A cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, a preparation method and application thereof

Abstract

The application belongs to the field of advanced oxidation treatment of organic matters, and particularly relates to a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, a preparation method and application thereof. The photocatalytic material comprises cerium dioxide and nitrogen-doped carbon nitride, the cerium dioxide has a sheet structure, and the mass percentage of the cerium dioxide in the photocatalytic material is 0.5-1.5%. The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is mixed with wastewater containing polyvinyl alcohol and subjected to dark treatment, and after saturation adsorption, the photocatalytic degradation reaction is carried out under light. The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has the advantages of good dispersibility and easy recycling and reuse, and is a novel composite photocatalytic material with excellent photocatalytic performance, environmental friendliness and wide application range.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of advanced oxidation treatment of organic matters, and particularly relates to a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material and a preparation method and application thereof. BACKGROUND

[0002] Polyvinyl alcohol is an important industrial raw material, has good physical and chemical properties, and is widely used in the production of products such as coatings, adhesives, paper processing, emulsifiers, dispersants, and the application range covers steel, textile, food, medicine, building, papermaking, high polymer chemical industry and other industries. In recent years, the vigorous development of these industries has driven the rapid increase of polyvinyl alcohol production capacity. However, polyvinyl alcohol is a typical biodegradable polymer, which makes the polyvinyl alcohol wastewater have high COD and poor biodegradability, and direct discharge will seriously pollute the water body. The pollution of polyvinyl alcohol to the environment is not because of its toxicity, but because of its biodegradation. Its large surface activity can increase the foam on the surface of the polluted water body and increase the viscosity, which is not conducive to the water recovery behavior, thereby inhibiting the respiratory activity of aquatic organisms. In addition, the discharge of polyvinyl alcohol-containing wastewater into the water body will also promote the release and migration of deposited heavy metals, enhance their activity, and cause more serious environmental problems. Therefore, finding an effective method to remove polyvinyl alcohol in water environment has become an urgent task.

[0003] As a new advanced oxidation-reduction technology, photocatalysis technology has the technical characteristics of using green energy, room temperature deep reaction, wide spectrum, complete purification and long service life of photocatalyst, and is considered to be a reliable and efficient method. In the prior art, photocatalytic degradation of polyvinyl alcohol in water mainly focuses on the research of TiO2 and its modification to obtain good polyvinyl alcohol degradation efficiency. However, there are some common problems in these studies: (1) limited by the large band gap of TiO2, its light absorption performance is limited, and it can only be excited by ultraviolet light to achieve photocatalytic degradation. However, ultraviolet light only accounts for 7% of solar radiation energy, while visible light and infrared light account for 50% and 43% of solar radiation energy, respectively. Therefore, TiO2 cannot fully utilize solar radiation energy, which limits its practical application; (2) the photocatalytic degradation of TiO2 is limited by the rapid recombination of photo-generated carriers, and the degradation efficiency of polyvinyl alcohol is not ideal in a short time. After 4h ultraviolet light irradiation, the degradation efficiency of polyvinyl alcohol is only 50%; (3) in order to improve the photocatalytic activity of TiO2, many studies use metal ions and noble metals to modify the surface of TiO2 to improve the photocatalytic degradation activity of polyvinyl alcohol. However, the loading of heteroatoms inevitably introduces impurities and structural defects, which adversely affects the stability of the catalyst; in addition, noble metals also limit the large-scale application of materials. Therefore, it is still a great challenge to obtain a photocatalytic material for treating polyvinyl alcohol with good economic benefit, high degradation efficiency and recyclability.

[0004] In recent years, carbon nitride (C3N4) has been widely applied in photocatalytic water splitting, CO2 reduction, nitrogen fixation, artificial photosynthesis and environmental remediation due to its suitable energy band structure, excellent thermal and chemical stability, easy availability of constituent elements and environmental friendliness. However, the photocatalytic activity of carbon nitride monolayer prepared by direct calcination of precursor is not ideal due to its high recombination rate of photo-generated carriers and limited visible light absorption range (λ < 470 nm). In order to overcome these difficulties, element doping, cocatalyst loading and construction of heterojunction are used to optimize the photocatalytic performance of carbon nitride monolayer. Among them, element doping can effectively adjust the energy band structure and light absorption performance of carbon nitride, and loading cocatalyst can effectively improve the separation efficiency of photo-generated carriers. However, the process of element doping and cocatalyst loading inevitably introduces impurities and structural defects, thereby affecting the stability of the photocatalyst. Therefore, it is of great significance to construct a carbon nitride-based photocatalyst with good light absorption performance, high quantum efficiency and stable catalytic performance. SUMMARY

[0005] The technical problems to be solved by the present application are to overcome the shortcomings of the prior art and provide a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, a preparation method and application thereof. The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is used to treat polyvinyl alcohol in water, which is simple in operation, short in cycle, easy to recycle and reuse, and high in degradation efficiency.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] In one aspect, the present application provides a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, which comprises cerium dioxide and nitrogen-doped carbon nitride, and the cerium dioxide has a sheet structure. The mass percentage of cerium dioxide in the photocatalytic material is 0.5-1.5%.

[0008] In another aspect, the present application provides a preparation method of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material according to claim 1, which comprises the following steps:

[0009] S1. Dissolve cerium salt in deionized water, add a nitrogen-containing compound, ultrasonic, and stir to obtain a cerium salt precursor;

[0010] S2. Perform hydrothermal reaction on the cerium salt precursor obtained in step S1 to obtain cerium carbonate hydroxide slurry, cool and remove the supernatant, and then wash, filter and dry the remaining slurry to obtain a cerium carbonate hydroxide precursor;

[0011] S3. Calcine the cerium carbonate hydroxide precursor obtained in step S2, and grind to obtain cerium dioxide nanoparticles;

[0012] S4, mixing citric acid with deionized water, constant temperature stirring until the water evaporates, citric acid powder is obtained;

[0013] S5, mixing the cerium dioxide nanoparticles obtained in step S3 with the citric acid powder obtained in step S4, adding urea, grinding, calcining, washing, filtering, drying, to obtain a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material.

[0014] The above technical solution, further, in step S1, the cerium salt is cerium nitrate hexahydrate, and the nitrogen-containing compound is hexamethylenetetramine, or the cerium salt is cerium carbonate, and the nitrogen-containing compound is ammonia water; the mass ratio of the cerium salt to the nitrogen-containing compound is 1:1.5-2.5; the ultrasonic time is 5-15 min; the stirring is carried out under the condition that the rotating speed is 600-800 r / min, and the stirring time is 5-7 h.

[0015] The above technical solution, further, in step S2, the hydrothermal reaction temperature is 140-180 DEG C, and the hydrothermal reaction time is 9-15 h; the drying temperature is 60-80 DEG C, and the drying time is 12-20 h.

[0016] The above technical solution, further, in step S3, the calcining temperature is 500-600 DEG C, the temperature rising rate is 2-5 DEG C / min, and the calcining time is 2-4 h; the grinding time is 10-20 min.

[0017] The above technical solution, further, in step S4, the constant temperature stirring temperature is 60-70 DEG C, the time is 4-6 h, the stirring rotating speed is 1000-1200 r / min; the dosage ratio of citric acid to deionized water is 1 g:20 ml.

[0018] The above technical solution, further, in step S5, the mass ratio of cerium dioxide, citric acid powder and urea is 6-12:0.5-1.5:100; the calcining temperature is 500-600 DEG C, the temperature rising rate in the calcining process is 2-5 DEG C / min, and the calcining time is 2-4 h; the grinding time is 20-40 min; the drying temperature is 60-80 DEG C, and the drying time is 12-20 h.

[0019] The application also provides an application of the above cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material in treating polyvinyl alcohol in water, and the application method comprises the following steps:

[0020] The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is mixed with wastewater containing polyvinyl alcohol and is subjected to dark treatment, after reaching adsorption saturation, the photocatalytic degradation reaction is carried out under light irradiation.

[0021] The technical scheme further includes that the concentration of polyvinyl alcohol in the wastewater containing polyvinyl alcohol is 10-30 mg / L; and the mass ratio of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material to polyvinyl alcohol is 9-15:1.

[0022] The technical scheme further includes that the dark treatment is stirring for 30-60 min under dark conditions; the photocatalytic degradation reaction is performed under stirring conditions at a rotation speed of 400-1000 r / min, the photocatalytic degradation reaction is performed under light conditions at a wavelength of 420-850 nm, and the photocatalytic degradation reaction time is 60-90 min.

[0023] The present application has the following advantages:

[0024] 1. The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material includes cerium dioxide and nitrogen-doped carbon nitride, the nitrogen-doped carbon nitride material is doped with nitrogen elements, and the cerium dioxide is loaded on the nitrogen-doped carbon nitride material. Compared with doping other elements, the doping of nitrogen elements can not only adjust the inherent optical / electrical properties of the carbon nitride monomer material and enhance the light absorption performance of the carbon nitride monomer, but also avoid the introduction of foreign impurities and defects without affecting the stability of the photocatalyst; in order to inhibit the recombination of photo-generated carriers in the photocatalytic process, a cheap and stable cerium dioxide is introduced. Since the conduction band position of the cerium dioxide is lower than that of the carbon nitride, it can be foreseen that the coupling of the cerium dioxide and the carbon nitride can gather the photo-generated electrons on the cerium dioxide in the reaction process, thereby promoting the separation of the photo-generated electron-hole pairs. On the other hand, due to the unique electronic structure of Ce 3+ (4f 1 5d 0 ) and Ce 4+ (4f 0 5d 0 ), the original Ce 4+ position in the cerium dioxide can be easily replaced by Ce 3+ and stably coexist with Ce 4+ , and the two can be converted into each other. Therefore, the existence of the Ce 4+ / Ce 3+ redox pair can further promote the transfer of electrons as a charge transfer medium, thereby improving the photocatalytic activity. Compared with the carbon nitride monomer material, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has a lower electron-hole recombination rate, a wider light response range, and enhanced stability, and exhibits better photocatalytic performance. The cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has the advantages of strong stability, wide light response range, high electron-hole pair separation efficiency, excellent photocatalytic performance, and environmental friendliness.

[0025] 2、The preparation method of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material of the application first synthesizes cerium dioxide monomers by using cerium salt and nitrogen-containing compounds as raw materials through a hydrothermal-calcination method, and then the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material with excellent electron conduction performance and photocatalytic performance is prepared by directly calcining a mixture of the cerium dioxide, citric acid and urea. The preparation method of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has a simple process flow and is green and environmentally friendly. Meanwhile, the method does not require special equipment and will not affect the crystal form of cerium dioxide, so that the properties of the synthesized material can be ensured unchanged, and the method is suitable for large-scale preparation and is convenient for industrial utilization.

[0026] 3、When the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is used to treat polyvinyl alcohol in water, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material can be uniformly dispersed in the wastewater, showing good dispersibility, so that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material can be ensured to fully contact with the organic pollutants polyvinyl alcohol to be treated. Meanwhile, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material can be separated from the reaction solution through a simple centrifugal process, so that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material can be recycled and reused. In addition, the degradation efficiency of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material on polyvinyl alcohol within 1h is as high as 73.09%, so that the polyvinyl alcohol can be effectively and rapidly degraded.

[0027] In summary, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has the advantages of good dispersibility and easy recycling and reuse, and is a new composite photocatalytic material with excellent photocatalytic performance, environmental friendliness and wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 TEM image of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material prepared in Example 2;

[0029] Figure 2 Degradation effect diagram of polyvinyl alcohol by the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material prepared in Example 1;

[0030] Figure 3 Degradation effect diagram of polyvinyl alcohol by the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material prepared in Example 2 under different water source environments, wherein DW is pure water, TW is tap water, LW is lake water and RW is river water;

[0031] Figure 4 Degradation effect diagram of polyvinyl alcohol by the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material prepared in Example 3 under different ion conditions. DETAILED DESCRIPTION

[0032] The application will be further described in conjunction with the accompanying drawings and specific preferred embodiments of the application, but the protection scope of the application is not limited thereby.

[0033] The materials and instruments used in the following examples are commercially available, and the raw materials are of analytical purity. In the following examples, the obtained data are the average values of three or more repeated tests, unless otherwise specified.

[0034] Example 1

[0035] According to the mass ratio of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material to polyvinyl alcohol in the polyvinyl alcohol solution being 9:1, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is added to the polyvinyl alcohol solution with an initial concentration of 10 mg / L, and stirred in the dark for 30 min, i.e. dark treatment for 30 min. After the adsorption equilibrium of the polyvinyl alcohol is reached, the polyvinyl alcohol solution is subjected to photocatalytic degradation reaction under light irradiation with a wavelength of 420-800 nm at a rotation speed of 800 r / min for 60 min. The polyvinyl alcohol concentration is tested at 0 min, 15 min, 30 min, 45 min and 60 min of the photocatalytic treatment. After the reaction is completed, solid-liquid separation is performed, and the degradation of the polyvinyl alcohol is completed.

[0036] In this example, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material used includes cerium dioxide and nitrogen-doped carbon nitride. The nitrogen-doped carbon nitride material is doped with nitrogen elements, and the cerium dioxide is loaded on the nitrogen-doped carbon nitride material. The mass percentage content of the cerium dioxide in the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is 1.

[0037] In this example, the preparation method of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material includes the following steps:

[0038] I. Preparation of cerium dioxide monomer material

[0039] (1) 6.5 g of cerium carbonate (Ce2(CO3)3) is dissolved in 80 ml of deionized water, and ultrasonic treatment is performed for 10 min to obtain a cerium carbonate solution, wherein the concentration of the cerium carbonate solution is 0.215 mol / L;

[0040] (2) 20 ml of ammonia water is added to the cerium carbonate solution prepared in step (1), and stirring is performed at a rotation speed of 750 r / min for 6 h to obtain a cerium carbonate / ammonia water precursor mixture;

[0041] (3) The cerium carbonate / ammonia water precursor mixture obtained in step (2) is transferred to a reaction kettle, and hydrothermal reaction is performed at 160℃ for 12 h. The obtained product is cooled to room temperature, repeatedly washed with deionized water and ethanol, and dried in a 70℃ oven for 16 h to obtain an alkaline cerium carbonate precursor;

[0042] (4) The basic cerium carbonate precursor obtained in step (3) is transferred to a crucible and placed in a muffle furnace. The temperature is increased to 550°C at a heating rate of 2°C / min and calcined at 550°C for 2 hours. After the calcination is completed, the material is cooled to room temperature and then washed three times with deionized water and anhydrous ethanol respectively. The material is then dried in a forced-air drying oven for 12 hours. After drying, the material is ground for 10 minutes to obtain powder, thus obtaining cerium dioxide nanoparticles.

[0043] II. Preparation of cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic materials:

[0044] (1) Dissolve citric acid (C6H8O7·H2O) in 20 ml of deionized water and stir for 15 min at 600 r / min to obtain citric acid solution; then stir and evaporate the obtained citric acid at 60 °C and 1200 r / min for 4 h to obtain citric acid powder.

[0045] (2) Mix 90mg of cerium dioxide obtained in step (1) with 10mg of citric acid powder obtained in step (2) evenly, add 10g of urea, grind for 40min to obtain cerium dioxide / citric acid / urea precursor;

[0046] (3) The cerium dioxide / citric acid / urea precursor obtained in step (2) is transferred to a crucible and heated to 550°C at a heating rate of 2°C / min. The product is then calcined at 550°C for 3 hours. The product is cooled to room temperature, washed repeatedly with deionized water and ethanol, and dried at 70°C for 16 hours to obtain a cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst material, denoted as CeNCN1. The mass percentage of cerium dioxide in this cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst material is 1%.

[0047] Figure 2 This image shows the degradation effect of polyvinyl alcohol by the cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst (CeNCN1) in Example 1 of this invention. Figure 2 As can be seen, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst of this invention exhibits good photocatalytic effect on polyvinyl alcohol, with a removal rate of 73.09% within 60 minutes. This is partly because nitrogen doping effectively broadens the photoresponse range of the photocatalyst material. On the other hand, since the conduction band position of cerium dioxide is lower than that of carbon nitride, its coupling with carbon nitride can concentrate photogenerated electrons onto cerium dioxide during the reaction, thereby promoting the separation of photogenerated electron-hole pairs. Furthermore, thanks to Ce... 3+ (4f 1 5d 0 ) and Ce 4+ (4f 0 5d0 )Unique electronic structure, Ce 4+ position in cerium dioxide is easy to be replaced by Ce 3+ and Ce 4+ stable and coexist, and can be converted between each other. Therefore, Ce 4+ / Ce 3+ The presence of redox pair can further promote electron transfer as charge transfer medium.

[0048] Example 2

[0049] According to the mass ratio of cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material to polyvinyl alcohol in the polyvinyl alcohol solution is 15:1, 4 parts of cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material are added to four kinds of solutions of polyvinyl alcohol pure water (DW), tap water (TW), lake water (LW), and river water (RW) with an initial concentration of 30 mg / L. Stirring is carried out in the dark for 60 min, i.e. dark treatment for 60 min. After the adsorption equilibrium of polyvinyl alcohol is reached, photocatalytic treatment is carried out under stirring conditions at a speed of 400 r / min and light conditions with a wavelength of 420 nm-850 nm for 90 min. The polyvinyl alcohol concentration is tested at 0 min, 15 min, 30 min, 45 min, 60 min, 75 min, and 90 min of photocatalytic treatment. After the reaction is completed, solid-liquid separation is carried out, and the degradation of polyvinyl alcohol is completed.

[0050] In this embodiment, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material used includes cerium dioxide and nitrogen-doped carbon nitride. The nitrogen-doped carbon nitride material is doped with nitrogen elements, and the cerium dioxide is loaded on the nitrogen-doped carbon nitride material. The mass percentage content of cerium dioxide in the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is 0.5.

[0051] In this embodiment, the preparation method of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material includes the following steps:

[0052] I. Preparation of cerium dioxide monomer material

[0053] (1) Dissolve 5 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) in 70 ml of deionized water, and ultrasonically treat for 5 min to obtain a cerium nitrate solution, wherein the concentration of the cerium nitrate solution is 0.165 mol / L;

[0054] (2) Add 8.2 g of hexamethylenetetramine to the cerium nitrate solution prepared in step (1), and stir at a speed of 650 r / min for 7 h to obtain a cerium nitrate / hexamethylenetetramine precursor mixed solution;

[0055] (3) The cerium nitrate / hexamethylenetetramine precursor mixture obtained in step (2) is transferred to a reaction kettle, and hydrothermal reaction is carried out at 180℃ for 9h. The obtained product is cooled to room temperature, repeatedly washed with deionized water and ethanol, and dried in a 80℃ oven for 12h to obtain the basic cerium carbonate precursor;

[0056] (4) The basic cerium carbonate precursor obtained in step (3) is transferred to a crucible and placed in a muffle furnace, and heated to 600℃ at a heating rate of 5℃ / min, and calcined at 600℃ for 2h. After the calcination is completed and the material is cooled to room temperature, it is washed with deionized water and anhydrous ethanol for three times respectively, and dried in a blast drying oven for 12h. After the drying is completed, the material is ground for 15min to obtain a powder, i.e. cerium dioxide nanoparticles are obtained.

[0057] II. Preparation of cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material:

[0058] (1) Citric acid (C6H8O7·H2O) is dissolved in 20ml deionized water, and stirred at a rotation speed of 600r / min for 15min to obtain a citric acid solution. Then the obtained citric acid is evaporated under stirring at 70℃ and 1100r / min for 5h to obtain citric acid powder;

[0059] (2) 60mg of cerium dioxide obtained in step (1) is uniformly mixed with 15mg of citric acid powder obtained in step (2.1), and 10g of urea is added and ground for 30min to obtain a cerium dioxide / citric acid / urea precursor;

[0060] (3) The cerium dioxide / citric acid / urea precursor obtained in step (2) is transferred to a crucible, heated to 600℃ at a heating rate of 2℃ / min, and calcined at 600℃ for 2h. The obtained product is cooled to room temperature, repeatedly washed with deionized water and ethanol, and dried at 80℃ for 12h to obtain a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, which is recorded as CeNCN2. In the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, the mass percentage of cerium dioxide is 0.5%.

[0061] Figure 3 The figure shows the degradation effect of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material (CeNCN2) in different water source environments on polyvinyl alcohol in Example 2 of the present application, wherein DW is pure water, TW is tap water, LW is lake water, and RW is river water. Figure 3 The ordinate is the ratio of the concentration of polyvinyl alcohol after degradation at a certain time to the initial concentration. From the figure, it can be seen that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material (CeNCN2) has the best degradation effect on polyvinyl alcohol in pure water. Figure 3As can be seen, the removal rates of the prepared cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material (CeNCN2) on polyvinyl alcohol in pure water, tap water, lake water and river water are 86.39%, 80.93%, 68.61% and 69.89% respectively, which indicates that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material has high photocatalytic performance on polyvinyl alcohol in different water environments and can effectively degrade polyvinyl alcohol in different water environments, and also indicates that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material can be widely used for treating polyvinyl alcohol in different water environments, has good application prospect in the field of photocatalysis and has good practical availability.

[0062] Example 3

[0063] According to the mass ratio of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material to polyvinyl alcohol in the polyvinyl alcohol solution of 12:1, 5 portions of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material are added into the polyvinyl alcohol solution containing SO4 2- , CO3 2- , Cl - , NO3 - (the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 20 mg / L, and the concentrations of SO4 2- , CO3 2- , Cl - , NO3 - are 0.5 mmol / L) to stir for 30 min in the dark, i.e. dark treatment for 30 min, and then the photocatalytic degradation reaction is carried out under the stirring condition of 1000 r / min and the light irradiation condition of 420 nm-800 nm for 60 min, the polyvinyl alcohol concentration is measured at 0 min, 15 min, 30 min, 45 min and 60 min of the photocatalytic treatment, and the degradation of polyvinyl alcohol is completed after the reaction is completed.

[0064] In this embodiment, the used cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material includes cerium dioxide and nitrogen-doped carbon nitride, wherein the nitrogen-doped carbon nitride material is doped with nitrogen element in carbon nitride, and the cerium dioxide is loaded on the nitrogen-doped carbon nitride material, and the mass percentage content of cerium dioxide in the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material is 1.5%.

[0065] In this embodiment, the preparation method of the used cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material includes the following steps:

[0066] I. Preparation of cerium dioxide monomer material

[0067] (1) Dissolve 1.5 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) in 30 ml of deionized water, and ultrasonically treat for 15 min to obtain a cerium nitrate solution, wherein the concentration of the cerium nitrate solution is 0.165 mol / L;

[0068] (2) Add 2.8 g of hexamethylenetetramine to the cerium nitrate solution obtained in step (1), and stir at a rotation speed of 800 r / min for 5 h to obtain a cerium nitrate / hexamethylenetetramine precursor mixed solution.

[0069] (3) Transfer the cerium nitrate / hexamethylenetetramine precursor mixed solution obtained in step (2) into a reaction kettle, and hydrothermally react at 140℃ for 15 h. The obtained product is cooled to room temperature, repeatedly washed with deionized water and ethanol, and dried in a 60℃ oven for 20 h to obtain a basic cerium carbonate precursor;

[0070] (4) Transfer the basic cerium carbonate precursor obtained in step (3) into a crucible, and place it in a muffle furnace. Heat it to 500℃ at a heating rate of 5℃ / min, and calcine at 500℃ for 4 h. After the calcination is completed and the material is cooled to room temperature, wash it with deionized water and anhydrous ethanol for three times respectively, and dry it in a blast drying oven for 12 h. After the drying is completed, grind the material for 20 min to obtain a powder, i.e. cerium dioxide nanoparticles.

[0071] II. Preparation of cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material:

[0072] (1) Dissolve citric acid (C6H8O7·H2O) in 20 ml of deionized water, and stir at a rotation speed of 600 r / min for 15 min to obtain a citric acid solution. Then evaporate the obtained citric acid at 80℃ under stirring at 1000 r / min for 6 h to obtain citric acid powder;

[0073] (2) Mix 120 mg of cerium dioxide obtained in step (1) with 5 mg of citric acid powder obtained in step (2.1) uniformly, add 10 g of urea, and grind for 20 min to obtain a cerium dioxide / citric acid / urea precursor;

[0074] (3) Transfer the cerium dioxide / citric acid / urea precursor obtained in step (2) into a crucible, heat it to 500℃ at a heating rate of 5℃ / min, and calcine at 500℃ for 4 h. The obtained product is cooled to room temperature, repeatedly washed with deionized water and ethanol, and dried at 60℃ for 20 h to obtain a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, which is recorded as CeNCN3. In the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, the mass percentage of cerium dioxide is 1.5.

[0075] Figure 4The graph shows the degradation effect of cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst (CeNCN3) on polyvinyl alcohol under different ionic conditions in Example 3 of this invention. Figure 4 In the graph, the vertical axis represents the ratio of the concentration of polyvinyl alcohol after degradation to its initial concentration at a certain moment. From... Figure 4 As can be seen from the above, the cerium dioxide-nitrogen-doped carbon nitride composite photocatalyst material prepared by this invention exhibits good performance in deionized water and in water containing SO4. 2- CO3 2- Cl - NO3 - The removal rates of polyvinyl alcohol (PVA) in water bodies were 71.07%, 65.83%, 73.66%, and 66.41%, respectively. This was excluding Cu, which competes with PVA. 2+ In addition, all of them exhibited highly efficient photocatalytic performance, which indicates that the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material of the present invention has good practical applicability.

[0076] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material, characterized in that, The photocatalytic material comprises cerium dioxide and nitrogen-doped carbon nitride, the cerium dioxide is in a sheet structure, and the mass percentage of the cerium dioxide in the photocatalytic material is 0.5-1.5 %; The preparation method comprises the following steps: S1, dissolving cerium salt in deionized water, adding a nitrogen-containing compound, ultrasonicating, and stirring to obtain a cerium salt precursor; S2, performing hydrothermal reaction on the cerium salt precursor obtained in step S1 to obtain cerium carbonate hydroxide slurry, cooling and removing supernatant, and then washing, filtering, and drying the remaining slurry to obtain a cerium carbonate hydroxide precursor; S3, calcining, grinding the cerium carbonate hydroxide precursor obtained in step S2 to obtain cerium dioxide nanoparticles; S4, mixing citric acid with deionized water, constant-temperature stirring until the water evaporates to obtain citric acid powder; S5, mixing the cerium dioxide nanoparticles obtained in step S3 with the citric acid powder obtained in step S4, adding urea, grinding, calcining, washing, filtering, and drying to obtain a cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material. 2.The ceria-carbon nitride composite photocatalytic material according to claim 1, characterized in that, In step S1, the cerium salt is cerium nitrate hexahydrate, and the nitrogen-containing compound is hexamethylenetetramine, or the cerium salt is cerium carbonate, and the nitrogen-containing compound is ammonia water; The mass ratio of the cerium salt to the nitrogen-containing compound is 1:1.5-2.5; The ultrasonicating time is 5-15 min; The stirring is performed at a rotating speed of 600-800 r / min, and the stirring time is 5-7 h. 3.The CeO 2 -C 3 N 4 composite photocatalytic material according to claim 1, characterized in that, In step S2, the hydrothermal reaction temperature is 140-180 ℃, and the hydrothermal reaction time is 9-15 h; The drying temperature is 60-80 ℃, and the drying time is 12-20 h. 4.The ceria-carbon nitride composite photocatalytic material according to claim 2, characterized in that, In step S3, the calcining temperature is 500-600 ℃, the heating rate is 2-5 ℃ / min, and the calcining time is 2-4 h; The grinding time is 10-20 min.

5. The CeO2-C3N4 composite photocatalytic material according to claim 2, characterized in that, In step S4, the constant-temperature stirring temperature is 60-70 ℃, the time is 4-6 h, and the stirring rotating speed is 1000-1200 r / min; The dosage ratio of citric acid to deionized water is 1 g:20 ml. 6.The CeO 2 -C 3 N 4 composite photocatalytic material of claim 2, wherein, In step S5, the mass ratio of cerium dioxide, citric acid powder, and urea is 6-12:0.5-1.5:100; The calcining temperature is 500-600 ℃, the heating rate in the calcining process is 2-5 ℃ / min, and the calcining time is 2-4 h; The grinding time is 20-40 min; The drying temperature is 60-80 ℃, and the drying time is 12-20 h.

7. The use of the ceria-nitrogen-doped carbon nitride composite photocatalytic material according to any one of claims 1-6 in the treatment of polyvinyl alcohol in water, characterized in that, The application method comprises the following steps: mixing the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material with polyvinyl alcohol-containing wastewater and performing dark treatment, and then performing photocatalytic degradation reaction under light irradiation after adsorption saturation.

8. Use according to claim 7, characterized in that, The concentration of polyvinyl alcohol in the polyvinyl alcohol-containing wastewater is 10-30 mg / L; The mass ratio of the cerium dioxide-nitrogen-doped carbon nitride composite photocatalytic material to polyvinyl alcohol is 9-15:

1.

9. Use according to claim 7, characterized in that, The dark treatment is stirring in the dark for 30-60 min; The photocatalytic degradation reaction is carried out under stirring at a rotating speed of 400-1000 r / min, the photocatalytic degradation reaction is carried out under light irradiation at a wavelength of 420-850 nm, and the photocatalytic degradation reaction is carried out for 60-90 min.

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