A nitrogen-oxygen co-coordinated iron monatomic catalyst, a preparation method thereof and application thereof in degrading phenolic pollutants

Abstract

The application discloses a nitrogen-oxygen co-coordinated iron monatomic catalyst and a preparation method and application in degrading phenolic pollutants thereof. The preparation method of the nitrogen-oxygen co-coordinated iron monatomic catalyst comprises the following steps: (1) dispersing o-phenylenediamine and salicylaldehyde in a first organic solvent to obtain a mixed solution, heating and reacting to obtain a salofen type Schiff base ligand; (2) dispersing iron salt, the salofen type Schiff base ligand and a template agent in a second organic solvent to obtain a mixed solution, heating and reacting to obtain a pyrolysis precursor; (3) heat-treating the pyrolysis precursor obtained in the step (2) and cooling to obtain a crude product; and (4) washing and drying the crude product obtained in the step (3) to obtain the nitrogen-oxygen co-coordinated iron monatomic catalyst Fe-N2O2. The catalyst can effectively activate peroxymonosulfate, has high degradation efficiency on various phenolic pollutants, and has strong anti-interference ability and low metal leaching level.

Description

Technical Field

[0001] This invention relates to the fields of catalysts and organic wastewater treatment technology, and in particular to a nitrogen-oxygen co-coordinated iron single-atom catalyst, its preparation method, and its application in the degradation of phenolic pollutants. Background Technology

[0002] Phenolic compounds and their derivatives are widely found in wastewater from industries such as chemical, coking, coatings, and pharmaceuticals. They are characterized by high toxicity, strong stability, and difficulty in natural degradation, and improper treatment can easily have adverse effects on the ecological environment and human health. Persulfate-based advanced oxidation technologies (PMS-AOPs) have attracted attention due to their strong oxidizing power and wide applicable pH range; however, their treatment effect largely depends on the activity and stability of the catalyst. Single-atom catalysts (SACs) show good application potential in this type of system due to their high atom utilization, well-defined active sites, and tunable coordination environment. Among them, iron-based SACs have good application potential due to the low cost, abundant sources, and good environmental compatibility of iron. However, traditional iron-based SACs still suffer from limited active site utilization, secondary pollution caused by metal leaching, and difficulty in precisely controlling the catalytic reaction pathway, which restricts their application in practical wastewater treatment.

[0003] Existing research indicates that by constructing a nitrogen-oxygen co-coordination structure, the local electronic environment of the iron center can be tuned, thereby affecting the activation process of persulfate and the degradation efficiency of pollutants. Compared to a single nitrogen coordination structure, the nitrogen-oxygen co-coordination structure has potential advantages in improving catalytic activity and reaction selectivity. Therefore, it is necessary to develop a nitrogen-oxygen co-coordinating iron single-atom catalyst with a defined coordination environment, a controllable preparation process, and suitability for the degradation of phenolic pollutants. Summary of the Invention

[0004] To address the problems of uncontrollable coordination environment, complex preparation process, and insufficient catalytic stability of existing iron-based single-atom catalysts, this invention proposes a nitrogen-oxygen co-coordinated iron single-atom catalyst, its preparation method, and its application in the degradation of phenolic pollutants. This invention, through a strategy combining "ligand pre-design" and "inert template anchoring," can obtain a nitrogen-oxygen co-coordinated iron single-atom catalyst with a more defined coordination environment. This catalyst exhibits high degradation efficiency for various phenolic pollutants, strong anti-interference ability, and low metal leaching level.

[0005] The first objective of this invention is to provide a method for preparing a nitrogen-oxygen co-coordinated iron single-atom catalyst, comprising the following steps: (1) Disperse o-phenylenediamine and salicylaldehyde in a first organic solvent to obtain a mixture, heat the mixture to react, and then remove the first organic solvent to obtain a saprofen-type Schiff base ligand; (2) Disperse the iron salt, the saprofen-type Schiff base ligand and the template agent described in step (1) in a second organic solvent to obtain a mixture, heat the mixture to react, and then remove the second organic solvent to obtain the pyrolysis precursor; (3) Heat-treat the pyrolysis precursor obtained in step (2) and cool it to obtain the crude product; (4) The crude product obtained in step (3) is washed and dried to obtain the nitrogen-oxygen co-coordinated iron single-atom catalyst Fe-N2O2.

[0006] Preferably, in step (1), the first organic solvent is selected from at least one of methanol and ethanol; the molar ratio of o-phenylenediamine to salicylaldehyde is 1:2, and the molar concentration of salicylaldehyde in the mixture is 0.04~4 mol / L; the heating reaction conditions are: temperature of 60℃~80℃, time of 4~6 h.

[0007] In step (1), o-phenylenediamine and salicylaldehyde are dispersed in a first organic solvent, and then ultrasonically dispersed and heated and stirred to form a homogeneous mixture. The first organic solvent is removed by rotary evaporation and filtration. The ultrasonic dispersion frequency is 10~50 kHz and the time is 10~60 min.

[0008] Further preferred, in step (1), the molar concentration of salicylaldehyde in the mixture is 0.4 mol / L; the heating reaction conditions are: temperature 70℃, time 4 h.

[0009] Preferably, in step (2), the iron salt is selected from at least one of ferric acetate, ferric chloride and ferric nitrate; the template agent (inert template agent) is selected from at least one of magnesium oxide, sodium chloride and silicon dioxide; and the second organic solvent is selected from at least one of methanol and ethanol.

[0010] In step (2), the iron salt, saprofen-type Schiff base ligand, and template agent are dispersed in a second organic solvent. After ultrasonic dispersion and heating and stirring, a homogeneous mixture is formed. The second organic solvent is removed by rotary evaporation to obtain the pyrolysis precursor. The ultrasonic dispersion frequency is 10~50 kHz, and the time is 10~60 min.

[0011] Preferably, in step (2), the molar ratio of the iron salt to the saprofen-type Schiff base ligand is 1:12 to 3:1, the molar ratio of the saprofen-type Schiff base ligand to the template agent is 1:40 to 60, and the molar concentration of the iron salt in the mixture is 0.01 to 0.12 mol / L; the heating reaction conditions are: temperature of 60℃ to 80℃ and time of 6 to 12 h.

[0012] Further preferred, in step (2), the molar ratio of the iron salt to the saprofen-type Schiff base ligand is 1:1 to 3:1, the molar ratio of the saprofen-type Schiff base ligand to the template agent is 1:53, and the molar concentration of the iron salt in the mixture is 0.06 mol / L; the heating reaction conditions are: temperature 80℃ and time 8 h.

[0013] Preferably, in step (3), the heat treatment conditions are as follows: under an inert atmosphere, the temperature is increased to 500℃~800℃ at a heating rate of 2~5℃ / min and held for 60~180 min. The inert atmosphere is nitrogen, argon or hydrogen.

[0014] Further preferred, in step (3), the heat treatment conditions are: under an inert atmosphere, the temperature is raised to 600°C at a heating rate of 2°C / min and held for 120 min.

[0015] Preferably, the specific conditions for washing and drying in step (4) are as follows: the inorganic acid solution is heated and acid-washed, followed by washing and drying. The inorganic strong acid used for acid washing is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid. The concentration of the inorganic strong acid is 0.5~1.5 mol / L, the solid-liquid ratio of acid washing is 30~40 g / L, the acid washing temperature is 60℃~80℃, and the time is 6~8 h.

[0016] Further optimization involves using an inorganic strong acid concentration of 1 mol / L, a solid-liquid ratio of 35 g / L, a pickling temperature of 80℃, and a pickling time of 8 h.

[0017] The second objective of this invention is to provide a nitrogen-oxygen co-coordinated iron single-atom catalyst prepared by the aforementioned preparation method, wherein iron is dispersed in the form of single atoms on the surface of a carbon-based support, and the iron active center is formed by two nitrogen atoms and two oxygen atoms coordinating to form a Fe-N2O2 structure, and the iron loading in the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.036~2.008 wt%.

[0018] A third object of the present invention is to provide the application of the nitrogen-oxygen co-coordinated iron single-atom catalyst in the degradation of phenolic pollutants, wherein the phenolic pollutants are selected from at least one of phenol (PN), bisphenol A (BPA), tetrabromobisphenol A (TBBPA), fluorophenols (e.g., 4-fluorophenol (4-FP)), chlorophenols (e.g., 4-chlorophenol (4-CP), 3-chlorophenol (3-CP), 2-chlorophenol (2-CP), 3,5-dichlorophenol (3,5-DCP), 2,3,5-trichlorophenol (2,3,5-TCP) and 3,4,5-trichlorophenol (3,4,5-TCP)) and bromophenols (e.g., 4-bromophenol (4-BP)).

[0019] Preferably, the nitrogen-oxygen co-coordinated iron single-atom catalyst and persulfate are added to the wastewater containing phenolic pollutants to degrade the phenolic pollutants. The dosage of the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.02~0.30 g / L, the mass ratio of the nitrogen-oxygen co-coordinated iron single-atom catalyst to persulfate is 1:1.0~1:4.5, and the pH value of the wastewater is 3.0~11.0. The dosage of the nitrogen-oxygen co-coordinated iron single-atom catalyst refers to the amount of nitrogen-oxygen co-coordinated iron single-atom catalyst added per liter of wastewater.

[0020] Further optimization resulted in the following: the dosage of the nitrogen-oxygen co-coordinated iron single-atom catalyst was 0.15 g / L, and the mass ratio of the nitrogen-oxygen co-coordinated iron single-atom catalyst to persulfate was 1:4.098. The persulfate was a potassium persulfate complex salt.

[0021] This invention involves adding a nitrogen-oxygen co-coordinated iron single-atom catalyst and persulfate to the wastewater to be treated, selectively generating singlet oxygen (…). 1 O2 can efficiently degrade various phenolic pollutants, especially in the treatment of phenol and halogenated phenolic pollutants. It has strong resistance to water matrix interference, and the metal leaching amount is less than 2.0 μg / L; further combined with electrospinning technology, a catalytic membrane (Fe-N2O2@PAN) can be prepared, which can achieve stable operation in a continuous flow reactor for 24 h with low pollutant detection.

[0022] This invention also protects a catalyst membrane for electrospinning, wherein the catalyst membrane is formed by supporting the nitrogen-oxygen co-coordinated iron single-atom catalyst on a fiber support, and is prepared by the following steps: the nitrogen-oxygen co-coordinated iron single-atom catalyst is mixed with polyacrylonitrile (PAN), dimethylformamide (DMF) and acetone, and ultrasonically stirred to prepare a casting solution, and the catalyst membrane (Fe-N2O2@PAN) is prepared by electrospinning.

[0023] The catalytic membrane is prepared by the following steps: dissolving polyacrylonitrile in dimethylformamide to obtain solution A, wherein the concentration of polyacrylonitrile in solution A is 0.1~0.4 g / mL; mixing dimethylformamide and acetone in a volume ratio of 1~2:1 to obtain solution B; mixing the nitrogen-oxygen co-coordinated iron single-atom catalyst, dimethylformamide, and acetone to obtain solution C, wherein the volume ratio of dimethylformamide to acetone in solution C is 1~2:1, and the concentration of the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.03~0.05 g / mL; mixing solutions A, B, and C in a volume ratio of 1:1:1~5:1:1, stirring for 6~12 h to form a casting solution, and finally electrospinning and calcining to obtain the catalytic membrane.

[0024] Further preferably, the catalytic membrane is prepared by the following steps: dissolving polyacrylonitrile in dimethylformamide to obtain solution A, wherein the concentration of polyacrylonitrile in solution A is 0.17~0.18 g / mL; mixing dimethylformamide and acetone in a volume ratio of 1.5:1 to obtain solution B; mixing the nitrogen-oxygen co-coordinated iron single-atom catalyst, dimethylformamide, and acetone to obtain solution C, wherein the volume ratio of dimethylformamide to acetone in solution C is 1.5:1, and the concentration of the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.04 g / mL; mixing solutions A, B, and C in a volume ratio of 4:1:1, stirring for 6~12 h to form a casting solution, and finally electrospinning and calcining to obtain the catalytic membrane.

[0025] The electrospinning process parameters are as follows: rotation speed: 800~1200 r / min, positive high voltage: 15.0~16.5 kV, negative high voltage: 5.5~10.5 kV, pump flow rate: 0.5~1.5 mL / h, and spinning time: 7~8 h under the conditions of a spray spacing of 10~15 cm. The entire membrane is hot-pressed and then calcined at 600°C for 2 h under a nitrogen atmosphere with a heating rate of 2°C / min to obtain the catalytic membrane.

[0026] The present invention also protects the application of the catalytic membrane in the degradation of phenolic pollutants in a continuous flow reactor, wherein the phenolic pollutants are selected from at least one of phenol, bisphenol A, tetrabromobisphenol A, fluorophenol, chlorophenol, and bromophenol.

[0027] The catalytic membrane is encapsulated in a continuous flow reactor, and a mixed solution containing persulfate and phenolic pollutants with a concentration of 0.8-1.2 mg / L is fed into it at a flow rate of 0.5-1.5 mL / min. The catalytic membrane is placed in the continuous flow reactor to achieve continuous degradation treatment of wastewater.

[0028] The specific steps are as follows: The catalytic membrane is encapsulated in the membrane reactor. Using a peristaltic pump, wastewater containing phenolic pollutants with a concentration of 0.8-1.2 mg / L and a 1 mM PMS solution are fed into the membrane reactor at a flow rate of 0.5-1.5 mL / min through the delivery pipe. The wastewater and 1 mM PMS solution are then fed into the same outlet for continuous degradation treatment.

[0029] The catalytic membrane proposed in this invention can achieve stable operation for up to 24 hours under continuous flow conditions, and has good prospects for practical application.

[0030] Compared with the prior art, the present invention has the following advantages: (1) The present invention uses a strategy combining “ligand pre-design” and “inert template anchoring” to obtain nitrogen-oxygen co-coordinated iron single-atom catalysts with a clear coordination environment. The preparation process is relatively simple and has good reproducibility.

[0031] (2) The catalyst proposed in this invention can effectively activate persulfate, has a high degradation efficiency for a variety of phenolic pollutants, and exhibits strong anti-interference ability and low metal leaching level.

[0032] (3) The catalyst proposed in this invention can be further made into a catalytic membrane to achieve stable operation for up to 24 hours under continuous flow conditions, and has good prospects for practical application. Attached Figure Description

[0033] Figure 1 This is a graph showing the iron loading of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Examples 1-5; Figure 2 The graph shows the performance of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Examples 1-5 in removing phenol using an advanced oxidation process. Figure 3 This is a scanning electron microscope image of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Example 1; Figure 4 These are transmission electron microscope images and mapping diagrams of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Example 1. Figures a and b show the morphology of Fe-N2O2 at 200 nm, 50 nm, 20 nm and 5 nm, respectively. Figure e shows the region scanned by energy dispersive spectroscopy at the 50 nm scale. The mapping diagram in Figure fi shows the elemental distribution of C, N, O and Fe in Fe-N2O2. Figure 5 This is a spherical aberration electron microscope image of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Example 1; Figure 6 These are high-resolution Fe 2p X-ray photoelectron spectra of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Example 1 before and after use; Figure 7 The graph shows the removal performance of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in Example 1 using an advanced oxidation process for different phenolic pollutants. Figure 8 This is a graph showing the removal performance of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in Example 2 using an advanced oxidation process for different halogenated phenol pollutants; Figure 9 This is a graph showing the effect of pH on the application of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in the advanced oxidation process in Example 3. Figure 10This is a diagram showing the common cation and anion effects of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in advanced oxidation processes, as shown in Example 4. Figure 11 This is a quenching experiment diagram of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in the advanced oxidation process in Example 5; Figure 12 The electron paramagnetic resonance (EPR) spectrum of persulfate activated by the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in Example 5 is shown. Figure 13 This is a cyclic experimental diagram of the application of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) in the advanced oxidation process in Example 6; Figure 14 This is a scanning electron microscope image of the nitrogen-oxygen co-coordinated iron single-atom catalytic membrane (Fe-N2O2) in Application Example 7; Figure 15 This is a graph showing the phenol removal performance of the nitrogen-oxygen co-coordinated iron single-atom catalytic membrane (Fe-N2O2@PAN) in the continuous advanced oxidation process application of Example 7. Detailed Implementation

[0034] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental materials and reagents used herein are commercially available products conventionally available in this technical field.

[0036] A method for preparing a nitrogen-oxygen co-coordinated iron single-atom catalyst includes the following steps: (1) Disperse o-phenylenediamine and salicylaldehyde in a first organic solvent, and form a uniform mixture by ultrasonic dispersion and heating and stirring. Remove the first organic solvent by rotary evaporation and filtration to obtain an orange saprofen-type Schiff base ligand. (2) The iron salt, the saprofen-type Schiff base ligand and the inert template agent are dispersed in the second organic solvent, and a uniform mixture is formed by ultrasonic dispersion and heating and stirring. After the second organic solvent is removed by rotary evaporation, the pyrolysis precursor is obtained. (3) The precursor obtained in step (2) is ground, sieved and then calcined to obtain a black solid; (4) The black solid obtained in step (3) is heated and acid-washed with an inorganic acid solution, and then washed, dried and ground to obtain a nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2).

[0037] In the following preferred embodiments, the first organic solvent in step (1) is selected from one or more of methanol and ethanol, the molar ratio of o-phenylenediamine to salicylaldehyde is 1:2, the molar concentration of salicylaldehyde in the mixture is 0.04~4 mol / L, the ultrasonic dispersion frequency is 10~50 kHz, the time is 10~60 min, and the heating and stirring temperature is 60℃~80℃, the time is 4~6 h.

[0038] In the following preferred embodiments, in step (2), the iron salt is selected from one or more of ferric chloride, ferric sulfate, and ferric acetate; the inert template agent is selected from one or more of sodium chloride, silicon dioxide, and magnesium oxide; the second organic solvent is selected from one or more of methanol, ethanol, and acetonitrile; the molar ratio of iron salt to saprofen-type Schiff base ligand is 1:12 to 3:1, the molar ratio of saprofen-type Schiff base ligand to inert template agent is 1:40 to 60, the molar concentration of iron salt in the mixture is 0.01 to 0.12 mol / L; the ultrasonic dispersion frequency is 10 to 50 kHz, the time is 10 to 60 min; the heating and stirring temperature is 60℃ to 80℃, and the time is 6 to 12 h.

[0039] In the preferred embodiment described below, the calcination conditions in step (3) are as follows: the temperature is increased to 500℃~800℃ at a rate of 2~10℃ / min under an inert atmosphere (nitrogen, argon or hydrogen) and held for 60~180 min; the inorganic strong acid used for pickling is one or more of hydrochloric acid, sulfuric acid or nitric acid, with a concentration of 0.5~1.5 mol / L, a solid-liquid ratio of 7 g / L, a pickling temperature of 60℃~80℃, and a pickling time of 6~8 h.

[0040] The above-mentioned catalyst has environmental applications in the degradation of phenolic pollutants in persulfate-based advanced oxidation systems, including the addition of the catalyst and persulfate to wastewater to be treated to selectively generate singlet oxygen. 1 O2 can efficiently degrade a variety of phenolic pollutants, especially in the treatment of phenol and halogenated phenolic pollutants.

[0041] A method for preparing a catalytic membrane by electrospinning includes the following steps: mixing Fe-N2O2 catalyst with polyacrylonitrile (PAN), dimethylformamide (DMF) and acetone, preparing a casting solution by ultrasonic stirring, and calcining by electrospinning to prepare a catalytic membrane (Fe-N2O2@PAN).

[0042] In the preferred embodiment described below, the casting solution preparation process is as follows: 10-20 g of polyacrylonitrile (PAN) is dissolved in 50-100 mL of dimethylformamide (DMF) to obtain solution A; 5-10 mL of DMF and 5-10 mL of acetone are mixed to obtain solution B; 150-300 mg of Fe-N2O2, 5-10 mL of DMF and 5-10 mL of acetone are mixed to obtain solution C; solutions A, B and C are mixed in a ratio of 1:1:1 to 5:1:1 and stirred for 6-12 h to form the casting solution, which is then subjected to electrospinning.

[0043] The electrospinning process parameters were as follows: rotation speed: 800~1200 r / min, positive high voltage: 15.0~16.5 kV, negative high voltage: 5.5~10.5 kV, pump flow rate: 0.5~1.5 mL / h, and spinning time: 8 h under the conditions of a jetting distance of 5~10 cm. The entire film was then hot-pressed and calcined at 600°C for 2 h under a nitrogen atmosphere with a heating rate of 2°C / min.

[0044] In the preferred embodiments described below, the catalyst dosage is 0.02~0.30 g / L, the mass ratio of nitrogen-oxygen co-coordinated iron single-atom catalyst to persulfate is 1:1.0~1:4.5, the persulfate concentration is 0.5~4.0 mM, and the wastewater pH range is 3.0~11.0.

[0045] The iron loading in the iron single-atom catalyst proposed in this invention is calculated as: (mass of iron / total mass of catalyst) × 100%. The specific steps are as follows: the iron single-atom catalyst is added to aqua regia and digested using a microwave digester. After digestion, only a solution containing metallic iron remains. The solution is then brought to a final volume and tested using an ICP-OES instrument to calculate the mass of metallic iron.

[0046] The specific steps are as follows: Weigh 10 mg of iron single-atom catalyst into a microwave digestion vessel, then add 5 mL of nitric acid, 2 mL of hydrochloric acid, and 1 mL of hydrofluoric acid sequentially. Assemble the digestion vessel and prepare a blank sample simultaneously. Turn on the microwave digester and set the program to: pressure 30 bar, power 500 W, temperature 200℃, and a heating program of 10 min to reach 200℃, followed by 30 min of constant temperature, and then cooling. After digestion is complete and the temperature drops to room temperature, only a solution containing metallic iron remains. Remove the solution from the digestion vessel and evaporate it to 2 mL on a hot plate. Finally, make up the volume with 10 mL. After volume adjustment, use an ICP-OES instrument to test and calculate the mass of metallic iron.

[0047] Example 1 A method for preparing a nitrogen-oxygen co-coordinated iron single-atom catalyst includes the following steps: (1) 20 mmol o-phenylenediamine was dispersed in 100 mL methanol, followed by the addition of 40 mmol salicylaldehyde. The mixture was ultrasonically dispersed (ultrasonic dispersion frequency of 30 kHz) for 30 min. The mixture was stirred in an oil bath at 70 °C for 4 h. Methanol was then removed by rotary evaporation and vacuum filtration to obtain orange saprofen-type Schiff base ligand.

[0048] (2) 6.0 mmol ferric acetate and 6.0 mmol saprofen-type Schiff base ligand were dissolved in 100 mL ethanol, stirred for 5 min, and then ultrasonically dispersed for 30 min. Subsequently, 320 mmol magnesium oxide was added, and the mixture was ultrasonically dispersed again (ultrasonic dispersion frequency of 30 kHz) for 30 min, and then stirred in an oil bath at 80 ℃ for 8 h. After the reaction was completed, the ethanol was removed by rotary evaporation to obtain the pyrolysis precursor.

[0049] (3) The obtained precursor was ground in an agate grinding bowl and sieved through a 100-mesh sieve. It was then placed in a quartz boat and heated to 600 ℃ at a heating rate of 2 ℃ / min under a nitrogen atmosphere and held for 120 min. After cooling to room temperature, a black solid was obtained.

[0050] (4) Weigh 7 g of black solid and mix it with 200 mL of 1.0 M sulfuric acid solution. Wash it with acid at 80 °C for 8 h. Then wash the resulting solid until neutral, dry and grind it to obtain nitrogen-oxygen co-coordinated iron single-atom catalyst, denoted as (1:1)Fe-N2O2.

[0051] The nitrogen-oxygen co-coordinated iron single-atom catalyst was tested, and the Fe-N2O2 metal loading was as follows: Figure 1 As shown, the scanning electron microscope image is as follows: Figure 3 As shown, the transmission electron microscope (TEM) image and mapping diagram are as follows: Figure 4 As shown, the spherical aberration electron microscope image is as follows: Figure 5 As shown, the detection results indicate that the iron loading in the obtained Fe-N2O2 catalyst is 2.008 wt%. Aberration-corrected electron microscopy results show that no obvious iron nanoparticles and clusters were observed in the sample, indicating that the iron species exist in a highly dispersed state; elemental mapping results show that iron, carbon, nitrogen and oxygen elements are relatively uniformly distributed.

[0052] High-resolution Fe 2p X-ray photoelectron spectroscopy of Fe-N2O2 is shown below. Figure 6 As shown, the bimodal characteristic peak at 709.7 eV is attributed to Fe. 2+ The double characteristic peak at 711.4 eV is attributed to Fe. 3+ Other peaks are considered satellite peaks.

[0053] Example 2 Compared to Example 1, the difference was that the molar amount of iron acetate was 0.5 mmol. A single-atom iron catalyst was obtained, named (1:12)Fe-N2O2, with the metal loading of (1:12)Fe-N2O2 as follows... Figure 1 As shown, the iron loading is 0.036 wt%; only single-atom iron structures exist on the surface.

[0054] Example 3 Compared to Example 1, the difference is that the molar amount of iron acetate is 2 mmol. A single-atom iron catalyst was obtained, named (1:3)Fe-N2O2, and the metal loading of (1:3)Fe-N2O2 is as follows: Figure 1 As shown, the iron load is 1.804 wt%; only single-atom iron structures exist on the surface.

[0055] Example 4 Compared to Example 1, the difference is that the molar amount of iron acetate is 3 mmol. A single-atom iron catalyst was obtained, named (1:2)Fe-N2O2, and the metal loading of (1:2)Fe-N2O2 is as follows: Figure 1 As shown, the iron loading is 1.506 wt%; only single-atom iron structures exist on the surface.

[0056] Example 5 Compared to Example 1, the difference is that the molar amount of iron acetate is 18 mmol. The resulting iron catalyst was named (3:1)Fe-N2O2, and the metal loading of (3:1)Fe-N2O2 was as follows... Figure 1 As shown, the iron loading is 0.818 wt%; the surface only has iron single-atom structures. The catalyst obtained by the molar ratio of iron acetate to saprofen-type Schiff base ligand of 3:1 has iron agglomeration during the catalyst synthesis reaction due to the excessive amount of iron salt added. Iron clusters or nano-iron particles are easily dissolved and eluted by sulfuric acid during the acid washing process, resulting in a low metal loading in the catalyst.

[0057] Example 6 Compared with Example 1, the differences are as follows: In step (1), the molar concentration of salicylaldehyde in the mixture is 0.04 mol / L; the heating reaction conditions are: temperature 60℃, time 6 h; In step (2), the molar ratio of saprofen-type Schiff base ligand to template agent is 1:40; the heating reaction conditions are: temperature 60℃, time 12 h; In step (3), the heat treatment conditions are: under an inert atmosphere, the temperature is raised to 500℃ at a heating rate of 2℃ / min and held for 180 min.

[0058] Example 7 Compared with Example 1, the differences are as follows: In step (1), the molar concentration of salicylaldehyde in the mixture is 4 mol / L; the heating reaction conditions are: temperature 80℃, time 4 h; In step (2), the molar ratio of salicylaldehyde-type Schiff base ligand to template agent is 1:60; the heating reaction conditions are: temperature 80℃, time 6 h; In step (3), the heat treatment conditions are: under an inert atmosphere, the temperature is raised to 800℃ at a heating rate of 5℃ / min and held for 60 min.

[0059] Application Example 1 The degradation experiments were conducted in 100 mL containers with shaking at 25 °C and 150 rpm. 7.5 mg of the Fe-N₂O₂ (iron single-atom catalyst) obtained in Examples 1-5 was added to 50 mL of 10 mg L⁻¹ solution. -1 A solution of phenol or other novel pollutants (4-chlorophenol (4-CP), bisphenol A (BPA), tetrabromobisphenol A (TBBPA)) (pH 7.0) was prepared by sonication for 30 s to ensure uniform catalyst dispersion. Subsequently, 0.2 mL of a 250 mM potassium persulfate complex solution was added to the solution, marking the start of the degradation reaction. Samples of the reaction solution were taken at 0, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 min. The samples were filtered through a 0.22 μm aqueous filter, and the concentrations of phenol or other novel pollutants were detected by high-performance liquid chromatography (HPLC) or HPLC-MS / MS. All experiments were performed in triplicate, and the removal efficiency of the novel pollutants was calculated.

[0060] Phenol was degraded using Fe-N2O2 catalysts with different proportions, and the experimental results are as follows: Figure 2 As shown, the degradation efficiency of (1:12) Fe-N2O2 was only 20.89%, while the degradation rates of (1:3) Fe-N2O2, (1:2) Fe-N2O2, (1:1) Fe-N2O2 and (3:1) Fe-N2O2 were 54.56%, 87.60%, 100% and 100%, respectively.

[0061] Experimental results are as follows Figure 7 As shown, (1:1) Fe-N2O2 can effectively activate potassium persulfate composite salt. Within 5 min, its removal rate for four phenolic pollutants was higher than 93%, with phenol (PN) and 4-chlorophenol (4-CP) both achieving 100% removal rates, bisphenol A (BPA) at 96.29%, and tetrabromobisphenol A (TBBPA) at 93.79%. These results indicate that the catalyst has a good removal effect on various phenolic pollutants.

[0062] Application Example 2 The difference from Application Example 1 is that the contaminants are 4-fluorophenol (4-FP), 4-bromophenol (4-BP), 4-chlorophenol (4-CP), 3-chlorophenol (3-CP), 2-chlorophenol (2-CP), 3,5-dichlorophenol (3,5-DCP), 2,3,5-trichlorophenol (2,3,5-TCP) and 3,4,5-trichlorophenol (3,4,5-TCP).

[0063] Experimental results are as follows Figure 8 As shown, within 5 min, the removal efficiency of (1:1) Fe-N2O2 for eight halogenated phenolic pollutants was higher than 97%, with removal efficiencies of 99.21% for 4-fluorophenol (4-FP), 100% for 4-bromophenol (4-BP), 100% for 4-chlorophenol (4-CP), 98.98% for 3-chlorophenol (3-CP), 98.51% for 2-chlorophenol (2-CP), 97.12% for 3,5-dichlorophenol (3,5-DCP), 99.95% for 2,3,5-trichlorophenol (2,3,5-TCP), and 98.63% for 3,4,5-trichlorophenol (3,4,5-TCP). This indicates that the catalyst has a good degradation effect on different halogenated phenols.

[0064] Application Example 3 Compared with Application Example 1, the difference is that the pollutant is phenol, and the reaction pH values ​​are 3, 5, 6.7, 9, and 11, respectively.

[0065] Experimental results are as follows Figure 9 As shown, (1:1)Fe-N2O2 can activate potassium persulfate complex salt to completely remove phenol in the pH range of 3 to 9, and has broad pH application potential.

[0066] Application Example 4 Compared to Application Example 1, the difference lies in that the pollutant is phenol, and the reaction process involves common anions and cations, such as 10 mMCl. - NO3 - SO4 2- H2PO4 - HPO4 2- Na + Fe 3+ Ca 2+ Mg 2+ Ni + and K + One of them.

[0067] Experimental results are as follows Figure 10As shown, some coexisting ions have less than 3% effect on the removal of phenol by (1:1) Fe-N2O2-activated potassium persulfate composite salt, while the remaining ions show a certain promoting effect on phenol removal. These results indicate that Fe-N2O2 still possesses good anti-interference ability under common ion coexistence conditions.

[0068] Application Example 5 The difference compared to Application Example 1 is that the pollutant is phenol, and the reaction process involves a common quencher, such as methanol (MeOH), which can quench H₂O• and SO₄•. - tert-butanol (TBA) can quench HO•, and p-BQ (p-benzoquinone) can quench O2•. - Furfural (FFA) can quench [the virus]. 1 O2 and dimethyl sulfoxide (DMSO) can quench high-valence metal species.

[0069] Experimental results are as follows Figure 11 As shown, the effects of 100 mM methanol (MeOH), 100 mM tert-butanol (TBA), and 5 mM dimethyl sulfoxide (DMSO) on the degradation of phenol by (1:1) Fe-N2O2 activated potassium persulfate complex salt were all less than 5%. However, in the presence of 5 mM p-benzoquinone (p-BQ) and 5 mM furfural (FFA), the degradation rate of phenol decreased from 100% to 27.24% and 45.27%, respectively, indicating that O2• - and 1 O2 species are active species that cause phenol degradation.

[0070] In addition, such as Figure 12 As shown, electron paramagnetic resonance (EPR) before and after p-BQ quenching further confirmed the existence of singlet oxygen species and demonstrated that some... 1 O2 is produced by O2• - It was transformed.

[0071] Application Example 6 Compared to Application Example 1, the difference lies in the following: the new contaminant is phenol. The used (1:1) Fe-N2O2 is sequentially recovered by centrifugation, washed with ethanol, and dried overnight before the next cycle, accumulating four cycles. Subsequently, it undergoes heat treatment for reuse, at 2°C min under nitrogen atmosphere. -1 The temperature was increased to 600℃ and held for 120 min. After cooling to room temperature, the cooled black solid was ground and sieved to further degrade phenol.

[0072] Experimental results are as follows Figure 13As shown, (1:1) Fe-N2O2 maintained a phenol removal performance of over 90% after three applications, with the leaching concentration of metallic iron below 2.0 μg / L. After a fourth degradation application, the degradation performance decreased, but through heat recovery, it was restored to 95%. Therefore, Fe-N2O2 exhibits good stability.

[0073] Application Example 7 To explore the continued application potential of (1:1) Fe-N2O2. 15 g of polyacrylonitrile (PAN) was dissolved in 85 mL of dimethylformamide (DMF), heated to 60 °C and stirred for 6 h. 20 mL of this mixture was taken to obtain solution A. Dimethylformamide and acetone were mixed in a volume ratio of 3:2 to obtain solution B. 200 mg of the nitrogen-oxygen co-coordinated iron single-atom catalyst (Fe-N2O2) obtained in Example 1, 3 mL of dimethylformamide, and 2 mL of acetone were mixed and stirred to obtain solution C. Solution C was then poured into solution A and rinsed with solution B. Solutions A, B, and C were mixed in a volume ratio of 4:1:1 and stirred for 6 h to form a casting solution. Electrospinning was then performed using an electrospinning machine at a speed of 1000 r / min, a positive voltage of 15 kV, a negative voltage of 7.5 kV, a pump flow rate of 1 mL / h, and a jet spacing of 10 cm for 8 h. The entire membrane was hot-pressed and then calcined at 600°C for 2 h under a nitrogen atmosphere at a rate of 2°C / min to obtain a nitrogen-oxygen co-coordinated iron single-atom catalytic membrane (Fe-N2O2@PAN). Figure 14 ).

[0074] The nitrogen-oxygen co-coordinated iron single-atom catalytic membrane was placed in a continuous flow device. The specific steps were as follows: the nitrogen-oxygen co-coordinated iron single-atom catalytic membrane was encapsulated in a membrane reactor. Using a peristaltic pump, wastewater containing phenol with a concentration of 1 mg / L and a 1 mM potassium persulfate complex salt solution were pumped into the membrane reactor at a flow rate of 1.0 mL / min through a delivery pipe. The solutions were then converged into the same outlet and flowed into the membrane reactor for continuous degradation treatment. The effluent solution from the continuous flow device was collected at a given time, filtered through a 0.22 μm aqueous filter, and the phenol concentration was detected by high performance liquid chromatography.

[0075] Experimental results are as follows Figure 15 As shown, phenol was completely removed during the 22 h operation of Fe-N2O2@PAN in the continuous flow unit, indicating that the catalytic membrane has good continuous operation stability and application potential.

[0076] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. The application of nitrogen-oxygen co-coordinated iron single-atom catalysts in the degradation of phenolic pollutants in persulfate-based advanced oxidation systems, characterized in that, The phenolic pollutants are selected from at least one of phenol, bisphenol A, tetrabromobisphenol A, fluorophenol, chlorophenol, and bromophenol; in the nitrogen-oxygen co-coordinated iron single-atom catalyst, iron is dispersed in single-atom form on the surface of the carbon-based support, and the iron active center is coordinated by two nitrogen atoms and two oxygen atoms to form a Fe-N2O2 structure. The iron loading in the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.036~2.008 wt%. The preparation method of the nitrogen-oxygen co-coordinated iron single-atom catalyst includes the following steps: (1) Disperse o-phenylenediamine and salicylaldehyde in a first organic solvent to obtain a mixture, heat the mixture to react, and then remove the first organic solvent to obtain a saprofen-type Schiff base ligand. The first organic solvent is selected from at least one of methanol and ethanol. The molar ratio of o-phenylenediamine to salicylaldehyde is 1:2, and the molar concentration of salicylaldehyde in the mixture is 0.04~4 mol / L. The heating reaction conditions are: temperature 60℃~80℃, time 4~6 h. (2) The iron salt, the saprofen-type Schiff base ligand and the template agent described in step (1) are dispersed in a second organic solvent to obtain a mixture, heated to react, and then the second organic solvent is removed to obtain a pyrolysis precursor. The template agent is selected from at least one of magnesium oxide and sodium chloride. The molar ratio of the iron salt to the saprofen-type Schiff base ligand is 1:2 to 1:1, and the molar ratio of the saprofen-type Schiff base ligand to the template agent is 1:40 to 60. (3) Heat-treat the pyrolysis precursor obtained in step (2) and cool it to obtain the crude product. The heat treatment conditions are: under an inert atmosphere, heat the product to 500℃~800℃ at a heating rate of 2~5℃ / min and hold it for 60~180 min. (4) The crude product obtained in step (3) is washed and dried to obtain the nitrogen-oxygen co-coordinated iron single-atom catalyst Fe-N2O2. The specific conditions for washing and drying are: acid washing with an inorganic acid solution, followed by washing and drying. The inorganic acid used for acid washing is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid.

2. The application according to claim 1, characterized in that, In step (2), the iron salt is selected from at least one of ferric acetate, ferric chloride and ferric nitrate; the second organic solvent is selected from at least one of methanol and ethanol.

3. The application according to claim 1 or 2, characterized in that, In step (2), the molar concentration of iron salt in the mixture is 0.01~0.12 mol / L; the heating reaction conditions are: temperature 60℃~80℃, time 6~12 h.

4. The application according to claim 1, characterized in that, The nitrogen-oxygen co-coordinated iron single-atom catalyst and persulfate are added to the wastewater containing phenolic pollutants to degrade the phenolic pollutants. The dosage of the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.02~0.30 g / L, the mass ratio of the nitrogen-oxygen co-coordinated iron single-atom catalyst to persulfate is 1:1.0~1:4.5, and the pH value of the wastewater is 3.0~11.

0.

5. The application of an electrospun catalytic membrane in the degradation of phenolic pollutants in a continuous flow reactor, characterized in that, The catalytic membrane is formed by supporting a nitrogen-oxygen co-coordinated iron single-atom catalyst on a fiber support and is prepared by the following steps: the nitrogen-oxygen co-coordinated iron single-atom catalyst is mixed with polyacrylonitrile, dimethylformamide and acetone, and ultrasonically stirred to prepare a casting solution, and the catalytic membrane is prepared by electrospinning. In the nitrogen-oxygen co-coordinated iron single-atom catalyst, iron is dispersed in single-atom form on the surface of a carbon-based support. The iron active center is formed by two nitrogen atoms and two oxygen atoms coordinating to form a Fe-N2O2 structure. The iron loading in the nitrogen-oxygen co-coordinated iron single-atom catalyst is 0.036~2.008 wt%. The preparation method of the nitrogen-oxygen co-coordinated iron single-atom catalyst includes the following steps: (1) Disperse o-phenylenediamine and salicylaldehyde in a first organic solvent to obtain a mixture, heat the mixture to react, and then remove the first organic solvent to obtain a saprofen-type Schiff base ligand. The first organic solvent is selected from at least one of methanol and ethanol. The molar ratio of o-phenylenediamine to salicylaldehyde is 1:2, and the molar concentration of salicylaldehyde in the mixture is 0.04~4 mol / L. The heating reaction conditions are: temperature 60℃~80℃, time 4~6 h. (2) The iron salt, the saprofen-type Schiff base ligand and the template agent described in step (1) are dispersed in a second organic solvent to obtain a mixture, heated to react, and then the second organic solvent is removed to obtain a pyrolysis precursor. The template agent is selected from at least one of magnesium oxide and sodium chloride. The molar ratio of the iron salt to the saprofen-type Schiff base ligand is 1:2 to 1:1, and the molar ratio of the saprofen-type Schiff base ligand to the template agent is 1:40 to 60. (3) Heat-treat the pyrolysis precursor obtained in step (2) and cool it to obtain the crude product. The heat treatment conditions are: under an inert atmosphere, heat the product to 500℃~800℃ at a heating rate of 2~5℃ / min and hold it for 60~180 min. (4) The crude product obtained in step (3) is washed and dried to obtain the nitrogen-oxygen co-coordinated iron single-atom catalyst Fe-N2O2. The specific conditions for washing and drying are: acid washing with an inorganic acid solution, followed by washing and drying. The inorganic acid used for acid washing is selected from one or more of hydrochloric acid, sulfuric acid and nitric acid. The catalytic membrane is encapsulated in a continuous flow reactor, and a mixed solution containing persulfate and phenolic pollutants with a concentration of 0.8-1.2 mg / L is fed into it at a flow rate of 0.5-1.5 mL / min. The catalytic membrane is placed in the continuous flow reactor to achieve continuous degradation treatment of wastewater. The phenolic pollutants are selected from at least one of phenol, bisphenol A, tetrabromobisphenol A, fluorophenol, chlorophenol, and bromophenol.

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