Preparation and application of Fe-Fe3C@nitrogen-doped porous carbon composite material supported on BiOBr nanosheets
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANCHANG UNIV
- Filing Date
- 2026-02-06
- Publication Date
- 2026-07-17
Smart Images
Figure CN121715205B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental functional materials and pollution control technology, specifically relating to the preparation of Fe-Fe3C@nitrogen-doped porous carbon composite material supported on BiOBr nanosheets and its application as a highly efficient photocatalyst. Background Technology
[0002] With the continued deepening of global industrialization, various pollutants are constantly entering water bodies, leading to increasingly severe water pollution problems. Among them, phenols in wastewater, as small-molecule, recalcitrant, and highly toxic organic compounds, have become a recognized major environmental challenge. Currently, various treatment technologies have been developed for phenol removal, such as volatilization, adsorption, biodegradation, and electrochemical degradation. However, these methods often have limitations such as insufficient mineralization capacity, highly toxic intermediate products, or demanding conditions. In contrast, photocatalytic oxidation technology, with its strong oxidizing properties, potential for complete mineralization, and mild conditions, shows significant potential and has a broad prospect in the field of phenol pollution control.
[0003] Bismuth-based materials, as a current hot topic in photocatalysis research, exhibit broad application prospects and significant research value due to their advantages such as low cost, simple preparation process, environmental friendliness (non-toxicity), and high chemical stability. In particular, bismuth oxybromine (BiOBr), with its suitable bandgap structure and layered topology, shows significant potential in visible light photocatalysis. This layered structure can induce atomic orbital polarization, forming a structure perpendicular to the Br⁻ layer and [Bi₂O₂]. 2+ The built-in electric field of the layer efficiently drives the migration of photogenerated electrons. However, BiOBr still suffers from drawbacks such as small specific surface area, limited visible light absorption, and weak conduction band reduction ability. Carbon-based materials, with their high conductivity and tunable pore structure, can overcome the above-mentioned defects of BiOBr, making them ideal composite modification materials.
[0004] Metal-organic frameworks (MOFs), as a class of emerging porous crystalline materials with tunable composition and structure and excellent metal dispersion, have shown application potential in multiple fields. However, pure MOFs often face problems such as difficult recycling, limited regeneration capacity, and low adsorption efficiency in practical applications. Amino-functionalized MIL-101(Fe) (NH2-MIL-101(Fe)) is a typical Fe-based MOF with regular channels, abundant amino functional groups, and uniformly dispersed iron metal sites. In previous studies, the inventors found that composite materials prepared directly using NH2-MIL-101(Fe) as the matrix did not exhibit ideal adsorption and photocatalytic degradation performance for representative phenols. Summary of the Invention
[0005] This invention addresses the limitations of single BiOBr semiconductor materials and MOF-derived materials in practical applications by significantly enhancing the synergistic adsorption-photocatalytic degradation performance of composite materials for phenolic pollutants through the synergistic effect between components. It provides a novel composite photocatalytic material capable of achieving efficient adsorption-photocatalytic synergistic degradation of phenolic pollutants in water under sunlight, and enabling rapid separation and recovery with the aid of an external magnetic field. This material not only overcomes key bottlenecks in the current photocatalytic degradation treatment of phenolic wastewater but also achieves efficient degradation and deep mineralization of water-soluble persistent phenolic pollutants, thus providing important technical support for promoting sustainable socio-economic development.
[0006] This invention discloses a method for preparing a nitrogen-doped porous carbon composite material (BiOBr / Fe-Fe3C@NC) loaded with BiOBr nanosheets and its application. The preparation method of this composite material is as follows: First, using an equimolar ratio of FeCl3·6H2O and 2-aminoterephthalic acid (NH2-BDC) as precursors via a hydrothermal method, NH2-MIL-101(Fe) with a regular octahedral morphology was synthesized based on the self-assembly characteristics of metal-organic frameworks (MOFs). Subsequently, high-temperature carbonization was performed in a nitrogen atmosphere, and under specific calcination conditions, the organic components of NH2-MIL-101(Fe) underwent decomposition, accompanied by in-situ reduction of Fe species, ultimately forming a nitrogen-doped porous carbon material encapsulating Fe-Fe3C nanoparticles, denoted as Fe-Fe3C@NC. Furthermore, using Bi(NO3)3·5H2O and KBr as raw materials, BiOBr nanosheets were self-assembled and grown on the surface of Fe-Fe3C@NC through a secondary hydrothermal reaction, thus preparing a composite material loaded with BiOBr nanosheets, denoted as BiOBr / Fe-Fe3C@NC.
[0007] The preparation method of the composite material (BiOBr / Fe-Fe3C@NC) of the present invention specifically includes the following steps:
[0008] (1) Preparation of NH2-MIL-101(Fe): The precursor FeCl3·6H2O and 2-aminoterephthalic acid (NH2-BDC) were dispersed in an N,N-dimethylformamide (DMF) solvent system in an equimolar ratio and acetic acid was added for hydrothermal crystallization. After drying and sieving, NH2-MIL-101(Fe) powder was obtained.
[0009] (2) Preparation of N-doped porous carbon (Fe-Fe3C@NC) encapsulating Fe-Fe3C nanoparticles: The powder obtained in step (1) was calcined under N2 protection and then naturally cooled to obtain Fe-Fe3C@NC powder;
[0010] (3) Preparation of Fe-Fe3C@nitrogen-doped porous carbon composite material (BiOBr / Fe-Fe3C@NC) loaded with BiOBr nanosheets: The powder obtained in step (2) was dispersed in a mixed solvent system of ethylene glycol and ethanol containing Bi(NO3)3·5H2O and KBr by hydrothermal method, and the BiOBr / Fe-Fe3C@NC powder was obtained after drying and sieving.
[0011] Further, step (1) specifically involves weighing FeCl3·6H2O and NH2-BDC at a molar ratio of 1:1 at room temperature, and ultrasonically dissolving FeCl3·6H2O and NH2-BDC in N,N-dimethylformamide (DMF) according to a solute-solvent ratio of 1 mmol:10 mL. Under magnetic stirring, acetic acid with a ratio of 0.25~0.5 mL:1 mmol of acetic acid and the ultrasonically dispersed FeCl3 solution are added to the NH2-BDC solution at a constant rate and stirred continuously until homogeneous. The mixture is then transferred to a sealed high-pressure reactor, sealed, and placed in an oven at 110 ℃ for hydrothermal crystallization for 20 h. After centrifugation, washing, vacuum drying, and sieving through a 100-mesh sieve, particles with a particle size of 0.5-1 μm and a specific surface area of 2100~2200 m² are obtained. 2 / g, a reddish-brown NH2-MIL-101(Fe) powder with an octahedral morphology.
[0012] Furthermore, the constant dropping rate is 0.05~0.1 mL / s, and the high-pressure reactor is lined with polytetrafluoroethylene.
[0013] Furthermore, in step (1), the cleaning is performed by alternating washing with hot DMF at 50-60 ℃ and anhydrous ethanol at least 4 times; the vacuum drying is performed at 60-80 ℃ for 10-12 h.
[0014] Further, step (2) specifically involves placing the sample obtained in step (1) in a tube furnace and carbonizing it to 600-750 ℃ for 3-6 h under N2 protection at a flow rate of 80-100 mL / min and a heating rate of 3-10 ℃ / min. After natural cooling, a particle size of 500 nm and a specific surface area of 280-300 m² are obtained. 2 / g, N-doped porous carbon (Fe-Fe3C@NC) black powder with a rough surface and a quasi-octahedral structure and coated with magnetic Fe-Fe3C nanoparticles.
[0015] Further, step (3) specifically involves ultrasonically dissolving Bi(NO3)3·5H2O in ethylene glycol at a ratio of 0.1~0.3 mmol:50 mL; then, weighing the Fe-Fe3C@NC powder prepared in step (2) at a ratio of Fe-Fe3C@NC:Bi(NO3)3·5H2O=0.15 g: 0.1~0.3 mmol and adding it to the above Bi(NO3)3·5H2O ethylene glycol solution and ultrasonically dispersing it to form a Fe-Fe3C@NC and Bi(NO3)3·5H2O mixed system; simultaneously weighing KBr in an equimolar ratio with Bi(NO3)3·5H2O, and ultrasonically dissolving it in a 1:1 volume ratio ethylene glycol-ethanol mixed solution at a ratio of 0.1~0.3 mmol:80~100 mL; under magnetic stirring, dissolving the resulting KBr solution at 0.5~1 The Fe-Fe3C@NC and Bi(NO3)3·5H2O mixture was added dropwise at a constant rate of mL / s to the above mixture and stirred until homogeneous to obtain a ternary mixture. The ternary mixture was then placed in a high-pressure reactor, sealed, and placed in an oven at 140~160 ℃ for hydrothermal reaction for 8~12 h. After centrifugation, washing, vacuum drying, and sieving through a 100-mesh sieve, BiOBr / Fe-Fe3C@NC was obtained.
[0016] Furthermore, in step (3), the washing process involves alternating washing with anhydrous ethanol and deionized water at least four times; vacuum drying is performed at 60-80 °C for 10-12 h.
[0017] The specific surface area of the BiOBr / Fe-Fe3C@NC composite material prepared by this invention ranges from 150 to 220 m². 2 / g, with an average pore size distribution between 3.5 and 3.8 nm. The theoretical amount of BiOBr generated is based on the theoretical amount of Fe-Fe3C@NC in the composite, with a mass ratio between the two ranging from 1:5 to 3:5. The construction of this composite structure not only effectively inhibits the aggregation of BiOBr and provides abundant reactive sites, but also constructs a sufficient amount of S-shaped heterojunction through the tight interfacial contact between BiOBr and the support Fe-Fe3C@NC, which helps to enhance visible light absorption, thereby significantly improving the photocatalytic degradation performance of the material.
[0018] This invention further provides the application of the above-mentioned composite material in the field of photocatalytic degradation of pollutants. Under simulated sunlight (300 W xenon lamp) irradiation conditions, the composite material exhibits excellent and stable photocatalytic degradation performance of typical pollutants in phenolic wastewater, namely catechol and β-naphthol, characterized by rapid mineralization rate and high mineralization efficiency, with virtually no secondary pollution. Simultaneously, thanks to its magnetic response characteristics, the composite material can be rapidly recovered under the action of an external magnetic field, maintaining good photocatalytic activity and stability even after multiple reuses. Furthermore, the material also shows good degradation effects on the above two pollutants under real sunlight irradiation, demonstrating high practical application potential and industrialization prospects.
[0019] The beneficial effects of this invention:
[0020] (1) This invention uses NH2-MIL-101(Fe) as a precursor, which is pyrolyzed at high temperature under specific conditions to obtain nitrogen-doped porous carbon coated with magnetic Fe-Fe3C nanoparticles as a material carrier. This carbon matrix not only retains the octahedral framework structure of the NH2-MIL-101(Fe) precursor, but also has abundant porous features on its surface. This porous structure is conducive to the high dispersion of active components and provides sufficient active sites for adsorption and catalytic reactions. In addition, after carbonization, a large number of conjugated graphite-like nitrogen-doped carbon frameworks are formed, which form a stronger "electron cloud overlap" with the π electrons of phenolic aromatic rings, and the π-π stacking effect is significantly enhanced, which is conducive to the adsorption of pollutants and thus accelerates the degradation rate.
[0021] (2) This invention achieves uniform dispersion of the active component BiOBr by in-situ growing sufficient BiOBr nanosheets on a special carbon matrix under specific hydrothermal crystallization conditions, which effectively inhibits excessive self-assembly and the formation of nanoflower-like structures. This method significantly reduces the amount of BiOBr used while ensuring catalytic degradation performance, thereby reducing material costs.
[0022] (3) The composite photocatalytic material of this invention possesses a unique photocatalytic structure. By embedding Fe-Fe3C nanoparticles into an N-doped porous carbon matrix and tightly combining them with the active photocatalytic component BiOBr, a sufficient amount of S-shaped heterojunction is successfully constructed. This structure can effectively regulate the band structure of the material, enhance the response to the visible light region, and promote the efficient separation and migration of photogenerated carriers in space, thereby retaining carriers with high redox capabilities and generating abundant active species for the deep degradation and rapid mineralization of pollutants. In addition, the introduced N-doped porous carbon matrix not only provides chemical protection for the Fe-Fe3C nanoparticles and improves their stability in the photocatalytic process, but also acts as an electron trap, rapidly transferring photogenerated electrons separated at the heterojunction interface to the reactive active sites. Under mild conditions, this material can generate a large number of nucleophilic active species (such as •O2).- It achieves highly efficient attack on phenolic organic pollutants (•OH), ultimately rapidly and thoroughly mineralizing them into CO2 and H2O, exhibiting significantly enhanced photocatalytic performance.
[0023] (4) The composite photocatalyst material of the present invention contains magnetic Fe-Fe3C nanoparticles, which can be rapidly separated from the solution under the action of an external magnetic field and can be reused multiple times. The catalyst exhibits good photochemical stability, which provides strong support for its practical application. Attached Figure Description
[0024] Figure 1 The graph shows the adsorption and removal efficiency of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention for β-naphthol aqueous solution under visible light.
[0025] Figure 2 The graph shows the adsorption and removal efficiency of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention for catechol aqueous solution under visible light.
[0026] Figure 3 The graph shows the adsorption-photocatalytic synergistic removal efficiency of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention for β-naphthol aqueous solution under visible light.
[0027] Figure 4 The graph shows the adsorption-photocatalytic synergistic removal efficiency of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention for catechol aqueous solution under visible light.
[0028] Figure 5 The mineralization efficiency of BiOBr / Fe-Fe3C@NC1:5 prepared in Example 1 of this invention for different pollutants under different light exposure times;
[0029] Figure 6 X-ray photoelectron spectroscopy (XPS) of Fe in the BiOBr / Fe-Fe3C@NC1:5 catalyst prepared in Example 1 and the catalyst prepared in Comparative Example 1 of this invention. 2p Spectral comparison and peak division results;
[0030] Figure 7 The X-ray photoelectron spectroscopy (XPS) of BiOBr / Fe-Fe3C@NC1:5 prepared in Example 1 and the catalyst prepared in Comparative Example 2 of this invention are shown. 4f Spectral comparison and peak division results;
[0031] Figure 8 This is a scanning electron microscope image of BiOBr / Fe-Fe3C@NC1:5 prepared in Example 1 of this invention;
[0032] Figure 9The graph shows the magnetic properties of BiOBr / Fe-Fe3C@NC1:5 obtained in Example 1 of this invention.
[0033] Figure 10 This is an experimental diagram of the reuse of BiOBr / Fe-Fe3C@NC1:5 prepared in Example 1 of this invention for the degradation of β-naphthol and catechol aqueous solution;
[0034] Figure 11 A schematic diagram of the process of this invention. Detailed Implementation
[0035] The present invention will be further described below with reference to specific embodiments.
[0036] Example 1
[0037] Preparation of BiOBr / Fe-Fe3C@NC composite photocatalyst:
[0038] (1) Preparation of NH2-MIL-101(Fe): FeCl3·6H2O and NH2-BDC were weighed at a molar ratio of 1:1 at room temperature. The FeCl3·6H2O and NH2-BDC were dissolved separately in N,N-dimethylformamide (DMF) using ultrasonication at a solute-solvent ratio of 1 mmol:10 mL. Under magnetic stirring, acetic acid in a ratio of 0.25~0.5 mL:1 mmol (acetic acid:NH2-BDC = 1 mmol) and the ultrasonically dispersed FeCl3 solution were added to the NH2-BDC solution at a constant rate and stirred continuously until homogeneous. The mixture was then transferred to a sealed high-pressure reactor, sealed, and placed in an oven at 110 ℃ for hydrothermal crystallization for 20 h. After the reaction was completed and cooled to room temperature, the mixture was centrifuged at high speed, and the reddish-brown solid was collected. To remove surface-adsorbed unreacted substances, residual acetic acid, and further purified products, the solid was washed six times alternately with hot DMF at 50~60 ℃ and anhydrous ethanol. Finally, the solid was dried at 60–80 °C under vacuum for 10–12 h. The resulting solid was then sieved through a 100-mesh sieve to obtain particles with a diameter of approximately 0.5–1 μm and a specific surface area of 2100–2200 m². 2 / g, a reddish-brown powder of NH2-MIL-101(Fe) with an octahedral morphology.
[0039] (2) N-doped porous carbon encapsulating Fe-Fe3C nanoparticles: The sample obtained in step (1) was placed in a tube furnace and carbonized at 600-750 ℃ for 3-6 h under N2 protection at a flow rate of 80-100 mL / min and a heating rate of 3-10 ℃ / min. After natural cooling, a particle size of approximately 500 nm and a specific surface area of 280-300 m² were obtained. 2 / g, N-doped porous carbon (Fe-Fe3C@NC) black powder with a rough surface and a quasi-octahedral structure and coated with magnetic Fe-Fe3C nanoparticles.
[0040] (3) Fe-Fe3C@nitrogen-doped porous carbon composite material (BiOBr / Fe-Fe3C@NC) loaded with BiOBr nanosheets: Bi(NO3)3·5H2O was ultrasonically dissolved in ethylene glycol at a ratio of 0.1~0.3 mmol:50 mL; then, Fe-Fe3C@NC powder prepared in step (2) was weighed and added to the above Bi(NO3)3·5H2O ethylene glycol solution at a ratio of Fe-Fe3C@NC:Bi(NO3)3·5H2O = 0.15 g:0.1~0.3 mmol and ultrasonically dispersed to form a mixed system of Fe-Fe3C@NC and Bi(NO3)3·5H2O; at the same time, KBr was weighed in an equimolar ratio with Bi(NO3)3·5H2O at a ratio of 0.1~0.3 mmol. The KBr solution was ultrasonically dissolved in a 1:1 volume ratio of ethylene glycol to ethanol at a ratio of 80-100 mL. Under magnetic stirring, the resulting KBr solution was added dropwise at a constant rate of 0.5-1 mL / s to the above Fe-Fe3C@NC and Bi(NO3)3·5H2O mixture, and stirred until homogeneous to obtain a ternary mixture. The ternary mixture was then placed in a high-pressure reactor, sealed, and placed in an oven at 140-160 °C for hydrothermal reaction for 8-12 h. After the reaction, the system was cooled to room temperature, and the product was separated by high-speed centrifugation to obtain a black solid. The solid was washed six times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 60-80 °C for 10-12 h. Finally, the dried powder was passed through a 100-mesh sieve to obtain BiOBr / Fe-Fe3C@NC.
[0041] Following the method provided in step (3), based on the theoretical amount of Fe-Fe3C@NC in the composite, the dosage of Bi(NO3)3·5H2O and KBr was calculated when the theoretical amount of BiOBr was generated and the mass ratio of Fe-Fe3C@NC was 1:5, 2:5 and 3:5, respectively. The prepared materials were named BiOBr / Fe-Fe3C@NC1:5, BiOBr / Fe-Fe3C@NC2:5 and BiOBr / Fe-Fe3C@NC3:5, respectively.
[0042] Comparative Example 1:
[0043] Preparation of pure Fe-Fe3C@NC:
[0044] The NH2-MIL-101(Fe) prepared in Example 1(1) was placed in a tube furnace and carbonized at 600-750 °C for 3-6 h under N2 protection at a flow rate of 80-100 mL / min and a heating rate of 3-10 °C / min, thus obtaining N-doped porous carbon (denoted as Fe-Fe3C@NC) coated with magnetic Fe-Fe3C nanoparticles.
[0045] Comparative Example 2:
[0046] Preparation of pure BiOBr:
[0047] 0.1–0.3 mmol Bi(NO3)3·5H2O was dissolved in 50 mL ethylene glycol. Simultaneously, an equimolar ratio of KBr was dissolved in 80–100 mL of a 1:1 (v / v) ethylene glycol-ethanol mixture, and the solution was sonicated at room temperature for 5–10 min to ensure complete dissolution. Under magnetic stirring at 25 °C and 500–1000 r / min, the KBr solution was added dropwise to the Bi(NO3)3·5H2O system at a constant rate of 0.5–1 mL / s, and stirring was continued for 1 h to ensure homogeneous mixing. The mixture was then transferred to a 200 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), sealed, and placed in an oven at 140–160 °C for a hydrothermal reaction for 8–12 h. After the reaction, the system was cooled to room temperature, and the product was centrifuged to obtain a white solid. The solid was washed six times alternately with anhydrous ethanol and deionized water, and then dried under vacuum at 60–80 °C for 10–12 h. Finally, the dried powder was passed through a 100-mesh sieve to obtain BiOBr.
[0048] Example 2:
[0049] The degradation performance of β-naphthol and catechol aqueous solutions was investigated using uncalcined NH2-MIL-101(Fe), the catalysts prepared in Example 1 and Comparative Examples 1-2 under xenon lamp irradiation.
[0050] (1) The adsorption removal and adsorption-photocatalytic synergistic removal experiments of β-naphthol were carried out in two steps:
[0051] (i) Adsorption experiment: 20 mg of catalyst was added to 40 mL of 20 mg / L β-naphthol aqueous solution, and the mixture was magnetically stirred (500 rpm) under light-protected conditions until the set time. Then, 2 mL of the reaction solution was taken, filtered through a 0.22 μm filter membrane, and the concentration of β-naphthol was measured at 274 nm using a UV-Vis spectrophotometer. The adsorption removal efficiency was calculated using formula (1). This experiment was also used to determine the adsorption-desorption equilibrium time.
[0052] (ii) Adsorption-photocatalytic synergistic experiment: Take another 40 mL of β-naphthol aqueous solution with a concentration of 20 mg / L, add 20 mg of catalyst, and place it directly under a 300 W xenon lamp for irradiation. Stir magnetically (500 rpm) and react for the set time. After the reaction is completed, take 2 mL of suspension, filter it through a 0.22 μm filter membrane, and measure the concentration of β-naphthol at 274 nm. Calculate the adsorption-photocatalytic synergistic removal efficiency using formula (1).
[0053]
[0054] Among them, C0 (mg / L) and C t (mg / L) represent the initial concentration of the solution and the concentration of the filtrate at time t (min), respectively.
[0055] (2) Adsorption removal and adsorption-photocatalytic synergistic removal experiments of catechol: 20 mg / L β-naphthol in (1) was replaced with 20 mg / L catechol, the absorption wavelength was replaced with 276 nm, and other conditions remained unchanged.
[0056] The adsorption performance of different catalysts for aqueous solutions of β-naphthol and catechol is as follows: Figure 1 and Figure 2 As shown in the figure. The data indicate that Fe-Fe3C@NC and its three composites with BiOBr (BiOBr / Fe-Fe3C@NC 1:5, 2:5, and 3:5 obtained in Example 1) all exhibit superior adsorption capacity for single β-naphthol and catechol. In contrast, under the same conditions, pure BiOBr and NH2-MIL-101 (Fe) (Comparative Examples 1 and 2) showed poor adsorption performance.
[0057] The relatively weak adsorption capacity of BiOBr is mainly attributed to its small specific surface area. While NH2-MIL-101(Fe) has a higher specific surface area, its adsorption performance is still inferior to that of Fe-Fe3C@NC formed after calcination. The main reasons can be summarized as follows:
[0058] Firstly, regarding the π-π stacking effect, the ligand conjugation system of NH2-MIL-101(Fe) is limited to a single benzene ring and separated by Fe metal nodes, resulting in a weak π electron overlap between it and the phenolic aromatic ring. However, the Fe-Fe3@NC obtained by calcination forms a large-scale continuous conjugated nitrogen-doped carbon skeleton through ligand carbonization. The N atom doping further increases the π electron density of the carbon skeleton, thereby significantly enhancing the electron cloud overlap effect with the phenolic aromatic structure.
[0059] Secondly, regarding hydrogen bonding, the N in NH2-MIL-101(Fe) exists in the form of an amino group (-NH2), primarily acting as a hydrogen bond donor, i.e., through the H on the -NH2 group. + It forms a hydrogen bond with the O of the phenolic hydroxyl group. However, due to H... + The electron-donating ability of the amine is relatively weak, resulting in weak hydrogen bond strength. However, in the Fe-Fe3C@NC formed by calcination, N is transformed from an amino donor to a strong hydrogen bond acceptor such as pyridine N, forming hydrogen bonds with hydroxyl groups of phenols with significantly increased strength. At the same time, the N atoms are more dispersed in the carbon skeleton, freeing them from the spatial constraints of the NH2-MIL-101 (Fe) structure, and greatly increasing the probability of contact with phenol molecules.
[0060] Thirdly, the Fe-Fe3C nanoparticles in Fe-Fe3C@NC have a large number of exposed Fe sites on their surface. These sites have low empty orbital energy and high exposure, making them easy to accept the lone pair electrons of the phenolic hydroxyl O atom, thus forming a stable coordinate bond. In NH2-MIL-101(Fe), the Fe atom acts as the core of the secondary building block (Fe3O cluster), and is bonded by the carboxyl group (-COO) of the organic ligand. - With tight coordination, the empty orbitals are almost completely occupied or shielded, making it difficult to form effective coordination with the O atom of the neutral phenolic hydroxyl group.
[0061] Based on the above analysis, the excellent adsorption performance of Fe-Fe3C@NC for β-naphthol and catechol stems from the multiple synergistic effects brought about by its unique structural characteristics. Furthermore, the adsorption rates of all materials were relatively rapid in the first 5 minutes, gradually decreasing thereafter. After 30 minutes of adsorption, most materials reached adsorption equilibrium; even after extending to 60 minutes, no significant desorption was observed. Among the six materials, BiOBr / Fe-Fe3C@NC1:5 showed the most outstanding adsorption performance for β-naphthol and catechol, achieving adsorption removal rates of 83.7% and 88.4%, respectively, within 30 minutes.
[0062] Figure 3 and Figure 4 The adsorption-photocatalytic synergistic effect of different catalysts on the removal efficiency of β-naphthol and catechol aqueous solutions was demonstrated. It can be clearly seen that the removal efficiency of pure NH2-MIL-101 (Fe) for 20 mg / L β-naphthol and 20 mg / L catechol is only 17.9% and 20.3%, respectively, while Fe-Fe3C@NC improves the removal efficiency of the two pollutants to 84.5% and 87.9%, respectively.
[0063] The above results indicate that calcination modification can improve the material's removal capacity for target pollutants, a phenomenon closely related to changes in the material's adsorption capacity. Since adsorption is a prerequisite step in photocatalytic degradation, the strength of adsorption directly affects subsequent photocatalytic efficiency. This is the key reason why Fe-Fe3C@NC exhibits superior adsorption-photocatalytic synergistic performance compared to NH2-MIL-101 (Fe). Furthermore, pure BiOBr showed relatively low removal efficiencies for both pollutants, at only 25.3% and 29.3%, respectively. However, the removal efficiency of the products obtained by combining Fe-Fe3C@NC and BiOBr (BiOBr / Fe-Fe3C@NC 1:5~3:5) was significantly improved. Among them, BiOBr / Fe-Fe3C@NC 1:5 exhibited the strongest adsorption-photocatalytic synergistic removal performance, achieving final degradation removal efficiencies of 98.1% and 100.0% for β-naphthol and catechol, respectively, far exceeding the removal capabilities of pure Fe-Fe3C@NC and pure BiOBr.
[0064] The superior performance mentioned above is attributed to two main factors: firstly, the material itself exhibits excellent adsorption performance for phenolic pollutants; secondly, the sufficient S-type heterojunctions constructed on the material surface promote efficient spatial separation and migration of photogenerated carriers, thereby retaining carriers with high redox capabilities and generating abundant active species. Furthermore, the introduced N-doped porous carbon not only provides chemical protection for the Fe-Fe3C nanoparticles, enhancing their stability during photocatalysis, but also acts as an electron trap, rapidly transferring photogenerated electrons separated at the heterojunction interface to reactive sites, thus ensuring rapid and complete mineralization of adsorbed pollutants. However, with further increases in BiOBr content, the adsorption-photocatalytic synergistic performance of the composite material gradually decreases. This is because excessive BiOBr forms a thicker coating on the Fe-Fe3C@NC surface, reducing the effective contact between the composite material and pollutants and lowering the adsorption and enrichment capacity. Moreover, BiOBr aggregation also leads to a decrease in light absorption efficiency and an increase in carrier recombination probability, thereby weakening the synergistic catalytic effect of the heterojunction.
[0065] The total organic carbon (TOC) removal rate of the BiOBr / Fe-Fe3C@NC1:5 prepared in Example 1 on simulated wastewater containing mixed β-naphthol and catechol under different light exposure times is shown in the figure. Figure 5 As shown in the figure, the mineralization efficiency of the mixed solution was 70.3% after 60 min of illumination, and further increased to 88.2% after 120 min. This result indicates that even in complex systems with multiple phenolic pollutants, BiOBr / Fe-Fe3C@NC1:5 still exhibits excellent deep oxidation capabilities, and can efficiently convert most phenolic organic pollutants into inorganic small molecules such as CO2 and H2O.
[0066] High-resolution XPS spectra of Fe 2p and Bi 4f ( Figure 6 and Figure 7 This confirmed the existence of strong electronic interactions at the interface of the composite material. Compared with Fe-Fe3C@NC, the characteristic peak of Fe 2p in BiOBr / Fe-Fe3C@NC1:5 shifted significantly towards the direction of higher binding energy. Figure 6 This indicates that the electron cloud density around the Fe sites is reduced, and the Fe element is in an electron-deficient state; conversely, compared with pure BiOBr, the characteristic peak of Bi 4f in the composite material shifts towards the direction of lower binding energy ( Figure 7 This indicates that the electron cloud density around Bi element increases, placing it in an electron-rich state. This result strongly demonstrates that at the BiOBr / Fe-Fe3C@NC1:5 heterojunction interface, electrons undergo a directional transfer from Fe-Fe3C@NC to BiOBr, thus constructing a built-in electric field at the two-phase interface. Through photoexcitation, electrons in the valence bands (VB) of Fe-Fe3C@NC and BiOBr will jump to their respective conduction bands (CB). Under the influence of the built-in electric field, electrons in the conduction band of Fe-Fe3C@NC are accelerated to transfer to the conduction band of BiOBr. Simultaneously, according to the S-type heterojunction electron migration pathway, photogenerated holes in the valence band of BiOBr migrate to the conduction band of Fe-Fe3C@NC and recombine with electrons there. This unique carrier migration pathway not only achieves efficient spatial separation of electron-hole pairs, but also retains the BiOBr conduction band electrons with strong reducing power and the Fe-Fe3C@NC valence band holes with strong oxidizing power, thus making it easier to generate a large number of highly active free radicals, ultimately achieving efficient degradation and mineralization of small molecule recalcitrant organic pollutants.
[0067] The scanning electron microscope (SEM) image of BiOBr / Fe-Fe3C@NC1:5 obtained in Example 1 is shown below. Figure 8 As shown, BiOBr nanosheets can be observed to grow dispersedly on the surface of the Fe-Fe3C@NC substrate. Due to the low amount of BiOBr added and the steric hindrance effect of Fe-Fe3C@NC, BiOBr failed to self-assemble into a complete nanoflower-like structure.
[0068] Table 1 lists the specific surface area (S) of Example 1 (BiOBr / Fe-Fe3C@NC1:5), Comparative Example 1 (Fe-Fe3C@NC), Comparative Example 2 (BiOBr), and NH2-MIL-101 (Fe). BETThe data shows that the specific surface areas of NH2-MIL-101 (Fe), BiOBr, Fe-Fe3C@NC, and BiOBr / Fe-Fe3C@NC1:5 are 2148.4, 24.7, 289.6, and 215.0 m², respectively. 2 / g. Compared to Fe-Fe3C@NC, the specific surface area of BiOBr / Fe-Fe3C@NC1:5 is slightly decreased. This may be due to the tight adhesion between BiOBr and Fe-Fe3C@NC, which blocks some of the originally open pore structures of Fe-Fe3C@NC. Nevertheless, BiOBr / Fe-Fe3C@NC1:5 still possesses a relatively large specific surface area and abundant pore structure, providing sufficient active sites for photocatalytic reactions, enhancing its adsorption performance, and thus synergistically improving the removal efficiency of phenolic pollutants.
[0069] Table 1. Specific surface area, pore volume, and average pore size of BiOBr, Fe-Fe3C@NC, and BiOBr / Fe-Fe3C@NC 5:1
[0070] sample <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore size (nm) <![CDATA[NH2-MIL-101(Fe)]]> 2148.4 1.222 2.0 BiOBr 24.7 0.038 5.0 <![CDATA[Fe / Fe3C@NC]]> 289.6 0.317 3.1 <![CDATA[Fe / Fe3C@NC / BiOBr 5:1]]> 215.0 0.310 3.5
[0071] The magnetic property curve of the BiOBr / Fe-Fe3C@NC1:5 sample prepared in Example 1 is shown in the figure. Figure 9 The results showed that the saturation magnetization (Ms) of BiOBr / Fe-Fe3C@NC1:5 was 61.47 emug. -1 The curves also show its hysteresis behavior. Furthermore, as illustrated in the inset, BiOBr / Fe-Fe3C@NC1:5 exhibits excellent magnetization response performance, rapidly separating and enriching from the reaction solution under an applied magnetic field. This characteristic endows the catalyst with convenient separation and recovery capabilities, effectively solving the problems of difficult catalyst recovery and secondary pollution during photocatalysis, laying an important foundation for its practical water treatment applications.
[0072] The BiOBr / Fe-Fe3C@NC1:5 sample prepared in Example 1 was recovered under an external magnetic field, and the adsorption-photocatalytic synergistic removal of β-naphthol and catechol was reproducibly investigated under the same conditions. Figure 10 It can be seen that the degradation rates of BiOBr / Fe-Fe3C@NC 1:5 remained at 91.2% and 93.4% respectively after being reused 5 times, and the catalyst still had excellent recovery rate in multiple cycles, showing high adsorption-photocatalytic synergistic removal efficiency and reusability.
[0073] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent changes and modifications made without departing from the spirit and scope of the present invention are covered within the scope of the present invention.
Claims
1. An application of a Fe-Fe3C@nitrogen-doped porous carbon composite material supported on BiOBr nanosheets, characterized in that: The composite material BiOBr / Fe-Fe3C@NC was applied to the degradation of phenols β-naphthol and catechol in wastewater; the preparation steps of BiOBr / Fe-Fe3C@NC are as follows: (1) Preparation of NH2-MIL-101-Fe: The precursor FeCl3·6H2O and 2-aminoterephthalic acid (NH2-BDC) were dispersed in an N,N-dimethylformamide (DMF) solvent system in an equimolar ratio, and acetic acid with a ratio of 0.25~0.5 mL:1 mmol was added. The mixture was then hydrothermally crystallized at 110 °C for 20 h. After drying and sieving, NH2-MIL-101-Fe powder was obtained. (2) Preparation of N-doped porous carbon (Fe-Fe3C@NC) encapsulating Fe-Fe3C nanoparticles: The powder obtained in step (1) was heated to 600-750 ℃ for 3-6 h under N2 protection at a heating rate of 3-10 ℃ / min, and Fe-Fe3C@NC powder was obtained after natural cooling. (3) Preparation of Fe-Fe3C@nitrogen-doped porous carbon composite material (BiOBr / Fe-Fe3C@NC) loaded with BiOBr nanosheets: The powder obtained in step (2) was dispersed in a mixed solvent system of ethylene glycol and ethanol with equimolar ratio of Bi(NO3)3·5H2O and KBr by hydrothermal method. The hydrothermal synthesis reaction was carried out at 140-160 °C for 8-12 h. After drying and sieving, BiOBr / Fe-Fe3C@NC powder was obtained.
2. The application according to claim 1, characterized in that: Step (1) specifically involves weighing FeCl3·6H2O and NH2-BDC at a molar ratio of 1:1 at room temperature, and dissolving FeCl3·6H2O and NH2-BDC in N,N-dimethylformamide (DMF) by ultrasonication according to a solute-solvent ratio of 1 mmol:10 mL. Under magnetic stirring, acetic acid with a ratio of 0.25~0.5 mL:1 mmol and the ultrasonically dispersed FeCl3 solution are added to the NH2-BDC solution at a constant rate and stirred continuously until homogeneous. The mixture is then transferred to a sealed high-pressure reactor, sealed, and placed in an oven at 110 ℃ for hydrothermal crystallization for 20 h. After centrifugation, washing, vacuum drying, and sieving through a 100-mesh sieve, NH2-MIL-101-Fe powder is obtained.
3. The application according to claim 2, characterized in that: The constant dropping rate in step (1) is 0.05~0.1 mL / s, and the high-pressure reactor is lined with polytetrafluoroethylene.
4. The application according to claim 2, characterized in that: The cleaning in step (1) is performed by alternating washing with hot DMF at 50~60 ℃ and anhydrous ethanol; the vacuum drying conditions are 60~80 ℃ for 10~12 h.
5. The application according to claim 1, characterized in that: Step (3) specifically involves ultrasonically dissolving Bi(NO3)3·5H2O in ethylene glycol at a ratio of 0.1~0.3 mmol:50 mL; then, weighing the Fe-Fe3C@NC powder prepared in step (2) and adding it to the above Bi(NO3)3·5H2O ethylene glycol solution at a ratio of Fe-Fe3C@NC:Bi(NO3)3·5H2O = 0.15 g:0.1~0.3 mmol, and ultrasonically dispersing it to form a mixed system of Fe-Fe3C@NC and Bi(NO3)3·5H2O; simultaneously, weighing KBr in an equimolar ratio with Bi(NO3)3·5H2O, and ultrasonically dissolving it in a 1:1 volume ratio ethylene glycol-ethanol mixed solution at a ratio of 0.1~0.3 mmol:80~100 mL; and, under magnetic stirring, dissolving the resulting KBr solution at a ratio of 0.5~1... The Fe-Fe3C@NC and Bi(NO3)3·5H2O mixture was added dropwise at a constant rate of mL / s to the above mixture and stirred until homogeneous to obtain a ternary mixture. The ternary mixture was then placed in a high-pressure reactor, sealed, and placed in an oven at 140~160 ℃ for hydrothermal reaction for 8~12 h. After centrifugation, washing, vacuum drying, and sieving through a 100-mesh sieve, BiOBr / Fe-Fe3C@NC was obtained.
6. The application according to claim 5, characterized in that: The cleaning in step (3) involves alternating washing with anhydrous ethanol and deionized water; the vacuum drying conditions are 60~80 ℃ for 10~12 h.
7. The application according to any one of claims 1-6, characterized in that: The composite material BiOBr / Fe-Fe3C@NC used has a specific surface area ranging from 150 to 220 m². 2 / g, with an average pore size distribution of 3.5~3.8 nm. The theoretical amount of BiOBr generated is based on the theoretical amount of Fe-Fe3C@NC in the composite, and the mass ratio of the two is 1:5~3:5.