Preparation method and application of mn-mn atomic pair catalyst

Abstract

This invention discloses a method for preparing Mn-Mn atom-pair catalysts and their applications. It proposes a novel "dual-ligand synergy" design strategy for the first time: based on the anchoring of Mn ions by phenanthroline ligands, a C2-C6 short-chain diamine is directionally introduced as a second ligand. Utilizing its bidentate coordination ability and the "molecular ruler" function of the short carbon chain, it synergistically constructs Mn-Mn atom pairs with a proximity effect with phenanthroline. By controlling the feed ratio of phenanthroline to C2-C6 short-chain diamine, the Mn-Mn atom pair spacing can be precisely controlled within the range of 2.3 Å to 4.5 Å. This Mn-Mn diatomic structure provides a two-site adsorption configuration and achieves bridged activation of PDS through the electronic synergistic effect between Mn and Mn, fundamentally breaking through the single-atom-site SRL, and showing promising application prospects in the field of advanced oxidation water treatment.

Description

Technical Field

[0001] This invention relates to the field of catalysts and wastewater treatment technology, specifically to a method for preparing a Mn-Mn atom-pair catalyst and its application. Background Technology

[0002] Currently, emerging pollutants such as tetrabromobisphenol A (TBBPA) pose a serious threat to aquatic environmental safety, and traditional wastewater treatment technologies struggle to effectively degrade them. Heterogeneous advanced oxidation technologies, with persulfate activation at their core, are an effective means of degrading such pollutants. Among these, single-atom catalysts (SACs) exhibit extremely high catalytic potential due to their maximized atom utilization efficiency. However, SACs face an intrinsic theoretical bottleneck: scaling relation limitation (SRL). In multi-step catalytic reactions, the adsorption energies of multiple intermediates at the same isolated metal site are linearly correlated, making it impossible to simultaneously achieve optimal adsorption, fundamentally limiting catalytic reaction efficiency. To overcome this limit, diatomic catalysts (DACs) have emerged. By introducing a second neighboring metal atom, DACs can overcome SRL through electronic effects, synergistic catalytic effects, and adsorption configuration regulation effects, achieving a leap in catalytic performance.

[0003] In the rational design of DACs, precise control of the interatomic spacing is the core to fully releasing the aforementioned effects, but this remains a major challenge in synthetic chemistry. Existing methods have failed to achieve the controllable transformation of Mn atoms from "isolated dispersion" to "dimeric pairing," resulting in low catalyst activation efficiency for oxidants, incomplete pollutant degradation, and high operating costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing Mn-Mn atom-pair catalysts and their applications, which solves the problem of low activation efficiency of existing Mn single-atom catalysts for persulfate.

[0005] This invention is achieved through the following technical solutions: A method for preparing a Mn-Mn atom-pair catalyst, the method comprising the following steps: (1) Manganese salt, first ligand, second ligand and heavy magnesium oxide template are dispersed in an organic solvent and subjected to ultrasonic treatment and heating and stirring at 60~80℃ to allow manganese ions to undergo a complexation reaction with the two ligands to form Mn-dual ligand complexes, which are uniformly loaded on the surface and pores of the heavy magnesium oxide template. The organic solvent is then removed by rotary evaporation to obtain the pyrolysis precursor. The first ligand is a nitrogen heterocyclic compound containing a phenanthroline skeleton and the second ligand is a saturated C2-C6 short-chain diamine compound containing a primary amine group at each end. (2) The pyrolysis precursor obtained in step (1) is ground and sieved, and then subjected to high-temperature carbonization treatment at 550~650 °C under an inert atmosphere. After cooling, a carbonized product containing a template is obtained. (3) The carbonized product containing the template obtained in step (2) is acid washed with an inorganic acid solution at 60~80℃ to remove the heavy magnesium oxide template and unstable metal nanoparticles. After washing to neutrality, drying and grinding, the Mn-Mn atom pair catalyst is obtained.

[0006] In step (1), the molar ratio of the first ligand to the second ligand can be adjusted to precisely regulate the spacing and pairing ratio of Mn-Mn atomic pairs in the final product. Preferably, the molar ratio of the first ligand to the second ligand is 1:0.25 to 1:2, more preferably 1:0.5 to 1:2, and most preferably 1:0.5.

[0007] Preferably, in step (1), the manganese salt is selected from manganese acetate, manganese chloride, or manganese nitrate; the first ligand is selected from 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, or 2,9-dimethyl-1,10-phenanthroline; the second ligand is selected from ethylenediamine, 1,3-propanediamine, or 1,4-butanediamine, preferably ethylenediamine; the molar ratio of the manganese salt, the first ligand, and heavy magnesium oxide is 0.5~3.0:3.0~9.0:300~1200; the organic solvent is one or more of methanol, ethanol, or acetonitrile, and the concentration of the manganese salt is 0.001~0.03 mol / L.

[0008] Preferably, the ultrasonic frequency in step (1) is 10~50 kHz, the ultrasonic time is 10~60 min, and the heating and stirring time is 6~12 h.

[0009] Preferably, the inert atmosphere in step (2) is nitrogen, argon, or helium; the carbonization process is: at 2~5 °C for min -1 The temperature is increased to 550~650 ℃ at a rate of [temperature value], and held for 60~120 min.

[0010] Preferably, the inorganic acid used for pickling in step (3) is one or more of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 0.5~2.0 M and a pickling solid-liquid ratio of 5~10 g / L. -1 The pickling temperature is 60~80 ℃ and the time is 4~8 h.

[0011] A second objective of this invention is to provide a Mn-Mn atom-pair catalyst prepared by the above method, wherein manganese is dispersed in the form of atom pairs on a nitrogen-doped carbon support, the average spacing between Mn-Mn atom pairs is 2.3 to 4.5 Å, preferably 3.4 Å, and the loading of manganese is 0.3 to 2.0 wt%, particularly 0.76 to 0.92 wt%.

[0012] This invention innovatively introduces a second ligand (e.g., ethylenediamine, EA) into the ligand system. Utilizing the bidentate coordination ability of the amino groups at both ends of the second ligand molecule, it "bridges" and confines two spatially separated Mn ions within a specific distance, forming a stable Mn-dual-ligand complex together with the phenanthroline ligand. During subsequent pyrolysis, the short carbon chain of the second ligand (e.g., ethylenediamine approximately 4.6 Å) acts as a "molecular ruler" to precisely limit the interposition distance between the two Mn atoms on the carbon-nitrogen skeleton, thereby controllably constructing Mn-Mn atom pairs. This Mn-Mn diatomic structure with proximity effect can provide a two-site adsorption configuration for persulfate (PDS) and optimize the adsorption energy of the active center for reaction intermediates through electronic synergistic effects. This breaks through the scaling relation limitation (SRL) of traditional Mn single-atom catalysts, significantly improving the activation efficiency for PDS and the oxidative degradation ability for new pollutants.

[0013] Therefore, a third objective of this invention is to provide the application of the Mn-Mn atom-pair catalyst in the degradation of novel pollutants in wastewater within a persulfate-based advanced oxidation system. The novel pollutants include at least one of tetrabromobisphenol A (TBBPA), bisphenol A (BPA), phenol, sulfamethoxazole (SMX), and chlorobenzene (4-CP). The persulfate is either permonosulfate or perdisulfate.

[0014] Preferably, the dosage of the Mn-Mn atom-pair catalyst is 0.02~0.20 g / L. -1 The persulfate concentration is 0.1~2.0mM, the wastewater pH range is 3.0~11.0, the Mn-Mn atom pair catalyst has an activation efficiency of over 85% for persulfate, and a degradation efficiency of nearly 100% for new pollutants.

[0015] The beneficial effects of this invention are as follows: 1) This invention proposes a novel design strategy of "dual ligand synergy": Based on the anchoring of Mn ions by phenanthroline ligands, a C2-C6 short-chain diamine compound containing a primary amine group at each end is introduced for the first time as a second ligand. Utilizing its bidentate coordination ability and the "molecular ruler" function of the short carbon chain, it synergistically constructs a Mn-Mn atom pair with a proximity effect with phenanthroline, bridging and confining the two Mn atoms to a specific spacing. This Mn-Mn diatomic structure provides a two-site adsorption configuration, and through the electronic synergistic effect between Mn-Mn, it achieves bridged activation of PDS, fundamentally breaking through the single-atom site SRL. The catalytic performance exhibits a volcanic change, with the catalyst at the optimal spacing of 3.4 Å achieving an activation efficiency of 85.2% for PDS, which is 3.65 times higher than that of the single-atom catalyst, and can completely degrade new pollutants such as tetrabromobisphenol A within 30 min. This invention breaks through the limitation that traditional single ligands (such as 1,10-phenanthroline) can only form isolated metal single-atom sites, and breaks through the activity limit of traditional Mn single-atom catalysts. It provides a new paradigm for controlling the atomic pair spacing of single-atom catalysts and has good application prospects in the field of advanced oxidation water treatment.

[0016] 2) This invention provides a novel strategy for the synthesis of Mn-Mn atom pairs with controllable interatomic spacing. Existing methods struggle to achieve the controllable transformation of Mn atoms from "isolated distribution" to "precise pairing." This invention, for the first time, introduces the molecular scale function of C2-C6 short-chain diamine ligands into the Mn-based catalyst synthesis system. By controlling the feed ratio of phenanthroline to C2-C6 short-chain diamine, the interatomic spacing of the two Mn atoms on the carbon-nitrogen framework can be precisely defined, achieving precise control of the Mn-Mn atom pair spacing within the range of 2.3 Å to 4.5 Å. This method requires no precious metals or complex equipment, and the process is simple and controllable, opening a practical new path for the design and large-scale preparation of high-performance Mn-based diatomic catalysts. It solves the problem of the difficulty in achieving the controllable transformation of Mn atoms from "isolated distribution" to "precise pairing" using existing methods. Attached Figure Description

[0017] Figure 1 The image is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC-HAADF-STEM) image of the Mn-Mn atom pair catalyst (Mn-NC-EA-1) prepared in Example 1, which visually shows that Mn atoms are dispersed on the support surface in the form of atom pairs.

[0018] Figure 2 The image shows the elemental distribution (mapping) of the Mn-Mn atom-pair catalyst (Mn-NC-EA-1) prepared in Example 1, which shows that Mn, N, C and O elements are uniformly distributed on the catalyst surface.

[0019] Figure 3The X-ray diffraction (XRD) patterns of the Mn-Mn atom pair catalysts prepared in Examples 1-3 and the manganese single atom catalysts prepared in Comparative Examples 1-2 are shown.

[0020] Figure 4 The X-ray photoelectron spectroscopy (XPS) N 1s spectrum of the Mn-Mn atom pair catalyst (Mn-NC-EA-1) prepared in Example 1 reveals the influence of Mn-N coordination configuration and the introduction of dual ligands on the nitrogen chemical state.

[0021] Figure 5 This is a comparison chart of the metal loading of the Mn-Mn atom pair catalysts prepared in Examples 1-3 and the manganese single atom catalysts prepared in Comparative Examples 1-2.

[0022] Figure 6 The diagram shows the statistical distribution of the interpair spacing of Mn-Mn atom pair catalysts with different ligand ratios prepared in Examples 1-3, demonstrating that the Mn-Mn spacing can be precisely adjusted by controlling the ethylenediamine ratio.

[0023] Figure 7 The graph shows a comparison of the activation efficiency of persulfate (PDS) by the Mn-Mn atom pair catalysts prepared in Examples 1-3 and the manganese single atom catalysts prepared in Comparative Examples 1-2.

[0024] Figure 8 The graph shows a comparison of the degradation performance of the Mn-Mn atom-pair catalysts prepared in Examples 1-3 and the manganese single-atom catalysts prepared in Comparative Examples 1-2 on PDS activated by the catalysts for the degradation of tetrabromobisphenol A (TBBPA).

[0025] Figure 9 The graph shows the degradation efficiency of PDS activated by the Mn-Mn atom-pair catalyst (Mn-NC-EA-1) prepared in Example 1 for various new pollutants (tetrabromobisphenol A, bisphenol A, phenol, chlorobenzene and sulfamethoxazole, etc.). Detailed Implementation

[0026] The following is a further description of the invention, but not a limitation thereof.

[0027] Example 1: 1) Dissolve 3.0 mmol manganese acetate, 3.0 mmol ethylenediamine and 6.0 mmol 1,10-phenanthroline in 100 mL ethanol and sonicate for 30 min; then add 600 mmol heavy magnesium oxide and sonicate for 30 min; stir the mixture in an oil bath at 80 °C for 8 h, and then remove the ethanol by rotary evaporation to obtain the pyrolysis precursor; 2) Grind and sieve the precursor (100 mesh). Place the sieved powder in a quartz boat in a tube furnace and heat it at 2 °C for 1 minute under nitrogen atmosphere.-1 Heat to 600 °C at the set heating rate, hold for 120 min, and then cool to room temperature. 3) Grind and sieve the cooled black solid, weigh 5 g of black solid and mix it with 500 mL of 1.0 M H2SO4 solution. Mix at 80 °C for 8 h. Wash the remaining acid-washed solid until neutral, then dry and grind it to obtain the Mn-Mn atom pair catalyst, named Mn-NC-EA-1.

[0028] Aberration-corrected electron micrograph of Mn-NC-EA-1 is shown below. Figure 1 As shown, the corresponding mapping graph is as follows: Figure 2 As shown, the X-ray diffraction pattern is as follows: Figure 3 As shown, the N 1s XPS spectrum is as follows Figure 4 As shown, the metal loading is as follows Figure 5 As shown, the interatomic spacing is as follows Figure 6 As shown in the figure. The results show that the metal loading of Mn-NC-EA-1 is 0.76 wt%, and the surface does not contain metal nanoparticles or nanoclusters. The metal manganese exists in an atomically dispersed form, mainly in the form of Mn-Mn atomic pairs with an average interpair spacing of ~3.4 Å, and forms Mn-N coordination with nitrogen.

[0029] Example 2: Compared to Example 1, the difference lies in the molar amounts of ethylenediamine and 1,10-phenanthroline, both being 4.5 mmol (EA:Phen = 1:1), resulting in a catalyst named Mn-NC-EA-2. Mn-NC-EA-2 has a metal loading of 0.76 wt%, with manganese metal highly dispersed in atomic pairs. Due to the increased proportion of EA, its "molecular scale" bridging effect is enhanced, and the average interatomic distance decreases to ~3.1 Å.

[0030] Example 3: Compared to Example 1, the difference lies in the molar amounts of ethylenediamine and 1,10-phenanthroline, which are 6.0 mmol and 3.0 mmol, respectively (EA:Phen = 2:1), resulting in a catalyst named Mn-NC-EA-3. The metal loading of Mn-NC-EA-3 is 0.92 wt%, where EA becomes the dominant ligand, bridging most Mn-Mn pairs and further reducing the average interatomic distance to ~2.8 Å.

[0031] Comparative Example 1: Referring to Example 1, the difference lies in replacing ethylenediamine with an equimolar amount of 1,10-phenanthroline (i.e., using only 9.0 mmol of 1,10-phenanthroline without adding ethylenediamine), resulting in a catalyst named Mn-NC-Phen. Mn-NC-Phen has a metal loading of 1.02 wt%, exists in single-atom site form, no Mn-Mn atom pairs were observed, and the interatomic distance between adjacent Mn atoms is greater than 5.0 Å.

[0032] Comparative Example 2: Compared to Example 1, the difference lies in replacing all of the 1,10-phenanthroline with an equimolar amount of ethylenediamine (i.e., using only 9.0 mmol EA, without adding Phen), resulting in a catalyst named Mn-NC-EA-4. Mn-NC-EA-4 has a metal loading of 0.50 wt%, with manganese metal dispersed in atomic pairs, all bridged by EA, and the atomic pairs pulled to their closest distance, with an average spacing of ~2.2 Å.

[0033] Application Example 1: The reaction was carried out in a 100 mL container, shaken at 25 °C and 150 rpm. 5 mg of the catalyst prepared in Example 1, Examples 2-3, or Comparative Examples 1-2 was added to 50 mL of a 0.1 mM sodium persulfate (PDS) solution (at which point the catalyst concentration was 0.1 g / L). -1 The pH value was 7.0, which was used as the starting point for the degradation reaction. The reaction solution was sampled at 0, 2, 5, 10, 15, 20 and 30 min of reaction. The samples were filtered through a 0.22 μm water filter and the PDS concentration was detected by UV spectrophotometer using the iodometric method. All experiments were performed in triplicate, and the results are expressed as average values. The PDS activation efficiency was calculated.

[0034] Experimental results are as follows Figure 7 As shown, the activation efficiencies of Mn-NC-Phen, Mn-NC-EA-1, Mn-NC-EA-2, Mn-NC-EA-3, and Mn-NC-EA-4 for PDS were 23.3%, 85.2%, 42.0%, 36.4%, and 3.9%, respectively. Compared with Mn-NC-Phen, which contains only a single atomic site, the activation efficiency of Mn-NC-EA-1 for PDS was increased by 3.65 times.

[0035] The above results clearly reveal the volcano-like variation of catalytic activity with Mn-Mn atomic spacing, and confirm that ~3.4 Å is the optimal atomic pair spacing for achieving efficient PDS activation.

[0036] Application Example 2: The degradation experiment was performed in the same manner as in Application Example 1, except that the solution contained 10 mg L. -1Tetrabromobisphenol A (TBBPA). Samples were taken at different time points during the reaction, and the concentration of TBBPA was detected by high-performance liquid chromatography.

[0037] Experimental results are as follows Figure 8 As shown, the Mn-NC-EA-1 / PDS system achieved a 100% degradation rate of TBBPA within 30 min, while the Mn-NC-Phen / PDS system only achieved a 41.3% degradation rate. The performance enhancement trend is completely consistent with the PDS activation efficiency. Furthermore, the Mn-NC-EA-1 / PDS system also achieved nearly 100% degradation efficiency for novel pollutants such as bisphenol A (BPA) and phenol (Phenol). Figure 9 It exhibits excellent broad-spectrum applicability.

Claims

1. A method for preparing a Mn-Mn atom-pair catalyst, characterized in that, The method includes the following steps: (1) Manganese salt, first ligand, second ligand and heavy magnesium oxide template are dispersed in an organic solvent, and subjected to ultrasonic treatment and heating and stirring at 60~80℃. Then the organic solvent is removed by rotary evaporation to obtain a pyrolysis precursor. The first ligand is a nitrogen heterocyclic compound containing a phenanthroline skeleton, and the second ligand is a saturated C2-C6 short-chain diamine compound containing a primary amine group at each end. (2) The pyrolysis precursor obtained in step (1) is ground and sieved, and then subjected to high-temperature carbonization treatment at 550~650 °C under an inert atmosphere. After cooling, a carbonized product containing a template is obtained. (3) The carbonized product containing the template obtained in step (2) is acid-washed with an inorganic acid solution under heating conditions of 60~80℃, washed until neutral, dried and ground to obtain the Mn-Mn atom pair catalyst.

2. The preparation method according to claim 1, characterized in that, Step (1) The molar ratio of the first ligand to the second ligand is 1:0.25~1:2; the manganese salt is selected from manganese acetate, manganese chloride or manganese nitrate; the first ligand is selected from 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline or 2,9-dimethyl-1,10-phenanthroline; the second ligand is selected from ethylenediamine, 1,3-propanediamine or 1,4-butanediamine; the molar ratio of the manganese salt, the first ligand and heavy magnesium oxide is 0.5~3.0:3.0~9.0:300~1200; the organic solvent is one or more of methanol, ethanol or acetonitrile; the concentration of the manganese salt is 0.001~0.03mol / L.

3. The preparation method according to claim 1, characterized in that, Step (1) The molar ratio of the first ligand to the second ligand is 1:0.5~1:

2.

4. The preparation method according to claim 1, characterized in that, In step (1), the ultrasonic frequency is 10~50 kHz, the ultrasonic time is 10~60 min, and the heating and stirring time is 6~12 h.

5. The preparation method according to claim 1, characterized in that, The inert atmosphere mentioned in step (2) is one of nitrogen, argon, or helium; the carbonization procedure is: at 2~5 ℃ min -1 The temperature is increased to 550~650 ℃ at a rate of [temperature value], and held for 60~120 min.

6. The preparation method according to claim 1, characterized in that, In step (3), the inorganic acid used for pickling is one or more of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 0.5~2.0 M and a solid-liquid ratio of 5~10 g / L. -1 The pickling time is 4-8 hours.

7. The Mn-Mn atom-pair catalyst prepared by the method of claim 1, characterized in that, In the catalyst, manganese is dispersed in the form of atomic pairs on a nitrogen-doped carbon support, with an average Mn-Mn atomic pair spacing of 2.3 to 4.5 Å; the manganese loading is 0.3 to 2.0 wt%.

8. The application of the Mn-Mn atom-pair catalyst prepared by the method of claim 1 in the degradation of new pollutants in wastewater in a persulfate-based advanced oxidation system.

9. The application according to claim 8, characterized in that, The new pollutant includes at least one of tetrabromobisphenol A, bisphenol A, phenol, sulfamethoxazole, and chlorobenzene; the persulfate is permonosulfate or perdisulfate.

10. The application according to claim 8, characterized in that, The dosage of Mn-Mn atom-pair catalyst is 0.02~0.20 g / L. -1 The persulfate concentration is 0.1~2.0 mM, and the pH value of the wastewater is 3.0~11.0.

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