A Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge, and its preparation method and application

Abstract

The present invention belongs to the technical field of hydrogen production catalysts and discloses a Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge, as well as its preparation method and application, including: preparing Co-CdS QDs; preparing MIL; dispersing the MIL and Co-CdS QDs in a mixed solution of ethanol and water, stirring evenly, heating the reaction, filtering, washing, and vacuum drying to obtain the Z-type heterojunction photocatalyst constructed with the N-Co-S electron bridge. By uniformly loading the Co-CdS QDs on the surface of the MIL, a photocatalyst with a high redox potential was prepared, achieving efficient photocatalytic ammonia decomposition and hydrogen production at low temperatures, with a maximum hydrogen production rate of 18 μmol·g −1 ·s −1 .

Description

Technical Field

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

[0002] Green hydrogen (H2), as a clean energy with zero carbon emissions, has broad prospects in the future energy system. However, H2 storage and transportation face challenges such as high energy consumption, high costs, 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 precious 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 promotion. Photocatalytic ammonia decomposition technology (Review of the Decomposition of Ammonia to Generate Hydrogen, Industrial & Engineering Chemistry Research, 2021, 60(51): 18560-18611) is a truly green hydrogen production solution, as it further reduces dependence on fossil energy due to its efficient use of solar energy. By directly driving the NH3 decomposition reaction via photocatalysts, H2 is efficiently generated under mild conditions, significantly reducing energy consumption while avoiding the environmental problems that may arise from traditional high-temperature and high-pressure processes.

[0003] Defects and shortcomings of existing technology:

[0004] 1. Traditional thermal catalytic NH3 decomposition to produce hydrogen 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. Traditional thermal catalytic NH3 decomposition to produce hydrogen mainly relies on precious metal catalysts, such as Ru, Pt, Ir and other precious metals, which are expensive and have limited reserves, thus restricting industrialization;

[0006] 3. When the catalyst is operated at high temperature for a long time, it is easy to sinter, poison or carbonize, resulting in decreased activity and affecting stability. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge, a preparation method and application thereof. By uniformly loading Co-CdS QDs on the surface of MIL, a Z-type heterojunction photocatalyst Co-CdS QDs / MIL with high redox potential is prepared, achieving efficient photocatalytic ammonia decomposition to produce hydrogen at low temperature.

[0008] The technical solution adopted by the present invention to solve the technical problem is:

[0009] In one aspect, the present invention provides a method for preparing a Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge, comprising the following steps:

[0010] (1) Cd(CH3COO)2·2H2O and CoCl2·6H2O with a mass ratio of 18-22:1 were dispersed in ethanol and stirred evenly by ultrasonication. The mixture was heated to 343-363 K. After the temperature stabilized, 0.03-0.05 mol / L thioacetamide solution was added dropwise. The mixture was reacted at 343-363 K for 1-2 h. The mixture was separated by filtration and dried in vacuum to obtain cobalt-doped cadmium sulfide quantum dots (Co-CdSQDs).

[0011] (2) Al(NO3)3·9H2O and H2N-H2BDC were dissolved in DMF at a mass ratio of 1-2:1-2, stirred at room temperature, and then transferred to a high-pressure reactor for reaction at 420-425 K for 10-14 h. After the reaction, the reaction was cooled to room temperature to obtain the product, which was washed with DMF. The product was then dispersed in DMF and further treated at 420-425 K for 5-8 h, washed, and vacuum dried to obtain the final product MIL (amino-functionalized MIL-53 (aluminum)).

[0012] (3) MIL and Co-CdS QDs with a mass ratio of 1-3:1 were dispersed in a mixed solution of ethanol and water, stirred evenly, heated to 343-363 K for 1-2 h, filtered, washed, and vacuum dried to obtain a Z-type heterojunction photocatalyst (Co-CdS QDs / MIL) constructed with an N-Co-S electron bridge.

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

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

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

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

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

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

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

[0020] The second aspect of the present invention provides a Z-type heterojunction photocatalyst prepared by the above preparation method, wherein the internal structure is constructed by an N-Co-S electron bridge.

[0021] The third aspect of the present invention provides the use of the Z-type heterojunction photocatalyst in a photocatalytic ammonia decomposition reaction.

[0022] Furthermore, the Z-type heterojunction photocatalyst was placed in a quartz glass reactor at 24-26 °C, 100 sccm NH3 was used as the reaction gas, a 300 W xenon lamp was used as the light source, and the light intensity was 3 W·cm −2 Before the reaction started, 15-20 miM of NH3 was continuously introduced into the reactor, and then the illumination was started. The reaction products were analyzed by gas chromatography, and the gas composition was determined by TCD detector.

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

[0024] The present invention addresses the high temperature and precious metal catalysis relied upon in existing ammonia decomposition hydrogen production technologies. By uniformly loading Co-CdS QDs on the surface of MIL, a Z-type heterojunction photocatalyst Co-CdS QDs / MIL with high redox potential was prepared. This catalyst retains the highest reduction potential of Co-CdS QDs and the lowest oxidation potential of MIL, achieving efficient photocatalytic ammonia decomposition and hydrogen production at room temperature, with a maximum hydrogen production rate of 18 μmol·g −1 ·s −1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 High-resolution transmission electron micrographs of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4, wherein a is an electron micrograph of CdS QDs, b is an electron micrograph of Co-CdS QDs, c is an electron micrograph of MIL, d is an electron micrograph of CdS QDs / MIL, and e is an electron micrograph of Co-CdS QDs / MIL;

[0026] Figure 2 The spherical aberration correction transmission electron microscopy image of the photocatalyst Co-CdS QDs / MIL prepared in Example 1 is corrected for spherical aberration by the condenser lens. a is a spherical aberration correction transmission electron microscopy image of the Co-CdS QDs / MIL, and b is a quantitative analysis of the integrated pixel intensity of the rectangular area in Figure a.

[0027] Figure 3 The 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) are shown in Figure 1. a is the X-ray absorption near-edge structure spectra, and b is the Fourier transform extended X-ray absorption fine structure spectra.

[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 The X-ray photoelectron spectra of N atoms and S atoms in the Co-CdS QDs / MIL photocatalyst prepared in Example 1 are shown in Figures a and b, respectively, as shown in Figure 1.

[0030] Figure 6 DMPO spin-trapping • O2 of the photocatalyst prepared in Example 1 and Comparative Examples 1 to 4 − Electron paramagnetic resonance spectrum of

[0031] Figure 7 The activity diagram of ammonia decomposition and hydrogen production of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4;

[0032] Figure 8 This is a cycle experiment diagram of the photocatalyst prepared in Example 1;

[0033] Figure 9 Graphs showing the hydrogen production rates of control experiments of photocatalytic ammonia decomposition reactions conducted under dark conditions, without catalyst, and without NH3. DETAILED DESCRIPTION

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

[0035] Example 1

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

[0037] (1) Co-CdS QDs were synthesized by a hydrothermal method. 92 mg of Cd(CH3COO)2·2H2O and 4.6 mg of CoCl2·6H2O were dispersed in 10 mL of ethanol and stirred continuously for 20 min. The solution was then ultrasonicated for 10 min. The solution was then 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. The mixture was reacted at 353 K for another 1 h. The sample was separated by filtration and dried in vacuum to obtain Co-CdS QDs.

[0038] (2) MIL was synthesized by a hydrothermal method. 1.576 g Al(NO3)3·9H2O and 1.112 g H2N-H2BDC were dissolved in 60 mL DMF, stirred at room temperature, and then transferred to a 100 mL polytetrafluoroethylene-lined autoclave for reaction at 423 K for 12 h. After the reaction, the mixture was slowly cooled to room temperature, and the product was washed with DMF. The product was then redispersed in 50 mL DMF and treated at 423 K for another 6 h. Finally, the mixture was washed with acetone several times and dried in vacuum at 373 K overnight 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 for 1 h. After the reaction, the product was filtered and washed with water and ethanol several times, and then dried in vacuum at 333 K for 12 h to obtain the final product, Co-CdS QDs / MIL.

[0040] Example 2

[0041] A Z-type heterojunction photocatalyst constructed with an N-Co-S electronic 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 stirred continuously for 20 min. The solution was then ultrasonicated for 10 min. The solution was then 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. The mixture was reacted at 353 K for another 1 h. The sample was separated by filtration and dried in vacuum to obtain Co-CdS QDs.

[0043] (2) MIL was synthesized by a hydrothermal method. 1.4184 g Al(NO3)3·9H2O and 1.0 g H2N-H2BDC were dissolved in 54 mL DMF, stirred evenly at room temperature, and then transferred to a 100 mL polytetrafluoroethylene-lined autoclave for reaction at 423 K for 12 h. After the reaction, the mixture was slowly cooled to room temperature, and the product was washed with DMF. The product was then redispersed in 60 mL DMF and treated at 423 K for another 6 h. Finally, it was washed with acetone several times and dried in vacuum 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 for 1 h. After the reaction, the product was filtered and washed with water and ethanol several times, and then dried in vacuum at 333 K for 12 h to obtain the final product, Co-CdS QDs / MIL.

[0045] Comparative Example 1

[0046] A method for preparing a photocatalyst (CdS QDs) is disclosed. The method comprises a hydrothermal method in which 92 mg of Cd(CH3COO)2·2H2O is dispersed in 10 mL of ethanol and stirred continuously for 20 minutes. The solution is then ultrasonicated for 10 minutes. The solution is then placed in a beaker and heated to 353 K. After the temperature stabilizes, 10 mL of a 0.03 mol / L thioacetamide solution is added dropwise. The reaction is continued at 80°C for another 1 hour. The sample is then filtered and separated, and vacuum dried 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 method for preparing a photocatalyst (MIL) is the same as that in Example 1.

[0051] Comparative Example 4

[0052] A method for preparing a photocatalyst CdS QDs / MIL is disclosed. The MIL and CdS QDs are prepared by a hydrothermal method as in Example 1. 40 mg of the synthesized MIL and 20 mg of the synthesized CdS QDs are dispersed in a mixture of 40 mL of ethanol and 20 mL of water and uniformly dispersed under stirring. The mixed solution is then heated to 353 K for 1 hour. After the reaction, the product is filtered and washed multiple times with water and ethanol. Finally, the product is dried in vacuo at 333 K for 12 hours to obtain the final product, CdS QDs / MIL.

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

[0054] The photocatalyst Co-CdS QDs / MIL prepared in Example 1 was scanned by a transmission electron microscope with spherical aberration correction. Figure 2 As shown in Figure a, a single Co atom can be directly observed to be stably anchored on the surface of CdS QDs. The integrated pixel intensity of the rectangular area in Figure a is selected for quantitative analysis. The results are shown in Figure b, which confirms the atomic-level precise doping and integration of Co species in the heterogeneous interface.

[0055] The photocatalyst prepared in Example 1 and Co foil, CoS, and CoPc were tested by X-ray absorption near edge structure (XANES) and Fourier transform extended X-ray absorption fine structure (FT-EXAFS). Figure 3 (a) is the X-ray absorption near-edge structure spectrum, and (b) is the Fourier transform extended X-ray absorption fine structure spectrum. Analysis shows that the average oxidation state of Co species in Co-CdS QDs / MIL is between CoS and CoPc, and the Co atoms are in a heterogeneous coordination environment acted upon by N and S, proving the formation of an N–Co–S coordination structure.

[0056] The photocatalyst samples prepared in Example 1 and the comparative example were subjected to X-ray diffraction analysis. Figure 4 As 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] The X-ray photoelectron spectroscopy of N atoms and S atoms in the Co-CdS QDs / MIL photocatalyst prepared in Example 1 was analyzed. Figure 5 As shown in Figure 1, it can be seen from a that the N–Co bond was observed in the X-ray photoelectron spectrometer of the N atom, and from b, it can be seen that the S–Co bond was observed in the X-ray photoelectron spectrometer spectrum of the S atom, proving that the N–Co–S structure really exists.

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

[0059] Application Examples

[0060] Implementation 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 weighed and placed in a quartz glass reactor. 100 sccm NH3 was used as the reaction gas. A 300 W xenon lamp (light intensity 3 W·cm −2 ) was used as the light source. Before the reaction began, 15 miM of NH3 was continuously introduced into the reactor, and then illumination was initiated. The reaction products were analyzed by gas chromatography (GC 9790Ⅱ), and the gas composition was determined using a TCD detector.

[0061] Figure 7The activity diagram of ammonia decomposition and hydrogen production of the photocatalysts prepared in Example 1 and Comparative Examples 1 to 4 shows that the photocatalytic hydrogen production efficiency of the Co-CdS QDs / MIL prepared in Example 1 is significantly higher than that of the comparative examples, with a hydrogen production rate of up to 18 μmol·g −1 ·s −1 .

[0062] The photocatalyst prepared in Example 1 was subjected to a catalytic cycle experiment. The results are as follows: Figure 8 As shown in the figure, it can be seen that after 20 hours of circulation, the hydrogen production rate is still maintained at 18 μmol·g −1 ·s −1 .

[0063] The photocatalytic ammonia decomposition reaction control test was carried out under the experimental conditions of darkness, no catalyst, and no NH3 (using only Ar). Other conditions were the same as those in the application example. The photocatalytic hydrogen production efficiency was as follows: Figure 9 As shown in the figure, it can be seen that the hydrogen production rates under dark conditions, without catalyst and without 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 Co-CdS QDs / MIL catalyst, NH3 and light irradiation conditions in the photocatalytic reaction are clarified.

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

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

[0066]

[0067] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. Application of a Z-type heterojunction photocatalyst constructed with an N-Co-S electronic bridge in a photocatalytic ammonia decomposition reaction, characterized in that: The steps of preparing the catalyst are as follows: (1) Cd(CH3COO)2·2H2O and CoCl2·6H2O with a mass ratio of 18-22:1 were dispersed in ethanol and stirred evenly by ultrasonication. The mixture was heated to 343-363 K. After the temperature stabilized, 0.03-0.05 mol / L thioacetamide solution was added dropwise. The mixture was reacted at 343-363 K for 1-2 h. The mixture was separated by filtration and dried in vacuum to obtain Co-CdS QDs. (2) Al(NO3)3·9H2O and H2N-H2BDC were dissolved in DMF at a mass ratio of 1-2:1-2, stirred at room temperature, and then transferred to a high-pressure reactor for reaction at 420-425 K for 10-14 h. After the reaction, the mixture was cooled to room temperature to obtain the product, which was washed with DMF. The product was then dispersed in DMF and further treated at 420-425 K for 5-8 h, washed, and vacuum dried to obtain the final product MIL. (3) MIL and Co-CdS QDs with a mass ratio of 1-3:1 were dispersed in a mixed solution of ethanol and water, stirred evenly, heated to 343-363 K for 1-2 h, filtered, washed, and vacuum dried to obtain a Z-type heterojunction photocatalyst constructed with an N-Co-S electron bridge.

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

3. The use according to claim 1, characterized in that The volume ratio of the ethanol to the thioacetamide solution is 1-2:1-2.

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

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

1.

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

7. The use according to claim 1, characterized in that The Z-type heterojunction photocatalyst was placed in a quartz glass reactor at 24-26 °C, with 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, 15-20 miM of NH3 was continuously introduced into the reactor, and then the illumination was started. The reaction products were analyzed by gas chromatography, and the gas composition was determined by TCD detector.

Images