查看更多>>摘要：Direct dual Z-scheme heterostructured nanocomposite TiO_2-WO_3-CeO_2 (NC) and pristine metal oxides na-nostructures (NSs) were fabricated using a facile co-precipitation route. XRD, FTIR, and Raman data have confirmed the formation of NSs and NC. FESEM images showed quasi-mesoporous morphology of as-grown nanocomposite. EDX analysis confirmed the existence of titanium (Ti), cerium (Ce), and tungsten (W) in grown NC. The energy bandgap of NC was narrow 2.45 eV as compared to NSs. The higher electrical conductivity and lower recombination rate of NC were observed in IV and PL analysis. The photodegradation efficiency of NC was recorded 99.8% after 60 min under sunlight radiation against methylene blue (MB), which was significantly higher than NSs. NC catalyst has shown excellent photodegradation against other organic pollutants and has superior recyclability up to 7th cycle toward MB dye with a ~ 6% deficit in photodegradation efficiency. The antimicrobial activity results indicated the higher inhibition ability of NC against E. coli, K. pneumoniae, S. aureus, P. Vulgaris, and P. aeruginosa with maximum inhibition zone diameter 25, 29, 26, 28, and 27 mm, respectively. The electrochemical tests including CV, EIS, and GCD exhibited the superior capacitive behaviour of NC. These results demonstrate that grown NC is an efficient material for electrochemical devices, water purification, and biomedical applications.
查看更多>>摘要：Despite the ultrahigh theoretical capacity of Si anodes, their commercial application is severely restricted due to the lack of scalable and low-cost methods to overcome their considerable volume deformation and poor electrical connectivity. Herein, a novel hierarchical porous silicon/N-doped carbon composite (Si/N-PC) is successfully fabricated via simple biomass fermentation with inexpensive wheat flour, and this composite is then used as a high-performance lithium-ion battery (LIB) anode. Wheat flour blended with silicon na-noparticles can be fermented under the action of yeast while releasing carbon dioxide to construct a unique hierarchical porous structure. The added cationic surfactant hexadecyltrimethylammonium bromide not only helps uniformly deposit the Si particles in the wheat flour under the action of electrostatic forces but also forms an N-doped carbon layer in combination with the protein in the wheat flour, realizing full utilization of the raw materials. Systematic tests verify that the N-doped hierarchical porous structure contributes to mitigating the volume change, ensuring electrode stability and enhancing the electrical conductivity of the Si/N-PC composite during the charge-discharge process. As anticipated, the obtained Si/ N-PC composite electrode can maintain a reversible discharge capacity of 696.1 mAh g~(-1) for over 300 cycles at a current density of 1 A g~(-1) exhibiting a 0.17% capacity loss per cycle from the 3rd to 300th cycle. Additionally, this composite electrode delivers a superior rate capability of 946.1 mAh g~(-1) at a high current density of 2 A g~(-1), showing the synergistic benefit of the hierarchical porous structure and N doping. This is the first time that a hierarchical porous silicon/N-doped carbon composite has been prepared via biomass fermentation treatment for use in high-performance LIBs. The overall fabrication process of the Si/N-PC composites is low cost and scalable, providing a sustainable strategy for the production of high-performance Si/C anode materials.
查看更多>>摘要：The CO gas sensing characteristics of polar GaN (P-GaN) and non-polar GaN (NP-GaN) thin-films grown by RF-plasma assisted molecular beam epitaxy on c-Al_2O_3 and r-Al_2O_3 substrate is analyzed. The temperature-dependent (27-300 °C) current-voltage (I-V) measurements were performed for both (P-GaN & NP-GaN) Schottky barrier diodes having identical device dimensions with Au as the metal contact. The Schottky barrier height increases with the increment in temperature, while vice versa was perceived for the ideality factor and series resistance. The I-V characteristics dictated that the terminal current for P-GaN is 25 times that of NP-GaN, further corroborated by simulation results. The I-V curve fitting suggests the initial emission of charge carrier from a trapped state to a continuum of electronic state, following the Frenkel-Poole emission model for P-GaN. The NP-GaN demonstrated a higher surface-to-volume ratio and native (shallow and deep level) defects corresponding to V_(Ga) and O_N as compared to the P-GaN. The sensing response obtained for the NP-GaN for 100 ppm CO gas at 300 °C is ~ 33%, which is about seven times the response in the case of P-GaN. The role of native defects and the potentiality of the fabricated NP-GaN over P-GaN films in providing a better sensing characteristic by reducing the current conduction paths are elaborated.
查看更多>>摘要：Tungsten carbide-cobalt (WC-Co) mixtures is the most critical material for cemented carbide. However, traditional preparation methods by using various carbon sources (e, g. carbon black, glucose, methane, carbon monoxide) cause severe carbon deposition. Consequently, traditional WC-Co mixtures exhibits uncontrollable carbon content. To address the challenge, we investigate the in-situ synthesis of WC-Co mixtures by supplying successive liquid methanol as a carbon source and nitrogen gas as a diluent. The as-prepared WC-Co mixture possesses clean surface and controllable carbon content, which are no need for removing excess carbon deposition by washing with water. The carbon nanolayers derived from methanol cracking gas appear on the surface of the intermediates, which can effectively prevent particle aggregation, efficiently increase the intimate contact probability of WC particles and Co particles, and greatly reduce the appearance of excess carbon deposition during subsequent carbonization processes. The present study offers insights on employing quantitative methanol cracking gas as reductive and carbonaceous atmosphere to mediate carbon content in the WC-Co composite powder, which presents a more economical and efficient pathway for large-scale synthesis of high-quality WC-Co mixtures with clean surface and controllable carbon content.
查看更多>>摘要：CdSe-reduced Graphene Oxide (CdSe-rGO) nanocomposite was synthesized using a facile hot injection method with excellent control over the size and morphology. The superb distribution of the CdSe quantum dots (CdSe QPs) and the tightly anchoring to the graphene sheets enhance their optical properties. Therefore, the effect of reduced Graphene oxide (rGO) on the structure and optical properties of CdSe nanoparticles is studied by X-ray diffraction (XRD), UV-visible spectroscopy, and transmission electron microscopy (TEM). As well as Effective mass approximation model (EMA) and Polynomial Fitting Functions (PFF) were used to calculate the sizes of nanoparticles, yielding particle sizes ranging from 4.64 to 5.46 nm and 2.74-3.72 nm, respectively. These values were comparable to those obtained by TEM and XRD. Furthermore, the data revealed that the direct energy gap of the CdSe QDs was reduced from 2.33 eV for the smallest size to 2.17 eV for the largest size. The optical parameters of CdSe-rGO nanocomposite such as the refractive index and extinction coefficient were increased with the particle size growth. As well, optical dielectric constant and optical conductivity were improved due to the increase of the particle size of CdSe Q_Ds in the CdSe-rGO nanocomposite. So, the capability of CdSe-rGO nanocomposite to tune the optical parameters makes it a suitable candidate for a wide range of applications, specifically optoelectronics.
查看更多>>摘要：The post-dynamic recrystallization (PDRX) behavior of a powder metallurgy (PM) Ni-Co-Cr based super-alloy was researched by thermal compression tests at the temperature range of 1020-1080 °C within the strain rates of 0.01-1 s~\ followed by heat preservation for 0-45 s after deformed to 10%-50%. Electron backscatter diffraction (EBSD) and Transmission Electron Microscope (TEM) techniques were employed to investigate the effect of the deformation conditions on PDRX behavior. The results show that the deformation conditions (strain rate, temperature, degree of deformation and holding time) have great impact on the PDRX kinetics. Increasing deformation temperature, strain or holding time can result in the effective release of residual deformation stored energy, promoting the PDRX course. The irregular energy storage release of the superalloy deformed at different strain rates is mainly concerned with the various micro-structure evolution during heat preservation. The evolution of twin boundary (?3) during PDRX exhibits the similar regularity with that of recrystallization fraction. The formation of ?3 boundary induces the recrystallized nucleation, leading to further release of deformation storage energy. Meta-dynamic recrystallization (MDRX) and static recrystallization (SRX) are the dominant mechanisms of PDRX, and the nucleation induced by undissolved γ' precipitates or assisted by twins also play certain roles in microstructure evolution during heat preservation of the deformed superalloy.
查看更多>>摘要：The development of high energy density Li-O_2 batteries is restricted by the sluggish kinetics of both the oxygen reduction reaction and the oxygen evolution reaction, and developing an efficient cathode catalyst is the key to resolving this issue. In present study, interconnected honeycomb-like NiCo_2O_4 nanoflakes are synthesized by facile electrochemical deposition on carbon cloth (CC) and subsequent heat treatment. Compared with NiO and Co_3O_4, suitably sized NiCo_2O_4 nanoflakes benefit from a vital synergistic effect of components Co and Ni and are expected to show superior OER/ORR performance. The presence of redox couples Co~(3+)/Co~(2+) and Ni~(2+)/Ni~(3+) and abundant oxygen vacancies in NiCo_2O_4 allow Li-O_2 batteries deliver satisfactory cycle durability and high discharge/recharge capacities. Li-O_2 batteries that use the NiCo_2O_4/CC cathodes exhibit high specific discharge capacities of 8388 mA h g~(-1) and 5238 mA h g~(-1) at 200 mA g~(-1) and 400 mA g~(-1) respectively, and deliver a long lifetime of 102 cycles with a capacity limit of 500 mA h g~(-1) at 340 mA g~(-1) thereby suggesting that honeycomb-like NiCo_2O_4 nanoflakes are a promising cathode catalyst.
查看更多>>摘要：Metal-organic framework (MOF) based materials are a fascinating candidate in the sensor field. In this work, we successfully synthesized Co-MOF/BP-RGO nanocomposite by simple hydrothermal method and fabricated on glassy carbon electrode (GCE) for the detection of chlorogenic acid (CGA). The Co-MOF/BP-RGO nanocomposite was characterized by the powder x-ray diffraction (XRD), micro-Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The electrochemical performance of Co-MOF/BP-RGO was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The Co-MOF/BP-RGO/GCE exposed good sensitivity, and great selectivity towards CGA under optimized conditions. The Co-MOF/BP-RGO/GCE exhibited a wide linear range and excellent LOD 0.001-391 uM and 0.014 uM respectively, and it exposed strong long-term stability also. Hence all these findings indicate that the Co-MOF/BP-RGO nanocomposite is a novel electrocatalyst for the highly sensitive CGA electrochemical sensor. Additionally, our proposed sensor was applied for the detection of CGA in the real samples, such as coffee powder and green tea leaves and it displayed excellent sensitivity and good recovery results.
查看更多>>摘要：Lithium metal has been considered as one of the most promising anodes for the endeavoring pursuit of advanced batteries due to its ultra-high capacity of-3860 mAh g~(-1). To solve the current problems of lithium metal anode (LMA), such as unreliable dendritic growth, dead Li accumulation, and the resulted pulverization, three-dimensional frameworks have been adopted to maintain the structural integrity of LMA, but the issues including interfacial stability and affinity, undesired Li-ion deletion at the electrolyte/electrode interface are still challenging. Herein, by adopting hierarchical porous graphitic carbon (HPGC) as LMA skeleton and the atomic-level MgO for interface modification, the ideally uniform interface with strong Li affinity can effectively regulate the nucleation and deposition behavior of Li metal; while with the large quantity of Li~+ storage in the micro-porous of HPGC, both the spatial confinement of Li~+ flux and the increase in Li~+ concentration at electrode/electrolyte interface can be achieved to facilitate the planer Li metal electrodeposition. Furthermore, the delithiation of HPGC with slightly higher potential can effectively reduce the formation of dead-Li via preventing the depletion of Li with inexhaustible Li~+ storage during stripping process. The superiority of MgO@HPGC hosted LMA can be demonstrated both as coating layer and interior skeleton for different kinds of LMA applications, with enhancement in both long term cycling stability (-650 h) and high coulombic efficiency (-97%) over 390 cycles.
查看更多>>摘要：In this work, a novel method of mechanochemistry is used to directly prepare high-performance Ni-Fe based catalysts for oxygen evolution reaction (OER) in an environmental-friendly borate electrolyte with near-neutral pH. Such a procedure is simple, effective, and time-saving. The effect of iron-based raw materials and mechanochemical reaction on OER of catalysts are investigated. It shows that iron nitrate nonahydrate is the best iron resource compared to iron hydroxide and iron oxide due to amorphous iron species in catalysts for strengthening the "Fe inductive effect" and generating active Ni species with high valence. Besides, the grinding time can control the mechanochemical reaction from mixed reaction to solid reaction in the catalyst synthesis process. When the time is 30 min, the catalyst is composed with amorphous Ni(OH)_2 and the precursors of NiFe-LDH. This catalyst only needs 413 mV overpotential to reach 1 mA cm~(-2) in 0.1 M K-Bi (pH=9.2), which is better than precious RuO_2. It is proven that the mechanochemical approach is an alternative method for synthesizing superior OER catalysts.
NSTL
Elsevier