Showing papers by "Taiyuan University of Technology published in 2017"

Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction

Abstract: The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.

MoSe2‐Covered N,P‐Doped Carbon Nanosheets as a Long‐Life and High‐Rate Anode Material for Sodium‐Ion Batteries

Abstract: MoSe2 grown on N,P-co-doped carbon nanosheets is synthesized by a solvothermal reaction followed with a high-temperature calcination. This composite has an interlayer spacing of MoSe2 expanded to facilitate sodium-ion diffusion, MoSe2 immobilized on carbon nanosheets to improve charge-transfer kinetics, and N and P incorporated into carbon to enhance its interaction with active species upon cycling. These features greatly improve the electrochemical performance of this composite, as compared to all the controls. It presents a specific capacity of 378 mAh g−1 after 1000 cycles at 0.5 A g−1, corresponding to 87% of the capacity at the second cycle. Ex situ Raman spectra and high-resolution transmission electron microscopy images confirm that it is element Se, rather than MoSe2, formed after the charging process. The interaction of the active species with modified carbon is simulated using density functional theory to explain this excellent stability. The superior rate capability, where the capacity at 15 A g−1 equals ≈55% of that at 0.5 A g−1, could be associated with the significant contribution of pseudocapacitance. By pairing with homemade Na3V2(PO4)3/C, this composite also exhibits excellent performances in full cells.

Green synthesis of carbon dots from rose-heart radish and application for Fe3+ detection and cell imaging

Abstract: Herein, a simple, green, and low-cost way was developed in the synthesis of fluorescent carbon dots (CDs) with well-distributed size, using one-pot hydrothermal treatment of rose-heart radish. The as-prepared carbon dots exhibit exceptional advantages including high fluorescent quantum yield (13.6%), excellent biocompatibility, low-toxicity, and satisfactory chemical stability. More strikingly, as-synthesized N-CDs generate strong response to Fe 3+ ions and gives rise to the fluorescence quenching. This phenomenon was used to develop a fluorescent method for facile detection of Fe 3+ with a linear range from 0.02 to 40 μM and a detection limit of 0.13 μM (S/N = 3), and further extended to measure environmental water samples with satisfactory recoveries. Eventually, the low toxicity and strongly fluorescent carbon dots were applied for cell imaging and the quenched fluorescence by adding Fe 3+ , demonstrating their potential towards diverse applications.

Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Abstract: Selective separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties We report a microporous material [Zn(dps)2(SiF6)] (UTSA-300, dps = 4,4′-dipyridylsulfide) with two-dimensional channels of about 33 A, well-matched for the molecular sizes of C2H2 After activation, the network was transformed to its closed-pore phase, UTSA-300a, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF62– pillars Strong C–H···F and π–π stacking interactions are found in closed-pore UTSA-300a, resulting in shrinkage of the structure Interestingly, UTSA-300a takes up quite a large amounts of acetylene (764 cm3 g–1), while showing complete C2H4 and CO2 exclusion from C2H2 under ambient conditions Neutron powder diffraction and molecular modeling studies clea

Flexible-Robust Metal-Organic Framework for Efficient Removal of Propyne from Propylene.

Abstract: The removal of trace amounts of propyne from propylene is critical for the production of polymer-grade propylene We herein report the first example of metal–organic frameworks of flexible–robust nature for the efficient separation of propyne/propylene mixtures The strong binding affinity and suitable pore confinement for propyne account for its high uptake capacity and selectivity, as evidenced by neutron powder diffraction studies and density functional theory calculations The purity of the obtained propylene is over 999998%, as demonstrated by experimental breakthrough curves for a 1/99 propyne/propylene mixture

Highly Efficient Gas Sensor Using a Hollow SnO2 Microfiber for Triethylamine Detection.

Abstract: Triethylamine (TEA) gas sensors having excellent response and selectivity are in great demand to monitor the real environment. In this work, we have successfully prepared a hollow SnO2 microfiber by a unique sustainable biomass conversion strategy and shown that the microfiber can be used in a high-performance gas sensor. The sensor based on the hollow SnO2 microfiber shows a quick response/recovery toward triethylamine. The response of the hollow SnO2 microfiber is up to 49.5 when the concentration of TEA gas is 100 ppm. The limit of detection is as low as 2 ppm. Furthermore, the sensor has a relatively low optimal operation temperature of 270 °C, which is lower than those of many other reported sensors. The excellent sensing properties are largely attributed to the high sensitivity provided by SnO2 and the good permeability and conductivity of the one-dimensional hollow structure. Thus, the hollow SnO2 microfiber using sustainable biomass as a template is a significant strategy for a unique TEA gas sensor.

Molybdenum carbide as alternative catalyst for hydrogen production – A review

Abstract: Hydrogen energy has become an important research area worldwide for environmental-friendly and sustainable energy development. A large number of studies can be found in the literature regarding the development of novel functional catalysts for hydrogen production from various reactions such as hydrocarbon reforming, water gas shift reaction, and water decomposition reaction. Due to the unique surface and electronic properties of molybdenum carbide, it has been attracted more and more attentions as a potential catalyst. This article reviews the latest research progress on the molybdenum carbide catalyst for hydrogen production. Two main parts are included in this review: preparation of molybdenum carbide and application of it in hydrogen production technology. In the first part, various molybdenum carbide preparation methods and the strategies to modify the physicochemical properties of molybdenum carbide are described. It is concluded that solid-solid reaction method could provide high surface area and the synthesis process is relatively easy and safe. Furthermore, the addition of second metal could increase molybdenum carbide surface area and adjust catalyst surface electronic condition. In the second part, the applications of molybdenum carbide based catalysts for various reactions for hydrogen production are described. The catalytic activity, stability, and deactivation and reaction mechanism over molybdenum carbide catalyst are critically reviewed and discussed. It indicates that molybdenum carbide should be an alternative catalyst with high efficiency for hydrogen production.

Highly stable supercapacitors with MOF-derived Co9S8/carbon electrodes for high rate electrochemical energy storage

Abstract: Co9S8 has received intensive attention as an electrode material for electrical energy storage (EES) systems due to its unique structural features and rich electrochemical properties. However, the instability and inferior rate capability of the Co9S8 electrode material during the charge/discharge process has restricted its applications in supercapacitors (SCs). Here, MOF-derived Co9S8 nanoparticles (NPs) embedded in carbon co-doped with N and S (Co9S8/NS–C) were synthesized as a high rate capability and super stable electrode material for SCs. The Co9S8/NS–C material was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the Co9S8/NS–C material possessed a unique nanostructure in which Co9S8 NPs were encapsulated in porous graphitic carbon co-doped with N and S. The N/S co-doped porous graphitic carbon of composite led to improved rate performance by enhancing the stability of the electrode material and shortening the ion diffusion paths due to a synergistic effect. The as-prepared Co9S8/NS–C-1.5 h material exhibited a high specific capacitance of 734 F g−1 at a current density of 1 A g−1, excellent rate capability (653 F g−1 at 10 A g−1) and superior cycling stability, i.e., capacitance retention of about 99.8% after 140 000 cycles at a current density of 10 A g−1. Thus, a new approach to fabricate promising electrode materials for high-performance SCs is presented here.

Effects of graphene oxide aggregates on hydration degree, sorptivity, and tensile splitting strength of cement paste

Abstract: It has recently been found the graphene oxide (GO) aggregates form in cement paste due to the chemical cross-linking of calcium cations. Therefore, the effects of GO addition on the properties of cement based materials should be dependent on the properties of GO aggregates rather than GO nanosheets. In this study, GO aggregates were first characterized by particle size measurement. Then, the effects of GO aggregates on the degree of hydration, sorptivity, and tensile strength of cement paste were investigated. The aspect ratio of GO aggregates is much larger than that of the original GO nanosheets. Compared to plain cement paste, the increase of non-evaporable water content of the cement paste was found to be very limited, around 1.17% and 3.90% for cement pastes containing 0.02% and 0.04% by weight GO, respectively. The sorptivity of cement paste, especially the secondary sorptivity, was notably reduced for GO incorporated cement paste. The tensile strength was significantly improved by GO aggregates. Incorporation of 0.04% by weight GO increased the tensile strength by 67% compared to that of plain cement paste.

Interface engineering of 3D BiVO4/Fe-based layered double hydroxide core/shell nanostructures for boosting photoelectrochemical water oxidation

Abstract: Photoelectrochemical water oxidation driven by photocatalysts is one of the most effective ways for converting solar energy into fuels and chemicals. However, to date, the solar conversion efficiency using the established photocatalysts is still low. Herein, we report a new strategy for making a class of three-dimensional (3D) BiVO4/Fe-based (Ni1−xFex and Co1−xFex) layered double hydroxide (LDH) interface heterostructures for boosting the photoelectrocatalytic water oxidation performance. Compared with the BiVO4, the BiVO4/Ni0.5Fe0.5–LDH interface photoanode exhibits about 4-fold photocurrent enhancement at 1.23 V vs. the reversible hydrogen electrode and remarkable negative shift (320 mV) of the onset potential for the oxygen evolution reaction (OER). Theoretical calculations reveal that the enhanced photocatalysis for the OER is mainly attributed to the optimal light absorption and the acceleration of electron–hole separation enabled by the strong electronic coupling at the BiVO4/NiFe–LDH interface. The present work first highlights the importance of tuning the light absorption and the separation of carriers using interface engineering in enhancing the solar photocatalytic performance.

Yb3+-Concentration dependent upconversion luminescence and temperature sensing behavior in Yb3+/Er3+ codoped Gd2MoO6 nanocrystals prepared by a facile citric-assisted sol–gel method

Abstract: Yb3+/Er3+ codoped Gd2MoO6 upconversion nanocrystals were synthesized via the traditional citric-assisted sol–gel method. X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and upconversion emission spectroscopy were employed to characterize the final products. Under the irradiation of 980 nm light, the synthesized nanocrystals emitted visible green and red upconversion emissions arising from the intra-4f transitions of Er3+ ions. The upconversion emission intensities were found to be dependent on the dopant concentration and the emission colour gradually changed from green to yellow, and finally to red on elevating the Yb3+ doping concentration. The involved upconversion luminescence mechanism was systematically studied and the steady-state rate expressions were applied to analyze the influence of energy back transfer on the multicolour upconversion emissions. Moreover, the temperature dependent emission intensity ratio of the (2H11/2, 4S3/2) thermally coupled levels of the Er3+ ion in the range of 303–703 K was recorded to study the optical thermometric properties of the resultant nanocrystals. The maximum sensor sensitivity of the Yb3+/Er3+ codoped Gd2MoO6 nanocrystals was determined to be as high as 0.0053 K−1 at 350 K. In addition, the temperature sensing performance of the synthesized compounds was found to be greatly dependent on the Yb3+ doping concentration. These results reveal that the Yb3+/Er3+ codoped Gd2MoO6 nanocrystals with high sensor sensitivity and wide operation range are suitable for non-contact optical thermometry.

Tuning the Shell Number of Multishelled Metal Oxide Hollow Fibers for Optimized Lithium-Ion Storage

Abstract: Searching the long-life transition-metal oxide (TMO)-based materials for future lithium-ion batteries (LIBs) is still a great challenge because of the mechanical strain resulting from volume change of TMO anodes during the lithiation/delithiation process To well address this challenging issue, we demonstrate a controlled method for making the multishelled TMO hollow microfibers with tunable shell numbers to achieve the optimal void for efficient lithium-ion storage Such a particularly designed void can lead to a short diffusion distance for fast diffusion of Li+ ions and also withstand a large volume variation upon cycling, both of which are the key for high-performance LIBs Triple-shelled TMO hollow microfibers are a quite stable anode material for LIBs with high reversible capacities (NiO: 6981 mA h g–1 at 1 A g–1; Co3O4: 9402 mA h g–1 at 1 A g–1; Fe2O3: 9978 mA h g–1 at 1 A g–1), excellent rate capability, and stability The present work opens a way for rational design of the void of multiple she