A photocatalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic functional materials, and discloses a kind of photocatalyst and its preparation method and application. Through the high-temperature liquid phase environment of molten salt, the heavy rare earth oxide is effectively dissolved and dispersed, the atomic dispersion of heavy rare earth elements in g-C3N4 skeleton is realized, so as to give full play to its advantages, utilize the unique coordination of rare earth single atom and nitrogen skeleton N of carbon nitride, and the performance of photocatalytic preparation of hydrogen peroxide is improved by strong electron interaction.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic functional materials technology, specifically relating to a photocatalyst, its preparation method, and its applications. More specifically, it relates to a heavy rare earth single-atom coordinated carbon nitride photocatalyst, its preparation method, and its applications. Background Technology

[0002] Photocatalysis, an environmentally friendly technology that utilizes solar energy to drive chemical reactions, has shown broad application prospects in energy conversion and environmental remediation. Graphitic carbon nitride (g-C3N4) has become a research hotspot in photocatalysis due to its suitable bandgap structure, good chemical and thermal stability, and wide availability of precursor sources. However, pure g-C3N4 suffers from severe recombination of photogenerated electron-hole pairs and insufficient surface active sites in photocatalytic reactions, limiting its quantum efficiency and practical application performance.

[0003] To overcome these problems, researchers have developed various modification strategies, such as heavy rare earth atom modification, to expand the photoresponse range of the photocatalyst, prolong the lifetime of photogenerated carriers, and reduce the recombination degree of photogenerated carriers. However, existing preparation methods, such as impregnation-pyrolysis, physical mixing, traditional solid-state calcination, and molten salt modification, suffer from problems such as complex operation, easy detachment of weak metals at the interface, poor controllability of rare earth single atoms, and easy masking of active sites. These methods struggle to balance the integrity of the carbon nitride framework with the stability and uniform doping of rare earth single atoms, making it difficult to achieve breakthroughs in catalyst activity. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a photocatalyst, its preparation method, and its application. By effectively dissolving and dispersing heavy rare earth oxides in a high-temperature liquid phase environment of molten salt, atomic-level dispersion of heavy rare earth elements in the g-C3N4 framework is achieved, thereby fully leveraging its advantages. The unique coordination of rare earth single atoms with carbon nitride framework N and the strong electronic interaction enhance the performance of photocatalytic preparation of hydrogen peroxide.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution: A photocatalyst, wherein the catalyst uses graphitic carbon nitride as a support and rare earth elements are anchored in the carbon nitride framework in the form of single atoms through MN coordination bonds.

[0006] More specifically, the catalyst consists of a graphitic carbon nitride substrate and heavy rare earth single-atom sites anchored on the substrate. The heavy rare earth single-atom sites are bonded to nitrogen atoms in the carbon nitride framework through MN coordination bonds.

[0007] The present invention also claims protection for the preparation method of the above-mentioned photocatalyst, comprising the following steps: melamine, lithium chloride, cesium chloride, and rare earth oxides are placed together in a mortar and ground thoroughly until uniformly mixed; heat treatment is performed using a tube furnace at a temperature of 550~560°C for 3~3.5h, with a heating rate of 5~10°C / min; cooling is performed; the product is collected, washed, and centrifuged; this process is repeated 2~3 times; the washed product is dried; and the product is ground and collected to obtain a rare earth single-atom coordinated carbon nitride photocatalyst.

[0008] Furthermore, the rare earth oxide is any one of Gd2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3.

[0009] Furthermore, the mass ratio of lithium chloride to cesium chloride is 1:1.2 to 1:1.5, preferably 1:1.33.

[0010] Furthermore, the mass ratio of melamine to rare earth oxides is 5:1 to 7:1, preferably 6:1.

[0011] Furthermore, the washing process uses hot ultrapure water for washing, and the washing is repeated 3 to 5 times to remove residual LiCl / CsCl molten salt.

[0012] Furthermore, the centrifugation conditions were: rotation speed 7000~7500 r / min, centrifugation time 4~6 min.

[0013] Furthermore, the drying conditions are as follows: the oven temperature is set to 60~70°C, and the drying time is 11~12 hours.

[0014] This invention also claims protection for the application of the photocatalyst prepared by the above method in the photocatalytic reduction of O2 to H2O2. Specifically, in this application, the mass ratio of the catalyst to deionized water is 1:4000-1:5000, and the reaction is carried out at 25°C for 30 min. The reaction system is a mixture of ethanol and deionized water.

[0015] The advantages of this invention compared to the prior art are: The preparation method provided by this invention utilizes a one-step molten salt calcination process, which is simple and effectively suppresses the migration and aggregation of rare earth atoms by leveraging the high-temperature liquid phase environment of the molten salt. This achieves atomic-level dispersion of heavy rare earth atoms within the carbon nitride framework. HAAD-STEM images of the catalysts prepared in various embodiments show that rare earth atoms are uniformly dispersed on the carbon nitride matrix without significant aggregation. This invention anchors rare earth single atoms within the carbon nitride framework using the molten salt method. The rare earth single atoms and the carbon nitride framework form a unique MN coordination structure, resulting in strong electronic interactions between the rare earth single atom sites and the matrix, thereby effectively controlling the local electronic structure of carbon nitride. Figure 8XPS high-resolution N-wave spectra showed that the N1s main peak of the Yb / PTI sample after the introduction of rare earth single atoms shifted towards higher binding energies. Simultaneously, the relative content of framework nitrogen decreased, while the ratio of bridging nitrogen to amino-deficient nitrogen significantly increased, indicating a strong electronic interaction between Yb and framework nitrogen. The Yb / PTI catalyst prepared in this invention exhibits the lowest electron transport resistance, a lower recombination probability of photogenerated carriers, and a faster transfer rate of photogenerated electrons to active sites, resulting in a higher photocatalytic hydrogen peroxide production rate. The photocatalytic hydrogen peroxide production rate is 4.82 times that of Yb / PTI-LiNa and 3.92 times that of Yb / PTI-LiCsNa. Attached Figure Description

[0016] Figure 1 Aberration-corrected transmission electron microscope image of GdPTI prepared in Example 1.

[0017] Figure 2 Aberration-corrected transmission electron microscope image of Dy / PTI prepared in Example 2.

[0018] Figure 3 Aberration-corrected transmission electron microscope image of the Ho / PTI prepared in Example 3.

[0019] Figure 4 Aberration-corrected transmission electron microscope image of Er / PTI prepared in Example 4.

[0020] Figure 5 Aberration-corrected transmission electron microscope image of Tm / PTI prepared in Example 5.

[0021] Figure 6 Aberration-corrected transmission electron microscope image of Yb / PTI prepared in Example 6.

[0022] Figure 7 Aberration-corrected transmission electron microscope image of Lu / PTI prepared in Example 7.

[0023] Figure 8 The XPS high-resolution N spectrum of the catalysts prepared in Example 6 and Comparative Example 1 is shown.

[0024] Figure 9 Impedance spectra of the catalysts prepared in Example 6 and Comparative Examples 1, 4, and 5. Detailed Implementation

[0025] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0026] Example 1 Accurately weigh 1.20g of melamine, 0.20g of gadolinium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Gd / PTI catalyst.

[0027] Example 2 Accurately weigh 1.20g of melamine, 0.20g of dysprosium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Dy / PTI catalyst.

[0028] Example 3 Accurately weigh 1.20g of melamine, 0.20g of holmium oxide, 1.20g of lithium chloride, and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge it, repeating the process 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Ho / PTI catalyst.

[0029] Example 4 Accurately weigh 1.20g of melamine, 0.20g of erbium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Er / PTI catalyst.

[0030] Example 5 Accurately weigh 1.20g of melamine, 0.20g of thulium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Tm / PTI catalyst.

[0031] Example 6 Accurately weigh 1.20g of melamine, 0.20g of ytterbium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Yb / PTI catalyst.

[0032] Example 7 Accurately weigh 1.20g of melamine, 0.20g of lutetium oxide, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials, place them together in a mortar and grind them thoroughly until they are uniformly mixed. Heat treat them in a tube furnace at 550°C for 3 hours with a heating rate of 5°C / min. After cooling, collect the product, wash and centrifuge, repeat 3 times. Dry the washed and centrifuged product, grind and collect it to obtain the 6-Lu / PTI catalyst.

[0033] Comparative Example 1 Based on Example 1, but unlike Example 1, only 1.40g of melamine, 1.20g of lithium chloride and 1.60g of cesium chloride raw materials were added, without adding any rare earth oxides, to obtain the PTI catalyst.

[0034] Comparative Example 2 Based on Comparative Example 1, the difference is that the added molten salt was changed from lithium chloride and cesium chloride to lithium chloride and sodium chloride molten salt, resulting in the PTI-LiNa catalyst. Everything else is the same as in Comparative Example 1.

[0035] Comparative Example 3 Based on Comparative Example 1, the difference is that the added molten salt was changed from lithium chloride and cesium chloride to a molten salt of lithium chloride, cesium chloride, and sodium chloride, resulting in the PTI-LiCsNa catalyst. Everything else is the same as in Comparative Example 1.

[0036] Comparative Example 4 Based on Example 6, the difference is that the added molten salt was changed from lithium chloride and cesium chloride to lithium chloride and sodium chloride molten salt, resulting in a Yb / PTI-LiNa catalyst. Everything else is the same as in Example 6.

[0037] Comparative Example 5 Based on Example 6, the difference from Example 6 is that the added molten salt is changed from lithium chloride and cesium chloride to a molten salt of lithium chloride, cesium chloride and sodium chloride (Cs / Na mass ratio of 1:1), to obtain the Yb / PTI-LiCsNa catalyst, otherwise the same as in Example 6.

[0038] Application Example 1 0.020 g of the 6-Gd / PTI catalyst prepared in Example 1 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 3.77 mmol g. -1 h -1 .

[0039] Application Example 2 0.020 g of the 6-Dy / PTI catalyst prepared in Example 2 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 3.21 mmol g. -1 h -1 ...

[0040] Application Example 3 0.020 g of the 6-Ho / PTI catalyst prepared in Example 3 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 3.62 mmol g. -1 h -1 ...

[0041] Application Example 4 0.020 g of the 6-Er / PTI catalyst prepared in Example 4 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 4.03 mmol g. -1 h -1 .

[0042] Application Example 5 0.020 g of the 6-Tm / PTI catalyst prepared in Example 5 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 4.96 mmol g. -1h -1 .

[0043] Application Example 6 0.020 g of the catalyst 6-Yb / PTI prepared in Example 6 was weighed into a centrifuge tube, 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 7.18 mmol g. -1 h -1 ...

[0044] Application Example 7 0.020 g of the 6-Lu / PTI catalyst prepared in Example 7 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. The mixture was then transferred to a reactor, and high-purity O2 was bubbled through it for 30 min in the dark. A photocatalytic reduction experiment was conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the photocatalytic hydrogen peroxide generation rate was calculated to be 5.76 mmol g. -1 h -1 ...

[0045] Application Comparative Example 1 0.020 g of the PTI catalyst prepared in Comparative Example 1 was weighed into a centrifuge tube, and 90.00 mL of ultrapure water and 10.00 mL of ethanol were added and mixed well. High-purity O2 was bubbled through the tube for 30 min in the dark. A photocatalytic reduction experiment was then conducted under xenon lamp illumination. The H2O2 concentration was determined by iodometric titration, and the calculated photocatalytic hydrogen peroxide generation rate was 0.69 mmol g. -1 h -1 .

[0046] Application Comparative Example 2 Based on Comparative Example 1, but differing from Comparative Example 1 in that the catalyst was replaced with the PTI-LiNa catalyst prepared in Comparative Example 2, and the H2O2 concentration was determined by iodometric titration. The calculated photocatalytic hydrogen peroxide generation rate was 0.26 mmol g. -1 h -1 .

[0047] Application Comparative Example 3 Based on Comparative Example 1, but differing from Comparative Example 1 in that the catalyst was replaced with the PTI-LiCsNa catalyst prepared in Comparative Example 3, and the H2O2 concentration was determined by iodometric titration. The calculated photocatalytic hydrogen peroxide generation rate was 0.48 mmol g. -1 h -1 .

[0048] Application Comparative Example 4 Based on Comparative Example 1, but differing from Comparative Example 1 in that the catalyst was replaced with the Yb / PTI-LiNa catalyst prepared in Comparative Example 4, and the H2O2 concentration was determined by iodometric titration. The calculated photocatalytic hydrogen peroxide generation rate was 1.49 mmol / g. -1 h -1 .

[0049] Application Comparative Example 5 Based on Comparative Example 1, but differing from Comparative Example 1 in that the catalyst was replaced with the Yb / PTI-LiCsNa catalyst prepared in Comparative Example 5, and the H2O2 concentration was determined by iodometric titration. The calculated photocatalytic hydrogen peroxide generation rate was 1.83 mmol / g. -1 h -1 .

[0050] Depend on Figure 1-7 It can be seen that the catalysts prepared by the present invention all achieve atomic-level distribution of rare earth atoms on carbon nitride substrate. Figure 8 The XPS high-resolution N spectrum showed that the N1s main peak of the Yb / PTI sample after the introduction of rare earth single atoms shifted towards the direction of higher binding energy. At the same time, the relative content of framework nitrogen decreased, and the ratio of bridging nitrogen to amino defect nitrogen increased significantly, indicating that strong electronic interactions were formed between Yb and framework nitrogen. Figure 9 The results show that the Yb / PTI catalyst prepared by this invention has the lowest electron transport resistance, resulting in a lower recombination probability of photogenerated carriers, a faster transfer rate of photogenerated electrons to active sites, and a higher photocatalytic hydrogen peroxide production rate. The photocatalytic hydrogen peroxide production rate is 4.82 times that of Yb / PTI-LiNa and 3.92 times that of Yb / PTI-LiCsNa. This is in comparison to the 2.74 mmol g of K and S modified carbon nitride materials used in existing technologies. -1 h -1 (P. Zhang et al., Heteroatom dopants-promoted two-electron O2 reduction for photocatalytic production of H2O2 on polymeric carbon nitride. Angew. Chem. Int. Ed. 59, 2-11(2020).), the performance was improved by 2.62 times.

[0051] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A photocatalyst, characterized in that, The catalyst uses graphitic carbon nitride as a support, and rare earth elements are anchored in the carbon nitride framework in the form of single atoms through MN coordination bonds.

2. The photocatalyst as described in claim 1, characterized in that, The catalyst consists of a graphitic carbon nitride substrate and heavy rare earth single-atom sites anchored on the substrate. The heavy rare earth single-atom sites are bonded to nitrogen atoms in the carbon nitride framework through MN coordination bonds.

3. The method for preparing a photocatalyst as described in claim 1, characterized in that, Includes the following steps: Melamine, lithium chloride, cesium chloride, and rare earth oxides were placed together in a mortar and ground thoroughly until uniformly mixed. The mixture was then heat-treated in a tube furnace at 550-560°C for 3-3.5 hours with a heating rate of 5-10°C / min. After cooling, the product was collected, washed, and centrifuged. This process was repeated 2-3 times. The washed product was dried, ground, and collected to obtain the rare earth single-atom coordinated carbon nitride photocatalyst.

4. The method for preparing a photocatalyst as described in claim 1, characterized in that, The rare earth oxides are any one of Gd2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3.

5. The method for preparing a photocatalyst as described in claim 1, characterized in that, The mass ratio of lithium chloride to cesium chloride is 1:1.2 to 1:1.

5.

6. The method for preparing a photocatalyst as described in claim 1, characterized in that, The mass ratio of melamine to rare earth oxides is 5:1 to 7:

1.

7. The method for preparing a photocatalyst as described in claim 1, characterized in that, Centrifugation conditions: 7000~7500 r / min, centrifugation time 4~6 min.

8. The method for preparing a photocatalyst as described in claim 1, characterized in that, The drying conditions are as follows: the oven temperature is set to 60~70°C, and the drying time is 11~12 hours.

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