Preparation of Li4Ti5O12 Yolk–Shell Powders by Spray Pyrolysis and their Electrochemical Properties

We have reported for the first time the preparation of yolk–shell‐structured Li₄Ti₅O₁₂ powders for use as anode materials in lithium‐ion batteries. One Li₄Ti₅O₁₂ yolk–shell‐particle powder is directly formed from each droplet containing lithium, titanium, and carbon components inside the hot wall reactor maintained at 900 °C. The precursor Li₄Ti₅O₁₂ yolk–shell‐particle powders, which are directly prepared by spray pyrolysis, have initial discharge and charge capacities of 155 and 122 mA h g^?1, respectively, at a current density of 175 mA g^?1. Post‐treatment of the yolk–shell‐particle powders at temperatures of 700 and 800 °C improves the initial discharge and charge capacities. The initial discharge capacities of the Li₄Ti₅O₁₂ powders with a yolk–shell structure and a dense structure post‐treated at 800 °C are 189 and 168 mA h g^?1, respectively. After 100 cycles, the corresponding capacities are 172 and 152 mA h g^?1, respectively (retentions of 91 and 90 %).     

A Self‐Standing and Flexible Electrode of Yolk–Shell CoS2 Spheres Encapsulated with Nitrogen‐Doped Graphene for High‐Performance Lithium‐Ion Batteries

Flexible lithium‐ion batteries (LIBs) have recently attracted increasing attention with the fast development of bendable electronic systems. Herein, a facile and template‐free solvothermal method is presented for the fabrication of hybrid yolk–shell CoS₂ and nitrogen‐doped graphene (NG) sheets. The yolk–shell architecture of CoS₂ encapsulated with NG coating is designed for the dual protection of CoS₂ to address the structural and interfacial stability concerns facing the CoS₂ anode. The as‐prepared composite can be assembled into a film, which can be used as a binder‐free and flexible electrode for LIBs that does not require any carbon black conducting additives or current collectors. When evaluating lithium‐storage properties, such a flexible electrode exhibits a high specific capacity of 992 mAh g^?1 in the first reversible discharge capacity at a current rate of 100 mA g^?1 and high reversible capacity of 882 mAh g^?1 after 150 cycles with excellent capacity retention of 89.91 %. Furthermore, a reversible capacity as high as 655 mAh g^?1 is still achieved after 50 cycles even at a high rate of 5 C due to the yolk–shell structure and NG coating, which not only provide short Li‐ion and electron pathways, but also accommodate large volume variation.     

Preparation of Yolk‐Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties

In this study, we report the first preparation of phase‐pure Co₉S₈ yolk–shell microspheres in a facile two‐step process and their improved electrochemical properties. Yolk–shell Co₃O₄ precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co₉S₈ yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co₉S₈ microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co₉S₈ microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m² g^?1 with a mean pore size of 16 nm. The yolk–shell Co₉S₈ microspheres have initial discharge and charge capacities of 1008 and 767 mA h g^?1 at a current density of 1000 mA g^?1, respectively, while the filled Co₉S₈ microspheres have initial discharge and charge capacities of 838 and 638 mA h g^?1, respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g^?1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %.     

A Yolk–Shell Structured Silicon Anode with Superior Conductivity and High Tap Density for Full Lithium‐Ion Batteries

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si‐based anodes. Herein, we report for the first time of a new yolk–shell structured high tap density composite made of a carbon‐coated rigid SiO₂ outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe₂O₃ nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe₂O₃ NPs, and CNTs Li⁺ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs “highway”. Half cells can achieve a high area capacity of 3.6 mAh cm^?2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li‐rich Li₂V₂O₅ cathode can achieve a high reversible capacity of 260 mAh g^?1 after 300 cycles.     

Electrochemical Properties of Yolk–Shell‐Structured Zn–Fe–S Multicomponent Sulfide Materials with a 1:2 Zn/Fe Molar Ratio

Yolk–shell‐structured Zn–Fe–S multicomponent sulfide materials with a 1:2 Zn/Fe molar ratio were prepared applying a sulfidation process to ZnFe₂O₄ yolk–shell powders. The Zn–Fe–S powders had mixed sphalerite (Zn,Fe)S and hexagonal FeS crystal structures. The discharge capacities of the Zn–Fe–S powders sulfidated at 350 °C at a constant current density of 500 mA g^?1 for the first, second, and fiftieth cycles were 1098, 912, and 913 mA h g^?1, respectively. The powders exhibited a high discharge capacity of 602 mA h g^?1 even at the high current density of 10 A g^?1. The synergistic effect of yolk–shell structure and multicomponent composition improved the electrochemical properties of Zn–Fe–S powders.     

Polyoxometalate Ionic Liquids as Self‐Repairing Acid‐Resistant Corrosion Protection

Corrosion is a global problem for any metallic structure or material. Herein we show how metals can easily be protected against acid corrosion using hydrophobic polyoxometalate‐based ionic liquids (POM‐ILs). Copper metal disks were coated with room‐temperature POM‐ILs composed of transition‐metal functionalized Keggin anions [SiW₁₁O₃₉TM(H₂O)]^n? (TM=Cu^II, Fe^III) and quaternary alkylammonium cations (C_nH_{2 n+1})₄N⁺ (n=7–8). The corrosion resistance against acetic acid vapors and simulated “acid rain” was significantly improved compared with commercial ionic liquids or solid polyoxometalate coatings. Mechanical damage to the POM‐IL coating is self‐repaired in less than one minute with full retention of the acid protection properties. The coating can easily be removed and recovered by rinsing with organic solvents.     

Kilogram‐Scale Production of SnO2 Yolk–Shell Powders by a Spray‐Drying Process Using Dextrin as Carbon Source and Drying Additive

A simple and general method for the large‐scale production of yolk–shell powders with various compositions by a spray‐drying process is reported. Metal salt/dextrin composite powders with a spherical and dense structure were obtained by spray drying and transformed into yolk–shell powders by simple combustion in air. Dextrin plays a key role in the preparation of precursor powders for fabricating yolk–shell powders by spray drying. Droplets containing metal salts and dextrin show good drying characteristics even in a severe environment of high humidity. Sucrose, glucose, and polyvinylpyrrolidone are widely used as carbon sources in the preparation of metal oxide/carbon composite powders; however, they are not appropriate for large‐scale spray‐drying processes because of their caramelization properties and adherence to the surface of the spray dryer. SnO₂ yolk–shell powders were studied as the first target material in the spray‐drying process. Combustion of tin oxalate/dextrin composite powders at 600 °C in air produced single‐shelled SnO₂ yolk–shell powders with the configuration SnO₂@void@SnO₂. The SnO₂ yolk–shell powders prepared by the simple spray‐drying process showed superior electrochemical properties, even at high current densities. The discharge capacities of the SnO₂ yolk–shell powders at a current density of 2000 mA g^?1 were 645 and 570 mA h g^?1 for the second and 100th cycles, respectively; the corresponding capacity retention measured for the second cycle was 88 %.     

Yolk–shell microspheres assembled from Preyssler‐type NaP5W30O11014− polyoxometalate and MIL‐101(Cr) metal–organic framework: A new inorganic–organic nanohybrid for fast and selective removal of cationic organic dyes from aqueous media

Novel inorganic–organic yolk–shell microspheres based on Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate and MIL‐101(Cr) metal–organic framework (P₅W₃₀/MIL‐101(Cr)) were synthesized by reaction of K_12.5Na_1.5[NaP₅W₃₀O₁₁₀], Cr(NO₃)₃·9H₂O and terephthalic acid under hydrothermal conditions at 200°C for 24 h. The as‐prepared yolk–shell microspheres were fully characterized using various techniques. All analyses confirmed the incorporation of the Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate into the three‐dimensional porous MIL‐101(Cr) metal–organic framework. The results revealed that P₅W₃₀/MIL‐101(Cr) demonstrated rapid adsorption of cationic methylene blue (MB) and rhodamine B (RhB) with ultrahigh efficiency and capacity, as well as achieving rapid and highly selective adsorption of MB from MB/MO (MO = methyl orange), MB/RhB and MB/RhB/MO mixtures. The P₅W₃₀/MIL‐101(Cr) adsorbent not only exhibited a high adsorption capacity of 212 mg g^?1, but also could quickly remove 100% of MB from a dye solution of 50 mg l^?1 within 8 min. The effects of some key parameters such as adsorbent dosage, initial dye concentration and initial pH on dye adsorption were investigated in detail. The equilibrium adsorption data were better fitted by the Langmuir isotherm. The adsorption kinetics was well modelled using a pseudo‐second‐order model. Also, the inorganic–organic hybrid yolk–shell microspheres could be easily separated from the reaction system and reused up to four times without any change in structure or adsorption ability. The stability and robustness of the adsorbent were confirmed using various techniques.     

Synergy of Epoxy Chemical Tethers and Defect‐Free Graphene in Enabling Stable Lithium Cycling of Silicon Nanoparticles

We report a new approach for nanosilicon–graphene hybrids with uniquely stable solid electrolyte interphase. Expanded graphite is gently exfoliated creating “defect‐free” graphene that is non‐catalytic towards electrolyte decomposition, simultaneously introducing high mass loading (48 wt. %) Si nanoparticles. Silane surface treatment creates epoxy chemical tethers, mechanically binding nano‐Si to CMC binder through epoxy ring‐opening reaction while stabilizing the Si surface chemistry. Epoxy‐tethered silicon pristine–graphene hybrid “E‐Si‐pG” exhibits state‐of‐the‐art performance in full battery opposing commercial mass loading (12 mg cm^?2) LiCoO₂ (LCO) cathode. At 0.4 C, with areal capacity of 1.62 mAh cm^?2 and energy of 437 Wh kg^?1, achieving 1.32 mAh cm^?2, 340.4 Wh kg^?1 at 1 C. After 150 cycles, it retains 1.25 mAh cm^?2, 306.5 Wh kg^?1. Sputter‐down XPS demonstrates survival of surface C‐Si‐O‐Si groups in E‐Si‐pG after repeated cycling. The discovered synergy between support defects, chemical‐mechanical stabilization of Si surfaces, and SEI‐related failure may become key LIB anode design rule.     

Thermochromism of CuI Tetrakisguanidine Complexes: Reversible Activation of Metal‐to‐Ligand Charge‐Transfer Bands

Tetranuclear, intensely blue‐coloured Cu^I complexes were synthesised in which two Cu₂X₃^? units (X=Br or I) are bridged by a dicationic GFA (guanidino‐functionalised aromatic) ligand. The UV/Vis spectra show a large metal‐to‐ligand charge‐transfer (MLCT) band around 638 nm. The tetranuclear “low‐temperature” complexes are in a temperature‐dependent equilibrium with dinuclear Cu^I “high‐temperature” complexes, which result from the reversible elimination of two CuX groups. A massive thermochromism effect results from the extinction of the strong MLCT band upon CuX elimination with increasing temperature. For all complexes, quantum chemical calculations predict a small and method‐dependent energy difference between the possible electronic structures, namely Cu^I and dicationic GFA ligand (closed‐shell singlet) versus Cu^II and neutral GFA ligand (triplet or broken‐symmetry state). The closed‐shell singlet state is disfavoured by hybrid‐DFT functionals, which mix in exact Hartree–Fock exchange, and is favoured by larger basis sets and consideration of a polar medium.     

Polymer‐based fluoride‐selective chemosensor: Synthesis,sensing property,and its use for the design of molecular‐scale logic devices

A new styryl‐type monomer, 2‐(4‐vinylbenzyloxy)‐1 ‐naphthaldehyde thiosemicarbazone (VNT), was synthesized and then copolymerized with methyl methacrylate (MMA) by reversible addition fragmentation chain transfer polymerization affording a series of poly(MMA‐co‐VNT)s with different functional unit content, predetermined molecular weight, and narrow molecular‐weight distribution. The desired copolymers were structurally confirmed by various spectroscopic characterizations. Colorimetric and fluorescent titration spectra revealed that the copolymers are highly selective toward fluoride anions over other competitive species including Cl^?, Br^?, I^?, H₂PO₄^?, AcO^?, and HSO₄^?. On addition of F^?, a remarkable colorless‐to‐yellow color change is easily observed by naked eyes. The influence of the copolymer composition and molecular weight on its sensing capacity was then carefully investigated. The results showed that higher VNT‐incorporation amount within the copolymer chains leads to higher sensitivity toward F^? ions. Interestingly, the chromogenic process of the polymeric sensor can be switched back and forth by successively adding F^? and HSO₄^? anions into the dimethyl sulfoxide solution of the polymer, which may be represented by a complementary “IMPLICATION/INHIBIT” logic gate at molecular level using both the ions as the chemical inputs. Based on such a reversible and reproducible sensing system, we designed a molecular‐scale sequential information processing circuit displaying “writing–reading–erasing–reading” behavior and “multiwrite” function in the form of binary logic. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation and characterization of Fe3O4@SiO2/APTPOSS core–shell composite nanomagnetics as a novel family of reusable catalysts and their application in the one‐pot synthesis of 1,3‐thiazolidin‐4‐one derivatives

Octakis[3‐(3‐aminopropyltriethoxysilane)propyl]octasilsesquioxane (APTPOSS) as a polyhedral oligomeric silsesquioxane derivative was prepared and used as a pioneer reagent to obtain a novel core–shell composite using magnetic iron oxide nanoparticles as the core and the inorganic–organic hybrid polyhedral oligomeric silsesquioxane as the shell. Fe₃O₄@SiO₂/APTPOSS were confirmed using Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, dynamic light scattering, thermogravimetric analysis, X‐ray diffraction and vibrating sample magnetometry. The inorganic–organic hybrid polyhedral oligomeric silsesquioxane magnetic nanoparticles were used as an efficient new heterogeneous catalyst for the one‐pot three‐component synthesis of 1,3‐thiazolidin‐4‐ones under solvent‐free conditions. Moreover, these nanoparticles could be easily separated using an external magnet and then reused several times without significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and Properties of Azide‐Functionalized Ionic Liquids as Attractive Hypergolic Fuels

Hypergolic ionic liquids (ILs) have shown a great promise as viable replacements for toxic and volatile hydrazine derivatives used as propellant fuels, and hence, have attracted increasing interest over the last decade. To take advantage of the reactivity and high energy density of the azido group, a family of low‐cost and easily prepared azide‐functionalized cation‐based ILs, including fuel‐rich anions, such as nitrate, dicyanamide, and nitrocyanamide anions, were synthesized and characterized. All the dicyanamide‐ and nitrocyanamide‐based ILs exhibited spontaneous combustion upon contact with 100 % HNO₃. The densities of these hypergolic ILs varied in the range 1.11–1.29 g cm^?3, and the density‐specific impulse, predicted based on Gaussian 09 calculations, was between 289.9 and 344.9 s g cm^?3. The values of these two key physical properties are much higher than those of unsymmetrical dimethylhydrazine (UDMH). Among the studied compounds, compound IL‐3b, that is, 1‐(2‐azidoethyl)‐1‐methylpyrrolidin‐1‐ium dicyanamide, shows excellent integrated properties including the lowest viscosity (30.9 M Pa s), wide liquid operating range (?70 to 205 °C), shortest ignition‐delay time (7 ms) with 100 % HNO₃, and superior density specific impulse (302.5 s g cm^?3), suggesting promising applications with potential as bipropellant formulations.     

Fabrication of Efficient Hydrogenation Nanoreactors by Modifying the Freedom of Ultrasmall Platinum Nanoparticles within Yolk–Shell Nanospheres

The synthesis of silica‐based yolk–shell nanospheres confined with ultrasmall platinum nanoparticles (Pt NPs) stabilized with poly(amidoamine), in which the interaction strength between Pt NPs and the support could be facilely tuned, is reported. By ingenious utilization of silica cores with different surface wettability (hydrophilic vs. ‐phobic) as the adsorbent, Pt NPs could be confined in different locations of the yolk–shell nanoreactor (core vs. hollow shell), and thus, exhibit different interaction strengths with the nanoreactor (strong vs. weak). It is interesting to find that the adsorbed Pt NPs are released from the core to the hollow interiors of the yolk–shell nanospheres when a superhydrophobic inner core material (SiO₂?Ph) is employed, which results in the preparation of an immobilized catalyst (Pt@SiO₂?Ph); this possesses the weakest interaction strength with the support and shows the highest catalytic activity (88 500 and 7080 h^?1 for the hydrogenation of cyclohexene and nitrobenzene, respectively), due to its unaffected freedom of Pt NPs for retention of the intrinsic properties.     

Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium‐sized [NTf₂]^? (0.230 nm³; Tf=CF₃SO₃^?) and the large [Al(hfip)₄]^? (0.581 nm³; hfip=OC(H)(CF₃)₂) anions were synthesized and characterized. Their temperature‐dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel–Fulcher–Tammann (VFT) behavior. Ion‐specific self‐diffusion constants were measured at room temperature by pulsed‐gradient stimulated‐echo (PGSTE) NMR experiments. In general, self‐diffusion constants of both cations and anions in [Al(hfip)₄]^?‐based ILs were higher than in [NTf₂]^?‐based ILs. Ionicities were calculated from self‐diffusion constants and measured bulk conductivities, and showed that [Al(hfip)₄]^?‐based ILs yield higher ionicities than their [NTf₂]^? analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)₄]^?‐based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)₄]^?. Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions.     

Nitration of Simple Aromatics with NO2 under Air Atmosphere in the Presence of Novel Brønsted Acidic Ionic Liquids

Abstract

Aromatics nitrate with NO₂/air catalyzed by novel Brønsted acidic ionic liquids (ILs) without any volatile chlorinated organic solvent under mild conditions. The ILs employed were caprolactam based, [Caprolactam]X (X^?=pTSO^?, BSO^?, BF₄ ^?, NO₃ ^?), which are of relatively lower cost and lower toxicity than traditional imidazolium‐based ILs. The nitration reactions were carried out at ?15 to ?0°C first, then at room temperature for a longer time with a little excessive NO₂ (ca. 1.4 eqv.) for moderate yield (for toluene). The IL could be reused four times.     

Elucidating Interactions between DMSO and Chelate‐Based Ionic Liquids

The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D₆]DMSO) and the C₂?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C₁₀mim]⁺ and anion [Mn(hfac)₃]^? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C₂?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution.     

Design and synthesis of "dumb-bell" and "triangular" inorganic-organic hybrid nanopolyoxometalate clusters and their characterisation through ESI-MS analyses

A series of tris(hydroxymethyl)aminomethane (TRIS)‐based linear (bis(TRIS)) and triangular (tris(TRIS)) ligands has been synthesised and were covalently attached to the Wells–Dawson type cluster [P₂V₃W₁₅O₆₂]^9? to generate a series of nanometer‐sized inorganic–organic hybrid polyoxometalate clusters. These huge hybrids, with a molecular mass similar to that of small proteins in the range of ≈10–16 kDa, were unambiguously characterised by using high‐resolution ESI‐MS. The ESI‐MS spectra of these compounds revealed, in negative ion mode, a characteristic pattern showing distinct groups of peaks corresponding to different anionic charge states ranging from 3^? to 8^? for the hybrids. Each peak in these individual groups could be unambiguously assigned to the corresponding hybrid cluster anion with varying combinations of tetrabutylammonium (TBA) and other cations. This study therefore highlights the prowess of the high‐resolution ESI‐MS for the unambiguous characterisation of large, nanoscale, inorganic–organic hybrid clusters that have huge mass, of the order of 10–16 kDa. Also, the designed synthesis of these compounds points to the fact that we were able to achieve a great deal of structural pre‐design in the synthesis of these inorganic–organic hybrid polyoxometalates (POMs) by means of a ligand design route, which is often not possible in traditional “one‐pot” POM synthesis.     

Polymerizable Molecular Silsesquioxane Cage Armored Hybrid Microcapsules with In Situ Shell Functionalization

We prepared core–shell polymer–silsesquioxane hybrid microcapsules from cage‐like methacryloxypropyl silsesquioxanes (CMSQs) and styrene (St). The presence of CMSQ can moderately reduce the interfacial tension between St and water and help to emulsify the monomer prior to polymerization. Dynamic light scattering (DLS) and TEM analysis demonstrated that uniform core–shell latex particles were achieved. The polymer latex particles were subsequently transformed into well‐defined hollow nanospheres by removing the polystyrene (PS) core with 1:1 ethanol/cyclohexane. High‐resolution TEM and nitrogen adsorption–desorption analysis showed that the final nanospheres possessed hollow cavities and had porous shells; the pore size was approximately 2–3 nm. The nanospheres exhibited large surface areas (up to 486 m² g^?1) and preferential adsorption, and they demonstrated the highest reported methylene blue adsorption capacity (95.1 mg g^?1). Moreover, the uniform distribution of the methacryloyl moiety on the hollow nanospheres endowed them with more potential properties. These results could provide a new benchmark for preparing hollow microspheres by a facile one‐step template‐free method for various applications.     

Challenges in predicting ΔrxnG in solution: Hydronium,hydroxide, and water autoionization

Standard non‐semiempirical continuum‐dielectric orbital‐based methods horribly overpredict, by 26‐50 kcal mol⁻¹, the Gibbs energy for the water autoionization reaction 2 H₂O_(l) → H₃O⁺_(aq) + OH^–_(aq). Here, we demonstrate these errors, fully investigate the reasons for these errors, and show that the use of 4 explicit solvent within the continuum (the “semicontinuum,” “cluster‐continuum,” or “hybrid” technique) can reduce the error of a standard continuum model from 50 to 2 kcal mol⁻¹. Results from pure cluster, pure continuum (several versions including semiempirical ones), and semicontinuum modeling are each presented and discussed. We recommend use of 3 waters around hydronium and 4 waters around hydroxide with standard continua whenever these ions are involved in reaction. To the possible surprise of some, time‐consuming molecular‐dynamics simulations are not needed to reproduce this problematic energy.