Light magnetic persulfate catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a light magnetic persulfate catalyst, and belongs to the technical field of preparation of catalytic materials. A sol-gel method and a coprecipitation method are adopted, the steps are simple, the conditions are mild, the method is simple and clear, and the whole preparation process is non-toxic and harmless and is controllable in the whole process; the preparation conditions are mild, the process is simple and convenient, and the efficient PMS activation capability is achieved; the catalyst not only has specific magnetism, but also shows certain photocatalytic performance; the TiO2 porous membrane layer firmly loads magnetic components and is not easy to fall off, and the catalyst can still keep efficient activity after being used for multiple times; the mass of the catalyst is light, the catalyst can float on the surface layer of sewage in the water treatment process, and the catalyst can be conveniently recycled and reused by utilizing the magnetic characteristic, so that the use cost is reduced; in conclusion, the invention solves the problems of difficult catalyst recovery, complex preparation, poor stability and the like in the prior art, and has significant application potential in the field of water treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic material preparation, and in particular relates to a light magnetic persulfate catalyst and a preparation method and application thereof. Background Art

[0002] Persulfate catalyst plays a vital role in the field of water pollution control. Its core value lies in its ability to generate highly active free radicals, such as sulfate radicals (SO4 - ·) and hydroxyl radicals (·OH). These free radicals have strong oxidizing ability and can effectively decompose organic matter in water, including organic solvents, color substances and difficult-to-degrade organic matter. When treating sewage, the catalyst exhibits a fast reaction speed and can treat sewage in a short time, significantly improving treatment efficiency, and is especially suitable for emergency treatment needs. In addition, since the operation is carried out at room temperature, high temperature conditions are not required, thereby reducing energy consumption and operating costs. The reaction products produced by this technology are mostly non-toxic and harmless substances, and will not cause secondary pollution to the environment. This is particularly important for environmental protection and effectively avoids the secondary pollution problems that may be caused by traditional treatment methods.

[0003] Persulfate-catalyzed wastewater treatment technology is applicable to all types of organic wastewater, including industrial wastewater, rural sewage and domestic sewage, and shows a wide range of applicability. This technology oxidizes organic matter in water through the generation of active free radicals, without the need for additional oxygen or oxidants, thereby reducing treatment costs. Persulfate activators, as key components in advanced oxidation technologies, effectively degrade difficult-to-treat organic pollutants by generating strong oxidizing substances such as sulfate radicals, and have become a research focus for treating environmental problems such as wastewater containing antibiotics. In recent years, research has also revealed the existence of non-radical oxidation processes in persulfate-based advanced oxidation technologies. This discovery provides a new research direction and mechanism understanding for the application of persulfate activators. Persulfate activators are of great value in environmental pollution control. They can not only effectively treat various types of organic wastewater, but are also environmentally friendly and energy-saving. They are one of the important development directions of current and future water treatment technologies.

[0004] Patent CN116212916 A describes a cobalt-manganese-based composite catalyst, its preparation method, and its use in activating peroxymonosulfate to degrade antibiotics, addressing the high energy consumption and low pollutant degradation efficiency of traditional activators. The preparation method comprises: mixing melamine, cyanuric acid, and water, followed by annealing to produce a three-dimensional porous g-C3N4; then, mixing an ethanol solution of the three-dimensional porous g-C3N4, cobalt chloride hexahydrate, manganese chloride tetrahydrate, and ammonium bicarbonate, followed by annealing to produce the cobalt-manganese-based composite catalyst. The cobalt-manganese-based composite catalyst prepared by this invention has a high specific surface area, a rich pore structure, and numerous active sites, which facilitates the activation of PMS and the degradation of pollutants. However, the catalyst prepared by this method is difficult to recycle and has high costs, making it unsuitable for industrial application. Patent CN117258789 A discloses a CoFe2O4-based composite catalyst and its preparation method. The preparation steps include: dissolving a cobalt source, an iron source, a surfactant, and an alkali source in a solvent to obtain a mixed solution; adding a carbon material to the mixed solution to obtain a suspension; and post-treating the suspension to produce a CoFe2O4-based composite catalyst. The CoFe2O4 in the prepared CoFe2O4-based composite catalyst is CoFe2O4 quantum dots. The quantum dots are supported on the carbon material, effectively preventing the aggregation of CoFe2O4, thereby improving catalytic performance. However, the catalyst preparation process is complex and requires high preparation conditions. Furthermore, the catalyst has a weak binding force with the carbon material, and the catalytic material easily falls off during use, resulting in reduced reusability. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a light magnetic persulfate catalyst and a preparation method and application thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a light magnetic persulfate catalyst comprises the following steps:

[0008] Step 1: First, the hollow glass microspheres are dispersed in a dilute acid solution (mass fraction 10%) and stirred; then, the hollow glass microspheres are separated by filtration and washed with deionized water until they reach a neutral state; finally, the treated hollow glass microspheres are placed in an oven at 80°C for drying to obtain acid-washed hollow glass microspheres;

[0009] Step 2: adding anhydrous ethanol, glacial acetic acid, and deionized water to a beaker and mixing them uniformly to form a first solution; then, adding anhydrous ethanol, triethanolamine, and tetrabutyl titanate to another beaker in sequence and mixing them uniformly to form a second solution; adding the first solution dropwise to the second solution under continuous stirring, and finally adding polyethylene glycol to the mixture after the addition is complete, stirring at room temperature for 3 hours to obtain a uniform, transparent, light yellow TiO2 sol;

[0010] Step 3: adding the acid-washed hollow glass microspheres obtained in step 1 to the TiO2 sol obtained in step 2, stirring and mixing, and then standing for a period of time; then, separating the hollow glass microspheres by filtration and drying them in an oven; then, placing the dried hollow glass microspheres in a muffle furnace for calcination, and after naturally cooling to room temperature, obtaining TiO2 / hollow glass microspheres coated with a layer of TiO2 porous structure film;

[0011] Step 4: adding ferrous chloride, ferric chloride, and cobalt nitrate to deionized water and stirring uniformly; then, immersing the TiO2 / hollow glass microspheres prepared in step 3 in the above solution and stirring for 1 hour; and during the stirring process, adding an alkaline solution to the system to obtain a pretreatment system;

[0012] Step 5: Place the pretreatment system in step 4 into a water bath for water bath treatment, and then filter, wash and dry to obtain a light magnetic persulfate catalyst.

[0013] Furthermore, the dilute acid in step 1 is at least one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid.

[0014] Furthermore, in step 2, the molar ratio of anhydrous ethanol, glacial acetic acid and deionized water is 2-5:1:4-8.

[0015] Furthermore, in step 2, the molar ratio of anhydrous ethanol, triethanolamine and tetrabutyl titanate is 10-30:1:1-2.

[0016] Furthermore, in step 3, the mass ratio of the hollow glass microspheres to the titanium dioxide sol is 1:10-30.

[0017] Furthermore, in step 3, the drying treatment temperature is 60-120° C. and the time is 2-8 hours; the calcination treatment temperature is 500-600° C. and the time is 2-4 hours.

[0018] Furthermore, in step 4, the mass ratio of ferrous chloride, ferric chloride, cobalt nitrate, TiO2 / hollow glass microspheres, ammonia water and deionized water is 1:2-4:2-6:5-20:30-60:120-250; the sum of the molar masses of ferric chloride and ferrous chloride is equal to 2-4 times the molar mass of cobalt nitrate.

[0019] Furthermore, the alkaline solution in step 4 is aqueous ammonia with a concentration of 25-28 wt%.

[0020] Furthermore, in step 5, the temperature of the water bath treatment is 80-100° C., and the water bath time is 0.5-2 hours; the drying temperature is 50-80° C., and the drying time is 2-24 hours.

[0021] Hollow glass microspheres are used as the core carrier of the catalyst. Hollow glass microspheres have the characteristics of low density, high specific surface area and porous structure, which can significantly reduce the overall weight of the catalyst, thereby achieving lightweight. In addition, their porous structure provides a good foundation for the subsequent loading of active components.

[0022] Iron sources (ferrous chloride and ferric chloride) and cobalt sources (cobalt nitrate) are co-precipitated onto the surface of hollow glass microspheres to form magnetic components. These magnetic oxides enable the catalyst to be rapidly separated under an external magnetic field, facilitating recovery and reuse.

[0023] Coating a TiO2 porous film layer on the surface of the hollow glass microspheres not only enhances the stability of the carrier, but also synergizes with the magnetic components to improve the catalytic activity. TiO2 can also play a photocatalytic role under light conditions, further promoting the activation of persulfate.

[0024] Beneficial effects of the present invention:

[0025] The present invention proposes a lightweight magnetic CoFe2O4-TiO2 / / hollow glass microsphere PMS catalyst, as well as a preparation method and application of the catalyst;

[0026] 1. The sol-gel method and co-precipitation method are simple in steps, mild in conditions, and concise in methods. The entire preparation process is non-toxic and harmless, and is fully controllable.

[0027] 2. Mild preparation conditions, simple process, and efficient PMS activation ability;

[0028] 3. The catalyst not only has specific magnetic properties, but also exhibits certain photocatalytic properties;

[0029] 4. The TiO2 porous membrane layer firmly loads the magnetic components and is not easy to fall off. The catalyst can still maintain high efficiency and activity after repeated use;

[0030] 5. The catalyst is light in weight. During the water treatment process, the catalyst can float on the surface of the sewage. By utilizing its magnetic properties, the catalyst can be easily recovered and reused, thereby reducing the cost of use.

[0031] In summary, the present invention solves the problems of difficult catalyst recovery, complex preparation, poor stability and the like in the prior art, and has significant application potential in the field of water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below with reference to the accompanying drawings.

[0033] Figure 1 This is a SEM comparison image of the hollow glass microspheres before and after pickling in step 1 of Example 1.

[0034] Figure 2 This is the SEM image of the TiO2 / hollow glass microspheres prepared in step 3 of Example 1.

[0035] Figure 3 These are SEM images of the light magnetic persulfate catalyst prepared in Example 1 at different magnifications.

[0036] Figure 4 This is the XRD pattern of the light magnetic persulfate catalyst prepared in Example 1.

[0037] Figure 5 VSM hysteresis loop diagram of the light magnetic persulfate catalyst prepared in Example 1.

[0038] Figure 6 This is a photo of the light magnetic persulfate catalyst prepared in Example 1 being adsorbed on a magnet.

[0039] Figure 7 The degradation curve of tetracycline by the light magnetic persulfate catalyst prepared in Examples 1-5 is shown.

[0040] Figure 8 The degradation efficiency curve of tetracycline by the light magnetic persulfate catalyst prepared in Example 1 when recycled is shown in FIG.

[0041] Figure 9 The degradation curve of tetracycline by the light magnetic persulfate catalyst prepared in Examples 1-5 under ultraviolet light is shown. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] Example 1

[0044] Step 1: Take 100g of density as 0.2g / cm 3Hollow glass microspheres with a particle size of 20 μm were dispersed in 10% dilute nitric acid and stirred for 6 hours. The hollow glass microspheres were then filtered out and washed with deionized water until neutral. The hollow glass microspheres were placed in an oven at 80°C and dried to obtain acid-washed hollow glass microspheres. The hollow glass microspheres before and after acid washing were scanned using a scanning electron microscope, and the SEM images obtained were as shown below. Figure 1 As shown;

[0045] Step 2: 0.05 mol of anhydrous ethanol, 0.01 mol of glacial acetic acid, and 0.08 mol of deionized water were added to a beaker, and stirred to obtain a first solution. 0.39 mol of anhydrous ethanol, 0.02 mol of triethanolamine, and 0.02 mol of tetrabutyl titanate were added to the beaker in sequence, and stirred to obtain a second solution. The first solution was added dropwise to the second solution under stirring to obtain a mixed solution. 0.02 mmol of polyethylene glycol was added to the mixed solution, and the mixture was stirred at room temperature for 3 h to obtain a uniform, transparent, light yellow TiO2 sol.

[0046] Step 3: Add 10 g of the hollow glass microspheres obtained in step 1 to the TiO2 sol obtained in step 2, stir and mix for 2 hours, and then let it stand for 12 hours. Then filter the hollow glass microspheres, dry them in an oven at 80°C for 2 hours, put them in a muffle furnace, heat them to 530°C at a rate of 5°C / min, calcine them for 3 hours, and then naturally cool them to room temperature to obtain TiO2 / hollow glass microspheres; use a scanning electron microscope to scan the TiO2 / hollow glass microspheres, and the obtained SEM image is as follows: Figure 2 As shown;

[0047] Step 4: 0.86 g of FeCl2·4H2O, 2.05 g of FeCl3·6H2O, and 1.65 g of Co(NO3)2·6H2O were placed in a 500 ml beaker, and then 200 ml of deionized water was added and stirred to obtain a magnetic solution;

[0048] Step 5: 2 g of the TiO2 / hollow glass microspheres obtained in step 3 were added to the magnetic solution in step 4, stirred for 1 hour, and then 40 ml of 25% ammonia water was added dropwise. The beaker was placed in a water bath at 85°C for 1 hour, filtered, and then the sample obtained after centrifugation was washed with deionized water and anhydrous acetic acid, respectively. The above steps were repeated 3 times. Finally, the sample was placed in an oven at 80°C and dried for 12 hours to obtain a lightweight magnetic persulfate catalyst.

[0049] The light magnetic persulfate catalyst was scanned using a scanning electron microscope, and the SEM image obtained was as follows: Figure 3 As shown; X-ray diffraction pattern as shown Figure 4As shown; using a vibrating sample magnetometer, the VSM hysteresis loop diagram of the light magnetic persulfate catalyst is measured, as shown Figure 5 As shown; Use magnets to adsorb light magnetic persulfate catalysts, as shown in the photo Figure 6 As shown; explain with the accompanying drawings: Figure 1 It can be seen from the figure that there are many impurity particles on the surface of the hollow glass microspheres before pickling, and these impurities are removed after pickling; Figure 2 It can be seen that a certain thickness of TiO2 film is coated on the surface of the hollow glass microspheres; Figure 6 It can be seen that the light magnetic persulfate catalyst can be adsorbed by a magnet and has magnetic properties.

[0050] Example 2

[0051] The difference from Example 1 is that the mass of FeCl3·6H2O added in step 4 is 3 g, and the amount of ammonia water added in step 5 is 50 ml. The rest is the same as Example 1.

[0052] Example 3

[0053] The difference from Example 1 is that the mass of Co(NO3)2·6H2O added in step 4 is 2.4 g, and the amount of ammonia water added in step 5 is 50 ml. The rest is the same as in Example 1.

[0054] Example 4

[0055] The difference from Example 1 is that;

[0056] The operation of step 4 is as follows: 0.86g FeCl2·4H2O, 3g FeCl3·6H2O and 2.4g Co(NO3)2·6H2O are placed in a 500ml beaker, and then 300ml deionized water is added and stirred to obtain a magnetic solution;

[0057] The operation of step 5 is as follows: 2 g of the TiO2 / hollow glass microspheres obtained in step 3 are added to the magnetic solution of step 4, stirred for 1 hour, and then 60 ml of 25% ammonia water is added dropwise. The beaker is then placed in a water bath at 85°C for 1 hour, filtered, and then the sample obtained after centrifugation is washed with deionized water and anhydrous acetic acid, respectively. The above steps are repeated 3 times. Finally, the sample is placed in an oven at 80°C and dried for 12 hours to obtain a light magnetic persulfate catalyst. The rest is the same as in Example 1.

[0058] Example 5

[0059] The difference from Example 1 is that;

[0060] The operation of step 4 is as follows: 0.86g FeCl2·4H2O, 2.05g FeCl3·6H2O and 2.4g Co(NO3)2·6H2O are placed in a 500ml beaker, and then 400ml deionized water is added and stirred to obtain a magnetic solution;

[0061] The operation of step 5 is as follows: 2 g of the TiO2 / hollow glass microspheres obtained in step 3 are added to the magnetic solution of step 4, stirred for 1 hour, and then 50 ml of 25% ammonia water is added dropwise. The beaker is then placed in a water bath at 85°C for 1 hour, filtered, and then the sample obtained after centrifugation is washed with deionized water and anhydrous acetic acid, respectively. The above steps are repeated 3 times. Finally, the sample is placed in an oven at 80°C and dried for 12 hours to obtain a light magnetic persulfate catalyst. The rest is the same as in Example 1.

[0062] The catalytic performance of Examples 1-5 was tested using the following method:

[0063] 2mM peroxymonosulfate was added to 50mL of a tetracycline solution with an initial concentration of 50mg / L. After stirring, 30mg of the sample catalyst was added to the solution and stirred for degradation experiments. 2mL of the sample was taken at regular intervals, and 20μL of a 1M sodium sulfate solution was added to the sample to terminate the degradation reaction. The tetracycline concentration in the sample was measured using an ultraviolet spectrophotometer. Finally, the degradation rate was calculated; degradation rate (%) = (initial tetracycline concentration - tetracycline concentration after degradation) / initial tetracycline concentration × 100%; the degradation rate of Examples 1-5 was measured over time, as shown in the following figure. Figure 7 The degradation rate at 1 min was measured, as shown in Table 1:

[0064] Table 1

[0065]

[0066]

[0067] According to the above standards, Example 1 was subjected to five cycle tests, and a line graph showing the degradation rate versus the number of cycles was obtained, as shown in FIG. Figure 8 shown.

[0068] The catalytic performance of Examples 1-5 was tested under ultraviolet light, and the test method was as follows:

[0069] 2mM peroxymonosulfate was added to 50mL of a tetracycline solution with an initial concentration of 50mg / L. After stirring, 30mg of the sample catalyst was added to the above solution. The ultraviolet lamp was turned on (100W high-pressure mercury lamp, irradiation distance 10cm), and the degradation experiment was carried out by stirring. 2mL of the sample was taken at intervals, and 20μL of a 1M sodium sulfate solution was added to the sample to terminate the degradation reaction. The tetracycline concentration in the sample was then measured using an ultraviolet spectrophotometer. Finally, the degradation rate was calculated; degradation rate (%) = (initial tetracycline concentration - tetracycline concentration after degradation) / initial tetracycline concentration × 100%; the degradation rate of Examples 1-5 was measured over time, as shown in the following figure. Figure 9 shown.

[0070] This paper describes five detailed examples, each of which optimizes catalyst performance by precisely adjusting key parameters such as the raw material mass ratio, water bath temperature, and stirring speed. These examples not only demonstrate the adaptability of the preparation process but also demonstrate the stability and efficiency of the catalyst under different conditions.

[0071] To more intuitively demonstrate the properties of the catalyst, this document includes the SEM image of Example 1, the XRD pattern, and the VSM hysteresis loop of Example 1. These images not only confirm the microstructure and composition of the catalyst but also reveal its magnetic properties, providing important information for catalyst recovery and reuse.

[0072] According to the degradation rate test results of tetracycline in Examples 1-5 in Table 1, Figure 7 The degradation curve and Figure 8 It can be seen from the graph of the change in degradation efficiency of recycling that the catalysts obtained by the preparation methods of all the embodiments of this application all exhibit excellent catalytic performance and magnetism, among which the degradation rate of Example 1 is as high as 91.2%, and the magnetism is 1.5emu / g. After 5 recycling uses, the degradation rate is still as high as 89.2%. It is worth mentioning that the catalysts prepared in all the embodiments can degrade tetracycline by more than 78.8% within 1 minute, which proves the high efficiency and high stability of the catalyst. Under ultraviolet light irradiation, the degradation rates of tetracycline prepared in Examples 1-5 are as follows: Figure 9 As shown in the figure, it can be seen that the degradation rate of the catalyst under ultraviolet light is increased by about 5%, indicating that the catalyst not only has a high PMS catalytic performance, but also has a certain photodegradation ability and a strong ability to degrade pollutants.

[0073] In summary, the catalyst obtained by the present invention has high catalytic efficiency, and the entire preparation process is non-toxic and controllable. The catalyst not only has certain magnetic properties but also exhibits certain photocatalytic properties, solving the problems of difficult catalyst recovery, complex preparation, and poor stability in the prior art, and has significant application potential in the field of water treatment.

[0074] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0075] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a light magnetic persulfate catalyst, characterized in that: The following steps are involved: Step 1: First, the hollow glass microspheres are dispersed in a dilute acid solution, stirred, filtered, and washed with deionized water until they reach a neutral state; finally, the treated hollow glass microspheres are dried to obtain acid-washed hollow glass microspheres; Step 2: adding anhydrous ethanol, glacial acetic acid, and deionized water to a beaker and mixing them uniformly to form a first solution; then, adding anhydrous ethanol, triethanolamine, and tetrabutyl titanate to another beaker in sequence and mixing them uniformly to form a second solution; adding the first solution dropwise to the second solution under continuous stirring; after the addition is complete, adding polyethylene glycol to the mixture and stirring at room temperature for 3 hours to obtain a uniform, transparent, light yellow TiO2 sol; Step 3, adding the acid-washed hollow glass microspheres obtained in step 1 to the TiO2 sol obtained in step 2, stirring and mixing, letting it stand for a period of time, filtering, drying, calcining the dried hollow glass microspheres, and cooling them naturally to obtain TiO2 / hollow glass microspheres; Step 4: Add ferrous chloride, ferric chloride and cobalt nitrate to deionized water and stir evenly; then, immerse the TiO2 / hollow glass microspheres prepared in step 3 in the above solution and stir for 1 hour; and adding an alkaline solution to the system during the stirring process to obtain a pretreatment system; Step 5: Place the pretreatment system in step 4 into a water bath for water bath treatment, and then filter, wash and dry to obtain a light magnetic persulfate catalyst.

2. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein The dilute acid in step 1 is at least one of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid.

3. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein In step 2, the molar ratio of anhydrous ethanol, glacial acetic acid and deionized water is 2-5:1:4-8.

4. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein In step 2, the molar ratio of anhydrous ethanol, triethanolamine and tetrabutyl titanate is 10-30:1:1-2.

5. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein In step 3, the mass ratio of the hollow glass microspheres to the titanium dioxide sol is 1:10-30; the drying temperature is 60-120° C., and the time is 2-8 hours; and the calcination temperature is 500-600° C., and the time is 2-4 hours.

6. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein: In step 4, the mass ratio of ferrous chloride, ferric chloride, cobalt nitrate, TiO2 / hollow glass microspheres, ammonia water and deionized water is 1:2-4:2-6:5-20:30-60:120-250; the sum of the molar masses of ferric chloride and ferrous chloride is equal to 2-4 times the molar mass of cobalt nitrate; and the alkaline solution is ammonia water with a concentration of 25-28wt%.

7. The method for preparing a light magnetic persulfate catalyst according to claim 1, wherein: In step 5, the temperature of the water bath treatment is 80-100° C., and the water bath time is 0.5-2 hours; the drying temperature is 50-80° C., and the drying time is 2-24 hours.

8. A light magnetic persulfate catalyst, characterized in that Prepared according to the method according to any one of claims 1 to 7.

9. Use of the light magnetic persulfate catalyst according to claim 8 in the field of water treatment.

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