Accurate preparation method and system of composite water treatment agent based on humic acid

Abstract

The invention discloses a precise preparation method and system of a composite water treatment agent based on humic acid, and the method comprises the following steps: firstly, simultaneously guiding humic acid fragments and functional components such as metal ions in a water phase by using template molecules with bifunctional binding sites, such as carboxylated beta-cyclodextrin, to carry out spatial specific pre-assembly; then, a light triggering condition is applied to the assembly system, thiol-ene and other click chemical reactions are induced to occur, and a dynamic pre-assembly structure is instantly locked in situ through a covalent cross-linked network; and finally, adjusting the pH value, removing and recycling the template to obtain the composite water treatment agent with an accurate structure. The method realizes normal form transformation from random mixing to directional construction, and the prepared product has the outstanding advantages of high complexing capacity, strong stability and good batch consistency, and is especially suitable for high-standard heavy metal wastewater treatment and resource recovery.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and fine chemical technology, specifically relating to a method for preparing a humic acid-based composite functional agent for water treatment. Background Technology

[0002] Humic acid is a widely available and environmentally friendly natural organic macromolecule. Its structure contains abundant active functional groups such as carboxyl and phenolic hydroxyl groups, which give it excellent complexing, adsorption, and flocculation properties for various heavy metal ions and pollutants. Therefore, developing humic acid into a highly efficient and low-cost water treatment agent, especially a specialized complexing agent for heavy metal wastewater treatment, has always been an important research goal in this field.

[0003] To achieve this goal, existing technologies generally employ mechanical blending to prepare humic acid composites. This involves macroscopically mixing humate solutions with target functional components (such as metal salt solutions) through physical stirring, ultrasound, or high shear, relying on random molecular collisions to form complexes. However, this traditional method has inherent and deep-seated technical defects. First, because it relies entirely on a random physical mixing process, the resulting product is a mixture of various complex forms, coordination structures, and stability, with a highly disordered molecular structure. This leads to the embedding of numerous active sites or the formation of weak bonds, resulting in low utilization of the effective components and a performance ceiling that is difficult to break through. Second, the structure and performance of the product are highly uncontrollable, with significant batch-to-batch and batch-to-batch differences, failing to meet the stringent requirements of modern water treatment processes for agent efficiency and stability. Third, this method is essentially a random mixing process, unable to perform reverse design and precise construction targeting the microstructure of specific pollutants (such as the electronic configuration and ionic radius of different metal ions), limiting the ability to develop high-performance, highly selective specialized agents.

[0004] The aforementioned shortcomings stem from the underlying logic of existing technologies, which merely mix but do not construct. Therefore, developing a new method capable of actively guiding and precisely immobilizing the composite structure of humic acid and functional components at the molecular level, fundamentally overcoming the series of bottlenecks caused by structural disorder, has become a key technical problem urgently needing to be solved to improve the performance of humic acid-based water treatment agents and expand their high-end applications. Related improvements are imperative. Summary of the Invention

[0005] To address the technical problems and shortcomings of existing technologies, this invention provides a precise preparation technology based on template guidance and photocuring locking. By introducing a designable molecular template, the active sites are pre-assembled in a programmed manner, and the structure is solidified in situ using a photoclick chemical reaction. Finally, the template is removed to obtain a composite agent with a well-defined structure and excellent performance, thereby fundamentally solving the aforementioned technical problems.

[0006] The solution to the technical problem of this invention is a method for preparing a composite water treatment agent based on humic acid, comprising the following steps: S1. Template-guided pre-assembly: Humic acid, functional components, and template molecules are mixed in a liquid phase, so that the template molecules simultaneously bind to the humic acid and the functional components to form a pre-assembled composite; the template molecules have a first binding site for binding to the humic acid and a second binding site for binding to the functional components; S2. Structure solidification: A triggering condition is applied to the system containing the pre-assembled composite obtained in step S1 to induce a cross-linking reaction between the humic acid and the functional components, and / or within the humic acid and / or the functional components, thereby fixing the structure of the pre-assembled composite; S3. Template removal: The template molecules are removed from the product obtained in step S2 to obtain the composite water treatment agent.

[0007] Preferably, the template molecule is a cyclodextrin or a derivative thereof.

[0008] Preferably, the cyclodextrin or its derivative is a carboxylated β-cyclodextrin.

[0009] Preferably, the functional component is a metal ion.

[0010] Preferably, the metal ion is selected from copper ions, iron ions, lead ions, or cadmium ions.

[0011] Preferably, in step S2, the triggering condition is photo-triggered; the crosslinking reaction is a photo-initiated click chemistry reaction.

[0012] Preferably, the photo-initiated click chemistry reaction is a thiol-ene click chemistry reaction or a thiol-alkyne click chemistry reaction.

[0013] Preferably, in step S3, the template molecules are precipitated by adjusting the pH value of the system, and the template molecules are removed by solid-liquid separation.

[0014] Another system for implementing the preparation method includes a pre-assembly reaction unit for mixing humic acid, functional components, and template molecules and performing a pre-assembly reaction; a structure curing unit connected to the pre-assembly reaction unit for receiving the pre-assembly reaction product and applying triggering conditions to induce a cross-linking reaction; the structure curing unit is a photochemical reactor; and a template separation unit connected to the structure curing unit for separating and removing template molecules from the cured reaction product.

[0015] The beneficial effects of this invention are as follows: 1. By using a template-guided and photocuring-locking method, precise control of the microstructure of the humic acid composite agent is directly achieved, breaking through the performance bottleneck caused by traditional random mixing. The prepared humic acid copper complexing agent increases the saturated complexing capacity of Cu²⁺ by 50%-80%, and the stability constant of the complex is increased by more than an order of magnitude. The standard deviation of performance fluctuation between product batches is less than 5%, achieving a qualitative change and high stability in performance.

[0016] 2. In terms of practical applications, the simple step of pH adjustment and precipitation separation enables the efficient recovery and recycling (≥20 times) of template molecules, reducing the potentially high costs of the core innovation to an acceptable level and significantly improving the economics of the process. Simultaneously, it promotes the transformation of the entire preparation process from extensive mixing to refined molecular engineering, providing a scalable and universal platform for customizing a series of products with different functions as needed.

[0017] 3. Based on the optimized scheme of pulsed light illumination and online feedback control, the system maintains extreme stability in continuous production, and the standard deviation of product uniformity within a batch can be further optimized to within 3%, verifying its robustness in industrial scale-up. This provides a reliable technical foundation for the subsequent application of such precisely structured reagents in demanding scenarios with extremely high requirements for reagent performance consistency, such as the deep treatment of electronic electroplating wastewater and the selective recovery of valuable metals. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the preparation method of the present invention.

[0019] Figure 2 This is a schematic diagram of the core molecular-level mechanism of action in this invention.

[0020] Figure 3 This is a schematic diagram of the structure of the continuous flow photochemical reactor preferred for use in this invention.

[0021] Figure 4 This is a flowchart of the main steps of the preparation method of the present invention.

[0022] in Figure 2 (a) shows the template combining with humic acid and metal ions respectively, (b) shows the formation of a ternary pre-assembled composite, and (c) shows photocuring crosslinking and template removal. Figure 3 1-Reaction tube; 2-Inlet; 3-Outlet; 4-LED array; 5-Prior monitoring probe. Detailed Implementation

[0023] The following detailed description, in conjunction with the accompanying drawings, provides a precise preparation method and system for a humic acid-based composite water treatment agent provided by this invention. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0024] In the field of environmental water treatment, humic acid, as a widely available and environmentally friendly natural high-molecular-weight organic compound, is extensively studied for the complexation removal of heavy metal ions due to its rich content of active functional groups such as carboxyl and phenolic hydroxyl groups. Currently, mainstream humic acid-based water treatment agents (such as iron humate and copper humate) are mainly prepared through a simple mechanical blending method, which involves physically mixing humate salt solutions with target metal salt solutions in a reaction vessel, relying on random collisions between molecules to form complex products. However, through in-depth research, the inventors have realized that the above-mentioned traditional methods have a deep-seated and long-neglected technical bottleneck. Because they rely entirely on random macroscopic physical mixing, the prepared humic acid-metal complexes are essentially mixtures of various complexation forms, different coordination structures, and varying stability, with their molecular structures in a highly disordered and random state. This inherent structural disorder results in a low proportion of effective active sites, a ceiling on performance (such as complexation capacity), and large batch-to-batch fluctuations, making it difficult to meet the increasingly stringent wastewater treatment standards for agent efficiency and stability. The industry typically attributes performance bottlenecks to insufficient mixing, but the applicant discovered that the root cause lies in the lack of proactive control over the molecular-level composite structure. Therefore, achieving precise construction of the microstructure of humic acid composites has become crucial for improving their performance. This invention addresses this technical problem by proposing a novel preparation paradigm, aiming to achieve precise design and controllable synthesis of the active site structure of the final product from a molecular engineering perspective.

[0025] The core of the method provided by this invention lies in a three-step strategy of guiding, locking, and removing, such as... Figure 4 As shown, its basic process can be found in [reference needed]. Figure 1 . Figure 1 This is a process flow diagram of the preparation method of the present invention. As shown in the figure, the entire process begins with the input of humic acid raw material, functional components (such as metal salts), and template molecules, and sequentially passes through a pre-assembly reaction zone, a photocuring reaction zone, and a template separation and product post-processing zone, ultimately yielding a composite water treatment agent product with a precise structure. The arrows in the figure clearly show the flow direction of materials between each step.

[0026] Template-guided pre-assembly steps correspond to Figure 1 The pre-assembled reaction zone in the liquid phase aims to pre-arrange humic acid and functional components (such as target metal ions) into an ideal spatial configuration by utilizing the specific binding ability of template molecules.

[0027] The specific operation involves adding humic acid (usually in the form of its water-soluble salts, such as sodium humate or potassium humate), a solution containing functional components (e.g., a metal salt solution), and a template molecule solution to a reaction vessel equipped with a gentle stirrer and temperature and pH control devices, according to a predetermined stoichiometric ratio. The humic acid can be derived from an alkaline extract of weathered coal, lignite, or peat, and its carboxyl content is preferably between 3-6 mmol / g. The functional components are mainly metal ions that need to be removed or utilized, such as iron ions (Fe³⁺) for phosphorus removal and decolorization, copper ions (Cu²⁺), lead ions (Pb²⁺), or cadmium ions (Cd²⁺) for heavy metal removal. These are added in the form of soluble salts, such as nitrates, chlorides, or sulfates. The template molecule is the core for achieving precise pre-assembly. It must simultaneously possess a first binding site for humic acid and a second binding site for the functional component. A preferred embodiment uses cyclodextrin or its derivatives as the template. More preferably, carboxylated β-cyclodextrin is used. Its mechanism of action can be found in [reference needed]. Figure 2 .

[0028] The molecular interaction mechanism is shown in the figure. Figure 2 A schematic diagram illustrating the core molecular-level mechanism of action of this invention is shown. For example... Figure 2 As shown in (a), the carboxylated β-cyclodextrin molecule possesses a hydrophobic cavity (serving as the first binding site), which can selectively accommodate and locate aromatic structural fragments in humic acid molecules through non-covalent forces such as hydrophobic interactions and π-π stacking. Simultaneously, its edge-modified carboxyl groups (serving as the second binding site) can reversibly capture target metal ions (Mⁿ⁺) in solution through ionic or coordinate bonds under appropriate pH conditions (e.g., pH 7.0-8.5). Thus, a template molecule acts like a molecular clamp, simultaneously capturing humic acid fragments and metal ions, forcing them to approach each other with specific spatial geometry, forming a well-defined humic acid-template-metal ion ternary pre-assembled complex, such as... Figure 2 As shown in (b).

[0029] This step is carried out at room temperature to 40°C, with the pH value controlled between 7.0 and 8.5. The stirring speed should be just enough to ensure the homogeneity of the solution, without high-intensity shearing. The reaction time is approximately 20-60 minutes. The molar ratio of the raw materials (based on the molar number of active groups of humic acid, metal ions, and template) is usually in the range of (1-4):1:(0.5-2). The specific ratio needs to be optimized experimentally based on the performance of the target product.

[0030] Structural solidification corresponds to Figure 1The photocuring reaction zone is used to permanently fix the spatial structure of the pre-assembled composite that is in dynamic equilibrium. Specifically, the pre-assembled reaction mixture is transferred to a photochemical reaction device. Before entering the device or at the inlet of the device, a photoinitiator and active monomers (i.e., crosslinking agents) that can participate in the crosslinking reaction are added to the mixture.

[0031] The preferred triggering condition and reaction type is photo-triggered. More specifically, a photo-initiated click chemistry reaction, such as a thiol-alkene click chemistry reaction, is used. For this, it is necessary to ensure that the system contains carbon-carbon double bonds (alkene) and thiol groups (-SH). This can be achieved by slightly modifying humic acid before the pre-assembly step, introducing alkenyl groups into its molecular chain (e.g., reacting some of the carboxyl groups of humic acid with allyl glycidyl ether). A multifunctional thiol compound, such as pentaerythritol tetra-3-mercaptopropionate, is chosen as the crosslinking agent. 2-hydroxy-2-methylphenylacetone (HMPP) can be used as the photoinitiator. The curing process involves pumping a mixture containing the pre-assembled body, crosslinking agent, and photoinitiator into a photochemical reactor (see schematic diagram). Figure 3 The humic acid is exposed to ultraviolet light of a specific wavelength (such as 365 nm, which matches the absorption peak of HMPP). Under photoexcitation, the initiator generates free radicals, rapidly initiating a click chemistry reaction between thiols and alkenes, forming a strong covalent network between humic acid molecules and between humic acid and metal ions (through cross-linking near coordination sites). Figure 2 As shown in (c), this process is like putting a rigid covalent skeleton on a pre-assembled body, freezing its ideal configuration in situ.

[0032] Regarding photochemical reactors, such as Figure 3 This is a simplified structural diagram of the continuous flow photochemical reactor preferred for use in this invention. The reactor includes a transparent reaction tube 1 (such as a quartz glass tube), through which the reaction liquid flows in from inlet 2 and out from outlet 3. An array of ultraviolet LEDs 4 is arranged around the outside of the reaction tube 1 to provide uniform, high-intensity, and wavelength-controllable irradiation. To precisely control the curing process, an online monitoring probe 5, such as a UV-Vis spectroscopy probe, can be integrated into the reactor to monitor changes in characteristic absorption in the reaction liquid in real time, indirectly providing feedback on the progress of the crosslinking reaction. This design ensures that the fluid receives uniform illumination during flow, which is crucial for achieving batch-to-batch product consistency.

[0033] The template removal step corresponds to Figure 1The template separation and post-processing zone aims to separate the template molecules, which have completed their guiding function, from the solidified product for recycling, thereby obtaining the final product. The photocured reaction solution is transferred to a separation container. Template separation is achieved by adjusting the pH of the system. Specifically, an acid (such as dilute hydrochloric acid or dilute sulfuric acid) is added to the reaction solution to adjust the pH to an acidic range of 2.0-4.0. Under these conditions, the carboxyl groups on the carboxylated β-cyclodextrin template undergo protonation, significantly weakening or even eliminating the ionic / coordinate bonds between the template and metal ions. Simultaneously, the solubility of the protonated template molecules in water is significantly reduced, causing them to precipitate from the solution as a solid.

[0034] The precipitated template solid can then be separated from the liquid phase containing the target product using conventional solid-liquid separation methods, such as filtration or centrifugation. The separated template solid can be recycled for the next preparation after simple alkali dissolution, neutralization, and regeneration, significantly reducing raw material costs. The separated liquid phase (i.e., the product liquid) may still contain small amounts of small molecule salts or reagents, which can be further purified and processed into a finished product using methods well-known to those skilled in the art, such as dialysis, ultrafiltration, or spray drying, to obtain a solid, powdered humic acid composite water treatment agent.

[0035] In implementing the above basic scheme, the applicant further discovered that precise control of the photocuring process is crucial to obtaining products with extremely uniform structure and excellent performance. Based on this, a better implementation method can be adopted to optimize the curing step by combining pulsed light irradiation with online spectral feedback control. Specifically, instead of continuously and uniformly irradiating the flowing reaction liquid, the ultraviolet LED array 4 is configured to emit pulsed light at a preset frequency and duty cycle. Simultaneously, an online ultraviolet-visible spectral probe 5 integrated on the reactor is used to monitor in real time the absorbance value of the reaction liquid flowing through the monitoring point at a specific wavelength (e.g., a characteristic absorption wavelength associated with a certain intermediate or product in the reaction system).

[0036] The absorbance data is transmitted in real time to a feedback controller, which stores a pre-built absorbance-crosslinking degree correlation model established through previous experiments. The controller compares the real-time monitored absorbance value with the target value and dynamically adjusts the frequency, duty cycle, or switching of certain sections of the LED array in subsequent pulses. For example, if the rate of change of absorbance in a certain fluid segment is lower than expected, indicating that its crosslinking reaction may be slower due to uneven local concentration or light intensity, the controller can immediately increase the light pulse frequency of the LED section through which the fluid segment will flow to provide more photon energy and promote the completion of the reaction; conversely, it can reduce the light intensity to avoid excessive crosslinking or side reactions.

[0037] This optimization method yields additional and significant technical benefits, fundamentally solving the problem of batch-specific product structural inhomogeneity caused by minute differences in the light exposure history of fluid microclusters in continuous flow production. Through this adaptive feedback control, it ensures that the complex in every microliter of fluid flowing from the reactor achieves a nearly identical degree of cross-linking and solidification, resulting in an unprecedented level of molecular structural consistency in the final product. Experiments show that, with this optimized control, the standard deviation of complexation capacity fluctuation at different sampling points for the same batch of product can be further reduced to below 3%, far superior to the level without control, providing a solid quality guarantee for applications in high-end water treatment scenarios.

[0038] Through the implementation of the aforementioned specific technical means, the introduction of template molecules with bifunctional binding sites (such as carboxylated β-cyclodextrin) actively guides humic acid and metal ions to form spatially accurate complexes during the pre-assembly step, changing the traditional random collision recombination mode and significantly increasing the proportion of effective active sites (i.e., structurally correct and accessible complexing sites) in the final product. The use of rapid and efficient photo-triggered click chemistry to covalently lock the pre-assembled structure in situ transforms the ideal metastable molecular arrangement into a permanently stable covalent network, resulting in a qualitative change in the chemical stability of the product. Potentiometric titration tests show that the complex stability constant (LogK) of the product is more than an order of magnitude higher than that of traditional products. This means that it has extremely strong resistance to interference from other coexisting ions when treating complex wastewater, and the effluent heavy metal concentration is more stable. The highly homogeneous product resulting from the above structural control, combined with the recyclable template design, ensures excellent batch repeatability of product performance and effectively controls raw material costs. The relative deviation of key performance indicators (complexation capacity) between batches of products can be kept stable at less than 5%. Meanwhile, the guiding efficiency of the template does not show a significant decrease after 20 cycles of use, and the cost of a single template can be reduced to a negligible level. Furthermore, due to the aforementioned optimized scheme of pulsed light irradiation and online feedback control, microscopic dynamic regulation of the photocuring process is achieved, resulting in a new level of product structural consistency. The standard deviation of uniformity within batches is less than 3%, thus providing the possibility of achieving stable and reliable high-standard effluent in demanding scenarios such as the deep treatment of electronic electroplating wastewater.

[0039] It should be noted that the above embodiments and accompanying drawings are merely illustrative examples of the core principles and key structures of the precise preparation method and system for a humic acid-based composite water treatment agent of the present invention. The accompanying drawings are simplified schematic diagrams, intended to clearly illustrate the structural, process, or data flow relationships related to the innovative points of the technical solution, and are not intended to limit the complete form of the actual product. This specification focuses on the innovative technical means necessary to achieve the purpose of the invention and solve the technical problem. While auxiliary or common-sense details that can be implemented by those skilled in the art without creative effort, such as the conventional heating / cooling jacket design of the reaction vessel, the selection and connection of pumps and valves, the installation of pH meters and thermometers, the selection of filtration equipment models, and the conventional parameter settings for spray drying, are not described in detail, they should all be understood as naturally included in the specific implementation of the present invention and fall within the protection and implementation scope of this technical solution.

Claims

1. A method for preparing a composite water treatment agent based on humic acid, characterized in that, Includes the following steps: S1. Template-guided pre-assembly: Humic acid, functional components and template molecules are mixed in a liquid phase, so that the template molecules simultaneously bind to the humic acid and the functional components to form a pre-assembled complex; the template molecules have a first binding site for binding to the humic acid and a second binding site for binding to the functional components. S2. Structure solidification: Apply triggering conditions to the system containing the pre-assembled composite obtained in step S1 to induce cross-linking reactions between the humic acid and the functional components, and / or within the humic acid and / or functional components, thereby fixing the structure of the pre-assembled composite. S3. Template Removal: Remove the template molecule from the product obtained in step S2 to obtain the composite water treatment agent.

2. The preparation method according to claim 1, characterized in that, The template molecule is a cyclodextrin or its derivative.

3. The preparation method according to claim 2, characterized in that, The cyclodextrin or its derivatives are carboxylated modified β-cyclodextrins.

4. The preparation method according to claim 1, characterized in that, The functional component is a metal ion.

5. The preparation method according to claim 4, characterized in that, The metal ions are selected from copper ions, iron ions, lead ions, or cadmium ions.

6. The preparation method according to any one of claims 1, characterized in that, In step S2, the triggering condition is photo-triggered; the crosslinking reaction is a photo-initiated click chemistry reaction.

7. The preparation method according to claim 6, characterized in that, The photo-initiated click chemistry reaction is either a thiol-ene click chemistry reaction or a thiol-alkyne click chemistry reaction.

8. The preparation method according to any one of claims 1, characterized in that, In step S3, the template molecules are precipitated by adjusting the pH value of the system, and the template molecules are removed by solid-liquid separation.

9. A system for carrying out the preparation method according to any one of claims 1-8, characterized in that, include: Pre-assembly reaction unit, used to mix humic acid, functional components and template molecules and carry out pre-assembly reaction; A structure curing unit, connected to the pre-assembly reaction unit, is used to receive the pre-assembly reaction products and apply triggering conditions to induce a cross-linking reaction; the structure curing unit is a photochemical reactor. The template separation unit, connected to the structure curing unit, is used to separate and remove template molecules from the cured reaction products.

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