Self-Assembled Organic Nanowires for High Power Density Lithium Ion Batteries

The electroactive organic materials are promising alternatives to inorganic electrode materials for the new generation of green Li-ion batteries due to their sustainability, environmental benignity, and low cost. Croconic acid disodium salt (CADS) was used as Li-ion battery electrode, and CADS organic wires with different diameters were fabricated through a facile synthetic route using antisolvent crystallization method to overcome the challenges of low electronic conductivity of CADS and lithiation induced strain. The CADS nanowire exhibits much better electrochemical performance than its crystal bulk material and microwire counterpart. CADS nanowire with a diameter of 150 nm delivers a reversible capability of 177 mAh g^–1 at a current density of 0.2 C and retains capacity of 170 mAh g^–1 after 110 charge/discharge cycles. The nanowire structure also remarkably enhances the kinetics of croconic acid disodium salt. The CADS nanowire retains 50% of the 0.1 C capacity even when the current density increases to 6 C. In contrast, the crystal bulk and microwire material completely lose their capacities when the current density merely increases to 2 C. Such a high rate performance of CADS nanowire is attributed to its short ion diffusion pathway and large surface area, which enable fast ion and electron transport in the electrode. The theoretical calculation suggests that lithiation of CADS experiences an ion exchange process. The sodium ions in CADS will be gradually replaced by lithium ions during the lithiation and delithiation of CADS electrode, which is confirmed by inductively coupled plasma test

PEGylated Graphene Oxide-Mediated Protein Delivery for Cell Function Regulation

Delivery of proteins into cells may alter cellular functions as various proteins are involved in cellular signaling by activating or deactivating the corresponding pathways and, therefore, can be used in cancer therapy. In this study, we have demonstrated for the first time that PEGylated graphene oxide (GO) can be exploited as a nanovector for efficient delivery of proteins into cells. In this approach, GO was functionalized with amine-terminated 6-armed polyethylene glycol (PEG) molecules, thereby providing GO with proper physiological stability and biocompatibility. Proteins were then loaded onto PEG-grafted GO (GO-PEG) with high payload via noncovalent interactions. GO-PEG could deliver proteins to cytoplasm efficiently, protecting them from enzymatic hydrolysis. The protein delivered by GO-PEG reserves its biological activity that regulates the cell fate. As a result, delivery of ribonuclease A (RNase A) led to cell death and transport of protein kinase A (PKA) induced cell growth. Taken together, this work demonstrated the feasibility of PEGlyated GO as a promising protein delivery vector with high biocompatibility, high payload capacity and, more importantly, capabilities of protecting proteins from enzymatic hydrolysis and retaining their biological functions

Graphene-Catalyzed Direct Friedel–Crafts Alkylation Reactions: Mechanism, Selectivity, and Synthetic Utility

Transition-metal-catalyzed alkylation reactions of arenes have become a central transformation in organic synthesis. Herein, we report the first general strategy for alkylation of arenes with styrenes and alcohols catalyzed by carbon-based materials, exploiting the unique property of graphenes to produce valuable diarylalkane products in high yields and excellent regioselectivity. The protocol is characterized by a wide substrate scope and excellent functional group tolerance. Notably, this process constitutes the first general application of graphenes to promote direct C–C bond formation utilizing polar functional groups anchored on the GO surface, thus opening the door for an array of functional group alkylations using benign and readily available graphene materials. Mechanistic studies suggest that the reaction proceeds via a tandem catalysis mechanism in which both of the coupling partners are activated by interaction with the GO surface

Combined Effect of Porosity and Surface Chemistry on the Electrochemical Reduction of Oxygen on Cellular Vitreous Carbon Foam Catalyst

A new mechanism of O₂ reduction, which follows principles different from those generally accepted for describing ORR reduction on heteroatom-doped carbons, is suggested. It is based on the ability of oxygen to strongly adsorb in narrow hydrophobic pores. In this respect, a cellular vitreous carbon foam–graphene oxide composite was synthesized. The materials were doped with sulfur and nitrogen and/or heat-treated at 950 °C in order to modify their surface chemistry. The resultant samples presented a macro-/microporous nature and were tested as ORR catalysts. To understand the reduction process, their surfaces were extensively characterized from texture and chemistry points of view. The treatment applied markedly changed the volumes of small micropores and the surface hydrophilicity/polarity character. The results showed that the electron transfer number was between 3.87 and 3.96 and the onset potential reached 0.879 V for the best-performing sample. It is noteworthy that the best-performing sample has the highest volume of pores smaller than 0.7 nm while there was no heteroatom doping. The hydrophobicity and the strong adsorption forces provided by these pores to pull oxygen inside are the possible reasons for the observed excellent performance. A decrease in the volume of these pores resulted in a decrease in the catalytic performance. When the surface was modified with heteroatoms, the performances worsened further because of the induced hydrophilicity

Structural Transformation of Li-Excess Cathode Materials via Facile Preparation and Assembly of Sonication-Induced Colloidal Nanocrystals for Enhanced Lithium Storage Performance

A surfactant-free sonication-induced route is developed to facilely prepare colloidal nanocrystals of Li-excess layered Li_1.2Mn_0.54Ni_0.13­Co_0.13O₂ (marked as LMNCO) material. The sonication process plays a critical role in forming LMNCO nanocrystals in ethanol (ethanol molecules marked as EtOHs) and inducing the interaction between LMNCO and solvent molecules. The formation mechanism of LMNCO–EtOH supramolecules in the colloidal dispersion system is proposed and examined by the theoretical simulation and light scattering technique. It is suggested that the as-formed supramolecule is composed of numerous ethanol molecules capping the surface of the LMNCO nanocrystal core via hydrogen bonding. Such chemisorption gives rise to dielectric polarization of the absorbed ethanol molecules, resulting in a negative surface charge of LMNCO colloids. The self-assembly behaviors of colloidal LMNCO nanocrystals are then tentatively investigated by tuning the solvent evaporation condition, which results in diverse superstructures of LMNCO materials after the evaporation of ethanol. The reassembled LMNCO architectures exhibit remarkably improved capacity and cyclability in comparison with the original LMNCO particles, demonstrating a very promising cathode material for high-energy lithium-ion batteries. This work thus provides new insights into the formation and self-assembly of multiple-element complex inorganic colloids in common and surfactant-free solvents for enhanced performance in device applications

P‑Doped Porous Carbon as Metal Free Catalysts for Selective Aerobic Oxidation with an Unexpected Mechanism

An extremely simple and rapid (seconds) approach is reported to directly synthesize gram quantities of P-doped graphitic porous carbon materials with controlled P bond configuration. For the first time, it is demonstrated that the P-doped carbon materials can be used as a selective metal free catalyst for aerobic oxidation reactions. The work function of P-doped carbon materials, its connectivity to the P bond configuration, and the correlation with its catalytic efficiency are studied and established. In direct contrast to N-doped graphene, the P-doped carbon materials with higher work function show high activity in catalytic aerobic oxidation. The selectivity trend for the electron donating and withdrawing properties of the functional groups attached to the aromatic ring of benzyl alcohols is also different from other metal free carbon based catalysts. A unique catalytic mechanism is demonstrated, which differs from both GO and N-doped graphene obtained by high temperature nitrification. The unique and unexpected catalytic pathway endows the P-doped materials with not only good catalytic efficiency but also recyclability. This, combined with a rapid, energy saving approach that permits fabrication on a large scale, suggests that the P-doped porous materials are promising materials for “green catalysis” due to their higher theoretical surface area, sustainability, environmental friendliness, and low cost

Direct Production of Graphene Nanosheets for Near Infrared Photoacoustic Imaging

Hummers method is commonly used for the fabrication of graphene oxide (GO) from graphite particles. The oxidation process also leads to the cutting of graphene sheets into small pieces. From a thermodynamic perspective, it seems improbable that the aggressive, somewhat random oxidative cutting process could directly result in graphene nanosheets without destroying the intrinsic π-conjugated structures and the associated exotic properties of graphene. In Hummers method, both KMnO₄ and NO₂⁺ (nitronium ions) in concentrated H₂SO₄ solutions act as oxidants <i>via</i> different oxidation mechanisms. From both experimental observations and theoretical calculations, it appears that KMnO₄ plays a major role in the observed oxidative cutting and unzipping processes. We find that KMnO₄ also limits nitronium oxidative etching of graphene basal planes, therefore slowing down graphene fracturing processes for nanosheet fabrication. By intentionally excluding KMnO₄ and exploiting pure nitronium ion oxidation, aided by the unique thermal and kinetic effects induced by microwave heating, we find that graphite particles can be converted into graphene nanosheets with their π-conjugated aromatic structures and properties largely retained. Without the need of any postreduction processes to remove the high concentration of oxygenated groups that results from Hummers GO formation, the graphene nanosheets as-fabricated exhibit strong absorption, which is nearly wavelength-independent in the visible and near-infrared (NIR) regions, an optical property typical for intrinsic graphene sheets. For the first time, we demonstrate that strong photoacoustic signals can be generated from these graphene nanosheets with NIR excitation. The photo-to-acoustic conversion is weakly dependent on the wavelength of the NIR excitation, which is different from all other NIR photoacoustic contrast agents previously reported