Qiaoliang Bao

The chemistry of graphene

A review on the latest developments on graphene, written from the perspective of a chemist, is presented. The role of chemistry in bringing graphene research to the next level is discussed.

Electrocatalytically Active Graphene–Porphyrin MOF Composite for Oxygen Reduction Reaction

Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORR) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron-porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron-porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron-porphyrin. The graphene-metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell.

Large energy soliton erbium-doped fiber laser with a graphene-polymer composite mode locker

Due to its unique electronic property and the Pauli blocking principle, atomic layer graphene possesses wavelength-independent ultrafast saturable absorption, which can be exploited for the ultrafast photonics application. Through chemical functionalization, a graphene-polymer nanocomposite membrane was fabricated and first used to mode lock a fiber laser. Stable mode locked solitons with 3 nJ pulse energy, 700 fs pulse width at the 1590 nm wavelength have been directly generated from the laser. We show that graphene-polymer nanocomposites could be an attractive saturable absorber for high power fiber laser mode locking.

Large energy mode locking of an erbium-doped fiber laser with atomic layer graphene

We report on large energy pulse generation in an erbium-doped fiber laser passively mode-locked with atomic layer graphene. Stable mode locked pulses with single pulse energy up to 7.3 nJ and pulse width of 415 fs have been directly generated from the laser. Our results show that atomic layer graphene could be a promising saturable absorber for large energy mode locking.

Z-scan measurement of the nonlinear refractive index of graphene

Han Zhang, Stéphane Virally, Qiaoliang Bao, Kian Ping Loh, Serge Massar, Nicolas Godbout, and Pascal Kockaert OPERA-photonics, Université libre de Bruxelles, 50 Av. F. D. Roosevelt, CP 194/5, B-1050 Bruxelles, Belgium Engineering Physics Department, École polytechnique de Montréal, P.O. Box 6079, Station Centre-ville, Montréal (Québec), H3C 3A7 Canada Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 Laboratoire d’information quantique, CP 225, Université libre de Bruxelles, 50 Av. F. D. Roosevelt, B-1050 Bruxelles, Belgium ∗Corresponding author: hzhang@ulb.ac.be, smassar@ulb.ac.beUnder strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n(2)≃10(-7) cm(2) W(-1), almost 9 orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.

Electrochemical delamination of CVD-grown graphene film: toward the recyclable use of copper catalyst.

The separation of chemical vapor deposited (CVD) graphene from the metallic catalyst it is grown on, followed by a subsequent transfer to a dielectric substrate, is currently the adopted method for device fabrication. Most transfer techniques use a chemical etching method to dissolve the metal catalysts, thus imposing high material cost in large-scale fabrication. Here, we demonstrate a highly efficient, nondestructive electrochemical route for the delamination of CVD graphene film from metal surfaces. The electrochemically delaminated graphene films are continuous over 95% of the surface and exhibit increasingly better electronic quality after several growth cycles on the reused copper catalyst, due to the suppression of quasi-periodical nanoripples induced by copper step edges. The electrochemical delamination process affords the advantages of high efficiency, low-cost recyclability, and minimal use of etching chemicals.

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.

Graphene mode locked, wavelength-tunable, dissipative soliton fiber laser

Atomic layer graphene possesses wavelength-insensitive ultrafast saturable absorption, which can be exploited as a “full-band” mode locker. Taking advantage of the wide band saturable absorption of the graphene, we demonstrate experimentally that wide range (1570–1600 nm) continuous wavelength tunable dissipative solitons could be formed in an erbium doped fiber laser mode locked with few layer graphene.

A Graphene Oxide–Organic Dye Ionic Complex with DNA‐Sensing and Optical‐Limiting Properties

Graphene oxide (GO), a nonstoichiometric, two-dimensionalcarbonsheetresultingfromacidexfoliationofgraphite,offersa new class of solution-dispersible polyaromatic platform forperforming chemistry. Graphene oxide bears covalentlybound epoxide (1,2-ether) and hydroxyl functional groupson either side of its basal plane, while carboxyl groups arelocated at the edge sites.

Microstructuring of Graphene Oxide Nanosheets Using Direct Laser Writing

Graphene(G),a single atomiclayer ofaromatic carbon atoms,has attracted much attention recently owing to its fascinating properties such as massless fermions, ballistic electronic transport, and ultrahigh electron mobility. [1] Currently, there are many approaches to the synthesis of graphene ranging from chemical vapor deposition from hydrocarbon to solution phase methods involving the chemical exfoliation of graphite. [2] One commonly used solution-processing route to graphene involved the chemical reduction of graphene oxide (GO). GO is produced by the oxidative treatment of graphite. [2] The basal planes of GO are decorated with epoxide and hydroxyl groups, while carboxylic and carbonyl groups are located at the edges. These oxygen functionalities render GO hydrophilic and improve its solubility, however they destroy the aromaticity of the graphene framework. As a result, GO is insulating, and a chemical reduction and thermal annealing treatment is needed before electronic conductivity could be recovered. The presence of oxygen functional groups also reduces the thermal stability of GO relative to that of G, since GO can be thermally pyrolized at high temperatures and transformed into volatile carbonaceous oxides. The thermal instability of GO motivates us to consider a strategy for the microstructuing of GO nanosheets using laser-assisted etching. The microstructuring of GO is relevant to the challenges of lithographically patterning G, since GO and G are interconvertible to some extent. Recently, promising approaches for the patterned assemblies of G on substrates have been developed. [3–8] Micro-contact printing using molecular templates was used to transfer GO sheets onto the pre-defined areas of the substrate surfaces via electrostatic attachment. [3] Large-scale G films were recently synthesized on patterned nickel layers using chemical vapor deposition. [7] All the patterning methods reported so far involved conventional lithographic techniques or employment of masks for the definition of patterns on substrates. To date, there are few demonstrations of a maskless, direct ‘‘writing’’ pattern on G-related materials using electron beam or optical methods.