Agcl / biocla@diatomite s-type heterostructure and application thereof in photocatalytic degradation

Abstract

The application discloses a preparation method of an AgCl / BiOCl@diatomite S-type heterostructure, which is prepared by a two-step method, BiOCl nanosheets are loaded on diatomite through simple electrostatic self-assembly, and then AgCl is in-situ deposited through a photochemical method, diatomite can increase the specific surface area of the composite material and enhance the recyclability, an S-type heterostructure can be formed between AgCl and BiOCl, the S-type heterostructure can retain the highest redox potential of photogenerated carriers in the composite material, and has high carrier separation capacity, compared with pure BiOCl, the degradation capacity of the AgCl / BiOCl@diatomite S-type heterostructure on rhodamine b, tetracycline, norfloxacin and levofloxacin is greatly improved.

Description

TECHNICAL FIELD

[0001] The application relates to an AgCl / BiOCl@diatomite S-type heterostructure and application thereof in photocatalytic degradation, and belongs to the technical field of photocatalytic materials. BACKGROUND

[0002] The serious influence of wastewater of azo dyes and pharmaceutically active compounds on the ecosystem and the potential threat to human health have attracted global attention in recent decades. Since the mid-1990s, antibiotic-containing organic pharmaceutical wastewater has become one of the focuses of people. Among them, fluoroquinolone antibiotics containing quinolone core structures such as norfloxacin, levofloxacin and ciprofloxacin have been widely used in livestock husbandry, health care industry and aquaculture to treat infectious diseases. Therefore, a large amount of wastewater containing fluoroquinolone antibiotics and residual molecules is released into the environment, resulting in a series of unknown environmental effects and serious environmental pollution; carbamazepine (CBZ) is a stable structure and difficult-to-biodegrade substance widely studied in emerging pollutants, which exists for a long time in the wild. In addition, the presence of CBZ in water bodies poses a major threat to human health and other natural organisms. However, traditional wastewater treatment technologies are difficult to remove CBZ. Based on this, it is urgent to solve the drugs and organic pollutants in wastewater, and many methods including biological treatment, physical adsorption, chemical adsorption, Fenton-like oxidation and other methods have been applied, but there are still some problems to be solved. Therefore, it is of great significance to develop an efficient and safe technology for removing organic pollutants in wastewater.

[0003] Photocatalytic oxidation technology has attracted widespread attention due to its efficient degradation of organic pollutants, and therefore many types of photocatalysts have been reported. Recently, bismuth-based catalysts such as BiVO4 (BVO), Bi2WO6 and BiOCl have received increasing attention. Among them, BiOCl with a layered structure exhibits unique photocatalytic activity and stability. However, due to the small specific surface area of monomer BiOCl, easy agglomeration, low recovery rate, wide band gap of energy band, and high probability of electron and hole recombination, it can only respond to ultraviolet light, which seriously limits its application in real life. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of existing photocatalytic materials in degrading organic pollutants, and to provide an AgCl / BiOCl@diatomite S-type heterostructure and application thereof in photocatalytic degradation.

[0005] The AgCl / BiOCl@diatomite S-type heterostructure described in this invention includes silver chloride-modified BiOCl molar superlattice nanosheets supported on alkali-treated diatomite. Using the molar superlattice material BiOCl nanosheets as the AgCl support, it exhibits high exposure of the (001) crystal plane. According to the crystal structure of BiOCl, the terminal chlorine on the (001) plane has the highest exposure, allowing Ag ions to anchor to the terminal chlorine. Furthermore, the Bi-Cl bonds in the BiOCl nanosheet structure can briefly break under visible light, forming a metastable state, thereby promoting the formation of silver chloride. This results in a closer contact than with an additional chlorine source. Further characterization demonstrates its unique S-type heterojunction mechanism, effectively enhancing catalytic performance.

[0006] In embodiments of the present invention, the preparation of the AgCl / BiOCl@diatomite S-type heterostructure is achieved through the following steps:

[0007] (1) BiOCl nanosheets and alkali-treated diatomaceous earth were dispersed in deionized water respectively;

[0008] (2) The diatomaceous earth suspension was slowly added to the BiOCl nanosheet suspension, stirred for 12 hours, and centrifuged and dried to obtain the BiOCl@diatomaceous earth composite material; wherein, the mass of alkali-treated diatomaceous earth accounted for (5~30) / 100 of the total mass of BiOCl nanosheets and alkali-treated diatomaceous earth.

[0009] (3) Disperse the BiOCl@diatomite composite material in water, add silver nitrate, stir evenly, and irradiate under visible light for 40 minutes; the mass ratio of BiOCl@diatomite composite material to silver nitrate is 20: (1~16.9).

[0010] (4) After centrifugation and washing, the mixture was dried in a vacuum drying oven at 60°C to obtain an AgCl / BiOCl@diatomite S-type heterostructure.

[0011] Furthermore, the BiOCl nanosheets of the moiré superlattice were obtained using the following steps:

[0012] (1.1.1) Disperse 9.6 ml of 20 wt% PDDA (400000-500000) aqueous solution in 160 ml of ethylene glycol, add 0.19404 g of Bi(NO3)3•5H2O, and stir magnetically for 30 min;

[0013] (1.1.2) Place the above mixed solution in a 200°C oil bath and heat under reflux for 2 hours;

[0014] (1.1.3) After the above solution has cooled to room temperature, it is centrifuged using a high-speed centrifuge, washed three times with deionized water, and placed in a vacuum drying oven at 60°C for 12 hours to obtain BiOCl nanosheets.

[0015] Furthermore, the alkali-treated diatomaceous earth is obtained through the following steps:

[0016] (1.2.1) Mix natural diatomaceous earth with a 5% NaOH solution at a liquid-to-solid mass ratio of 3:1;

[0017] (1.2.2) Heat oil in a 95°C bath, stir and maintain for 90 minutes.

[0018] (1.2.3) After cooling to room temperature, rinse with a large amount of distilled water until neutral, and then vacuum dry at 60°C for 6 hours to obtain alkali-treated diatomaceous earth.

[0019] Preferably, the mass of alkali-treated diatomite accounts for 10% of the total mass of BiOCl nanosheets and alkali-treated diatomite.

[0020] Preferably, the mass ratio of BiOCl@diatomite composite material to silver nitrate is 20:4.5.

[0021] This invention also relates to the application of the aforementioned AgCl / BiOCl@diatomite S-type heterostructure in the photocatalytic degradation of azo dyes and pharmaceutically active compounds. The dyes include, but are not limited to, rhodamine B, and the pharmaceutically active compounds include, but are not limited to, tetracycline, levofloxacin, carbamazepine, and norfloxacin.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) Unlike the previous method of adding chlorine source, we used the end chlorine plate on the structure of BiOCl molar superlattice nanosheet as chlorine source to prepare AgCl in situ. A close contact was formed between AgCl and BiOCl, forming an S-type heterostructure, which has a unique charge transfer mechanism, high carrier separation ability and high redox ability, significantly improving the effective removal of various organic pollutants.

[0024] (2) This invention creatively utilizes the properties of BiOCl molar superlattice nanosheets to construct a closely contacted AgCl / BiOCl S-type heterostructure. The method is simple and easy to operate. Attached Figure Description

[0025] Figure 1The figures show the morphology and structure of BiOCl nanosheets, alkali-treated diatomaceous earth, BiOCl@diatomaceous earth composite material (J-10), and AgCl / BiOCl@diatomaceous earth S-type heterostructure (J-10-2), respectively. Figure a shows the X-ray diffraction analysis of the initial material and the composite material. Figures b, c, and d are scanning electron microscope images of alkali-treated diatomaceous earth, BiOCl nanosheets, and the preferred AgCl / BiOCl@diatomaceous earth S-type heterostructure (J-10-2), respectively. Figure e is a TEM image of the BiOCl nanosheets, which shows that it has a moiré superlattice structure.

[0026] Figure 2 It is a zeta potential diagram of natural diatomaceous earth, alkali-treated diatomaceous earth, and BiOCl nanosheets, used to characterize surface electrical properties.

[0027] Figure 3 The graphs show nitrogen adsorption-desorption curves and corresponding pore size distribution data for raw diatomaceous earth, alkali-treated diatomaceous earth, BiOCl nanosheets, and BiOCl@diatomaceous earth composite material (J-10).

[0028] Figure 4 The UV-Vis diffuse reflectance spectra of BiOCl nanosheets, BiOCl@diatomite composite materials, and AgCl / BiOCl@diatomite S-type heterostructure (J-10-2).

[0029] Figure 5 a and b are the electrochemical impedance spectroscopy and photocurrent measurements of BiOCl and AgCl / BiOCl@diatomite S-type heterostructures (J-10-2), respectively.

[0030] Figure 6 a and b are the valence band spectra of AgCl and BiOCl, respectively, used to determine their band structures.

[0031] Figure 7 These are the X-ray photoelectron spectra of BiOCl and the in-situ X-ray photoelectron spectra of the AgCl / BiOCl@diatomite S-type heterostructure (J-10-2). Where 'a' represents pure BiOCl, the AgCl / BiOCl@diatomite S-type heterostructure (J-10-2) in darkness, and the AgCl / BiOCl@diatomite S-type heterostructure (J-10-2) under illumination. 4f Spectrum, b is the corresponding O 1S Spectrum, c represents the corresponding Cl 2p Spectrum, d represents AgCl / BiOCl@diatomite S-type heterostructure (J-10-2) under dark and light conditions. 3d Spectrum.

[0032] Figure 8 These are the ultraviolet photoelectron spectra of BiOCl and AgCl.

[0033] Figure 9 Figures a, b, c, d, e, f, and g show the catalytic properties and stability of BiOCl nanosheets, BiOCl@diatomaceous earth, and AgCl / BiOCl@diatomaceous earth S-type heterostructures. Figure a shows the degradation effect of Rhodamine b by BiOCl composites with different proportions of diatomaceous earth; Figure b shows the degradation effect of Rhodamine b by the AgCl / BiOCl@diatomaceous earth S-type heterostructure; Figures c, d, e, and f show the catalytic effects of BiOCl nanosheets, BiOCl@diatomaceous earth, and AgCl / BiOCl@diatomaceous earth S-type heterostructures on tetracycline, levofloxacin, carbamazepine, and norfloxacin, respectively; and Figure g shows the cyclic stability test results for the degradation of Rhodamine b. Detailed Implementation

[0034] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0035] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0036] In the following examples, the photocatalytic testing method is as follows: Rhodamine B solution (10 mg / L), carbamazepine solution (20 mg / L), norfloxacin (10 mg / L), tetracycline (10 mg / L), and levofloxacin (15 mg / L) were used as target degradation products. 50 mL of each solution was placed in a glass reactor. The outer layer of the container was kept at a constant temperature using condensate water. A 300W xenon lamp (filter > 400 nm) with visible light was used as the light source. 15 mg of the sample was added to each. The reactor was dark-treated for 30 min to reach adsorption-desorption equilibrium. Samples were taken at 20, 40, 60, 80, and 100 minutes. The samples were centrifuged at 10000 r / min for 10 min. The supernatant was collected, and the change in pollutant concentration (C / CO) was plotted using a UV-8500 ultraviolet-visible spectrophotometer (UV-Vis). Example 1

[0037] This embodiment prepares the AgCl / BiOCl@diatomite S-type heterostructure, specifically including the following steps:

[0038] 1. Preparation of alkali-treated diatomaceous earth

[0039] (1.1) Pour 1g of natural diatomaceous earth into a 250ml double-necked flask, then weigh 3g of 5% NaOH solution using a balance, and add it dropwise into the double-necked flask using a dropper. Mix the mixture in an oil bath at 95℃, stirring and maintaining the temperature for 90 minutes.

[0040] (1.2) After cooling to room temperature, rinse with a large amount of distilled water until neutral, and then vacuum dry at 60°C for 6 hours to obtain alkali-treated diatomaceous earth.

[0041] 2. Preparation of BiOCl nanosheets, specifically:

[0042] (2.1) Measure 160 ml of ethylene glycol solution using a 100 ml graduated cylinder, then pour it into a 250 ml double-necked flask and stir. Use a pipette to take 9.6 ml of a 20 wt% aqueous solution of PDDA (molecular weight 400,000-500,000) and add it dropwise into the double-necked flask. Continue stirring vigorously, then add Bi(NO3)3•5H2O and stir magnetically for 30 min.

[0043] (2.2) Transfer the above mixed solution to an oil bath at 200°C and heat under reflux for 2 hours.

[0044] (2.3) After the above mixed solution has cooled to room temperature, centrifuge, wash and dry. Centrifuge for 15 min with a high-speed centrifuge, wash 3 times with deionized water, and dry in a vacuum drying oven at 60°C for 4 h.

[0045] 3. Preparation of BiOCl nanosheets loaded on alkali-treated diatomaceous earth

[0046] (3.1) Take 1.2, 2.4, 4.8, 7.2 and 9.6 mg of alkali-treated diatomaceous earth and sonicate for one hour and disperse in 30 ml of deionized water. Then take 22.8, 21.6, 19.2, 16.8 and 14.4 mg of BiOCl nanosheets and sonicate for 10 minutes and disperse in 20 ml of deionized water.

[0047] (3.2) At room temperature and with a stirring speed of 450 rpm, the BiOCl nanosheet solution was slowly added dropwise to the alkali-treated diatomaceous earth solution. The mixture was stirred for 12 h. The resulting catalysts were labeled as J-5 (1.2 mg alkali-treated diatomaceous earth + 22.8 mg BiOCl nanosheets), J-10 (2.4 mg alkali-treated diatomaceous earth + 21.6 mg BiOCl nanosheets), J-20 (4.8 mg alkali-treated diatomaceous earth + 19.2 mg BiOCl nanosheets), J-30 (7.2 mg alkali-treated diatomaceous earth + 16.8 mg BiOCl nanosheets), and J-40 (9.6 mg alkali-treated diatomaceous earth + 14.4 mg BiOCl nanosheets).

[0048] (3.3) Centrifuge the final solution, wash and dry it. Centrifuge for 5 minutes with a high-speed centrifuge, wash once with deionized water, and dry in a vacuum drying oven at 60°C for 4 hours.

[0049] Figure 9In our initial exploration of the optimal ratio for BiOCl@diatomite composite materials, we first conducted a photodegradation experiment on diatomite treated with soda ash. We found that the alkali-treated diatomite primarily exhibited physical adsorption with no significant photodegradation performance, and that adsorption-desorption equilibrium was reached within 30 minutes. Secondly, we conducted a 100-minute photodegradation test using different diatomite input ratios. The degradation efficiency in the first 60 minutes showed a trend of first increasing and then decreasing with the amount of alkali-treated diatomite added. J-10 showed the highest degradation efficiency. This is mainly because adding a suitable ratio of diatomite to BiOCl nanosheets increases their specific surface area. However, diatomite itself has almost no degradation performance, and excessive diatomite hinders the light absorption of BiOCl nanosheets, thus reducing the degradation efficiency of the composite material.

[0050] 4. Preparation of AgCl / BiOCl@diatomite S-type heterostructure

[0051] (4.1) Disperse 20mg BiOCl@diatomite composite material J-10 in 50ml of water by ultrasonication for ten minutes.

[0052] (4.2) Add 1 mg, 4.5 mg and 16.9 mg of silver nitrate to the above solution, stir for ten minutes, and irradiate for 40 minutes under a 300 W xenon lamp (wavelength greater than 400 nm). Label them as J-10-1, J-10-2 and J-10-3 respectively.

[0053] (4.3) Centrifuge the final solution, wash and dry it. Centrifuge for 5 minutes with a high-speed centrifuge, wash 3 times with deionized water, and dry in a vacuum drying oven at 60°C for 4 hours.

[0054] The test results for the AgCl / BiOCl@diatomite S-type heterostructure are as follows: Figure 9 As shown in b, when the initial silver nitrate dosage is 4.5 mg (J-10-2), after continuous irradiation for 30 min, the degradation rate of Rhodamine b reaches as high as 98% (and it also has a significant catalytic effect on several other pollutants, namely...). Figure 9 cTetracycline, Figure 9 d Levofloxacin, Figure 9 e-carbazepine, Figure 9 Compared to the J-10 composite catalyst, the degradation effect of J-10-2 (for norfloxacin) is significantly improved compared to the original BiOCl nanosheets. This is because AgCl and BiOCl form an S-type heterojunction, which, due to its unique charge transfer mechanism, results in faster carrier separation and stronger carrier redox ability, further enhancing photocatalytic activity.

[0055] Figure 9g is a reaction diagram of the degradation of Rhodamine B by J-10-2 after three repeated uses. It can be seen that the degradation of Rhodamine B can be completed within 40 minutes after three repeated uses, which shows that the composite material has excellent stability and recyclability.

[0056] from Figure 7 X-ray photoelectron spectroscopy reveals that, compared to the original BiOCl, the binding energies of the Bi 4f, O 1s, and Cl 2p orbitals in the AgCl / BiOCl@diatomite S-type heterostructure (J-10-2) show a certain degree of shift. This indicates a change in electron cloud density caused by the close contact between AgCl and BiOCl. Furthermore, compared to the original BiOCl, both Bi orbitals in the AgCl / BiOCl@diatomite S-type heterostructure (J-10-2) shift towards higher binding energies, while under illumination, they shift towards lower binding energies compared to in darkness. Figure 7 The same phenomenon was also found in b and c, but Ag under illumination conditions had a 3d 3 / 2 3D 5 / 2 The contrast between the dark areas and the high binding energy regions, combined with these four images, demonstrates that the prepared AgCl / BiOCl@diatomite composite material (J-10-2) conforms to an S-shaped heterostructure. That is, when BiOCl is combined with AgCl, the work function of BiOCl is smaller than that of AgCl. Figure 8 Electrons in BiOCl spontaneously flow to AgCl, causing the binding energies of both Bi and O orbitals to shift towards higher binding energies. This further induces band bending at the contact interface. Due to the higher electron density in AgCl and the higher hole density in BiOCl, a strong built-in electric field is formed at the contact interface, driving the separation and migration of photogenerated carriers. When illuminated, due to the built-in electric field, electrons flow to BiOCl, as shown in the figure, after illumination, the binding energies of both Bi and O orbitals shift towards lower binding energies, while the binding energies of both Ag orbitals shift towards higher binding energies. 7b O in composite materials 1s A new peak appears at 531.8 in the spectrum, which is believed to be a Si-O bond, proving that the composite material was successfully prepared.

[0057] from Figure 8 The work function can be calculated from the formula Φ=hv+E. cutoff -E F (where hv = 21.22 eV), it can be seen that the work function of BiOCl is less than that of AgCl. Combined with the above X-ray photoelectron spectroscopy, it is confirmed that the AgCl / BiOCl@diatomite S-type heterostructure was successfully prepared.

[0058] from Figure 1Analysis of X-ray diffraction pattern (a), scanning electron microscope image (1c) of BiOCl nanosheets (1e), and transmission electron microscope image (1e) of BiOCl shows that the synthesized BiOCl nanosheets grow along a uniaxial axis and exhibit moiré fringes, successfully forming a moiré superlattice structure. Figure 1 As can be seen in b, the porous and disc-like structure of the diatomaceous earth after alkali treatment is well preserved. Figure 1 As shown in Figure c, BiOCl nanosheets are loaded onto the surface of diatomaceous earth. Furthermore, silver chloride nanoparticles are also loaded onto the BiOCl / alkali-treated diatomaceous earth composite material. The XRD diffraction peaks of the J-10 and J-10-2 composite materials remain basically unchanged. The J-10-2 composite material only shows the characteristic peak of silver chloride, and does not damage the original crystal structure, proving that the material synthesis was successful.

[0059] from Figure 2 The zeta potential shows that BiOCl nanosheets are positively charged, while alkali-treated diatomaceous earth is more negatively charged than natural diatomaceous earth, which proves the theoretical feasibility of electrostatic self-assembly.

[0060] from Figure 3 As can be seen, the specific surface area and average pore size of diatomite are significantly increased after alkali treatment, and the specific surface area and pore size of the preferred BiOCl@diatomite composite material (J-10) are further improved compared with BiOCl nanosheets.

[0061] from Figure 4 The UV-Vis diffuse reflectance spectrum shows that the AgCl / BiOCl@diatomite S-type heterostructure has a narrower band gap and a wider light absorption range compared to the initial BiOCl nanosheets.

[0062] from Figure 5 The electrochemical impedance spectroscopy (a) and photocurrent (b) show that the AgCl / BiOCl@diatomite S-type heterostructure has a higher photocurrent and a smaller carrier transfer resistance, indicating that it has a better carrier separation capability.

[0063] from Figure 6 Combining the valence band spectrum with the previous UV-Vis diffuse reflectance spectrum, the calculated positions of the valence band and conduction band of AgCl are 2 and -0.96, respectively; while those of BiOCl are 1.1 and -1.5, respectively. This demonstrates that the valence band and conduction band structures of AgCl and BiOCl are well-matched, meeting the requirements of an S-type heterojunction.

[0064] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. An AgCl / BiOCl@diatomite S-type heterostructure, characterized in that, It is prepared through the following steps: (1) BiOCl nanosheets and alkali-treated diatomite were dispersed in deionized water respectively; the alkali-treated diatomite suspension was added dropwise to the BiOCl nanosheet suspension, stirred for 12 hours, and centrifuged and dried to obtain BiOCl@diatomite composite material; wherein, the mass of alkali-treated diatomite accounted for (5~30) / 100 of the total mass of BiOCl nanosheets and alkali-treated diatomite. (2) Disperse the BiOCl@diatomite composite material in water, add silver nitrate, stir evenly, and irradiate under visible light for 40 minutes; the mass ratio of BiOCl@diatomite composite material to silver nitrate is 20: (1~16.9). (3) After centrifugation and washing, the sample was dried in a vacuum drying oven at 60℃ to obtain an AgCl / BiOCl@diatomite S-type heterostructure. The BiOCl nanosheets in step (1) are prepared by the following steps: (1.1) Disperse 9.6 ml of 20 wt% PDDA aqueous solution in 160 ml of ethylene glycol, add 0.19404 g of Bi(NO3)3•5H2O, and stir magnetically for 30 min; (1.2) Place the above mixed solution in a 200°C oil bath and heat under reflux for 2 hours; (1.3) After the above solution is cooled to room temperature, it is centrifuged, washed 3 times with deionized water, and placed in a vacuum drying oven at 60°C for 12 hours to obtain molar superlattice BiOCl nanosheets.

2. The AgCl / BiOCl@diatomite S-type heterostructure according to claim 1, characterized in that, The alkali-treated diatomaceous earth in step (1) is prepared by the following steps: (2.1) Mix natural diatomaceous earth with a 5% NaOH solution by mass, with a liquid-to-solid mass ratio of 3:1; (2.2) Heat oil in a 95°C bath, stir and maintain for 90 minutes; (2.3) After cooling to room temperature, rinse with water until neutral, and dry under vacuum at 60°C to obtain alkali-treated diatomaceous earth.

3. The AgCl / BiOCl@diatomite S-type heterostructure according to claim 1, characterized in that, The mass of alkali-treated diatomite accounts for 10% of the total mass of BiOCl nanosheets and alkali-treated diatomite.

4. The AgCl / BiOCl@diatomite S-type heterostructure according to claim 1, characterized in that, The mass ratio of BiOCl@diatomite composite material to silver nitrate is 20:4.

5.

5. The application of the AgCl / BiOCl@diatomite S-type heterostructure as described in claim 1 in the photocatalytic degradation of azo dyes and pharmaceutical active compounds.

6. The application according to claim 5, characterized in that, The dye is Rhodamine B, and the active pharmaceutical compound is tetracycline, levofloxacin, carbamazepine, or norfloxacin.

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