R&sultats d'une &tude prospective multicentrique sur la ponction guid&e par &choendoscopie de tumeurs pancr&atiques de moins de 3cm de diam&tre (PDF Download Available)
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05/12/2017 JFHOD | SNFGE.org - Société savante médicale fran?aise d&hépato-gastroentérologie et d’oncologie digestivehttps://www.snfge.org/content/resultats-dune-etude-prospective-multicentriqu 1/2ACCUEIL PROFESSIONNELS CONGR?S LES JFHOD
R?SULTATS D&UNE ?TUDE PROSPECTIVE MULTICENTRIQU...Retour aux résultatsP0 - Résultats d&une étude prospective multicentrique sur la ponctionguidée par échoendoscopie de tumeurs pancréatiques de moins de 3 cm dediamètreGiovannini Marc, Monges Geneviève, Arcidiacono P, Ardengh C, Deprez P, Guaraldi S, Fogel R, Karamboulis J, Bories E,Pesenti CH, Moutardier Vincent, Delpero Jean-RobertButLe
multicentrique
échoendoscopie
massespancréatiques (& 3 cm). Sept centres (2 au Brésil, 1 en Belgique, 1 au Venezuela, 1 en Italie, 1 en Grèce et 1 en France) ont participé à cette étude. Patients et MéthodesDe mai 2002 à mai
patients (78 H, 77 F) d&?ge moyen 60,72 ans (extrêmes : 22 - 88 ans) ont été inclus dans l&étude. Ils présentaient tous unetumeur pancréatique de moins de 3 cm de diamètre. 51/155 lésions n&ont été diagnostiquées uniquement
lors de l&échoendoscopie (EE) soit 32,9 %. Lataille moyenne de la tumeur pancréatique était de 21,12 mm (extrêmes : 6 - 29 mm). On notait 6 lésions de moins de 10 mm, 16 entre 10 et 15 mm, 31entre 15 et 20 mm, 37 entre 20 et 25 mm et 65 de plus de 25 mm. La tumeur siégeait 18 fois au niveau du crochet, 74 fois au niveau de la tête, 21 foisau niveau de l&isthme, 24 fois au niveau
et 18 fois au niveau
queue. La ponction a toujours
été réalisée avec une aiguille de 22
gauges(Wilson-Cook) .60/155 patients ont été opérés (38,7 %). Le diagnostic final a été porté sur le résultat de la PGEE seule dans 91 cas, sur les données dela chirurgie et de la PGEE dans 43 cas, sur les données de la chirurgie seule dans 17 cas et sur l&évolution clinique dans 4 cas. RésultatsQuatre complications bénignes
sont survenues (douleurs
épigastriques 3 fois, fièvre 1 fois), elles ont
toutes été régressives sous traitement médical enmoins de 48
heures. La PGEE n&a
pas été contributive dans
17 cas soit 10,9
diagnostic final des
155 lésions pancréatiques
a été le suivant
:adénocarcinome du pancréas (n = 88, 56,8 %), tumeur endocrine (n = 34, 21,9 %), cystadénome (n = 11, 7,1 %), nodule de pancréatite chronique (PCC)(n = 13, 8,4 %), métastase pancréatique (n = 4, 2,6 %), tumeur bénigne (n = 4, 2,6 %) et lymphome pancréatique (n = 1, 0,6 %). Aucun faux positif de laPGEE n&a été noté. Pour le diagnostic de malignité, la sensibilité, la spécificité, la valeur prédictive positive et la valeur prédictive négative de la PGEE aété respectivement de 86,7 %, 100 %, 100 % et
La fiabilité
de la technique a été de 89 %. Si on compare
les résultats
en fonction
taille(moins de 20 mm vs plus de
existe une différence significative de la fiabilité (92,4 % pour les lésions de moins de 20 mm vs 87,2 %
pour lestumeurs de plus de 20 mm, p & 0,001). Par ailleurs, la fiabilité de la PGEE est
meilleure pour le diagnostic d&adénocarcinome que pour celui
de tumeurendocrine (93,2 % vs 70,6 %, p & 0,001). Par contre, il n&existe aucune différence en fonction de la localisation de la tumeur dans la glande pancréatique. ConclusionLa PGEE des petites tumeurs pancréatiques est faisable, sure et trouve des chiffres de sensibilité et spécificité équivalents à ceux des séries englobantdes
plus volumineuses.
étude trouve
de tumeurs
endocrines
publiées (10
moins demétastases
pancréatiques
lesadénocarcinomes
endocrines.
conclusion
intéressante
développement
radiochimiothérapie pré-opératoire des adénocarcinomes du pancréas. JFHOD
05/12/2017 JFHOD | SNFGE.org - Société savante médicale fran?aise d&hépato-gastroentérologie et d’oncologie digestivehttps://www.snfge.org/content/resultats-dune-etude-prospective-multicentriqu 2/2
ArticleFeb 2007ChapterApr 2009ProjectProjectCarcinoma of the pancreas remains a great challenging. Disease is diagnosed in an advanced stage in the majority of cases. MicroRNAs (miRs) are small non-coding RNAs that regulate the expression of…& [more]ProjectMany imaging methods complement each and other to confirm the correct diagnosis of the solid or cystic tumors of the pancreas. The major challenge is to accurately identify prior to the adoption of…& [more]Project[...]The therapeutic EUS-guided therapy has evolved incontestably. The use of imaging methods for the staging of tumors that affect the digestive system allows the adoption of a therapeutic measures rat…& [more]ArticleMarch 2005 · ArticleMarch 2005 · ArticleMarch 2006 · ArticleMarch 2006 · Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.This publication is from a journal that may support self archiving.Last Updated: 05 Dec 17PREPARATION OF FUNCTIONALISED MATERIALS
WIPO Patent Application WO/
The invention provides for a method of preparing a covalently functionalised carbon nanomaterial, comprising the steps of (i) treating a carbon material with a reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and (ii) treating the resulting reduced-carbon material solution with a functionalising reagent to form a covalently functionalised carbon nanomaterial, wherein (a) the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L, and (b) the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1. A method of preparing a covalently functionalised carbon nanomaterial using N,N-dimethylacetamide as a solvent is also provided.
Inventors:
SHAFFER, Milo Sebastian Peter (Imperial Innovations Limited, 52 Princes Gate, London SW7 2PG, GB)
MORISHITA, Takuya (Imperial Innovations Limited, 52 Princes Gate, London SW7 2PG, GB)
CLANCY, Adam Justin (Imperial Innovations Limited, 52 Princes Gate, London SW7 2PG, GB)
Application Number:
Publication Date:
05/21/2015
Filing Date:
11/14/2014
Export Citation:
IMPERIAL INNOVATIONS LIMITED (52 Princes Gate, London SW7 2PG, GB)
International Classes:
View Patent Images:
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Other References:
BAI ET AL., ADV. MATER., vol. 23, 2011, pages 1089
KHAN ET AL., SMALL, vol. 6, 2010, pages 864
VALLES ET AL., J. AM. CHEM.SOC., vol. 130, 2008, pages 15802
ENGLERT ET AL., NAT. CHEM., vol. 3, 2011, pages 279
ENGLERT ET AL., CHEM. COMM., vol. 48, 2012, pages 5025
NOVOSELOV ET AL., NATURE, vol. 490, 2012, pages 192
KHAN ET AL., SMALL, vol. 6, 2013, pages 864
COLEMAN ET AL., NATURE MATERIALS, vol. 13, pages 624 - 630
Y. HERNANDEZ ET AL., NAT. NANOTECHNOL., vol. 3, 2008, pages 563
HODGE ET AL., FARADAY DISCUSSIONS, 2014
Attorney, Agent or Firm:
HARRIS, Jennifer Lucy (Kilburn & Strode LLP, 20 Red Lion Street, London Greater London WC1R 4PJ, GB)
1. A method of preparing a covalently functionalised carbon nanomaterial, comprising the steps of
(i) treating a carbon material with a reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial,
the solvent S is Ν,Ν-dimethyl acetamide.
2. A method according to claim 1 , wherein the carbon material comprises carbon nanotubes.
3. A method according to claims 1 or 2, wherein the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L. 4. A method according to claim 1 , 2 or 3, wherein the ratio of carbon material to alkali metal (CM) in solution in step (i) is at least 2:1.
5. A method of preparing a covalently functionalised carbon nanomaterial, comprising the steps of
(i) treating a carbon material with a reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial,
(a) the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L, and
(b) the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1.
6. A method according to any preceding claim, wherein the carbon material comprises graphite, graphene, graphene nanoribbons or carbon nanotubes.
7. A method according to any one of claims 5 to 6, wherein the covalently
functionalised carbon nanomaterial is soluble in solvent S.
8. A method according to any of claims 5 to 7, wherein the solvent S is a coordinating solvent. 9. A method according to claim 8, wherein the coordinating solvent comprises a cyclic ether, preferably THF, 1 ,4-dioxane or a crown ether.
10. A method according to claim 6, wherein the carbon material comprises graphite, graphene, or graphene nanoribbons and the concentration of alkali metal in step (i) is between 0.003 mol/L and 0.015 mol/L.
1 1 . A method according to claim 10, wherein the concentration of alkali metal in step (i) is between 0.006 mol/L and 0.012 mol/L.
12. A method according to claim 1 1 , wherein the concentration of alkali metal in step (i) is between 0.007 mol/L and 0.01 1 mol/L.
13. A method according to claim 12, wherein the concentration of alkali metal in step (i) is about 0.009 mol/L.
14. A method according to claim 6, wherein the carbon material comprises a carbon nanotube and the concentration of alkali metal in step (i) is between 0.015 mol/L and 0.05 mol/L.
15. A method according to claim 14, wherein the concentration of alkali metal in step (i) is between 0.020 mol/L and 0.035 mol/L.
16. A method according to claim 15, wherein the concentration of alkali metal in step (i) is between 0.025 mol/L and 0.030 mol/L.
17. A method according to any of claims 14 to 16, wherein the solvent S comprises an amide.
18. A method according to claim 17, wherein the amide is N,N-dimethylacetamide.
19. A method according to any preceding claim wherein the functionalising reagent is an electrophile.
20. A method according to claim 19, wherein the electrophile is a compound comprising a moiety R, wherein R is an organic moiety. 21 . A method according to claim 20, wherein R comprises an aliphatic, heteroaliphatic, aromatic, heteroaromatic, carbonyl, epoxy, disulphide or peroxide moiety.
22. A method according to claim 19, wherein the electrophile is a compound comprising a moiety R-X, wherein R is an organic moiety and X is a leaving group.
23. A method according to claim 22, wherein R comprises an aliphatic, heteroaliphatic, aromatic, heteroaromatic moiety, or combinations thereof, and X is a halide.
24. A method according to any preceding claim, wherein the C/M ratio is at least 5:1 .
25. A method according to claim 24, wherein the C/M ratio is at least 10:1.
26. A method according to any preceding claim, wherein prior to step (i), the carbon material is subjected to purification, the purification comprising the steps of:
contacting the carbon material with a reducing solution to dissolve impurities, the reducing solution comprising a solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
27. A method of purifying a carbon nanomaterial, the method comprising the steps of: contacting the carbon nanomaterial with a reducing solution to dissolve impurities, the reducing solution comprising an amide solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
28. A method according to claim 26 or 27, wherein the purification comprises a step of determining the concentration of alkali metal required to dissolve impurities without dissolving a desired fraction of carbon material, prior to contacting the carbon material with a reducing solution.
29. A method according to any one of claims 26 to 28, wherein the carbon material comprises carbon nanotubes.
30. A method according to any one of claims 26 to 29, wherein the solvent is N,N- dimethyl acetamide. 31 . A method according to any preceding claim, wherein the reducing agent comprises an alkali metal and a charge transfer agent.
32. A method according to any preceding claim, wherein the alkali metal M comprises lithium, sodium, potassium or an alloy thereof.
33. A method according to claim 31 or 32, wherein the charge transfer agent is naphthalene.
34. A functionalised carbon nanomaterial produced by the method according any one of claims 1 to 26 or 31 to 33.
35. A functionalised carbon nanomaterial according to claim 34, wherein the carbon material comprises graphite, graphene, graphene nanoribbons or carbon nanotubes. 36. A method as substantially described herein with reference to or as illustrated in any one or more of the examples or accompanying figures.
37. A functionalised carbon nanomaterial as substantially described herein with reference to or as illustrated in any one or more of the examples or accompanying figures.
Description:
Preparation of functionalised materials
Technical field
The present invention generally relates to the field of carbon nanomaterials.
Background
Carbon nanomaterials, such as graphene and carbon nanotubes, have attracted immense attention in a wide range of promising potential applications. In many cases, such as nanocomposite materials, electronic inks, display devices, drug delivery and biosensors, the graphene must be individually dispersed in solvents or matrices by a scalable method. However, graphene itself has extremely low solubilities in common solvents, and therefore functionalization is crucial to avoid restacking and enable processing.
Functionalization by the production of graphene oxide by acid exfoliation is popular but this method damages the intrinsic structure and degrades the properties of the graphene (Bai et al. Adv. Mater., 201 1 , 23, 1089). Alternative milder wet-chemical approaches generate graphenes from graphite by exploiting exfoliation and stabilisation using carefully selected surfactants or solvents (Khan et al., Small, 4). However such graphenes typically involve extended sonication which leads to the formation of structural defects and reduced flake size.
An approach to retain the bonded network and the lateral dimensions of graphenes involves the formation of electrostatically-stabilised dispersions by protonation in superacids or reduction and dissolution in polar aprotic solvents. For example, graphite is intercalated with liquid potassium-ammonia followed by dissolution in tetrahydrofuran (THF) as well as the dissolution of potassium-based graphite intercalation compounds (GICs) in N-methyl pyrrolidone (Valles et al., J. Am. Chem.Soc, , 15802). The resulting solutions contain individually solvated graphenes (graphenides) and are stable as long as air is excluded.
Covalent functionalization of these graphenides has been achieved through reaction with a suitable electrophile (Englert et al., Nat. Chem., 201 1 , 3, 279; Englert et al., Chem. Comm. 25). In these reactions, an excess of Na/K was used for reducing the graphite. However, low grafting ratio and low solubility of the functionalised products was observed.
l Single walled carbon nanotubes (SWNTs) have shown excellent potential in electronic, mechanical, and other functional applications. Semiconducting SWNTs are of particular relevance in the field of nano-electronics, for example in the form of thin film transistors (TFTs)
networks of metallic tubes are widely considered as transparent conducting films (TCFs) for displays, touch screens, and solar cells.
Functionalization of the sidewalls of SWNTs is challenging due to their relatively poor reactivity and dispersibility. Synthesized carbon nanotubes also routinely contain impurities both in the form of non-nanotube carbon (amorphous and graphitic carbon, and short defective nanotubes) and residual catalytic particles, often contained within graphitic shells and carbon nanotube caps. Although functionalization has been achieved, many processes require ultrasonication of the carbon nanotubes during the functionalization process, which may damage the nanotubes. Exfoliating bundles of SWNTs presents similar challenges to the case of graphene, albeit with different geometry.
There is therefore a need for improved methods for purifying carbon nanomaterials and preparing functionalised carbon nanomaterials. Summary of the Invention
It has been determined that in a process involving reduction of a carbon nanomaterial, followed by covalent functionalization thereof, control of the absolute alkali metal concentration in the reduction of a carbon nanomaterial results in an improved process. Accordingly, in a first aspect, the present invention provides a method of preparing a covalently functionalised carbon nanomaterial, comprising the steps of
(i) treating a carbon material with reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial,
wherein the solvent S is N,N-dimethylacetamide. The use of N, N-dimethylacetamide allows for the use of a single solvent in the preparation of functionalised carbon nanomaterial and allows for significant improvements in yield. Preferably, the carbon material comprises a carbon nanotube.
Preferably, the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L.
Preferably, the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1 . In a second aspect, the present invention provides a method of preparing a covalently functionalised carbon nanomaterial, comprising the steps of
(i) treating a carbon material with reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial,
(a) the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L, and
(b) the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1.
Optimisation of the concentration of alkali metal in step (i) as well as the ratio of the carbon material to alkali metal allows for enhanced exfoliation and improved grafting ratio of the carbon nanomaterial.
Preferably the reducing agent comprises an alkali metal and a charge transfer agent, which may be, for example, a compound comprising one or more aromatic rings.
Preferably, the charge transfer agent comprises naphthalene.
Preferably, the carbon material comprises graphite, graphene, graphene nanoribbons or carbon nanotubes.
Preferably, the covalently functionalised carbon nanomaterial is soluble in solvent S. Preferably, the solvent S is a coordinating solvent. Preferably, the coordinating solvent comprises a cyclic ether, THF, 1 , 4-dioxane or a crown ether.
Preferably, wherein the carbon material comprises graphite, graphene, or graphene nanoribbons, the concentration of alkali metal in step (i) is between 0.003 mol/L and 0.015 mol/L. Preferably, the concentration of alkali metal in step (i) is between 0.006 mol/L and 0.012 mol/L. Preferably, the concentration of alkali metal in step (i) is between 0.007 mol/L and 0.01 1 mol/L. More preferably, the concentration of alkali metal in step (i) is about 0.009 mol/L.
Preferably, wherein the carbon material comprises a carbon nanotube, the concentration of alkali metal in step (i) is between 0.015 mol/L and 0.05 mol/L. More preferably, the concentration of alkali metal in step (i) is between 0.020 mol/L and 0.035 mol/L. More preferably, the concentration of alkali metal in step (i) is between 0.025 mol/L and 0.030 mol/L.
Preferably, wherein the carbon material comprises a carbon nanotube or a pre-exfoliated graphene, the solvent S comprises an amide. More preferably, the amide is N,N- dimethylacetamide (DMAC).
In any aspects of the invention and in any preferred embodiment, the method may further comprise a step (i)(a) comprising sonicating the reduced carbon material solution prior to step (ii). In all aspects of the invention, preferably, the functionalising reagent is an electrophile. Preferably, the electrophile is a compound comprising a moiety R, wherein R is an organic moiety. Preferably, R comprises an aliphatic, heteroaliphatic, aromatic, heteroaromatic, carbonyl, epoxy, disulphide or peroxide moiety. Preferably, the electrophile is a compound comprising a moiety R-X, wherein R is an organic moiety and X is a leaving group.
Preferably, R comprises an aliphatic, heteroaliphatic, aromatic, heteroaromatic moiety and X is a halide. In some embodiments, the functionalising reagent is R-X, wherein R is Ci-30 aliphatic (e.g. Cio-24 alkyl) and X is a halide. In all aspects of the invention, preferably, the alkali metal M comprises lithium, sodium, potassium or an alloy thereof.
Preferably, the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1 . More preferably, the C/M ratio is at least 5:1. More preferably, the C/M ratio is at least 10:1.
Preferably, prior to step (i), the carbon material is subjected to purification, the purification comprising the steps of:
contacting the carbon nanomaterial with a reducing solution to dissolve impurities, the reducing solution comprising a solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
Preferably, the solvent in the reducing solution is an amide solvent, for example DMAc.
In a third aspect, the invention is directed to a method of purifying carbon nanomaterial, the method comprising the steps of
contacting the carbon nanomaterial with a reducing solution to dissolve impurities, the reducing solution comprising an amide solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
Preferably, the carbon material comprises carbon nanotubes. Preferably, the purification comprises a step of determining the concentration of alkali metal required to dissolve impurities without dissolving a desired fraction of carbon material prior to contacting the carbon material with a reducing solution.
Preferably, the solvent in the reducing solution is an amide solvent, for example DMAc. In a fourth aspect, the present invention relates to a functionalised carbon nanomaterial produced by the method according to the first or second aspect.
Preferably, the carbon material comprises graphite, graphene, graphene nanoribbons or carbon nanotubes.
In a fifth aspect, the present invention relates to a method as substantially described herein with reference to or as illustrated in any one or more of the examples or accompanying figures.
In a sixth aspect, the present invention relates to a functionalised carbon nanomaterial as substantially described herein with reference to or as illustrated in any one or more of the examples or accompanying figures. Brief Description of the Figures
The invention may be put into practice in various ways and a number of specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying figures, in which:
Figure 1 shows a schematic representation of the synthesis of alkylated graphene using Na-reduced graphite. Bilayers represent unexfoliated stacks of two or more layers.
Figure 2 shows a table with the properties of various alkylated graphenes.
Figure 3 shows thermogravimetric analysis data (TGA) for eicosylated graphene, pristine graphite and eicosane.
Figure 4 shows (a) the Raman spectra (laser wavelength 531 nm, normalized by the intensity of the G peak) and (b) XRD patterns of pristine graphite and eicosylated graphenes 1f, 1j, 1 k, and 11 (grafted after a brief bath sonication (5 min)).
Figure 5 shows TGA data for Na-THF-GIC.
Figure 6 shows the FT-IR spectroscopy of eicosylated graphene and pristine graphite. Figure 7 shows (a) the relation between n number of CnH2n+iBr used and the C/R value obtained CnH2n+i grafted graphenes, and (b) the relation between C/Na and C/R.
Figure 8 shows Raman spectra of pristine graphite, eicosylated graphene and eicosylated graphene after TGA measurement.
Figure 9 shows englarged XRD diffractogram of eicosylated graphene.
Figure 10 shows (a) the (a) XRD patterns of pristine graphite and dodecylated graphenes (C/Na = 1 , 4, 12, and 24), and (b) the effect of diluting the graphite concentration (the standard condition: 0.1 M) on the relation between C/Na and C/R.
Figure 1 1 shows SEM images of pristine graphite and eicosylated graphene. Figure 12 shows XRD patterns of pristine graphite and dodecylated graphenes.
Figure 13 shows the effect of changing the graphite concentration in the reaction.
Figure 14 shows the concentration of supernatant after mild centrifugation of eicosylated graphene.
Figure 15 shows the relation between the alkyl chain of alkylated graphenes and their solubility.
Figure 16 shows the UV-vis spectra of supernatant solutions after mild centrifugation of butylated graphene in DCB.
Figure 17 shows a graph which illustrates the effect of changing the sodium concentration on the C/R for dodecylated single walled carbon nanotubes.
Figure 18 shows the impact of different sodium concentrations on the grafting ratio C/R for SWNTs.
Figure 19 shows the UV spectra of 1 mg/ml preexfoliated graphene disposed in 12.5mM sodium naphthalide in THF, 12mM sodium naphthalide in DMAC, and neat DMAC.
Figure 20 shows the UV spectra of equimolar sodium and naphthalene (of ~ 1 mg (Na)ml" 1) added to a selection of solvents (top) and cuvettes containing the Na/Ci0H8 solutions of (a) THF, (b) DMAC(C) DMF (d) NMP () DMSO (f) CHP (bottom).
Figure 21 shows the impact of C/Na ratio on the concentration of nanotubide solution starting with 3.5 mgml"1 loading of SWCNT (top) and the yield and concentration of nanotubide solution against initial SWCNT loadings with 20:1 C/Na (bottom).
Figure 22 shows the alkyl chain length of 1-bromoalkanes (CnH2n+iBr) and 1 -halide octanes (C8H17X where X = F, CI, Br or I) versus grafting ratios on 20:1 charges SWCNT, calculated from TGA in N2.
Figure 23 shows the grafting ratios of reduced SWCNTs added to 1-bromododecane versus (a) C/Na ratio, (b) sodium concentration.
Figure 24 shows (a) the absorbance (660 nm) of NaNp/DMAC and SWCNTs at a given SWCNT to sodium ratio versus time (b) percentage material dissolved versus C/Na after 48h percentage material dissolved versus C/Na after 48h soaking of 1 mg ml"1 SWCNT in DM Ac.
Figure 25 shows the Raman of residual SWCNTs and removed material after purification of SWCNTs at 20:1 and 10:1 C/Na ratios.
Figure 26 shows the weight of the dissolved SWCNTs as a percentage of the total weight put in at different C/Na ratios.
Figure 27 shows the Ramon D/G peak ratios of SWCNTs, DMAC sodium naphthalide purified nanotubes, nanotubes purified by heating to 350°C in air for 1 h and washing with HCI, and Tuball purified by reflux in nitric acid (6M, 1 mg (SWCNT)/ml, 48h) and washed with NaOH (0.1 M) and excess D1 water. Detailed Description of the Invention
The present invention is defined in the accompanying claims. In a first aspect, the invention relates to a method of preparing functionalized carbon materials, comprising the steps of
(i) treating a carbon material with a reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial, wherein
(a) the concentration of alkali metal [M] in step (i) is between 0.003 mol/L and 0.05 mol/L, and
(b) the ratio of carbon material to alkali metal (C/M) in solution in step (i) is at least 2:1.
In a second aspect, the invention relates to a method of preparing a covalently
functionalised carbon nanomaterial, comprising the steps of
(i) treating a carbon material with a reducing agent comprising an alkali metal M in the presence of a solvent S to form a reduced-carb and
(ii) treating the resulting reduced-carbon material solution with a
functionalising reagent to form a covalently functionalised carbon nanomaterial,
wherein the solvent S is N,N-dimethylacetamide. Carbon material may be carbon nanomaterial. Carbon material according to the present invention, may comprise graphite, graphene, or carbon nanotubes. Graphene carbon material may comprise graphene sheets or graphene nanoribbons. Carbon nanotubes, according to the present invention, include, but are not limited to, single-wall carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), small diameter carbon nanotubes, and combinations thereof.
Nanomaterials are materials with at least one external dimension in the size range from about 1 to 100 nm.
The nanotube may be any type of nanotube, that is, it may be any hollow tubular structure having at least one dimension measuring on the nanometer scale. For example, the nanotube may have a smallest inner diameter measuring between about 0.5 nm to about 50 nm, such as about 0.5 nm to about 20 nm, for example between about 0.7 nm to about 10 nm, e.g. between about 0.8 nm to about 2 nm. Small diameter carbon nanotubes are defined herein as carbon nanotubes having diameters of at most about 3 nm, regardless of the number of walls. The nanotube may be of any length. For example, the nanotube may have a length between about 5 nm to about 500 μηη.
The solvent S is aprotic, for example an ether, an amide or an amine solvent, or a mixture thereof. The ether may comprise alkyl or cycloalkyi ethers. Exemplary ethers include tetrahydrofuran (THF), dioxane, diethyl ether, diisopropyl ether, di-n-butyl ether, di-sec- butyl ether, methyl t-butyl ether, 1 ,2-dimethoxyethane, 1 ,2-dimethoxypropane, 1 ,3- dimethoxypropane, 1 ,2-diethoxyethane, 1 ,2-diethoxypropane, 12-crown-4 ether, 15- crown-5 ether, 18-crown-6 ether or combinations thereof. Amine solvents may be used and may comprise tertiary amines. Useful amines may comprise tertiary alkyl or cycloalkyi amines. Exemplary amines include tertiary amine including n-methyl piperidine, n-methyl morpholine, N,N,N',N'-tetramethyl-1 ,2-diaminoethane, or combinations thereof. Amide solvents may be used. Exemplary amides include dimethylformamide, N-methyl-2- pyrrolidone, N,N-dimethylacetamide. Amide solvents should preferably be inert towards the alkali metal. The solvent should be stable in the presence of both the change transfer agent and the charged carbon material (formed by treatment with a reducing agent). A preferable amide solvent includes N-N-dimethylacetamide.
The solvent S may be a coordinating solvent. The coordinating solvent is aprotic, and is substantially free of protic contaminants such as moisture, alcohols, protic amines, hydroperoxides, or other reactive species including carbonyl compounds such as acids, ketones, aldehydes, esters. The coordinating solvent comprises an ether, an amine or a combination thereof. In one embodiment, the coordinating solvent is a cyclic ether.
Preferably, the cyclic ether comprises THF or a crown ether.
The reducing agent may further comprise a charge transfer agent. The charge transfer agent is an agent which supports electride formation. Charge transfer agents may comprise aromatics. Examples of such charge transfer agents are naphthalene, anthracene, phenanthrene, 4,4'-di-tert-butylbiphenyl, azulene or combinations thereof. Preferably, the charge transfer agent is naphthalene.
The alkali metal comprises lithium, sodium, potassium or an alloy thereof. The total alkali metal in step (i) is as defined above. It will be apparent that a mixture of one or more alkali metal may be present. The ratio of carbon material to alkali metal (C/M) refers to the ratio of carbon material (mol) to alkali metal (mol).
In some embodiments, wherein the carbon material comprises graphite, graphene, or graphene nanoribbons, the concentration of alkali metal in step (i) is between 0.003 mol/L and 0.015 mol/L. The concentration of alkali metal in step (i) may be between 0.006 mol/L and 0.012 mol/L. The concentration of alkali metal in step (i) may be between 0.007 mol/L and 0.01 1 mol/L. The concentration of alkali metal in step (i) may be about 0.009 mol/L. In some embodiments, wherein the carbon material comprises a carbon nanotube, the concentration of alkali metal in step (i) may be between 0.015 mol/L and 0.05 mol/L. The concentration of alkali metal in step (i) may be between 0.020 mol/L and 0.035 mol/L. The concentration of alkali metal in step (i) may be between 0.025 mol/L and 0.030 mol/L. In one embodiment, the functionalised carbon nanomaterial has a grafting ratio GR of at least 0.7.
Step (ii) of the method comprises treating the reduced carbon nanomaterial solution with a functionalizing reagent to form a covalently functionalized carbon nanomaterial. The above-described reductive functionalization method allows various functional groups (e.g. alkyl-, aryl-, allyl-, and benzyl-) to be covalently linked to the carbon material. The functional group may be a monomer. Functionalization is covalent functionalization, involving covalent bonding of the functional group to the carbon material. The functionalizing reagent may comprise an aliphatic, heteroaliphatic, aromatic, heteroaromatic, carbonyl, epoxy, disulfide or peroxide moiety. The aliphatic,
heteroaliphatic, aromatic, heteroaromatic, carbonyl, epoxy moieties may be optionally substituted with aliphatic, heteroaliphatic, aromatic, heteroaromatic, carbonyl, epoxy, disulfide or peroxide moieties. The carbonyl moiety may comprise an ester, amide, carbonate, aldehyde, or acyl moiety. The ester moiety may be saturated or unsaturated.
The term "aliphatic", as used herein, means a substituted or unsubstituted straight-chain, branched, or cyclic hydrocarbon, which is completely saturated or which contains one or more units of unsaturation, but which is not aromatic. For example, suitable aliphatic groups include substituted or unsubstituted linear, branched or cyclic alkyl, alkenyl, or alkynyl groups and hybrids thereof, such as (cycloalkyl)alkyl, (cycloalkenyl)alkyl or (cycloalkyl)-alkenyl. In certain embodiments, a straight chain or branched chain alkyl has about 30 or fewer carbon atoms in its backbone (e.g., C1-C30 for straight chain, C3-C30 for branched chain), and alternatively, about 24 or fewer. Likewise, cycloalkyls have from about 3 to about 10 carbon atoms in their ring structure, and alternatively about 5, 6 or 7 carbons in the ring structure. Exemplary alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, cyclopropyl, and cyclobutyl, dodecyl, eicosyl. The term aliphatic may also refer to an alkyl group that is substituted with at least one halogen. Exemplary haloalkyl groups include -CH2F, -CHF2, -CF3, -CH2CF3, -CF2CF3, and the like. The term "hydroxyalkyl" refers to an alkyl group that is substituted with at least one hydroxyl group. Exemplary hydroxyl alkyl groups include -CH2OH, -CH2CH2OH, -C(H)(OH)C(OH)H2, and the like. The term aliphatic may also refer to polyether groups. Exemplary polyether groups include poylethyleneglycol. The term aliphatic may also refer to an alkyl group substituted with an aryl group. The term aliphatic may also refer to an alkyl group substituted with a heteroaryl group. In one embodiment, the aliphatic group comprises C4H9, C12H25, or C20H41.
The term "heteroraliphatic" or "heteroalkyl" refers to aliphatic groups that include at least one heteroatom. In certain instances, a heteroaliphatic group contains 1 , 2, 3, or 4 heteroatoms, N, O, S or P. The term "aromatic" refers to a carbocyclic aromatic group. Representative aromatic groups include phenyl, naphthyl, anthracenyl, and the like. Unless specified otherwise, the aromatic ring may be substituted at one or more ring positions with, for example, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, carboxylic acid, -C(0)alkyl, -C02alkyl, carbonyl, carboxyl, alkylthio, sulfonyl, sulfonamido, sulfonamide, ketone, aldehyde, ester, heterocyclyl, aryl or heteroaryl moieties, -CF3, -CN, or the like. The term "aryl" also includes polycyclic aromatic ring systems having two or more carbocyclic rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein all of the fused rings are aromatic rings, e.g., in a naphthyl group.
The term "heteroromatic" or "heteroaryl" refers to aromatic groups that include at least one ring heteroatom. In certain instances, a heteroaromatic group contains 1 , 2, 3, or 4 ring heteroatoms, N, O, S or P. Representative examples of heteroaryl groups include pyrrolyl, furanyl, thiophenyl, imidazolyl, oxazolyl, thiazolyl, triazolyl, pyrazolyl, pyridinyl, pyrazinyl, pyridazinyl and pyrimidinyl, and the like. Unless specified otherwise, the heteroaryl ring may be substituted at one or more ring positions with, for example, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino, amido, carboxylic acid, -C(0)alkyl, -C02alkyl, carbonyl, carboxyl, alkylthio, sulfonyl, sulfonamido, sulfonamide, ketone, aldehyde, ester, heterocyclyl, aryl or heteroaryl moieties, -CF3, -CN, or the like. The term "heteroaryl" also includes polycyclic aromatic ring systems having two or more rings in which two or more carbons are common to two adjoining rings (the rings are "fused rings") wherein all of the fused rings are
heteroaromatic, e.g., in a naphthyridinyl group.
In some embodiments, the functionalizing reagent comprises a compound comprising a moiety R-X, wherein R is an organic moiety and X is a leaving group. X may comprise a halide, sulfoxide, or tosylate. R may comprise aliphatic, heteroaliphatic, aromatic or heteroaromatic moiety, or combinations thereof.
In some embodiments, the functionalizing reagent may comprise an alkyl halide, alkyl sulphoxide. In other embodiments, the aromatic moiety may comprise an aralkyl halide. In some embodiments, the acyl moiety may be an acyl halide, acyl tosylate, or acid anhydride.
The halide may be selected from the group consisting of -F, -CI, -Br, -I. In some embodiments, the functionalizing reagent, the charged carbon nanomaterial and the resulting functionalized carbon nanomaterial are soluble in solvent S.
In some embodiments, the ratio of carbon material to alkali metal (C/M) in solution in step (i) may be at least 2:1 . More preferably, the moles of carbon to moles of alkali metal (C/M) ratio may be at least 5:1. More preferably, the C/M ratio may be at least 10:1 . In some embodiments, the upper range of the C/M ratio may be 100:1 , 80:1 , 60:1 or 45:1. In some embodiments, for graphene, the C/M ratio may be between 22:1 and 32:1.
In some embodiments, the method may further comprise a step (i)(a) comprising sonicating the reduced carbon material solution prior to step (ii), i.e. prior to the treatment with a functionalizing reagent. The sonication step may be a mild sonication, for example the sonication may be bath sonication, preferably for up to ten minutes, i.e. approximately 5 minutes. In some embodiments, further (subsequent) functionalization of the functionalized carbon nanomaterial is possible. For example, in another embodiment of the present invention, the method allows for the polymerization of monomers from an initially grafted functionalization group or by direct anionic polymerization from the charged carbon material. In such embodiments, the method allows for the in situ polymerization of monomeric material via reductive pathway to form polymer chains attached to the carbon material. Various monomeric species or combination of species can be used.
For the purposes of this invention, a monomer may be selected from a monomer which is accessible by free radical or anionic polymerization, such as a (meth)acrylate monomer or a vinyl monomer, a polymer, a fluorescent dye, a coupling agent, a surfactant, a free radical tag/trap (such as nitroxides, organic halides and especially organic iodides for example 1-iodododecane) or a free radical initiator (such as azo compounds, persulfates and organic peroxides). The vinyl monomer is preferably one or more selected from the group comprising ethylene, propylene, methyl methacrylate, styrene, (3,5,5- trimethylcyclohex-2-enylidene)malononitrile, 1 ,1-dichloroethylene, 1-(3-sulfopropyl)-2- vinylpyridinium hydroxide, 1-vinyl-2-pyrrolidinone, vinylnaphthalene 2-isopropenyl-2- oxazoline, 2-vinyl-1 ,3-dioxolane, vinylnaphthalene, vinylpyridine, 4-vinyl-1-cyclohexene 1 ,2-epoxide, 4-vinyl-1 -cyclohexene, vinylanthracene, vinylcarbazole, divinyl sulfone, ethyl vinyl sulfide, N-ethyl-2-vinylcarbazole, N-methyl-N-vinylacetamide, N-vinylformamide, N- vinylphthalimide, trichlorovinylsilane, vinyl bromide, vinyl chloride, vinylcyclohexane, vinylcyclopentane, vinylphosphonic acid, vinylsulfonic acid, vinyltrimethylsilane, cis-1 ,3- dichloropropene, vinyl acetate, acrylic acid, acrylonitrile, (dimethylamino)
ethylmethacrylate, lauryl methacrylate, 2-(methylthio)ethyl methacrylate, trimethylsilyl methacrylate, 2-hydroxyethyl methacrylate, hydroxy propyl methylacrylate, acrylamide, oleic acid, glycidyl methacrylate (GMA) and maleic anhydride. In some embodiments, prior to step (i), the carbon material is subjected to purification, the purification comprising the steps of:
contacting the carbon nanomaterial with a reducing solution to dissolve impurities, the reducing solution comprising a solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
In a third aspect, the invention is directed to a method of purifying carbon nanomaterial, the method comprising the steps of contacting the carbon nanomaterial with a reducing solution to dissolve impurities, the reducing solution comprising an amide solvent and a reducing agent comprising an alkali metal M;
allowing impurities to be dissolved to provide a mixture comprising undissolved carbon material and a supernatant comprising
removing the supernatant.
The carbon nanomaterial may be carbon nanotubes. The alkali metal M may be provided in an amount sufficient to solubilise impurities without solubilising the desired carbon material. Impurities may comprise amorphous carbon, graphitic carbon, short defective nanotubes, and residual catalytic particles.
The impurities may require less charge to solubilise than a desired fraction of carbon material. Accordingly, the alkali metal M may be provided in an amount insufficient to dissolve a desired fraction of the carbon material. The alkali metal may be provided in an amount such that the C/M ratio is at least 10:1 , 30:1 , 40:1 , 50:1 , 60:1 , 70:1 , 80:1 , 100:1.
The amount of M and desired fraction may be determined by a fractionation process. For example, the carbon material may be exposed to different concentrations of alkali metal. The amount of dissolved impurities in the supernatant may be assessed, for example by UV vis spectroscopy. The concentration of alkali metal is determined at which impurities are dissolved without dissolving a desired fraction of carbon material. This fractionation process may involve the steps of:
exposing samples of carbon material to different concentrations of alkali metal to provide a mixture comprising undissolved carbon material and a supernatant comprising
assessing the percentage (by weight) of carbon material dissolve
determining the concentration of alkali metal required to leave a desired percentage fraction of carbon material undissolved.
The solvent for purification may be N,N-dimethylacetamide.
The contacting of the carbon nanomaterial with a reducing solution may take place without stirring. The purification may further comprise a step of quenching the carbon material following removal of the supernatant. Quench occurs to remove residual charge on the carbon material. The purified carbon material may be quenched with dry oxygen. Following purification, and optionally following quenching, the carbon material may be subjected to the functionalization method of the first or second aspect of the present invention.
A functionalized carbon material is soluble in a solvent under conditions used in the claimed method. The functionalized carbon material may preferably be dissolved in solvent, optionally by sonication at room temperature or by application of stirring, sonication or other methods.
The following examples of the invention are provided to aid understanding of the invention but should be not taken to limit the scope of the invention.
Graphite (Graphexel natural crystalline flake graphite, grade: 2369, Graphexel Ltd., UK) was obtained from the manufacturer and used without any further purification. Elicarb single walled carbon nanotubes (PR929, batch 10851 1/g) were supplied by Thomas Swan Ltd and were dried under vacuum (-10"2 mbar) at 300 °C for 1 h and 16 h at room temperature before use.
1-Chlorododecane (&97%), 1-bromododecane (&98%) and 1-chloroeicosane (&96%) were purchased from Tokyo Chemical Industry Co., Ltd. 1-Bromobutane (99%), 1- bromoeicosane (98%), 1-iodododecane (98%) and anhydrous THF were obtained from Sigma-Aldrich. 1-Chloroeicosane and 1-bromoeicosane were dried at room temperature for at least 4 days under vacuum before using in the glove box. 1 -Chlorododecane, 1- bromobutane, 1-bromododecane, 1-iodododecane, DMSO and THF were degassed via a freeze-pump-thaw method and dried over 20% wt, molecular sieves 4 A. Sodium (99.95%, ingot, No. 262714) and naphthalene (99%) were purchased from Sigma-Aldrich.
Naphthalene was dried under vacuum in the presence of P205.
All work is carried out in a nitrogen glovebox. If not supplied anhydrous, solids are dried under vacuum in the presence of P205 whilst liquids are degassed via freeze-pump-thaw and dried with molecular sieves. Measurements
Thermogravimetric analysis (TGA) was performed using a Perkin Elmer Pyris 1 TGA under perfect N2 atmosphere (samples were held at 100°C for 90 min at the N2 flow rate = 60 ml min"1, ramped 10 °C min"1 to 800 °C (N2 flow rate = 60 ml min"1). FT-IR spectra were measured using a Perkin Elmer Spectrum 100 with universal ATR sampling accessary. X-ray powder diffraction (XRD) was recorded at a scan rate of 0.1087s with the Cu Ka (1.542 A) line using a PANalytical X'Pert PRO diffractometer. UV-vis-NIR absorption spectra were measured using a Perkin Elmer Lambda 950 UVA is
spectrometer. Sonication was performed using an ultrasonic cleaner (USC300T, 80 W). Raman spectra were measured using an ISA Jobin Yvon SPEX Raman spectrometer equipped with a 532 nm excitation laser source. Typical tapping-mode atomic force microscopy (AFM) measurements were taken using Bruker MultiMode 8 AFM. Samples for AFM images were prepared by drop-casting dilute graphene-dispersed chloroform solutions on silica substrates.
Grafting ratio
The grafting ratio is the molar ratio of grafted moiety against molar ratio of carbon within the raw carbon nanomaterial with both these values taken from the weights calculated from the TGA as described below.
The derivative of percentage weight with respect to temperature of the TGA was taken and smoothed with a Savitzky-Golay filter. The resultant peak(s) allowed the
determination of an onset and ending temperatures of the grafted moiety degradation, whilst the plateau of the derivative game the rate of degradation of the grafted species which was presumed to be constant. The percentage weight loss between the two temperatures was calculated and the contribution of thermal degradation (calculated using the plateau rate multiplied by the difference in temperature) was subtracted. This weight loss was attributed to the grafting species minus the leaving group. For graphite, the sample weight minus the grafted weight was attributed to graphite. For CNTs, the remaining weight was normalized to take into account the residual catalyst calculated from the residual weight of an oxidative TGA of the as received material.
Functionalisation of graphene
69 mg (3 mmol) of sodium and 384.5 mg (3 mmol) of dried naphthalene were added into 30 ml. of degassed anhydrous THF in a N2 filled glove box, and stirred for 1 day forming a green Na/naphthalene solution. A pre-made sodium naphthalide THF solution was used to allow for accurate, simple addition of sodium to the carefully dried nanocarbon. Typically, a Schlenk tube including graphite (36 mg, 3 mmol of carbon) together with a magnetic bar was flame-dried, and placed in a glove box. A variable mass of the Na/naphthalene solution (1 :1 in THF) was added into the Schlenk tube containing graphite and the concentration of graphite in THF adjusted to 0.1 M (mmol ml"1) by addition of degassed anhydrous THF. The suspension was stirred for 1 day, and alkyl halides (9 mmol, 3 equiv. per sodium) were added to the tube. Then, the reaction was stirred at room temperature for 1 day under N2. After bubbling dry 02 into the solution for 15 min, the solution was stirred for 1 day under dry 02 for oxidation of any remaining charges on the functionalized graphenes. The solution was stirred as ethanol (10 ml) was added slowly followed by water (20 ml). After neutralization using 0.1 N HCI, the functionalized graphenes were extracted into hexane and washed several times with water. The mixture was filtered through a 0.1 mm PTFE membrane filter, washed thoroughly with hexane, THF, ethanol and water. After washing the sample with ethanol and THF again, the product was obtained after drying overnight under vacuum at 80 °C.
As shown in Figure 2, a clear trend of increasing reactivity down the group of the order RCI & RBr & Rl was observed with alkyl iodides giving the greatest GR. As shown in Figure 2 and Figure 7a, decreasing the chain length led to a significant increase in the GR. Butylated graphenes (1 g) showed high GR values attaining a maximum of 22.1 graphene carbons per grafted chain. This trend demonstrates that steric factors play an important role in determining the outcome of these 'grafting to' reactions. In the theta state, of a free-jointed linear polymer chain, the mean-square radius of gyration (&S2&) is proportional to the number of bond (n) (&S2& = kn). Therefore, the graphene area occluded by one grafting chain (C/R) might also be expected to be approximately proportional to n, as observed in the data (Figure 7a). However, the conformation of the alkyl chains near the graphene is unknown and may vary as t the availability of the graphene surface and negative charge also vary with reaction conditions. In the case of well exfoliated C/Na = 12 samples (vide infra), for very short chains, the reaction appears to approach the limit of available charge (C/R = 12). For higher metal content systems (C/R = 1 ) the observed GR is unexpectedly lower, and more sensitive to the steric effects of chain length. This trend indicates a more limited surface area available for grafting which may be attributed to poorer exfoliation. The C/M ratio (i.e. the ratio of moles of carbon material used to moles of alkali metal) was varied. A systematic study of the effect of the charge ratio on the degree of grafting (Figure 7b) shows that the optimal C/Na ratio for maximum grafting density is -12. As shown in Scheme 1 , when the C/Na value is small, the total negative charge on the graphene
however, most of the charges are condensed and screened by the high concentration of Na cations. This 'salting out' leads to incomplete exfoliation and lower GR, and is consistent with the assumption that grafting only occurs on exposed surfaces. In contrast, when the C/Na value is large, the total negative charge on the graphene is low, resulting in incomplete exfoliation and a low GR. Between these extremes lies an optimum for graphene exfoliation and grafting. As shown in Figure 4b, both above (1 k, C/Na = 24) and below (1f, C/Na = 1 ) this 12:1 ratio, the diffractogram indicates remaining graphite as illustrated by the (002) peak. In contrast, at the optimal charge (C/Na = 12), the (002) diffraction of the alkylated graphene 1j is almost absent. In these samples, a very small stage-1 peak originating from remaining GICs was observed, probably due to physical connections between some layers limiting exfoliation. However, a brief weak sonication (5- minute's bath-sonication) at the optimal charge ratio before the addition of eicosyl bromides led to apparently no detectable interlayer peaks remain in the 11 XRD data. The loss of the layer peaks can be explained by near full exfoliatio peak intensity can be affected by various factors, but all XRD samples were prepared and measured identically, in the same shape and volume: the only difference is the state of exfoliation and functionalization.
Figure 3 shows TGA data (heating rate = 10°C min"1, under N2) for eicosylated graphene 1f, pristine graphite, and eicosane. A pure eicosane control decomposed predominantly below 200°C with a small amount of char disappearing about ~550°C. A very small weight loss of 1f below 210°C can be ascribed to decomposition of remaining physical adsorbed alkane. Na-THF-GIC after the same work-up procedure as 1f has no weight loss above 100°C to 800°C (Figure 5). The weight loss of 1f observed from 210°C to 800°C is ascribed to decomposition of eicosyl chains to graphenes. Alkyl chains grafted to graphene nanoribbons [1 a] and SWNTs [1 b] synthesized by reacting with alkyl iodide, are also known to show two or more weight loss components from ~200°C to ~650°C.
Figure 5 shows TGA data (heating rate = 10°C min"1, under N2) for Na-THF-GIC
(synthesized with C/Na ratio = 12) after the same work-up procedure as eicosylated graphene, eicosylated graphene 1f, 1j, 1 k, and 11. Na-THF-GIC prepared by the same work-up procedure as 1f does not show any weight loss above 100°C. However, there is a 5.3 wt% loss during holding at 100°C for 90min before ramping 10°C min"1 to 800°C, which is ascribed to intercalate (THF) volatilization of remaining Na-THF-GICs. For comparison, a weight loss due to intercalate volatilization of stage-1 Na-alkyldiamine-GICs is known (Novoselov et al., Nature, , 192) to be observed from 50°C to ~100°C. During the work-up procedure using dry 02, most the Na cations reacted with dry 02 producing Na20 during charge quenching (Na-THF-GICs can be converted into the pristine graphite), and the resulting Na20 was removed by washing with water several times. Most of the remaining THF between layers can be removed by drying at 80 °C under vacuum overnight, and therefore, the weight loss of the intercalate (THF) volatilization was small (-5.3 wt%). There is no further weight loss in the range 100°C to 800°C under N2, which might confound signals from the grafting alkyl chains. Note that the amount of Na-GIC remaining unreacted in the alkyl reacted samples is very small (&0.1wt%).
Figure 8, top, shows Raman spectra (laser wavelength: 532 nm) of (a) pristine graphite, (b) eicosylated graphene 1f, and (c) 1f after TGA measurement. After TGA measurement of 1f, dealkylation of 1f led to restoration of the pristine sp2 carbon network (negligible D peak), but with less perfect stacking (broadened 2D peak). Figure 8, bottom, shows 2D bands (normalised by the intensity of the G peak) of pristine graphite and eicosylated graphenes 1f, 1j, 1 k, and 11. The 2D peaks of 1j and 11 have a single symmetric
Lorentzian line profile: this characteristic 2D peak indicates the existence of a single layer graphene sheet. In the case of a single-layer graphene, the 2D peak is generally higher than the intensity of G peak.
Figure 9 shows enlarged XRD diffractogram of eicosylated graphene 1f. Remaining stage-1 structure peaks are indexed as (001 ) lines by using two values of the identity period lc, 1.12 and 0.72 nm, indicated as stage-1 phases A (S1 A) and B (S1 B), respectively, in the figure. The thickness of intercalate layer is calculated as 0.79 nm for phase A, and 0.39 nm for phase B, by a subtraction of the thickness of carbon layers (0.335 nm). Phase B is formed by exposing phase A to air. From these values of lc, both phases are reasonably supposed to have the stage-1 structure (Khan et al., Small, 4). The content of remaining Na-THF-GIC in 1f is very small (the remaining intercalate (THF) volatilization of 1f, which is calculated from the weight loss at -100 °C by TGA, is estimated as -0.1 wt%). The same optimal C/Na ratio (C/Na = 12) is also observed for dodecylated graphenes. At this charge ratio, the (002) diffraction peak of the dodecylated graphene is almost absent (Figure 3a) and GR shows the highest value (Figure 10b). However, the optimal C/Na ratios have been shown to be dependent on the concentration of graphite. Diluting the graphite concentration in THF led to the shift of optimal C/Na ratio (Figure 10b). This shows that controlling Na concentration decided by both C/Na ratio and graphite concentration is important when enhancing the exfoliation and GRs (Figure 1 1 ). Lower Na concentration leads to decreased charge condensation, however it also decreases the total charge av the optimal Na concentration for exfoliation and grafting of GIC is~0.009 M for each graphite concentration (Figure 1 1 ), corresponding to the calculated Debye length of -1 .0 nm (Figure 1 1 ) Figure 1 1 shows SEM images of pristine graphite (G2369) and eicosylated graphene 1j (C/Na = 12). The SEM image of 1j shows crumpled sheets with blunter, less distinct edges, due to the exfoliation reaction and functionalization.
Figure 12 shows XRD patterns of pristine graphite and dodecylated graphenes (C/Na = 1 , 4, 12, and 24).
Figure 13 shows the effect of changing the graphite concentration in the reaction (0.1 M (the standard concentration) (·), 0.02 M (■), 0.04 M (A ), and 0.3 M (?)) on the relation between C/Na and C/R of dodecylated graphenes.
Figure 14 shows concentrations of supernatant after mild centrifugation (1 ,000 rpm (87 g), 5 min) of eicosylated graphene 1j-dispersed DCB solution (initial concentration: 0.2, 1 , and 2 mg/ml). Figure 15 shows the relation between the alkyl chain length of alkylated graphenes and their solubility (after mild centrifugation (1 ,000 rpm (87 g), 5 min) to remove non-dispersed particles). Alkylated graphenes (C/Na = 12) in DCB (A ) and chloroform (·), and alkylated graphenes (C/Na = 1 ) in DCB (Δ) and chloroform (o). Photographs show the supernatants of each alkylated graphene dispersion.
Figure 16 shows the UV-vis spectra of supernatant solutions after mild centrifugation of butylated graphene (1 g) in DCB, dodecylated graphene (1 h) in DCB, and eicosylated graphene (1j) in DCB. Graphene that has been pre-exfoliated, for example by treatment in the presence of surfactant under high shear (Coleman ef a/, Nature Materials, 13, 624-630), can be reduced and dispersed in a one pot method by sonication in solutions of sodium naphthalide in DMAc. In an inert environment, 20 mg of graphene was added to 20 ml of 12.5 mM sodium naphthalide (1 :1 Na/Ci0H8) in DMAc and bath sonicated for 30 min. The solution was then centrifuged at 10,000 g for 30 min to sediment the undissolved fraction, and the solution was pipetted off by hand. Figure 19 shows the UV spectra of 1 mg/ml graphene dispersed in 12.5 mM sodium naphthalide in THF, 12.5 mM sodium naphthalide in DMAc, and neat DMAc. The measurements were made with 4 mm path length. Sodium naphthalide measurements were carried out at 10x dilution in appropriate solvent.
The pre-exfoliated graphene can also be functionalised. For example, in an inert environment, 20 mg of graphene was added to 20 ml of 12.5 mM sodium naphthalide (1 :1 Na/Ci0H8) in DMAc or THF and bath sonicated for 30 min. 1 -iodododecane (250 mg) was added to the solution and stirred overnight with a glass stirrer bar. The material was filtered and washed with THF, ethanol and water. The solubility of the functionalized graphene was assessed by UV-vis. The samples were prepared as follows: the functionalised graphene was bath sonicated for 30 min in chloroform at an initial concentration of 0.5 mg/ml and lightly centrifuged (1000g, 5 min).
The absorbances and concentrations of the reductively dodecylated and as received graphene dispered in chloroform in table 1. Graphene concentrations were calculated from ε600 = 2460 L g"1 m"1 (Y. Hernandez et al., Nat. Nanotechnol., 3) with 10 mm pathlength
Functionalisation of single wall carbon nanotubes
Lumps of sodium and dried naphthalide powder in one to one molar ratio were stirred overnight with a glass stirrer bar in dried N,N-dimethylacetamide to form a bulk 1 mgNa ml-1 sodium naphthalide solution. Within minutes, a dark green solution (indicative of the formation of a naphthalide radical anion) is formed which is stable for over a month under inert atmosphere. The solution is diluted down to the desired concentration and poured over dried single walled carbon nanotube (SWCNT) powder and stirred overnight. Within 30 minutes, dissolution of the SWCNTs is evident from the solution turning black and after overnight stirring an increase in viscosity is seen (if solutions of &1 mg SWCNT/ml are being created). The solutions were centrifuged at 10,000 g for 30 min in PTFE centrifuge tubes before pipetting off the SWCNT solution.
Dry and degassed dodecyl bromide (3 eq. vs. Na) was added to the reduced SWCNT solution and stirred overnight. The solution was quenched with dry oxygen, filtered under vacuum and washed with THF, water and acetone. The sodium naphthalide/DMAc solution can lead to higher concentrations by starting with a higher loading of nanotubes. By starting with 5.5 mg/ml of SWCNTs and charging at 10:1 C/Na, a solution of 5.1 mg/ml was obtained after centrifugation.
Figure 17 shows the impact of increasing the sodium to carbon ratio on yield. A charge ratio of 200:1 SWCNT to Na is sufficient to enable dissolution of the SWNT, although the yield of dissolved material is low in this scenario and contains predominantly the more defective SWCNTs in the initial sample. The yield can be increased by increasing the ratio of sodium naphthalide added.
Figure 18 shows the impact of different sodium concentrations on the grafting ratio C/R. At low sodium concentrations, the grafting ratio is low due to limited charge on the SWCNTs available for the grafting reaction whilst increasing the sodium concentration leads to condensation of the charge on the nanotubes also leading to a decrease in grafting. These phenomena lead to an idealised sodium concentration (-0.025 mol dm"3).
SWCNT reductive dissolution
A bulk solution of sodium naphthalide (NaNp) in DMAc was prepared by stirring sodium (50 mg) and naphthalene (278 mg) in DMAc (50 ml) using a glass stirrer bar. For high levels of charging at high SWCNT loadings, higher concentration solutions may be necessary. Sodium naphthalide solutions were used within a week of preparation. For a 1 mg ml"1 loading of SWCNTs charged to a C:Na ratio of 10:1 , 19.2 ml of 1 mg(Na) ml"1 sodium naphthalide was diluted to 100 ml added to SWCNTs (100 mg). The mixture was stirred with a glass stirrer bar overnight before pipetting into fluorinated ethylene propylene (FEP) centrifuge tubes with PTFE tape sealing the cap thread and centrifuging at 10,000 g for 30 min and solutions were then pipetted off by hand. Concentrations were measured by quenching 10 ml of solution by bubbling with dry oxygen for -20 min and filtering over a tared 100 nm pore PTFE membrane and washing with copious ethanol, Dl water, and acetone ensuring the sample did not dry out between washings. The sample was then dried at 150 °C for 3 hours and weighed. A membrane put through this procedure using 10 ml of DMAc in lieu of the SWCNT solution returned the tared weight.
Nanotubide solubilising solvents include tertiary/cyclic amides, most commonly N,N- dimethylformamide (DMF), N-menthyl-2-pyrrolidone (NMP), and N-cyclohexyl-2- pyrrolidone (CHP). Sodium naphthalide (NaNp) was selected as the reductant as it can be easily visually identified by a characteristic green colour. When equimo