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Nanocarbon Chemistry
Nanostructured allotropic forms of carbon (Carbon Nanostructures - CNS) and in particular carbon nanotubes (CNTs) are promising active components of light-weight, flexible and resistant functional materials in such application as photoelectrochemical cells, electrochemical sensors, photodetectors and organic light-emitting diodes. Despite their high electrical and thermal conductivity, the lack of solubility and strong absorption in the visible region (350-800 nm) of carbon nanotubes prevents them to be effectively and extensively employed in commercial devices.
In order to exploit CNS properties towards practical applications, it is required to understand their chemical behavior and to develop strategies for their chemical modification. Main goals of CNS chemistry are the improvement of their processability and the tuning of their properties in view of the specific application.
Functional
Polymer Nanocomposite Materials
Polymer composite materials based on nanosized fillers can be designed to perform specific and complex functions by controlling the physical and chemical interactions between the phases.
We follow three different strategies to couple carbon nanotubes and organic moieties, as following.
The exohedral covalent approach
We exploit both the carboxylic approach [1, 2, 3] (Fig. 1) and other synthetic strategies, such as the readily accessible 1,3-dipolar cycloaddition of azomethine ylides or the addition of diazonium salts to introduce functional groups in sp2-bonded carbon surfaces and to convey additional chemical and physical properties to the starting material. We also improved reaction times through an early implementation of microwave heating.
Fig. 1: Soluble and functional CNT derivatives obtained through carboxylic chemistry. (Ref. 1,2)
We implemented the use of a controllable, high throughput, environmentally friendly technology, based on continuous flow processes, (Fig. 2) to obtain functionalized CNSs with a considerable improvement in productivity compared to traditional reactors.[4, 5, 6, 13]
Fig. 2: An efficient continuous-flow method for the exohedral functionalisation of carbon nanotubes. (Ref. 4, 5, 6)
Controlling diazonium chemistry
The derivatisation of materials including iron, gold, and carbon by addition of diazonium salts is a reliable process to tune their interfacial interaction with the surrounding media. In this regard, the functionalisation of carbon nanostructures by diazonium chemistry is a versatile strategy to obtain soluble nanomaterials with degrees of functionalisation among the highest ever reported. Starting from these premises we have studied the functionalisation of multi-walled carbon nanotubes by addition of the aryl diazonium salts generated in situ by treatment of 4-methoxyaniline with isopentylnitrite. Following a thorough purification and characterisation protocol (UV–vis, TGA, ATR-IR, cyclic voltammetry, AFM and other surface analytical techniques), we have investigated the key parameters to obtain both functionalised multi-walled carbon nanotubes, where the amount of functional groups anchored to the carbon surface is less than a monolayer, and superfunctionalised carbon nanotubes, with a carbon nanotube core and a multilayered aryl coating. The results outlined provide the basis for the design and controlled processing of novel decorated carbon nanostructures that would be useful for a number of technological applications.[12]
The exohedral non-covalent approach
We exploited, for example, the interaction between CNT walls and pyrene derivatives [7] (Fig. 3). Another example is based on the coupling of a porphyrin-cyclodextrin conjugated (TPPCD) and CNTs to obtain stable water dispersions. We repeatedly observed, in this case, the formation of complexes with a fixed stoichiometry suggesting that a selective recognition occurs between TPPCD and CNTs. (collab. with Prof. Tommaso Carofiglio)
Fig. 3: Supramolecular hybrids of [60]Fullerene and Single Wall Carbon Nanotubes (Rif. 7)
The endohedral approach
It consists of the encapsulation of different types of organic molecules (fullerene derivatives [8] and polycyclic aromatic molecules[9, 10, 11]) inside the inner space of the single wall CNTs (SWNTs) to obtain supramolecular entities, usually referred as “peapods” (Fig. 4). The incapsulation is achieved by means of solvents, through vapor-phase techniques or using supercritical CO2.
We studied the novel peapods by means of steady-state and time-resolved UV-vis-NIR absorption and emission spectroscopy, Raman spectroscopy, and HR-TEM.
Fig. 4: Nanohybrids for photonic devices: encapsulation of conjugated oligomers in SWNTs (Ref. 9, 10, 11)
References
[1] M. D'Este, M. De Nardi, E. Menna; "A co-functionalization approach to soluble and functional Single-Walled Carbon Nanotubes", Eur. J. Org. Chem. 2006, 2517-2522.
[2] F. Cordella, M. De Nardi, E. Menna, C. Hébert, M.A. Loi; "Tuning the photophysical properties of soluble single-wall carbon nanotube derivatives by co-functionalization with organic molecules", Carbon 2009, 47, 1264-1269
[3] A. Gambetta, C. Manzoni, E. Menna, M. Meneghetti, G. Cerullo, G. Lanzani, S. Tretiak, A. Piryatinski, A. Saxena, R. L. Martin, A. R. Bishop; "Real-time observation of nonlinear coherent phonon dynamics in single-walled carbon nanotubes", Nature Phys. 2006, 2, 515-520.
[4] P. Salice, D. Fenaroli, C. C. De Filippo, E. Menna, G. Gasparini, M. Maggini; "Efficient functionalization of carbon nanotubes: an opportunity enabled by flow chemistry", Chimica Oggi-Chemistry Today 2012, 30, 37-39.
[5] P. Salice, P. Maity, E. Rossi, T. Carofiglio, E. Menna, M. Maggini; "The continuous-flow cycloaddition of azomethine ylides to carbon nanotubes", Chem. Commun. 2011, 9092-9094.
[6] M. Maggini, P. Salice, E. Rossi, E. Menna, T. Carofiglio; "Method for synthesis of functionalised carbon nanotubes by cycloaddition under continuous flow conditions and apparatus for the method", WO 2012156297.
[7] D. M. Guldi, E. Menna, M. Maggini, M. Marcaccio, D. Paolucci, F. Paolucci, S. Campidelli, M. Prato, G. M. A. Rahman, S. Schergna; " Supramolecular hybrids of [60]Fullerene and Single Wall Carbon Nanotubes", Chem.-Eur. J. 2006, 12, 3975-3983..
[8] S. Campestrini, C. Corvaja, M. De Nardi, C. Ducati, L. Franco, M. Maggini, M. Meneghetti, E. Menna, G. Ruaro; "Investigation of the Inner Environment of Carbon Nanotubes with a Fullerene-Nitroxide Probe", Small 2008, 4, 350-356.
[9] M. A. Loi, J. Gao, F. Cordella, P. Blondeau, E. Menna, B. Bartova, C. Hebert, S. Lazar, G. A. Botton, M. Milko, C. Ambrosch-Draxl; "Encapsulation of Conjugated Oligomers in Single-Wall Carbon Nanotubes: Towards Nanohybrids for Photonic Devices", Adv. Mater. 2010, 22, 1635-1639.
[10] J. Gao, P. Blondeau, P. Salice, E. Menna, B. Bártová, C. Hébert, J. Leschner, U. Kaiser, M. Milko, C. Ambrosch-Draxl, M. A. Loi; "Electronic Interactions between “Pea” and “Pod”: The Case of Oligothiophenes Encapsulated in Carbon Nanotubes", Small 2011, 7, 1807-1815.
[11] M. Milko, P. Puschnig, P. Blondeau, E. Menna, J. Gao, M. A. Loi, C. Draxl; "Evidence of Hybrid Excitons in Weakly Interacting Nano-Peapods", J. Phys. Chem. Lett. 2013, 2664-2667.
[12] P. Salice, E. Fabris, C. Sartorio, D. Fenaroli, V. Figà, M. P. Casaletto, S. Cataldo, B. Pignataro, E. Menna; "An Insight into the Functionalisation of Carbon Nanotubes by Diazonium Chemistry: Towards a Controlled Decoration", Carbon 2014, DOI:10.1016/j.carbon.2014.02.084.
[13] P. Salice, E. Rossi, A. Pace, P. Maity, T. Carofiglio, E. Menna, M. Maggini; "Chemistry of carbon nanotubes in flow",J. Flow Chem. 2014, DOI:10.1556/JFC-D-13-00031
Continuous Flow Processing of Carbon Nanotubes and Graphene
A simple and scalable approach for a fast chemical functionalization of carbon nanotubes (patent application PD2011A000153) and graphene nanoplatelets.
Microwave Functionalization of Carbon Nanotubes
Microwave heating can impressively enhance reaction rates with carbon nanotubes. We have reported one of the first example of application.