Preparation method and application of cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst

Abstract

The present invention discloses a preparation method and application of a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst. The preparation process is as follows: boron nitride flower and copper nitrate are dispersed in water, copper nitrate is chemically reduced by hydrazine hydrate on the surface of the boron nitride flower, cuprous oxide is grown in situ, and then freeze-dried to obtain a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst. The present invention successfully constructs a boron nitride flower and cuprous oxide heterojunction, utilizes a catalytic interface formed by the composite of the two catalysts, regulates a multivalent Cu(I) / Cu(II) site, promotes the directional transmission and accumulation of photogenerated carriers to the Cu(I) / Cu(II) site, and finally realizes the ability of photocatalytic CO2 ethanolization. The present invention is easy to operate and repetitively stable.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of S-type heterojunction composite photocatalytic materials, and relates to a cuprous oxide-boron nitride flower composite photocatalyst capable of photocatalytically reducing CO2 to ethanol and a preparation method thereof. Background Art

[0002] The application of artificial photosynthesis to convert CO2 into high-value-added chemicals, combined with clean solar energy as a driving force, has been identified as a promising strategy to address the current energy shortage problem and mitigate the rising carbon dioxide levels in the atmosphere. Photocatalytic CO2 reduction can produce a variety of chemicals (such as CO, CH4, C2H4, EtOH), among which the liquid product EtOH is highly anticipated due to its high energy density and easy storage. However, due to the rapid recombination of electron holes, photocatalytic CO2 reduction is difficult to provide sufficient power to generate C2 products through the multi-electron reduction pathway. In addition, the formation of CC bonds requires overcoming a large reaction energy barrier. Therefore, in photocatalytic CO2 reduction, reducing CO2 to liquid compounds remains a worthy of attention and challenging issue.

[0003] To date, copper-based catalysts are considered to be the most effective catalysts for converting CO2 to C2 products. Among them, manipulating the oxidation state to construct a synergistic catalytic site of Cu(I) / Cu(II) can effectively reduce the thermodynamic barrier. Based on direct bias voltage regulation in electrochemical reactions, the construction of heterojunctions in photocatalytic CO2 reduction can indirectly induce the formation of Cu(I) / Cu(II) by utilizing the mobile electrons during the bending of the Fermi level. During the irradiation process, the photogenerated electrons are directed to the Cu under the action of the built-in electric field. δ+ (1<δ<2) bit, keep Cu δ+ At present, there are no reports on the construction of S-type heterojunction to adjust the oxidation state of copper to achieve photocatalytic CO2 reduction to C2 products. Summary of the invention

[0004] The object of the present invention is to provide a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst and a preparation method and application thereof, so as to realize efficient photocatalytic reduction of CO2 into ethanol.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for preparing a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst comprises the following steps:

[0007] (1) Preparation of boron nitride flowers:

[0008] Melamine, boric acid and urotropine powders are dispersed in deionized water in proportion, heated in a water bath and stirred for a period of time until completely dissolved, and then freeze-dried to obtain a precursor, which is then calcined in two steps under a nitrogen atmosphere to obtain boron nitride flower;

[0009] (2) ultrasonically dispersing the boron nitride flower and copper nitrate obtained in step (1) in water and stirring at room temperature for a period of time, then adding an appropriate amount of hydrazine hydrate, chemically reducing the copper nitrate on the surface of the boron nitride flower using hydrazine hydrate, and in situ growing cuprous oxide; washing with water for multiple times and freeze-drying to obtain a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst.

[0010] In step (1), the molar ratio of melamine, boric acid and urotropine powder is 1:2:5, and the concentration of melamine after dissolution is 0.02 mol / L; the temperature of the water bath is 80-85°C, the stirring speed is 400-600 rpm, and the stirring time is 15-30 min; the freeze-drying time is 72-96 h; the nitrogen flow rate is 200-300 ml / min, the heating rate is 5°C / min, the initial calcination temperature is 550°C, the calcination time is 2 h, the final calcination temperature is 850-1050°C, and the calcination time is 3-4 h.

[0011] In step (2), the mass ratio of boron nitride flower to copper nitrate is 0.5-12:1, the ultrasonic time is 5-15 min, the stirring time is 1 h-2 h, the usage ratio of copper nitrate mass to hydrazine hydrate volume is 1 mg: 0.55-0.65 μL; washing with water 3-6 times, and freeze drying time is 18-24 h.

[0012] The cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst prepared by the present invention realizes the application of light-driven catalytic conversion of CO2 into ethanol under normal temperature and pressure conditions.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention uses n-type semiconductor boron nitride flower and p-type semiconductor cuprous oxide to construct an S-type heterojunction composite photocatalyst for photocatalytic reduction of CO2 to high value-added product ethanol. The present invention uses the constructed S-type heterojunction to fully retain the redox ability of the dual catalytic system, improve the separation and transfer efficiency of photogenerated carriers, promote the directional migration and accumulation of photoelectrons, have significant photocatalytic CO2 reduction performance, and the product has excellent economic value.

[0015] The preparation method provided by the invention is simple and convenient for mass synthesis. Water is used as a solvent in the preparation process, thereby ensuring green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is the XRD spectrum of the cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst in Example 2 of the present invention.

[0017] Figure 2 This is the SEM spectrum of the cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst in Example 2 of the present invention.

[0018] Figure 3 This is a photocatalytic performance diagram of the cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is not limited to the following specific embodiments. Researchers in the field can use other various embodiments to repeat the present invention based on the content disclosed in the present invention, or use the design ideas of the present invention to make modifiable or simplified operation paths, which all fall within the protection scope of the present invention. It should be noted that, under non-contradictory conditions, the embodiments and characterization diagrams provided by the present invention can be combined with each other. At the same time, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood.

[0020] Example 1

[0021] Preparation of Cuprous Oxide-Bron Nitride Flower S-Type Heterojunction Composite Photocatalyst

[0022] (1) 0.7 g of hexamethylenetetramine, 0.126 g of melamine and 0.1236 g of boric acid were dissolved in 50 ml of deionized water, stirred in a water bath at 80° C. for 30 min, and freeze-dried for 72 h to obtain a white flocculent precursor.

[0023] (2) 400 mg of the white flocculent precursor was calcined at 550°C for 2 h in a nitrogen atmosphere and then annealed at 950°C for 3 h to obtain a white powdery boron nitride flower.

[0024] (3) Disperse 50 mg of boron nitride flower in 50 ml of deionized water, add 8.5 mg of copper nitrate after ultrasonic treatment for 10 min, stir at room temperature for 1 h, drop 5 ul of hydrazine hydrate for chemical reduction, wash with water 4 times, and freeze-dry for 24 h to obtain 5 wt% cuprous oxide-boron nitride flower.

[0025] Example 2

[0026] Preparation of Cuprous Oxide-Bron Nitride Flower S-Type Heterojunction Composite Photocatalyst

[0027] (1) 0.7 g of hexamethylenetetramine, 0.126 g of melamine and 0.1236 g of boric acid were dissolved in 50 ml of deionized water, stirred in a water bath at 80° C. for 30 min, and freeze-dried for 72 h to obtain a white flocculent precursor.

[0028] (2) 400 mg of the white flocculent precursor was calcined at 550°C for 2 h in a nitrogen atmosphere and then annealed at 950°C for 3 h to obtain a white powdery boron nitride flower.

[0029] (3) Disperse 50 mg of boron nitride flower in 50 ml of deionized water, add 17 mg of copper nitrate after ultrasonic treatment for 10 min, stir at room temperature for 1 h, drop 10 ul of hydrazine hydrate for chemical reduction, wash with water 4 times, and freeze-dry for 24 h to obtain 10 wt% cuprous oxide-boron nitride flower.

[0030] Figure 1 This is the XRD pattern of the best cuprous oxide-loaded boron nitride flower material prepared in this example. The obvious cuprous oxide signal and boron nitride signal indicate that cuprous oxide has grown successfully on the boron nitride flower.

[0031] Figure 2 This is a SEM image of the BPQDs-loaded BNNF material prepared in this example, showing the three-dimensional flower-like structure of the boron nitride flower, the cubic block structure of the cuprous oxide, and the morphology in which the cuprous oxide is partially wrapped by the boron nitride flower when the two are combined.

[0032] Example 3

[0033] Preparation of Cuprous Oxide-Bron Nitride Flower S-Type Heterojunction Composite Photocatalyst

[0034] (1) 0.7 g of hexamethylenetetramine, 0.126 g of melamine and 0.1236 g of boric acid were dissolved in 50 ml of deionized water, stirred in a water bath at 80° C. for 30 min, and freeze-dried for 84 h to obtain a white flocculent precursor.

[0035] (2) 400 mg of the white flocculent precursor was calcined at 550°C for 2 h in a nitrogen atmosphere and then annealed at 950°C for 3 h to obtain a white powdery boron nitride flower.

[0036] (3) Disperse 50 mg of boron nitride flower in 50 ml of deionized water, add 34 mg of copper nitrate after ultrasonic treatment for 10 min, stir at room temperature for 1 h, drop 20 ul of hydrazine hydrate for chemical reduction, wash with water 4 times, and freeze-dry for 24 h to obtain 20 wt% cuprous oxide-boron nitride flower.

[0037] Example 4

[0038] Preparation of Cuprous Oxide-Bron Nitride Flower S-Type Heterojunction Composite Photocatalyst

[0039] (1) 0.7 g of hexamethylenetetramine, 0.126 g of melamine and 0.1236 g of boric acid were dissolved in 50 ml of deionized water, stirred in a water bath at 80° C. for 30 min, and freeze-dried for 96 h to obtain a white flocculent precursor.

[0040] (2) 400 mg of the white flocculent precursor was calcined at 550°C for 2 h in a nitrogen atmosphere and then annealed at 950°C for 3 h to obtain a white powdery boron nitride flower.

[0041] (3) Disperse 50 mg of boron nitride flower in 50 ml of deionized water, add 50 mg of copper nitrate after ultrasonic treatment for 10 min, stir at room temperature for 1 h, drop 20 ul of hydrazine hydrate for chemical reduction, wash with water 4 times, and freeze-dry for 24 h to obtain 30 wt% cuprous oxide-boron nitride flower.

[0042] The material obtained in Example 2 has the highest performance of photocatalytic CO2 reduction to ethanol compared with the materials obtained in Examples 1, 3 and 4, mainly because the appropriate cuprous oxide loading and the carrier boron nitride flower construct a sufficient reaction interface for photocatalytic CO2 cascade reaction, promote the formation of CC bonds and ultimately achieve the conversion of C2 products. The material in Example 2 is the best ratio material.

[0043] Figure 3 The activity diagram of the photocatalytic reduction of CO2 to ethanol by the boron nitride flower materials loaded with cuprous oxide in different proportions prepared by the present invention shows that the boron nitride flower material loaded with 10% cuprous oxide has the best photocatalytic performance, reaching 68.5 μmol / g / h.

Claims

1. A method for preparing a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst, characterized in that: The following steps are involved: (1) Preparation of boron nitride flowers: Melamine, boric acid and urotropine powders are dispersed in deionized water in proportion, heated in a water bath and stirred for a period of time until completely dissolved, and then freeze-dried to obtain a precursor, which is then calcined in two steps under a nitrogen atmosphere to obtain boron nitride flower; (2) ultrasonically dispersing the boron nitride flower and copper nitrate obtained in step (1) in water and stirring at room temperature for a period of time, then adding an appropriate amount of hydrazine hydrate, chemically reducing the copper nitrate on the surface of the boron nitride flower using hydrazine hydrate, and in situ growing cuprous oxide; washing with water for multiple times and freeze-drying to obtain a cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst.

2. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of melamine, boric acid and urotropine powder is 1:2:5, and the concentration of melamine after dissolution is 0.02 mol / L.

3. The preparation method according to claim 1, characterized in that: In step (1), the temperature of the water bath is 80-85° C., the stirring speed is 400-600 rpm, and the stirring time is 15-30 min.

4. The preparation method according to claim 1, characterized in that: In step (1), the freeze-drying time is 72 to 96 hours.

5. The preparation method according to claim 1, characterized in that: In step (1), the nitrogen flow rate is 200-300 ml / min, the heating rate is 5°C / min, the initial calcination temperature is 550°C, the calcination time is 2h, the final calcination temperature is 850-1050°C, and the calcination time is 3-4h.

6. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of boron nitride flower to copper nitrate is 0.5-12:

1.

7. The preparation method according to claim 1, characterized in that: In step (2), the ultrasonic time is 5 to 15 minutes, and the stirring time is 1 hour to 2 hours.

8. The preparation method according to claim 1, characterized in that: In step (2), the usage ratio of copper nitrate mass to hydrazine hydrate volume is 1 mg: 0.55-0.65 μL; the number of water washings is 3-6 times, and the freeze-drying time is 18-24 hours.

9. A cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. The use of the cuprous oxide-boron nitride flower S-type heterojunction composite photocatalyst as claimed in claim 9, characterized in that: Used for light-driven catalytic conversion of CO2 into ethanol under normal temperature and pressure conditions.

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