An oxygen vacancy-rich BiOBr photocatalytic material and its preparation method and application

Abstract

The present invention discloses an oxygen vacancy-rich BiOBr photocatalytic material, a preparation method thereof, and an application thereof. The preparation method of the photocatalytic material comprises the following steps: mixing polyethylene glycol and water to obtain a mixed solvent; dissolving a bismuth salt, a bromide salt, and lignin in the mixed solvent to obtain a reaction solution; and transferring the reaction solution to a reactor after uniform mixing to carry out a hydrothermal reaction to prepare a target product. The present invention uses polyethylene glycol as a reducing agent and uses lignin in combination. Oxygen vacancies can be generated simultaneously on the crystal surface and inside the crystal through a hydrothermal reaction, and the prepared product has good stability. The photocatalytic material prepared by the present invention can efficiently and simultaneously oxidize and reduce rhodamine B and Cr(VI) in water, and can effectively repair the water environment. The catalyst preparation method of the present invention is simple, the reaction conditions are mild, and it can be recycled multiple times, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis, and in particular relates to an oxygen vacancy-rich BiOBr photocatalytic material and a preparation method and application thereof. Background Art

[0002] Today's industrial wastewater contains a large amount of toxic heavy metal ions and organic matter, which poses a serious threat to public health and has a significant impact on the sustainable development of the environment. Among them: hexavalent chromium (Cr(VI)) has the characteristics of non-biodegradability, carcinogenicity, teratogenicity, mutagenicity, and easy enrichment through the food chain. It has been listed as a Class I carcinogen by the International Agency for Research on Cancer (IARC); dye wastewater such as rhodamine B and methyl orange has caused serious damage to the ecological environment due to its large discharge volume, poor biodegradability, and difficulty in degradation. Metal ions and dyes generally coexist in wastewater, and removing metal ions and dyes from wastewater at the same time is of special significance for pollution control and remediation. As an environmentally friendly and sustainable advanced oxidation technology, photocatalysis has strong redox ability and good stability, and has made great contributions to sewage treatment. Under the irradiation of visible light, photocatalysts can produce highly reactive oxygen species (ROS), such as hydroxyl (·OH) and superoxide (·O 2- ) free radicals, which can non-selectively oxidize organic pollutants without causing secondary pollution.

[0003] BiOBr is uniquely composed of [Bi2O2] 2+ The layered structure formed by the alternation of plates and dibromine atom plates has many active sites and high carrier separation efficiency. However, pure BiOBr has a weak ability to collect visible light and a large band gap energy, and its photocatalytic effect is not ideal in practical applications; especially when the sewage contains multiple pollutants, due to the mutual influence of different pollutants during the degradation process, BiOBr is not ideal in the treatment of sewage containing multiple pollutants. A large number of studies have shown that oxygen vacancies (OVs) play an important role in regulating the optical and electronic properties of photocatalysts. OVs can narrow the band gap by introducing defects at the edge of the conduction band or valence band, thereby enhancing the enrichment ability of visible light. In addition, OVs can act as capture sites, hindering the recombination of photogenerated carriers and enhancing the transfer of excited electrons to surface sites, thereby generating more active oxygen groups. How to introduce oxygen vacancies in BiOBr to improve its catalytic performance is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] The purpose of the present invention is to provide an oxygen vacancy-rich BiOBr photocatalytic material and a preparation method and application thereof, so as to solve the problem of unsatisfactory catalytic performance of BiOBr in the prior art.

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

[0006] A first object of the present invention is to provide a method for preparing an oxygen-vacancy-rich BiOBr photocatalytic material, comprising the following steps: mixing polyethylene glycol and water to obtain a mixed solvent; dissolving a bismuth salt, a bromide salt, and lignin in the mixed solvent to obtain a reaction solution; mixing the reaction solution uniformly and then transferring it to a reactor for a hydrothermal reaction; and cooling, separating, washing, and drying the reaction material to obtain the oxygen-vacancy-rich BiOBr photocatalytic material.

[0007] As a preferred technical solution, the polyethylene glycol is polyethylene glycol 200 or polyethylene glycol 400. The alcoholic hydroxyl groups contained in the alcohol reagent play a reducing role in the reaction, making it reducible. The polyethylene glycol molecular chain contains ether bonds. In the reaction, the number of alcoholic hydroxyl groups and the length of the carbon chain will affect the concentration of oxygen vacancies.

[0008] As a preferred technical solution, the lignin is at least one of alkali lignin and lignin sulfonate. Lignin is one of the most abundant renewable aromatic polymers in nature, and the pulp and paper industry produces large quantities of lignin as a byproduct annually. Lignin has a rich variety of functional groups and can act as a surface modifier for catalysts, regulating their growth. It can also act as a reducing agent, promoting the generation of oxygen vacancies.

[0009] As a preferred technical solution, the volume ratio of the polyethylene glycol to water is (1-4):(4-1); more preferably 4:1.

[0010] As a preferred technical solution, the bismuth salt is bismuth nitrate, bismuth sulfate or bismuth chloride; the bromide salt is potassium bromide or sodium bromide; and in the bismuth salt and the bromide salt, the atomic molar ratio of bismuth to bromine elements is 1:1.

[0011] As a preferred technical solution, the hydrothermal reaction temperature is 120-160°C and the time is 12-18 hours; the hydrothermal reaction operation is simple and easy to implement industrial production; the hydrothermal time and temperature will affect the concentration of oxygen vacancies and must be controlled within an appropriate temperature and time range.

[0012] The second object of the present invention is to provide an oxygen vacancy-rich BiOBr photocatalytic material, which is prepared by the preparation method described in the first object.

[0013] The third object of the present invention is to provide the oxygen vacancy-rich BiOBr photocatalytic material as described in the second object for catalytic degradation of pollutants in wastewater. Preferably, the pollutants in the wastewater include rhodamine B and Cr(VI).

[0014] The present invention has the following beneficial effects:

[0015] The present invention uses polyethylene glycol of a specific molecular weight as a reducing agent and uses lignin in combination. During the hydrothermal reaction, the alcoholic hydroxyl groups in the polyethylene glycol are oxidized to generate aldehydes and carboxylic acids, while the Bi-O bonds are broken and reduced to generate oxygen vacancies, causing electrons to rearrange inside the crystal, thereby affecting the optical properties of the crystal. The hydrothermal method can simultaneously generate oxygen vacancies on the crystal surface and inside the crystal, and the prepared product has good stability. The oxygen vacancy-rich BiOBr photocatalytic material prepared by the present invention can efficiently and simultaneously oxidize and reduce rhodamine B and Cr(VI) in water, and can effectively repair the water environment. The catalyst preparation method of the present invention is simple, the reaction conditions are mild, and it can be recycled multiple times, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD patterns of oxygen vacancy-rich BiOBr photocatalytic materials prepared in various examples and comparative examples;

[0017] Figure 2 This is the SEM image of BPG200 prepared in Example 1;

[0018] Figure 3 The EPR graphs of the oxygen vacancy-rich BiOBr photocatalytic materials prepared in various examples and comparative examples are shown;

[0019] Figure 4 UV-vis graphs of oxygen vacancy-rich BiOBr photocatalytic materials prepared in various examples and comparative examples. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0021] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional means in the prior art in this field, and therefore, they are not described in detail; the raw materials and reagents used in the following embodiments are all commercially available products and can be purchased.

[0022] Example 1

[0023] A method for preparing an oxygen vacancy-rich BiOBr photocatalytic material comprises the following steps:

[0024] 10 ml of distilled water and 40 ml of polyethylene glycol 200 were mixed to obtain a mixed solvent, 4 mmol of KBr and 0.0244 g of lignin were added to the mixed solvent and stirred evenly to obtain a dispersion. 4 mmol of Bi(NO3)3·5H2O was then dissolved in the dispersion, first ultrasonicated for 30 minutes, and then vigorously stirred for 30 minutes to obtain a reaction solution. The reaction solution was poured into a 100 mL stainless steel hydrothermal autoclave lined with polytetrafluoroethylene, placed in an oven and heated at 160°C for 12 hours to carry out a hydrothermal reaction. After the reaction was completed, the obtained product was separated, washed, and dried in sequence to obtain an oxygen-vacancy-rich BiOBr photocatalyst, labeled as BPG200.

[0025] Example 2

[0026] Compared with Example 1, the difference in Example 4 is that polyethylene glycol 200 is replaced by polyethylene glycol 400, and other conditions are the same as those in Example 1. The prepared product is marked as BPG400.

[0027] Example 3

[0028] Compared with Example 1, the difference of Example 7 is that the reaction time is extended to 18 hours. Other conditions are the same as those of Example 1. The prepared product is marked as BPG200-18h.

[0029] Comparative Example 1

[0030] Compared with Example 1, the difference of Comparative Example 1 is that the mixed solvent does not contain water, that is, the mixed solvent is 100% polyethylene glycol 200, and other conditions are the same as those of Example 1. The prepared product is marked as D1.

[0031] Comparative Example 2

[0032] Compared with Example 1, the difference of Comparative Example 2 is that the mixed solvent does not contain polyethylene glycol 200, that is, the mixed solvent is 100% water, and other conditions are the same as those of Example 1. The prepared product is marked as D2.

[0033] Comparative Example 3

[0034] Compared with Example 1, the difference of Comparative Example 3 is that polyethylene glycol 200 is replaced by ethylene glycol, and other conditions are the same as those of Example 1. The prepared product is marked as BEG.

[0035] Photocatalytic performance test

[0036] The photocatalytic performance of the photocatalysts prepared in the above examples and comparative examples was tested as follows: 100 mg of the catalyst was added to 250 mL of a mixed solution of Rhodamine B (30 mg / L) and Cr(VI) (50 mg / L). The solution was adjusted to pH 3 and stirred in the dark for 30 minutes to achieve adsorption equilibrium. The solution was then irradiated with a 300 W Xe lamp (with a 420 nm cutoff filter at the light source outlet). After 60 minutes, the degradation rates of Rhodamine B and Cr(VI) were measured. The results are shown in Table 1 below.

[0037] Table 1 Degradation rate of the photocatalysts prepared in Examples and Comparative Examples for the mixed solution of Rhodamine B and Cr(VI)

[0038]

[0039] The data in Table 1 show that the photocatalyst prepared when the solvent contained polyethylene glycol 200 exhibited the best photocatalytic efficiency. The catalyst prepared in Comparative Example 3, which contained ethylene glycol in the solvent, exhibited the worst photocatalytic effect. This difference in alcohol content leads to the formation of varying concentrations of oxygen vacancies in the catalyst, which in turn affects the photoelectric properties of the catalyst and results in varying catalytic effects.

[0040] 100 mg of BPG200 was added to a 250 ml mixed solution of Rhodamine B (30 mg / L) and Cr(VI) (50 mg / L). The solution pH was adjusted and stirred in the dark for 30 minutes to reach adsorption equilibrium. The solution was then irradiated with a 300 W Xe lamp (with a 420 nm cutoff filter at the light source outlet). After 60 minutes, the degradation rates of Rhodamine B and Cr(VI) were measured. The degradation rates under different pH conditions are shown in Table 2 below.

[0041] Table 2 Degradation rate of BPG200 on mixed solution of Rhodamine B and Cr(VI)

[0042]

[0043]

[0044] From the data in Table 2, it can be seen that when the pH value is low, the BPG200 prepared by the present invention has a good photocatalytic degradation rate for both Rhodamine B and Cr(VI); as the pH value increases, the degradation rate of BPG200 for Rhodamine B and Cr(VI) decreases significantly, and the degradation rate of BPG200 for Rhodamine B is inhibited. In an acidic environment, Cr2O7 2- It mainly exists in the form of Cr(VI), which can accept electrons and be easily reduced to Cr(III). Under neutral and alkaline conditions, Cr2O7 2- Mainly HCrO 4- and CrO42- It exists in the form of Cr(OH)3, which easily generates precipitates and deposits on the catalyst surface, resulting in a large number of active sites being covered, thereby inhibiting the photocatalytic efficiency of the catalyst for RhB and Cr(VI).

[0045] BPG200, which had undergone a catalytic experiment, was centrifuged from a mixed solution of Rhodamine B and Cr(VI), washed and dried, and then used to treat a 250 mL mixed solution of Rhodamine B (30 mg / L) and Cr(VI) (50 mg / L) three times. The solution was irradiated with a 300W Xe lamp (a 420 nm cutoff filter was installed at the light source outlet). The degradation rates of Rhodamine B and Cr(VI) after 60 minutes are shown in Table 3 below:

[0046] Table 3 Degradation rate of Rhodamine B after BPG200 was reused three times

[0047]

[0048] Table 3 shows that the catalytic effect of the catalyst was only slightly reduced after three series of repeated experiments, indicating that the catalyst has good repeatability and stability.

[0049] Material characterization

[0050] In order to study the crystalline structure of the products prepared in the above examples and comparative examples, we performed XRD characterization on them, and the results are as follows Figure 1 As shown. The obtained catalyst alcohol-induced oxygen vacancy-BiOBr all matches the tetragonal crystal JCPDF No.85-0862, without other impurity peaks, indicating that all samples are high-purity crystals. The typical diffraction peaks at 2θ values ​​of 31.7° and 32.3° correspond to the (102) and (110) planes, respectively. Compared with the standard peak, the peak intensity ratio of (102) and (110) has changed, and the characteristic diffraction peaks of all catalysts have slightly weakened and broadened, and the crystallinity has gradually decreased. This may be because the formation of oxygen vacancies affects the growth of the (102) crystal plane.

[0051] Figure 2 This is a SEM image of BPG200 prepared in Example 1. The image shows that BPG200 has a nano-flower structure, ranging in size from 300 to 500 nm. This micro-flower structure gives the catalyst a rich surface area and more active sites, increasing the contact area between the catalyst and pollutant molecules.

[0052] like Figure 3As shown, all samples exhibit a characteristic single Lorentzian line centered at g = 2.003, caused by unpaired electrons trapped by oxygen vacancies. The number of oxygen vacancies is proportional to the relative intensity of the EPR signal peak, with the relative intensities of the EPR peaks ranking approximately BPG400 > BPG200 > BEG. BPG400 produces the highest concentration of oxygen vacancies, while the most effective BPG200 has a lower concentration than that produced by BPG400, indicating that a higher oxygen vacancy concentration does not necessarily improve photocatalysis. Excessive oxygen vacancies can act as centers for photogenerated carriers, inhibiting the separation of photogenerated electrons and holes and leading to reduced photocatalytic efficiency.

[0053] Figure 4 The UV-vis absorption curves of the photocatalytic materials prepared in Examples and Comparative Examples are shown in Figure 2. The catalyst with the strongest visible light absorption capacity is obtained using ethylene glycol 200 as the solvent, indicating that an appropriate oxygen vacancy concentration can improve the visible light absorption capacity of the catalyst.

[0054] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. An oxygen vacancy-rich BiOBr photocatalytic material for catalytic degradation of pollutants in wastewater, characterized by: The pollutants in the wastewater include rhodamine B and Cr(VI); The preparation of the oxygen vacancy-rich BiOBr photocatalytic material comprises the following steps: Polyethylene glycol and water are mixed to obtain a mixed solvent, bismuth salt, bromide salt, and lignin are dissolved in the mixed solvent to obtain a reaction solution, the reaction solution is mixed evenly and then transferred to a reactor for a hydrothermal reaction, and the reaction material is cooled, separated, washed, and dried to obtain an oxygen vacancy-rich BiOBr photocatalytic material; The polyethylene glycol is polyethylene glycol 200; The volume ratio of the polyethylene glycol to water is (1-4): (4-1); The temperature of the hydrothermal reaction is 120-160° C., and the time is 12-18 hours.

2. The oxygen vacancy-rich BiOBr photocatalytic material according to claim 1 is used for catalytic degradation of pollutants in wastewater, characterized in that: The bismuth salt is bismuth nitrate, bismuth sulfate or bismuth chloride.

3. The oxygen vacancy-rich BiOBr photocatalytic material according to claim 1 is used for catalytic degradation of pollutants in wastewater, characterized in that: The bromine salt is potassium bromide or sodium bromide.

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