CN111266124B - Fluorine-doped porous carbon nanomaterial, and preparation method and application thereof - Google Patents
Fluorine-doped porous carbon nanomaterial, and preparation method and application thereof Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 103
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 103
- 239000002086 nanomaterial Substances 0.000 title claims abstract description 88
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 94
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 68
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 47
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 33
- 238000006243 chemical reaction Methods 0.000 claims abstract description 32
- 239000013207 UiO-66 Substances 0.000 claims abstract description 27
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 25
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000011737 fluorine Substances 0.000 claims abstract description 24
- 238000005530 etching Methods 0.000 claims abstract description 18
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 14
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical group [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims abstract description 9
- 230000009467 reduction Effects 0.000 claims abstract description 9
- 125000004432 carbon atom Chemical group C* 0.000 claims abstract description 7
- 125000001153 fluoro group Chemical group F* 0.000 claims abstract description 7
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 21
- 238000000034 method Methods 0.000 claims description 21
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical group [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 16
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 16
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 15
- 238000001354 calcination Methods 0.000 claims description 15
- -1 polytetrafluoroethylene Polymers 0.000 claims description 11
- KKEYFWRCBNTPAC-UHFFFAOYSA-N Terephthalic acid Chemical compound OC(=O)C1=CC=C(C(O)=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-N 0.000 claims description 10
- 239000011259 mixed solution Substances 0.000 claims description 10
- 239000002253 acid Substances 0.000 claims description 9
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 9
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 9
- 239000000243 solution Substances 0.000 claims description 9
- 229910052786 argon Inorganic materials 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 7
- 238000003786 synthesis reaction Methods 0.000 claims description 6
- DUNKXUFBGCUVQW-UHFFFAOYSA-J zirconium tetrachloride Chemical compound Cl[Zr](Cl)(Cl)Cl DUNKXUFBGCUVQW-UHFFFAOYSA-J 0.000 claims description 5
- 239000012298 atmosphere Substances 0.000 claims description 4
- 238000003763 carbonization Methods 0.000 claims description 4
- 230000001681 protective effect Effects 0.000 claims description 4
- 238000004321 preservation Methods 0.000 claims description 3
- 239000003054 catalyst Substances 0.000 abstract description 22
- 238000004519 manufacturing process Methods 0.000 abstract description 18
- 239000011943 nanocatalyst Substances 0.000 abstract description 11
- 230000003197 catalytic effect Effects 0.000 abstract description 8
- 238000010000 carbonizing Methods 0.000 abstract description 3
- 229910052755 nonmetal Inorganic materials 0.000 abstract description 3
- 238000010494 dissociation reaction Methods 0.000 abstract description 2
- 230000005593 dissociations Effects 0.000 abstract description 2
- 239000001257 hydrogen Substances 0.000 description 17
- 229910052739 hydrogen Inorganic materials 0.000 description 17
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 15
- 230000008569 process Effects 0.000 description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 10
- 238000012360 testing method Methods 0.000 description 10
- 238000006722 reduction reaction Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000000843 powder Substances 0.000 description 5
- 239000008367 deionised water Substances 0.000 description 4
- 229910021641 deionized water Inorganic materials 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 238000009210 therapy by ultrasound Methods 0.000 description 3
- 229910052726 zirconium Inorganic materials 0.000 description 3
- VRZJGENLTNRAIG-UHFFFAOYSA-N 4-[4-(dimethylamino)phenyl]iminonaphthalen-1-one Chemical compound C1=CC(N(C)C)=CC=C1N=C1C2=CC=CC=C2C(=O)C=C1 VRZJGENLTNRAIG-UHFFFAOYSA-N 0.000 description 2
- 239000002841 Lewis acid Substances 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 238000003795 desorption Methods 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 150000007517 lewis acids Chemical class 0.000 description 2
- 239000012621 metal-organic framework Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 238000000870 ultraviolet spectroscopy Methods 0.000 description 2
- 238000001291 vacuum drying Methods 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 1
- 239000004480 active ingredient Substances 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 239000012300 argon atmosphere Substances 0.000 description 1
- 150000001721 carbon Chemical group 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000010411 electrocatalyst Substances 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 239000000295 fuel oil Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 238000002173 high-resolution transmission electron microscopy Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 235000009566 rice Nutrition 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 238000013112 stability test Methods 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
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- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
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Abstract
The invention provides a fluorine-doped porous carbon nanomaterial, wherein fluorine atoms and carbon atoms of the porous carbon nanomaterial form bonds, and the porous carbon nanomaterial is obtained by carbonizing UiO-66 and etching zirconium atoms. The application also provides a preparation method and application of the fluorine-doped porous carbon nano material. The fluorine-doped porous carbon nano material provided by the application is used as a catalyst, and the introduction of fluorine improves the non-metal nano catalyst, and improves the catalytic activity and selectivity of the catalyst on the reaction of synthesizing ammonia by electrochemically reducing nitrogen; meanwhile, the introduction of fluorine can promote the dissociation of nitrogen, and the selectivity and the ammonia production rate of the catalyst in the electrochemical reduction nitrogen reaction are improved.
Description
Technical Field
The invention relates to the technical field of catalysts, in particular to a fluorine-doped porous carbon nano material, and a preparation method and application thereof.
Background
Synthetic ammonia is ammonia directly synthesized from nitrogen and hydrogen at high temperature and pressure in the presence of a catalyst. The main raw materials for producing synthetic ammonia include natural gas, naphtha, heavy oil and coal.
Currently, ammonia is synthesized industrially by the traditional haber method, and the process consumes a large amount of energy and emits a large amount of greenhouse gases. The reaction for synthesizing ammonia by electrochemically reducing nitrogen takes water as a hydrogen source, the reaction is carried out at normal temperature and normal pressure, the reaction can be regulated and controlled by changing voltage, the operation is easy, and the method is a promising method for synthesizing ammonia. However, the covalent triple bond of N ≡ N present in nitrogen molecules is difficult to activate, and the reaction for synthesizing ammonia competes with the reaction for hydrogen evolution during the reaction, so it is a very challenging task to develop a catalyst for electrochemically reducing nitrogen to synthesize ammonia with high selectivity and high activity.
In recent years, some metal-based catalysts, such as platinum (Pt), gold (Au), ruthenium (Ru), iron (Fe), molybdenum (Mo), and the like, have catalytic activity for electrochemically reducing nitrogen to synthesize ammonia, but these catalysts also have catalytic activity for hydrogen evolution reaction, resulting in low selectivity and yield of synthesized ammonia, and furthermore, theoretical calculations indicate that the activity for hydrogen evolution reaction of a non-metal catalyst is low, so that the non-metal catalyst can be used to suppress hydrogen evolution reaction. In view of the above, it is necessary to provide a catalyst for ammonia synthesis.
Disclosure of Invention
The invention aims to provide a fluorine-doped porous carbon nano material and a preparation method thereof, and the fluorine-doped porous carbon nano material provided by the invention has high selectivity and activity and good catalytic stability when used as a catalyst in the process of synthesizing ammonia by electrochemically reducing nitrogen.
In view of the above, the present application provides a fluorine-doped porous carbon nanomaterial, in which fluorine atoms are bonded to carbon atoms of the porous carbon nanomaterial, and the fluorine-doped porous carbon nanomaterial is obtained by etching away zirconium atoms after carbonization of a fluorine source and UiO-66.
Preferably, the average size of the fluorine-doped porous carbon nanomaterial is 800-1200 nm.
The application also provides a preparation method of the fluorine-doped porous carbon nanomaterial, which comprises the following steps:
and mixing the UiO-66 and a fluorine source, calcining, and etching by adopting acid liquor to obtain the fluorine-doped porous carbon nano material.
Preferably, the fluorine source is polytetrafluoroethylene, and the acid liquid is hydrofluoric acid.
Preferably, the calcination is performed in a protective atmosphere, the protective atmosphere is argon, and the flow rate of the argon is 20-100 mL/min.
Preferably, the calcining temperature is 500-1000 ℃, the calcining temperature rise rate is 1-5 ℃/min, and the calcining time is 1-10 h.
Preferably, the concentration of the hydrofluoric acid is 10-20 wt%, and the ratio of the UiO-66 to the polytetrafluoroethylene is (80-120) mg: 1 mL.
Preferably, the preparation method of the UiO-66 specifically comprises the following steps:
zirconium chloride and terephthalic acid are mixed in a mixed solution of acetic acid and dimethylformamide, and heat preservation is carried out after heating, thus obtaining UiO-66.
The application also provides the application of the fluorine-doped porous carbon nano material or the fluorine-doped porous carbon nano material prepared by the preparation method in the reaction of synthesizing ammonia by electrochemically reducing nitrogen.
The application provides a fluorine-doped porous carbon nanomaterial, wherein fluorine atoms and carbon atoms of the porous carbon nanomaterial form bonds, and the porous carbon nanomaterial is obtained by carbonizing UiO-66 and etching zirconium atoms. The fluorine-doped porous carbon nanomaterial provided by the application has a large number of Lewis acid sites, and in the process of synthesizing ammonia by electrochemically reducing nitrogen, the mutual repulsion between the Lewis acid sites and hydrogen ions can inhibit the competitive reaction of electrochemically decomposing water to produce hydrogen, so that the selectivity of synthesizing ammonia by electrochemically reducing nitrogen is increased; meanwhile, due to the doping of fluorine elements, the charge distribution of carbon atoms is uneven, and the adsorption capacity to nitrogen molecules is enhanced, so that the fluorine-doped porous carbon nano material has higher activity for electrochemically reducing nitrogen to synthesize ammonia; the fluorine-doped porous carbon nanomaterial has a unique 3D frame structure, so that the fluorine-doped porous carbon nanomaterial has good structural stability and good catalytic stability in the process of synthesizing ammonia by electrochemically reducing nitrogen.
Drawings
Fig. 1 is a scanning electron microscope picture of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention;
FIG. 2 is a TEM image of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention;
FIG. 3 is a high-resolution TEM image of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention;
fig. 4 is an X-ray diffraction pattern of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention and the original porous carbon nanomaterial;
fig. 5 is a raman spectrum of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention and the original porous carbon nanomaterial;
FIG. 6 is an X-ray photoelectron spectrum of the fluorine-doped porous carbon nanomaterial prepared in example 1 of the present invention and the original porous carbon nanomaterial;
fig. 7 is a temperature-rising desorption spectrum of the fluorine-doped porous carbon nano-catalyst and the original porous carbon nano-material prepared in example 1 of the present invention with respect to nitrogen adsorption;
fig. 8 is an effective current density curve of the fluorine-doped porous carbon nano-catalyst prepared in example 3 of the present invention and the original porous carbon nano-material under different overpotentials;
fig. 9 shows the faradaic efficiency of ammonia production by the fluorine-doped porous carbon nano-catalyst and the original porous carbon nano-material prepared in example 3 of the present invention under different overpotentials;
FIG. 10 shows the ammonia production rates of the fluorine-doped porous carbon nano-catalyst and the original porous carbon nano-material prepared in example 3 of the present invention under different overpotentials;
FIG. 11 shows the ammonia production rate of the fluorine-doped porous carbon nanomaterial prepared in example 4 of the present invention after reaction for 12 hours at an overpotential of-0.3V relative to a standard hydrogen electrode.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In view of the problems of low selectivity and low yield of the existing synthetic ammonia, the application provides a fluorine-doped porous carbon nano material, and the introduction of fluorine can promote the dissociation of nitrogen, so that the selectivity and the ammonia production rate of the fluorine-doped porous carbon nano material as a catalyst in the electrochemical reduction nitrogen reaction are improved; meanwhile, the structure of the fluorine-doped porous carbon nano material ensures that the fluorine-doped porous carbon nano material has good catalytic stability when being used as a catalyst in the process of synthesizing ammonia. Specifically, the embodiment of the invention discloses a fluorine-doped porous carbon nanomaterial, wherein fluorine atoms and carbon atoms of the porous carbon nanomaterial form bonds, and the fluorine-doped porous carbon nanomaterial is obtained by etching away zirconium atoms after carbonization of a fluorine source and UiO-66.
The application discloses a fluorine-doped porous carbon nanomaterial, wherein fluorine in the fluorine-doped porous carbon nanomaterial is not in a free state and is in an atomic state to form a bond with carbon atoms in the porous carbon nanomaterial. The porous carbon nanomaterial in the fluorine-doped porous carbon nanomaterial is obtained by carbonizing UiO-66 and etching zirconium atoms, namely the porous carbon nanomaterial in the fluorine-doped porous carbon nanomaterial does not contain other elements, and the zirconium element in the original metal organic framework material is etched. The fluorine-doped porous carbon nanomaterial is in an octahedral shape with the average size of 800-1200 nm.
The application also provides a preparation method of the fluorine-doped porous carbon nanomaterial, which comprises the following steps:
and mixing the UiO-66 and a fluorine source, calcining, and etching by adopting acid liquor to obtain the fluorine-doped porous carbon nano material.
In the process of preparing the fluorine-doped porous carbon nano material, the UiO-66 which has a three-dimensional framework, uniform pores, a large surface area and high stability is selected and is a metal organic framework material, the porous three-dimensional framework structure of the material can increase the surface area, and the material has a large active area and more active sites in the catalytic reaction process, so that the activity of the catalyst can be improved. The preparation method of the UiO-66 may be performed according to methods well known to those skilled in the art, and the application is not particularly limited, and in specific examples, the preparation method of the UiO-66 specifically comprises the following steps:
zirconium chloride and terephthalic acid are mixed in a mixed solution of acetic acid and dimethylformamide, and heat preservation is carried out after heating, thus obtaining UiO-66.
More specifically, dissolving zirconium chloride and terephthalic acid with equal mole numbers in a mixed solution of acetic acid and dimethylformamide, carrying out ultrasonic treatment on the mixed solution for 20-30 min, sealing, heating to 100-150 ℃, and keeping in an oven for 24 h; and centrifuging and cleaning the obtained sample for three times by sequentially adopting dimethylformamide and methanol, wherein the centrifugal rotating speed is 10000-12000 r/min, centrifuging for 5min, and drying the precipitate obtained by centrifuging at 90 ℃ overnight to obtain UiO-66.
The process of mixing the UiO-66 and the fluorine source is specifically as follows: mixing UiO-66, a fluorine source and a solvent, and stirring by magnetic force to form a gel state; the fluorine source is well known to those skilled in the art and in particular embodiments is selected from polytetrafluoroethylene. The ratio of the UiO-66 to the polytetrafluoroethylene is (80-120) mg: 1 mL; the ratio of the UiO-66 to the polytetrafluoroethylene affects the fluorine content of the fluorine-doped porous carbon nanomaterial. In the process, the stirring time is 8-10 h, and the stirring time can influence the uniformity of fluorine doping. The solvent is a common organic solvent well known to those skilled in the art, and the present application is not particularly limited thereto, and in a specific embodiment, the solvent is ethanol.
According to the invention, after the raw materials are mixed, the obtained mixture is calcined, and in order to avoid introducing additional impurities, the calcination is preferably carried out in an argon atmosphere, wherein the flow rate of argon is 20-100 mL/min, and in a specific embodiment, the flow rate of argon is 40-60 mL/min. The calcining temperature is 500-1000 ℃, the heating rate is 1-5 ℃/min, and the time is 1-10 h; in a specific embodiment, the calcining temperature is 700-800 ℃, the heating rate is 2-3 ℃/min, and the time is 3-7 h. The calcination process described above achieves the doping of fluorine atoms and the carbonization of UiO-66.
And finally, mixing the calcined powder with an acid solution for etching to remove Zr element. The acid solution is an acid solution capable of etching away the Zr element, and in a specific embodiment, the acid solution is selected from hydrofluoric acid. The etching process specifically comprises the following steps:
dispersing the calcined powder into a mixed solution of hydrofluoric acid and water, etching for 2-5 h, then centrifugally cleaning by using deionized water and ethanol, wherein the centrifugal rotating speed is 10000-15000 r/min, and finally, carrying out vacuum drying on the centrifuged precipitate at 50-100 ℃.
In the above process, the ratio of the calcined powder to the hydrofluoric acid is 100 mg: 2-10 mL, wherein the concentration of the hydrofluoric acid is 10-20 wt%; the etching material ratio and the etching time can affect the etching degree of zirconium, and the zirconium needs to be completely etched in the application.
The application also provides application of the fluorine-doped porous carbon nano material in the reaction of synthesizing ammonia by electrochemically reducing nitrogen; in the reaction of synthesizing ammonia by electrochemical reduction of nitrogen, the fluorine-doped porous carbon nano material is used as a catalyst.
Compared with the original porous carbon nano material which is treated in the same process but is not doped with fluorine, in the reaction of synthesizing ammonia by electrochemically reducing nitrogen, under the overpotential of-0.2V relative to the standard hydrogen electrode, the Faraday efficiencies of the ammonia production of the original porous carbon nano material and the fluorine-doped porous carbon nano material are respectively 18.3 percent and 54.8 percent, under the overpotential of-0.3V relative to the standard hydrogen electrode, the effective current densities respectively reach-0.064 milliampere/square centimeter and-0.225 milliampere/square centimeter, and the ammonia production rates respectively reach 56.1 microgram/milligramCatalyst and process for preparing sameHour and 197.7. mu.g/mgCatalyst and process for preparing sameIn terms of hours.
For further understanding of the present invention, the fluorine doped porous carbon nanomaterial, the preparation method thereof and the application thereof provided by the present invention are described in detail below with reference to the following examples, and the scope of the present invention is not limited by the following examples.
Example 1
The invention provides a fluorine-doped porous carbon nano catalyst with the average size of 800-1200 nm, and the synthesis method comprises the following steps:
dissolving 0.045 mmol of zirconium chloride and 0.045 mmol of terephthalic acid in a mixed solution of 1.2 ml of acetic acid and 10ml of dimethylformamide, carrying out ultrasonic treatment on the mixed solution for 30min, sealing, heating to 120 ℃, and keeping in an oven for 24 h; centrifuging and washing the obtained sample for three times by using dimethylformamide and methanol respectively, wherein the centrifugal rotating speed is 13000 r/min, centrifuging for 5min, and drying the precipitate obtained by centrifuging at 90 ℃ overnight to obtain UiO-66;
mixing 100mg of UiO-66, 1mL of polytetrafluoroethylene and 10mL of ethanol, magnetically stirring for 8 hours until the mixture is in a gel state, placing the mixture in argon gas to calcine for 3 hours at 700 ℃, wherein the argon gas flow is 50mL/min, the heating rate is 2 ℃/min, and cooling to room temperature; and dispersing 100mg of calcined powder in a mixed solution of 5 ml of HF and 10ml of deionized water for etching for 2h, wherein the concentration of HF is 15%, centrifugally cleaning the powder for three times by using deionized water and ethanol after etching, wherein the centrifugal speed is 13000 r/min every time for 10 min, and carrying out vacuum drying on the precipitate obtained by centrifugation at 90 ℃ overnight to obtain the fluorine-doped porous carbon nano material.
The preparation method of the original porous carbon nano material is the same as the method, and the difference is that: no polytetrafluoroethylene was introduced.
Fig. 1 shows a scanning electron microscope picture of the fluorine-doped porous carbon nanomaterial prepared in this embodiment, fig. 2 shows a transmission electron microscope picture, and fig. 3 shows a high-resolution transmission electron microscope picture, which are shown in fig. 1 and 2, it can be seen that the fluorine-doped porous carbon nanomaterial prepared in this embodiment is in an octahedral shape with an average size of 800-1200 nm, and as can be seen from fig. 3, carbon in the porous carbon nanomaterial of the fluorine-doped porous carbon nanomaterial is amorphous carbon; the X-ray diffraction patterns of the fluorine-doped porous carbon nanocatalyst and the original porous carbon nanocatalyst are shown in fig. 4; the Raman spectrum is shown in FIG. 5, and only the diffraction peak of carbon exists in FIG. 5, which shows that Zr in the material is completely etched; an X-ray photoelectron energy spectrum is shown in fig. 6, and as can be seen from fig. 6, a bond is formed between a fluorine atom and a carbon atom in the fluorine-doped porous carbon nanomaterial without the existence of a free fluorine ion, which proves that the fluorine is bonded with the carbon in the porous carbon nanomaterial in an atomic form, thereby realizing doping; the temperature programmed desorption spectrum for nitrogen adsorption is shown in fig. 7, and as can be seen from fig. 7, the introduction of fluorine enhances the adsorption of the porous carbon nanomaterial on nitrogen, thereby increasing the catalytic activity.
Example 2
1) Electrocatalyst with fluorine-doped porous carbon nanomaterial as active ingredient and electrochemical reduction nitrogen test condition
Dispersing 5 mg of fluorine-doped porous carbon nanomaterial prepared in example 1 and 40 microliters of 5% mass fraction Nafion solution in a mixed solution of 660 microliters of ethanol and 300 microliters of deionized water, and performing ultrasonic treatment for 1 hour to obtain a uniform solution; then, 10 microliter of the solution is uniformly dripped on a rotating disc electrode with the diameter of 0.5 cm; the rotating disc electrode is used as a working electrode, the silver/silver chloride electrode is used as a reference electrode, and the graphite rod is used as a counter electrode; the electrochemical reduction nitrogen reaction electrolyte is 30 ml of sulfuric acid solution with the concentration of 0.05 mol/L, nitrogen is introduced for at least 30min before reaction to remove other gases, and the catalytic reaction is carried out in an H-shaped electrolytic cell, wherein the electrolytic cell is separated by a Nafion 115 proton exchange membrane.
2) Current density and product selectivity tests of the fluorine-doped porous carbon nano catalyst in an electrochemical reduction nitrogen synthesis ammonia test:
under the reaction conditions, adopting a constant potential test; setting the overpotential of a relative standard hydrogen electrode to be-0.1V, and carrying out constant potential test for 2 h; during the reaction, nitrogen gas is required to be continuously introduced at the speed of 10 ml/min; oxygen generated by the anode in the reaction is discharged into the air; after the reaction is finished, the concentration of the generated ammonia is subjected to indophenol blue color development reaction and then is detected by an ultraviolet visible spectrophotometer; after the test is finished, the overpotential is changed to-0.2V, -0.3V, -0.4V, -0.5V, and the test is carried out under the unchanged other conditions. The effective current density of the fluorine-doped porous carbon nanomaterial for ammonia production under the overpotential is shown as 8, the faraday efficiency of ammonia production is shown as fig. 9, and the ammonia production rate is shown as fig. 10, as can be seen from fig. 8, under the overpotential of-0.3V relative to the standard hydrogen electrode, the effective current densities of the original porous carbon nanomaterial and the fluorine-doped porous carbon nanomaterial for ammonia production respectively reach-0.064 ma/cm and-0.225 ma/cm, as can be seen from fig. 9, under the overpotential of-0.2V relative to the standard hydrogen electrode, the faraday efficiencies of the original porous carbon nanomaterial and the fluorine-doped porous carbon nanomaterial for ammonia production are respectively 18.3% and 54.8%, which proves that the fluorine doping increases the selectivity of the catalyst in the electrochemical reduction reaction for ammonia synthesis from nitrogen gas, as can be seen from fig. 10, under the overpotential of-0.3V relative to the standard hydrogen electrode, raw porous carbon nanomaterial and fluorine-doped porous carbon nanomaterialThe ammonia generating rate of the rice material reaches 56.1 micrograms/milligram respectivelyCatalyst and process for preparing sameHour and 197.7. mu.g/mgCatalyst and process for preparing sameIn the case of the reaction, it was confirmed that the introduction of fluorine increased the ammonia production rate of the catalyst in the synthesis of ammonia by electrochemical reduction of nitrogen.
Example 3
Stability test of fluorine-doped porous carbon nano material in ammonia synthesis by electrochemical reduction of nitrogen under the condition that overpotential of relative standard hydrogen electrode is-0.3V
A potentiostatic test was carried out under the reaction conditions of example 2; setting the overpotential of a relative standard hydrogen electrode to be-0.3V, and carrying out constant potential test for 12 hours; in the reaction process, nitrogen is required to be continuously introduced at the speed of 10 ml/min, and oxygen generated by the anode in the reaction is discharged into the air; after the reaction is finished, the concentration of the generated ammonia is subjected to indophenol blue color development reaction and then is detected by an ultraviolet visible spectrophotometer; fig. 11 shows the graph of the change of the current density and the ammonia production rate of the fluorine-doped porous carbon nano-catalyst with the test time at the potential, and it can be known from fig. 11 that the fluorine-doped porous carbon nano-catalyst has good catalytic stability for electrochemically reducing nitrogen to synthesize ammonia.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. The preparation method of the fluorine-doped porous carbon nano material applied to the reaction of synthesizing ammonia by electrochemically reducing nitrogen comprises the following steps:
mixing UiO-66 and a fluorine source, calcining, and etching by adopting acid liquor to obtain a fluorine-doped porous carbon nano material;
the fluorine source is polytetrafluoroethylene, and the ratio of the UiO-66 to the polytetrafluoroethylene is (80-120) mg: 1 mL;
fluorine atoms and carbon atoms of the porous carbon nano material form bonds, and the fluorine-doped porous carbon nano material is obtained by etching away zirconium atoms after a fluorine source and UiO-66 carbonization.
2. The method according to claim 1, wherein the acid solution is hydrofluoric acid.
3. The preparation method according to claim 1, wherein the calcination is performed under a protective atmosphere, the protective atmosphere is argon, and the flow rate of the argon is 20-100 mL/min.
4. The preparation method according to claim 1, wherein the calcination temperature is 500-1000 ℃, the temperature rise rate of the calcination is 1-5 ℃/min, and the calcination time is 1-10 h.
5. The method according to claim 2, wherein the concentration of the hydrofluoric acid is 10 to 20 wt%.
6. The preparation method according to any one of claims 1 to 5, wherein the preparation method of UiO-66 specifically comprises:
zirconium chloride and terephthalic acid are mixed in a mixed solution of acetic acid and dimethylformamide, and heat preservation is carried out after heating, thus obtaining UiO-66.
7. The preparation method according to claim 1, wherein the fluorine-doped porous carbon nanomaterial has an average size of 800 to 1200 nm.
8. The application of the fluorine-doped porous carbon nanomaterial prepared by the preparation method of any one of claims 1 to 7 in ammonia synthesis reaction by electrochemical reduction of nitrogen.
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