ZnO / In2O3 heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to a ZnO / In2O3 heterojunction photocatalyst as well as a preparation method and application thereof. The method comprises the following steps: (1) ultrasonically dissolving KOH in absolute ethyl alcohol to form a solution A; dissolving zinc acetate in absolute ethyl alcohol to obtain a solution B; dropwise adding the solution A into the solution B at room temperature, stirring, adding ethyl acetate, continuously stirring, washing and centrifuging the prepared ZnO QDs-containing solution with ethanol and water respectively, and re-dispersing in absolute ethyl alcohol to obtain synthesized ZnO quantum dots; (2) dissolving indium nitrate and polyvinylpyrrolidone in a mixed solution of ethanol and N, N-dimethylformamide, and stirring at room temperature; putting the stirred solution into an electrostatic spinning instrument; drying the obtained fibers, and preserving heat in an air atmosphere to obtain In2O3 nanofibers; and (3) performing ultrasonic mixing on the ZnO quantum dots and the In2O3 nanofibers, and then performing centrifugal drying to obtain the ZnO QDs / In2O3 nanofiber heterojunction optical composite material catalyst. The photocatalytic performance is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and in particular to a ZnO / In2O3 heterojunction photocatalyst and a preparation method and application thereof. Background Art

[0002] Photocatalytic technology holds significant potential in energy conversion and environmental pollution control. ZnO quantum dots have attracted significant attention due to their high carrier mobility and ease of preparation, but their agglomeration and high recombination rate of photogenerated carriers limit their practical applications. In₂O₃ nanofibers, while possessing a continuous structure and large surface area, exhibit insufficient visible light responsiveness.

[0003] In existing technologies, heterojunction structures are widely used to improve photocatalytic efficiency, but there are still technical bottlenecks in how to simultaneously achieve efficient hydrogen production, heavy metal detection and reduction through material design. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a ZnO / In2O3 heterojunction photocatalyst and its preparation method and application, which significantly improves the photocatalytic performance by combining the composite structure with the sol-gel method and electrospinning technology.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst comprises the following steps:

[0007] Step (1): synthesizing ZnO quantum dots;

[0008] Potassium hydroxide (KOH) was ultrasonically dissolved in anhydrous ethanol (C2H5OH) to form solution A;

[0009] Zinc acetate (C4H 10 O6Zn) was dissolved in anhydrous ethanol to obtain solution B;

[0010] Solution A was added dropwise to solution B at room temperature and stirred, and ethyl acetate (C4H8O2) was added thereto and continued to stir. The ZnO QDs solution prepared above was washed with ethanol and water, centrifuged, and then redispersed in anhydrous ethanol to obtain synthesized ZnO quantum dots.

[0011] Step (2): preparing In2O3 nanofibers;

[0012] Indium nitrate (In(NO)3·4.5H2O) and polyvinylpyrrolidone ((C6H9NO)n, PVP, K=1300000)) were dissolved in a mixed solution of ethanol and N,N-dimethylformamide (HCON(CH)3, DMF) and stirred at room temperature;

[0013] The stirred solution is placed in an electrospinning apparatus; the obtained fibers are dried and then kept warm in an air atmosphere to obtain In2O3 nanofibers;

[0014] Step (3): Preparation of ZnO QDs / In2O3 nanofiber heterojunction photocomposite catalyst (IZO):

[0015] The ZnO quantum dots and the In2O3 nanofibers are ultrasonically mixed and then centrifugally dried to obtain a heterojunction photocomposite material catalyst.

[0016] In the step (1), the molar ratio of potassium hydroxide (KOH) to anhydrous ethanol (C2H5OH) is 1:60±5;

[0017] Zinc acetate and anhydrous ethanol is 1:900±50;

[0018] The ratio of potassium hydroxide, zinc acetate and ethyl acetate is: 3±0.5:1±0.5:50±5.

[0019] In the step (2), the mass ratio of indium nitrate to polyvinyl pyrrolidone is 1:1±0.5; the volume ratio of the mixed solution of ethanol and N,N-dimethylformamide is 1:1±0.5.

[0020] In step (2), the electrospinning instrument is set to a voltage of 16-18 kV and a flow rate of 0.3-0.5 mL·h -1 After drying, the obtained fiber was kept at 500-550℃ in air atmosphere for 4h, with a heating rate of 5℃·min -1 .

[0021] The ultrasonic time in step (3) is 2-4 hours, and the ZnO quantum dot loading amount is controlled by adjusting the volume of the ZnO QDs solution.

[0022] The molar ratio of the ZnO quantum dots to the In2O3 nanofibers is 0.3±0.05:1.

[0023] A ZnO QDs / In2O3 nanofiber heterojunction photocatalyst, which is a composite of ZnO quantum dots prepared by a sol-gel method and In2O3 nanofibers prepared by an electrospinning method;

[0024] The cubic indium oxide phase is composed of the In2O3 (440) crystal plane and the wurtzite phase ZnO (110) crystal plane. The heterojunction structure between In2O3 and ZnO forms an important interface for charge transfer between the two semiconductors.

[0025] A self-generated electric field is formed at the heterojunction interface, driving the directional separation of electrons and holes and inhibiting recombination. Among them, the diameter of In2O3 nanofibers is about 110nm, and the average particle size of ZnO quantum dots is 4.96nm. After loading, a porous structure is formed. The absorption range of the composite material is extended to the visible light region (λ>400nm), and the photocurrent intensity is significantly improved.

[0026] ZnO QDs / In2O3 nanofiber heterojunction photocatalysts are used for Cr(VI) detection and reduction; ZnO QDs achieve Cr(VI) self-detection via fluorescence quenching (linear detection range 0-0.9 μM, R 2 =0.998), the IZO composite material has a Cr(VI) reduction efficiency of 92% within 30 minutes under visible light.

[0027] Beneficial effects of the present invention:

[0028] This invention promotes the directional separation of photogenerated carriers through the self-generated electric field at the heterojunction interface. Due to differences in the band structures of ZnO QDs and In2O3, the bands bend upon photoexcitation, leading to directional carrier movement between the two materials and forming a self-generated electric field. Positively charged holes flow to the In2O3 surface, while negatively charged electrons flow to the ZnO surface. Combining the quantum confinement effect with the high specific surface area of ​​nanofibers significantly enhances photocatalytic performance. This catalyst demonstrates high efficiency in the fluorescence detection and simultaneous reduction of the heavy metal Cr(VI), providing an innovative solution for energy conversion and environmental governance.

[0029] ZnO quantum dots enable rapid self-detection of Cr(VI), and the composite material simultaneously completes detection and reduction, making it suitable for wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 TEM morphology of In2O3 nanofibers, ZnO QDs and IZO composites.

[0031] Figure 2 Schematic diagram of Raman spectroscopy characterization results of IZO composite catalyst.

[0032] Figure 3 Schematic diagram of the fluorescence lifetime curve of Cr(VI) detection in IZO composite materials.

[0033] Figure 4 Schematic diagram of the Cr(VI) reduction rate curve of IZO composite material. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the embodiments.

[0035] Example 1

[0036] Preparation of ZnO quantum dots:

[0037] 3.0 mmol of potassium hydroxide (KOH) was ultrasonically dissolved in 10 mL of anhydrous ethanol (C2H5OH) to form solution A;

[0038] Solution B is composed of 1.0 mmol zinc acetate (C4H 10 O6Zn) was dissolved in 50 mL of anhydrous ethanol.

[0039] Solution A was added dropwise to solution B at room temperature and stirred for 3 h, followed by addition of 5 mL of ethyl acetate (C4H8O2) and continued stirring for 1 h. The ZnO QDs solution prepared above was washed with ethanol and water, centrifuged, and redispersed in 15 mL of anhydrous ethanol.

[0040] Preparation of In2O3 nanofibers:

[0041] 0.5 g of indium nitrate (In(NO)3·4.5H2O) and 0.68 g of polyvinylpyrrolidone ((C6H9NO)n, PVP, K=1300000)) were dissolved in a mixed solution of 5 mL of ethanol and 5 mL of N,N-dimethylformamide (HCON(CH)3, DMF) and stirred at room temperature for 8 h.

[0042] The stirred solution was placed in a 10 mL electrospinning instrument and the voltage was set to 16 kV and the flow rate was 0.4 mL h. -1 The obtained fiber was dried and kept at 550℃ in air atmosphere for 4h, with a heating rate of 1℃·min -1 Preparation of ZnO QDs / In2O3 nanofiber composite catalyst (IZO):

[0043] The ZnO QDs solution obtained above was diluted 12 times with ethanol.

[0044] A certain amount of In2O3 nanofibers were ultrasonically dispersed in 50 mL of ethanol, 30 mL of diluted ZnO QDs solution was added dropwise and ultrasonic stirring was continued for 3 h.

[0045] The IZO composite catalyst was obtained by centrifugation and drying.

[0046] Example 2:

[0047] Preparation of ZnO quantum dots:

[0048] 3.5 mmol of potassium hydroxide (KOH) was ultrasonically dissolved in 10 mL of anhydrous ethanol (C2H5OH) to form solution A;

[0049] Solution B was composed of 1.5 mmol zinc acetate (C4H 10O6Zn) was dissolved in 50 mL of anhydrous ethanol.

[0050] Solution A was added dropwise to solution B at room temperature and stirred for 3 h, followed by addition of 5 mL of ethyl acetate (C4H8O2) and continued stirring for 1 h. The ZnO QDs solution prepared above was washed with ethanol and water, centrifuged, and redispersed in 18 mL of anhydrous ethanol.

[0051] Preparation of In2O3 nanofibers:

[0052] 0.45 g of indium nitrate (In(NO)3·4.5H2O) and 0.7 g of polyvinylpyrrolidone ((C6H9NO)n, PVP, K=1300000)) were dissolved in a mixed solution of 5.5 mL of ethanol and 5 mL of N,N-dimethylformamide (HCON(CH)3, DMF) and stirred at room temperature for 10 h.

[0053] The stirred solution was placed in a 10 mL electrospinning instrument and the voltage was set to 18 kV and the flow rate was 0.45 mL h. -1 The obtained fiber was dried and kept at 500℃ in air atmosphere for 4h, with a heating rate of 5℃·min -1 Preparation of ZnO QDs / In2O3 nanofiber composite catalyst (IZO):

[0054] The ZnO QDs solution obtained above was diluted 12 times with ethanol.

[0055] A certain amount of In2O3 nanofibers were ultrasonically dispersed in 40 mL of ethanol, 25 mL of diluted ZnOQDs solution was added dropwise and ultrasonic stirring was continued for 3 h.

[0056] The IZO composite catalyst was obtained by centrifugation and drying.

[0057] The IZO composite material was used to treat wastewater containing Cr(VI). The detection results were as follows: the average fluorescence lifetime of pure ZnO quantum dots was 40.39ns, and when Cr(VI) was added, the average fluorescence lifetime decayed to 36.42ns ( Figure 3 ). After 30 minutes of adsorption in the dark, the Cr(VI) removal rate was about 20%; after 30 minutes of visible light irradiation, the composite material had a Cr(VI) reduction efficiency of 92% ( Figure 4 ).

[0058] Figure 1: a is the electrospun In2O3 nanofiber obtained in the implementation case, which has a high aspect ratio; b is the ZnO QDs prepared by the gel-sol method, d is the TEM image of the ZnO QDs / In2O3 composite material, indicating that the material is successfully composited; e is the lattice fringe image of the composite material, further proving the heterojunction interface of the two materials.

[0059] The HRTEM image in Figure e shows that the lattice fringes of the contact surface are composed of cubic indium oxide with the (440) crystal plane of In2O3 and wurtzite ZnO with the (110) crystal plane, showing the heterojunction structure between In2O3 and ZnO, forming an important interface for charge transfer between the two semiconductors.

[0060] Figure 2 : Raman map of the composite material shows that IZO is composed of cubic indium oxide wurtzite phase ZnO.

Claims

1. A ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst, characterized in that: The following steps are included: Step (1): Potassium hydroxide (KOH) is ultrasonically dissolved in anhydrous ethanol (C2H5OH) to form solution A; zinc acetate (C4H 10 O6Zn) was dissolved in anhydrous ethanol to obtain solution B; solution A was added dropwise to solution B at room temperature and stirred, ethyl acetate (C4H8O2) was added thereto and continued to stir, the prepared ZnO QDs solution was washed with ethanol and water respectively, centrifuged, and then redispersed in anhydrous ethanol to obtain synthesized ZnO quantum dots; Step (2): dissolving indium nitrate (In(NO)3·4.5H2O) and polyvinyl pyrrolidone in a mixed solution of ethanol and N,N-dimethylformamide and stirring at room temperature; The stirred solution is placed in an electrospinning apparatus; the obtained fibers are dried and then kept warm in an air atmosphere to obtain In2O3 nanofibers; Step (3): ultrasonically mixing the ZnO quantum dots and the In2O3 nanofibers and then centrifugally drying them to obtain a ZnO QDs / In2O3 nanofiber heterojunction photocomposite material catalyst.

2. The ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst according to claim 1, characterized in that: In the step (1), the molar ratio of potassium hydroxide (KOH) to anhydrous ethanol (C2H5OH) is 1:60±5; Zinc acetate and anhydrous ethanol is 1:900±50; The ratio of potassium hydroxide, zinc acetate and ethyl acetate is: 3±0.5:1±0.5:50±5.

3. The ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst according to claim 1, characterized in that: In the step (2), the mass ratio of indium nitrate to polyvinyl pyrrolidone is 1:1±0.5; the volume ratio of the mixed solution of ethanol and N,N-dimethylformamide is 1:1±0.

5.

4. The ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst according to claim 1, characterized in that: In step (2), the electrospinning instrument is set to a voltage of 16-18 kV and a flow rate of 0.3-0.5 mL·h -1 After drying, the obtained fiber was kept at 500-550℃ in air atmosphere for 4h, with a heating rate of 5℃·min -1 .

5. The ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst according to claim 1, characterized in that: The ultrasonic time in step (3) is 2-4 hours, and the ZnO quantum dot loading amount is controlled by adjusting the volume of the ZnO QDs solution.

6. The ZnO quantum dot / In2O3 nanofiber heterojunction photocatalyst according to claim 1, characterized in that: The molar ratio of the ZnO quantum dots to the In2O3 nanofibers is 0.3±0.05:

1.

7. A ZnO QDs / In2O3 nanofiber heterojunction photocatalyst, characterized in that: The cubic indium oxide phase is composed of the In2O3 (440) crystal plane and the wurtzite phase ZnO (110) crystal plane. There is a heterojunction structure between In2O3 and ZnO, which forms an important interface for charge transfer between the two semiconductors. A self-generated electric field is formed at the heterojunction interface, driving the directional separation of electrons and holes and inhibiting recombination. Among them, the diameter of In2O3 nanofibers is about 110nm, and the average particle size of ZnO quantum dots is 4.96nm. After loading, a porous structure is formed, and the absorption range of the composite material is extended to the visible light region (λ>400nm).

8. An application of a ZnO QDs / In2O3 nanofiber heterojunction photocatalyst, characterized in that: ZnO QDs / In2O3 nanofiber heterojunction photocatalyst for Cr(VI) detection and reduction.

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