Sludge biochar / titanium dioxide composite photocatalyst, floating photocatalyst and method for treating cyanobacteria

Abstract

This application discloses a sludge biochar / titanium dioxide composite photocatalyst, a floating photocatalyst, and a method for controlling cyanobacteria. The sludge biochar / titanium dioxide composite photocatalyst is prepared by ball milling raw materials comprising sludge biochar powder and nano-titanium dioxide in a mass ratio of 1:(1-2). The floating photocatalyst is loaded with the sludge biochar / titanium dioxide composite photocatalyst, capable of floating on the water surface and fully absorbing and utilizing sunlight energy to synthesize low-concentration hydrogen peroxide. This allows for the continuous and spontaneous production of low-concentration hydrogen peroxide in waters contaminated by cyanobacteria, thereby inhibiting and killing the algae. The synthesized hydrogen peroxide, upon decomposition, generates new oxygen, increasing the dissolved oxygen content of the water and promoting the growth of other aquatic organisms.

Description

Technical Field

[0001] The present application relates to the field of cyanobacteria control, and in particular to a sludge biochar / titanium dioxide composite photocatalyst, a floating photocatalyst, and a method for controlling cyanobacteria. Background Art

[0002] Cyanobacterial blooms are becoming increasingly frequent due to environmental factors such as eutrophication, rising carbon dioxide concentrations, and global warming. These blooms can cause serious water quality problems, making it difficult for aquatic organisms to survive, disrupting the aquatic ecosystem, and releasing a variety of cyanobacterial toxins into the aquatic environment that are carcinogenic and teratogenic to humans and animals, resulting in severe ecological damage.

[0003] Existing methods for controlling cyanobacteria blooms include manual or mechanical salvage, chemical dosing, nitrogen and phosphorus reduction, ultrasonic treatment, aquatic biological treatment, and chemical oxidation. Adding low-concentration hydrogen peroxide to water bodies is an effective method for controlling cyanobacteria. However, hydrogen peroxide solutions are prone to decomposition at room temperature, and excessively high concentrations can harm aquatic life. Frequent dosing is costly and operationally dangerous. Summary of the Invention

[0004] In order to solve the problems of difficult control of dosage, high cost and dangerous operation in the process of hydrogen peroxide treatment of cyanobacteria, the present application provides a sludge biochar / titanium dioxide composite photocatalyst, a floating photocatalyst and a method for treating cyanobacteria.

[0005] In a first aspect, a sludge biochar / titanium dioxide composite photocatalyst is provided. The sludge biochar / titanium dioxide composite photocatalyst is prepared by ball milling raw materials including sludge biochar powder and nano-titanium dioxide in a mass ratio of 1:(1-2).

[0006] Preferably, the particle size of the sludge biochar / titanium dioxide composite photocatalyst is 20 to 38 μm.

[0007] By adopting the above technical solution, nano-titanium dioxide has long-term thermodynamic stability, is non-toxic, and has relatively effective photocatalytic activity compared to other photocatalytic materials, making it a highly efficient photocatalytic material. However, nano-titanium dioxide has a wide band gap and can only absorb ultraviolet light below 385nm, resulting in a very low utilization rate of sunlight. In addition, due to the wide band gap, the photocatalytic efficiency of nano-titanium dioxide decreases due to the rapid recombination of electrons and holes in the photocatalytic reaction. In practical applications, due to the high surface energy of nano-titanium dioxide, it is in an energy unstable state and is very prone to forming agglomerates, which has brought great obstacles to the practical application of nano-titanium dioxide materials.

[0008] Sludge biochar is a low-cost carbon material that recycles waste biomass. It contains a large number of adsorption sites and ion exchange sites, is loose and porous, and has a large specific surface area. Biochar also contains a variety of functional groups, including carboxyl, phenolic hydroxyl, acid anhydride, etc., which have good adsorption properties. Nano-titanium dioxide material uses sludge biochar as a carrier, which can effectively prevent the agglomeration of nano-titanium dioxide. The sludge biochar / titanium dioxide composite photocatalyst has a large specific surface area and photocatalytic efficiency, can absorb sunlight across a wide spectrum, and efficiently utilize the energy of sunlight. At the same time, sludge biochar has a good ability to transmit electrons. It provides an electron transfer channel for the nano-titanium dioxide material during the photocatalytic reaction, which can quickly transfer photogenerated electrons, thereby reducing the recombination of electron and hole pairs and improving the photocatalytic efficiency.

[0009] The resulting sludge biochar / titanium dioxide composite photocatalyst uses sludge biochar as a carrier, with titanium dioxide nanomaterials dispersed on the surface of the sludge biochar. Using solar energy as its primary energy source and oxygen from water and air as raw materials, the catalyst converts light energy into chemical energy under the stimulation of sunlight, synthesizing low-concentration hydrogen peroxide. This allows for the continuous and spontaneous production of low-concentration hydrogen peroxide in waters contaminated by cyanobacteria, thereby inhibiting and killing the algae and oxidizing and decomposing some cyanobacterial toxins, achieving the goal of sustainable cyanobacterial control. Furthermore, the synthesized hydrogen peroxide, after decomposition, produces new oxygen, increasing the dissolved oxygen content of the water, promoting the growth of other aquatic organisms in the water, improving the diversity of aquatic organisms in the water, and creating a well-circulated ecosystem.

[0010] At the same time, compared with the chemical method, the ball milling method has a simple preparation process and does not require the use of a large amount of compounds to achieve the composite of sludge biochar and nano-titanium dioxide materials.

[0011] Preferably, the preparation method of the sludge biochar / titanium dioxide composite photocatalyst is as follows:

[0012] Preparation of sludge biochar powder: The sludge is naturally air-dried and then placed in a muffle furnace at 500-600°C for pyrolysis for 1.5-2.5 hours. The sludge biochar powder is then washed, dried, and ground to obtain the sludge biochar powder.

[0013] Preparation of sludge biochar / titanium dioxide composite photocatalyst: The obtained sludge biochar powder and nano-titanium dioxide are mixed evenly and added to a ball mill, and ball milled for 5 to 12 hours at a ball milling speed of 300 to 600 rpm. Dispersant and deionized water are added during the ball milling process. After the ball milling is completed, the sludge biochar / titanium dioxide composite photocatalyst is obtained by cooling, drying and sieving.

[0014] Preferably, the dispersant includes one or a combination of sodium hexametaphosphate, sodium tripolyphosphate, and sodium pyrophosphate; and the added amount of the dispersant is 0.5% to 2% of the total mass of the sludge biochar powder and nano-titanium dioxide.

[0015] Preferably, during the ball milling process, the ball-to-material ratio is (20-30):1.

[0016] Preferably, the ball mill is a zirconia ball mill with a wall thickness of 8 mm.

[0017] Preferably, during the ball milling process, the ball milling direction is switched every 30 minutes.

[0018] Preferably, the product needs to be sieved through a 400-mesh sieve after the ball milling process.

[0019] Preferably, the ratio of the mass of deionized water to the total mass of the sludge biochar powder and nano-titanium dioxide is (0.8-1.2):1.

[0020] By adopting the above technical solution, the sludge undergoes pyrolysis reaction under high temperature environment to generate sludge biochar with a porous structure. The organic matter and beneficial elements originally contained in the sludge are also enriched in the sludge biochar generated by pyrolysis, which is conducive to the adsorption of nano-titanium dioxide materials.

[0021] At the same time, this application adopts the ball milling method to prepare the sludge biochar / titanium dioxide composite photocatalytic material. Compared with the chemical method, this method has a simple preparation process and does not require the use of a large amount of compounds to achieve the composite of sludge biochar and nano-titanium dioxide materials. The forced force during the ball milling process will introduce a large amount of strain and reorganization of the nano-scale microstructure, and the small-particle nano-titanium dioxide material can be evenly dispersed on the sludge biochar.

[0022] Preferably, a terminated carbamate polyester is further added during the ball milling process; the added amount of the terminated carbamate polyester is 1.5% to 2.5% of the total mass of the sludge biochar powder and the nano-titanium dioxide.

[0023] Preferably, the preparation process of the carbamate-terminated polyester is as follows:

[0024] S1. Maleic anhydride, ethanol and catalyst A were mixed under a nitrogen atmosphere, and then propylene oxide was added, the temperature was raised to 80-100 ° C, and the reaction was stirred for 5-8h to obtain a pre-reactant;

[0025] S2. Add the pre-reactant to the solvent, adjust the temperature to 60-80°C, add methyl diisocyanate and catalyst B, and stir the reaction for 2-3 hours. Then add the polyethylene polyamine compound and continue stirring the reaction for 2-3 hours to obtain the terminated carbamate polyester.

[0026] Preferably, the mass ratio of maleic anhydride, propylene oxide and ethanol is (65-75):(45-55):100.

[0027] Preferably, catalyst A is sodium hydroxide, and the addition amount is 1% to 2% of the mass of ethanol; catalyst B includes one or a combination of dibutyltin dilaurate and stannous octoate, and the addition amount is 0.1% to 0.2% of the mass of methyl diisocyanate.

[0028] Preferably, the solvent includes one or a combination of acetone and ethyl acetate; the mass ratio of the solvent to ethanol is (1.2-1.5):1.

[0029] Preferably, the mass of methyl diisocyanate is 30% to 40% of the mass of ethanol.

[0030] Preferably, the polyethylene polyamine compound is a co-product of ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine; the mass of the polyethylene polyamine compound is 10% to 20% of the mass of ethanol.

[0031] By adopting the above technical solution, maleic anhydride is further reacted with propylene oxide in ethanol to generate a hydroxyl-terminated polymer, and the hydroxyl groups on the polymer react with methyl diisocyanate and are capped with polyethylene polyamine to obtain a carbamate-terminated polyester.

[0032] During the ball milling process, sludge biochar has strong adsorption capacity, and nano-titanium dioxide is fixedly distributed on the surface of sludge biochar through ball milling and surface potential energy. However, under this connection, the nano-titanium dioxide material is easy to fall off due to external force during use. Therefore, terminal carbamate polyester is also added during the ball milling process. On the one hand, the terminal carbamate polyester can enhance the dispersibility of nano-titanium dioxide during ball milling. The solvated chains contained in the terminal carbamate polyester can form sufficient spatial steric hindrance on the particle surface, so that the nano-titanium dioxide material can be evenly dispersed on the sludge biochar; on the other hand, deionized water is used as the ball milling medium during the ball milling process, and the amino group in the terminal carbamate polyester is the anchoring group. The amino group can form hydrogen bonds with the hydroxyl groups on the surface of the nano-titanium dioxide material and the oxygen-containing groups on the surface of the sludge biochar with the participation of deionized water. Under the action of hydrogen bonds, the nano-titanium dioxide and the sludge biochar are tightly combined, thereby reducing the risk of nano-titanium dioxide falling off during use.

[0033] In a second aspect, a floating photocatalyst is provided, wherein the floating photocatalyst is a polyester fiber non-woven fabric loaded with any one of the sludge biochar / titanium dioxide composite photocatalysts of claims 1 to 6.

[0034] Preferably, the loading amount of the sludge biochar / titanium dioxide composite photocatalyst on the polyester fiber non-woven fabric is 20 to 40 g / m2 .

[0035] Preferably, the preparation method of the floating photocatalyst is as follows: polyester fiber and sludge biochar / titanium dioxide composite photocatalyst are melt-spinned and extruded into a mesh to obtain the floating photocatalyst.

[0036] By adopting the above technical solution, polyester fibers are spun into a web to obtain non-woven fabrics. During this process, the sludge biochar / titanium dioxide composite photocatalyst is loaded on the non-woven fabric and placed in water to achieve the floating of the photocatalyst. On the one hand, it can absorb the energy of sunlight to the greatest extent and make full use of sunlight for photocatalytic reactions; on the other hand, the low concentration of hydrogen peroxide produced by the photocatalyst can also promptly remove cyanobacteria floating on the water surface, inhibiting the survival and reproduction of cyanobacteria floating on the water surface, and facilitating recycling in the later stage.

[0037] In a third aspect, a method for treating cyanobacteria using a sludge biochar / titanium dioxide composite photocatalyst is provided, wherein any floating photocatalyst according to claims 7 to 9 is placed into a cyanobacteria treatment water area for treatment.

[0038] In summary, this application has the following beneficial effects:

[0039] 1. The sludge biochar / titanium dioxide composite photocatalyst in this application is able to float on the water surface by being loaded on a polyester fiber non-woven fabric, and can fully absorb and utilize the energy of sunlight. In addition, the low-concentration hydrogen peroxide produced by the photocatalyst can promptly remove the cyanobacteria floating on the water surface, and is also easy to recycle after treatment.

[0040] 2. The sludge biochar / titanium dioxide composite photocatalyst uses solar energy as its main energy source and oxygen from water and air as raw materials to synthesize low-concentration hydrogen peroxide. This allows the continuous and spontaneous production of low-concentration hydrogen peroxide in waters contaminated by cyanobacteria, thereby inhibiting and killing cyanobacteria. It can also oxidize and decompose a portion of cyanobacterial toxins, achieving the goal of continuous treatment of cyanobacteria. Furthermore, the synthesized hydrogen peroxide will produce new oxygen after decomposition, increasing the dissolved oxygen content of the water and promoting the growth of other aquatic organisms in the water. At the same time, the present application uses a ball milling method to prepare the sludge biochar / titanium dioxide composite photocatalytic material. This method has a simple preparation process, and small-particle nano-titanium dioxide materials can be evenly dispersed on the sludge biochar.

[0041] 3. The sludge biochar / titanium dioxide composite photocatalyst in this application is also added with terminal aminocarbamate polyester during the ball milling process, which can enhance the dispersibility of the nano-titanium dioxide material and form hydrogen bonds between the nano-titanium dioxide and the sludge biochar, thereby strengthening the combination of nano-titanium dioxide and sludge biochar, making the nano-titanium dioxide less likely to fall off during use. DETAILED DESCRIPTION

[0042] Preparation Example of Carbamate-Terminated Polyester

[0043] Preparation Example 1-1, a carbamate-terminated polyester was prepared according to the following method:

[0044] Take 70g of maleic anhydride, 100g of ethanol and 1.5g of sodium hydroxide, mix them evenly under a nitrogen atmosphere, then add 50g of propylene oxide, raise the temperature to 100°C, and stir to react for 6h to obtain a pre-reacted product;

[0045] Take 130g of acetone, add the obtained pre-reactant to the acetone, mix well and adjust the temperature to 70°C, then add 35g of methyl diisocyanate and 0.05g of dibutyltin dilaurate and stir to react for 2h, then add 15g of polyethylene polyamine compound and continue stirring to react for 3h to obtain terminal carbamate polyester.

[0046] Preparation example of sludge biochar / titanium dioxide composite photocatalyst

[0047] Preparation Example 2-1: A sludge biochar / titanium dioxide composite photocatalyst was prepared according to the following method:

[0048] 30 g of sludge was weighed and air-dried, then placed in a muffle furnace at 500 °C for 2 h for pyrolysis, washed with deionized water to remove ash and impurities, and then dried in an oven at 105 °C. The powder was then ground through a 200-mesh sieve to obtain sludge biochar.

[0049] Take 100g of the obtained sludge biochar powder and 150g of nano-titanium dioxide, mix them evenly and add them to a zirconia ball mill with a wall thickness of 8mm. The ball-to-material ratio is 30:1. The ball milling is carried out for 8h. The ball milling speed is set to 500rpm. The ball milling direction is changed every 30min. During the ball milling process, 2.5g of sodium hexametaphosphate, 5g of the terminal aminoformate polyester prepared in Preparation Example 1-1 and 250g of deionized water are also added. After the ball milling is completed, it is cooled, dried and ground, and passed through a 400-mesh sieve to obtain a sludge biochar / titanium dioxide composite photocatalyst with an average particle size of 30μm.

[0050] Preparation Example 2-2, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the added amount of nano-titanium dioxide is 100 g.

[0051] Preparation Example 2-3, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the amount of nano-titanium dioxide added is 200 g.

[0052] Preparation Example 2-4, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the amount of sodium hexametaphosphate added is 1.3 g.

[0053] Preparation Example 2-5, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the amount of sodium hexametaphosphate added is 5 g.

[0054] Preparation Example 2-6, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the added amount of the terminal carbamate polyester prepared in Preparation Example 1-1 is 3.8 g.

[0055] Preparation Example 2-7, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the added amount of the terminal carbamate polyester prepared in Preparation Example 1-1 is 6.2 g.

[0056] Preparation Example 2-8, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the ball-to-material ratio during the ball milling process is 20:1.

[0057] Preparation Example 2-9, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the ball-to-material ratio during the ball milling process is 25:1.

[0058] Preparation Example 2-10, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the added amount of nano-titanium dioxide is 50 g.

[0059] Preparation Example 2-11, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the added amount of nano-titanium dioxide is 300 g.

[0060] Preparation Example 2-12, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the ball-to-material ratio during the ball milling process is 35:1.

[0061] Preparation Example 2-13, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the ball-to-material ratio during the ball milling process is 15:1.

[0062] Preparation Example 2-14, a sludge biochar / titanium dioxide composite photocatalyst, differs from Preparation Example 2-1 only in that the terminal carbamate polyester prepared in Preparation Example 1-1 is not added.

[0063] Example

[0064] Example 1, a method for treating cyanobacteria using a sludge biochar / titanium dioxide composite photocatalyst, wherein the floating photocatalyst is prepared according to the following method:

[0065] A certain amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1 was mixed with polyethylene terephthalate (Sinopec TFW100) and melt-spun to produce polyester fibers. This was then extruded into a web to produce a polyester fiber non-woven fabric loaded with the sludge biochar / titanium dioxide composite photocatalyst, i.e., a floating photocatalyst. The melt-spinning process temperature was 255°C to 275°C.

[0066] The loading amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1 on the polyester fiber non-woven fabric is 20 g / m 2 .

[0067] Example 2, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-2 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0068] Example 3, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-3 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0069] Example 4, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-4 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0070] Example 5, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-5 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0071] Example 6, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-6 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0072] Example 7, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-7 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0073] Example 8, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-8 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0074] Example 9, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-9 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0075] Example 10, a method for treating cyanobacteria using a sludge biochar / titanium dioxide composite photocatalyst, the floating photocatalyst used differs from that in Example 1 only in that the loading amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1 on the polyester fiber nonwoven fabric is 30 g / m 2 .

[0076] Example 11, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst, the floating photocatalyst used differs from that in Example 1 only in that the loading amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1 on the polyester fiber nonwoven fabric is 40 g / m 2 .

[0077] Example 12, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-10 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0078] Example 13, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-11 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0079] Example 14, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-12 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0080] Example 15, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-13 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0081] Example 16, a method for treating cyanobacteria with a sludge biochar / titanium dioxide composite photocatalyst. The floating photocatalyst used is different from that in Example 1 only in that an equal amount of the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-14 is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0082] Comparative Example

[0083] Comparative Example 1, a method for treating cyanobacteria using a sludge biochar / titanium dioxide composite photocatalyst, the floating photocatalyst used differs from that in Example 1 only in that an equal amount of nano-titanium dioxide is used to replace the sludge biochar / titanium dioxide composite photocatalyst prepared in Preparation Example 2-1.

[0084] Performance testing

[0085] 1. Algae removal test:

[0086] (1) Sample preparation: The floating photocatalysts obtained in Examples 1 to 16 and Comparative Example 1 were cut into square samples of 4×4 cm in size.

[0087] (2) Experimental process: 100 ml of Microcystis aeruginosa solution (initial algal cell density was 6.48 × 10 6 cells / ml), and then the prepared sample was added to a beaker, placed in a dark place for 1 hour, and then placed under a xenon lamp for photocatalytic algae removal test. Samples were taken every 1 hour, and the concentration of chlorophyll a in the solution was detected by UV-visible spectrophotometer to characterize the content of Microcystis aeruginosa.

[0088] The xenon lamp used was a 300W xenon lamp equipped with a 420nm filter, with a light intensity of 100mW / cm 2 , the distance between the xenon lamp light source and the liquid surface in the beaker is 10 cm.

[0089] The test results are shown in Table 1.

[0090] 2. Photocatalyst Durability Test: Based on Experiment 1, a photocatalytic algae removal test was conducted under a xenon lamp. The solution in the beaker was stirred at a low speed of 140 rpm. After 9 hours of testing, the removal rate of Microcystis aeruginosa was measured. The test results are shown in Table 2.

[0091] Table 1 Algae removal test results

[0092]

[0093]

[0094] Table 2 Durability test results of photocatalyst

[0095]

[0096] According to Tables 1 and 2, in combination with Example 1 and Comparative Example 1, it can be seen that the removal rate of Microcystis aeruginosa in the algae removal test of Comparative Example 1 is significantly lower than that of Example 1, and the removal rate is also significantly reduced in the durability test. This indicates that the algae removal efficiency and durability of Comparative Example 1 are significantly reduced compared to Example 1. The reason for this may be that the nano-titanium dioxide photocatalyst in Comparative Example 1 does not use sludge biochar as a carrier, and loses the assisting effect of biochar. The utilization rate of nano-titanium dioxide for light is significantly reduced, and the recombination of electrons and holes in the photocatalytic process is difficult, resulting in a significant decrease in the overall photocatalytic efficiency. In addition, the nano-titanium dioxide is composited with polyester fiber, and the connection between the two is not tight enough, which also reduces the durability.

[0097] Combining Example 1 with Examples 2 to 7, it can be seen that the removal rates of Microcystis aeruginosa in Examples 2 to 7 in the algae removal test did not change significantly compared to Example 1, and in the durability test, the removal rate did not decrease significantly. This indicates that there was no significant change in the algae removal efficiency and durability of Examples 2 to 7 compared to Example 1. The reason for this may be that in Examples 2 to 7, only the ratio of the raw materials used in the preparation of the sludge biochar / titanium dioxide composite photocatalyst was varied within the required range, indicating that varying the ratio of the raw materials within the required range had no significant effect on the final algae removal effect.

[0098] Combining Examples 1, 8, and 9, it can be seen that the removal rates of Microcystis aeruginosa in Examples 8 and 9 in the algae removal test did not change significantly compared to Example 1, and in the durability test, the removal rates did not decrease significantly. This indicates that there was no significant change in the algae removal efficiency and durability of Examples 8 and 9 compared to Example 1. This may be because in Examples 8 and 9, only the ball-to-material ratio during the ball milling of the sludge biochar / titanium dioxide composite photocatalyst was varied within the required range, indicating that varying the ball-to-material ratio within the required range had no significant effect on the final algae removal effect.

[0099] Combining Examples 1, 10, and 11, it can be seen that the removal rates of Microcystis aeruginosa in Examples 10 and 11 did not change significantly compared to Example 1 in the algae removal test, and the removal rates did not decrease significantly in the durability test. This indicates that there was no significant change in the algae removal efficiency and durability of Examples 10 and 11 compared to Example 1. This may be because Examples 10 and 11 only varied the loading of the sludge biochar / titanium dioxide composite photocatalyst on the polyester fiber non-woven fabric in the floating photocatalyst within the required range. This indicates that varying the photocatalyst loading within the required range has no significant effect on the final algae removal effect.

[0100] Combining Examples 1, 12, and 13, it can be seen that the removal rates of Microcystis aeruginosa in Examples 12 and 13 decreased compared to Example 1 in the algae removal test, while the removal rate did not decrease significantly in the durability test. This indicates that the algae removal efficiency of Examples 12 and 13 decreased compared to Example 1. This may be because, in Example 12, the amount of nano-titanium dioxide added during the preparation of the sludge biochar / titanium dioxide composite photocatalyst was reduced, resulting in a decrease in the content of titanium dioxide in the resulting floating photocatalyst, and thus a decrease in photocatalytic efficiency. In Example 13, the amount of titanium dioxide added during the preparation of the sludge biochar / titanium dioxide composite photocatalyst was increased. During the biochar composite process, the increased amount of titanium dioxide added easily caused agglomeration, which reduced the content of titanium dioxide in the resulting floating photocatalyst, and thus reduced the photocatalytic efficiency.

[0101] Combining Example 1, Example 14, and Example 15, it can be seen that the removal rates of Microcystis aeruginosa in Example 14 and Example 15 in the algae removal test were lower than those in Example 1, while the removal rates did not decrease significantly in the durability test. This indicates that the algae removal efficiency of Example 14 and Example 15 decreased compared to that in Example 1. This may be because the ball-to-material ratio in Example 14 was increased, i.e., the proportion of titanium dioxide and sludge biochar added during the ball milling process was too small, resulting in a poor composite effect during the ball milling process, which in turn led to a decrease in the algae removal efficiency of the resulting floating photocatalyst. In contrast, the ball-to-material ratio in Example 15 was decreased, i.e., the proportion of titanium dioxide and biochar added during the ball milling process was too large, resulting in insufficient ball milling of some materials, a decreased composite effect, and a decreased photocatalytic effect of the resulting floating photocatalyst.

[0102] Combining Example 1 and Example 16, it can be seen that the removal rate of Microcystis aeruginosa in Example 16 in the algae removal test is lower than that in Example 1, and the removal rate is also lower in the durability test. This indicates that the algae removal efficiency and durability of Example 16 are lower than those of Example 1. The reason for this may be that in Example 16, no terminal carbamate polyester was added during the ball milling process of the sludge biochar / titanium dioxide composite photocatalyst, resulting in an insufficient connection between the sludge biochar and the nano-titanium dioxide material. This resulted in separation during the subsequent preparation of the floating photocatalyst, resulting in a decrease in photocatalytic efficiency. At the same time, in the durability test, separation was triggered by external force, resulting in a decrease in durability.

[0103] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A sludge biochar / titanium dioxide composite photocatalyst, characterized in that: The sludge biochar / titanium dioxide composite photocatalyst is prepared by ball milling raw materials including sludge biochar powder and nano-titanium dioxide in a mass ratio of 1: (1-2); The preparation method of the sludge biochar / titanium dioxide composite photocatalyst is as follows: Preparation of sludge biochar powder: The sludge is naturally air-dried and then pyrolyzed at 500-600°C for 1.5-2.5 hours, and then washed, dried, and ground to obtain sludge biochar powder; Preparation of sludge biochar / titanium dioxide composite photocatalyst: The obtained sludge biochar powder and nano-titanium dioxide are mixed evenly and added to a ball mill, and ball milled for 5 to 12 hours at a ball milling speed of 300 to 600 rpm. A dispersant, a terminal carbamate polyester and deionized water are added during the ball milling process. After the ball milling, the sludge biochar / titanium dioxide composite photocatalyst is obtained by cooling, drying and sieving. The added amount of the terminal carbamate polyester is 1.5% to 2.5% of the total mass of the sludge biochar powder and nano-titanium dioxide; The preparation process of the terminal carbamate polyester is as follows: S1. Maleic anhydride, ethanol and catalyst A were mixed under a nitrogen atmosphere, and then propylene oxide was added, the temperature was raised to 80-100 ° C, and the reaction was stirred for 5-8h to obtain a pre-reactant; S2. Add the pre-reactant to the solvent, adjust the temperature to 60-80°C, add methyl diisocyanate and catalyst B, and stir to react for 2-3 hours. Then add the polyethylene polyamine compound and continue stirring to react for 2-3 hours to obtain the terminated carbamate polyester.

2. The sludge biochar / titanium dioxide composite photocatalyst according to claim 1, characterized in that: The particle size of the sludge biochar / titanium dioxide composite photocatalyst is 20 to 38 μm.

3. The sludge biochar / titanium dioxide composite photocatalyst according to claim 1, characterized in that: The dispersant includes one or a combination of sodium hexametaphosphate, sodium tripolyphosphate, and sodium pyrophosphate; the added amount of the dispersant is 0.5% to 2% of the total mass of the sludge biochar powder and nano-titanium dioxide.

4. A floating photocatalyst, characterized in that: The floating photocatalyst is a polyester fiber non-woven fabric loaded with any one of the sludge biochar / titanium dioxide composite photocatalysts according to claims 1 to 3.

5. The floating photocatalyst according to claim 4, characterized in that The loading amount of the sludge biochar / titanium dioxide composite photocatalyst on the polyester fiber non-woven fabric is 20 to 40 g / m 2 .

6. The floating photocatalyst according to claim 4, characterized in that The preparation method of the floating photocatalyst is as follows: polyester fiber and sludge biochar / titanium dioxide composite photocatalyst are melt-spinned and extruded into a net to obtain the floating photocatalyst.

7. A method for treating cyanobacteria using a sludge biochar / titanium dioxide composite photocatalyst, characterized in that: Any floating photocatalyst according to claims 4 to 6 is placed into a water area for blue algae treatment.

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