An oxygen-doped carbon nitride / ytterbia heterojunction photocatalyst

Abstract

This invention discloses an oxygen-doped carbon nitride / ytterbium oxide (OCN / Yb₂O₃) heterojunction photocatalyst, its preparation method, and its applications, belonging to the field of photocatalytic materials technology. The process involves thermally treating a carbapenemhydrazine to obtain the intermediate HTIC; then, HTIC is uniformly mixed with Yb₂O₃ and a water-soluble molten salt, followed by molten salt thermal treatment to obtain the target catalyst OCN / Yb₂O₃. This method is simple, the molten salt can be washed and recovered with water, it is environmentally friendly, and has low cost. The OCN / Yb₂O₃ photocatalyst obtained by this invention exhibits a broad spectral response, high carrier separation and migration efficiency, and excellent all-water splitting activity under visible light, showing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to an oxygen-doped carbon nitride / ytterbium oxide (OCN / Yb2O3) heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] Photocatalytic water splitting for hydrogen production is a green pathway to convert solar energy into hydrogen energy. Polymer carbon nitride (PCN) is an important photocatalyst due to its suitable energy band, good stability, and low cost. However, the light absorption edge of traditional PCN is limited to around 460 nm, making it difficult to utilize long-wavelength visible and near-infrared light, and photogenerated carriers are prone to recombination, which restricts its photocatalytic efficiency. Non-metallic doping (such as oxygen doping) can effectively broaden the photoresponse range; constructing heterojunctions can promote charge separation and suppress recombination. Ytterbium oxide (Yb₂O₃) has an energy band that is staggered with PCN, and its wide bandgap does not compete with PCN for light absorption, making it suitable for recombination with oxygen-doped carbon nitride (OCN) to form OCN / Yb₂O₃ heterojunctions, achieving broadband and efficient photocatalysis. Therefore, developing a simple, low-cost, and environmentally friendly OCN / Yb₂O₃ preparation method is of great significance. Summary of the Invention

[0003] The present invention aims to provide a method for preparing an oxygen-doped carbon nitride / ytterbium oxide (OCN / Yb₂O₃) heterojunction photocatalyst and its applications. This method is simple, the molten salt can be washed and recovered with water, it is environmentally friendly and low-cost, and easily scalable. The obtained catalyst, OCN / Yb₂O₃, exhibits a broad spectral response, high carrier separation efficiency, and excellent photocatalytic activity, making it suitable for photocatalytic water splitting for hydrogen production, carbon dioxide reduction, and degradation of organic pollutants.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an OCN / Yb2O3 heterojunction photocatalyst: HTIC powder intermediate is obtained by heat treatment of carbazide; HTIC, Yb2O3, and water-soluble molten salt are then thoroughly ground and mixed in a mortar, transferred to a covered corundum crucible, and subjected to molten salt heat treatment in a muffle furnace, followed by natural cooling to room temperature; the product is washed with deionized water until the ion concentration is below 10 ppm, and dried at 60-80 ℃ for 3-10 h to obtain the OCN / Yb2O3 heterojunction photocatalyst.

[0005] The mass of the carbazide is 5-30 g.

[0006] The heat treatment temperature is 300~450 ℃, the heating rate is 1~10 ℃ / min, and the treatment time is 0.5~3 h.

[0007] The mass ratio of Yb2O3, HTIC and water-soluble molten salt is 1:(0.5~10):(1~20).

[0008] The water-soluble molten salt is one or more of lithium chloride, potassium chloride, and sodium chloride.

[0009] The molten salt heat treatment temperature is 450~600 ℃, the heating rate is 1~10 ℃ / min, and the treatment time is 1~6h.

[0010] The resulting OCN / Yb2O3 heterojunction photocatalyst is suitable for photocatalytic water splitting to produce hydrogen, carbon dioxide reduction, and organic matter degradation.

[0011] The beneficial effects of this invention are as follows: (1) This invention is the first to prepare an OCN / Yb2O3 heterojunction photocatalyst.

[0012] (2) The OCN / Yb2O3 heterojunction photocatalyst prepared in this invention significantly broadens the photoresponse range and effectively promotes the separation and migration of photogenerated carriers, realizing visible light-driven total water splitting; while pure OCN has no such activity.

[0013] (3) The preparation process of this invention is simple, the molten salt can be washed and recycled, it is environmentally friendly, low in cost, and easy to scale up. Attached Figure Description

[0014] Figure 1 X-ray powder diffraction pattern of the OCN / Yb2O3 heterojunction photocatalyst prepared in Example 1; Figure 2 Fourier transform infrared spectra of the samples from Example 1 (OCN / Yb2O3), Comparative Example 1 (OCN), and Comparative Example 2 (Yb2O3); Figure 3 The UV-Vis diffuse reflectance spectra of Comparative Example 1 (OCN) and Comparative Example 3 (PCN) samples are shown. Figure 4 Comparison of the catalytic activity of Example 1 (OCN / Yb2O3), Comparative Example 1 (OCN), and Comparative Example 2 (Yb2O3) in the complete water splitting process under visible light; Figure 5 The activity stability of the OCN / Yb2O3 heterojunction photocatalyst prepared in Example 1 for complete water splitting under visible light. Detailed Implementation

[0015] To make the content of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with specific embodiments, but this invention is not limited thereto.

[0016] Example 1: Preparation of OCN / Yb2O3 heterojunction photocatalyst (1) Preparation of HTIC intermediate: Weigh 10 g of carbonyl hydrazine, place it in a covered corundum crucible, heat it to 450 ℃ at 5 ℃ / min, and keep it at the temperature for 2 h; after cooling, grind it into powder to obtain HTIC.

[0017] (2) OCN / Yb2O3 heterojunction: Weigh 1 g HTIC, 0.5 g Yb2O3, 2 g lithium chloride and 2 g potassium chloride, grind and mix them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, keep the temperature constant for 3 h, cool naturally, wash with deionized water until the ion concentration is <10 ppm, dry at 70 ℃ for 6 h to obtain OCN / Yb2O3 heterojunction.

[0018] Figure 1 The X-ray powder diffraction pattern of the photocatalyst obtained in Example 1 shows the characteristic diffraction peaks of typical cubic Yb2O3 (JCPDS: 43-1037), with no PCN characteristic peaks observed.

[0019] Example 2: Preparation of OCN / Yb2O3 heterojunction photocatalyst (1) Preparation of HTIC intermediate: Weigh 10 g of carbonyl hydrazine, place it in a covered corundum crucible, heat it to 450 ℃ at 5 ℃ / min, and keep it at the temperature for 2 h; after cooling, grind it into powder to obtain HTIC.

[0020] (2) OCN / Yb2O3 heterojunction: Weigh 1 g HTIC, 0.5 g Yb2O3, 2 g lithium chloride and 2 g potassium chloride, grind and mix them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, keep the temperature constant for 1 h, cool naturally, wash with deionized water until the ion concentration is <10 ppm, dry at 70 ℃ for 6 h to obtain OCN / Yb2O3 heterojunction.

[0021] Example 3: Preparation of OCN / Yb2O3 heterojunction photocatalyst (1) Preparation of HTIC intermediate: Weigh 10 g of carbonyl hydrazine, place it in a covered corundum crucible, heat it to 450 ℃ at 5 ℃ / min, and keep it at the temperature for 2 h; after cooling, grind it into powder to obtain HTIC.

[0022] (2) OCN / Yb2O3 heterojunction: Weigh 1 g HTIC, 0.5 g Yb2O3, 2 g lithium chloride and 2 g potassium chloride, grind and mix them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, keep the temperature constant for 6 h, cool naturally, wash with deionized water until the ion concentration is <10 ppm, dry at 70 ℃ for 6 h to obtain OCN / Yb2O3 heterojunction.

[0023] Comparative Example 1: Preparation of OCN (1) Preparation of HTIC intermediate: Weigh 10 g of carbonyl hydrazine, place it in a covered corundum crucible, heat it to 450 ℃ at 5 ℃ / min, and keep it at the temperature for 2 h; after cooling, grind it into powder to obtain HTIC.

[0024] (2) OCN synthesis: Weigh 1 g HTIC, 2 g lithium chloride and 2 g potassium chloride, grind and mix them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, keep the temperature for 3 h, cool naturally, wash with deionized water until the ion concentration is <10 ppm, dry at 70 ℃ for 6 h to obtain OCN.

[0025] Comparative Example 2: Preparation of Yb2O3 Weigh 0.5 g Yb2O3, 2.0 g lithium chloride, and 2.0 g potassium chloride, grind them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, hold at that temperature for 3 h, and allow to cool naturally to room temperature; wash the product with deionized water until the ion concentration is <10 ppm, and dry at 70 ℃ for 6 h to obtain Yb2O3.

[0026] Figure 2 The Fourier transform infrared spectra of samples from Example 1 (OCN / Yb2O3), Comparative Example 1 (OCN), and Comparative Example 2 (Yb2O3) are shown. As can be seen from the figures, both OCN / Yb2O3 and OCN exhibit characteristic peaks of polymeric carbon nitride.

[0027] Comparative Example 3: Preparation of PCN (1) Place 6 g of melamine in a covered corundum crucible and heat it to 450 °C at 5 °C / min, and hold it at that temperature for 2 h. After cooling, grind it to obtain the intermediate Melon.

[0028] (2) Take 2.0 g lithium chloride, 2.0 g potassium chloride and 1.0 g Melon, mix them thoroughly in a mortar, transfer them to a covered corundum crucible, heat to 550 ℃ at 5 ℃ / min, keep the temperature for 3 h, cool naturally, wash with deionized water until the ion concentration is <10 ppm, dry at 70 ℃ for 6 h to obtain PCN.

[0029] Figure 3 The UV-Vis diffuse reflectance spectra of Comparative Example 1 (OCN) and Comparative Example 3 (PCN) are shown. The absorption band edge of PCN is located at 456 nm; OCN exhibits a double absorption band: 300-450 nm belongs to π→π* electronic transitions, and 450-800 nm belongs to n→π* transitions, indicating that its photoresponse range is significantly broadened.

[0030] Application Example 1: Visible Light-Based Complete Water Splitting Hydrogen Production Performance of OCN / Yb2O3 Heterojunction Photocatalyst (1) The OCN / Yb2O3 heterojunction prepared in Example 1 was used as the catalyst, and the OCN of Comparative Example 1 and the Yb2O3 of Comparative Example 2 were used as controls. All samples were first loaded with 0.5 wt.% Pt and 0.1 wt.% Co co-catalyst by photodeposition: 100 mg of sample was dispersed in 100 ml of deionized water, 1 mL of methanol, appropriate amounts of H2PtCl6 (corresponding to Pt content) and CoCl2 (corresponding to Co content) were added, vacuumed and irradiated for 1 h, then washed with deionized water and dried.

[0031] (2) The photocatalytic reaction was carried out in a 250 mL sealed circulation system, using a 300 W xenon lamp with a 420 nm filter as the light source. 50 mg of the modified catalyst and 100 mL of ultrapure water were added to the system, magnetically stirred until homogeneous, and the lamp was turned on after evacuation. The gaseous product was introduced into the gas chromatograph for online analysis via a four-way valve at regular intervals. Figure 4 The results showed that OCN and Yb2O3 alone had no visible light-based water splitting activity; however, the OCN / Yb2O3 heterojunction exhibited high activity, with a hydrogen production rate of 12.5 μmol g. -1 h -1 The oxygen production rate was 5.9 μmol g. -1 h -1 .

[0032] Application Example 2: The OCN / Yb2O3 heterojunction photocatalyst prepared in Example 1 was subjected to a 5-cycle total water splitting test under visible light (3 hours each time). Between each cycle, the lights were turned off, the pump was stopped, and a vacuum was applied for 10 minutes before restarting. Figure 5 The results show that the hydrogen production activity of OCN / Yb2O3 through water splitting remains essentially unchanged, demonstrating excellent stability.

[0033] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing an oxygen-doped carbon nitride / ytterbium oxide heterojunction, characterized in that: Includes the following steps: (1) The carbonyl hydrazine was heat-treated to obtain the intermediate HTIC; (2) The intermediate HTIC and ytterbium oxide obtained in step (1) are uniformly mixed with water-soluble molten salt and subjected to molten salt heat treatment to obtain the oxygen-doped carbon nitride / ytterbium oxide heterojunction.

2. The preparation method according to claim 1, characterized in that: The heat treatment temperature in step (1) is 300~450℃, the heating rate is 1~10℃ / min, and the treatment time is 0.5~3 h.

3. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of ytterbium oxide, intermediate HTIC and water-soluble molten salt is 1:0.5~10:1~20.

4. The preparation method according to claim 1, characterized in that... The water-soluble molten salt mentioned in step (2) is at least one of lithium chloride, potassium chloride, and sodium chloride.

5. The preparation method according to claim 1, characterized in that: The molten salt heat treatment in step (2) is performed at a temperature of 450~600 ℃, a heating rate of 1~10 ℃ / min, and a treatment time of 1~6 h.

6. An oxygen-doped carbon nitride / ytterbium oxide heterojunction prepared by the method according to any one of claims 1-5.

7. The application of an oxygen-doped carbon nitride / ytterbium oxide heterojunction prepared by the method according to any one of claims 1 to 5 in a photocatalyst.

8. The application according to claim 7, characterized in that: The oxygen-doped carbon nitride / ytterbium oxide heterojunction is used for photocatalytic water splitting to produce hydrogen, carbon dioxide reduction, and organic matter degradation.

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