Photocatalyst, its production method and application in tetracycline wastewater treatment

Abstract

The application provides a production method of a photocatalyst, and steps are as follows: tetrabutyl titanate and anhydrous ethanol are mixed into an ester alcohol mixed solution; calcium carbonate is used to prepare a calcium carbonate solution by mixing with an ethanol aqueous solution, the calcium carbonate solution is added dropwise into the ester alcohol mixed solution for reaction, and after filtration, drying and calcination, calcium titanate-titanium dioxide composite microparticles are obtained; rare earth waste residues are calcined and ground to obtain waste residue powder, the waste residue powder is leached and filtered by using dilute sulfuric acid to obtain a leaching solution; the leaching solution is extracted, the raffinate is precipitated by using oxalic acid, and after filtration, a modified solution is obtained; the calcium titanate-titanium dioxide composite microparticles are put into the modified solution, and after drying and calcination, the photocatalyst is obtained. The application also discloses the catalyst prepared by using the method and application of the catalyst in tetracycline wastewater treatment. The application reduces pollution to the environment, widens the type of titanium photocatalysts, and the photocatalyst has high degradation efficiency on tetracycline wastewater.

Description

Technical Field

[0001] This invention relates to a photocatalyst, its production method, and its application in tetracycline wastewater treatment. Background Technology

[0002] With the continuous development of industrial production, the application of rare earth elements is becoming increasingly widespread. Along with the expanding processing volume, a large amount of rare earth waste is generated. Statistics show that processing one ton of Bayan Obo rare earth concentrate produces over 0.6 tons of rare earth waste. This waste contains no more than 0.5 wt% thorium oxide and more than 3-6 wt% rare earth elements. Currently, this waste is stored in designated slag pits, causing environmental pollution and preventing the recycling of valuable rare earth elements, resulting in significant waste. Therefore, reducing the volume of rare earth waste and extracting and recovering rare earth elements is of great practical significance. Although there are many methods for recovering rare earth elements, the similar properties of iron and rare earth elements increase the difficulty of separation and extraction. Furthermore, due to the solubility product of insoluble substances, even deep recycling of adsorbed waste cannot completely remove rare earth elements, ultimately causing significant adverse environmental impacts from the discharged rare earth waste. Summary of the Invention

[0003] To reduce the environmental impact of rare earth waste and recover valuable metals from it, this application first proposes a method for producing a photocatalyst, which includes the following steps:

[0004] (1) Tetrabutyl titanate and anhydrous ethanol are mixed evenly to form an ester-alcohol mixture;

[0005] (2) Calcium carbonate powder is added to an ethanol aqueous solution to form a calcium carbonate solution with a concentration of 3-5 wt%. Then, the calcium carbonate solution is added dropwise to the ester-alcohol mixture. After reacting at 30-50℃ for 20-30 h, the mixture is filtered. After drying the filter residue, the filter residue is calcined at 700-800℃ for 2-3 h. After cooling and washing, calcium titanate-titanium dioxide composite particles are obtained. The ethanol aqueous solution is composed of distilled water and anhydrous ethanol in a volume ratio of 1:(3-5).

[0006] (3) After roasting the rare earth waste residue at 500-600℃ for 2-3 hours, grind it to obtain waste residue powder. Use dilute sulfuric acid to leach the waste residue powder, filter it, and obtain leachate. The mass ratio of rare earth waste residue to tetrabutyl titanate is 1:1.

[0007] (4) Add an extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth remain in the first raffinate. Use primary amine N1923 to extract thorium from the first raffinate. Thorium enters the primary amine N1923, while trivalent rare earth remains in the second raffinate.

[0008] Oxalic acid is added to the second raffinate to form rare earth oxalate precipitate, which is then filtered to obtain rare earth oxalate and rare earth filtrate. Alkali solution is added dropwise to the rare earth filtrate to bring its pH to 7-8, which is then used as a modification solution.

[0009] (5) The calcium titanate-titanium dioxide composite particles are added to the modification liquid to form a mixture. The mixture is evaporated and dried to obtain the catalyst precursor. The catalyst precursor is calcined, cleaned, dried and ground to obtain the photocatalyst.

[0010] In step (2), the drying temperature for the filter residue is 80-200℃, and the drying time is 10-20h. The preferred particle size of calcium carbonate is 1250-2000 mesh. After grinding the photocatalyst, the particle size is controlled at 800-1500 mesh. In step (4), the alkaline solution can be prepared using materials such as sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate. In step (5), distilled water or deionized water is used for cleaning, and the drying temperature is controlled at 80-150℃ for 3-5h.

[0011] In this application, titanium dioxide is deposited on the surface of calcium carbonate particles, followed by calcination. This allows some of the titanium dioxide to react with the calcium carbonate to form calcium titanate, thus creating a composite structure of calcium titanate and titanium dioxide. Since calcium titanate has a typical perovskite structure, it possesses a large internal space. Furthermore, during calcination, the carbon dioxide produced by the decomposition of calcium carbonate leaves pores on the composite particles, facilitating the absorption of rare earth elements from the modification solution. During calcination, calcium carbonate first reacts with the titanium dioxide on its surface to form calcium titanate, creating a calcium titanate shell. Due to the obstruction of this shell, titanium dioxide particles farther from the calcium carbonate adhere to its surface. Because calcium titanate and titanium dioxide are deeply integrated, forming a fused composite structure, calcium carbonate decomposes and reacts with titanium dioxide to produce calcium titanate. Some of the larger calcium carbonate particles only decompose into calcium oxide in their center and do not participate in the reaction to form calcium titanate. They are removed in the subsequent washing process. The resulting pores can be used to absorb rare earth elements in the modified liquid. After forming a photocatalyst, it can also serve as a cavity for adsorbing harmful substances in wastewater.

[0012] In processing rare earth waste residue, the residue is first roasted to activate the metal elements. Then, it is leached with dilute sulfuric acid, and the metal elements in the leachate are recovered. Finally, the remaining filtrate is used as a modified liquid to produce a photocatalyst. After recovery, the rare earth filtrate still contains trace amounts of thorium and rare earth elements, as well as other symbiotic elements, such as oxides of silicon, titanium, lead, zirconium, calcium, iron, magnesium, sodium, and aluminum. Except for titanium, these elements simultaneously participate in the modification of calcium titanate and titanium dioxide in the calcium titanate-titanium dioxide composite particles. During the subsequent roasting process, these elements undergo elemental substitution of calcium titanate and titanium dioxide, forming a doped structure. The rare earth elements, in their reaction with titanium dioxide and calcium titanate, form a complex doped structure, exhibiting excellent photocatalytic degradation effects on tetracycline.

[0013] Because the aforementioned elements accumulate together in the same mineral, they can replace each other like particles in the mineral lattice without changing the mineral structure. These elements are usually not the main and stable components in the mineral lattice, but rather, due to their crystallization chemical properties being similar to those of a major element in the mineral, they enter the mineral lattice as minor or trace elements under certain conditions. After entering the mineral lattice, these elements do not change the crystal structure of the mineral. Therefore, trace elements in the same mineral can dope the same crystal to different degrees, forming a co-doped structure.

[0014] However, some of the aforementioned metallic elements may not combine with titanium dioxide in the form of doping. For example, SiO2 and ZrO2, these two oxides are insulators and may mainly act as carriers to increase the pore size and specific surface area of ​​the photocatalyst. A small number of TiO2 molecules will adsorb on the surface of SiO2 or ZrO2 to form composite grains, thereby increasing the contact area with tetracycline and thus improving the degradation effect of tetracycline. Other elements, as symbiotic elements, have similar properties in certain aspects and can dope titanium dioxide in multiple ways. For example, calcium, iron, magnesium, aluminum, lanthanum, and cerium can all dope titanium dioxide, thereby introducing defects or changing the crystallinity in CaTiO3 and TiO2, thus changing the structure and surface properties of the particles. This not only affects the recombination rate of electron-hole pairs but also expands the absorption wavelength range of CaTiO3 and TiO2 into the visible light region, promoting the separation of photogenerated electrons and holes, improving the efficiency of light energy conversion and utilization, and ultimately enhancing the activity of the photocatalyst.

[0015] Because the calcium titanate-titanium dioxide composite microparticles contain numerous pores, they can adsorb harmful substances in wastewater, effectively improving photocatalytic efficiency. When using the photocatalyst provided in this application to degrade tetracycline in wastewater, when the tetracycline concentration is below 30 mg / L and the amount of photocatalyst is 16 times the total amount of tetracycline, the degradation rate of tetracycline can reach over 98% within 120 minutes, demonstrating high degradation efficiency. This application not only reduces environmental pollution but also provides a novel structure for a photocatalyst doped with calcium titanate-titanium dioxide composites, broadening the types of titanium-based photocatalysts.

[0016] Specifically, in order to fully disperse tetrabutyl titanate and form a chelate, in step (1), the mass ratio of tetrabutyl titanate to anhydrous ethanol is 1:(3-5).

[0017] Specifically, in order to ensure the formation of a complete calcium titanate shell and to ensure the content of titanium dioxide, in step (2), the mass ratio of calcium carbonate to tetrabutyl titanate is 1:(6-8).

[0018] Specifically, for proper use of the production method in this application, the rare earth waste residue contains, by oxides, 0.3-0.5 wt% ThO2, 2.8-3.3 wt% CeO2, 1.1-2.5 wt% TiO2, 1.5-2.1 wt% P2O5, 1.3-1.7 wt% La2O3, and 0.5-0.6 wt% Pr6O2. 11 The rare earth tailings containing the above composition can effectively recover rare earth elements and remove thorium, and can form a photocatalyst with good photocatalytic effect.

[0019] Specifically, in order to remove thorium and rare earth elements from rare earth waste residue as much as possible, in step (3), the leaching temperature is 25-40℃, the concentration of dilute sulfuric acid is 0.45-0.55mol / L, 4-6mL of dilute sulfuric acid is used for leaching per gram of waste residue powder, and the leaching time is 5-8h.

[0020] Specifically, in step (4), the volume ratio of extractant P923 to TBP is 100:(5-10), the volume ratio of extract to leachate is (2-4):1; the volume ratio of primary amine N1923 to the first raffinate is (2-3):1; the mass ratio of rare earth waste residue to oxalic acid is 1:(1-1.5), and the oxalic acid concentration is 9-12wt%. Under the above conditions, thorium can be successfully separated and processed separately, reducing the difficulty of separation.

[0021] Specifically, in order to facilitate the replacement of rare earth elements with some titanium elements to form a doped structure, in step (5), when the catalyst primary body is calcined, the calcination temperature is 400-500℃ and the calcination time is 2-3h.

[0022] Secondly, this application also discloses photocatalysts prepared using any of the above-described production methods.

[0023] Furthermore, this application also discloses the application of the aforementioned photocatalyst in the treatment of tetracycline wastewater. Specifically, the concentration of tetracycline in the wastewater is 1-35 mg / L, and the concentration of the photocatalyst in the wastewater is 0.16-0.64 g / L.

[0024] When using the photocatalyst provided in this application to degrade tetracycline in wastewater, when the concentration of tetracycline is less than 50 mg / L, and the amount of photocatalyst is 10 times the total amount of tetracycline, the degradation rate of tetracycline can reach more than 97% within 120 minutes, which has a high degradation efficiency. Attached Figure Description

[0025] Figure 1 This is a SEM image of the calcium titanate-titanium dioxide composite microparticles obtained in Example 1.

[0026] Figure 2 This is the XRD pattern of the calcium titanate-titanium dioxide composite microparticles obtained in Example 1.

[0027] Figure 3 This is the EDS image of the photocatalyst obtained in Example 1. Detailed Implementation

[0028] Example 1

[0029] Production of #1 photocatalyst:

[0030] (1) Mix 5g of tetrabutyl titanate and 20g of anhydrous ethanol evenly to form an ester-alcohol mixture;

[0031] (2) 0.7g of calcium carbonate with a particle size of 1500 mesh was added to an ethanol aqueous solution and stirred evenly to form a calcium carbonate solution with a concentration of 4wt%. Then the calcium carbonate solution was added dropwise to the ester alcohol mixture and reacted at 40℃ for 25h. After filtration, the filter residue was dried at 100℃ for 15h and then calcined at 700℃ for 3h. After the material was cooled to room temperature, it was washed with distilled water to obtain calcium titanate-titanium dioxide composite particles. The ethanol aqueous solution was composed of distilled water and anhydrous ethanol with a volume ratio of 1:4.

[0032] (3) After calcining 5g of rare earth waste residue at 550℃ for 2.5h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 30℃ for 6h, filter, and obtain leachate. Use 5mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0033] Based on oxides, the rare earth waste residue contains 0.42 wt% ThO2, 3.1 wt% CeO2, 2.1 wt% TiO2, 1.8 wt% P2O5, 1.5 wt% La2O3, and 0.52 wt% Pr6O. 11 0.98wt% Nd2O3, 0.24wt% ZrO2.

[0034] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add sodium hydroxide solution dropwise to the rare earth filtrate at a pH of 7.1 as a modification solution.

[0035] The volume ratio of extractant P923 to TBP in the extract is 100:8; the volume ratio of extract to leachate is 3:1; the volume ratio of primary amine N1923 to the first raffinate is 2:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.2, and the oxalic acid concentration is 10wt%.

[0036] Thorium and rare earth oxalates that enter organic cerium, primary amine N1923 can all be recovered and refined. In the following examples, the same method is used to recover cerium, thorium and other rare earths.

[0037] The rare earth filtrate contained 4.2 mg Th, 2.2 mg Ce, 1.5 mg La, 0.9 mg Pr, and 1.3 mg Nd. The recoveries of Th, Ce, La, Pr, and Nd were over 77%, 98%, 97%, 95%, and 96%, respectively.

[0038] (5) The calcium titanate-titanium dioxide composite microparticles were added to the modification liquid to form a mixture. The mixture was evaporated and dried to obtain the catalyst precursor. The catalyst precursor was calcined at 400℃ for 2.5h, cooled, washed three times with distilled water, dried at 90℃ for 5h, and then ground to 900 mesh to obtain the photocatalyst.

[0039] Example 2

[0040] Production of photocatalyst #2:

[0041] (1) Mix 5g of tetrabutyl titanate and 15g of anhydrous ethanol evenly to form an ester-alcohol mixture;

[0042] (2) 0.8g of calcium carbonate with a particle size of 1250 mesh was added to an ethanol aqueous solution and stirred evenly to form a calcium carbonate solution with a concentration of 3wt%. Then the calcium carbonate solution was added dropwise to the ester alcohol mixture and reacted at 50℃ for 20h. After filtration, the filter residue was dried at 150℃ for 14h and then calcined at 800℃ for 2h. After the material was cooled to room temperature, it was washed with distilled water to obtain calcium titanate-titanium dioxide composite particles. The ethanol aqueous solution was composed of distilled water and anhydrous ethanol with a volume ratio of 1:4.

[0043] (3) After calcining 5g of rare earth waste residue at 500℃ for 3h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 25℃ for 7h, filter, and obtain leachate. Use 6mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0044] Based on oxides, the rare earth waste residue contains 0.35 wt% ThO2, 3.3 wt% CeO2, 1.5 wt% TiO2, 1.5 wt% P2O5, 1.6 wt% La2O3, and 0.55 wt% Pr6O. 11 0.91wt% Nd2O3, 0.27wt% ZrO2.

[0045] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add sodium carbonate solution dropwise to the rare earth filtrate at a pH of 7.3 as a modification solution.

[0046] The volume ratio of extractant P923 to TBP in the extract is 100:5; the volume ratio of extract to leachate is 4:1; the volume ratio of primary amine N1923 to the first raffinate is 2.5:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.3, and the oxalic acid concentration is 12wt%.

[0047] The rare earth filtrate contained 3.8 mg Th, 2.5 mg Ce, 1.5 mg La, 0.8 mg Pr, and 1.4 mg Nd. The recoveries of Th, Ce, La, Pr, and Nd were over 75%, 98%, 97%, 96%, and 96%, respectively.

[0048] (5) The calcium titanate-titanium dioxide composite microparticles were added to the modification liquid to form a mixture. The mixture was evaporated and dried to obtain the catalyst precursor. The catalyst precursor was calcined at 500℃ for 2 hours, cooled, washed 4 times with distilled water, dried at 120℃ for 3 hours, and then ground to 1500 mesh to obtain the photocatalyst.

[0049] Example 3

[0050] Production of photocatalyst #3:

[0051] (1) Mix 5g of tetrabutyl titanate and 25g of anhydrous ethanol evenly to form an ester-alcohol mixture;

[0052] (2) 0.63g of calcium carbonate with a particle size of 2000 mesh was added to an ethanol aqueous solution and stirred evenly to form a calcium carbonate solution with a concentration of 5wt%. Then the calcium carbonate solution was added dropwise to the ester alcohol mixture and reacted at 30℃ for 30h. After filtration, the filter residue was dried at 200℃ for 10h and then calcined at 750℃ for 3h. After the material was cooled to room temperature, it was washed with distilled water to obtain calcium titanate-titanium dioxide composite particles. The ethanol aqueous solution was composed of distilled water and anhydrous ethanol with a volume ratio of 1:5.

[0053] (3) After calcining 5g of rare earth waste residue at 600℃ for 2h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 40℃ for 5h, filter, and obtain leachate. Use 4mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0054] Based on oxides, the rare earth waste residue contains 0.48 wt% ThO2, 2.9 wt% CeO2, 2.4 wt% TiO2, 2.0 wt% P2O5, 1.6 wt% La2O3, and 0.56 wt% Pr6O. 11 0.95wt% Nd2O3, 0.26wt% ZrO2.

[0055] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add potassium hydroxide solution dropwise to the rare earth filtrate at a pH of 7.9 as a modification solution.

[0056] The volume ratio of extractant P923 to TBP in the extract is 100:10; the volume ratio of extract to leachate is 3:1; the volume ratio of primary amine N1923 to the first raffinate is 3:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.1, and the oxalic acid concentration is 11wt%.

[0057] The rare earth filtrate contained 4.4 mg Th, 2.1 mg Ce, 1.6 mg La, 1.0 mg Pr, and 1.1 mg Nd. The recoveries of Th, Ce, La, Pr, and Nd were over 79%, 98%, 97%, 95%, and 97%, respectively.

[0058] (5) The calcium titanate-titanium dioxide composite microparticles were added to the modification liquid to form a mixture. The mixture was evaporated and dried to obtain the catalyst precursor. The catalyst precursor was calcined at 450°C for 3 hours, cooled, washed three times with distilled water, dried at 150°C for 3 hours, and then ground to 1000 mesh to obtain the photocatalyst.

[0059] Example 4

[0060] Production of photocatalyst #4:

[0061] (1) Mix 5g of tetrabutyl titanate and 20g of anhydrous ethanol evenly to form an ester-alcohol mixture;

[0062] (2) 0.74 g of calcium carbonate with a particle size of 1250 mesh was added to an ethanol aqueous solution and stirred evenly to form a calcium carbonate solution with a concentration of 4 wt%. Then, the calcium carbonate solution was added dropwise to the ester alcohol mixture and reacted at 35°C for 25 h. After filtration, the filter residue was dried at 80°C for 20 h and then calcined at 730°C for 2.5 h. After the material was cooled to room temperature, it was washed with distilled water to obtain calcium titanate-titanium dioxide composite particles. The ethanol aqueous solution was composed of distilled water and anhydrous ethanol in a volume ratio of 1:3.

[0063] (3) After calcining 5g of rare earth waste residue at 520℃ for 3h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 35℃ for 8h, filter, and obtain leachate. Use 6mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0064] Based on oxides, the rare earth waste residue contains 0.31 wt% ThO2, 3.0 wt% CeO2, 1.8 wt% TiO2, 1.6 wt% P2O5, 1.7 wt% La2O3, and 0.59 wt% Pr6O. 11 1.1wt% Nd2O3, 0.29wt% ZrO2.

[0065] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add sodium bicarbonate solution dropwise to the rare earth filtrate at pH 7.5 as a modification solution.

[0066] The volume ratio of extractant P923 to TBP in the extract is 100:6; the volume ratio of extract to leachate is 2:1; the volume ratio of primary amine N1923 to the first raffinate is 3:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.5, and the oxalic acid concentration is 9wt%.

[0067] The rare earth filtrate contained 3.2 mg Th, 3.1 mg Ce, 1.4 mg La, 0.7 mg Pr, and 1.5 mg Nd. The recoveries of Th, Ce, La, Pr, and Nd were over 76%, 97%, 97%, 97%, and 96%, respectively.

[0068] (5) The calcium titanate-titanium dioxide composite microparticles were added to the modification liquid to form a mixture. The mixture was evaporated and dried to obtain the catalyst precursor. The catalyst precursor was calcined at 480℃ for 2.1h, cooled, washed 5 times with distilled water, dried at 120℃ for 4h, and then ground to 1250 mesh to obtain the photocatalyst.

[0069] Comparative Example 1

[0070] Preparation of photocatalyst #5:

[0071] (1) Add 5g tetrabutyl titanate to 20g anhydrous ethanol, then add 1g glacial acetic acid, and add 3mol / L hydrochloric acid dropwise to make the pH of the solution 2.5-3. Mix well to obtain solution A.

[0072] Add 20 mL of an ethanol aqueous solution dropwise to solution B while stirring to obtain a sol; the volume ratio of anhydrous ethanol to distilled water in the ethanol aqueous solution is 3:1.

[0073] (2) The sol was aged at room temperature for 24 h to obtain a gel, which was then dried at 80 °C for 6 h and calcined at 400 °C for 4 h to obtain photocatalyst #5. This comparative example uses the method of Example 1 to prepare pure TiO2 photocatalyst without dopants.

[0074] Comparative Example 2

[0075] Preparation of photocatalyst #6:

[0076] (1) Add 5g tetrabutyl titanate to 20g anhydrous ethanol, then add 1g glacial acetic acid, and add 3mol / L hydrochloric acid dropwise to make the pH of the solution 2.5-3. Mix well to obtain solution A.

[0077] Add 20 mL of an ethanol aqueous solution dropwise to solution B while stirring to obtain a sol; the volume ratio of anhydrous ethanol to distilled water in the ethanol aqueous solution is 3:1.

[0078] (2) The sol was aged at room temperature for 24 hours to obtain a gel, the gel was dried at 80°C for 20 hours, and then the gel was calcined at 400°C for 4 hours to obtain pure TiO2.

[0079] (3) After calcining 5g of rare earth waste residue at 550℃ for 2.5h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 30℃ for 6h, filter, and obtain leachate. Use 5mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0080] Based on oxides, the rare earth waste residue contains 0.42 wt% ThO2, 3.1 wt% CeO2, 2.1 wt% TiO2, 1.8 wt% P2O5, 1.5 wt% La2O3, and 0.52 wt% Pr6O. 11 0.98wt% Nd2O3, 0.24wt% ZrO2.

[0081] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add sodium hydroxide solution dropwise to the rare earth filtrate at a pH of 7.1 as a modification solution.

[0082] The volume ratio of extractant P923 to TBP in the extract is 100:8; the volume ratio of extract to leachate is 3:1; the volume ratio of primary amine N1923 to the first raffinate is 2:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.2, and the oxalic acid concentration is 10wt%.

[0083] (5) Pure TiO2 is added to the modification liquid to form a mixture. The mixture is evaporated and dried to obtain the catalyst precursor. The catalyst precursor is calcined at 400℃ for 2.5h, cooled, washed 3 times with distilled water, dried at 90℃ for 5h, and then ground to 900 mesh to obtain the photocatalyst.

[0084] Comparative Example 3

[0085] Preparation of photocatalyst #7:

[0086] Calcium titanate was prepared using the sol-gel method. 20g of anhydrous ethanol was added to 5g of tetrabutyl titanate, and the mixture was stirred. Then, 0.4g of anhydrous citric acid was added until the citric acid was completely dissolved to obtain solution A. 2.42g of calcium nitrate was dissolved in deionized water to obtain solution B. Solutions A and B were mixed and stirred until a transparent gel was formed. The gel was then dried at 130℃ for 5 hours and calcined at 750℃ for 7 hours. The resulting powder was calcium titanate.

[0087] Comparative Example 4

[0088] Preparation of photocatalyst #8:

[0089] (1) Calcium titanate was prepared by sol-gel method. 20g of anhydrous ethanol was added to 5g of tetrabutyl titanate and stirred with a stirrer. Then 0.4g of anhydrous citric acid was added until the citric acid was completely dissolved to obtain solution A. 2.42g of calcium nitrate was dissolved in deionized water to obtain solution B. Solution A and solution B were mixed and stirred until a transparent gel was formed. Then the gel was dried at 130℃ for 5h and calcined at 750℃ for 7h. The resulting powder was calcium titanate.

[0090] (2) After calcining 5g of rare earth waste residue at 550℃ for 2.5h, grind it to 800 mesh to obtain waste residue powder. Then, leach the waste residue powder with 0.5mol / L dilute sulfuric acid at 30℃ for 6h, filter, and obtain leachate. Use 5mL of dilute sulfuric acid per gram of waste residue powder for leaching.

[0091] Based on oxides, the rare earth waste residue contains 0.42 wt% ThO2, 3.1 wt% CeO2, 2.1 wt% TiO2, 1.8 wt% P2O5, 1.5 wt% La2O3, and 0.52 wt% Pr6O. 11 0.98wt% Nd2O3, 0.24wt% ZrO2.

[0092] (4) Add the extractant formed by extractant P923 and TBP to the leachate. Cerium ions enter the organic phase, while thorium and trivalent rare earth elements remain in the first raffinate. Extract the thorium in the first raffinate with primary amine N1923. The thorium enters the primary amine N1923, while the trivalent rare earth elements remain in the second raffinate. Add oxalic acid to the second raffinate to form a rare earth oxalate precipitate. Filter to obtain rare earth oxalate and rare earth filtrate. Add sodium hydroxide solution dropwise to the rare earth filtrate at a pH of 7.1 as a modification solution.

[0093] The volume ratio of extractant P923 to TBP in the extract is 100:8; the volume ratio of extract to leachate is 3:1; the volume ratio of primary amine N1923 to the first raffinate is 2:1; the mass ratio of rare earth waste residue to oxalic acid is 1:1.2, and the oxalic acid concentration is 10wt%.

[0094] (5) Add calcium titanate to the modification solution to form a mixture. After evaporating and drying the mixture, the catalyst precursor is obtained. The catalyst precursor is calcined at 400°C for 2.5 hours, cooled, washed three times with distilled water, dried at 90°C for 5 hours, and then ground to 900 mesh to obtain the photocatalyst.

[0095] Comparative Example 5

[0096] Preparation of photocatalyst #9:

[0097] This comparative example is basically the same as Example 1, except that the amount of rare earth waste residue used is 7g.

[0098] Comparative Example 6

[0099] Preparation of photocatalyst #10:

[0100] This comparative example is basically the same as the example, except for the amount of rare earth waste residue used. In this comparative example, the amount of rare earth waste residue used is 4g.

[0101] Please see Figure 2 , Figure 2 The image shows the XRD pattern of the calcium titanate-titanium dioxide composite microparticles prepared in Example 1, indicating a composite structure of TiO2 and calcium titanate, with TiO2 exhibiting a composite crystal form of anatase and rutile. Figure 2 The diffraction peaks in the spectrum are not very sharp, indicating that the calcium titanate-titanium dioxide composite microparticles are very small, resulting in a very small photocatalyst particle size. Please refer to [link / reference]. Figure 3 The EDS diagram of the photocatalyst obtained in Example 1 is derived from... Figure 3 It is known that in addition to Th, Ce, Ti, La, Pr and Nd elements, trace amounts of Si and Zr elements are also present in the photocatalyst, indicating that the photocatalyst prepared in this application is a multi-element co-doped material.

[0102] Degradation effect test:

[0103] In this invention, the photocatalytic efficiency of the photocatalyst is evaluated by observing the degradation of the tetracycline solution. First, 100 mL of tetracycline solution (40 mg / L) is poured into a jacketed beaker, and 50 mg of photocatalyst is added. The mixture is stirred in a dark room for 30 min to establish an adsorption-desorption equilibrium through a dark reaction.

[0104] Then, turn on the 300W xenon lamp located 25cm above the jacketed beaker, and simultaneously start the circulating water pump connected to the jacketed beaker to keep the solution inside the jacketed beaker at room temperature, so as to avoid the thermal effect from affecting the photocatalytic performance of the sample.

[0105] Every 30 minutes, 5 ml of sample was extracted from the suspension and then filtered through a 0.22 μm filter membrane to obtain a clear solution. The clear solution was then analyzed using a spectrophotometer to measure the absorbance of the liquid, thus providing the photocatalytic efficiency of the photocatalyst. The photocatalytic efficiency was calculated using the following formula:

[0106] (C0-C) / C0×100%, where C is the concentration of tetracycline in the supernatant at a certain time point, and C0 is the initial concentration of tetracycline at the beginning of the reaction.

[0107] Using the above method, the degradation efficiency of photocatalysts 1-10 was measured. Photocatalysts 1-4 showed good catalytic degradation effects. After 120 minutes of illumination, the degradation efficiency of photocatalyst 1 was 97.4%, 2 was 97.2%, 3 was 97.1%, 4 was 96.9%, 5 was 58.6%, 6 was 76.2%, 7 was 47.2%, 8 was 71.1%, 9 was 97.1%, and 10 was 84.3%.

[0108] Based on the above degradation efficiency, when the proportion of rare earth waste residue is too low, the doping ratio of the photocatalyst will be too low, which will not effectively improve the catalytic effect of the photocatalyst. However, when the proportion of rare earth waste residue is too high, the efficiency of photocatalysis will no longer be improved.

[0109] Using the above detection method, 100 mL of tetracycline solutions with concentrations of 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, and 55 mg / L were poured into five beakers, respectively. 50 mg of the No. 1 photocatalyst prepared in Example 1 was added to each of the five beakers. The degradation rate of each tetracycline was then measured within 120 minutes. The degradation rates were 97.3%, 97.4%, 96.7%, 95.1%, and 83.2%, respectively. The data are listed in Table 1. It was found that the degradation rate began to decrease when the tetracycline concentration exceeded 45 mg / L.

[0110] Table 1

[0111]

[0112] Using the above detection method, 100 mL of tetracycline solution with a concentration of 45 mg / L was poured into five beakers. Then, 25 mg, 30 mg, 35 mg, 40 mg, 45 mg, 50 mg, 55 mg, and 60 mg of photocatalyst #1 were added to each beaker, respectively. The degradation rate of each tetracycline was then measured over 120 minutes. The degradation rates were 66.1%, 78.3%, 89.4%, 93.7%, 97.4%, 97.6%, 92.3%, and 83.4%, respectively. It was found that when the amount of photocatalyst reached 45 mg, the degradation of the 45 mg / L tetracycline solution reached its optimal effect within 120 minutes. As the amount of catalyst increased, the photocatalytic degradation effect initially remained unchanged, then began to decrease, likely due to the influence of excessively high concentrations of photocatalyst on the light intensity. Excessive catalyst usage would also be wasteful. Considering both degradation capacity and economic factors, a catalyst dosage of 45 mg was optimal. That is, when the catalyst concentration is 0.45 g / L and the tetracycline concentration is 45 mg / L, the degradation efficiency reaches its best within 120 minutes, which is the better choice. The dosage of photocatalyst #1 and the photocatalytic tetracycline degradation efficiency are summarized in Table 2.

[0113] Table 2

[0114]

[0115] Using the above detection method, 100 mL of tetracycline solutions with concentrations of 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, and 60 mg / L were poured into five beakers, respectively. Then, 30 mg, 35 mg, 40 mg, 45 mg, 50 mg, 55 mg, and 60 mg of photocatalyst #1 were added to each beaker, respectively. The degradation rate of each tetracycline was then measured within 120 minutes. The degradation rates were 97.9%, 97.9%, 97.7%, 97.4%, 97.4%, 91.1%, and 82.2%, respectively. Within a certain range, increasing the concentration of tetracycline proportionally with the increase of photocatalyst can achieve the highest degradation rate within the same timeframe. However, when the tetracycline concentration reaches 50 mg / L, the degradation efficiency begins to decline, requiring an increase in the proportion of catalyst added, which reduces the efficiency of the photocatalyst. In practical applications, the tetracycline concentration should be controlled below 50 mg / L to ensure optimal degradation of tetracycline while maintaining the efficiency of the photocatalyst. However, when a high degradation rate of tetracycline is not required, the concentration of tetracycline can be appropriately increased, and the amount of photocatalyst added can be adjusted as needed.

Claims

1. A method for producing a photocatalyst, characterized by, The method comprises the following steps: (1) uniformly mixing tetrabutyl titanate and anhydrous ethanol to form an ester-alcohol mixture; (2) adding calcium carbonate powder into the ethanol aqueous solution to form a calcium carbonate solution with a concentration of 3-5 wt%, then adding the calcium carbonate solution into the ester-alcohol mixture, and reacting at 30-50°C for 20-30 h, then filtering, drying the residue, calcining the residue at 700-800°C for 2-3 h, and then cooling and washing to obtain calcium titanate-titania composite particles; the ethanol aqueous solution is composed of distilled water and anhydrous ethanol with a volume ratio of 1:(3-5); (3) calcining the rare earth waste residue at 500-600°C for 2-3 h, grinding to obtain waste residue powder, leaching the waste residue powder with dilute sulfuric acid, and filtering to obtain a leaching solution; the mass ratio of the rare earth waste residue to tetrabutyl titanate is 1:1; 0.3-0.5 wt% ThO2, 2.8-3.3 wt% CeO2, 1.1-2.5 wt% TiO2, 1.5-2.1 wt% P2O5, 1.3-1.7 wt% La2O3, 0.5-0.6 wt% Pr6O 11 0.9-1.1 wt% Nd2O3, 0.2-0.3 wt% ZrO2; (4) adding an extractant P923 and TBP to form an extractant solution into the leaching solution, and cerium ions enter the organic phase, while thorium and trivalent rare earths remain in the first raffinate; using primary amine N1923 to extract thorium in the first raffinate, and thorium enters the primary amine N1923, while trivalent rare earths remain in the second raffinate; adding oxalic acid into the second raffinate to form a rare earth oxalate precipitate, filtering to obtain a rare earth oxalate and a rare earth filtrate; adding lye into the rare earth filtrate to make the pH value of the rare earth filtrate reach 7-8, as a modified solution; (5) adding the calcium titanate-titania composite particles into the modified solution to form a mixture, evaporating and drying the mixture to obtain a catalyst precursor, and then calcining, washing, drying and grinding the catalyst precursor to obtain a photocatalyst.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of tetrabutyl titanate to anhydrous ethanol is 1:(3-5).

3. The production method according to claim 1, characterized by, In step (2), the mass ratio of calcium carbonate to tetrabutyl titanate is 1:(6-8).

4. The production method according to claim 1, characterized by, In step (3), the leaching temperature is 25-40°C, the concentration of dilute sulfuric acid is 0.45-0.55 mol / L, 4-6 mL of dilute sulfuric acid is used for leaching per gram of waste residue powder, and the leaching time is 5-8 h.

5. The production method according to claim 1, characterized by, In step (4), the volume ratio of extractant P923 to TBP is 100:(5-10), the volume ratio of the extractant solution to the leaching solution is (2-4):1, the volume ratio of primary amine N1923 to the first raffinate is (2-3):1, and the mass ratio of the rare earth waste residue to oxalic acid is 1:(1-1.5), and the concentration of oxalic acid is 9-12 wt%.

6. The production method according to claim 1, characterized by, In step (5), when calcining the catalyst precursor, the calcination temperature is 400-500°C, and the calcination time is 2-3 h.

7. The photocatalyst produced by the production method of any one of claims 1-6.

8. The photocatalyst of claim 7 for use in tetracycline wastewater treatment.

9. Use according to claim 8, characterized in that, The concentration of tetracycline in the wastewater is 1-35 mg / L, and the concentration of the photocatalyst in the wastewater is 0.16-0.64 g / L.

Images