multi‐scale porous structure that improves the space utilization of the host. The corresponding symmetric cells adopting such 3D anode demonstrate excellent cycling performance, especially at a high rate (300 cycles at 10 mA cm−2 with a capacity of 5 mA h cm−2). A full cell with LiFePO4 cathode shows a capacity retention of 98% after cycling at 1C for 300 cycles. This method provides an effective design strategy for 3D hosting electrodes in dendrite‐free alkali metal anode applications.
A 3D host of Zn, O, and N co‐doped carbon fibers fabricated by a facile method of electrospinning followed by carbonization is reported. The design of the “built‐in” lithiophilic sites provides long lasting sites favoring lithiation upon the repeated charging/discharging process, restricting the Li dendrite grow and improving the cycle performance of the electrode.
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