Flexible aerogel-coated iron porphyrin carbon dot composite material and preparation method thereof

Abstract

This invention discloses a flexible aerogel-coated iron porphyrin carbon dot composite material and its preparation method, relating to the field of environmental functional materials. The invention employs an organosilicon-based flexible aerogel and iron porphyrin carbon dots prepared within a specific raw material mass ratio range, compounded at a certain mass-volume ratio. The resulting flexible aerogel-coated iron porphyrin carbon dot composite material can significantly adsorb Fe²⁺. + Zn² + Cd² + It contains heavy metal ions, possesses good mechanical flexibility, and has unique fluorescence response characteristics. It can detect the concentration of heavy metal ions through fluorescence spectroscopy, meeting the integrated needs of environmental remediation for heavy metal ion adsorption and ion concentration detection, and has the potential for recycling and reuse.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials, and in particular to a flexible aerogel-coated iron porphyrin carbon dot composite material and its preparation method. Background Technology

[0002] Heavy metal ion pollution has become a critical issue that urgently needs to be addressed in the global environmental protection field. Traditional adsorption materials (such as activated carbon and single resins) have drawbacks such as low adsorption efficiency, poor ion selectivity, high preparation cost, and easy secondary pollution after adsorption, making it difficult to meet the needs of efficient treatment in complex environments.

[0003] Iron porphyrin carbon dots have specific adsorption activity for some heavy metal ions due to their unique optical properties (such as fluorescence properties) and abundant surface functional groups (carboxyl groups, amino groups, etc.). However, they are prone to aggregation when used alone, resulting in small adsorption capacity and difficulty in recycling, making it impossible to achieve recycling. Summary of the Invention

[0004] The main objective of this invention is to propose a flexible aerogel-coated iron porphyrin carbon dot composite material and its preparation method, which can overcome the problems of poor selectivity and low adsorption efficiency of traditional heavy metal ion adsorption materials, as well as the problems of easy aggregation, insufficient stability and difficulty in recycling of iron porphyrin carbon dots when used alone.

[0005] To achieve the above objectives, this invention proposes a method for preparing a flexible aerogel-coated iron porphyrin carbon dot composite material, comprising the following steps: S1. Preparation of organosilicon-based flexible aerogels; S2. Preparation of iron porphyrin carbon dot solution: A nitrogen-containing polymer is dissolved in deionized water, a porphyrin compound and a carbon source reagent are added, and the mixture is ultrasonically mixed. The mixture is then heated and reacted in a high-pressure reactor. After the reaction is completed, the mixture is cooled and stored under cold storage to obtain an iron porphyrin carbon dot solution. The mass ratio of the nitrogen-containing polymer, the porphyrin compound and the carbon source reagent is 40~60:1~2:0.3~0.5. S3. The organosilicon-based flexible aerogel and the iron porphyrin carbon dot solution are mixed at a mass-volume ratio of 1.8~2.2 g:1 mL, ultrasonically treated, and then dried under normal pressure to obtain a flexible aerogel-coated iron porphyrin carbon dot composite material.

[0006] Specifically, the nitrogen-containing polymer is one of polyethyleneimine and polyamide; the porphyrin compound is heme chloride; and the carbon source reagent is one of sodium citrate, glucose, and citric acid.

[0007] This invention employs a flexible organosilicon-based aerogel, combined with iron porphyrin carbon dots prepared within a specific raw material mass ratio range, at a certain mass-volume ratio. The resulting flexible aerogel-coated iron porphyrin carbon dot composite material can significantly adsorb Fe²⁺. + Zn² + Cd² + It contains heavy metal ions, possesses good mechanical flexibility, and has unique fluorescence response characteristics. It can achieve visual detection of ion concentration through fluorescence spectroscopy, meeting the integrated needs of environmental remediation for heavy metal ion adsorption and ion concentration detection, and has the potential for recycling and reuse.

[0008] The preparation process adopts atmospheric pressure drying technology, which does not require supercritical equipment. It is simple to operate, has low energy consumption, and reduces costs by more than 40% compared with traditional supercritical drying. In addition, the raw materials are readily available (such as triethoxymethylsilane [MTES] and heme chloride, which are all commercially available conventional reagents), making it suitable for large-scale production.

[0009] Flexible aerogel-coated iron porphyrin carbon dot composites expose the adsorption sites of iron porphyrin carbon dots through the porous framework structure of organosilicon-based flexible aerogels, thus solving the carbon dot aggregation problem that exists when iron porphyrin carbon dots are used alone. The functional groups of iron porphyrin carbon dots enhance the ion-selective adsorption capacity of the composite material, constructing a composite system with high adsorption capacity, strong ion selectivity, and fluorescence response. This effectively overcomes the shortcomings of traditional materials and meets the urgent need for efficient, environmentally friendly, and monitorable adsorption materials in environmental remediation. The use of organosilicon-based flexible aerogels greatly avoids the weakness of conventional rigid aerogels, which are prone to breakage under stress, effectively enhancing the load stability of carbon dots (maintaining a certain adsorption effect even if broken). During the desorption phase (the process of releasing adsorbed heavy metal ions), it exhibits a certain degree of compressive elasticity during extrusion, thus endowing the flexible aerogel-coated iron porphyrin carbon dot composite material with potential for recycling and reuse.

[0010] In the specific embodiment, this invention utilizes the "porous framework-active site" composite structure formed by iron porphyrin carbon dots and organosilicon-based flexible aerogel, and the synergistic effect of the carboxyl and amino groups on the surface of the iron porphyrin carbon dots with the porous structure of the aerogel, enabling the flexible aerogel-coated iron porphyrin carbon dot composite material to utilize the Fe²⁺... + Zn² + Cd² +The composite material exhibits significant selective adsorption capacity for heavy metal ions, with adsorption capacities reaching 180–200 mg / g, 160–180 mg / g, and 150–170 mg / g, respectively. The adsorption process conforms to the Langmuir monolayer adsorption model, with a short equilibrium time (≤60 min). The composite material's fluorescence response characteristics result in a gradient increase in fluorescence intensity after adsorption of the target ions (2–3 times higher than the original carbon dots). Ion concentration can be detected via fluorescence spectroscopy (detection limit as low as 0.1 μmol / L), thus meeting the integrated requirement of heavy metal ion adsorption and concentration detection.

[0011] Furthermore, in step S2, the reaction temperature of the heating reaction is 160~200℃, the reaction time is 8~12 h, and the refrigeration temperature is 2~6℃. The preferred reaction temperature, time, and refrigeration temperature parameters in S2 are beneficial for the synthesis of iron porphyrin carbon dot solution. In this invention, when the temperature is below 160℃, the reaction is incomplete, resulting in poor fluorescence performance of the carbon dots; when the temperature is above 200℃, the active sites of the carbon dots are destroyed, resulting in low product purity. If the reaction time is less than 8 h, the precursor reaction is incomplete; if it exceeds 12 h, the carbon dots are prone to aggregation and decreased stability. Refrigeration at 2~6℃ can effectively avoid carbon dot aggregation and oxidation, extending the storage period. Preferably, after the reaction, purification is required: after the reaction solution cools to room temperature, it is first centrifuged to remove large particle precipitates, then filtered through a filter membrane to obtain a clear solution, followed by dialysis to remove residual impurities. The purified carbon dot solution is then stored at 2~6℃ in the dark. Furthermore, in step S1, the step of preparing the organosilicon-based flexible aerogel includes: S101. Mix organosilicon mixed precursor, alcohol solvent and deionized water in a molar ratio of 1:5~9:14~18, stir at room temperature and add acid regulator dropwise to adjust the pH to 2~3 to obtain silica sol; S102. Add an alkaline regulator to the silica sol obtained in step S1 to adjust the pH to 8-10, stir to form a block gel, use a volatile organic solvent to perform multiple solvent replacements and aging on the block gel, and then dry it under normal pressure to obtain an organosilicon-based flexible aerogel.

[0012] The optimized raw material molar ratio and pH process parameters in S1 are beneficial for the synthesis of organosilicon-based flexible aerogels. When the raw material molar ratio is too low, the silicon source cannot form a continuous framework structure, resulting in aerogels with poor strength and brittleness. When the molar ratio is too high, the framework becomes too dense, losing flexibility and significantly reducing porosity. When the pH value is too low, the silicon source reacts too quickly, easily forming large particle precipitates and failing to form a uniform aerogel network. When the pH value is too high, the reaction rate is too slow, the framework cross-linking is incomplete, the aerogel has poor formability, and it is difficult to obtain a complete flexible material. Furthermore, the organosilicon mixed precursor is a mixture of triethoxymethylsilane (MTES) and tetraethyl orthosilicate (TEOS), wherein the molar ratio of triethoxymethylsilane to tetraethyl orthosilicate is 0.8:0.2 to 0.9:0.1.

[0013] Preferably, the molar ratio of the triethoxymethylsilane to the tetraethyl orthosilicate is 0.8:0.2.

[0014] By optimizing the precursor ratio and preparation process of the flexible hot melt adhesive, its mechanical flexibility and porous structure stability were balanced. Further adjusting the molar ratio of MTES to TEOS to 0.8:0.2, combined with an atmospheric pressure drying process, the resulting flexible aerogel achieved a specific surface area of ​​321.48 m² / g and an average pore size of 4.42 nm. It possesses both high porosity (≥95%) and good mechanical flexibility (only 10% irreversible strain loss after 20 cycles of cyclic compression at 50% strain), providing a stable attachment carrier for iron porphyrin carbon dots, effectively preventing carbon dot aggregation, achieving uniform dispersion of iron porphyrin carbon dots within the aerogel channels, and fully exposing adsorption active sites.

[0015] Furthermore, in step S101, the alcohol solvent is one or more of anhydrous ethanol, methanol, and propanol; The acid regulator is one of dilute hydrochloric acid and dilute nitric acid; the stirring temperature is 45~55℃; and the stirring time is 2~4h. In step S102, the alkaline regulator is one of ammonia solution or sodium hydroxide solution, with a concentration of 4~8 mol / L; The volatile organic solvent is one or more of ethanol, n-hexane, and acetone; the solvent replacement is performed 2 to 4 times, and the aging time for each replacement is 6 to 14 hours; the temperature for atmospheric pressure drying is 70 to 90°C, and the drying time is 40 to 50 hours.

[0016] The optimized process parameters in S1 ensure the successful synthesis and stable performance of silicone-based flexible aerogels. Controlling the stirring temperature and time within a reasonable range allows for thorough and uniform mixing of the silica sol, preventing uneven material properties caused by excessively rapid or slow local reactions. Appropriate solvent replacement and aging parameters stabilize the internal structure of the gel, preventing shrinkage and cracking during subsequent drying. Moderate drying temperature and time ensure complete drying of the gel without damaging its porous structure and mechanical flexibility, guaranteeing the aerogel possesses excellent performance characteristics.

[0017] Specifically, in step S3, the duration of ultrasonic treatment is 2-4 minutes; the temperature of atmospheric pressure drying is 85-95°C; and the drying duration is 2-4 hours.

[0018] The optimal ultrasonic treatment duration, ambient pressure drying temperature, and duration in S3 are beneficial for the composite material of iron porphyrin carbon dots coated with flexible aerogel. Ultrasonic treatment of 2-4 minutes ensures uniform dispersion and full loading of iron porphyrin carbon dots into the pores of the organosilicon-based flexible aerogel. Too short a treatment time leads to uneven carbon dot loading, while too long a time can damage the porous framework structure of the aerogel. A ambient pressure drying temperature of 85-95℃ and a duration of 2-4 hours ensures thorough drying of the composite material while avoiding damage to the fluorescence properties and adsorption activity of the iron porphyrin carbon dots from high temperatures or prolonged heating. This ensures a strong bond between the carbon dots and the aerogel, resulting in a composite material with both excellent heavy metal adsorption performance and fluorescence response characteristics.

[0019] This invention proposes a flexible aerogel-coated iron porphyrin carbon dot composite material, which is prepared using the preparation method for flexible aerogel-coated iron porphyrin carbon dot composite materials as described in any of the above-mentioned schemes. It possesses all the beneficial effects of the aforementioned schemes, which will not be elaborated upon here.

[0020] Based on the relevant properties of the flexible aerogel-coated iron porphyrin carbon dot composite material, this invention proposes that the prepared flexible aerogel-coated iron porphyrin carbon dot composite material can be applied to the adsorption and concentration detection of heavy metal ions, and is suitable for environmental remediation scenarios such as industrial wastewater treatment and soil remediation. The heavy metal ions include Fe²⁺. + Zn² + and Cd² + The flexible aerogel-coated iron porphyrin carbon dot composite material adsorbs heavy metal ions, and the concentration is detected using fluorescence spectroscopy. For example, under ultraviolet light, the carbon dots in the composite material adsorbing heavy metal ions emit visible blue light. By detecting the change in the intensity of the blue light, the concentration of the adsorbed heavy metal ions can be reflected, with a detection limit as low as 0.1 μmol / L. Furthermore, the aforementioned flexible aerogel-coated iron porphyrin carbon dot composite material is recyclable. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a scanning electron microscope image of the flexible aerogel-coated iron porphyrin carbon dot composite material of the present invention; Figure 2 The fluorescence response spectra of the flexible aerogel-coated iron porphyrin carbon dot composite material of the present invention to various ions are shown. Figure 3The flexible aerogel-coated iron porphyrin carbon dot composite material of this invention is effective for Fe²⁺. + Zn² + Cd² + Adsorption standard curve; Figure 4 This is a transmission electron microscope (TEM) image of the flexible aerogel-coated iron porphyrin carbon dot composite material of the present invention. Figure 5 This is a DLS particle size distribution table of the flexible aerogel-coated iron porphyrin carbon dot composite material of the present invention.

[0023] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0025] To overcome the problems of poor selectivity and low adsorption efficiency of traditional heavy metal ion adsorption materials, as well as the tendency of iron porphyrin carbon dots to aggregate, insufficient stability, and difficulty in recycling when used alone, this application proposes a method for preparing a flexible aerogel-coated iron porphyrin carbon dot composite material, comprising the following steps: S1. Preparation of organosilicon-based flexible aerogels; S2. Preparation of iron porphyrin carbon dot solution: Dissolve nitrogen-containing polymer in deionized water, add porphyrin compound and carbon source reagent, mix ultrasonically, and then heat and react in a high-pressure reactor. After the reaction is completed, cool and store under cold storage to obtain iron porphyrin carbon dot solution; the mass ratio of nitrogen-containing polymer, porphyrin compound and carbon source reagent is 40~60:1~2:0.3~0.5; S3. Mix organosilicon-based flexible aerogel with iron porphyrin carbon dot solution at a mass-to-volume ratio of 1.8~2.2 g:1 mL, sonicate, and then dry under normal pressure to obtain flexible aerogel-coated iron porphyrin carbon dot composite material.

[0026] The nitrogen-containing polymer is one of polyethyleneimine and polyamide; the porphyrin compound is heme chloride; and the carbon source reagent is one of sodium citrate, glucose, and citric acid.

[0027] In step S2, the reaction temperature of the heating reaction is 160~200 ℃, the reaction time is 8~12 h, and the refrigeration temperature is 2~6 ℃.

[0028] Step S1, the step of preparing organosilicon-based flexible aerogel includes: S101. Mix organosilicon mixed precursor, alcohol solvent and deionized water in a molar ratio of 1:5~9:14~18, stir at room temperature and add acid regulator dropwise to adjust the pH to 2~3 to obtain silica sol; S102. Add an alkaline regulator to the silica sol obtained in step S1 to adjust the pH to 8-10, stir to form a block gel, use a volatile organic solvent to perform multiple solvent replacements and aging on the block gel, and then dry it under normal pressure to obtain an organosilicon-based flexible aerogel.

[0029] In a preferred embodiment, the organosilicon mixed precursor is a mixture of triethoxymethylsilane and tetraethyl orthosilicate, wherein the molar ratio of triethoxymethylsilane to tetraethyl orthosilicate is 0.8:0.2 to 0.9:0.1.

[0030] In a preferred embodiment, the molar ratio of triethoxymethylsilane to tetraethyl orthosilicate is 0.8:0.2.

[0031] In step S101, the alcohol solvent is one or more of anhydrous ethanol, methanol, and propanol; The acid regulator is one of dilute hydrochloric acid or dilute nitric acid; the stirring temperature is 45~55℃; and the stirring time is 2~4 h. In step S102, the alkaline regulator is either an ammonia solution or a sodium hydroxide solution, with a concentration of 4-8 mol / L; The volatile organic solvent is one or more of ethanol, n-hexane, and acetone; the number of solvent replacements is 2 to 4 times, and the single aging time is 6 to 14 hours; the temperature for drying under normal pressure is 70 to 90°C, and the drying time is 40 to 50 hours.

[0032] In step S3, the ultrasonic treatment lasts for 2 to 4 minutes; the temperature for atmospheric pressure drying is 85 to 95°C, and the drying time is 2 to 4 hours.

[0033] This application proposes a flexible aerogel-coated iron porphyrin carbon dot composite material, which is prepared by any of the above-mentioned methods for preparing flexible aerogel-coated iron porphyrin carbon dot composite materials.

[0034] The aforementioned flexible aerogel-coated iron porphyrin carbon dot composite material can be applied to the selective adsorption and concentration detection of heavy metal ions. The technical solution of the present invention will be further described in detail below with reference to specific embodiments or comparative examples. In the following embodiments and comparative examples, the raw materials and reagents, unless otherwise specified, are all obtained commercially available, and the same batch of raw materials or reagents are used in the embodiments and comparative examples. The preparation methods without special conditions are all prepared by conventional and well-known preparation methods.

[0035] The indicators and testing methods used to characterize the performance are shown in the table below: Example 1 Weigh 7.74g of MTES and 2.26g of TEOS according to the MTES:TEOS ratio of 0.8:0.2 (molar ratio). Add 25mL of anhydrous ethanol and 18mL of deionized water, and stir magnetically at room temperature for 15min to form a homogeneous mixture. Slowly add 0.3mol / L dilute hydrochloric acid to the mixture to adjust the pH to 2.5. After sealing, stir at 50℃ for 3h to obtain a transparent silica sol. Add 6mol / L ammonia solution to the silica sol to adjust the pH to 9.5 to form a block gel. Perform solvent replacement twice with ethanol, soaking for 6h each time. Then perform solvent replacement twice with n-hexane, soaking for 4h each time to complete solvent replacement and aging. Then dry at 80℃ for 48h to obtain a flexible aerogel. Weigh 2.0g of polyethyleneimine and 50.0mg of TEOS according to the mass ratio of nitrogen-containing polymer:porphyrin compound:carbon source reagent = 40:1:0.4. Heme chloride and 20.0 mg sodium citrate were used to dissolve polyethyleneimine in 10 mL of deionized water. Heme chloride and sodium citrate were added, and the mixture was sonicated for 10 min. The mixture was then subjected to high pressure reaction at 180 °C for 10 h and refrigerated at 4 °C for later use. 10 g of flexible aerogel was mixed with 5 mL of iron porphyrin carbon dot solution, sonicated for 3 min, and dried at 90 °C for 3 h to obtain the target composite material.

[0036] Example 2 Weigh 8.30 g of MTES and 1.70 g of TEOS according to a molar ratio of MTES:TEOS = 0.85:0.15. Add 25 mL of anhydrous ethanol and 18 mL of deionized water, and stir magnetically at room temperature for 15 min to form a homogeneous mixture. Slowly add 0.3 mol / L dilute hydrochloric acid to the mixture to adjust the pH to 2.5. After sealing, stir at 50℃ for 3 h to obtain a transparent silica sol. Add 6 mol / L ammonia solution to the silica sol to adjust the pH to 9.5 to form a block gel. Perform solvent replacement twice with ethanol, soaking for 4 h each time. Then perform solvent replacement twice with n-hexane, soaking for 2 h each time to complete solvent replacement and aging. Then dry at 80℃ for 48 h to obtain a flexible aerogel. Weigh 2.5 g of polyamide and 62.5 mg of porphyrin compound and carbon source reagent according to a mass ratio of nitrogen-containing polymer:porphyrin compound:carbon source reagent = 50:1.25:0.375. Polyamide was dissolved in 10 mL of deionized water, and heme chloride and glucose were added. The mixture was sonicated for 10 min, reacted under high pressure at 180℃ for 10 h, and then refrigerated at 4℃ for later use. 10 g of flexible aerogel was mixed with 5 mL of iron porphyrin carbon dot solution, sonicated for 3 min, and dried at 90℃ for 3 h to obtain the target composite material.

[0037] Example 3 Weigh 8.85g of MTES and 1.15g of TEOS according to a molar ratio of MTES:TEOS = 0.9:0.1. Add 25mL of anhydrous ethanol and 18mL of deionized water, and stir magnetically at room temperature for 15min to form a homogeneous mixture. Slowly add 0.3mol / L dilute hydrochloric acid to the mixture to adjust the pH to 2.0. After sealing, stir at 55℃ for 4h to obtain a transparent silica sol. Add 6mol / L ammonia solution to the silica sol to adjust the pH to 10.0 to form a block gel. Perform solvent replacement twice with ethanol, soaking for 6h each time. Then perform solvent replacement twice with n-hexane, soaking for 4h each time to complete solvent replacement and aging. Then dry at 90℃ for 48h to obtain a flexible aerogel. Weigh 3.0g of polyethyleneimine and 100.0mg of TEOS according to a mass ratio of nitrogen-containing polymer:porphyrin compound:carbon source reagent = 60:2:0.5. Heme chloride and 25.0 mg citric acid were used to dissolve polyethyleneimine in 10 mL of deionized water. Heme chloride and citric acid were added, and the mixture was sonicated for 10 min. The mixture was then subjected to high pressure reaction at 200 °C for 12 h and refrigerated at 4 °C for later use. 10 g of flexible aerogel was mixed with 5 mL of iron porphyrin carbon dot solution, sonicated for 4 min, and dried at 95 °C for 4 h to obtain the target composite material.

[0038] Comparative Example 1 Weigh 7.74 g of MTES and 2.26 g of TEOS according to a molar ratio of MTES:TEOS = 0.8:0.2. Add 25 mL of anhydrous ethanol and 18 mL of deionized water, and stir magnetically at room temperature for 15 min to form a homogeneous mixture. Slowly add 0.3 mol / L dilute hydrochloric acid to the mixture to adjust the pH to 2.5. After sealing, stir at 50 °C for 3 h to obtain a transparent silica sol. Add 6 mol / L ammonia solution to the silica sol to adjust the pH to 9.5 to form a block gel. Perform solvent replacement twice with ethanol, soaking for 6 h each time. Then perform solvent replacement twice with n-hexane, soaking for 4 h each time to complete the solvent replacement and aging. Finally, dry at 80 °C for 48 h to obtain a pure flexible aerogel without carbon dot composite step.

[0039] Comparative Example 2 The preparation method of the flexible aerogel is the same as in Example 1; conventional carbon dots are used instead of iron porphyrin carbon dots. Conventional carbon dot preparation: 2.0 g of polyethyleneimine is dissolved in 10 mL of deionized water, 20.0 mg of sodium citrate is added, heme chloride is not added, and the mixture is sonicated for 10 min; the mixture is then reacted under high pressure at 180 °C for 10 h and refrigerated at 4 °C for later use; 10 g of flexible aerogel is mixed with 5 mL of conventional carbon dot solution, sonicated for 3 min, and dried at 90 °C for 3 h to obtain conventional carbon dot composite aerogel material.

[0040] The materials obtained in the above embodiments and comparative examples were subjected to performance testing, and the results are shown in Tables 1 and 2: Table 1 Table 2 As can be seen from the specific embodiments and the effect data in Tables 1 and 2 above, the composite materials obtained by combining iron porphyrin carbon dots with organosilicon-based flexible aerogels in Embodiments 1 to 3 of this application can significantly adsorb Fe²⁺. + Zn² + Cd² + It contains heavy metal ions and has good mechanical flexibility. After adsorbing the target ions, the fluorescence intensity is significantly enhanced.

[0041] Compared to Example 1, Comparative Example 1, which did not have composite carbon dots, showed poor selectivity for heavy metal ions and a lower adsorption capacity.

[0042] Compared to Example 1, Comparative Example 2, which uses a flexible aerogel combined with conventional carbon dots, shows a significant decrease in heavy metal adsorption performance compared to Example 1: Fe² + Zn² + Cd² +The saturated adsorption capacities decreased from 192 mg / g, 175 mg / g, and 168 mg / g in Example 1 to 125 mg / g, 110 mg / g, and 100 mg / g, respectively, representing a decrease of 35%–40%. Simultaneously, the adsorption equilibrium time increased from 50 min in Example 1 to 65 min, indicating a significant deterioration in adsorption kinetics. Furthermore, conventional carbon dots lack the specific heavy metal binding sites provided by the iron porphyrin structure, resulting in weak selective adsorption of target ions. Moreover, during repeated recycling cycles, insufficient binding force easily leads to a rapid decline in adsorption efficiency, failing to meet the dual requirements of high efficiency and stability for adsorption materials.

[0043] It is evident that the use of iron porphyrin carbon dots combined with flexible aerogel in the preparation of the composite material is crucial for its practical application in heavy metal adsorption scenarios. In Example 1, the flexible aerogel enhances the loading stability of the carbon dots and possesses excellent mechanical flexibility, giving the composite material potential for recycling and reuse. It performs significantly better under internal / external forces such as compression and rebound, and can withstand a certain degree of compression during the desorption process (releasing adsorbed heavy metal ions) (conventional aerogels are difficult to withstand compression operations). Therefore, the combination of flexible aerogel and iron porphyrin carbon dots in this application can significantly improve the overall effect.

[0044] Comparative Example 3 The specific preparation method is the same as in Example 1, except that the mass and mass ratio of the nitrogen-containing polymer, porphyrin compound and carbon source reagent are different.

[0045] Performance tests were conducted on examples 3-1 to 3-8, and the results were compared with those of example 1. The data are shown in Tables 3 and 4. Table 3 Table 4 As can be seen from the data in Tables 3 and 4. Compared to Example 1, when the mass of nitrogen-containing polymer raw materials in the raw material formulation is too low or too high, such as in Comparative Examples 3-1 and 3-6, it affects the surface amino content and dispersion stability of the prepared iron porphyrin carbon dots, resulting in a decrease in the heavy metal adsorption performance of the composite material: insufficient amino groups lead to a reduction in binding sites, or excessively dense amino groups cause steric hindrance, making the carbon dots prone to agglomeration and uneven particle size, significantly reducing the adsorption capacity, and making them prone to detachment during cycling, resulting in poor stability.

[0046] Compared to Example 1, when the mass of porphyrin compound raw materials in the raw material formulation is too low or too high, such as in Comparative Examples 3-2 and 3-7, it affects the number and uniformity of iron porphyrin-specific binding sites and particle size of the prepared iron porphyrin carbon dots. The adsorption performance and selectivity of heavy metals in the composite material decrease. Due to insufficient iron porphyrin sites, the specific adsorption capacity is weakened, or the aggregation of porphyrin groups causes carbon dot agglomeration. Not only is the adsorption capacity reduced, but the selectivity for target heavy metal ions is also significantly reduced, and the anti-interference ability is poor.

[0047] Compared to Example 1, when the carbon source reagent is too low or too high in the raw material formulation, such as in Comparative Examples 3-3 and 3-8, it affects the integrity of the carbon dot skeleton structure and the exposure of surface active sites of the prepared iron porphyrin carbon dots. The adsorption performance of heavy metals in the composite material decreases. Due to insufficient carbon source, the carbon dot skeleton is poorly developed and the particle size is uneven. Or, the carbon source excessively coats the active sites, which reduces the effective adsorption sites of the carbon dots, significantly reduces the adsorption capacity, prolongs the adsorption equilibrium time, and deteriorates the kinetic performance.

[0048] In summary, the mass ratio of nitrogen-containing polymer:porphyrin compound:carbon source reagent in the iron porphyrin carbon dot raw material needs to be controlled at 40-60:1-2:0.3-0.5, as in Example 1 and Comparative Examples 3-4 to 3-5. This ensures that the iron porphyrin carbon dots are uniformly dispersed with good particle size uniformity. At the same time, it has sufficient amino groups and iron porphyrin specific binding sites. The composite material has high heavy metal adsorption capacity, good selectivity, and fast adsorption kinetics. Moreover, the carbon dots are not easy to agglomerate and are not easy to fall off during recycling. It has excellent adsorption performance and stability, which can meet the requirements of high efficiency and durability for actual heavy metal adsorption.

[0049] Comparative Example 4 The specific preparation method is the same as in Example 1, except that the molar ratio of MTES to TEOS is the same (the sum of the masses of the two raw materials is the same as in Example 1).

[0050] Performance tests were conducted on Comparative Examples 4-1 to 4-3, and compared with Example 1. The performance data are shown in Tables 5 and 6. Table 5 Table 6 As can be seen from Tables 5 and 6. Compared to Example 1, when the molar ratio of MTES and TEOS in the organosilicon aerogel precursor formulation is too low or too high, such as in Comparative Examples 4-1 and 4-3, it affects the uniformity of the pore structure, crosslinking density, and mechanical stability of the prepared organosilicon flexible aerogel. The adsorption performance and adsorption kinetics of heavy metals in the composite material decrease, or other defects may occur: when the MTES ratio is too low, the aerogel skeleton is too hydrophilic and easily absorbs water and collapses, the carbon dot loading is uneven, and the effective adsorption sites are greatly reduced; when the MTES ratio is too high, the aerogel crosslinking degree is insufficient, the skeleton structure is loose, the carbon dots are easy to fall off, and the adsorption equilibrium time is significantly prolonged. After cyclic compression, the irreversible deformation increases significantly, and the mechanical stability is extremely poor.

[0051] In summary, the molar ratio of the precursor raw materials for organosilicon aerogel needs to be controlled at 0.8:0.2~0.9:0.1, as in Example 1 and Comparative Examples 4-2. By optimizing the precursor ratio and preparation process of the flexible hot melt adhesive, its mechanical flexibility and porous structure stability can be balanced.

[0052] As attached Figure 1 As shown in Figure 1, the morphology of different samples is obtained by scanning electron microscopy (SEM). The test conditions were as follows: the samples were vacuum sputtered with gold, the accelerating voltage was 5 kV, and the magnification was 4.0~4.35 k times. Among them, a is the cross-sectional morphology of the composite material of Example 1, b is the morphology of the sample of Comparative Example 4-1, c is the morphology of the sample of Comparative Example 4-2, and d is the morphology of the sample of Comparative Example 4-3. As can be seen from the figure, the samples of Example 1 and Comparative Example 4-2 exhibit a continuous and uniform three-dimensional interconnected porous network structure with regular pores without collapse, and carbon dots are uniformly loaded on the surface of the aerogel framework without agglomeration. The pores of the sample of Comparative Example 4-1 have local collapse and poor connectivity, while the framework of the sample of Comparative Example 4-3 is loose and the pore size distribution is uneven. This verifies that the MTES:TEOS molar ratio specified in this application can effectively construct a stable and uniform porous structure, providing sufficient channels for carbon dot loading and heavy metal adsorption.

[0053] As attached Figure 2 As shown in Figure 2, the fluorescence response spectrum of the composite material was obtained under the following conditions: room temperature, excitation wavelength of 365 nm, and heavy metal ion concentration of 0.5 mmol / L. Figure a shows the fluorescence response spectrum of different heavy metal ions, and Figure b shows the fluorescence response spectrum of the composite material adsorbing Fe²⁺ in Example 1. + The fluorescence spectrum after adsorption, c represents the adsorbed Zn²⁺. + The fluorescence spectrum after adsorption, d represents the adsorbed Cd². + The fluorescence spectrum after the experiment; as can be seen from the figure, the composite material of Example 1 reacts with Fe²⁺. + Zn² + Cd² +All exhibit significant fluorescence response, with fluorescence intensity increasing by 2 to 3 times compared to the original state. Furthermore, the fluorescence peak shape and intensity corresponding to different ions show characteristic differences, verifying that the composite material can achieve the identification and concentration detection of heavy metal ions through fluorescence spectroscopy, meeting the integrated adsorption-detection requirements.

[0054] As attached Figure 3 As shown in Figure 3, the adsorption standard curves of the composite material for different heavy metal ions were obtained under the following conditions: room temperature 25℃, solution pH=6, adsorption time 120 min, and initial concentration gradient of heavy metal ions 0~1.0 mmol / L; where a represents Fe²⁺. + Adsorption standard curve (fitting equation: y = -5.57x + 52.17, R² = 0.961), b represents Zn² + Adsorption standard curve (fitting equation: y = -10.5x + 65.29, R² = 0.933), c is Cd² + Adsorption standard curve (fitting equation: y=-9.569x+64.21, R²=0.917); As shown in the figure, all three curves exhibit good linear correlation, with a goodness of fit R² greater than 0.91, which can accurately quantify the concentration of heavy metal ions with a detection limit as low as 0.1 μmol / L, verifying that the composite material has excellent quantitative detection performance of heavy metal ions.

[0055] As attached Figure 4 As shown, attached Figure 4 The image is a transmission electron microscope (TEM) image. The black spherical spots are carbon dots. The carbon dots are uniformly dispersed and of uniform size, and no aggregation is observed.

[0056] As attached Figure 5 As shown, the DLS particle size distribution results indicate that the carbon dots exhibit a unimodal distribution, concentrated in the range of 2–7 nm, with an average particle size of approximately 4.5 nm. The distribution is narrow and the monodispersity is good.

[0057] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a flexible aerogel-coated iron porphyrin carbon dot composite material, characterized in that, Includes the following steps: S1. Preparation of organosilicon-based flexible aerogels; S2. Preparation of iron porphyrin carbon dot solution: A nitrogen-containing polymer is dissolved in deionized water, a porphyrin compound and a carbon source reagent are added, and the mixture is ultrasonically mixed. The mixture is then heated and reacted in a high-pressure reactor. After the reaction is completed, the mixture is cooled and stored under cold storage to obtain an iron porphyrin carbon dot solution. The mass ratio of the nitrogen-containing polymer, the porphyrin compound and the carbon source reagent is 40~60:1~2:0.3~0.

5. S3. The organosilicon-based flexible aerogel and the iron porphyrin carbon dot solution are mixed at a mass-volume ratio of 1.8~2.2 g:1 mL, ultrasonically treated, and dried to obtain a flexible aerogel-coated iron porphyrin carbon dot composite material.

2. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 1, characterized in that, The nitrogen-containing polymer is one of polyethyleneimine and polyamide; the porphyrin compound is heme chloride; and the carbon source reagent is one of sodium citrate, glucose, and citric acid.

3. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 2, characterized in that, In step S2, the reaction temperature of the heating reaction is 160~200 ℃, the reaction time of the heating reaction is 8~12h; the temperature of the cold storage is 2~6 ℃.

4. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 1, 2, or 3, characterized in that, In step S1, the step of preparing the organosilicon-based flexible aerogel includes: S101. Mix organosilicon mixed precursor, alcohol solvent and deionized water in a molar ratio of 1:5~9:14~18, stir at room temperature and add acid regulator dropwise to adjust the pH to 2~3 to obtain silica sol; S102. Add an alkaline regulator to the silica sol obtained in step S1 to adjust the pH to 8-10, stir to form a block gel, use a volatile organic solvent to perform multiple solvent replacements and aging on the block gel, and then dry it under normal pressure to obtain an organosilicon-based flexible aerogel.

5. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 4, characterized in that, The organosilicon mixed precursor is a mixture of triethoxymethylsilane and tetraethyl orthosilicate, wherein the molar ratio of triethoxymethylsilane to tetraethyl orthosilicate is 0.8:0.2~0.9:0.

1.

6. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 5, characterized in that, The molar ratio of the triethoxymethylsilane to the tetraethyl orthosilicate is 0.8:0.

2.

7. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 4, characterized in that, In step S101, the alcohol solvent is one or more of anhydrous ethanol, methanol, and propanol; The acid regulator is one of dilute hydrochloric acid and dilute nitric acid; the stirring temperature is 45~55℃; and the stirring time is 2~4 h. In step S102, the alkaline regulator is one of ammonia solution or sodium hydroxide solution, with a concentration of 4~8 mol / L; The volatile organic solvent is one or more of ethanol, n-hexane, and acetone; the solvent replacement is performed 2 to 4 times, and the aging time for each replacement is 6 to 14 hours; the temperature for atmospheric pressure drying is 70 to 90°C, and the drying time is 40 to 50 hours.

8. The method for preparing the flexible aerogel-coated iron porphyrin carbon dot composite material according to claim 1, characterized in that, In step S3, the duration of ultrasonic treatment is 2-4 min; the drying temperature is 85-95℃; the drying duration is 2-4 h; and the drying pressure is atmospheric pressure.

9. A flexible aerogel-coated iron porphyrin carbon dot composite material, characterized in that, It was prepared using the preparation method of the flexible aerogel-coated iron porphyrin carbon dot composite material as described in any one of claims 1 to 8.

10. The flexible aerogel-coated iron porphyrin carbon dot composite material as described in claim 9, characterized in that, The flexible aerogel-coated iron porphyrin carbon dot composite material was applied to the adsorption and concentration detection of heavy metal ions.

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