Chenliang Su

Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored.

Cell‐Assembled Graphene Biocomposite for Enhanced Chondrogenic Differentiation

Graphene-based nanomaterials are increasingly being explored for use as biomaterials for drug delivery and tissue engineering applications due to their exceptional physicochemical and mechanical properties. However, the two-dimensional nature of graphene makes it difficult to extend its applications beyond planar tissue culture. Here, graphene-cell biocomposites are used to pre-concentrate growth factors for chondrogenic differentiation. Bone marrow-derived mesenchymal stem cells (MSCs) are assembled with graphene flakes in the solution to form graphene-cell biocomposites. Increasing concentrations of graphene (G) and porous graphene oxide (pGO) are found to correlate positively with the extent of differentiation. However, beyond a certain concentration, especially in the case of graphene oxide, it will lead to decreased chondrogenesis due to increased diffusional barrier and cytotoxic effects. Nevertheless, these findings indicate that both G and pGO could serve as effective pre-concentration platforms for the construction of tissue-engineered cartilage and suspension-based cultures in vitro.

Tandem Catalysis of Amines Using Porous Graphene Oxide

Porous graphene oxide can be used as a metal-free catalyst in the presence of air for oxidative coupling of primary amines. Herein, we explore a GO-catalyzed carbon-carbon or/and carbon-heteroatom bond formation strategy to functionalize primary amines in tandem to produce a series of valuable products, i.e., α-aminophosphonates, α-aminonitriles, and polycyclic heterocompounds. Furthermore, when decorated with nano-Pd, the Pd-coated porous graphene oxide can be used as a bifunctional catalyst for tandem oxidation and hydrogenation reactions in the N-alkylation of primary amines, achieving good to excellent yields under mild conditions.

Heck Reactions Catalyzed by Ultrasmall and Uniform Pd Nanoparticles Supported on Polyaniline

Using air as the oxidant instead of the traditionally employed persulfates, the smaller and more uniform Pd nanoparticles (around 2 nm) supported on polyaniline (Pd@PANI) can be easily fabricated by the oxidation-polymerization of aniline with PdCl2. This material is an efficient and environmentally friendly catalyst for Heck reactions due to its recyclability, low loading, and ligand-free and mild reaction conditions. It was even tolerant to sulfur-containing substrates. This work reports the Pd@PANI-catalyzed Heck reactions with very wide substrate scopes, and discloses the catalytic mechanisms based on experimental findings and results of catalyst analysis and characterization.

Graphene Oxide and Its Functionalized Derivatives as Carbocatalysts in the Multicomponent Strecker Reaction of Ketones

Functionalized graphene oxide derivatives are found to be efficient and reusable carbocatalysts for the one‐pot multicomponent Strecker reaction of aldehydes and ketones under neat and open‐air conditions.

Properties of Strained Structures and Topological Defects in Graphene

Strain and defect engineering of graphene can modify the topological features of electronic states, leading to novel properties such as pseudomagnetism in bubbles and metallicity in extended topological defects. A consequence of graphene being a soft membrane is that it can be strain-engineered to become highly corrugated by modifying its adhesion to the substrate. Extended grain boundaries in graphene can be constructed from periodic combinations of nonhexagonal rings (5-7 pairs). However, a controlled method of producing these defects is not currently available. In this Perspective, we discuss some of the recent advances in studying the properties and formation mechanisms of strained structures and defects in graphene, extending across both physics and chemistry.

Recent advances in Fe (or Co)/N/C electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of fuel cells, especially polymer electrolyte membrane fuel cells. The recent emergence of Fe (or Co)/N/C catalysts has created tremendous opportunities for the development of non-precious metal catalysts for ORR in acidic media and thus presents great potential in the application of fuel cells. In this review, we summarize the recent advances in the Fe (or Co)/N/C catalysts for ORR in acidic media that have demonstrated comparable activity to the commercial Pt catalyst. The synthesis, structural characterization and underlying mechanism of Fe (or Co)/N/C catalysts are discussed. In addition, we highlight the interesting microstructures of the active site, new synthesis approaches, and the catalytic performances tuned by nonmetal heteroatom dopants. Finally, perspectives on the challenges and future opportunities are also discussed.

Polyquinoneimines for lithium storage: more than the sum of its parts

A straightforward synthetic strategy for the construction of electrode materials is demonstrated by the polymerization of two kinds of electrochemically active organic monomers without sacrificing specific capacity. Polyquinoneimines (PQIs), synthesised by the polycondensation reaction of 2,6-diaminoanthraquinone and the anhydrides, were used as a cathode in lithium ion batteries (LIBs). Electrochemical analysis such as CV and galvanostatic cycling reveals that PQIs exhibit the combined electrochemical properties of the two monomers. The mechanism of lithiation/delithiation of the PQIs has been investigated by means of electrochemical and spectroscopic (FTIR) analytical techniques. The as-prepared PQI-1 exhibits a higher specific capacity of 210 mA h g−1 and a better cycling performance (136 mA h g−1 after 200 cycles) compared with their polymeric precursors.

Room‐Temperature Ice Growth on Graphite Seeded by Nano‐Graphene Oxide

Water wetting on a hydrophobic surface at ambient conditions is disallowed by the non-polar nature of the surface and high vapor pressure of water. However, the presence of sub-millimeter sized hydrophilic patches allows the waxy wings of desert beetles to become wettable by morning mist. 5] Herein, we show that a sprinkle of graphene oxide nanoflakes (nanoGOs) is effective in condensing water nanodroplets and seeding ice epitaxy on graphite at ambient conditions. By controlling the relative humidity and nanoGO density, we are able to study the formation of a complete ice wetting layer on a time scale of 20 h. This presents an unprecedented opportunity to visualize ice nucleation and growth in real time using non-contact atomic force microscopy. The stages of crystallization, as proposed by Ostwald in 1897, are fully unfolded at a microscopic level for the first time. We obtain real-time imaging of the sequential phase transition from amorphous ice to a transient cubic ice Ic stage, and finally to the stable hexagonal ice Ih. Most interestingly, we discover that ice nucleation and growth can be influenced by modifying the functional groups of nanoGO and by intermolecular hydrogen-bonding between nanoGOs. This affords a strategy to control heterogeneous ice nucleation and snow crystal formation. 8] The interaction of water with solid surfaces is one of the most pervasive natural phenomena which underpins, for example, rain precipitation, snow formation, rock erosion. The wetting of surfaces by ambient water is also of crucial importance in many processes, such as heterogeneous catalysis, photocatalysis, microelectronics, and drug development. 3] In bulk ice which is formed below 0 8C, water molecules pack in a hexagonal ice Ih structure with four hydrogen bonds arranged in tetrahedral geometry. Above 0 8C, vibrational lattice instability leads to the liquid phase. 10] A new idea emerged recently, that the ice-toliquid phase transition crossing the freezing point may not apply in the two dimensional (2D) limit. Recent research revealed that at a hydrophilic interface, or by nanoconfinement, ice Ih wetting layers can persist even at ambient conditions. To date, insights into the hydration structure and wetting dynamics of ambient water on solids is derived mainly from studies on single-crystal metal surfaces carried out at cryogenic temperatures in vacuum conditions. 3,14] Molecular level studies of water/ice nucleation and growth on solid surfaces at ambient conditions remain a formidable challenge owing to the highly mobile nature of water molecules and its high vapor pressure. In our ice growth experiments, we use nanoGOs as ice nucleation seeds. These nanoGOs were heated in base and had a higher degree of restored sp conjugation than the assynthesized nanoGOs as well as carboxylate (COO ) groups on their periphery, as shown by vibrational spectroscopy (Figure S1 in the Supporting Information). After spin coating nanoGOs on a freshly peeled highly ordered pyrolytic graphite (HOPG), the samples were dried at 80 8C for 15 min before amplitude-modulated non-contact atomic force microscopy (NCAFM) imaging. The typical NCAFM amplitude setpoint for direct imaging of ice epitaxial domains is 2–3 nm. Using higher setpoints results in a perturbation of the wetting layer or even penetration of the water films (see Figure S2 for setpoints of 6 nm and > 10 nm). Penetration allows us to directly image the underlying substrate and determine the physical dimensions of nanoGOs, which have heights varying from 0.5 nm to several nm (Figure S2 and S3). Figure 1a illustrates the dynamic processes involved in room-temperature ice formation on graphite seeded by superhydrophilic nanoGOs. We modify the graphite substrate with 1–10% surface coverage of nanoGOs. The advantages of using the graphite surface as a template include its atomic flatness which does not disrupt the fragile hydrogen bonding in ice structures, and its ability to conduct the latent heat produced by ice condensation rapidly. The triangular sublattice of graphite (2.46 ) matches the natural ice structure very well. All these factors favor the epitaxial growth of a commensurate ffiffiffi

CAN-Mediated Highly Regio- and Stereoselective Oxidation of Vinylidenecyclopropanes: A Novel Method for the Synthesis of Unsymmetrical Divinyl Ketone and Functional Enone Derivatives

CAN-mediated oxidative rearrangement of various vinylidenecyclopropanes under mild conditions generates unsymmetrical divinyl ketone and functional enone derivatives in moderate to good yields with excellent regio- and stereoselectivities. The reaction mechanism was investigated on the basis of an oxygen-18 tracer experiment.