The presently disclosed subject matter relates generally to the preparation of substrates comprising carbon nanotube sheets and to derivatization of highly-aligned carbon nanotube sheets with one or more transition metal centers.
Since the discovery of carbon nanotubes (CNTs) in 1991, CNTs have been used in various fields including energy storage, molecular electronics, nanoprobes, sensor, and composite materials. The excellent mechanical, electrical, and thermal properties of CNTs have also led to the emergence of CNTs as electrocatalysts, either as a stand-alone electrode with the necessary binder or as additionally modified with metal centers with added binders. CNT sheets have been prepared that are flexible, stackable with multi-layers, reusable, much lighter than metal, and are conductive.
However, CNTs are still challenged with the controllability in alignment-dependent, interconnection-dependent, and layered thickness-dependent electrical conductivity. Although it has been shown that chemical vapor deposition (CVD) can be used to fabricate CNT arrays (see for example, Jakubinek, M. B., Johnson, M. B., White, M. A., Jayasinghe, C., Li, G., Cho, W., Schulz, M. J., and Shanov. “Thermal and electrical conductivity of array-spun multi-walled carbon nanotube yarns.” Carbon 50, no. 1 (2012): 244-248), it is challenging to fabricate low resistance and thin layer CNT sheets. Specific challenges include: 1) handling CNT sheets, in particular for cutting, bonding, and electrically connecting the sheets, and 2) transporting CNT sheets from one place to other without damaging them.
The present application is generally directed to methods for the preparation of CNT sheets substrates as well as the deposition of metal centers on CNT sheets or CNT substrates and the products resulting therefrom.
In one aspect, the present application discloses a method of preparing a CNT sheet substrate comprising between about 5 and about 100 CNT sheets. In one variation, the 5-100 CNT sheet substrate is prepared from a CNT sheet substrate comprising at least about 200 CNT sheets.
In a further aspect, the present application discloses a CNT sheet or CNT substrate derivatized with one or more metal centers selected from the group of Cu, Pt, Ru, Ti, Pd, Sn, Ag, Au, CuO, Cu2O, TiO2, PdO, SnO, AgO, AuO, Ag/Ti, Pt/Ru, Ag/TiO2, Sn/TiO2, Pt/TiO2, Au/TiO2, and Pt/Al2O3. In another aspect, the present application discloses a catalyst comprising a metal-derivatized CNT sheet substrate. In yet another aspect, the present application discloses a method of converting carbon dioxide to one or more or carbon monoxide, methane, ethane, higher order hydrocarbons or a combination comprising exposing carbon dioxide to a catalyst comprising a metal-derivatized CNT sheet substrate. Alternately, the present application discloses each of a method of filtering biological contaminants from a biological sample and a method of filtering volatile organic compounds from a non-biological sample comprising passing the biological sample or non-biological sample comprising biological or VOC contaminants respectively through or past a metal-derivatized CNT sheet or a metal-derivatized CNT substrate as disclosed herein and separating the unwanted contaminants from the sample. In yet another aspect, the present application discloses each of an energy storage device, a fuel cell electrode, and a biosensor each of which comprise a metal-derivatized CNT sheet or CNT substrate as disclosed herein.
In another aspect, the present application discloses a method of preparing a CNT sheet or CNT substrate derivatized with one or more transition metal centers comprising: (a) treating a CNT sheet or CNT substrate with oxygen plasma yielding a functionalized CNT sheet or functionalized CNT substrate; and (b) depositing one or more transition metals on the functionalized CNT sheet or functionalized CNT substrate.
In another aspect, the present application discloses electrochemically depositing one or more metal centers on CNT sheets or CNT substrates as disclosed herein, without a prior treatment step, such as oxygen plasma.
In another aspect, the present application discloses a method for fabricating of a CNT sheet substrate, the method comprising: (a) providing a first CNT sheet substrate having a first thickness defined by a number of CNT sheets; (b) providing a template sheet having an aperture therein, the aperture having a predetermined dimension; (c) adhering the template sheet to the first CNT sheet substrate; and (d) pulling the template sheet away from the first CNT sheet substrate to form a second CNT sheet substrate of a second thickness and having the predetermined dimension of the aperture, wherein the second thickness is not as great as the first thickness.
Accordingly, it is an object of the presently disclosed subject matter to provide methods for the preparation of CNT sheets and CNT substrates, as well as the deposition of metal centers on CNT sheet and CNT substrates and products resulting therefrom. This object is achieved in whole or in part by the presently disclosed subject matter will become apparent to those skilled in the art after a reading of the following description of the disclosure when considered with the drawings.
It will be understood that the drawings are for the purpose of describing a preferred embodiment of the inventions and are not intended to limit the inventions thereto.
The Nyquist plots show the imaginary part (Y axis) versus the real part (X axis) of impedance. The inset using the same symbols shows an expanded view of the high frequency range. Data were collected in the frequency range of 1.0 MHz to 0.1 Hz at AC amplitude of 10 rms mV in 0.1 M KCl electrolyte, 2.68 mW/cm2 light intensity, the solutions had been purged with inert gas (either argon or nitrogen).
The light intensity was 2.68 mW/cm2 and the solution was 0.1M KCl electrolyte purged with N2.
Each response was measured with a UV lamp intensity of 2.68 mW/cm2 in 0.1M KCl electrolyte purged with N2 or CO2.
In accordance with the present application and as used herein, the following terms are defined with the following meanings, unless explicitly stated otherwise.
As used herein, “CNT sheet” refers to a roughly 3-dimensional arrangement of highly aligned multiwalled carbon nanotubes. Methods of preparation of CNT sheets have been reported, including but not limited to: (a) Pöhls, J. H., Johnson, M. B., White, M. A., Malik, R., Ruff, B., Jayasinghe, C., Schulz, M. & Shanov, V. (2012). “Physical properties of carbon nanotube sheets drawn from nanotube arrays.” Carbon, 50(11), 4175-4183; (b) Malik, R et al., “Manufacturing and Applications of Carbon Nanotube Sheet” Recent Advances in Circuits, Communications and Signal Processing, from the February 2013 Proceedings of the 5th International Conference on Nanotechnology, (c) Koo, Y.; Malik, R.; Alvarez, N.; White, L.; Shanov, V. N.; Schulz, M.; Collins, B.; Sankar, J.; Yun, Y. RSC Advances 2014, 4, 16362-16367, each of which is incorporated in its entirety. Other examples of CNT sheet preparations can be found in Zhang, et al., “Strong, Transparent, Multifunctional, Carbon Nanotube Sheets” Science 19, 1215-1219 (2005).
As used herein, “substrate” or “CNT sheet substrate” or “CNT substrate” refers to multiple layers of CNT sheets, wherein the layers are held together either physically or chemically, generally via Van der Waals forces. As used herein, “substrate” or “CNT sheet substrate” or “CNT substrate” does not refer to a nanocomposite and nor does it refer to a composition containing polymer components.
Typically, the substrate contains at least two CNT sheets. In one variation, the CNT sheet substrate contains at least about 5 CNT sheets, at least about 10 CNT sheets, at least about 25 CNT sheets, at least about 50 CNT sheets; in another variation at least about 100, or at least about 200, or at least about 300, or at least about 400; in yet another variation, the CNT sheet substrate contains at least about 500 CNT sheets or at least about 600, or at least about 700, or at least about 800, or at least about 900, or at least about 1000 CNT sheets. In another variation, the substrate comprises between about 5 and about 1000 CNT sheets or between about 10 and about 500 CNT sheets or between about 25 and about 200 CNT sheets or between about 50 and about 100 CNT sheets. In another variation, the substrate comprises between about 5 and about 10 CNT sheets or between about 10 and about 15 CNT sheets or between about 10 and about 25 CNT sheets or between about 15 and about 20 CNT sheets or between about 20 and about 30 CNT sheets or between about 40 and about 60 CNT sheets or between about 75 and about 150 CNT sheets or between about 90 and about 110 CNT sheets.
As used herein, “pristine” when used in reference to a CNT sheet or CNT substrate, as in ‘a pristine CNT sheet or substrate” refers to a CNT sheet or substrate that has not been chemically modified, that is, the surface of the sheet/substrate has not been functionalized or derivatized, as defined herein. Generally, the CNT sheets prepared or received as disclosed herein were used as received or as prepared according to the methods disclosed herein (see “Preparation of a CNT sheet substrate” in Example 1) and are considered ‘pristine.’
As used herein, “functionalized” when used in reference to a CNT sheet or a CNT substrate, as in ‘a functionalized CNT sheet’ or ‘functionalized CNT substrate’ refers to a chemical modification of the top and/or the bottom surface of a CNT sheet or CNT substrate. In one variation, the CNT sheet is functionalized to facilitate chemically affixing the metal centers to the sheet surface. Alternately, functionalization enables improved deposition of the metal centers on the CNT sheet.
As used herein, “derivatized” when used in reference to a CNT sheet or CNT substrate, as in ‘a derivatized CNT sheet’ or ‘a derivatized CNT substrate,’ refers to a CNT sheet or substrate in which metal and/or metal oxide centers are affixed or deposited on the top and/or the bottom of a CNT sheet surface. The metal and/or metal oxide centers can be in the form of, but are not limited to, nanoparticles as agglomerates, homogeneous or mostly homogeneous dispersions, or aggregates. In one variation, the derivatization refers to a CNT sheet or CNT substrate in which no more than 10% or no more than about 25% of the CNT surface area exposed to the derivatization process is covered by the metal and/or metal oxide. In another variation, no more than about 50% of the chemically available CNT surface area is covered; alternately, no more than about 75% is covered.
When a derivatized CNT sheet or CNT substrate is referred to as a catalyst, the composition has the effect of enabling a chemical reaction, such as, but not limited to, the conversion of carbon dioxide to one or more of carbon monoxide, methane, ethane, higher order hydrocarbons or any combination thereof, to proceed at a faster rate or under different conditions (e.g. at a lower temperature) than otherwise possible. As an electrocatalyst, the derivatized CNT sheet or CNT substrate responds to the application of current by initiating catalytic activity.
As used herein, ‘electrode structure’ typically refers to a printed circuit board (‘PCB’) electrically connected to a CNT sheet substrate; the CNT sheet substrate may be pristine, functionalized, derivatized, or otherwise treated as disclosed herein. One example of an electrode structure is shown by the cartoon in
In one aspect, the present application discloses a method of preparing ‘thin’ fabricated CNT sheet substrates comprising between about 5 and about 100 CNT sheets from ‘thick’ CNT sheet substrates comprising at least about 200 CNT sheets. Thin fabricated CNT sheet substrates were prepared according to the methods disclosed herein; the resulting substrate was electrochemically stable and had enhanced capacitive performance compared to a CNT sheet substrate comprising 200 CNT sheets. As shown herein, the experimental data displayed correlation between decreasing number of CNT sheets in the substrate and larger specific capacitances. Energy and power density correspondingly increased as the number of CNT sheets in the substrate decreased.
In another aspect, the present application discloses a CNT sheet or CNT substrate derivatized with one or more metal centers. In one embodiment, the one or more metal centers comprises one or more of Cu, Pt, Ru, Fe, Zn, Ti, Pd, Mn, Mg, Sn, Ni, Rh, Al, Ag, Au, CuO, Cu2O, TiO2, MnO2, MgO, Al2O3, Fe2O3, PdO, SnO, NiO, AgO, AuO, Ag/Ti, Pt/Ru, Ag/TiO2, Pt/Al2O3, Rh/Al2O3, and Pd/Fe2O3. In another embodiment, the one or more metal centers comprises one or more of Cu, Pt, Ru, Fe, Zn, Ti, Pd, Mg, Sn, Ni, Rh, Al, Ag, Au, CuO, Cu2O, TiO2, MgO, Al2O3, Fe2O3, PdO, SnO, NiO, AgO, AuO, Ag/Ti, Pt/Ru, Ag/TiO2, Pt/Al2O3, Rh/Al2O3, and Pd/Fe2O3. In yet another embodiment, the one or more metal centers comprises one or more of Cu, Pt, Ru, Fe, Zn, Ti, Pd, Mn, Mg, Sn, Ni, Rh, Al, Ag, Au, Ag/Ti and Pt/Ru. In another embodiment, the one or more metal centers comprises one or more of Cu, Pt, Ru, Fe, Zn, Ti, Pd, Mg, Sn, Ni, Rh, Al, Ag, Au, Ag/Ti and Pt/Ru. In another variation, the one or more metal centers comprises one or more of Cu, Ti, Pt, Ag, and Au or alternately comprises one or more of CuO, Cu2O, TiO2, MgO, Al2O3, Fe2O3, PdO, SnO, NiO, AgO, and AuO. Alternately, the one or more metal centers comprises one or more of Ag/TiO2, Pt/Al2O3, Rh/Al2O3, and Pd/Fe2O3. In yet another variation, the one or more metal centers comprises Cu or Ti or alternately comprises one or more of CuO, Cu2O, or TiO2, or alternately comprises Ag/TiO2. In a further variation, the one or more metal centers comprises Cu, CuO, Cu2O, TiO2, Ag/TiO2, Pt, Ag, Au or combinations thereof.
In another aspect, the present application discloses a CNT sheet or CNT substrate derivatized with one or more metal centers selected from the group of Cu, Pt, Ru, Ti, Pd, Sn, Ag, Au, CuO, Cu2O, TiO2, PdO, SnO, AgO, AuO, Ag/Ti, Pt/Ru, Ag/TiO2, Sn/TiO2, Pt/TiO2, Au/TiO2, and Pt/Al2O3. In one embodiment, the one or more metal centers comprises one or more of Cu, Pt, Ti, Pd, Ag, Au, Ag/Ti and Pt/Ru. In another embodiment, the one or more metal centers comprises one or more of Cu, Ti, Pt, Ag, and Au. In yet another embodiment, the one or more metal centers comprises one or more of CuO, Cu2O, TiO2, PdO, SnO, AgO, and AuO. Alternately, the one or more metal centers comprises one or more of Ag/TiO2, Sn/TiO2, Pt/TiO2, Au/TiO2, and Pt/Al2O3.
In one aspect, the present application discloses a catalyst comprising any metal-derivatized CNT sheet or a metal-derivatized CNT substrate as described above. In one variation, the catalyst is an electrocatalyst; in another variation, the catalyst is a photoelectrocatalyst.
In one embodiment, the metal-derivatized CNT substrates disclosed herein are used in the conversion of carbon dioxide to one or more of carbon monoxide, methane, ethane, higher order hydrocarbons or any combination thereof. In another embodiment, the catalyst of the present application is used in an energy storage device, in a fuel cell electrode, in the filtration of biological contaminants from a biological sample, in the filtration of volatile organic compounds from a sample, or as a biosensor.
In one aspect, the present application discloses a method of converting carbon dioxide to one or more or carbon monoxide, methane, ethane, higher order hydrocarbons or a combination thereof comprising exposing carbon dioxide to a catalyst as described above or exposing carbon dioxide to a metal-derivatized CNT sheet or metal-derivatized CNT sheet substrate as described above. Alternately, the present application discloses each of a method of filtering biological contaminants from a biological sample and a method of filtering volatile organic compounds from a non-biological sample comprising passing the biological sample or non-biological sample comprising biological or VOC contaminants respectively through or past a metal-derivatized CNT sheet or a metal-derivatized CNT substrate as disclosed herein and separating the unwanted contaminants from the sample. In yet another aspect, the present application discloses each of an energy storage device, a fuel cell electrode, and a biosensor each of which comprise a metal-derivatized CNT sheet or a metal-derivatized CNT substrate as disclosed herein.
In another aspect, the present application discloses a method of preparing a CNT sheet or CNT substrate derivatized with one or more transition metal centers comprising: (a) treating a CNT sheet or CNT substrate with oxygen plasma yielding a functionalized CNT sheet or functionalized CNT substrate; and (b) depositing one or more transition metals on the functionalized CNT sheet or functionalized CNT substrate. In one variation, the depositing comprises sol-gel deposition, electrodeposition, physical vapor deposition or chemical vapor deposition; in another variation, the depositing is only sol-gel deposition, electrodeposition, physical vapor deposition or chemical vapor deposition. In one embodiment, the electrodeposition comprises pulsed electrodeposition. In one variation the disclosed method further comprises activating the functionalized CNT sheet or functionalized CNT substrate. In one embodiment, the activation is electrochemical activation, wherein the activation optionally uses cyclic voltammetry.
In another aspect, the present application discloses a method of preparing a CNT sheet or CNT substrate derivatized with one or more transition metal centers comprising: (a) treating a CNT sheet or CNT substrate with oxygen plasma yielding a functionalized CNT sheet or functionalized CNT substrate; and (b) depositing one or more transition metals on the functionalized CNT sheet or functionalized CNT substrate via electrodeposition, wherein the method does not comprise electrochemically activating the functionalized CNT sheet or functionalized CNT substrate.
Using a CNT sheet substrate with excellent electrical conductivity, thermal, and chemical stability properties yields a flexible 3D electrode. Metals which can be deposited onto CNT sheets in accordance with the methods of the present application include but are not limited to Cu, Pt, Ru, Fe, Zn, Ti, Pd, Mn, Mg, Sn, Ni, Rh, Al, Co, Ag, and Au. The metal centers can be deposited as metal-oxides, such as CuO, Cu2O, TiO2, MnO2, MgO, Al2O3, Fe2O3, PdO, SnO, NiO, AgO, and AuO, as mixed metal systems, such as Ag/Ti or Pt/Ru, or as mixed metal-oxides, including, but not limited to, Ag/TiO2, Pt/Al2O3, Rh/Al2O3, and Pd/Fe2O3. As exemplified herein, some of the metal centers can be used as electrocatalysts for the conversion of carbon dioxide to hydrocarbons. In one embodiment, the metal affixed to the CNT sheet substrate is copper; in another embodiment, the metal is TiO2 or alternately is Ag/TiO2.
When the metal deposited on the CNT sheets is TiO2, the deposition pH and deposition time of the TiO2 nanoparticles can be varied, thereby influencing the photoresponse of the resulting CNT-TiO2 sheet substrates.
An SEM image of a CNT sheet substrate (top view) is shown in
As disclosed herein, a CNT sheet substrate has been treated to enable efficient deposition of metal and metal oxides on the CNT surface. When the deposited metal is copper, it acts as a highly effective catalytic reaction site for the electrochemical reduction of CO2 to CH4 (as well as CO and C2H4) without requiring any binder or an additional metal layer. A cartoon of an electrode as disclosed herein is shown in
The metal derivatized CNT sheet substrates, prepared according the methods disclosed herein, have a variety of different applications, due to the electrocatalytic properties and structural robustness of the products. In particular, the metal-derivatized CNT sheets and metal-derivatized CNT substrates disclosed can be used in fuel cell electrodes, as composites for energy storage devices, as filters to remove contaminants, either biological or VOCs (volatile organic compounds). In addition, the products of the current application can be used as biosensors.
In another aspect, the present application discloses a method for fabricating of a CNT sheet substrate, the method comprising: (a) providing a first CNT sheet substrate having a first thickness defined by a number of CNT sheets; (b) providing a template sheet having an aperture therein, the aperture having a predetermined dimension; (c) adhering the template sheet to the first CNT sheet substrate; and (d) pulling the template sheet away from the first CNT sheet substrate to form a second CNT sheet substrate of a second thickness and having the predetermined dimension of the aperture, wherein the second thickness is not as great as the first thickness. In one embodiment, the number of CNT sheets that define the first thickness of the first CNT sheet substrate is less than about 1000 CNT sheets or less than about 500 CNT sheets or less than about 250 CNT sheets. In yet another embodiment, the number of CNT sheets that define the first thickness of the first CNT sheet substrate ranges from about 25 to about 200 sheets. In another embodiment, step (b) comprises providing two template sheets, each having an aperture therein, each aperture having a predetermined dimension therein, optionally wherein the predetermined dimension of each aperture is same. Alternately, or in addition, step (c) comprises adhering one template sheet to a first surface of the first CNT sheet substrate and adhering the other template sheet to a second surface of the first CNT sheet substrate opposite the first surface. Alternately or in addition, step (d) comprises pulling the template sheets away from the first CNT sheet substrate to form a second CNT sheet substrate of a second thickness and having the predetermined dimension of the aperture, wherein the second thickness is not as great as the first thickness. In one variation of any of the disclosed aspects or embodiment, the method comprises repeating steps (a)-(d) one or more additional times, with each repeat starting with the CNT sheet substrate formed at the completion of steps (a)-(d).
The CNT sheets used in the following examples were prepared generally according to the methods disclosed in Pöhls, J. H., Johnson, M. B., White, M. A., Malik, R., Ruff, B., Jayasinghe, C., Schulz, M. & Shanov, V. (2012). “Physical properties of carbon nanotube sheets drawn from nanotube arrays.” Carbon, 50(11), 4175-4183 or as disclosed in Malik, R.; Alvarez, N.; Haase, M.; Ruff, B.; Song, Y.; Suberu, B.; Shereen, D.; Mast, D.; Gilpin, A.; Schulz, M.; Shanov, V. Recent Advances in Circuits, Communications and Signal Processing 2013, ISBN: 978-1-61804-164-7, 327-335.
Typically, the CNT sheets were produced from multi-walled carbon nanotubes (MWCNT) arrays. The sheets were drawn from 0.5 mm high CNT arrays, synthesized by a water-assisted chemical vapor deposition (CVD) process. Ethylene (C2H4) gas was used as a carbon precursor in order to obtain spinnable CNT arrays. The synthesized CNT arrays were aligned perpendicularly to the substrate, which consisted of several layers (Si/SiO2/Al2O3/Fe alloy catalyst). The free-standing CNT sheet substrate was fabricated from the 0.5 mm length MWCNT array by pulling a bundle of nanotubes from one side of the aligned CNT array. The sheet was then attached to a Teflon® belt and drawn at a rate of ca. 17 mm/s. The rotation of the belt caused accumulation of the formed CNT ribbon on the Teflon® belt and formation of a CNT sheet substrate with controllable dimensions and thickness. The array on the platform was linearly translated by one half of its width per revolution of the belt thus allowing newly formed sheets to overlap previously laid ribbon and thereby securing lateral uniformity within the substrate. The fabricated 200 layer CNT sheets were densified layer by layer using acetone while the ribbon was located on the belt and simultaneously exposed to the tension caused by the drawing procedure, thereby maintaining the longitudinal nanotube orientation and the original dimensions obtained during densification. The 200 layer CNT sheet substrates were characterized by scanning electron microscopy (SEM). The obtained images revealed good tube alignment and a cross-section thickness of about 10 μm.
Referring now to
In an alternative method of preparation, the CNT sheet substrate prepared as above is not affixed to the PCB, but is treated according to the method outlined below and is thereafter attached to the PCB.
The O2 plasma treatment of the CNT substrate electrode was performed in a discharge chamber (M4L™ RF gas plasma system, PVA TePla America, Corona, Calif., United States of America). The 200 layered pristine CNT sheet substrate was exposed to the plasma produced from O2 (50 sccm) and Ar (50 sccm) gas with a nominal power of about 35 W. The pressure was fixed at 500 mTorr. Typically, the exposure lasted for 5 minutes.
To activate the CNT sheet substrate that had been treated with oxygen plasma, the sheet, held by the PCB, was electrochemically cycled (10 cycles) from about −1.5 to about +1.5 V at room temperature and atmosphere in 0.1 mM CuSO4.5H2O at pH 2.8, adjusted by 0.1 M H2SO4 with KCl.
Each CNT sheet electrode was immersed in the solution for 5 min. A standard electrochemical cell using a potentiostat (Gamry Instruments, Warminster, Pa.) was used with a counter electrode (a platinum plate of 2 cm×2 cm) and an Ag/AgCl reference electrode. All experiments were carried out at atmospheric pressure and room temperature (25±1° C.) and solutions were pre-purged with nitrogen for 15 min to reduce the concentration of oxygen. Pulsed electrodeposition (PED) of copper was performed in 0.1 mM CuSO4.5H2O at pH 2.8, adjusted by 0.1 M H2SO4 with KCl. at −0.8 V and 5 Hz for 5 min. The Cu-derivatized CNT sheet substrates were then rinsed with DI water and ethanol.
Three electrocatalysts were thus prepared:
Based on data from Raman spectra the defect/graphite ratios (ID/IG ratios) of the various CNT substrates, P-CNT sheets, O-CNT sheets and OE-CNT sheets, were 0.83, 1.15, and 1.25 respectively.
The copper was deposited, coalesced and formed crystalline islands (grain formation and anisotropic growth) on P-CNT sheets and O-CNT sheets. However, the metal centers of O-CNT/Cu sheets was larger and more homogeneous. Without being bound by theory, it is believed that the presence of weakly bound oxygen atoms and oxidized defects at the CNT sheet surface created by O2 plasma induced formation of Cu—O bonds and promoted nucleation for strong Cu binding The copper particles on OE-CNT/Cu sheets were observed as agglomerated spheres. Without being bound by theory, it is believed that electrochemical redox cycling following O2 plasma increased the defect area of CNT sheets and chemically activated sites on the surface for metal deposition. From the population density, surface area and diameter estimation from SEM images, the metal centers of P-CNT/Cu sheets were generally spherical bundles with an average diameter of about 130 nm. The copper particles on O-CNT/Cu sheets were cylinders of different size with an average diameter and height of about 400 nm and 1 μm, respectively. The copper particles on OE-CNT/Cu sheets were hemispheres with an average diameter of about 80 nm. Noting that copper was deposited on both the top and bottom of the CNT sheets and assuming similar shapes/distributions on both surfaces, the surface areas of copper particles were calculated to be approximately 5.4 cm2, 24.7 cm2, and 12.2 cm2 respectively. Average grain sizes were calculated using the Debye-Scherrer equation on (111), (200) reflections from X-ray diffraction (XRD) patterns, yielding an average of about 37.8 nm for the Cu deposited on CNT sheets; only signals for copper peaks were observed in the XRD. The average grain size was consistent with SEM imaging.
CO2 reduction of CNT substrates, P-CNT sheets and three different CNT/Cu sheets, were determined by various applied currents in CO2 saturated 0.1 M NaHCO3 (380 mL) aqueous solution with pH of 6.7. Electrochemical reduction experiments were conducted in a three electrode electrochemical cell. The electrolyte (0.1 M NaHCO3, 380 mL) was saturated with ultra pure CO2 (99.9999%, Airgas, Greensboro, N.C., United States of America) at a continuous flow rate of 10 mL/min CO2 for 1 hour (298 K, pH 7.0). During the 15 minutes of CO2 reduction, the electrolyte was kept under constant stirring at a current range of −1.5 to −5.0 V and voltage range of −1.0 to −70 mA/cm2. At the end of the electrolysis, the gaseous products were immediately sampled and analyzed by gas chromatography. The gas chromatograph was equipped with a Hayesep-D and MS13X column and HID (Helium Ionization Detector) detector.
The CNT/Cu sheet substrates were reused without poisoning during electrocatalytic reduction of CO2. The gas products from the P-CNT sheets and three different CNT/Cu sheets are summarized in
To promote the growth of metal particles on CNT sheets/substrates, well-defined nucleation site and spatial distribution of nucleation site were both found to be variables; these properties also were found to increase electro-catalytic reactivity. Both oxygen plasma and electrochemical modification were good methods to modify CNT sheet surfaces for nucleation sites. After activating the CNT surface using the electrochemical method and treatment with oxygen plasma, smaller sized Cu centers were deposited more uniformly and without aggregation. After treating a CNT sheet only with oxygen plasma, copper particles deposited on the surface grew directionally as a 3D crystal. The CNT sheet electrode treated with O2 plasma but without subsequent electrochemical activation of the surface showed both a large catalytic surface area and large metallic contact area, and was shown to provide improved reactivity of CO2 at the Cu particles, more effectively converting carbon dioxide to hydrocarbons.
A PCB pattern was designed and electrically connected to a CNT sheet substrate comprising about 200 CNT layers (2 cm×2 cm×10 μm) as described in Example 1.
In an alternative method of preparation, the CNT sheet substrate prepared as in Example 1 is not affixed to the PCB, but is treated according to the method outlined below and is thereafter attached to the PCB.
The O2 plasma treatment of the CNT substrate was performed as described above.
TiO2 Deposition with O2 Plasma Treatment
In one variation, in which O2 plasma treatment was used, the treated CNT sheet substrate was derivatized with TiO2 using electrochemical methods.
A stable electrolytic suspension was prepared: a solution of 25 mL EtOH, 0.2 mmol H2O2, and 0.2 mmol titanium(IV) isopropoxide was added slowly with stirring to a solution of 1.2 mmol TiO2 (P25) in 25 mL of H2O, which was stirred vigorously for 5 minutes. The final solution was sonicated for 10 minutes; it had a pH of between 10 and 11 and maintained a homogenous medium without stirring at 298K.
All electrolytic experiments were conducted in the potentiostatic mode using a Gamry reference 600 potentiostat/galvanostat. A constant cell voltage was applied (2.0 V). After electrodeposition, CNT sheets coated with TiO2 nanoparticles were rinsed with Milli-Q™ water and then dried in an open atmosphere.
The TiO2-derivatized CNT sheet substrate was characterized using SEM, XRD, EDX, and XPS and Raman spectroscopies.
TiO2 Deposition without O2 Plasma Treatment
In one variation, in which O2 plasma treatment was not used, the CNT sheet substrate was derivatized with TiO2 using electrochemical methods as described above.
The TiO2-derivatized CNT sheet substrate was characterized using SEM and EDX (
Generally treatment with oxygen plasma yielded stable thinner layers of TiO2, while TiO2 deposited without oxygen plasma treatment was found to be thicker, but less stable.
A PCB pattern was designed and electrically connected to a CNT sheet substrate comprising about 200 CNT layers (2 cm×2 cm×10 μm) as described in Example 1.
In an alternative method of preparation, the CNT sheet substrate prepared as in Example 1 is not affixed to the PCB, but is treated according to the method outlined below and is thereafter attached to the PCB.
Ag/TiO2 nanoparticles were synthesized according to the methods previously described [Ko, et al., (2011). “Photochemical synthesis and photocatalytic activity in simulated solar light of nanosized Ag doped TiO2 nanoparticle composite.” Composites Part B: Engineering, 42(3), 579-583]. Typically, 0.3 g of P25 TiO2 particles were added to 50 mL of 15 mM AgNO3 aqueous solution with stirring; the solution pH (between 10 and 11) was reached via drop-wise addition of NH4OH. The solution was irradiated in a dark room under black light blue UV lamp (GE, 15 W) with stirring at room temperature for 4-5 hr. The Ag loaded TiO2 particles were collected via centrifugation, rinsed with distilled water, and dried overnight at 80° C. under vacuum. The Ag/TiO2 nanoparticles were characterized by methods disclosed in Ko et al.
The O2 plasma treatment of the CNT substrate was performed as described above.
Ag/TiO2 Nanoparticle Deposition with O2 Plasma Treatment
In one variation, in which O2 plasma treatment was used, the treated CNT sheet substrate was derivatized with Ag/TiO2 nanoparticles using electrochemical methods.
A stable electrolytic suspension was prepared comprising 1.2 nmol Ag/TiO2 nanoparticles suspended in an equal mixture of EtOH and H2O, which was stirred vigorously for 5 minutes, with optional sonication.
The electrolytic experiment was conducted in potentiostatic mode using a Gamry reference 600 potentiostat/galvanostat. A constant cell voltage was applied (2.0 V). After electrodeposition, CNT sheets coated with Ag/TiO2 nanoparticles were rinsed with Milli-Q™ water and then dried in an open atmosphere. The Ag/TiO2-derivatized CNT sheet substrate was characterized using SEM and XPS.
Ag/TiO2 Nanoparticle Deposition without O2 Plasma Treatment
In one variation, in which O2 plasma treatment was not used, the CNT sheet substrate was derivatized with Ag/TiO2 using electrochemical methods as described above.
The Ag/TiO2-derivatized CNT sheet substrate was characterized using SEM and EDX (
A PCB pattern is designed and electrically connected to a CNT sheet substrate comprising about 200 CNT layers (2 cm×2 cm×10 μm) as described in Example 1.
In an alternative method of preparation, the CNT sheet substrate prepared as in Example 1 is not affixed to the PCB, but is treated according to the method outlined below and is thereafter attached to the PCB.
Sn/TiO2 nanoparticles are synthesized according to methods known in the art (see for example, Xiufeng, Zhou, et al. “Preparation of crystalline Sn-doped TiO2 and its application in visible-light photocatalysis.” Journal of Nanomaterials 2011 (2011): 47.)
The electrodeposition of Sn/TiO2 nanoparticles on a CNT substrate is conducted as generally described above for the deposition of Ag/TiO2 on a CNT substrate electrode.
The Sn/TiO2-derivatized CNT sheet substrate is characterized using SEM, XRD, EDX, XPS, Raman, CV and other methods disclosed herein.
Using methods known to those of skill in the art, Pt/TiO2 nanoparticles or Au/TiO2 nanoparticles are prepared and deposited on a CNT substrate according to the methods disclosed herein.
The M/TiO2-derivatized CNT sheet substrate is characterized using SEM, XRD, EDX, XPS, Raman, CV and other methods disclosed herein.
A PCB pattern was designed and electrically connected to a CNT sheet substrate comprising about 200 CNT layers (2 cm×2 cm×10 μm) as described in Example 1.
In an alternative method of preparation, the CNT sheet substrate prepared as in Example 1 is not affixed to the PCB, but is treated according to the method outlined below and is thereafter attached to the PCB.
The O2 plasma treatment of the CNT substrate is optionally performed as described herein.
The optionally oxygen plasma treated CNT substrate is derivatized with Au or Pt using electrochemical methods disclosed herein, wherein the metal source solution is HAuCl4 or H2PtCl6.x H2O respectively. Alternately, the optionally treated CNT substrate is derivatized with a combination of Au and Pt, in which the source solution is comprised of both HAuCl4 and H2PtCl6.x H2O
The M-derivatized CNT sheet substrate is characterized using SEM, XRD, EDX, XPS, Raman, CV and other methods disclosed herein.
A highly-aligned CNT sheet was synthesized (see above). The CNT substrate comprising 200 CNT sheets were drawn from 0.5 mm multi-walled carbon nanotubes (MWCNT) arrays synthesized by a water-assisted chemical vapor deposition (CVD).
A electrolyte solution was prepared from two solutions, 1) solution A was prepared by mixing with 0.2 mmol H2O2 (CH3CH2OH, 99.5%, Fisher Scientific) and 0.2 mmol titanium (IV) isopropoxide (TTIP, Fisher Scientific) with absolute ethanol (CH3CH2OH, 99.5%, Fisher Scientific) for 15 min, 2) solution B was prepared by stirring a solution of 1.2 mmol TiO2 (nanosized bicrystalline P25 50 m2/g, 80% anatase, 20% rutile, Dugussa) in Milli-Q™ deionized water (Millipore) for 15 minutes. Solution B was slowly added into Solution A and 0.2 mmol ammonium hydroxide (NH4OH, 30% v/v aqueous solution, Sigma Aldrich) was added to adjust pH between 10 and 11. The final solution was homogeneously dispersed at room temperature.
Deposition of TiO2 on the CNT substrate prepared above was conducted using a potentiostat (Reference 600, Gamry Instrument, USA). The electrolyte was bubbled with purified N2 (99.9%. Airgas, USA) for 1 hour with 5 mL/min flow rate. The CNT sheet substrate (2 cm×2 cm) served as a substrate of the working electrode. A platinum plate of 2 cm×2 cm and Ag/AgCl electrodes were used as a counter electrode and reference electrode respectively. The deposition of TiO2 on the CNT sheet was carried out in the potential at 5.0 V. The CNT sheet substrates deposited with TiO2 were rinsed with de-ionized water to reduce/eliminate the residual components of the suspension. The final CNT-TiO2 sheet substrates were dried in air.
Raman analysis (using a LabRAM ARAMIS (HORIBA Scientific, Edison, N.J. United States of America) with excitation laser beam (wavelength, 633 nm)) revealed the structure of the CNT sheet substrate. The surface morphology as well as the thicknesses of the prepared CNT-TiO2 sheet substrates were characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi 8000, 10 kV). The atomic component analysis data were obtained with energy dispersive X-ray spectroscopy (EDS) with Bruker AXS (XFlash detector 5030). Structural changes of the CNT-TiO2 sheet substrates were characterized using an X-ray diffractometer (XRD, Bruker, Discover D8) with Cu Kα radiation (40 kV, 40 mA).
The morphology of top view and cross view with the four different CNT-TiO2 sheets is shown in
In cyclic voltammetry testing, CNT-TiO2 sheet substrates were used as a working electrode, using an electrolyte of 2.5 mM K3[Fe(CN)6] in 0.1 M KCl solution in a three-electrode cell with an Ag/AgCl reference electrode and a platinum plate counter electrode. Prior to evaluating photoelectrochemical activity, the electrolyte was purged with N2 for 1 hour at a 5 mL/min flow rate.
Cyclic voltammetry (CV) was used to characterize electrochemical properties of the CNT and the CNT-TiO2-4 sheets.
where A represents the area of the electrode (cm2), n is the number of electrons participating in the reaction, D is the diffusion coefficient of the molecule, C is the concentration of the probe molecule, and v is the scan rate (Vs−1), F is Faraday's constant, R is the universal gas constant and T is temperature (K). The peak current was plotted against the square root of the scan rate and the slope of the linear fit (a=ip/v1/2) was used to determine the diffusion coefficient. The surface area of CNT-TiO2 sheets electrodes was calculated (8.0004 cm2) based on electrode geometry and thickness. The calculated diffusion coefficient for [Fe(CN)6]3− at the CNT substrates was 4.27×10−6 cm2 s−1 at the CNT sheet and 2.56×10−6 cm2 s−1 at the CNT-TiO2-4 sheet respectively.
Photoactivity of the CNT-TiO2 sheets was measured using the electrochemical cell in combination with pulsed ultraviolet exposure. The 100 W, 365 nm ultraviolet (UV) lamp (UVP Inc.) was used as light source (2.68 mW/cm2). The illumination light intensity was measured by a UVX radiometer (UVP Inc. UVX-36 sensor). Electron impedance spectra and photocurrent densities were measured both in the dark and under illumination. The electrolyte was purged with CO2 for 1 hour at a 5 mL/min flow rate before testing.
Nyquist plots for the CNT sheet substrate and the four different CNT-TiO2 sheet electrodes with UV on/off exposure are shown in
A lower interfacial charge transfer resistance was observed for the CNT sheet substrate than for the four different CNT-TiO2 sheet substrates, indicating an interfacial nature of the deposited TiO2 nanoparticles on the CNT substrate. As shown in
The photocurrent responses on CNT sheet substrate and CNT-TiO2-3 sheet substrates in the 0.1M KCl were recorded (see
As demonstrated herein, CNT-TiO2 can be used as a photoactive catalyst of as a component part in a photoactive catalyst. In particular, CNT-TiO2 has applications including, but not limited to solar energy conversion and storage, fuel cells, and environment remediation.
The CNT sheet substrates derivatized with metal and/or metal oxides disclosed herein can be used in the conversion of carbon dioxide to one or more of carbon monoxide, methane, ethane, higher order hydrocarbons or any combination thereof. in the filtration of biological contaminants from a biological sample, or in the filtration of volatile organic compounds from a sample. Alternately, the derivatized CNT sheet substrates disclosed herein can used in an energy storage device, in a fuel cell electrode, or as a biosensor.
A CNT sheet substrate comprising about 200 CNT layers (2 cm×2 cm×10 μm) was prepared according to the method described in Example 1 (“Preparation of a CNT sheet substrate”). Typically, the CNT sheet substrate used in the following was cut to about 30 mm×5 mm.
Fabrication of a CNT Sheet Substrate Comprising Fewer than 200 CNT Sheets
Referring now to
As-prepared 200 CNT sheet substrate, SH, was cut to 20 mm width×30 mm length. Two template sheets (each being self-adhesive) AS1 and AS2, were adhered to the CNT sheet substrate, SH— one to the top and one to the bottom (see
The repeating of steps is referred to generally in
Additional template sheets were cut as above and in
After reaching a substrate comprising approximately 12.5 CNT sheets, the substrate was transparent as well as free-standing, meaning that the substrate had three dimensional structural robustness and no additional binder was necessary to hold the CNT sheets together. A free-standing substrate did not require either binder, glass or silicon support to maintain its physical integrity.
The electrochemical properties of each substrate comprising varying number of CNT sheets were explored. Using the free-standing substrates prepared according to the methods disclosed herein, the electrochemical measurements did not require any added binder or conductive physical support.
Raman analysis was performed on pristine 200 CNT sheet substrates using a LabRAM ARAMIS (HORIBA Scientific) with excitation laser beam wavelength of 633 nm. The surface morphology was characterized by field-emission scanning electron microscope (FE-SEM, Hitachi 8000, 10 kV).
Raman analysis showed three characteristic peaks corresponding to the D, G, and G′ bands observed at 1328 cm−1, 1580 cm−1, and 2641 cm−1 (
The electrochemical measurements were done in a three-electrode setup: a CNT sheet substrate was the working electrode, a platinum wire electrode and an Ag/AgCl electrode served as counter and reference electrodes respectively. The cyclic voltammetry (CV), constant current charge-discharge, and electrochemical impedance spectroscopy (EIS) were measured using Reference 600TM potentiostat (Gamry Instrument, United States of America) in 6 M KOH aqueous electrolyte at room temperature.
The specific capacitances of the electrodes, Cspe were calculated according to:
where I (in Ampere) is the constant discharge current, Δt (in seconds) is the time for a full discharge, m (in grams) indicates the weight of the active materials in the electrode, and ΔV (in Volts) represents the potential drop during discharge.
The energy density (E) and power density (P) were calculated from the charge/discharge data according to:
where C is the calculated specific capacitance, V is the voltage window (0.6 V minus the IR drop), and Δt is the discharge time.
The columbic efficiency, η, was estimated as:
where Δtd and Δtc represent the discharge and charge time, respectively.
As measured, the resistance of the 200 CNT sheet substrate as affixed to the PCB as disclosed herein (2 cm×2 cm) is less than 1Ω, which includes both the bulk resistance of the substrate and the contact resistance to the PCB.
As shown in
The peak current response of the electrode comprising about 200 CNT sheets is roughly 80 times larger than that of the substrate comprising about 12.5 CNT sheets.
Electrochemical impedance measurements were carried out to understand the electrochemical performance of the CNT sheet substrates as a supercapacitor.
In
A comparison of the results of the different substrates prepared according to the methods disclosed herein are summarized in Table 5. Substrates comprising between about 25 and about 50 CNT sheets have better supercapacitor performance than the other substrates measured at constant current of 1.5 mA. Specific capacitance of the substrate comprising approximately 12.5 CNT sheets, 10.10 F g−1 was also measured at relatively low current such as 0.15 mA. The electrochemical properties of the substrate comprising about 12.5 CNT sheets decreased, as shown in Table 5. Poor interfacial contact of the about 12.5 CNT sheets in the substrate might be one reason for the high internal resistance of the supercapacitor due to increasing resistance due to the loose connections between layers (
A ‘thin’ CNT sheet substrate comprising between about 12.5 and about 100 CNT sheets is prepared according to the methods of Example 8.
The thin CNT sheet substrate is derivatized with copper metal centers according to the methods of Example 1.
The Cu-derivatized thin CNT sheet substrate is characterized using standard electrochemical methods disclosed herein, including cyclic voltammetry and EIS charge/discharge response, as well as SEM, XRD, EDX, and Raman spectroscopy.
A ‘thin’ CNT sheet substrate comprising between about 12.5 and about 100 CNT sheets is prepared according to the methods of Example 8.
The thin CNT sheet substrate is derivatized with TiO2 according to the methods of Example 2 or Example 5.
The TiO2-derivatized thin CNT sheet substrate is characterized using standard electrochemical methods disclosed herein, including cyclic voltammetry and EIS charge/discharge response, as well as SEM, XRD, EDX, and Raman spectroscopy.
A ‘thin’ CNT sheet substrate comprising between about 12.5 and about 100 CNT sheets is prepared according to the methods of Example 8.
The thin CNT sheet substrate is derivatized with Ag/TiO2, Sn/TiO2, Pt/TiO2, or Au/TiO2, according to the methods of Example 3.
The M/TiO2-derivatized thin CNT sheet substrate is characterized using standard electrochemical methods disclosed herein, including cyclic voltammetry and EIS charge/discharge response, as well as SEM, XRD, EDX, and Raman spectroscopy.
A ‘thin’ CNT sheet substrate comprising between about 12.5 and about 100 CNT sheets is prepared according to the methods of Example 8.
The thin CNT sheet substrate is derivatized with Pt or Au according to the methods of Example 4.
The Pt- or Au-derivatized thin CNT sheet substrate is characterized using standard electrochemical methods disclosed herein, including cyclic voltammetry and EIS charge/discharge response, as well as SEM, XRD, EDX, and Raman spectroscopy.
The ‘thin’ CNT sheet substrates derivatized with metal and/or metal oxides disclosed herein can be used in the conversion of carbon dioxide to one or more of carbon monoxide, methane, ethane, higher order hydrocarbons or any combination thereof. in the filtration of biological contaminants from a biological sample, or in the filtration of volatile organic compounds from a sample. Alternately, derivatized CNT sheets substrates disclosed herein can used in an energy storage device, in a fuel cell electrode, or as a biosensor.
The patents and publications listed herein describe the general skill in the art and are hereby incorporated by reference in their entireties for all purposes and to the same extent as if each was specifically and individually indicated to be incorporated by reference. In the case of any conflict between a cited reference and this specification, the specification shall control. In describing embodiments of the present application, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/936,129 filed Feb. 5, 2014 and 62/020,690, filed Jul. 3, 2014, the disclosure of each of which is incorporated herein by reference in its entirety.
Work described herein was supported by the Office of Naval Research (N0001411103151) The United States Government therefore has certain rights in the inventions.
Filing Document | Filing Date | Country | Kind |
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PCT/US15/14621 | 2/5/2015 | WO | 00 |
Number | Date | Country | |
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61936129 | Feb 2014 | US | |
62020690 | Jul 2014 | US |