A cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants and a preparation method thereof

Abstract

The application discloses a preparation method of a cobalt-doped bismuth oxychloride photocatalyst. Cobalt nitrate hexahydrate and bismuth nitrate pentahydrate are dissolved in water under magnetic stirring, and then dilute nitric acid and sodium chloride are added in sequence to obtain a precursor solution. The precursor solution is loaded into a polytetrafluoroethylene liner, and a hydrothermal reaction is carried out, and then natural cooling is carried out to room temperature. The cobalt-doped bismuth oxychloride photocatalyst can be obtained by washing and drying with water and ethanol. The raw material used in the application has low cost, the method is mature and stable, and no harmful organic solvent is used in the reaction, so that the application is a high-efficiency and green synthesis method. The cobalt-doped bismuth oxychloride photocatalyst synthesized in the application changes the energy band structure of bismuth oxychloride, the absorption capacity of sunlight spectrum is improved through the introduction of cobalt-doped energy level, and then the photocatalytic degradation capacity of organic pollutants is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants and a preparation method thereof, and belongs to the technical field of photocatalytic materials. BACKGROUND

[0002] With the advancement of industrialization, the solution of environmental and energy problems has become urgent. Photocatalytic technology, with the help of inexhaustible solar energy, generates electrons and holes on the conduction band and valence band of semiconductors, respectively, and has made a lot of achievements in treating water pollution, hydrogen production by water photolysis, etc.

[0003] Among many photocatalysts, bismuth oxychloride (BiOCl) based photocatalytic materials have attracted the attention of researchers due to their special layered structure and non-toxicity, wide source, etc. Among them, Bi and O atoms form [Bi2O2] 2+ layer, and Cl atoms form [Cl] 2- layer, and the layered structure formed by the interlacing of the two layers has a large number of active sites. However, as a semiconductor material with a band gap as high as 3.2 eV, bismuth oxychloride can only absorb 4% of the ultraviolet light of solar energy, limiting its large-scale application.

[0004] Morphology control, crystal face regulation, composite heterojunction and element doping are common means to modify photocatalytic materials, among which element doping often forms a new energy level between the conduction band and the valence band, so that the photocatalytic material can absorb light with a larger wavelength. Among the commonly used doped elements, transition metals have greater application prospects due to their uncompleted d orbit. Patent CN106563472A discloses a composite material in which gold nanoparticles are loaded on bismuth oxychloride nanosheets or micrometer flowers for degrading organic pollutants under visible light irradiation. The preparation method in this patent uses laser irradiation of a gold target, which is complex. Patent CN112958120A discloses a silver-loaded bismuth oxychloride nanomaterial for degrading gaseous pollutants such as NOx. The above patents all use noble metal doping, which is expensive. Variable valence elements such as iron, cobalt and nickel can further separate photo-generated electron-hole pairs by changing their valence states, thereby improving the photocatalytic performance. For example, patent CN109550510A discloses a tantalum-doped bismuth oxychloride prepared by dissolving bismuth nitrate pentahydrate and tantalum chloride in organic solvents, respectively, and then mixing the two solutions for hydrothermal reaction, for degrading organic pollutants.

[0005] The conventional synthesis method of bismuth oxychloride often needs to use organic solvents, which have certain toxicity and can pollute the environment, such as ethylene glycol (Applied Surface Science 543 (2021) 148798), glycerol (Environmental Research 216 (2023) 114808), isopropyl alcohol (Applied Surface Science 465 (2019) 1019-1027) and the like. Therefore, developing a synthesis method without organic solvents to dope the variable element into bismuth oxychloride and improve its absorption of sunlight is one of the focuses of widening the application scenarios of bismuth oxychloride photocatalysts. SUMMARY

[0006] The application provides a preparation method of a cobalt-doped bismuth oxychloride photocatalyst, which widens the absorption spectrum of bismuth oxychloride to the visible light region and improves the photocatalytic activity of the material through the doping of cobalt elements.

[0007] The technical scheme adopted by the application is a preparation method of a cobalt-doped bismuth oxychloride photocatalyst, comprising the following steps:

[0008] Step 1: A certain amount of cobalt nitrate hexahydrate and bismuth nitrate pentahydrate are dissolved in water under magnetic stirring, and then dilute nitric acid and a certain amount of sodium chloride are added in sequence to obtain a precursor solution;

[0009] Step 2: The precursor solution is loaded into a polytetrafluoroethylene liner, and a hydrothermal reaction is carried out at a certain temperature for a certain time, and then the solution is naturally cooled to room temperature;

[0010] Step 3: The solution is washed and dried with water and ethanol to obtain the cobalt-doped bismuth oxychloride photocatalyst.

[0011] In step 1, the molar ratio of cobalt nitrate hexahydrate, bismuth nitrate pentahydrate and sodium chloride is 0.02-0.2:1:4. Preferably, the molar ratio of cobalt nitrate hexahydrate, bismuth nitrate pentahydrate and sodium chloride is 0.05-0.1:1:4.

[0012] The molar concentration of dilute nitric acid is 1 mol / L, and the volume ratio of dilute nitric acid to water is 1:14.

[0013] Preferably, the magnetic stirring rate in step 1 is 300-600 r / min, and the stirring time is 10-30 min.

[0014] Preferably, the hydrothermal reaction temperature in step 2 is 150-180℃, and the reaction time is 8-16 h.

[0015] Preferably, the washing solvent in step 3 is a mixed solvent of water and ethanol in a volume ratio of 1:1, and the washing is performed 3-6 times.

[0016] Preferably, the drying temperature in step 3 is 50-70℃, and the drying time is 12-24h.

[0017] The beneficial effects of the present application are as follows:

[0018] 1. The raw materials used in the present application are all common and inexpensive materials, the method used is a mature hydrothermal synthesis method, and no organic solvent that may cause continuous harm to the environment and human body is used in the reaction, which is a highly efficient and green synthesis method.

[0019] 2. In the present application, dilute nitric acid is used instead of organic solvent to provide hydrogen ions and promote the doping of Co elements, thereby further improving the catalytic activity of Co-BiOCl.

[0020] 3. The cobalt-doped bismuth oxychloride photocatalyst synthesized in the present application changes the energy band structure of bismuth oxychloride, and through the introduction of cobalt-doped energy levels, the solar spectrum absorption capacity is improved, thereby greatly improving the photocatalytic degradation of organic pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 XRD patterns of Co-BiOCl prepared in Examples 1-4 of the present application and BiOCl prepared in Comparative Example 1; wherein (a) is the XRD pattern at 10-80°, and (b-d) are enlarged views of (a) at different angles.

[0022] Figure 2 Scanning electron microscope photograph of 10% Co-BiOCl synthesized in Example 3 of the present application.

[0023] Figure 3 UV-visible absorption spectrum of Co-BiOCl prepared in Examples 1-4 of the present application and BiOCl prepared in Comparative Example 1.

[0024] Figure 4 Comparison chart of photocatalytic performance of Co-BiOCl prepared in Examples 1-4 of the present application and BiOCl prepared in Comparative Example 1, wherein (a) is the degradation percentage, and (b) is the kinetic curve.

[0025] Figure 5 Comparison chart of photocatalytic performance of 10% Co-BiOCl prepared in Example 3 of the present application and 10% Co-BiOCl prepared in Comparative Example 2.

[0026] Figure 6 Energy band structure diagram of BiOCl and Co-BiOCl. DETAILED DESCRIPTION

[0027] For a further understanding of the present application, the application will be described in greater detail below with reference to the embodiments. These embodiments are described by way of example only and merely to further explain the features and advantages of the present application, and are not used to limit the scope of the claims of the present application. Example 1

[0028] (1) 0.1 mmol of cobalt nitrate hexahydrate and 5 mmol of bismuth nitrate pentahydrate were dissolved in 70 mL of water under magnetic stirring at 300 r / min, and then 5 mL of dilute nitric acid (1 mol / L) and 20 mmol of sodium chloride were sequentially added, and stirred for 10 min to obtain a precursor solution;

[0029] (2) The precursor solution was loaded into a 100 mL polytetrafluoroethylene liner, and a hydrothermal reaction was carried out at 160°C for 12 h, and then naturally cooled to room temperature;

[0030] (3) The sample was washed 3 times with a mixed solvent of water and ethanol in a volume ratio of 1:1, and dried at 60°C for 24 h, and the obtained sample was recorded as 2% Co-BiOCl. Example 2

[0031] In this embodiment, the amount of cobalt nitrate hexahydrate was 0.25 mmol, and the other steps were the same as in Example 1, and the obtained sample was recorded as 5% Co-BiOCl. Example 3

[0032] In this embodiment, the amount of cobalt nitrate hexahydrate was 0.5 mmol, and the other steps were the same as in Example 1, and the obtained sample was recorded as 10% Co-BiOCl. Example 4

[0033] In this embodiment, the amount of cobalt nitrate hexahydrate was 1 mmol, and the other steps were the same as in Example 1, and the obtained sample was recorded as 20% Co-BiOCl. Comparative Example 1

[0034] In this comparative example, no cobalt nitrate hexahydrate was added, and the other steps were the same as in Example 1, and the obtained sample was recorded as BiOCl. Comparative Example 2

[0035] In this comparative example, no dilute nitric acid was added, and the other steps were the same as in Example 3, and the obtained sample was recorded as 10% Co-BiOCl-N.

[0036] Figure 1 The XRD patterns of different embodiments of the present application are shown in Figure 1 As can be seen from (a), all the samples have good crystallinity, and are all bismuth oxychloride tetragonal structure (JCPDS: 73-2060), and the cobalt-doped samples do not have characteristic peaks of other crystal phases, indicating that cobalt enters bismuth oxychloride in the form of doping, rather than forming a new substance. Figure 1(b-d) all show that the doping of cobalt makes the position of the XRD peak shift to high angle, which is due to the smaller cobalt ions entering the bismuth lattice, causing lattice distortion, further proving the successful synthesis of cobalt-doped bismuth oxychloride of the examples.

[0037] Figure 2 The scanning electron microscope photo of 10% Co-BiOCl synthesized in Example 3 of the present application. The photo shows that Example 3 is a nanosheet structure with a diameter of 400-800 nm and a thickness of about 100 nm.

[0038] Figure 3 The ultraviolet-visible absorption spectrum of Examples 1-4 and Comparative Example 1 of the present application. It can be found that the pure BiOCl synthesized in Comparative Example 1 only has absorption in the ultraviolet region, while Examples 1-4 all have obvious absorption enhancement in the visible region.

[0039] The photocatalytic degradation of organic pollutants was evaluated by photocatalytic degradation of methyl orange solution, and the specific operation was as follows: 10 mg of photocatalyst was ultrasonically dispersed into 50 mL of methyl orange solution, a 300 W full-spectrum xenon lamp was used to simulate sunlight, and the light irradiation reaction was carried out for 60 min. Figure 4 The photocatalytic performance comparison chart of Examples 1-4 and Comparative Example 1 of the present application. It can be seen that the doping of cobalt significantly improves the photocatalytic performance. Figure (a) is the degradation percentage, and Comparative Example 1 pure BiOCl only degrades 39.1% of methyl orange in 60 min, and the degradation rates of 5%-20% Co-BiOCl in the same time are 52.5%, 69.2%, 77.7%, and 65.1%, respectively, and it can be seen that the performance of 10% Co-BiOCl is the best. As measured by the kinetic curve in Figure (b), the reaction rate constant of Example 3 is 3.02 times that of Comparative Example 1.

[0040] Figure 5 The photocatalytic performance comparison chart of Example 3 and Comparative Example 2 of the present application. The degradation rate of the sample added with dilute nitric acid in Example 3 reaches 77.7%, while the degradation rate of the sample without dilute nitric acid in Comparative Example 2 is only 43.7%, close to the performance of pure BiOCl. The doping of variable valence elements often requires the participation of organic solvents such as ethylene glycol (see Background Art). In the present application, the role of dilute nitric acid is to replace the organic solvent, to provide hydrogen ions, to promote the doping of Co element, and to further improve the catalytic activity of 10% Co-BiOCl.

[0041] Figure 6 The band structure diagram of BiOCl and Co-BiOCl. It can be seen that the doping of cobalt maintains the original energy structure on the conduction band of BiOCl, while introducing new doping energy levels between the conduction bands, providing better conditions for electron transition, which is beneficial to broaden the absorption spectrum.

[0042] The above examples and comparative examples are only the preferred embodiments of the present application, and are not intended to limit the scope of the present application. Any improvement and substitution based on the technical solution of the present application without creative labor by those skilled in the art falls within the protection scope of the present application.

Claims

1. A method for the preparation of a cobalt-doped bismuth oxychloride photocatalyst for the degradation of organic pollutants, characterized by, The cobalt-doped bismuth oxychloride photocatalyst is composed of cobalt nanoparticles and bismuth oxychloride nanosheets, and has a nanosheet structure with a diameter of 400-800 nm and a thickness of 50-100 nm; the molar percentage of cobalt element to bismuth ion in the cobalt-doped bismuth oxychloride photocatalyst is 5%-20%; the preparation method comprises the following specific steps: dissolving cobalt nitrate hexahydrate and bismuth nitrate pentahydrate in water, adding dilute nitric acid and sodium chloride in sequence to obtain a precursor solution; hydrothermally reacting the precursor solution at 150-180 DEG C for 8-16 h, naturally cooling, washing, and drying to obtain the cobalt-doped bismuth oxychloride photocatalyst.

2. The method for preparing the cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The molar ratio of cobalt nitrate hexahydrate, bismuth nitrate pentahydrate and sodium chloride is 0.02-0.2:1:

4.

3. The method for preparing the cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The cobalt nitrate hexahydrate and bismuth nitrate pentahydrate are dissolved in water, and stirred at a magnetic stirring speed of 300-600 r / min for 10-30 min.

4. The method for preparing the cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The concentration of the dilute nitric acid is 1 mol / L; the volume ratio of the dilute nitric acid to water is 1:

14.

5. The method for preparing the cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The washing solvent is a mixed solvent of water and ethanol with a volume ratio of 1:1, and the washing is performed for 3-6 times.

6. The method for preparing the cobalt-doped bismuth oxychloride photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The drying temperature is 50-70 DEG C, and the drying time is 12-24 h.

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