MoO2@CoFe LDHs photocatalyst and its application in synergistic degradation of tetracycline with persulfate

Abstract

The invention discloses an application of a hydrotalcite composite as a photocatalytic material and a persulfate for synergistically degrading tetracycline. The hydrotalcite composite product is MoO2@CoFe LDH, and discloses an application of the hydrotalcite composite and a persulfate for photocatalytic degradation of antibiotics. The reaction conditions are mild, the pollutant removal rate is high and the speed is fast, and the material after catalytic degradation is easy to recycle.

Description

Technical Field

[0001] The invention relates to the field of photocatalytic degradation, and in particular to a novel hydrotalcite-based composite material and application thereof as a photocatalytic material for synergistically degrading antibiotics in water with persulfate. Background Art

[0002] The annual production of industrial wastewater in my country has reached more than 200 billion tons, and most of the organic pollutants contained in the wastewater, including dyes, phenols, antibiotics, etc., are stable in structure and difficult to degrade. Antibiotics are widely used in medicine, health, agriculture, biology and other fields, but in recent years, due to improper use in medicine, animal husbandry and other fields, their threats to environmental safety, ecosystems and human health have become increasingly serious. Tetracycline, as one of the antibiotics, cannot be fully absorbed by the human body and will enter the environment through urine and feces. In addition, tetracycline is not easy to degrade and has strong chemical stability. Therefore, it is very necessary to degrade tetracycline in water systems. The mainstream treatment technologies include chemical catalytic oxidation, physical adsorption and biodegradation, but these methods have the limitations of secondary pollution, long cycle and high cost. Photocatalytic technology has become a research hotspot in energy and environment due to its green environmental protection, simple operation and high efficiency.

[0003] Compared with other methods, photocatalysis has the advantages of mild reaction conditions, simple equipment, less secondary pollution, and the use of sunlight as the only external energy input. It is a very promising pollution control technology.

[0004] Semiconductor photocatalysis has been widely studied. In the system based on semiconductor catalysts, layered double hydroxide (LDHs)-based materials have a special layered structure and include advantages such as good material dispersion, high specific surface area, small grain size, suitable acidity and alkalinity, and high thermal stability. Under visible light excitation, LDHs materials can generate a large number of photogenerated electrons and holes for the degradation of pollutants. However, single-phase LDHs still have many limitations, such as slow electron transfer rate and easy recombination and annihilation of electron-hole pairs, which curb their photocatalytic performance. To solve this problem, different semiconductor materials can be used for compounding, heterojunctions can be constructed, and built-in electric fields can be formed to promote electron transfer and inhibit the recombination of electrons and holes. On the one hand, electrons and holes are accumulated at higher energy levels and have stronger redox ability; on the other hand, more electrons and holes are used to generate active free radicals to act on subsequent degradation reactions. In addition, although the photocatalytic process has a good effect on the degradation of pollutants, it has low efficiency in light energy utilization and limited active free radicals, so the process is relatively slow. At present, SO-based 4 · - The photocatalytic method is widely used to degrade organic pollutants. 4 · -Persulfate can usually be activated and produced by light, microwaves, ultrasound, heating, transition metal ions, metal and metal-free catalysts. Among them, light energy is used to activate SO 4 · — It will not cause secondary pollution, nor does it require additional energy, which greatly saves the cost of degrading pollutants. PS has a high electron affinity, and the photogenerated electrons generated by semiconductors can be quickly captured by PS to form highly oxidizing SO4 — The degradation effect on pollutants in water is very significant, and the time is shortened to a quarter of the original time, greatly improving the degradation efficiency.

[0005] Therefore, coupling the LDHs / persulfate system with photocatalysis to construct a multi-reaction coupled advanced oxidation system for efficient degradation of organic pollutants in water is a hot topic in current research. 2 @LDHs composite materials, and construct a multi-reaction coupled advanced oxidation system (photocatalysis + persulfate activation) by coupling persulfate. Summary of the invention

[0006] The present invention aims to provide a novel MoO 2 @CoFe LDHS composite materials and their application as photocatalytic materials for synergistic degradation of antibiotics and azo dyes with persulfate.

[0007] The technical solution adopted by the present invention is:

[0008] The MoO 2 @CoFe LDHs are usually prepared as follows:

[0009] (1) MoO 2 Preparation

[0010] Weigh 1.0 ~ 1.5g of ammonium molybdate tetrahydrate and disperse it in 30 ~ 50mL of deionized water. Stir at room temperature for 30 ~ 60 min until the solution becomes transparent, which is called solution A. Weigh 0.1 ~ 0.15g of CTAB (hexadecyltrimethylammonium bromide) and dissolve it in ethanol (about 3 ~ 5mL) to form a homogeneous solution, which is called solution B. Add solution B drop by drop into solution A and continue stirring. 3 Add dropwise to the mixed solution and adjust the pH to 1.5. Pour the solution into a 100 mL Teflon stainless steel autoclave and hydrothermal at 180 °C for 48 hours. After the reaction is completed, cool the autoclave to room temperature. Wash with ethanol and distilled water three times respectively, and dry at 50 ~ 60 °C.

[0011] (2) MoO 2 Preparation of @LDHs:

[0012] Take Co(NO 3 ) 2 6H 2 O 4mmol, Fe(NO 3 ) 3 · 9H 2 O 2mmol, a certain amount of MoO 2 , dissolved in 50 mL of water, stirred magnetically for 30 min to form a uniform solution, and then 15 mmol NH 4 F, stir again for 30 min to make it evenly mixed, recorded as solution A; take 21mmol NaOH, 3mmol Na 2 CO 3 , dissolved in 50mL of distilled water, recorded as solution B; under continuous stirring, solution B was added dropwise to solution A, pH was adjusted to 9.5, and further stirred for 5h. The precipitate was then aged at room temperature for 12h. It was washed three times with ethanol and distilled water respectively, and dried at 50-60℃.

[0013] The present invention provides MoO 2 @CoFe LDHs synergistically with persulfate can be applied to degrade antibiotics, more specifically, tetracycline.

[0014] Further, the application method of the present invention is: 5 to 30 mg MoO 2 @LDHs and 0.01 ~ 1 g sodium persulfate were placed in an organic aqueous solution, irradiated under a xenon lamp for 0.5 ~ 2 h, and stirred to degrade the pollutants; the initial mass concentrations of the pollutants were 10 ~ 100 mg / L.

[0015] The MoO provided by the present invention 2 @CoFe LDHs have relatively small bandgap and grain size, and can generate catalytically active electron-hole pairs under appropriate light. When pollutants (tetracycline) are adsorbed on the surface of hydrotalcite, they will capture electron-hole pairs, activate persulfate ions, and degrade pollutants, thereby achieving the purpose of purifying wastewater.

[0016] The MoO of the present invention 2 @CoFe LDHs and its use as photocatalytic materials to synergistically degrade pollutants in water with persulfate. The above method is used to calculate the degradation rate. The reaction conditions are mild, the degradation efficiency is high, the effect is significant, and the materials after catalytic degradation are easy to recycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is MoO in Example 1 2 , CoFe LDH, MoO 2@X-ray diffraction pattern of CoFe LDHs;

[0018] Figure 2 is a degradation rate curve diagram of tetracycline in Example 2;

[0019] Figure 3 This is the standard curve diagram of tetracycline in Example 3. DETAILED DESCRIPTION

[0020] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0021] (1) MoO 2 Preparation

[0022] Weigh 1.0 ~ 1.5g of ammonium molybdate tetrahydrate and disperse it in 30 ~ 50mL of deionized water. Stir at room temperature for 30 ~ 60 min until the solution becomes transparent, which is called solution A. Weigh 0.1 ~ 0.15g of CTAB (hexadecyltrimethylammonium bromide) and dissolve it in ethanol (about 3 ~ 5mL) to form a homogeneous solution, which is called solution B. Add solution B drop by drop into solution A and continue stirring. 3 Add dropwise to the mixed solution and adjust the pH to 1.5. Pour the solution into a 100 mL Teflon stainless steel autoclave and hydrothermal it at 180 °C for 48 h. After the reaction is completed, cool the autoclave to room temperature. Wash with ethanol and distilled water three times respectively, and dry at 50 ~ 60 °C to obtain MoO 2 .

[0023] Take Co(NO 3 ) 2 · 6H 2 O 4mmol, Fe(NO 3 ) 3 · 9H 2 O 2mmol, magnetic stirring for 30min to form a uniform solution, and then 15mmol NH 4 F, stir again for 30 min to make it evenly mixed, recorded as solution A; take 21mmol NaOH, 3mmol Na 2 CO 3 , dissolved in 50mL of distilled water, recorded as solution B; under continuous stirring, solution B was added dropwise to solution A, pH was adjusted to 9.5, and further stirred for 5h. The precipitate was then aged at room temperature for 12h. It was washed three times with ethanol and distilled water respectively, and dried at 50-60℃.

[0024] (3) MoO 2 Preparation of @LDHs:

[0025] Take Co(NO 3 ) 2 6H 2 O 4mmol, Fe(NO 3 ) 3 9H 2 O 2mmol, a certain amount of MoO 2 , dissolved in 50 mL of water, stirred magnetically for 30 min to form a uniform solution, and then 15 mmol NH 4 F, stir again for 30 min to make it evenly mixed, recorded as solution A; take 21mmol NaOH, 3mmol Na 2 CO 3 , dissolved in 50 mL of distilled water, recorded as solution B; under continuous stirring, solution B was added dropwise to solution A, the pH was adjusted to 9.5, and further stirred for 5 h. The precipitate was then aged at room temperature for 12 h. It was washed with ethanol and distilled water three times respectively, and dried at 50 ~ 60 °C to obtain MoO 2 @CoFe LDHS.

[0026] The degradation of tetracycline by simulated sunlight was used as a model reaction. The absorbance of the tetracycline solution at 357 nm was measured by a UV-visible spectrophotometer to determine its relative concentration, thereby evaluating the photocatalytic performance of the material. The light source was a 300 W xenon lamp (using a filter to filter out ultraviolet light and retain visible light of 400 nm<λ<800 nm), and the light source was 25 cm away from the reaction solution. At a certain temperature and pH value, 10 mg of catalytic material was added to a double-layer quartz reaction tube containing 100 mL of 40 mg / L tetracycline solution, followed by 0.0238 g of sodium persulfate. The xenon lamp was then turned on to carry out the photocatalytic experiment under continuous illumination and magnetic stirring. After the reaction started, samples were taken every 5 min, and the absorbance of the filtrate at 357 nm was measured by a UV-visible spectrophotometer after filtration through a 0.22 μm organic filter membrane. According to the standard curve, it was converted to the relative mass concentration C (mg / L) of tetracycline. According to C / C 0 Calculate the degradation rate of tetracycline (η%), C 0 (mg / L) is the initial mass concentration of tetracycline.

[0027] η=C / C 0 (1)

[0028] In the experiment, the

[0029] 1. Blank experiment (no catalyst);

[0030] 2. Add only catalyst MoO 2 、MoO 2@LDHs;

[0031] 3. Adding catalyst MoO 2 、CoFe-LDH MoO 2 @LDHs and Na persulfate 2 S 2 O 8 ;

[0032] 4. Add catalyst MoO2@LDHs and persulfate Na2S2O8 under light-free conditions.

[0033] The degradation rate curve is given by Figure 2 As shown in the figure, under the condition of no light, the catalyst has no degradation effect on tetracycline. 2 S 2 O8 is slightly activated under light, and its degradation effect on tetracycline is weak, about 20%. 2 The material has a certain promoting effect under light, but the activation effect on persulfate is not obvious, and the degradation rate is 48%. 2 The effect is significantly improved by compounding, and the degradation rate in 30 minutes is increased to 85%-90%. Compared with conventional photodegradation, the treatment time for pollutants is shorter and energy consumption is reduced.

[0034] Based on the tetracycline solution with an initial concentration of 100 mg / L, solutions with concentrations of 5.00 mg / L, 10.00 mg / L, 20.00 mg / L, 30.00 mg / L, 40.00 mg / L, and 50.00 mg / L were prepared. Deionized water was used as a blank reference. The absorbance of each solution was measured at 357 nm using a Shimadzu 2550 UV-Vis spectrophotometer. A standard curve of tetracycline solution absorbance A-concentration C was obtained by linear fitting, see Figure 3 shown.

Claims

1. A MoO2@CoFe LDHs photocatalyst, characterized in that: The photocatalyst is prepared by the following method: (1) Preparation of MoO2: MoO2 is obtained by reacting ammonium molybdate tetrahydrate with CTAB; (2) Preparation of MoO2@CoFe LDHs: Take Co(NO3)2·6H2O, Fe(NO3)3·9H2O, and dissolve the MoO2 obtained in step (1) in water, stir magnetically to form a uniform solution, then add NH4F and mix well, which is recorded as solution A; Take NaOH and Na2CO3 and dissolve them in 50mL of distilled water, which is called solution B; Under continuous stirring, solution B was added dropwise into solution A, and the pH was adjusted to 8-11. After further stirring, the precipitate was aged at room temperature, washed, and dried to obtain the MoO2@CoFe LDHs photocatalyst.

2. The MoO2@CoFe LDHs photocatalyst according to claim 1, characterized in that: The preparation of MoO2 in step (1) comprises the following method: weighing 1.0-1.5 g of ammonium molybdate tetrahydrate, dispersing it in 30-50 mL of deionized water, stirring at room temperature for 30-60 min until the solution becomes transparent, which is referred to as solution A; weighing 0.1-0.15 g of CTAB, dissolving it in 3-5 mL of ethanol, forming a homogeneous solution, which is referred to as solution B; dropping solution B into solution A drop by drop while stirring continuously; dropping concentrated HNO3 into the mixed solution, adjusting the pH to 1.5; pouring the solution into a high-pressure reactor, and hydrothermally reacting it at 180°C for 48 h; after the reaction is completed, cooling the reactor to room temperature, washing it with ethanol and distilled water for 3 times respectively, and drying it at 50-60°C.

3. The MoO2@CoFe LDHs photocatalyst according to claim 2, characterized in that: Step (2) The preparation of MoO2@CoFeLDHs includes the following method: 4 mmol of Co(NO3)2·6H2O, 2 mmol of Fe(NO3)3·9H2O, and a certain amount of MoO2 are dissolved in 50 mL of water, and magnetically stirred for 30 min to form a uniform solution, and then 15 mmol of NH4F is added, and stirred again for 30 min to make it mix evenly, which is recorded as solution A; 21 mmol of NaOH and 3 mmol of Na2CO3 are dissolved in 50 mL of distilled water, which is recorded as solution B; under continuous stirring, solution B is added dropwise into solution A, the pH is adjusted to 9.5, and further stirred for 5 h. The precipitate is then aged at room temperature for 12 h, washed 3 times with ethanol and distilled water respectively, and dried at 50 ~ 60 °C.

4. Use of the MoO2@CoFe LDHs photocatalyst according to any one of claims 1 to 3 in combination with sodium persulfate as a photocatalytic material for degrading tetracycline.

5. The use according to claim 4, characterized in that: 10 ~ 100 mg MoO2@CoFe LDHs and 0.01 ~ 1 g sodium persulfate were placed in a tetracycline aqueous solution, irradiated under a xenon lamp for 0.5 ~ 2 h, and stirred to degrade tetracycline; the initial mass concentration of the tetracycline was 10 ~ 100 mg / L.

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