Z-type heterojunction photocatalyst constructed by N-Co-S electron bridge as well as preparation method and application of Z-type heterojunction photocatalyst

Abstract

The invention belongs to the technical field of hydrogen production catalysts, and discloses a Z-type heterojunction photocatalyst constructed by an N-Co-S electron bridge and a preparation method and application of the Z-type heterojunction photocatalyst constructed by the N-Co-S electron bridge. Preparing an MIL; the preparation method comprises the following steps: dispersing MIL and Co-CdS QDs in a mixed solution of ethanol and water, uniformly stirring, carrying out a heating reaction, filtering, washing, and carrying out vacuum drying to obtain the Z-type heterojunction photocatalyst constructed by the N-Co-S electron bridge. The Co-CdS QDs are uniformly loaded on the surface of the MIL to prepare the photocatalyst with high oxidation-reduction potential, so that high-efficiency photocatalytic ammonia decomposition for hydrogen production at low temperature is realized, and the highest hydrogen production rate reaches 18 [mu] mol.g1.s1.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen-producing catalysts, and relates to a Z-scheme heterojunction photocatalyst constructed with an N-Co-S electron bridge, a preparation method thereof, and an application thereof. Background Art

[0002] Green hydrogen (H2), as a clean energy source with zero carbon emissions, has broad prospects in the future energy system. However, the storage and transportation of H2 face challenges such as high energy consumption, high cost, and safety risks. Ammonia (NH3), as a carbon-free hydrogen storage carrier (Recent progress in ammonia fuel cells and their potential applications, Journal of Materials Chemistry A, 2021, 9(2): 727-752), has a high hydrogen storage density (17.6%) and can be stored in liquid form at room temperature and atmospheric pressure. Relying on a mature production and transportation network, it is expected to reduce the cost of hydrogen energy infrastructure. However, traditional ammonia decomposition relies on noble metal high-temperature catalysis (Chemical Looping Ammonia Decomposition Mediated by Alkali Metal and Amide Pairs for H2 Production and Thermal Energy Storage, Advanced Energy Materials, 2024, 14(43): 2401252), which limits its popularization. Photocatalytic ammonia decomposition technology (Review of the Decomposition of Ammonia to Generate Hydrogen, Industrial & Engineering Chemistry Research, 2021, 60(51): 18560-18611), due to its efficient utilization of solar energy and further reduction of dependence on fossil energy, is a truly green hydrogen production solution. By directly driving the NH3 decomposition reaction with a photocatalyst to efficiently generate H2 under mild conditions, this not only significantly reduces energy consumption but also avoids environmental problems that may be caused by traditional high-temperature and high-pressure processes.

[0003] Defects and deficiencies of the prior art:

[0004] 1. Traditional thermal catalytic NH3 decomposition for hydrogen production mainly relies on high-temperature catalysis, usually requiring 600–900 °C to achieve efficient decomposition, resulting in high energy consumption and high economic costs;

[0005] 2. The traditional thermal catalytic NH3 decomposition for hydrogen production mainly relies on noble metal catalysts such as Ru, Pt, Ir and other noble metals, which are expensive and limited in reserves, restricting industrialization;

[0006] 3. During the long-term high-temperature operation of the catalyst, it is prone to sintering, poisoning or carbon deposition, resulting in a decrease in activity and affecting stability. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Z-scheme heterojunction photocatalyst constructed by an N-Co-S electron bridge, its preparation method and application. By uniformly loading Co-CdS QDs on the surface of MIL, a Z-scheme heterojunction photocatalyst Co-CdS QDs / MIL with high redox potential is prepared, realizing efficient photocatalytic ammonia decomposition for hydrogen production at low temperature.

[0008] The technical solution adopted by the present invention to solve the technical problems is as follows:

[0009] On the one hand, the present invention provides a preparation method of a Z-scheme heterojunction photocatalyst constructed by an N-Co-S electron bridge, and the steps are as follows:

[0010] (1) Disperse Cd(CH3COO)2·2H2O and CoCl2·6H2O with a mass ratio of 18~22:1 in ethanol, stir and ultrasonically mix evenly, heat to 343~363 K, and after the temperature is stable, dropwise add 0.03~0.05 mol / L thioacetamide solution, and react at 343~363 K for 1~2 h, filter and separate, and vacuum dry to obtain cobalt-doped cadmium sulfide quantum dots (Co-CdS QDs);

[0011] (2) Dissolve Al(NO3)3·9H2O and H2N-H2BDC with a mass ratio of 1~2:1~2 in DMF, stir evenly at room temperature and transfer to a high-pressure reaction kettle, react at 420~425 K for 10~14 h, cool to room temperature after the reaction, obtain the product, wash the product with DMF, then disperse the product in DMF, and continue to treat at 420~425 K for 5~8 h, wash, and vacuum dry to obtain the final product MIL (amino-functionalized MIL-53(aluminum));

[0012] (3) Disperse MIL and Co-CdS QDs with a mass ratio of 1~3:1 in a mixed solution of ethanol and water, stir evenly, heat to 343~363 K and react for 1~2 h, filter, wash, and vacuum dry to obtain a Z-scheme heterojunction photocatalyst constructed by an N-Co-S electron bridge (Co-CdS QDs / MIL).

[0013] Further, the ratio of the total mass of Cd(CH3COO)2·2H2O and CoCl2·6H2O to the volume of ethanol is 90 - 100 mg: 10 mL.

[0014] Further, the volume ratio of ethanol to the thioacetamide solution is 1 - 2: 1 - 2.

[0015] Further, the ratio of the total mass of Al(NO3)3·9H2O and H2N-H2BDC to the volume of DMF is 2 - 3 g: 60 mL.

[0016] Further, in the mixed solution of ethanol and water in step (3), the volume ratio of ethanol to water is 2 - 3: 1.

[0017] Further, the ratio of the total mass of MIL and Co-CdS QDs to the volume of the mixed solution of ethanol and water is 40 - 60 mg: 60 mL.

[0018] Further, the solvent for washing in step (2) is acetone, and the vacuum drying is carried out at 370 - 375 K for 12 - 20 h.

[0019] Further, the solvents for washing in step (3) are water and ethanol, and the vacuum drying is carried out at 330 - 335 K for 12 - 20 h.

[0020] In the second aspect of the present invention, a Z-scheme heterojunction photocatalyst prepared by the above preparation method is provided, and an N-Co-S electron bridge is constructed inside the structure.

[0021] In the third aspect of the present invention, an application of the Z-scheme heterojunction photocatalyst in a photocatalytic ammonia decomposition reaction is provided.

[0022] Further, at 24 - 26 °C, the Z-scheme heterojunction photocatalyst is placed in a quartz glass reactor, 100 sccm NH3 is used as the reaction gas, a 300 W xenon lamp is used as the light source, and the light intensity is 3 W·cm −2 , before the reaction starts, NH3 is continuously introduced into the reactor for 15 - 20 min, and then light irradiation is started. The reaction products are analyzed by a gas chromatograph, and the gas composition is measured using a TCD detector.

[0023] The advantages and positive effects of the present invention are:

[0024] In view of the phenomenon of relying on high temperature and noble metal catalysis in the existing ammonia decomposition hydrogen production technology, a Z-scheme heterojunction photocatalyst Co-CdS QDs / MIL with a high redox potential was prepared by uniformly loading Co-CdS QDs on the surface of MIL. This catalyst retains the highest reduction potential of Co-CdS QDs and the lowest oxidation potential of MIL, achieving efficient photocatalytic ammonia decomposition hydrogen production at room temperature, with the highest hydrogen production rate reaching 18 μmol·g −1 ·s −1 . Description of the Drawings

[0025] Figure 1 High-resolution transmission electron microscopy images of the photocatalysts prepared in Example 1 and Comparative Examples 1-4, where a is the TEM image of CdS QDs, b is the TEM image of Co-CdS QDs, c is the TEM image of MIL, d is the TEM image of CdS QDs / MIL, and e is the TEM image of Co-CdS QDs / MIL;

[0026] Figure 2 Converging lens spherical aberration corrected transmission electron microscopy images of the photocatalyst Co-CdS QDs / MIL prepared in Example 1, where a is the converging lens spherical aberration corrected transmission electron microscopy image of Co-CdS QDs / MIL, and b is the image obtained by quantitatively analyzing the integral pixel intensity of the rectangular region selected in Figure a;

[0027] Figure 3 X-ray absorption near-edge structure spectra and Fourier transform extended X-ray absorption fine structure spectra of the photocatalyst Co-CdS QDs / MIL prepared in Example 1 and reference samples (Co foil, CoS, CoPc), where a is the X-ray absorption near-edge structure spectrum and b is the Fourier transform extended X-ray absorption fine structure spectrum;

[0028] Figure 4 X-ray diffraction patterns of the photocatalysts, where a is the X-ray diffraction pattern of MIL, CdS QDs / MIL, and Co-CdS QDs / MIL, and b is the X-ray diffraction pattern of CdS QDs, CdS QDs / MIL, and Co-CdS QDs / MIL;

[0029] Figure 5 X-ray photoelectron spectra of N atoms and S atoms in the Co-CdS QDs / MIL photocatalyst prepared in Example 1, where a is the X-ray photoelectron spectrum of N atoms; b is the X-ray photoelectron spectrum of S atoms;

[0030] Figure 6 Electron paramagnetic resonance spectra of DMPO spin trapping •O2 − for the photocatalysts prepared in Example 1 and Comparative Examples 1-4;

[0031] Figure 7 Hydrogen production activity diagrams of the photocatalysts prepared in Example 1 and Comparative Examples 1-4;

[0032] Figure 8 Cyclic experiment diagram of the photocatalyst prepared in Example 1;

[0033] Figure 9 Hydrogen production rate diagrams of the photocatalytic ammonia decomposition reaction control experiments carried out under the experimental conditions of darkness, without catalyst, and without NH3, respectively. Specific implementation manners

[0034] The present invention will be further described in detail below through specific examples. The following examples are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0035] Example 1

[0036] A Z-scheme heterojunction photocatalyst constructed with an N-Co-S electron bridge, the steps are as follows:

[0037] (1) Synthesize Co-CdS QDs by hydrothermal method. Disperse 92 mg of Cd(CH3COO)2·2H2O and 4.6 mg of CoCl2·6H2O in 10 mL of ethanol and continuously stir for 20 min, then ultrasonically treat the solution for 10 min. Subsequently, place the solution in a beaker and heat it to 353 K. After the temperature is stabilized, dropwise add 10 mL of 0.03 mol / L thioacetamide solution, and react for another 1 h at 353 K. Filter the sample by suction and dry it under vacuum to obtain Co-CdS QDs;

[0038] (2) Synthesize MIL by hydrothermal method. Dissolve 1.576 g of Al(NO3)3·9H2O and 1.112 g of H2N-H2BDC in 60 mL of DMF, stir evenly at room temperature and then transfer it to a 100 mL polytetrafluoroethylene-lined autoclave, and react at 423 K for 12 h. After the reaction is completed, slowly cool it to room temperature, and wash the obtained product with DMF. Subsequently, redisperse the product in 50 mL of DMF and continue to treat it at 423 K for 6 h. Finally, wash it with acetone multiple times and dry it overnight under vacuum at 373 K to obtain the final product MIL;

[0039] (3) Co-CdS QDs / MIL was synthesized by a hydrothermal method. 40 mg of the synthesized MIL and 20 mg of the synthesized Co-CdS QDs were dispersed in a mixed solution of 40 mL of ethanol and 20 mL of water and uniformly dispersed under stirring. Subsequently, the mixed solution was heated to 353 K and reacted for 1 h. After the reaction, the product was filtered and washed repeatedly with water and ethanol, and dried in vacuo at 333 K for 12 h to obtain the final product Co-CdS QDs / MIL.

[0040] Example 2

[0041] A Z-scheme heterojunction photocatalyst constructed with an N-Co-S electron bridge, the steps are as follows:

[0042] (1) Co-CdS QDs were synthesized by a hydrothermal method. 82.8 mg of Cd(CH3COO)2·2H2O and 4.14 mg of CoCl2·6H2O were dispersed in 9 mL of ethanol and continuously stirred for 20 min, then the solution was ultrasonicated for 10 min. Subsequently, the solution was placed in a beaker and heated to 353 K. After the temperature stabilized, 10 mL of 0.03 mol / L thioacetamide solution was added dropwise, and the reaction was continued at 353 K for 1 h. The sample was separated by suction filtration and dried in vacuo to obtain Co-CdS QDs;

[0043] (2) MIL was synthesized by a hydrothermal method. 1.4184 g of Al(NO3)3·9H2O and 1.0 g of H2N-H2BDC were dissolved in 54 mL of DMF, stirred evenly at room temperature and then transferred to a 100 mL polytetrafluoroethylene-lined autoclave and reacted at 423 K for 12 h. After the reaction, it was slowly cooled to room temperature, and the obtained product was washed with DMF. Subsequently, the product was redispersed in 60 mL of DMF and further treated at 423 K for 6 h. Finally, it was washed repeatedly with acetone and dried in vacuo at 373 K overnight to obtain the final product MIL;

[0044] (3) Co-CdS QDs / MIL was synthesized by a hydrothermal method. 43.6 mg of the synthesized MIL and 18 mg of the synthesized Co-CdS QDs were dispersed in a mixed solution of 40 mL of ethanol and 20 mL of water and uniformly dispersed under stirring. Subsequently, the mixed solution was heated to 353 K and reacted for 1 h. After the reaction, the product was filtered and washed repeatedly with water and ethanol, and dried in vacuo at 333 K for 12 h to obtain the final product Co-CdS QDs / MIL.

[0045] Comparative Example 1

[0046] A preparation method of a photocatalyst (CdS QDs) is synthesized by a hydrothermal method. 92 mg of Cd(CH3COO)2·2H2O is dispersed in 10 mL of ethanol and continuously stirred for 20 min, then the solution is ultrasonicated for 10 min. Subsequently, the solution is placed in a beaker and heated to 353 K. After the temperature is stabilized, 10 mL of 0.03 mol / L thioacetamide solution is added dropwise, and the reaction is continued for 1 h at 80 °C. The sample is separated by suction filtration and dried in vacuum to obtain CdS QDs;

[0047] Comparative Example 2

[0048] A preparation method of a photocatalyst (Co-CdS QDs) is the same as that in Example 1.

[0049] Comparative Example 3

[0050] A preparation method of a photocatalyst (MIL) is the same as that in Example 1.

[0051] Comparative Example 4

[0052] A preparation method of a photocatalyst CdS QDs / MIL is synthesized by a hydrothermal method. The preparation methods of MIL and CdS QDs are the same as those in Example 1. 40 mg of the synthesized MIL and 20 mg of the synthesized CdS QDs are dispersed in a mixed solution of 40 mL of ethanol and 20 mL of water and uniformly dispersed under stirring. Subsequently, the mixed solution is heated to 353 K and reacted for 1 h. After the reaction, the product is filtered and washed with water and ethanol multiple times. Finally, it is dried in vacuum at 333 K for 12 h to obtain the final product CdS QDs / MIL.

[0053] The photocatalysts prepared in Example 1 and Comparative Examples 1-4 are scanned by high-resolution transmission electron microscopy, as Figure 1 shown. Among them, a is the electron micrograph of CdS QDs, b is the electron micrograph of Co-CdS QDs, c is the electron micrograph of MIL, d is the electron micrograph of CdS QDs / MIL, and e is the electron micrograph of Co-CdS QDs / MIL. In e, we found that Co-CdS QDs are uniformly loaded on the surface of MIL. Such a design improves the dispersion of Co-CdS QDs in the reaction medium and is beneficial to enhancing the catalytic effect.

[0054] The photocatalyst Co-CdS QDs / MIL prepared in Example 1 is scanned by a condenser spherical aberration corrected transmission electron microscope, as Figure 2 shown. In a, a single Co atom can be directly observed to be stably anchored on the surface of CdS QDs. The integral pixel intensity of the rectangular region in Figure a is selected for quantitative analysis, and the result is shown in Figure b, which confirms the atomic-level precise doping and integration of Co species at the heterojunction interface.

[0055] X-ray absorption near-edge structure spectra (XANES) and Fourier transform extended X-ray absorption fine structure spectra (FT-EXAFS) were respectively performed on the photocatalyst prepared in Example 1, Co foil, CoS, and CoPc. As Figure 3 shown in a, which is the X-ray absorption near-edge structure spectrum, and b, which is the Fourier transform extended X-ray absorption fine structure spectrum. Through analysis, it can be seen that the average oxidation state of Co species in Co-CdS QDs / MIL is between CoS and CoPc, and Co atoms are in a hetero-coordination environment jointly affected by N and S, proving the formation of an N–Co–S coordination structure.

[0056] X-ray diffraction analysis was performed on the photocatalyst samples prepared in Example 1 and the comparative examples. As Figure 4 shown in a and b, the existence of two phases, Co-CdS QDs and MIL, can be clearly observed in the Co-CdS QDs / MIL spectrum.

[0057] X-ray photoelectron spectroscopy of N atoms and S atoms in the Co-CdS QDs / MIL photocatalyst prepared in Example 1 was analyzed. As Figure 5 shown, from a, it can be seen that an N–Co bond was observed in the X-ray photoelectron spectrum of N atoms, and from b, it can be seen that an S–Co bond was observed in the X-ray photoelectron spectrometer spectrum of S atoms, proving the real existence of the N–Co–S structure.

[0058] Figure 6 is the electron paramagnetic resonance spectrum of DMPO spin trapping •O2 − for the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4. It can be found from the spectrum that the peak intensity of Co-CdS QDs / MIL is higher than that of CdS QDs / MIL, indicating that a Z-scheme heterojunction is formed in Co-CdSQDs / MIL, which has a stronger redox potential.

[0059] Application Example

[0060] Details of the photocatalytic ammonia decomposition reaction. At 25 °C, 70 mg of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4 were respectively weighed and placed in a quartz glass reactor, and 100 sccm NH3 was used as the reaction gas. A 300 W xenon lamp (light intensity 3W·cm −2 −2) was used as the light source. Before the reaction started, NH3 was continuously introduced into the reactor for 15 min, and then light irradiation was started. The reaction products were analyzed by a gas chromatograph (GC 9790Ⅱ), and a TCD detector was used to measure the gas composition.

[0061] Figure 7Hydrogen production activity diagrams of the photocatalysts prepared in Example 1 and Comparative Examples 1-4 are shown. It can be seen that the photocatalytic hydrogen production efficiency of Co-CdS QDs / MIL prepared in Example 1 is significantly higher than that of the comparative examples, and the hydrogen production rate is as high as 18 μmol·g −1 ·s −1 。

[0062] The photocatalyst prepared in Example 1 was subjected to a catalytic cycle experiment, and the results are as Figure 8 shown. It can be seen that after 20 hours of cycling, the hydrogen production rate still remains at 18 μmol·g −1 ·s −1 。

[0063] Photocatalytic ammonia decomposition reaction control experiments were carried out under the experimental conditions of dark conditions, no catalyst, and no NH3 (only using Ar) respectively. Other conditions were the same as those in the application example. The photocatalytic hydrogen production efficiency is as Figure 9 shown. It can be seen from the figure that the hydrogen production rates under the experimental conditions of dark conditions, no catalyst, and no NH3 are not as good as those in the application example, and the three hydrogen production rate curves basically overlap. Through systematic control experiments, the key roles of the Co-CdS QDs / MIL catalyst, NH3, and light irradiation conditions in the photocatalytic reaction were clarified.

[0064] The photocatalytic hydrogen production efficiency of Example 1 is higher than the photocatalytic ammonia decomposition hydrogen production efficiency of the existing discovered photocatalysts without adding additional auxiliary photothermal carrier catalysts. The yields of photocatalytic NH3 decomposition by different catalysts are shown in Table 1.

[0065] Table 1 Yields of photocatalytic NH3 decomposition by different catalysts

[0066]

[0067] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of a Z-scheme heterojunction photocatalyst constructed by an N-Co-S electron bridge, characterized in that, The steps are as follows: (1) Disperse Cd(CH3COO)2·2H2O and CoCl2·6H2O with a mass ratio of 18 - 22:1 in ethanol, stir and ultrasonically homogenize, heat to 343 - 363 K. After the temperature stabilizes, dropwise add 0.03 - 0.05 mol / L thioacetamide solution, react at 343 - 363 K for 1 - 2 h, perform suction filtration for separation, and vacuum dry to obtain Co-CdS QDs; (2) Dissolve Al(NO3)3·9H2O and H2N-H2BDC with a mass ratio of 1 - 2:1 - 2 in DMF, stir evenly at room temperature and then transfer to a high-pressure reactor, react at 420 - 425 K for 10 - 14 h. After the reaction ends, cool to room temperature to obtain the product, wash the product with DMF, then disperse the product in DMF, and continue to treat at 420 - 425 K for 5 - 8 h, wash, and vacuum dry to obtain the final product MIL; (3) Disperse MIL and Co-CdS QDs with a mass ratio of 1 - 3:1 in a mixed solution of ethanol and water, stir evenly, heat to 343 - 363 K and react for 1 - 2 h, filter, wash, and vacuum dry to obtain a Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge.

2. The preparation method according to claim 1, wherein The ratio of the total mass of Cd(CH3COO)2·2H2O and CoCl2·6H2O to the volume of ethanol is 90 - 100 mg:10 mL.

3. The preparation method according to claim 1, wherein The volume ratio of ethanol to thioacetamide solution is 1 - 2:1 - 2.

4. The preparation method according to claim 1, characterized in that, The ratio of the total mass of Al(NO3)3·9H2O and H2N-H2BDC to the volume of DMF is 2 - 3 g:60 mL.

5. The preparation method according to claim 1, characterized in that, In the mixed solution of ethanol and water in step (3), the volume ratio of ethanol to water is 2 - 3:

1.

6. The preparation method according to claim 1, characterized in that, The ratio of the total mass of MIL and Co-CdS QDs to the volume of the mixed solution of ethanol and water is 40 - 60 mg:60 mL.

7. The Z-type heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The interior of the structure is constructed by an N-Co-S electron bridge.

8. Application of the Z-type heterojunction photocatalyst according to claim 7 in the photocatalytic ammonia decomposition reaction.

9. The application according to claim 8, wherein At 24-26 °C, the Z-scheme heterojunction photocatalyst was placed in a quartz glass reactor. Using 100 sccm NH3 as the reaction gas and a 300 W xenon lamp as the light source with a light intensity of 3 W·cm −2 , before the reaction started, NH3 was continuously introduced into the reactor for 15-20 min, and then light irradiation was started. The reaction products were analyzed by a gas chromatograph, and a TCD detector was used to determine the gas composition.

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