CN112593203B - Preparation method and application of sulfur and/or nitrogen doped graphene nanosheet - Google Patents
Preparation method and application of sulfur and/or nitrogen doped graphene nanosheet Download PDFInfo
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- CN112593203B CN112593203B CN202011347785.1A CN202011347785A CN112593203B CN 112593203 B CN112593203 B CN 112593203B CN 202011347785 A CN202011347785 A CN 202011347785A CN 112593203 B CN112593203 B CN 112593203B
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Abstract
The application discloses a preparation method and application of sulfur and/or nitrogen doped graphene nanosheets, wherein the method comprises the following steps: under an inactive atmosphere, carrying out chemical deposition and reaction on a raw material containing a doping source and a carbon source in the presence of a catalyst, and then removing the catalyst to obtain the sulfur and/or nitrogen doped graphene nanosheet; the doping source is at least one selected from a sulfur source and a nitrogen source. The S and/or N doped graphene nanosheet synthesized based on Chemical Vapor Deposition (CVD) method strategy provided by the application is used as a catalyst to show extraordinary electrocatalytic oxidation reduction of H in an acidic medium 2 O 2 The performance of (a) is the highest rate and faradaic efficiency reported in acidic media at present.
Description
Technical Field
The application relates to a preparation method and application of sulfur and/or nitrogen doped graphene nanosheets, belonging to the technical field of composite materials.
Background
As a green chemical, the hydrogen peroxide has wide application and rapid demand in the industries of paper making, textile, chemical industry, environmental protection and the like, and the main component of the hydrogen peroxide (H) is hydrogen peroxide 2 O 2 ) Has become one of the fastest growing chemicals in use in the last decade. The traditional industrial anthraquinone process comprises complex organic system reaction and post-treatment steps: high danger, high energy consumption and the like. The method for electrochemically synthesizing the hydrogen peroxide has the characteristics of simple equipment, high efficiency, low consumption, environmental protection and the like, and is expected to replace the traditional industrial anthraquinone method.
The electrochemical reduction of oxygen to hydrogen peroxide is to combine oxygen and water (H) + ) Conversion to H 2 O 2 The presence of concomitant competitive four-electron oxygen reduction side reactions, results in poor energy efficiency and product selectivity. More remarkably, most of catalysts reported in the past are noble metals, such as Pd-Au, Pt-Pd, W-Au, Pd-Hg, Pt-Hg, Ag-Hg and other alloy catalysts, and particularly Pd-Hg has high selectivity and stability under an acidic condition and is the best two-electron reduction catalyst at present, but the high cost and the harm of mercury loss to the environment limit the wide application of the catalysts.
Some carbon materials with low raw material cost and electrochemical stability and transition metal composite nano carbon materials reported recently are expected to be developed into the most potential two-electron oxygen reduction catalysts, such as oxidized multi-wall carbon nanotubes and graphene, N-doped carbon nanohorns, N-doped mesoporous carbon and the like. However, most of these catalysts show excellent performance (such as low overpotential and large current) for producing hydrogen peroxide by oxygen reduction under alkaline/neutral medium conditions, and show mediocre performance in acidic medium. Unfortunately, the hydrogen peroxide product is unstable and prone to decomposition in alkaline and neutral media. But can coexist for a long time under the acidic condition, thereby being beneficial to the collection of products. For this reason, the development of highly efficient non- (noble) metals in acidic media is of great practical interest.
Disclosure of Invention
According to one aspect of the application, a preparation method of sulfur and/or nitrogen doped graphene nanoplatelets is provided, S and/or N doped graphene nanoplatelets are synthesized based on a Chemical Vapor Deposition (CVD) method strategy, and the S and/or N doped graphene nanoplatelets can be used as a catalyst to show extraordinary electrocatalytic oxidation and reduction of H in an acidic medium 2 O 2 The performance of (A): in which the starting potential reaches 0.616V (acidic medium favors H 2 O 2 Stable), higher than most of the reported materials such as N-doped carbon nanohorns (0.4V), N-doped mesoporous carbon (0.55V) and mesoporous carbon spheres (0.37V). The hydrogen peroxide production selectivity is higher than 90% in the electrochemical window (0.2-0.55V interval), and the velocity reaches 4.79mol g -1 ·h -1 Faradaic efficiency of 92% is the highest rate and faradaic efficiency reported in acidic media at present.
According to a first aspect of the present application, there is provided a method of preparing sulfur-and/or nitrogen-doped graphene nanoplatelets, the method comprising: under an inactive atmosphere, carrying out chemical deposition and reaction on a raw material containing a doping source and a carbon source in the presence of a catalyst, and then removing the catalyst to obtain the sulfur and/or nitrogen doped graphene nanosheet;
the doping source is at least one selected from a sulfur source and a nitrogen source.
Optionally, the catalyst comprises an active component and a support; the active component is loaded on the carrier; the active component is selected from metal elements; the metal element is selected from at least one of iron, cobalt and nickel;
the carrier is selected from gamma-Al 2 O 3 、SiO 2 At least one of MgO;
the sulfur source is at least one selected from thiophene and thiourea;
the carbon source is selected from at least one of thiophene, pyrimidine, pyridine, thiourea and pyrrole;
the nitrogen source is at least one selected from pyrimidine, pyridine and pyrrole.
Optionally, the reaction conditions are: the reaction temperature is as follows: 500 ℃ and 800 ℃; the reaction time is 6-24 h; the heating rate is 1-5 ℃/min.
Optionally, the mass content of the active component in the catalyst is 11.5-17.4%.
Optionally, the sulfur source is selected from thiophene; the carbon source comprises thiophene and pyrimidine; the nitrogen source is selected from pyrimidines.
Optionally, the doping source comprises a sulfur source and a nitrogen source; the volume ratio of the nitrogen source to the sulfur source is 2-9: 1;
the mass ratio of the catalyst to the nitrogen source is 0.08-0.2: 1.6-4.0.
Optionally, the doping source comprises any one of a sulfur source and a nitrogen source; the mass ratio of the doping source to the catalyst is 2.4-4.0: 0.08-0.2.
Optionally, the upper volume ratio limit of the nitrogen source and the sulfur source is independently selected from 9: 1. 8: 1. 7: 1. 6: 1. 5: 1. 4: 1. 3: 1, the lower limit is independently selected from 2:1. 8: 1. 7: 1. 6: 1. 5: 1. 4: 1. 3: 1.
optionally, the removing the catalyst comprises the steps of:
(1) placing the reacted material in a solution containing strong base, refluxing I, and etching to remove the carrier to obtain an intermediate product;
(2) and (3) placing the intermediate product in a solution containing strong acid, refluxing II, and removing active components to obtain the sulfur and/or nitrogen doped graphene nanosheet.
Optionally, the conditions of reflux I and reflux II are both selected from: the temperature is 110-140 ℃; the time is 24-48 h.
Optionally, the concentration of the solution containing strong base and the concentration of the solution containing strong acid are both 4-10M.
Optionally, the active component comprises iron and cobalt; the carrier comprises gamma-Al 2 O 3 。
Optionally, the particle size of the carrier is 20-50 nm.
Alternatively, the catalyst in the present application is prepared as follows:
FeCo/γ-Al 2 O 3 preparation of the catalyst:
taking 1-2 g of gamma-Al 2 O 3 With 1mol Fe (NO) 3 ) 3 And 2mol of Co (NO) 3 ) 3 Uniformly mixing the aqueous solution, stirring and drying, transferring the mixture into a porcelain boat, heating the porcelain boat to 500-800 ℃ at 3-5 ℃ in air, carrying out heat treatment, preserving heat for 6-24 hours, and naturally cooling to obtain FeCo/gamma-Al 2 O 3 And grinding the catalyst for later use.
According to a second aspect of the application, provided is a sulfur and/or nitrogen doped graphene nano sheet, wherein the size of a single sheet in the sulfur and/or nitrogen doped graphene nano sheet is 19-21 nm; the size of the stack was 300-500 nm.
Optionally, in the sulfur and/or nitrogen-doped graphene nanosheet, the atomic percentage of nitrogen is 0-12%; the atomic percentage of sulfur is 0-2%; the atomic percentage of oxygen is 8-17%.
According to a third aspect of the present application, there is provided a sulfur-and/or nitrogen-doped graphene nanoplatelet prepared according to the above-described method, and a use of any of the above-described sulfur-and/or nitrogen-doped graphene nanoplatelets in the electrochemical preparation of hydrogen peroxide.
Alternatively, hydrogen peroxide is produced using an electrolytic cell;
the electrolytic cell comprises an anode electrode slice, a cathode electrode slice, a reference electrode, a bipolar membrane, anode chamber electrolyte and cathode chamber electrolyte;
wherein the cathode electrode sheet comprises a cathode catalyst selected from sulfur and/or nitrogen doped graphene nanoplatelets;
the anode electrode plate is selected from any one of a platinum sheet and a graphite rod;
the reference electrode is selected from Ag/AgCl, Hg/HgSO 4 Any one of (a) to (b);
the electrolyte in the anode chamber and the electrolyte in the cathode chamber are both selected from solutions containing acidic substances;
the acidic substance is at least one of perchloric acid and sulfuric acid;
when the electrolytic cell is adopted to prepare the hydrogen peroxide, oxygen is introduced into the cathode electrode plate.
Preparation of catalyst with 20nm of gamma-Al 2 O 3 As carrier, removing gamma-Al in alkali washing process 2 O 3， Generating mesopores which are beneficial to mass transfer; cracking a carbon source on the surface of catalyst particles by taking Fe and Co as catalysts, carrying out catalytic growth to obtain a carbon nano material, and then carrying out acid washing to remove Fe and Co.
The hydrogen peroxide generated by electrochemistry is more stable in an acid medium and is beneficial to collection. The invention aims to overcome the defects that the existing single-doped carbon catalyst has good catalytic performance (such as low overpotential and large current) when hydrogen peroxide is generated by two-electron oxygen reduction in an alkaline medium, and shows mediocre technical problems in an acidic medium.
The application is based on a traditional Chemical Vapor Deposition (CVD) synthesis method, pyrimidine and/or thiophene are/is used as a raw material, a doping strategy is adopted to synthesize surface S and N co-doped graphene nanosheets, and the catalyst shows high starting potential (0.616V) and high selectivity (C and N are respectively mixed with N and N to obtain the graphene nanosheet)>90%) and yield H 2 O 2 Rate (4.79 mol. g) -1 ·h -1 ) The Faraday efficiency also reaches 92%.
The beneficial effects that this application can produce include:
(1) the invention provides a catalyst of S and/or N doped graphene nanosheets, which improves the catalytic selectivity of two electrons by S and/or N doping. More importantly, the catalyst shows extraordinary electrocatalytic oxidation reduction of H in an acidic medium 2 O 2 The performance of (A): wherein the initiation potential reaches 0.616V, higher than most of the reported materials such as N-doped carbon nanohorn (0.4V), N-doped mesoporous carbon (0.55V) and mesoporous carbonPorous carbon spheres (0.37V). The hydrogen peroxide production selectivity is higher than 90% in the electrochemical window (0.2-0.55V interval), and the velocity reaches 4.79mol g -1 ·h -1 Faradaic efficiency of 92% is the highest rate and faradaic efficiency reported in acidic media at present.
(2) Based on a CVD method, nitrogen and/or sulfur are doped under the condition of low temperature (700 ℃) through catalyst auxiliary growth, the method is different from most reported S, N co-doped graphene which is obtained by stripping graphene from graphite by a hummers method and then mixing N-containing and S-containing precursors for high-temperature heat treatment (above 900 ℃) to realize doping, and the process is simpler.
(3) The doping concentration is higher, the N doping concentration reaches 8.08 at%, the S doping concentration reaches 0.92 at%, the oxygen content reaches 8.92 at%, and is higher than N4.5 at% and S2.0 at% O4.6 at% reported in the literature.
Drawings
Fig. 1 XRD of sulfur-nitrogen co-doped graphene nanoplatelets (SNGL-20) prepared in example 1, nitrogen-doped graphene Nanoplatelets (NGL) prepared in example 4, and sulfur-doped graphene nanoplatelets (SGL) prepared in example 5.
FIG. 2 is a transmission electron micrograph (a) and a high resolution transmission electron micrograph (b) of SNGL-20 prepared in example 1.
Fig. 3N of sulfur and nitrogen co-doped graphene nanoplatelets (SNGL-20) prepared in example 1, nitrogen-doped graphene Nanoplatelets (NGL) prepared in example 4, and sulfur-doped graphene nanoplatelets (SGL) prepared in example 5 2 Adsorption curve (a) and pore size distribution (b).
Fig. 4 is sulfur and nitrogen co-doped graphene nanoplatelets (SNGL-20) prepared in example 1, example nitrogen-doped graphene Nanoplatelets (NGL) and sulfur-doped graphene nanoplatelets (SGL) based on linear sweep voltammograms measured by the cyclic disk technique (a) and their calculated two-electron selectivities (b). Fig. 5 is a linear sweep voltammogram (a) and a calculated two-electron selectivity (b) of sulfur-nitrogen co-doped graphene nanoplates SNGL-20, SNGL-10 and SNGL-30 prepared in examples 1,2 and 3 based on a ring-disk technique.
FIG. 6 example 1 preparation of SNGL-20 assembled H-type electrolytic cell for electrocatalytic H production 2 O 2 And (4) quantifying. (a) Under different potential conditions, (0.1-0.4V) current-time curve and (b) H production 2 O 2 The rate.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
1. The synthesis method comprises the following steps: at a molecular weight of 20nm gamma-Al 2 O 3 The loaded FeCo alloy is used as a catalyst, sulfur and/or nitrogen doped graphene nanosheets (SNGL) are synthesized by a Chemical Vapor Deposition (CVD) method at a low temperature (700 ℃), and the method realizes in-situ S and/or N doping in the growth process of graphene. The method is different from most reported S and N co-doped graphene, the graphene is firstly stripped from graphite by a hummers method, then N-containing and S-containing precursors are mixed for high-temperature heat treatment (above 900 ℃), and doping is realized, so that the process is simpler.
2. The material appearance: few layers of S and/or N doped graphene nano sheets copied by the template are formed by stacking single sheets with the size of about 20nm, wherein the size of the stacked sheets is about 300-500nm, and the size of the single sheets of graphene peeled by the hummers method is larger and usually reaches several micrometers or even tens of micrometers.
3. In composition, the doping concentration is higher, the N doping concentration reaches 8.08 at%, the S doping concentration reaches 0.92 at%, and the oxygen content reaches 8.92 at%, which is higher than the N4.5 at% and S2.0 at% O4.6 at% reported in the literature.
4. The application comprises the following steps: most importantly, the sulfur and/or nitrogen doped graphene nano-sheets synthesized by the method are firstly applied to electrochemical synthesis of hydrogen peroxide in an acid medium, and the material is subjected to electrocatalytic oxidation and reduction in the acid medium to produce H 2 O 2 The starting potential of (2) reaches 0.616V (the acidic medium is favorable for H 2 O 2 Stable), higher than most of the reported materials such as N-doped carbon nanohorns (0.4V), N-doped mesoporous carbon (0.55V) and mesoporous carbon spheres (0.37V). The hydrogen peroxide production selectivity is higher than 90% in an electrochemical window (0.2-0.55V interval), and 0.55V is close to 100%. Produce H 2 O 2 The rate reaches 4.79mol g -1 ·h -1 Faradaic efficiency of 92% is the highest rate and faradaic efficiency reported in acidic media at present.
1. The method synthesizes the graphene nanosheet with high-concentration defects at a lower temperature, and particularly, S and/or N are codoped to regulate and control the surface electronic state, so that the performance of the material is greatly exerted.
2. The sulfur and/or nitrogen-doped graphene nanosheet (SNGL) synthesized by the method is applied to electrochemical synthesis of hydrogen peroxide in an acidic medium for the first time, and H is produced by electrocatalytic oxidation and reduction of the material in the acidic medium 2 O 2 The starting potential of (2) reaches 0.616V (the acidic medium is favorable for H 2 O 2 Stable), higher than most of the reported materials such as N-doped carbon nanohorns (0.4V), N-doped mesoporous carbon (0.55V) and mesoporous carbon spheres (0.37V). The selectivity of hydrogen peroxide production is higher than 90% in the electrochemical window (0.2-0.55V interval), and H is produced 2 O 2 The highest speed reaches 4.79mol g -1 ·h -1 Faradaic efficiency of 92% is the highest rate and faradaic efficiency reported in acidic media at present.
The preparation of S and/or N doped graphene carbon material for electrocatalytic hydrogen peroxide production in acidic medium includes the following steps:
(a1)FeCo/gamma-Al 2 O 3 preparing a catalyst;
taking a plurality of gamma-Al 2 O 3 With Fe (NO) 3 ) 3 And Co (NO) 3 ) 3 Mixing the water solution uniformly, stirring and drying, transferring into a porcelain boat, heating to 450 ℃ in air at 3-5 ℃, carrying out heat treatment, preserving heat for 5 hours, and naturally cooling to obtain FeCo/gamma-Al 2 O 3 And grinding the catalyst for later use.
(b1) Synthesizing S and/or N doped graphene nanosheets by a chemical vapor deposition method;
taking a plurality of FeCo/gamma-Al 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and the nitrogen gas flow is used for blowing and removing oxygen. Then heating to the target temperature at a heating speed of 3-5 ℃/min and keeping the temperature constant. The gas flow was switched and vapor deposition was carried out by nitrogen entrainment (pyrimidine and/or thiophene) into the quartz glass tube. And after the reaction is finished, naturally cooling to obtain a black product.
(c1) Removal of the support and catalyst.
Grinding the product obtained in the step b1, ultrasonically dispersing the product in a 5-10M NaOH solution, refluxing the product in an oil bath kettle at the temperature of 110-140 ℃ for 24-48h, and etching to remove the carrier gamma-Al 2 O 3 . Filtering and washing the product, continuously dispersing the product in 5-10M HCl, refluxing for 24-48h, and removing the metal active components. The product was washed to neutrality (pH 7.0) with deionized water and dried at 60 ℃ for 12 h.
According to the invention, in the step (a1), the proportion concentration of the impregnated FeCo catalyst is adjustable, and the Fe/Co molar ratio of the FeCo catalyst ranges from 1:1 to 1:3, and the Fe/Co molar ratio is preferably 1: 2. With 1 gram of gamma-Al 2 O 3 The total amount of the supportable metal catalyst is 1-4mmol, preferably 3mmol, as the carrier.
According to the invention, in said step (b1), the added material may be a single pyrimidine or thiophene, obtaining a single doped product NGL, SGL. The ratios of the starting materials can also be adjusted (pyrimidine/thiophene volume ratio: 9: 1; 8: 2; 7:3) to obtain SNGL-10, SNGL-20 and SNGL-30, respectively. By preference, SNGL-20 has the highest catalytic selectivity and electrocatalytic production of H 2 O 2 The rate is the best.
According to the present invention, in the step (c1), the optional alkali solution may be NaOH or KOH. The concentration is adjustable within the range of 4-10M, preferably 6M. The optional washing container is a round bottom flask or a polytetrafluoroethylene cup, preferably a polytetrafluoroethylene cup to prevent the SiO generated by the etching of glassware with alkaline solution 2 Contaminating the sample. The reflux time is from 24 to 60 hours, preferably 48 hours. The concentration of the optional hydrochloric acid solution is in the range of 4-10M, preferably 6M. The reflux time is from 24 to 60 hours, preferably 48 hours.
Examples the drug pyrimidine used was purchased from the company Aladdin pharmaceuticals and thiophene from the company alpha-Angsa pharmaceuticals. gamma-Al 2 O 3 ，Fe(NO 3 ) 3 And Co (NO) 3 ) 3 Purchased from the national drug group and used directly.
The apparatus used in the examples was a magnetic stirrer model ZNCL-G190 x 90, a vacuum drying oven model DZF-6020.
Example 1 (preparation of SNGL-20)
(a1) Taking 1 g of gamma-Al 2 O 3 (particle diameter of 20nm) withFe(NO 3 ) 3 (1mmol) and Co (NO) 3 ) 3 (2mmol) water solution is evenly mixed, stirred and dried, then transferred into a porcelain boat to be heated to 450 ℃ in air at the temperature of 3 ℃, and then heat treatment is carried out, and the temperature is naturally reduced after 5 hours of heat preservation, thus obtaining FeCo/gamma-Al 2 O 3 And grinding the catalyst (the mass content of the active component is 7.74%) for later use.
(b1) Synthesizing an S and N codoped graphene nanosheet by a chemical vapor deposition method;
200 mg of FeCo/gamma-Al are taken 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and nitrogen gas flow is used for blowing and removing oxygen. Then heating to 700 ℃ at a heating speed of 5 ℃/min and keeping the temperature constant. The gas flow was switched and vapor deposition was carried out by nitrogen gas (3.38g pyrimidine +0.84g thiophene, volume ratio 8:2) into a quartz glass tube. After the reaction is finished for 12h, naturally cooling to obtain a black product.
(c1) Removal of the support and catalyst.
Grinding the product obtained in the step b1, ultrasonically dispersing the product in 6M KOH solution, refluxing the product in an oil bath kettle at the temperature of 110 ℃ for 48 hours, and etching to remove the carrier gamma-Al 2 O 3 . The product was filtered and washed and further dispersed in 6M HCl for reflux for 48h to remove the metal catalyst. The product was washed to neutrality (pH 7.0) with deionized water and dried at 60 ℃ for 12 h. The product was found by X-ray photoelectron spectroscopy: in the sulfur and nitrogen co-doped graphene nanosheet (SNGL-20), the atomic percentage of nitrogen is 8.0%; the atomic percentage of sulfur is 0.92%; the atomic percent of oxygen is 8.9%.
Example 2 (preparation of SNGL-10)
(a1) Same as example 1
(b1) 200 mg of FeCo/gamma-Al are taken 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and nitrogen gas flow is used for blowing and removing oxygen. Then heating to 700 ℃ at a heating speed of 5 ℃/min and keeping the temperature constant. The gas flow was switched and vapor deposition was carried out by nitrogen gas (3.80g pyrimidine +0.42g thiophene, volume ratio 9:1) into a quartz glass tube. After the reaction is finished for 12h, naturally cooling to obtain a black product.
(c1) The same as in example 1. The product was found by X-ray photoelectron spectroscopy: in the sulfur and nitrogen co-doped graphene nanosheet (SNGL-10), the atomic percentage of nitrogen is 8.0%; the atomic percentage of sulfur is 0.5%; the atomic percent of oxygen was 17.2%.
Example 3 (preparation of SNGL-30)
(a1) Same as example 1
(b1) 200 mg of FeCo/gamma-Al are taken 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and the nitrogen gas flow is used for blowing and removing oxygen. Then heating to 700 ℃ at a heating speed of 5 ℃/min and keeping the temperature constant. The gas flow was switched and vapor deposition was carried out by nitrogen gas (2.96g of pyrimidine +1.26g of thiophene, volume ratio 7:3) into a quartz glass tube. After the reaction is finished for 12h, naturally cooling to obtain a black product.
(c1) The same as in example 1. The product was found by X-ray photoelectron spectroscopy: in the sulfur-nitrogen co-doped graphene nanosheet (SNGL-30), the atomic percentage of nitrogen is 3.7%; the atomic percentage of sulfur is 2.0 percent; the atomic percent of oxygen is 12.6%.
Example 4
(a1) Same as example 1
(b1) 200 mg of FeCo/gamma-Al are taken 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and the nitrogen gas flow is used for blowing and removing oxygen. Then heating to 700 ℃ at a heating speed of 5 ℃/min and keeping the temperature constant. The gas flow is switched, and nitrogen carries 0.053mol of pyrimidine to enter a quartz glass tube for vapor deposition. After the reaction is finished for 12h, naturally cooling to obtain a black product.
(c1) The obtained nitrogen-doped graphene nanoplatelets sample was named NGL as in example 1. The product was found by X-ray photoelectron spectroscopy: in the sulfur-nitrogen co-doped graphene nano sheet (NGL), the atomic percentage content of nitrogen is 12.0 percent; the sulfur content was not detected; the atomic percent of oxygen was 9.7%.
Example 5
(a1) Same as example 1
(b1) 200 mg of FeCo/gamma-Al are taken 2 O 3 The catalyst is placed in the middle of the quartz glass tube, and nitrogen gas flow is used for blowing and removing oxygen. Then heating to 700 ℃ at a heating speed of 5 ℃/min and keeping the temperature constant. Switching air flow, and introducing the nitrogen carrying thiophene of 0.052mol into the quartz glass tubeVapor deposition is performed. After the reaction is finished for 12h, naturally cooling to obtain a black product.
(c1) The obtained sample of sulfur-doped graphene nanoplatelets was named SGL as in example 1. The product was found by X-ray photoelectron spectroscopy: in the sulfur-doped graphene nanosheet (SGL), the atomic percentage of nitrogen is 4.7%; the atomic percentage of sulfur is 1.4%; the atomic percent of oxygen is 6.4%.
Example 6
XRD characterization is performed on the samples prepared in examples 1 to 5, and is typically represented by the samples prepared in examples 1, 4 and 5, fig. 1 is XRD (a) and X-ray photoelectron spectrum (b) of the sulfur-nitrogen co-doped graphene nanoplate (SNGL-20) prepared in example 1, the nitrogen-doped graphene Nanoplate (NGL) prepared in example 4 and the sulfur-doped graphene nanoplate (SGL) prepared in example 5, and as can be seen from fig. (a), only a carbon peak exists, indicating that γ -Al as a carrier exists 2 O 3 Active components Fe and Co can be completely removed; as can be seen from the graph (b), sulfur and nitrogen are supported on the graphene nanoplatelets.
Example 7
The samples prepared in examples 1 to 5 are subjected to transmission electron microscope tests, the samples prepared in example 1 are taken as typical representatives, and FIG. 2 is a transmission electron microscope picture (a) and a high-resolution transmission electron microscope picture (b) of SNGL-20 prepared in example 1, and as can be seen from the pictures, the size of a single sheet of the material is 19-21 nm, the size of a stacked body is 300-500nm, and the material has a layered structure and does not contain residual metal catalysts and other pyrolysis impurities.
Example 8
The samples prepared in examples 1 to 5 were subjected to specific surface area tests, represented by the samples prepared in examples 1, 4 and 5, and fig. 3 is N-doped graphene nanoplatelets (SNGL-20) prepared in example 1, N-doped graphene Nanoplatelets (NGL) prepared in example 4 and N-doped graphene nanoplatelets (SGL) prepared in example 5 2 The adsorption curve (a) and the pore size distribution can be seen from the figure that the single doping or the codoping both have larger specific surface area and canMore active sites are exposed and therefore have higher selectivity.
Example 9
Samples SNGL-20, NGL and SGL were subjected to a linear sweep voltammogram (a) measured based on a disk-on-disk technique and a two-electron selectivity (b) test calculated therefrom, and fig. 4 is a plot of sulfur-nitrogen co-doped graphene nanosheet (SNGL-20) prepared in example 1, and a plot of a linear sweep voltammogram (a) measured based on a disk-on-disk technique and a two-electron selectivity (b) measured based on a nitrogen-doped graphene Nanosheet (NGL) and a sulfur-doped graphene nanosheet (SGL) in example 1. As can be seen from the graph (a), the current of the catalyst disk is the largest when sulfur-doped graphene nanosheets (SGL) are used, the current of the catalyst disk is the second time when sulfur-nitrogen-doped graphene nanosheets (SNGL-20) are used, and the current of the catalyst disk is the smallest when N-doped graphene Nanosheets (NGL) are used; but the catalytically produced hydrogen peroxide was found by ring current detection: the ring current of the sulfur-nitrogen co-doped graphene nano sheet (SNGL-20) is the largest, namely the generated hydrogen peroxide is the largest. Accordingly, it is found by 2 electron selectivity calculation formula (fig. b): the electronic selectivity of oxygen reduction 2 of the sulfur-nitrogen co-doped graphene nanosheet (SNGL-20) is the highest (> 90%), the electronic selectivity of the nitrogen-doped graphene nanosheet 2 is the second highest (80-85%), and the electronic selectivity of the sulfur-doped graphene nanosheet 2 is the lowest (65-70%). Indicating that the sulfur-nitrogen co-doping improves the 2 electron selectivity of the material for electrocatalytic oxygen reduction.
The samples prepared in examples 1 to 5 are subjected to electrochemical tests, and typically represented by the samples prepared in examples 1, 4 and 5, fig. 5 is a plot of linear sweep voltammetry curves (a) and calculated two-electron selectivity (b) of the sulfur-nitrogen co-doped graphene nanosheets (SNGL-20) prepared in example 1, the nitrogen-doped graphene Nanosheets (NGL) prepared in example 4 and the sulfur-doped graphene nanosheets (SGL) prepared in example 5, and it can be seen from the plots that when a voltage window is 0.2 to 0.55V, the selectivity of SGL is higher than 60%, the selectivity of NGL is higher than 80%, and the selectivity of SNGL-20 is higher than 90%.
Example 10
Preparation H 2 O 2 Examples of the invention
Examples the pharmaceutical sodium oxalate standard solution (0.05M) used was purchased from alatin pharmaceuticals,perchloric acid, isopropanol, Nafion were purchased from Alphaesar Chemicals, concentrated sulfuric acid and KMnO 4 Purchased from the national drug group.
1.KMnO 4 Preparing and calibrating a standard solution:
a) 1.6 g of KMnO are taken 4 Dissolving in 500 ml deionized water, boiling and stirring for 2 hours, then stirring for 7 days at room temperature, removing filter residue, and preparing 500 ml KMnO 4 And (4) standard solution.
b) 30 ml of 0.05M sodium oxalate standard solution and 15 ml of 3M sulfuric acid solution are mixed uniformly for KMnO 4 The concentration of the solution is calibrated, and the calibration solubility is 0.023M.
Quantitative test for hydrogen peroxide prepared by H-type electrolytic cell electrochemistry
(a1) 3mg of the cathode catalyst (sample prepared in example 1) was ultrasonically dispersed in a mixed solution of 0.54 ml of isopropyl alcohol and 60. mu.l of Nafion to form an ink, 20. mu.l of the ink was dropped on carbon paper, and dried naturally.
(b1) 25 ml of 0.1M perchloric acid solution is respectively placed at two ends of an H-shaped electrolytic cell, and a three-electrode system which takes carbon paper coated with a catalyst as a working electrode anode, a platinum sheet as a counter electrode and Ag/AgCl as a reference electrode is connected with an electrochemical workstation. After 30 minutes of oxygen was introduced into one end of the working electrode, a test for hydrogen peroxide production was carried out.
(c1) Respectively setting working voltages of 0.1V, 0.2V, 0.3V and 0.4V (based on a standard hydrogen electrode) to carry out voltage-current test for 30 minutes, taking 20 ml of electrolyte after electrosynthesis, uniformly mixing with 10 ml of 3M sulfuric acid solution, and adopting KMnO according to GB method 4 Standard solution for H in the above electrolyte 2 O 2 Titrating the concentration, and calculating to obtain different voltages for half an hour H 2 O 2 The hydrogen peroxide production rate.
The samples prepared in examples 1 to 5 were subjected to a hydrogen peroxide yield test, and fig. 6 is a sulfur and nitrogen co-doped graphene nanoplatelets (SNGL-20) prepared in example 1, a nitrogen-doped graphene Nanoplatelet (NGL) prepared in example 4, and a sulfur-doped graphene nanoplatelet (S) prepared in example 5, which are typical of the samples prepared in examples 1, 4, and 5GL) and its different voltages H 2 O 2 Yield (b) is shown, as can be seen from the graph, at different voltages for half an hour H 2 O 2 The hydrogen peroxide production rates of (a) are respectively 4.79mol/g/h, 4.11mol/g/h, 2.19mol/g/h and 0.96 mol/g/h.
Although the present invention has been described with reference to a few preferred embodiments, it should be understood that various changes and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (12)
1. The application of sulfur and/or nitrogen-doped graphene nanoplatelets in electrochemical synthesis of hydrogen peroxide in an acidic medium is characterized in that the preparation method of the sulfur and/or nitrogen-doped graphene nanoplatelets comprises the following steps: under an inactive atmosphere, carrying out chemical deposition and reaction on a raw material containing a doping source and a carbon source in the presence of a catalyst, and then removing the catalyst to obtain the sulfur and/or nitrogen doped graphene nanosheet;
the doping source is at least one selected from a sulfur source and a nitrogen source;
the catalyst comprises an active component and a carrier; the active component is loaded on the carrier; the active component is selected from metal elements; the metal element is selected from at least one of iron, diamond and nickel;
the carrier is selected from gamma-Al 2 O 3 、SiO 2 At least one of MgO; the sulfur source is at least one selected from thiophene and thiourea;
the carbon source is selected from at least one of thiophene, pyrimidine, pyridine, thiourea and pyrrole;
the nitrogen source is at least one selected from pyrimidine, pyridine and pyrrole.
2. Use according to claim 1, characterized in that the reaction conditions are: the reaction temperature is as follows: 500 ℃ and 800 ℃; the reaction time is 6-24 h; the heating rate is 1-5 ℃/min.
3. The use according to claim 1, wherein the mass content of active components in the catalyst is 11.5-17.4%.
4. The use of claim 1, wherein the dopant source comprises a sulfur source and a nitrogen source; the volume ratio of the nitrogen source to the sulfur source is 2-9: 1;
the mass ratio of the catalyst to the nitrogen source is 0.08-0.2: 1.6-4.0.
5. The use of claim 1, wherein the doping source comprises any one of a sulfur source, a nitrogen source; the mass ratio of the doping source to the catalyst is 2.4-4.0: 0.08-0.2.
6. Use according to claim 1, wherein said removal of the catalyst comprises the steps of:
(1) placing the reacted material in a solution containing strong base, refluxing I, and etching to remove the carrier to obtain an intermediate product;
(2) and (3) placing the intermediate product in a solution containing strong acid, refluxing II, and removing active components to obtain the sulfur and/or nitrogen doped graphene nanosheet.
7. The use according to claim 6, wherein the conditions of reflux I and reflux II are each selected from: the temperature is 110-140 ℃; the time is 24-48 h.
8. The use according to claim 6, wherein the concentration of the solution containing a strong base and the concentration of the solution containing a strong acid are both 4 to 10M.
9. The use according to claim 6, wherein the carrier has a particle size of 20 to 50 nm.
10. The use according to claim 1, wherein in the sulfur and/or nitrogen doped graphene nanoplatelets, the size of individual sheets is 19-21 nm; the size of the stack was 300-500 nm.
11. The application of claim 1, wherein in the sulfur and/or nitrogen doped graphene nano sheets, the nitrogen content is 0-12% by atomic percentage; the atomic percentage of sulfur is 0-2%; the atomic percentage of oxygen is 8-17%.
12. Use according to claim 1, characterized in that hydrogen peroxide is produced in an electrolytic cell;
the electrolytic cell comprises an anode electrode slice, a cathode electrode slice, a reference electrode, a bipolar membrane, anode chamber electrolyte and cathode chamber electrolyte;
wherein the cathode electrode sheet comprises a cathode catalyst selected from sulfur and/or nitrogen doped graphene nanoplatelets;
the anode electrode plate is selected from any one of a platinum sheet and a graphite rod;
the reference electrode is selected from Ag/AgCl, Hg/HgSO 4 Any one of (a) to (b);
the electrolyte in the anode chamber and the electrolyte in the cathode chamber are both selected from solutions containing acidic substances;
the acidic substance is at least one selected from perchloric acid and sulfuric acid;
when the electrolytic cell is adopted to prepare the hydrogen peroxide, oxygen is introduced into the cathode electrode plate.
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