Advances in K-Q (Q = S,Se and SexSy) batteries

Metal-sulfur batteries are advanced energy storage systems featuring intriguingly high theoretical capacity and high energy density. Spurred on by the failures in commercializing Li-S and Na-S batteries, K-Q (Q = S, Se, and Se_xS_y) batteries have entered the sights of researchers because of the low redox potential and natural abundance of element K and its synergistic reaction with S or Se. Unfortunately, the current K-Q battery still suffers from several drawbacks, such as drastic volume change, shuttling phenomenon, relatively low reactivity, and dendrite growth. To help to push forward progress of the K-Q battery, here in this review, we first introduce the operation principle and the fundamental challenges faced by the current K-Q batteries, followed by a comprehensive review of effective strategies that have been developed, including engineering of the electrode structure and optimization of the battery composition. Discussions of the mechanism are also included to deepen the understanding of such battery systems. Finally, we discuss the perspectives and challenges for practical application of K-Q batteries. We hope the insights provided in this review can shed light on this new yet rapidly developing field and offer guidance for the development of future high-performance K-Q batteries.     

Emerging opportunities in the two-dimensional chalcogenide systems and architecture

Inspired by the triumphs - and motivated by the need to overcome the limitations - of graphene, the science and engineering community is rapidly exploring the landscape of other potential two-dimensional materials, particularly in their single - or few layer form. Dominating this landscape are the layered chalcogenides; diverse in chemistry, structure and properties, there are well over 100 primary members of this materials family. Driven by quantum confinement, single layers (or few, in some cases) of these materials exhibit electronic, optical, and transport properties that diverge dramatically from their bulk counterparts. The field has evolved considerably since the time when single or few layer flakes were “synthesized” by the scotch-tape mechanical cleavage method. New and more sophisticated methods for controlled synthesis (or thinning), deposition and chemical exfoliation have been developed that can “dial” the number of layers with large areal coverage on diverse substrates. Further, the 2D chalcogenide layers are being used as “substrates” onto which other dimensionally confined structures are being integrated in the spirit of nanoscale composites. Some composite structures exhibit synergy of multiple functionalities of the individual components, while in other cases they represent quantum coupling or unusual behavior that is contrary to nominal synergy or the proportional contribution of individual components. Last but not the least, there remain many structural and chemical combinations that are yet to be explored with deeply intriguing properties or phenomena that are waiting to be revealed. Thus, it is timely to review the status of the field; particularly in the context of synthesis, geometric architecturing and characterization of 2D layered systems.Herein we review the evolving architecture of two-dimensional chalcogenide materials. We outline classes of specific materials and the evolution of their properties as they transition from nominally three to two-dimensionality, and especially in their single (or few) layer form. A variety of vapor-phase synthetic methods for the direct growth of large area single layers and the typical techniques for their characterization are presented. Lastly, we examine the potential of these materials as the fundamental building blocks of two-dimensional heterostructures and multi-dimensional nanocomposites. However, we also emphasize the need for fundamental experimental and theoretical undertaking to probe the classical problems like basic characterization and the dynamics of nucleation and growth in these 2D systems for realizing complex architecturing and resultant technologically useful phenomena and properties.     

Effect of morphology on the photocatalytic activity of g-C3N4 photocatalysts under visible-light irradiation

Graphite-like carbon nitride (g-C₃N₄) photocatalysts with different morphologies have been synthesized using melamine as a precursor using a template-free wet chemical method. The as-prepared g-C₃N₄ nanorods, g-C₃N₄ microcones and porous g-C₃N₄ quadruple prisms were characterized by XRD, FESEM, FT-IR and UV–vis absorption spectrophotometer. These nanostructured g-C₃N₄ photocatalysts show better photocatalytic activity than bulk g-C₃N₄ under visible light irradiation in view of degrading Rhodamine B (RhB). The porous g-C₃N₄ quadruple prisms show the highest photocatalytic efficiency. We deduce that the surface area of the catalysts and their adsorption ability of target molecules play important roles in improving the photocatalytic activity of the g-C₃N₄ photocatalysts.     

Structures and electronic properties of symmetric and nonsymmetric graphene grain boundaries

The graphene grain boundaries with periodic length up to 18 Å have been studied using density functional theory. Atomic structures, thermodynamic stabilities and electronic properties of 40 grain boundaries with symmetric and nonsymmetric structures were investigated. According to the arrangements of pentagons and heptagons on the boundary, grain boundaries were cataloged into four classes. Some nonsymmetric grain boundaries constructed here have identical misorientation angles to the experimentally observed ones. The formation energies of grain boundaries can be correlated with the misorientation angle and inflection angle. Nonsymmetric grain boundaries possess comparable formation energies to their symmetric counterparts when the periodic length along the defect line is larger than 1 nm. Analysis of electronic density of states shows that the existence of a grain boundary usually increases the density of states near the Fermi level, whereas some symmetric grain boundaries can open a small band gap due to local sp²-to-sp³ rehybridization.     

A simple method for preparing graphene nano-sheets at low temperature

Graphene nano-sheets (GNs) with high quality were successfully synthesized in a Teflon-lined container through a low temperature expansion process. The influence factors of expansion temperature, expansion mode and reduction time on the morphology and structure of products have been systematically investigated, and an optimum experimental condition for the synthesis of GNs has been obtained. The results showed that the Teflon-lined container is an effective apparatus for preparing GNs at relative low temperature (<300 °C). The low temperature synthetic process is simple, inexpensive and easy to scale up in comparison with the traditional method which often consume more energy, use more complicated instruments, or more costly. The electrochemical properties of the as-synthesized products were investigated as anode materials for lithium ion batteries.     

Bio-hydrogen production from cornstalk wastes by orthogonal design method

One-factor-at-a-time design and orthogonal design were used in the experimental design methods to optimize bio-hydrogen (bio-H₂) production from cornstalk wastes by anaerobic fermentation. Three series of experiments were designed to investigate the effects of substrate concentration, initial pH and orthogonal design on the bio-H₂ production by using the natural sludge as inoculant. Experimental results indicate that substrate concentration was the most significant condition for optimal hydrogen production. The optimum orthogonal design method was proposed to be at an enzymatic temperature of 50 °C, an enzymatic time of 72 h, an initial pH of 7.0 and a substrate concentration of 10 g/L. The proposed method facilitated the optimization of optimum design parameters, only with a few well-defined experimental sets. Under the proposed condition, the maximum cumulative H₂ yield was 141.29 ml g^?1-CS (cornstalk, or 164.48 ml g^?1-TS, total solid, TS = 0.859 W_{dried cornstalk}), with an average H₂ production rate of 12.31 ml g^?1-CS h^?1. The hydrogen content reached 57.85% and methane was not detected in the biogas.     

凝胶法制备纳米氧化锌颗粒及其光谱分析

就尝试利用溶胶-凝胶法制备纳米氧化锌颗粒,并且运用各种表征技术和测试手段(扫描电镜(SEM)及X射线衍射技术(XRD))对所制备的纳米材料进行了表征、分析和性能研究,主要得出以下结论:(1)验证纳米氧化锌是纤锌矿结构,以六边形貌存在。(2)观察到氧化锌的光谱图与已知的氧化锌的光谱图一致。并且看出不同烧结温度对它的光谱有一定的影响。(3)氧化锌在不同波长的激发下所得到的光谱与现有理论保持一致,这也再一次验证了理论的正确性。     

用于油井激光射孔的10 kW激光19×1空间非相干合束

激光射孔是油井完井工程领域一项具有前瞻性的技术,对提高石油资源采收率具有重要的应用价值。为提高油井激光射孔所使用的激光功率和激光传输的安全性,利用19台光纤传输972 nm半导体激光器实现了10 kW级激光空间非相干合束。通过分析参与合束的准直激光束的半径、间距与合束激光的光斑重叠率之间的变化规律以及模拟合束激光横截面能量分布,完成激光空间非相干合束器的结构设计。在300 mm的合束长度内实现了具有单一光束形态且最大合束功率达到10.441 kW、焦斑直径21 mm、线宽2.46 nm的空间非相干合束激光输出,合束效率达到98.2%。利用10 kW空间非相干合束激光完成了针对砂岩和钢板的地面激光射孔实验,射孔深度分别达到570 mm和70 mm。     

Amplified spontaneous emission from single CdS nanoribbon with low symmetric cross sections

CdS nanoribbons with various cross sections offer the opportunity to deeply understand the interaction between optical cavity and spontaneous emission. Herein, long tapered nanoribbons with the cross sections gradually changing were synthesized by a simple physical vapour deposition method. Morphology dependent micro-region photoluminescence (PL) spectroscopy is employed to show Purcell effect along different low symmetry cross sections. Spikes on the PL spectra reveal that local density of optical modes increases when the mode match happens between optical cavity and spontaneous emission. Bound exciton complex related amplified spontaneous emission is observed in a single CdS nanoribbon with well-defined elliptical cross sections and optimized width/thickness ratio ～1.45. Polarized Raman and TEM confirmed that the nanoribbon with the elliptical cross section adopts the [0002] growth direction with good quality. The results suggest that the cross section resonant cavity would be of importance for both fundamental and practical application of cavity quantum electrodynamics in CdS nanoribbon.     

White-light emission lead-free perovskite phosphor Cs2ZrCl6:Sb3+

Obtaining phosphors with white-light emission is a promising and economical approach for phosphor-conversion light emitting diodes (pc-LEDs), but traditional single-phase white light emission phosphors are inefficient. Here a white-light-emission phosphor was prepared via a co-precipitation method by doping Sb³⁺ into lead-free and vacancy-ordered double perovskite Cs₂ZrCl₆. X-ray diffraction, X-ray photoelectron spectroscopy, and formation energy calculations confirmed that Sb³⁺ ions replaced the Zr⁴⁺sites in the [ZrCl₆]^2? octahedron. The optical properties of Cs₂ZrCl₆:Sb³⁺ were investigated and compared with those of blank Cs₂ZrCl₆. The origination of the emission bands was determined according to their fluorescence spectra and decay-time at an approximate temperature of 4 K Sb³⁺-doped Cs₂ZrCl₆ exhibited white-light emission with double emission bands at 495 and 622 nm due to the ¹P₁ → ¹S₀ and ³P_{2, 1, 0} → ¹S₀ transitions of Sb³⁺, respectively. The intensity ratios of cyan light (495 nm) and the red light emission bands (622 nm) were tunable by adjusting the Sb³⁺concentration. The red component increased with increasing Sb³⁺ concentration in the present experimental range. Moreover, 10% Sb³⁺-doped Cs₂ZrCl₆ showed the strongest emission with a photoluminescence quantum yield of approximately 78% under excitation of 333-nm light White LED devices with different correlated color temperatures were achieved by combining 1% or 10% Sb³⁺-doped Cs₂ZrCl₆ with a 310-nm ultraviolet chip, suggesting that the synthesized samples have potential applications in white-illumination LEDs.