Floating photocatalytic material, preparation method and application in blue-green algae treatment

Abstract

This invention relates to a floating photocatalytic material, its preparation method, and its application in cyanobacteria control. The method includes the following steps: uniformly mixing a phenolic compound, an aldehyde solution, a solvent, and an alkaline catalyst, followed by a prepolymerization reaction to obtain a prepolymer; adding a foaming agent to the prepolymer and mixing uniformly to obtain an emulsion; adding an acidic catalyst to the emulsion and undergoing a gelation reaction to obtain a wet gel; and curing the wet gel by heating to obtain the floating photocatalytic material. This invention utilizes an integrated foaming process to simultaneously form a porous structure with interconnected internal components during synthesis, giving the material sufficient low density to achieve self-floating. The material itself is the photocatalytically active component, simultaneously possessing structural support and buoyancy functions, achieving integrated construction of material function and structure. This effectively avoids problems such as active component shedding, loss, and secondary pollution, resulting in high catalytic efficiency. This material can be directly used as a floating board for cyanobacteria control, achieving efficient and eco-friendly continuous inhibition of cyanobacteria.

Description

Technical Field

[0001] This invention relates to the fields of water environment management and photocatalysis technology, specifically to a floating photocatalytic material and its preparation method, and its application in cyanobacteria control. Background Technology

[0002] With the increasing severity of eutrophication, cyanobacteria blooms are frequently occurring in lakes, reservoirs, and landscape water bodies, not only disrupting the balance of aquatic ecosystems but also potentially releasing algal toxins that threaten drinking water safety. Existing technologies for treating cyanobacteria include chemical treatments, physical removal, and biological regulation, but these methods generally suffer from drawbacks such as high ecological risks, high costs, and difficulty in maintaining long-term effectiveness.

[0003] In recent years, floating photocatalytic algae removal technology has attracted attention. This type of technology involves placing photocatalytic materials on the water surface and utilizing the active species generated under light conditions to inhibit or remove cyanobacteria. However, existing floating photocatalytic technologies mostly employ methods such as coating or bonding the photocatalyst to the surface of inert floating carriers like foam plastics or pontoons. Their structure and function are independent, and the following problems still exist in practical water applications: (1) The bonding strength between the photocatalyst and the floating carrier is limited. Under conditions of long-term immersion, water flow disturbance and algae attachment, it is easy to fall off or peel off, resulting in rapid decay of catalytic performance and may cause secondary pollution risk. (2) Conventional floating carriers are mostly inert materials. The carrier itself does not have catalytic function, resulting in a low proportion of effective active ingredients in the material and limited catalytic efficiency per unit area. In addition, in some composite processes, the catalytic active components are easily wrapped or buried by the matrix, making it difficult to fully expose them to light and reactants, which further reduces their utilization rate. (3) Existing floating photocatalytic materials are mostly used in the form of overall deployment, which has poor structural adaptability and is not conducive to modular installation, replacement and maintenance, thus restricting their application in engineering water treatment.

[0004] Therefore, there is an urgent need to develop a floating photocatalytic material that is structurally stable, has good catalytic efficiency, and is easy to integrate, in order to achieve the long-term stable operation of cyanobacteria control technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a floating photocatalytic material, its preparation method, and its application in cyanobacteria control, thereby solving the technical problems of easy photocatalyst detachment and limited catalytic efficiency in existing floating photocatalytic materials.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for preparing a floating photocatalytic material, comprising the following steps: S1, mixing a phenolic compound, an aldehyde solution, a solvent and an alkaline catalyst uniformly, and obtaining a prepolymer through a prepolymerization reaction; S2, adding a foaming agent to the prepolymer and mixing uniformly to obtain an emulsion; S3, adding an acidic catalyst to the emulsion and obtaining a wet gel through a gelation reaction; S4, heating and curing the wet gel to obtain a floating photocatalytic material.

[0007] Secondly, the present invention provides a floating photocatalytic material prepared by the above-described preparation method.

[0008] Thirdly, the present invention provides an application of the above-mentioned floating photocatalytic material in the treatment of cyanobacteria.

[0009] Compared with the prior art, the beneficial effects of the present invention include: (1) In this invention, phenolic compounds undergo alkali-catalyzed polycondensation with aldehydes to obtain linear or low-crosslinking prepolymers. A foaming agent is then added to the prepolymers to fully emulsify and disperse the foaming agent in the prepolymers to form a uniform emulsion. A three-dimensional network wet gel is obtained by rapid gelation catalysis with acid. Finally, the material is cured by heating to form a floating photocatalytic material with a porous structure. In this invention, the integrated foaming process enables the material to form an internally interconnected porous structure during synthesis. This structure gives the material a sufficiently low density to achieve self-floating without relying on any external buoyancy carrier. The preparation process is simple, the raw materials are widely available, the reaction conditions are mild, no complicated post-processing is required, the cost is controllable, the size is adjustable and it has the ability to form large sizes, making it suitable for large-scale continuous production. (2) The floating photocatalytic material of the present invention is the photocatalytic active component itself, and has both structural support and floating functions. It realizes the integrated construction of material function and structure, effectively avoiding problems such as active component shedding, loss, and secondary pollution, and has high catalytic efficiency. The material can be directly used as a floating plate for cyanobacteria control. Through the design of the material's integral porous structure, a gas-liquid-solid three-phase reaction interface is actively and stably constructed on the water surface. This not only optimizes the mass transfer of oxygen and water, but more importantly, it promotes the synergy of the "oxygen reduction" and "water oxidation" dual reaction pathways based on this interface, thereby significantly improving the in-situ generation efficiency of key active species such as hydrogen peroxide (H2O2). It can achieve efficient and ecologically mild continuous inhibition of cyanobacteria and has high algae removal efficiency. Attached Figure Description

[0010] Figure 1 This is a description of the changes in lake water during the treatment process of the floating plate of the present invention; wherein, (a) is a water sample before treatment, (b) is a water sample of the long-term treatment group (total 18h) after 6h of treatment, and (c) is a water sample of the long-term treatment group (total 18h) after treatment is completed. Figure 2This describes the changes in water quality indicators within 21 days after the lake water was treated. Figure 3 This study analyzes the changes in community structure and toxicity factors of cyanobacteria at the genus level before and after the treatment of lake water samples. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0013] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0014] To address the shortcomings of existing photocatalyst materials, such as easy photocatalyst detachment and limited catalytic efficiency, this invention provides a floating photocatalytic material, its preparation method, and its application in cyanobacteria control. A monolithic functional material based on resorcinol-formaldehyde (RF) resin is prepared through an integrated sol-gel and foaming process. The resorcinol-formaldehyde resin forms the main framework of the material and imparts photocatalytic activity. Furthermore, its low density allows it to be directly used as a floating board. This floating board has the following characteristics: (1) Integrated structure: Under photocatalytic conditions, low-concentration hydrogen peroxide is continuously generated in situ on the water surface by the photocatalytic component resorcinol-formaldehyde resin, which can achieve mild inhibition of cyanobacteria and avoid the ecological impact caused by one-time high-dose addition; (2) Built-in porous floating structure: Through controllable foaming, low-density, high-porosity interconnected channels are formed inside the material, giving the material self-floating ability and large specific surface area; (3) Good environmental stability: The RF resin matrix has good water resistance and chemical corrosion resistance, and is suitable for maintaining stable performance in water for a long time; (4) It can be molded and processed: it can be directly prepared into plate-shaped components with regular shape and stable structure, which is convenient for large-scale production and use.

[0015] Therefore, this floating photocatalytic material integrates material buoyancy, structural strength and photocatalytic function, and is superior to existing photocatalytic materials in terms of stability, service life and engineering applicability.

[0016] In a first aspect, the present invention provides a method for preparing a floating photocatalytic material, comprising the following steps: S1, phenolic compounds, aldehyde solution, solvent and alkaline catalyst are mixed evenly and then subjected to a prepolymerization reaction to obtain a prepolymer; S2, add foaming agent to prepolymer and mix evenly to obtain emulsion; S3, add an acid catalyst to the emulsion, and obtain a wet gel through a gelation reaction; S4, the wet gel is cured by heating to obtain a floating photocatalytic material.

[0017] It should be noted that the shape of the wet gel can be changed according to the mold. During the preparation process, the wet gel can be directly molded into a structure with specific macroscopic size and shape (such as a plate) by casting. The size can be controlled and scaled up by adjusting the process parameters to prepare a large-size photocatalytic floating plate suitable for large-area water applications, while maintaining good mechanical strength and dimensional stability. Therefore, this invention has good processing adaptability, which is convenient for modular production, transportation, deployment and replacement. It effectively overcomes the limitations of photocatalytic materials such as MOF in terms of molding and processing, structural stability and engineering cost, and provides a practical material basis for large-scale water body cyanobacteria control projects.

[0018] In this invention, phenolic compounds and aldehydes undergo alkali-catalyzed condensation polymerization to form a soluble and fusible linear or low-crosslinked prepolymer. A foaming agent is then added to this prepolymer, allowing it to fully emulsify and disperse, forming a uniform emulsion. Rapid gelation via acid catalysis yields a three-dimensional network-like wet gel. Finally, heating and curing result in a floating photocatalytic material with a porous structure. This invention utilizes an integrated foaming process to simultaneously form a porous structure within the material during synthesis. This structure provides the material with sufficiently low density to achieve self-floating without relying on any external buoyancy support. The preparation process is simple, with widely available raw materials, mild reaction conditions, no complex post-processing required, controllable cost, adjustable dimensions, and large-scale molding capability. It exhibits good processability and engineering application prospects, and is particularly suitable for large-scale continuous production.

[0019] The floating photocatalytic material of this invention is the photocatalytic active component itself, and also has structural support and buoyancy functions, realizing the integrated construction of material function and structure, effectively avoiding problems such as active component shedding, loss, and secondary pollution; it uses phenol-aldehyde resin with good water resistance and chemical corrosion resistance as the matrix, and the material can resist the complex chemical environment in natural water bodies and the effects of long-term light and immersion, significantly improving the material's environmental adaptability and service life.

[0020] In some embodiments, in step S1, the phenolic compound includes one or more of resorcinol, phenol, catechol, hydroquinone, phloroglucinol, etc.; the aldehyde compound in the aldehyde solution is selected from one or more of formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, etc., preferably formaldehyde.

[0021] In some embodiments, in step S1, the molar ratio of phenolic compound to aldehyde is 1:(1-3), more preferably 1:(1.5-2.5).

[0022] In some embodiments, in step S1, the mass concentration of the aldehyde solution is 35-40%.

[0023] In some embodiments, in step S1, the solvent is water, and the mass ratio of the phenolic compound to water is 1:(0.5-10), more preferably 1:(1-4).

[0024] In some embodiments, in step S1, the alkaline catalyst includes one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, sodium hydroxide, and ammonia.

[0025] In some embodiments, step S1 involves mixing the phenolic compound, aldehyde solution, solvent, and alkaline catalyst evenly, specifically including: dissolving the phenolic compound in the solvent under a water bath at 40–60°C, then adding the alkaline catalyst to adjust the pH value to 8–10, and subsequently adding the aldehyde solution dropwise under stirring and mixing evenly.

[0026] In some embodiments, in step S1, the prepolymerization reaction is carried out at 15–30°C for 30–720 min.

[0027] In some embodiments, in step S2, the foaming agent includes n-pentane, n-hexane, cyclohexane, dichloromethane, or petroleum ether (boiling range 30-60°C). The present invention uses hydrophobic foaming agents such as n-pentane, which have a low boiling point, making it easy to cooperate with subsequent heat treatment and ensure the foaming effect.

[0028] In some embodiments, the ratio between the foaming agent and the phenolic compound is (2-6) mL : 10g.

[0029] In some embodiments, step S2, adding a foaming agent to the prepolymer and mixing it evenly, specifically includes: adding a foaming agent to the prepolymer and stirring at a speed of 1000-1500 rpm for 5-10 min. This invention, by continuously stirring at a significantly increased stirring speed for 5-10 min, allows the foaming agent to be fully emulsified and dispersed in the continuous phase of the prepolymer (RF sol) in the form of tiny droplets, forming a uniform emulsion (yellow turbid liquid).

[0030] In some embodiments, in step S3, the acid catalyst includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, p-toluenesulfonic acid, etc., preferably phosphoric acid; the acid catalyst is added to the emulsion to adjust the pH value to 2-4.5. This invention adds an acid catalyst to the emulsion to initiate gelation, causing the RF prepolymer to rapidly crosslink and form a three-dimensional network-like wet gel, and the rapidly formed gel network encapsulates and locks the foaming agent droplets inside.

[0031] In some embodiments, in step S4, the heat curing involves pre-curing at 30–40°C for 1.5–2.5 h, followed by curing at 40–80°C for another 1.5–2.5 h. This invention uses heat treatment to solidify and shape the resin network, while the foaming agent vaporizes to create pores. Specifically, the process is divided into two stages: the first stage is at a lower temperature, where the resin initially solidifies, and the foaming agent begins to vaporize, expanding within the gel network to form bubbles; the second stage is at a higher temperature, where the resin is fully cross-linked and cured, and the foaming agent completely vaporizes and escapes or dissolves into the resin skeleton, ultimately forming a dry, hard, porous pink RF floating photocatalyst material that can be used directly as a floating plate.

[0032] Secondly, the present invention provides a floating photocatalytic material prepared by the above-described preparation method.

[0033] Thirdly, the present invention provides an application of the above-mentioned floating photocatalytic material in the treatment of cyanobacteria.

[0034] The main mechanisms of action and advantages of this invention include: (1) This invention uses resorcinol-formaldehyde (RF) resin system as the core material, which is chosen based on the following comprehensive advantages: RF resin has a superior intrinsic photoresponse capability compared to traditional TiO2 under sunlight (especially in the visible light region), and can more effectively utilize the solar spectrum, overcoming the fundamental defects of inorganic semiconductor materials, such as strong dependence on ultraviolet light and low overall utilization rate of sunlight. Compared with other organic photocatalytic materials, the network structure formed by RF resin through three-dimensional cross-linking has excellent chemical stability and resistance to photocorrosion, and can withstand long-term immersion in water, pH fluctuations and continuous light exposure, fundamentally solving the problems of easy degradation and short service life of organic materials. Compared with MOFs and COFs materials, which are complex to synthesize, expensive and generally have poor water stability, RF resin raw materials are readily available, the synthesis process is mature and the cost is low, and its cross-linked polymer nature endows it with excellent water resistance and long-term structural stability. Most importantly, the RF resin system can be molded into a low-density porous structure through an integrated in-situ foaming process, which enables the material to float. This allows it to be directly molded into an integral material with macroscopic dimensions, regular shape, self-floating and controllable porous structure, without relying on an external buoyancy carrier, thus eliminating the failure problem caused by the instability of the carrier-catalyst interface. (2) The resorcinol-formaldehyde (RF) resin of the present invention is the photocatalytic active component. Therefore, the buoyancy, structural strength and photocatalytic function of the material are all derived from the single RF resin body. Its buoyancy is given by the porous structure formed by the foaming of the resin itself, and the catalytic activity comes from the photoresponse characteristics of the resin itself. Thus, it eliminates the various failure risks caused by the unstable bonding of heterogeneous materials at the interface, fundamentally solves the technical problem of easy shedding and loss of traditional powder or supported photocatalysts, and eliminates the risk of secondary pollution. (3) In the preparation method of the present invention, firstly, the hydrophobic foaming agent droplets are encapsulated and locked in the network by rapid gelation, and finally, the simultaneous curing and foaming are achieved by controlled heat treatment; the method of the present invention can prepare phenolic resin foam photocatalytic materials with both high porosity and suitable pore size distribution. (4) By controlling the foaming conditions and molding process parameters, the material can be molded in a controllable manner, so that it can be prepared into plate-shaped structures of different specifications and sizes, including large-size floating plates suitable for large-area water applications; the preparation method has a simplified process flow, controllable cost, and is suitable for large-scale continuous production. (5) The floating photocatalytic material of this invention can be directly used as a floating plate for cyanobacteria control. It can not only provide sufficient buoyancy and high specific surface area to optimize mass transfer and light utilization, but also actively and stably construct a gas-liquid-solid three-phase reaction interface on the water surface through the design of the material's integral porous structure. This not only optimizes the mass transfer of oxygen and water, but more importantly, promotes the synergistic effect of the "oxygen reduction" and "water oxidation" dual reaction pathways based on this interface. This significantly improves the in-situ generation efficiency of key active species such as hydrogen peroxide (H2O2), achieving efficient and ecologically mild treatment of cyanobacteria. The invention provides continuous inhibition of cyanobacteria; the photocatalytic material is driven by solar energy, requiring no chemical agents, making the treatment process green, safe, and with low ecological risk; the floating structure is highly compatible with the enrichment characteristics of cyanobacteria on the surface, resulting in high light energy utilization and superior algae removal efficiency compared to traditional methods; it can operate for a long time under natural conditions, providing continuous inhibition of cyanobacteria recurrence; the system has a simple structure, low energy consumption, and low maintenance costs, making it particularly suitable for the inhibition and removal of cyanobacteria in lakes, reservoirs, landscape water bodies, and other eutrophic water bodies. It also possesses good modularity and engineering adaptability, facilitating large-scale promotion and comprehensive treatment applications.

[0035] Therefore, the floating photocatalytic material of this invention possesses excellent water resistance, chemical corrosion resistance, and resistance to photoaging. It can maintain the integrity of its physical structure and the stability of its photocatalytic function over a long period in complex aquatic environments. It is a photocatalytic material that integrates floating function, structural strength, and stable photocatalytic activity. The method of this invention mainly includes an integrated sol-gel and foaming step, realizing the direct molding from raw materials into materials with specific macroscopic shapes (such as plates) and microscopic porous structures. This method is simple, cost-controllable, and suitable for large-scale production. The floating photocatalytic material obtained by this invention can be used for cyanobacteria control, effectively suppressing algae while maximizing the maintenance of the aquatic ecosystem's balance and self-repair capabilities.

[0036] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0037] The formaldehyde solution is a 37% (w / w) aqueous solution of formaldehyde with a density of 1.09 g / mL.

[0038] Test-related instructions for this invention: Photocatalytic activity test (H2O2 generation): The floating plate sample (8 cm × 8 cm) was placed in a reactor containing 100 mL of deionized water and irradiated under simulated sunlight (xenon lamp, light intensity ~800 mW / cm²). Samples were taken at 1, 2, 4, 8, and 12 hours after irradiation, and the concentration of hydrogen peroxide in the aqueous solution was determined by titanium salt spectrophotometry. The results are expressed in mg / L.

[0039] Cyanobacterial inhibition experiment: Using Microcystis aeruginosa as a model organism, floating plate samples (10 cm × 10 cm) were placed in 1 L of algal solution with the appropriate density (initial algal density: 1.0 × 10⁻⁶). 6 Algal cells were collected in glass dishes (cells / mL) and irradiated under simulated sunlight (xenon lamp, light intensity ~800 mW / cm²). Samples were taken at 1, 2, 4, 8, and 12 hours after irradiation, and the algal cell density was determined by microscopic counting.

[0040] Example 1 A method for preparing a floating photocatalytic material includes the following steps: S1. Preparation of the prepolymer: Add 20.0 g of deionized water to a beaker and heat to 50°C on a magnetic stirrer. Add 10.00 g of resorcinol and stir until the white solid is completely dissolved and the solution becomes clear. Then add 0.072 g of anhydrous sodium carbonate to adjust the pH of the system to approximately 10. While stirring continuously (400 rpm), slowly add 13.6 mL of a 37% (w / w) formaldehyde aqueous solution (i.e., the molar ratio of resorcinol to formaldehyde is approximately 1:2). After the addition is complete, continue stirring at room temperature for 90 minutes to obtain a uniform, pale yellow prepolymer.

[0041] S2. Dissolving the foaming agent: Add 4.0 mL of n-pentane as a foaming agent to the above pale yellow prepolymer, increase the stirring speed to 1200 rpm, disperse it evenly in the solution, and stir for 10 minutes to obtain a yellow emulsion.

[0042] S3. Acid-catalyzed gelation: After the n-pentane has partially dissolved, slowly add 2.0 mL of a 25% phosphoric acid solution dropwise to the emulsion. The system color rapidly turns white. After the acid is added, continue stirring for 5 minutes. At this point, the pH of the system is 3.2, and a wet gel is obtained. Immediately pour the wet gel into a flat mold with dimensions of 8 cm × 8 cm × 1 cm or 10 cm × 10 cm × 1 cm.

[0043] S4. Curing, Foaming, and Drying: Place the mold in a forced-air drying oven and treat it at 40°C for 2 hours to complete preliminary curing and foaming; then raise the temperature to 60°C for 2 hours to allow the resin to fully crosslink and dry completely. After demolding, a pink, hard, and porous floating photocatalytic material is obtained, denoted as RF floating plate.

[0044] Example 2 Compared with Example 1, the only difference is that the feed ratio of hydroquinone and formaldehyde (R / F) in step S1 is adjusted to 1:1, 1:1.5, 1:2.5 and 1:3 respectively, while the other steps and conditions are the same as in Example 1.

[0045] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments, and the results are shown in Table 1 below.

[0046] Table 1. Effect of different R / F molar ratios on the photocatalytic performance of the floating plate

[0047] As shown in Table 1, the H2O2 generation rate was highest when the R / F molar ratio was 1:2, accumulating to 4.5 mg / L within 12 h, corresponding to the most significant decrease in cyanobacteria density (down to 0.52 × 10⁻⁶). 6 When the molar ratio is reduced to 1:1, insufficient cross-linking may lead to insufficient exposure of catalytic active sites and poor stability, resulting in weak H2O2 production capacity. When the ratio is increased to 1:3, excessively rapid gelation may lead to excessively deep catalytic embedding or poor pore structure, which also limits mass transfer and light utilization, thus reducing performance. Therefore, the molar ratio of phenolic compounds to aldehydes in this invention is preferably 1:(1-3), and more preferably 1:(1.5-2.5).

[0048] Example 3 Compared with Example 1, the only difference is that the pH value during acid-catalyzed gelation in step S3 is changed to 4.5, 3.8, 2.8 and 2.3 respectively, while the other steps and conditions are the same as in Example 1.

[0049] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments, and the results are shown in Table 2 below.

[0050] Table 2. Effect of different gel pH on the photocatalytic performance of the floating plate

[0051] As shown in Table 2, the gel exhibits optimal performance at a pH of 3.2. Increasing the pH (4.5) leads to a loose gel network, weak resin bonding, uneven pore size, and low H2O2 production. Decreasing the pH (2.3) results in the rapid formation of numerous closed pores, hindering mass transfer and light penetration of reactants, thus reducing performance. Therefore, in this invention, the gel pH is 2–4.5, preferably 2.8–3.8.

[0052] Example 4 Compared with Example 1, the only difference is that the curing temperature in step S4 is changed to 40°C, 50°C, 70°C and 80°C respectively, while the other steps and conditions are the same as in Example 1.

[0053] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments, and the results are shown in Table 3 below.

[0054] Table 3. Effects of different curing temperatures in the second stage on the photocatalytic performance of the floating plate.

[0055] As shown in Table 3, 60℃ is the optimal curing temperature. When the temperature is lowered (40℃), foaming may be insufficient, the resin may not cure completely, resulting in fewer and smaller pores, or even failure to form the expected open-pore structure. When the temperature is higher (80℃), foaming is too fast, leading to pore structure deterioration (co-forming or cracking), both of which affect the continuous generation of H2O2 and the inhibitory effect on algal cells. Therefore, the temperature of the second stage of heating curing in this invention is 40-80℃, and considering energy consumption, 50-70℃ is further preferred.

[0056] Example 5 Compared with Example 1, the only difference is that different foaming agents are used in step S2, namely n-hexane, cyclohexane, dichloromethane and petroleum ether, while the other steps and conditions are the same as in Example 1.

[0057] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments, and the results are shown in Table 4 below.

[0058] Table 4. Effects of different foaming agents on the photocatalytic performance of the floating plate

[0059] As shown in Table 4, low-boiling-point n-pentane can effectively and uniformly vaporize and foam under curing conditions of 60℃, forming an ideal interconnected open-cell structure. Hexane and cyclohexane have higher boiling points and insufficient vaporization at the curing temperature, resulting in low porosity, numerous closed cells, severely limiting mass transfer, and relatively poor performance. Although dichloromethane has a suitable boiling point, it may participate in side reactions or affect resin curing; petroleum ether is a mixture, and its foaming behavior is not as uniform and controllable as n-pentane, therefore its effect is not as good as n-pentane. Therefore, the foaming agent of this invention can be selected from n-pentane, n-hexane, cyclohexane, dichloromethane, or petroleum ether, with n-pentane being more preferred.

[0060] Example 6 Compared with Example 1, the only difference is that the reaction time for generating the prepolymer in step S1 is changed to 30 minutes, 60 minutes, 180 minutes, 360 minutes and 720 minutes respectively, while the other steps and conditions are the same as in Example 1.

[0061] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments, and the results are shown in Table 5 below.

[0062] Table 5. Effect of different prepolymer reaction times on the photocatalytic performance of the floating plate.

[0063] As shown in Table 5, the prepolymerization reaction time has a significant impact on the molecular weight, viscosity, and reactivity of the prepolymer. If the reaction time is too short (30 minutes), the condensation reaction is incomplete, resulting in low molecular weight oligomers. This leads to insufficient cross-linking density of the three-dimensional network formed during the subsequent acid-catalyzed gelation process, resulting in poor mechanical stability of the final material. Furthermore, the loose network structure may affect catalyst fixation and mass transfer efficiency, leading to low H2O2 yield and limited algae inhibition. Conversely, if the reaction time is too long, it may cause over-polymerization of the prepolymer, resulting in an excessively large molecular weight and high system viscosity. This also hinders the uniform dispersion of the foaming agent and limits the uniform expansion of the network during acid-catalyzed gelation, leading to dense structures in some areas or the precipitation of white solids, thus reducing photocatalytic performance. Therefore, the preferred prepolymerization reaction time in this invention is 30–720 min, more preferably 60–180 min, with 90 minutes being the optimal time. At this time, the RF prepolymer has suitable molecular weight and reactivity, forming a uniform, moderately cross-linked, and porous network, thus exhibiting optimal photocatalytic performance.

[0064] Example 7 Compared with Example 1, the only difference is that the amount of deionized water in step S1 is adjusted to 5 mL, 10 mL, 20 mL, 40 mL, 100 mL and 200 mL respectively, while the other steps and conditions are the same as in Example 1.

[0065] The RF floating plate samples obtained in this embodiment were subjected to photocatalytic activity tests and cyanobacterial inhibition experiments (initial algae density: 1.0 × 10⁻⁶). 6 (cells / mL), the results are shown in Table 6 below.

[0066] Table 6. Effects of different deionized water dosages on the photocatalytic performance of the floating plate.

[0067] As shown in Table 6, the amount of deionized water is the core determining factor for the successful preparation and functional realization of the foamed photocatalytic phenolic resin material. If the water content is too low, hydroquinone will be difficult to dissolve, resulting in an extremely high solid content (>60%) and viscosity. This leads to uneven dispersion of the foaming agent, inability of bubbles to grow, and ultimately the formation of a nearly solid resin block. With an appropriate water volume (20 mL, W / R = 2.0), the solid content (~38%) and viscosity reach an optimal balance, resulting in a thorough and uniform foaming process that forms a stable open-cell structure with high porosity and high specific surface area. Excessive deionized water (40 mL, W / R = 4.0) reduces the solid content (~25%), weakening the resin network skeleton due to the decreased polymer concentration. Although the initial porosity may not be low, the structural strength is insufficient, and long-term immersion in an aqueous environment may lead to swelling or deformation, affecting its durability and the stability of its catalytic performance. Excessive deionized water results in an excessively low reactant concentration, failing to reach the critical point of sol-gel transition, keeping the system in a solution state, and preventing solidification and formation of the target floating plate material. Therefore, this invention preferably uses a resorcinol to water mass ratio of 1:(0.5~10), more preferably 1:(1~4).

[0068] Comparative Example 1 Compared with Example 1, the only difference is that step S3 is omitted, that is, the yellow emulsion obtained in step S2 is directly poured into the mold for curing, foaming and drying in step S4. The other steps and conditions are the same as in Example 1.

[0069] The results showed that the emulsion failed to form a stable gel network throughout the entire heat treatment process. The blowing agent (n-pentane) directly escaped to the system surface and volatilized upon heating, failing to be effectively encapsulated and utilized. The final product was a loose, weak, and non-porous phenolic resin layer, unable to form a floating plate with mechanical strength. This comparative example demonstrates that the acid-catalyzed rapid gelation step is indispensable for locking the blowing agent and constructing a three-dimensional network structure.

[0070] Application Example 1 The floating board obtained in Example 1 was added to the water of Houhu Lake to verify its algae removal performance. At the same time, various water quality indicators were tested to provide further guidance for the application of the floating board in engineering projects.

[0071] Water samples were taken from Houhu Lake. After sampling, the lake water was left to stand in a transparent plastic container for later use. The specific experimental procedure was as follows: a prepared pure RF flotation board was added to 600 ml of lake water, and its effect on algae control in the Houhu Lake water was tested under simulated light. The light intensity was 800 W / m². 2 Two experimental groups were set up: a control group without floating board treatment and experimental groups treated with floating boards for 6 h (low level) and 18 h (high level). Chlorophyll a and other routine water quality indicators were measured in the lake water within 21 days after treatment to assess the impact of floating board treatment on the aquatic ecosystem. For a detailed comparison of the effects during the experiment, see [link to experimental data]. Figure 1 The test results are shown below. Figure 2 .

[0072] Depend on Figure 1 It can be seen that as the treatment time increases, the algae in the lake water decreases, and the water gradually becomes clearer from green.

[0073] Depend on Figure 2 It was found that the chlorophyll a content in the lake water before treatment was 160.45 μg / L. Monitoring showed that the COD of the lake water after treatment was 250.48 mg / L, TP was 1.247 mg / L, and NH4+ was... + -N, NO3 - -N, NO2 - -N were 13.01, 1.23, and 0.02 mg / L, respectively. The Technical Specification for Surface Water Resources Quality Assessment (SL395-2007) stipulates that when the chlorophyll a content in lake water reaches 64-160 μg / L, it is a moderately eutrophic water body, and when its total phosphorus content exceeds 0.9 mg / L, it is a severely eutrophic water body. It can be seen that algae are proliferating and growing in large quantities in Houhu Lake, and the water body is seriously eutrophic.

[0074] One day after treatment, the chlorophyll a content in the lake water decreased to 58.73 μg / L, with a removal rate of 63.4%, and its content remained stable in the following weeks, which verified the algae removal performance of the floating board.

[0075] To assess the impact of the floating board on the aquatic microbial community, metagenomic testing was conducted on lake water samples. Analysis of cyanobacterial community structure changes and virulence factors at the genus level was also performed. Figure 3 As shown in the figure (Note: Group A1 in the figure is the water sample before long-term treatment, C1 is the water sample 4 days after long-term treatment, and C2 is the water sample 20 days after treatment). After long-term RF floating plate treatment, the species structure of cyanobacteria underwent significant changes and migrations. Figure 3 (Left); In untreated lake water, the dominant cyanobacterial species include Cyanobacterium (Cyanobacteria) Okeania (Octenia) Scytonema(Pseudobranchium) Synechococcus (Synechococcus) Microcystis etc. Among them. Microcystis Microcystis species are widely distributed in eutrophic freshwater lakes and are highly prone to forming harmful algal blooms. Some strains produce microcystin, a potent hepatotoxin that can cause liver damage or even death in mammals upon ingestion. After RF floating board treatment, the relative abundance of most cyanobacteria decreased, among which... Anabaena (Anabaena genus) Aphanizomenon (The genus *Tricholoma*) are all harmful algal bloom species widely reported globally. Anabaena It is one of the most toxic cyanobacteria genera, often appearing successively during cyanobacterial blooms, and Aphanizomenon Some species can produce paralytic shellfish toxins and sarcotoxins, which harm aquatic ecosystems. A comparison between group C2 and group C1 showed that, except... Alkalinema , Oxynema Except for a few specific genera, the relative abundance of most cyanobacteria did not increase significantly, suggesting that RF floating board treatment may have been able to prevent secondary algal blooms within weeks of treatment. (Temporality factor heatmap) Figure 3 (Right) Overall, sample A1 showed high relative abundance (orange-red, z-score>0) for most virulence factor genes, while samples C1 and C2 showed low relative abundance (cyan-blue, z-score<0) for most genes. This indicates that functional genes related to the movement, diffusion, and colonization of pathogens in the aquatic microbial community are highly enriched. Overall, the relative abundance of most virulence factors decreased after treatment, which suggests that RF floating board treatment has a certain disinfection effect and can reduce the potential pathogen risk in the water.

[0076] In this experiment, RF floating boards were added to the water of Houhu Lake to evaluate their performance in treating algae-contaminated water. Overall, extending the treatment time removed nearly 70% of chlorophyll a from the water, and it is expected that further extending the treatment time will further enhance the chlorophyll a removal efficiency of the RF floating boards. Meanwhile, metagenomic testing results showed that the relative abundance of cyanobacteria at the genus level was significantly reduced after treatment, and the relative content of virulence factors also decreased significantly. Therefore, the RF floating boards can play a certain disinfection role while killing algae in the water, and have the potential for practical engineering applications.

[0077] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a floating photocatalytic material, characterized in that, Includes the following steps: S1, phenolic compounds, aldehyde solution, solvent and alkaline catalyst are mixed evenly and then subjected to a prepolymerization reaction to obtain a prepolymer; S2, add a foaming agent to the prepolymer and mix evenly to obtain an emulsion; S3, add an acidic catalyst to the emulsion, and obtain a wet gel through a gelation reaction; S4, the wet gel is heated and cured to obtain a floating photocatalytic material.

2. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S1, the phenolic compound is selected from one or more of resorcinol, phenol, catechol, hydroquinone, and phloroglucinol; the aldehyde compound in the aldehyde solution is selected from one or more of formaldehyde, paraformaldehyde, acetaldehyde, and propionaldehyde; and / or, The molar ratio of the phenolic compound to the aldehyde is 1:(1-3); and / or, The aldehyde solution has a mass concentration of 35-40%.

3. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S1, the solvent is water, and the mass ratio of the phenolic compound to water is 1:(0.5-10); and / or, The alkaline catalyst includes one or more of sodium carbonate, potassium carbonate, sodium bicarbonate, sodium hydroxide, and ammonia water; and / or, The process of uniformly mixing phenolic compounds, aldehyde solutions, solvents, and alkaline catalysts specifically includes: dissolving phenolic compounds in a solvent under a water bath at 40–60°C, then adding an alkaline catalyst to adjust the pH value to 8–10, and subsequently adding the aldehyde solution dropwise under stirring and mixing uniformly.

4. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S1, the prepolymerization reaction is carried out at 15–30°C for 30–720 min.

5. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S2, the foaming agent includes n-pentane, n-hexane, cyclohexane, dichloromethane, or petroleum ether; and / or, The ratio between the foaming agent and the phenolic compound is (2-6) mL : 10 g.

6. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S2, the step of adding a foaming agent to the prepolymer and mixing it evenly specifically includes: adding a foaming agent to the prepolymer and stirring at a speed of 1000-1500 rpm for 5-10 minutes.

7. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S3, the acidic catalyst includes one or more of phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and p-toluenesulfonic acid; the acidic catalyst is added to the emulsion to adjust the pH value to 2-4.

5.

8. The method for preparing the floating photocatalytic material according to claim 1, characterized in that, In step S4, the heating curing involves pre-curing at 30–40°C for 1.5–2.5 h, followed by curing at 40–80°C for another 1.5–2.5 h.

9. The floating photocatalytic material prepared by the preparation method according to any one of claims 1-8.

10. The application of the floating photocatalytic material as described in claim 9 in the control of cyanobacteria.

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