Graphene Oxide Facilitates Solvent‐Free Synthesis of Well‐Dispersed,Faceted Zeolite Crystals

Zeolites with molecular dimension pores are widely used in petrochemical and fine‐chemical industries. While traditional solvothermal syntheses suffer from environmental, safety, and efficiency issues, the newly developed solvent‐free synthesis is limited by zeolite crystal aggregation. Herein, we report well‐dispersed and faceted silicalite ZSM‐5 zeolite crystals obtained using a solvent‐free synthesis facilitated by graphene oxide (GO). The selective interactions between the GO sheets and different facets, which are confirmed by molecular dynamics simulations, result in oriented growth of the ZSM‐5 crystals along the c‐axis. More importantly, the incorporation of GO sheets into the ZSM‐5 crystals leads to the formation of mesopores. Consequently, the faceted ZSM‐5 crystals exhibit hierarchical pore structures. This synthetic method is superior to conventional approaches because of the features of the ZSM‐5 zeolite.     

Deformation of single‐walled carbon nanotubes by interaction with graphene: A first‐principles study

The interaction between single‐walled carbon nanotubes (SWNTs) and graphene were studied with first‐principles calculations. Both SWNTs and single‐layer graphene (SLG) or double‐layer graphene (DLG) display more remarkable deformations with the increase of SWNT diameter, which implies a stronger interaction between SWNTs and graphene. Besides, in DLG, deformation of the upper‐layer graphene is less than in SLG. Zigzag SWNTs show stronger interactions with SLG than armchair SWNTs, whereas the order is reversed for DLG, which can be interpreted by the mechanical properties of SWNTs and graphene. Density of states and band structures were also studied, and it was found that the interaction between a SWNT and graphene is not strong enough to bring about obvious influence on the electronic structures of SWNTs. © 2015 Wiley Periodicals, Inc.     

Direct Patterning and Biofunctionalization of a Large‐Area Pristine Graphene Sheet

Direct patterning of streptavidin and NIH 3T3 fibroblast cells was successfully achieved over a large‐area pristine graphene sheet on Si/SiO₂ by aryl azide‐based photografting with the conventional UV lithographic technique and surface‐initiated, atom transfer radical polymerization of oligo(ethylene glycol) methacrylate.     

Reactivity of Graphene and Hexagonal Boron Nitride In‐Plane Heterostructures with Oxygen: A DFT Study

A density‐functional study has been undertaken to investigate the chemical properties of in‐plane heterostructures of graphene and hexagonal boron nitride. The interactions of armchair and zigzag linking edges with oxygen are looked at in detail. The results of the calculations indicate that the linking edges are highly reactive to oxygen atoms and predict that oxygen molecules can accordingly be adsorbed dissociatively. Furthermore, because oxygen atoms cooperatively interact with the heterostructures, the process can lead to opening of the linking edges, thus splitting the two materials.     

Oxidative Degradation of trans‐1,4‐Polyisoprene Cast Films and Single Crystals by Enzyme‐Mediator Systems

Depolymerization and morphological changes of cast films and single crystals of trans‐1,4‐polyisoprene with three enzyme‐mediator systems, lipoxygenase/linoleic acid (LPO/LH), horseradish peroxidase/1‐hydroxybenzotriazole (HRP/1‐HBT) and laccase/1‐hydroxybenzotriazole/linoleic acid (laccase/1‐HBT/LH), were investigated by scanning electron microscopy and gel permeation chromatography. Treatment of cast film with a LPO/LH system involving radical generation via lipid peroxidation led to a marked decrease in the molecular weight of polymers. LPO/LH system resulted in the morphological damage of single crystals of trans‐1,4‐polyisoprene. Laccase/1‐HBT/LH also destroyed the single crystals and depolymerized emulsified trans‐1,4‐polyisoprene. On the contrary, spherulites appeared on the surface of cast films and the molecular weight slightly decreased after treatment with HRP/1‐HBT, indicating that the amorphous region was predominantly degraded and the crystal region remained unchanged. The morphology of single crystals remained unchanged during the treatment of HRP/1‐HBT system for 6 d. In addition, Fenton reagent/linoleic acid was used as a chemical initiator of lipid peroxidation for degradation of trans‐1,4‐polyisoprene cast films. This system reduced molecular weight of the cast films, as well as LPO/LH system.

Scanning electron micrographs of trans‐1,4‐polyisoprene single crystals before (A) and after (B) treatment with the lipoxygenase/linoleic acid system.     

Functionalizing Single Crystals: Incorporation of Nanoparticles Inside Gel‐Grown Calcite Crystals

Synthetic single crystals are usually homogeneous solids. Biogenic single crystals, however, can incorporate biomacromolecules and become inhomogeneous solids so that their properties are also extrinsically regulated by the incorporated materials. The discrepancy between the properties of synthetic and biogenic single crystals leads to the idea to modify the internal structure of synthetic crystals to achieve nonintrinsic properties by incorporation of foreign material. Intrinsically colorless and diamagnetic calcite single crystals are turned into colored and paramagnetic solids, through incorporation of Au and Fe₃O₄ nanoparticles without significantly disrupting the crystalline lattice of calcite. The crystals incorporate the nanoparticles and gel fibers when grown in agarose gel media containing the nanoparticles, whereas the solution‐grown crystals do not. As such, our work extends the long‐history gel method for crystallization into a platform to functionalize single‐crystalline materials.     

Visualizing Phase Segregation in Mixed‐Halide Perovskite Single Crystals

Mixed organolead halide perovskites (MOHPs), CH₃NH₃Pb(Br_xI_1?x)₃, have been shown to undergo phase segregation into iodide‐rich domains under illumination, which presents a major challenge to their development for photovoltaic and light‐emitting devices. Recent work suggested that phase‐segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm³) monocrystalline MAPb(Br_xI_1?x)₃ single crystals is presented. The direct visualization of the growth of nanocluster‐like I‐rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time‐resolved spectroscopy provided new insight into the nature of the phase‐segregated domains and the collective impact on the optoelectronic properties.     

Characteristic Spectral Patterns in the Carbon‐13 Nuclear Magnetic Resonance Spectra of Hexagonal and Crenellated Graphene Fragments

Nuclear magnetic resonance (NMR) spectroscopy is an important molecular characterisation method that may aid the synthesis and production of graphenes, especially the molecular‐scale graphene nanoislands that have gathered significant attention due to their potential electronic and optical applications. Herein, carbon‐13 NMR chemical shifts were calculated using density functional theory methods for finite, increasing‐size fragments of graphene, hydrogenated graphene (graphane) and fluorinated graphene (fluorographene). Both concentric hexagon‐shaped (zigzag boundary) and crenellated (armchair) fragments were investigated to gain information on the effect of different types of flake boundaries. Convergence trends of the ¹³C chemical shift with respect to increasing fragment size and the boundary effects were found and rationalised in terms of low‐lying electronically excited states. The results predict characteristic behaviour in the ¹³C NMR spectra. Particular attention was paid to the features of the signals arising from the central carbon atoms of the fragments, for graphene and crenellated graphene on the one hand and graphane and fluorographene on the other hand, to aid the interpretation of the overall spectral characteristics. In graphene, the central nuclei become more shielded as the system size increases whereas the opposite behaviour is observed for graphane and fluorographene. The ¹³C signals from some of the perimeter nuclei of the crenellated fragments obtain smaller and larger chemical shift values than central nuclei for graphene and graphane/fluorographene, respectively. The diameter of the graphenic quantum dots with zigzag boundary correlates well with the predicted carbon‐13 chemical shift range, thus enabling estimation of the size of the system by NMR spectroscopy. The results provide data of predictive quality for future NMR analysis of the graphene nanoflake materials.     

Heterostructures through Divergent Edge Reconstruction in Nitrogen‐Doped Segmented Graphene Nanoribbons

Atomically precise engineering of defined segments within individual graphene nanoribbons (GNRs) represents a key enabling technology for the development of advanced functional device architectures. Here, the bottom‐up synthesis of chevron GNRs decorated with reactive functional groups derived from 9‐methyl‐9H‐carbazole is reported. Scanning tunneling and non‐contact atomic force microscopy reveal that a thermal activation of GNRs induces the rearrangement of the electron‐rich carbazole into an electron‐deficient phenanthridine. The selective chemical edge‐reconstruction of carbazole‐substituted chevron GNRs represents a practical strategy for the controlled fabrication of spatially defined GNR heterostructures from a single molecular precursor.     

Concise,Single‐Step Synthesis of Sulfur‐Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

The concise synthesis of sulfur‐enriched graphene for battery applications is reported. The direct treatment of graphene oxide (GO) with the commercially available Lawesson's reagent produced sulfur‐enriched‐reduced GO (S‐rGO). Various techniques, such as X‐ray photoelectron spectroscopy (XPS), confirmed the occurrence of both sulfur functionalization and GO reduction. Also fabricated was a nanohybrid material by using S‐rGO with polyoxometalate (POM) as a cathode‐active material for a rechargeable battery. Transmission electron microscopy (TEM) revealed that POM clusters were individually immobilized on the S‐rGO surface. This battery, based on a POM/S‐rGO complex, exhibited greater cycling stability for the charge‐discharge process than a battery with nanohybrid materials positioned between the POM and nonenriched rGO. These results demonstrate that the use of sulfur‐containing groups on a graphene surface can be extended to applications such as the catalysis of electrochemical reactions and electrodes in other battery systems.     

Truxene‐Based Columnar Liquid Crystals: Self‐Assembled Structures and Electro‐Active Properties

Columnar liquid‐crystalline (LC) truxene derivatives containing branched flexible alkyl chains have been designed and synthesized. The dicyanomethylene and dithiafulvene substituents have been introduced into the π‐conjugated truxene framework to tune their electronic and redox properties as well as the molecular assembled structures. The π‐conjugated cores of dicyanomethylene‐ and dithiafulvene‐appended truxenes adopt bowl‐shaped conformations, giving rise to a large intrinsic dipole moment perpendicular to the aromatic framework. These molecules form stable columnar LC structures through intermolecular dipole–dipole interactions. The redox properties of LC truxene derivatives have been examined by cyclic voltammetry. The dicyanomethylene‐appended truxene shows the reversible four‐step electrochemical reductions, whereas the dithiafulvene‐appended truxene undergoes three‐step oxidations.     

“Click”‐Triggered Self‐Healing Graphene Nanocomposites

Strategies to compensate material fatigue are among the most challenging issues, being most prominently addressed by the use of nano‐ and microscaled fillers, or via new chemical concepts such as self‐healing materials. A capsule‐based self‐healing material is reported, where the adverse effect of reduced tensile strength due to the embedded capsules is counterbalanced by a graphene‐based filler, the latter additionally acting as a catalyst for the self‐healing reaction. The concept is based on “click”‐based chemistry, a universal methodology to efficiently link components at ambient reaction conditions, thus generating a “reactive glue” at the cracked site. A capsule‐based healing system via a graphene‐based Cu₂O (TRGO‐Cu₂O‐filler) is used, acting as both the catalytic species for crosslinking and the required reinforcement agent within the material, in turn compensating the reduction in tensile strength exerted by the embedded capsules. Room‐temperature self‐healing within 48 h is achieved, with the investigated specimen containing TRGO‐Cu₂O demonstrating significantly faster self‐healing compared to homogeneous (Cu(PPh₃)₃F, Cu(PPh₃)₃Br), and heterogeneous (Cu/C) copper(I) catalysts.

     

Enhanced Oxygen Reduction Reactions in Fuel Cells on H‐Decorated and B‐Substituted Graphene

In the light of recent experimental research on the oxygen reduction reaction (ORR) with carbon materials doped with foreign atoms, we study the performance of graphene with different defects on this catalytic reaction. In addition to the reported N‐graphene, it is found that H‐decorated and B‐substituted graphene can also spontaneously promote this chemical reaction. The local high spin density plays the key role, facilitating the adsorption of oxygen and OOH, which is the start of ORR. The source of the high spin density for all of the doped graphene is attributed to unpaired single π electrons. Meanwhile, the newly formed C? H covalent bond introduces a higher barrier to the p electron flow, leading to more localized and higher spin density for H‐decorated graphene. At the same time, larger structural distortion should be avoided, which could impair the induced spin density, such as for P‐substituted graphene.     

Direct‐methanol Fuel Cell Based on Functionalized Graphene Oxide with Mono‐metallic and Bi‐metallic Nanoparticles: Electrochemical Performances of Nanomaterials for Methanol Oxidation

The catalysts based on 2‐aminoethanethiol functionalized graphene oxide (AETGO) with several mono‐metallic and bi‐metallic nanoparticles such as rod gold (rAuNPs), rod silver (rAgNPs), rod gold‐platinum (rAu‐Pt NPs) and rod silver‐platinum (rAg‐Pt NPs) were synthesized. The successful synthesis of nanomaterials was confirmed by various methods. The effective surface area (ESA) of the rAu‐Pt NPs/AETGO is 1.44, 1.64 and 2.40 times higher than those of rAg‐Pt NPs/AETGO, rAuNPs/AETGO and rAgNPs/AETGO, respectively, under the same amount of Pt. The rAu‐Pt NPs/AETGO exhibited a higher peak current for methanol oxidation than those of comparable rAg‐Pt NPs/AETGO under the same amount of Pt loading.