Preparation method and application of CoO / black phosphorus catalyst

Abstract

The invention belongs to the technical field of photocatalytic water treatment in environmental chemical industry, and discloses a preparation method and application of a CoO / black phosphorus catalyst, and a series of CoO / BP composite photocatalysts are prepared by taking CoO and Black Phosphoru (BP) as precursor reactants. The preparation method comprises the following steps: preparing a BP catalyst by a simple hydrothermal method, calcining Co (CH3COO) 2.4 H2O and BP in different proportions to generate a composite CoO / BP photocatalyst, and analyzing that CoO is loaded on a BP layer and forms a composite structure. Under the condition of visible light, tetracycline hydrochloride is degraded by using the prepared catalysts, and then the catalytic activity of the composite photocatalyst is observed. Results show that in CoO / BP photocatalysts with different loading capacities, the photocatalytic degradation effect of 50%-CoO / BP is the best, the degradation rate within 4 hours reaches 86.55% and is 7.76 times and 2.06 times of the degradation rates of pure CoO and BP respectively, and it is indicated that the efficient composite catalyst is successfully prepared through the method.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic water treatment in environmental chemical engineering, and relates to the generation of clean gas by visible light treatment, in particular to a preparation method and application of a CoO / black phosphorus catalyst. Background Art

[0002] With the need of production, industrialization has continuously expanded production, and the discharge of industrial wastewater from industries such as papermaking, petrochemical, and printing and dyeing has been increasing year by year. A considerable part of this is that organic pollutants in organic pollution wastewater exist in water bodies for a long time, and the scope of influence is extensive, involving a large number and types of chemicals, and the reaction mechanisms and physical and chemical properties involved in the degradation of organic matter are very complex. At present, the traditional methods for treating organic pollutants usually have high costs. As an environmental protection method, photocatalysts have rapidly emerged and are a cost-effective tool that can utilize solar renewable energy. Due to their great availability for collecting solar energy for various uses, sustainability, and cleanliness, they have developed rapidly in the world. Their outstanding function in solar energy conversion: having the potential to convert solar energy into renewable energy, overcoming the problems of environmental pollution and energy-driven shortages, and being consistent with the "100%" utilization plan in the water / wastewater industry.

[0003] Black Phosphorus (BP) is a form of phosphorus in nature and is an allotrope of common flammable red phosphorus. The preparation of BP crystals started as early as 100 years ago. BP crystals are composed of single-layer black phosphorus lamellae. BP is a p-type semiconductor. It has been found through research that its properties are independent of the number and size of the lamellae, but its band gap is related to the number of layers of the lamellae. Therefore, the band gap width of BP can be adjusted by controlling the number of lamellae of BP. So BP is a semiconductor with an adjustable band gap, and its band gap can range from 2.1 eV of a single-layer BP lamella to 0.3 eV of a bulk crystal. By adjusting the band gap of BP, the range of light absorption can cover the ultraviolet-visible-near-infrared range, and the adjustable range has great advantages compared with other semiconductors. Although BP has excellent photocatalytic properties, because it is easily oxidized and decomposed and fails in oxygen-containing air, water, and visible light, and its properties are unstable, it is necessary to continue to explore and study the modification of BP, which can not only retain its original photocatalytic properties but also improve its stability.

[0004] Cobalt, as a common metal material, has attracted extensive attention in recent years. Cobalt oxide is a promising electrocatalytic material and one of the most intensively studied materials in electrocatalysis. In recent years, cobalt oxide has also been used in the field of photocatalysis and is a current research hotspot. Nevertheless, only a few studies have used CoO as a candidate material for the photocatalytic degradation of organic pollutants because the synthesis method of CoO nanoparticles is complex, the synthesis conditions are harsh, and due to the severe aggregation and chemical instability of CoO nanoparticles, they are prone to inactivation, resulting in an extremely short lifespan of as low as 1 hour. Therefore, the problem of preparing an efficient, stable and easily obtainable CoO photocatalyst remains to be solved. Summary of the Invention

[0005] Since BP is easily oxidized and decomposed and becomes ineffective in oxygen-containing air, water and visible light, and its properties are unstable, exploring and researching the modification of BP can not only retain its original photocatalytic characteristics but also improve its stability. The synthesis method of CoO nanoparticles is complex, the synthesis conditions are harsh, and due to the severe aggregation and chemical instability of CoO nanoparticles, they are prone to inactivation, resulting in an extremely short lifespan of as low as 1 hour. BP with a large specific surface area and a flexible two-dimensional structure can effectively prevent the aggregation of nanoparticles, and some studies have shown that after the BP lamellae are wrapped by CoO nanoparticles, the lone pair electrons will be protected, which may improve the stability of BP. The present invention combines the two to avoid their respective disadvantages and produces a composite metal photocatalyst with high efficiency. The effects of the combination of CoO with different concentrations and BP on the degradation of tetracycline hydrochloride wastewater and photocatalytic performance were studied through experiments.

[0006] In order to solve the problems mentioned in the background art, the purpose of the present invention is to provide a CoO / BP catalyst and a preparation method thereof with good photocatalytic properties, which can provide new ideas for the subsequent degradation of wastewater.

[0007] The present invention mainly realizes the above purpose by improving the catalyst composition and preparation method. To achieve this purpose, the present invention provides:

[0008] A CoO / black phosphorus catalyst, first synthesize BP particles, and then synthesize CoO particles and finally load them on BP. The CoO material is in the shape of nanoparticles, BP is in a clear layered structure, and the composite CoO / BP is in the shape of a layered structure inlaid with nanoparticles.

[0009] On the other hand, a preparation method of the above composite photocatalyst CoO / BP is provided, including the following steps:

[0010] (1) Preparation of BP: 0.25 - 0.75 g of red phosphorus was first ground into powder with a pestle and mortar, and then 70 - 80 mL of ethylenediamine was added. After vigorously stirring with a magnetic stirrer for 30 min, the mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, placed in a constant temperature drying oven, heated at 165 °C for 24 h, quickly cooled to room temperature, and the product was collected with cold water. After centrifugation, it was washed three times with ethanol to remove the residual solvent ethylenediamine. The final product was dried in vacuo at 40 °C;

[0011] (2) Preparation of CoO / BP: Composites of BP and CoO with different mass ratios were prepared by changing the content of CoO in the mixed solution before firing while keeping the BP content constant. The CoO / BP composite catalyst was prepared by the following method: 0.27 - 7.75 g of Co(CH 3 COO) 2 ·4H 2 O and 1 g of the prepared BP powder were added to a mixed solvent containing 10 - 20 mL of n-octanol and 60 - 70 mL of ethanol, and stirred with a magnetic stirrer for 2 h. The resulting slurry was transferred to a 100 mL stainless steel autoclave lined with tetrafluoroethylene, and then placed in a vacuum drying oven and heated at 220 °C for 4 h. The formed mixture was centrifuged to obtain the composite material, washed three times with ethanol, and finally dried in an oven at 70 °C. Pure CoO without BP was prepared using the same method, and finally the sample preparation was completed.

[0012] On the other hand, provided is an application of a CoO / black phosphorus catalyst for photocatalytic degradation of antibiotic wastewater.

[0013] More specifically, it is applied to the photocatalytic degradation of tetracycline hydrochloride wastewater. First, 3 - 5 mg of pure CoO, pure BP, and CoO / BP composites with different ratios were respectively added to 100 mL of tetracycline hydrochloride (10 mg / L). The 3 - 5 mg of the synthesized catalyst was dispersed in 100 mL of tetracycline hydrochloride (10 mg / L) by ultrasonic treatment, and then stirred for 60 min under dark conditions to establish the adsorption - desorption equilibrium between the catalyst and the tetracycline hydrochloride solution. A 500 w xenon lamp was vertically placed 15 cm above the solution. 4 mL of the sample was taken at regular intervals and transferred to a centrifuge tube, and the photocatalyst was separated by centrifugation. Finally, the absorbance at 356 nm was measured using a UV - visible spectrophotometer, and the change in the concentration of tetracycline hydrochloride was determined by the absorbance to analyze the degradation efficiency of the photocatalyst.

[0014] The present invention has the following advantages compared with the prior art:

[0015] 1. The composite CoO / BP catalyst is composed of CoO particles and BP particles. First, the BP particles are prepared, and finally CoO is loaded.

[0016] 2. The composite CoO / BP catalyst has strong light adsorption ability and high electron-hole separation efficiency, so that the material structure is stable, the photo-generated carriers are transported quickly, and the recombination of photo-generated carriers can be effectively inhibited.

[0017] 3. Compared with the common photocatalyst g-C 3 N 4 and pure CoO and BP, the composite CoO / BP catalyst has better visible light absorption performance and greatly improves the photocatalytic degradation of tetracycline hydrochloride solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a scanning electron microscope image. (a) is the scanning electron microscope image of CoO in Example 1, (b) is the transmission electron microscope image of BP at 50 nm, (c) is the transmission electron microscope image of BP at 5 nm, (d) is the scanning electron microscope image of CoO / BP, (e) is the transmission electron microscope image at 100 nm, and (f) is the transmission electron microscope image at 500 nm;

[0019] Figure 2 It is the X-ray photoelectron spectroscopy of CoO, BP and CoO / BP in Example 1. Figure (a) is the total spectrum, Figure (b) is the Co 2p spectrum, Figure (c) is the O1s spectrum, and Figure (d) is the P 2p spectrum;

[0020] Figure 3 It is the fluorescence spectrum of all samples in Example 1;

[0021] Figure 4 It is the UV-Vis diffuse reflection spectrum of all samples in Example 1;

[0022] Figure 5 It is the X-ray diffraction spectrum of all samples in Example 1;

[0023] Figure 6 It is the degradation effect diagram of different catalysts under visible light irradiation. (a) is the removal rate diagram of different catalysts for degrading tetracycline hydrochloride under visible light irradiation in Example 1, and (b) is the first-order kinetic curve of different catalysts for degrading tetracycline hydrochloride under visible light irradiation in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0024] The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0025] Example 1

[0026] The preparation method of the composite CoO / BP photocatalyst is specifically as follows:

[0027] The prepared photocatalyst is denoted as CoO / BP(x:y), where x:y is the mass ratio of CoO to BP. The CoO / BP composite catalysts with different mass ratios (0%, 7.5%, 15%, 30%, 50%, and 70%) were prepared by the following method: Different masses of Co(CH 3 COO) 2 ·4H 2 O (0, 0.27, 0.58, 1.43, 3.32, and 7.75 g) and 1 g of the prepared BP powder were added to a mixed solvent containing 16 mL of n-octanol and 64 mL of ethanol, and stirred for 2 h by a magnetic stirrer. The resulting slurry was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene, and then placed in a vacuum drying oven and heated at 220 °C for 4 h. The formed mixture was centrifuged to obtain the composite material, washed three times with ethanol, and finally dried in an oven at 70 °C. Pure CoO was prepared using the same method but without BP, and finally the sample preparation was completed.

[0028] Example 2

[0029] 0.5 g of red phosphorus was first ground into powder with a pestle and mortar, and then 75 mL of ethylenediamine was added. After vigorously stirring for 30 min with a magnetic stirrer, the mixture was transferred to a 100 mL stainless steel high-pressure reaction kettle lined with polytetrafluoroethylene, placed in a constant temperature drying oven, and heated at 165 °C for 24 h. Then it was quickly cooled to room temperature, and the product was collected with cold water. After centrifugation, it was washed three times with ethanol to remove the residual solvent ethylenediamine. The final product was dried in vacuo at 40 °C; finally, BP was obtained. Figure 1 Figures are the SEM images of CoO, the TEM images of BP, and the SEM and TEM images of CoO / BP in Example 1; as Figure 1 a, the SEM image of CoO nanomaterial at 1 μm. It can be seen from the figure that the CoO material is in the form of nanoparticles. Figure 1 b, the TEM image of BP material at 50 nm. It can be seen from the figure that BP has a clear layered structure. According to Figure 1 c, the TEM image of BP at 5 nm, it can be seen that the lattice spacing of the prepared BP material is approximately 0.256 nm, corresponding to the (040) crystal plane, which is consistent with the XRD pattern of BP. Through (d), (e), (f), the 1 μm SEM image, 100 nm TEM image, and 500 nm TEM image of the CoO / BP composite material, it is obvious that the surface of the composite material is rougher. By analyzing the structure of the CoO / BP composite material, it is found that CoO nanoparticles are adsorbed on the layered BP.

[0030] Figure 2XPS spectra of CoO, BP, and CoO / BP in Example 1; it is confirmed that Co, O, and P elements exist in the CoO / BP structure.

[0031] Figure 3 Fluorescence spectra of all samples in Example 1; as shown in the figure, the PL intensity of BP is higher than that of the CoO / BP composite material. The PL intensity of the CoO / BP composite material decreases, and 50%-CoO / BP has the lowest PL intensity, indicating that the presence of CoO reduces the PL intensity, effectively separates the photo-generated electron-hole pairs, reduces the recombination of photo-generated electron-hole pairs, and realizes effective electron transfer. The 70%-CoO / BP is slightly higher than 50%-CoO / BP, indicating that it also has a good electron transfer effect.

[0032] Figure 4 UV-Vis diffuse reflectance spectra of all samples in Example 1; black phosphorus has a wide absorption range of light and excellent light absorption ability. The absorption range of CoO is 400-600 nm, and its light absorption ability is weak. For the composites 50%, 70%, and 30%-CoO / BP, the absorption edge has a red shift compared to that of pure CoO material, and the light absorption range is 450-700 nm. The light absorption ability of the CoO / BP-50% composite material is stronger than that of CoO. It shows that the visible light utilization rate of the 50%-CoO / BP composite material is significantly improved compared to CoO.

[0033] Figure 5 X-ray diffraction patterns of all samples in Example 1; as shown in the figure, the characteristic peaks are 16.9°, 26.5°, and 35.0°, corresponding to the (020), (021), and (040) crystal planes respectively, indicating the successful preparation of BP. In the XRD pattern of the CoO nanomaterial, all diffraction peaks at 36.4°, 42.3°, 61.4°, 73.6°, and 77.5° correspond to the (111), (200), (220), (311), and (222) crystal planes, and no impurity peaks appear, indicating the successful preparation of the CoO nanomaterial. In the pattern of the CoO / BP composite material in the figure, the characteristic peaks of BP and CoO nanomaterial can be observed, indicating the successful combination of the layered BP material and CoO nanomaterial. The crystal structures of the BP material and CoO nanomaterial are not changed in the synthesized composite materials. In the composite, the characteristic peak of the CoO material at (220) becomes more and more obvious with the increase of the proportion of CoO, indicating the successful synthesis of the CoO component in the composite component.

[0034] Figure 6 Removal rate diagram and first-order kinetic curve of different catalysts for the degradation of tetracycline hydrochloride under visible light irradiation in Example 1;

[0035] Application Example 1

[0036] First, 3 mg of pure CoO, pure BP, and CoO / BP composite catalysts with different ratios (0%, 7.5%, 15%, 30%, 50%, and 70%) were separately added to 100 mL of tetracycline hydrochloride (10 mg / L). The 3 mg of synthesized catalyst was dispersed in 100 mL of tetracycline hydrochloride (10 mg / L) by ultrasonic treatment, and then stirred for 60 min under dark conditions to establish the adsorption-desorption equilibrium between the catalyst and the tetracycline hydrochloride solution. A 500-w xenon lamp was vertically placed 15 cm above the solution. Samples of 4 mL were taken at regular intervals and transferred to a centrifuge tube to separate the photocatalyst by centrifugation. Finally, the absorbance at 356 nm was measured using a UV-visible spectrophotometer, and the change in the concentration of tetracycline hydrochloride was determined by the absorbance to analyze the degradation efficiency of the photocatalyst.

[0037] The experimental results are shown in Figure 6 As shown, the mixture of the catalyst and tetracycline hydrochloride was placed under a 500-w xenon lamp for irradiation. It can be clearly seen from the figure that the degradation efficiencies of pure black phosphorus and CoO for tetracycline hydrochloride are only 41.45% and 11.14% respectively, while the composite material of CoO / BP is significantly higher than the two pure samples. Among them, the highest composite material, 50%-CoO / BP, has an effect as high as 86.55%. The degradation rate of the common photocatalyst g-C 3 N 4 for the degradation of tetracycline hydrochloride solution is 44%, and the degradation rate of 50%-CoO / BP is 1.97 times that of g-C 3 N 4 . The degradation percentages of the composite materials are in the order of 50%-CoO / BP (86.55%) > 30%-CoO / BP (78.38%) > 70%-CoO / BP (72.36%) > 15% CoO / BP (55.46%) > 7.5%-CoO / BP (47.67). It can be analyzed from this that as the proportion of CoO added to black phosphorus increases, the degradation efficiency of photocatalytic degradation of tetracycline hydrochloride gradually increases, but the degradation efficiency decreases when the CoO ratio increases to 70%, indicating that loading too high CoO nanoparticles will cause a burden on the composite material. Too many CoO arranged together will increase the recombination efficiency of photoelectrons and holes and reduce the photocatalytic activity. Using the kinetic first-order model ln(C / C 0 ) = kt to fit the Figure 6 (b) shown fitting curve, the reaction rate of photocatalytic degradation can be obtained from the slope of the fitting curve. Among them, the degradation rate of the composite material 50%-CoO / BP is the highest at 0.172 h -1 , and the degradation rates of pure black phosphorus and cobalt oxide are 0.053 h -1 and 0.029 h -1 .

[0038] The above-described embodiments are only the preferred embodiments of the present invention, rather than all the feasible embodiments of the present invention. For those of ordinary skill in the art, any obvious changes made without departing from the principle and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A CoO / black phosphorus catalyst, characterized in that: BP particles are synthesized first, then CoO particles are synthesized and finally BP is loaded. The CoO material is in the form of nanoparticles, BP has a clear layered structure, and the composite CoO / BP is in the form of nanoparticles inlaid with a layered structure.

2. A method for preparing a CoO / black phosphorus catalyst, characterized in that: The following steps are involved: (1) Preparation of BP: 0.25-0.75 g of red phosphorus powder was added with 70-80 mL of ethylenediamine, mixed well, heated at 165°C for 24 h, and then quickly cooled to room temperature, the product was collected with cold water, centrifuged, and washed with ethanol to remove the residual solvent ethylenediamine. The final product was dried at 40°C in a vacuum; (2) Preparation of CoO / BP: 0.27-7.75 g of Co(CH3COO)2·4H2O and 1 g of prepared BP powder were added to a mixed solvent containing 10-20 mL of n-octanol and 60-70 mL of ethanol, and the resulting slurry was heated at 220°C for 4 h. The resulting mixed solution was centrifuged to obtain the composite material, which was washed with ethanol and finally dried in an oven at 70°C.

3. The method for preparing the CoO / black phosphorus catalyst according to claim 2, characterized in that: The heating reactions in step (1) and step (2) are both carried out in a constant temperature drying oven.

4. The method for preparing the CoO / black phosphorus catalyst according to claim 2, characterized in that: The mixture of the heating reaction in step (1) is mixed evenly and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and placed in a constant temperature drying oven.

5. The method for preparing the CoO / black phosphorus catalyst according to claim 2, characterized in that: The slurry of the heating reaction in step (2) is transferred to a tetrafluoroethylene-lined stainless steel autoclave and placed in a vacuum drying oven.

6. The method for preparing the CoO / black phosphorus catalyst according to claim 2, characterized in that: In step (1) and step (2), the sample was washed with ethanol three times.

7. An application of CoO / black phosphorus catalyst, characterized in that: Used for photocatalytic degradation of antibiotic wastewater.

8. The use of the CoO / black phosphorus catalyst according to claim 7, characterized in that: Application in photocatalytic degradation of tetracycline hydrochloride wastewater.

9. The use of the CoO / black phosphorus catalyst according to claim 7, characterized in that: 3-5 mg of the synthesized catalyst was dispersed in 100 mL of a 10 mg / L tetracycline hydrochloride solution by ultrasonic treatment, and the adsorption-desorption equilibrium between the catalyst and the tetracycline hydrochloride solution was established by stirring for 60 min in the dark, and a xenon lamp was used for vertical irradiation.

10. The use of the CoO / black phosphorus catalyst according to claim 8, characterized in that: Add a magnetic stirrer to the tetracycline hydrochloride solution and place it on a magnetic stirrer to continue stirring the reaction.

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