High-performance electrocatalyst of vanadium-iron bimetal organic framework arrays on nickel foam for overall water splitting

The development of active,low-cost and durable bifunctional electrocatalysts toward both oxygen evolution reaction(OER) and hydro gen evolution react ion(HER) a re important for overall water splitting.Here,well-defined arrays of vanadium-iron bimetal organic frameworks(VFe-MOF) with controllable stoichiometry have been successfully prepared on nickel foam(NF).The as-fabricated VFe-MOF@NF electrode exhibits excellent electrocatalytic activity and durability for OER and HER in alkaline medium.The material's overpotentials of 10 mA/cm~2 are 246 mV for OER and 147 mV for HER,respectively.The electrolyzer made from the VFe-MOF@NF electrodes as both the cathode and anode in 1 mol/L KOH needs only a voltage of 1.61 V to reach a current density of 10 mA/cm~2.The superior performance of VFeMOF@NF can be attributed to the morphological control and electronic regulation of the bimetals,that is,1) the exposure of the active sites at electrocatalyst/electrolyte interfaces due to the array structure;2)the synergistic effect of vanadium and iron metals on electro-catalyzing the overall water splitting.     

Cellulose-based fluorescent macromolecular sensors and their ability in 2, 4, 6-trinitrophenol detection

This article deals with three cellulose-based fluorescent macromolecular sensors by introducing 1,8-naphthalimide fluorophore to cellulose. First, through the etherification reaction of cellulose with BrCH₂CH₂NH₂, –NH₂ group–bearing cellulose CS 1 was obtained. Then, the –NH₂ group reacts with 4-bromo-1,8-naphthalic anhydride to synthesize a naphthalimide cellulose derivative (CS 2). Finally, the recognition group was introduced by substituting Br atoms, and three cellulose fluorescent probes (CS 3, CS 4, and CS 5) were obtained eventually. Structure and fluorescence properties of the macromolecular sensors were characterized and confirmed. Fluorescence detection measurements show that these probes can be used as selective and sensitive fluorescent sensors to 2,4,6-trinitrophenol (TNP). The detection limits are 0.52 μM, 0.76 μM, and 0.81 μM, indicating good detection performance. This work provides a new method for the selective detection of TNP and also a method to enlarge the application scope of cellulose.     

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection

The development of nanoscaled luminescent metal–organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu - and csq -type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH₂ as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH₂-substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.     

Study of Intermolecular Reconfiguration of Flexible COF-5 Film and Its Ultra-high Chemiresistive Humidity Sensitivity

Recently, abundant active materials are developed to achieve the wearable detection of human body humidity. However, the limited response signal and sensitivity restrict further application due to their moderate affinity to water. Herein, we propose a flexible COF-5 film synthesized by a brief vapor-assisted method at room temperature. Intermediates are calculated by DFT simulation to investigate the interaction between COF-5 and water. The adsorption and desorption of water molecule result in a reversible deformation of COF layers while creating new conductive path by π–π stacking. The as-prepared COF-5 films are applied to the flexible humidity sensors, exhibiting a resistance change in 4 orders of magnitude with remarkable linear relation between log function of resistance and relative humidity (RH) in 11 %–98 % RH range. Applications including respiratory monitoring and non-contact switch are tested, providing a promising prospect for the detection of human body humidity.     

碱性聚合物电解质膜的表面锥形阵列结构提升燃料电池性能

燃料电池作为一种清洁高效的能量转换装置,被认为是构建未来社会可再生能源结构的关键一环。不同于质子交换膜燃料电池(PEMFC),碱性聚合物电解质燃料电池(APEFC)的出现使非贵金属催化剂的使用成为可能,因而受到了日益广泛的关注和研究。APEFC的关键结构是膜电极,主要由聚合物电解质膜和阴阳极(含催化层、气体扩散层)组成,膜电极是电化学反应发生的场所,其优劣直接决定着电池性能的好坏。因此,基于现有的碱性聚合物电解质及催化剂体系,如何构筑更加优化的膜电极结构,使APEFC发挥出更高的电池性能是亟待开展的研究。本文首先通过模板法在碱性聚合物电解质膜的表面构建出有序的锥形阵列,再将具有阵列结构的一侧作为阴极来构筑膜电极,同时,作为对比,制备了由无阵列结构的聚合物电解质膜构筑而成的膜电极,最后对基于两种不同膜电极的APEFC的电化学性能进行了对比研究。实验结果表明,锥形阵列结构可以将APEFC的峰值功率密度由1.04 W·cm-2显著提高到1.48 W·cm-2,这主要归因于在APEFC的阴极侧具有锥形阵列结构的聚合物电解质膜的亲水性的提升和催化剂电化学活性面积的增加。本工作为碱性聚合物电解质燃...     

可见/近红外实时成像光谱仪控制系统设计

针对高光谱成像需求,设计了一套可见/近红外实时成像光谱仪.光谱仪基于声光可调谐滤波器(Acousto-Optic Tunable Filter,AOTF)分光器件进行设计,光谱带宽为1.3μm,其中可见光相机工作在400～1000 nm波段,近红外相机工作在1000～1700 nm波段.光谱仪控制系统以现场可编程门阵列...     

适用于声呐阵形估计的姿态传感器网络设计

设计了一种基于姿态传感器网络的声呐阵形估计系统,给出了系统设计的整体方案并对系统的软硬件设计进行了论述。实验结果证明了该设计的可行性。     

改进自适应遗传算法的平面传声器阵列优化

针对传声器位置的离散性和遗传算法二进制的编码特点,本文提出改进的自适应遗传算法,对自适应交叉概率和变异概率作了重新设计,并将本文改进自适应遗传算法和传统标准遗传算法以及文献中提到的改进自适应遗传算法进行了比较,发现本文方法能够快速得到更优的结果。此外,本文提出了随频率变化的主瓣宽度和旁瓣水平折中的适应度函数R3,通过与适应度函数R1和R2的仿真结果对比,发现适应度函数R3能够有效地平衡阵列主瓣宽度和旁瓣水平。最后,本文设计了5臂均匀圆阵和5臂螺旋阵,并与本文随机阵进行仿真实验对比,进一步验证本文方法的有效性和可行性。     

Investigations of Linearly Chirped Fiber Bragg Gratings for Time-Steered Array Antennas

The use of linearly chirped fiber Bragg gratings as dispersive delay line elements in optical true time-delay beamformers is investigated. Two different dispersive prism beamforming architectures are considered as is their impact on the grating specifications. Microwave double-sideband and single-sideband characterization is carried out on gratings suitable for both architectures with an emphasis on the group delay ripple of single and cascaded gratings. Results indicate that commercially available gratings are suitable for beamforming applications.     

Finite Element Analysis of Piezoelectric Polymer-Coated D-Fiber Intended for Electric Field Sensing

We report, for the first time, the advantage of using a polymer-coated D-fiber over conventional circular fiber as the sensing element in an all-fiber electric field sensor. Finite element analysis has been used to studythe strains in a D-fiber subjected to an external electric field. The optical D-fiber carrying a transversely poled piezoelectric poly(vinylidene fluoride) polymer coating was modeled by using three-dimensional stress analysis. The response of the D-fiber electric field sensor was determined over a wide frequency range from 100 Hz to 50 MHz. The modeling predicts that the resulting strains will cause a phase shift of 0.06 rad V m in the low-frequency (axially unconstrained) region and 0.002 rad V m in the high-frequency (axially constrained)region. An increase in the phase modulation sensitivity by a factor of 3 compared to conventional circular fiber has been achieved by utilizing the unique properties of the D-fiber structure.