Preparation method and application of double-heterojunction catalytic material for efficiently degrading chlorinated flame retardant through photo-Fenton

Abstract

The invention discloses a preparation method and application of a dual-heterojunction catalytic material for efficiently degrading a chlorinated flame retardant through photo-Fenton. According to the method, BC is introduced into modified g-C3N4 containing N defects to construct p-n-n double heterojunctions, so that a band gap structure can be optimized, and dissolution of Co metal in a CoSe semiconductor material clamped between the band gap structure and the p-n-n double heterojunctions is remarkably inhibited by utilizing a sandwich structure of the p-n-n double heterojunctions. Besides, a p-n / n-n built-in electric field can promote directed migration and efficient separation of photon-generated carriers, and a relatively high oxidation-reduction potential of the composite material is maintained, so that under the condition of visible light, a reaction energy barrier for adsorbing H2O2 to be converted into. OH by nitrogen vacancies on the surface of the modified g-C3N4 is effectively activated, the generation capacity of. OH is enhanced, and efficient degradation and dechlorination of a chlorinated flame retardant are realized. Under the visible light Fenton condition, the prepared catalyst can degrade 10 mg / L of TCBPA by 99% or above within 25 min, and the dechlorination rate can reach 69.6% within 60 min.

Description

Technical Field

[0001] The present invention belongs to the field of environmental engineering technology, and relates to the research on the preparation technology of black phosphorus nanosheets, cobalt diselenide and modified graphite phase carbon nitride (PNN) double heterojunction photocatalytic materials, and the innovation of a method for efficiently degrading chlorinated flame retardants by visible light Fenton catalysis using the double heterojunction photocatalytic materials. Background Art

[0002] Tetrachlorobisphenol A (TCBPA) is a persistent pollutant widely used in the organic synthesis industry as a chlorinated flame retardant, accounting for approximately 60% of the entire market. It has a long half-life, biotoxicity, bioaggregation and long-distance migration ability, which seriously affects people's life and health.

[0003] At present, the main treatment methods are: biological method, physical adsorption method, Fenton method and photocatalytic method. The article "Optimization of parameters for anaerobic co-metabolic degradation of TBBPA" by Peng et al. shows that the use of biological methods can achieve the degradation and mineralization of halogenated flame retardants in water bodies, and can effectively reduce their biological toxicity. However, the biological method still has problems such as large footprint, poor microbial selectivity, limited available strains and difficulty in enriching trace microorganisms in the environment, which hinders its practical application. Chen et al. "Functional PVDFultrafiltration membrane for Tetrabromobisphenol-A (TBBPA) removal with highwater recovery." The article uses nano-ZrO2 to functionalize the surface of commercial PVDF ultrafiltration membranes, making it obtain a membrane permeation flux 4 times stronger than that of unmodified PVDF membranes, and removes TBBPA from water bodies through the screening function of the membrane. The physical adsorption method is simple and easy, with low cost, but it cannot degrade this type of pollutants, and the adsorbent is easily deactivated. He et al. "Preparation of bifunctional hollow mesoporous Fe 0 @C@MnFe2O4 as Fenton-like catalyst for degradation of Tetrabromobisphenol A. The article loaded nano-iron element (nZVI) on the magnetic hollow mesoporous C@MnFe2O4 material to prepare Fe 0 @C@MnFe2O4 bimetallic Fenton catalyst can remove 90% of typical halogenated flame retardants in 120 minutes. While the Fenton process can rapidly remove these halogenated flame retardants, it also involves metal dissolution, potentially causing secondary pollution.

[0004] Compared to the aforementioned methods, photo-Fenton is an emerging Fenton-like advanced oxidation technology. It converts solar energy into chemical energy, which then reacts with hydrogen peroxide (H2O2) to catalyze its conversion to hydroxyl radicals (·OH). The catalysts used in this technology can be made from a wide range of non-metallic semiconductor materials, which avoids metal dissolution. Furthermore, it is environmentally friendly and sustainable, and is considered a viable solution to environmental water pollution. However, its practical application is hampered by issues such as high carrier recombination rates and low light utilization. Currently, researchers are optimizing the performance of this type of catalytic material through methods such as morphology control, element doping, and heterostructure construction. For example, Weng et al. reported efficient mineralization of TBBPA via an integrated photocatalytic reduction / oxidation process mediated by MoS2 / SnIn4S8 photocatalyst. The article combines MoS2 nanosheets with SnIn4S8 to reduce the recombination rate of photogenerated electron-hole pairs, making the MoS2 / SnIn4S8 composite material have excellent carrier separation ability. However, the material still has problems such as low spectral utilization and low dehalogenation and mineralization rates.

[0005] Therefore, the present invention selects graphite carbon nitride (GCN) as a non-metallic semiconductor material and synthesizes a PNN double heterojunction photocatalytic material with different types of semiconductors. This creates a unique built-in electric field that promotes the directional migration of photogenerated carriers and broadens the material's spectral utilization. This improves the separation efficiency of photogenerated carriers while maintaining a high redox capacity, thereby achieving rapid and low-cost degradation and dechlorination of TBBPA in the environment. Furthermore, the double heterojunction catalytic material forms a sandwich structure. Summary of the Invention

[0006] This invention provides a method for preparing a pn / nn double heterojunction photocatalytic material composed of black phosphorus nanosheets, cobalt diselenide, and modified graphitic carbon nitride. The material also achieves TCBPA degradation and dechlorination via visible light Fenton reaction. First, p-type semiconductor black phosphorus nanosheets (Bpn) and n-type semiconductor cobalt diselenide (CoSe) are combined to form a pn heterojunction precursor. This precursor is then bonded to an n-type non-metallic modified graphitic carbon nitride (g-C3N4) substrate to form a pn / nn double heterojunction. This extends the composite's light absorption range and inhibits the recombination of photogenerated carriers. Furthermore, the modified g-C3N4 surface possesses numerous defect sites, effectively capturing H2O2. The unique pn / nn built-in electric field not only promotes the directional migration of photogenerated carriers but also maintains a high redox capacity in the composite. This, in turn, promotes the conversion of adsorbed H2O2 molecules into hydroxyl radicals (•OH), achieving efficient degradation and removal of TCBPA from water.

[0007] The technical solution of the present invention:

[0008] A method for preparing a double heterojunction catalytic material for efficient photo-Fenton degradation of chlorinated flame retardants, comprising the following steps:

[0009] Step 1: Dark yellow modified g-C3N4 was obtained by referring to the preparation method in the reference “A General Synthesis of Porous Carbon Nitride Filmswith Tunable Surface Area and Photophysical Properties”.

[0010] Step 2: Synthesize co-catalyst Bpn liquid and CoSe powder;

[0011] Bpn liquid: In an N2 atmosphere, black phosphorus solid was ground into powder, dispersed in N-methylpyrrolidone, and sonicated until uniformly dispersed. The resulting mixture was then centrifuged at 8000-12000 rpm, and the supernatant was collected to obtain a Bpn liquid with a lamellar structure at a concentration of 1.0-5.0 mg / L.

[0012] CoSe powder: First, two solutions need to be prepared separately; Co(NO3)2 solid is dispersed in deionized water to obtain solution 1 with a concentration of 0.1-0.3 mol / L; selenium powder is dissolved in deionized water to obtain solution 2 with a concentration of 0.12-0.36 mol / L; solution 1 and solution 2 are fully stirred to completely dissolve them; then, during the stirring process, solution 1 is added dropwise to solution 2 to form a uniform mixed liquid, the volume ratio of solution 1 to solution 2 is 1:1, and the molar ratio of Co(NO3)2 to selenium in the solution is 1:1-1:1.5; the mixed liquid is transferred to a polytetrafluoroethylene reactor and maintained at a temperature of 200-300°C for hydrothermal reaction for 18-25 hours; after it is cooled to room temperature, it is washed three times with deionized water and vacuum dried to obtain black CoSe powder;

[0013] Step 3: The CoSe powder obtained in step 2 is dispersed into the Bpn liquid and mixed evenly. After the mixed liquid is vacuum dried, it is calcined at 150-250 ° C for 1-2 h in a N2 atmosphere. After cooling to room temperature, it is taken out to obtain a Bpn / CoSe heterojunction (BC); then, the Bpn / CoSe heterojunction is mixed with the modified g-C3N4 obtained in step 1 and ground and dispersed in anhydrous ethanol. The mass ratio of modified g-C3N4, CoSe powder and Bpn is controlled to be 200:5:1-10:1:1, and then ultrasonically treated for 30-60 min to obtain a uniform suspension; after the suspension is vacuum dried, the obtained solid is ground into powder and placed in a porcelain boat. In a N2 atmosphere, it is kept at 300-450 ° C for 2-5 h, and after cooling to room temperature, the product was taken out and washed three times with deionized water and ethanol to remove residual precursor ions. After vacuum drying, a double heterojunction catalytic material, namely, a pnn double heterojunction photocatalytic material Bpn / CoSe / g-C3N4 (BCC), was obtained.

[0014] The double heterojunction catalytic material prepared by the above preparation method is used as a photo-Fenton catalyst, and visible light activates H2O2 to degrade chlorinated flame retardants in water and achieve detoxification and dechlorination; H2O2 aqueous solution is added at room temperature and visible light irradiation conditions (λ>420 nm).

[0015] The chlorinated flame retardant, tetrachlorobisphenol A (TCBPA), degraded over 99% of 10 mg / L TCBPA within 25 minutes. Furthermore, a 69.6% TCBPA dechlorination rate was achieved within 60 minutes.

[0016] Beneficial effects of the present invention: The method of the present invention is the first to achieve the visible light Fenton fast and efficient degradation of the typical chlorinated flame retardant TCBPA using the pnn double heterojunction catalytic material BCC. The modified g-C3N4 prepared by the method in step 1 is optimized in morphology compared to the bulk graphite phase carbon nitride prepared by the traditional method. It exhibits a two-dimensional porous layered structure with a large specific surface area, which can effectively improve the surface mass transfer efficiency and light absorption intensity of the material. In addition, a large number of nitrogen defect structures can induce electron cloud migration and enrichment, and the electron-rich environment is conducive to the construction and stability of the g-C3N4 surface heterojunction. Then, using p-type semiconductor Bpn and n-type semiconductor CoSe as raw materials, BC with a pn-type heterojunction is synthesized by simple calcination. It not only has good conductivity and a wide light response range, but also forms a unique pn heterojunction that can guide the efficient and directional migration of photogenerated carriers. It is then further calcined with an n-type semiconductor modified g-C3N4 substrate to synthesize a pnn double heterojunction catalytic material BCC, which can effectively optimize the band gap structure of the composite material and extend the spectral response range. The improvement in conductivity promotes the improvement of surface mass transfer efficiency. The sandwich structure of the pnn double heterojunction can significantly inhibit the dissolution of Co metal in the CoSe sandwiched in the middle. In addition, the construction of the pn / nn built-in electric field can promote the directional migration and efficient separation of photogenerated carriers, and maintain a high redox potential of the composite material, so that it can effectively activate the reaction energy barrier of the nitrogen vacancies on the surface of the modified g-C3N4 to adsorb H2O2 and convert it into •OH under visible light conditions, enhance the production of •OH, and efficiently degrade TCBPA. The modified g-C3N4 can also catalyze the conversion of O2 molecules in water into superoxide radicals (O2 ·- ), can selectively attack the β-C site in the TCBPA structure and accelerate the degradation of target pollutants. ·- Under the synergistic effect, efficient degradation and dechlorination of TCBPA can be achieved. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is described below in conjunction with the technical solution.

[0018] Example 1

[0019] Preparation method of pnn dual photocatalytic material BCC:

[0020] 5.0 g of cyanuric chloride, 5.0 g of dicyandiamide and 0.8 g of barbituric acid were dispersed in 80 ml of deionized water in sequence. Each component was added at intervals of 30 min, and the resulting mixed liquid was stirred for 6 h until fully mixed. After the obtained mixed liquid was dried at 60 ° C to remove all moisture, it was ground evenly and placed in a tube furnace for calcination in a N2 atmosphere. The temperature was controlled at 500 ° C for 5 h. After it was cooled to room temperature, it was taken out and soaked in 1 wt% dilute hydrochloric acid for 30 min. It was then washed with deionized water and ethanol three times respectively, and dried in an oven at 60 ° C to obtain a dark yellow modified g-C3N4 powder. A series of characterizations, such as solid 13 C nuclear magnetic resonance, electron spin resonance spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to investigate the morphology and structural characteristics of the prepared modified g-C3N4 substrate. It was found that the prepolymerization process reduced the stacking and agglomeration of the modified g-C3N4, and the material tended to a two-dimensional lamellar structure. The surface exhibited a sponge-like porous structure, and the presence of a large number of N vacancies increased the specific surface area of ​​the composite material, improved the utilization of incident light, and enhanced the surface mass transfer efficiency. Furthermore, the acid wash process removed residual oxygen-containing groups in the structure and improved the surface charge distribution of the material.

[0021] Cocatalyst Bpn liquid and CoSe powder were prepared. For the Bpn liquid, 200 mg of black phosphorus solid was ground into a powder under a nitrogen atmosphere and then dispersed in 150 ml of N-methylpyrrolidone. Ultrasonication was performed until uniformly dispersed. The resulting mixture was then centrifuged at 8000 rpm, and the supernatant was collected to obtain a lamellar Bpn liquid with a concentration of 1.0 mg / L. For the CoSe powder, two separate solutions were prepared. Solution 1: 1.8 g of Co(NO₃)₂ solid was dispersed in deionized water. Solution 2: 0.8 g of selenium powder was added to deionized water and solutions 1 and 2 were thoroughly stirred to dissolve. Then, while stirring, solution 1 was added dropwise to solution 2 to form a uniform mixture. The mixture was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 200°C for 22 hours. After cooling to room temperature, it was washed three times with deionized water and dried in a vacuum oven at 40°C to obtain black CoSe powder.

[0022] The CoSe powder obtained in step 2 was dispersed into the Bpn liquid and mixed uniformly. The mixture was then dried in a vacuum oven at 40°C and calcined at 200°C for 1 h under an N2 atmosphere. After cooling to room temperature, the Bpn / CoSe heterojunction (BC) was obtained. BC was then mixed with 0.20 g-C3N4 obtained in step 1, ground, and dispersed in anhydrous ethanol (the mass ratio of modified g-C3N4:CoSe:Bpn was 20:1:1). Ultrasonication was then performed for 30 min to obtain a uniform suspension. The mixture was dried in a vacuum oven at 40°C. The solid was then ground into a powder and calcined in a tube furnace at 400°C for 2 h under an N2 atmosphere. After cooling to room temperature, the product was washed three times with deionized water and ethanol to remove residual precursor ions. After vacuum drying, the Bpn / CoSe / modified g-C3N4-1 (BCC-1) double heterojunction catalyst was obtained.

[0023] Reference group catalyst: The above preparation method was used to prepare the BCC catalyst reference group, with only the mass ratio of modified g-C3N4:CoSe:Bpn being changed. The mass ratios of the three were 20:0.1:0.1, 20:0.5:0.5, 20:2:2, and 20:3:3, respectively. The reference group catalysts were named BCC-0.1, BCC-0.5, BCC-2, and BCC-3, respectively.

[0024] Example 2

[0025] Visible-light Fenton degradation of TCBPA: The BCC-1 heterojunction catalyst was dispersed into a reactor containing 100 mL of a 10 mg / L TCBPA solution (catalyst concentration 0.2 mg / L). Prior to the degradation experiment, the reactor was stirred in the dark for 30 minutes to allow the catalyst and TCBPA to reach adsorption saturation. 100 μL of a 30% H₂O₂ aqueous solution was then added dropwise to the solution. The photo-Fenton degradation test was conducted under visible light (λ > 420 nm). The reaction time was 60 minutes at a temperature of 25°C. The reaction solution was sampled every 10 minutes, filtered through a 0.22 μm filter, and 1 mL of the sample was collected for later use. The degradation and dechlorination rates were then measured using an instrument.

[0026] High-performance liquid chromatography (HPLC) analysis of TCBPA concentrations revealed that the degradation rate of TCBPA reached over 99% by 25 minutes. Ion chromatography analysis of the dechlorination rate during the reaction revealed that the dechlorination rate reached 69.6% by 60 minutes.

[0027] Comparative Example 1

[0028] The same test method as in Example 2 was used, except that BCC-0.1, BCC-0.5, BCC-2, and BCC-3 were used instead of BCC-1 to perform degradation and dechlorination performance tests.

[0029] After 25 min of reaction, the degradation rates of BCC-0.1, BCC-0.5, BCC-2, and BCC-3 were 31.5%, 58%, 88.5%, and 79.3%, respectively.

[0030] After 60 min of reaction, the dechlorination rates of BCC-0.1, BCC-0.5, BCC-2, and BCC-3 were 7%, 13.2%, 28.1%, and 21%, respectively.

[0031] Compared with the reference catalyst, BCC-1 exhibited the best degradation and dechlorination performance for TCBPA. This is due to the suitable heterojunction structure, which maximizes the separation of charge carriers and promotes the reaction rate of H2O2 to OH.

[0032] Example 3

[0033] Degradation quenching experiment: The BCC-1 heterojunction catalyst was subjected to degradation test according to the method of Example 2. When H2O2 aqueous solution was added, 1 mmol / L quenchers (p-benzoquinone, isopropanol, sodium oxalate and potassium dichromate) were added respectively. Their effects on the active species O2 generated in the quenching reaction were as follows: ·- , ·OH, photogenerated holes, and photogenerated electrons. Other operating conditions remained unchanged, with a reaction time of 60 min. The reaction solution was collected every 10 min, filtered through a 0.22 μm filter membrane, and 1 mL was collected for later use. The removal rate was then determined by instrument testing.

[0034] The TCBPA concentration was determined by high performance liquid chromatography. Combining the effects of various quenchers on the TCBPA removal rate and the results of electron spin resonance spectroscopy, it was found that ·OH played a major role in the entire degradation system, contributing 70% to the degradation; O2 ·- The contribution rate to degradation is 25%, and the remaining contribution rate to degradation is photogenerated electrons and photogenerated holes.

Claims

1. A method for preparing a double heterojunction catalytic material for efficient photo-Fenton degradation of chlorinated flame retardants, characterized in that: Here are the steps: Step 1: Preparation of modified g-C3N4; Step 2: Synthesize co-catalyst Bpn liquid and CoSe powder; Bpn liquid: In an N2 atmosphere, black phosphorus solid is ground into powder, dispersed in N-methylpyrrolidone, and sonicated until uniformly dispersed. The resulting mixed liquid is then centrifuged at 8000-12000 rpm, and the supernatant is collected to obtain a Bpn liquid with a lamellar structure at a concentration of 1.0-5.0 mg / L. CoSe powder: Prepare two solutions: an aqueous solution of Co(NO3)2 and an aqueous solution of selenium powder. Mix the two solutions and transfer them to a polytetrafluoroethylene reactor. Maintain a temperature of 200-300°C for a hydrothermal reaction for 18-25 hours. After cooling to room temperature, wash with deionized water and vacuum dry to obtain black CoSe powder. Step 3: The CoSe powder obtained in step 2 is dispersed into the Bpn liquid and mixed evenly. After the mixed liquid is vacuum dried, it is calcined at 150-250°C for 1-2 h under N2 atmosphere, and taken out after cooling to room temperature to obtain a Bpn / CoSe heterojunction; then, the Bpn / CoSe heterojunction is mixed with the modified g-C3N4 obtained in step 1 and ground and dispersed in anhydrous ethanol, followed by ultrasonic treatment to obtain a uniform suspension; after the suspension is vacuum dried, the obtained solid is ground into powder and placed in a porcelain boat, and calcined at 300-450°C for 2-5 h under N2 atmosphere, and then taken out after cooling to room temperature. The product is washed continuously with deionized water and ethanol to remove residual precursor ions, and a double heterojunction catalytic material, i.e., a pnn double heterojunction photocatalytic material Bpn / CoSe / g-C3N4, is obtained after vacuum drying.

2. The preparation method according to claim 1, characterized in that In step 2, The concentration of Bpn liquid is 1.0-5.0 mg / L.

3. The preparation method according to claim 1, characterized in that In step 2, The concentration of Co(NO3)2 aqueous solution is 0.1-0.3 mol / L; The concentration of the aqueous solution of selenium powder is 0.12-0.36 mol / L; The volume ratio of the aqueous solution of Co(NO3)2 to the aqueous solution of selenium powder is 1:1; The molar ratio of Co(NO3)2 to selenium in the mixed solution is 1:1-1:1.

5.

4. The preparation method according to claim 1, characterized in that In step 3, The mass ratio of modified g-C3N4, CoSe powder and Bpn is 200:5:1-10:1:

1.

5. The preparation method according to claim 1, characterized in that In step 3, Ultrasonic treatment for 30-60 min.

6. Use of the double heterojunction catalytic material obtained by the preparation method according to any one of claims 1 to 5 as a photo-Fenton catalyst, characterized in that: Visible light activated H2O2 degraded chlorinated flame retardants in water and achieved detoxification and dechlorination; H2O2 aqueous solution was added at room temperature and under visible light irradiation conditions.

7. The use according to claim 6, characterized in that The chlorinated flame retardant is tetrachlorobisphenol A.