Plasmonic metal Bi / oxygen vacancy-biobr photocatalytic material and preparation method and application thereof

Abstract

This invention discloses a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, its preparation method, and its applications. The preparation method includes the following steps: dissolving a bromide salt in 1,2-propanediol to obtain a dispersion; adding a bismuth salt to the dispersion and mixing thoroughly to obtain a reaction solution; subjecting the reaction solution to a hydrothermal reaction; and cooling, separating, washing, and drying the resulting material to obtain the target product. This invention uses 1,2-propanediol as a solvent and a reducing agent, simultaneously introducing plasma metal Bi and oxygen vacancies into BiOBr through a hydrothermal reaction to enhance its catalytic performance. Furthermore, the addition of lignin to the reaction system further promotes the formation of plasma metal Bi and oxygen vacancies. The material prepared by this invention can be used for the oxidation-reduction of 2,4-dichlorophenol in water and for CO2 reduction, effectively remediating the environment and achieving energy conversion, showing great application potential.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis, and in particular relates to a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, its preparation method and application. Background Technology

[0002] Human activities and the use of fossil fuels have led to a dramatic increase in atmospheric carbon dioxide levels over the past few decades, resulting in global warming, glacial melting, rising sea levels, and the greenhouse effect. Finding feasible strategies to curb the rapid increase in carbon dioxide is of paramount importance. Photocatalytic reduction of CO2 to hydrocarbon fuels using water vapor has become a promising approach to alleviating global warming and energy shortages. Unfortunately, the high dissociation energy of the C=O bond (750 kJ mol⁻¹) poses a significant thermodynamic barrier to the activation and reduction of CO2. While many semiconductor materials have been proven suitable for the photoreduction of carbon dioxide, the development of semiconductors as potential photocatalysts remains inherently limited by light collection and utilization constraints. Therefore, it is necessary to develop new alternative materials or intelligent strategies to avoid the drawbacks of semiconductor photocatalysts. Furthermore, industrial development has caused significant damage to the aquatic environment. Chlorophenols (CPs) are a class of organic pollutants characterized by high toxicity, carcinogenicity, teratogenicity, and poor biodegradability. 2,4-Dichlorophenol (2,4-DCP) is widely present in industries such as pesticides, herbicides, dyes, pulp and paper making. Due to its high mutagenicity, carcinogenicity, and adverse effects on human health, many countries have listed it as a key pollutant. Therefore, it is necessary to develop an environmentally friendly method to simultaneously achieve the effective degradation of 2,4-dichlorophenol and CO2 reduction.

[0003] Photocatalysis, as a green and pollution-free advanced oxidation technology, utilizes solar energy to effectively degrade pollutants. Under visible light irradiation, the catalyst absorbs energy, and photogenerated electrons transition from the conduction band to the valence band, thereby producing highly oxidizing free radicals, such as hydroxyl (·OH) and superoxide (·O). 2- Free radicals and holes (h) + BiOBr can non-selectively oxidize organic pollutants without producing secondary pollution. It is unique in that it is composed of [Bi₂O₂]. 2+The layered structure formed by alternating plates and dibromo atom plates possesses numerous active sites and high carrier separation efficiency, making it widely used in photocatalysis. However, pure BiOBr exhibits weak visible light collection ability and a large band gap energy, resulting in less than ideal photocatalytic performance in practical applications. Generally, catalyst modification is employed to enhance its catalytic effect. Numerous studies have shown that the deposition of plasmonic metallic Bi and the generation of oxygen vacancies (OVs) play crucial roles in enhancing the catalytic performance of photocatalysts. Elemental Bi can improve catalytic performance by enhancing the absorption of visible light through the plasmonic effect and accelerating the separation efficiency of photogenerated carriers. OVs, on the other hand, can narrow the band gap by introducing defects at the conduction or valence band edges, thereby enhancing the enrichment of visible light. Furthermore, OVs can act as trapping sites, hindering the recombination of photogenerated carriers and enhancing the transfer of excited electrons to surface sites, thus generating more active oxygen groups. How to simultaneously introduce plasmonic metallic Bi and oxygen vacancies into BiOBr to improve its catalytic performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, its preparation method, and its application, so as to solve the problem of unsatisfactory catalytic performance of BiOBr in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first objective of this invention is to provide a method for preparing a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, comprising the following steps: dissolving a bromide salt in 1,2-propanediol to obtain a dispersion; adding a bismuth salt to the dispersion and mixing them evenly to obtain a reaction solution; transferring the reaction solution evenly to a reaction vessel and carrying out a hydrothermal reaction at a temperature of 120–200°C for 6–18 h; and cooling, separating, washing, and drying the resulting material to obtain the plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material.

[0007] As a preferred technical solution, lignin is further added to the dispersion, and the amount of lignin added is 1wt% to 10wt% of the mass of BiOBr. More preferably, the lignin is alkali lignin or lignin sulfonate.

[0008] As a preferred technical solution, the bromide salt is potassium bromide or sodium bromide; the bismuth salt is bismuth nitrate, bismuth sulfate or bismuth chloride; the atomic molar ratio of bismuth to bromine in the bismuth salt and the bromide salt is 1:1.

[0009] The second objective of this invention is to provide a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, which is prepared using the preparation method described in the first objective.

[0010] A third object of the present invention is to provide the application of the plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material as described in the second object. This photocatalytic material can be used for the catalytic degradation of pollutants in wastewater, including 2,4-dichlorophenol; the photocatalytic material can also be used for the reduction of carbon dioxide.

[0011] The present invention has the following beneficial effects:

[0012] This invention uses 1,2-propanediol as a solvent and reducesr. In the hydrothermal reaction, the hydroxyl groups of 1,2-propanediol induce the breaking of Bi-O bonds, thereby generating oxygen vacancies. This leads to the rearrangement of electrons within the crystal and simultaneously promotes the gain of electrons by trivalent Bi ions to form elemental Bi, which is then loaded onto the BiOBr surface. This achieves the simultaneous introduction of plasmonic metallic Bi and oxygen vacancies into BiOBr, resulting in a plasmonic metallic Bi / oxygen vacancy-BiOBr photocatalytic material. According to our research, the polarity of the solvent weakens the generation of oxygen vacancies during catalyst formation; therefore, the catalyst prepared using only 1,2-propanediol as a solvent has the highest oxygen vacancy concentration. Furthermore, a moderate increase in the number of hydroxyl groups and α-C atom branches is beneficial for oxygen vacancy generation, but an excessive increase significantly alters the properties of the alcohol, making it more viscous and increasing its boiling point. These factors are detrimental to the contact between precursors in the hydrothermal reaction and the generation of oxygen vacancies and elemental Bi. When an appropriate amount of lignin is added to the reaction system, due to the large number of functional groups in lignin, it can synergistically interact with 1,2-propanediol, further promoting the formation of homoionic metal Bi and oxygen vacancies in the catalyst. The BiOBr photocatalytic material prepared by this invention can efficiently oxidize and reduce 2,4-dichlorophenol in water and be used for CO2 reduction, effectively repairing the environment. The photocatalytic material preparation method provided by this invention is simple, can be recycled multiple times, and has good prospects for widespread application. Attached Figure Description

[0013] Figure 1 XRD patterns of the materials prepared in each embodiment and comparative example;

[0014] Figure 2 SEM images of BP0 and BPL7 photocatalysts at 120℃;

[0015] Figure 3 EPR diagrams of materials prepared in some of the embodiments and comparative examples;

[0016] Figure 4 XPS images of photocatalysts BP0, BP50, BPL7, BPL9, BPL7-120℃, BPL7-200℃, BPL7-6h, and BPL7-18h. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0018] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; the raw materials and reagents used in the following embodiments are all commercially available products.

[0019] Example 1

[0020] A method for preparing an alcohol-induced plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material includes the following steps:

[0021] 4 mmol KBr was added to 50 mL of 1,2-propanediol solvent and stirred until homogeneous to obtain a dispersion. Then, 4 mmol Bi(NO3)3·5H2O was dissolved in the dispersion, sonicated for 30 min, and then stirred vigorously for 30 min to obtain a reaction solution. The reaction solution was poured into a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene and placed in an oven at 160 °C for 12 h to carry out a hydrothermal reaction. After the reaction was completed, the obtained product was separated, washed, and dried to obtain an alcohol-rich induced plasma metal Bi / oxygen vacancy-BiOBr photocatalyst, labeled BP50.

[0022] Example 2

[0023] Compared with Example 1, the difference in Example 2 is that 1,2-propanediol is replaced with propanol, while all other conditions are the same as in Example 1, and the product prepared is labeled as BP.

[0024] Comparative Example 1

[0025] Compared with Example 1, the difference in Comparative Example 1 is that 1,2-propanediol was replaced with glycerol, and all other conditions were the same as in Example 1. The product prepared was labeled as BG.

[0026] Comparative Example 2

[0027] Compared with Example 1, the difference in Comparative Example 2 is that the 50 ml 1,2-propanediol solvent was replaced with a mixed solution of 1,2-propanediol and pure water, and the volume ratio of 1,2-propanediol to water was 1:4, 2:3, 3:2, and 4:1. All other conditions were the same as in Example 1, and the products obtained were labeled as BP10, BP20, BP30, and BP40, respectively.

[0028] Comparative Example 3

[0029] Compared with Example 1, the difference in Comparative Example 3 is that 50 ml of 1,2-propanediol was replaced with 50 ml of pure water, while all other conditions were the same as in Example 1. The product prepared was labeled as BPO.

[0030] Example 3

[0031] 4 mmol KBr and 0.0122 g alkali lignin were added to 50 mL of 1,2-propanediol and stirred until homogeneous to obtain a dispersion. Then, 4 mmol Bi(NO3)3·5H2O was added to the dispersion and mixed until homogeneous to obtain a reaction solution. The reaction solution was poured into a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene and heated in an oven at 160 °C for 12 h to complete the reaction. After the reaction was completed, the product was separated, washed, and dried sequentially. The separated product was labeled as BPL1.

[0032] Example 4

[0033] 4 mmol KBr and 0.0854 g alkali lignin were added to 50 mL of 1,2-propanediol and stirred until homogeneous to obtain a dispersion. Then, 4 mmol Bi(NO3)3·5H2O was added to the dispersion and mixed until homogeneous to obtain a reaction solution. The reaction solution was poured into a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene and heated in an oven at 120 °C for 12 h to complete the reaction. After the reaction was completed, the product was separated, washed, and dried. The separated product was labeled as BPL7-120 °C.

[0034] Example 5

[0035] Compared with Example 3, the difference in this example is that the amount of lignin added is 0.0366g, 0.061g, 0.0854g, and 0.1098g, respectively. All other conditions are the same as in Example 3, and the products obtained are labeled as BPL3, BPL5, BPL7, and BPL9 in sequence.

[0036] Example 6

[0037] Compared with Example 4, the difference in this example is that the reaction conditions are 200℃ and 12h, 160℃ and 6h, and 160℃ and 18h, respectively. All other conditions are the same as in Example 4. The products obtained are labeled as BPL7-200℃, BPL7-6h, and BPL7-18h, respectively.

[0038] Photocatalytic performance test

[0039] Degradation of 1,2,4-dichlorophenol

[0040] The pollutant degradation performance of the photocatalytic materials prepared in the above embodiments and comparative examples was tested as follows: 150 mg of catalyst was added to 200 ml of 2,4-dichlorophenol (10 mg / L) solution. The solution was stirred in the dark for 30 minutes to reach adsorption equilibrium. Then, it was irradiated with a 300 W Xe lamp (the light source outlet was equipped with a 420 nm cutoff filter). After 120 minutes, the degradation rate of 2,4-dichlorophenol was tested. The results are shown in Table 1 below.

[0041] Table 1. Degradation rates of 2,4-dichlorophenol solution by the photocatalysts prepared in each example and comparative example.

[0042] Photocatalytic materials 2,4-DCP degradation rate / % BP0 16.29 BP10 16.33 BP20 22.90 BP30 23.08 BP40 23.39 BP50 36.36 BP 31.21 BG 2.28 BPL1 48.52 BPL3 51.73 BPL5 53.69 BPL7 65.32 BPL9 55.70 BPL7-120℃ 61.33 BPL7-200℃ 22.12 BPL7-18h 59.02 BPL7-6h 61.03

[0043] Table 1 shows that BPL7 exhibits the best photocatalytic efficiency, but the reaction rate calculated from the experimental data indicates that BPL7 has the fastest reaction rate at -120℃. Due to its large specific surface area, BPL7 demonstrates a strong adsorption capacity for pollutants, thus showing the best degradation effect within the first 120 minutes of reaction time. With increasing degradation time, BPL7 at -120℃ continues to show the best degradation effect. In Comparative Example 1, the photocatalytic effect of the obtained catalyst was the worst when glycerol was used as the solvent. In Comparative Example 2, the addition of water to 1,2-propanediol also led to a decrease in the catalytic effect of the obtained product. This is because the difference in the ratio of alcohol to pure water and the number of alcohol hydroxyl groups resulted in the formation of different concentrations of plasma Bi and oxygen vacancies on the catalyst, thus affecting the photoelectric properties of the catalyst and producing different catalytic effects.

[0044] 2. CO2 reduction performance test

[0045] The CO2 reduction performance of the photocatalytic materials prepared in the above examples and comparative examples was tested as follows: The photocatalytic CO2 reduction reaction was carried out in a 200 mL sealed quartz round-bottom flask with water circulation at 5 °C. 40 mg of the catalyst material was dispersed in 20 mL of pure water and irradiated under a 300 W xenon lamp using a 420 nm cutoff filter (Beijing Perfectlight Technology Co., Ltd.). Before illumination, a degassing process was performed to remove impurities from the system, and then CO2 was bubbled into the system for 10 minutes to saturate it. The gaseous products were quantitatively analyzed using a gas chromatograph equipped with a flame ionization detector (FID). The results are shown in Table 2 below.

[0046] Table 2 shows the CO yield from CO2 reduction using the photocatalysts prepared in the examples and comparative examples.

[0047] Photocatalytic materials <![CDATA[CO production rate (μmol g -1 h -1 )]]> BP0 22.64 BP10 33.13 BP20 13.38 BP30 28.21 BP40 16.50 BP50 35.40 BPL1 26.03 BPL3 30.53 BPL5 45.17 BPL7 44.45 BPL9 37.44 BPL7-120℃ 62.94 BPL7-200℃ 11.61 BPL7-18h 36.52 BPL7-6h 74.25

[0048] As shown in Table 2, BPL7 exhibits the best CO2 reduction efficiency at 120℃, while BPL7 at 200℃ shows the worst. This is because differences in lignin content and hydrothermal reaction conditions lead to the formation of varying concentrations of plasma Bi and oxygen vacancies on the catalyst, thus affecting its photoelectric properties and resulting in different reduction effects. The excessively high reaction temperature at 200℃ damages the catalyst's morphology and structure, leading to very poor catalytic efficiency.

[0049] BPL7-120℃, which had undergone one catalytic experiment, was separated from its respective solution by centrifugation, washed, and dried. This process was repeated three times to treat 200 mL of 2,4-dichlorophenol (10 mg / L) solution and CO2 reduction. The results are shown in Table 3 below:

[0050] Table 3

[0051] Loop count 1st time 2nd time 3rd 2,4-DCP degradation rate / % 36.36 36.21 35.91 <![CDATA[CO production rate (μmol g -1 h -1 )]]> 62.94 62.69 62.53

[0052] Table 3 shows that the catalytic effect of the catalyst only decreased slightly after three repeated experiments. This indicates that the catalyst has good repeatability and stability.

[0053] Material characterization

[0054] To investigate the crystal phase structure of the products prepared in the above embodiments and comparative examples, we performed XRD characterization, and the results are as follows: Figure 1 As shown. The obtained plasma metal Bi / oxygen vacancy-BiOBr catalysts all matched the quadrilateral crystal JCPDF No. 85-0862, with no other impurity peaks, indicating that all samples were high-purity crystals. The typical diffraction peaks with 2θ values ​​at 31.7° and 32.3° corresponded to the (102) and (110) planes, respectively. Compared with the standard peaks, the peak intensity ratio of (102) and (110) changed, and the characteristic diffraction peaks of all catalysts were slightly weakened and broadened, indicating a gradual decrease in crystallinity. Except for BPO, BP, and BG samples, the characteristic peaks of Bi (JCPDF No. 85-01329) were detected in the other catalysts, indicating that the catalytic material prepared in this invention contains plasma Bi. No obvious characteristic peaks of Bi (JCPDF No. 85-01329) were observed in the BP and BG samples, possibly because the concentration of Bi was too low to be detected by XRD. Therefore, not all alcohols are suitable for the generation of plasma Bi.

[0055] Figure 2SEM images of catalysts BPO and BPL7-120℃ are shown. The images reveal that BPO exhibits a layered nanosheet structure, while BPL7-120℃ displays a nanofloral structure. The addition of 1,2-propanediol and lignin promotes the self-reorganization of the catalyst. The nanofloral structure endows the catalyst with a richer specific surface area, more active sites, and increased contact area between the catalyst and pollutant molecules.

[0056] like Figure 3 As shown, all samples exhibited a characteristic single Lorentz line centered at g = 2.003, caused by unpaired electrons trapped by oxygen vacancies. The number of oxygen vacancies was proportional to the relative intensity of the EPR signal peaks, with the relative intensities of the EPR peaks approximately BPL7 > BPL9 > BPL5 > BPL3 > BPL1 > BP50 > BP0 > BP40 > BP30 > BP20 > BP10, and BPL7-200℃ > BPL7-18h > BPL7 > BPL7-6h > BPL7-120℃. Before the addition of lignin, the catalyst prepared using only 1,2-propanediol as a solvent had the highest oxygen vacancy concentration, while the catalyst prepared using pure water as a solvent had a higher oxygen vacancy concentration than other catalysts. This is because 1,2-propanediol has a boiling point of 184.8℃, while water has a boiling point of 100℃. Under the hydrothermal conditions of this experiment, pure water vaporizes, which facilitates sufficient contact of the precursors, resulting in a more complete reaction and thus a higher oxygen vacancy concentration in the resulting catalyst. The addition of lignin significantly increased the oxygen vacancy concentration. Moderately increasing the hydrothermal temperature and time also facilitated the generation of oxygen vacancy. This indicates that a higher oxygen vacancy concentration is not necessarily more conducive to photocatalysis. Excessive oxygen vacancy can become the overlap center of the photogenerated carrier, which inhibits the separation of photogenerated electrons and holes, leading to a decrease in photocatalytic efficiency.

[0057] Figure 4 Table 4 shows the XPS spectra of Bi at BP0, BP50, BPL7, BPL9, BPL7-200℃, BPL7-18h, BPL7-6h, and BPL7-120℃. Table 4 also shows the fitting results of the Bi 4f XPS spectrum. The data in the table indicate that 1,2-propanediol and lignin are beneficial to the formation of plasmonic metal Bi. The synergistic effect of plasmonic metal Bi and oxygen vacancies promotes the separation of photogenerated carriers in the catalyst, thereby improving the photocatalytic efficiency.

[0058] Table 4. Fitting results of Bi 4f XPS spectra

[0059]

[0060] Note: R(%) represents the area ratio of Bi to the total area, and ζ represents the surface oxygen vacancy concentration.

[0061] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, characterized in that: Includes the following steps: Bromine salt was dissolved in 1,2-propanediol to obtain a dispersion. Bismuth salt was added to the dispersion and mixed evenly to obtain a reaction solution. After the reaction solution was mixed evenly, it was transferred to a reaction vessel for hydrothermal reaction. The material obtained from the reaction was cooled, separated, washed, and dried to obtain a plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material. The dispersion also contains lignin, and the amount of lignin added is 1wt% to 10wt% of the mass of BiOBr. The atomic molar ratio of bismuth to bromine in the bismuth and bromide salts is 1:

1. The hydrothermal reaction is carried out at a temperature of 120~160℃ for a duration of 6~18h.

2. The preparation method of the plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material according to claim 1, characterized in that: The lignin is alkali lignin or lignin sulfonate.

3. The method for preparing the plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material according to claim 1, characterized in that: The bromide salt is potassium bromide or sodium bromide.

4. The method for preparing the plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material according to claim 1, characterized in that: The bismuth salt is bismuth nitrate, bismuth sulfate, or bismuth chloride.

5. A plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material, characterized in that: It is prepared by the preparation method as described in any one of claims 1 to 4.

6. The plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material as described in claim 5 is used for the catalytic degradation of pollutants in wastewater, characterized in that: The pollutants in the wastewater include 2,4-dichlorophenol.

7. The plasma metal Bi / oxygen vacancy-BiOBr photocatalytic material as described in claim 5 is used for the reduction of carbon dioxide.

Images