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Graphene Coated Nanoparticles and Nanograins

Periodic Reporting for period 4 - GRANN (Graphene Coated Nanoparticles and Nanograins)

Reporting period: 2020-01-01 to 2020-06-30

The aim of GRANN was to synthesize graphene nanostructures and nanoparticles with tunable electronic, optical and chemical properties, to utilize graphene and functionalized graphene as a coating material for metal nanostructures and nanoparticles and to explore the catalytic properties of such structures for interstellar chemistry.

Under the project we have brought our knowledge and expertise with graphene synthesis, graphene coatings and control of graphenes’ electronic properties on macroscopic samples into the realm of nanoparticles and nano-grains. The output of this high-risk, high gain research project has been the development of synthesis routes for formation of graphene coated Nanoparticles, development of novel methods to synthesize graphene nanodot structures, exploration the chemical reactivity of nanographenes and PAHs under interstellar conditions, development of novel methods to engineer a tunable band gap opeening in graphene by the formation of hydrogen functionalization structures on the nanoscale and with tunable symmetry. Furthermore, we have demonstrated the existance of novel chemical reaction routes and functionalization motifs for graphene on metal substrates - specifically we have shown that graphene mediates the catalytic activity of the underlying metal surface enabling chemical functionalization with excited molecular hydrogen and stabilizing a novel binding motif for atomic oxygen on graphene - a so-called enolate bond. Finally, we have demonstrated that graphene can act as a protective coating on industrial grade metal alloys and demonstrated how hydrogen functionalization nanostructures can enhance the protective properties of such coatings. The project has demonstrated the potential for graphene coatings and functionalization enhanced graphene coatings for use as anti-corrosion coatings of surfaces of industrial relevance and may thus point to the use of this technology in future applications.
Exploiting symmetry in functionalization patterns to engineer a band gap opening in graphene: A method was developed to control hydrogen functionalization of graphene so that nanostructured graphene with varying symmetry could be produced. The obtained symmetry variations were demonstrated to result in the opening of a band gap of varying width in graphene. Overall, the band gap in graphene can be engineered to have values ranging from 0 eV and up to at least 450 meV using this method. The results are reported in J. H. Jørgensen et al., Symmetry Driven Band Gap Engineering in Hydrogen Functionalized Graphene, ACS Nano 10, 10798 (2016).

New graphene functionalization routes and motifs: A novel route to functionalize graphene using excited molecular hydrogen was identified and explained via density functional theory calculations. New functionalization motifs for oxygen functionalized graphene were observed. Specifically, oxygen on graphene on Ir(111) was found to bind to the surface via an enolate bond. As a result both excited H2 molecules and oxygen was found to induce a stronger coupling between graphene and the underlying metal, just as the underlying metal were seen to catalyze novel reactions over and on graphene - i.e. molecular hydrogen dissociative adsorption and enolate bond formation. These results are reported in L. Kyhl et.al. Exciting H2 Molecules for Graphene Functionalization, ACS Nano 12, 513 (2018) and A. Cassidy et al., Patterned formation of enolate functional groups on the graphene basal plane. Phys. Chem. Chem. Phys. 20, 28370 (2018).

Growing selfassembled graphene nanodots: A novel method for growing self assembled graphene nanodots in a boron-nitrogen-carbon alloy matrix were demonstrated. The results of this work is presented in L. Camilli et al., Self-assembly of ordered graphene nanodot arrays. Nat. Comm. 8, 47 (2017).

Identifying stable hydrogenation structures on and catalytic activity of graphene nanodots/PAHs: Hydrogen functionalization structures on graphene nanodots in the form of PAH molecules were observed to be governed by a novel concept of retained aromaticity. This new concept is expected to be valid for a broad range of functionalization structures on aromatic carbonaceous compounds. Furthermore, the PAH molecules were found to be catalytically active in the formation of molecular hydrogen under interstellar conditions. The experiments and theory leading to the development of this new concept are described in papers P. A. Jensen et al., Identification of Stable Configurations in the Superhydrogenation Sequence of Polycyclic Aromatic Hydrocarbon Molecules. Mon. Not. Roy. Astron. Soc. 486, 5492 (2019) and D. Campisi et al., Superhydrogenation of Pentacene: the reactivity of zigzag-edges. Phys. Chem. Chem. Phys. 22, 1557 (2020).

Graphene as an anti-corrosive coating: A low temperature synthesis pathway to graphene corrosive coatings on industrial grade metal substrates (Inconel) were demonstrated and the coating performance against different corrosive environments were investigated. Hydrogen functionalization of graphene coatings were demonstrated to yield superior coating performance since it increases the adhesion between graphene and the metal substrate, thereby preventing intercalation. These results are reported in S. Halkjær et al., Low-temperature synthesis of a graphene-based, corrosion-inhibiting coating on an industrial grade alloy. Corrosion Science 152, 1 (2019) and L. Kyhl et al., Enhancing Graphene Protective Coatings by Hydrogen Induced Chemical Bond Formation, ACS Applied Nano Materials, DOI: 10.1021/acsanm.8b00610 (2018).
We have demonstrated a novel way to increase graphene coating performance by chemically functionalizing graphene with hydrogen to achieve a stronger graphene-metal bond. The increased binding between graphene and the metal results in prevention of intercalation of reactive species at the graphene-metal interface.

We have developed new methods to control the electronic properties of graphene by Controlling the symmetry of the chemical functionalization structures of graphene on metal substrates allowing for band gap engineering.

We have developed a novel method to produce highly vibrationally excited molecular hydrogen and have demonstrated that the catalytic activity of graphene covered metal substrates allows for their functionalization by these molecules.

We have demonstrated the formatuon of enolate bonds in oxygen functionalization of graphene on metal substrates.

We have demonstrated a novel method for growing self assembled graphene nanodots in a boron-nitrogen-carbon alloy matrix.