A Mn, Co single atom pair modified carbon nitride photocatalyst and its preparation method and application
By constructing a Mn, Co single atom pair modified carbon nitride photocatalyst, the problem of low electron transfer efficiency of single atom catalysts was solved, and efficient catalytic degradation and hydrogen production performance was achieved.
Patent Information
- Application Number
- CN202311391464.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-24
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2043-10-24
AI Technical Summary
Existing single-atom catalysts with a single active site have low efficiency in the electron transfer process in complex reactions. The metal ions in cobalt-manganese-based composite catalysts do not exist in single-atom form, resulting in low catalytic conversion efficiency and reaction rate.
A preparation method for carbon nitride photocatalyst modified with Mn and Co single atom pairs was adopted. Co atoms were preassembled with thiourea precursor and Mn atoms were introduced by thermal polymerization to construct Mn, Co single atom pairs, increase the electron transfer pathway, and utilize MOF cracking to promote carbon nitride stripping to form non-covalent Mn, Co single atom pairs.
The catalytic activity and reaction rate of the catalyst were improved, and the efficiency of catalytic degradation of antibiotic pollutants and decomposition of water to produce hydrogen was significantly improved.
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Figure CN117443424B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of photocatalysis, and in particular to a Mn and Co single-atom-pair modified carbon nitride photocatalyst, a preparation method and an application thereof. Background Art
[0002] Semiconductor nanomaterial photocatalysis is a green and sustainable technology that has been widely used in energy conversion and pollutant degradation.
[0003] Graphitic carbon nitride (GCN) is a semiconductor material with advantages such as being non-toxic, readily available, responsive to visible light, and having a tunable band gap. It has been widely used in photocatalysis. It is composed of planar, conjugated 3-s-triazine units. The six lone pairs of electrons on the nitrogen atoms in the 3-s-triazine structure can effectively anchor metal atoms, offering significant advantages in the precise construction of single-atom catalysts.
[0004] Single-atom catalysts have attracted widespread attention due to their atomic-scale dispersion and unique electronic properties. However, having only a single active site still limits the electron transfer process of complex reactions. For example, Chinese patent application No. 202211561855.2 discloses a cobalt-manganese-based composite catalyst. Although this catalyst uses cobalt and manganese to dope modified carbon nitride, the nitrogen lone electron pair of the carbon nitride acts as an electron donor to form a metal-nitrogen (MN) bond with the metal ion. Cobalt and manganese do not exist in the form of single atoms, but rather as metal clusters supported on the carbon nitride. Therefore, the conversion efficiency and reaction rate of this catalyst are still relatively low. Summary of the Invention
[0005] The main purpose of the present invention is to provide a Mn, Co single atom pair modified carbon nitride photocatalyst with higher catalytic reaction rate, as well as a preparation method and application thereof.
[0006] To achieve the above object, the present invention provides a method for preparing a carbon nitride photocatalyst modified by a Mn and Co single atom pair, comprising the following steps:
[0007] (1) adding thiourea and cobalt sulfate to an ethanol aqueous solution, and then evaporating to dryness under constant temperature and stirring;
[0008] (2) cooling the evaporated mixture to room temperature, and then grinding it to obtain a light blue powder;
[0009] (3) mixing the light blue powder and Mn-MOF, and then grinding them to obtain a premix powder;
[0010] (4) The premix powder is placed in a crucible with a cover, heated in a muffle furnace, and ground after cooling to obtain the Mn and Co single atom pair modified carbon nitride photocatalyst.
[0011] Furthermore, in step (1), the mass ratio of thiourea to cobalt sulfate is 250-1000:1.
[0012] Furthermore, in step (1), the concentration of the ethanol aqueous solution is 60-70vt%, and the amount of the ethanol aqueous solution added is such that the volume mass ratio of the ethanol aqueous solution to the cobalt nitrate reaches 5-6ml:1mg.
[0013] Furthermore, in step (1), the temperature conditions for the constant temperature stirring evaporation treatment are 60-80° C., the stirring speed is 400-600 rpm, and the time is 12-18 hours. During this process, the ethanol aqueous solution is evaporated to dryness.
[0014] Furthermore, in step (3), the mass ratio of Mn-MOF to light blue powder is 1:250-1000.
[0015] Furthermore, in step (3), the grinding treatment time is 15 to 30 minutes.
[0016] Furthermore, in step (4), the heating conditions are: air atmosphere, heating temperature 500-550°C, heating time 4-5h, and heating rate 2-4°C.
[0017] Furthermore, both Mn and Co exist in single-atom form and form a non-covalent bond relationship.
[0018] The present invention also provides a Mn and Co single atom pair modified carbon nitride photocatalyst prepared according to the above preparation method.
[0019] The present invention also provides the use of the carbon nitride photocatalyst modified by the above-mentioned Mn and Co single atom pairs as a catalyst in catalytic degradation of antibiotic pollutants or decomposition of water to produce hydrogen.
[0020] This invention provides a method for modifying graphite-phase carbon nitride with two metal atoms. Co atoms are preassembled with a thiourea precursor to facilitate their entry into the carbon nitride sextuple cavity. Thermal polymerization then allows the entry of Mn atoms from the MOF, thereby forming Mn, Co single-atom pairs. The Mn, Co single-atom pairs create new electron transfer pathways, while MOF cracking promotes carbon nitride exfoliation, thereby enhancing catalytic activity.
[0021] The beneficial effects of the present invention are embodied in:
[0022] 1. In the present invention, the single atoms are selected from two metals, Mn and Co, which have the advantages of low cost compared with precious metals, and the preparation process and operation method are simple.
[0023] 2. Compared with single-atom-doped graphite-phase carbon nitride, the present invention constructs double-single-atom-pair-doped graphite-phase carbon nitride through preassembly-thermal polymerization, with a higher single-atom loading and more increased electron transfer pathways. By constructing Mn, Co nitrogen atom pairs in the carbon nitride 3-s-triazine structure, the electron migration rate of the graphite-phase carbon nitride is effectively improved. At the same time, MOF cracking promotes the exfoliation of carbon nitride to obtain a cluster structure, thereby effectively improving the catalytic activity of the graphite-phase carbon nitride.
[0024] 3. In the present invention, Mn and Co atoms exist in the form of non-covalent bonds, which not only maximizes the utilization of atoms, but also effectively promotes charge transfer by constructing an internal electric field through unique and asymmetric atomic pairs, resulting in a higher reaction rate.
[0025] 4. Compared with original carbon nitride and single atom doping, the catalyst's hydrogen production efficiency and pollutant degradation efficiency are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 These are the N2- adsorption-desorption isotherms of Mn, Co-CN, Mn-CN, Co-CN, and CN.
[0027] Figure 2 SEM and TEM images of CN and Mn,Co-CN.
[0028] Figure 3 XRD diffraction analysis diagram of Mn, Co-CN, (a) HAADF-STEM image of Mn, Co-CN (the bright spots in the isolated red rectangles are Mn, Co single atom pairs), (b) line scanning intensity distribution diagram in areas A, B, C, and D, and (c) energy dispersive X-ray (EDS) element mapping.
[0029] Figure 4 These are the XRD patterns of Mn, Co-CN, Mn-CN, Co-CN, and CN.
[0030] Figure 5 (a) Mn k-edge XANES spectra of Mn, Co-CN, and Mn-CN, (b) Mn k-edge FT-EXAFS spectra, (c) Co k-edge XANES spectra of Mn, Co-CN, and Co-CN, (d) Co k-edge FT-EXAFS spectra, Mn and Co (e) k-edge EXAFS fitting of Mn and Co-CN, (f) R-edge EXAFS fitting, (g) WT diagram of Mn and Co elements in Mn, Co-CN, Mn foil, and Co foil.
[0031] Figure 6 The degradation test results of Mn, Co-CN, Mn-CN, Co-CN, and CN are shown.
[0032] Figure 7 The graph shows the hydrogen production test results of Mn, Co-CN, Mn-CN, Co-CN, and CN. DETAILED DESCRIPTION
[0033] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.
[0034] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial channels or by existing known methods; unless otherwise specified, the methods used in the examples of the present invention are methods known to those skilled in the art.
[0035] Example 1
[0036] Preparation of Mn-MOF
[0037] 0.156 g of manganese chloride tetrahydrate and 0.261 g of 1,3,5-benzenetricarboxylic acid were weighed and dissolved in 30 ml and 40 ml of NN dimethylacetamide solution respectively. After ultrasonication for five minutes, the mixture was mixed and stirred for 20 minutes. The mixture was transferred to a 100 ml reactor and hydrothermally treated at 140 ° C for 12 hours. The mixture was naturally cooled to room temperature. The obtained mixed solution was centrifuged, washed with dimethylacetamide and methanol three times respectively, and dried in a vacuum drying oven at 60 ° C. Finally, the obtained solid was ground into a powder to obtain Mn-MOF.
[0038] Example 2
[0039] Preparation of Mn and Co Single Atom Pair Modified Carbon Nitride Photocatalyst
[0040] Take 10 mg of cobalt nitrate and 5 g of thiourea and dissolve them in 50 ml of 70vt% ethanol aqueous solution. After ultrasonication for five minutes, the mixed solution is stirred at a constant temperature of 60°C and 600 rpm for 12 hours, then cooled to room temperature, and the obtained solid is placed in an agate mortar and ground for 30 minutes to obtain a light blue powder. 2.5 g of blue powder is mixed with 10 mg of Mn-MOF and ground in an agate mortar for 15 minutes to obtain a premix powder. The premix powder is placed in a crucible with a lid, and the temperature is increased to 550°C at a rate of 2°C / min in a muffle furnace, kept warm for 4 hours, and finally cooled naturally to room temperature. Place it in an agate mortar and grind for 15 minutes to obtain a light yellow powder, which is the Mn and Co single atom pair modified carbon nitride photocatalyst, recorded as Mn,Co-CN.
[0041] Example 3
[0042] Preparation of Mn and Co Single Atom Pair Modified Carbon Nitride Photocatalyst
[0043] Take 10 mg of cobalt nitrate and 10 g of thiourea and dissolve them in 55 ml of 65vt% ethanol aqueous solution. After ultrasonication for five minutes, the mixed solution is stirred at a constant temperature of 70°C and 500 rpm for 15 hours, then cooled to room temperature, and the obtained solid is placed in an agate mortar and ground for 30 minutes to obtain a light blue powder. 5 g of blue powder is mixed with 10 mg of Mn-MOF and ground in an agate mortar for 15 minutes to obtain a premix powder. The premix powder is placed in a crucible with a lid, and the temperature is increased to 500°C at a rate of 3°C / min in a muffle furnace, kept warm for 5 hours, and finally cooled naturally to room temperature. Place it in an agate mortar and grind for 15 minutes to obtain a light yellow powder, which is the Mn and Co single atom pair modified carbon nitride photocatalyst.
[0044] Example 4
[0045] Preparation of Mn and Co Single Atom Pair Modified Carbon Nitride Photocatalyst
[0046] Take 20 mg of cobalt nitrate and 5 g of thiourea and dissolve them in 60 ml of 60vt% ethanol aqueous solution. After ultrasonication for five minutes, the mixed solution is stirred at a constant temperature of 80°C and 400 rpm for 18 hours, then cooled to room temperature, and the obtained solid is placed in an agate mortar and ground for 30 minutes to obtain a light blue powder. 2.5 g of blue powder is mixed with 2.5 mg of Mn-MOF and ground in an agate mortar for 15 minutes to obtain a premix powder. The premix powder is placed in a crucible with a lid, and the temperature is increased to 550°C at a rate of 2°C / min in a muffle furnace, kept warm for 4 hours, and finally cooled naturally to room temperature. Place it in an agate mortar and grind for 15 minutes to obtain a light yellow powder, which is the Mn and Co single atom pair modified carbon nitride photocatalyst.
[0047] Comparative Example 1
[0048] Preparation of Mn Single Atom Modified Carbon Nitride Photocatalyst
[0049] 5 g of thiourea was dissolved in 50 ml of 70 vt% ethanol aqueous solution. After ultrasonication for five minutes, the mixed solution was stirred at a constant temperature of 60 ° C and 600 rpm for 12 hours, then cooled to room temperature, and the obtained solid was placed in an agate mortar and ground for 30 minutes until it was in a powder state. 2.5 g of the obtained powder was mixed with 10 mg of Mn-MOF and ground in an agate mortar for 15 minutes to obtain a premix powder. The premix powder was placed in a crucible with a lid, and the temperature was increased to 550 ° C at a rate of 2 ° C / min in a muffle furnace. The temperature was kept for 4 hours, and finally cooled to room temperature naturally. The powder was placed in an agate mortar and ground for 15 minutes to obtain a light yellow powder, which is the Mn single atom modified carbon nitride photocatalyst, recorded as Mn-CN.
[0050] Comparative Example 2
[0051] Preparation of Co Single Atom Modified Carbon Nitride Photocatalyst
[0052] 10 mg of cobalt nitrate and 5 g of thiourea were dissolved in 50 ml of 70 vt% ethanol aqueous solution. After ultrasonication for five minutes, the mixed solution was stirred at 60 ° C and 600 rpm for 12 hours, then cooled to room temperature, and the obtained solid was placed in an agate mortar and ground for 30 minutes until it was in a powder state. The obtained powder was placed in an agate mortar and ground for 15 minutes, then placed in a covered crucible, and heated to 550 ° C at a rate of 2 ° C / min in a muffle furnace. The temperature was kept for 4 hours and finally cooled naturally to room temperature to obtain a light yellow powder, which is a Co single atom modified carbon nitride photocatalyst, denoted as Co-CN.
[0053] Comparative Example 3
[0054] Preparation of carbon nitride
[0055] Dissolve 5g of thiourea in 50ml of 70wt% ethanol-water solution. After ultrasonication for five minutes, stir the mixture at 60°C and 600rpm for 12h, then cool to room temperature. Grind the resulting solid in an agate mortar for 30min until it becomes a powder. Grind the powder in an agate mortar for 15min, place it in a covered crucible, and heat it to 550°C in a muffle furnace at a rate of 2°C / min. Hold the temperature for 4h, and finally cool it naturally to room temperature to obtain a light yellow powder, which is carbon nitride, denoted as CN. Structure determination of the catalyst:
[0056] In order to understand the structure of the catalyst of the present invention, the Mn and Co-CN prepared in Example 2 and the Mn-CN, Co-CN, and CN prepared in Comparative Examples 1-3 were analyzed by N2-adsorption-desorption, XRD, and high-magnification transmission electron microscopy. Figures 1 to 4 shown.
[0057] Figure 1 is the N2-adsorption-desorption isotherm curve and the pore size distribution diagram of the carrier. Figure 1 It can be seen that the nitrogen adsorption-desorption curve of the catalyst of the present invention is a type IV isotherm with an H3 type hysteresis loop, indicating that the sample has a mesoporous structure. The Mn, Co-CN catalyst of the present invention has a large specific surface area of 110.52 m 2 / g, and the pore volume reaches 0.68cm 3 / g, indicating that the catalyst prepared by the present invention is a mesoporous material.
[0058] exist Figure 2It can be observed that CN is a bulk structure formed by nanosheet accumulation. The introduction of Mn and Co promotes the exfoliation of the sheet accumulation. Mn, Co-CN forms a thin sheet structure, and no related metal nanoclusters and metal particles are observed on the surface, indicating that Mn and Co atoms do not form metal oxides or metal agglomerates, but instead enter the carbon nitride crystal structure.
[0059] The state of the metal atoms in the catalyst of the present invention was further clarified by aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images. Figure 3 As shown in the figure, Mn atoms and Co atoms are evenly distributed on Mn, Co-CN. They appear in pairs (red circles), indicating that Mn and Co exist in the form of bimetallic atomic pairs in Mn, Co-CN. In addition, the distances between the fluorescent spots (representing metal atoms) are measured by randomly selected sites A, B, C, and D, respectively. It shows that specific single atom pairs (SAPs) of Mn-Co are formed in Mn,Co-CN.
[0060] In order to further prove the structure of the catalyst, the present invention conducted XRD diffraction analysis, and the results are as follows Figure 4 As shown, all samples have two similar diffraction peaks, located at 12.7°(100) and 27.6°(002), respectively, which are attributed to the intralayer connection of the 3-s-triazine structure and the interlayer superposition of the conjugated aromatic system. At the same time, there are no peaks related to Mn, Co metals and their compounds in the XRD spectrum, which proves that the addition of Mn and Co does not destroy the basic structure of carbon nitride. The catalyst maintains the hexagonal unit cell structure of graphite phase carbon nitride, and Mn and Co exist in the form of metal coordination in carbon nitride. This is consistent with the above analysis results.
[0061] The coordination environment of the prepared catalyst and the electronic effect between Mn and Co were further confirmed by X-ray near-edge structure (XANES) spectroscopy. Figure 5As shown, the front curve of the Mn k-edge X-ray absorption near-edge structure spectrum of Mn,Co-CN lies between that of MnO and Mn2O3, indicating that Mn in the catalyst exists in +2 and +3 valence states. The front curve of the Co k-edge XANES spectrum of Mn,Co-CN lies between that of Co foil and CoO, and close to that of CoO, indicating that the valence state of Co in Mn,Co-CN is close to +2, which is consistent with the XPS analysis results. In addition, compared with Mn-CN, the front edge peak intensity of the Mn k-edge XANES spectrum of Mn,Co-CN is blue-shifted, indicating that the valence state of Mn in Mn,Co-CN is reduced and the D4h symmetry of the Mn atoms is slightly distorted. Conversely, compared with Co-CN, the front edge peak of the Co k-edge XANES spectrum of Mn,Co-CN is red-shifted, indicating that the Co atoms have lost electrons.
[0062] Catalyst degradation performance test of pollutants:
[0063] The catalytic activity of the catalyst was evaluated by the degradation efficiency of tetracycline hydrochloride under visible light. In each reaction, 10 mg of the catalyst (Mn, Co-CN prepared in Example 2) was weighed and dispersed into 100 ml of a 10 mg / L pollutant solution (tetracycline hydrochloride). Before the light reaction, the suspension was placed in a dark box and stirred for 30 minutes to reach adsorption equilibrium, and then the light reaction was carried out (60 minutes). During the entire reaction process, 3 ml of the sample was sampled every 10 minutes, and the pollutant concentration was measured using a spectrophotometer after centrifugation. Each experiment was repeated 3 times, and the results are shown as the average value and error bars. Figure 6 shown.
[0064] Photocatalytic hydrogen evolution reaction test of catalyst:
[0065] 10 mg of catalyst (Mn, Co-CN prepared in Example 2) was dispersed in 50 ml of triethanolamine (10%) aqueous solution, and 3 wt% Pt was in situ deposited on the catalyst surface by photodeposition. Before the photoreaction, the mixture was aerated with nitrogen for 15 minutes to remove oxygen from the solution. The reaction light source was 300 W, equipped with a 420 filter, and the reaction temperature was controlled by a constant temperature (25°C) circulating water system. Samples were taken every 1 hour, and the H2 content was detected by an online gas chromatograph using a high-purity nitrogen carrier gas thermal conductivity detector (TCD). The results are as follows: Figure 7 shown.
[0066] All samples can produce hydrogen, among which Mn, Co-CN has the highest H2 production rate of 14092.6 μmol g -1 h -1 , is CN (208.7 μmol g -1 h -1) was 94.5 times higher than that of Mn-CN (12097.3 μmol g -1 h -1 ), and Co-CN (10263.9 μmol g -1 h -1 The sample doped with Mn and Co double atoms showed a degradation ability for tetracycline that exceeded that of the original graphitic carbon nitride and Mn and Co single atom doping.
[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A method for preparing a carbon nitride photocatalyst modified by a single atom pair of Mn and Co, characterized in that: The following steps are involved: (1) Add thiourea and cobalt sulfate to an ethanol aqueous solution, and then evaporate to dryness under constant temperature and stirring; The temperature conditions of the constant temperature stirring evaporation treatment are 60-80°C, the stirring speed is 400-600 rpm, and the time is 12-18 hours; (2) The evaporated mixture was cooled to room temperature and then ground to obtain a light blue powder; (3) Mixing the light blue powder and Mn-MOF, and then grinding them to obtain a premix powder; (4) placing the premix powder in a crucible with a cover, heating it in a muffle furnace, cooling it, and then grinding it to obtain the Mn and Co single atom pair modified carbon nitride photocatalyst; The heating conditions are: air atmosphere, heating temperature 500-550°C, heating time 4-5h, and heating rate 2-4°C.
2. The method for preparing the Mn and Co single atom pair modified carbon nitride photocatalyst according to claim 1, wherein: In step (1), the mass ratio of thiourea to cobalt sulfate is 250-1000:
1.
3. The method for preparing the Mn and Co single atom pair modified carbon nitride photocatalyst according to claim 1, wherein: In step (1), the concentration of the ethanol aqueous solution is 60-70% by volume, and the amount of the ethanol aqueous solution added is such that the volume mass ratio of the ethanol aqueous solution to the cobalt nitrate reaches 5-6 ml:1 mg.
4. The method for preparing the carbon nitride photocatalyst modified by Mn and Co single atom pairs according to claim 1, wherein: In step (3), the mass ratio of Mn-MOF to light blue powder is 1:250-1000.
5. The method for preparing the carbon nitride photocatalyst modified by Mn and Co single atom pairs according to claim 1, wherein: In step (3), the grinding treatment time is 15 to 30 minutes.
6. The method for preparing the carbon nitride photocatalyst modified by Mn and Co single atom pairs according to claim 1, wherein: Both Mn and Co exist in single-atom form and form a non-covalent bond relationship.
7. A carbon nitride photocatalyst modified by a Mn and Co single atom pair prepared by the preparation method according to any one of claims 1 to 6.
8. Use of the Mn and Co single atom pair modified carbon nitride photocatalyst as claimed in claim 7 as a catalyst in the catalytic degradation of antibiotic pollutants or the decomposition of water to produce hydrogen.