Preparation method and application of cobalt-based catalyst suitable for preparing singlet oxygen through visible light chemistry

Abstract

The invention belongs to the field of preparation and application of nano composite materials, and discloses a preparation method and application of a cobalt-based catalyst suitable for preparing singlet oxygen through visible light chemistry. The supported cobalt-based monatomic photocatalyst is prepared by using the eutectic component molten salt to assist pyrolysis of the cobalt chloride precursor and the graphite phase carbon nitride carrier, and the visible light absorption range and the charge transfer state life are remarkably increased. Under the conditions of visible light and O2, the prepared catalyst can efficiently promote generation of singlet active oxygen species. The preparation steps are simple, environment-friendly and cheap, the defect of narrow spectral response of a traditional carbon nitride material is overcome, and practical application is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of preparation and application of nanocomposites, and relates to a preparation method of a cobalt-based catalyst suitable for visible light chemical preparation of singlet oxygen. A supported cobalt-based single-atom photocatalyst is prepared by a molten salt-assisted pyrolysis method and used for the generation of singlet reactive oxygen species under visible light. Background Art

[0002] Singlet oxygen ( 1 O2) is an important reactive oxygen species and shows important application values in the fields of fine chemical synthesis, organic pollutant degradation, and targeted photodynamic therapy (Adv. Mater. 2016, 28, 6940 - 6945). Currently 1 The preparation technologies of O2 include enzymatic method and chemical oxidation, etc., but generally have problems such as high energy consumption, complex equipment, and biological toxicity. In contrast, visible light-driven technology has advantages such as environmental protection, low cost, and sustainability, and has become a research hotspot of new photocatalytic systems in recent years.

[0003] Single-atom catalysts can precisely regulate the local coordination environment of metal active centers by embedding active metals in the form of atomic dispersion into semiconductor supports (such as graphitic carbon nitride or metal-organic frameworks), forming a homogeneous complex-like structure (Nat. Rev. Chem., 2018, 2, 65 - 81). In the research of cobalt-based single-atom catalysts, some strategies for precisely regulating the coordination structure of metal centers have been realized, such as the synergistic regulation of axial chlorine (Cl) and second-shell sulfur (S), which improves the catalytic activity of Co single-atom catalysts (Nature. Water. 2025, 3, 211–221). Co atoms are coordinated by 4 N atoms and an asymmetric P atom, forming a unique Co-N4P SAC site (Adv. Funct. Mater. 2022, 32, 2207408) and cobalt-based single-atom catalysts with nitrogen-sulfur co-coordination, etc. However, limited by the structural stability of photosensitive supports (especially organic polymers, etc.) under conditions such as temperature / atmosphere and the limitations of spectral absorption, it is still a great challenge to develop a metal / support interface coordination structure to realize the electron transfer at the metal-support interface under visible light excitation to form a high-density charge separation state, laying a foundation for the target chemical oxidation / reduction process (Acc. Chem. Res. 2024, 57, 2915 - 2927), thereby improving the photocatalytic activity and stability.

[0004] Therefore, there is an urgent need to develop a catalyst with stable photosensitivity and construct a monodisperse metal-support interface structure with both long-lived charge transfer states and chemical stability to promote the generation of visible light-driven singlet oxygen. Summary of the Invention

[0005] To address the above problems, the present invention utilizes a molten salt-assisted pyrolysis strategy to successfully prepare a novel cobalt-based catalyst by high-temperature roasting of a composite system of cobalt chloride precursor (CoCl2) and graphite carbon nitride support (CN). It has a special Co-C coordination structure (with a low-spin Co center), which can significantly increase the visible light absorption range and the excited state lifetime of ligand-to-metal charge transfer (LMCT). Molten salt chemistry provides an innovative and precise synthesis route for the development of highly efficient visible light chemical preparation 1 of O2 catalysts.

[0006] Photochemical preparation of the cobalt-based single-atom catalyst of the present invention 1 of O2 basic photophysical / photochemical processes:

[0007] (1) Photoinduced excitation and efficient charge separation: When the cobalt-based catalyst absorbs visible light, the photoexcited electrons migrate efficiently from the ligand C to the metal Co center due to the ligand-to-metal charge transfer (LMCT) mechanism. This process forms metal ions enriched with electrons and ligands with radicals (R·), significantly reducing the recombination probability of photoexcited electrons and holes, thereby enhancing the separation efficiency of photogenerated charges.

[0008] (2) Oxygen activation and formation of singlet oxygen:

[0009] O2+ * →O2 * (1)

[0010] O2 * +e - →·O2 -* (2)

[0011] O2 * +e - +H + →·OOH * (3)

[0012] ·OOH * → * +·OOH (4)

[0013] ·O2 - / ·OOH+·O2 - / ·OOH→H2O2+ 1 O2 (5)

[0014] A preparation method of a cobalt-based catalyst suitable for visible light chemical preparation of singlet oxygen, the steps are as follows:

[0015] Step (1): Synthesis of graphite carbon nitride (CN) photocatalyst precursor

[0016] Urea and melamine are mixed and ground, then calcined in an inert atmosphere at high temperature for 2 h to 3 h. After the calcined sample is filtered and washed with a mixed solution of ethanol and deionized water, it is vacuum dried to obtain a graphite-phase carbon nitride (CN) photocatalyst precursor;

[0017] Among them, the mass ratio of urea to melamine is 1:2 to 1:3;

[0018] The calcination temperature is 500 to 550 °C;

[0019] The heating rate is (2 to 10) °C / min -1 ;

[0020] The inert atmosphere is argon / nitrogen;

[0021] The volume ratio of ethanol to deionized water is 1:1 to 1:3;

[0022] The drying temperature is 60 °C to 80 °C, and the drying time is 3 h to 4 h;

[0023] Step (2): Preparation of cobalt-based catalyst by doping graphite-phase carbon nitride with cobalt

[0024] The graphite-phase carbon nitride photocatalyst precursor prepared in step (1) is added to a mixture of lithium chloride, potassium chloride and cobalt chloride hexahydrate, and ground to make it evenly mixed; the evenly mixed powder is calcined in an inert atmosphere from room temperature to 400 °C to 600 °C for 2 h to 3 h, then filtered and washed with deionized water, and vacuum dried to obtain a cobalt-based catalyst;

[0025] Among them, the inert atmosphere is argon / nitrogen;

[0026] The heating rate is (2 to 10) °C / min -1 ;

[0027] The mass ratio of graphite-phase carbon nitride to cobalt chloride hexahydrate: 50:1 to 10:1;

[0028] The molar ratio of lithium chloride to potassium chloride is 3:2;

[0029] The drying temperature is 60 °C to 80 °C, and the drying time is 3 h to 4 h.

[0030] The cobalt-based catalyst obtained by the above preparation method is used for the application of producing 1 O2 under visible light irradiation, and the steps are as follows:

[0031] Step (1): Ultrasonically disperse the cobalt-based catalyst in a mixed solution of deionized water and the hole sacrificial agent isopropanol (IPA), where the concentration of the cobalt-based catalyst is 0.3 mg / mL, and the volume ratio of H2O to IPA is 3:1 to 5:1; place the mixed solution in a magnetic stirrer and stir, and the whole process is carried out in a completely light-shielded environment;

[0032] Step (2): Add the singlet oxygen scavenger 2,2,6,6-tetramethylpiperidine (TEMP) with a concentration of 50 mM to the mixed solution in step (1) and stir, and place the above solution under one of the following two conditions:

[0033] 2.1) Irradiate under a 300 W xenon lamp with a CUT420 nm filter for 2 min to 6 min;

[0034] 2.2) Irradiate under a 300 W xenon lamp with a QD500 nm filter for 2 min to 6 min;

[0035] After irradiating for 2 min to 6 min under each condition, accurately take out 50 μL of the solution and filter it through a filter head. Subsequently, carefully suck the filtered liquid with a capillary tube and transfer it to a paramagnetic tube for detection on an electron paramagnetic resonance spectrometer (EPR).

[0036] Advantages of the present invention:

[0037] (1) The present invention has successfully developed a new cobalt-based single-atom catalyst for photocatalytic generation of singlet oxygen ( 1 O2) under visible light irradiation. By using graphitic carbon nitride as a carrier and calcining at high temperature by molten salt-assisted pyrolysis, carbonization, nitrogen loss, and metal cobalt occur, and thus the metal is anchored at the sites, realizing precise regulation of the metal / support interface site structure and solving the problem of the structural stability of the photosensitive support under conditions such as temperature / atmosphere.

[0038] (2) A new type of metal / support coordination structure has been developed, which has a special Co-C coordination structure (the Co center is in a low-spin state), can significantly increase the visible light absorption range and the ligand-metal charge transfer (LMCT) excited state lifetime. It effectively overcomes the limitations of traditional carbon nitride materials in spectral response and greatly improves the efficiency of photocatalytic generation of singlet oxygen ( 1 O2) under visible light irradiation, and has significant application value.

[0039] (3) The preparation method of this catalyst is not only environmentally friendly, economical, and simple in process, but also after the introduction of single-atom cobalt metal, the formation of the metal / support coordination structure shows an obvious contrast to the support for visible light-driven singlet oxygen generation, and the single-atom cobalt metal is effectively utilized. Description of the Drawings

[0040] Figure 1 Scanning electron microscope (SEM) image of the Co-based single-atom catalyst (Co1 / CN(V)-600) prepared by calcination at 600 °C.

[0041] Figure 2 X-ray diffraction spectrum (XRD) of the support CN and the cobalt-based catalyst in the temperature range of 400 °C to 600 °C.

[0042] Figure 3 Shows the Fourier transform infrared spectrum (FTIR) of the sample in the wavenumber range of 500 - 4000 cm -1 Wave number.

[0043] Figure 4 UV-vis spectrum of the sample.

[0044] Figure 5 For TEMP capture 1 Electron paramagnetic spectrum (EPR) of O2. Among them, a is the comparison of the singlet oxygen generation intensity of CN-400, CN(V)-600, Co1 / CN-400 and Co1 / CN(V)-600 under CUT420nm. b is the comparison of the singlet oxygen generation intensity of Co1 / CN-400 and Co1 / CN(V)-600 under CUT420nm and QD500nm. Specific implementation mode

[0045] The following further illustrates the specific implementation mode of the present invention in combination with the attached drawings and technical solutions. (The attached drawing description is written in)

[0046] Example 1: Urea and melamine are mixed and ground in a ratio of 1:3, and then heated at a rate of 5 °C / min under an argon atmosphere at 500 °C -1 Calcined for 2 h, and the calcined sample is filtered and washed with a mixed solution of ethanol and deionized water in a volume ratio of 1:1, and then vacuum dried at 60 °C for 4 h to obtain a graphitic carbon nitride (CN) photocatalyst precursor.

[0047] Example 2: Based on Example 1, the calcination temperature is changed to 550 °C to obtain a graphitic carbon nitride (CN) photocatalyst precursor.

[0048] Example 3: Based on Example 1, the ratio of urea to melamine is changed to 1:2, and the calcination temperature is changed to 550 °C to obtain a graphitic carbon nitride (CN) photocatalyst precursor.

[0049] Example 4: (1) Place the CN precursor prepared in Example 3 in reserve. Weigh 1 g of CN in a mortar, add 2.7 g of lithium chloride, 2.3 g of potassium chloride and 20 mg of cobalt chloride hexahydrate, and grind them together;

[0050] (2) Place the ground powder in a tube furnace and calcine it from room temperature to 400 °C for 2 h in an argon atmosphere with a heating rate of 5 °C / min. -1 ;

[0051] (3) Post-treat the obtained sample. Ultrasonically dissolve the sample in deionized water and filter and wash it. After repeating this process 2 - 3 times, place it in a vacuum drying oven and dry it at 60 °C for 4 h to obtain the cobalt-based single-atom catalyst (Co1 / CN-400) calcined at 400 °C.

[0052] Example 5: On the basis of Example 4, change the calcination temperature in step (2) to 450 °C and keep other conditions unchanged to obtain the cobalt-based single-atom catalyst (Co1 / CN-450) calcined at 450 °C.

[0053] Example 6: On the basis of Example 4, change the calcination temperature in step (2) to 500 °C and keep other conditions unchanged to obtain the cobalt-based single-atom catalyst (Co1 / CN(V)-500) calcined at 500 °C.

[0054] Example 7: On the basis of Example 4, change the calcination temperature in step (2) to 550 °C and keep other conditions unchanged to obtain the cobalt-based single-atom catalyst (Co1 / CN(V)-550) calcined at 550 °C.

[0055] Example 8: On the basis of Example 4, change the calcination temperature in step (2) to 600 °C and keep other conditions unchanged to obtain the cobalt-based single-atom catalyst (Co1 / CN(V)-600) calcined at 600 °C.

[0056] Example 9: On the basis of Example 4, do not add 20 mg of cobalt chloride hexahydrate in step (1) and keep other conditions unchanged to obtain the support catalyst (CN-400) calcined at 400 °C.

[0057] Example 10: On the basis of Example 8, do not add 20 mg of cobalt chloride hexahydrate in the preparation conditions and keep other conditions unchanged to obtain the support catalyst (CN(V)-600) calcined at 600 °C.

[0058] Example 11: (1) Ultrasonically disperse the samples obtained in Example 4, Example 8, Example 9, and Example 10 in a mixed solution of deionized water and the hole sacrificial agent isopropyl alcohol (IPA), where the concentration of the catalyst is 0.3 mg / mL and the volume ratio of H2O to IPA is 3:1; place the mixed solution on a magnetic stirrer and stir, and the whole process is in a completely light-shielded environment;

[0059] Step (2): Add 1 mL of a 50 mM singlet oxygen scavenger 2,2,6,6 - tetramethylpiperidine (TEMP) to the mixed solution in step (1) and stir. Place the above solution under one of the following two conditions:

[0060] 2.1) Irradiate under a 300 W xenon lamp with a CUT420 nm filter for 2 min;

[0061] 2.2) Irradiate under a 300 W xenon lamp with a QD500 nm filter for 2 min;

[0062] Application Example 1: The cobalt - based single - atom catalyst (Co1 / CN(V)-600) prepared by calcining at 8600 °C in Example 8 was tested by scanning electron microscopy (SEM). The results are as Figure 1 shown. Its morphology shows a rod - like shape, which is significantly different from that of ordinary CN, indicating that temperature and the introduction of single - atom cobalt have a certain impact on the morphology.

[0063] Application Example 2: The samples obtained in Examples 3 - 8 were tested by X - ray diffraction (XRD). The results are as Figure 2 shown. For CN, two peaks were observed at 12.9° and 27.5°, corresponding to the inter - planar filling of the (100) crystal plane and the inter - layer stacking of the (002) crystal plane, respectively. As the calcination temperature of the sample increased, the (100) peak shifted from 12.9° to 8°, which may be due to the formation of N vacancies leading to an increase in the inter - planar spacing. This indicates that the increase in temperature has a certain impact on the crystal structure.

[0064] Application Example 3: Fourier transform infrared spectroscopy (FTIR) tests were performed on the cobalt - based single - atom catalysts (Co1 / CN - 400, Co1 / CN(V)-600) and supports (CN - 400, CN(V)-600) prepared by calcining at 400 and 600 °C in Examples 1 - 2 in the wavenumber range of 500 - 4000 cm -1 . The results are as Figure 3 shown. With the increase of the experimental temperature and the introduction of metallic cobalt, the inherent structural characteristics of each sample generally remain consistent. The significant absorption peaks observed in the range of 1200 to 1650 cm -1 are closely related to the stretching vibration of carbon - nitrogen heterocyclic molecules. At the same time, the sharp absorption peak at 806 cm -1 clearly indicates the characteristic bending vibration mode of the heptazine unit.

[0065] Application Example 4: The samples obtained in Examples 4, 8 - 10 were tested by ultraviolet diffuse reflectance spectroscopy (UV - vis). The results are as Figure 4As shown, Co1 / CN(V)-600 has a strong absorption peak in the visible light region of 450 - 800 nm while other samples do not. Combining experiments and theoretical calculations proves that it can be attributed to ligand-to-metal charge transfer (LMCT) transitions.

[0066] Application Example 5: Visible light-driven O2 production performance tests were carried out on the cobalt-based single-atom catalysts (Co1 / CN-400, Co1 / CN(V)-600) and supports (CN-400, CN(V)-600) prepared by calcination at 400 °C and 600 °C obtained in Implementation 11. The samples were measured using electron paramagnetic resonance (EPR) technology. During this process, 2,2,6,6-tetramethylpiperidine (TEMP) was used as a specific scavenger to detect the generation of singlet oxygen ( 1 1O2). 1 O2). The results are as Figure 5 shown. The observed 1:1:1 triplet signal coincides with the characteristic signal of tetramethylpiperidine oxide, thus precisely confirming the 1 formation of 1O2. In addition, the research focused on investigating the generation of 1O2 within the visible light spectrum range. This signal was detected through the screening of CUT420 nm and QD500 nm filters. The analysis results clearly indicate that the Co1 / CN(V)-600 catalyst exhibits higher efficiency in the generation of 1 1O2. 1 O2.

[0067] Comprehensive analysis shows that the cobalt-based single-atom photocatalyst prepared in this invention has a significant visible light absorption range and charge transfer state lifetime, and can efficiently promote the generation of singlet reactive oxygen species.

Claims

1. A preparation method of a cobalt-based catalyst applicable to the visible-light chemical preparation of singlet oxygen, characterized in that, The steps are as follows: Step (1): Synthesis of graphitic carbon nitride photocatalyst precursor Mix urea and melamine and grind them, then calcine them in an inert atmosphere at a high temperature for 2 h to 3 h. After filtering and washing the calcined sample with a mixed solution of ethanol and deionized water, vacuum dry it to obtain the graphitic carbon nitride photocatalyst precursor; Step (2): Preparation of cobalt-based catalyst by doping graphitic carbon nitride with metal cobalt Add the graphitic carbon nitride photocatalyst precursor prepared in step (1) to a mixture of lithium chloride, potassium chloride and cobalt chloride hexahydrate, and grind to make them evenly mixed; heat the evenly mixed powder from room temperature to 400 °C to 600 °C in an inert atmosphere and calcine for 2 h to 3 h, then filter and wash with deionized water, and vacuum dry to obtain the cobalt-based catalyst.

2. The preparation method according to claim 1, wherein in step (1), the mass ratio of urea to melamine is 1:2 to 1:3; the calcination temperature is 500 to 550 °C; The heating rate is (2 to 10) °C / min -1 ; the inert atmosphere is argon / nitrogen; the volume ratio of ethanol to deionized water is 1:1 to 1:3; the drying temperature is 60 °C to 80 °C, and the drying time is 3 h to 4 h.

3. The preparation method according to claim 1, wherein in step (2), the inert atmosphere is argon / nitrogen; The heating rate is (2 to 10) °C / min -1 ; the mass ratio of graphitic carbon nitride to cobalt chloride hexahydrate is 50:1 to 10:1; the molar ratio of lithium chloride to potassium chloride is 3:2; the drying temperature is 60 °C to 80 °C, and the drying time is 3 h to 4 h.

4. Use of the cobalt-based catalyst obtained by the preparation method according to any one of claims 1-3 for producing 1 O2 under visible light irradiation, characterized in that The steps are as follows: Step (1): Ultrasonically disperse the cobalt-based catalyst in a mixed solution of deionized water and hole sacrificial agent isopropanol, wherein the concentration of the cobalt-based catalyst is 0.3 mg / mL, and the volume ratio of deionized water to isopropanol is 3:1 to 5:1; place the mixed solution in a magnetic stirrer and stir, and the whole process is in a completely light-shielded environment; Step (2): Add a 50 mM singlet oxygen scavenger 2,2,6,6-tetramethylpiperidine (TEMP) to the mixed solution in step (1) and stir, and place the above solution under one of the following two conditions: 2.1) Irradiate under a 300 W xenon lamp with a CUT420 nm filter for 2 min to 6 min; 2.2) Irradiate under a 300 W xenon lamp with a QD500 nm filter for 2 min to 6 min.

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