CN117867560A - Method for preparing formic acid by using composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl proportion for carbon dioxide electroreduction - Google Patents
Method for preparing formic acid by using composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl proportion for carbon dioxide electroreduction Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 84
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 58
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims abstract description 44
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 title claims abstract description 42
- 230000002829 reductive effect Effects 0.000 title claims abstract description 36
- 239000003054 catalyst Substances 0.000 title claims abstract description 35
- 229910000416 bismuth oxide Inorganic materials 0.000 title claims abstract description 24
- TYIXMATWDRGMPF-UHFFFAOYSA-N dibismuth;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Bi+3].[Bi+3] TYIXMATWDRGMPF-UHFFFAOYSA-N 0.000 title claims abstract description 24
- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000001569 carbon dioxide Substances 0.000 title claims abstract description 22
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims abstract description 22
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 title claims abstract description 21
- 235000019253 formic acid Nutrition 0.000 title claims abstract description 21
- 125000002887 hydroxy group Chemical group [H]O* 0.000 title claims abstract description 21
- 239000002131 composite material Substances 0.000 title claims abstract description 13
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 claims description 47
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- 238000006243 chemical reaction Methods 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 21
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- 239000010439 graphite Substances 0.000 claims description 18
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- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 15
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 15
- 238000005406 washing Methods 0.000 claims description 14
- 239000000047 product Substances 0.000 claims description 13
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 13
- -1 lithium aluminum hydride Chemical compound 0.000 claims description 12
- 239000012280 lithium aluminium hydride Substances 0.000 claims description 11
- 238000004108 freeze drying Methods 0.000 claims description 10
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
- DLYUQMMRRRQYAE-UHFFFAOYSA-N tetraphosphorus decaoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 claims description 10
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 9
- 238000003756 stirring Methods 0.000 claims description 9
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 6
- 238000001354 calcination Methods 0.000 claims description 5
- 230000007935 neutral effect Effects 0.000 claims description 5
- 239000012286 potassium permanganate Substances 0.000 claims description 5
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 claims description 5
- 238000002360 preparation method Methods 0.000 claims description 5
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- 239000006185 dispersion Substances 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 4
- RXPAJWPEYBDXOG-UHFFFAOYSA-N hydron;methyl 4-methoxypyridine-2-carboxylate;chloride Chemical compound Cl.COC(=O)C1=CC(OC)=CC=N1 RXPAJWPEYBDXOG-UHFFFAOYSA-N 0.000 claims description 4
- 239000002244 precipitate Substances 0.000 claims description 4
- FFRBMBIXVSCUFS-UHFFFAOYSA-N 2,4-dinitro-1-naphthol Chemical compound C1=CC=C2C(O)=C([N+]([O-])=O)C=C([N+]([O-])=O)C2=C1 FFRBMBIXVSCUFS-UHFFFAOYSA-N 0.000 claims description 3
- 239000003638 chemical reducing agent Substances 0.000 claims description 3
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- 239000006228 supernatant Substances 0.000 claims description 3
- 238000009210 therapy by ultrasound Methods 0.000 claims description 3
- 238000001291 vacuum drying Methods 0.000 claims description 3
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 2
- 230000009467 reduction Effects 0.000 abstract description 16
- 239000000243 solution Substances 0.000 description 12
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 11
- 229910052760 oxygen Inorganic materials 0.000 description 11
- 239000001301 oxygen Substances 0.000 description 11
- 125000000524 functional group Chemical group 0.000 description 9
- 238000003917 TEM image Methods 0.000 description 8
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- 229910010082 LiAlH Inorganic materials 0.000 description 3
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- 125000004432 carbon atom Chemical group C* 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
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- YQNQTEBHHUSESQ-UHFFFAOYSA-N lithium aluminate Chemical compound [Li+].[O-][Al]=O YQNQTEBHHUSESQ-UHFFFAOYSA-N 0.000 description 3
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- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000008346 aqueous phase Substances 0.000 description 2
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- WMWLMWRWZQELOS-UHFFFAOYSA-N bismuth(iii) oxide Chemical compound O=[Bi]O[Bi]=O WMWLMWRWZQELOS-UHFFFAOYSA-N 0.000 description 2
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- BDAGIHXWWSANSR-UHFFFAOYSA-M Formate Chemical compound [O-]C=O BDAGIHXWWSANSR-UHFFFAOYSA-M 0.000 description 1
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- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
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- Inorganic Compounds Of Heavy Metals (AREA)
Abstract
The invention provides a method for preparing formic acid by using a composite catalyst of bismuth oxide supported by reduced graphene oxide rich in hydroxyl proportion for carbon dioxide electroreduction, and relates to the field of electrocatalytic reduction of carbon dioxide.
Description
Technical Field
The invention relates to the field of electrocatalytic reduction of carbon dioxide, and in particular relates to a method for preparing formic acid by using a composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl proportion in carbon dioxide electroreduction.
Background
The continued reliance of humans on fossil energy has long resulted in a large amount of the greenhouse gas carbon dioxide (CO 2 ) The resulting greenhouse effect creates a significant disturbance to the global climate. Renewable resources such as solar energy, wind energy and tidal energy are utilized to convert into electric energy for carbon dioxide electroreduction (CO 2 ER), not only can slow down the greenhouse effect, but also can realize the conversion from electric energy to chemical energy, and accords with the concept of current sustainable development.
In CO 2 In the ER field, the design of efficient catalysts is first to be understood as the problem faced. 1) The carbon dioxide molecules are inert due to the high bond energy of c=o, and therefore are active in CO 2 When more energy is required to be input, namely more overpotential is 2) CO 2 The equilibrium potential of ER to produce different products is very close to the theoretical potential of hydrogen evolution reaction while CO is in aqueous phase 2 The lower the solubility, the slower the rate at which it diffuses to the electrode surface, and thus the more prone the hydrogen evolution reaction in the aqueous phase occurs, and the faraday efficiency of the target product decreases. 3) The long-time electrolysis causes the agglomeration, shedding and even deactivation of particles on the surface of the catalyst electrode, which is still quite different from the requirement of the catalyst in industrialization. Thus, it is difficult and challenging to design a catalyst that is good in selectivity, high in activity, and excellent in stability.
Bismuth-based catalysts are now being reported to be increasingly widespread due to their high selectivity to the product and low cost. Theoretical calculation results show that bismuth oxide (Bi 2 O 3 ) The Bi-O bond in the catalyst has a certain promotion effect on the adsorption of carbon dioxide, and the existence of Bi-O can improve the CO of an intermediate 2 -stability. However, the poor conductivity and the susceptibility to agglomeration of metal oxides have presupposed that they cannot exist independently. In recent years, carbon-based materials such as carbon nanotubes, graphene, and porous carbon have been widely used for catalyst synthesis due to good conductivity and good dispersibility of active components. Among them, graphene stands out from a large number of carbon carriers due to its excellent conductivity and large specific surface area. However, unmodified graphene is free of any catalytic activity due to its stable presence of conjugated large pi bonds, often requiring modification of the charge distribution of internal carbon atoms by incorporation of heteroatoms or introduction of defects, making it an active center. Currently, the modification of graphene is usually oxidation treatment, and a large number of oxygen-containing functional groups are generated on the surface of the graphene as sites of anchoring metal while introducing defects, but the oxygen-containing functional groups also damage the graphite to a certain extentThe original conjugated structure of the graphene leads to the reduction of the conductivity of oxidized graphene. To improve this problem, graphene after oxidation often needs to be reduced to solve the coexistence problem of defects and conductivity. Therefore, consider Bi 2 O 3 For CO 2 The catalytic performance of the catalyst and the conductivity and specific surface area of the reduced graphene oxide are subjected to intensive research and exploration on a composite catalyst composed of the two.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for preparing formic acid by using a composite catalyst of reduced graphene oxide loaded bismuth oxide with a hydroxyl group-enriched proportion for carbon dioxide electroreduction, which aims to overcome the defects of insufficient conductivity and easy agglomeration of metal oxides and improve the adsorption problem of carbon dioxide, and oxygen-containing functional groups on graphene oxide are removed mostly by virtue of strong reduction nonselective of lithium aluminum hydride to obtain reduced graphene oxide with hydroxyl groups as a main component, and then the catalyst obtained by loading bismuth oxide nano particles has high Faraday efficiency of the catalyst to formic acid and good stability under long-time electrolysis.
In order to achieve the above purpose, the invention is realized by the following technical scheme: a method for preparing formic acid by using a composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl proportion for carbon dioxide electroreduction comprises the following steps:
(1) Slowly adding concentrated sulfuric acid into a mixture containing graphite, potassium persulfate and phosphorus pentoxide, then reacting for 5 hours at 80 ℃ in an oil bath, washing with deionized water to be neutral after the reaction is finished, and vacuum drying for 12 hours at 80 ℃ to obtain preoxidized graphite;
(2) Slowly adding concentrated sulfuric acid into the preoxidized graphite and stirring for 0.5h, then gradually adding potassium permanganate into the solution in batches, transferring to a water bath for reaction for 2h, slowly adding deionized water after the reaction is finished, stirring at the same time, dropwise adding hydrogen peroxide after the solution is completely exothermic, centrifugally washing with hydrochloric acid until the supernatant becomes transparent after the solution turns golden yellow, washing with deionized water until the pH is about 6, and freeze-drying for two days to obtain Graphene Oxide (GO);
(3) Adding graphene oxide and lithium aluminum oxide into a flask 1 and a flask 2 filled with anhydrous tetrahydrofuran respectively, performing ultrasonic dispersion, then dropwise adding tetrahydrofuran dissolved with lithium aluminum oxide into a graphene oxide solution under N2, continuously reacting for 24 hours, washing with hydrochloric acid solution and deionized water in sequence until the solution is neutral, and finally, performing freeze drying to obtain a product, namely reduced graphene oxide (rGO-OH, wherein OH indicates that oxygen elements in the reduced graphene oxide by lithium aluminum oxide mainly exist in a hydroxyl form, and the number of non-hydroxyl groups is increased);
(4) Adding N, N-dimethylformamide into reduced graphene oxide, performing ultrasonic treatment to obtain a dispersion liquid, adding bismuth nitrate, stirring overnight, transferring to an autoclave for hydrothermal reaction, washing the precipitate obtained by the reaction with ethanol and deionized water for multiple times, performing freeze drying to obtain a pre-product, and calcining to obtain the final catalyst (Bi) 2 O 3 /rGO-OH)。
As a preferable technical scheme of the invention, in the preparation process of the pre-oxidized graphite, the mass of graphite, potassium persulfate and phosphorus pentoxide is 5-15g, and the dosage of concentrated sulfuric acid is 150-450mL.
As a preferable technical scheme of the invention, in the preparation process of the graphene oxide, the mass of the pre-oxidized graphite is 5-15g, the dosage of concentrated sulfuric acid is 150-450mL, and the dosages of potassium permanganate, deionized water and hydrogen peroxide are 25-75g, 75-225mL and 20-60mL respectively. In addition, the concentration of hydrochloric acid is 0.5-1.5mol/L.
As the preferable technical scheme of the invention, the added amounts of graphene oxide and anhydrous tetrahydrofuran in the flask 1 are 125-375mg and 50-150mL respectively, the added amount of anhydrous tetrahydrofuran in the flask 2 is 25-75mL, lithium aluminum hydride in the flask 2 is taken as a variable, the selected mass is 0-500mg, 400mg of reduced graphene oxide is taken as an example, and the catalyst is marked as rGO-OH-0.4 (0.4 represents the added amount of reducing agent and takes g as a unit), therefore, the catalyst corresponding to the supported bismuth oxide is named as Bi 2 O 3 /rGO-OH-0.4。
As a preferable technical scheme of the invention, in the hydrothermal synthesis, the mass of the reduced graphene oxide is 20-30mg, the mass of the bismuth nitrate is 15-20mg, the dosage of the N, N-dimethylformamide is 15-20mL, and the hydrothermal synthesis condition is that the reaction is carried out for 12h at 180 ℃.
As a preferable technical scheme of the invention, the calcination process is to raise the temperature to 300 ℃ at a heating rate of 5 ℃/min under the condition of introducing air and continuously calcine for 4 hours.
The beneficial effects of the invention are as follows:
1. the invention adopts LiAlH 4 The reduction method is used for reducing GO to prepare reduced graphene oxide with hydroxyl-rich surface proportion, and Bi is built by in-situ bismuth oxide loading 2 O 3 The rGO-OH catalyst has the advantages of simple operation, small experimental error and excellent electrocatalytic performance.
2. Bi prepared by the invention 2 O 3 Catalyst rGO-OH for CO 2 ER exhibits excellent properties: bi at-1.0V (vs. RHE) and high potential 2 O 3 The Faraday efficiency of the catalyst is best for formic acid of/rGO-OH-0.4, and at-1.1V (vs. RHE), the Faraday efficiency reaches 97 percent, which is about 18 percent higher than that of the bismuth oxide catalyst loaded by unmodified graphene oxide.
Drawings
FIG. 1 is a Fourier transform infrared spectrum of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5;
FIG. 2 is a fine O1s spectra of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5;
FIG. 3 is Bi 2 O 3 TEM image of rGO-OH-X;
FIG. 4 is a Raman spectrum of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5;
FIG. 5 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 XRD pattern of/rGO-OH-0.5;
FIG. 6 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 R GO-OH-0.5 inA faraday efficiency plot of conversion to formic acid at different potentials;
FIG. 7 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 Formic acid current density diagram of/rGO-OH-0.5 at different potentials.
Detailed Description
Embodiments of the present invention are described in further detail below with reference to the accompanying drawings and examples. The following examples are illustrative of the invention but are not intended to limit the scope of the invention.
In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front," "rear," "head," "tail," and the like are used as an orientation or positional relationship based on that shown in the drawings, merely to facilitate description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "connected," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
Example 1:
step one: in the preoxidation process, 10g of graphite, 10g of phosphorus pentoxide and 10g of potassium persulfate are sequentially added into a 500mL three-neck flask, 200mL of concentrated sulfuric acid is slowly added into the three-neck flask while mechanical stirring is carried out, and the three-neck flask is placed in an oil bath at 80 ℃ for reaction for 5 hours after uniform mixing. And after the reaction is finished and cooled to room temperature, carrying out suction filtration and separation by using a sand core funnel, washing the obtained filter cake by using deionized water until the pH value of the filtrate reaches neutrality, and then carrying out vacuum drying at 80 ℃ for 24 hours to obtain the preoxidized graphite.
Step two: in the oxidation process, 10g of pre-oxidized graphite is added into a 1000mL three-neck flask and placed in an ice water bath, 300mL of concentrated sulfuric acid is slowly added into the three-neck flask while mechanical stirring is carried out, 50g of potassium permanganate is slowly added into a dispersion liquid in batches after uniform stirring, then the mixture is transferred to a room temperature water bath for stirring for a moment, and then the temperature is raised to 35 ℃ for reaction for 2 hours. After the reaction is finished, the solution is dark green, a container is placed in an ice-water bath, 150mL of deionized water is slowly added for dilution, 40mL of hydrogen peroxide (30%) is dropwise added after stirring until the solution releases heat completely, after the solution becomes golden yellow, dilute hydrochloric acid (volume concentration 10%) is used for centrifugal washing for 6 times, the supernatant is in a clear and transparent state, deionized water is used for washing until the pH=5-6, the collected dark brown product is Graphene Oxide (GO), and a freeze drying method can be adopted to obtain fluffy solid GO.
Step three: in the preparation process of the reduced graphene oxide, 250mg of GO after freeze drying is firstly dispersed in a three-neck flask containing 100mL of anhydrous Tetrahydrofuran (THF) and is subjected to ultrasonic treatment for 2 hours to obtain GO suspension, and simultaneously 400mg of LiAlH is additionally taken 4 Disperse to 50mL of anhydrous THF. Subsequently, the sonicated GO is vigorously stirred while at N 2 Dropwise addition of LiAlH under an atmosphere as a protective gas 4 Is a solution of THF. Continuing to feed for 10min N after the addition is finished 2 The gas was then turned off and the reaction was continued for 24 hours, noting that the three-necked flask had to be completely sealed during this procedure. After the reaction is finished, the product is respectively washed by THF, 1mol/L hydrochloric acid solution and deionized water for a plurality of times until the filtrate is neutral, the precipitate is collected, and freeze drying treatment is adopted, so that the obtained final product is marked as rGO-OH-0.4.
Step four: bi is loaded by adopting a solvothermal method 2 O 3 The method comprises the following specific steps: firstly, 30mg of rGO-OH-0.4 is dispersed in 20mL of N, N-dimethylformamide solution, treated by ultrasonic for 3h, and 20mg of Bi (NO) is added after the dispersion is uniform 3 ) 3 Vigorously stirred overnightThen transferred to an autoclave with a polytetrafluoroethylene lining and reacted at 180℃for 12 hours. After the reaction is finished, cooling the reaction kettle to room temperature, centrifugally collecting precipitate, repeatedly washing with ethanol and deionized water for a plurality of times, and freeze-drying to obtain a pre-product. Secondly, grinding the pre-product to powder, placing the powder in a tube furnace, introducing air, heating to 300 ℃ at a heating rate of 5 ℃ min < -1 >, calcining for 4 hours, and marking the final product as Bi after finishing 2 O 3 /rGO-OH-0.4。
Example 2:
the addition amount of lithium aluminum hydride in the step III of the example 1 is changed to 300mg, the obtained reduction product is rGO-OH-0.3, and the final product is Bi after the solvothermal method of the step IV 2 O 3 R GO-OH-0.3, the other operations are the same as in example 1.
Example 3:
the addition amount of lithium aluminum hydride in the step III of the example 1 is changed to 500mg, the obtained reduction product is rGO-OH-0.5, and the final product is Bi after the solvothermal method of the step IV 2 O 3 R GO-OH-0.5, and the other operations were the same as in example 1.
Comparative examples 1-3:
the addition amount of lithium aluminum hydride in the step III in the example 1 is changed to 0mg, namely, graphene oxide is not reduced, and the final product is Bi after the solvothermal method in the step IV 2 O 3 The other operations of/GO are the same as those of example 1.
FIG. 1 is a Fourier transform infrared spectrum of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5 of the present invention for characterizing oxygen-containing functional groups. GO is 3000-3700cm -1 There is a broader, stronger absorption band within the range, which is attributed to the stretching vibrational peak of O-H, which is the result of adsorbing free and associated hydroxyl groups on water and graphene oxide. At 1677cm -1 The absorption peak at the location is a stretching vibration peak of-COOH at 1591cm -1 The absorption peak at the position belongs to the stretching vibration peak of C=O in aromatic hydrocarbon, and is 1385cm -1 Bending vibration peak belonging to C-OH at 1340cm -1 The stretching vibration peak belongs to C-O-C and is 768cm -1 The absorption peak at this point belongs to the bending vibration peak of O-H. After reduction, the peak intensity of all oxygen-containing functional groups is greatly reduced at the same time; wherein, -COOH telescopic vibration peaks are basically disappeared, and main O-H telescopic and vibration peaks indicate that the surface of the carrier after reduction is mainly hydroxyl.
FIG. 2 is a graph of O1s fine spectra of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5 and Table 1 is oxygen-containing functional group duty cycle data of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5 based on the graph of O1s fine spectra. Five peaks were fitted to each of the four vectors. Binding energies at 531eV, 531.8eV, 532.25eV, 532.85eV and 534.7eV correspond to C=O, -OH, C-O, -COOH and H, respectively 2 O. Comparing the peak areas of graphene oxide and any reduced graphene oxide, the remarkable reduction of the C-O content from 44% to about 20% can be observed; the carboxyl content is slightly reduced, whereas the-OH content is increased from 23% to more than 45%, which indicates that the hydroxyl group is the main oxygen-containing functional group through the strong reduction of lithium aluminum hydride.
Table 1: oxygen-containing functional groups of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5 account for the proportion of oxygen elements:
FIG. 3 is a TEM image of Bi2O3/rGO-OH-X, where FIG. 3a is Bi 2 O 3 TEM image of the/rGO-OH-0.3 vector, FIG. 3b is Bi 2 O 3 Particle size distribution of the/rGO-OH-0.3 carrier, FIG. 3c shows Bi at high resolution 2 O 3 TEM image of/rGO-OH-0.3, FIG. 3d is Bi 2 O 3 TEM image of the/rGO-OH-0.4 vector, FIG. 3e is Bi 2 O 3 Particle size distribution of the/rGO-OH-0.4 carrier, FIG. 3f is Bi at high resolution 2 O 3 TEM image of/rGO-OH-0.4, FIG. 3g is Bi 2 O 3 TEM image of the/rGO-OH-0.5 vector, FIG. 3h is Bi 2 O 3 Particle size distribution of the/rGO-OH-0.5 carrier, FIG. 3i shows Bi at high resolution 2 O 3 TEM image of rGO-OH-0.5; it can be seen that the bismuth oxide nanoparticles are uniformly distributed on the surface of the sheet-like support. Then for metal oxideThe particle size statistics of the particles shows that Bi is found 2 O 3 The average particle size of the rGO-OH-0.4 is 6.82nm and is smaller than Bi distributed on other two carriers 2 O 3 Average particle diameter, at the same time Bi 2 O 3 The distribution range of the/rGO-OH-0.4 is narrow.
FIG. 4 is a Raman spectrum of GO, rGO-OH-0.3, rGO-OH-0.4 and rGO-OH-0.5. At about 1335cm -1 And 1585cm -1 Two broad peaks, respectively a disordered D peak and an ordered G peak, were observed, where the ratio of peak heights of the two peaks was used (I D /I G ) Reflecting the carbon defects of the support. I as the reduction degree of graphene oxide increases D /I G Gradually increase, and the reduction time is prolonged, the I of the obtained graphene D /I G The ratio gradually increases. Theoretically, when graphene oxide is reduced, oxygen-containing functional groups on the graphite flake are removed, sp 2 The degree of ordering of the carbon network structure is increased, sp 2 The area becomes larger, I D /I G The value of (c) will decrease. The possible reason for this opposite trend of change to the theoretical prediction is that after the graphene oxide is reduced, a large amount of sp 3 New sp is formed after the hybridized carbon atoms are deoxidized 2 Hybridization of regions to reform sp 2 The area is smaller than that of graphene oxide (carbon atoms can be removed while deoxidizing, so that intrinsic defects are caused), so that the average sp of the reduced graphene 2 The size of the region is reduced, the number is increased, and the region is reflected on the I of the Raman spectrogram D /I G Gradually enhancing.
FIG. 5 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 XRD pattern of/rGO-OH-0.5. The four catalysts all have relatively wide amorphous peaks at about 26.2 degrees, namely graphite carbon (002), and the diffraction angles are 27.9 degrees, 31.7 degrees, 32.7 degrees, 46.2 degrees, 46.9 degrees, 54.2 degrees and 55.5 degrees correspond to Bi 2 O 3 (201) The (002), (220), (222), (400), (203), (421) and (402) crystal planes indicate that the bismuth oxide nanoparticle crystal belongs to a tetragonal structure.
Table 2 shows Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 Bismuth oxide loading data of/rGO-OH-0.5. Comparing the loadings of the four catalyst active components, wherein Bi 2 O 3 The loading of/rGO-OH-0.4 was the largest and was consistent with TEM characterization result analysis.
Table 2: bi (Bi) 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 Load of bismuth oxide/rGO-OH-0.5:
FIG. 6 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 Faraday efficiency plot of conversion of/rGO-OH-0.5 to formic acid at various potentials. Bi at-1.0V and high overpotential 2 O 3 Faraday efficiency of/rGO-OH-0.4 for formate is best shown, followed by Bi 2 O 3 rGO-OH-0.5 shows that the reduced graphene oxide rich in hydroxyl proportion adsorbs more carbon dioxide on the surface of the reduced graphene oxide through hydrogen bonds, thereby promoting more efficient CO 2 ER。
FIG. 7 is Bi 2 O 3 /GO、Bi 2 O 3 /rGO-OH-0.3、Bi 2 O 3 rGO-OH-0.4 and Bi 2 O 3 Partial current density plot of formic acid at different potentials for/rGO-OH-0.5. As the reduction degree of graphene oxide increases, the partial current density of formic acid also gradually increases. After the amount of lithium aluminum hydride added reached 0.4g, the current density hardly changed any more, and it was considered that the amounts of the reducing agents of 0.4 and 0.5g contributed equally to the current density.
From the above examples we can know that the catalyst obtained by carrying bismuth oxide on graphene oxide with different reduction degrees shows the process of increasing and then decreasing the Faraday efficiency of formic acid with the increase of reduction degree, and the method comprises the steps of adding 400mg of lithium aluminum hydride stripsThe maximum value is reached under the piece, mainly the hydroxyl plays a key role in the adsorption of carbon dioxide, and simultaneously Bi 2 O 3 The rGO-OH-0.4 has the maximum bismuth oxide load, improves the stability of the carbon dioxide intermediate, and realizes the Faraday efficiency of formic acid higher than 90% under the synergistic effect of the two.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (6)
1. A method for preparing formic acid by using a composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl proportion for carbon dioxide electroreduction is characterized by comprising the following steps: the method specifically comprises the following steps:
step one: slowly adding concentrated sulfuric acid into a mixture containing graphite, potassium persulfate and phosphorus pentoxide, then reacting for 5 hours at 80 ℃ in an oil bath, washing with deionized water to be neutral after the reaction is finished, and vacuum drying for 12 hours at 80 ℃ to obtain preoxidized graphite;
step two: slowly adding concentrated sulfuric acid into the preoxidized graphite and stirring for 0.5h, then gradually adding potassium permanganate into the solution in batches, transferring to the water bath for reaction for 2h, slowly adding deionized water after the reaction is finished, stirring at the same time, dropwise adding hydrogen peroxide after the solution is completely exothermic, centrifugally washing with hydrochloric acid until the supernatant becomes transparent after the solution turns to golden yellow, washing with deionized water until the pH is about 6, and freeze-drying for two days to obtain Graphene Oxide (GO);
step three: adding graphene oxide and lithium aluminum hydride into a flask 1 and a flask 2 filled with anhydrous tetrahydrofuran respectively, performing ultrasonic dispersion, then dropwise adding the tetrahydrofuran dissolved with the lithium aluminum hydride into a graphene oxide solution under N2, continuously reacting for 24 hours, washing the solution with hydrochloric acid solution and deionized water in sequence until the solution is neutral, and finally, performing freeze drying for two days to obtain a product, namely reduced graphene oxide (rGO-OH);
step four: adding N, N-dimethylformamide into reduced graphene oxide, performing ultrasonic treatment to obtain a dispersion liquid, adding bismuth nitrate, stirring overnight, transferring to an autoclave for hydrothermal reaction, washing the precipitate obtained by the reaction with ethanol and deionized water for multiple times, performing freeze drying to obtain a pre-product, and calcining to obtain the final catalyst (Bi) 2 O 3 /rGO-OH)。
2. The method for preparing formic acid by carbon dioxide electroreduction by using the composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl group proportion as claimed in claim 1, which is characterized in that: in the preparation process of the pre-oxidized graphite, the mass of graphite, potassium persulfate and phosphorus pentoxide is 5-15g, and the dosage of concentrated sulfuric acid is 150-450mL.
3. The method for preparing formic acid by carbon dioxide electroreduction by using the composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl group proportion as claimed in claim 1, which is characterized in that: in the preparation process of the graphene oxide, the mass of the pre-oxidized graphite is 5-15g, the dosage of concentrated sulfuric acid is 150-450mL, and the dosages of potassium permanganate, deionized water and hydrogen peroxide are 25-75g, 75-225mL and 20-60mL respectively; in addition, the concentration of hydrochloric acid is 0.5-1.5mol/L.
4. The method for preparing formic acid by carbon dioxide electroreduction by using the composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl group proportion as claimed in claim 1, which is characterized in that: the added amounts of the graphene oxide and the anhydrous tetrahydrofuran in the flask 1 are 125-375mg and 50-150mL respectively; the addition amount of anhydrous tetrahydrofuran and lithium aluminum hydride in the flask 2 is 25-75mL and 0-500mg respectively, taking 400mg of reduced graphene oxide as an example, and marking as rGO-OH-0.4 (0.4 represents the addition amount of the reducing agent and is expressed in g); therefore, the catalyst corresponding to the supported bismuth oxide is named Bi 2 O 3 /rGO-OH-0.4。
5. The method for preparing formic acid by carbon dioxide electroreduction by using the composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl group proportion as claimed in claim 1, which is characterized in that: in the hydrothermal synthesis, the mass of the reduced graphene oxide is 20-30mg, the mass of bismuth nitrate is 15-20mg, the dosage of N, N-dimethylformamide is 15-20mL, and the hydrothermal synthesis condition is that the reaction is carried out for 12h at 180 ℃.
6. The method for preparing formic acid by carbon dioxide electroreduction by using the composite catalyst of reduced graphene oxide loaded bismuth oxide rich in hydroxyl group proportion as claimed in claim 1, which is characterized in that: the calcination process is to raise the temperature to 300 ℃ at a heating rate of 5 ℃/min under the condition of introducing air and continuously calcine for 4 hours.
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