Preparation method of hollow carbon sphere epitaxial growth bi4o5br2 nanosheet confined reactor and CO2 hydrogenation application thereof

Abstract

The application belongs to the field of design and synthesis of nano-confined reactors and application of CO2 hydrogenation, and relates to a preparation method of a hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor and application of the reactor in photocatalytic CO2 hydrogenation. A hollow nitrogen-doped carbon sphere NC is used as a template, and Bi4O5Br2 nanosheets are in-situ grown on the surface of the template by an oil bath method to construct a supported hollow carbon sphere confined reactor BOB@NC. The photo-generated electrons generated by the Bi4O5Br2 nanosheets are transferred to the inside of the hollow carbon sphere (NC) by the action of the built-in electric field and the Bi-C bond. The N sites in the NC can simultaneously act as an electron enrichment center and a CO2 spontaneous adsorption-activation center, effectively reducing the CO2 activation energy barrier and promoting the hydrogenation reduction reaction. Under simulated sunlight irradiation, the CO and CH4 yields generated by the reduction of CO2 by the BOB@NC are 3.31 and 14.91 times those of the monomer BOB, respectively. The work provides a new idea for constructing high-performance artificial photosynthesis catalysts.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanometer confined reactor material preparation and artificial photosynthesis, and particularly relates to a preparation method of a hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor and application of the reactor to photocatalytic CO2 reduction and hydrogenation. BACKGROUND

[0002] With clean solar energy as the driving force, greenhouse gas CO2 is converted into carbon-based fuels by simulating plant photosynthesis, which is a frontier technology for relieving the current energy crisis and environmental pollution. However, CO2 is an extremely stable linear molecule, and the C=O binding energy is 750 kJ mol -1 . At the same time, the photocatalyst has low photo-generated carrier separation efficiency and poor CO2 adsorption-activation-hydrogenation active site, resulting in poor CO2 reduction activity. Therefore, constructing a photocatalyst that combines effective directional separation of photo-generated carriers and rich CO2 activation and reduction sites is the key to further development of artificial photosynthesis technology. SUMMARY

[0003] The purpose of the application is to controllably construct a hollow BOB@NC nanometer confined reactor, to realize effective light absorption, improve the directional migration and separation efficiency of photo-generated electrons, and strengthen the CO2 adsorption-activation capacity, so as to realize high-performance photocatalytic CO2 reduction and hydrogenation to carbon-based fuels and relieve the fossil energy crisis.

[0004] The patent controllably constructs a hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet (BOB@NC) confined reactor by a template method. The ultrathin BOB nanosheet grows uniformly and vertically on the outer surface of the NC. The photo-generated electrons of the BOB nanosheet converge to the edge from the surface under light excitation, and the edge electrons migrate to the surface of the NC through the Bi-C bond. The photo-generated electrons on the NC quickly undergo an e-h exciton state generation and transfer to a defect state process, thereby effectively separating the photo-generated electrons of the BOB. The NC acts as a photo-generated electron enrichment center, and at the same time, captures a large number of CO2 molecules in the cavity. Under simulated sunlight, the yield of CO and CH4 produced by the reduction of CO2 by the BOB@NC is 3.31 and 14.91 times that of the BOB, respectively. The construction of the BOB@NC nanometer confined reactor opens up a new way for the design of a high-efficiency artificial photosynthesis catalyst.

[0005] The technical scheme of the application is as follows:

[0006] A preparation method of a hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor, comprising the following steps:

[0007] (1) adding hollow nitrogen-doped carbon spheres and urotropine into a mannitol aqueous solution to prepare a solution A;

[0008] (2) Dissolve bismuth nitrate, bismuth acetate, bismuth sulfate or bismuth citrate in a mannitol solution to form solution B;

[0009] (3) Add an inorganic or organic bromide salt to the mannitol solution to form solution C;

[0010] (4) Add solution B in step (2) and solution C in step (3) to solution A in step (1) in sequence, and stir to obtain a mixed solution D.

[0011] (5) Transfer solution D in step (4) to an oil bath pot and heat for several hours. Centrifuge the obtained product, wash it with distilled water and anhydrous ethanol several times, and dry to obtain Bi4O5Br2 nanosheet loaded hollow carbon sphere confined reactor material, namely, hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor, denoted as BOB@NC.

[0012] In step (1), the amount ratio of the hollow nitrogen-doped carbon sphere, urotropine and the mannitol aqueous solution is 5-20 mg: 0.5-3 mmol: 10-150 mL, wherein the concentration of the mannitol aqueous solution is 0.2-2.0 mmol / L.

[0013] In step (2), the amount ratio of the bismuth salt and the mannitol aqueous solution is 0.2-4 mmol: 10-150 mL, wherein the concentration of the mannitol aqueous solution is 0.2-2.0 mmol / L.

[0014] In step (3), the amount ratio of the bromide salt and the mannitol aqueous solution is 0.2-4 mmol: 10-150 mL, wherein the concentration of the mannitol aqueous solution is 0.2-2.0 mmol / L.

[0015] In step (3), the inorganic bromide salt is one of KBr, NaBr or NH4Br.

[0016] In step (3), the organic bromide salt is one of cetyltrimethylammonium bromide, 1,3-dimethylimidazole bromide salt, 1-ethyl-3-methylimidazole bromide salt, 1-propyl-3-methylimidazole bromide iodide salt, 1-butyl-3-methylimidazole bromide iodide salt or 1-dodecyl-3-methylimidazole bromide salt.

[0017] In step (4), the proportion of each raw material in solutions A, B and C is that the amount ratio of the hollow nitrogen-doped carbon sphere, the bismuth salt and the bromide salt is 5-20 mg: 0.2-4 mmol: 0.2-4 mmol.

[0018] In step (5), the reaction temperature is 60-120℃, the reaction time is 1-24 h, the drying temperature is 40-80℃, and the drying time is 4-12 h.

[0019] The hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor prepared in the application has a diameter of 100-1000 nm.

[0020] The hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor prepared in the application is used for photocatalytic CO2 reduction and hydrogenation to generate CO and CH4.

[0021] The application has the following beneficial effects:

[0022] The application uses hollow nitrogen-doped carbon spheres (NC) as a template to epitaxially and uniformly grow Bi4O5Br2 (BOB) ultrathin nanosheets to construct a hollow confined reactor (BOB@NC). The BOB@NC improves the utilization rate of light absorption and promotes the migration of photo-generated electrons from the BOB to the surface of the NC through the built-in electric field and Bi-C bond. The photo-generated electrons on the surface of the NC undergo rapid e-h exciton state generation and transfer to the defect state, realizing the directional migration and effective separation of the photo-generated electrons. The doped nitrogen in the NC acts as an enrichment center for photo-generated electrons and an active site for CO2 adsorption-activation-hydrogenation, effectively reducing the energy barrier of the reaction rate-determining step and spontaneously inducing the hydrogenation of CO intermediates until CH4 is generated. The construction of the BOB@NC nanoreactor opens up a new way for the design of high-efficiency artificial photosynthesis catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The XRD pattern of the prepared hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor material.

[0024] Figure 2 The SEM and TEM images of the prepared BOB@NC-0.3 material.

[0025] Figure 3 The SEM and TEM images of the prepared BOB@NC-0.1 material.

[0026] Figure 4 The SEM and TEM images of the prepared BOB@NC-0.5 material.

[0027] Figure 5 The TEM image of the prepared Bi4O5Br2 nanosheet.

[0028] Figure 6 The solid ultraviolet image of the prepared BOB@NC-0.3.

[0029] Figure 7 The yield of the prepared hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor material for photocatalytic reduction of CO2 to produce CO and CH4. DETAILED DESCRIPTION

[0030] The application will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] The preparation method of the hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor comprises the following steps:

[0033] First, 9 mL of ammonia water, 16.5 mL of water, and 4.5 mL of tetraethoxysilane are mixed into 70 mL of ethanol and stirred for 2 hours, then centrifuged, washed with deionized water and ethanol, and dried to obtain SiO2 nanospheres. Next, 0.5 g of SiO2 nanospheres are dispersed in a tris-hydroxymethyl aminomethane buffer solution with a pH of 8.5, stirred for 22 h, then centrifuged, washed with deionized water and ethanol, and dried. The obtained solid is calcined at 800°C for 2 h under N2 protection, and the calcined product is etched with 4M NH4HF2 for 24 h to remove the SiO2 template, thereby obtaining hollow nitrogen-doped carbon spheres (NC).

[0034] 10 mg of hollow nitrogen-doped carbon spheres, 1.5 mmol of urotropine, and 20 mL of a mannitol solution (0.1M) are added to a 100 mL round-bottom flask, stirred for 15 min, and solution A is prepared.

[0035] 0.3 mmol of Bi(NO3)3·5H2O is dissolved in 10 mL of a mannitol solution (0.1M) to prepare solution B.

[0036] 0.3 mmol of KBr is dissolved in 10 mL of a mannitol solution (0.1M) to prepare solution C.

[0037] First, solution B is added dropwise to solution A and stirred for 15 min, and then solution C is added, and stirred for 30 min. The mixture is placed in a 90°C oil bath and reacted for 6 h. The product is separated, washed, and dried to obtain the nanometer confined reactor BOB@NC-0.3.

[0038] Example 2

[0039] The preparation method of the BOB@NC-0.1 material comprises the following steps:

[0040] 10 mg of hollow nitrogen-doped carbon spheres, 1.5 mmol of urotropine, and 20 mL of a mannitol solution (0.1M) are added to a 100 mL round-bottom flask, stirred for 15 min, and solution A is prepared.

[0041] 0.1 mmol of Bi(NO3)3·5H2O is dissolved in 10 mL of a mannitol solution (0.1M) to prepare solution B.

[0042] Solution C was prepared by dissolving 0.1 mmol of KBr in 10 mL of a mannitol solution (0.1 M).

[0043] Solution B was first added to solution A dropwise and stirred for 15 min, then solution C was added, and after stirring for 30 min, the mixture was placed in a 90 °C oil bath for 6 h. The product was isolated, washed, and dried to obtain the nanoscopic confinement reactor BOB@NC-0.1.

[0044] Example 3:

[0045] The method for preparing the BOB@NC-0.5 material included the following steps:

[0046] Solution A was prepared by adding 10 mg of hollow nitrogen-doped carbon spheres, 1.5 mmol of urotropine, and 20 mL of a mannitol solution (0.1 M) into a 100 mL round-bottom flask and stirring for 15 min.

[0047] Solution B was prepared by dissolving 0.5 mmol of Bi(NO3)3·5H2O in 10 mL of a mannitol solution (0.1 M).

[0048] Solution C was prepared by dissolving 0.5 mmol of KBr in 10 mL of a mannitol solution (0.1 M).

[0049] Solution B was first added to solution A dropwise and stirred for 15 min, then solution C was added, and after stirring for 30 min, the mixture was placed in a 90 °C oil bath for 6 h. The product was isolated, washed, and dried to obtain the nanoscopic confinement reactor BOB@NC-0.5.

[0050] Comparative Example 1:

[0051] The method for preparing Bi4O5Br2nanosheets included the following steps:

[0052] Solution A was prepared by adding 1.5 mmol of urotropine and 20 mL of a mannitol solution (0.1 M) into a 100 mL round-bottom flask and stirring for 15 min.

[0053] Solution B was prepared by dissolving 0.5 mmol of Bi(NO3)3·5H2O in 10 mL of a mannitol solution (0.1 M).

[0054] Solution C was prepared by dissolving 0.5 mmol of KBr in 10 mL of a mannitol solution (0.1 M).

[0055] Solution B was first added to solution A dropwise and stirred for 15 min, then solution C was added, and after stirring for 30 min, the mixture was placed in a 90 °C oil bath for 6 h. The product was isolated, washed, and dried to obtain Bi4O5Br2nanosheets, denoted as BOB.

[0056] Figure 1 XRD patterns of the Bi4O5Br2nanosheets prepared by the nanoreactor BOB@NC-0.3, BOB@NC-0.1, BOB@NC-0.5 of the present application and the Bi4O5Br2nanosheets prepared by Comparative Example 1. It can be found that the XRD diffraction peaks of the prepared materials are all characteristic peaks of Bi4O5Br2.

[0057] Figure 2 SEM and TEM images of the BOB@NC-0.3 material prepared by the present application Example 1. It can be found that the Bi4O5Br2nanosheets grow uniformly on the surface of the hollow nitrogen-doped carbon spheres.

[0058] Figure 3 SEM and TEM images of the BOB@NC-0.1 material prepared by the present application Example 2. It can be found that a small amount of Bi4O5Br2nanosheets grow vertically on the surface of the hollow nitrogen-doped carbon spheres.

[0059] Figure 4 SEM and TEM images of the BOB@NC-0.5 material prepared by the present application Example 3. It can be found that a large amount of Bi4O5Br2nanosheets grow randomly on the surface of the hollow nitrogen-doped carbon spheres.

[0060] Figure 5 TEM image of the Bi4O5Br2nanosheets prepared by the present application Comparative Example 1. It can be found that the Bi4O5Br2nanosheets are ultra-thin sheet structures.

[0061] Figure 6 Solid UV-vis spectra of the nanoreactor BOB@NC-0.3 and the Bi4O5Br2nanosheets prepared by the present application Example 1 and Comparative Example 1. It can be found that the light absorption edge of the Bi4O5Br2nanosheets is 550 nm, while the light absorption edge of the nanoreactor BOB@NC-0.3 can be widened to near-infrared light.

[0062] Figure 7 Yield chart of the photocatalytic reduction of CO2 to generate CO and CH4 by the nanoreactor BOB@NC-0.3, BOB@NC-0.1, BOB@NC-0.5 of the present application Examples 1-3 and the Bi4O5Br2nanosheets (BOB) prepared by Comparative Example 1. It can be found that the nanoreactor BOB@NC-0.3 generates the highest yield of CO and CH4, and the yield of CO and CH4 generated by the reduction of CO2 by BOB@NC-0.3 is 28.34 and 3.13 μmol h -1 g -1 , respectively, which is 3.31 and 14.91 times that of the monomer BOB, respectively, after 5 h of illumination.

Claims

1. A method for preparing a hollow carbon sphere epitaxial growth Bi4O5Br2 nanosheet confined reactor, characterized by, Includes the following steps: (1) Add hollow nitrogen-doped carbon spheres and hexamethylenetetramine to an aqueous mannitol solution to prepare solution A; (2) Prepare solution B using bismuth nitrate, bismuth acetate, bismuth sulfate or bismuth ammonium citrate as the bismuth source and mannitol aqueous solution as the solvent; (3) Prepare solution C using inorganic bromide and organic bromide as halogen sources and mannitol aqueous solution as solvent; (4) Inject solution B from step (2) and solution C from step (3) into solution A from step (1) in sequence, and stir to obtain mixed solution D; The proportions of each raw material in solutions A, B, and C are as follows: the ratio of hollow nitrogen-doped carbon spheres, bismuth salt, and bromide salt is 5-20 mg. 0.2-4 mmol; (5) Transfer the solution D from step (4) to an oil bath, heat it at 60-120℃ for 1-24 hours, centrifuge the obtained product, wash it several times with distilled water and anhydrous ethanol, and vacuum dry it to obtain the Bi4O5Br2 nanosheet supported hollow carbon sphere confined reactor material, namely the hollow carbon sphere epitaxially grown Bi4O5Br2 nanosheet confined reactor.

2. The method of claim 1, wherein, In step (1), the ratio of hollow nitrogen-doped carbon spheres, hexamethylenetetramine, and mannitol aqueous solution is 5-20 mg: 0.5-3 mmol: 10-150 mL, wherein the concentration of mannitol aqueous solution is 0.2-2.0 mmol / L.

3. The preparation method according to claim 1, characterized in that, In step (2), the ratio of bismuth salt to mannitol aqueous solution is 0.2-4 mmol: 10-150 mL, wherein the concentration of mannitol aqueous solution is 0.2-2.0 mmol / L.

4. The preparation method according to claim 1, characterized in that, In step (3), the inorganic bromine salt is one of KBr, NaBr or NH4Br.

5. The preparation method according to claim 1, characterized in that, In step (3), the organic bromide is one of the following: hexadecyltrimethylammonium bromide, 1,3-dimethylimidazolium bromide, 1-ethyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide iodide, 1-butyl-3-methylimidazolium bromide iodide, or 1-dodecyl-3-methylimidazolium bromide.

6. The preparation method according to claim 1, characterized in that, In step (3), the ratio of bromide salt to mannitol aqueous solution is 0.2-4 mmol: 10-150 mL, wherein the concentration of mannitol aqueous solution is 0.2-2.0 mmol / L.

7. The preparation method according to claim 1, characterized in that, In step (5), the drying temperature is 40-80℃ and the drying time is 4-12h.

8. A confined reactor for epitaxial growth of Bi4O5Br2 nanosheets using hollow carbon spheres, characterized in that, It is prepared by the preparation method described in any one of claims 1-7, and the diameter of the confined reactor for epitaxial growth of Bi4O5Br2 nanosheets by hollow carbon spheres is 100-1000 nm.

9. The use of the confined reactor for epitaxial growth of Bi4O5Br2 nanosheets from hollow carbon spheres as described in claim 8 for photocatalytic reduction of CO2 to produce CO and CH4.

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