Shape‐Assisted 2D MOF/Graphene Derived Hybrids as Exceptional Lithium‐Ion Battery Electrodes

Herein, a novel polymer‐templated strategy is described to obtain 2D nickel‐based MOF nanosheets using Ni(OH)₂, squaric acid, and polyvinylpyrrolidone (PVP), where PVP has a dual role as a structure‐directing agent, as well as preventing agglomeration of the MOF nanosheets. Furthermore, a scalable method is developed to transform the 2D MOF sheets to Ni₇S₆/graphene nanosheet (GNS) heterobilayers by in situ sulfidation using thiourea as a sulfur source. The Ni₇S₆/GNS composite shows an excellent reversible capacity of 1010 mAh g^?1 at 0.12 A g^?1 with a Coulombic efficiency of 98% capacity retention. The electrochemical performance of the Ni₇S₆/GNS composite is superior not only to nickel sulfide/graphene‐based composites but also to other metal disulfide–based composite electrodes. Moreover, the Ni₇S₆/GNS anode exhibits excellent cycle stability (≈95% capacity retention after 2000 cycles). This outstanding electrochemical performance can be attributed to the synergistic effects of Ni₇S₆ and GNS, where GNS serves as a conducting matrix to support Ni₇S₆ nanosheets while Ni₇S₆ prevents restacking of GNS. This work opens up new opportunities in the design of novel functional heterostructures by hybridizing 2D MOF nanosheets with other 2D nanomaterials for electrochemical energy storage/conversion applications.     

Using Deep Machine Learning to Understand the Physical Performance Bottlenecks in Novel Thin‐Film Solar Cells

There is currently a worldwide effort to develop materials for solar energy harvesting which are efficient and cost effective, and do not emit significant levels of CO₂ during manufacture. When a researcher fabricates a novel device from a novel material system, it often takes many weeks of experimental effort and data analysis to understand why any given device/material combination produces an efficient or poorly optimized cell. It therefore takes the community tens of years to transform a promising material system to a fully optimized cell ready for production (perovskites are a contemporary example). Herein, developed is a new and rapid approach to understanding device/material performance, which uses a combination of machine learning, device modeling, and experiment. Providing a set of electrical device parameters (charge carrier mobilities, recombination rates, trap densities, etc.) in a matter of seconds thus offers a fast way to directly link fabrication conditions to device/material performance, pointing a way to further and more rapid optimization of light harvesting devices. The method is demonstrated by using it to understand annealing temperature and surfactant choice and in terms of charge carrier dynamics in organic solar cells made from the P3HT:PCBM, PBTZT‐stat‐BDTT‐8:PCBM, and PTB7:PCBM material systems.     

Mechanochemical syntheses of LiFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript>-based nanocomposite and novel nanoglassy LiFeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>

Two members of the pyroxene family, the germanate-type LiFeGe₂O₆ and the titanate-type LiFeTi₂O₆, are prepared for the first time via non-conventional one-step mechanosynthesis. The evolution of the as-prepared materials in the course of mechanosynthesis and their structural state on the long-range and local atomic scales are characterized by X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy, respectively. Both, the nanocrystalline nature of LiFeGe₂O₆ and the nanoglassy state of LiFeTi₂O₆ are revealed.     

Modified progressive random walk with chaotic PRNG

Abstract

In this paper, two modifications are proposed to the Progressive Random Walk (PRW) algorithm in order to address its potentially insufficient search space coverage. The first modification replaces the Pseudo-Random Number Generator (PRNG) with the uniform distribution by the chaotic map based PRNG for generating of the offset values and the second modification is called direction switching and is based on experiment observation. The modifications are implemented into the PRW and the resulting algorithm is called modified Progressive Random Walk. The search space coverage of the two algorithms is compared. Both algorithms are used in macro ruggedness estimation of the CEC2015 benchmark set and the results are discussed.     

Phase transition in swollen gels

Summary The photoelastic behaviour of two networks — polyacrylamide (PAAm) and of a network prepared by the copolymerization of acrylamide with 5 mol.% sodium methacrylate — was investigated in water-acetone mixtures. For the PAAm network the dependence of all photoelastic characteristics on the composition of the mixture is continuous. At 54 vol.% acetone in the mixture, the ionized network undergoes a transition which gives rise to jumpwise changes in the shear modulus, deformational-optical coefficient, C, and in the refractive index of the gel, n_g. While in the collapsed state the optical anisotropy of the statistical segment is negative, –3×10^–24 cm³ (indicating an interaction between the side chains), in the expanded state it is positive, 0.5 × 10^–24 cm³. The dependence of all optical characteristics on the composition of the mixtures suggests that: (a) in both networks we have a transition between two conformational states of the chain; while for the ionized network the transition is a discrete one, for the nonionized network it takes place in the range between 30 and 45 vol.% acetone in the mixture; (b) in both networks the gels are optically homogeneous throughout the whole range of compositions of the mixtures (and thus also in the close vicinity of the collapse of the ionized network).     

Micro axial tomography: a miniaturized, versatile stage device to overcome resolution anisotropy in fluorescence light microscopy

With the development of novel fluorescence techniques, high resolution light microscopy has become a challenging technique for investigations of the three-dimensional (3D) micro-cosmos in cells and sub-cellular components. So far, all fluorescence microscopes applied for 3D imaging in biosciences show a spatially anisotropic point spread function resulting in an anisotropic optical resolution or point localization precision. To overcome this shortcoming, micro axial tomography was suggested which allows object tilting on the microscopic stage and leads to an improvement in localization precision and spatial resolution. Here, we present a miniaturized device which can be implemented in a motor driven microscope stage. The footprint of this device corresponds to a standard microscope slide. A special glass fiber can manually be adjusted in the object space of the microscope lens. A stepwise fiber rotation can be controlled by a miniaturized stepping motor incorporated into the device. By means of a special mounting device, test particles were fixed onto glass fibers, optically localized with high precision, and automatically rotated to obtain views from different perspective angles under which distances of corresponding pairs of objects were determined. From these angle dependent distance values, the real 3D distance was calculated with a precision in the ten nanometer range (corresponding here to an optical resolution of 10-30 nm) using standard microscopic equipment. As a proof of concept, the spindle apparatus of a mature mouse oocyte was imaged during metaphase II meiotic arrest under different perspectives. Only very few images registered under different rotation angles are sufficient for full 3D reconstruction. The results indicate the principal advantage of the micro axial tomography approach for many microscopic setups therein and also those of improved resolutions as obtained by high precision localization determination.     

High‐Performance Supercapacitors Based on a Zwitterionic Network of Covalently Functionalized Graphene with Iron Tetraaminophthalocyanine

Graphene derivatives are promising candidates as electrode materials in supercapacitor cells, therefore, functionalization strategies are pursued to improve their performance. A scalable approach is reported for preparing a covalently and homogenously functionalized graphene with iron tetraaminophthalocyanine (FePc‐NH₂) with a high degree of functionalization. This is achieved by exploiting fluorographene's reactivity with the diethyl bromomalonate, producing graphene‐dicarboxylic acid after hydrolysis, which is conjugated with FePc‐NH₂. The material exhibits an ultrahigh gravimetric specific capacitance of 960 F g^?1 at 1 A g^?1 and zero losses upon charging–discharging cycling. The energy density of 59 Wh kg^?1 is eminent among supercapacitors operating in aqueous electrolytes with graphene‐based electrode materials. This is attributed to the structural and functional synergy of the covalently bound components, giving rise to a zwitterionic surface with extensive π–π stacking, but not graphene restacking, all being very beneficial for charge and ionic transport. The safety of the proposed system, owing to the benign Na₂SO₄ aqueous electrolyte, the high capacitance, energy density, and potential of preparing the electrode material on a large‐scale and at low cost make the reported strategy very attractive for development of supercapacitors based on the covalent attachment of suitable molecules onto graphene toward high‐synergy hybrids.     

Antibacterial LDPE Nanocomposites Based on Zinc Oxide Nanoparticles/Vermiculite Nanofiller

Polyethylene (PE) nanocomposites with the zinc oxide-nanoparticles/vermiculite nanofiller were prepared in two-steps. In first step, the ZnO-np/V nanofiller were prepared by the mechanochemical method followed by a heat treatment at 650?°C for 90 min. In second step, this nanofiller was used in concentration 3, 6, 10 and 15 wt% for PE nanocomposites preparation via melt compounding technique, the nanocomposites plates were pressed. The particles morphology of the ZnO-np/V nanofiller, arrangement of the ZnO-np/V nanofiller and surface of the PE plates were studied using scanning electron microscopy, optical light microscopy and atomic force microscopy. The surface roughness of the PE plates was evaluated from AFM measurements. Structural changes of the ZnO-np/V nanofiller in PE nanocomposites were monitored using X-ray diffraction analysis and Fourier transform infrared analysis. The gradual and long-term antibacterial effect of PE nanocomposites was tested on the Gram positive bacteria E. faecalis by counting the colony forming units number.