EP3038976A1 - Préparation en masse d'allotropes perforés du carbone par oxydation catalytique contrôlée - Google Patents

Préparation en masse d'allotropes perforés du carbone par oxydation catalytique contrôlée

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Publication number
EP3038976A1
EP3038976A1 EP13892744.7A EP13892744A EP3038976A1 EP 3038976 A1 EP3038976 A1 EP 3038976A1 EP 13892744 A EP13892744 A EP 13892744A EP 3038976 A1 EP3038976 A1 EP 3038976A1
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Prior art keywords
carbon
graphene
nanoparticles
oxidation catalyst
acid
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German (de)
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EP3038976A4 (fr
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Watson KENT
Yi Lin
Sayata Ghose
John Connell
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National Institute of Aerospace Associates
National Aeronautics and Space Administration NASA
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National Institute of Aerospace Associates
National Aeronautics and Space Administration NASA
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    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/00—Carbon; Compounds thereof
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
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    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/198—Graphene oxide
    • C—CHEMISTRY; METALLURGY
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    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/44—Carbon
    • C09C1/48—Carbon black
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
    • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
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    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
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    • H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon

Definitions

  • the present invention relates to holey graphenes, graphene nanomeshes, holey carbon nanotubes, or holey carbon nanofibers, and, more particularly to holey graphenes, graphene nanomeshes, holey carbon nanotubes, or holey carbon nanofibers formed by controlled catalytic oxidation.
  • Graphene sheets are two-dimensional, conjugated carbon structures which are only one or a few atoms thick. They are currently among the most studied nanomaterials for potential applications in electronics, energy harvesting, conversion, and storage, polymer composites, and others. 1"4 Graphene sheets with the most ideal structures are experimentally obtained via mechanical exfoliation (the "Scotch Tape” method), which only produces very small quantities. 1 For the bulk preparation of graphene, one of the most popular methods usually starts with strong oxidation of natural graphite into graphene oxide (GO) that is dispersible in aqueous solutions as an exfoliated monolayer or few-layered sheets.
  • GO graphene oxide
  • the exfoliated GO sheets may then be chemically or thermally converted into graphene - or more accurately “reduced graphene oxide” (rGO).
  • rGO reduced graphene oxide
  • chemically exfoliated rGO sheets usually have more defects.
  • 3 ' 5,6 [05] graphene sheets prepared from any method always contain intrinsic defects. Typical types of defects on graphene surface are Stone-Wales (pentagon-heptagon pairs) or vacancy sites, which are mostly of nanometer sizes. 5 ' 6 Recently, there have been a few reports on novel types of graphene structures which are featured with large pore openings (i.e., holes) on the conjugated carbon surface.
  • porous Si0 2 mask on top of a graphene flake, was then placed under oxygen plasma for the removal of exposed carbon atoms underneath. This resulted in supported or freestanding (upon lift-off) graphene nanomeshes with spherical holes of a few to tens of nm in diameter with various periodicities.
  • metallic nanoparticles such as silver (Ag), gold (Au), or platinum (Pt) nanoparticles, or metallic oxide nanoparticles, or combinations thereof.
  • the present invention addresses these needs by providing a method for forming holey graphenes by a controlled catalytic oxidation of the graphene surface using metallic or metal oxide nanoparticles.
  • the method includes the steps of providing a carbon allotrope in solid form, depositing carbon oxidation catalyst nanoparticles on the surface of the carbon allotrope sheet in a facile, controllable, and solvent-free process to yield an carbon oxidation catalyst-carbon allotrope material, subjecting the resulting carbon oxidation catalyst-carbon allotrope material to a thermal treatment in air, selectively oxidizing the carbons in contact with the carbon oxidation catalyst nanoparticles into gaseous byproducts, and removing the carbon oxidation catalyst nanoparticles such that the holes remain in the surface of the carbon allotrope.
  • the carbon allotrope is preferably graphene, graphene oxide, reduced graphene oxide, thermal exfoliated graphene, graphene nanoribbons, graphite, exfoliated graphite, expanded graphite, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, carbon fibers, carbon black, amorphous carbon, or fullerenes.
  • the carbon oxidation catalyst may be a transition metal, a rare earth metal, an oxides, or a
  • the carbon oxidation catalyst is Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, or Au.
  • the carbon oxidation catalyst nanoparticle -carbon allotrope is prepared by heating a mixture of a metal salt precursor and a carbon allotrope at an elevated temperature whereby the metal salt precursor is decomposed in an inert atmosphere with the elevated temperature being between 100 to 500°C and most preferably 350°C.
  • the metal salt precursor is preferably a compound with organic groups or inorganic groups and more preferably metal acetate, metal acetyl acetonate, metal nitrate, metal halides, or combinations thereof.
  • the heating may be provided by energy input such as thermal, electrical, mechanochemical, electrochemical, electron bombardment, ion bombardment, electromagnetic, or combinations of those.
  • the carbon oxidation catalyst nanoparticle is in a concentration of between 0.1 mol% and 20 mol%.
  • the oxidation step preferably occurs at a temperature between 150°C and 500°C.
  • the carbon oxidation catalyst nanoparticles may preferably be removed by treatment in acid at temperatures between ambient and the temperature to reflux the acid and the acid is most preferably nitric acid, hydrochloric acid, sulfuric acid, acetic acid, chlorosulfonic acid, phosphorous acid or combinations thereof.
  • the resulting holey carbon allotrope is incorporated into an electrode as a platform for an electrochemical device. Electrodes may be prepared according to the method described herein. In particular, this method may be use to form hole graphene by providing a graphene sheet and depositing Ag
  • the steps are as set out previously.
  • the Ag nanoparticles are in the form of metallic silver in a concentration of between 0.1 mol% and 20 mol%.
  • the Ag nanoparticles are removed by treatment in diluted nitric acid at temperatures between ambient and the temperature to reflux the acid.
  • Fig. la shows a TEM image of (Ag-G)i samples
  • Fig. lb shows a TEM image of (Ag-G) !0 samples, the inset is a SEM image showing the flat interface morphology of a Ag nanoparticle on a graphene sheet;
  • Fig. lc shows XRD patterns of the same samples: (Ag-G)i (bottom) and (Ag-G)io
  • Fig. Id shows an XPS spectrum in the Ag 4d core level region for the (Ag-G)io sample
  • Fig. 2a shows a lower magnification SEM image of a (Ag-G)io sample subjected to air oxidation at 300°C for 3 hours showing both holes and tracks;
  • FIG. 2b shows SEM images of a (Ag-G)io sample subjected to air oxidation at 300°C for 3 hours showing areas enriched with lower aspect ratio holes;
  • Fig. 2c shows SEM images of a (Ag-G)io sample subjected to air oxidation at 300°C for 3 hours showing areas enriched with high aspect ratio holes (i.e., tracks);
  • Fig. 2d shows a TEM image at higher magnification of a (Ag-G) 10 sample subjected to air oxidation at 300°C for 3 hours showing the morphology of a hole;
  • Fig. 3a shows DTG curves (air, 5.4°C/min) of the (Ag-G)io (top) and (Ag-G)i (middle) samples in comparison with the starting graphene sample (G, bottom);
  • Fig. 3b shows the isothermal regions of the TGA traces of the same (Ag-G)io sample heated to and held at the denoted temperatures (from top to bottom: 250, 300, 350, 400, 450, 500°C) in air for 3-10 h;
  • Fig. 4a shows a TEM image of the same (Ag-G)io sample oxidized in air at
  • Fig. 4b shows a TEM image of the same (Ag-G)io sample oxidized in air at
  • Fig. 4c shows a TEM image of the same (Ag-G)]o sample oxidized in air at 400°C, shown in the inset are two graphene sheets with small ( ⁇ 500 nm) lateral dimensions as a result of catalytic oxidation;
  • Fig. 5a shows XRD patterns of a (Ag-G)io sample before (black) and after (red) catalytic oxidation in air, the inset shows the enlarged Ag (1 11) peak region;
  • Fig. 5b shows XPS Ag 4d spectra of the same (Ag-G)io sample after catalytic oxidization in air at various temperatures: 250, 300, 350 and 400°C (from bottom to top);
  • Fig. 6a shows a SEM image of a hGj sample
  • Fig. 6b shows a TEM image of a hGj sample acquired at the exactly the same location as the corresponding image shown in Fig. 6a;
  • Fig. 6c shows a SEM image of a hG 10 sample
  • Fig. 6d shows a TEM image of a hGjo sample acquired at the exactly the same location as the corresponding image shown in Fig. 6c;
  • Fig. 6e shows a SEM image of a control graphene sample
  • Fig. 6f shows a TEM image of a control graphene sample acquired at the exactly the same location as the corresponding image shown in Fig. 6e;
  • Fig. 7a shows a TEM image of a hGio sheet
  • Fig. 7b shows an electron diffraction pattern taken from the area indicated in Fig.
  • Fig. 7c shows an electron diffraction partem taken from the area indicated in Fig.
  • Fig. 7d shows an electron diffraction pattern taken from the area indicated in Fig.
  • Fig. 8a shows XPS C Is spectra of a hGio sample (top, red), a hGj sample
  • Fig. 8b shows Raman spectra of a hGio sample (top), a hGi sample (middle), and a control graphene sample that was only refluxed in nitric acid under the same Step III conditions (bottom);
  • Fig. 9a shows a SEM image of a hG 10 sheet obtained from a larger scale (-2.1 g) preparation
  • Fig. 9b shows a photo of melt-extruded ribbons of neat Ultem (golden colored) and 1% hGio-filled Ultem composite (black colored);
  • Fig. 9c shows a comparison of the ultimate strengths of neat Ultem, 1 wt% graphene-filled Ultem composite (1% G-Ultem), and 1 wt% hGio-filled Ultem composite (1% hGio-Ultem);
  • Fig. 9d shows a comparison of Young's moduli of neat Ultem, 1 wt% graphene- filled Ultem composite (1% G-Ultem), and 1 wt% hG 10 -filled Ultem composite (1% hGio- Ultem);
  • Fig. 10a shows a SEM image showing the catalytic oxidation of MWNTs in air at 300°C of with 10 mol% Ag;
  • Fig. 10b shows a SEM image showing the catalytic oxidation of MWNTs in air at 300°C of with 5 mol% Au;
  • Fig. 10c shows a SEM image showing the catalytic oxidation of graphene in air at 300°C of with 5 mol% Au;
  • Fig. lOd shows a SEM image showing the catalytic oxidation of graphene in air at 300°C of with 5 mol% Pt;
  • Fig. 11 shows a SEM image of a (Ag-G)io sample subjected to thermal treatment at 300°C in air for 10 hours;
  • Fig. 12 shows DTG curves (air, 5.4°C/min) of the hGlO and hGl samples in comparison with the starting graphene sample;
  • Fig. 13a shows preliminary electrochemical evaluations in the form of cyclic voltammetry curves of a hGl 0 electrode at scanning rates from 10 (most inner curve) to 500 mV s-1 (most outer curve);
  • Fig. 13b shows preliminary electrochemical evaluations in the form of specific capacitance values of hGl 0 in comparison with those of a control graphene sample (with 2 hours nitric acid reflux only);
  • Fig. 14 shows the steps of the method described herein.
  • a straightforward yet highly scalable method is described to prepare bulk quantities of "holey graphenes", which are graphene sheets with holes ranging from a few to over 100 nm in diameter.
  • the approach to their preparation takes advantage of the catalytic properties of certain metal oxides or metals, such as silver (Ag), nanoparticles toward the air oxidation of graphitic carbons.
  • Ag nanoparticles were first deposited onto the graphene sheet surface in a facile, controllable, and solvent-free process. The catalyst- loaded graphene samples were then subjected to thermal treatment in air.
  • the graphitic carbons in contact with the Ag nanoparticles were selectively oxidized into gaseous byproducts such as CO or C0 2 , leaving the graphene surface with holes.
  • the Ag catalysts were then removed via refluxing in diluted nitric acid to obtain the final holey graphene products.
  • the average size of the holes on the graphene was found to strongly correlate with the size of the Ag nanoparticles and thus could be conveniently controlled as previously established by adjusting the silver precursor concentration.
  • the temperature and time of the air oxidation step as well as the catalyst removal treatment conditions were found to strongly affect the morphology of the holes. Characterization results of the holey graphene products suggested that the hole generation might have started from defect-rich regions present on the starting graphene sheets. As a result, the remaining graphitic carbons on the holey graphene sheets were highly crystalline, with no significant increase of the overall defect density despite the presence of structural holes.
  • This invention is a facile and well controllable procedure to prepare holey graphene structures, which contain holes on the graphene surfaces etched via catalytic oxidation of graphitic carbon by deposited metal oxide or metallic nanoparticles.
  • the technique described herein is not only versatile in that it provides controlled hole sizes on the graphitic surface, but also readily scalable. This enables more convenient use of these materials in many applications that require bulk quantities, such as polymeric composites and energy storage.
  • the commercially available starting graphene material is prepared from a process similar to the thermal reduction/exfoliation of GO ["thermally exfoliated graphene” (TEG) 19 ].
  • the preparation of holey graphenes (hG) is a 3-step process from the starting graphene material, namely the catalyst deposition, the catalytic oxidation, and the catalyst removal. Detailed observations from each step are discussed below.
  • Step I Catalyst Deposition.
  • catalytic nanoparticles such as Ag
  • MWNTs multi-walled carbon nanotubes
  • the nanoparticle growth in the Ag-G samples appears to use the local graphene surface as a template, as suggested by the flat interface indicating an intimate contact between Ag nanoparticles and the graphene support.
  • a scanning electron microscopy (SEM) image of an example with an Ag nanoparticle "sitting" on a wrinkled part of graphene is shown in the Figure lb inset.
  • the contact angle between the Ag nanoparticle and the graphene surface is smaller than 90°. In other words, the diameter of the contact area is somewhat smaller than that of the Ag nanoparticle. This is typically seen for all Ag-G samples as well as those using other metal salt precursors such as gold acetate, palladium acetate, or platinum acetyl acetonate .
  • Step II Catalytic Oxidation.
  • the metal oxide or metal nanoparticle decorated graphene samples are subjected to controlled air oxidation via heating in an open- ended tube furnace.
  • a significant number of holes appeared on the originally intact graphene surfaces. Most of the holes are associated with at least one Ag nanoparticle. Some holes also appeared as tracks, which are apparently associated with the directional movements of the attached Ag nanoparticles under the given conditions ( Figure 2b), likely due to etching-induced motions (see more below). Nevertheless, Ag nanoparticles with larger sizes typically yield holes of larger diameters (or tracks of larger widths).
  • the diameter of the Ag-graphene contact area is smaller than the corresponding Ag nanoparticle
  • the diameters of the holes could be equivalent or even slightly larger than the diameter of the corresponding Ag nanoparticles at higher oxidation degrees. This might be due to the unbalanced etching- induced motions of non-spherical Ag nanoparticles.
  • the motions of Ag nanoparticles on graphitic surfaces should be self-rotations along with movements in a slightly spiral and sometimes zigzag fashion.
  • the rather rough edges of the holes and tracks might also have originated from such unbalanced movements of Ag.
  • the weight loss threshold significantly reduces to ⁇ 370°C (peak at 534°C) for a (Ag-G)i sample and further to ⁇ 250°C (peak at 468°C) for a (Ag-G)io sample.
  • the remaining weight percentages of the (Ag-G)io samples heated to 250 and 350°C in air and held for 3 hours were 93 and 83 wt%, respectively.
  • the weight loss after 3 hours is ⁇ 50 wt%, indicating that there was a nearly complete oxidation of graphene with essentially no carbon left behind considering that Ag consisted of -47 wt% of the starting (Ag-G)io sample.
  • Step III Catalyst Removal.
  • the partially oxidized Ag-G samples from Step II (oxidation temperature at 300°C) are refluxed with diluted (2.6 M) nitric acid.
  • the solid is then extensively washed with water followed by drying.
  • the catalytic Ag nanoparticles are completely removed from the samples since nitric acid oxidized metallic Ag into Ag + (i.e., AgN0 3 ).
  • the Ag salt is soluble in the aqueous dispersion and effectively removed with repeated washing. No Ag nanoparticle is found by microscopic analysis of the final products.
  • the lack of Ag signals for these samples analyzed using both XPS and XRD confirms the complete removal of the metal.
  • Electron microscopy images shown in Figure 6 are from an instrument (Hitachi S- 5200) that is equipped with capabilities of acquiring images under both secondary electron (SE) and transmitted electron (TE) modes (i.e., SEM and TEM) conveniently at the same area.
  • SE secondary electron
  • TE transmitted electron
  • the SEM images ( Figure 6 left side, a, c, e) emphasize the top surface morphology, while the corresponding TEM images of the same area ( Figure 6 right side, b, d, f) allow observations through the thickness of the specimens. It is apparent from these images (Figure 6a - d) that the final samples after Step III catalyst removal exhibit distinct hole structures on the Ag-free graphitic surfaces. Therefore, these samples are referred to as "holey graphene" samples, or hGs.
  • the relative sizes of the holes in the hG samples inherit such dependence.
  • the hole sizes of the hG sample from a (Ag-G) ⁇ sample (designated as hGio) ranges from -10 to over 100 nm ( ⁇ 22 nm in average diameter), much larger than that of one started with (Ag-G)i (designated as hGj), which is ⁇ 5 nm in average diameter.
  • the hGi sample has a lower oxidation degree with the same treatment temperature, making its average hole size closer to the Ag-graphene contact area (smaller than the average diameter of catalytic Ag nanoparticles).
  • the hG 10 sample with a higher oxidation degree - due to large Ag- graphene contact area as well as lower oxidation threshold - has holes with diameters closer (and sometimes even larger due to hole merging) than the sizes of the original catalytic Ag
  • the wider size distribution of the holes in the hGio sample is a combined result from the initial wide distribution of the catalytic Ag nanoparticles and the inhomogeneous etching of the graphene sheets due to the irregular shapes of the catalysts as previously discussed. Nevertheless, this result demonstrates that the hole sizes of the hG samples can be controlled, to a consistent degree, by varying the loading, and thus the average size, of the catalytic Ag nanoparticles.
  • the retained graphitic crystallinity of the hG samples in this study suggests that many important properties of the starting graphene sample, such as electron mobility, electrical conductivity, thermal conductivity, and mechanical properties, are largely preserved. It is these properties of graphene that make it such an attractive material, so the fact that the hG samples retain them is very important for their subsequent applications that are dependent upon these properties.
  • the above 3 -step procedure to prepare hG samples is readily scalable. The first two steps are both conducted in the solid-state, so the limitations only come from the sizes of the mixing and heating devices. The last step, catalyst removal via nitric acid treatment, is a straightforward wet process that can be very conveniently scaled up to the level of multiple grams.
  • This large scale hGio product also shows comparable microscopic and spectroscopic characteristics as compared to the samples from the smaller scale batches discussed above.
  • the average hole size for the hGio sheets in the sample is -20 nm ( Figure 9a), comparable to that for a sample prepared from a smaller scale ( Figure 6c).
  • the Raman spectrum and the XPS spectrum of the sample are also very similar (not shown).
  • the hG sheets may be viewed as "graphene nets" that are more flexible than plain sheets, just like the comparison of a netbag vs. a regular bag but at a microscopic scale.
  • hGs might also be advantageous to intact graphene sheets.
  • the hole structures might allow polymer penetration or enhanced entanglement sites leading to more enhanced interactions, which could potentially be further improved by hole-edge functionalization.
  • the 3-step method to prepare hGs is versatile and applicable to various carbon allotropes since the Ag-catalyzed air oxidation of carbon is not unique to graphene sheets. For example, by heating a Ag nanoparticle-decorated multi-walled carbon nanotube ("MWNT”) sample at 300°C for 3 hours, significant Ag-induced oxidation of the nanotubes is observed ( Figure 10a). This method may also be followed to use these partially oxidized samples to prepare "holey carbon nanotubes".
  • MWNT multi-walled carbon nanotube
  • graphene oxide examples include graphene oxide, reduced graphene oxide, thermal exfoliated graphene, graphene nanoribbons, graphite, exfoliated graphite, expanded graphite single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, carbon fibers, carbon black, amorphous carbon, and fullerenes.
  • the carbon oxidation catalyst is not restricted to Ag; transition metals including rare earth metals, and their oxides may also be used as the catalyst.
  • the metals from Group VIIIA Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt
  • Group IB Cu, Ag, and Au
  • Pt and Au nanoparticles are both effective catalysts toward MWNTs and graphene under similar experimental conditions ( Figure 10b - d). More surveys are being conducted on the search for lower cost replacements for the noble metal catalysts. 23 It is interesting to note that some transition metal nanoparticles (such as Fe, Ni, and Co) have been used for graphene surface etching under reductive conditions in hydrogen atmosphere. 29"32 The movements of these nanoparticles on the highly crystalline graphene surface seemed to follow chirality patterns, as similarly observed by Booth et al.
  • the metals can be deposited onto the carbon allotropes in various ways, including but not limited to sputtering, electrochemical deposition, replacement reaction, spontaneous deposition, and solventless deposition. Solventless deposition is especially preferred for bulk preparation. It is preferable to use a metal compound as the precursor.
  • the preferable metal compounds include but are not limited to halides, nitrates, carboxylates, oxalates, acetates, acetylacetonates, and those with any other inorganic or organic functional groups.
  • the preferred range of temperature for carrying out the catalytic oxidation is between 150°C and 500°C.
  • the specific surface area (in m 2 g _1 ) of a hG sheet should be the same as an intact graphene sheet.
  • the actual surface area of carbon nanomaterials is strongly affected by post-processing methods. 34"38
  • the starting graphene sample is from a thermal exfoliation process and thus very lightweight and fluffy with a reasonably high specific surface area of -590 m 2 g " ' measured from the nitrogen adsorption-desorption isotherms using the Brunauer-Emmett-Teller (BET) method.
  • BET Brunauer-Emmett-Teller
  • the method disclosed herein is a straightforward procedure to controllably prepare hG sheets with holes of various sizes.
  • the 3-step procedure includes the deposition of Ag nanoparticles onto graphene sheets, the Ag-catalyzed oxidation of graphene in air under elevated temperature (typically at 300°C), and the refluxing with dilute nitric acid to remove Ag catalysts.
  • elevated temperature typically at 300°C
  • the hole sizes of the hG sheet products could be tuned in a wide range (average diameter from ⁇ 5 to tens of nm demonstrated in current work).
  • the air oxidation temperature and time duration in the second step and the intensity of the acid treatment in the last step may also affect the hole morphology of the final hG sheets.
  • the procedure was found highly scalable and used to produce multiple grams of hG sheets routinely. It is important that the hG sheets, despite their holey structures, largely retain the two- dimensional graphitic crystallinity as evidenced from a combination of microscopic and spectroscopic analyses. Therefore, the hG sheets have preserved the important properties of intact graphene sheets such as electrical, thermal, and mechanical properties. This finding has profound implications on the potential applications of hGs. For example, the preliminary experiments show that the hG sheets are better reinforcements for polymer composites than the starting intact graphene sheets due to their lower volume density but retained mechanical strength, as well as possible contributions from their unique "graphene net' ike structures in addition to enhanced matrix-filler interactions with the presence of the holes. The conductive nature of hG sheets and their porous structure may allow them to be used as advanced electrode materials in energy storage applications, for which more detailed research is currently underway.
  • XPS spectra were obtained on a ThermoFisher ESCAlab 250 X-ray Photoelectron Spectrometer.
  • Raman spectra were acquired on a Thermo-Nicolet-Almega Dispersive Raman Spectrometer equipped with excitation lasers with wavelengths of 532 and 785 nm.
  • BET surface area measurements were conducted on a Quantachrome Nova 2200e Surface Area and Pore Size Analyzer system.
  • Thermogravimetric (TGA) and differential thermogravimetric (DTG) traces were obtained on a Seiko TG/DTA 220 (SSC/5200) system.
  • Polymer ribbons specimens were cut into strips of ⁇ 5 cm ⁇ 5 mm for mechanical tests, which were conducted at room temperature using at least 5 specimens on an Instron 5848 Microtester at a gauge length and a crosshead speed at 20 mm and 10 mm min "1 , respectively.
  • Step I Catalyst Deposition: Ag Nanoparticle-Decorated Graphene (Ag-G).
  • the as-obtained graphene powder (100 mgj and silver acetate powder of the desired ratio (1 or 10 mol% Ag-to-C, corresponding to ⁇ 9 or ⁇ 47 wt%) were mechanically mixed for 5 min using a zirconia vial-ball set (SPEX CertiPrep, ⁇ 20 cm mixing load, 2 balls) with a SPEX CertiPrep 8000D high-energy shaker mill.
  • the solid mixture was then transferred to an appropriate container (e.g.
  • Step II Catalytic Oxidation: Air-Oxidized Ag-G.
  • a Ag-G sample 100 mg
  • a given temperature 250 - 400°C
  • Step HI - Catalyst Removal Holey Graphene (hG).
  • an air-oxidized Ag-G sample 50 mg was refluxed in diluted nitric acid (2.6 M, 30 mL) for 2 hours to remove Ag.
  • diluted nitric acid 2.6 M, 30 mL
  • the slurry was centrifuged and the supernatant was discarded.
  • the solid was then repeatedly washed with water in up to ten more redispersion - centrifugation cycles until the supernatant reached neutral (pH > 6).
  • the solid was then carefully dried to obtain the final hG product.
  • Typical overall yields in terms of carbon weight were approximately 80% and 68% for hG] and hGio samples (air oxidation at 300°C for 3 h), respectively.
  • the mixing equipment used was a 30 mL half sized mixer equipped with roller blades (C.W. Brabender) attached to a RS7500 drive/ data collection system (Rheometer

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Abstract

La présente invention concerne un procédé évolutif permettant de préparer de grandes quantités d'allotropes perforés du carbone comprenant des trous de diamètre compris entre quelques nm et plus de 100 nm. Des nanoparticules de catalyseur d'oxydation du carbone sont d'abord déposées sur une surface allotrope du carbone selon un procédé simple, contrôlable, et exempt de solvants. Les carbones chargés en catalyseur sont ensuite soumis à un traitement thermique en présence d'air. Les carbones en contact avec les nanoparticules de catalyseur d'oxydation du carbone sont oxydés sélectivement en produits secondaires gazeux tels que CO ou CO2, laissant la surface avec des trous. Le catalyseur est ensuite éliminé par reflux dans de l'acide nitrique dilué afin d'obtenir les allotropes perforés du carbone finaux. La taille moyenne des trous est corrélée fortement à la taille des nanoparticules de catalyseur et est contrôlée en ajustant la concentration en précurseur de catalyseur. La température et la durée de l'étape d'oxydation en présence d'air, et les conditions du traitement d'élimination du catalyseur, affectent fortement la morphologie des trous.
EP13892744.7A 2013-08-28 2013-08-28 Préparation en masse d'allotropes perforés du carbone par oxydation catalytique contrôlée Withdrawn EP3038976A4 (fr)

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