CNT-coated Bi2Fe4O9 confinement material as well as preparation and application of CNT-coated Bi2Fe4O9 confinement material

Abstract

The invention discloses a CNT-coated Bi2Fe4O9 confinement material as well as preparation and application thereof. The preparation method comprises the following steps: performing strong acid treatment on an original carbon nanotube CNT to generate an open-end CNT, adding bismuth salt into an open-end CNT solution, adjusting the pH value of the open-end CNT solution and a bismuth salt and ferric salt mixed solution, and performing hydrothermal reaction in a NaOH solution; and centrifugally collecting the precipitate, drying and calcining to obtain the CNT-coated Bi2Fe4O9 confinement composite material. According to the material, Bi2Fe4O9 is confined in an endogenous channel of CNT, the problems that a traditional electro-catalytic material is low in efficiency and prone to inactivation in practical application are solved, and the material has efficient catalytic performance, can be used for reduction reaction of CO2 and meanwhile has good stability and recyclability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic materials, and in particular to a preparation method and application of a CNT@Bi2Fe4O9 confined composite material for electrocatalytic CO2 reduction. Background Art

[0002] In recent years, CO2 catalytic reduction technology has attracted widespread attention due to its potential applications in reducing greenhouse gas emissions and producing renewable energy. Although traditional catalytic materials, such as TiO2, have certain electrocatalytic activity, their conversion efficiency is low and they are prone to electrocorrosion in practical applications, which limits their large-scale application. Therefore, it is particularly important to develop a new type of electrocatalytic material that is efficient, stable and easy to recycle.

[0003] As a new type of catalytic material, bismuth ferrite (Bi2Fe4O9) has become a research hotspot due to its unique crystal structure and excellent electrocatalytic performance. However, Bi2Fe4O9 is prone to agglomeration in practical applications, resulting in a decrease in specific surface area and reduced catalytic activity. In addition, Bi2Fe4O9 is easily oxidized during the catalytic process, resulting in catalyst deactivation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and the purpose of the present invention is to provide a method for preparing a CNT@Bi2Fe4O9 confined composite material and its application in electrocatalytic CO2 reduction. By confining Bi2Fe4O9 in the endogenous channels of CNT, not only the electrocatalytic performance of the material is improved, but also the stability and recyclability of the material are enhanced, solving the problems of low efficiency and easy deactivation of traditional electrocatalytic materials in practical applications.

[0005] The present invention is achieved through the following technical solutions.

[0006] In one aspect, the present invention provides a method for preparing a CNT@Bi2Fe4O9 confined material, comprising the following steps:

[0007] A. Preparation of open-ended carbon nanotubes CNT:

[0008] a. Add the original carbon nanotubes CNT to a strong acid solvent in a mass ratio of (2-4): (300-500), disperse by ultrasound, reflux in an oil bath, cool naturally after the reaction is complete, collect the precipitate by centrifugation, and wash the precipitate with deionized water until it is neutral;

[0009] b. The product obtained in step a is uniformly dispersed in deionized water, and freeze-dried at low temperature to obtain open-ended CNTs;

[0010] B. Preparation of CNT@Bi2Fe4O9 confined composite materials:

[0011] c. preparing an open-ended CNT solution, a bismuth salt solution and an iron salt solution;

[0012] d. adding the bismuth salt solution to the open-ended CNT solution in a mass ratio of (1-2): (10-20) to obtain a solution A;

[0013] e. Under ultrasonic conditions, slowly add the iron salt solution dropwise to solution A in a mass ratio of (2-3): (20-40), and adjust the pH of the mixed solution to 9-11 using an alkaline solution; collect the precipitate by centrifugation, and place the precipitate in a NaOH solution for hydrothermal reaction;

[0014] f. Collect the product by centrifugation, dry and calcine the product to obtain CNT@Bi2Fe4O9 confined composite material.

[0015] Preferably, the strong acid solvent is a mixed solution of nitric acid and sulfuric acid in a volume ratio of 1:1.

[0016] Preferably, the bismuth salt is bismuth nitrate or bismuth chloride; and the bismuth salt solution solvent is ethanol or ethylene glycol.

[0017] Preferably, the iron salt is ferric sulfate, ferric nitrate or ferric chloride; and the iron salt solution solvent is water or ethanol.

[0018] Preferably, the concentration of the open-ended CNT solution is 0.2-0.5 g / L; the concentration of the bismuth salt solution is 5-10 g / L; and the concentration of the iron salt solution is 15-30 g / L.

[0019] Preferably, in step a, the reaction mixture is refluxed in an oil bath at 120-200° C. for 15-20 hours, and then cooled naturally to room temperature after the reaction is completed.

[0020] Preferably, in step b, the low-temperature freezing temperature is -40 to -55°C, and the freeze-drying time is 40 to 50 hours.

[0021] Preferably, in step e, the alkaline solution is aqueous ammonia or sodium hydroxide solution; the precipitate is placed in a NaOH solution and subjected to a hydrothermal reaction at 180±10° C. for 40-50 hours.

[0022] Preferably, in step f, after drying at 80-100° C. for 10-12 hours, calcination is performed at 500-600° C. for 1-2 hours.

[0023] In another aspect of the present invention, a CNT@Bi2Fe4O9 confined composite material prepared by the method is provided.

[0024] In another aspect of the present invention, a CNT@Bi2Fe4O9 confined composite material is provided for use in an electrocatalytic CO2 reduction reaction.

[0025] The present invention adopts the above technical solution, which has the following beneficial effects:

[0026] 1. The present invention adjusts the crystal structure of bismuth ferrite by adjusting the pH of the hydrothermal reaction solvent to produce bismuth ferrite (Bi2Fe4O9) with a mullite structure, further improving the metal atom utilization efficiency of bismuth ferrite and improving the electrocatalytic activity of the catalyst.

[0027] 2. The present invention confines and encapsulates Bi2Fe4O9 in the CNT endogenous channel, and by utilizing the efficient electron transmission efficiency of CNT, it can effectively overcome the limitation that Bi2Fe4O9 is easily oxidized as a metal oxide during the catalytic reaction.

[0028] 3. The present invention confines and encapsulates Bi2Fe4O9 in the endogenous channel of CNT, and utilizes the internal filling of Bi2Fe4O9 to confine and adjust the electron density and characteristics of CNT. The composite material exhibits efficient catalytic activity and good stability, thereby improving the rate of CO2 electrocatalytic reduction reaction.

[0029] 4. The catalyst of the present invention has strong stability, is easy to separate and recover, can be repeatedly recycled, and still has a high catalytic efficiency after multiple cycles.

[0030] 5. The catalyst of the present invention has high environmental compatibility and low metal leaching rate during use, thereby reducing the risk of secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1 The following are scanning electron microscope images (SEM), (d) element energy spectrum surface scanning (EDS-mapping) and (e) element energy spectrum point scanning of (a) CNT, (b) open-CNT and (c) CNT@BFO confined nanocatalysts in Example 1 of the present invention;

[0033] Figure 2 is the X-ray diffraction pattern (XRD) of the catalyst prepared in Example 1 of the present invention;

[0034] Figure 3 is the Fourier transform infrared spectrum (FT-IR) of the catalyst prepared in Example 1 of the present invention;

[0035] Figure 4 is the Faraday efficiency of the electrocatalytic reduction of CO prepared by the catalyst prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0037] A method for preparing a CNT@Bi2Fe4O9 confined composite material provided in an embodiment of the present invention comprises the following steps:

[0038] Step A. Preparation of open-ended carbon nanotubes CNT:

[0039] a. Add the original carbon nanotubes to a strong acid solvent in a mass ratio of (2-4): (300-500), wherein the strong acid solvent is a mixed solution of nitric acid and sulfuric acid in a volume ratio of 1:1, disperse by ultrasound, reflux in an oil bath at 120-200°C for 15-20 hours, cool naturally to room temperature after the reaction is completed, collect the precipitate by centrifugation, and rinse the precipitate with deionized water until it is neutral;

[0040] b. The product obtained in step a is uniformly dispersed in deionized water, frozen at (-55±5°C), and then dried in a freeze dryer at -40--55°C for 40-50 hours to obtain open-end CNTs.

[0041] B. Preparation of CNT@Bi2Fe4O9 confined composite materials:

[0042] c. Dissolve the open-ended CNT in water to prepare an open-ended CNT solution with a concentration of 0.2-0.5 g / L;

[0043] Dissolve bismuth nitrate or bismuth chloride in ethanol or ethylene glycol to prepare a bismuth salt solution with a concentration of 5-10 g / L;

[0044] Dissolve ferric sulfate, ferric nitrate or ferric chloride in water or ethanol to prepare an iron salt solution with a concentration of 15-30 g / L;

[0045] d. adding the bismuth salt solution to the open-ended CNT solution in a mass ratio of (1-2): (10-20) to obtain a solution A;

[0046] e. Under ultrasonic conditions, slowly drop the iron salt solution into solution A in a mass ratio of (2-3): (20-40), and adjust the pH of the mixed solution to 9-11 using an alkaline solution; the alkaline solution is one of ammonia water or sodium hydroxide solution; collect the precipitate by centrifugation, place the precipitate in a NaOH solution, and perform a hydrothermal reaction at 180±10°C for 40-50 hours;

[0047] f. Collect the product by centrifugation, dry the product at 80-100°C for 10-12 hours, and calcine at 500-600°C for 1-2 hours to obtain the CNT@Bi2Fe4O9 confined composite material.

[0048] In step A, the common original carbon nanotube is a nanoscale tubular structure formed by curling graphene sheets, which usually appears closed and closed at both ends by hemispherical fullerene structures; during the strong acid treatment process, the oxidizing components in the acid will react with the carbon atoms at the ends of the carbon nanotubes to form functional groups such as carboxyl and hydroxyl groups. This process will gradually etch the ends of the carbon nanotubes, opening their closed structures and forming open-ring structures; oil bath heating can not only accelerate the penetration of acidic substances on the surface and inside of the carbon nanotubes, but also increase the vibration energy of the carbon nanotubes and accelerate the breaking of carbon-carbon bonds.

[0049] Since the surface energy of the ring-opened carbon nanotubes is high and the stability is poor, by evenly dispersing the ring-opened carbon nanotubes in water and collecting them through freeze-drying technology, the aggregation ability of the ring-opened carbon nanotubes can be suppressed to the maximum extent, and a single ring-opened carbon nanotube can be prepared.

[0050] In step B, Bi ions enter the carbon nanotubes through both ends of the ring-opened carbon nanotubes and are attached to the inner wall of the carbon nanotubes through bonding. Further adding Fe solution allows it to enter the ring-opened carbon nanotubes and react with Bi ions. Ultrasonic conditions can accelerate the entry of Fe ions into the carbon nanotubes, promote their reaction with Bi ions attached to the inner wall, and increase their reaction rate. The crystal type of the product generated by the reaction can be changed by adjusting the pH of the system, and the hydrothermal reaction can promote the generation of Bi2Fe4O9 with a mullite structure in the carbon nanotubes to generate a confined composite material with high stability.

[0051] Since the Bi and Fe ions that are not completely reacted in step g and the by-products generated during the reaction process can be removed by high-temperature calcination, in addition, high-temperature calcination can also remove the functional groups generated on the surface of the carbon nanotubes during the reaction process, further improving the stability of CNT@Bi0Fe4O9.

[0052] At the same time, the efficient electron transport characteristics of CNTs are used to enhance the electrocatalytic performance of the composite material, solving the shortcoming of Bi2Fe4O9 being easily oxidized. Confining Bi2Fe4O9 in carbon nanotubes (CNTs) can not only improve its catalytic performance, but also enhance the stability and recyclability of the material.

[0053] The preparation of CNT@Bi2Fe4O9 confined materials according to the present invention is further described below through specific examples.

[0054] Example 1

[0055] Step A. Preparation of open-ended carbon nanotubes CNT:

[0056] a. Add the original carbon nanotubes to a strong acid solvent at a mass ratio of 3:300, disperse by ultrasonication, reflux in an oil bath at 160°C for 18 hours, cool to room temperature, collect the precipitate by centrifugation and rinse to neutrality;

[0057] b. The product was evenly dispersed in deionized water, frozen at -55°C, and dried at -45°C for 40 hours to obtain open-end CNTs.

[0058] B. Preparation of CNT@Bi2Fe4O9 confined composite materials:

[0059] c. Dissolve the open-ended CNT in water to prepare an open-ended CNT solution with a concentration of 0.3 g / L;

[0060] Dissolve bismuth nitrate in ethanol to prepare a bismuth nitrate solution with a concentration of 10 g / L;

[0061] Dissolve ferric sulfate in ethanol to prepare a 15 g / L ferric sulfate solution;

[0062] d. adding the bismuth nitrate solution to the open-ended CNT solution at a mass ratio of 1:15 to obtain solution A;

[0063] e. Under ultrasonic conditions, slowly add the ferric sulfate solution to solution A at a mass ratio of 2:30, and adjust the pH of the mixed solution to 9 with aqueous ammonia; collect the precipitate by centrifugation, place the precipitate in a NaOH solution, and perform hydrothermal reaction at 190°C for 40 hours;

[0064] f. Collect the product by centrifugation, dry it at 90°C for 11 hours, and calcine it at 500°C for 2 hours to obtain the CNT@Bi2Fe4O9 confined composite material.

[0065] Example 2

[0066] Step A. Preparation of open-ended carbon nanotubes CNT:

[0067] a. Add the original carbon nanotubes to a strong acid solvent at a mass ratio of 2:400, disperse by ultrasonication, reflux in an oil bath at 120°C for 20 hours, cool to room temperature, collect the precipitate by centrifugation and rinse to neutrality;

[0068] b. The product was evenly dispersed in deionized water, frozen at -60°C, and dried at -40°C for 45 hours to obtain open-end CNTs.

[0069] B. Preparation of CNT@Bi2Fe4O9 confined composite materials:

[0070] c. Dissolve the open-ended CNT in water to prepare an open-ended CNT solution with a concentration of 0.4 g / L;

[0071] Dissolve bismuth chloride in ethylene glycol to prepare a bismuth chloride solution with a concentration of 5 g / L;

[0072] Dissolve ferric nitrate in water to prepare a 18 g / L ferric nitrate solution;

[0073] d. adding the bismuth chloride solution to the open-ended CNT solution at a mass ratio of 2:10 to obtain solution A;

[0074] e. Under ultrasonic conditions, slowly add the ferric nitrate solution to solution A at a mass ratio of 2.5:20, and adjust the pH of the mixed solution to 10 using sodium hydroxide solution; collect the precipitate by centrifugation, place the precipitate in a NaOH solution, and perform hydrothermal reaction at 170°C for 45 hours;

[0075] f. Collect the product by centrifugation, dry it at 100°C for 10 hours, and calcine it at 550°C for 2 hours to obtain the CNT@Bi2Fe4O9 confined composite material.

[0076] Example 3

[0077] Step A. Preparation of open-ended carbon nanotubes CNT:

[0078] a. Add the original carbon nanotubes to a strong acid solvent at a mass ratio of 4:500, disperse them ultrasonically, reflux them in an oil bath at 200°C for 15 hours, cool them to room temperature, collect the precipitate by centrifugation and rinse them to neutrality;

[0079] b. The product was evenly dispersed in deionized water, frozen at -50°C, and dried at -55°C for 50 hours to obtain open-ended CNTs.

[0080] B. Preparation of CNT@Bi2Fe4O9 confined composite materials:

[0081] c. Dissolve the open-ended CNT in water to prepare an open-ended CNT solution with a concentration of 0.1 g / L;

[0082] Dissolve bismuth chloride in ethanol to prepare a bismuth chloride solution with a concentration of 8 g / L;

[0083] Dissolve ferric chloride in ethanol to prepare a 30 g / L ferric chloride solution;

[0084] d. adding the bismuth chloride solution to the open-ended CNT solution at a mass ratio of 1.5:20 to obtain solution A;

[0085] e. Under ultrasonic conditions, slowly add the ferric chloride solution to solution A at a mass ratio of 3:40, and adjust the pH of the mixed solution to 11 using sodium hydroxide solution; collect the precipitate by centrifugation, place the precipitate in a NaOH solution, and perform hydrothermal reaction at 180°C for 50 hours;

[0086] f. Collect the product by centrifugation, dry it at 80°C for 12 hours, and calcine it at 600°C for 1 hour to obtain the CNT@Bi2Fe4O9 confined composite material.

[0087] The performance of the composite material prepared by the present invention is further illustrated by experiments below.

[0088] Test Example 1

[0089] The electrochemical properties of all materials in Examples 1, 2, and 3 were obtained by testing using an electrochemical workstation (CHI660E), and the electrochemical test system was a classic three-electrode electrolytic cell system. CO2 gas was continuously delivered to the cathode electrolyte at an average rate of 5 mL / min, and then delivered to a gas chromatograph (RAMIN, GC2060) through a pipeline. The gas products were analyzed by GC gas chromatograph every 15 minutes. The scanning electron microscopy images (SEM), (d) elemental energy spectrum surface scans (EDS-mapping), and (e) elemental energy spectrum point scans of (a) CNT, (b) open-CNT, and (c) CNT@BFO confined nanocatalysts in Example 1 of the present invention are shown in Figure 1 The X-ray diffraction pattern (XRD) of the catalyst prepared in Example 1 of the present invention is shown in Figure 2 The Fourier transform infrared spectrum (FT-IR) of the catalyst prepared in Example 1 of the present invention is shown in Figure 3 As shown; Figure 4 The Faradaic yields of CO produced by the catalysts prepared in Example 1, Example 2 and Example 3 at different voltages are shown in Table 1. Figure 4 It can be seen that the Faraday efficiency of CNT@Bi2Fe4O9 for electrocatalytic reduction of CO is significantly higher than that of CNT and Bi2Fe4O9. CNT@Bi2Fe4O9 has the highest FE in the entire potential range. CO In the potential range of -0.7 to -0.9 V vs. RHE, the Faraday efficiency of CO is above 80%. At -1.0 V vs. RHE, the Faraday efficiency of CO reaches a maximum of 88.7%, which is the highest FE of BFO catalyst. CO The FE of CNT catalyst is 2.10 times of the peak value (42.3%). CO The peak value (34.5%) is 2.57 times that of the previous peak value, indicating that the composite structure greatly improves the electrocatalytic performance of the material and improves the selectivity of CO production.

[0090] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. A CNT@Bi 2 Fe 4 O 9 Method for preparing confined material, It is characterized in that The following steps are involved: A. Preparation of open-ended carbon nanotubes CNT: a. Add the original carbon nanotubes CNT to a strong acid solvent in a mass ratio of (2-4): (300-500), disperse by ultrasound, reflux in an oil bath, cool naturally after the reaction is complete, collect the precipitate by centrifugation, and wash the precipitate with deionized water until it is neutral; b. The product obtained in step a is uniformly dispersed in deionized water, and freeze-dried at low temperature to obtain open-ended CNTs; B. Preparation of CNT@Bi 2 Fe 4 O 9 Confined composite materials: c. preparing an open-ended CNT solution, a bismuth salt solution and an iron salt solution; d. adding the bismuth salt solution to the open-ended CNT solution in a mass ratio of (1-2): (10-20) to obtain a solution A; e. Under ultrasonic conditions, slowly add the iron salt solution dropwise to solution A in a mass ratio of (2-3): (20-40), and adjust the pH of the mixed solution to 9-11 using an alkaline solution; collect the precipitate by centrifugation, and place the precipitate in a NaOH solution for hydrothermal reaction; f. Collect the product by centrifugation, dry it and calcine it to obtain CNT@Bi 2 Fe 4 O 9 Confined composite materials.

2. The preparation method according to claim 1, It is characterized in that The strong acid solvent is a mixed solution of nitric acid and sulfuric acid in a volume ratio of 1:

1.

3. The preparation method according to claim 1, It is characterized in that The bismuth salt is bismuth nitrate or bismuth chloride; the bismuth salt solution solvent is ethanol or ethylene glycol.

4. The preparation method according to claim 1, It is characterized in that The iron salt is iron sulfate, iron nitrate or iron chloride; the iron salt solution solvent is water or ethanol.

5. The preparation method according to claim 1, It is characterized in that The concentration of the open-end CNT solution is 0.2-0.5 g / L; the concentration of the bismuth salt solution is 5-10 g / L; and the concentration of the iron salt solution is 15-30 g / L.

6. The preparation method according to claim 1, It is characterized in that In the step a, reflux in an oil bath at 120-200° C. for 15-20 hours; In the step b, the low-temperature freezing temperature is -40--55°C, and the freeze-drying time is 40-50 hours.

7. The preparation method according to claim 1, It is characterized in that In the step e, the alkaline solution is ammonia water or sodium hydroxide solution; the precipitate is placed in a NaOH solution and subjected to a hydrothermal reaction at 180±10° C. for 40-50 hours.

8. The preparation method according to claim 1, It is characterized in that In the step f, after drying at 80-100° C. for 10-12 hours, calcination is performed at 500-600° C. for 1-2 hours.

9. A CNT@Bi prepared by the method according to any one of claims 1 to 8 2 Fe 4 O 9 Restricted materials.

10. A CNT@Bi as claimed in claim 9 2 Fe 4 O 9 Confined materials in electrocatalytic CO 2 Used in reduction reactions.

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