A method and system for regenerating rare earth-doped ZnO photocatalytic materials

Abstract

This invention discloses a method and system for regenerating rare-earth-doped ZnO photocatalytic materials. The method includes the following steps: Step 1, preparing a weak acid buffer solution of hydrochloric acid and sodium acetate; Step 2, washing the solid waste of rare-earth-doped ZnO photocatalyst with the aforementioned weak acid buffer solution; Step 3, filtering after washing; Step 4, collecting and processing the filtrate, drying the filter residue to obtain larger-particle rare-earth-doped ZnO catalyst solids; Step 5, calcining the rare-earth-doped ZnO catalyst solids to obtain the regenerated rare-earth-doped ZnO photocatalyst. This invention effectively solves the problem of regenerating rare-earth-doped ZnO photocatalytic materials, enabling the effective regeneration of solid waste. It utilizes a method and system that dissolves a thin layer of zinc oxide on the surface, followed by lattice annealing, to restore the photocatalytic material's strong photocatalytic ability. The process is simple, saves raw materials and water resources, and has good continuity.

Description

Technical Field

[0001] This invention belongs to the field of waste recycling technology, specifically to a method and system for regenerating rare earth-doped ZnO photocatalytic materials. Background Technology

[0002] Photocatalytic degradation technology utilizes light energy to degrade organic matter into products such as water and carbon dioxide. Due to its advantages of low energy consumption, environmental friendliness, and high efficiency, it is an ideal environmental degradation technology and has attracted widespread attention. Currently, more and more photocatalysts are being developed, among which rare-earth-doped ZnO nanocatalysts have received extensive research interest due to their excellent catalytic performance. However, studies have found that the secondary photocatalytic effect of rare-earth-doped ZnO photocatalysts is not significant, which is not conducive to the repeated application of photocatalytic materials. As recorded in existing technology (Lei Yang, Ruijiang Ding, Chunshui Hong, Wencai Zhu, Synthesis, Optical and Photocatalytic Properties of ZnO:Tb Nanopartic Lithology, Solid State Sciences 2022, 131:106957(1-11)), the degradation rate k of the Tb-doped ZnO nanocatalyst prepared by the authors during primary and secondary photocatalysis is compared, as shown in Table 1. The photodegradation rate of all samples decreases by more than an order of magnitude.

[0003] Table 1. Degradation rates k of Tb-doped ZnO nanocatalysts during primary and secondary photocatalysis.

[0004]

[0005] The above results indicate that photocatalysts gradually lose their photocatalytic activity and become inactive as the reaction time increases, resulting in solid waste. After one or more photocatalytic processes, the internal composition and crystal structure of the photocatalyst particles do not change significantly. The reason for the reduced photocatalytic ability is that after one photocatalytic process, some uncatalyzed dye particles adhere to the surface of the material particles, and some lattice sites lose their activity due to the adsorption of small amounts of other ions during the photocatalytic process.

[0006] From a material perspective, rare earth elements are relatively expensive, the preparation process is relatively difficult, and the cost of replacing the catalyst with a fresh one is high. Therefore, the recycling and regeneration process of the photocatalyst is very important. Currently, there are no reports on the technology for regenerating rare earth-doped ZnO nanophotocatalysts. Summary of the Invention

[0007] In view of this, the present invention provides a method and system for regenerating rare earth-doped ZnO photocatalytic materials, which regenerates failed rare earth-doped ZnO photocatalytic materials to reduce costs. This application provides the following technical solution:

[0008] A method for regenerating rare earth-doped ZnO photocatalyst material includes the following steps: Step 1, preparing a weak acid buffer solution of hydrochloric acid and sodium acetate; Step 2, washing the solid waste of rare earth-doped ZnO photocatalyst with the weak acid buffer solution by stirring; Step 3, filtering after washing; Step 4, collecting and processing the filtrate, and drying the filter residue to obtain a solid rare earth-doped ZnO catalyst with larger particles; Step 5, calcining the solid rare earth-doped ZnO catalyst to obtain the regenerated rare earth-doped ZnO photocatalyst.

[0009] Preferably, the pH of the weak acid buffer solution is between 5.5 and 6.5.

[0010] Preferably, the calcination temperature is controlled at 500°C.

[0011] Preferably, the filtrate in step 4 is centrifuged, and the separated solid is repeatedly washed and separated. The solid obtained is dried to obtain a small-particle rare earth-doped ZnO catalyst solid. The washing wastewater in step 2 and the wastewater in the filtrate treatment in step 4 are mixed and then treated by a reverse osmosis device to obtain pure water and high-concentration wastewater for reuse.

[0012] Preferably, the wastewater mixture further includes a Zn ion concentration detection step, and the high-concentration wastewater is treated as follows based on the detected concentration: when the Zn ion concentration is less than 0.1M, a weakly acidic hydrochloric acid-sodium acetate buffer washing solution is prepared for reuse; when the Zn ion concentration is higher than 0.1M, calcined small-particle rare earth-doped ZnO catalyst solid is added, stirred evenly, and allowed to stand under light.

[0013] Preferably, the wastewater mixture further includes a sodium chloride concentration detection step, and when the sodium chloride reaches a saturation concentration of 95%, evaporation and desalination are performed.

[0014] This invention also discloses a regeneration system for rare earth-doped ZnO photocatalytic materials, comprising: a dissolution and washing system, a filtration system, and a calcination system for surface treatment of solid waste from rare earth-doped ZnO photocatalysts. The dissolution and washing system includes a reaction tank for surface dissolution and washing of the solid waste from rare earth-doped ZnO photocatalysts. The filtration system includes a filter and a multi-stage treatment device for the filtrate, and the treated wastewater and waste residue are reused. Pipelines and pumps connect the reaction tank, the filter, and the filtrate treatment device, and a centrifugal filter, which can be used in the prior art. The calcination system includes a pulverizing dryer for drying the filter residue and a muffle furnace for high-temperature calcination after drying.

[0015] Working principle of the invention:

[0016] The reason for the decrease in photocatalytic activity of photocatalysts is that after one photocatalytic process, some uncatalyzed dye particles and a small amount of other ions adhere to the surface of the material particles, resulting in loss of activity. Therefore, this invention employs a method to restore the strong photocatalytic activity of the photocatalytic material by dissolving the zinc oxide surface layer and then performing lattice annealing. By using a weakly acidic hydrochloric acid-sodium acetate buffer, a thin layer on the surface of rare earth-doped ZnO is slowly dissolved, exposing the core components. After filtration, drying, and calcination at a low temperature (500℃), the rare earth-doped ZnO can be restored to its state before one photocatalytic process. Rare earth ions (mainly Eu) 3+ Tb 3+ and Ce 3+ Ions are widely distributed in the ZnO lattice. Due to the imbalance of charge and the difference in atomic radius, a large number of lattice defects are easily formed in the ZnO lattice. Some of these lattice defects are located on the crystal surface of ZnO, forming active sites.

[0017] The wastewater from washing rare-earth-doped ZnO catalysts mainly contains hydrochloric acid, sodium acetate, small amounts of zinc ions and rare-earth ions, and small amounts of uncatalyzed organic matter. In the initial washing processes, the levels of these small amounts of zinc ions, rare-earth ions, and uncatalyzed organic matter are relatively low and do not affect the washing process. They are removed once the zinc ion content reaches a certain level.

[0018] Uncatalyzed organic matter, after being decomposed by a photocatalyst, forms water and carbon dioxide, leaving hydrochloric acid, sodium acetate, and small amounts of zinc and rare earth ions. Adding sodium acetate to this wastewater makes it alkaline, increasing the Zn content. 2+ and RE 3+ It precipitates. The chemical reaction formula is as follows:

[0019] CH3COONa→CH3COO–+Na +

[0020] CH3COO–+H2℃H3COOH+OH –

[0021] Zn 2+ +2OH – →Zn(OH)2↓

[0022] RE 3+ +3OH – →RE(OH)3↓

[0023] After solid-liquid separation, the wastewater contains only acetic acid and sodium acetate. At this point, adding sodium acetate and hydrochloric acid can prepare a buffer solution for further washing.

[0024] However, each time zinc is removed, a small amount of NaCl is generated. When sodium chloride accumulates to a certain level, desalination is necessary.

[0025] The beneficial effects of this invention are:

[0026] This invention proposes a method for regenerating rare-earth-doped photocatalysts. The process is simple: by slightly dissolving a thin layer of zinc oxide on the surface followed by lattice annealing, the photocatalytic material can regain its strong photocatalytic activity. This method allows for the recycling of raw materials and water, conserving resources and promoting resource recycling and environmental protection. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram of the regeneration method for rare earth-doped ZnO photocatalytic materials. Detailed Implementation

[0029] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0030] The regeneration method for rare earth-doped ZnO photocatalyst material provided in this embodiment includes the following steps: Step 1, preparing a weak acid buffer solution of hydrochloric acid and sodium acetate; Step 2, washing the solid waste of rare earth-doped ZnO photocatalyst with the weak acid buffer solution by stirring; Step 3, filtering after washing; Step 4, collecting and processing the filtrate, and drying the filter residue to obtain a solid rare earth-doped ZnO catalyst with larger particles; Step 5, calcining the solid rare earth-doped ZnO catalyst to obtain the regenerated rare earth-doped ZnO photocatalyst.

[0031] The filtrate from step 4 is centrifuged, and the separated solid is repeatedly washed and separated. The resulting solid is dried to obtain a small-particle rare earth-doped ZnO catalyst solid. The washing wastewater from step 2 is mixed with the wastewater from the filtrate treatment in step 4 and then treated by a reverse osmosis device to obtain pure water and high-concentration wastewater for reuse.

[0032] The wastewater mixture also includes a Zn ion concentration detection step. Based on the detected concentration, the wastewater is treated as follows: when the Zn ion concentration is less than 0.1M, a weakly acidic hydrochloric acid-sodium acetate buffer washing solution is prepared for reuse; when the Zn ion concentration is higher than 0.1M, calcined small-particle rare earth-doped ZnO catalyst solid is added, stirred evenly, and placed in a place where sunlight can irradiate it, and left to stand for 3 hours.

[0033] When the Zn ion concentration is less than 0.1 M, the wastewater mainly contains Cl-, acetate, Na+, and H+, and can be recycled for use as a washing solution. When the Zn ion concentration is higher than 0.1 M, the wastewater contains Cl-, acetate, Na+, H+, and a certain amount of Zn2+ washed off. In addition, it contains some organic dyes and other organic matter remaining from the photocatalytic process. Before washing, these organic substances are mainly adsorbed on the surface of the photocatalyst and enter the wastewater after washing. After adding calcined rare-earth-doped ZnO catalyst solid to this wastewater and placing it under sunlight, the rare-earth-doped ZnO photocatalyst decomposes these organic substances into water and carbon dioxide, thus removing them.

[0034] Please refer to Figure 1 The diagram shows a processing system for the regeneration of rare-earth-doped ZnO photocatalytic materials. This system includes a dissolution and washing system, a filtration system, and a calcination system for surface treatment of solid waste from rare-earth-doped ZnO photocatalysts. The dissolution and washing system comprises a powder tank, a reaction tank, a storage tank (No. 1), and a mixing tank. The mixing tank is piped to the storage tank (No. 1) and is used to prepare a weak acid buffer solution. The powder tank stores the solid waste from rare-earth-doped ZnO photocatalysts. The reaction tank is used for surface dissolution and washing of the solid waste. The storage tank (No. 1) and the powder tank are connected to the reaction tank. The filtration system includes a filter and a multi-stage treatment device for the filtrate, allowing for the reuse of treated wastewater and residue. The calcination system includes a pulverizer and dryer for drying the filter residue, and a muffle furnace for high-temperature calcination after drying.

[0035] The regeneration method of the present invention will be illustrated below through specific embodiments:

[0036] Example 1

[0037] 1) In the mixing tank, dissolve 20 mol of sodium acetate in a certain amount of purified water, add an appropriate amount of water to prepare approximately 1000 L of sodium acetate solution, at which point the pH value is controlled at 8.52. Then, add an appropriate amount of hydrochloric acid to the sodium acetate to prepare a weakly acidic hydrochloric acid-sodium acetate buffer solution with a pH value of 6.1. After stirring evenly, pump the solution into storage tank No. 1.

[0038] 2) Take 50 kg of rare earth-doped ZnO micro / nano structured photocatalyst from the powder container and add it to the reaction vessel through the feed port. Draw 500 L of weakly acidic hydrochloric acid-sodium acetate buffer solution from storage tank No. 1 (or storage tank No. 3 or No. 4) into the reaction vessel, stir continuously, and wash for 1 hour.

[0039] 3) The rare earth-doped ZnO micro / nano structured photocatalyst in the reaction vessel is drawn out from the outlet and enters the filter. The filter uses a filter cloth with a filtration accuracy of 0.5 micrometers and a thickness of 2 mm. After filtration, pure water is introduced from storage tank No. 2 to wash the catalyst three times, and then the catalyst is filtered and separated.

[0040] 4) The filtered residue is flash-dried in a pulverizer and dryer with an inlet air temperature of 180℃ to form dry, larger particles of rare earth-doped ZnO powder.

[0041] 5) The filtrate after filtration contains small particles with a diameter of less than 0.5 micrometers. These small particles are separated into solid and liquid by a nano-powder dehydration centrifuge No. 1, with the speed controlled at 3000-4000 r / min. 100L of pure water is introduced from storage tank No. 2 and centrifuged again. This process is repeated three times with clean water.

[0042] 6) The filter residue after solid-liquid separation by centrifugation is fed into a flash dryer / pulverizer / dryer with an inlet air temperature of 180℃, forming dry, smaller-particle rare earth-doped ZnO powder. The centrifuged particles are relatively small and need to be dried separately from the filter residue.

[0043] 7) The larger rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0044] 8) The smaller rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0045] 9) Draw the weakly acidic hydrochloric acid-sodium acetate buffer solution wastewater from the filter and centrifuge into wastewater tank No. 1 for storage and collection. The wastewater in wastewater tank No. 1 mainly contains hydrochloric acid, sodium acetate, small amounts of zinc ions and rare earth ions, and small amounts of uncatalyzed organic matter, etc.

[0046] 10) The wastewater used for cleaning the filter and centrifuge sediment is drawn out and passed through the reverse osmosis unit to obtain pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0047] 11) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is less than 0.1 M, pump 500 L of wastewater from wastewater tank No. 1 into mixing tank No. 2, measure the acetate content, add an appropriate amount of sodium acetate to bring the total acetate content in the wastewater to approximately 0.02 M, then add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 6.1, and stir well. Add this solution to storage tank No. 3; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0048] 12) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is higher than 0.1M, pump 500L of wastewater from wastewater tank No. 1 into the photocatalytic tank, add 25g of calcined small-particle rare earth doped ZnO powder, stir evenly, place in a place where sunlight can shine, and let stand for 3 hours.

[0049] 13) Pump the wastewater in the catalytic tank into wastewater tank No. 2 and collect and store it.

[0050] 14) Pump 500L of wastewater from wastewater tank No. 2 and put it into batching tank No. 2. Take a small amount of wastewater sample and measure the acetate content. Add an appropriate amount of sodium acetate to make the total acetate content in the wastewater reach about 0.02M. Then add an appropriate amount of sodium hydroxide to control the pH value of the solution at 8.52 while stirring.

[0051] 15) After stirring, the wastewater containing sodium acetate is introduced into the No. 2 nanoparticle dehydration centrifuge for solid-liquid separation and washed three times.

[0052] 16) After solid-liquid separation, the solid can be collected and dried in a flash dryer or a pulverizing and drying integrated machine, and then calcined at 500°C to form a photocatalyst.

[0053] 17) The wastewater from centrifuge No. 2 enters mixing tank No. 3. Add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 6.1, then stir thoroughly. Add this mixture to storage tank No. 4; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0054] 18) The cleaning wastewater from centrifuge No. 2 is processed through a reverse osmosis unit to produce pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0055] 19) Continuously monitor the sodium chloride concentration in wastewater tank No. 1. When the sodium chloride concentration reaches 95% of its saturation level, the wastewater from wastewater tank No. 2 needs to be introduced into evaporation tank No. 1 for evaporation and desalination. Considering that the concentration of sodium acetate in the wastewater tank is approximately 0.02M, while the concentration of a saturated sodium acetate solution at room temperature and pressure is approximately 3.69 mol / L, the solution can be concentrated to 1 / 100 of its original volume during desalination.

[0056] Example 2

[0057] 1) In mixing tank No. 1, dissolve 20 mol of sodium acetate in a certain amount of purified water, add an appropriate amount of water to prepare approximately 1000 L of sodium acetate solution, at which point the pH value is controlled at 8.52. Then, add an appropriate amount of hydrochloric acid to the sodium acetate to prepare a weakly acidic hydrochloric acid-sodium acetate buffer solution with a pH value of 6.0. After stirring evenly, pump the solution into storage tank No. 1.

[0058] 2) Take 75 kg of rare earth-doped ZnO micro / nano structured photocatalyst from the powder container and add it to the reaction vessel through feed port 0. Draw 500 L of weakly acidic hydrochloric acid-sodium acetate buffer solution from storage tank 1 (or storage tank 3 or 4) and introduce it into the reaction vessel through port 1. Stir continuously for 1 hour to wash the product.

[0059] 3) The rare earth-doped ZnO micro / nano structured photocatalyst in the reaction vessel is drawn out from the bottom outlet and enters the filter. The filter uses a filter cloth with a filtration accuracy of 0.5 micrometers and a thickness of 2 mm. After filtration, pure water is introduced from storage tank No. 2 to wash the catalyst three times, and then the mixture is filtered and separated.

[0060] 4) The filtered residue enters a flash dryer pulverizer-dryer with an inlet air temperature of 180℃, forming dry, larger particles of rare earth-doped ZnO powder.

[0061] 5) The filtrate after filtration contains small particles with a diameter of less than 0.5 micrometers. These small particles are separated into solid and liquid by a nano-powder dehydration centrifuge No. 1, with the speed controlled at 3000-4000 r / min. 100L of pure water is introduced from storage tank No. 2 and centrifuged again. This process is repeated three times with clean water.

[0062] 6) The filter residue after solid-liquid separation by centrifugation is fed into a flash dryer / pulverizer / dryer with an inlet air temperature of 180℃, forming dry, smaller-particle rare earth-doped ZnO powder. The centrifuged particles are relatively small and need to be dried separately from the filter residue.

[0063] 7) The larger rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0064] 8) The smaller rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0065] 9) Draw the weakly acidic hydrochloric acid-sodium acetate buffer solution wastewater from the filter and centrifuge into wastewater tank No. 1 for storage and collection. The wastewater in wastewater tank No. 1 mainly contains hydrochloric acid, sodium acetate, small amounts of zinc ions and rare earth ions, and small amounts of uncatalyzed organic matter, etc.

[0066] 10) The wastewater used for cleaning the filter and centrifuge sediment is drawn out and passed through the reverse osmosis unit to obtain pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0067] 11) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is less than 0.1 M, pump 500 L of wastewater from wastewater tank No. 1 into mixing tank No. 2, measure the acetate content, add an appropriate amount of sodium acetate to bring the total acetate content in the wastewater to approximately 0.02 M, then add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 6.0, and stir well. Add this solution to storage tank No. 3; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0068] 12) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is higher than 0.1M, pump 500L of wastewater from wastewater tank No. 1 into the photocatalytic tank, add 25g of calcined small-particle rare earth doped ZnO powder, stir evenly, place in a place where sunlight can shine, and let stand for 3 hours.

[0069] 13) Pump the wastewater in the catalytic tank into wastewater tank No. 2 and collect and store it.

[0070] 14) Pump 500L of wastewater from wastewater tank No. 2 and put it into batching tank No. 2. Take a small amount of wastewater sample and measure the acetate content. Add an appropriate amount of sodium acetate to make the total acetate content in the wastewater reach about 0.02M. Then add an appropriate amount of sodium hydroxide to control the pH value of the solution at 8.52 while stirring.

[0071] 15) After stirring, the wastewater containing sodium acetate is introduced into the No. 2 nanoparticle dehydration centrifuge for solid-liquid separation and washed three times.

[0072] 16) After solid-liquid separation, the solid can be collected and dried in a flash dryer or a pulverizing and drying integrated machine, and then calcined at 500°C to form a photocatalyst.

[0073] 17) The wastewater from centrifuge No. 2 enters mixing tank No. 3. Add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 6.0, then stir thoroughly. Add this mixture to storage tank No. 4; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0074] 18) The cleaning wastewater from centrifuge No. 2 is processed through a reverse osmosis unit to produce pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0075] 19) Continuously monitor the sodium chloride concentration in wastewater tank No. 1. When the sodium chloride concentration reaches 95% of its saturation level, the wastewater from wastewater tank No. 2 needs to be introduced into evaporation tank No. 1 for evaporation and desalination. Considering that the concentration of sodium acetate in the wastewater tank is approximately 0.02M, while the concentration of a saturated sodium acetate solution at room temperature and pressure is approximately 3.69 mol / L, the solution can be concentrated to 1 / 100 of its original volume during desalination.

[0076] Example 3

[0077] 1) In mixing tank No. 1, dissolve 20 mol of sodium acetate in a certain amount of purified water, add an appropriate amount of water to prepare approximately 1000 L of sodium acetate solution, at which point the pH value is controlled at 8.52. Then, add an appropriate amount of hydrochloric acid to the sodium acetate to prepare a weakly acidic hydrochloric acid-sodium acetate buffer solution with a pH value of 5.9. After stirring evenly, pump the solution into storage tank No. 1.

[0078] 2) Take 80 kg of rare earth-doped ZnO micro / nano structured photocatalyst from the powder container and add it to the reaction vessel through feed port 0. Draw 500 L of weakly acidic hydrochloric acid-sodium acetate buffer solution from storage tank 1 (or storage tank 3 or 4) and introduce it into the reaction vessel through port 1. Stir continuously for 1 hour to wash the product.

[0079] 3) The rare earth-doped ZnO micro / nano structured photocatalyst in the reaction vessel is drawn out from the bottom outlet and enters the filter. The filter uses a filter cloth with a filtration accuracy of 0.5 micrometers and a thickness of 2 mm. After filtration, pure water is introduced from storage tank No. 2 to wash the catalyst three times, and then the mixture is filtered and separated.

[0080] 4) The filtered residue enters a flash dryer pulverizer-dryer with an inlet air temperature of 180℃, forming dry, larger particles of rare earth-doped ZnO powder.

[0081] 5) The filtrate after filtration contains small particles with a diameter of less than 0.5 micrometers. These small particles are separated into solid and liquid by a nano-powder dehydration centrifuge No. 1, with the speed controlled at 3000-4000 r / min. 100L of pure water is introduced from storage tank No. 2 and centrifuged again. This process is repeated three times with clean water.

[0082] 6) The filter residue after solid-liquid separation by centrifugation is fed into a flash dryer / pulverizer / dryer with an inlet air temperature of 180℃, forming dry, smaller-particle rare earth-doped ZnO powder. The centrifuged particles are relatively small and need to be dried separately from the filter residue.

[0083] 7) The larger rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0084] 8) The smaller rare earth-doped ZnO powder particles after crushing and drying are placed in a large muffle furnace for calcination. The calcination temperature is set at 500℃ and the calcination time is controlled at 2 hours.

[0085] 9) Draw the weakly acidic hydrochloric acid-sodium acetate buffer solution wastewater from the filter and centrifuge into wastewater tank No. 1 for storage and collection. The wastewater in wastewater tank No. 1 mainly contains hydrochloric acid, sodium acetate, small amounts of zinc ions and rare earth ions, and small amounts of uncatalyzed organic matter, etc.

[0086] 10) The wastewater used for cleaning the filter and centrifuge sediment is drawn out and passed through the reverse osmosis unit to obtain pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0087] 11) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is less than 0.1 M, pump 500 L of wastewater from wastewater tank No. 1 into mixing tank No. 2, measure the acetate content, add an appropriate amount of sodium acetate to bring the total acetate content in the wastewater to approximately 0.02 M, then add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 5.9, and stir well. Add this solution to storage tank No. 3; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0088] 12) Detect the Zn ion concentration in wastewater tank No. 1. When the Zn ion concentration is higher than 0.1M, pump 500L of wastewater from wastewater tank No. 1 into the photocatalytic tank, add 25g of calcined small-particle rare earth doped ZnO powder, stir evenly, place in a place where sunlight can shine, and let stand for 3 hours.

[0089] 13) Pump the wastewater in the catalytic tank into wastewater tank No. 2 and collect and store it.

[0090] 14) Pump 500L of wastewater from wastewater tank No. 2 and put it into batching tank No. 2. Take a small amount of wastewater sample and measure the acetate content. Add an appropriate amount of sodium acetate to make the total acetate content in the wastewater reach about 0.02M. Then add an appropriate amount of sodium hydroxide to control the pH value of the solution at 8.52 while stirring.

[0091] 15) After stirring, the wastewater containing sodium acetate is introduced into the No. 2 nanoparticle dehydration centrifuge for solid-liquid separation and washed three times.

[0092] 16) After solid-liquid separation, the solid can be collected and dried in a flash dryer or a pulverizing and drying integrated machine, and then calcined at 500°C to form a photocatalyst.

[0093] 17) The wastewater from centrifuge No. 2 enters mixing tank No. 3. Add an appropriate amount of hydrochloric acid to control the pH of the wastewater solution at 5.9, then stir thoroughly. Add this mixture to storage tank No. 4; it can be used as a weakly acidic hydrochloric acid-sodium acetate buffer washing solution.

[0094] 18) The cleaning wastewater from centrifuge No. 2 is processed through a reverse osmosis unit to produce pure feed water, which is then introduced into storage tank No. 2. The high-concentration water obtained from the reverse osmosis unit enters wastewater tank No. 1.

[0095] 19) Continuously monitor the sodium chloride concentration in wastewater tank No. 1. When the sodium chloride concentration reaches 95% of its saturation level, the wastewater from wastewater tank No. 2 needs to be introduced into evaporation tank No. 1 for evaporation and desalination. Considering that the concentration of sodium acetate in the wastewater tank is approximately 0.02M, while the concentration of a saturated sodium acetate solution at room temperature and pressure is approximately 3.69 mol / L, the solution can be concentrated to 1 / 100 of its original volume during desalination.

[0096] Photocatalysis experiment

[0097] Take 50g of raw ZnO:Eu powder and perform the first photocatalytic performance test as follows: First, prepare a 15ppm Rhodamine B (RhB) solution. Add 50mg of photocatalyst to 50mL of RhB solution (catalyst concentration is only about 0.1%), and stir at a constant speed in the dark for 1 hour to reach adsorption equilibrium. Then, place the beaker under a 125W UV lamp for 60 minutes until RhB is completely degraded. Centrifuge the sample and take the supernatant. Take 3mL of the supernatant each time and measure the absorbance of Rhodamine B at the absorption peak (550nm) using a UV-spectrum spectrophotometer to calculate the degradation rate. The test is conducted according to the "Test Method for Aqueous Purification Performance of Photocatalytic Materials" (GB / T 23762-2020). After testing the photocatalytic performance, separate the solid and liquid phases by centrifugation, repeatedly wash the photocatalyst with deionized water, and then separate again. After repeatedly measuring the photocatalytic performance of ZnO:Eu, the average value of the RhB concentration (ppm) after degradation was taken to calculate the photodegradation rate. Simultaneously, the ZnO:Eu photocatalytic powder was collected. After repeating this process three times, the photocatalyst was regenerated according to the method of this invention. Wherein:

[0098] Recovery rate = Degradation rate after regeneration / Degradation rate during the first catalysis

[0099] Table 1. Catalytic performance and regeneration photocatalytic performance of ZnO:Eu

[0100]

[0101] Table 1 shows the catalytic performance and regeneration photocatalytic performance of ZnO:Eu. Although the catalytic efficiency of the photocatalyst after regeneration varies slightly in different implementation methods, the overall regeneration recovery capacity reaches 99.63-99.75%, indicating that the method of the present invention has a good regeneration effect.

[0102] This embodiment has the following advantages: the method is simple, it effectively regenerates the solid waste of rare earth-doped ZnO photocatalytic material, the wastewater in the regeneration process is recycled and treated, the raw materials and water are effectively recycled, saving raw materials and water resources, it has good continuity, it can be scaled up for industrial production, and it has certain economic and social benefits.

[0103] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for regenerating rare earth-doped ZnO photocatalytic materials, characterized in that: The process includes the following steps: Step 1, preparing a weak acid buffer solution of hydrochloric acid and sodium acetate; Step 2, adding the rare earth-doped ZnO photocatalyst solid waste to the weak acid buffer solution and stirring and washing; Step 3, filtering after washing; Step 4, collecting and processing the filtrate from Step 3, drying the filter residue to obtain larger rare earth-doped ZnO catalyst solid particles, centrifuging the filtrate, repeatedly washing and separating the separated solid, and finally collecting and drying the solid to obtain smaller rare earth-doped ZnO catalyst solid particles; Step 5, calcining the dried rare earth-doped ZnO catalyst solid to obtain the regenerated rare earth-doped ZnO photocatalyst.

2. The method for regenerating rare earth-doped ZnO photocatalytic material according to claim 1, characterized in that: The pH of the weak acid buffer solution should be controlled between 5.5 and 6.

5.

3. The method for regenerating rare earth-doped ZnO photocatalytic material according to claim 2, characterized in that: The calcination temperature is controlled at 500℃.

4. The method for regenerating rare earth-doped ZnO photocatalytic material according to claim 1, characterized in that: The regeneration method further includes the following steps: mixing the washing wastewater in step 2 with the wastewater in the filtrate treatment in step 4, and then treating them through a reverse osmosis device to obtain pure water and high-concentration wastewater, which are then reused separately.

5. The method for regenerating rare earth-doped ZnO photocatalytic material according to claim 4, characterized in that: After the wastewater is mixed, a Zn ion concentration detection step is also included. Based on the detected concentration, the high-concentration wastewater is treated as follows: when the Zn ion concentration is less than 0.1 M, a weakly acidic hydrochloric acid-sodium acetate buffer washing solution is prepared for reuse; when the Zn ion concentration is higher than 0.1 M, calcined small-particle rare earth-doped ZnO catalyst solid is added, stirred evenly, and allowed to stand under light.

6. The method for regenerating rare earth-doped ZnO photocatalytic material according to claim 4, characterized in that: The wastewater mixture also includes a sodium chloride concentration detection step. When the sodium chloride concentration reaches 95% of the saturation concentration, evaporation and desalination are carried out.

7. A method for regenerating rare-earth-doped ZnO photocatalytic material according to any one of claims 1-6, characterized in that: The following system is used to regenerate rare earth-doped ZnO photocatalyst solid waste through surface treatment. This system includes a dissolution and washing system, a filtration system, and a calcination system. The dissolution and washing system includes a reaction tank for surface dissolution and washing of the rare earth-doped ZnO photocatalyst solid waste. The filtration system includes a filter and a multi-stage treatment device for the filtrate, allowing for the reuse of treated wastewater and waste residue. The washing system is connected to the filtration system via pipelines. The calcination system includes a pulverizing dryer for drying the filter residue and a muffle furnace for high-temperature calcination after drying.

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