Electron-rich copper site layered supramolecular photocatalytic material as well as preparation and application thereof

Abstract

The invention discloses a supramolecular catalytic material containing uniform and electron-rich copper sites, a preparation method of the supramolecular catalytic material and application of the supramolecular catalytic material in photocatalytic reduction of carbon dioxide into ethane. According to the material, a pi-conjugated organic framework is self-assembled to form a layered structure, and copper and a carboxylic acid-containing ligand form a Cu-O4 coordination environment; the center-to-center distance R (Cu... Cu) of adjacent copper active sites is a powder X-ray diffraction pattern (radiated by Cu K alpha) and has an interlayer stacking characteristic peak at the position of 2theta = 25.2-26.4 degrees. The structure stabilizes a key intermediate and promotes C-C coupling through geometric and electronic dual regulation, so that ethane is selectively generated. Under representative conditions, the generation rate of ethane reaches 250.9 [mu] mol.g <-1 >. H <-1 >, and the electron selectivity is 85.5%. The method is simple and convenient, can be amplified, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic reduction of carbon dioxide, specifically to an organic supramolecular catalytic material containing uniform and electron-rich copper active sites, its preparation method, and its application in the photocatalytic reduction of carbon dioxide to ethane. Background Technology

[0002] Photocatalytic CO2 reduction (PCR) driven by solar energy is considered a potential pathway for coupling carbon cycling and energy storage. Performance evaluations in academia and engineering typically focus on product distribution (selectivity), product formation rate, apparent quantum efficiency (AQE), and solar-to-chemical energy conversion efficiency (SCC), supplemented by 13CO2 isotope tracing and durability / cycle stability testing to ensure comparability and verifiability. Existing research indicates that most photocatalytic systems more readily generate C1 products such as CO, HCOOH, and CH4; while the formation of C2 and higher (C2+) products requires multi-electron / multi-proton cooperative transfer and crucial C–C coupling, resulting in complex reaction pathways, numerous competing side reactions, and easy deactivation of intermediates, with the stable and directional formation of ethane being particularly challenging.

[0003] Among numerous candidate systems, copper-based active centers have attracted attention due to their ability to adsorb and stabilize *CO with moderate intensity, thereby promoting C–C coupling under certain conditions. However, existing copper sites are often heterogeneous in structure and electronic environment, and are prone to reconstruction or aggregation during illumination and reaction processes, leading to time-dependent drift in selectivity and rate. Meanwhile, the generation and transport of photogenerated carriers remain limited in some organic or hybrid frameworks, and electron-hole recombination restricts the electron flux required for deep hydrogenation. The spatial relationships (distance and orientation) between adjacent active sites are difficult to accurately construct and maintain over a long period at a characterizable scale, further exacerbating the uncertainty of the reaction pathway. Furthermore, mass transfer issues such as limited CO2 solubility and diffusion under gas-liquid-solid three-phase conditions, local pH fluctuations, and product precipitation also affect the continued advancement of the target pathway.

[0004] Supramolecular self-assembly and the layered stacking of π-conjugated organic frameworks offer the possibility of simultaneously controlling geometry and electronic structure at the molecular scale, potentially yielding reproducible coordination microenvironments and characterizable site geometry. However, publicly available technologies still lack material and structural paradigms capable of achieving sub-nanometer control over the geometric relationship between adjacent copper sites and maintaining stable transport channels under mild conditions, particularly for stable and efficient systems that selectively reduce CO2 to ethane. Therefore, the industry still needs to develop photocatalytic materials and construction strategies that achieve synergistic optimization among structural stability, site controllability, and carrier / mass transfer management to improve the selectivity and reproducible yield of C2+ (especially ethane). Summary of the Invention

[0005] Technical problems to be solved

[0006] This invention aims to provide a layered organic supramolecular photocatalytic material, its preparation method, and its applications. This material possesses uniform and electron-rich copper active sites, and the spacing between adjacent sites can be precisely defined to improve the generation rate and electron selectivity of the selective reduction of carbon dioxide to ethane.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In one aspect of the invention, a supramolecular photocatalytic material with a layered π-conjugated organic structure is provided, wherein copper and a carboxylic acid-containing ligand construct a Cu–O4 coordination environment; the central spacing R (Cu···Cu) between adjacent copper active sites is limited to [missing information]. The powder X-ray diffraction pattern (Cu Kα) shows characteristic peaks of interlayer stacking at 2θ = 25.2–26.4° (corresponding to interlayer spacing of 0.34–0.36 nm). Preferably, R(Cu···Cu) is... Extended X-ray absorption fine structure (EXAFS) fitting shows that the bond length of the first coordination shell of Cu–O is In X-ray photoelectron spectroscopy (XPS) tests, the binding energy of Cu 2p3 / 2 showed a negative shift of 0.2–0.8 eV compared to the unself-assembled coordination compound sample.

[0010] In another aspect of the invention, a method for preparing the material is provided: the material can be obtained through antisolvent-induced self-assembly. For example, a coordination precursor formed in an aqueous phase from a dicarboxylic acid ligand and divalent copper ions under pH 8–11 is dissolved in tetrahydrofuran and slowly added dropwise to methanol or ethanol for self-assembly for 2–6 hours, followed by separation and drying to obtain a layered material. Figure 1 As shown, this process consists of ligand source / and Cu 2+ Layered structures were obtained by coordination to form coordination precursors / antisolvent-induced self-assembly, corresponding to Examples 1–3.

[0011] In another aspect of the invention, a method is provided for using the material for photocatalytic CO2 reduction to prepare ethane: dispersing the material in water or a water / alcohol mixture in a closed reactor, introducing CO2 with a purity ≥99.9%, and reacting under ultraviolet-visible light irradiation; preferably using a 300W xenon lamp and adding triethanolamine as a sacrificial agent.

[0012] Beneficial effects

[0013] Compared with the closest technology, the present invention has the following advantages:

[0014] (1) Uniform and electron-rich copper sites are constructed through dual geometric and electronic regulation, and the spacing between adjacent sites is limited to a range that is conducive to C–C coupling. Preferred This enhances the stability and coupling ability of key intermediates such as *CO. Under representative light conditions, the ethane formation rate reaches 250.9 μmol·g⁻¹. -1 ·h -1 The electron selectivity is 85.5%; the ethane formation rate in an aqueous system is 18.9 μmol·g⁻¹. -1 ·h -1 It retains ≥90% of its initial activity after 10 cycles.

[0015] (2) The above results are supported by the structural-electronic evidence chain of "XRD-EXAFS-XPS three-in-one": XRD shows interlayer stacking characteristic peaks at 2θ=25.2–26.4° (d=0.34–0.36nm); EXAFS fitting shows the Cu–O first coordination shell bond length The controlled spacing R (Cu···Cu) between adjacent copper sites is given; XPS analysis shows a negative shift of 0.2–0.8 eV in Cu2p3 / 2 compared to the unself-assembled control sample, comprehensively demonstrating that the sites are uniform, electron-enriched, and consistent with the layered geometry. Figure 8 As shown in the schematic diagram of the reaction mechanism, the pathway for the promotion of *CO adsorption, activation and C–C coupling by the electron-rich copper sites is illustrated, demonstrating how the dual regulation of geometry and electronics can enhance ethane selectivity.

[0016] To avoid ambiguity, unless otherwise stated, all numerical ranges in this document include endpoints. Attached Figure Description

[0017] Figure 1 The material of this invention is a commercially available ligand and Cu 2+ A schematic diagram of the process for coordination to form a precursor and self-assembly to obtain a layered structure / film under antisolvent induction; this process corresponds sequentially to the steps of Examples 1–3.

[0018] Figure 2 The powder XRD pattern (Cu Kα) shows interlayer stacking characteristic peaks at 2θ = 25.2–26.4° (d = 0.34–0.36 nm).

[0019] Figure 3 The X-ray photoelectron spectroscopy (Cu 2p region) shows the changes in binding energy of the self-assembled sample before and after illumination, as well as the results for the control sample.

[0020] Figure 4 Schematic diagram of Cu K-edge EXAFS fitting results and local coordination structure: (a) XANES spectrum comparison: HCDS and reference samples (Cu foil, Cu2O, CuO); (b) k-space weighted oscillation spectrum. 3 χ(k); (c) R-space Fourier transform amplitude |FT(k) 3 χ(k))|(hollow dots represent experimental data, red line represents the fitted curve), the inset plot represents the local coordination structure model. The fitting uses the Hanning window function, with k ranging from... R range Amplitude reduction factor S0 2 =0.9, global energy displacement ΔE0 = 9.2eV; the corresponding fitting parameters are shown in Table 2.

[0021] Figure 5 The SEM / TEM images show the layered stacked structure and particle size distribution.

[0022] Figure 6 The optical and electrochemical characterization diagrams include UV–Vis DRS, transient photocurrent, EIS, and steady-state / transient PL.

[0023] Figure 7 The figures show the ethane formation rate and electron selectivity over time, along with cycle stability results: (a) C2H6 formation rate and electron selectivity of the sacrificial HCDS system; (b) C2H6 formation rate of the sacrificial HCDS system; (c) Cyclic stability of the sacrificial HCDS system (10 cycles); (d) C2H6 formation rate and electron selectivity of the pure water HCDS system. All other conditions are consistent with Example 5 unless otherwise specified.

[0024] Figure 8 This is a schematic diagram of the reaction mechanism, illustrating the pathway by which electron-rich copper sites promote *CO coupling.

[0025] Figure 9 This diagram illustrates step A (bromination at the 2,5-position of thiophene-3,4-dicarboxylic acid) in the ligand synthesis. Detailed Implementation

[0026] The following examples are for illustrative purposes only and are not intended to limit the scope of protection of the invention. Unless otherwise stated, percentages are by mass, temperatures are in Celsius (°C), and pressures are in standard atmospheres. Reagents used in the experiments were analytical grade and had not undergone further purification; the water used in the experiments was deionized water. Test methods and parameters followed conditions generally accepted in the art, or were specified in the relevant paragraphs.

[0027] Example 1: Ligand Source and Confirmation

[0028] The dicarboxylic acid ligand DDA used in this invention is a commercially available compound (purity ≥95%), which was purchased and then processed... 1 The results were confirmed by H NMR and FT-IR.

[0029] Example 2: Preparation of Coordination Precursors

[0030] The dicarboxylic acid ligand obtained in Example 1 was dissolved in deionized water, and triethylamine was added to adjust the pH to 8–11; copper sulfate pentahydrate was added, and the mixture was stirred at 500 rpm. -1 Stirring under certain conditions for 8 hours yielded a coordination precursor (denoted as SCDA), which was then separated into solid and liquid components and dried for later use.

[0031] Example 3: Self-assembly of layered supramolecular materials

[0032] The coordination precursor obtained in Example 2 was dissolved in tetrahydrofuran and slowly added dropwise to methanol with stirring. Self-assembly was carried out for 2–6 h. The mixture was then filtered and dried to obtain layered supramolecular material (denoted as HCDS) powder. The self-assembly temperature was 15–35 °C, and the dropping rate was 0.3–2.0 mL·min. -1 .

[0033] Example 4: Structure and Photophysical Characterization

[0034] Instruments and General Settings

[0035] XRD: Commercial X-ray powder diffractometer (e.g., Bruker D8 Advance or equivalent), Cu Kα Step size 0.02°, scan rate 2°·min -1 The 2θ scan range is 5–80°; 2θ is calibrated using high-purity Si standards (such as the NIST SRM 640 series).

[0036] XPS: Monochromatic Al Kα (hv = 1486.6 eV), channel energy 20 eV, beam spot approximately 400 μm; charge neutralization enabled; binding energy calibration using C1s = 284.8 eV as a reference. If the sample is an insulator, a low-energy electron / ion gun is used to suppress surface charging.

[0037] EXAFS / XANES: Tested at the copper k-edge (approximately 8979 eV); can be performed in a synchrotron radiation beamline or equivalent laboratory setup; data processing uses IFEFFIT (Athena / Artemis) or equivalent software, k-range R range Hanning window function, S0 2 =0.9; global ΔE0 = 9.2eV.

[0038] SEM / TEM: Field emission scanning electron microscope and transmission electron microscope (e.g., Zeiss or JEOL or equivalent), accelerating voltage 5–200 kV; sample is drop-coated onto conductive carrier or carbon film copper mesh with low loading.

[0039] UV–Vis DRS: Integrating sphere attachment, wavelength 300–900 nm, with BaSO4 as blank reference; PL (steady-state / transient) can be obtained using a fluorescence spectrometer or a transient absorption system, with excitation wavelength and bandwidth given in the figure caption.

[0040] Electrochemistry and transient photocurrent: Three-electrode system, working electrode is FTO or ITO substrate coated with sample, reference electrode is Ag / AgCl or saturated calomel, electrolyte is 0.5 mol·L⁻¹ -1 Na2SO4 (or equivalent), AC amplitude 10mV, frequency 10 5 -10 - 1 Hz.

[0041] GC / GC-MS: Carbon molecular sieve or equivalent column is used, and TCD / FID (with methanator) is used for joint detection; multi-point calibration is performed using external standard mixture with metrological traceability; chromatographic peak assignment and detection limit are explained in the figure notes or tables.

[0042] Light intensity measurement: The light intensity on the sample surface was measured using a calibrated power meter (example: 58 mW·cm). -2 The reactor's airtightness was confirmed by helium detection or purging tests, with a leakage rate ≤10%. -5 s -1 .

[0043] Representative results and figure captions

[0044] XRD: Interlayer stacking characteristic peaks were observed at 2θ = 25.2–26.4° (corresponding to d = 0.34–0.36 nm), consistent with layered self-assembly (see [link to XRD pattern]). Figure 2 ).

[0045] XPS: Copper is predominantly divalent; a negative shift of 0.2–0.8 eV in the Cu 2p3 / 2 binding energy after illumination was observed only in self-assembled samples compared to before illumination; this phenomenon was not observed in the non-self-assembled control (see...). Figure 3 ).

[0046] EXAFS (Cu K-edge) results show that the first coordination shell is Cu–O, with a bond length of approximately The spacing R (Cu···Cu) between adjacent copper sites corresponding to the second shell scattering is approximately (After phase correction). The fitting path and parameters are shown in Table 2.

[0047] Morphology: SEM / TEM shows the layered stacked structure and particle size distribution (see...). Figure 5 ).

[0048] An overview of the structure and main characterization results is shown in Table 1. No interlayer stacking characteristic peaks were observed in the control sample, and R(Cu···Cu) could not be defined.

[0049] Table 1 Summary of Structure and Representation

[0050]

[0051] Note: This table is a simplified summary for easy reference; see Table 2 for complete parameters.

[0052] Note codes: A = pH 8–11; B = self-assembly 2–6h; C = antisolvent MeOH / EtOH; D = non-self-assembly control.

[0053] Figure 4 The XANES and k of HCDS are given. 3 χ(k) and its Fourier transform |FT(k) 3 χ(k))|; The range of k / R used for fitting and the key parameters are shown in Table 2.

[0054] Table 2 EXAFS Fitting Parameters

[0055]

[0056] Note: This table corresponds to Figure 4 The fitting results; k range R range S0 2 =0.9, ΔE0 =9.2eV; the parameters are representative results and are allowed to fluctuate within ±10–20% due to differences between samples and instruments.

[0057] Example 5: Photocatalytic Carbon Dioxide Reduction Test

[0058] The catalyst was dispersed in water or a water / TEOA mixture in a closed reactor; CO2 with a purity ≥99.9% was introduced and pre-bubbled for 15 min; the sample surface was irradiated with a 300W xenon lamp, achieving a light intensity of 58 mW·cm². -2 The reaction was carried out at a temperature of 25℃ and a pressure of approximately 100 kPa (~1 atm). 1 mL of gas phase sample was taken every 60 min, and CO, CH4, C2H4, C2H6, and other products were analyzed using GC. Catalyst-free, dark reaction, and inert gas conditions were set as controls.

[0059] Example 6 Performance Results

[0060] In the sacrificial agent (TEOA 25%) system, the C2H6 formation rate of HCDS was 250.9 μmol·g.-1 ·h -1 Electron selectivity 85.5%; rate of action 18.9 μmol·g in pure water system. -1 ·h -1 After 10 cycles, the activity retention rate was ≥90%. The corresponding time-series curves are shown below. Figure 7 Representative reaction conditions and control data are summarized in Table 3 (Table 3 and...). Figure 7 (Mutual correspondence)

[0061] Table 3 Summary of photocatalytic performance and testing conditions

[0062]

[0063] Note: Code 0 = no catalyst; 1 = dark reaction; 2 = inert atmosphere. Unless otherwise specified, the other conditions are the same as in Example 5.

[0064] Example 7 Doping Regulation

[0065] Introducing Ag during self-assembly + and / or Au 3+ Doping was performed with a doping amount ≤10% of the molar fraction of copper. Characterization and testing were carried out according to the methods of Examples 4–6.

[0066] Example 8: Ligand Substitution

[0067] The triphenylamine fragment was replaced with a ligand having a larger π plane (such as porphyrin, phthalocyanine, or bipyridine derivative), or thiophene dicarboxylic acid was replaced with a symmetrical polydentate carboxylic acid (such as pyromellitic acid or biphenyltetracarboxylic acid) to regulate R(Cu···Cu) and the light absorption range; the remaining conditions were performed as described in the above examples.

[0068] Data integrity and duplicate description

[0069] Each test was repeated at least three times; error was expressed as standard deviation or 95% confidence interval; external standard calibration curve R0 2 ≥0.995; Baseline, drift, and background subtraction methods follow the instrument manual and industry standards.

[0070] Industrial applicability

[0071] The material can be prepared from readily available raw materials using a mild process, and is scalable and repeatable; it selectively generates ethane under visible light conditions, making it suitable for carbon dioxide resource utilization and distributed chemical energy storage.

Claims

1. A supramolecular photocatalytic material, characterized in that: The material includes uniformly distributed copper active sites, wherein the copper forms a Cu–O4 coordination environment with a carboxylic acid-containing ligand; the center-to-center distance R(Cu···Cu) between adjacent copper active sites is [missing value]. The material has a π-conjugated organic layered structure, and its powder X-ray diffraction pattern (Cu Kα) shows interlayer stacking characteristic peaks at 2θ = 25.2–26.4° (corresponding to interlayer spacing of 0.34–0.36 nm).

2. The material according to claim 1, wherein R(Cu···Cu) is Furthermore, EXAFS shows that the first coordination shell bond length of Cu–O is 3. The material according to claim 1 or 2, wherein the organic framework comprises a triphenylamine fragment and a thiophene dicarboxylic acid fragment.

4. The material according to any one of claims 1–3, wherein the layered structure is obtained by antisolvent-induced self-assembly, the antisolvent being methanol or ethanol; and may contain Ag and / or Au doping, with a doping amount ≤10%.

5. The material according to any one of claims 1–4, wherein the material is formed by antisolvent self-assembly of a coordination precursor obtained by adjusting the pH of a dicarboxylic acid ligand to divalent copper ions with triethylamine in an aqueous phase to 8–11.

6. A method for preparing the material according to any one of claims 1–5, comprising: (1) The dicarboxylic acid ligand is coordinated with divalent copper ions in an alkaline aqueous phase to obtain a coordination precursor; (2) Dissolve the precursor in tetrahydrofuran and slowly add it dropwise to an alcohol antisolvent, and self-assemble for 2–6 hours; (3) Separate and dry to obtain a layered material.

7. The method according to claim 6, wherein the antisolvent is methanol, and the dropping rate is 0.3–2.0 mL·min. -1 The self-assembly temperature is 15–35℃, and it is vacuum dried at 25–80℃ for 4–12 hours.

8. A method for photocatalytic reduction of carbon dioxide to ethane, characterized in that: Under ultraviolet-visible light irradiation, the material described in any one of claims 1–5 is dispersed in water or a water / alcohol mixture, and CO2 with a purity ≥99.9% is introduced to carry out the reaction.

9. The method according to claim 8, wherein the light source is a 300W xenon lamp with triethanolamine added as a sacrificial agent, and the electron selectivity of ethane is ≥70%.

10. The method according to claim 8 or 9, wherein the rate of ethane formation in an aqueous system only is ≥10 μmol·g -1 • h⁻¹, or the rate of ethane formation in a system containing a sacrificial agent ≥ 100 μmol·g -1 ·h-1.

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