Graphene & 2D Materials
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Since the isolation of graphene in 2004, other layered materials such as transition metal dichalcogenides, graphitic carbon nitride or boron nitride have attracted a great attention due to their unique properties. However, one of the drawbacks of these materials is that their outstanding features (electronic, mechanical and thermal) appear when the bulk counterparts are exfoliated into mono- or few layers. Exfoliation of the bulk materials is possible due to the weak van der Waals interactions that maintain the layers together. In addition, the properties can be tailored using different strategies. One of the most common is the chemical modification, allowing the application of these 2D materials in a great number of fields (optoelectronics, sensing, catalysis, energy storage, etc.) This modification can be carried out covalently or non-covalently and employing metals, organic or inorganic moieties and even other nanostructures. In case of covalent modification, the formation of new bonds modifies the pristine skeleton of the materials and their intrinsic properties. In the non-covalent functionalization, the structure does not suffer modifications. Our group is interested in the topic of the 2D materials, as a consequence of the great number of possibilities that they offer in different research fields.
Graphene is a single layer of graphite, a monolayer of sp2 hybridized carbon atoms arranged into a 2D honeycomb structure. Due to its outstanding mechanical, electronic and thermal properties, graphene has attracted the interest of the scientific community. In fact, the Graphene Flagship is a funded project by the European Commission, in which over 150 research groups collaborates in different divisions and work packages. Our group is one of these collaborators, and is integrated in two work packages: Health and Environment (WP4) and Biomedical Technologies (WP5). Despite of its properties, one of the major drawbacks of graphene is its lack of solubility that hampers its manipulation and possible applications. The chemical modification allows to overcome this inconvenient due to the tuning of the chemical and physical properties of graphene. This tuning can take place by covalent or non-covalent functionalization. The most common reactions for the covalent functionalization of graphene are cycloadditions. Recently, we have reported the covalent functionalization of graphene employing microwave irradiation, this approach allows to reduce the reaction times that are used for the functionalization in classic thermal conditions, and in addition to control the functionalization degree of this kind of nanomaterials. [1,2]
Another interesting 2D material is graphitic carbon nitride (g-C3N4), a π-conjugated 2D polymeric material formed by carbon and nitrogen (with a variable content of hydrogen) organized in triazine units. Its excellent properties (moderate bandgap, visible light absorption, chemical stabilit, etc.) make it a widely used semiconductor photocatalytic material allowing several catalytic processes for energy conversion, environmental remediation and organocatalysis, among others. In collaboration with the group of Prof. Fornasiero, we have started to study the photocatalytic performances of this material and how its modification affect its catalytic behavior. [3] The collaboration with the group of Prof. Fornasiero is not limited to the g-C3N4, but extends to the use of other carbon nanostructures (for example carbon nanotubes and carbon nanohorns) as components in the assembly of multi-phase materials for various electro- and photo-catalytic reactions.
We are also interested in molybdenum disulfide (MoS2), an inorganic 2D material composed by layers of Mo atoms sandwiched between two layers of sulfur atoms covalently bonded. This material is present as two different polytypes: the 2H phase, which has a semiconductor character and the 1T phase with a metallic character. Both phases present interesting electronic, optical and thermal properties, allowing the use of MoS2 in a great number of fields like sensing and catalysis. Like in the case of the other 2D materials, the chemical modification of MoS2 allows to tune its properties for different applications. Recently, our group has reported the preparation and exfoliation of the 1T phase, its application for surface-enhanced Raman scattering (SERS) and the covalent functionalization. [4]
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Highlighted contributions:
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[1] Microwave-induced covalent functionalization of few-layer graphene with arynes under solvent-free conditions.
M. V. Sulleiro, S. Quirog, D. Peña, D. Pérez, E. Guitián, A. Criado, M. Prato. Chem. Commun. 54, 2086-2089 (2018). Link
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[2] Ionic liquids plus microwave irradiation: a general methodology for the retro-functionalization of single-walled carbon nanotubes.
M. Barrejón, Z. Syrgiannis, M. Prato. Nanoscale 10, 15782-15787 (2018). Link
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[3] Metal-free dual-phase full organic carbon nanotubes/g-C3N4 heteroarchitectures for photocatalytic hydrogen production.
K.C. Christoforidis, Z. Syrgiannis, V. La Parola, T. Montini, C. Petit, E. Stathatos, R. Godin, J.R. Durrant, M. Prato, P. Fornasiero. Nano Energy 50, 468-478. (2018). Link
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[4] High-Yield Preparation of Exfoliated 1T-MoS2 with SERS Activity.
E. Er, H. Hou, A. Criado, J. Langer, M. Möller, N. Erk, L.M. Liz-Marzán, M. Prato. Chem. Mater. 31, 5725-5734 (2019). Link