Porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect as well as preparation method and application of porphyrin single molecule / hydrotalcite composite material

Abstract

The invention discloses a porphyrin single molecule / hydrotalcite composite material with a built-in electric field enhancement effect as well as a preparation method and application of the porphyrin single molecule / hydrotalcite composite material. Through a novel supramolecular assembly strategy combining electrostatic interaction and hydrogen-bond interaction, porphyrin monomolecules are assembled on two-dimensional matrix hydrotalcite to construct a porphyrin monomolecule / hydrotalcite junction. The porphyrin single molecule / hydrotalcite junction can obviously increase the contact surface of the photocatalyst, the porphyrin single molecule and hydrotalcite are tightly bonded, the interface action is strong, the constructed porphyrin single molecule / hydrotalcite junction is beneficial to establishment of an effective interface BEF, photon-generated carrier separation is greatly promoted, and the overall photocatalytic performance is improved; meanwhile, the electron structure of the active site of the catalyst can be adjusted through the strong interface BEF, the adsorption and desorption process of an intermediate is optimized, and high-selectivity conversion of CO2 is facilitated; more importantly, the strong interface BEF effect can greatly reduce the energy barrier of the photocatalytic CO2 reduction reaction speed control step, so that CO2 reduction is easier.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and particularly relates to a porphyrin single molecule / hydrotalcite composite material with an enhanced built-in electric field effect, a preparation method thereof, and an application thereof. Background Art

[0002] With economic growth, the overuse of non-renewable fossil energy by humans has led to an energy crisis and huge CO 2 emissions. The increase in the content of CO 2 in the atmosphere has caused many problems, including sea level rise, global warming, and climate change, endangering human health. To solve the above problems, it is urgent to develop advanced technologies to convert CO 2 into chemical fuels with significant added value to maintain the balance between energy and the environment. Currently, researchers have developed some important strategies, such as traditional thermochemical, electrochemical, and photocatalytic technologies. Among them, thermochemical and electrochemical CO 2 conversion requires energy consumption and increases costs; at the same time, electrochemical CO 2 reduction is often accompanied by hydrogen production from water decomposition, affecting the purity of reaction products. Photocatalysis has a series of advantages such as mild reaction conditions, simple system structure, no need for additional power input, low operating cost, and green sustainability, and has attracted much attention in recent years.

[0003] Photocatalytic reduction of CO 2 is essentially an oxidation-reduction reaction process under the action of photons, and the reaction involves a complex multi-electron reduction process. Although various photocatalysts have been developed currently, due to problems such as low efficiency, low selectivity, and poor stability, the development of the field of photocatalytic CO 2 reduction has been severely hindered. Therefore, new types of efficient catalysts should continue to be developed to achieve higher conversion efficiency. Most semiconductor photocatalysts have the disadvantages of high recombination and inactivation of photo-generated carriers during the photocatalytic CO 2 reduction process, which greatly limits the conversion efficiency of CO 2 . When carriers cannot migrate to the catalyst surface within a short time, electrons will quickly return to the valence band to recombine with holes. The rapid migration of carriers is beneficial to promoting the separation and transfer of photo-generated carriers and ensuring that more photo-generated electrons migrate to the semiconductor surface to quickly occur reactions. Therefore, the design and optimization of the surface electronic state and carrier dynamics of semiconductor photocatalysts are crucial for improving photocatalytic CO 2Reduction performance is particularly crucial. By reducing the diffusion distance of photo-generated carriers or constructing an interfacial electric field (BEF), the recombination of electrons and holes can be effectively reduced. The BEF can significantly enhance photocatalysis by promoting the separation of charges in the spatial domain, reducing the recombination of photo-generated charges, and facilitating electron transfer. The currently widely adopted method for constructing BEF is to construct heterojunctions. However, the limited contact area and weak interfacial bonding of most heterojunctions hinder the formation of BEF and effective charge transfer at the interface. Summary of the Invention

[0004] Aiming at the problems of low intrinsic activity, poor stability, low separation efficiency of photo-generated carriers, low selectivity and yield of photocatalytic products in the prior art, the present invention provides a porphyrin single molecule / magnesium aluminum layered double hydroxide composite material with an enhanced built-in electric field effect, a preparation method thereof, and an application thereof. Through a novel supramolecular assembly strategy that combines electrostatic interaction and hydrogen bond interaction, porphyrin single molecules are assembled onto a two-dimensional matrix of magnesium aluminum layered double hydroxide to construct a porphyrin single molecule / magnesium aluminum layered double hydroxide junction. This supramolecular assembly technology can avoid many problems of traditional chemical synthesis and has advantages such as a simple synthesis process, low cost, easy large-scale production, and stable structural integrity. The porphyrin single molecule / magnesium aluminum layered double hydroxide junction can significantly increase the contact surface of the photocatalyst, and the porphyrin single molecule is tightly bonded to the magnesium aluminum layered double hydroxide with strong interfacial interaction. The constructed porphyrin single molecule / magnesium aluminum layered double hydroxide junction is conducive to establishing an effective BEF, greatly promoting the separation of photo-generated carriers, and improving the overall photocatalytic performance; at the same time, the strong interfacial BEF can adjust the electronic structure of the active sites of the catalyst, optimize the adsorption and desorption process of intermediates, and is conducive to the high-selectivity conversion of CO 2 ; more importantly, the strong interfacial BEF effect can greatly reduce the energy barrier of the rate-determining step of the photocatalytic CO 2 reduction reaction, which makes the CO 2 reduction easier and can greatly increase the chemical fuel production.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention: provides a preparation method of a porphyrin single molecule / magnesium aluminum layered double hydroxide composite material with an enhanced built-in electric field effect, including the following steps:

[0007] First, synthesize carbonate-intercalated magnesium aluminum layered double hydroxide; then, use nitrate to replace carbonate through an ion exchange method to obtain nitrate-intercalated magnesium aluminum layered double hydroxide; then, exfoliate the nitrate-intercalated magnesium aluminum layered double hydroxide to obtain a colloidal solution of nitrate-intercalated magnesium aluminum layered double hydroxide, and then add porphyrin single molecules for self-assembly to obtain a porphyrin single molecule / magnesium aluminum layered double hydroxide composite material with an enhanced built-in electric field effect.

[0008] The reason for using nitrate to replace carbonate in the present invention is as follows: The interaction force between carbonate ions and the lamellar is very strong, and it is difficult to break the interlayer interaction force to strip into LDH lamellae. After replacing with nitrate, the interaction force is greatly weakened, and it can be stripped into hydrotalcite lamellae in the dispersion medium to form a colloidal solution.

[0009] Preferably, the bimetallic combination of the carbonate-intercalated hydrotalcite is nickel-aluminum or nickel-iron.

[0010] More preferably, when preparing nickel-aluminum carbonate-intercalated hydrotalcite, the molar ratio of Ni 2+ and Al 3+ is 3:1 to 1:1; when preparing nickel-iron carbonate-intercalated hydrotalcite, the molar ratio of Ni 2+ and Fe 3+ is 5:1 to 3:1.

[0011] Preferably, concentrated nitric acid is used to provide nitrate in the ion exchange method, and the dosage ratio of the concentrated nitric acid to the carbonate-intercalated hydrotalcite is 0.6 to 1.0 mL:1 g.

[0012] This concentration is more conducive to replacing the carbonate ions with stronger affinity between the hydrotalcite layers, inducing the formation of nitrate-intercalated hydrotalcite, and at the same time avoiding the damage to the hydrotalcite lamellar structure by the over-acidic environment.

[0013] Preferably, the solvent used for stripping is formamide.

[0014] Preferably, the porphyrin single-molecule raw materials include: tetrakis(4-carboxyphenyl)porphyrin (TCPP), tetrakis(4-carboxyphenyl)zinc porphyrin (ZnTCPP), tetrakis(4-carboxyphenyl)nickel porphyrin (NiTCPP), or tetrakis(4-carboxyphenyl)manganese porphyrin (MnTCPP).

[0015] Preferably, the porphyrin single molecule is added in the form of being dissolved in an alkaline solution with a pH of 9 to 10.

[0016] Preferably, the mass ratio of the porphyrin single molecule to the nitrate-intercalated hydrotalcite in the colloidal solution of the nitrate-intercalated hydrotalcite is 0.15 to 0.45:1.

[0017] Preferably, in the stripping and self-assembly steps, an operation to exclude CO 2 that interferes with the stripping or self-assembly is included. For example, using N 2 or Ar 2 for purging can avoid the stacking and sedimentation of the stripped hydrotalcite lamellae.

[0018] The second technical solution of the present invention: Provide a porphyrin single molecule / hydrotalcite composite material with an enhanced built-in electric field effect prepared by the preparation method of the above-mentioned porphyrin single molecule / hydrotalcite composite material with an enhanced built-in electric field effect.

[0019] The third technical solution of the present invention: Provide an application of the above-mentioned porphyrin single molecule / hydrotalcite composite material with an enhanced built-in electric field effect in photocatalytic reduction of CO 2 in.

[0020] The beneficial technical effects of the present invention are as follows:

[0021] The BEF of the porphyrin single molecule / hydrotalcite composite material provided by the present invention has a bifunctional effect. It not only accelerates the transfer of photo-generated carriers from the photosensitizer to the supramolecular assembly, but also enhances the inherent activity of the supramolecular assembly by regulating the electronic structure of the active sites. The lattice structure of the hydrotalcite in the porphyrin single molecule / hydrotalcite composite material is also distorted, with a specific electronic structure. The charge redistribution increases the density of states near the Fermi level, resulting in an increase in the conductivity of the assembled supramolecular structure and optimizing its adsorption and desorption process of reaction intermediates, thereby realizing the efficient and highly selective conversion of CO 2 The design idea can provide a new perspective for improving photocatalytic performance by using molecular / two-dimensional matrix junctions to induce interfacial electric fields. Brief Description of the Drawings

[0022] Figure 1 XRD pattern of NiAl-ZnTCPP prepared in Example 1.

[0023] Figure 2 Transmission electron micrograph of NiAl-ZnTCPP prepared in Example 1.

[0024] Figure 3 Transmission electron micrograph of NiAl-ZnTCPP prepared in Example 1.

[0025] Figure 4 Transmission electron micrograph of NiAl-ZnTCPP prepared in Example 1.

[0026] Figure 5 XRD pattern of NiFe-MnTCPP prepared in Example 2.

[0027] Figure 6 Transmission electron micrograph of NiFe-MnTCPP prepared in Example 2.

[0028] Figure 7 Transmission electron micrograph of NiFe-MnTCPP prepared in Example 2.

[0029] Figure 8Isotope detection spectrum with NiAl-ZnTCPP prepared in Example 1 as the photocatalyst.

[0030] Figure 9 Four-cycle stability test chart with NiAl-ZnTCPP prepared in Example 1 as the photocatalyst.

[0031] Figure 10 Photocurrent curve measured by a three-electrode system in a sodium sulfate solution under simulated solar light irradiation for NiAl-ZnTCPP prepared in Example 1 and NiAl-LDH prepared in Comparative Example 1.

[0032] Figure 11 For NiAl-ZnTCPP prepared in Example 1 and NiAl-CO 3 -LDH, Electrochemical impedance Nyquist diagram tested in a sodium sulfate solution.

[0033] Figure 12 For NiAl-ZnTCPP prepared in Example 1 and NiAl-CO 3 -LDH, Surface photovoltage diagram. Detailed implementation mode

[0034] Now, various exemplary implementation modes of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms used in the present invention are only for describing specific implementation modes and are not used to limit the present invention.

[0035] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0036] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0037] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0038] Example 1

[0039] Preparation of Tetrakis(4-carboxyphenyl)zinc Porphyrin / NiAl Hydrotalcite (NiAl-ZnTCPP):

[0040] Weigh 0.3 g of Ni(NO 3 ) 2 ·6H 2 O, 0.15 g of Al(NO 3 ) 3 ·9H 2 O and 0.1 g of urea, dissolve them in 70 mL of deionized water to form a homogeneous solution. Put the solution into a stainless-steel container lined with Teflon and carry out a hydrothermal reaction at 110 °C for 24 h. After the reaction is completed, centrifuge the product and wash it 3 times with deionized water, then dry it in a vacuum oven at 60 °C for 24 h to obtain NiAl-CO 3 -LDH.

[0041] Disperse 1.0 g of the above-synthesized NiAl-CO 3 -LDH sample into 90 mL of methanol and stir vigorously at room temperature for several hours to form a suspension. Then add a mixed solution containing 615 μL of concentrated HNO 3 and 10 mL of methanol to the above suspension and stir continuously for 6 h. After centrifuging the product, wash it with methanol until the solution is neutral, and then dry it in a vacuum drying oven at 60 °C to obtain NiAl-NO 3 -LDH solid powder.

[0042] Mix 80 mg of the above NiAl-NO 3 -LDH with 80 mL of formamide in a conical beaker, cover it tightly after purging with N 2 . Stir the mixture vigorously for 2 days until the solid powder is uniformly dispersed and exfoliated into a colloidal state in the formamide solution.

[0043] Purify the above-exfoliated NiAl-NO 2 -LDH colloidal dispersion with N 3 to eliminate the interference of CO 2 in the atmosphere. Add 20 mL (1 mM) of the alkaline solution of ZnTCPP (pH = 9 - 10) to 80 mL of the LDH colloidal dispersion and stir for 2 hours. Centrifuge the precipitate, wash it with deionized water to completely remove the formamide. Dry it in a vacuum drying oven at 60 °C to obtain NiAl-ZnTCPP solid powder.

[0044] The XRD pattern of NiAl-ZnTCPP prepared in Example 1 is shown in Figure 1 . Figure 1It is shown that the NiAl-ZnTCPP assembly prepared in Example 1 has a hydrotalcite structure and no other diffraction peaks, indicating that ZnTCPP does not accumulate and crystallize significantly on the surface of NiAl-LDH, but binds to the surface of LDH in the form of molecules.

[0045] The transmission electron micrograph of NiAl-ZnTCPP prepared in Example 1 is shown in Figure 2 、 Figure 3 and Figure 4 . From Figure 2 and Figure 3 , it can be seen that the assembly structure is hexagonal, with a lateral dimension of about 200 nm and a thickness of about 10 nm; compared with the hydrotalcite synthesized by traditional methods (hydrothermal method, electrodeposition method, coprecipitation method, etc.), this exfoliated-assembled hydrotalcite has a larger specific surface area, which is more conducive to the mass transfer process in catalysis. From Figure 4 , it can be seen that the lattice fringes observed at 0.23 nm correspond to the characteristic (015) crystal plane of LDH, which is formed by the sharing of edges of nickel oxide and aluminum oxide octahedra within the NiAl-LDH lamellar; in addition, no additional lattice spacing is detected over a large range, which confirms that ZnTCPP does not accumulate or aggregate on the surface of hydrotalcite.

[0046] Example 2

[0047] Preparation of tetra(4-carboxyphenyl)manganese porphyrin / NiFe hydrotalcite (NiFe-MnTCPP):

[0048] Weigh 0.3 g of Ni(NO 3 ) 2 ·6H 2 O, 0.1 g of Fe(NO 3 ) 3 ·9H 2 O and 0.1 g of urea and dissolve them in 70 mL of deionized water to form a homogeneous solution. Put the solution into a stainless-steel container lined with Teflon and carry out hydrothermal reaction at 120 °C for 24 h. After the reaction is completed, centrifuge the product and wash it 3 times with deionized water, and dry it in a vacuum oven at 60 °C for 24 h to obtain NiFe-CO 3 -LDH.

[0049] Disperse 1.0 g of the above-synthesized NiFe-CO 3 -LDH sample into 90 mL of methanol and stir vigorously at room temperature for several hours to form a suspension. Then add a mixed solution containing 615 μL of concentrated HNO 3 and 10 mL of methanol to the above suspension and stir continuously for 6 h. After centrifuging the product, wash it with methanol until the solution is neutral, and dry it in a vacuum drying oven at 60 °C to obtain the NiFe-NO 3 -LDH solid powder.

[0050] Mix the above NiFe-NO 3 -LDH (80 mg) with 80 mL of formamide in a conical beaker, and cover it tightly after purging with N 2 . Stir the mixture vigorously for 2 days until the solid powder is uniformly dispersed and exfoliated into a colloidal state in the formamide solution.

[0051] Purge with N 2 to further purify the exfoliated NiFe-NO 3 -LDH colloidal dispersion to eliminate CO 2 interference in the atmosphere. Add 20 mL (1 mM) of the alkaline solution of Mn-TCPP (pH = 9 - 10) to 80 mL of the LDH colloidal dispersion and stir for 2 hours. Centrifuge the precipitate, wash it with deionized water to completely remove formamide. Dry it in a vacuum drying oven at 60 °C to obtain NiFe-MnTCPP solid powder.

[0052] The XRD pattern of NiFe-MnTCPP prepared in Example 2 is shown in Figure 5 . Figure 5 It shows that the NiFe-MnTCPP assembly prepared in Example 5 has a hydrotalcite structure and no other diffraction peaks, indicating that MnTCPP does not accumulate and crystallize significantly on the surface of NiFe-LDH, but binds to the surface of LDH in the form of molecules.

[0053] The transmission electron micrograph of NiFe-MnTCPP prepared in Example 2 is shown in Figure 6 and Figure 7 . It can be seen from Figure 6 that the assembly has a hexagonal flake structure with a lateral size of about 50 nm. Compared with the hydrotalcite synthesized by traditional methods (hydrothermal method, electrodeposition method, coprecipitation method, etc.), this exfoliated-assembled hydrotalcite has a larger specific surface area, which is more conducive to the mass transfer process in catalysis. It can be seen from Figure 7 that the lattice fringes observed at 0.23 nm correspond to the characteristic (015) crystal plane of LDH, which is formed by the sharing of edges of nickel oxide and iron oxide octahedra within the NiFe-LDH layer; in addition, no additional lattice spacing is detected in a large range, which confirms that MnTCPP does not accumulate or aggregate on the surface of the hydrotalcite.

[0054] Example 3

[0055] Preparation of tetra(4-carboxyphenyl)porphyrin / NiAl hydrotalcite (NiAl-TCPP):

[0056] Weigh 0.3 g of Ni(NO 3 ) 2 ·6H 2O, 0.15 g of Al(NO 3 ) 3 ·9H 2 O and 0.1 g of urea were dissolved in 70 mL of deionized water to form a homogeneous solution. The solution was placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 110 °C for 24 h. After the reaction was completed, the product was centrifuged and washed 3 times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain NiAl-CO 3 -LDH.

[0057] 1.0 g of the synthesized NiAl-CO 3 -LDH sample was dispersed in 90 mL of methanol and vigorously stirred at room temperature for several hours to form a suspension. Then, a mixed solution containing 615 μL of concentrated HNO 3 and 10 mL of methanol was added to the above suspension and continuously stirred for 6 h. After centrifugation, the product was washed with methanol until the solution was neutral, and then dried in a vacuum drying oven at 60 °C to obtain NiAl-NO 3 -LDH solid powder.

[0058] The above NiAl-NO 3 -LDH (80 mg) was mixed with 80 mL of formamide in a conical beaker, purged with N 2 and then covered tightly. The mixture was vigorously stirred for 2 days until the solid powder was uniformly dispersed and exfoliated into a colloidal state in the formamide solution.

[0059] Using N 2 to further purify the above exfoliated NiAl-NO 3 -LDH colloidal dispersion to eliminate the interference of CO 2 in the atmosphere. 20 mL (1 mM) of the alkaline solution of TCPP (pH = 9 - 10) was added to 80 mL of the LDH colloidal dispersion and stirred for 2 hours. The precipitate was centrifuged and washed with deionized water to completely remove formamide. It was dried in a vacuum drying oven at 60 °C to obtain NiAl-TCPP solid powder.

[0060] Example 4

[0061] Preparation of nickel tetrakis(4-carboxyphenyl)porphyrin / NiAl hydrotalcite (NiAl-NiTCPP):

[0062] Weigh 0.3 g of Ni(NO 3 ) 2 ·6H 2 O, 0.15 g of Al(NO 3 ) 3 ·9H 20.3 g of Ni(NO₃)₂·6H₂O and 0.1 g of urea were dissolved in 70 mL of deionized water to form a homogeneous solution. The solution was placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 110 °C for 24 h. After the reaction was completed, the product was centrifuged and washed 3 times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain NiAl-CO 3 -LDH.

[0063] 1.0 g of the as-synthesized NiAl-CO 3 -LDH sample was dispersed in 90 mL of methanol and vigorously stirred at room temperature for several hours to form a suspension. Then, a mixed solution containing 615 μL of concentrated HNO₃ 3 and 10 mL of methanol was added to the above suspension, and the mixture was continuously stirred for 6 h. After centrifugation, the product was washed with methanol until the solution was neutral, and then dried in a vacuum drying oven at 60 °C to obtain NiAl-NO 3 -LDH solid powder.

[0064] The above NiAl-NO 3 -LDH (80 mg) was mixed with 80 mL of formamide in a conical beaker, and after purging with N₂ 2 and covering it tightly. The mixture was vigorously stirred for 2 days until the solid powder was uniformly dispersed and exfoliated into a colloidal state in the formamide solution.

[0065] The exfoliated NiAl-NO 2 -LDH colloidal dispersion was further purified with N₂ 3 to eliminate the interference of CO₂ 2 in the atmosphere. 20 mL (1 mM) of the basic solution of Ni-TCPP (pH = 9 - 10) was added to 80 mL of the LDH colloidal dispersion and stirred for 2 h. The precipitate was centrifuged and washed with deionized water to completely remove formamide. It was dried in a vacuum drying oven at 60 °C to obtain NiAl-NiTCPP solid powder.

[0066] Example 5

[0067] Preparation of tetra(4-carboxyphenyl)manganese porphyrin / NiAl hydrotalcite (NiAl-MnTCPP):

[0068] Weigh 0.3 g of Ni(NO₃)₂ 3 ·6H₂O and 0.15 g of Al(NO₃)₃ 2 ·9H₂O 2 O, 0.15 g of Al(NO₃)₃ 3 ·9H₂O 3 ·9H₂O 20.3 g of Ni(NO₃)₂·6H₂O and 0.1 g of urea were dissolved in 70 mL of deionized water to form a homogeneous solution. The solution was placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 110 °C for 24 h. After the reaction was completed, the product was centrifuged and washed 3 times with deionized water, and then dried in a vacuum oven at 60 °C for 24 h to obtain NiAl-CO 3 -LDH.

[0069] 1.0 g of the synthesized NiAl-CO 3 -LDH sample was dispersed in 90 mL of methanol and vigorously stirred at room temperature for several hours to form a suspension. Then, a mixed solution containing 615 μL of concentrated HNO₃ 3 and 10 mL of methanol was added to the above suspension, and the mixture was continuously stirred for 6 h. After centrifugation, the product was washed with methanol until the solution was neutral, and then dried in a vacuum drying oven at 60 °C to obtain NiAl-NO 3 -LDH solid powder.

[0070] 80 mg of the above NiAl-NO 3 -LDH was mixed with 80 mL of formamide in a conical beaker, and then purged with N₂ 2 and covered tightly. The mixture was vigorously stirred for 2 days until the solid powder was uniformly dispersed and exfoliated into a colloidal state in the formamide solution.

[0071] The exfoliated NiAl-NO 2 -LDH colloidal dispersion was further purified with N₂ 3 to eliminate the interference of CO₂ 2 in the atmosphere. 20 mL (1 mM) of the alkaline solution of Mn-TCPP (pH = 9 - 10) was added to 80 mL of the LDH colloidal dispersion and stirred for 2 h. The precipitate was centrifuged and washed with deionized water to completely remove formamide. Then it was dried in a vacuum drying oven at 60 °C to obtain NiAl-MnTCPP solid powder.

[0072] Comparative Example 1

[0073] Preparation of NiAl hydrotalcite (NiAl-CO 3 -LDH):

[0074] Weigh 0.3 g of Ni(NO₃)₂ 3 ·6H₂O and 0.15 g of Al(NO₃)₃ 2 ·9H₂O 2 O, 0.15 g of Al(NO₃)₃ 3 ·9H₂O 3 ·9H₂O 20.3 g of Ni(NO₃)₂·6H₂O, 0.1 g of urea are dissolved in 70 mL of deionized water to form a homogeneous solution. The solution is placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 110 °C for 24 h. After the reaction is completed, the product is centrifuged and washed 3 times with deionized water, and dried in a vacuum oven at 60 °C for 24 h to obtain NiAl-CO 3 -LDH.

[0075] Comparative Example 2

[0076] Preparation of NiFe hydrotalcite (NiFe-CO 3 -LDH):

[0077] Weigh 0.3 g of Ni(NO₃)₂·6H₂O, 0.1 g of Fe(NO₃)₃·9H₂O and 0.1 g of urea and dissolve them in 70 mL of deionized water to form a homogeneous solution. The solution is placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 120 °C for 24 h. After the reaction is completed, the product is centrifuged and washed 3 times with deionized water, and dried in a vacuum oven at 60 °C for 24 h to obtain NiFe-CO 3 ) 2 ·6H 2 O, 0.1 g of Fe(NO₃)₃·9H₂O and 0.1 g of urea are dissolved in 70 mL of deionized water to form a homogeneous solution. The solution is placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 120 °C for 24 h. After the reaction is completed, the product is centrifuged and washed 3 times with deionized water, and dried in a vacuum oven at 60 °C for 24 h to obtain NiFe-CO 3 ) 3 ·9H 2 O and 0.1 g of urea are dissolved in 70 mL of deionized water to form a homogeneous solution. The solution is placed in a stainless-steel container lined with Teflon and hydrothermally reacted at 120 °C for 24 h. After the reaction is completed, the product is centrifuged and washed 3 times with deionized water, and dried in a vacuum oven at 60 °C for 24 h to obtain NiFe-CO 3 -LDH.

[0078] Comparative Example 3

[0079] TCPP is directly purchased from Aladdin.

[0080] Comparative Example 4

[0081] Preparation of zinc tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP):

[0082] 0.15 g of TCPP is heated and dissolved in 12 mL of 0.1 M sodium hydroxide solution, then 62.4 mg of zinc acetate is added, and the mixture is refluxed at 120 °C for 2 h. After cooling to room temperature, the reaction solution is quickly added to 100 mL of deionized water containing 100 μL of concentrated hydrochloric acid and 72.89 mg, and stirred at room temperature and in the dark for 20 h; the product is centrifuged, washed, and dried in a vacuum oven at 70 °C for 24 h to obtain ZnTCPP.

[0083] Comparative Example 5

[0084] Preparation of nickel tetrakis(4-carboxyphenyl)porphyrin (NiTCPP):

[0085] Dissolve 0.15 g of TCPP by heating in 12 mL of 0.1 M sodium hydroxide solution, then add 70.8 mg of nickel acetate. Reflux at 120 °C for 2 h. After cooling to room temperature, quickly add the reaction solution to 100 mL of deionized water containing 100 μL of concentrated hydrochloric acid and 72.89 mg. Stir at room temperature in the dark for 20 h; centrifuge and wash the product, and dry it in a vacuum oven at 70 °C for 24 h to obtain NiTCPP.

[0086] Comparative Example 6

[0087] Preparation of manganese tetrakis(4-carboxyphenyl)porphyrin (MnTCPP):

[0088] Dissolve 0.15 g of TCPP by heating in 12 mL of 0.1 M sodium hydroxide solution, then add 56.3 mg of manganese chloride. Reflux at 120 °C for 2 h. After cooling to room temperature, quickly add the reaction solution to 100 mL of deionized water containing 100 μL of concentrated hydrochloric acid and 72.89 mg. Stir at room temperature in the dark for 20 h; centrifuge and wash the product, and dry it in a vacuum oven at 70 °C for 24 h to obtain MnTCPP.

[0089] Each metal porphyrin used in the examples was also prepared by the methods of Comparative Examples 4 to 6.

[0090] Test Example

[0091] Using the samples of Examples 1 to 5 and Comparative Examples 1 to 6 as photocatalysts respectively, carry out CO 2 reduction photocatalytic experiments in a 50 mL special photoreactor. The reaction system mainly consists of 10 mg of catalyst, 0.005 mmol of photosensitizer (ruthenium terpyridine) dissolved in 6 mL of acetonitrile, and 2 mL of sacrificial agent (triethanolamine). The experimental process includes three steps. First, connect the reactor containing all reaction components to a vacuum pump and CO 2 gas, and carry out three cycles of evacuation and gas filling to make the pressure reach 1.8 bar. Second, irradiate the reactor with visible light (λ > 400 nm) using a 300 W xenon lamp. Finally, after irradiation for 1 h, collect the gas-phase products and inject them into a gas chromatograph for analysis. The types, yields, and selectivities of the photocatalytic products of all example samples are shown in Table 1. The types, yields, and selectivities of the photocatalytic products of all comparative example samples are shown in Table 2.

[0092] Table 1

[0093]

[0094]

[0095] Table 2

[0096]

[0097] The results in Table 1 and Table 2 show that compared with the unassembled monomeric catalysts, the assembled catalysts with the BEF effect all show an enhanced photocatalytic CO 2 efficiency phenomenon. This highlights the universality of the enhanced activity of single-molecule metal TCPP / LDH assemblies.

[0098] Using 13 CO 2 and 12 CO 2 as reactant gases, photocatalysis was carried out according to the method of the reference test example, and the products were detected by mass spectrometry. The isotope detection spectrum of the NiAl-ZnTCPP prepared in Example 1 as the photocatalyst is shown in Figure 8 .

[0099] As can be seen from Figure 8 , when 13 CO 2 is used as the reactant gas, a peak corresponding to 13 CO is detected at m / z = 29; in addition, the peak at m / z = 13 corresponds to 13 CO 2 produced 13 C. It should be noted that the fragment peaks related to 13 CO are significantly shifted relative to the fragment peaks from conventional 12 CO. This evidence confirms that 2 CO is the carbon source of the reaction. The above conclusions also hold for the samples prepared in Examples 2 to 5.

[0100] Four photocatalytic cycle experiments were carried out using the samples prepared in Examples 1 to 5 as photocatalysts. The four-cycle stability test chart of the NiAl-ZnTCPP prepared in Example 1 as the photocatalyst is shown in Figure 9 .

[0101] As Figure 9 shown, after four cycles, there are no obvious changes in the selectivity and yield of photocatalytic CO 2 reduction to produce chemical fuels. The above conclusions also hold for the samples prepared in Examples 2 to 5.

[0102] Using an electrochemical workstation and a three-electrode system, the porphyrin single molecule / hydrotalcite assembly prepared in Example 1 and the hydrotalcite prepared in Comparative Example 1 were used as the working electrodes, the Pt electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The electrolyte was Na 2 SO 4 , and electrochemical tests were carried out and compared. The electrochemical tests mainly included: photocurrent test and electrochemical impedance test of the prepared porphyrin single molecule / hydrotalcite assembly.

[0103] The NiAl-ZnTCPP prepared in Example 1 and the NiAl-CO prepared in Comparative Example 1 3 -LDH, the photocurrent curves measured in a three-electrode system in a sodium sulfate solution under simulated solar light irradiation are shown in Figure 10 .

[0104] Figure 10 Show that the samples prepared in Example 1 and Comparative Example 1 both show transient photocurrent responses during repeated light on / off cycles. In contrast, the photocurrent response of the sample prepared in Example 1 is stronger, which highlights the key role of the BEF effect in promoting charge transfer.

[0105] The NiAl-ZnTCPP prepared in Example 1 and the NiAl-CO prepared in Comparative Example 1 3 -LDH, the Nyquist plot of the electrochemical impedance measured in a sodium sulfate solution is shown in Figure 11 .

[0106] Figure 11 Show that the sample prepared in Example 1 has a smaller arc radius, which means a smaller charge transfer resistance, indicating that the assembly prepared by the preparation method of the present invention has a stronger charge transport ability.

[0107] The NiAl-ZnTCPP prepared in Example 1 and the NiAl-CO prepared in Comparative Example 1 3 -LDH, the surface photovoltage map is shown in Figure 12 .

[0108] Figure 12 Show that the sample prepared in Example 1 has a stronger surface photovoltage (SPV) signal. And the more obvious SPV signal usually represents a higher carrier separation efficiency, indicating that the sample prepared in Example 1 can significantly promote the interfacial charge transfer process and greatly increase the carrier transport efficiency.

[0109] The porphyrin single molecule / hydrotalcite assembly formed by the present invention has high-quality interfacial contact, and a strong BEF pointing from the hydrotalcite to the porphyrin molecule is formed in the porphyrin single molecule / hydrotalcite supramolecular assembly. This strong BEF significantly enhances the photocatalytic CO 2 reduction activity and selectivity. Under visible light irradiation, the CO production yields of NiAl-ZnTCPP are 25 times and 5.6 times that of ZnTCPP and NiAl-CO 3 -LDH respectively, and the selectivity is as high as 98%; the CH production yields of NiFe-MnTCPP are 4 respectively those of MnTCPP and NiAl-CO 3- 10 times and 2.5 times of LDH, with a selectivity as high as 91%. In addition, BEF has a bifunctional effect. It not only accelerates the transfer of photo-generated carriers from the photosensitizer to the supramolecular assembly, but also enhances the inherent activity of the supramolecular assembly by regulating the electronic structure of the active sites. The lattice structure of the hydrotalcite in the porphyrin single molecule / hydrotalcite assembly is also distorted, with a specific electronic structure. The charge redistribution increases the density of states near the Fermi level, resulting in an increase in the conductivity of the assembled supramolecular structure and optimizing its adsorption and desorption process of reaction intermediates, thus realizing the 2 efficient and highly selective conversion. This design concept provides a new perspective for using the molecular / two-dimensional matrix junction to induce an interfacial electric field to improve the photocatalytic performance.

[0110] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a porphyrin single molecule / hydrotalcite composite material with a built-in electric field enhancement effect, characterized in that: The following steps are involved: First, carbonate intercalated hydrotalcite is synthesized; then, carbonate is replaced by nitrate by ion exchange to obtain nitrate intercalated hydrotalcite; then, the nitrate intercalated hydrotalcite is stripped to obtain a colloidal solution of nitrate intercalated hydrotalcite, and then porphyrin single molecules are added for self-assembly to obtain a porphyrin single molecule / hydrotalcite composite material with a built-in electric field enhancement effect.

2. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: The bimetallic combination of the carbonate intercalated hydrotalcite is nickel-aluminum or nickel-iron.

3. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 2, characterized in that: When preparing carbonate-intercalated nickel-aluminum hydrotalcite, Ni 2+ and Al 3+ The molar ratio of Ni is 3:1 to 1:1; when preparing carbonate-intercalated nickel-iron hydrotalcite, Ni 2+ and Fe 3+ The molar ratio is 5:1 to 3:

1.

4. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: In the ion exchange method, concentrated nitric acid is used to provide nitrate, and the usage ratio of the concentrated nitric acid to the carbonate-intercalated hydrotalcite is 0.6-1.0 mL:1 g.

5. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: The porphyrin monomolecular raw material includes: tetrakis(4-carboxyphenyl)porphyrin, tetrakis(4-carboxyphenyl)zincporphyrin, tetrakis(4-carboxyphenyl)nickelporphyrin or tetrakis(4-carboxyphenyl)manganeseporphyrin.

6. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: The porphyrin single molecule is added in the form of being dissolved in an alkaline solution.

7. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: The mass ratio of the porphyrin single molecule to the nitrate-intercalated hydrotalcite in the colloidal solution of the nitrate-intercalated hydrotalcite is 0.15-0.45:

1.

8. The method for preparing the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to claim 1, characterized in that: The stripping and self-assembly steps include an operation of eliminating the interference of CO2 on the stripping or the self-assembly.

9. A porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect obtained according to the method for preparing a porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect according to any one of claims 1 to 8.

10. Use of the porphyrin single molecule / hydrotalcite composite material with built-in electric field enhancement effect as claimed in claim 9 in photocatalytic reduction of CO2.

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