A Self‐Assembled Superhydrophobic Electrospun Carbon–Silica Nanofiber Sponge for Selective Removal and Recovery of Oils and Organic Solvents

An oil spill needs timely cleanup before it spreads and poses serious environmental threat to the polluted area. This always requires the cleanup techniques to be efficient and cost‐effective. In this work, a lightweight and compressible sponge made of carbon–silica nanofibers is derived from electrospinning nanotechnology that is low‐cost, versatile, and readily scalable. The fabricated sponge has high porosity (>99 %) and displays ultra‐hydrophobicity and superoleophilicity, thus making it a suitable material as an oil adsorbent. Owing to its high porosity and low density, the sponge is capable of adsorbing oil up to 140 times its own weight with its sorption rate showing solution viscosity dependence. Furthermore, sponge regeneration and oil recovery are feasible by using either cyclic distillation or mechanical squeezing.     

A 116-Nuclear Metallosupramolecular Cage-of-Cage Showing Multistep Single-Crystal-to-Single-Crystal Transformation

Here a unique single-crystal-to-single-crystal (SCSC) transformation of a 116-nuclear Au^I₇₂Cd^II₄₀Na^I₄ cage-of-cage ( 2 _CdNa) is reported, which was created from a trigold(I) metalloligand with d -penicillamine by way of a 9-nuclear Au^I₆Cd^II₃ cage ( 1 ). Cage-of-cage 2 _CdNa is composed of 12 cages of 1 that are linked by 4 Cd²⁺ and 4 Na⁺ ions, with its surface being covered by 12 NO₃⁻ ions to form a discrete, spherical molecule with a diameter ca. 4.7 nm. In crystal 2 _CdNa, the cage-of-cage molecules are packed in a cubic lattice with a huge cell volume of ca. 4.5×10⁵ ų_, so as to have large interstices with diameters of more than 3 nm. Upon soaking crystals 2 _CdNa in aqueous Cu(NO₃)₂, all Cd²⁺ and Na⁺ were quickly exchanged by Cu²⁺ to produce an analogous Au^I₇₂Cu^II₄₄ cage-of-cage ( 2 _Cu) in a SCSC manner. Prolonged soaking led to the SCSC transformation to another supramolecular structure ( 2′ _Cu) consisting of 152-nuclear Au^I₇₂Cu^II₈₀ cage-of-cages that are alternately H-bonded with the Au^I₇₂Cu^II₄₄ cage-of-cages. 2′ _Cu showed the accommodation of MoO₄²⁻ and the conversion of MoO₄²⁻ to β-Mo₈O₂₆⁴⁻ in the crystal, with retention of single-crystallinity.     

Solid‐state drawing of β‐nucleated polypropylene: Effect of additives on drawability and mechanical properties

Isotactic polypropylene (i‐PP) can crystallize in different crystal modifications. In this article, the effect of sepiolite (one‐dimensional) and carbon black (three‐dimensional) fillers on the solid‐state drawability of i‐PP is discussed. The cross‐hatched structure of thermodynamically most stable α‐crystal phase in i‐PP does not allow for perfect chain alignment during solid‐state drawing. The β‐phase i‐PP, obtained by addition of specific nucleating agents, crystallizes in a non‐cross‐hatched spherulitic structure and allows more easy drawing. Depending on the filler type, β–α transformation takes place at different draw ratios, as was observed by in situ wide‐angle X‐ray diffraction measurements. It was observed that β‐nucleated i‐PP has a lower yield stress and can be drawn further than i‐PP crystallized in the α‐crystal phase. If added in the right amount, both carbon black and sepiolite have a reinforcing effect on PP tapes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1071–1082     

Asymptotics in percolation on high‐girth expanders

We consider supercritical bond percolation on a family of high‐girth ‐regular expanders. The previous study of Alon, Benjamini and Stacey established that its critical probability for the appearance of a linear‐sized (“giant”) component is . Our main result recovers the sharp asymptotics of the size and degree distribution of the vertices in the giant and its 2‐core at any . It was further shown in the previous study that the second largest component, at any , has size at most for some . We show that, unlike the situation in the classical Erd?s‐Rényi random graph, the second largest component in bond percolation on a regular expander, even with an arbitrarily large girth, can have size for arbitrarily close to 1. Moreover, as a by‐product of that construction, we answer negatively a question of Benjamini on the relation between the diameter of a component in percolation on expanders and the existence of a giant component. Finally, we establish other typical features of the giant component, for example, the existence of a linear path.     

Electronic structural studies of pyrrolidinium-based ionic liquids for electrochemical application

Electrochemical stability and noncovalent interactions escorting the cyclic ammonium-based ionic liquids composed of N-alkyl-substituted N-methyl pyrrolidinium (P_yr1R) (R = methyl, ethyl, propyl, butyl, pentyl, hexyl) cations and four anions hexafluorophosphate (PF₆), tetrafluoroborate (BF₄), bis(trifluoromethylsulfonyl-imide (TFSI), and trifluoromethane sulfonate (TFO) have been analyzed using the density functional theory. Electronic structures, electrochemical window, frontier orbital energy difference (HOMO-LUMO gap), binding energies, vibrational spectra of these ion pairs were characterized. It has been established that ion pair formation is largely reigned by C H⋯F interactions between anionic fluorine for BF₄⁻ and PF₆⁻ anions and C H⋯O interactions between anionic oxygen for TFSI and TFO anions and pyrrolidinic proton, methyl, or alkyl group protons of the cations. The effect of alkyl chain length and pairing anions of the alkyl substituted N-methyl pyrrolidinium-based ionic liquids on the electrochemical window was investigated. The results revealed that the HOMO energy of pairing anions is the key factor to decide the electrochemical window. Further quantification of noncovalent interactions in terms of electrostatic and hydrogen bonding interactions has been brought out employing a novel method with the aid of Mulliken and Merz-Singh-Kollman charges, prevailed in pyrrolidinium-based ionic liquids.     

Electrosprayed NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles for long cycle life and high-power Li-ion battery anode

Electrospraying-based synthesis of NiCo₂O₄ (NCO-ES) nanoparticles that exhibit long cycle life and high rate capability is reported. The results are compared with a conventionally prepared NiCo₂O₄ sample by direct annealing (NCO-DA). The structure and morphology of NCO-ES and NCO-DA nanoparticles have been characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy to confirm the size, morphology, structure, and surface chemistry of the as-prepared samples. Electrochemical testing established that the NCO-ES sample displayed enhanced Li-ion storage performance. The NCO-ES delivered a discharge capacity of almost 370 mAh/g at the end of 50 cycles at 1C rate (890 mA/g) while only 180 mAh/g was retained for the NCO-DA sample at the same condition. At a high rate of 5C (4450 mA/g), NCO-ES electrodes delivered a stabilized specific capacity of 225 mAh/g with almost 100% Coulombic efficiency over 1000 cycles. Its rate capability and cycle life were found to be superior to NCO-DA electrodes. The nanoscale grain boundaries in the NCO-ES sample enhanced the lithium-ion diffusion and enabled high rate capability. The impedance analysis at different stages of lithiation/delithiation indicates a lower impedance and better kinetics as one of the reasons for better performance of the NCO-ES sample.