Fe-N-C catalyst and application thereof in degradation of perfluorinated and polyfluoroalkyl substances

Abstract

The invention discloses a Fe-N-C catalyst and application thereof in degradation of perfluorinated and polyfluoroalkyl substances, and belongs to the technical field of water treatment. The preparation method comprises the following steps: taking nitrogen-doped carbon derived from pine cones as a substrate, dissolving aminated pine cones, FeCl36H2O, sodium acetate and polyethylene glycol in ethylene glycol, reacting at 200 DEG C for 10 hours, putting in an inert gas atmosphere, and calcining at 900 DEG C for 2 hours; the Fe-N-C catalyst which simultaneously contains Fe nano particles (Fe NPs) and Fe-N single atoms (Fe SAs) and has different sizes and double sites is prepared. The catalyst and PMS are mixed and then added into water, and perfluoro and polyfluoroalkyl substances in the water can be degraded; the catalyst can activate PMS to promote formation of a non-free radical pathway, depends on a degradation mechanism of Fe (IV) = O and singlet oxygen (O), the degradation rate of PFOA within 2 hours reaches 90.5%, and the catalyst also shows relatively strong tolerance in different natural water bodies; a key thought is provided for designing the efficient catalyst, and a new technical direction is expected to be provided for environmental treatment of persistent organic pollutants such as PFOA.

Description

Technical Field

[0001] This application relates to the field of new environmental materials, in particular to an Fe-N-C catalyst coexisting with nanoparticles and single-atom sites for highly selective generation of non-radical pathways to degrade perfluorooctanoic acid and its application in degrading per- and polyfluoroalkyl substances. Background Art

[0002] Per- and polyfluoroalkyl substances (PFASs), as important chemical raw materials, have been widely used in industrial fields such as textiles, papermaking, firefighting, and electronics, as well as in daily consumer products such as non-stick pans, waterproof clothing, and food packaging. Among them, perfluorooctanoic acid (PFOA) has strong chemical stability and bioaccumulation. Long-term exposure can cause a series of health risks: not only may it lead to liver and kidney function damage and immune function suppression, but it is also closely related to reproductive system abnormalities and cancer occurrence. On April 10, 2024, the US Environmental Protection Agency (USEPA) officially issued the first mandatory drinking water standard for PFOA, setting its maximum contaminant level (MCL) at 4.0 parts per trillion (4.0 ppt). Therefore, there is an urgent need to develop efficient and economical PFOA removal technologies to ensure public drinking water safety.

[0003] Currently, technologies such as adsorption, advanced oxidation processes (AOPs), advanced reduction processes, and thermal decomposition have been used to remove perfluorooctanoic acid (PFOA) in water. Among them, the advanced oxidation process based on peroxymonosulfate (PMS) (PMS-AOPs) has become a research hotspot due to its low cost, high efficiency, and ability to generate reactive species in situ at room temperature. Heterogeneous catalysts in the PMS-AOPs system do not require complex equipment and are easy to operate. Moreover, PMS can degrade PFOA through two pathways on the catalyst surface: free radicals (such as ·SO4 - , ·OH) and non-free radicals (such as 1 O2, Fe(IV)=O, electron transfer). Among them, the free radical pathway has the defects of high PMS consumption and short free radical lifetime, which not only reduces the degradation efficiency but also increases the cost. In contrast, the non-free radical pathway has the advantages of fewer side reactions, high reactive species yield, and wide application range. Therefore, regulating the reaction pathway from free radicals to non-free radicals is the key to improving the degradation efficiency.

[0004] The selectivity of the non-radical pathway mainly depends on the activation mode of PMS by the catalyst active sites. Iron-nitrogen-carbon (Fe-N-C) catalysts have become the most promising PMS activation materials due to their unique metal-nitrogen-carbon structure. The research has adopted strategies such as regulating the coordination environment of Fe active centers (such as FeN4 → FeN5), increasing the density of active sites (Fe loading reaches 11.2 wt%), and introducing heteroatom doping (such as Fe@N / C-S, Fe-Co dual-atom catalysts). However, the design of such catalysts relies on specific carbon precursors, and the synthesis conditions are harsh and the raw material costs are high, severely restricting their large-scale application. Summary of the Invention

[0005] In view of the above problems, this application uses pinecone-derived nitrogen-doped carbon as the substrate to prepare an Fe 0 / NC catalyst containing different-sized double sites of Fe nanoparticles (Fe NPs) and Fe-N4 single atoms (Fe SAs) to activate PMS to promote the formation of the non-radical pathway and improve the degradation effect of perfluoro- and polyfluoroalkyl substances based on PMS. SAs-NPs Specifically, this application realizes the above invention purpose through the following scheme:

[0006] Specifically, this application realizes the above invention purpose through the following scheme:

[0007] First, this application provides an Fe-N-C (Fe SAs-NPs / NC) catalyst, which is prepared by the following method:

[0008] Dissolve aminated pinecones, FeCl3·6H2O, sodium acetate, and polyethylene glycol (PEG-20000) in ethylene glycol; stir evenly, place in a reaction kettle, and react at 200 °C for 10 hours; then place it in an inert gas (such as an argon protection atmosphere), heat it to 900 °C at a heating rate of 10 °C / min, and calcine at this temperature for 2 hours to finally successfully prepare the above-mentioned Fe SAs-NPs / NC catalyst.

[0009] Furthermore, the above-mentioned aminated pinecones are prepared by the following method: Add 10.0 g of pinecones, 20 mL of 0.4 mol / L NaOH, 3 mL of triethylenetetramine (TETA), and 1 mL of formaldehyde to a flask, and stir and react at 70 °C for about 4 h; subsequently, add an acid (such as conventional acids like hydrochloric acid, nitric acid, etc.) dropwise to the solution to produce a brown precipitate. After the precipitate is washed and dried (dried at about 105 °C), the aminated pinecones are obtained. Amination can provide nitrogen elements to make the subsequent Fe addition reaction more uniform.

[0010] Furthermore, in the above preparation steps, the mass ratio of aminated pinecones, FeCl3·6H2O, sodium acetate, and polyethylene glycol is 10:0.05:3.6:0.5 in sequence.

[0011] In the above reaction, ethylene glycol serves as a solvent to provide a reduction reaction environment. In one embodiment of the present application, the mass-volume ratio of aminated pinecone to ethylene glycol is 10:40, and the unit of the mass-volume ratio is g / mL.

[0012] Secondly, the present application provides the use of the above-mentioned Fe SAs-NPs / NC catalyst in the degradation of perfluoro and polyfluoroalkyl substances (PFAS) in water. The Fe SAs-NPs / NC catalyst can activate PMS to selectively generate a non-radical pathway, thereby degrading PFAS in water.

[0013] Furthermore, the above-mentioned polyfluoroalkyl substances include at least one of perfluorooctanoic acid (PFOA, C8HF 15 O2), perfluorohexanoic acid (PFHxA), and perfluorobutyric acid (PFBA).

[0014] Furthermore, the application steps are as follows: Mix 10 mg of Fe SAs-NPs / NC catalyst with peroxysulfate and add it to water to degrade PFAS in water. The above-mentioned peroxysulfate is preferably KHSO5·0.5KHSO4·0.5K2SO4.

[0015] Further preferably, the dosages of Fe SAs-NPs / NC catalyst and PMS are 100 mg / L (water body) and 60 mg / L (water body) respectively, and the pH of the reaction system is 7; the content of PFOA in the water body is preferably not more than 1 mg / L.

[0016] The present application successfully couples single-atom Fe and Fe 0 (110) NPs to nitrogen-doped carbon derived from pinecone (carbon substrate) through in-situ Fe anchoring and carbothermal reduction method, and constructs a novel Fe SAs-NPs / NC catalyst for activating PMS to generate non-radicals to achieve efficient removal of PFOA.

[0017] The Fe SAs-NPs / NC catalyst prepared by the above method exhibits excellent performance in PFOA degradation, with a high degradation rate and the reaction process being almost completely achieved through a non-radical path. This degradation process mainly relies on Fe(IV)=O and singlet oxygen ( 1O2) degradation mechanism. Experimental and theoretical analyses show that when the initial concentration of PMS in water is 0.2 mM, the active species generated in this system mainly follow a non-radical pathway (accounting for nearly 100%), and a PFOA degradation rate of 90.5% can be achieved within 2 hours. This innovative research provides a key idea for designing efficient catalysts based on specific non-radical degradation pathways, and is expected to provide a new technical direction for the environmental treatment of persistent organic pollutants such as PFOA. Description of the Drawings

[0018] Figure 1 Schematic diagram of the preparation process of Fe SAs-NP / NC.

[0019] Figure 2 Characterization results of the FeSAs-NPs / NC catalyst;

[0020] Among them, a transmission electron microscope (TEM) image; b aberration-corrected scanning transmission electron microscope (AC-STEM) image; c AC-STEM-EDS image with elemental mapping; d X-ray absorption near-edge structure (XANES) spectra of FeSAs-NPs / NC, reference sample iron foil, FeO, iron phthalocyanine (FePc), and Fe2O3 at the Fe K-edge; e Fourier-transformed extended X-ray absorption fine structure (EXAFS) spectra at the Fe K-edge; f high-resolution N1s X-ray photoelectron spectra of NC and FeSAs-NPs / NC.

[0021] Figure 3 Test results of the effect of PMS concentration on PFOA degradation.

[0022] Figure 4 Test results of the effect of catalyst dosage on PFOA degradation.

[0023] Figure 5 Test results of the effect of pH on PFOA degradation.

[0024] Figure 6 For Fe SAs-NPs / NC catalyst recycling test results.

[0025] Figure 7 Test results of the removal of PFOA from natural water by FeSAs-NPs / NC.

[0026] Figure 8 For 1 mM singlet oxygen ( 1 O2) quencher effect on the change in PFOA removal efficiency.

[0027] Figure 9 For 10 mM singlet oxygen ( 1Results of the change in the removal efficiency of PFOA under the action of the quenching agent.

[0028] Figure 10 For the electron paramagnetic resonance (EPR) signal of TEMP- 1 O2 when the quenching agent was added and the reaction was carried out for 10 minutes.

[0029] Figure 11 For the quantification of Fe(IV)=O.

[0030] Figure 12 For the quantification results of the active species.

[0031] Figure 13 For the proportion of each active species.

[0032] Figure 14 For the results of the degradation of PFHxA and PFBA by the Fe SAs-NPs / NC+PMS system. Detailed implementation manners

[0033] Materials involved in the examples:

[0034] Sodium acetate (NaAc), hydrochloric acid (HCl, mass concentration 37%), ethylene glycol (EG), methanol (MeOH), ethanol (EtOH), tert-butanol (TBA), dimethyl sulfoxide (DMSO), and isopropanol (IPA) were all purchased from Kaitong Chemical Reagent Company in Tianjin, China.

[0035] Potassium monopersulfate compound salt (KHSO5·0.5KHSO4·0.5K2SO4), L-histidine (L-His), furfuryl alcohol (FFA), aniline, cerium(IV) sulfate, cerium(III) sulfate, terephthalic acid (TA), methyl phenyl sulfoxide (PMSO), methyl phenyl sulfone (PMSO2), perfluorohexanoic acid (PFHxA), perfluorobutyric acid (PFBA), and perfluorooctanoic acid (PFOA) were all purchased from Aladdin Biochemical Technology Co., Ltd. in Shanghai, China.

[0036] β-carotene (β-car), superoxide dismutase (SOD), nitroblue tetrazolium (NBT), iron(III) chloride hexahydrate (FeCl3·6H2O), and triethylenetetramine (TETA) were all from Macklin Biochemical Technology Co., Ltd. (Shanghai, China).

[0037] The water used in the examples was directly taken from the pipeline of the Nanjing University laboratory (conventional municipal water); the river water was collected at the confluence of the Jiuxiang River and the Yangtze River; the groundwater was extracted from the Xianlin Campus of Nanjing University in Nanjing, China, and its ion composition is shown in Table 1. The water used in the experiment was filtered through a 0.22 μm PES filter membrane before use.

[0038] Table 1 Ion Concentrations in Natural Water Samples

[0039]

[0040] Experimental Equipment and Detection Methods Involved in the Examples:

[0041] Scanning electron microscope (SEM, Quanta400FEG, FEI, USA), high-resolution transmission electron microscope (FEI Tecnai F20, USA), ζ potential of the material was measured using ZetaSizer Nano Nano 90 (Malvern Instruments), relevant absorption spectral data were recorded using a Shimadzu UV-3600 UV-visible spectrometer, Fourier transform infrared (FT-IR) spectra were obtained using a Nicolet 67FT-IR spectrometer (TensorII, Bruker, Germany), and X-ray diffraction (XRD) patterns were analyzed using a D8 Advance X-ray diffractometer (Bruker, Germany) with a Cu Kα radiation source.

[0042] The specific surface area of the material was determined by the Brunauer-Emmett-Teller (BET) method, and the pore size distribution was obtained by the Barrett-Joyner-Halenda (BJH) method (ASAP 2020V4.02, Micromeritics, USA).

[0043] X-ray photoelectron spectroscopy (XPS) was measured using a K-Alpha XPS system (ESCALAB 250Xi, Thermo Fisher Scientific, USA), and all XPS spectra were calibrated based on the C1s line at 284.6 eV.

[0044] Raman spectra were measured using a DXR confocal Raman spectrometer from Thermo Fisher Scientific. Aberration-corrected scanning transmission electron microscope (AC-STEM) images and energy-dispersive spectroscopy (EDS) analysis were performed using a JEM-ARM 300F microscope (USA). Synchrotron radiation spectra were collected at the Shanghai Synchrotron Radiation Facility.

[0045] Example 1 Synthesis of Fe-N-C (Fe SAs-NPs / NC) Catalyst

[0046] The synthesis process of the Fe SAs-NPs / NC catalyst in this example is as Figure 1 shown, and the specific steps are as follows:

[0047] 1) Add 10.0 g of pinecones (picked from Mount Tai), 20 mL of 0.4 mol / L NaOH, 3 mL of triethylenetetramine (TETA), and 1 mL of formaldehyde into a flask, and stir at 70 °C for 4 h; subsequently, add hydrochloric acid dropwise into the solution to produce a brown precipitate; wash the precipitate with deionized water and then dry it in a blast oven at 105 °C to obtain aminated pinecones for standby.

[0048] 2) Dissolve 10.0 g of aminated pinecones, 0.05 g of FeCl3·6H2O, 3.6 g of sodium acetate, and 0.5 g of polyethylene glycol (PEG-20000) in 40 mL of ethylene glycol, stir in a beaker for 30 minutes to fully mix all components evenly, then transfer the obtained mixture to a high-pressure reactor and react at 200 °C for 10 h;

[0049] 3) After the reaction, place the product in an argon protection atmosphere, heat it to 900 °C at a heating rate of 10 °C / min, and calcine at this temperature for 2 h to finally successfully prepare the FeSAs-NPs / NC catalyst (experimental group).

[0050] The control group (NC) prepares the NC material without adding FeCl3·6H2O under exactly the same experimental conditions.

[0051] Example 2 Characterize the FeSAs-NPs / NC catalyst

[0052] The TEM image of the FeSAs-NPs / NC catalyst prepared in Example 1 is as Figure 2 shown in a of [Figure]. The presence of Fe NPs can be clearly observed in the randomly selected observation area. Use aberration-corrected scanning transmission electron microscopy (AC-STEM) to deeply study the atomic-scale distribution of Fe species, and it is found that the Fe NPs present a regular spherical structure, and its interlayer spacing is measured to be 0.201 nm, corresponding to the (110) crystal plane of zero-valent iron (Fe 0 ) (as Figure 7 shown).

[0053] Figure 2 The enlarged image shown in b of [Figure] more intuitively shows the state of the close distribution of iron atoms (marked with purple circles), indicating the presence of Fe SAs in FeSAs-NPs / NC.

[0054] The energy-dispersive X-ray spectroscopy (EDS) analysis results further confirm that Fe NPs (marked with pink circles) and Fe SAs (marked with yellow circles) are uniformly distributed and coexist in the NC support (as Figure 2 shown in c of [Figure]).

[0055] In order to further explore the local coordination environment and valence state information of Fe species in FeSAs-NPs / NC, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were used for analysis. Figure 2 As shown in (d), the Fe K-edge X-ray absorption near-edge structure (XANES) spectrum of FeSAs-NPs / NC shows that the absorption threshold position of FeSAs-NPs / NC is between that of iron phthalocyanine (FePc) and ferric oxide (Fe2O3) reference samples (in the valence range of +2 to +3), and is closer to the absorption threshold position of FePc. This result indicates that the valence state of the Fe element in FeSAs-NPs / NC is similar to that of the Fe element in FePc (+2 valence).

[0056] Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectra of FeSAs-NPs / NCs ( Figure 2 (shown in e) There is a main peak corresponding to the Fe-N scattering path and a peak related to the Fe-Fe bond. The small peaks confirm the coexistence of NPs and SAs in FeS-NP / NC, in which SAs dominate. The inconsistent position of Fe-Fe in FeSAs-NPs / NC compared with Fe foil may be due to the coordination of Fe SAs with nitrogen and the effect of N-doped carbon matrix on Fe0 NPs, which change the electronic structure and thus affect the characteristics and position of Fe-Fe bonds.

[0057] In addition, compared with the NC sample without Fe element, the N1s XPS spectrum of FeSAs-NPs / NC (e.g. Figure 2 (f) shows a new characteristic peak at 399.1eV, which corresponds to pyrrolic nitrogen. This phenomenon indicates that in FeSAs-NPs / NC, Fe atoms may have coordinated with pyridinic nitrogen. Based on the above characterization results, it is fully confirmed that the isolated Fe-N4 and Fe 0 Coexistence status of NPs(110).

[0058] Example 3 Optimization of PFOA removal experimental parameters

[0059] Batch degradation experiments were conducted in a 200 mL conical flask to systematically study the removal effect of FeSAs-NPs / NC+PMS system on PFOA.

[0060] At the beginning of the experiment, in a 100 mL solution, the concentration of PFOA was set at 1 mg / L. First, the catalyst prepared in Example 1 was used to adsorb PFOA in the solution, and the solution was shaken at 150 rpm for 30 minutes. Subsequently, a certain amount of KHSO5·0.5KHSO4·0.5K2SO4 (hereinafter referred to as PMS) was added to officially start the degradation reaction. During the reaction process, samples were collected at different time intervals. All the collected samples were filtered through a 0.22 μm polyethersulfone (PES) membrane, and the concentration of PFOA in the solution was accurately measured. The conditions of the degradation experiment were optimized, and the entire experiment was repeated twice.

[0061] The analysis and detection of PFOA were carried out using a liquid chromatography-mass spectrometry (LC-MS) instrument according to the revised GB / T 29493.2-2021 method. The specific experimental instrument was an Agilent 1200 high-performance liquid chromatography (HPLC) system equipped with a 1.7 μm, 2.1 mm×50 mm C18 column (Waters Corporation, BEH series, USA), which was coupled with an API 4000 mass spectrometer (ABSciex Company). During the analysis, the mobile phase was a mixture of acetonitrile and ammonium acetate aqueous solution, the flow rate was set at 0.1 mL / min, and the column temperature was maintained at 30 °C. The parameter settings of the mass spectrometer were as follows: spray voltage was -4500 V, probe heater temperature was 350 °C, ion pair (m / z) was 412.9 / 368.9, and other related specific settings. By systematically studying the effects of PMS concentration (as Figure 3 shown), catalyst dosage (as Figure 4 shown), and solution pH value (as Figure 5 shown) on the removal rate of PFOA, the results showed that there were optimal operating conditions for the FeSAs-NPs / NC catalyst during the PMS conversion process, specifically, the PMS dosing concentration was 0.2 mM (dosage 60 mg / L), the catalyst dosage was 100 mg / L, and the solution pH value was 7 (in the examples, the reaction system pH was adjusted with hydrochloric acid and sodium hydroxide), and the best degradation rate was 90.46%.

[0062] Example 4 Recycling of FeSAs-NPs / NC for the Removal of PFOA

[0063] In this example, to comprehensively evaluate the reusability performance of the FeSAs-NPs / NC catalyst, a systematic recycling experiment was carried out (the relevant experimental results are as Figure 6 shown).

[0064] The reaction conditions in this example were the same as those in Example 3, with a PMS dosage of 60 mg / L, a catalyst dosage of 100 mg / L, a solution pH value of 7, and shaking adsorption at 150 rpm for 30 minutes. After one adsorption reaction, the catalyst was separated by filtration and washed three times with ethanol to remove the adsorbed substrates, intermediate products, or PMS residues on the surface; then the recovered catalyst was added to a new reaction system under the same conditions (PFOA, catalyst, PMS concentration the same as the first time) for a recycling test.

[0065] Experimental data showed that even after four consecutive cycles of use, the removal rate of PFOA by the FeSAs-NPs / NC catalyst could still be maintained above 80%. This result fully demonstrated that the FeSAs-NPs / NC catalyst had good reusability and stability.

[0066] Example 5 Application of FeSAs-NPs / NC in Removing PFOA from Natural Water

[0067] To deeply explore the influence of environmental interference factors on the degradation performance of the FeSAs-NPs / NC+PMS system, this example selected tap water, Yangtze River water, and groundwater as different reaction matrices for experimental research. The reaction conditions were the same as those in Example 3, with a PMS dosage of 60 mg / L, a catalyst dosage of 100 mg / L, a solution pH value of 7, and shaking adsorption at 150 rpm for 30 minutes.

[0068] The experimental results showed that the removal rates of the target pollutant PFOA by the FeSAs-NPs / NC+PMS system in tap water, Yangtze River water, and groundwater reached 87.58%, 74.67%, and 63.48% respectively (the detection results are as Figure 7 shown, where a-c are tap water, Yangtze River water, and groundwater in sequence).

[0069] This result indicated that the FeSAs-NPs / NC catalyst showed strong tolerance in the face of a complex natural water environment. Further analysis found that the removal rate of PFOA was relatively the lowest in the groundwater environment among different natural waters.

[0070] Example 6 Non-Free Radical Reaction Mechanism

[0071] The following experimental reaction conditions were the same as those in Example 3, with a PMS dosage of 60 mg / L, a catalyst dosage of 100 mg / L, a solution pH value of 7, and shaking adsorption at 150 rpm for 30 minutes.

[0072] 6.1) Dominant Role Test of Singlet Oxygen ( 1 O2)

[0073] In this example, L-histidine (L-His), furfuryl alcohol (FFA), and β-carotene (β-car) were used as 1 O2 quenchers, and it was found that the PFOA removal rate decreased significantly with the increase in the scavenger concentration, and the inhibitory effect was concentration-dependent ( Figure 8 、 Figure 9 ), directly indicating that 1 O2 plays a dominant role in the reaction.

[0074] Electron paramagnetic resonance (EPR) tests further observed the 1:1:1 triplet characteristic signal of TEMP- 1 O2 in the FeSAs-NPs / NC + PMS system ( Figure 10 ), verifying the 1 generation and participation of O2 at the molecular spectral level.

[0075] 6.2 Oxidation of high-valent iron species (Fe(IV)=O)

[0076] In this example, the methyl phenyl sulfoxide (PMSO) probe method was used to confirm the presence of Fe(IV)=O: PMSO was quantitatively oxidized to methyl phenyl sulfone (PMSO2) through the Fe(IV)-mediated oxygen transfer reaction, and its generation efficiency reached 92.65% - 100%, corresponding to the Fe(IV)=O concentration of 226 μM in the system ( Figure 11 ), indicating that Fe(IV)=O is generated by the complex oxidation of PMS with the ≡Fe(II) / ≡Fe(III) active sites on the catalyst surface.

[0077] 6.3) Quantitative experiments on reactive species

[0078] In the reactive species detection experiment, this example used furfuryl alcohol (FFA), cerium (III), terephthalic acid (TA), and nitroblue tetrazolium (NBT) to quantitatively determine singlet oxygen ( 1 O2), sulfate radical (·SO4 2- ), hydroxyl radical (·OH), and superoxide anion radical (·O2 - ), respectively.

[0079] Probe quantitative analysis showed that within 120 minutes, 1 the generation amount of O2 was 48.02 μM, while the concentrations of ·OH (0.254 μM), ·SO4 2- (0.810 μM), and ·O2 - (4.681 μM) were all 1 - 2 orders of magnitude lower ( Figure 12 ). Combining with the results of Figure 11 further confirmed that non-radical species ( 1 O2 and Fe(IV)=O) are the main active components, while radical substances (·OH, ·SO42- , ·O2 - ) The contribution is negligible. Combining the above data analysis, in the Fe SAs-NPs / NC + PMS system, the proportion of non-free radicals is 97.9% ( Figure 13 ), approaching 100%.

[0080] Example 7 Application of FeSAs-NPs / NC + PMS System in Degrading Short-chain Perfluorinated Compounds

[0081] The FeSAs-NPs / NC + PMS system also showed good removal ability for other perfluoro- and polyfluoroalkyl substances (PFAS), such as perfluorohexanoic acid (PFHxA) and perfluorobutyric acid (PFBA), which are more difficult to be adsorbed compared with PFOA (the relevant results are as Figure 14 shown).

[0082] The reaction conditions were the same as those in Example 3, with the PMS dosage of 60 mg / L, the catalyst dosage of 100 mg / L, the solution pH value of 7, and shaking adsorption at 150 rpm for 30 minutes. The initial concentrations of both PFHxA and PFBA were 1 mg / L.

[0083] Further experimental results showed that the removal rates of PFHxA and PFBA reached 75.6% and 83.3% respectively, which fully indicated that the FeSAs-NPs / NC + PMS system had wide applicability and excellent catalytic activity.

[0084] The above examples successfully prepared an FeSAs-NPs / NC catalyst that simultaneously contained Fe 0 nanoparticles (Fe NPs) and Fe-N4 single atoms (FeSAs) dual active sites, and coupled it onto a pinecone-derived nitrogen-doped carbon substrate through in-situ Fe anchoring and carbothermal reduction method. Experimental results showed that the system constructed by this catalyst and PMS exhibited excellent PFOA degradation performance: under the conditions of PMS concentration of 0.2 mM, catalyst dosage of 100 mg / L, and pH = 7, the degradation rate of 1 mg / L PFOA could reach 90.5% within 2 hours, and the reaction process mainly followed the non-free radical path (accounting for nearly 100%), mainly relying on singlet oxygen ( 1Efficient oxidation is achieved by O2 and high-valent iron species (Fe(IV)=O). This catalyst has significant technical advantages: firstly, the dual-site structure design enables specific activation of PMS, overcoming the defects of high PMS consumption and short lifespan in the traditional free radical pathway; secondly, using natural pinecones as carbon precursors, the raw material source is extensive and the synthesis conditions are mild, significantly reducing the catalyst preparation cost; thirdly, it shows good removal ability for short-chain perfluorinated compounds (such as PFHxA, PFBA), and the removal rate of PFOA still remains above 80% after four cycles of use, and it also shows strong environmental tolerance and anti-interference ability in complex natural waters such as tap water, Yangtze River water, and groundwater. This invention first reveals the regulation mechanism of the coupling of iron active sites with different sizes on the non-free radical pathway, providing a new strategy for the design of efficient PMS activation catalysts. Its excellent degradation performance, stability, and practical application potential are expected to become the key technology for the environmental treatment of persistent organic pollutants such as PFOA, and have important scientific significance and engineering application value in the field of water pollution control.

Claims

1. A Fe-N-C catalyst, characterized in that, The catalyst is prepared by the following method: The aminated pinecones, FeCl3·6H2O, sodium acetate and polyethylene glycol are dissolved in ethylene glycol, reacted at 200 °C for 10 h, and then placed in an inert gas atmosphere and calcined at 900 °C for 2 h to obtain the Fe-N-C catalyst.

2. The Fe-N-C catalyst according to claim 1, wherein The aminated pinecones are prepared by the following method: 10.0 g of pinecones, 20 mL of 0.4 mol / L NaOH, 3 mL of triethylenetetramine and 1 mL of formaldehyde are mixed and stirred at 70 °C; then acid is added dropwise to produce a precipitate; the precipitate is taken, washed and dried to obtain the aminated pinecones.

3. The Fe-N-C catalyst according to claim 1, wherein The mass ratio of the aminated pinecones, FeCl3·6H2O, sodium acetate and polyethylene glycol is 10:0.05:3.6:0.5 in sequence.

4. The Fe-N-C catalyst according to claim 1, wherein The calcination at 900 °C for 2 h means heating to 900 °C at a heating rate of 10 °C / min and then calcining for 2 h.

5. The Fe-N-C catalyst according to claim 2, wherein The acid is hydrochloric acid or nitric acid.

6. The application of the Fe-N-C catalyst according to any one of claims 1-5 in the degradation of perfluoro- and polyfluoroalkyl substances in water.

7. The application according to claim 6, characterized in that, The application means that the Fe-N-C catalyst and permonosulfate are jointly added into the water body to degrade the perfluoro- and polyfluoroalkyl substances in the water body.

8. The application according to claim 6, wherein The perfluoro- and polyfluoroalkyl substances include at least one of perfluorooctanoic acid, perfluorohexanoic acid and perfluorobutyric acid.

9. The application according to claim 7, characterized in that, The permonosulfate is KHSO5·0.5KHSO4·0.5K2SO4.

10. The application according to claim 9, characterized in that, The dosage of the Fe-N-C catalyst and permonosulfate is 100 mg / L and 60 mg / L respectively.

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