An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers’ method (KMnO4, NaNO3, H2SO4) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 mixture of H2SO4/H3PO4 improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers’ method or Hummers’ method with additional KMnO4. Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers’ method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers’ method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the ...

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Improved Synthesis of Graphene Oxide

The reduction of graphene oxide

Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Face-to-face crosslinking of graphdiyne and related carbon sheets toward integrated graphene nanoribbon arrays

Fullerenols possess excellent antioxidant activity, in which they can scavenge all of the major physiologically relevant reactive oxygen species (ROS). However, the underlying ROS-scavenging mechanisms of C60 fullerenols are not completely understood. Using density functional theory calculations, we investigated •OH-, O2•--, and H2O2-scavenging mechanisms of C60 fullerenols and the correlations between hydroxyl distributions and radical-scavenging ability. For scavenging •OH and O2•-, H• donation and electron transfer via hydrogen bonds, respectively, are the dominant mechanisms for C60 fullerenols. Although the obtained fullerenols simultaneously contain radicals and anions, there is an isolated OH anion which possesses the activity of eliminating H2O2. The •OH-scavenging activity depends on the distribution of hydroxyls according to the calculations for ten C60(OH)24 isomers. Fullerenols, in which the distribution of hydroxyls leads to low redox potential (e) values, possess high scavenging activity. For the nonmagnetic fullerenols, activity relies on the number of sp2 substructures, in which the greater their number is, the lower the activity of the fullerenols. The results will be of fundamental importance in understanding the antioxidant activities of fullerenols.

Mechanisms of Antioxidant Activities of Fullerenols from First-Principles Calculation.

Graphene has diverse applications in molecular electronics due to its unique electronic, thermal, and mechanical properties. Lattice imperfections are introduced into graphene unavoidably during graphene growth or when a graphene sheet is irradiated with high-energy particles. These structural defects are known to significantly affect electronic and chemical properties. A comprehensive understanding of graphene defects is thus of critical importance. In particular, the monovacancy defect has attracted great attention due to its fundamental nature. Recent studies have established that monovacancies exist in graphene as a planar 5/9 isomer with lowered symmetry. The 5/9 isomer is generated by formation of an elongated carbon–carbon bridge across the hole that results from removal of a single carbon atom, which leads to fusion of a fiveand a nine-membered ring (Figure 1b). Each 5/9 isomer contributes an intrinsic magnetic moment of about 1 mB. [4] Here we report that the stability and therefore electronic structure of the monovacancy defect is determined by the distance from the graphene periphery: The magnetic, planar 5/9 isomer is most stable in the center of graphene flakes, whereas the nonmagnetic spiro isomer (Figure 1b) is more stable when the shortest center-to-periphery distance d of the vacancy is less than 7 (for definition of d, see Figure 1a). Creation of spiro isomers in the planes of graphene nanoribbons (GNRs) paves the way to achieving novel nanoarchitectures such as spiral helices. To investigate the low-lying structural and electronic conformation of graphene monovacancies, monovacant graphene flakes 1–6 with peripheries terminated by hydrogen atoms were used as model systems (Figure 1a). The largest flake, 1, contains 351 carbon and 46 hydrogen atoms (Table 1). With decreasing molecular size from 1 to 6, the d value decreases from 15.6 to 4.2 (Table 1). Thus, 1–6 provide reasonable models for monovacancy defects in graphenes with shrinking size and decreasing d. Geometry optimizations and energy calculations were performed by four methods: B3LYP/6-31G(d), GGA-PBE/DZP, and selfconsistent-charge density functional tight binding with finite Figure 1. a) 1–6 : Hydrogen-terminated graphene flakes with monovacancies; the empty circle designates the vacant carbon position; d is the shortest center-to-periphery distance. b) 6F and 6S : Structures derived from 6 with 5/9 and spiro defects. Hydrogen atoms of all structures are omitted for clarity.

Carbon Spiral Helix: A Nanoarchitecture Derived from Monovacancy Defects in Graphene

Opening a large band gap for graphene by covalent addition

The water-resistant adhesion of mussel adhesive proteins (MAPs) to a wet surface requires a cross-linking step, where the catecholic ligands of MAPs coordinate to various transition-metal ions. Fe(III), among the range of metal ions, induces particularly strong cross-linking. The molecular details underlying this cross-linking mediated by transition-metal ions are largely unknown. Of particular interest is the metal–ligand binding energy, which is the molecular origin of the mechanical properties of cross-linked MAPs. Using density functional theory, this study examined the structures and binding energies of various trivalent metal ions (Ti–Ga) forming coordination complexes with a polymeric ligand similar to a MAP. These binding energies were 1 order of magnitude larger than the physisorption energy of a catechol molecule on a metallic surface. On the other hand, the coordination strength of Fe(III) with the ligand was not particularly strong compared to the other metal ions studied. Therefore, the stron...

Xingfa Gao

Papers

Face-to-face crosslinking of graphdiyne and related carbon sheets toward integrated graphene nanoribbon arrays

Mechanisms of Antioxidant Activities of Fullerenols from First-Principles Calculation.

Carbon Spiral Helix: A Nanoarchitecture Derived from Monovacancy Defects in Graphene

Opening a large band gap for graphene by covalent addition

Density Functional Theory Study on the Cross-Linking of Mussel Adhesive Proteins