Precious metal continuous recovery method based on photochemical regenerated polyphenol interface composite aerogel

Abstract

The invention discloses a precious metal continuous recovery method based on photochemical regenerated polyphenol interface composite aerogel, and belongs to the field of precious metal ion adsorption-reduction and recovery. The preparation method comprises the following steps: preparing aerogel with photoelectrochemical activity, depositing a metal polyphenol network coating on an aerogel skeleton by taking the aerogel as a substrate to obtain polyphenol interface composite aerogel, and introducing a phenol-quinone structure group capable of generating redox cycle conversion to obtain the polyphenol interface composite aerogel. And continuous adsorption-reduction of precious metal ions is realized through light-driven electron transfer and proton coupling oxidation-reduction cycle so as to recover precious metal. The prepared polyphenol interface composite aerogel material can realize multiple adsorption cycles of noble metal ions, shows ultrahigh adsorption capacity, and has wide applicability to various noble metals such as gold, silver, platinum, palladium and the like.

Description

Technical Field

[0001] This invention relates to a method for continuous recovery of precious metals based on photochemically regenerated polyphenol interface composite aerogel, belonging to the field of metal ion adsorption-reduction and recovery. Background Technology

[0002] Precious metals (such as gold and silver) are widely used in aerospace, medical, and energy fields due to their excellent electrical conductivity, chemical stability, and catalytic properties. With the continued growth in demand for electronic products and the gradual depletion of mineral resources, recovering precious metals from secondary resources such as discarded electronic devices and industrial waste liquids has become an important research direction. However, existing precious metal recycling technologies still have many shortcomings.

[0003] Traditional methods such as extraction, electrochemical separation, and chemical precipitation typically require complex equipment, expensive reagents, and organic solvents. These processes are energy-intensive and highly polluting, making it difficult to meet the requirements of green, sustainable, and recyclable utilization.

[0004] In recent years, adsorbent-based recovery methods have attracted widespread attention due to their ease of operation, environmental friendliness, and high capture efficiency for low concentrations of metal ions. Traditional adsorbents, such as those containing functional groups like thiol, hydroxyl, or imine groups that can undergo redox reactions, can reduce noble metal ions to elemental metals. However, the redox processes of these adsorbents are mostly irreversible, resulting in limited adsorption capacity (typically less than 3500 mg / g) and short lifespan (generally less than 24 hours), making long-term, efficient recycling difficult. Therefore, developing a noble metal adsorbent material with reversible redox properties and self-renewal capabilities is crucial for improving the efficiency and sustainability of noble metal recovery.

[0005] Adsorbents containing polyphenol structures have attracted widespread attention in the field of noble metal ion adsorption-reduction due to their unique redox properties. Polyphenols, represented by tannic acid (TA), possess moderate redox potentials (approximately 0.5–0.7 V, relative to the standard hydrogen electrode). The catechol group can form a coordination complex with noble metal ions and convert the catechol to a quinone group through its own oxidation reaction, simultaneously reducing the noble metal ions to elemental metals. Although polyphenol-containing adsorbents offer advantages such as low cost and environmental friendliness when used for noble metal adsorption, the following problems remain: powder samples are difficult to recover; the adsorption sites cannot spontaneously regenerate after oxidation; and intermittent operation makes continuous recovery of noble metals difficult, thus limiting their further application. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a photochemical in-situ regeneration method for continuous recovery of precious metals based on polyphenol-modified conductive carbon nanogels. This method utilizes photoelectrons generated by the conductive carbon nanoframework under illumination to in-situ reduce oxidized quinone groups in the polyphenol coating to phenolic hydroxyl groups, thereby achieving the cyclic regeneration of phenolic hydroxyl groups and realizing the efficient and continuous recovery of precious metals.

[0007] This invention provides a method for preparing a polyphenol interface composite aerogel material, comprising the following steps: (1) Add 1~10 mL of graphene oxide (GO, 10 mg / mL) aqueous dispersion and 8 mL of ultrapure water to a 50 mL hydrothermal reactor, add 1~6 mg of carboxylated multi-walled carbon nanotubes (MWCNT), ultrasonically disperse for 30 min, and then carry out hydrothermal reduction reaction in an oven (90~240 ℃) for 2~24 h to prepare nano-carbon composite hydrogel; (2) After the reaction is complete, the nano-carbon composite hydrogel is rapidly frozen with liquid nitrogen for a certain period of time. After it is completely frozen, it is placed in a freeze dryer and dried for 72 h to obtain nano-carbon composite aerogel. (3) The nano-carbon composite aerogel was immersed in a polyphenol aqueous solution, soaked, and ferrous salt aqueous solution was added. The mixture was shaken and co-deposited for a period of time, and then washed to obtain the nanomaterial composite aerogel. The concentration of the polyphenol aqueous solution was 0.8~80 mg / mL, and the concentration of the ferrous salt aqueous solution was 0.98~98 mg / mL. (4) The obtained aerogel was then placed in glutaraldehyde solution (GA) for cross-linking for a period of time (0~24 h), thoroughly washed with ultrapure water, and then rapidly frozen with liquid nitrogen and dried in a freeze dryer to obtain polyphenol interface composite aerogel.

[0008] In one embodiment of the present invention, in step (1), the volume of the graphene oxide aqueous dispersion is any volume between 1 and 10 mL; preferably 2 mL.

[0009] In one embodiment of the present invention, in step (1), the molar ratio of polyphenol to ferrous salt is 1:1 to 1:100.

[0010] In one embodiment of the present invention, in step (1), the graphene oxide material can be replaced with a photocatalytic material with photoelectric properties, such as any one or more of titanium carbide (MXene), graphitized carbonitride (g-C3N4), titanium dioxide (TiO2), metal-organic framework (MOF) or covalent organic framework (COF).

[0011] In one embodiment of the present invention, in step (1), the metal-organic framework is any one of UiO-66-NH2, ZIF-8, and MIL-101(Cr).

[0012] In one embodiment of the present invention, in step (1), the covalent organic framework is any one of TpBpy-COF, Py-Bpy-COF, and Bp-COF.

[0013] In one embodiment of the present invention, in step (1), the mass of the carboxylated multi-walled carbon nanotube is any mass of 1 to 6 mg; preferably 3 mg.

[0014] In one embodiment of the present invention, in step (1), the hydrothermal reduction temperature is any temperature from 90 to 240 °C; preferably 180 °C.

[0015] In one embodiment of the present invention, in step (1), the hydrothermal reduction time is any time from 2 to 24 hours; preferably 9 hours.

[0016] In one embodiment of the present invention, in step (3), the polyphenol is any one of tannic acid, phytic acid, gallic acid, dopamine, tea polyphenols, and pyrogallol.

[0017] In one embodiment of the present invention, in step (3), the ferrous salt can be replaced by any one of cobalt chloride, aluminum chloride, zinc chloride, copper chloride, zirconium chloride, and cerium nitrate hexahydrate.

[0018] In one embodiment of the present invention, in step (3), the polyphenol aqueous solution is obtained by dissolving polyphenols in ultrapure water.

[0019] In one embodiment of the present invention, in step (3), the ferrous salt aqueous solution is obtained by dissolving ferrous salt in ultrapure water.

[0020] In one embodiment of the present invention, in step (3), the concentration of the polyphenol aqueous solution is 40 mg / mL.

[0021] In one embodiment of the present invention, the ferrous salt aqueous solution in step (3) is 9.8 mg / mL.

[0022] In one embodiment of the present invention, the oscillating co-deposition time in step (3) is 0 to 6 h, and is not 0; preferably 2 h.

[0023] In one embodiment of the present invention, in step (3), ultrapure water is used for cleaning.

[0024] In one embodiment of the present invention, in step (4), glutaraldehyde can be replaced by any one of terephthalaldehyde, 2,6-pyridinedialdehyde, p-phenylenediamine, and formaldehyde.

[0025] In one embodiment of the present invention, in step (4), the GA concentration is 2~70 wt%; preferably 30 wt%.

[0026] In one embodiment of the present invention, in step (4), the GA crosslinking time is 6 h.

[0027] This invention provides a polyphenol interface composite aerogel prepared by the method described above.

[0028] This invention provides the application of the polyphenol interface composite aerogel described above in the adsorption of noble metals.

[0029] The advantages of the photochemical in-situ regeneration method for continuous recovery of noble metals from polyphenol interface composite aerogels proposed in this invention are: (1) This invention achieves continuous adsorption and reduction reactions of noble metals by constructing a photochemically renewable phenolic hydroxyl-quinone cyclic interface. Compared with traditional non-renewable adsorbents, the adsorption capacity of this material is increased by more than 3 times; for example, the adsorption capacity for gold ions can exceed 12500 mg g. -1 Especially when the adsorption atmosphere is changed and a hole scavenger is added, the adsorption capacity for gold ions can exceed 15000 mg g. -1 Meanwhile, its continuous use time exceeds 500 hours, which is more than 10 times longer than that of conventional materials, effectively reducing energy consumption and material loss.

[0030] (2) The material of the present invention can achieve a recovery efficiency of nearly 100% for a variety of precious metal ions (including gold, silver, platinum, palladium, etc.) under light conditions. It can simultaneously deal with precious metal ions of different valence states and different sources, and has excellent selectivity and universality.

[0031] (3) The photochemical self-regenerating precious metal recycling system proposed in this invention can efficiently recycle precious metal resources from diverse sources, including central processing unit (CPU) waste, industrial catalysts, mine wastewater, and natural seawater. The process is mild and environmentally friendly, and can be widely promoted and applied, showing good potential for sustainable development.

[0032] (4) Specifically, this invention prepares photochemically active aerogels by freeze-drying. Then, using the aerogel as a substrate, a metal polyphenol network coating is deposited on the surface of the aerogel framework to obtain a polyphenol interface composite aerogel, thereby introducing a phenol-quinone structure that can undergo reversible redox cycle transformation into the system. This allows for the continuous adsorption-reduction of noble metal ions through light-driven electron transfer and proton-coupled redox cycle. Attached Figure Description

[0033] Figure 1These are photographs and scanning electron microscope images of the polyphenol interface composite aerogel prepared in Example 1 of this invention.

[0034] Figure 2 This is a scanning electron microscope image of the polyphenol interface composite aerogel prepared in Example 1 of the present invention after adsorption and reduction of gold, silver, platinum and palladium. Detailed Implementation

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] The reagents used in the various embodiments of this invention are as follows: Graphene oxide (GO) aqueous dispersion was purchased from Hangzhou Gaoxi Technology Co., Ltd.; carboxyl multi-walled carbon nanotubes (MWCNTs), titanium carbide (Ti3C2Tx) MXene multilayer nanosheets, graphitic carbon nitride (g-C3N4), UiO-66-NH2 (MOF), ZIF-8, MIL-101 (Cr), Py-Bpy-COF, and Bp-COF were all purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.; chloroauric acid (HAuCl4) and silver nitrate (AgNO3) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; tannic acid (TA) was purchased from Sigma-Aldrich; and platinum chloride (PtCl4) and palladium chloride (PdCl2) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Ferrous chloride tetrahydrate (Iron(II) chloride tetrahytdrate) and glutaraldehyde (50 wt% aqueous solution), along with other materials used in the experiment, were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0037] Preparation of COF (TpBpy): The preparation method of TpBpy is described in the article "Linker Modulation of Covalent Organic Frameworks at Atomic Level for Enhanced and Selective Photocatalytic Oxidation of Thioether".

[0038] The polyphenol interface composite aerogel prepared in this invention is used for noble metal adsorption. Adsorption capacity is the main parameter for evaluating adsorption performance. The adsorption capacity test methods in Examples 1-66 include: Under xenon lamp irradiation at 1 Sun intensity, different concentrations of noble metal ion solutions were used as feed solutions. At an optimized pH of 4, 30 mg of adsorbent was added to 300 mL of the feed solution, and samples were taken at set time intervals to measure the change in the concentration of noble metal ions in the solution. The amount of metal ions adsorbed by the adsorbent was calculated based on the difference in metal ion concentration before and after the reaction, and the adsorption capacity was defined as the ratio of the adsorbed amount to the adsorbent mass, expressed in mg / g. The adsorption atmosphere was air. Based on the saturated adsorption capacity (q) of the material e The saturation adsorption capacity and recovery efficiency (η) are used as the main performance evaluation indicators, and the time required to reach saturation adsorption capacity is used as the criterion for the material's service life. The saturation adsorption capacity and recovery efficiency are calculated using the following formulas:

[0039]

[0040] Where, q e η is the saturated adsorption capacity of the adsorbent (mg / g), η is the metal ion recovery efficiency (%), C0 is the initial metal ion concentration in the solution (mg / L), and C e denoted as , where is the concentration of metal ions at adsorption equilibrium (mg / L), m is the mass of the adsorbent (g), and V is the volume of the solution (L).

[0041] Example 1 (1) 2 mL of graphene oxide (GO, 10 mg / mL) aqueous dispersion and 8 mL of ultrapure water were added to a 50 mL hydrothermal reactor, and 3 mg of carboxylated multi-walled carbon nanotubes (MWCNTs) were added. The mixture was ultrasonically dispersed for 30 min. Then, a hydrothermal reduction reaction was carried out in an oven at 180 °C for 9 h to prepare a nano-carbon composite hydrogel.

[0042] (2) After the reaction is complete, the nano-carbon composite hydrogel obtained in (1) is rapidly frozen with liquid nitrogen. After it is completely frozen, it is placed in a freeze dryer and dried for 72 h to obtain nano-carbon composite aerogel.

[0043] (3) Weigh 1.2 g of tannic acid and dissolve it in 30 mL of ultrapure water to obtain a tannic acid aqueous solution with a concentration of 40 mg / mL; weigh 0.298 g of ferrous chloride tetrahydrate and dissolve it in 30 mL of ultrapure water to obtain a ferrous chloride salt solution with a concentration of 9.8 mg / mL. Deposit the composite aerogel obtained in (2) in the tannic acid aqueous solution and soak it for 10 min, then add the ferrous salt aqueous solution, wherein the molar ratio of tannic acid to ferrous chloride is 5:10, and shake and deposit at 25 ℃ for 2 h, then transfer it to a vacuum oven for thermal crosslinking for 20 min.

[0044] (4) The obtained aerogel was then crosslinked in a 30 wt% GA solution for 6 h, thoroughly washed with ethanol and ultrapure water, and then rapidly frozen in liquid nitrogen and dried in a freeze dryer for 72 h to obtain a polyphenol interface composite aerogel.

[0045] Examples 2-10 By changing the type of optoelectronic material (as shown in Table 1) and keeping the other conditions the same as in Example 1, a polyphenol interface composite aerogel was obtained.

[0046] Test Example 1 The nanocomposite aerogels prepared in Examples 1-10 were tested, and the results are shown in Table 1.

[0047] Table 1. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 1-10

[0048] As shown in Table 1, any type of optoelectronic material can achieve the conversion of phenol-quinone adsorption sites for noble metal ions, thus exhibiting excellent adsorption capacity.

[0049] Examples 11-15 Adjust the amount of graphene oxide aqueous dispersion added (as shown in Table 2), and keep the other conditions the same as in Example 1 to obtain polyphenol interface composite aerogel.

[0050] Test Example 2 The polyphenol interface composite aerogels prepared in Examples 11-15 were tested, and the results are shown in Table 2.

[0051] Table 2. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 11-15

[0052] Table 2 shows that the GO content significantly affects the noble metal adsorption capacity of the composite aerogel. The composite aerogel reaches its maximum adsorption capacity when the GO mass is 2 mg, exhibiting the best adsorption and in-situ reduction performance. When the GO mass is below 2 mg, the adsorption performance decreases significantly, mainly due to insufficient conductive framework, reduced electron transport efficiency, and insufficient number of active sites, leading to decreased adsorption and reduction efficiencies. When the GO mass is above 2 mg, the adsorption capacity per unit mass gradually decreases. This is due to factors such as excessive stacking of GO sheets leading to reduced specific surface area and pore accessibility, and relative dilution of TA active sites, thus affecting the adsorption-reduction-regeneration cycle efficiency. Although a high GO content may improve the overall mechanical stability of the material, it is detrimental to the adsorption capacity per unit mass.

[0053] Examples 16-20 The amount of carboxylated multi-walled carbon nanotubes added was adjusted (as shown in Table 3), and the other conditions were the same as in Example 1, to obtain polyphenol interface composite aerogel.

[0054] Test Example 3 The polyphenol interface composite aerogels prepared in Examples 16-20 were tested, and the results are shown in Table 3.

[0055] Table 3. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 16-20

[0056] As shown in Table 3, the amount of MWCNT added has a significant impact on the noble metal adsorption performance of the composite aerogel. When the MWCNT content is too low (<3 mg), the electron transport capacity is insufficient, and the adsorption and reduction efficiency decreases; when the MWCNT content is too high (>3 mg), aggregation is likely to occur, leading to a decrease in the utilization rate of active sites.

[0057] Examples 21-25 Adjust the hydrothermal reduction temperature of the nano-carbon aerogel (as shown in Table 4), and keep the other conditions the same as in Example 1 to obtain a polyphenol interface composite aerogel.

[0058] Test Example 4 The polyphenol interface composite aerogels prepared in Examples 21-25 were tested, and the results are shown in Table 4.

[0059] Table 4. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 21-25

[0060] As shown in Table 4, hydrothermal temperature has a significant impact on the noble metal adsorption performance of the composite aerogel. When the temperature is below the optimal value (<180℃), the reduction of GO is insufficient, the conductive network of the composite aerogel is imperfect, and the electron transport efficiency is low, resulting in a decrease in the adsorption and in-situ reduction efficiency of noble metals. When the hydrothermal temperature is above the optimal value (>180℃), excessive reduction or local aggregation of GO may cause a decrease in specific surface area or pore blockage, which is also detrimental to the improvement of adsorption capacity.

[0061] Examples 26-30 Adjust the hydrothermal reduction time of the nano-carbon aerogel (as shown in Table 5), and keep the other conditions the same as in Example 1 to obtain a polyphenol interface composite aerogel.

[0062] Test Example 5 The polyphenol interface composite aerogels prepared in Examples 26-30 were tested, and the results are shown in Table 5.

[0063] Table 5. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 26-30

[0064] As shown in Table 5, when the hydrothermal time is short (<9 h), the reduction degree of GO is insufficient, graphitization and conductive network are not fully formed, and the electron transport efficiency and active site exposure of the material are low, resulting in a decrease in the adsorption and in-situ reduction efficiency of noble metals. With the extension of hydrothermal time, the reduction degree and conductivity of GO gradually improve, and the pore structure and specific surface area tend to be optimized. At a hydrothermal time of about 9 h, the obtained aerogel has a good conductive network, suitable specific surface area and permeable pore structure, and the interfacial electron transport and the utilization rate of phenolic hydroxyl active sites are well balanced, thus exhibiting the highest adsorption capacity and the best photochemical regeneration performance. When the hydrothermal time is further extended to a longer period (>9 h), excessive heat treatment may lead to local rearrangement or agglomeration of rGO sheets, deterioration of pore structure and partial loss of surface active sites, which will reduce the adsorption capacity and regeneration efficiency per unit mass.

[0065] Examples 31-35 By adjusting the type of polyphenols (as shown in Table 6) and using the same conditions as in Example 1, a polyphenol interface composite aerogel was obtained.

[0066] Test Example 6 The polyphenol interface composite aerogels prepared in Examples 31-35 were tested, and the results are shown in Table 6.

[0067] Table 6. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 31-35.

[0068] As shown in Table 6, compared with tannic acid, tea polyphenols possess a high density of phenolic hydroxyl groups and a large π-conjugated structure, enabling multi-site coordination and effective electron transfer, thus exhibiting excellent adsorption performance for noble metal ions. While gallic acid and dopamine possess catechol structures, allowing for stable complexation and partial photoreduction, their smaller molecular weight or polymerization leads to decreased porosity and reduced adsorption capacity. Phytic acid, primarily composed of phosphate groups, relies mainly on electrostatic adsorption, exhibiting insufficient electron transfer capacity and significantly reduced adsorption performance. Pyrogallol, with its simple structure and limited coordination sites, also shows a significantly reduced adsorption capacity.

[0069] Examples 36-40 Adjust the tannic acid concentration (as shown in Table 7), and keep the other conditions the same as in Example 1 to obtain polyphenol interface composite aerogel.

[0070] Test Example 7 The polyphenol interface composite aerogels prepared in Examples 36-40 were tested, and the results are shown in Table 7.

[0071] Table 7. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 36-40

[0072] As shown in Table 7, when the TA concentration is low (<40 mg / mL), the coordination reaction is insufficient, the MPN framework is incomplete, the coating is thin and unevenly distributed, resulting in a limited number of active phenolic hydroxyl groups and weak adsorption and reduction capabilities. With increasing TA concentration (up to 40 mg / mL), the coordination ratio between TA and iron ions becomes more reasonable, forming a stable and uniformly distributed TA–Fe network layer. At this point, the density of phenolic hydroxyl groups in the system is moderate, the electron transfer pathway is unobstructed, the complexation and reduction efficiency of noble metal ions is highest, and the adsorption capacity and recycling performance of the material are optimal. When the TA concentration further increases (>40 mg / mL), excess TA leads to over-coordination and cross-linking, forming a thicker or locally agglomerated coating, causing a decrease in porosity and an increase in diffusion resistance. Simultaneously, some phenolic hydroxyl groups are shielded, reducing electron transfer efficiency and consequently lowering adsorption performance.

[0073] Examples 41-45 The types of metal salts in the solution were adjusted (as shown in Table 8), and the other conditions were the same as in Example 1, to obtain polyphenol interface composite aerogels.

[0074] Test Example 8 The polyphenol interface composite aerogels prepared in Examples 41-45 were tested, and the results are shown in Table 8.

[0075] Table 8. Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 41-45

[0076] As shown in Table 8, compared with the system using FeCl2 as the coordinating metal, CuCl2 and Ce(NO3)3·6H2O significantly improved the adsorption capacity of noble metals, mainly due to CuCl2. 2+ Strong coordination with polyphenols and electron relaying role in redox reactions, as well as Ce 3+ / Ce 4+ The reversible redox properties and multi-coordination structure of the phenolic compounds enhance electron transfer and metal complexation capabilities. Conversely, the coordination networks formed by CoCl2, ZnCl2, and ZrCl4 are relatively dense or have weak electronic coupling, and some phenolic hydroxyl groups are passivated, resulting in a reduction in active sites and limited mass transfer, thus reducing adsorption capacity.

[0077] Examples 46-50 The concentration of ferrous chloride in the solution was adjusted (as shown in Table 9), and the other conditions were the same as in Example 1, to obtain a polyphenol interface composite aerogel.

[0078] Test Example 9 The polyphenol interface composite aerogels prepared in Examples 46-50 were tested, and the results are shown in Table 9.

[0079] Table 9 shows the adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 46-50.

[0080] As shown in Table 9, when the FeCl2 concentration is low (<9.8 mg / mL), there are insufficient metal coordination centers, resulting in incomplete and discontinuous MPN layer formation. This leads to a limited number of exposed phenolic hydroxyl active sites on the surface, low interfacial coordination / crosslinking degree, and reduced complexation and in-situ reduction efficiency of noble metal ions, resulting in unsatisfactory adsorption capacity and cycling stability. With increasing FeCl2 concentration, the MPN structure gradually improves. When the FeCl2 concentration further increases (>9.8 mg / mL), excess metal ions lead to over-coordination and excessive crosslinking density, forming a thicker or locally dense polyphenol layer. This causes a decrease in porosity, an increase in diffusion resistance, and the shielding of some active sites, resulting in a decrease in interfacial electron transfer efficiency, thereby reducing the adsorption capacity per unit mass and regeneration performance.

[0081] Examples 51-54 The deposition time of the metal polyphenol network was adjusted (as shown in Table 10), and the other conditions were the same as in Example 1, to obtain a polyphenol interface composite aerogel.

[0082] Test Case 10 The polyphenol interface composite aerogels prepared in Examples 51-54 were tested, and the results are shown in Table 10.

[0083] Table 10. Adsorption capacity of noble metal ions of polyphenol interfacial composite aerogels prepared in Examples 51-54

[0084] As shown in Table 10, the deposition time of MPN has a significant impact on the degree of coating formation and adsorption performance. When the deposition time is short (<2 h), the TA–Fe metal polyphenol network is not fully cross-linked, the coating coverage is incomplete, and the active sites on the aerogel surface are insufficiently exposed, resulting in low complexation and reduction capabilities of noble metal ions. With the extension of deposition time, the coordination and cross-linking reactions of MPN are gradually completed, and a continuous and stable polyphenol network layer is formed on the material surface. When the deposition time is 2 h, the MPN coating is uniform, dense, and structurally stable, and the noble metal adsorption rate of the composite aerogel reaches its highest value. When the deposition time is further extended (>2 h), the change in adsorption rate tends to be gradual, indicating that MPN has basically completed deposition and cross-linking at 2 h. Extending the time will not significantly increase the amount of MPN deposited, and may even cause some pores to be covered, thus slightly hindering mass transfer.

[0085] Examples 55-58 By adjusting the type of crosslinking agent (as shown in Table 11) and keeping the other conditions the same as in Example 1, a polyphenol interface composite aerogel was obtained.

[0086] Test Example 11 The polyphenol interface composite aerogels prepared in Examples 55-58 were tested, and the results are shown in Table 11.

[0087] Table 11 Adsorption capacity of noble metal ions for the polyphenol interfacial composite aerogels prepared in Examples 55-58

[0088] As shown in Table 11, both terephthalaldehyde and 2,6-pyridinedicarboxaldehyde contain aromatic conjugated structures, which can form π–π stacking and conjugated bridging with polyphenol molecules, enhancing electron delocalization and coordinated electron transfer, thereby increasing their adsorption capacity for metal ions. p-phenylenediamine, possessing both aromatic and amino rings, can participate in hydrogen bonding and coordination, further enhancing interfacial activity and electronic coupling. In contrast, formaldehyde, being a small-molecule non-conjugated aldehyde, has a fast cross-linking rate but easily consumes phenolic hydroxyl groups and disrupts the π-conjugated system, leading to limited electron transfer pathways and a reduction in effective coordination sites, thus significantly decreasing its adsorption capacity.

[0089] Examples 59-62 The concentration of glutaraldehyde was adjusted (as shown in Table 12), and the other conditions were the same as in Example 1, to obtain a polyphenol interface composite aerogel.

[0090] Test Example 12 The polyphenol interface composite aerogels prepared in Examples 59-62 were tested, and the results are shown in Table 12.

[0091] Table 12 Adsorption capacity of noble metal ions for the polyphenol-interfacial composite aerogels prepared in Examples 59-62

[0092] As shown in Table 12, when the crosslinking agent concentration is low (<30 wt%), the crosslinking is incomplete, leading to reduced stability of the polyphenol coating and decreased adsorption capacity during long-term use. When the crosslinking agent concentration is high (>30 wt%), excessive crosslinking of glutaraldehyde will occupy some of the phenolic hydroxyl adsorption sites of the polyphenols, thus reducing the adsorption capacity. Examples 63-66 The crosslinking time of glutaraldehyde was adjusted (as shown in Table 13), and the other conditions were the same as in Example 1, to obtain polyphenol interface composite aerogel.

[0093] Test Example 13 The polyphenol interface composite aerogels prepared in Examples 63-66 were tested, and the results are shown in Table 13.

[0094] Table 13. Adsorption capacity of noble metal ions of polyphenol interfacial composite aerogels prepared in Examples 63-66

[0095] As shown in Table 13, when the crosslinking time is short (<6 h), the phenolic hydroxyl groups in the MPN coating do not react completely with glutaraldehyde, resulting in poor network structure stability. This leads to coating peeling and performance degradation in long-term cycling or acidic environments. With the extension of crosslinking time, the structure of the MPN layer gradually becomes denser, and the chemical stability is significantly improved. However, when the crosslinking time is too long (>6 h), excessive crosslinking consumes some of the surface phenolic hydroxyl groups, reducing the number of exposed active sites, thereby reducing the adsorption capacity of noble metal ions.

[0096] Test Example 14 The adsorption capacity of the polyphenol interface composite aerogel prepared in Example 1 was tested. The method for testing the adsorption capacity was the same as that for Example 1, except that the adsorption atmosphere was changed, or the adsorption atmosphere was changed and an electron capture agent, ROS capture agent and hole capture agent were added (30 mg of adsorbent was added to 300 mL of raw material solution and then multiple capture agents were added), as shown in the table below.

[0097] Table 14 Adsorption capacity of polyphenol interfacial composite aerogel in Example 1 under different adsorption atmospheres, or under different adsorption atmospheres and with the addition of hole scavengers.

[0098] Table 14 shows that we conducted a series of free radical scavenging experiments. When methanol was added as a hole scavenger, the adsorption capacity significantly increased, indicating that hole removal can promote more efficient use of photogenerated electrons in AuCl4. – The reduction and regeneration of phenolic groups were observed; conversely, the adsorption performance decreased significantly after the introduction of the electron scavenger K2S2O8, further verifying the key role of photogenerated electrons in the reaction process. Regarding the influence of reactive oxygen species (ROS), isopropanol (•OH scavenger) showed a significantly stronger inhibitory effect on adsorption than p-benzoquinone (•O2 scavenger). – (Scavenging agent), indicating that •OH free radicals have a greater impact on weakening the adsorption performance of polyphenol-coated aerogels. Furthermore, excessive ROS and photogenerated holes can hinder the continuous regeneration of the system by re-oxidizing phenolic hydroxyl groups or consuming electrons.

[0099] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a polyphenol interfacial composite aerogel, characterized in that, Includes the following steps: (1) Add 1~10 mL of graphene oxide aqueous dispersion and 8 mL of ultrapure water to a hydrothermal reactor, add 1~6 mg of carboxylated multi-walled carbon nanotubes, sonicate until completely dispersed, and then carry out a hydrothermal reduction reaction to prepare nano-carbon composite hydrogel; the concentration of graphene oxide aqueous dispersion is 10 mg / mL; the hydrothermal reduction reaction temperature is 90~240℃, and the time is 2~24 h; (2) After the reaction is complete, the nano-carbon composite hydrogel is rapidly frozen with liquid nitrogen. After it is completely frozen, it is placed in a freeze dryer and dried for a period of time to obtain nano-carbon composite aerogel. (3) The nano-carbon composite aerogel was immersed in a polyphenol aqueous solution, soaked, and a ferrous salt aqueous solution was added. The mixture was shaken and co-deposited for a period of time, and then washed to obtain the nanomaterial composite aerogel. The concentration of the polyphenol aqueous solution was 0.8~80 mg / mL, and the concentration of the ferrous salt aqueous solution was 0.98~98 mg / mL. (4) Subsequently, the obtained nanomaterial composite aerogel was placed in glutaraldehyde solution for cross-linking for a period of time, then rapidly frozen with liquid nitrogen, and dried in a freeze dryer to obtain polyphenol interface composite aerogel. The concentration of glutaraldehyde solution was 2~70 wt%, and the cross-linking time was 4~24 h.

2. The method according to claim 1, characterized in that, In step (1), graphene oxide can be replaced with photocatalytic materials with photoelectric properties, including one or more of titanium carbide, graphitized carbonitride, titanium dioxide, metal-organic framework, and covalent organic framework.

3. The method according to claim 2, characterized in that, The metal-organic framework is one of UiO-66-NH2, ZIF-8, and MIL-101(Cr), and the covalent organic framework is one of TpBpy-COF, Py-Bpy-COF, and Bp-COF.

4. The method according to claim 1, characterized in that, In step (1), the volume of the graphene oxide aqueous dispersion is 2 mL; the mass of the carboxylated multi-walled carbon nanotubes is 3 mg.

5. The method according to claim 1, characterized in that, In step (1), the hydrothermal reduction temperature is 180℃ and the time is 9 h.

6. The method according to claim 1, characterized in that, In step (3), the polyphenol is any one of tannic acid, phytic acid, gallic acid, dopamine, tea polyphenols, or pyrogallol; the ferrous salt can be replaced by any one of cobalt chloride, aluminum chloride, zinc chloride, copper chloride, zirconium chloride, or cerium nitrate hexahydrate.

7. The method according to claim 1, characterized in that, In step (3), the concentration of polyphenol aqueous solution was 40 mg / mL; the concentration of ferrous salt aqueous solution was 9.8 mg / mL; and the shaking co-deposition time was 0.5~6 h.

8. The method according to claim 1, characterized in that, In step (4), glutaraldehyde can be replaced by any one of terephthalaldehyde, 2,6-pyridinedicarboxaldehyde, p-phenylenediamine, or formaldehyde; the mass fraction of the glutaraldehyde solution is 30 wt%.

9. The polyphenol interface composite aerogel prepared by any one of claims 1 to 8.

10. The application of the polyphenol interface composite aerogel according to claim 9 in the adsorption and recovery of precious metals.

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