A method for preparing an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst and its application in water purification.

Abstract

This invention discloses a method for preparing an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst and its application in water purification, belonging to the field of organic wastewater removal. The preparation method includes preparing negatively charged ultrathin BiOCl-OV and positively charged CoAl-LDH surfaces via ultrasonic exfoliation and co-precipitation, respectively. Utilizing Coulomb attraction, an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction with a thickness of only about 10 nm is synthesized using electrostatic self-assembly. The unique Z-type charge transfer pathway accelerates the reduction of Co(III) to Co(II) within the catalyst itself, thereby promoting the two-electron transfer of Co(II) to form Co(IV)=O. In a synergistic system of light and PMS, Co(IV)=O participates in the degradation reaction as the main active species, achieving 100% RhB degradation in 9 minutes. Meanwhile, this heterojunction exhibits excellent degradation performance against a variety of organic pollutants and strong resistance to interference from inorganic ions. Furthermore, the raw materials are inexpensive, non-toxic, and harmless, demonstrating high practical value and application prospects in the field of organic wastewater removal.

Description

Technical Field

[0001] This invention relates to the field of organic wastewater removal, specifically to a method for preparing an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst with synergistic degradation performance of photocatalysis and persulfate oxidation, and its application in water purification. Background Technology

[0002] Insoluble and recalcitrant organic pollutants in wastewater pose a serious threat to human life and ecosystems, even at low concentrations. Therefore, there is an urgent need to develop effective pollutant remediation strategies for aquatic environments. Among these, advanced oxidation technologies (AOPs) based on peroxymonosulfate (PMS) have attracted widespread attention due to their strong oxidizing power against organic pollutants. Activation methods include UV activation, thermal activation, electrochemical activation, carbon material activation, photocatalytic activation, and transition metal ion activation. Transition metal Co(II) ions and Co-based heterogeneous catalysts have been proven to be among the most effective catalysts for PMS activation. However, traditional Co(II) / PMS systems often employ a radical pathway, generating sulfate radicals (·SO4) through single-electron transfer. - While pollutants are degraded by hydroxyl radicals (·OH), this pathway suffers from drawbacks such as low steady-state concentration of free radicals, poor resistance to interference, rapid consumption, and poor selectivity. Therefore, a non-radical pathway dominated by high-valence Co(IV)=O species generated through two-electron transfer holds promise as an effective solution. Furthermore, this pathway exhibits high selectivity, wide pH adaptability, excellent pollutant removal capacity, and superior chemical stability.

[0003] However, the formation of high-valence Co(IV)=O is severely restricted by the breaking of the high-energy-barrier OO bonds in the Co(II)-PMS intermediate, and Co(VI)=O is unstable, easily undergoing reduction reactions with pollutants to transform into low-valence Co(III). The formed Co(III) can only be converted into Co(IV)=O through a single electron transfer process in the Co / PMS system, during which abundant ·SO4 is generated. - This is not conducive to the formation of Co(IV)=O. Therefore, finding a suitable method to achieve a rapid conversion of Co(III) to Co(II) is crucial for the formation of high-valence Co(IV)=O through two-electron transfer.

[0004] Photocatalysis, as an advanced oxidation technology, boasts advantages such as being green, environmentally friendly, safe, and energy-efficient, showing broad application prospects in the removal of organic pollutants from water. Catalysts, through photoexcitation, generate holes and hydroxyl radicals, which possess strong oxidizing capabilities against organic pollutants. However, traditional photocatalysts exhibit low efficiency in the separation and transfer of photogenerated carriers. It has been reported that constructing heterojunctions with two-dimensional ultrathin structures is an effective strategy to improve the separation and transfer efficiency of photogenerated electron-hole pairs, as the ultrathin structure can significantly shorten the transport distance of photogenerated electrons and holes. Furthermore, compared to traditional type II heterojunctions, type Z heterojunctions exhibit higher separation and transfer efficiency of photogenerated carriers, while also possessing stronger redox capabilities.

[0005] Coupled photocatalytic degradation with PMS oxidation, the strong mineralization power of photocatalysis and the rapid degradation performance of PMS can effectively improve the removal efficiency of organic pollutants in water. Furthermore, for some Co-based catalytic materials, the internal electric field of photocatalysis can directionally drive photogenerated electrons to specific sites. These photogenerated electrons can not only rapidly activate PMS but also quickly reduce Co(III) to Co(II), thereby promoting the formation of Co(IV)=O, effectively improving the oxidation performance of organic pollutants.

[0006] In summary, a Co-based Z-type heterojunction catalyst with a two-dimensional ultrathin structure was constructed using BiOCl (BiOCl-OV) and CoAl-LDH, which are simple to prepare, highly stable, use inexpensive raw materials, and have matching band structures and oxygen-rich vacancies. This catalyst is used for the synergistic degradation of organic pollutants in water through photocatalysis and PMS oxidation. The photogenerated electrons produced by the catalyst can accelerate the conversion of Co(III) to Co(II) and generate high-valence Co(IV)=O species through two-electron transfer. This catalyst design is of great significance for water purification technology. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst and its application in water purification. The key feature is that this ultrathin Z-type heterojunction catalyst can effectively couple photocatalysis and persulfate oxidation degradation systems, and rapidly reduce Co(III) to Co(II) through photogenerated electrons, accelerating the continuous generation of Co(IV)=O. Through a non-radical pathway dominated by high-valence Co(IV)=O species, it achieves 100% degradation efficiency of Rhodamine B (RhB) within 9 minutes. Furthermore, this system exhibits excellent degradation performance for various organic pollutants such as phenol, methylene blue, tetracycline, and methyl orange.

[0008] To achieve the above objectives, embodiments of the present invention provide a method for preparing an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst, comprising the following steps:

[0009] (1) Weigh out Bi(NO3)2·5H2O and polyvinylpyrrolidone, dissolve them in water, stir until homogeneous, then add 1-butyl-3-methylimidazolium chloride to the above mixed solution and stir until homogeneous;

[0010] (2) The solution obtained in step (1) was transferred to a reaction vessel, subjected to hydrothermal treatment, washed and dried to obtain BiOCl nanosheets;

[0011] (3) Disperse the BiOCl obtained in step (2) into a 1-methyl-2-pyrrolidone solution, sonicate, wash and dry to obtain ultrathin BiOCl nanosheets;

[0012] (4) Irradiate the ultrathin BiOCl obtained in step (3) under a mercury lamp to obtain ultrathin BiOCl-OV nanosheets rich in oxygen vacancies.

[0013] (5) Mix the Co(NO3)2·6H2O and Al(NO3)3·9H2O solutions thoroughly according to the Co:Al molar ratio of 2:1;

[0014] (6) The mixed solution from step (5) was added dropwise to a mixed solution of NaNO3 and formamide, heated, washed and dried to obtain ultrathin CoAl-LDH nanosheets;

[0015] (7) Dissolve the BiOCl-OV obtained in step (4) and the CoAl-LDH obtained in step (6) in water respectively, and sonicate them. Then add the CoAl-LDH solution dropwise to the BiOCl-OV solution, heat it, wash and dry it to obtain the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction material.

[0016] The embodiments of the present invention have the following advantages:

[0017] The ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst provided in this invention can efficiently couple photocatalytic degradation and persulfate oxidation technologies. Simultaneously, the electrons generated by photocatalysis can accelerate the conversion of Co(III) to Co(II) and generate high-valence Co(IV) species through two-electron transfer. In a synergistic system of light and PMS, 100% of RhB is degraded within 9 minutes via Co(IV)=O. Furthermore, this catalyst exhibits excellent degradation performance for various organic pollutants such as phenol, methylene blue, tetracycline, and methyl orange, and also demonstrates strong resistance to interference from inorganic ions in solution. The raw materials for this ultrathin Z-type heterojunction are inexpensive, non-toxic, and harmless, possessing high practical value and application prospects. Attached Figure Description

[0018] Figure 1This is a schematic diagram illustrating the fabrication of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in an embodiment of the present invention.

[0019] Figure 2 X-ray diffraction pattern of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in an embodiment of the present invention.

[0020] Figure 3 Transmission electron microscopy (TEM) image of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in an embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of the KPFM of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in an embodiment of the present invention.

[0022] Figure 5 The graph shows the RhB degradation performance of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in the embodiments of the present invention.

[0023] Figure 6 The image shows the capture performance of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in the embodiments of the present invention.

[0024] Figure 7 The graph shows the degradation performance of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction for different pollutants, as provided in the embodiments of the present invention.

[0025] Figure 8 The graph shows the performance of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction provided in the embodiments of the present invention in degrading RhB under different ionic environments. Detailed Implementation

[0026] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0027] Example 1

[0028] 1.0 g of polyvinylpyrrolidone and 1.94 g of Bi(NO3)2·5H2O were dissolved in 40 mL of deionized water at room temperature and stirred for 30 minutes. Then, 1.94 g of 1-butyl-3-methylimidazolium chloride was added to the above solution, and stirring was continued for another 30 minutes. Subsequently, the mixture was transferred to a 100 mL Teflon-lined stainless steel reactor and kept at 160 °C for 16 hours. After naturally cooling to room temperature, the mixture was washed and vacuum dried for 10 hours to obtain BiOCl. Then, 1.0 g of BiOCl was dispersed in 100 mL of 1-methyl-2-pyrrolidone solution and sonicated in ice water for 24 hours. After sonication, the mixture was centrifuged at 4000 rpm for 5 minutes, and then the supernatant was further centrifuged at 10000 rpm for 10 minutes. The solid BiOCl product was collected, washed several times with ethanol, and vacuum dried to obtain ultrathin BiOCl. Ultrathin BiOCl was irradiated under a 300W mercury lamp for 30 minutes to obtain ultrathin BiOCl-OV rich in oxygen vacancies.

[0029] Example 2

[0030] Ultrathin CoAl-LDH was prepared by coprecipitation: 40 mL of 0.04 M Co(NO3)2·6H2O and 80 mL of 0.01 M Al(NO3)3·9H2O were mixed in a beaker and stirred for 30 minutes to obtain solution A. 120 mL of 0.01 M NaNO3 solution and 36 mL of formamide were mixed in a beaker and stirred for 30 minutes to obtain solution B. Then, solution A was added dropwise to solution B, maintaining the pH at 10 during the addition. After the addition was complete, the reaction was continued for 20 minutes. The solid product was then collected, washed, and dried to obtain ultrathin CoAl-LDH.

[0031] Example 3

[0032] 0.1 g of BiOCI-OV and a certain amount of CoAl-LDH were dispersed in 50 mL and 30 mL of deionized water, respectively, and sonicated for 4 h. Subsequently, the CoAl-LDH mixed solution was added dropwise to the BiOCI-OV solution under stirring in an 80 °C water bath, and treated at 80 °C for 1 h. After washing and drying, ultrathin BiOCI-OV / CoAl-LDH Z-type heterojunction materials were obtained. Based on the amount of CoAl-LDH added, X (X = 10 mg, 30 mg, 60 mg), the synthesized composites were labeled B-CoAl-1, B-CoAl-2, and B-CoAl-3, respectively.

[0033] Example 4

[0034] The preparation process of BiOCl / CoAl-LDH heterojunction is the same as that of B-CoAl-2 in Example 3, except that BiOCl is used instead of BiOCl-OV.

[0035] Example 5

[0036] Figure 1 This diagram illustrates the preparation of an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction. Ultrathin BiOCl-OV with a negatively charged surface and ultrathin CoAl-LDH with a positively charged surface were prepared by ultrasonic exfoliation and co-precipitation methods, respectively. The ultrathin 2D heterojunction was then synthesized by electrostatic self-assembly using Coulomb attraction.

[0037] Example 6

[0038] The phase composition of the samples was characterized using a D8 ADVANCE X-ray diffractometer manufactured by Bruker AXS GmbH, Germany. Figure 2 The image shows the X-ray diffraction pattern of the prepared samples. As can be seen from the figure, characteristic peaks of BiOCl and CoAl-LDH can be observed in both BiOCl-OV / CoAl-LDH and BiOCl / CoAl-LDH heterojunctions, and no other impurity peaks were observed, indicating that the heterojunction was successfully prepared by electrostatic self-assembly.

[0039] Example 7

[0040] The microstructure of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction was characterized using a JEOL JEM-2010 transmission electron microscope manufactured by Nippon Electronics Corporation. Figure 3 The image shows a transmission electron microscope (TEM) image of the prepared ultrathin B-CoAl-2. As can be seen from the image, ultrathin CoAl-LDH nanosheets were successfully loaded onto ultrathin BiOCl-OV nanosheets.

[0041] Example 8

[0042] The surface potential of B-CoAl-2 was measured using in-situ Kelvin probe force microscopy (KPFM) under both dark and visible light conditions. Figure 4 (a) It can be seen that a tight heterojunction is formed between BiOCl-OV and CoAl-LDH. Figure 4 (b) shows that, under dark conditions, there are two distinct phases and a potential difference can be observed on the surface of the heterojunction, with the magnitude of the potential pointing from CoAl-LDH(A) to BiOCl-OV(B). Figure 4 (c, d) shows that under illumination, photogenerated electrons are transferred from BiOCl-OV to CoAl-LDH, which confirms the Z-type carrier migration path of the B-CoAl-LDH heterojunction.

[0043] Example 9

[0044] Degradation experiments were conducted using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. Figure 5 The graph shows the performance of the prepared sample in degrading RhB. This involved the addition of 5 mg of catalyst and 5 mg of PMS to degrade 50 mL of RhB at a concentration of 20 mg / L. Figure 5 It is known that B-CoAl-2 has the highest degradation activity, and can achieve 100% degradation of RhB within 9 minutes.

[0045] Example 10

[0046] The capture experiment was conducted using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. Figure 6 The image shows the capture performance of the prepared B-CoAl-2. Tert-butanol (TBA), methanol (MeOH), L-tryptophan, sodium iodate, and sodium oxalate were selected to capture ·OH and ·SO4, respectively. - , 1 O2, e - h + And Co(IV) = O, as shown in the figure, Co(IV) is the most important active species.

[0047] Example 11

[0048] Degradation experiments on different pollutants were conducted using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. Figure 7 The graph shows the degradation performance of the prepared B-CoAl-2 on methylene blue (MB), rhodamine B (RhB), methyl orange (MO), tetracycline (TC), and phenol. The results show that B-CoAl-2 has high degradation performance on a variety of organic pollutants.

[0049] Example 12

[0050] The degradation of RhB by B-CoAl-2 was carried out using a Phchem photocatalytic reactor manufactured by Beijing Newbit Technology Co., Ltd. under different anion conditions. Figure 8 Showing Cl - NO3 - HCO3 - HPO4 - and SO4 - The effects on degradation experiments showed that B-CoAl-2 has good environmental resistance.

[0051] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. The application of an ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst in the degradation of organic pollutants, characterized in that, Under the synergistic effect of light and persulfate, organic pollutants in water are efficiently degraded by Co(IV)=O species. The specific steps of the preparation method of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction catalyst are as follows: (1) Weigh Bi(NO3)2·5H2O and polyvinylpyrrolidone and dissolve them in water, stir well, then add 1-butyl-3-methylimidazolium chloride to the above mixed solution and stir well; (2) The solution obtained in step (1) is transferred to a reaction vessel, subjected to hydrothermal treatment, washed and dried to obtain BiOCl nanosheets; (3) Disperse the BiOCl obtained in step (2) into a 1-methyl-2-pyrrolidone solution, sonicate, wash and dry to obtain ultrathin BiOCl nanosheets; (4) Irradiate the ultrathin BiOCl obtained in step (3) under a mercury lamp to obtain ultrathin BiOCl-OV nanosheets rich in oxygen vacancies; (5) Mix the Co(NO3)2·6H2O and Al(NO3)3·9H2O solutions thoroughly at a Co:Al molar ratio of 2:1; (6) The mixed solution from step (5) was added dropwise to a mixed solution of NaNO3 and formamide, heated, washed and dried to obtain ultrathin CoAl-LDH nanosheets; the pH was kept at 10 during the dropwise addition process; (7) Dissolve the BiOCl-OV obtained in step (4) and the CoAl-LDH obtained in step (6) in water respectively, sonicate them, then add the CoAl-LDH solution dropwise to the BiOCl-OV solution, heat it, wash and dry it to obtain the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction material.

2. The application as described in claim 1, characterized in that, The thickness of the ultrathin BiOCl-OV / CoAl-LDH Z-type heterojunction material prepared in step (7) is about 10 nm.

3. The application as described in claim 1, characterized in that, The unique Z-type carrier charge transfer pathway of the prepared ultrathin BiOCl-OV / CoAl-LDH accelerates the conversion of Co(III) to Co(II) and promotes the two-electron transfer of Co(II) to generate Co(IV)=O.

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