A quasi-one-dimensional hydrogel composite material, a preparation method and application thereof

Abstract

This invention belongs to the field of functional composite materials and resource recycling technology, specifically relating to a quasi-one-dimensional hydrogel composite material, its preparation method, and its application. The quasi-one-dimensional hydrogel composite material comprises: a hydrophilic hydrogel matrix with long-range microchannels arranged in the same direction, the long-range microchannels forming a continuous, interconnected three-dimensional network structure with a pore size of 5-20 μm; conductive fibers penetrating and embedded within the hydrophilic hydrogel matrix, extending along the arrangement direction of the long-range microchannels; and a photothermal conversion nanofiber network composed of one-dimensional photothermal nanomaterials dispersed within the hydrophilic hydrogel matrix, forming an interconnected fibrous network structure. This invention achieves integrated treatment for the simultaneous recovery of fertilizer, freshwater, and electricity from nitrogen- and phosphorus-containing wastewater, demonstrating promising industrial application prospects.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials and resource recycling technology, specifically relating to a quasi-one-dimensional hydrogel composite material with conductive fibers, long-range microchannels and photothermal conversion nanofiber networks, its preparation method, and the application of this material in the synergistic recovery of slow-release fertilizer, fresh water and electricity in solar-driven interfacial struvite reaction. Background Technology

[0002] The global crises of water scarcity, phosphorus depletion, and energy demand are becoming increasingly severe. Recovering nutrients (such as struvite, MgNH4PO4·6H2O) from nitrogen- and phosphorus-containing wastewater as slow-release fertilizer, while simultaneously purifying water and generating energy, is key to solving the water-energy-food linkage problem. Current mainstream technologies fall into five categories: chemical crystallization precipitation, nitrogen recovery via stripping / membrane processes, adsorption / ion exchange, bioaccumulation, and evaporative crystallization. Among these, struvite crystallization precipitation is a commonly used method.

[0003] Traditional struvite sedimentation involves adding a magnesium source and an alkaline agent to nitrogen- and phosphorus-containing wastewater to reduce Mg content. 2+ NH4 + and PO4 3- Directly mixing the precipitate in solution to form struvite. This method has the following drawbacks:

[0004] 1) The reaction usually requires an excessive amount of magnesium salt and alkali to drive the reaction forward, resulting in reagent residues and secondary pollution;

[0005] 2) Crystals rapidly nucleate and grow in bulk solution, producing fine crystals of sub-100 μm, which are difficult to separate and recover, resulting in high energy consumption;

[0006] 3) During the reaction, NH4 + Volatile loss leads to incomplete ammonia nitrogen recovery;

[0007] 4) It has a single function, only able to recover nutrients, and cannot achieve water purification and energy recovery. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a quasi-one-dimensional hydrogel composite material, its preparation method and application. This material constructs a three-in-one structure through directional freezing and phase separation synergistic regulation, which integrates conductive fibers, long-range microchannels and photothermal conversion nanofiber networks. It can couple struvite reaction with solar evaporation to achieve synergistic integration of nutrient recovery, water purification and energy output.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a quasi-one-dimensional hydrogel composite material, comprising:

[0011] A hydrophilic hydrogel matrix having long-range microchannels arranged in the same direction inside, wherein the long-range microchannels are a continuous three-dimensional network structure with a pore size of 5~20 μm;

[0012] Conductive fibers penetrate and are embedded in the hydrophilic hydrogel matrix, extending along the arrangement direction of the long-range microchannels;

[0013] The photothermal conversion nanofiber network is composed of one-dimensional photothermal nanomaterials dispersed in the hydrophilic hydrogel matrix and forms an interconnected fibrous network structure.

[0014] The hydrophilic hydrogel matrix is ​​formed by cross-linking hydrophilic polymers to achieve rapid capillary water transport and ion transport. The conductive fibers are continuous fibrous conductive materials, whose surfaces serve as interfaces for preferential nucleation and growth of target crystals, while also providing electron transport channels. The conductive fibers run through the entire hydrophilic hydrogel matrix, with both ends exposed outside the hydrogel for connecting electrodes. The fibrous network structure is formed through rapid phase separation and is interspersed with the long-range microchannels to absorb sunlight and convert it into heat, while also acting as thermal antennas to enhance the absorption of latent heat from the environment.

[0015] Preferably, the hydrophilic hydrogel matrix is ​​formed by crosslinking chitosan and polyacrylic acid; and / or,

[0016] The hydrophilic hydrogel matrix has a water content of 80-95 wt%, a negatively charged surface, and an isoelectric point of pH 4.2-4.5; and / or,

[0017] The conductive fiber is carbon fiber with a diameter of 5~10 μm; and / or,

[0018] The photothermal conversion nanofiber network is composed of carboxyl-functionalized multi-walled carbon nanotubes, wherein the length of the carboxyl-functionalized multi-walled carbon nanotubes is 5–15 μm and the diameter is 10–20 nm; and / or,

[0019] The carboxyl-functionalized multi-walled carbon nanotubes constitute 5-15% of the composite material by mass.

[0020] Preferably, the quasi-one-dimensional hydrogel composite material has a quasi-one-dimensional ribbon structure with a length of 5-50 cm, a width of 1-5 mm, a thickness of 0.5-2 mm, and an aspect ratio greater than 100:1.

[0021] This invention also provides a method for preparing quasi-one-dimensional hydrogel composite materials, comprising the following steps:

[0022] (1) Prepare a precursor solution containing a hydrophilic polymer, a crosslinkable monomer, a photothermal nanomaterial and an initiator;

[0023] (2) Immerse the conductive fiber in the precursor solution to allow the fiber to fully adsorb the precursor;

[0024] (3) Take out the conductive fiber adsorbed with the precursor, perform cross-linking treatment, and form a wet gel encapsulating the fiber;

[0025] (4) The wet gel obtained in step (3) is directionally immersed in liquid nitrogen at a constant speed of 12~18 cm / min for directional freezing. The frozen sample is then freeze-dried to obtain a quasi-one-dimensional hydrogel composite material.

[0026] Preferably, step (1) includes: dissolving chitosan in acetic acid solution, stirring magnetically until completely dissolved, then adding acrylic acid solution, carboxyl-functionalized multi-walled carbon nanotubes and potassium persulfate solution, and ultrasonically dispersing for 30 minutes to form a uniform precursor solution;

[0027] In step (3), the conductive fiber adsorbed with the precursor is transferred into a 5% glutaraldehyde aqueous solution for crosslinking for 20 minutes.

[0028] More preferably, the acetic acid solution has a volume percentage of 1%, the chitosan to acetic acid solution mass-to-volume ratio is 1:100, the carboxyl-functionalized multi-walled carbon nanotubes to chitosan mass ratio is 1:2, the acrylic acid solution has a volume percentage of 20%, the potassium persulfate solution mass-to-volume concentration is 1%, and the volume ratio of the potassium persulfate solution, the acrylic acid solution, and the acetic acid solution is 1:5:25.

[0029] The present invention also provides the application of the above-mentioned quasi-one-dimensional hydrogel composite material or the quasi-one-dimensional hydrogel composite material prepared by the above method in the synergistic recovery of struvite, fresh water and electricity.

[0030] The present invention also provides a solar-driven interface reaction system, comprising any of the above-described quasi-one-dimensional hydrogel composite materials or quasi-one-dimensional hydrogel composite materials prepared by any of the above-described methods.

[0031] Preferably, the solar-driven interface reaction system includes a first storage tank and a second storage tank. One end of the quasi-one-dimensional hydrogel composite material is connected to a first electrolyte solution in the first storage tank and the other end is connected to a second electrolyte solution in the second storage tank. The first electrolyte solution is a solution containing magnesium ions, and the second electrolyte solution is nitrogen and phosphorus wastewater. The liquid level in the first storage tank is higher than the liquid level in the second storage tank.

[0032] More preferably, the quasi-one-dimensional hydrogel composite material is inclined at an angle of -15° to 0° to the horizontal plane.

[0033] This invention also provides a method for the synergistic recovery of struvite, fresh water, and electricity, achieved through the aforementioned solar-driven interface reaction system. The method includes: using solar energy to irradiate a quasi-one-dimensional hydrogel composite material to drive water evaporation; under capillary action, magnesium ions are transported from a first storage tank along the long-range microchannel to the evaporation interface, while ammonium and phosphate ions are transported from a second storage tank along conductive fibers to the same interface, resulting in struvite precipitation; collecting the struvite crystallized on the conductive fibers, simultaneously collecting the fresh water formed by the condensation of the water vapor generated during evaporation, and collecting the current generated during the reaction through electrodes connected to both ends of the conductive fibers.

[0034] Compared with the prior art, the present invention has the following significant advantages:

[0035] 1. Material Structure Innovation: For the first time, a quasi-one-dimensional hydrogel composite material integrating through-fiber conductive fibers, long-range microchannels, and a photothermal conversion nanofiber network was constructed through the synergistic regulation of directional freezing and phase separation. The through-fiber conductive fibers serve as an independent conductive substrate and crystal growth interface, the long-range microchannels are used for mass transport, and the photothermal conversion nanofiber network is used for thermal management. The three functional structures are interspersed at the microscale, realizing the multifunctional integration of mass transport, electronic conduction, thermal management, and crystal-induced growth.

[0036] 2. Significant Ion Gradient Effect: By utilizing the continuous consumption of interfacial ions through the struvite precipitation reaction, an ion concentration gradient of up to 727 times is formed within the material. Comparative experiments show that the gradient is only 1.8 times for the absence of through-fibers (Comparative Example A), only 2.1 times for the absence of photothermal conversion nanofiber network (Comparative Example B), and only 3.5 times for the absence of directional microchannels (Comparative Example C). This demonstrates that the 727-fold gradient is a direct result of the synergistic effect of the three-in-one structure of this invention.

[0037] 3. High efficiency of struvite recovery: The continuous interfacial reaction results in struvite crystal size exceeding 900 μm, which is much larger than the ~100 μm of traditional precipitation methods. It can be easily scraped and recovered without high-energy centrifugation separation, with a recovery efficiency of ≥99%.

[0038] 4. High-quality freshwater production: ammonia nitrogen rejection rate >99%, ammonia nitrogen concentration in the produced water <0.5 mg / L, meeting drinking water standards.

[0039] 5. Excellent power generation performance: Reaction-induced ion gradient driven power generation, with a power density of 9.7 μW cm⁻¹. -2 It is 6.5 times better than traditional concentration systems.

[0040] 6. Good cycle stability: It can be used more than 50 times without performance degradation. Attached Figure Description

[0041] Figure 1Scanning electron microscope images of the quasi-one-dimensional hydrogel composite material 1d-DFH@CFs in Example 1 of this invention: (a) Longitudinal cross section showing long-range microchannels; (b) High-magnification image showing carbon nanotube fiber network.

[0042] Figure 2 Photograph of the simplified reaction apparatus of this invention.

[0043] Figure 3 : Schematic diagram of the working principle of the quasi-one-dimensional hydrogel composite material of the present invention.

[0044] Figure 4 The test results in the test examples of this invention are as follows: (a) is the XRD pattern of struvite crystals obtained using the materials of Example 1 and Comparative Example A; (b) is the SEM image of struvite crystals obtained using 1d-DFH@CFs of Example 1; and (c) is the SEM image of struvite obtained using the materials of Comparative Example A.

[0045] Figure 5 Size distribution diagram of the struvite generated in Example 1 and Comparative Example A of this application.

[0046] Figure 6 The yield and photothermal evaporation rate of struvite after 50 cycles using the quasi-one-dimensional hydrogel composite material 1d-DFH@CFs from Example 1 of this invention.

[0047] Figure 7 The concentrations of total nitrogen, total phosphorus, available nitrogen, and available phosphorus in saline-alkali soil were measured 26 days after adding the struvite obtained in Example 1. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1: Preparation of Quasi-One-Dimensional Hydrogel Composite Material

[0050] Dissolve 1.0 g of chitosan (product model MS0816, degree of deacetylation >90%) in 100 mL of 1% (v / v) acetic acid solution and stir magnetically until completely dissolved. Then add 20 mL of 20% (v / v) acrylic acid solution, 0.5 g of carboxyl-functionalized multi-walled carbon nanotubes (product model XFM15, diameter 10~20 nm, length ~10 μm) and 4 mL of 1% (w / v) potassium persulfate solution, and sonicate for 30 minutes at a frequency of 20 kHz (15~25 kHz is also acceptable) and a power of 350 W, using intermittent sonication (on for 3 s / off for 3 s) to form a homogeneous precursor solution.

[0051] A mixture of 50 wt% deionized water and 50 wt% ethanol was prepared. Carbon fibers were completely immersed in the mixture and soaked at room temperature for 10–20 min for pretreatment. The pretreated carbon fibers (approximately 7 μm in diameter) were then immersed in the precursor solution and subjected to ultrasonic-assisted adsorption for 30 min. The ultrasonic frequency was 20 kHz (20–25 kHz is acceptable), the power was 350 W, and the ultrasonic treatment was intermittent (on for 3 s, off for 3 s) to ensure sufficient fiber adsorption of the precursor. After removal, the fibers were transferred to a 5% glutaraldehyde aqueous solution for crosslinking for 20 min, forming a wet gel encapsulating the fibers. The crosslinked wet gel was then directionally immersed in liquid nitrogen at 77 K (-196 °C) at a controlled speed of 14 cm / min for directional freezing. This caused solvent crystallization, forming oriented ice crystals, and simultaneously induced phase separation of carboxyl-functionalized multi-walled carbon nanotubes, forming a fibrous network. The frozen sample was immediately transferred to a freeze dryer and dried for 48 hours to remove the solvent crystals, yielding a quasi-one-dimensional hydrogel composite material (denoted as 1d-DFH@CFs). Scanning electron microscope images of the composite material are as follows: Figure 1 As shown, Figure 1 The arrow in Figure (a) indicates a long-range microchannel obtained by the directional ice template method, with a pore size of 5–20 μm. Figure 1 The arrow in Figure (b) shows the thermal antenna formed by phase separation of carbon nanotubes, which enhances the absorption of latent heat from the environment.

[0052] Comparative Example A: Preparation of ordinary hydrogel composite materials

[0053] The preparation steps were the same as in Example 1, except that the directional freezing step was replaced with slow freezing at -20°C for 12 hours, without directional freezing. The resulting sample was denoted as r-DFH@CFs.

[0054] Comparative Example B: Preparation of Carbon Nanotube-Free Hydrogel Composite Materials

[0055] The preparation steps were the same as in Example 1, except that carbon nanotubes were not added to the precursor solution. The resulting sample was designated 1d-DFH@CFs (CNT-free).

[0056] Comparative Example C: Preparation of Ultra-Fast Freezing Hydrogel Composite Materials

[0057] The preparation steps were the same as in Example 1, except that the directional immersion speed in liquid nitrogen was changed to 20 cm / min. The resulting sample was designated 1d-DFH@CFs (ultra-fast).

[0058] Test Example: Solar-Driven Interface Struvite Reaction Performance Test

[0059] 1. Constructing a photothermal-driven struvite reaction system

[0060] The system employs a decoupled reaction tank, comprising a first storage tank and a second storage tank; the first electrolyte solution in the first storage tank is an 80 mM MgCl2 solution, and the second electrolyte solution in the second storage tank is a solution containing 24 mM PO4. 3- -P and 20 mMNH4 + Simulated wastewater (pH 9.0) with -N concentration was used to adjust the liquid level in the first storage tank to be higher than that in the second storage tank, so that the tilt angle of the quasi-one-dimensional hydrogel composite material was -15°. A simple device was then prepared based on this. Figure 2 As shown.

[0061] One end of the hydrogel composite material prepared in Example 1 and Comparative Examples A, B, and C was immersed in MgCl2 solution, and the other end was immersed in simulated wastewater. The hydrogel side was irradiated with 1 sun intensity for 18 hours.

[0062] The working principle of the quasi-one-dimensional hydrogel composite material of the present invention is as follows: Figure 3 As shown. In the system of this invention, magnesium ions and nitrogen and phosphorus wastewater are physically isolated in space, forming a decoupled transport path. Under solar irradiation, water evaporates on the surface of the hydrogel evaporator, generating capillary forces that carry the magnesium ions from the first storage tank... 2+ The NH4+ in the second storage tank is pumped to the evaporation interface through long-range microchannels in the hydrogel matrix. + and PO4 3- The reactants are pumped to the same interface via conductive fibers. Due to the excellent hydroconductivity and hydrophilicity of the conductive fibers, the reactants meet at the interface, resulting in a struvite precipitation reaction (Mg...). 2+ + NH4 + + PO4 3- +6H2O → MgNH4 PO4·6H2O↓).

[0063] The extremely low solubility product of struvite (Ksp = 2.5 × 10⁻⁶) -13 This makes Mg at the interface 2+As ions are continuously consumed, a stable concentration gradient forms within the material, flowing from the reservoir (high concentration) to the reaction interface (low concentration). The long-range microchannel provides a low-resistance directional transport path for ions, ensuring the efficient transport of Mg consumed at the reaction interface. 2+ It can be replenished in a timely manner; the carbon nanotube (CNT) thermal antenna network provides efficient evaporation drive, providing a continuous power source for the entire system. This interfacial reaction has multiple synergistic effects, including complete nutrient recovery, controllable crystal growth, reaction-enhanced power generation, and water purification.

[0064] 2. Strombite recycling performance

[0065] A white precipitate forms at the carbon fiber interface, such as Figure 4 As shown in Figure (a), the precipitate was confirmed by XRD and Raman spectroscopy to be pure phase struvite (PDF #15-0762) without impurities. The precipitate of Comparative Example A contained magnesium phosphate impurities (PDF #35-0186). Figure 4 Figure (b) shows that the struvite crystals obtained in Example 1 have a size >900 μm, while the struvite crystals obtained in Comparative Example A have a size of approximately 50~100 μm. Figure 4 As shown in Figure (c), the curve of struvite size changing with reaction time is as follows. Figure 5 As shown, as the reaction time increased from 0 h to 16 h, the struvite size in Example 1 increased from 0 to 900 μm; while in Comparative Example A, the struvite reaction ended within 2 h, the struvite crystal size was about 100 μm, and the size no longer increased in the subsequent time.

[0066] Struvite yield: In Example 1, the struvite yield was 37 mg m³. -2 h -1 The water evaporation rate is 5.01 kg / m³. -2 h -1 ,like Figure 6 As shown, after 50 cycles, the struvite yield in Example 1 remained stable at 35 mg / m³. -2 h -1 The water evaporation rate is 4.96 kg / m³. -2 h -1 Additionally, comparative example A was tested and found to be 21 mg m. -2 h -1 Comparative Example B was 15 mg m -2 h -1 Comparative example C is 25 mg m -2 h -1 .

[0067] Fertilizer effect of struvite: The coastal saline-alkali soil tested was collected from Rudong County, Jiangsu Province, China, with a salt content of 3.1‰ and a pH of 8.2. To evaluate the slow-release performance, struvite from Example 1 was used at a concentration of 0.2 g·kg⁻¹. -1 The mixture was added to the soil in the specified proportions. Soil moisture was adjusted to 70% of field capacity, sealed, and stored at room temperature in the dark for 26 days. Subsequently, total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus (AP) in the soil were determined using standard methods. Figure 7 As shown, the guanostone obtained in Example 1 was recycled at a rate of 0.2 g / kg. -1 When the appropriate proportion was added to the tested coastal saline-alkali soil (salinity 3.1‰, pH 8.2), after 26 days, the total nitrogen in the soil increased from 520 mg / Kg to 737 mg / Kg, and the total phosphorus increased from 172 mg / Kg to 305 mg / Kg, both increasing by more than 50%; the available nitrogen increased from 35 mg / Kg to 74 mg / Kg, and the available phosphorus increased from 5.6 mg / Kg to 18 mg / Kg, increasing by 2.1 times and 3.5 times, respectively.

[0068] In the plant cultivation experiment, seeds of Chinese cabbage (Brassica rapa subsp. chinensis) were sown in plastic pots, each containing 0.5 kg of the tested coastal saline-alkali soil, and 0.2 g·kg⁻¹ of [unspecified ingredient] was added. -1 The guanoite was derived from Example 1. Plants were cultivated in an artificial climate greenhouse with a day / night temperature of 25 / 18°C, a photoperiod of 14 hours per day, and a relative humidity of 60%. The experiment employed a completely randomized design, with eight replicates for each treatment. All pots were irrigated with deionized water to maintain soil moisture at 70% of field capacity. After 26 days of growth, the plants were carefully harvested. Root length, leaf length, stem length, and stem diameter were immediately measured. The plants were then separated into root and above-ground parts, and their fresh weight was measured separately. Each part was dried at 70°C to constant weight, and its dry weight was measured. The results of the pakchoi planting experiment are shown in Table 1. Seedlings in soil with added guanoite showed significantly better root length, leaf length, stem length, and stem diameter than the control group, with a 48% increase in fresh weight and an 81% increase in dry weight.

[0069] Table 1. Statistical results of the bok choy planting experiment in the experimental and control groups of this invention.

[0070] 3. Freshwater production performance

[0071] Collect the condensate and determine the ion concentration, including NH4+. + The results of -N are shown in Table 2.

[0072] Table 2. NH4 in Example 1 and different comparative examples + -N measurement results

[0073] Meanwhile, PO4 in the water produced in Example 1 3- -P<0.05 mg / L, Mg 2+ <0.1 mg / L, meeting drinking water standards and showing better results than the control group.

[0074] 4. Power generation performance and ion gradient testing

[0075] Electrodes were connected to both ends of the carbon fiber, and the open-circuit voltage and short-circuit current were measured. In Example 1, the open-circuit voltage reached 0.91 V and the power density was 9.7 μW cm⁻¹ in a SISR (Surface In-situ Reconstruction) configuration. -2 (Load 10 kΩ). Comparative examples A, B, and C all have a voltage of 0.32 V and a power density of 1.5 μW cm⁻¹ under the same configuration. -2 .

[0076] The Mg content at the reaction interface was measured by cutting the evaporator in sections. 2+ Concentration, Mg in Example 1 2+ The concentration gradient was as high as 727 times (concentration at the reservoir end was 80 mmol / L). -1 / Concentration at the reaction interface: 0.11 mmol / L -1 ), that is, the struvite reaction at the interface of this application causes Mg 2+ The concentration difference reached over 720 times, compared to only 1.8 times for Comparative Example A, 2.1 times for Comparative Example B, and 3.5 times for Comparative Example C. The results are shown in Table 3.

[0077] Table 3. Comparison of structure and ion gradient between Example 1 of the present invention and Comparative Examples A, B and C

[0078] The results show that only Example 1, which simultaneously possesses the three structural features of through-fiber, directional microchannel, and CNT network, can achieve an ion gradient of 727 times. The absence of any one structural element causes the gradient to drop sharply to below 10 times, proving that the 727-fold gradient is a direct result of the synergistic effect of the three-in-one structure of this invention.

[0079] Application example: Practical wastewater treatment applications

[0080] 150 strands of the composite material 1d-DFH@CFs from Example 1 were integrated into a pilot-scale device. The first storage tank contained 80 mL of MgCl2, and the second storage tank contained actual aquaculture biogas slurry (pretreated by nanofiltration, PO4). 3- -P 24 mM, NH4 +-N 20 mM). Outdoor operation for 8 hours (9:00-17:00), average solar intensity is about 0.8 sun.

[0081] Results: Freshwater production was 15.8 kg m³. -2 The water quality meets drinking water standards; 140 gm³ of struvite was recovered. -2 The average voltage measured at both ends of the carbon fiber is 0.65 V, which can power a miniature light intensity meter.

[0082] A comprehensive comparison of this invention with the traditional struvite sedimentation method is presented:

[0083] The reaction process of the traditional struvite precipitation method is as follows: the source of chemical reagents is the same as in the test example. The molar concentrations of phosphorus (P) and nitrogen (N) in the simulated wastewater are set to 20 mM and 20 mM, respectively; the magnesium (Mg) source solution contains Mg... 2+ The concentration was 24 mM. First, the pH of the simulated wastewater was adjusted to 9.0, and then a magnesium source solution was added. Next, the mixture was continuously stirred on a magnetic stirrer for 30 minutes. After the reaction was completed, the resulting struvite precipitate was collected by centrifugation.

[0084] Table 4. Comparison of the effects of the present invention and the traditional struvite sedimentation method

[0085] The results show that the present invention has significant advantages in terms of ion gradient, nutrient recovery rate, product quality, product water quality, functional integration and carbon emissions.

[0086] The above description is merely a specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A quasi-one-dimensional hydrogel composite material, characterized in that, include: A hydrophilic hydrogel matrix having long-range microchannels arranged in the same direction inside, wherein the long-range microchannels are a continuous three-dimensional network structure with a pore size of 5~20 μm; Conductive fibers penetrate and are embedded in the hydrophilic hydrogel matrix, extending along the arrangement direction of the long-range microchannels; The photothermal conversion nanofiber network is composed of one-dimensional photothermal nanomaterials dispersed in the hydrophilic hydrogel matrix and forms an interconnected fibrous network structure.

2. The quasi-one-dimensional hydrogel composite material according to claim 1, characterized in that, The hydrophilic hydrogel matrix is ​​formed by crosslinking chitosan and polyacrylic acid; and / or, The hydrophilic hydrogel matrix has a water content of 80-95 wt%, a negatively charged surface, and an isoelectric point of pH 4.2-4.5; and / or, The conductive fiber is carbon fiber with a diameter of 5~10 μm; and / or, The photothermal conversion nanofiber network is composed of carboxyl-functionalized multi-walled carbon nanotubes, wherein the length of the carboxyl-functionalized multi-walled carbon nanotubes is 5–15 μm and the diameter is 10–20 nm; and / or, The carboxyl-functionalized multi-walled carbon nanotubes constitute 5-15% of the composite material by mass.

3. The quasi-one-dimensional hydrogel composite material according to claim 1, characterized in that, The quasi-one-dimensional hydrogel composite material has a quasi-one-dimensional ribbon structure with a length of 5-50 cm, a width of 1-5 mm, a thickness of 0.5-2 mm, and an aspect ratio greater than 100:

1.

4. A method for preparing quasi-one-dimensional hydrogel composite materials, characterized in that, Includes the following steps: (1) Prepare a precursor solution containing a hydrophilic polymer, a crosslinkable monomer, a photothermal nanomaterial and an initiator; (2) Immerse the conductive fiber in the precursor solution to allow the fiber to fully adsorb the precursor; (3) Take out the conductive fiber adsorbed with the precursor, perform cross-linking treatment, and form a wet gel encapsulating the fiber; (4) The wet gel obtained in step (3) is directionally immersed in liquid nitrogen at a constant speed of 12~18 cm / min for directional freezing. The frozen sample is then freeze-dried to obtain a quasi-one-dimensional hydrogel composite material.

5. The method according to claim 4, characterized in that, Step (1) includes: dissolving chitosan in acetic acid solution, stirring magnetically until completely dissolved, then adding acrylic acid solution, carboxyl-functionalized multi-walled carbon nanotubes and potassium persulfate solution, and ultrasonically dispersing for 30 minutes to form a uniform precursor solution; In step (3), the conductive fiber adsorbed with the precursor is transferred into a 5% glutaraldehyde aqueous solution for crosslinking for 20 minutes.

6. The method according to claim 5, characterized in that, The acetic acid solution has a volume percentage of 1%, the chitosan to acetic acid solution mass-volume ratio is 1:100, the carboxyl-functionalized multi-walled carbon nanotubes to chitosan mass ratio is 1:2, the acrylic acid solution has a volume percentage of 20%, the potassium persulfate solution mass-volume concentration is 1%, and the volume ratio of the potassium persulfate solution, the acrylic acid solution, and the acetic acid solution is 1:5:

25.

7. The application of the quasi-one-dimensional hydrogel composite material according to any one of claims 1 to 3 or the quasi-one-dimensional hydrogel composite material prepared by the method according to any one of claims 4 to 6 in the synergistic recovery of struvite, fresh water and electricity.

8. A solar-driven interface reaction system, characterized in that, The quasi-one-dimensional hydrogel composite material includes the quasi-one-dimensional hydrogel composite material according to any one of claims 1 to 3 or the quasi-one-dimensional hydrogel composite material prepared by the method according to any one of claims 4 to 6.

9. The solar-driven interface reaction system according to claim 8, characterized in that, The solar-driven interface reaction system includes a first storage tank and a second storage tank. One end of the quasi-one-dimensional hydrogel composite material is connected to a first electrolyte solution in the first storage tank and the other end is connected to a second electrolyte solution in the second storage tank. The first electrolyte solution is a solution containing magnesium ions, and the second electrolyte solution is nitrogen and phosphorus wastewater. The liquid level in the first storage tank is higher than the liquid level in the second storage tank.

10. A method for the synergistic recycling of guano, fresh water, and electricity, characterized in that, The solar-driven interface reaction system described in claim 8 is implemented by: using solar energy to irradiate a quasi-one-dimensional hydrogel composite material to drive water evaporation; under capillary action, magnesium ions are transported from the first storage tank along the long-range microchannel to the evaporation interface, and ammonium and phosphate ions are transported from the second storage tank along the conductive fiber to the same interface, resulting in a struvite precipitation reaction; the struvite crystallized on the conductive fiber is collected, and the fresh water formed by the condensation of the water vapor generated during evaporation is collected, and the current generated during the reaction is collected through electrodes connected to both ends of the conductive fiber.

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