WO2017011873A1 - Procédés et matériaux pour capturer et stocker du gaz - Google Patents

Procédés et matériaux pour capturer et stocker du gaz Download PDF

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WO2017011873A1
WO2017011873A1 PCT/AU2016/050645 AU2016050645W WO2017011873A1 WO 2017011873 A1 WO2017011873 A1 WO 2017011873A1 AU 2016050645 W AU2016050645 W AU 2016050645W WO 2017011873 A1 WO2017011873 A1 WO 2017011873A1
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gas
potential
graphitic
adsorbent
graphitic material
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PCT/AU2016/050645
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English (en)
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Sean C SMITH
Xin Tan
Hassan TAHINI
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Newsouth Innovations Pty Limited
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Priority claimed from AU2015902863A external-priority patent/AU2015902863A0/en
Application filed by Newsouth Innovations Pty Limited filed Critical Newsouth Innovations Pty Limited
Publication of WO2017011873A1 publication Critical patent/WO2017011873A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/0203—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04
    • B01J20/0259—Compounds of N, P, As, Sb, Bi
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • B01J20/205—Carbon nanostructures, e.g. nanotubes, nanohorns, nanocones, nanoballs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/3085—Chemical treatments not covered by groups B01J20/3007 - B01J20/3078
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3202—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
    • B01J20/3204—Inorganic carriers, supports or substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3234—Inorganic material layers
    • B01J20/324—Inorganic material layers containing free carbon, e.g. activated carbon
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
    • C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
    • C10L3/10—Working-up natural gas or synthetic natural gas
    • C10L3/101—Removal of contaminants
    • C10L3/102—Removal of contaminants of acid contaminants
    • C10L3/104—Carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C11/00—Use of gas-solvents or gas-sorbents in vessels
    • F17C11/005—Use of gas-solvents or gas-sorbents in vessels for hydrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C11/00—Use of gas-solvents or gas-sorbents in vessels
    • F17C11/007—Use of gas-solvents or gas-sorbents in vessels for hydrocarbon gases, such as methane or natural gas, propane, butane or mixtures thereof [LPG]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/10—Inorganic adsorbents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
    • B01D2253/10—Inorganic adsorbents
    • B01D2253/102—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/10—Nitrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/24—Hydrocarbons
    • B01D2256/245—Methane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/504—Carbon dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/40—Further details for adsorption processes and devices
    • B01D2259/40083—Regeneration of adsorbents in processes other than pressure or temperature swing adsorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/80—Employing electric, magnetic, electromagnetic or wave energy, or particle radiation
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
    • C10L2290/00—Fuel preparation or upgrading, processes or apparatus therefore, comprising specific process steps or apparatus units
    • C10L2290/54—Specific separation steps for separating fractions, components or impurities during preparation or upgrading of a fuel
    • C10L2290/542—Adsorption of impurities during preparation or upgrading of a fuel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

  • the present invention relates to materials that can be used for gas capture and storage.
  • the material is gas permeable graphitic material comprising at least two elements such as carbon and nitrogen; or carbon and boron.
  • the material can be used for capturing gases such as carbon dioxide and/or hydrogen.
  • the material is a hydrogen storage material.
  • Materials that can store gas have been used for a wide variety of applications, including energy storage and pollution control. Gases can be adsorbed onto a material for storage and the gas can subsequently be desorbed when the gas storage is no longer required.
  • the materials that are used for such adsorption/desorption of gas typically have stringent requirements including that they preferably should be able to store a gas reversibly with large gravimetric and volumetric densities, and the adsorption/desorption process should not require significant energy inputs.
  • Light metal hydrides and chemical hydrides have been used as materials for gas adsorption/desorption.
  • a gas that can be stored by these materials is hydrogen.
  • molecular H 2 typically needs to be split for adsorption.
  • the intrinsic free energy barrier for H recombination to form H 2 from the hydride needs to be overcome.
  • the materials can be heated e.g. to greater than 200 °C to encourage desorption of the H 2 gas, but this presents a significant energy input.
  • the kinetics and thermodynamics of these adsorption/desorption processes is not favourable and can prevent the material from meeting requirements for commercial use.
  • Light-element-based materials including carbon nanotubes or other carbon-based nanostructures, non-carbonaceous nanotubes, mesoporous silica, metal-organic frameworks, and covalent-organic frameworks can also be used as materials for gas adsorption/desorption.
  • molecular H 2 is usually weakly bound to the materials with adsorption energies in the meV range and hence the gas desorbs at very low temperatures.
  • weak adsorption energetics requires the use of high pressures for sufficient storage to be achieved. Increasing the pressure can be a significant energy input, as well as presenting safety hazards in the event of storage failure.
  • Incorporating metals into the materials can improve the adsorption/desorption characteristics, but issues of clustering of the metal atoms and consequent degradation of the performance of the materials remains a challenge.
  • a method of adsorbing gas from a gas stream comprising the steps of: providing a gas permeable graphitic material comprising carbon and at least one other element; allowing a gas to contact the graphitic material; applying a first potential to the graphitic material to adsorb at least some of the gas thereby producing a gas loaded material; and applying a second potential to the gas loaded material to desorb at least some of the gas.
  • the at least one other element can be nitrogen and the graphitic material can be carbon nitride or nitrogen-doped graphene.
  • the at least one other element can be boron and the material can be boron-doped graphene.
  • an electrically conductive or semi-conductive adsorbent comprising a gas permeable graphitic material comprising carbon and at least one other element, when used under the influence of an electrical potential to adsorb a gas.
  • the at least one other element can be nitrogen.
  • the graphitic material can therefore be a graphitic C-N material having a band gap less than about 2.5eV.
  • the graphitic C-N material can have the formula CXNY, wherein X is ⁇ 5 and Y is ⁇ 5.
  • the graphitic material can be nitrogen-doped graphene.
  • the at least one other element is boron.
  • the graphitic material can be boron-doped graphene. There can be less than about 25, 20, 15, 15, 5 wt% nitrogen or boron doping.
  • a system for storing gas in an adsorbent comprising:
  • the gas is adsorbed to the graphitic material thereby producing a gas loaded material, and wherein at the second potential at least some of the gas is desorbed from the gas loaded graphitic material.
  • the graphitic material comprises carbon and at least one other element.
  • the at least one other element can be nitrogen and the graphitic material can be carbon nitride or nitrogen- doped graphene.
  • the first potential is the injection of electrons in order to modulate the charge on the material; and the second potential is the removal of electrons in order to modulate the charge on the material.
  • the at least one other element can be boron and the material can be boron-doped graphene.
  • the first potential is the removal of electrons in order to modulate the charge on the material; and the second potential is the injection of electrons in order to modulate the charge on the material.
  • Figure 1 shows embodiments of graphitic material comprising carbon and nitrogen.
  • Figure 1 is a top (upper) and side (lower) view of a 6x6 single N-doped graphene supercell.
  • the top and side views of the energy-optimized configurations of a single C0 2 molecule are shown absorbed on (b) neutral, (c) 2e ⁇ , (d) 4e " (N site), (e) 4e " (C site), and (f) 6e " N-doped graphene.
  • the distance between the C atom of C0 2 and the adsorption atom (C or N) and the adsorption energies of each configuration are listed.
  • Figure 1 h shows a g-C 4 N 3 supercell.
  • Figure 1j shows a g-C 3 N 4 supercell.
  • Figure 1 k shows a g-C 2 N supercell.
  • Figure 1 m shows a g-CN supercell.
  • Figure 2 shows the H-H bond length (Figure 2a), the distance between N atom and H 2 molecule ( Figure 2b), the induced dipole moment of H 2 molecule (Figure 2c), and the adsorption energy of H 2 molecule (Figure 2d) as a function of the charge state of g-C 4 N 3 .
  • Figure 3a shows the relaxation of the physisorbed H 2 molecule to a chemisorbed structure when 3e- negative charge has been introduced into the g-C 4 N 3 supercell.
  • Figure 3b shows the relaxation of the chemisorbed H 2 molecule (3e- charged g-C 4 N 3 supercell) back to a physisorbed structure when the electrons are removed from the supercell.
  • Figure 4a shows the average adsorption energy of H 2 molecules on 3e " negatively charged g-C 4 N 3 at different hydrogen coverages - up to 12 molecules in the supercell.
  • Figure 4b shows the variation of the average adsorption energy of H 2 molecules at full coverage as the negative charge in the g-C 4 N 3 supercell is increased from zero to 3e-.
  • Figure 5 shows the maximum number and the average adsorption energies of captured C0 2 molecules on negatively charged g-C 4 N 3 with different negative charge densities.
  • Figure 6 shows the adsorption energies of C0 2 , CH 4 , H 2 and N 2 and H 2 0 on neutral, 1 e “ and 2e " negatively charged g-C 4 N 3 .
  • Figure 7 shows top and side views of the lowest-energy configurations of three C0 2 molecules absorbed onto the three C atoms adjacent to the N-dopant site in Figure 1 (a) when 6 electrons are added.
  • the distance between the C atom of C0 2 and the C atoms of graphitic N-doped graphene and the average adsorption energy are listed.
  • Figure 8 shows the adsorption energies of C0 2 , CH 4 , H 2 , N 2 and H 2 0 on the neutral, 2e-, 4e- and 6e- N-doped graphene structure of Figure 1 (a).
  • Figure 9(a) shows top views of the lowest-energy configurations and the calculated band structure of BC 49 .
  • Figure 9(b) shows top views of the lowest-energy configurations and the calculated band structure of BC 7 .
  • Figure 9(c) shows top views of the lowest-energy configurations and the calculated band structure of BC 5 .
  • Figure 9(d) shows top views of the lowest-energy configurations and the calculated band structure of BC 3 .
  • Figure 10(a) shows top and side views of the lowest-energy configurations of a single H 2 molecule absorbed on neutral BC 49 .
  • Figure 10(b) shows top and side views of the lowest-energy configurations of a single H 2 molecule absorbed on 5e positively charged BC 49 .
  • Figure 1 1 (a) shows isosurface (0.06 e/au) of HOMO of neutral BC 49 .
  • Figure 1 1 (b) shows the differences in electron density distribution of 5e positively charged BC 49 relative to neutral BC 49 using frozen atomic geometry.
  • Figure 1 1 (c) shows the differences in electron density distribution of a H 2 molecule adsorbed on 5e positively charged BC 49 relative to neutral BC 49 using frozen atomic geometry.
  • Figure 12(a) shows the adsorption energy of H 2 molecule for BC 49 .
  • Figure 12(b) shows H-H bond length for BC 49 .
  • Figure 12(c) shows induced dipole moment of H 2 molecule for BC 49 .
  • Figure 12(d) shows H-B distance as a function of the positive charges of BC 49 .
  • Figure 13(a) shows the energy change of the relaxation of a H 2 molecule on BC 49 after five extra positive charges are introduced.
  • Figure 13(b) the reverse relaxation process of a H 2 molecule from BC 49 after five extra positive charges are removed from the adsorbent.
  • Figure 14(a) shows top and side views of the lowest-energy configurations of 5e positively charged BC 49 with two H 2 molecules electrocatalytically adsorption on each B atom
  • Figure 14(b) shows the average adsorption energies of positively charged BC 49 with two adsorbed H 2 molecules as a function of the positive charges.
  • Figure 15(a) shows top and side views of the lowest-energy configurations of neutral BC 5 .
  • Figure 15(b) shows top and side views of the lowest-energy configurations of 0.8e positively charged BC 5 with two H 2 molecules adsorption on each B atom.
  • Figure 15(c) shows average adsorption energies of positively charged BC 5 with two adsorbed H 2 molecules in each unit cell as a function of the positive charges.
  • the graphitic material as described herein is carbonaceous and comprises carbon with at least one other element.
  • the material can have its surface charge modulated upon the application or removal of electrons as an applied potential.
  • the material is able to reversibly adsorb a gas to its surface.
  • the at least one other element can be nitrogen.
  • the graphitic material comprises carbon and nitrogen.
  • the material can be a carbon nitride.
  • the material can be a nitrogen-doped graphene, which is essentially graphene with nitrogen doped into the graphene lattice. Experimental and theoretical studies have shown that you can only push N-doped graphene up to about 30% N, after which the continuous graphene mesh motif is not stable. In an embodiment there is less than about 25, 20, 15, 15 or 5 wt% nitrogen doping.
  • Graphitic carbon nitride on the other hand, whilst being a 2D material, is structurally different.
  • Graphitic carbon nitride are based on hexagonal rings with alternating N-C-N-C and the structure has intrinsic pores in it rather than the continuous mesh that graphene and N-doped graphene have.
  • the graphitic carbon and nitrogen containing material can be in the form of graphitic nanosheets, multi- and/or single-walled nanotubes (SWCNT), and/or fullerenes. Combinations of structures could be employed, for example, graphitic nanosheets used together with SWCNT.
  • the at least one other element can be boron.
  • the graphitic material comprises carbon and boron.
  • the material can be a boron-doped graphene, which is essentially graphene with boron doped into the graphene lattice. In an embodiment there is less than about 25, 20, 15, 15 or 5 wt% nitrogen doping.
  • the graphitic carbon and boron containing material can be in the form of graphitic nanosheets, multi- and/or single-walled nanotubes (SWCNT), and/or fullerenes. Combinations of structures could be employed, for example, graphitic nanosheets used together with SWCNT.
  • graphitic carbon nitrides can have a variety of molecular architectures. This is because nitrogen present in the carbon nitride structure can cause the material to adopt different chemical structures by creating different types of bonding, for example primary, secondary and tertiary forms of nitrogen bonding.
  • the graphitic carbon nitride may include at least secondary and/or tertiary forms of nitrogen.
  • the carbonaceous graphitic material comprises nitrogen predominately in the secondary form.
  • the graphitic carbon nitride can be synthesised from precursor materials that are known to result in the desired chemical structure, which can be deduced by spectroscopy.
  • the method of the invention can include synthesising the graphitic material.
  • the unit cell is the repeat unit that makes up the graphitic carbon nitride.
  • the graphitic carbon nitride can be electrically conductive.
  • the graphitic carbon nitride can be an electrical semi-conductor.
  • Other graphitic carbon nitrides can be used, for example C 2 N and CN.
  • a mixture two or more graphitic carbon nitrides can be used e.g. a mixture of C 4 N 3 and C 3 N 4 materials.
  • Dopants can be added to the graphitic carbon nitride lattice.
  • the dopants can include boron, silicon, germanium. The presence of dopants can disrupt the unit cell formula. Introduction of dopants can be used to alter the electrical properties of the graphitic carbon nitride and may be used to adjust the band gap of the material. Metals such as lithium, beryllium, aluminium, palladium, platinum, ruthenium, (or any other metal known for use in conductors) can be included as a dopant. In some circumstances the dopant can also be a non-metal atom such as sulphur. A mixture of metal and non-metal dopants can be used. The dopant can be introduced during synthesis of the graphitic carbon nitride. The total amount of doping can be less than about 1 , 5, 10 or 20 % by weight.
  • N-doped graphene is the dominant energetically favoured defect site occurring when N is doped into graphene. It has been demonstrated both experimentally and theoretically that substitutional N doping can be pushed as high as 30 % nitrogen content.
  • the N-doped graphene material is conducting (metallic), which is a very important feature to effect the addition of charge to the material for the electrocata lytic gas binding.
  • conducting g-C 4 N 3 which has only been inferred in one experimental paper to date
  • B-doped graphene Hexagonal-like B-doped graphenes with B content less than 50 % have been synthesized.
  • the structure determines whether the B-doped graphene is a conductor (metallic) or a semiconductor. Typically, less than 30 wt% of boron doping results in a conductor.
  • metallic B-doped graphene has a structure ranging from BC 49 -BC 5
  • semiconductor graphene has a structure of BC 3 .
  • the gas permeable carbon and other element containing material is an adsorbent for gas.
  • gas molecules are able to interact with at least some of the atoms in the graphitic lattice.
  • the interaction of the gas with the graphitic material can be by a covalent, ionic and/or Van der Waals type of bonding.
  • the gas adsorption and desorption is performed by charge modulation of the underlying graphitic material.
  • the permeability to gas can be a result of the porosity of the gas permeable material.
  • Nanosheets such as graphitic carbon nitride, or N-or B-doped graphene, have a natural porosity along a 2D plane, while nanotubes have a natural porosity along a longitudinal axis of the tube. Accordingly, mixtures of different forms of graphitic material can be used to control the porosity of the gas permeable material, and this may alter the adsorption and/or desorption characteristics. Gas can be delivered to the material at a flow rate that allows at least some of the gas to permeate the material and be adsorbed thereon.
  • the gas that is adsorbed can be a pure gas, a substantially pure gas, or a mixture of gases.
  • the gas is selected from hydrogen, carbon dioxide, nitrogen, methane and mixtures thereof.
  • Other commercially relevant gases, such as argon, helium and oxygen, may also be adsorbed.
  • the gas adsorption can be for separation of a gas from a stream comprising a mixture of gases.
  • the carbonaceous absorbent material may selectively adsorb one gas.
  • the material may selectively adsorb carbon dioxide.
  • This selective adsorption property may enable the material and method to be used as or during a purifying step in gas production and/or separation, for example removal of carbon dioxide from natural gas in the liquefied natural gas industry.
  • This selective adsorption property may also allow for the selective adsorption of gases that are produced as a by-product from industrial application, for example carbon dioxide produced from coal fire power stations.
  • the graphitic material can also be used as an indicator and/or detector to detect the presence of a gas in a gas stream. It may be advantageous to detect trace amounts of a particular gas in a gas stream, for example detecting trace amounts of carbon dioxide in a nitrogen stream. Upon adsorption of a target gas the detector could indicate to the user that a particular gas has been adsorbed. This may be by detecting a change in the weight of the material. The change in weight might be known to only be possible upon the adsorption of the particular target gas.
  • the amount of gas that is adsorbed onto the graphitic material can be related to (and thus controlled) by the electrical and/or chemical characteristics of the graphitic material.
  • the graphitic material adsorbs at least about 3, 5, 6, 7, 8, 10, 20, 30 or 40 wt.% gas. The higher the molecular weight of the gas, the more wt% that the material may absorb.
  • a graphitic carbon nitride adsorbs about 6 to 7wt.% hydrogen.
  • an N-doped graphene material may adsorbs about 40 wt.% carbon dioxide.
  • B-doped graphene adsorbs about 5 to 6 wt% such as 5.3 wt.% hydrogen. For some gases, such as carbon dioxide, it may be advantageous to adsorb as much gas as the graphitic material will allow.
  • the graphitic carbon nitrides seem to be the most useful for adsorbing both H 2 and C0 2 .
  • the B-doped graphene can be useful for adsorbing hydrogen.
  • the loading of e.g. the graphitic carbon nitride or the B-doped graphene with at least 5 wt.% gas can mean that the graphitic materials are suitable for application as a hydrogen storage material.
  • Hydrogen storage materials find use for example in hydrogen powered cars. In terms of gas storage, the kinetics and thermodynamics of desorption is a critical step in being able to deliver gas on demand without significant delay.
  • the gas loaded material can be stored, handled, transported.
  • the gas-loaded material should remain in the loaded state, for as long as the first potential is applied to it.
  • the material can be stable for months, weeks or days.
  • C0 2 carbon dioxide
  • MOFs metal-organic frameworks
  • AIN aluminum nitride
  • h-BN hexagonal boron nitride
  • SiC silicon carbide
  • the N-doped graphene materials seem to be the most useful for absorbing C0 2 .
  • electrons can be injected or removed from the graphitic material depending upon the chemistry of the material.
  • electrons can be injected into the graphitic C-N material (carbon nitrides or N-doped graphenes) to encourage gas adsorption.
  • electrons can be removed from B-doped graphene to encourages gas adsorption to a positively charged surface.
  • the injection and removal of electrons can be by the application of an electrical current or voltage.
  • graphitic material has an inherent band gap then this will impact how much potential needs to be applied to encourage gas adsorption.
  • Lower band gap values usually means a relatively low electrical potential is required for adsorption of a gas compared to a higher band gap material. Accordingly, graphitic materials (semi-conductors e.g. carbon nitride) with band gaps less than about 5, 4, 3, 2.5 or 2 eV can be most suitable for gas
  • a first potential can be applied to adsorb at least some gas onto the graphitic material.
  • a second potential can be applied to desorb at least some of the adsorbed gas from the graphitic material.
  • the second potential can be applied subsequent to the first potential.
  • a first and second potential can be applied cyclically.
  • the graphitic material can be in contact with an electrical source.
  • the electrical source can be an electrode in direct contact with an inherently electrically conductive graphitic material.
  • the electrode can be a layer associated with the gas permeable material.
  • the gas permeable material can be applied as a thin film onto the surface of an electrically conductive substrate.
  • the layer of electrically conductive material can comprise a metal oxide, or a noble metal.
  • the layer can be e.g. ITO, or gold, or it could comprise an electrically conductive carbon material.
  • the gas permeable carbon and nitrogen; or carbon and boron containing material can increase in electrical conductivity by mixing it with a conductive material.
  • the conductive material can be carbon black or graphene.
  • the mixture can have the electrical potential applied by a point contact, and/or the mixture can be applied onto a surface of a conductive substrate in contact with the electrodes.
  • a conductive adhesive may be included in the conductive mixture to adhere the conductive mixture to the substrate.
  • Gas adsorption can occur upon exposure of the material to a first potential.
  • the first potential can be less than about 100, 80, 90, 70, 60, 50, 40, 30, 20 or 10 volts. In some embodiments, the first potential is less than about 10 volts.
  • the applied voltage is at most about 8, 6, 4, 2 volts from a standard hydrogen electrode. In another embodiment, about 1 volt is applied to cause the adsorption of gas.
  • the first potential is varied (this can be controlled) to adjust the amount of gas adsorbed. Prior experiments can be undertaken to determine how much gas will be adsorbed at various applied potentials. The advantage of relatively low voltage values is that they can help to reduce energy input and may make use of the carbonaceous material safer from an electrical hazard view point, for example minimizing electrical discharge which can be especially important for hydrogen storage or the storage of other combustible gases.
  • injected electrons can be removed from the graphitic material.
  • electrons can be injected into the B-doped graphene. Gas desorption can occur upon exposure to the second potential.
  • the second potential is determined relative to the first potential.
  • the potential values required to adsorb and desorb gas can be related to the band gap of the graphitic material.
  • the second potential can be less than the first potential. In one embodiment, the second potential is 80, 70, 60 or 50% less than the first potential. Optionally, the potential is varied (this can be controlled) to adjust the amount of gas desorbed. In one embodiment, the second potential is 0 volts (which means that any electrical potential is effectively removed from the system). The spontaneous discharge of excess electrons may need assistance. At 0 volts, substantially all of the adsorbed gas in the gas loaded graphitic material may be desorbed. The second potential can be greater than the first potential. In one embodiment, the second potential is 80, 70, 60 or 50% higher than the first potential. Optionally, the potential is varied (this can be controlled) to adjust the amount of gas desorbed
  • a vacuum may be applied before or after the second potential is reached to aid desorption of gas.
  • the volume of air surrounding the graphitic material may be flushed prior to desorption.
  • Desorption may be performed in steps to prevent a sudden increase in pressure.
  • the first and the second potential may alternatively be switched where the second potential is applied for a longer period of time than the first potential. In this way, release of the gas can be performed by repeated adsorption/desorption steps that result in a net desorption.
  • a gradient potential change between the second and first potential may be used to achieve a steady state release of gas. However, it may be desirable that the gas is desorbed in one sudden step.
  • An algorithm can be used to control the switching between applied potentials.
  • the graphitic C-N material may adsorb a particular gas from a gas stream, when a certain threshold of electrons are injected .
  • a second different gas may be adsorbed when more electrons are injected.
  • a first potential can cause the adsorption of a first gas; a further applied potential that is greater than the first potential can adsorb a second gas from a gas stream.
  • the relative potentials required for adsorption and desorption of each gas may be such that transitioning between the different potentials would adsorb/desorb only one gas.
  • An algorithm can be used to control the switching between the different potentials for multiple gas adsorption/desorption.
  • the graphitic C-B material may adsorb a particular gas from a gas stream, when a certain threshold of electrons are removed .
  • a second different gas may be adsorbed when more electrons are removed.
  • a first potential can cause the desorption of a first gas; a further applied potential that is less than the first potential can desorb a second gas from a gas stream.
  • the relative potentials required for adsorption and desorption of each gas may be such that transitioning between the different potentials would adsorb/desorb only one gas.
  • An algorithm can be used to control the switching between the different potentials for multiple gas adsorption/desorption.
  • a combination of carbonaceous materials e.g. a combination of N-doped graphene and B- doped graphene may be used to adsorb two or more different gases.
  • the amount of first gas adsorbed is generally less than the total adsorption capacity of the carbonaceous material. If the carbonaceous material is overloaded with the first gas, it may not be able to adsorb the second gas. If two different carbonaceous materials are used where each carbonaceous material selectively binds a different gas e.g. N-doped graphene for C0 2 adsorption and B-doped graphene for H 2 adsorption, then each carbonaceous material may be overloaded with adsorbed gas without affecting the loading capacity of the other carbonaceous material.
  • a different gas e.g. N-doped graphene for C0 2 adsorption and B-doped graphene for H 2 adsorption
  • the temperature required for gas desorption is greater than the temperature required for gas adsorption.
  • An advantage of the materials described here is that desorption may not require elevated temperatures and may instead rely only on the removal of the first potential to provide the second potential.
  • the second potential can be 0 volts.
  • desorption may be performed at temperatures approximate to that of the adsorption process. Accordingly, desorption may be performed at a temperature less than about 100 °C, 75 °C or 50 °C. In an embodiment, desorption is performed at approximately room temperature.
  • the temperatures used are related to the way in which the graphitic material binds the gas.
  • the graphitic materials can adsorb gas in its molecular form. This is in contrast with, for example, metal hydrides which typically require the use of catalysts to split gases such as hydrogen to adsorb the gas in elemental form.
  • Adsorbing gas in its molecular form may mean the use of graphitic materials can significantly reduce the energy barrier required for adsorption and desorption because there is no need to break and reform bonds i.e. energy inputs such as temperature can be significantly reduced.
  • the electrical response which mediates the strength of binding means that high pressures are not necessarily required to adsorb gas onto the graphitic carbon nitride.
  • the graphitic materials can be used in a system which comprises an electrical source to apply the first and second potentials.
  • the system may comprise sensors to determine the pressure of the gas before, during and/or after adsorption and/or desorption of the gas.
  • the sensors may communicate with a computer.
  • the computer may instruct the electrical source.
  • the computer may instruct the electrical source to apply the second potential to desorb gas.
  • the computer may instruct the electrical source to apply the first potential to adsorb more gas. More than one computer can be used to instruct the electrical source(s).
  • the system may comprise a temperature regulator.
  • the temperature regulator may heat and cool the system, and may also be instructed by a computer.
  • This computer may be the same or different to the computer that instructs the electrical source. Where different computers are used to instruct the temperature regulator and the electrical source, the two computers can communicate with one another.
  • the material can be contained in a voluminous body.
  • the desorbed gas may be stored in this voluminous body and/or stored in an intermediate chamber in
  • the system may comprise pressure relief valves in communication with the voluminous body. Pressure relief valves may operate when the system fails and there is sudden desorbing of gas. These valves may operate with and/or without the input from a computer. The values may communicate with the pressure sensors.
  • the graphitic carbon nitride can be synthesized by cross-linking nitride-containing anions in an ionic liquid or other suitable precursor materials such as ammonia. In situations where the graphitic C-N material is provided on a conductive substrate, the graphitic C-N material can be synthesized directly onto an electrically conductive substrate.
  • B-doped graphene can be prepared using solid phase, liquid phase, chemical vapour deposition, or post-functionalization of graphene.
  • a boron precursor such as mainly H 3 B0 3 , B 2 0 3 or B 4 C
  • boron doped graphite can be mechanically exfoliated in order to obtain single sheets of B-doped graphene.
  • B-doped graphene can be synthesized directly on to an electrical conductive substrate. Examples
  • 2x2 and 2x 1 supercells for g-C 4 N 3 were employed with periodic boundary conditions in the x-y plane.
  • the vacuum space was set to larger than 20 A in the z direction to avoid interactions between periodic images.
  • all the atomic coordinates were fully relaxed up to the residual atomic forces smaller than 0.001 Ha/A, and the total energy was converged to 10 ⁇ 5 Ha.
  • the Brillouin zone integration was performed on a (6x6x1 ) and (4x8x1 ) Monkhorst-Pack k-point mesh [Tan et al., ChemSusChem 2015 (in press)] for g-C 4 N 3 and g-C 3 N 4 , respectively.
  • the adsorption energy Eads of H 2 molecules on adsorbent was defined as
  • Eads (Eadsorbent+nEH2-Eadsorbent-nH 2 )/n, where Eadsorbent is the total energy of isolated g-C 4 N 3 or g-C 3 N 4 ; EH 2 is the total energy of an isolated H 2 molecule; Eadsorbent- nH2 is the total energy of adsorbent with adsorbed H 2 molecules; and n is the number of H 2 molecules adsorbed on adsorbent. According to this definition, a more positive adsorption energy indicates a stronger binding of H 2 molecule to adsorbent.
  • the electron distribution and transfer mechanism are determined using the Mulliken method [e.g. Du et al., Phys. Rev. Lett. 2012, 108, 197207].
  • the Brillouin zone integration was performed on a (5x5x1 ), (12x12x1 ), (13x13x1) and (12x12x1 ) Monkhorst-Pack k-point mesh [Monkhorst et al. Phys. Rev. B 1976, 13, 5188-5192] for BC49, BC7, BC5 and BC3, respectively.
  • the adsorption energy Eads of H 2 molecules on adsorbent was defined as
  • Eads (Eadsorbent+nEH2-Eadsorbent-nH 2 )/n, where Eadsorbent is the total energy of isolated g-C 4 N 3 or g-C 3 N 4 ; EH 2 is the total energy of an isolated H 2 molecule; Eadsorbent- nH2 is the total energy of adsorbent with adsorbed H 2 molecules; and n is the number of H 2 molecules adsorbed on adsorbent. According to this definition, a more positive adsorption energy indicates a stronger binding of the H 2 molecules to adsorbent.
  • the electron distribution and transfer mechanism are determined using the Mulliken method [Mulliken, J. Chem. Phys. 1955, 23, 1833-1840].
  • Nitrogen doped carbon nanotubes or graphenes with pyridinic-nitrogen defects have the advantage of relatively good electrical conductivity, so that charge can be readily added or removed by manipulating voltage.
  • pyridinic nitrogen is a minority defect structure in comparison with substitutional Nitrogen doping; hence the question arises: how to dope a sufficient density of pyridinic Nitrogen defect sites into carbon nanotubes or graphene so as to enable efficient gas capture.
  • the material design typically focuses on an approach of electrocatalytic gas capture that can offer advantages of controllable kinetics and reversibility.
  • C0 2 molecules are predicted to be weakly adsorbed (i.e., physisorbed) on neutral substitutional N-dopant or pyridinic N sites in graphenes; when negative charge is simulated in a supercell, density functional theory (DFT) calculations reveal that C0 2 adsorption can be dramatically enhanced via a charge-induced chemisorption interaction. C0 2 is not transformed chemically in this process (although this eventuality should not be excluded and could be highly desirable).
  • DFT density functional theory
  • electrocatalytic gas capture is likely most appropriate, since the presence of charge is both quantitatively and qualitatively changing the chemical interactions (i.e., the potential energy surface) in the system and thereby enabling formation of a new chemical bond between the material and the C0 2 .
  • the kinetics of uptake and release can be controlled by manipulating a simple physical variable - the charge in the material - since C0 2 capture/release occurs spontaneously once extra electrons are introduced or removed.
  • the need for a temperature swing and the associated energy cost can in some embodiments be obviated.
  • Example 1A N-doped graphitic carbon as in Figure 1 (a)
  • Example 1 B The graphitic carbon nitride
  • Embodiments of graphitic carbon nitride include g-C 4 N 3 and g-C 3 N 4 , g-C 2 N and g-CN.
  • Figures 1 (h)-(m) the darker balls represent nitrogen atoms and the lighter balls represent carbon atoms.
  • the unit cell for each of g-C 4 N 3 and g-C 3 N 4 , g-C 2 N and g-CN ( Figure 1 (h)- (m)) are indicated by the dark dashed lines.
  • the unit cell is repeated four times for form a graphitic nanosheet, represented by the light dashed line.
  • the scope of the disclosure is not limited to 4 unit cells and a plurality of unit cells can be used to form nanosheets of indefinite dimensions along a 2D plane.
  • the unit cell can be used to construct structures such as fullerenes, and these structures can be used to form higher order structures.
  • these structures can be arranged into a graphene- type structure where the nanosheets are arranged to be stacked on top of one another along a z direction. Different structures, such as nanotubes and/or fullerenes may be interlaced between the stacked nanosheets.
  • additional heteroatoms such as B, S, O and Si, and metals such as Li, Mg, Ge and Al are included into or associated with the graphitic nanosheets, then the unit cell will adopt a different structure.
  • Ci and C 2 denote different C atoms in g-C 4 N 3 unit cell
  • Figure 1j N 2 and N 3 denote different N atoms in g-C 3 N 4 unit cell.
  • Figure 9 shows the electronic structures of B-doped graphene nanosheets with increasing boron content, i.e., BC 49 ( Figure 9a) BC 7 ( Figure 9b), BC 5 ( Figure 9c) and BC 3 ( Figure 9d ), and details the lowest-energy configurations and the calculated band structures of these B- doped graphene nanosheets.
  • the light and dark grey balls represent B and C atoms, respectively, and the unit cells of each B-doped graphene are indicated by black dot lines.
  • the dashed horizontal line denotes the Fermi level in the respective eV level graphs for each type of B-doped graphene.
  • the calculations indicate that B-doped graphene with B content ranging from 0-16.7 atom % has good electrical conductivity and high electron mobility, which should readily facilitate charge/electron injection/release for charge-controlled switchable hydrogen storage.
  • the H 2 molecule When four electrons are injected into the g-C 4 N 3 supercell, the H 2 molecule is predicted to dissociate and atomically bond to the negatively charged g-C 4 N 3 , indicating that molecular hydrogen adsorption can be achieved only below a certain critical injected charge density.
  • the adsorption energies of a H 2 molecule are 0.25 and 0.50 eV, respectively. These values show that negatively charged g-C 4 N 3 can be an excellent media for hydrogen storage.
  • the interactions between H 2 molecules and negatively charged g-C 3 N 4 exhibit the similar behaviour.
  • the negatively charged g-C 3 N 4 can adsorb up to 14 H 2 molecules with small average adsorption energy decrease, and the configuration of adsorbent with 14 H 2 molecules was defined full hydrogen coverage.
  • FIG. 10 shows the lowest-energy configurations of a H 2 molecule absorbed on neutral and 5e positively charged BC 49 (corresponding to the charge density of 3.82x1014 cm "2 as defined in Tan et ai, Sci. Rep. 2015, 5, 17636).
  • the H 2 molecule aligns perpendicular to BC 49 nanosheet and on top of the doped B atom.
  • H 2 molecule The distance between the H 2 molecule and B atom is 2.760 A, and the H-H bond length is 0.753 A which is similar to isolated H 2 molecule (0.752 A from our calculation).
  • Mulliken population analysis suggests that the amount of transferred electron from BC 49 to absorbed H 2 is negligible (about 0.001 e-).
  • the H 2 molecule exhibits a weak interaction with BC 49 with an adsorption energy of 0.06 eV.
  • Figure 1 1 (a) shows the isosurface (0.06 e/au) of HOMO of neutral BC 49 .
  • the shades of the orbitals show the wave function of HOMO (lighter, positive; darker, negative).
  • Figure 1 1 (b) shows the differences in electron density distribution of 5e positively charged BC 49 relative to neutral BC 49 using frozen atomic geometry.
  • Figure 1 1 (c) shows the differences in electron density distribution of a H 2 molecule adsorbed on 5e positively charged BC 49 relative to neutral BC 49 using frozen atomic geometry.
  • the isosurface values are 2x10 "6 e/au, and darker and lighter shades refer to the electron-rich and -deficient areas, respectively.
  • the HOMO of neutral BC 49 is predominantly distributed on the doped B atom, which suggests that when an electron is extracted from the neutral BC 49 , the extracted electron is from p orbitals of B atom of the BC 49 . This is further confirmed by comparison of the difference in electron density distribution of 5e positively charged BC 49 relative to neutral BC 49 , as shown in Figure 1 1 (b).
  • the distance between the H 2 molecule and the B atom of BC 49 decreased significantly as the density of positive charges increased, as shown in Figure 12(d).
  • the H 2 molecule was predicted to dissociate and atomically bond to the positively charged BC 49 , indicating that molecular H 2 adsorption can be achieved only below a certain critical introduced positive charge density.
  • the adsorption energies of a H 2 molecule are 0.20, 0.41 and 0.79 eV, respectively, which are much larger than the optimal adsorption energy for H 2 on high-performance adsorbents (0.1-0.2 eV) (Zhou et al., Proc. Natl. Acad. Sci. USA 2010, 107, 2801-2806; Liu et ai, Appl. Phys. Lett. 2010, 96, 123101) indicating that positively charged B-doped graphene can be excellent media for hydrogen storage.
  • FIG. 13(a) depicts the lowest-energy configuration of neutral BC 49 with a weakly bounded H 2 molecule. Five positive charges were added to the neutral BC 49 , and Figure 13(a) shows the change in energy as the system relaxed to the 5e positively charged optimized state.
  • Figure 13b depicts the lowest-energy configuration of 5e positively charged BC 49 having a strongly bounded H 2 molecule. Five extra positive charges were removed, and the system was allowed to relax, forming a weakly bound H 2 molecule.
  • the maximal number of H 2 molecules that can be electrocatalytically adsorbed on each B atom is two.
  • the average adsorption energies of the positively charged BC49 with two adsorbed H2 molecules was calculated as a function of the positive charges, as shown in Figure 14(b). Similar to the case of a single adsorbed H 2 molecule, the average adsorption energy of H 2 molecules increases continuously from 0.06 eV/H 2 on neutral BC 49 to 0.51 eV/H 2 on 5e positively charged BC 49 .
  • the maximum number of captured C0 2 for each negatively charged g-C 4 N 3 was determined with different charge density by gradually increasing the number of C0 2 molecules on negatively charged g-C 4 N 3 until no more C0 2 can be absorbed, see for example Figure 5.
  • the average adsorption energy of captured C0 2 is calculated as the total adsorption energy divided by the maximum number of captured C0 2 .
  • No C0 2 molecules can be captured by negatively charged g-C 4 N 3 with small charge density ( ⁇ 12.3x10 13 cm "2 ).
  • the negatively charged g-C 4 N 3 can capture two, four and six C0 2 molecules with the average adsorption energy of captured C0 2 molecules ranging from 0.72 to 3.58 eV.
  • a further increase in the number of C0 2 molecules leads to some C0 2 molecules moving far away from the adsorbent during the geometry optimization even if the charge density of g-C 4 N 3 is increased further. Therefore, six C0 2 molecules are defined in each 4 unit cell nanosheet of Figure 1 h (i.e. C0 2 capture capacity 73.9x10 13 cm "2 ) as the likely saturation C0 2 capture coverage.
  • Substitutional N-doped graphene is conductive and is herein predicted to have electro- responsive switchable binding capacity for C0 2 , via the C sites adjacent to the N dopant atoms. Given that there is a limit to the fraction of N that can be doped into graphene of around 1/3, it is also significant to consider the binding capacity for C0 2 around the N site. There are three adjacent carbons that could potentially bind. Indeed, the calculations indicate that each of them can chemisorb a C0 2 molecule once the extra negative charge is introduced. Under the same charging conditions, three C0 2 can adsorb to the neighbouring carbons (optimally two above the plane and one below) as shown in Figure 7, with average adsorption energy -1 .81 eV per molecule. At the doping fraction indicated in Figure 1 (a) (i.e., 1 .6wt% of nitrogen), which is very conservative, this would yield a C0 2 binding capacity of ca. 13wt%.
  • the adsorption energies of CH 4 , H 2 and N 2 were calculated on neutral and negatively charged g-C 4 N 3 and compared with those of C0 2 .
  • Figure 6 the comparative adsorption energies of C0 2 , CH 4 H 2 H20 and N 2 on neutral, 1 e " and 2e " negatively charged g-C 4 N 3 are shown.
  • the adsorptions of CH 4 , H 2 and N 2 on neutral, 1 e " and 2e " g-C 4 N 3 are all physical rather than chemical.
  • the distance between the carbon atom of CH 4 (the hydrogen atom of H2, the nitrogen atom of N2) and g-C 4 N 3 is 3.157-3.159 (2.1 1 1 -2.539, 2.865-3.236) A, respectively.
  • the adsorption energies of CH 4 , H 2 and N 2 on neutral, 1 e- and 2 e- g-C 4 N 3 range from 0.06 to 0.39 eV.
  • C0 2 is physically adsorbed at neutral and 1 e " g-C 4 N 3 with small adsorption energy in the range from 0.24 to 0.32 eV
  • C0 2 is tightly chemisorbed on 2e " g-C 4 N 3 with large adsorption energy of 1 .20 eV.
  • the above comparisons demonstrate that negatively charged g-C 4 N 3 has very high selectivity for capturing C0 2 from CH 4 , H 2 and/or N 2 mixtures.
  • Figure 8 compares the adsorption energies of C0 2 , CH 4 , H 2 , N 2 and H 2 0 on neutral, 4e- and 6e- negatively charged N-doped graphene of Figure 1 .
  • both C0 2 and H 2 0 are favourably bound in comparison with the other gases.
  • 6e- C0 2 is strongly favoured over all the other gases. This implies that the N-doped graphene material could show superior selectivity for C0 2 binding - particularly for capturing C0 2 out of a gas stream containing water.

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Abstract

L'invention concerne un système pour stocker du gaz dans un adsorbant, le système comprenant un matériau graphitique perméable aux gaz. Le matériau graphitique comprend du carbone et au moins un autre élément tel que de l'azote et/ou du bore. Le système comprend également une source électrique qui permet l'application d'un premier et d'un second potentiel au matériau graphitique. Lors de l'application du premier potentiel, le gaz est adsorbé sur le matériau graphitique, ce qui produit un matériau chargé en gaz. Lors de l'application du second potentiel, au moins une partie du gaz est désorbée du matériau graphitique chargé en gaz.
PCT/AU2016/050645 2015-07-20 2016-07-20 Procédés et matériaux pour capturer et stocker du gaz WO2017011873A1 (fr)

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CN112897484B (zh) * 2021-01-14 2023-10-31 华南理工大学 一种无缺陷的g-C3N4纳米片、二维g-C3N4纳米片膜及制备方法与应用
CN114797926A (zh) * 2021-01-27 2022-07-29 中国科学院大连化学物理研究所 一种碳纳米管负载钴粒子复合催化剂的制备方法及其应用
WO2023022594A1 (fr) 2021-08-20 2023-02-23 Technische Universiteit Delft Procédé et système de capture de monoxyde de carbone avec un adsorbant électriquement commutable
NL2029016B1 (en) * 2021-08-20 2023-02-27 Univ Delft Tech Method and system for capturing carbon monoxide with an electrically switchable adsorbent
CN114878760A (zh) * 2022-07-11 2022-08-09 国网天津市电力公司电力科学研究院 一种用于一氧化碳在铑掺杂硒化铂上吸附分析方法

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