Composite hydrogel adsorbent with core-shell structure and preparation method thereof

Abstract

The invention belongs to the technical field of water treatment materials, particularly discloses a core-shell structure composite hydrogel adsorbent and a preparation method thereof, and aims to solve the technical problems of secondary pollution and poor material stability caused by easy dissolution of core metal ions in the existing active cross-linked hydrogel adsorbent. According to the technical scheme, the core-shell integrated structure is formed by taking cobalt-alginate gel loaded with coal cinder, cortex moutan charcoal and zeolite synergistic adsorption components as a functional core and taking genipin cross-linked sodium alginate-gelatin as a protective shell. According to the structure, through a synergistic mechanism of pre-fixation of an inner core and strong barrier of a shell, dissolution of cobalt ions is remarkably inhibited while organic dyes, antibiotics, heavy metal ions and micro-plastic pollutants in a water body are effectively removed, so that synchronous improvement of the adsorption performance and the application safety of the material is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment materials, and particularly relates to design and preparation of a composite hydrogel adsorbent, and more particularly relates to a composite hydrogel adsorbent with a core-shell structure and a preparation method thereof. BACKGROUND

[0002] With the rapid advancement of industrial civilization, the safety of water environment is under increasingly severe test while bringing material prosperity to society. Pollutants from industrial production, daily life and agricultural activities are more diverse and complex than ever before, showing new characteristics of diversification and compounding. Specifically, various types of azo and anthraquinone organic dyes discharged by the textile and dyeing industry have long plagued the water ecosystem due to their stable chemical structure and difficulty in natural degradation; the abuse and metabolites of antibiotics in the medical and livestock breeding fields enter the natural cycle through the sewage system, inducing the breeding and spread of drug-resistant bacteria, which poses a long-term hidden danger to public health safety; the wastewater containing heavy metal ions such as cadmium, lead, mercury and chromium generated by mining, electroplating and battery manufacturing is a direct threat to aquatic organisms and even human health due to its high biological accumulation and toxicity; in addition, microplastic particles generated by the degradation of daily chemical products and plastic waste have aroused high vigilance in the scientific community due to their carrier effect and ecological toxicity. These pollutants with different properties and diverse sources are entering rivers, lakes and seas at an unprecedented scale and rate, causing irreversible damage to the structure and function of the water ecosystem.

[0003] In the face of such a complex pollution pattern, among many water treatment technology routes, the adsorption method occupies an indispensable position in the field of environmental engineering due to its relatively simple operation process, wide applicability to pollutant molecular size and chemical properties, and comparative advantage in economic cost. The core performance of the adsorption method directly depends on the performance of the adsorbent itself, therefore, the development of new, efficient and economic adsorbents has always been one of the most active research frontiers in the field of environmental science and materials science. Among the family of adsorbents, biomass materials derived from natural high molecules are particularly favored by researchers due to their environmental friendliness, biodegradability and renewable raw materials. Among them, sodium alginate as a typical anionic polysaccharide is extracted from brown algae, and its molecular chain is composed of β -D-mannuronic acid (M unit) and α -L-guluronic acid (G unit) block copolymerized in different proportions. This unique molecular structure endows it with excellent physicochemical properties: wide sources and controllable cost, good biocompatibility, and most importantly, a large number of carboxyl (-COOH) functional groups on the molecular chain. These carboxyl groups can dissociate into carboxylate ions (-COO -), which can efficiently cross-link with multivalent cations to form a stable three-dimensional network structure, i.e. hydrogel, through the classic "egg-box" model. This gelation process is mild and does not require the use of toxic chemical cross-linking agents, making sodium alginate an ideal substrate for constructing environmentally friendly hydrogel adsorbents.

[0004] However, the simple use of Ca 2+ , etc. inert ion cross-linking to form hydrogels, whose adsorption mechanism mainly depends on physical embedding, electrostatic attraction and ion exchange, the adsorption capacity and selectivity are often limited. To break this performance bottleneck, a brilliant strategy called "active cross-linking" is proposed in the research frontier. The core idea of this strategy is to use transition metal ions such as Co 2+ , Cu 2+ or Fe 3+ , which have chemical adsorption activity, to replace the inert cross-linking ions that only play a structural supporting role in the traditional sense. The theoretical basis of this design is that the d orbitals of these transition metal ions are not completely filled with electrons, making them exhibit natural "Lewis acid" characteristics. They can act as efficient electron pair acceptors and form stable coordination bonds with pollutant molecules (such as organic compounds containing -NH2, -OH, -S-H groups) that are rich in lone pair electrons in water, thereby achieving strong and selective chemical capture. When these transition metal ions are used as cross-linking agents, their roles have undergone a fundamental transformation. They are no longer just "structural rivets" that maintain the three-dimensional network skeleton of the gel, but also "active centers" that are uniformly distributed in the entire material system at a very high density. This transformation has transformed the gel matrix from a passive physical carrier to an active chemical adsorption subject. Compared with traditional materials that rely on physical adsorption, the adsorption site density, binding strength and adsorption capacity of this "active cross-linking" hydrogel have been improved by orders of magnitude, showing great application potential.

[0005] However, while the high adsorption performance brought by the "active crosslinking" strategy is exciting, a technical problem associated with this mechanism and rooted in its chemical nature also emerges, and becomes a key bottleneck restricting its practical application. Ion crosslinking bonds, especially in the complex aqueous environment full of competing ions, are essentially a dynamic, reversible chemical equilibrium. This means that heavy metal ions, which are the core active sites and also bear the function of structural crosslinking, will inevitably gradually dissociate, dissolve, and eventually be released into the water being treated under the concentration gradient of the external solution, pH changes, or the action of complexing agents. This continuous loss of active components directly leads to irreversible decay of the adsorbent's adsorption performance over time, reducing its cycle life and long-term economy. More seriously, it introduces new secondary pollutants, high concentrations of heavy metal ions, into the water that is intended to be purified, which may have potential toxicity much higher than the original pollutants. This secondary pollution risk caused by "poisoning with poison" greatly limits the possibility of such high-performance adsorbents from the laboratory to large-scale engineering applications, trapping them in a typical technical dilemma of "high efficiency but uneasy, high energy but unstable."

[0006] In the face of this thorny ion leakage problem, a logical and intuitive solution is to build a dense physical barrier on the outside of the adsorbent particles, forming a so-called "core-shell" structure. The intention is to use the isolation of the shell to "imprison" the active components in the core area, thereby blocking their outward migration path. However, the challenges in practice are much more complex than theoretical assumptions. A protective shell that must be dense and thick enough to effectively block the penetration of smaller radius, more hydrated metal ions such as Co 2+ According to Fick's law of diffusion, the diffusion flux of a substance is proportional to the diffusion coefficient and concentration gradient, and inversely proportional to the diffusion path. A dense shell greatly increases the effective diffusion path length and may block the internal pore network. As a result, while successfully "locking" the active ions inside, it may also "close" the door for external pollutants to enter efficiently, ultimately leading to a sharp decline in the material's macroscopic adsorption rate and equilibrium adsorption capacity, and even completely losing its practical application value. This seems to form a sharp contradiction between adsorption performance and application stability, making it difficult to achieve both, and constitutes a core knot on the current technical development path.

[0007] Therefore, the current field is facing a specific and urgent technical need: how to break through the limitations of existing thinking and design a new and more sophisticated material structure that can maximize the excellent adsorption performance brought by "active crosslinking" and fundamentally solve the long-term stability problem of the large leakage of "active components", thereby harmonizing and efficiently unifying the two key indicators of adsorption performance and application safety in a unified material system. This is the core technical problem that the present application aims to solve. SUMMARY

[0008] The present application aims to provide a core-shell structure composite hydrogel adsorbent and its preparation method and application, aiming to overcome the secondary pollution risk caused by the easy dissolution of core metal ions in the "active crosslinking" hydrogel adsorbent in the prior art, and the technical defect of traditional core-shell structure sacrificing adsorption performance to improve stability, thereby realizing the synergistic unification of high-efficiency adsorption performance and application safety of the adsorbent.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The present application discloses a core-shell structure composite hydrogel adsorbent, which comprises a functional inner core and a protective shell completely covering the outside of the functional inner core.

[0010] The functional inner core is the core of high-efficiency adsorption. Its matrix is a cobalt-alginic acid salt gel network formed by ion crosslinking reaction of sodium alginate and cobalt nitrate hexahydrate. Co 2+ , not only as a structural crosslinking point to maintain the gel form, but also as a high-density Lewis acid active site that can coordinate with various pollutants in water. To overcome the limitations of single active component and enhance the adsorption capacity, the key of the present application is to innovatively load a synergistic adsorption component in the matrix. This component is not a single material, but a composite system composed of coal cinder, Danpi charcoal and zeolite, and the mass ratio is strictly limited to 1:1:1. In this ternary composite system, coal cinder and zeolite are both natural silico-aluminates with developed pore structure, which can provide large specific surface area and ion exchange capacity, realizing the synergistic effect of physical adsorption and ion exchange; and Danpi charcoal, as a kind of biomass charcoal, is rich in surface oxygen-containing functional groups and graphite-like structure, showing excellent π-π conjugation effect and hydrophobic adsorption force on organic pollutants (especially dye molecules). The three components are compounded with the cobalt-alginic acid salt matrix to build a multi-level adsorption network of physical adsorption, ion exchange, coordination chemical adsorption and π-π interaction, greatly improving the comprehensive capture capacity of the inner core for complex pollutants. At the same time, this composite structure also physically covers and sterically hinders the cobalt ions to a certain extent, achieving a "pre-fixing" effect.

[0011] The protective shell is a guarantee for application safety. 2+ The function of the protective shell is to build a selective permeation barrier, which effectively blocks the outward migration of Co

[0012] The application further provides a preparation method of the core-shell structure composite hydrogel adsorbent, and specifically comprises the following steps: a) construction of a functional core: disperse sodium alginate and the synergistic adsorption component in water to prepare a core mixture; dissolve cobalt nitrate hexahydrate in water to prepare a core crosslinking solution; then, introduce the core mixture into the core crosslinking solution in the form of droplets, and use ionic crosslinking to solidify the droplets in situ to form the functional core; b) coating of a protective shell: first, immerse the functional core obtained in step a) in a shell coating solution containing sodium alginate and gelatin to perform coating, and the treatment time is 10-12 h; then, take out the functional core and place it in a shell crosslinking solution containing genipin to perform chemical crosslinking, and the treatment time is also 10-12 h, so as to form the protective shell on the surface of the functional core; The component concentrations of the solutions are limited as follows: In the core mixture, the mass percentage of sodium alginate is 0.6-0.8%, and the mass percentage of the total amount of the synergistic adsorption component is 0.6-0.8%; In the core crosslinking solution, the mass percentage of cobalt nitrate hexahydrate is 2.8-3.0%; In the shell coating solution, the mass percentage of gelatin is 0.7-0.9%, and the mass percentage of sodium alginate is 0.7-0.9%; In the shell crosslinking solution, the mass percentage of genipin is 0.09-0.11%, and the solvent is an ethanol-water mixed solvent, in which the mass percentage of ethanol is 1.7-1.9%.

[0013] The application further discloses the use of the adsorbent. Due to excellent adsorption performance and reliable chemical stability, the adsorbent can be widely applied to the field of environmental remediation, and is particularly suitable for treating a complex wastewater system containing organic dyes, antibiotics, heavy metal ions and microplastics.

[0014] Compared with the prior art, the application has the following remarkable beneficial effects: (1) effectively inhibiting secondary pollution and being high in application safety: the application forms a solid physical and chemical barrier by constructing a compact protective shell cross-linked by genipin, so that the cobalt ions in the functional core are effectively "locked" inside, and the risk of elution of the cobalt ions in the water treatment process is greatly reduced. This fundamentally solves the core problem of traditional "active cross-linking" hydrogels, reduces secondary pollution caused by leakage of metal ions, and ensures the chemical stability and environmental safety of the adsorbent in the long-term use process.

[0015] (2) excellent adsorption performance and high treatment efficiency: the functional core of the application integrates multiple adsorption mechanisms. The cobalt-alginic acid salt matrix provides high-density coordination adsorption sites; the coal cinder and zeolite contribute to a large specific surface area and ion exchange capacity; and the cortex of cortex moutan efficiently captures organic matters through π-π conjugation and hydrophobic interaction. The synergistic effect of the four makes up a multi-level adsorption network from macro to micro and from physical to chemical, so that the adsorbent shows excellent adsorption capacity and removal efficiency for organic dyes, antibiotics, microplastics and heavy metal pollutants, which is significantly better than that of a single component or a traditional structure hydrogel adsorbent.

[0016] (3) successfully breaking through the dilemma between performance and stability: the application breaks the traditional contradiction between adsorption performance and application stability through the ingenious synergistic design of "core pre-fixing-shell strong barrier". The compact shell effectively guarantees the stability, and its optimized network pore size and high permeability to pollutants ensure the mass transfer efficiency, so that the high activity of the core can be fully utilized. This design makes the material have high stability without sacrificing adsorption capacity and rate, realizing the harmony of high efficiency and safety.

[0017] (4) controllable preparation process, conducive to large-scale production: the preparation method provided by the application adopts conventional operations such as droplet gelation and impregnation cross-linking, and the process flow is simple and the conditions are mild, without the need for complex equipment. Meanwhile, the main raw materials such as sodium alginate, gelatin and coal cinder used are low-cost, easily available biomass or industrial by-products, and the process parameters have been optimized, which makes the preparation of the adsorbent have good repeatability and large-scale amplification potential, laying a solid foundation for its industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1The figure is a structural schematic diagram of the core-shell structure composite hydrogel adsorbent of the present application. In the figure, 1 represents a functional core; 2 represents a protective shell; 3 represents a synergistic adsorption component loaded in the functional core; and 4 represents Co 2+ .

[0019] Figure 2 The figure is a preparation flowchart of the adsorbent of the present application. In the figure, S1 represents a construction step of the functional core, and S2 represents a coating step of the protective shell. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be clearly and completely described below in combination with the accompanying drawings and specific examples. The examples are intended to provide detailed guidance for understanding and reproducing the present application for those skilled in the art, and should not be interpreted as any limitation on the protection scope of the present application.

[0021] In the examples of the present application, the raw materials of the synergistic adsorption component used have the following specifications: Coal residue: the residue obtained after extracting humic acid and its salt from lignite according to the patent CN200810233669.X "Method for producing humic acid and its salt by oxidizing degradation of lignite", and sieved through a 100-mesh screen before use.

[0022] Paeonia suffruticosa charcoal: the residue after extracting traditional Chinese medicine Paeonia suffruticosa as raw material, calcined at 500℃ for 2h under nitrogen atmosphere, and ground through a 100-mesh screen after natural cooling.

[0023] Zeolite: commercially available ZSM-5 molecular sieve with an average particle size of about 1 μm.

[0024] Common conditions in the preparation method: in step a), the core mixture was uniformly added to the core crosslinking solution at a flow rate of 20 mL / min through a syringe needle with an inner diameter of 0.8 mm. Example 1

[0025] a) Construction of the functional core: sodium alginate and the synergistic adsorption component composed of coal residue, Paeonia suffruticosa charcoal and zeolite in a mass ratio of 1:1:1 were dispersed in water to prepare a core mixture; and cobalt nitrate hexahydrate was dissolved in water to prepare a core crosslinking solution. Then, the core mixture was introduced into the core crosslinking solution in the form of droplets at a constant speed, and the droplets were solidified in situ by ionic crosslinking between the cobalt nitrate hexahydrate and the sodium alginate to form the functional core; b) Coating of the protective shell: the functional core obtained in step a) was first immersed in a shell coating solution containing sodium alginate and gelatin for coating treatment for 10 h; and then taken out and placed in a shell crosslinking solution containing genipin for chemical crosslinking treatment for 10 h, so as to form the protective shell on the surface of the functional core. The component concentration of each solution is defined as follows: In the core mixing solution, the mass percentage of sodium alginate is 0.6%, and the mass percentage of the total amount of synergistic adsorption components is 0.8%; In the core cross-linking solution, the mass percentage of cobalt nitrate hexahydrate is 2.8%; In the shell coating solution, the mass percentage of gelatin is 0.7%, and the mass percentage of sodium alginate is 0.9%; The solvent of the shell cross-linking solution is an ethanol-water mixed solvent, in which the mass percentage of ethanol is 1.7%, and the mass percentage of genipin is 0.09%.

[0026] In the shell cross-linking solution, the mass percentage of genipin is 0.09%, and the solvent is an ethanol-water mixed solvent, in which the mass percentage of ethanol is 1.7%. Example 2

[0027] a) Construction of functional core: sodium alginate and synergistic adsorption components composed of coal cinder, cinnamomum cortex charcoal and zeolite in a mass ratio of 1:1:1 were dispersed in water to prepare a core mixing solution; cobalt nitrate hexahydrate was dissolved in water to prepare a core cross-linking solution. Then, the core mixing solution was introduced into the core cross-linking solution in the form of droplets at a constant speed, and the droplets were solidified in situ by ionic cross-linking between the cobalt nitrate hexahydrate and the sodium alginate to form the functional core; b) Coating of protective shell: the functional core obtained in step a) was first immersed in a shell coating solution containing sodium alginate and gelatin for coating treatment for 11 h; then, after taking out, it was placed in a shell cross-linking solution containing genipin for chemical cross-linking treatment for 11 h, thereby forming the protective shell on the surface of the functional core; The component concentration of each solution is defined as follows: In the core mixing solution, the mass percentage of sodium alginate is 0.7%, and the mass percentage of the total amount of synergistic adsorption components is 0.7%; In the core cross-linking solution, the mass percentage of cobalt nitrate hexahydrate is 2.9%; In the shell coating solution, the mass percentage of gelatin is 0.8%, and the mass percentage of sodium alginate is 0.8%; In the shell cross-linking solution, the mass percentage of genipin is 0.10%, and the solvent is an ethanol-water mixed solvent, in which the mass percentage of ethanol is 1.8%. Example 3

[0028] a) Construction of the functional core: disperse sodium alginate and the synergistic adsorption component composed of coal cinder, cortex moutan char and zeolite in a mass ratio of 1:1:1 in water to prepare a core mixing solution; and dissolve cobalt nitrate hexahydrate in water to prepare a core crosslinking solution. Then, introduce the core mixing solution into the core crosslinking solution system in the form of droplets at a constant speed, and use the ionic crosslinking effect between the cobalt nitrate hexahydrate and the sodium alginate to solidify the droplets in situ to form the functional core; b) Coating of the protective shell: immerse the functional core obtained in step a) in a shell coating solution containing sodium alginate and gelatin to perform coating treatment for 12 h; then, take out the functional core and immerse it in a shell crosslinking solution containing genipin to perform chemical crosslinking treatment for 12 h, thereby forming the protective shell on the surface of the functional core; In the above process, the component concentrations of each solution are limited as follows: In the core mixing solution, the mass percentage of sodium alginate is 0.8%, and the mass percentage of the total amount of the synergistic adsorption component is 0.6%; In the core crosslinking solution, the mass percentage of cobalt nitrate hexahydrate is 3.0%; In the shell coating solution, the mass percentage of gelatin is 0.9%, and the mass percentage of sodium alginate is 0.7%; In the shell crosslinking solution, the mass percentage of genipin is 0.11%, and the solvent is an ethanol-water mixed solvent, in which the mass percentage of ethanol is 1.9%.

[0029] To clearly demonstrate the functional contribution of each core structural unit, the following comparative examples are provided.

[0030] Comparative Example 1 The establishment of this comparative example aims to strip and evaluate the contribution of the synergistic adsorption component to the overall adsorption performance. The preparation method is basically the same as that of Example 2, except that no synergistic adsorption component (i.e., coal cinder, cortex moutan char and zeolite) is added to the functional core. The core mixing solution is only made of 0.7% sodium alginate by mass percentage, and the remaining steps and parameters are the same as those of Example 2.

[0031] Comparative Example 2 The establishment of this comparative example aims to verify the key role of the protective shell in inhibiting the dissolution of the active component and improving the overall performance. The difference between the preparation method of this comparative example and Example 2 is that only the functional core is prepared, and the encapsulation step of the protective shell is not performed. The core preparation steps and parameters are the same as those of Example 2.

[0032] Effect verification In order to objectively evaluate the performance of the adsorbent described in the present application, the following effect examples are designed and implemented. All adsorption experiments are carried out at 25°C under stirring at 200 r / min, and the adsorption time is 24 h, unless otherwise specified.

[0033] Table 1 Adsorption effect of methylene blue by 100 mg of adsorbent

[0034] Calculation of adsorption rate (R t ): R t = [(C0 - C t ) / C0] × 100%; Calculation of adsorption capacity (q t ): q t = [(C0 - C t ) × V] / m; Wherein, C0 is the initial concentration of the solution, C t is the concentration of the solution at time t, V is the volume of the solution, and m is the mass of the adsorbent.

[0035] Effect Example 1: Adsorption performance on organic dye (methylene blue) This example aims to investigate the removal capacity of the adsorbent on typical organic dyes, and preliminarily evaluate the influence of the synergistic adsorption component and protective shell on the adsorption performance. The experiment is divided into two groups, using 100 mg and 10 mg of adsorbent dosage respectively, to treat 100 mL of methylene blue solution with a concentration range of 10-40 mg / L. The absorbance of the solution is measured at 664 nm by ultraviolet spectrophotometer, and the adsorption capacity and adsorption rate at 24 h are calculated according to the standard curve (y=0.0414x+0.0498).

[0036] The data in Table 1 reveals the importance of the synergistic adsorption component on one hand. Compared with Comparative Example 1 which does not contain the synergistic adsorption component, Examples 1-3 and Comparative Example 2 which contain these components show significantly higher adsorption capacity when treating higher concentration (> 20 mg / L) of methylene blue. At the same time, a noteworthy phenomenon is that the adsorption capacity of Examples 1-3 (with shell) is generally higher than that of Comparative Example 2 (without shell), among which the effect of Example 2 is particularly obvious. This preliminarily indicates that the presence of the protective shell not only does not hinder the adsorption of methylene blue, but also may indirectly enhance the adsorption performance of the core by improving the dispersibility or stability of the material.

[0037] The above trend was further confirmed under more stringent conditions of small amount of adsorbent (Table 2). The adsorption performance of Examples 1-3 (with shell) was overall superior to Comparative Example 2 (without shell), again demonstrating the positive synergistic effect of the core-shell structure of the present application on the adsorption process of methylene blue, and the negligible mass transfer resistance of the outer shell.

[0038] Effect Example 2: Adsorption performance on antibiotics (tetracycline) This example aimed to investigate the removal effect of the adsorbent on another typical pollutant, antibiotics, and to focus on verifying the influence of the protective shell on the permeability of small molecule pollutants. The experimental method was similar to that of Effect Example 1, but the detection wavelength was 357 nm, and the standard curve was y = 0.0335x + 0.0081.

[0039] The experimental results in Tables 3 and 4 highly consistently showed that Examples 1-3 (with shell) of the present application and Comparative Example 2 (without shell) exhibited very close high adsorption capacity on tetracycline. For example, in Table 4, the maximum adsorption capacity of Example 2 (with shell) was 305.20 mg / g, while that of Comparative Example 2 (without shell) was 302.67 mg / g, with a very small difference. This key data powerfully proved that the protective shell designed by the present application had excellent permeability to small molecule pollutants such as tetracycline, and its existence almost did not affect the inherent high adsorption capacity of the inner core, successfully avoiding the common performance sacrifice problem of traditional coating layers. In addition, the low adsorption performance of Comparative Example 1 (not containing synergistic adsorption components) in Table 3 again highlighted the necessity of synergistic adsorption components for achieving high-efficiency and broad-spectrum adsorption.

[0040] Table 2 Adsorption effect of 10 mg of adsorbent on methylene blue

[0041] Effect Example 3: Adsorption performance on heavy metals (cadmium ion, Cd 2+ ) To investigate the removal capacity of the material on heavy metal ions, 10 mg of adsorbent was used to treat 1 mg / L and 10 mg / L of Cd 2+ solution. The concentration of cadmium ion was determined by a heavy metal detector, and the adsorption capacity and adsorption rate at 24 h were calculated.

[0042] The data in Table 5 revealed a unique performance of the adsorbent of the present application in treating heavy metal ions. At very low concentration (1 mg / L), the adsorption performance of Example 1 (with shell) and Comparative Example 2 (without shell) was almost equivalent, which indicated that under this condition, the mass transfer resistance of the protective shell to Cd 2+ was minimal. However, when the concentration of Cd 2+When the concentration was increased to 10 mg / L, the performance of the two began to differentiate significantly: the adsorption capacity of Example 1 was as high as 24.10 mg / g, more than twice that of Comparative Example 2 (11.40 mg / g). This great difference in performance under high concentration conditions strongly proves another key role of the protective shell - maintaining the long-term activity of the functional core. This can be attributed to the fact that, during the adsorption process lasting up to 24 h, the active cobalt ions in the core of Comparative Example 2 without the protection of the shell would have been significantly leached out (as confirmed by Effect Example 5), resulting in a large loss of its adsorption sites and a sharp decline in performance. In contrast, the protective shell of Example 1 effectively locks the active components, ensuring that the core can maintain a high density of effective adsorption sites throughout the adsorption period, thus exhibiting good adsorption efficiency in more challenging high-concentration wastewater.

[0043] Table 3 Adsorption effect of tetracycline using 100 mg of adsorbent

[0044] Effect Example 4: Adsorption performance on microplastics (polyvinylidene fluoride, PVDF) This example aims to verify the material's ability to remove emerging pollutants, microplastics. 20 mg and 100 mg doses of adsorbent were used to treat 200 mg / L of PVDF suspension. The turbidity of the solution was measured by turbidimeter, and the adsorption capacity and adsorption rate at 24 h were further calculated according to the standard curve (y = 0.2045x + 0.1381).

[0045] As can be seen from Table 6, the adsorption effect of Examples 1-3 of the present application is generally better than that of Comparative Example 2, especially when the dosage of adsorbent is larger (100 mg), the minimum adsorption capacity of the material of Example (113.82 mg / g) is still more than twice that of Comparative Example 2 (55.47 mg / g), which again proves the superiority of the structure of the present application in treating emerging microplastic pollutants.

[0046] Effect Example 5: Material chemical stability test This example is a key evaluation of the core innovation of the present application. 100 mg of each adsorbent material was placed in 100 mL of pure water, and samples were taken at different time points (6 h, 12 h, 24 h). The Co 2+ concentration in the supernatant was determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0047] Table 4 Adsorption effect of tetracycline using 10 mg of adsorbent

[0048] Table 5 Adsorption effect of Cd 2+ by each adsorbent

[0049] Table 6 Adsorption effect of each adsorbent on PVDF

[0050] Table 7 Co of each adsorbent in pure water 2+ Leakage concentration

[0051] The data in Table 7 directly reveals the synergistic technical effect of the core-shell structure of the present application in improving chemical stability. The Co 2+ The leakage concentration surged to 14.13 mg / L within 24 h, exposing the inherent chemical instability of the traditional "living crosslinking" structure. Although protected by the outer shell, the leakage of Comparative Example 1 (without synergistic components) was still as high as 5.63 mg / L, proving the limitations of a single protective mechanism.

[0052] In sharp contrast, the Co 2+ The leakage concentration was stably inhibited at a low level of 2.30-2.77 mg / L after 24 h. This value is not only much lower than that of Comparative Example 2, but also significantly better than that of Comparative Example 1. This result strongly proves that there is a "1+1>2" synergistic effect between the synergistic adsorption components in the functional core and the protective outer shell: the "pre-fixation" effect of the core and the "strong barrier" mechanism of the shell are complementary and indispensable. It is this overall design that enables the present application to maintain high adsorption performance while building a long-lasting kinetic barrier for the core active components, significantly improving the safety and durability of the material in practical applications.

[0053] In summary, the present application aims to address the technical challenges of the "active crosslinking" hydrogel in improving the adsorption performance, which is the easy dissolution of active components and the lack of stability. Unlike traditional optimization methods, a systematic and synergistic design is proposed to solve the above technical contradictions. The core highlight is to build a "core pre-fixing-shell strong barrier" double-layer synergistic system, which is reflected in the following two aspects: (1) The "multistage synergistic adsorption and pre-fixing" design of the functional core: In the cobalt-alginate gel matrix, the synergistic adsorption components composed of coal cinder, Danpi charcoal and zeolite are loaded. This design builds a multistage adsorption network integrating physical adsorption, ion exchange and chemical coordination, which significantly enhances the capture capacity of complex pollutants. In addition, the composite system forms a "pre-fixing" effect on active cobalt ions in the core, which improves the migration resistance of ions from the source and lays the foundation for subsequent protection. (2) The "selective strong barrier" design of the protective shell: Sodium alginate-gelatin crosslinked by genipin is used as the protective shell to form a covalent crosslinking network, which builds a physical and chemical barrier to effectively block cobalt ions. The design feature is that by adjusting the crosslinking degree, the shell realizes strong barrier to core ions while maintaining good permeability to target pollutants, thereby avoiding the performance sacrifice problem commonly seen in traditional coating technology.

Claims

1. A core-shell structured composite hydrogel adsorbent, characterized in that, Includes a functional core and a protective shell covering the functional core; The functional core has a matrix of cobalt-alginate gel formed by ion crosslinking of sodium alginate and cobalt nitrate hexahydrate, and the matrix is ​​loaded with a synergistic adsorption component, which consists of coal slag, peony charcoal and zeolite, with the mass ratio of the three limited to 1:1:

1. The protective shell is a network structure formed by the cross-linking reaction of sodium alginate and gelatin with genipin.

2. A method for preparing the core-shell structured composite hydrogel adsorbent of claim 1, characterized in that, The method includes the following steps: a) Construction of the functional core: Sodium alginate and the synergistic adsorption components were dispersed in water to prepare a core mixture; cobalt nitrate hexahydrate was dissolved in water to prepare a core crosslinking solution; Subsequently, the core mixture is introduced into the core crosslinking liquid system in the form of droplets, and the droplets are solidified in situ by ionic crosslinking to form the functional core. b) Coating of the protective shell: The functional core obtained in step a) is first immersed in a shell coating solution containing sodium alginate and gelatin for coating, and the treatment time is 10-12 h; after being removed, it is placed in a shell crosslinking solution containing genipin for chemical crosslinking, and the treatment time is also 10-12 h, thereby forming the protective shell on the surface of the functional core. The concentrations of the components in each solution are limited as follows: In the core mixture, the mass percentage of sodium alginate is 0.6-0.8%, and the mass percentage of the total amount of synergistic adsorption components is 0.6-0.8%. In the core crosslinking solution, the mass percentage of cobalt nitrate hexahydrate is 2.8-3.0%; In the outer shell coating liquid, the mass percentage of gelatin is 0.7-0.9%, and the mass percentage of sodium alginate is 0.7-0.9%. In the crosslinking liquid of the outer shell, the mass percentage of genipin is 0.09-0.11%, and the solvent is an ethanol-water mixture, wherein the mass percentage of ethanol is 1.7-1.9%.

3. The use of the core-shell structured composite hydrogel adsorbent according to claim 1, characterized in that, This adsorbent was applied to remove organic dyes, antibiotics, heavy metal ions, and microplastic pollutants from water.

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