A gradient composite type light regenerative water treatment flocculant and a preparation method and application thereof

Abstract

This invention discloses a gradient composite photocatalytic regeneration water treatment flocculant, its preparation method, and its application. The preparation method is as follows: 1. Mixing nano-chitin fibers, lignin-polyphenol complexes, and Fe3O4@TiO2 nanoparticles loaded on photocatalytic microspheres obtained from sodium alginate; 2. Crosslinking to form a homogeneous colloid; 3. Orienting in a magnetic field; 4. Gradient freeze-drying. This invention crosslinks nano-chitin fibers, lignin-polyphenol complexes, and photocatalytic microspheres to form a gradient composite photocatalytic regeneration water treatment flocculant, which possesses a four-dimensional adsorption mechanism of electrostatic attraction, π-π stacking, coordination complexation, and spatial sieving, enabling highly efficient removal of various pollutants such as heavy metal ions, organic pollutants, and suspended solids. Furthermore, the high crystallinity of the nano-chitin fibers in this invention provides mechanical support within the flocculant, preventing magnetic agglomeration of Fe3O4 magnetic nuclei.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a gradient composite photo-regenerated water treatment flocculant, its preparation method, and its application. Background Technology

[0002] In wastewater treatment technology systems, flocculants are key functional materials, and their performance directly affects pollutant separation efficiency and the economics of subsequent processes. Existing flocculation systems mainly rely on two major categories of traditional materials: inorganic and organic. However, significant technical bottlenecks exist in the synergistic removal of pollutants and resource recycling.

[0003] Inorganic flocculants, represented by aluminum-based compounds such as polyaluminum chloride (PAC), have advantages such as readily available raw materials and good economic efficiency, but they also have several application drawbacks: First, the dosage of the agent needs to reach a high concentration to form effective flocs (usually >200 mg / L), resulting in a 30%-50% increase in sludge production; second, the generated flocs have a loose structure, and their settling rate is generally less than 5 cm / min, which seriously affects the solid-liquid separation efficiency; third, they have weak complexation and capture capabilities for dissolved organic pollutants and heavy metal ions (such as Cr³⁺ and Cd²⁺) with a molecular weight <1000 Da, making it difficult to meet the advanced treatment standards of effluent CODcr <30 mg / L and heavy metal residue <0.1 mg / L.

[0004] In the field of organic flocculants, synthetic polymers such as polyacrylamide (PAM) are dominant. They can form dense flocs (settling rate > 15 cm / min) through long-chain bridging, but there are significant ecological risks: First, the inherent stability of the C-C bonds in the main chain of synthetic polymers results in a biodegradability rate of less than 5% and an environmental half-life of more than 180 days; second, the residual amount of unreacted monomers (such as acrylamide) during the production process can reach 0.05%-0.2%, which has significant neurotoxicity; third, conventional processes cannot achieve effective depolymerization of flocs after use, resulting in annual waste exceeding one million tons.

[0005] To address these issues, researchers have recently turned to the development of natural biomass-modified flocculants, with materials such as chitosan and starch attracting significant attention due to their biocompatibility (degradation rate >90%). However, these materials are limited by their single active site (amino or hydroxyl), resulting in a simultaneous removal rate of less than 60% for complex heavy metal-organic pollution systems. Furthermore, they exhibit poor thermal stability (thermal decomposition temperature <200℃), making them unsuitable for the high-load conditions of industrial wastewater treatment.

[0006] More concerning is the general lack of regenerability among existing flocculants. Industry statistics show that the recycling rate of traditional flocculants is less than 2%, resulting in annual resource waste amounting to billions of yuan. Current regeneration technologies mainly focus on chemical elution (hydrochloric acid / EDTA immersion) and high-temperature pyrolysis (500-800℃). However, the former requires 3-5 times the dosage of regeneration reagent and generates secondary polluting wastewater containing heavy metals (heavy metal leaching concentration >50 mg / L); while the latter can achieve >80% regeneration of deactivating agents, the high-temperature process causes molecular chain breakage (molecular weight decrease >60%), and the flocculation efficiency of the regenerator only maintains 40%-50% of the initial value.

[0007] This demonstrates that existing technologies suffer from systemic deficiencies in three dimensions: broad-spectrum pollutant removal, environmental friendliness, and resource recycling. With the continuous tightening of effluent quality requirements by regulations such as the Water Pollution Prevention and Control Action Plan (e.g., TP < 0.3 mg / L, TN < 10 mg / L), there is an urgent need to develop novel flocculants that combine efficient multi-pollutant synergistic removal, biodegradability, and mild regeneration conditions. This is of significant strategic importance for promoting the green transformation of the water treatment industry. Summary of the Invention

[0008] To meet the above requirements, the purpose of this invention is to provide a gradient composite photo-regenerated water treatment flocculant, its preparation method, and its application, which overcomes the shortcomings of existing flocculants, achieves efficient removal of various pollutants, and has good magnetic recovery performance, thereby reducing treatment costs and secondary pollution.

[0009] In a first aspect, the present invention provides a method for preparing a gradient composite photo-regenerated water treatment flocculant, comprising the following steps:

[0010] Step 1: Photocatalytic microspheres obtained by loading nano-chitin fibers, lignin-polyphenol complex, and Fe3O4@TiO2 nanoparticles onto sodium alginate are mixed in PBS buffer at a mass ratio of 1:(0.3~0.8):(0.1~0.5).

[0011] Step 2: Add a crosslinking agent to the mixture obtained in Step 1 and sonicate to form a homogeneous colloid.

[0012] Step 3: Place the colloid obtained in Step 2 in a magnetic field with a strength of 0.3~0.8T to make the Fe3O4 in the colloid oriented.

[0013] Step 4: Perform gradient freeze-drying on the product obtained in Step 3 to form and fix the mesoporous structure, and obtain the flocculant.

[0014] The three components in the obtained flocculant work synergistically to achieve efficient pollutant treatment: the positively charged amino groups on the nano-chitin fibers and the negatively charged groups on the lignin-polyphenol complex form a charge gradient field, adsorbing colloidal particles and heavy metals through electrostatic interactions; the three-dimensional sieve structure formed by the cross-linking of the three components intercepts suspended solids; simultaneously, the lignin-polyphenol complex utilizes phenolic hydroxyl groups to chelate heavy metals and utilizes the π-π stacking of lignin aromatic rings to improve COD removal rate. Meanwhile, TiO2 in component C generates electron-hole pairs under light irradiation, oxidizing organic matter and reducing heavy metals respectively; calcium alginate forms a gel barrier to protect the active components when the pH value is >6.

[0015] Furthermore, the nano-chitin fibers and lignin-polyphenol complex provide more attachment sites for the photocatalytic microspheres, improving the dispersion uniformity of the photocatalytic microspheres; the lignin-polyphenol complex has photosensitizing effect, which can improve the light absorption efficiency of TiO2, promote the generation of photogenerated carriers, and thus enhance the photocatalytic degradation effect, synergistically degrading organic pollutants with the photocatalytic microspheres.

[0016] Preferably, the preparation process of the nano-chitin fibers is as follows:

[0017] (1) Crush the shells of crustaceans (preferably shrimp shells or crab shells) to obtain chitin raw material particles.

[0018] (2) Remove calcium carbonate from chitin raw material particles in an acidic system to obtain decalcified particles.

[0019] (3) Deproteinization treatment: The decalcified particles are deproteinized in an alkaline system to remove protein, resulting in crude white chitin.

[0020] (4) Add crude chitin and cellulase to a buffer solution and apply microwave irradiation to obtain the enzymatic hydrolysis product.

[0021] (5) Pressurize the enzymatic hydrolysis product to form a nanofiber suspension, and then separate the solid and liquid to obtain nano-chitin fibers.

[0022] Preferably, the preparation process of the lignin-polyphenol complex is as follows:

[0023] (1) Pulverize the lignocellulosic biomass to obtain biomass raw material particles.

[0024] (2) Add biomass raw material particles to deionized water, adjust the temperature and pressure, and carry out subcritical water extraction.

[0025] (3) The product obtained in step (2) is fractionally purified to obtain a powdered lignin-polyphenol complex.

[0026] Preferably, the preparation process of the photocatalytic microspheres is as follows:

[0027] (1) Fe3O4 nanoparticles were obtained by reacting FeCl2·4H2O and FeCl3·6H2O in an alkaline system. Tetrabutyl titanate was mixed with anhydrous ethanol and then added dropwise to an ethanol dispersion containing Fe3O4 nanoparticles. The resulting product was calcined to obtain core-shell structured Fe3O4@TiO2 nanoparticles.

[0028] (2) After mixing Fe3O4@TiO2 nanoparticles with sodium alginate solution, they were dropped into CaCl2 solution and cross-linked and solidified to obtain photocatalytic microspheres.

[0029] Preferably, when the pollutant being treated by the flocculant is a heavy metal, the mass ratio of nano-chitin fibers, lignin-polyphenol complex, and photocatalytic microspheres is 1:(0.7~0.8):(0.1~0.3).

[0030] When the pollutants being treated by the flocculant are organic pollutants, the mass ratio of nano-chitin fibers, lignin-polyphenol complex, and photocatalytic microspheres is 1:(0.3~0.5):(0.4~0.5).

[0031] Preferably, the gradient freeze-drying process is as follows: the product obtained in step three is pre-frozen at -30 to -10°C, deep-frozen at -60 to -40°C, and then vacuum-dried.

[0032] Secondly, the present invention provides a gradient composite photo-regenerated water treatment flocculant, which is prepared by the aforementioned preparation method.

[0033] Thirdly, the present invention provides an application of a gradient composite photo-regenerated water treatment flocculant in the treatment of wastewater containing heavy metals and / or organic pollutants.

[0034] Fourthly, the present invention provides a wastewater treatment method, the process of which involves adding a gradient composite photo-regenerated water treatment flocculant to the wastewater to be treated; heavy metals and / or organic pollutants in the wastewater to be treated aggregate to form flocculent products.

[0035] Preferably, the wastewater to be treated is exposed to light to degrade organic pollutants in the flocculants; after flocculation, the flocculants are separated and placed in a regeneration system under light conditions to obtain regenerated flocculant. The pH value of the regeneration system is 2.5–4.

[0036] Preferably, the wastewater to be treated is dyeing and printing wastewater.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention crosslinks nano-chitin fibers (component A), lignin-polyphenol complexes (component B), and photocatalytic microspheres (component C) to form a gradient composite photo-regenerated water treatment flocculant, constructing a three-in-one synergistic system of "charge complementarity-adsorption catalysis-magnetic response regeneration". Specifically, the protonated amino groups on the surface of component A, carrying a positive charge, attract negatively charged colloidal particles in wastewater; component B, containing negatively charged groups, can chelate heavy metals through coordination bonds, and the aromatic rings of lignin form π-π stacking with the aromatic rings in organic pollutant molecules. The protonated amino groups on the surface of component A and the phenolic hydroxyl / carboxyl groups of component B form a dynamic charge gradient field, achieving the directional enrichment of pollutants through electrostatic attraction and π-π interactions; component C, through the photogenerated carrier separation effect of the Fe3O4@TiO2 core-shell heterojunction, simultaneously achieves the oxidative decomposition of enriched organic pollutants and the reduction of enriched heavy metal ions.

[0039] In this invention, component C is composed of Fe3O4@TiO2 nanoparticles with a core-shell structure loaded with calcium alginate. The interaction of these three components reduces the effective band gap of TiO2 and shifts the photoresponse range into the longer wavelength visible light region. In addition, the lignin aromatic rings and polyphenol groups in component B not only enhance pollutant adsorption, but their photosensitization effect further extends the photoresponse range of TiO2 into the visible light region.

[0040] The high crystallinity of the nano-chitin fibers (component A) in this invention not only improves the compressive strength of the flocculant in water flow impact or stirring environment, but also provides mechanical support for the flocculant, preventing magnetic agglomeration of component C, ensuring that component C is uniformly dispersed in the system, and maintaining good magnetic properties.

[0041] This invention features an "adsorption-photolysis-regeneration" cyclic mechanism. In the treatment stage (pH≈7), components A / B rapidly adsorb pollutants via amino / phenolic hydroxyl groups, while component C regenerates the active sites through photocatalytic degradation. In the regeneration stage (pH≈3), the calcium alginate gel barrier shrinks, releasing nascent TiO2 to aid flocculant regeneration, while component B chelates Fe. 3+ Inhibit magnetic core corrosion and ensure the removal rate of pollutants after material recycling. Attached Figure Description

[0042] Figure 1 This is a flowchart of Embodiment 1 of the present invention. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the embodiments.

[0044] Example 1

[0045] like Figure 1 As shown, a method for preparing a gradient composite photo-regenerated water treatment flocculant includes the following steps:

[0046] Step 1: Prepare raw materials consisting of three components, A, B, and C. Component A is nano-chitin fibers; component B is a lignin-polyphenol complex; and component C is photocatalytic microspheres.

[0047] The preparation process of the aforementioned nano-chitin fibers (component A) includes the following steps:

[0048] (1) Raw material cleaning: Take fresh shrimp shells, remove residual meat, crush them into particles with a diameter of 2-5 mm, and wash them 3 times with deionized water to remove impurities. In some other embodiments, shrimp shells can be replaced with crab shells or shells of other crustaceans, and shells of multiple crustaceans can be used in combination.

[0049] (2) Demineralization treatment: The raw material particles obtained in step (1) are soaked in 5% HCl at a liquid-solid ratio of 10:1 for 24 hours. The particles are then magnetically stirred at 300 rpm until no bubbles are generated and the CaCO3 in the particles is completely dissolved. After filtration, the particles are washed with deionized water until neutral (pH≈7) and dried at 60℃ to obtain decalcified particles.

[0050] (3) Deproteinization treatment: Immerse the decalcified particles in 3% NaOH solution and react at 90°C in a reaction vessel equipped with a reflux condenser for 4 hours (liquid-solid ratio 15:1); centrifuge (8000 rpm, 10 min), take the precipitate and wash it with water until neutral to obtain white crude chitin.

[0051] (4) Microwave-enzyme coupled treatment: Crude chitin was dispersed in an acetate-sodium acetate buffer solution at a solid-liquid ratio of 1:50 with a pH of 5.0; 0.5% cellulase (enzyme activity ≥500U / mg) was added, and the mixture was placed in a constant temperature water bath at 50℃; microwave radiation (800W, pulse mode: 2s on / 5s off) was applied simultaneously for 6 hours to obtain the enzymatic hydrolysis product. In this step, the local hot spots generated by the microwave can reduce the crystallinity of the chitin crystal structure, making it easier for enzyme molecules to penetrate the chitin crystal structure, accelerating the enzymatic hydrolysis reaction, and thus refining the chitin.

[0052] (5) High-pressure homogenization: The enzymatic hydrolysis product was subjected to a high-pressure homogenizer at 30 MPa for 5 cycles, with a 5-minute interval between each cycle, to obtain a nanofiber suspension. The diameter of the nano-chitin fibers in the nanofiber suspension obtained in this step is 50-100 nm. This step utilizes high-pressure shear force to further exfoliate the enzymatically refined chitin into nanofibers, exposing a large number of amino groups on the surface.

[0053] The preparation process of the lignin-polyphenol complex (component B) includes the following steps:

[0054] (1) Raw material pretreatment: The corn cob is crushed to 60 mesh and dried at 105°C to constant weight to obtain component B. In some other embodiments, the corn cob can be replaced with bagasse or other lignocellulosic biomass, and multiple lignocellulosic biomass can be mixed.

[0055] (2) Subcritical water extraction: The raw material of component B obtained in step (1) and deionized water were added to a high-pressure reactor at a mass ratio of 1:15. The reactor was set at 180℃ and 6MPa to allow the deionized water to reach a subcritical state for 30 minutes. In this step, the dielectric constant of the subcritical water is ε≈20, which can selectively dissolve the lignin-hemicellulose cross-linked structure. At the same time, its mild conditions can retain the polyphenolic antioxidant groups in the lignin-hemicellulose cross-linked structure.

[0056] (3) Fractional purification: The cooled crude extract was filtered through a 0.22 μm ceramic membrane to remove suspended particles; then the extract was concentrated to 1 / 5 of its original volume using a 10 kDa ultrafiltration membrane (tangential flow rate 2 m / s); finally, the concentrate was placed in a vacuum freeze dryer and dried at -50℃ and 0.1 Pa for 24 h to obtain a dark brown powder.

[0057] The method for synthesizing the photocatalytic microspheres (component C) includes the following steps:

[0058] (1) Preparation of core-shell Fe3O4@TiO2 nanoparticles: ①. Fe3O4 magnetic core synthesis: FeCl2·4H2O and FeCl3·6H2O were dissolved in deionized water at a molar ratio of 1:2, and 25% NH3·H2O was added dropwise at 80℃ until the pH value was 10. The mixture was aged for 1 h. After magnetic separation, the particles were washed three times with ethanol and dried under vacuum at 60℃ to obtain 50 nm Fe3O4 particles. ②. TiO2 coating: Tetrabutyl titanate and anhydrous ethanol were mixed at a molar ratio of 1:4 and added dropwise to an ethanol dispersion containing Fe3O4. The molar ratio of Fe to Ti was 1:3. The mixture was calcined at 500℃ for 2 h to obtain core-shell Fe3O4@TiO2 nanoparticles. As the main component of photocatalytic microspheres, Fe3O4@TiO2 exhibits a surface plasmon resonance effect under visible light irradiation. This enhances the absorption of visible light, strengthens the local electromagnetic field, promotes the generation and separation of photogenerated carriers, and enables the system to respond to visible light.

[0059] (2) Calcium alginate loading: Fe3O4@TiO2 nanoparticles and 2% sodium alginate solution were ultrasonically mixed at a mass ratio of 1:0.3 for 30 min; the resulting mixture was then dripped into a 2% CaCl2 solution at a rate of 2 mL / min using a syringe pump, and cross-linked and solidified for 2 h to form microspheres with a particle size of 200-400 μm. In this step, after Fe3O4@TiO2 nanoparticles were loaded with calcium alginate, the three interacted, which changed the electronic structure and energy level distribution of the system, reduced the effective band gap of TiO2, and shifted the photoresponse range to the longer wavelength visible light region; in addition, calcium alginate provided a stable dispersion environment for Fe3O4@TiO2. Under light irradiation, photogenerated carriers of Fe3O4@TiO2 were transferred to calcium alginate through the interface, reducing the recombination probability. At the same time, its functional groups interacted with Fe3O4@TiO2, promoting the separation and transport of photogenerated carriers and enhancing the photocatalytic activity in the visible light region.

[0060] The aforementioned reduction in recombination probability specifically refers to decreasing the probability of photogenerated carriers (i.e., photogenerated electrons and holes) recombinating after their generation. In photocatalytic reactions, the recombination of photogenerated carriers leads to a decrease in photocatalytic efficiency because a portion of the photogenerated carriers are consumed during recombination, preventing them from participating in subsequent redox reactions. Therefore, reducing the recombination probability can improve the utilization rate of photogenerated carriers, thereby enhancing photocatalytic performance.

[0061] Step 2: Perform gradient composite assembly of components A, B, and C, including the following steps:

[0062] 2-1. Mixing ratio: Mix components A, B, and C in a mass ratio of 1:0.6:0.3 and add PBS buffer; the pH of the PBS buffer is 7.4 and the solid content is 5%.

[0063] 2-2. Interfacial crosslinking: Add 0.5% by mass of glutaraldehyde crosslinking agent to the mixture obtained in step 2-1, and disperse by ultrasonication at 40 kHz for 30 min to form a homogeneous colloid.

[0064] 2-3. Magnetic field shaping: The colloid obtained in step 2-2 is injected into a polytetrafluoroethylene mold and placed in a permanent magnet array with a magnetic field strength of 0.5T. It is left to stand for 1 hour to allow the Fe3O4 in the colloid to align in a specific direction.

[0065] In this step, the permanent magnet array refers to multiple permanent magnets arranged in a specific manner to generate a magnetic field with a strength of 0.5T, thereby controlling specific properties of the material. The 0.5T magnetic field strength provides sufficient magnetic force to allow the Fe3O4 magnetic moments to overcome interference from thermal motion and other factors, aligning them in an orderly manner according to the magnetic field direction, thus laying the foundation for constructing the three-dimensional network structure of the flocculant. While Fe3O4 arranges itself to form electron transport channels under the rotating magnetic field, it also maintains good magnetic response characteristics throughout the material system. This characteristic allows for convenient separation and recycling of the material using an external magnetic field, enabling material reuse and reducing processing costs.

[0066] 2-4. Gradient freeze drying: Pre-freeze at -20℃ for 4 hours to form a large-size ice crystal template by utilizing the directional growth of ice crystals; deep freeze at -50℃ for 2 hours to further fix the mesoporous structure; finally, place it in a vacuum drying oven and dry it under 0.1 Pa for 24 hours to obtain a flocculant with a three-dimensional network structure.

[0067] In the flocculant obtained in this embodiment, there is a significant synergistic effect among the three components A, B, and C:

[0068] Firstly, there is the charge complementarity mechanism between components A and B. The protonated amino groups on the surface of component A carry a positive charge, which can attract negatively charged colloidal particles in wastewater through electrostatic interactions. Simultaneously, its high aspect ratio creates a three-dimensional sieve that can intercept suspended solids in the water. Component B contains negatively charged groups, such as phenolic hydroxyl and carboxyl groups, which can chelate heavy metals through coordination bonds. The aromatic rings of lignin can form π-π stacking with the aromatic rings in organic pollutant molecules, thereby improving COD removal efficiency. The positively charged regions on component A and the negatively charged regions on component B together form a charge gradient field, promoting the directional migration of pollutants under the influence of the electric field and accelerating the flocculation reaction.

[0069] Secondly, the adsorption-photocatalytic linkage mechanism driven by component C. Under light irradiation, TiO2 in component C generates electron-hole pairs. Photogenerated holes have strong oxidizing properties, capable of directly oxidizing and decomposing organic pollutants in wastewater; photogenerated electrons have strong reducing properties, reducing high-valence heavy metal ions, such as Cr(VI), to low-valence Cr(III). Furthermore, the calcium alginate network of component C forms a gel barrier at pH > 6, effectively blocking free radical attacks on components A and B, enhancing the flocculant's sustained effectiveness. Simultaneously, components A and B provide more attachment sites for component C, resulting in more uniform dispersion in water and increasing the contact area for the photocatalytic reaction. Moreover, component B has photosensitizing properties, improving the light absorption efficiency of TiO2, promoting the generation of photogenerated carriers, and thus enhancing the photocatalytic degradation effect, synergistically degrading organic pollutants with component C.

[0070] During the flocculation process, components A and B first adsorb and enrich pollutants based on their respective charge characteristics and chemical structures. Component C then undergoes photocatalytic in-situ degradation under light conditions, regenerating the adsorption sites and realizing a "adsorption-degradation-regeneration" cycle, which can continuously exert the purification efficiency of the flocculant.

[0071] Furthermore, in this embodiment, the three components A, B, and C of the flocculant are spatially interlocked, with different pore sizes complementing each other, exhibiting selective removal capabilities for pollutants of varying molecular weights, thus enhancing the flocculant's ability to remove complex pollutants. The high crystallinity of the nanofibers in component A imparts good compressive strength to the flocculant, maintaining structural stability even in humid environments, ensuring that the flocculant does not break down under the impact of water flow or agitation during water treatment. The Fe3O4 magnetic cores of component C endow the flocculant with magnetic response characteristics, enabling rapid aggregation and recovery under an external magnetic field. The mechanical support of component A prevents magnetic agglomeration of component C, ensuring uniform dispersion of component C in the system and maintaining good magnetic properties. The phenolic hydroxyl groups of component B can interact with the Fe3O4 cores of component C. 3+ Chelation occurs, forming a stable complex that inhibits photocorrosion of Fe3O4 during photocatalysis and protects the activity of component C. The magnetic properties of component C compensate for the insufficient settling performance of components A / B, enabling the flocculant to separate from the treated water in a short time, facilitating subsequent treatment operations.

[0072] Furthermore, the flocculant prepared in this embodiment possesses a unique regeneration synergistic effect: during the light irradiation stage (pH≈7), the phenolic hydroxyl groups of component B provide hydrogen atoms, which can react and combine with excess hydroxyl radicals (·OH), thereby preventing the oxidation of amino groups in component A and ensuring the stability and activity of component A in the water treatment process; during the regeneration stage (pH≈3), calcium alginate can also protect the photocatalytic structure inside component C to a certain extent, and has a slow-release characteristic in an acidic environment, which can continuously expose fresh TiO2 active sites, creating conditions for the regeneration of the flocculant and thus realizing the recycling of the flocculant. On the other hand, the TiO2 shell of component C and the Fe3O4 magnetic core can form a type II heterojunction. Under light irradiation, photogenerated electrons are transferred from TiO2 to Fe3O4, while holes are enriched on the TiO2 surface, thereby reducing the recombination probability of photogenerated carriers and improving the separation efficiency of photogenerated carriers. Furthermore, during the preparation of flocculants, the rotation of a magnetic field (0.5T) induces the arrangement of Fe3O4, forming a high-speed electron transport channel, which can promote the transport of photogenerated carriers, significantly improve photocatalytic efficiency, and further promote the regeneration and recycling of flocculants.

[0073] Comparative Example 1

[0074] A flocculant using chitosan flocculant with a purity of 90%.

[0075] Comparative Example 2

[0076] A flocculant using polyaluminum chloride with an Al2O3 content ≥30%.

[0077] The gradient composite photo-regenerated water treatment flocculant prepared in Example 1 was compared with the flocculants in Comparative Examples 1 and 2 in the following experiments:

[0078] (1) Preparation of simulated wastewater. In this embodiment, a 1L volume of simulated wastewater containing heavy metals and organic matter was used as a kaolin suspension. The heavy metals included Cr(VI) at a concentration of 50 mg / L and Cu at a concentration of 40 mg / L. 2+ The organic components include phenol. The simulated wastewater has a COD of 100 mg / L and a turbidity of 150 NTU.

[0079] (2) Flocculation experiment

[0080] The flocculant dosage was 0.5 g / L, pH value was 7.0, flocculation temperature was 25 ± 1℃, no light was applied, and the reaction was carried out by stirring at 150 rpm for 30 min.

[0081] (3) Determination of Cr(VI) and Cu 2+ The removal effects of COD and turbidity are shown in Table 1 below:

[0082] Table 1. Comparison of pollutant removal performance of Example 1, Comparative Examples 1 and 2

[0083]

[0084] Example 2:

[0085] A method for treating mixed wastewater containing heavy metals and organic matter, using the gradient composite photo-regenerated water treatment flocculant prepared in Example 1; the specific steps of this method are as follows:

[0086] (I) Preparation of flocculants

[0087] Component A (nano-chitin fibers), component B (lignin-polyphenol complex), and component C (photocatalytic microspheres) were prepared according to the scheme in Example 1 above.

[0088] Then, the components A, B, and C were assembled in a gradient manner: (1) Mixing ratio: Components A, B, and C were mixed in a mass ratio of 1:0.6:0.3, and PBS buffer with pH 7.4 and solid content of 5% was added. (2) Interfacial crosslinking: 0.5% glutaraldehyde crosslinking agent was added, and the mixture was ultrasonically dispersed at 40kHz for 30min to form a homogeneous colloid. (3) Magnetic field shaping: The colloid was injected into a polytetrafluoroethylene mold, placed in a 0.5T permanent magnet array, and left to stand for 1h to allow Fe3O4 to oriented. (4) Gradient freeze drying: Pre-freezing at -20℃ for 4h, deep freezing at -50℃ for 2h, and finally vacuum drying at 0.1Pa for 24h to obtain a flocculant with a three-dimensional network structure.

[0089] (ii) Using flocculants to remove pollutants from wastewater.

[0090] Flocculation treatment: 0.5g of the prepared flocculant was added to the wastewater, pH=7.0. The resulting mixture was placed in a photocatalytic reactor and irradiated with simulated sunlight. The mixture was stirred at 150rpm for 30min at 25℃. In this example, 1L of simulated wastewater containing 30mg / L Cu was used. 2+ A mixed wastewater containing 50 mg / L Cr (VI) and 100 mg / L phenol.

[0091] In this embodiment, the flocculation treatment and photocatalytic degradation processes can be carried out simultaneously or sequentially.

[0092] (3) Separation and detection: After the reaction is completed, an external magnetic field is applied to the mixture to cause the flocculation products in the mixture to aggregate rapidly and the supernatant is separated.

[0093] (iii) Flocculant regeneration.

[0094] Cleaning pretreatment: The separated saturated flocculant is washed multiple times with deionized water to remove large particulate impurities and easily soluble pollutants from the surface, so as to improve the efficiency of subsequent regeneration.

[0095] Photocatalytic treatment: Place the washed saturated flocculant and appropriate amount of deionized water (adjust the pH to around 3) into the photocatalytic reactor, turn on the dual-band light source, 365nm (ultraviolet light) and 450nm (visible light), and set the light intensity to 50 mW / cm² respectively. 2 With 100 mW / cm 2 The stirring speed was 100 rpm, the temperature was maintained at 35℃, and the irradiation time was 120 min. At the same time, the ORP was monitored in real time, and the light treatment was stopped when ∆ORP < 5.

[0096] Physical cleaning and magnetic separation: The flocculant suspension after photocatalytic regeneration is rapidly separated by a magnetic field, and then ultrasonically cleaned with deionized water for 10 minutes to remove loosely attached contaminants and photolysis products.

[0097] Surface activity remediation: The cleaned flocculant is immersed in a 0.5% lignin-polyphenol complex (component B) solution for 30 minutes to repair surface adsorption sites. (The polyphenolic hydroxyl groups in component B can replenish the active groups oxidized during regeneration, restoring the chelating ability for pollutants.)

[0098] Drying and structural reforming: Vacuum freeze drying (-50℃, 0.1Pa) to prevent the nanofiber network from collapsing due to capillary forces.

[0099] Performance verification and activation: 0.5g of regenerated flocculant was used to treat simulated wastewater, following the same procedure as in step (II). The results are shown in Table 2 below.

[0100] Table 2. Comparison of wastewater treatment efficiency before and after flocculant regeneration.

[0101] flocculants Cr (VI) removal rate <![CDATA[Cu 2+ Removal rate Phenol removal rate Before regeneration 91.6% 94.7% 82% After regeneration 90.2% 94% 80.7%

[0102] The Cu in the supernatant obtained in step (II) was determined using an atomic absorption spectrometer. 2+ The concentration of phenol was determined by high-performance liquid chromatography (HPLC) using Cu and Cr(VI) concentrations. The results were: Cu 2+ The concentration was reduced from 30 mg / L to 1.6 mg / L, with a removal rate of 94.7%; the Cr(VI) concentration was reduced from 50 mg / L to 4.2 mg / L, with a removal rate of 91.6%; and the phenol concentration was reduced from 100 mg / L to 18 mg / L, with a removal rate of 82%.

[0103] This demonstrates that the flocculant obtained by the gradient composite assembly of components A, B, and C in this invention can remove heavy metals and organic pollutants from wastewater.

[0104] In some embodiments, the shear strength is enhanced due to the formation of a dense three-dimensional network by the nano-chitin fibers. Therefore, for wastewater treatment scenarios with relatively turbulent water flow, the proportion of component A can be increased to improve the structural strength of the resulting flocculant.

[0105] Comparative Example 3

[0106] A method for preparing a flocculant, the difference between this comparative example and Example 1 is that only component A is prepared as a flocculant.

[0107] Comparative Example 4

[0108] A method for preparing a flocculant, the difference between this comparative example and Example 1 is that only component B is prepared as a flocculant.

[0109] Comparative Example 5

[0110] A method for preparing a flocculant, the difference between this comparative example and Example 1 is that only component B is prepared as a flocculant.

[0111] Comparative Example 6

[0112] A method for preparing a flocculant, the difference between this comparative example and Example 1 is that: in step one, component C is not prepared, and in step two, only components A and B are assembled. The assembly process is as follows: components A and B are mixed at a mass ratio of 1:0.6; PBS buffer with a pH of 7.4 and a solid content of 5% is added; glutaraldehyde crosslinking agent with a mass fraction of 0.5% is added; ultrasonic dispersion is performed at 40 kHz for 30 min; and then gradient freeze drying is performed (pre-freezing at -20℃ for 4 h, deep freezing at -50℃ for 2 h, and vacuum drying under 0.1 Pa for 24 h).

[0113] The flocculants prepared in Example 1 and Comparative Examples 3, 4, 5 and 6 were tested for flocculation effect. The testing process was the same as step (ii) in Example 2.

[0114] Cu was collected from each experimental group 2+ The concentrations of Cr (VI) and phenol were determined, and the results are shown in Table 2 below.

[0115] Table 2. Comparison of pollutant removal performance of Example 1, Comparative Examples 3, 4, 5, and 6

[0116] flocculants Cr (VI) removal rate <![CDATA[Cu 2+ Removal rate Phenol removal rate Comparative Example 3 (Component A only) 43.1% 36.7% 19.5% Comparative Example 4 (Component B only) 22.4% 80.6% 58.2% Comparative Example 5 (Component C only) 65.3% — 36.8% Comparative Example 6 (Components A + B) 75.9% 83.5% 60.1% Example 1 (Components A+B+C) 91.6% 94.7% 82%

[0117] Example 3

[0118] A method for treating dyeing and printing wastewater, using the gradient composite photo-regenerated water treatment flocculant prepared in Example 1;

[0119] (I) Preparation of flocculants

[0120] Component A (nano-chitin fibers), component B (lignin-polyphenol complex), and component C (photocatalytic microspheres) were prepared according to the scheme in Example 1 above, and then components A, B, and C were assembled in a gradient manner; the specific process was the same as in Example 1.

[0121] (ii) Using flocculants to remove pollutants from wastewater.

[0122] (1) Flocculation treatment: 0.6g of flocculant was added to 1L of dyeing and printing wastewater and stirred at 180rpm for 40min at 25℃. The wastewater in this embodiment was taken from the effluent of the secondary sedimentation tank of a textile factory. Its initial COD was 450mg / L and its color was 500 times.

[0123] (2) Photocatalytic degradation: The resulting mixture was placed in a photocatalytic reactor and irradiated with simulated sunlight for 150 min while being stirred.

[0124] (3) Separation and detection: After the reaction is completed, an external magnetic field is applied to the mixture to cause the flocculation products in the mixture to aggregate rapidly and the supernatant is separated.

[0125] (iii) Flocculant regeneration.

[0126] This step is the same as step (iii) in Example 2.

[0127] The COD value of the supernatant obtained in step (II) was tested. The results were as follows: the COD value decreased from 450 mg / L to 69 mg / L, with a removal rate of 84.7%; the color decreased from 500 times to 25 times, with a removal rate of 95%.

[0128] This demonstrates that the flocculant obtained by the gradient composite assembly of components A, B, and C in this invention can achieve efficient and thorough treatment of dyeing and printing wastewater.

[0129] Example 4

[0130] A method for preparing a gradient composite photo-regenerated water treatment flocculant is disclosed. The difference between this embodiment and Example 1 lies only in the mass ratio of components A, B, and C; in this embodiment, the mass ratio of components A, B, and C is 1:0.6:0.3. The flocculant prepared in this embodiment is suitable for conventional industrial wastewater treatment. Component B provides high-density adsorption sites, and the proportion of component C is moderate, ensuring visible light response efficiency during the regeneration stage.

[0131] Example 5

[0132] A method for preparing a gradient composite photo-regenerated water treatment flocculant is disclosed. The difference between this embodiment and Example 1 lies only in the mass ratio of components A, B, and C; in this embodiment, the mass ratio of components A, B, and C is 1:0.8:0.2. The flocculant prepared in this embodiment is suitable for surface water treatment primarily polluted by heavy metals. Increasing the proportion of component B to 40% increases the polyphenol hydroxyl content and enhances the adsorption capacity for heavy metal ions. Reducing the proportion of component C necessitates extending the photo-regeneration time to 3 hours.

[0133] Example 6

[0134] A method for preparing a gradient composite photo-regenerated water treatment flocculant is disclosed. The difference between this embodiment and Example 1 lies only in the mass ratio of components A, B, and C; in this embodiment, the mass ratio of components A, B, and C is 1:0.3:0.5. The flocculant prepared in this embodiment is suitable for treating wastewater with high organic loads requiring frequent regeneration. In this embodiment, the proportion of component C is increased to 28%, the Fe3O4@TiO2 loading is increased, the photogenerated carrier density is increased, and the regeneration time is shortened to 1.5 h. The reduction in component B leads to a decrease in adsorption capacity.

[0135] Example 7

[0136] A method for preparing a gradient composite photocatalytic regenerated water treatment flocculant is disclosed. The difference between this embodiment and Example 1 lies only in the mass ratio of components A, B, and C; in this embodiment, the mass ratio of components A, B, and C is 1:0.3:0.1. The flocculant prepared in this embodiment is suitable for treating high-turbulence, low-concentration wastewater. In this embodiment, component A has a relatively high proportion, and the nano-chitin fibers form a dense three-dimensional network, improving shear strength. The reduced dosage of components B and C lowers the overall production cost.

Claims

1. A method for preparing a gradient composite type light regenerative water treatment flocculant, characterized by: Includes the following steps: Step 1: Mix the nano-chitin fibers, lignin-polyphenol complex, and photocatalytic microspheres obtained by loading Fe3O4@TiO2 nanoparticles onto sodium alginate in a mass ratio of 1:(0.3~0.8):(0.1~0.5) and add them to PBS buffer. The preparation process of the lignin-polyphenol complex is as follows: (1) Pulverize lignocellulosic biomass to obtain biomass raw material pellets; (2) Add biomass raw material particles to deionized water, adjust the temperature and pressure, and carry out subcritical water extraction; (3) The product obtained in step (2) is fractionally purified to obtain a powdered lignin-polyphenol complex; Step 2: Add a crosslinking agent to the mixture obtained in Step 1 and sonicate to form a homogeneous colloid; Step 3: Place the colloid obtained in Step 2 in a magnetic field with a strength of 0.3~0.8T to make the Fe3O4 in the colloid oriented. Step 4: Perform gradient freeze-drying on the product obtained in Step 3 to obtain the flocculant.

2. The preparation method according to claim 1, characterized in that: The preparation process of the nano-chitin fibers is as follows: (1) The shells of crustaceans are crushed to obtain chitin raw material particles; (2) Remove calcium carbonate from chitin raw material particles in an acidic system to obtain decalcified particles; (3) Deproteinization treatment: The decalcified particles are subjected to alkaline system to remove protein, resulting in crude white chitin. (4) Add crude chitin and cellulase to a buffer solution and apply microwave irradiation to obtain the enzymatic hydrolysis product; (5) Pressurize the enzymatic hydrolysis product to form a nanofiber suspension, and then separate the solid and liquid to obtain nano-chitin fibers.

3. The method of claim 1, wherein: The preparation process of the photocatalytic microspheres is as follows: (1) Fe3O4 nanoparticles were obtained by reacting FeCl2·4H2O and FeCl3·6H2O in an alkaline system; tetrabutyl titanate was mixed with anhydrous ethanol and then added dropwise to an ethanol dispersion containing Fe3O4 nanoparticles; the resulting product was calcined to obtain core-shell structured Fe3O4@TiO2 nanoparticles. (2) After mixing Fe3O4@TiO2 nanoparticles with sodium alginate solution, they were dropped into CaCl2 solution and cross-linked and solidified to obtain photocatalytic microspheres.

4. The method of claim 1, wherein: When the pollutant being treated by the flocculant is heavy metal, the mass ratio of nano-chitin fibers, lignin-polyphenol complex, and photocatalytic microspheres is 1:(0.7~0.8):(0.1~0.3). When the pollutants being treated by the flocculant are organic pollutants, the mass ratio of nano-chitin fibers, lignin-polyphenol complex, and photocatalytic microspheres is 1:(0.3~0.5):(0.4~0.5).

5. The method of claim 1, wherein: The gradient freeze-drying process is as follows: the product obtained in step three is pre-frozen at -30 to -10℃, deep-frozen at -60 to -40℃, and then vacuum-dried.

6. A gradient composite type light regenerative water treatment flocculant, characterized by: It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the gradient composite photo-regenerated water treatment flocculant as described in claim 6 in the treatment of wastewater containing heavy metals and / or organic pollutants.

8. A method of wastewater treatment, characterized by: A gradient composite photo-regenerated water treatment flocculant as described in claim 6 is added to the wastewater to be treated; heavy metals and / or organic pollutants in the wastewater aggregate to form flocculent products.

9. A wastewater treatment method according to claim 8, characterized in that: Applying light to the wastewater being treated degrades organic pollutants in the flocculation products; After flocculation, the flocculated products are separated and placed in a regeneration system under light conditions to obtain regenerated flocculant; the pH value of the regeneration system is 2.5-4.

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