Sodide and Organic Halides Effect Covalent Functionalization of Single-Layer and Bilayer Graphene

International audienc

Sodide and Organic Halides Effect Covalent Functionalization of Single-Layer and Bilayer Graphene

International audienc

Mesoscopic magnetic iron oxide spheres for high performance Li-ion battery anode: a new pulsed laser induced reactive micro-bubble synthesis process

International audienc

Mesoscopic magnetic iron oxide spheres for high performance Li-ion battery anode: a new pulsed laser induced reactive micro-bubble synthesis process

International audienc

A comparative evaluation of differently synthesized high surface area carbons for Li-ion hybrid electrochemical supercapacitor application: Pore size distribution holds the key

We report a comparative evaluation of carbonaceous cathodes synthesized by different protocols in the context of Li-ion hybrid electrochemical supercapacitors (Li-HEC) application. The four cathode materials compared include hierarchically perforated graphene (HPGN), Polymer (Poly (4-styrene sulfonic acid-co-maleic acid) sodium salt) derived Graphene (PDG), dead Neem leaves derived carbon (LDC) and commercial activated carbon (CAC). All these carbons exhibit high specific surface area with excellent porosity. In the single electrode configuration (vs. Li), HPGN shows maximum specific capacitance of ∼155 F g−1 with good cycleability over 1000 cycles (99.5% retention). On the other hand, there is no obvious distinctive difference between the specific capacitance values for the rest of the carbonaceous materials tested. The Li-HEC is constructed with spinel phase Li4Ti5O12 anode and carbonaceous materials described above as cathode in a non-aqueous medium. Amongst the various cases the Li-HEC with HPGN delivered maximum energy and corresponding power density of 65 Wh kg–1 and 0.5 kW kg−1, respectively with excellent cycleability as compared to the rest of the materials, tested in the same configuration under the same testing conditions.NRF (Natl Research Foundation, S’pore)Accepted versio

Effect of Copper Substrate Surface Orientation on the Reductive Functionalization of Graphene

Although substrate composition can influence the chemical reactivity of graphene, substrate lattice orientation provides a valuable alternative. The effect of Cu surface orientation on the reactivity of graphene was explored through a reductive transformation. Among the substrates tested, only Cu(111) led to the efficient, fast and uniform functionalization of graphene, as demonstrated by Raman mapping, and this arose from compressive strain induced by Cu(111). Functionalization effectively relaxes the strain, which can be subsequently reintroduced after thermal treatment. Theoretical calculations showed how compression facilitates the reduction and hybridization of carbon atoms, while coupling experiments revealed how kinetics may be used to control the reaction. The number of graphene layers and their stacking modes were also found to be important factors. In a broader context, a description of how graphene undergoes chemical modification when positioned on certain metal substrates is provided

Birch-Type Hydrogenation of Few-Layer Graphenes: Products and Mechanistic Implications

Few-layer graphenes, supported on Si with a superficial oxide layer, were subjected to a Birch-type reduction using Li and H2O as the electron and proton donors, respectively. The extent of hydrogenation for bilayer graphene was estimated at 1.6-24.1% according to Raman and X-ray photoelectron spectroscopic data. While single-layer graphene reacts uniformly, few-layer graphenes were hydrogenated inward from the edges and/or defects. The role of these reactive sites was reflected in the inertness of pristine few-layer graphenes whose edges were sealed. Hydrogenation of labeled bilayer (12C/13C) and trilayer (12C/13C/12C) graphenes afforded products whose sheets were hydrogenated to the same extent, implicating passage of reagents between the graphene layers and equal decoration of each graphene face. The reduction of few-layer graphenes introduces strain, allows tuning of optical transmission and fluorescence, and opens synthetic routes to long sought-after films containing sp3-hybridized carbon.clos

Sodide and Organic Halides Effect Covalent Functionalization of Single-Layer and Bilayer Graphene

The covalent functionalization of single and bilayer graphene on SiO2 (300 nm)/Si was effected through sequential treatment with the alkalide reductant [K(15-crown-5)2]Na and electrophilic aryl or alkyl halides, of which the iodides proved to be the most reactive. The condensation reactions proceeded at room temperature and afforded the corresponding aryl- or alkyl-appended graphenes. For each sample, Raman and X-ray photoelectron spectroscopies were used to evaluate the degrees and uniformities of functionalization. Statistical analyses of the Raman data revealed that the introduction of the organic moieties was accompanied by sp3-rehybridization of the basal plane atoms. When bilayers consisting of 13C and 12C layers were treated, both the top and bottom sheets were decorated with organic groups. The reaction was followed using Raman spectroscopy, and the mechanism was studied by theoretical calculations. Indicative of its structure and reactivity, 4-pyridyl-decorated single-layer graphene was readily benzylated and appears to be an ideal platform to develop functional materials.clos

Controlled Folding of Single Crystal Graphene

Folded graphene in which two layers are stacked with a twist angle between them has been predicted to exhibit unique electronic, thermal, and magnetic properties. We report the folding of a single crystal monolayer graphene film grown on a Cu(111) substrate by using a tailored substrate having a hydrophobic region and a hydrophilic region. Controlled film delamination from the hydrophilic region was used to prepare macroscopic folded graphene with good uniformity on the millimeter scale. This process was used to create many folded sheets each with a defined twist angle between the two sheets. By identifying the original lattice orientation of the monolayer graphene on Cu foil, or establishing the relation between the fold angle and twist angle, this folding technique allows for the preparation of twisted bilayer graphene films with defined stacking orientations and may also be extended to create folded structures of other two-dimensional nanomaterials.clos