Ultrathin MnO2 nanosheets grown on hollow carbon spheres with enhanced capacitive performance

Ultrathin MnO₂ nanosheets grown on the surface of hollow carbon spheres (MnO₂/HCSs) were fabricated by the redox reaction between carbon spheres with KMnO₄ in aqueous solution. Due to the porous structure and large amounts of active sites, MnO₂/HCSs exhibit excellent capacitive performance with 227.5 F g⁻¹ at 1 A g⁻¹. After 5000 cycles, the capacity retention of MnO₂/HCSs remains 96%, indicating its good cycling stability. These results demonstrate that MnO₂/HCSs are promising supercapacitor electrode material and this work provide a facile method for growth of ultrathin MnO₂ nanosheets on carbon substrate.     

Self-trapped dynamics of a hollow Gaussian beam in metamaterials

We present a systematic investigation on the dynamics of a hollow Gaussian beam (HGB) in metamaterials. We predict self-trapped propagation of HGBs and evolution of the beam is highly influenced by dimensionless dispersion coefficient (κ), which determines the strength of dispersion over diffraction. The evolutions of HGBs such as disappearance of single ringed intensity pattern and appearance of patterns with a central bright spot are achievable with less propagation distance in metamaterials with higher values of κ. On the other hand, metamaterials with low values of κ can preserve single ring intensity distribution over a long propagation distance without focusing. When the strength of dispersion over diffraction increases, it significantly influences the evolution of the beam and may lead to the formation of tightly focussed beam with high peak intensity at the center. The phenomenon of tight focussing is found to have some applications in trapping of nanosized particles.     

中空MOFs材料制备及电催化应用的研究进展

水分裂、金属-空气电池和燃料电池等能源转换技术对解决未来的能源危机和环境问题至关重要.氧还原反应(ORR)、氧析出反应(OER)和氢析出反应(HER)作为其核心反应,存在反应动力学速率较慢的问题,因此,开发研制高效的非贵金属电催化剂具有重要意义.金属有机骨架(MOFs)材料因具有高度可调的组成和多孔晶体结构,在不同的应用领域引起了越来越多的关注.中空MOFs纳米材料具有MOFs材料高度可调的组成和结构优势,又具有中空结构纳米材料的优点(如更快的物质传输、更丰富的孔隙率、灵活多变的活性组分、更多的暴露活性位点及对苛刻条件的更好相容性等),在电催化领域显现出巨大的应用潜力.本文对近几年来基于中空结构MOFs材料的制备及在电催化方面应用的研究进展进行了综合评述,并对该领域面临的挑战和发展前景进行了总结和展望.     

CoO纳米颗粒/石墨烯纳米纤维复合材料的制备及电化学性能

用石墨烯和Co(CH₃COO)₂·4H₂O作为原料,利用超声辅助法合成了锂离子电池的负极材料CoO纳米颗粒/中空石墨烯纳米纤维复合物.采用X射线衍射(XRD)确定材料的物相组成,采用扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察材料的表面形貌和微观结构,采用X射线光电子能谱(XPS)确定材料的价态结构.采用循环伏安、恒电流充放电和交流阻抗谱表征材料的电化学性能.结果显示,在100 mA/g的电流密度下,循环了160次后,可逆容量仍超过800 mA/g,库仑效率保持在99%以上.该材料优异的电化学性能主要归因于石墨烯的中空纤维结构,中空内部可以容纳电解液,能直接将离子输送到颗粒表面,实现了离子的快速传输;二维中空纤维搭建成三维网络结构,实现了三维电子传导网络.     

Design of Hollow Nanoreactors for Size- and Shape-Selective Catalytic Semihydrogenation Driven by Molecular Recognition

Mimicking the structures and functions of cells to create artificial organelles has spurred the development of efficient strategies for production of hollow nanoreactors with biomimetic catalytic functions. However, such structure are challenging to fabricate and are thus rarely reported. We report the design of hollow nanoreactors with hollow multishelled structure (HoMS) and spatially loaded metal nanoparticles. Starting from a molecular-level design strategy, well-defined hollow multishelled structure phenolic resins (HoMS-PR) and carbon (HoMS-C) submicron particles were accurately constructed. HoMS-C serves as an excellent, versatile platform, owing to its tunable properties with tailored functional sites for achieving precise spatial location of metal nanoparticles, internally encapsulated (Pd@HoMS-C) or externally supported (Pd/HoMS-C). Impressively, the combination of the delicate nanoarchitecture and spatially loaded metal nanoparticles endow the pair of nanoreactors with size–shape-selective molecular recognition properties in catalytic semihydrogenation, including high activity and selectivity of Pd@HoMS-C for small aliphatic substrates and Pd/HoMS-C for large aromatic substrates. Theoretical calculations provide insight into the pair of nanoreactors with distinct behaviors due to the differences in energy barrier of substrate adsorption. This work provides guidance on the rational design and accurate construction of hollow nanoreactors with precisely located active sites and a finely modulated microenvironment by mimicking the functions of cells.     

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2O2 Production

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn−N₂O₂ moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N₂O₂−S). Systematic analyses demonstrate that the synergetic effects between the N₂O₂ species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O₂ reduction to H₂O₂. Remarkably, the Zn−N₂O₂ moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H₂O₂ generation. Consequently, the Zn−N₂O₂−S SAC exhibits impressive electrochemical H₂O₂ production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm⁻² in the flow cell, it shows a high H₂O₂ production rate of 6.924 mol g_cat⁻¹ h⁻¹ with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.     

聚氰基丙烯酸乙酯空心纳米纤维的制备

通过溶液聚合法制备了具有空心结构的聚氰基丙烯酸乙酯纳米纤维,纤维直径为50~100 nm.研究了3种溶液体系对形成聚氰基丙烯酸乙酯纳米纤维形貌与直径的影响,并探讨了其形成机理.通过调控溶液体系内外环境可得到不同形貌的聚合物纤维,且纤维表面表现出疏水性质.该方法适用于平整且具有粗糙结构的表面.所形成的聚氰基丙烯酸乙酯纳米纤维涂层可用于基底的疏水改性.     

Combination of hollow‐fiber‐supported liquid membrane and dispersive liquid–liquid microextraction as a fast and sensitive technique for the extraction of pesticides from grape juice followed by high‐performance liquid chromatography

The simultaneous use of a hollow‐fiber‐supported liquid membrane and dispersive liquid–liquid microextraction for the determination of pesticides directly in grape juice was investigated. The detection and quantification were performed by liquid chromatography with diode array detection. The optimum extraction condition was reached by filling the pores of the membrane wall with dodecanol and using hexane/acetone as extraction/dispersion solvents. Salt addition had a highly negative effect on the extraction efficiency and the optimum extraction time was 60 min. The volume of hexane/acetone mixture and the sample pH did not affect the signal at the levels studied. Therefore, an intermediate amount of these solvents (250 μL; 1:7.5 v/v) and pH 6 were selected. The optimum desorption condition was obtained with acetonitrile and 10 min of desorption time. The linear working range varied from 58 to 500 μg/L (parathion‐methyl), 62–500 μg/L (difenoconazole) and 107–500 μg/L (chlorpyrifos), with correlation coefficients ranging from 0.9980–0.9942. The limits of detection and quantification found were, respectively, 17 and 58 μg/L for parathion‐methyl, 19 and 62 μg/L for difenoconazole and 32 and 107 μg/L for chlorpyrifos. The relative standard deviation ranged between 3.5 and 11.2%.     

Hollow polyhedron structure of amorphous Ni-Co-S/Co(OH)_2 for high performance supercapacitors

In power storage technology,ion exchange is widely used to modify the electronic structures of electrode materials to stimulate their electrochemical properties.Here,we proposed a multistep ion exchange(cation exchange and anion exchange) strategy to synthesize amorphous Ni-Co-S and β-Co(OH)_2 hybrid nanomaterials with a hollow polyhedron structures.The synergistic effects of different components and the remarkable superiorities of hollow structure endow Ni-Co-S/Co(OH)_2 electrode with outstanding electrochemical performance,including ultra-high specific capacity(1440.0 C/g at 1 A/g),superior capacitance retention rate(79.1% retention at 20 A/g) and long operating lifespan(81.4% retention after5000 cycles).Moreover,the corresponding hybrid supercapacitor enjoys a high energy density of 58.4 Wh/kg at the power density of 0.8 kW/kg,and a decent cyclability that the capacitances are maintained at80.8% compared with the initial capacitance.This research presents a high-performance electrode material and provides a promising route for the construction of electrode materials for supercapacitors with both structural and component advantages.     

中空TiO_2微球的制备及对聚丙烯酸酯薄膜性能的影响

采用阳离子聚苯乙烯微球作为模板,钛酸四丁酯为钛源,氨水为催化剂,制备了中空TiO_2微球.采用X射线衍射、扫描电镜及比表面测定仪对其形貌和结构进行了表征,并考察了模板粒径、钛源用量以及催化剂用量对中空TiO_2微球形貌的影响.通过物理共混法将其引入至聚丙烯酸酯乳液中并成膜,研究了复合薄膜的保温性能、抗紫外性能及力学性能.结果表明,锐钛矿相中空TiO_2微球模板粒径、钛源用量以及催化剂用量影响中空TiO_2微球的空心尺寸、壁厚及壳层致密性.中空TiO_2微球可显著提升聚丙烯酸酯薄膜的保温性能、抗紫外性能和力学性能.采用不同粒径的模板制备的中空TiO_2微球对复合薄膜的各项性能均有影响,其中模板粒径为140 nm时复合薄膜性能最优,光反射率提升63%,导热系数降低27%,且在波长小于360 nm范围内,紫外透过率几乎为0,抗张强度增加100%,断裂伸长率提升62%.