Modified agar and method for preparing the same and scale inhibitor

Abstract

The application belongs to the technical field of water treatment, and particularly relates to a modified agar, a preparation method thereof and a scale inhibitor. The modified agar is formed by free radical grafting of carboxyl agar and protocatechuic acid; the carboxyl agar comprises carboxyl groups, the carboxyl groups comprise carboxymethyl groups, and are used for chelation with metal cations in water to inhibit scale formation; and the protocatechuic acid comprises hydroxyl groups, the hydroxyl groups comprise phenolic hydroxyl groups, and are used for destroying the structural integrity of bacteria in water to inhibit biological pollution of water. The modified agar as the scale inhibitor can effectively alleviate the scaling problem in the water treatment process through chelation, dispersion and other effects, improve the separation performance of lithium and magnesium ions, and reduce biological pollution; and the raw materials used are agar and protocatechuic acid, both of which are derived from natural plants, so the modified agar has the characteristics of non-toxicity and no secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a modified agar, its preparation method, and a scale inhibitor. Background Technology

[0002] Scale inhibitors are used to prevent or delay the deposition and scaling of insoluble inorganic salts on the surfaces of containers, pipes, or heat exchangers in water systems, thereby maintaining efficient system operation and extending the service life of equipment. Scale inhibitors typically possess multiple mechanisms of action, including dispersion, chelation, and lattice distortion. They can form stable complexes with calcium and magnesium ions in water, increasing their solubility and preventing them from combining with anions to form insoluble salt deposits, i.e., scale. However, existing scale inhibitors suffer from poor scale inhibition capabilities, inability to mitigate biological pollution, and poor biodegradability, easily leading to secondary pollution. Summary of the Invention

[0003] The purpose of this invention is to provide a modified agar, its preparation method, and a scale inhibitor. The modified agar provided in this application contains functional groups such as carboxyl and phenolic hydroxyl groups, wherein the carboxyl group can react with Ca in wastewater. 2+ Mg 2+ The chelation between plasmas allows the phenolic hydroxyl groups to effectively inhibit the growth of bacteria and other microorganisms, thereby reducing the risk of biofouling. This modified agar, as a scale inhibitor, can effectively alleviate scaling problems in water treatment processes through chelation and dispersion, improve the separation performance of lithium and magnesium ions, and reduce biofouling. Furthermore, the raw materials used are agar and protocatechuic acid, both derived from natural plants, giving the modified agar its non-toxic and non-polluting characteristics.

[0004] A first aspect of the present invention is to provide a modified agar formed by free radical grafting of carboxylated agar and protocatechuic acid; the carboxylated agar includes carboxyl groups, including carboxymethyl groups, for chelating with metal cations in water to inhibit scale formation; the protocatechuic acid includes hydroxyl groups, including phenolic hydroxyl groups, for disrupting the structural integrity of bacteria in water to inhibit biological pollution of water.

[0005] In some embodiments of this application, the mass ratio of carboxyl groups to phenolic hydroxyl groups in the modified agar is 3:1 to 20:1.

[0006] In some embodiments of this application, the structural formula of the modified agar includes: Where R1 is -H or -CH2COOH; R2 is .

[0007] In some embodiments of this application, the modified agar satisfies at least one of the following conditions: when used in water, it inhibits scale formation and biological pollution; at an effective dosage, the 24-hour inhibition rate against Escherichia coli is greater than or equal to 60%; at an effective dosage, the 24-hour inhibition rate against Staphylococcus aureus is greater than or equal to 60%; at an effective dosage, the bacterial mortality rate is greater than or equal to 30%; and the effective dosage is 10 mg / L to 50 mg / L.

[0008] The second aspect of the present invention is to provide a method for preparing modified agar, comprising the following steps: dissolving carboxylated agar and protocatechuic acid in pure water at a mass ratio of 1:(0.5~2) to obtain a mixed solution; purging the mixed solution with nitrogen gas to remove oxygen; adding hydrogen peroxide solution to initiate a free radical grafting reaction; heating to 60℃~70℃ and maintaining the temperature for 0.5h~6h to prepare modified agar; wherein the carboxylated agar includes carboxymethyl agar, and the degree of substitution of the carboxymethyl functional group of the carboxymethyl agar is 0.32~1.45.

[0009] In some embodiments of this application, the preparation method of carboxylated agar includes: dispersing agar and sodium hydroxide in an ethanol solution at a mass ratio of 1:(1~1.5) and reacting at 50-70°C for 0.5-1.5 h; adding chloroacetic acid at a mass ratio of chloroacetic acid to agar of (0.46~1.84):1 and reacting at 50-80°C for 0.5-6 h; separating and purifying to obtain carboxylated agar.

[0010] In some embodiments of this application, the volume percentage of hydrogen peroxide solution is 5% to 10% based on the volume of the mixed solution; the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%.

[0011] In some embodiments of this application, the mixed solution also includes ascorbic acid, and the mass ratio of ascorbic acid to protocatechuic acid is (0.06~0.25):1.

[0012] A third aspect of the present invention is to provide a scale inhibitor comprising the modified agar provided in the first aspect or a modified agar prepared by the method for preparing the modified agar provided in the second aspect.

[0013] In some embodiments of this application, scale inhibitors are used in industrial water treatment, cooling water systems, boiler water treatment, and desalination systems.

[0014] The beneficial effects of the present invention include at least one of the following: Compared with existing technologies, this invention prepares a modified agar by free radical grafting carboxylated agar with protocatechuic acid. The agar is a linear polysaccharide with galactose and 3,6-lactoether galactose as basic units forming a linear chain structure. The hydroxyl groups are linearly distributed without branching interference, providing uniform reaction sites for carboxymethylation, etherification, and protocatechuic acid free radical grafting, which is beneficial to the uniform distribution of functional groups on the molecular chain. It integrates the synergistic function of carboxyl (carboxymethyl) and phenolic hydroxyl groups. The carboxyl group can react with Ca in water. 2+ Mg 2+ The product utilizes strong chelation of metal cations, combined with lattice distortion and dispersion effects, to effectively inhibit the formation and aggregation of inorganic scale such as calcium sulfate and magnesium sulfate. At a dosage of 50 mg / L, the scale inhibition efficiency can reach over 98%, while simultaneously improving the separation performance of lithium and magnesium ions. The phenolic hydroxyl groups can disrupt the cell membrane integrity of microorganisms such as Escherichia coli and Staphylococcus aureus. At effective dosages of 10 mg / L to 50 mg / L, the 24-hour antibacterial rate is ≥60%, and the bacterial mortality rate is ≥30%, effectively reducing the risk of biological pollution in water treatment systems and achieving dual effects of scale inhibition and antibacterial action. The raw materials are all derived from natural plants, are non-toxic, do not cause secondary pollution, and are biodegradable, solving the problems of poor biodegradability and easy secondary pollution associated with traditional phosphorus-containing scale inhibitors and synthetic polymer scale inhibitors. The preparation method is simple and controllable, completed in two steps through etherification and free radical grafting reactions. The reaction parameters are clear, the raw materials are readily available, and key indicators such as the degree of carboxymethyl substitution and grafting ratio can be precisely controlled, making it suitable for large-scale industrial production. Furthermore, this modified agar exhibits good stability under normal industrial water treatment conditions with pH values ​​of 6-9 and temperatures of 40-60°C. The effective dosage is far lower than that of traditional natural polymer scale inhibitors, resulting in lower usage costs. It is suitable for various applications such as industrial water treatment, cooling water systems, boiler water treatment, and desalination systems. It can significantly reduce equipment scaling and membrane fouling, lower system energy consumption and maintenance costs, and has broad market application prospects. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0016] Figure 1 A flowchart illustrating the synthetic route of the modified agar provided in this application; Figure 2 Infrared spectrum of the modified agar provided in this application; Figure 3 A static scale inhibition efficiency diagram of the modified agar provided in this application; Figure 4 The effect of the modified agar provided in this application on scale morphology in static scale inhibition tests is shown in the figure. Figure 5 A graph showing the iron oxide dispersion properties of the modified agar provided in this application; Figure 6 A diagram showing the scale inhibition performance of the modified agar provided in this application during reverse osmosis experiments; Figure 7 Electron micrograph of the surface of the reverse osmosis membrane obtained after using the modified agar provided in this application in a reverse osmosis experiment; Figure 8 X-ray diffraction pattern of scale obtained after using the modified agar provided in this application for static scale inhibition testing; Figure 9 The antibacterial effect of the modified agar provided in this application is illustrated. Figure 10 The image shows the bactericidal effect of the modified agar provided in this application. Detailed Implementation

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] 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.

[0019] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0020] 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.

[0021] In industrial water treatment, cooling water systems, boiler water treatment, and desalination systems, the presence of pollutants such as salt ions, organic matter, and microorganisms in the water easily leads to the formation of inorganic scale, organic fouling, and biological fouling on equipment or membrane surfaces. This results in increased system energy consumption, shortened equipment and membrane lifespan, and significant economic losses to industrial production. Currently, physical or chemical methods are generally used to inhibit or remove scale to reduce the damage caused by scaling to cooling water and desalination systems. Physical methods mainly include ultrasonic, magnetic field, and electric field descaling methods, but their application is greatly limited due to problems such as unstable effectiveness and cumbersome equipment use. In contrast, chemical scale inhibitors have advantages such as ease of operation, low cost, and high efficiency in inhibiting scale formation, ensuring the stable operation of cooling water and desalination systems. Phosphorus-containing scale inhibitors and synthetic polymer scale inhibitors are currently the most widely used commercial scale inhibitors, but they have problems such as secondary pollution and poor biodegradability.

[0022] Developing biodegradable and non-toxic green scale inhibitors is a research hotspot in the water treatment field. Natural polymers such as starch, chitosan, and agar are excellent base materials for these scale inhibitors due to their wide availability, low cost, and renewability / biodegradability. However, directly using natural polymers as scale inhibitors suffers from low activity and uneven distribution of functional groups, resulting in poor scale inhibition efficiency against calcium sulfate (CaSO4) and magnesium sulfate (MgSO4) scale (e.g., unmodified chitosan has a scale inhibition rate of less than 30% for calcium sulfate). Furthermore, they exhibit weak chemical stability, are easily degraded and deactivated, and require large dosages (50 mg / L~200 mg / L), increasing costs and hindering engineering applications. For cooling water or desalination systems, there is also a risk of biofouling, and the performance of natural polymers directly used as scale inhibitors in preventing biofouling is limited.

[0023] To address the aforementioned issues, this application provides a modified agar, its preparation method, and a scale inhibitor, which exhibits excellent scale inhibition and biofouling suppression properties.

[0024] In a first aspect, the present invention provides a modified agar, which is formed by free radical grafting of carboxylated agar and protocatechuic acid; the carboxylated agar includes carboxyl groups, including carboxymethyl groups, which are used to chelate with metal cations in water to inhibit scale formation; the protocatechuic acid includes hydroxyl groups, including phenolic hydroxyl groups, which are used to disrupt the structural integrity of bacteria in water to inhibit biological pollution of water.

[0025] The modified agar provided in some embodiments of this application is formed by free radical grafting of carboxylated agar and protocatechuic acid. The carboxymethyl group in the carboxylated agar can react with Ca in water. 2+ Mg 2+The process involves chelation reactions between metal cations, and simultaneously, through lattice distortion and dispersion, it disrupts the crystal growth and aggregation of scale such as calcium sulfate and magnesium sulfate, thus inhibiting scale formation. The phenolic hydroxyl groups in protocatechuic acid act as active groups, disrupting the cell membrane integrity of bacteria such as Escherichia coli and Staphylococcus aureus, inhibiting microbial proliferation, and reducing the risk of biofouling. This addresses the problem of existing scale inhibitors only inhibiting scale or posing environmental hazards, achieving a dual effect of scale inhibition and antibacterial action.

[0026] In some embodiments of this application, the mass ratio of carboxyl groups to phenolic hydroxyl groups in the modified agar is 3:1 to 20:1. A suitable mass ratio of carboxyl groups to phenolic hydroxyl groups ensures both the scale inhibition function of the carboxyl groups and the antibacterial effect of the phenolic hydroxyl groups. This ratio range ensures that the carboxyl groups fully exert their chelating and dispersing effects, while maintaining a sufficient concentration of phenolic hydroxyl groups to achieve efficient antibacterial activity. It avoids functional redundancy due to an excessively high proportion of any one group or insufficient performance due to an excessively low proportion. For example, an excessively high proportion of phenolic carboxyl groups will reduce the antibacterial effect, while an excessively low proportion of carboxyl groups will affect the scale inhibition efficiency. This allows the modified agar to achieve a balance between scale inhibition and antibacterial performance, ensuring stable overall performance.

[0027] It should be noted that in some embodiments, the mass ratio of carboxyl groups to phenolic hydroxyl groups in the modified agar can be, for example, 3:1, 5:1, 7:1, 9:1, 11:1, 13:1, 13:1, 17:1, 19:1, 20:1 or a range of any two of these values, or other values ​​selected from the above range.

[0028] In some embodiments of this application, the structural formula of the modified agar includes: Wherein, R1 is selected from -H, -CH2COOH; R2 is... The -CH2COOH group is the core source of the carboxyl group, ensuring the structural basis for its chelating and scale-inhibiting function; R2 corresponds to the structure after grafting with protocatechuic acid, directly related to the presence and distribution of phenolic hydroxyl groups. This modified agar structure is beneficial for balancing scale inhibition and antibacterial properties.

[0029] In some embodiments of this application, the modified agar satisfies at least one of the following conditions: when used in water, it inhibits scale formation and biofouling; at an effective dosage, it exhibits a 24-hour inhibition rate of ≥60% against Escherichia coli; at an effective dosage, it exhibits a 24-hour inhibition rate of ≥60% against Staphylococcus aureus; at an effective dosage, it achieves a bacterial mortality rate of ≥30%; and the effective dosage is 10 mg / L to 50 mg / L. This facilitates improving the practicality and operability of the modified agar in industrial production and practical applications.

[0030] Effective dosage is defined as: in target application scenarios such as industrial water treatment, cooling water systems, boiler water treatment, and desalination systems, modified agar can fully exert its core functions (including its interaction with Ca in water).2+ Mg 2+ The modified agar inhibits the formation of inorganic scale such as calcium sulfate and magnesium sulfate by chelating with metal cations, and inhibits the growth and reproduction of microorganisms such as Escherichia coli and Staphylococcus aureus by disrupting the integrity of bacterial cell membranes through phenolic hydroxyl groups. It also meets the minimum to optimal dosage range required to achieve the preset performance indicators (24-hour inhibition rate of ≥60% for Escherichia coli and Staphylococcus aureus, bacterial mortality rate ≥30%, while simultaneously achieving efficient scale inhibition and iron oxide dispersion). This concentration range is determined based on data from static scale inhibition experiments, dynamic reverse osmosis experiments, and antibacterial experiments. This ensures that the functional groups of the modified agar fully function, avoids cost waste or performance redundancy due to excessive dosage, and meets the application requirements of non-toxicity and no secondary pollution.

[0031] It should be noted that in some embodiments, the effective dosage may be, for example, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, or a range of any two of these values, or other values ​​selected from the above range.

[0032] A second aspect of this invention is to provide a method for preparing modified agar. The specific synthetic route of the modified agar provided in this application is as follows: Figure 1 As shown. The preparation method includes the following steps: dissolving carboxylated agar and protocatechuic acid in pure water at a mass ratio of (0.5~2):1 to obtain a mixed solution; purging the mixed solution with nitrogen to remove oxygen; adding hydrogen peroxide solution to initiate a free radical grafting reaction; heating to 60℃~70℃ and maintaining the temperature for 0.5h~6h to prepare modified agar; the carboxylated agar includes carboxymethyl agar, and the degree of substitution of the carboxymethyl functional group of the carboxymethyl agar is 0.32~1.45.

[0033] The preparation method specifies a mass ratio of carboxylated agar to protocatechuic acid of 1:(0.5~2), preferably (0.8~1.8):1. This mass ratio affects the grafting degree and functional group ratio of protocatechuic acid, ensuring the performance of the modified agar. Nitrogen gas is introduced for deoxygenation to prevent oxygen quenching of free radicals, ensuring efficient grafting reaction. Hydrogen peroxide solution initiates the free radical reaction. A reaction temperature of 60℃~70℃ and a reaction time of 0.5h~6h ensure sufficient reaction while avoiding degradation of raw materials due to high temperature or prolonged reaction. The degree of substitution of the carboxymethyl functional group is 0.32~1.45, preferably 0.42~1.32, and more preferably 1~1.32, ensuring that the carboxyl group density meets the scale inhibition requirements. This method has clear steps and controllable parameters, solving the problems of low reaction efficiency and unstable product performance in traditional modification methods, and is suitable for large-scale industrial production.

[0034] The degree of substitution of the carboxymethyl functional group in this application refers to the average amount of active hydroxyl groups that are replaced by hydroxymethyl functional groups on each disaccharide repeating unit of carboxy agar. The degree of carboxymethyl substitution of the scale inhibitor sample can be roughly estimated from the integral area of ​​the characteristic peaks in the 1H NMR spectrum of the sample according to the following formula (1).

[0035] (1) The method for measuring the percentage content of protocatechuic acid and the percentage content of carboxymethyl functional groups in carboxylate in this application includes using conventional measurement methods in the art, such as chromatography or mass spectrometry.

[0036] The carboxymethyl agar in this application includes products obtained by modifying the carboxyl group of agar, wherein the agar includes, but is not limited to, food-grade agar. The protocatechuic acid in this application is 3,4-dihydroxybenzoic acid, which is mainly found in the leaves of plants such as *Pteris vittata* (family Lepidaceae) and *Ilex chinensis* (family Aquifoliaceae).

[0037] It should be noted that in some embodiments, the mass ratio of carboxylate to protocatechuic acid can be, for example, 0.5:1, 0.8:1, 1.1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, or any two of these values, or other values ​​selected from the above ranges. In some embodiments, the reaction temperature of the free radical reaction can be, for example, 60°C, 65°C, 70°C, or any two of these values, or other values ​​selected from the above ranges. The reaction time can be, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, or any two of these values, or other values ​​selected from the above ranges. The degree of substitution of the carboxymethyl functional group can be, for example, 0.32, 0.5, 0.8, 1.0, 1.1, 1.2, 1.3, 1.4, 1.45, or any two of these values, or other values ​​selected from the above ranges.

[0038] In some embodiments, based on the total mass of the modified agar, the mass percentage of carboxymethyl functional groups in the carboxy agar is 15% to 35%, preferably 16.5% to 32.5%, and more preferably 18% to 30%. It should be noted that in some embodiments, the mass percentage of carboxymethyl functional groups in the carboxy agar can be, for example, 15%, 16%, 16.5%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 32.5%, 33%, 34%, 35%, or a range consisting of any two of these values, or other values ​​selected from the above ranges.

[0039] In some embodiments of this application, the preparation method of carboxylated agar includes: dispersing agar and sodium hydroxide in an ethanol solution at a mass ratio of 1:(1~1.5) and reacting at 50-70°C for 0.5~1.5 h; adding chloroacetic acid at a mass ratio of chloroacetic acid to agar of (0.46~1.84):1 and reacting at 50-80°C for 0.5 h~6 h; separating and purifying to obtain carboxylated agar.

[0040] In some embodiments, in the preparation method of carboxylate agar, a suitable mass ratio of agar to sodium hydroxide can fully activate the active hydroxyl groups on the agar molecular chain, laying the foundation for the subsequent etherification reaction; a suitable mass ratio of chloroacetic acid to agar can precisely control the degree of substitution of the carboxymethyl functional group, ensuring that the carboxyl content meets the scale inhibition requirements; a reaction temperature of 50℃~80℃ and a reaction time of 0.5h~6h are adapted to the kinetic characteristics of the etherification reaction, ensuring a uniform and thorough reaction; the separation and purification step removes unreacted impurities, improving the purity of the carboxylate agar, thereby ensuring the efficiency of the subsequent grafting reaction and the final performance of the modified agar. This method is simple and uses readily available raw materials, providing a reliable guarantee for the preparation of high-quality carboxylate agar.

[0041] It should be noted that in some embodiments, the mass ratio of chloroacetic acid to agar can be, for example, 0.46:1, 0.8:1, 1:1, 1.5:1, 1.84:1 or a range of any two of these values, or other values ​​selected from the above range.

[0042] In some embodiments of this application, the volume percentage of hydrogen peroxide solution is 5% to 10% based on the volume of the mixed solution; the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%.

[0043] Based on the balance between initiator dosage and reaction efficiency: a 30% mass fraction provides sufficient reactive oxygen species to initiate free radical reactions, avoiding excessively high concentrations leading to violent reactions or insufficient concentrations leading to initiation; a 5%–10% volume fraction allows for precise control of the initiator dosage, ensuring a stable grafting reaction rate and preventing increased side reactions due to excessive initiator or incomplete reactions due to insufficient initiator. This limitation ensures appropriate initiator dosage, improving the reproducibility of the preparation method and the stability of the final modified agar.

[0044] It should be noted that in some embodiments, the volume percentage of hydrogen peroxide solution may be, for example, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two of these values, or other values ​​selected from the above range.

[0045] In some embodiments of this application, the mixed solution further includes ascorbic acid, and the mass ratio of ascorbic acid to protocatechuic acid is (0.06~0.25):1. Preferably, it is (0.1~0.25):1.

[0046] Ascorbic acid was added to the mixed solution, with a specific mass ratio of ascorbic acid to protocatechuic acid. Ascorbic acid, acting as a co-initiator, forms a redox system with hydrogen peroxide, significantly improving free radical generation efficiency and promoting the grafting reaction between carboxylated agar and protocatechuic acid, thus increasing the grafting rate. This ratio ensures effective initiation while avoiding excessive ascorbic acid that could increase costs or affect product purity. This improves reaction efficiency and product performance, resulting in a more uniform distribution of functional groups and more stable performance in the modified agar. It should be noted that in some embodiments, the mass ratio of ascorbic acid to protocatechuic acid can be, for example, 0.06:1, 0.08:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, or a range of any two values ​​thereof, or other values ​​selected from the above ranges.

[0047] In some embodiments, the mass percentage of protocatechuic acid is 5% to 15% based on the total mass of the modified agar, preferably 5.5% to 14%, and more preferably 6% to 13%. The mass percentage of protocatechuic acid can be, for example, 5%, 5.5%, 6%, 7%, 8%, 9%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of any two of these values, or other values ​​selected from the above ranges.

[0048] This application discloses in some embodiments the preparation process of carboxylated agar: agar is dispersed in an ethanol solution containing sodium hydroxide, the mass ratio of agar to sodium hydroxide is 1:(1~1.5), and alkalized at 60°C for 0.5 h; then, chloroacetic acid is added, the mass ratio of chloroacetic acid to agar is (0.46~1.84):1, and the reaction is carried out at 70°C for 3 h; after the reaction is completed, ethanol is used as a precipitant to separate the precipitate and obtain carboxylated agar.

[0049] This application discloses in some embodiments the preparation process of modified agar: the prepared carboxylated agar is dissolved with protocatechuic acid and ascorbic acid, the mass ratio of ascorbic acid to protocatechuic acid is (0.06~0.25):1, nitrogen gas is introduced, and the mixture is stirred at 65°C for 0.5h, the mass ratio of carboxylated agar to protocatechuic acid is 1:(0.5~2), 30% hydrogen peroxide solution is added, the mixture is stirred evenly, and the mixture is reacted at 70°C for 6h. Ethanol solution is used as a precipitant, and the precipitate is separated to obtain carboxylated agar grafted with protocatechuic acid.

[0050] A third aspect of the present invention is to provide a scale inhibitor comprising the modified agar provided in the first aspect or a modified agar prepared by the method for preparing the modified agar provided in the second aspect.

[0051] Based on the properties of modified agar, it is used in scale inhibitors, which have the advantages of scale inhibition and antibacterial function, non-toxicity, and no secondary pollution. It solves the problems of secondary pollution and poor biodegradability of traditional phosphorus-containing scale inhibitors and synthetic polymer scale inhibitors.

[0052] In some embodiments of this application, scale inhibitors are used in industrial water treatment, cooling water systems, boiler water treatment, and desalination systems.

[0053] This scale inhibitor is used in industrial water treatment, cooling water systems, boiler water treatment, and desalination systems to specifically address issues such as equipment scaling and membrane fouling. The non-toxic and non-polluting properties of modified agar avoid the environmental hazards associated with traditional scale inhibitors. Its highly efficient scale inhibition and antibacterial properties ensure stable system operation, reduce energy consumption and equipment maintenance costs, facilitate its promotion and application in related industries, and enhance the industrialization value of the invention.

[0054] Unless otherwise specified, the techniques or conditions described in the examples 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 whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. Unless otherwise specified, the experimental methods in the following examples are conventional methods. Unless otherwise specified, the experimental materials used in the following examples are all commercially available products. The agar used in the following examples is food-grade powdered agar.

[0055] In some embodiments of this application, the agar raw material used has hydroxyl groups. During the preparation of carboxylated agar, the hydroxyl groups in the agar raw material can react with chloroacetic acid to undergo a substitution reaction. During the reaction of carboxylated agar with protocatechuic acid, the carboxyl groups on the protocatechuic acid react with at least a portion of the remaining hydroxyl groups in the agar raw material that have not participated in the substitution reaction to form ester groups.

[0056] Example 1 In this embodiment, the method for preparing modified agar includes: (1) Preparation of carboxymethyl agar Agar was dispersed in an ethanol solution containing sodium hydroxide at a mass ratio of 1:1.12 and alkalized at 60°C for 0.5 h. Then, chloroacetic acid was added at a mass ratio of 1.65:1 to agar and reacted at 70°C for 3 h. After the reaction was completed, ethanol was used as a precipitant to separate the precipitate and obtain carboxymethyl agar. The degree of substitution of the carboxyl group was 1.32 according to NMR analysis.

[0057] (2) Modified agar The carboxymethyl agar obtained in step (1) was dissolved in a four-necked flask containing pure water, along with protocatechuic acid and ascorbic acid. Nitrogen gas was introduced, and the mixture was stirred at 65°C for 0.5 h. The mass ratio of ascorbic acid to protocatechuic acid was 0.24:1, and the mass ratio of carboxymethyl agar to protocatechuic acid was 1:0.5. Then, a 30% hydrogen peroxide solution was added, and the mixture was stirred until homogeneous. The mixture was reacted at 70°C for 6 h. Ethanol solution was used as a precipitant to separate the precipitate, and the modified agar was obtained, which was denoted as carboxymethyl agar grafted with protocatechuic acid (1).

[0058] Example 2 Compared with Example 1, the difference is that the carboxymethyl agar obtained in step (1) of Example 1 was dissolved with protocatechuic acid and ascorbic acid in a four-necked flask containing pure water, nitrogen gas was introduced, and the mixture was stirred at 65°C for 0.5 h. The mass ratio of ascorbic acid to protocatechuic acid was 0.12:1, and the mass ratio of carboxymethyl agar to protocatechuic acid was 1:1. Then, 30% hydrogen peroxide solution was added, stirred evenly, and reacted at 70°C for 6 h. Ethanol solution was used as a precipitant to separate the precipitate and obtain modified agar, which was denoted as carboxymethyl agar grafted with protocatechuic acid (2).

[0059] Example 3 Compared with Example 1, the difference is that the carboxymethyl agar obtained in step (1) of Example 1 was dissolved with protocatechuic acid and ascorbic acid in a four-necked flask containing pure water, nitrogen gas was introduced, and the mixture was stirred at 65°C for 0.5 h. The mass ratio of ascorbic acid to protocatechuic acid was 0.06:1, and the mass ratio of carboxymethyl agar to protocatechuic acid was 1:2. Then, 30% hydrogen peroxide solution was added, stirred evenly, and reacted at 70°C for 6 h. Ethanol solution was used as a precipitant to separate the precipitate and obtain modified agar, which was denoted as carboxymethyl agar grafted with protocatechuic acid (3).

[0060] Preparation and characterization: Infrared spectroscopy analysis was performed on agar, protocatechuic acid, carboxymethyl agar, and carboxymethyl agar grafted with protocatechuic acid (1)~(3), as shown in the figure. Figure 2 As shown, Figure 2 (b) and Figure 2 On curves (d) to (f), the wavenumber is 1599 cm⁻¹. 1 The nearby peak is the characteristic absorption peak of the C=O group on the carboxyl group. This characteristic peak is clearly observed in both carboxymethyl agar and the grafted product, indicating that the etherification reaction of agar with chloroacetic acid has successfully introduced the carboxymethyl group, and the preparation of carboxymethyl agar was successful. Figure 2 In curves (d) to (f), the wavenumber is 1744 cm⁻¹. 1 A characteristic absorption peak appears at the C=O group of the ester group. This peak appears in unmodified agar. Figure 2 (a) and carboxymethylated agar Figure 2 The absence of a significant peak in (b) indicates that protocatechuic acid has been successfully grafted onto the molecular chain of carboxymethyl agar via a free radical grafting reaction, forming an ester bond structure. These changes in infrared characteristic peaks confirm that both the carboxymethylation and etherification reactions of the agar and the protocatechuic acid grafting reaction of the carboxymethyl agar have been successfully carried out.

[0061] Example 4 Compared with Example 1, the difference is that the mass ratio of chloroacetic acid to agar is 0.55:1, and the mass ratio of carboxymethyl agar to protocatechuic acid is 1:1. The modified agar obtained is denoted as carboxymethyl agar grafted with protocatechuic acid (4).

[0062] Example 5 Compared with Example 1, the difference is that the mass ratio of chloroacetic acid to agar is 1.1:1, and the mass ratio of carboxymethyl agar to protocatechuic acid is 1:1. The modified agar obtained is denoted as carboxymethyl agar grafted with protocatechuic acid (5).

[0063] Example 6 Compared with Example 1, the difference is that the mass ratio of chloroacetic acid to agar is 0.55:1, and the mass ratio of carboxymethyl agar to protocatechuic acid is 1:0.5. The modified agar obtained is denoted as carboxymethyl agar grafted with protocatechuic acid (6).

[0064] The relevant parameters of the modified agar in Examples 1 to 6 are shown in Table 1.

[0065] Table 1

[0066] Application of modified agar The modified agar from Examples 1 to 6 was used as a component of the scale inhibitor for water treatment.

[0067] Static scale inhibition test Using calcium chloride, magnesium chloride, lithium chloride and sodium sulfate solutions as simulated saline samples, the scale inhibition of carboxymethyl agar grafted with protocatechuic acid (1) in the above water bodies was tested by static scale inhibition experiments.

[0068] The specific steps of the static scale inhibition experiment are as follows: Prepare a 100 mL simulated solution with a pH of 8, containing 3000 mg / L calcium ions, 3000 mg / L sulfate ions, 2000 mg / L magnesium ions, 100 mg / L lithium ions, and modified agar (as a scale inhibitor). Then, cool the solution to room temperature and filter it through 20 μm filter paper. Titrate with Chrome Black T standard solution to determine the concentration of calcium ions in the filtrate.

[0069] The formula (2) for calculating the scale inhibition efficiency of modified agar for calcium sulfate and magnesium sulfate is as follows: (2) in, V 0 (mL) represents the amount of Eriochrome Black T solution consumed without heating and without the addition of scale inhibitor; V 1 (mL) represents the amount of Eriochrome Black T consumed in the solution when scale inhibitor is added; V 2 (mL) represents the amount of Eriochrome Black T consumed in the solution without the addition of scale inhibitor.

[0070] like Figure 3 The table shows the scale inhibition performance of carboxymethyl agar and modified agar on mixed scale of CaSO4 and MgSO4. The scale inhibition efficiency of all scale inhibitors increases in an "S-shaped" manner with increasing scale inhibitor concentration. The scale inhibition efficiency increases rapidly in the concentration range of 0 mg / L to 20 mg / L, and tends to saturate in the concentration range of 20 mg / L to 50 mg / L. Among them, the performance of modified agar was significantly better than that of ungrafted carboxymethyl agar. At low concentrations (scale inhibitor concentration of 10 mg / L), the scale inhibition efficiency of carboxymethyl agar grafted with protocatechuic acid (2) (approximately 55%) far exceeded that of the ungrafted sample (approximately 40%). At medium to high concentrations (scale inhibitor concentration of 30 mg / L), the scale inhibition efficiency of carboxymethyl agar grafted with protocatechuic acid (2) (approximately 95%) was significantly higher than that of the ungrafted sample (approximately 90%). At a scale inhibitor concentration of 50 mg / L, the scale inhibition efficiency of carboxymethyl agar grafted with protocatechuic acid (2) was significantly higher than that of the ungrafted sample (approximately 90%). 2) The scale inhibition efficiency is stable at around 95%, further proving that the grafting modification of modified agar can significantly improve the scale inhibition performance, and the degree of grafting is positively correlated with the scale inhibition efficiency. Carboxymethyl agar grafted with protocatechuic acid (2) achieves the optimal balance between scale inhibition efficiency, structural stability and material cost, and is the scale inhibition material with the best comprehensive performance. When the dosage of carboxymethyl agar grafted with protocatechuic acid (2) is 50 mg / L, the scale inhibition efficiency reaches 98.16%, 98.36% and 96.58% respectively, which significantly inhibits the formation of calcium sulfate and magnesium sulfate scale.

[0071] The scale residue after the experiment was analyzed under a microscope, such as... Figure 4 As shown, modified agar, as a scale inhibitor, regulates the growth and aggregation of CaSO4 and MgSO4 crystals. Figure 4 In (a), the scale crystals are long needle-like / rod-like, with a size exceeding 100 μm, and they are interwoven into a network, showing the free growth and high aggregation of scale crystals without inhibition; Figure 4 Although the scale crystals in (b) are short, irregular, and have modified materials attached to their surface, they are still relatively large in size and show obvious aggregation. Figure 4 In (c), the scale crystals are significantly shorter and finer, with most being less than 100 μm in size. The aggregation state changes from intertwined to dispersed small clusters, which are approximately nanoscale fine scale crystals. This indicates that the degree of grafting can effectively inhibit crystal growth and aggregation. Figure 4In group (d), the scale crystals were further refined into needle-like structures, exhibiting radial aggregation, but the overall size remained smaller than that of the ungrafted group. In summary, grafting modification significantly alters the morphology and size of scale crystals. Among these, carboxymethyl agar grafted with protocatechuic acid (2) showed the best inhibitory effect on crystal growth and aggregation. This microstructural change also corresponds to the highly efficient scale inhibition performance of carboxymethyl agar grafted with protocatechuic acid (2) in the static scale inhibition experiment. Therefore, using the modified agar provided in this application as a scale inhibitor can more effectively alleviate scaling problems in water treatment processes.

[0072] Iron oxide dispersion experiment Carboxymethyl agar grafted with protocatechuic acid (1)~(3) was used as a water treatment agent. Calcium chloride and ferrous sulfate solutions were used as simulated water sample components. The dispersion performance of modified agar on ferrous oxide particles was determined through an ferrous oxide dispersion experiment.

[0073] The specific steps of the iron oxide dispersion experiment are as follows: First, prepare borax solution, scale inhibitor stock solution, calcium chloride solution, and ferrous sulfate solution for later use; mix calcium chloride solution, water, and borax solution in a beaker, adjust the pH to about 9.25, add different volumes of scale inhibitor stock solution to make the scale inhibitor concentration in the simulated water sample 0 mg / L, 2 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, and 100 mg / L respectively, adjust the pH to 9, add ferrous ion solution and make up to 100 mL, the final system calcium ion concentration is 150 mg / L and ferrous ion concentration is 10 mg / L; transfer the solution to an Erlenmeyer flask and stir for 15 min, let it stand in a constant temperature water bath at 50℃ for 5 h, take it out and let it stand for 5 min, take the supernatant and measure the transmittance at a wavelength of 420 nm, the lower the transmittance, the better the dispersion ability.

[0074] like Figure 5 As shown, the modified agar's ability to disperse iron oxide is evident. Specifically, at the tested concentrations, when the scale inhibitor concentration is greater than 20 mg / L, the dispersion performance of carboxymethyl agar grafted with protocatechuic acid (1)-(3) is significantly better than that of carboxymethyl agar, which can stably disperse iron oxide particles in the solution, thus exhibiting a lower solution transmittance. When the scale inhibitor concentration is 40 mg / L, the transmittance of carboxymethyl agar grafted with protocatechuic acid (2) (approximately 61%) is significantly lower than that of carboxymethyl agar grafted with protocatechuic acid (1) (approximately 63%), indicating that it has a higher dispersion efficiency; it is also slightly higher than that of carboxymethyl agar grafted with protocatechuic acid (3) (approximately 60%). However, the rapid decrease in transmittance of carboxymethyl agar grafted with protocatechuic acid (3) may be accompanied by the risk of agglomeration due to excessive particle dispersion, while the rate of decrease in transmittance of carboxymethyl agar grafted with protocatechuic acid (2) is more gradual, reflecting its superior dispersion stability for iron oxide particles.

[0075] Dynamic scale inhibition test Carboxymethyl agar-grafted protocatechuic acid (1) ~ carboxymethyl agar-grafted protocatechuic acid (3) were used as water treatment agents (scale inhibitors). Calcium chloride, anhydrous magnesium chloride, lithium chloride, and sodium sulfate solutions were used as simulated saline samples. The scale inhibition performance and membrane fouling control effect of this series of modified materials were determined through reverse osmosis (RO) experiments. The specific steps of the reverse osmosis experiment are as follows: 1000 mL of simulated saline sample with a pH of 7 ± 0.01 was prepared, containing 1200 mg / L calcium ions, 1000 mg / L magnesium ions, 50 mg / L lithium ions, and corresponding concentrations of sulfate ions. A certain amount of scale inhibitor was added. A commercial polyamide composite RO membrane (effective area 24 cm²) was used. 2 After pretreatment, the membrane was installed in a high-pressure flat-sheet membrane testing device and operated continuously for 180 minutes at a temperature of 30.0±0.5℃ and a pressure of 1.5MPa. The permeate mass was recorded in real time to calculate the normalized flux. After the experiment, the morphology of the fouling on the membrane surface was observed by scanning electron microscopy (SEM).

[0076] (3) (4) in, V for The volume of the internal permeate. A =24cm 2 , Let be the flux at time t. This represents the initial stable flux.

[0077] like Figure 6 As shown, the normalized flux experiment of the reverse osmosis membrane tested the scale inhibition performance of modified agar from two aspects: the degree of grafting and the dosage concentration. Figure 6 As shown in (a), with the increase of carboxymethyl agar-grafted protocatechuic acid (2) concentration, the flux stability increases with the concentration. When 5 mg / L of carboxymethyl agar-grafted protocatechuic acid (2) was added, the flux remained at around 85% after 180 minutes of reverse osmosis filtration. When 10 mg / L of carboxymethyl agar-grafted protocatechuic acid (2) was added, the flux stabilized above 90%. When 15 mg / L of carboxymethyl agar-grafted protocatechuic acid (2) was added, the flux fluctuation throughout the filtration process was minimal, remaining between 90% and 105%. This indicates that the scale inhibition performance of carboxymethyl agar-grafted protocatechuic acid (2) is concentration-dependent; at high concentrations, it can completely inhibit fouling deposition, ensuring the long-term stable operation of the reverse osmosis membrane. Figure 6In (b), the scale inhibitor concentration was 5 mg / L. The flux decay was the fastest in the group without scale inhibitor. The normalized flux dropped to below 60% at 180 min. The flux of the reverse osmosis membrane using carboxymethyl agar as scale inhibitor was maintained at about 70%. The flux stability of the reverse osmosis membrane using modified agar as scale inhibitor was significantly improved. Among them, the flux of carboxymethyl agar grafted with protocatechuic acid (1), carboxymethyl agar grafted with protocatechuic acid (2), and carboxymethyl agar grafted with protocatechuic acid (3) was maintained at about 80%, above 85%, and about 90% at 180 min, respectively. This shows that grafting modification can effectively alleviate membrane flux decay, and carboxymethyl agar grafted with protocatechuic acid (2) achieved a good balance between flux stability and structural stability.

[0078] Figure 7 This is a SEM image of the membrane surface after the reverse osmosis experiment, which visually shows the deposition morphology of mixed scale (CaSO4, MgSO4, etc.) on the reverse osmosis membrane surface and the scale inhibition and regulation effect of carboxymethyl agar grafted with protocatechuic acid. Figure 7 In the middle (a) is the original membrane, with a smooth surface, containing only trace impurities, and no obvious scaling. The control group did not use a scale inhibitor, such as... Figure 7 In (b), the reverse osmosis membrane surface is covered with a large number of long, rod-shaped mixed scale crystals, which are large in size and intertwined and aggregated, resulting in severe scaling. Figure 7 As shown in (c), when the dosage of scale inhibitor (ungrafted carboxymethyl agar) is 5 mg / L, although the scale on the reverse osmosis membrane surface is broken up, large crystals still remain. Figure 7 As shown in (d), when the dosage of scale inhibitor (carboxymethyl agar grafted protocatechuic acid (1)) is 5 mg / L, the scale on the reverse osmosis membrane surface forms a blocky aggregate. Figure 7 As shown in (e), when the dosage of scale inhibitor (carboxymethyl agar grafted protocatechuic acid (2)) is 5 mg / L, the scale on the reverse osmosis membrane surface consists of fine, dispersed needle-like crystals. Figure 7 As shown in (f), when the dosage of scale inhibitor (carboxymethyl agar-grafted protocatechuic acid (3)) is 5 mg / L, the scale on the reverse osmosis membrane surface exhibits a loose and porous structure, but there is a risk of pore blockage. Concentration gradient experiments on carboxymethyl agar-grafted protocatechuic acid (2) show that, as... Figure 7 As shown in (g), when the dosage of scale inhibitor (carboxymethyl agar grafted protocatechuic acid (2)) is 2 mg / L, there are flocculent scales on the surface of the reverse osmosis membrane; Figure 7 As shown in (h), when the antiscalant dosage is 10 mg / L, only a small amount of short rod-shaped crystals remain on the surface of the reverse osmosis membrane; Figure 7As shown in (i), when the antiscalant dosage is 15 mg / L, there is almost no obvious scale on the reverse osmosis membrane surface. In summary, carboxymethyl agar grafted with protocatechuic acid can effectively regulate the morphology and deposition of mixed scale. Among them, carboxymethyl agar grafted with protocatechuic acid (2) has the best antiscalant effect. Moreover, as its concentration increases, the scale size on the reverse osmosis membrane surface becomes smaller and the deposition amount becomes less, which can significantly alleviate the mixed scale fouling of the reverse osmosis membrane.

[0079] like Figure 8 As shown, XRD characterization of the scale in the static experiment, combined with spectral characteristics and standard diffraction data, revealed that: (020), (021), (040), and (042) crystal planes are typical characteristic peaks of calcium sulfate (gypsum dihydrate), (010) and (022) crystal planes correspond to magnesium sulfate (magnesium sulfate heptahydrate), and (041) and (043) crystal planes belong to lithium sulfate; among them, the characteristic peaks (010), (022), (041), and (043) in the group without scale inhibitor are sharp and have high intensity, indicating that the scale has high crystallinity and complete crystal structure; when only carboxymethyl agar is added, the intensity of these characteristic peaks is slightly weakened, indicating that it can only interfere with the nucleation and growth of scale to a limited extent; after adding modified agar, the effect of modified agar with different grafting degrees on the control of scale crystal form varies, among which carboxymethyl agar grafting degree of modified agar has a different effect on the control of scale crystal form. Protocatechuic acid (2) has the most significant destructive effect on scale crystal structure. The corresponding calcium sulfate (020), (021), (040), and (042) characteristic peaks show the largest decrease in intensity and the highest degree of peak broadening. The characteristic peak suppression effects of magnesium sulfate and lithium sulfate are also better than those of carboxymethyl agar grafted protocatechuic acid (1) and carboxymethyl agar grafted protocatechuic acid (3). It can be seen that the scale crystallinity decreases most significantly and the ordered crystal structure is most thoroughly destroyed under this degree of grafting, and the trend of crystal structure transforming into amorphous is the strongest. In contrast, carboxymethyl agar grafted protocatechuic acid (1) has a weaker regulatory effect on scale crystal structure due to insufficient grafting degree. Carboxymethyl agar grafted protocatechuic acid (3) may have a less effective effect than carboxymethyl agar grafted protocatechuic acid (2) because the scale inhibition active sites are masked due to excessive grafting degree. Modified agar exhibits a superior grafting degree in regulating the crystal form of multi-component sulfate scale. The grafting degree corresponding to carboxymethyl agar grafted with protocatechuic acid (2) is the best choice, and its scale inhibition performance is better than that of ungrafted carboxymethyl agar and other samples with different grafting degrees.

[0080] Antibacterial and bactericidal properties The antibacterial experiment used *Escherichia coli* (CMCC(B) 44102) and *Staphylococcus aureus* (CMCC(B) 26003) as test strains. The strains were first thawed on ice at -20℃ for 1 min, and then 1% of the bacterial culture was added to a 10 mL LB liquid medium glass tube. The tubes were then incubated at 37℃ with constant shaking at 200 rpm for 12-16 h to activate the bacteria to the logarithmic growth phase (OD). 595=0.5-0.8), OD was prepared by dilution in fresh LB medium. 595 =0.1 (concentration approximately 10) 7 CFU / mL ~10 8 The standard bacterial suspension (CFU / mL) was prepared and inoculated within 30 minutes. All LB liquid / solid culture media, glass tubes, centrifuge tubes, and other equipment used in the experiment were sterilized by autoclaving at 121℃ and 0.1MPa for 15 minutes. The experiment included a control group and experimental groups with different scale inhibitors, with three replicates per group. For each experimental group and control group, 10 mL of sterile LB liquid culture medium was added, along with 1% (volume fraction, i.e., 100 μL) of the above standard bacterial suspension. The experimental groups received a pre-set concentration of scale inhibitor (1 mg / mL), and the control group received an equal volume of sterile physiological saline. After mixing for 10-15 seconds, the mixture was incubated at 37℃ and 180-220 rpm. The bacteria were cultured in a constant-temperature shaker for 24 hours. At 0h, 1h, 2h, 4h, 8h, 12h, 16h, and 24h, the OD values ​​of each group of bacterial solutions were measured at 595nm using a microplate reader to characterize changes in bacterial density. After 24 hours of culture, each group of bacterial solutions was placed in a sterile centrifuge tube and centrifuged at 10000 rpm for 5 min. The supernatant was discarded, and the precipitate was gently resuspended by resuspending in a suitable amount of sterile PBS buffer. Then, PI sterilization staining agent was added according to the bacterial solution volume ratio and mixed thoroughly. The mixture was incubated at room temperature in the dark for 15-20 min. Flow cytometry was used to further quantify the proportion of dead bacteria to accurately evaluate the antibacterial effect of the scale inhibitor. Through antibacterial experiments, such as... Figure 9 and Figure 10 As shown, modified agar exhibits highly efficient and broad-spectrum antibacterial properties.

[0081] Figure 9 (Comparison of growth curve and density at 16h) From a kinetic perspective, the modified agar showed a time-dependent inhibitory effect on the proliferation of Escherichia coli and Staphylococcus aureus. The synergistic antibacterial effect of the modified agar was significantly better than that of carboxymethyl agar or protocatechuic acid alone. In the bacterial growth curve experiment, at 16h, the inhibition rate of carboxymethyl agar grafted with protocatechuic acid (2) against Escherichia coli (OD about 0.3) was significantly better than that of carboxymethyl agar grafted with protocatechuic acid (1) (OD about 0.35), and comparable to that of carboxymethyl agar grafted with protocatechuic acid (3) (OD about 0.3). The inhibition rate against Staphylococcus aureus (OD about 0.3) was also better than that of carboxymethyl agar grafted with protocatechuic acid (1) (OD about 0.32), and the difference with that of carboxymethyl agar grafted with protocatechuic acid (3) (OD about 0.28) was very small.

[0082] Figure 10(Flow cytometry and mortality analysis) confirmed at the mechanistic level through propidium iodide staining that modified agar mainly causes cell death by disrupting the integrity of bacterial cell membranes. The bacterial mortality rate of modified agar was significantly higher than that of the blank control group and the single-component group. Flow cytometry mortality data showed that the mortality rates of Escherichia coli (approximately 35%) and Staphylococcus aureus (approximately 35%) of carboxymethyl agar grafted with protocatechuic acid (2) were significantly higher than those of carboxymethyl agar grafted with protocatechuic acid (1) (approximately 25%), and only slightly lower than those of carboxymethyl agar grafted with protocatechuic acid (3) (approximately 38%). However, the low crystallinity of carboxymethyl agar grafted with protocatechuic acid (3) may lead to a decrease in the mechanical properties of modified agar, while carboxymethyl agar grafted with protocatechuic acid (2) maintains a more stable structural basis while ensuring high antibacterial activity. Overall, the grafting modification of carboxymethyl agar and protocatechuic acid produces a synergistic antibacterial effect, and this modified agar is an antibacterial agent with both good inhibitory activity and a clear mechanism of action.

[0083] In summary, the modified agar provided in this application can effectively alleviate scaling problems and reduce biofouling during water treatment through chelation and dispersion; details are provided in the aforementioned test data. More importantly, both agar and protocatechuic acid are derived from natural plants, possessing characteristics such as non-toxicity, no secondary pollution, and convenient biodegradability. Although specific biodegradation data is not provided in the specific tests, it can be inferred from the biodegradability characteristics of each monomer that it should possess relatively good biodegradability; this application will not elaborate further. This modified agar, as a scale inhibitor, is suitable for use as a water treatment agent in industrial water treatment, cooling water systems, boiler water treatment, desalination systems, etc. Furthermore, the preparation method for forming the modified agar provided in this application is simple to operate, has a short synthesis time, and uses abundant natural polymer materials as the main raw materials, resulting in low cost and suitability for large-scale industrial production; it is an economical and efficient preparation method.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A modified agar, characterized in that, The modified agar is formed by free radical grafting of carboxylated agar and protocatechuic acid; The modified agar has the following structural formula: ； Where R1 is -H or -CH2COOH; R2 is ; The carboxylated agar includes a carboxyl group, which includes a carboxylmethyl group, and is used to chelate with metal cations in water to inhibit scale formation. The protocatechuic acid includes hydroxyl groups, including phenolic hydroxyl groups, and is used to disrupt the structural integrity of bacteria in water and inhibit biological pollution of water bodies.

2. The modified agar according to claim 1, characterized in that, The mass ratio of carboxyl groups to phenolic hydroxyl groups in the modified agar is 3:1 to 20:

1.

3. The modified agar according to claim 1, characterized in that, At least one of the following conditions must be met: Used in water bodies to inhibit scale formation and biological pollution; At the effective dosage, the 24-hour inhibition rate against Escherichia coli is greater than or equal to 60%. At the effective dosage, the 24-hour inhibition rate against Staphylococcus aureus is greater than or equal to 60%. At the effective dosage, the bacterial mortality rate is greater than or equal to 30%; The effective dosage is 10 mg / L to 50 mg / L.

4. A method for preparing modified agar, characterized in that, Includes the following steps: Carboxylic agar and protocatechuic acid in a mass ratio of 1:(0.5~2) were dissolved in pure water to obtain a mixed solution; Nitrogen gas was introduced into the mixed solution to remove oxygen, and hydrogen peroxide solution was added to initiate a free radical grafting reaction. The temperature was raised to 60℃~70℃ and the reaction was maintained for 0.5h~6h to prepare modified agar. The carboxylated agar includes carboxymethyl agar, wherein the degree of substitution of the carboxymethyl functional group of the carboxymethyl agar is 0.32 to 1.

45.

5. The preparation method according to claim 4, characterized in that, The method for preparing the carboxylated agar includes: dispersing agar and sodium hydroxide in an ethanol solution at a mass ratio of 1:(1~1.5) and reacting at 50~70℃ for 0.5~1.5h; adding chloroacetic acid at a mass ratio of chloroacetic acid to agar of (0.46~1.84):1 and reacting at 50℃~80℃ for 0.5h~6h; separating and purifying to obtain the carboxylated agar.

6. The preparation method according to claim 4, characterized in that, Based on the volume of the mixed solution, the volume percentage of the hydrogen peroxide solution is 5% to 10%; the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%.

7. The preparation method according to claim 4, characterized in that, The mixed solution also includes ascorbic acid, and the mass ratio of ascorbic acid to protocatechuic acid is (0.06~0.25):

1.

8. A scale inhibitor, characterized in that, The scale inhibitor comprises the modified agar according to any one of claims 1 to 4 or the modified agar prepared by the method of preparing the modified agar according to any one of claims 4 to 7.

9. The scale inhibitor according to claim 8, characterized in that, The scale inhibitor is used in industrial water treatment, cooling water systems, boiler water treatment, and desalination systems.

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