Zirconium-based adsorption composite material and preparation method thereof

Abstract

This invention relates to the field of environmentally friendly adsorption materials technology, and discloses a zirconium-based adsorption composite material and its preparation method. The material uses diatomaceous earth as a matrix, modified with 3-aminopropyltriethoxysilane, and then copper-ammonia coordination sites are constructed on the carrier surface using copper sulfate pentahydrate. Subsequently, a complex solution formed by zirconium oxychloride octahydrate and citric acid monohydrate is added, followed by a two-stage programmed temperature-controlled hydrolysis with urea, causing the zirconium component to be electrostatically induced to target and deposit at specific sites. Finally, copper ions are removed in situ using ammonia complexation elution, and the final product is obtained after drying and calcination. This invention effectively suppresses spontaneous nucleation and aggregation of the zirconium source in the liquid phase through interface-induced deposition and post-copper removal pore-forming processes, opening up mass transfer pathways within the coating and significantly improving the actual specific surface area and effective adsorption site density of the composite material.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly adsorption materials technology, specifically to a zirconium-based adsorption composite material and its preparation method. Background Technology

[0002] Zirconium-based compounds possess abundant active hydroxyl groups on their surfaces, exhibiting excellent specific adsorption capabilities for certain anions and heavy metals in aqueous solutions. However, pure-phase amorphous zirconium-based or nanoscale zirconium oxide powders are prone to agglomeration in the liquid phase, leading to a significant decrease in the effective specific surface area of ​​the material and limitations in solid-liquid separation during practical water treatment applications. To overcome these application bottlenecks, porous inorganic minerals such as diatomaceous earth are typically introduced as framework carriers to load and solidify the zirconium active components.

[0003] In existing adsorbent material preparation processes, most methods employ direct chemical precipitation or impregnation coating to load the zirconium source onto the support surface. However, due to the excessively rapid hydrolysis kinetics of precursors such as zirconium oxychloride in aqueous environments, free zirconium ions within the system tend to undergo homogeneous nucleation reactions directly in the liquid phase, rapidly generating large-sized amorphous precipitates and flocs.

[0004] These large precipitates adhere disorderly to the outer layer of the carrier particles mainly through physical stacking. This not only makes it difficult to form a uniformly distributed active coating layer, but also directly blocks the original micropores of the porous carrier. This uncontrollable deposition mechanism causes a significant decrease in the overall specific surface area of ​​the composite material, resulting in the adsorption sites inside the coating layer being mutually masked and unable to contact the target pollutants, thus limiting the actual adsorption and utilization efficiency of the zirconium component.

[0005] Furthermore, due to the lack of effective chemical coordination anchoring between the carrier interface and the amorphous zirconium layer, the active coating obtained by conventional loading treatment is prone to peeling and loss when subjected to long-term fluid scouring, making it difficult to meet the requirements of long-term engineering use. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a zirconium-based adsorption composite material and its preparation method. The technical problem solved is that in the preparation process of existing zirconium-based adsorption materials, free zirconium ions are prone to spontaneous nucleation, which leads to the aggregation and uneven distribution of active components on the carrier surface, resulting in the decrease of the overall specific surface area of ​​the material and insufficient exposure of effective adsorption sites.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a zirconium-based adsorption composite material, which adopts the following technical solution:

[0009] A zirconium-based adsorption composite material is prepared from raw materials comprising the following parts by weight:

[0010] Based on 100.0 parts by weight of diatomaceous earth,

[0011] 3-Aminopropyltriethoxysilane: 2.0 to 6.0 parts by weight;

[0012] Copper sulfate pentahydrate: 1.57 to 2.70 parts by weight;

[0013] Zirconium oxychloride octahydrate: 20.0 to 50.0 parts by weight;

[0014] Citric acid monohydrate, wherein the molar ratio of citric acid monohydrate to zirconium in zirconium oxychloride octahydrate is 1.29:1 to 1.50:1;

[0015] Urea, wherein the molar ratio of urea to zirconium in zirconium oxychloride octahydrate is 8.4:1 to 12.1:1.

[0016] By employing the above technical solution, this material system utilizes the amino groups in the silane coupling agent to construct coordination sites on the diatomaceous earth surface. Based on this, copper ions are introduced to complex with the amino groups, making them induction centers for subsequent zirconium component deposition.

[0017] Normally, free zirconium ions readily undergo uncontrolled precipitation in the aqueous phase. However, this method utilizes the multidentate chelating action of citric acid to form a complex with zirconium oxychloride, thus suppressing this homogeneous nucleation side reaction. As urea decomposes upon heating, releasing alkaline substances, the negatively charged zirconium-citric acid complex, influenced by electrostatics, preferentially undergoes hydrolysis and condensation near the positively charged copper coordination sites.

[0018] After the zirconium-based active layer is constructed on the carrier surface, the original copper ions are eluted and removed using ammonia. This chemical displacement operation leaves pores and defects in situ on the material surface and inside the coating, effectively avoiding pore blockage that is easily caused by conventional impregnation methods, thereby significantly improving the actual specific surface area and adsorption capacity of the composite material.

[0019] Preferably, the weight ratio of the raw materials is as follows: based on 100.0 parts by weight of diatomaceous earth, the amount of 3-aminopropyltriethoxysilane is 4.0 parts by weight, the amount of copper sulfate pentahydrate is 1.57 parts by weight, and the amount of zirconium oxychloride octahydrate is 35.0 parts by weight.

[0020] By employing the above technical solution, the aforementioned dosage relationship represents the critical condition for maintaining a match between the surface modification reaction and the liquid-phase hydrolysis rate. If the zirconium precursor concentration is too high, the system reaction kinetics will still deviate from surface control and spontaneous liquid-phase nucleation will occur; while insufficient silane and copper ion dosages will lead to a decrease in the adhesion of the deposited layer. This specific ratio eliminates interference caused by material imbalance, ensuring that the zirconium oxide layer is firmly loaded onto the basic framework.

[0021] Preferably, the physicochemical parameters of the diatomaceous earth in the raw material are: a silica mass fraction of not less than 85%, a BET specific surface area of ​​10 to 25 square meters per gram, and a median particle size D50 of 10 to 50 micrometers.

[0022] The diatomaceous earth of this specification was selected by adopting the above technical solution mainly because its moderate initial porosity provides sufficient internal coating space. Furthermore, this particle size range prevents excessive agglomeration of the powder during the liquid-phase reaction and ensures that the final adsorbent exhibits good mass transfer kinetics performance in actual fluid separation applications.

[0023] Preferably, in the components constituting the composite material, the 3-aminopropyltriethoxysilane is pre-combined with diatomaceous earth and introduced in the form of amino-functionalized diatomaceous earth;

[0024] The preparation method of the amino-functionalized diatomaceous earth is as follows: the dried and activated diatomaceous earth is dispersed in anhydrous toluene, and after reflux azeotropic dehydration, the 3-aminopropyltriethoxysilane is slowly added dropwise under nitrogen protection and the reaction continues. The product is washed and dried to constant weight in a vacuum oven.

[0025] By employing the above technical solution, since trace amounts of moisture in the system can easily cause 3-aminopropyltriethoxysilane to undergo self-condensation and become ineffective, after forcibly removing physically adsorbed water through azeotropic operation, the alkoxy groups of the silane molecules can concentrate and undergo a condensation reaction with the silanol groups on the surface of diatomaceous earth. This liquid-phase grafting treatment under an anhydrous environment fundamentally ensures the effective immobilization of amino functional groups and the uniformity of modification density.

[0026] Secondly, the present invention provides a method for preparing a zirconium-based adsorption composite material, which adopts the following technical solution:

[0027] A method for preparing a zirconium-based adsorption composite material includes the following steps:

[0028] Aminofunctionalized diatomaceous earth with 3-aminopropyltriethoxysilane bonded to its surface was dispersed in a buffer solution, and an aqueous solution of copper sulfate pentahydrate was slowly added dropwise while stirring to obtain a slurry with cation-modified surface.

[0029] Zirconium oxychloride octahydrate and citric acid monohydrate were dissolved in water, and the pH of the solution was adjusted after stirring to form a clear complex solution.

[0030] The surface-cation-modified slurry was pumped into the complex solution, stirred and mixed, and then urea was added to carry out a urea slow-release hydrolysis reaction, using a two-stage programmed temperature rise.

[0031] After the reaction was completed, the solid product was separated, washed with hot water, and then added with dilute ammonia to perform a complexation and copper removal operation.

[0032] The solid product after copper removal is washed with water until neutral, then dried and calcined in sequence, and finally cooled to obtain the final product.

[0033] By employing the above technical solution, the chemical reaction mechanism of this preparation method is essentially an in-situ interfacial assembly process relying on a combination of steric hindrance and electrostatic induction. During the dispersion stage, some amino groups on the surface of the amino-functionalized diatomaceous earth are protonated. With the addition of copper sulfate, locally free amino groups undergo coordination substitution with copper ions, the reaction being: R-NH2 + Cu 2+ →[R-NH2-Cu] 2+ This step creates positively charged cation anchoring centers on the originally weakly charged carrier surface.

[0034] Meanwhile, zirconium oxychloride octahydrate in the liquid phase is readily hydrolyzed, but it combines with citric acid monohydrate to form a polydentate complex, forcing the zirconium source to maintain a homogeneous and transparent state.

[0035] When the two phases are mixed and heated, the slow hydrolysis of urea causes a gradual increase in the local pH of the system. Under the influence of opposite charges, the free zirconium-citric acid complex in the liquid phase continuously migrates towards the positively charged copper ammonia modification site. Upon approaching this interface, the increased pH promotes the dissociation of the complex and immediate hydrolytic condensation, forming a zirconium hydroxide coating.

[0036] After coating and molding, exposing the adsorption sites buried inside becomes crucial. To address this, this method incorporates ammonia elution. Ammonia molecules, with their stronger spatial penetration and coordination capabilities, penetrate the deposition layer, replacing the bottom solid copper ions with soluble tetraammine copper complex ions. This reverse removal process, where metal ions are pre-placed at fixed sites and then forcibly eluted through coordination competition, leaves interconnected mesoporous defects within the active coating layer.

[0037] Finally, after calcination, the amorphous precursor is dehydrated and shaped, transforming into a zirconium oxide adsorption layer with abundant internal pore activity.

[0038] Preferably, the buffer solution is an acetate-sodium acetate buffer solution with a pH of 5.8; when forming a clear complex solution, the pH of the system is pre-adjusted to 5.0 using ammonia.

[0039] By employing the above technical solution, the pH of the buffer solution is pre-fixed at 5.8 to prevent the amino groups from spontaneously aggregating under strongly alkaline conditions or completely deactivating under extremely acidic conditions. Meanwhile, the complex solution is pre-adjusted to pH 5.0, which places the citric acid molecules in the system in a semi-dissociation critical state, preserving their stable binding force on zirconium ions without directly triggering precipitation. The mixing of these two solutions effectively maintains the transparency of the reaction system in the initial stage.

[0040] Preferably, the specific process parameters for the two-stage temperature ramp are as follows: first, the temperature is increased to 70°C at a rate of 3°C / min and stirred at a constant temperature for 1 hour, and then the temperature is increased to 95°C at a rate of 1°C / min and reacted at a constant temperature for 8 hours.

[0041] By employing the above technical solution, the heating rate of the system is directly related to the kinetics of urea decomposition and alkali removal. The first stage maintains a low temperature of 70°C, providing only the basic energy to trigger the minute decomposition of urea, allowing zirconium hydroxide to slowly form discrete primary crystal nuclei on the solid surface. Upon transitioning to a high temperature of 95°C, the system releases a large amount of ammonia, prompting the remaining free zirconium source to rapidly grow and densify based on the existing crystal nuclei. This variable-temperature exfoliation control strategy completely avoids the problems of bulk agglomeration and coating peeling that are easily caused by conventional isothermal boiling operations.

[0042] Preferably, the specific implementation method of the complexation copper removal operation is as follows:

[0043] The washed solid product was redispersed in deionized water at a solid-liquid ratio of 1 g to 5 to 10 ml. Dilute ammonia was added dropwise to adjust the pH of the slurry to 9.5 while stirring continuously. The complexed eluent was collected by centrifugation.

[0044] Repeat the complexation copper removal operation until the copper ion concentration in the final complexation eluent is below 1.0 mg / L.

[0045] By employing the above technical solution, the effective permeation concentration of free ammonia molecules is directly linked to the elution efficiency of copper ions in the underlying layer. At pH 9.5, the concentration of activated ammonia molecules in the liquid phase is within the optimal operating range. Through repeated pulping and dispersion, combined with physical centrifugation and chemical displacement by an alkaline eluent, copper complexes located deep within the interlayer can be forcibly extracted and diffused into the external phase solution. This is a key engineering step in constructing mesoporous defects.

[0046] Preferably, the process parameters for the drying process are drying at 105°C for 12 hours; and the process parameters for the calcination process are heating to 450 to 500°C in air at a heating rate of 5°C / min, and calcining at a constant temperature for 2.5 to 3 hours.

[0047] By adopting the above technical solution, 450 to 500℃ is the thermodynamic window period for the crystal transformation of amorphous zirconium hydroxide into monoclinic or tetragonal zirconium dioxide. Isothermal calcination within this range allows the internal stress generated by lattice rearrangement to further increase the microporosity of the material, while simultaneously eliminating the structural risk of densification of the porous framework due to overheating.

[0048] Preferably, the amino-functionalized diatomaceous earth needs to be prepared in advance before preparing the surface cation-modified slurry;

[0049] The preparation parameters for the amino-functionalized diatomaceous earth are as follows: the raw diatomaceous earth is activated and dried at 150°C for 2 to 4 hours, and then transferred to a reaction vessel containing 800 to 1500 ml of anhydrous toluene for dehydration; after cooling the system to 80 to 90°C, 3-aminopropyltriethoxysilane of the corresponding proportion is added dropwise under a protective atmosphere, and the reaction is carried out continuously for 4 to 6 hours, and then vacuum dried to constant weight.

[0050] By adopting the above technical solution, the initial high-temperature baking at 150℃ not only forces the drainage of capillary water from the tube bundle but also prevents the degradation and loss of surface-bound water (silanol groups). The subsequent use of a large amount of toluene solvent and a micro-heating state of 80 to 90℃ significantly reduces the kinematic viscosity of the reaction solution, allowing sterically hindered silane molecules to fully penetrate into the deep pores of diatomaceous earth for in-situ grafting reactions, rather than merely adhering to the outer surface of the particles.

[0051] This invention provides a zirconium-based adsorption composite material and its preparation method. It possesses the following beneficial effects:

[0052] 1. This invention constructs positively charged copper-ammonia coordination sites on the surface of diatomaceous earth using 3-aminopropyltriethoxysilane and copper sulfate. Simultaneously, citric acid is used to lock the zirconium source into a stable complex. Combined with the slow-release hydrolysis of urea to achieve alkali removal, the zirconium component is electrostatically guided to migrate to specific modification sites on the carrier surface for hydrolysis. This interface-induced deposition method effectively inhibits the disordered spontaneous nucleation of free zirconium ions in the liquid phase, avoiding local aggregation of active components, thereby forming a uniformly dispersed and strongly adherent zirconium-based active layer on the carrier surface.

[0053] 2. In this invention, after the zirconium-based precursor is coated and molded, the solid-phase product is eluted with dilute ammonia. The ammonia molecules undergo a coordination substitution reaction with copper ions at the interface, converting the copper ions, which serve as the initial induction centers, into soluble complexes and removing them from the system. This chemical removal operation generates interconnected mesoporous channels in situ within the active coating and at its interface with the carrier, opening up internal mass transfer pathways and significantly increasing the actual specific surface area and effective adsorption site density of the composite material.

[0054] 3. The preparation method of this invention introduces a two-stage programmed temperature rise process in the hydrolysis deposition stage. First, the initial reaction rate is controlled at a relatively low temperature of 70°C to achieve slow discrete nucleation of zirconium hydroxide. Then, urea decomposition is accelerated at 95°C to promote the continuous growth and stabilization of the deposition layer on the existing crystal nuclei. This control strategy, which thermodynamically separates the nucleation and growth stages, eliminates the risk of bulk agglomeration that is easily caused by conventional isothermal violent reactions, improves the structural uniformity of the surface coating layer, and ensures the structural stability of the adsorbent material in fluid applications. Attached Figure Description

[0055] Figure 1 Fourier transform infrared spectra of pure diatomite, the product of preparation example 2, and the final product of example 1 of this invention;

[0056] Figure 2 The N2 adsorption-desorption isotherms and pore size distribution diagrams are shown for the pure diatomaceous earth carrier of the present invention, the product of Example 1 and the product of Comparative Example 4, wherein (a) is the N2 adsorption-desorption isotherm and (b) is the corresponding BJH pore size distribution curve. Detailed Implementation

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0059] Diatomaceous earth, calcined grade, CAS number 61790-53-2. The diatomaceous earth used in this invention has a SiO2 mass fraction of not less than 85% and a BET specific surface area of ​​10-25 m². 2 / g, with a median particle size (D50) ranging from 10 to 50 μm.

[0060] 3-Aminopropyltriethoxysilane (APTES), with the molecular formula H2N(CH2)3Si(OC2H5)3 and CAS number 919-30-2, has a purity of not less than 98.0%.

[0061] Zirconium oxychloride octahydrate, industrial grade, with the molecular formula ZrOCl2·8H2O and CAS number 13520-92-8, contains no less than 35% ZrO2. The molar ratios of citric acid monohydrate to zirconium and urea to zirconium in the following examples are calculated based on the theoretical chemical formula of zirconium oxychloride octahydrate. During industrial scale-up, the feed amounts can be corrected based on the actual ZrO2 content reported in the raw material testing report.

[0062] Citric acid monohydrate, industrial grade, molecular formula C6H8O7·H2O, CAS number 5949-29-1.

[0063] Toluene, anhydrous grade, CAS number 108-88-3, with a water content not exceeding 50 ppm.

[0064] Copper sulfate pentahydrate, analytical grade, molecular formula CuSO4·5H2O, CAS number 7758-99-8.

[0065] Ammonia water, analytical grade, CAS number 1336-21-6, with a mass concentration of 25-28%.

[0066] Urea, analytical grade, molecular formula CO(NH2)2, CAS number 57-13-6.

[0067] In a specific embodiment of the present invention, based on 100.0g of diatomaceous earth, the amount of 3-aminopropyltriethoxysilane used is 2.0-6.0g, preferably 4.0g; the amount of anhydrous toluene used is 800-1500mL, preferably 1000mL. The diatomaceous earth is activated and dried at 150℃ for 2-4 hours; the aminosilanization reaction temperature is 80-90℃ for 4-6 hours.

[0068] In a specific embodiment of the present invention, based on 100.0g of amino-functionalized diatomaceous earth, the amount of copper sulfate pentahydrate is 1.57-2.70g; the amount of zirconium oxychloride octahydrate is 20.0-50.0g, preferably 35.0g; the molar ratio of citric acid monohydrate to zirconium is 1.29:1-1.50:1; and the molar ratio of urea to zirconium is 8.4:1-12.1:1.

[0069] In a specific embodiment of the present invention, the pH value of the acetate-sodium acetate buffer solution used for surface cation modification is 5.8; the pre-adjusted pH value of the zirconium-citric acid complex solution is 5.0; the pH value of the slurry in the complexation copper removal step is adjusted to 9.5; and the final washing is performed until the pH of the filtrate is 7.0±0.2.

[0070] In a specific embodiment of the present invention, the urea slow-release hydrolysis reaction adopts a two-stage programmed temperature increase: first, the temperature is increased to 70°C at 3°C / min and held for 1 hour, then the temperature is increased to 95°C at 1°C / min and held for 8 hours. The drying temperature is 105°C and the drying time is 12 hours; the calcination temperature is 450-500°C and the calcination time is 2.5-3 hours, with a heating rate of 5°C / min.

[0071] The component proportions provided in this invention are characterized by parts by weight. In each embodiment and preparation example, there is a direct proportional relationship between the actual amount of material added in grams and the parts by weight. Specifically, when the amount of the reference raw material diatomaceous earth is 100.0 grams, it corresponds to 100.0 parts by weight, that is, 1 part by weight is equivalent to 1 gram. The parts by weight values ​​of the other components are equivalently replaced and converted with this reference ratio and the actual number of grams added.

[0072] Preparation Examples 1-3:

[0073] Preparation Example 1:

[0074] This preparation example provides a method for preparing low-grafted amino-functionalized diatomaceous earth (DE-NH2-L), including the following steps:

[0075] Place 100.0g of diatomaceous earth in an oven and dry it at a constant temperature of 150℃ for 2 hours. After cooling to room temperature, it is ready for use.

[0076] The activated diatomaceous earth was transferred to a reactor equipped with a mechanical stirrer, thermometer, Dean-Stark water separator and reflux condenser, and 800 mL of anhydrous toluene was added.

[0077] Start stirring and heat to the toluene reflux temperature for azeotropic dehydration until no water is separated. Cool the system to 80°C and slowly add 2.0 g of 3-aminopropyltriethoxysilane under nitrogen protection.

[0078] After the addition was complete, the reaction continued at this temperature for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the product was filtered, and washed twice with anhydrous toluene.

[0079] The resulting filter cake was dried to constant weight in a vacuum oven at 80°C to obtain low-grafted amino-functionalized diatomaceous earth (DE-NH2-L).

[0080] Preparation Example 2:

[0081] This preparation example provides a method for preparing amino-functionalized diatomaceous earth (DE-NH2-M) with a moderate grafting amount, including the following steps:

[0082] Place 100.0g of diatomaceous earth in an oven and dry it at a constant temperature of 150℃ for 3 hours. After cooling to room temperature, it is ready for use.

[0083] The activated diatomaceous earth was transferred to a reactor equipped with a mechanical stirrer, thermometer, Dean-Stark water separator and reflux condenser, and 1000 mL of anhydrous toluene was added.

[0084] Start stirring and heat to the toluene reflux temperature for azeotropic dehydration until no water is separated. Cool the system to 85°C and slowly add 4.0 g of 3-aminopropyltriethoxysilane under nitrogen protection.

[0085] After the addition was complete, the reaction continued at this temperature for 5 hours. After the reaction was completed, the mixture was cooled to room temperature, the product was filtered, and washed three times with anhydrous toluene.

[0086] The resulting filter cake was dried to constant weight in a vacuum oven at 80°C to obtain amino-functionalized diatomaceous earth with a medium grafting amount (DE-NH2-M).

[0087] Preparation Example 3:

[0088] This preparation example provides a method for preparing high-grafted amino-functionalized diatomaceous earth (DE-NH2-H), including the following steps:

[0089] Place 100.0g of diatomaceous earth in an oven and dry it at a constant temperature of 150℃ for 4 hours. After cooling to room temperature, it is ready for use.

[0090] The activated diatomaceous earth was transferred to a reactor equipped with a mechanical stirrer, thermometer, Dean-Stark water separator and reflux condenser, and 1500 mL of anhydrous toluene was added.

[0091] Start stirring and heat to the toluene reflux temperature for azeotropic dehydration until no water is separated. Cool the system to 90°C and slowly add 6.0 g of 3-aminopropyltriethoxysilane under nitrogen protection.

[0092] After the addition was complete, the reaction was continued at this temperature for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, the product was filtered, and washed three times with anhydrous toluene.

[0093] The resulting filter cake was dried to constant weight in a vacuum oven at 80°C to obtain high-grafted amino-functionalized diatomaceous earth (DE-NH2-H).

[0094] Examples 1-6:

[0095] Example 1:

[0096] This embodiment provides a method for preparing a zirconium-based adsorption composite material with reference parameters, including the following steps:

[0097] Prepare 1000 mL of a 0.1 M acetate-sodium acetate buffer solution and adjust its pH to 5.8. Disperse 100.0 g of the amino-functionalized diatomaceous earth (DE-NH2-M) obtained from Preparation Example 2 in the buffer solution to form a homogeneous slurry.

[0098] While stirring continuously, 50 mL of deionized water solution containing 1.57 g of copper sulfate pentahydrate was slowly added dropwise. After the addition was complete, stirring was continued at room temperature for 45 minutes to obtain a slurry with cation-modified surface.

[0099] In another container, 35.0 g of zirconium oxychloride octahydrate was dissolved in 500 mL of deionized water, and 29.68 g of citric acid monohydrate was slowly added and stirred until completely dissolved to form a clear and transparent complex solution.

[0100] Under pH meter monitoring, dilute ammonia solution with a concentration of 1 mol / L (NH3) was slowly added dropwise to pre-adjust the pH of the complex solution to 5.0, keeping the solution clear during the adjustment process.

[0101] The aforementioned surface-modified slurry was pumped into the pH-pre-adjusted complex solution under vigorous stirring, and stirring was continued at room temperature for 1.5 hours.

[0102] Then, 55.45g of urea was added to the mixture. The reactor was heated using a two-stage temperature program.

[0103] Heat to 70°C at a rate of 3°C / min and stir at that temperature for 1 hour;

[0104] The temperature was then increased to 95°C at a rate of 1°C / min and kept at that temperature for 8 hours.

[0105] After the reaction is complete, allow the mixture to cool naturally, centrifuge to collect the solid material, and wash it repeatedly with 70°C hot deionized water until no white precipitate is detected in the washing liquid using 0.1M silver nitrate solution.

[0106] The washed filter cake was redispersed in deionized water at a solid-liquid ratio of 1g:5-10mL. Dilute ammonia solution with a concentration of 1mol / L (NH3) was slowly added dropwise under mechanical stirring to adjust the pH of the slurry to 9.5, and stirring was continued for 1.5 hours. This complexation copper removal operation was repeated, with redispersing and pH adjustment to 9.5 for each round. After each round of complexation, the slurry was centrifuged and the complexation eluent was collected until the copper ion concentration in the final complexation eluent was lower than 1.0mg / L (the retention rate of zirconium in the solid before and after the complexation copper removal treatment was found to be greater than 95%).

[0107] The slurry was then centrifuged and washed with deionized water until the pH of the filtrate reached 7.0. The washed filter cake was dried in an oven at 105°C for 12 hours, then placed in a muffle furnace and calcined at 450°C for 2.5 hours under air atmosphere at a rate of 5°C / min. It was then allowed to cool naturally to obtain the final product.

[0108] Example 2:

[0109] This embodiment provides a method for preparing a zirconium-based adsorption composite material with low zirconium loading, including the following steps:

[0110] Prepare 1000 mL of 0.1 M acetate-sodium acetate buffer solution and adjust its pH to 5.8.

[0111] 100.0 g of DE-NH2-M obtained from Preparation Example 2 was dispersed in the buffer solution, and 50 mL of deionized water containing 1.57 g of copper sulfate pentahydrate was slowly added dropwise. The mixture was stirred at room temperature for 45 minutes.

[0112] In another container, 20.0 g of zirconium oxychloride octahydrate was dissolved in 300 mL of deionized water, and 16.9 g of citric acid monohydrate was slowly added until dissolved. The pH of the complex solution was pre-adjusted to 5.0 dropwise with dilute ammonia solution with a concentration of 1 mol / L (NH3).

[0113] The aforementioned slurry was pumped into the complex solution and stirred at room temperature for 1.5 hours. Then, 31.6 g of urea was added. The temperature was increased to 70°C at 3°C / min and held for 1 hour; then increased to 95°C at 1°C / min and held for 8 hours.

[0114] After the reaction is complete, the solid is collected by centrifugation and washed with 70°C hot water until no chloride ions are present.

[0115] After dispersing the filter cake in water, the pH was adjusted to 9.5 with dilute ammonia solution (NH3 concentration 1 mol / L), and the mixture was stirred for 1.5 hours. The elution was repeated until the copper ion concentration in the final complexed eluent was below 1.0 mg / L. After centrifugation, the mixture was washed with deionized water until neutral.

[0116] The filter cake was dried at 105℃ for 12 hours, then calcined in a muffle furnace at 450℃ for 2.5 hours with the temperature increased at 5℃ / min, and then naturally cooled to obtain the final product.

[0117] Example 3:

[0118] This embodiment provides a method for preparing a zirconium-based adsorption composite material with high zirconium loading, including the following steps:

[0119] Prepare 1000 mL of 0.1 M acetate-sodium acetate buffer solution and adjust its pH to 5.8.

[0120] 100.0 g of DE-NH2-M obtained from Preparation Example 2 was dispersed in the buffer solution, and 50 mL of deionized water containing 1.57 g of copper sulfate pentahydrate was slowly added dropwise. The mixture was stirred at room temperature for 45 minutes.

[0121] In another container, 50.0 g of zirconium oxychloride octahydrate was dissolved in 750 mL of deionized water, and 42.3 g of citric acid monohydrate was slowly added until dissolved. The pH of the complex solution was pre-adjusted to 5.0 dropwise with dilute ammonia solution with a concentration of 1 mol / L (NH3).

[0122] The aforementioned slurry was pumped into the complex solution and stirred at room temperature for 1.5 hours. Then, 79.1 g of urea was added. The temperature was increased to 70°C at 3°C / min and held for 1 hour; then increased to 95°C at 1°C / min and held for 8 hours.

[0123] The subsequent water washing, copper complexation removal, and water washing neutralization steps are the same as in Example 1.

[0124] The filter cake was dried at 105℃ for 12 hours, then calcined in a muffle furnace at 450℃ for 2.5 hours with the temperature increased at 5℃ / min, and then naturally cooled to obtain the final product.

[0125] Example 4:

[0126] This embodiment provides a method for preparing a zirconium-based adsorption composite material with a high proportion of surface cation modification, including the following steps:

[0127] Prepare 1000 mL of 0.1 M acetate-sodium acetate buffer solution and adjust its pH to 5.8. Disperse 100.0 g of DE-NH2-M obtained from Preparation Example 2 in the buffer solution, and slowly add 50 mL of deionized water solution containing 2.70 g of copper sulfate pentahydrate. Stir at room temperature for 45 minutes.

[0128] In another container, dissolve 35.0 g of zirconium oxychloride octahydrate in 500 mL of deionized water, add 29.68 g of citric acid monohydrate until dissolved, and pre-adjust the pH to 5.0 dropwise with 1 M dilute ammonia.

[0129] The aforementioned slurry was pumped into the complex solution, stirred for 1.5 hours, and then 55.45g of urea was added.

[0130] The temperature was increased to 70℃ at 3℃ / min and held for 1 hour, and then increased to 95℃ at 1℃ / min and held for 8 hours.

[0131] The subsequent washing, copper removal with ammonia, drying and calcination steps (calcination at 450℃ for 2.5 hours) were exactly the same as in Example 1.

[0132] Example 5:

[0133] This embodiment provides a method for preparing zirconium-based adsorption composite materials under conditions of strong chelation and high proportion of hydrolysate, including the following steps:

[0134] Prepare 1000 mL of 0.1 M acetate-sodium acetate buffer solution and adjust its pH to 5.8. Disperse 100.0 g of DE-NH2-M obtained from Preparation Example 2 in the buffer solution, add 50 mL of deionized water containing 1.57 g of copper sulfate pentahydrate, and stir for 45 minutes.

[0135] In another container, 35.0 g of zirconium oxychloride octahydrate was dissolved in 500 mL of deionized water, and 34.2 g of citric acid monohydrate was added until completely dissolved. The molar ratio of citric acid monohydrate to zirconium was approximately 1.50:1. The pH was pre-adjusted to 5.0 dropwise with 1 mol / L dilute ammonia solution (NH3 concentration).

[0136] The aforementioned slurry was pumped into the complex solution and stirred for 1.5 hours.

[0137] 78.3g of urea was added, with a molar ratio of urea to zirconium of approximately 12.0:1. The same temperature program was used for the reaction, and the subsequent washing, copper removal by complexation, drying, and calcination at 450°C were exactly the same as in Example 1.

[0138] Example 6:

[0139] This embodiment provides a method for preparing zirconium-based adsorption composite materials with high calcination temperature, including the following steps:

[0140] The initial feeding, mixing, controlled-release hydrolysis, washing, and complexation to remove copper until drying steps in this embodiment are exactly the same as in Example 1 (using 100.0g DE-NH2-M, 1.57g copper sulfate pentahydrate, 35.0g zirconium oxychloride octahydrate, 29.68g citric acid monohydrate and 55.45g urea).

[0141] The thoroughly washed and dried filter cake is placed in a muffle furnace and heated to 500°C at a rate of 5°C / min under air atmosphere and calcined at a constant temperature for 3 hours, then naturally cooled to obtain the final product.

[0142] Comparative Examples 1-6:

[0143] Comparative Example 1:

[0144] Compared with Example 1, the difference is that no surface amination modification and surface cation modification steps were performed, and an equal amount of unmodified original diatomaceous earth was used directly as the carrier, while all other aspects are the same.

[0145] Comparative Example 2:

[0146] Compared with Example 1, the difference is that the surface cation modification and nucleation site induction steps were omitted (i.e., copper sulfate pentahydrate solution was not added), and the prepared amino-functionalized diatomaceous earth was directly mixed with the zirconium precursor solution. All other aspects were the same.

[0147] Comparative Example 3:

[0148] Compared with Example 1, the difference is that citric acid monohydrate was not added for chelation during the preparation of the zirconium precursor solution, and pH pre-adjustment was not performed to maintain clarity; the zirconium oxychloride octahydrate aqueous solution was directly mixed with the surface modification slurry, and then urea was added and the temperature was programmed as in Example 1, with other post-treatment steps being the same.

[0149] Comparative Example 4:

[0150] Compared with Example 1, the difference is that urea was not added and the corresponding temperature-programmed reaction was cancelled. Instead, after mixing, the pH of the system was quickly adjusted to 9.0 by adding dilute ammonia water dropwise to induce rapid precipitation. After stirring at room temperature for 1.5 hours, solid-liquid separation was carried out. The remaining washing, copper complexation removal, drying and calcination steps were the same.

[0151] Comparative Example 5:

[0152] Compared with Example 1, the difference is that the complexation-targeted copper removal step in the post-processing is omitted, and after centrifugation, it is only washed with hot deionized water until neutral. Everything else is the same.

[0153] Comparative Example 6:

[0154] Compared with Example 1, the difference is that the entire synergistic control mechanism of carrier amination, surface copper modification, citric acid prechelation and urea slow-release hydrolysis was omitted. Instead, 100.0g of unmodified raw diatomaceous earth was directly impregnated in a zirconium salt aqueous solution prepared by 35.0g of zirconium oxychloride octahydrate and 500mL of deionized water. After stirring and evaporating to dryness, it was directly put into the subsequent drying and calcination process. All other processes were the same.

[0155] Test Examples 1-6:

[0156] Test Example 1:

[0157] This test case mainly examines the physicochemical processes related to support surface modification and coordination-induced nucleation. The specific experimental steps are as follows:

[0158] Sample pretreatment and Fourier transform infrared spectroscopy.

[0159] Take an appropriate amount of pure diatomaceous earth carrier that has been vacuum dried at 105℃ to constant weight, amino-functionalized diatomaceous earth obtained in Preparation Example 2, and the composite material finally prepared in Example 1. Mix them with potassium bromide at a mass ratio of 1:100 and grind them in an agate mortar. Press them into translucent sheets using a tablet press under a pressure of 10 MPa.

[0160] Using Fourier transform infrared spectroscopy in the range of 400 to 4000 cm⁻¹ -1 Transmission scanning was performed within the wavenumber range to record the vibrational absorption spectra of surface functional groups of the samples at each stage.

[0161] Zeta potential test.

[0162] 50.0 mg of pure diatomaceous earth carrier, amino-functionalized diatomaceous earth obtained in Preparation Example 2, and intermediate slurry extract after surface cation modification in Example 1 (the extract was separated by centrifugation and freeze-dried) were weighed out respectively. The above powders were added to 50 mL of sodium chloride background electrolyte solution with a concentration of 0.01 mol / L and ultrasonically dispersed for 10 minutes.

[0163] The pH of the suspension was adjusted to 5.8 using dilute hydrochloric acid and dilute sodium hydroxide, and then injected into a capillary electrophoresis tank. The average potential value was recorded by measuring the potential three times in parallel at 25°C using a Zeta potentiometer.

[0164] X-ray photoelectron spectroscopy analysis.

[0165] Pure diatomaceous earth, the product of Preparation Example 2, the surface-modified intermediate material of Example 1, and the final calcined product of Example 1 were selected as the test samples. The powder samples were pressed into tablets, fixed onto conductive tape, and then sent into the high-vacuum analysis chamber of an X-ray photoelectron spectroscopy (XPS) instrument. Monochromatic AlKα rays were used as the excitation source.

[0166] After completing the broad-spectral scan, narrow-region high-resolution scans were performed on the C1s, N1s, Cu2p, and Zr3d orbitals. The test spectra were charged using the C1s main peak of contaminated carbon (with a binding energy calibrated to 284.8 eV), and peak fitting was performed using a Gaussian-Lorentz mixture function.

[0167] Table 1. Surface charge and XPS binding energy parameters of pure support and products at each stage

[0168]

[0169] Note: "--" in the table indicates that the characteristic signal of the corresponding element was not detected under the test conditions.

[0170] Figure 1These are Fourier transform infrared spectra of the pure diatomaceous earth, the product of Preparation Example 2, and the final product of Example 1. The solid black line represents the pure diatomaceous earth carrier, the dashed blue line represents the amino-functionalized diatomaceous earth obtained in Preparation Example 2, and the dotted red line represents the zirconium-based adsorption composite material finally prepared in Example 1.

[0171] Experimental conclusions: Combining Table 1 and Figure 1 The data indicates that the chemical modification of the diatomaceous earth support surface and the subsequent coordination induction process occurred largely as expected. The original diatomaceous earth support exhibited the conventional characteristics of a silica matrix in the Fourier transform infrared spectrum, specifically at 1080 cm⁻¹. -1 Nearby Si-O-Si stretching vibrations and 3450 cm -1 The characteristic peaks of silanol groups and adsorbed water are observed at the location.

[0172] Because the silanol groups on the surface readily dissociate spontaneously in an aqueous environment, the measured Zeta potential of pure diatomaceous earth in the test system was -23.4 mV. After APTES modification, the infrared spectrum of the sample prepared in Example 2 showed an additional 2920 cm⁻¹. -1 CH vibration at 1560cm -1 The NH bending vibration signal at the location indicates that the aminosilane has been chemically bonded into the network structure of the support. This replacement of surface groups directly changes the surface charge state of the particles, with the Zeta potential turning into a positive value of +15.7 mV, which is also confirmed by the N1s binding energy signal of 399.6 eV appearing in the XPS analysis.

[0173] The introduction of copper sulfate for surface modification altered the local electronic environment of the amino group. Experiments recorded that the Zeta potential of the intermediate slurry extract from Example 1 increased to +31.2 mV, with the increase in surface positive charge density corresponding to copper ion fixation. XPS high-resolution spectroscopy data showed that the binding energy of N1s shifted from 399.6 eV to 400.3 eV towards higher binding energies. This chemical shift towards higher binding energies is typically interpreted in studies as the lone pair of electrons on the amino nitrogen atom participating in the binding with Cu. 2+ The coordination effect of the copper ions leads to a decrease in the electron cloud density outside the nitrogen atom nucleus. This energy spectrum change does not support the explanation that the copper ions are merely physically attached to the support surface, indicating that there is a coordination effect between the copper ions and the amino regions on the support surface, which in turn facilitates the formation of active coordination regions that can provide electrostatic attraction and nucleation targets.

[0174] At the end of the preparation process, the infrared spectrum of the final product of Example 1 was at 550 cm⁻¹. -1The presence of vibrational features of Zr-O bonds nearby indicates that zirconium species have been generated and loaded onto the support. The binding energy of Zr3d in the product is 182.4 eV, indicating that the supported phase exists in a relatively stable zirconium oxide form. Table 1 shows that after complexation elution, no Cu2p characteristic signals were detected on the surface of the final product under XPS detection conditions, indicating that the detectable copper species on the surface have been reduced to below the XPS detection limit; trace bulk phase residues can be further quantitatively confirmed by ICP-OES. These test results support the reaction pathway of precursor nucleation and growth guided by surface coordination sites in the early stages of preparation, in different dimensions.

[0175] Test Example 2:

[0176] This test case aims to verify the in-situ slow-release growth mechanism under steric hindrance control proposed in this invention by analyzing the pore structure and phase composition of the material.

[0177] N2 adsorption-desorption isotherm testing. Pure diatomaceous earth support, the final products of Example 1 and Comparative Example 4 were selected as test objects. Approximately 0.1 g of sample was placed in a sample tube and vacuum degassed at 200°C for 6 hours to remove physically adsorbed moisture and impurities.

[0178] Subsequently, the sample tubes were transferred to a fully automated physical adsorption instrument, where nitrogen adsorption and desorption tests were performed at 77K (liquid nitrogen). The relative pressure (P / P0) was recorded from 10... -5 The adsorption amount varies within the range of 0.995.

[0179] The specific surface area of ​​the samples was calculated using the Brunauer-Emmett-Teller (BET) multi-point method. The desorption branch data were processed using the Barrett-Joyner-Halenda (BJH) model to calculate the total pore volume and pore size distribution.

[0180] X-ray diffraction (XRD) analysis. Pure diatomaceous earth carrier, the final product powder of Example 1 (calcined at 450℃) and Example 6 (calcined at 500℃) were lightly ground in an agate mortar and then spread evenly and compacted in the sample trough.

[0181] Phase analysis was performed using a powder X-ray diffractometer equipped with a CuKα radiation source (λ=0.15406nm), with tube voltage and tube current set to 40kV and 40mA, respectively.

[0182] The scanning range of the diffraction angle 2θ is 10° to 80°, the scanning step size is 0.02°, and the scanning rate is 5° / min.

[0183] Table 2. Pore structure parameters and phase analysis of pure carriers and materials obtained by different preparation methods

[0184]

[0185] Figure 2 This is an N2 adsorption-desorption isotherm and pore size distribution diagram of the pure diatomaceous earth carrier of this invention, the product of Example 1, and the product of Comparative Example 4. Figure 2 (a) is the N2 adsorption-desorption isotherm. Figure 2 (b) shows the corresponding BJH pore size distribution curve; the solid line in the figure represents the pure diatomaceous earth carrier, the dashed line represents the product of Example 1, and the dotted line represents the product of Comparative Example 4.

[0186] In Table 2 above, This represents the specific surface area calculated using the BET method. This represents the total pore volume calculated at a relative pressure P / P0≈0.995. This represents the average pore size or peak value of the pore size distribution calculated using the BJH desorption branch.

[0187] Experimental conclusions: According to the data in Table 2, the pore structure parameters of the materials showed significant differences under different preparation methods. The original diatomaceous earth support, as a porous substrate, had a pore structure of 24.7 μm. 2 Specific surface area per g and 0.28 cm² 3 / g total pore volume. The product of Example 1, after being loaded with zirconium species, not only did not decrease in specific surface area, but actually increased significantly to 138.3m². 2 / g, while the total pore volume only decreased slightly to 0.23cm. 3 / g. This increase in specific surface area serves as important evidence that the active components are loaded onto the inner walls of the carrier pores in the form of highly dispersed nanoparticles or thin layers, rather than mainly blocking the pores with large-sized aggregates; the newly added nanostructures themselves contribute a huge amount of external surface area, and their increase exceeds the area lost due to occupying part of the pore space.

[0188] In stark contrast, the product of Comparative Example 4, prepared by the rapid precipitation method, exhibited a sharp decrease in specific surface area to 11.9 m². 2 / g, and the total pore volume also shrank to 0.09cm. 3 / g. This result indicates that, in the absence of synergistic control by citric acid chelation and urea slow-release hydrolysis, zirconium ions are prone to uncontrolled rapid nucleation and growth. The resulting zirconium hydroxyl precursors and the zirconium oxide aggregates formed after calcination easily block the original mesoporous channels of diatomaceous earth, leading to deterioration of the material's texture properties. This difference in pore structure is evident in... Figure 2 This is more intuitively demonstrated in the N2 adsorption-desorption behavior.

[0189] Figure 2(a) shows that the product of Example 1, like the pure support, exhibits a typical Type IV isotherm and an H3 hysteresis loop, indicating that the mesoporous structure of the material is well preserved. However, the isotherm of Comparative Example 4 shows extremely low overall adsorption capacity, with the hysteresis loop almost disappearing, tending towards the Type II isotherm characteristics of a non-porous solid. Figure 2 (b) Looking at the pore size distribution curve, the pore size distribution peak shape of Example 1 is similar to that of the pure carrier, with only the peak position slightly shifted to the left, while the pore size distribution curve of Comparative Example 4 is almost flattened and loses the concentrated pore distribution characteristics.

[0190] Furthermore, XRD phase analysis provides another dimension of support for the slow-release growth mechanism. Table 2 shows that under calcination at 450℃, the supported phase in Example 1 is mainly amorphous, indicating that the controlled slow hydrolysis process inhibits further growth and crystallization of the nuclei. When the calcination temperature is increased to 500℃ (Example 6), the amorphous phase begins to transform into the more crystalline tetragonal ZrO2 phase, and the specific surface area also decreases slightly, which is consistent with the general law of crystallization and particle growth during calcination. These comparative data collectively demonstrate that the preparation method of the present invention can effectively control the growth mode of the active component, which is conducive to achieving high dispersion and amorphous loading on the surface of the support, thereby better preserving and utilizing the pore structure of the support, which is consistent with the in-situ growth process under steric hindrance control.

[0191] Test Example 3:

[0192] This test case mainly analyzes the content of specific metal elements in the product, verifies the problem of residual directing agent introduced in the coordination-induced nucleation mechanism, and the actual separation efficiency of the ammonia-targeted complexation copper removal process.

[0193] Microwave digestion of solid samples.

[0194] Accurately weigh 0.1000 g of the final product powder dried to constant weight at 105 °C, including samples from Examples 1, 3, and 4, and Comparative Example 5 (without ammonia elution), and place them separately in polytetrafluoroethylene digestion vessels. Add 6.0 mL of concentrated nitric acid and 2.0 mL of hydrofluoric acid sequentially to each vessel. After sealing, place them in a microwave digester and heat to 190 °C using a programmed temperature rise mode, maintaining the temperature for 30 minutes to completely dissolve the solid matrix. After digestion, remove the acid to near dryness on a hot plate at 150 °C. After cooling, dilute to a volumetric flask with 2% (v / v) dilute nitric acid and mix well before analysis.

[0195] Element concentration determination and calculation.

[0196] In the copper removal process of this embodiment, the supernatant after ammonia washing and centrifugation was collected, filtered through a 0.45 μm aqueous microporous membrane, and an appropriate amount of the filtrate was acidified with nitric acid. The mass concentrations of Cu and Zr in the digest and liquid samples were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). A series of concentration gradients containing mixed Cu and Zr standard solutions were prepared before testing to establish a standard curve. Based on the measured concentrations and corresponding dilution factors, the actual mass fraction of elements in the solid products at each stage was calculated.

[0197] Table 3. Elemental mass fractions in the final composite solid powder under different processing techniques

[0198]

[0199] Experimental Conclusion: According to the data in Table 3, 0.3842% copper residue was detected in the solid product of Comparative Example 5 without targeted complexation elution treatment. This phenomenon corresponds to the coordination binding state revealed in the previous spectroscopic tests, indicating that the copper ions introduced as nucleation guides can coordinate and fix with the amino regions on the support surface in the early stage of preparation, and that some copper species remain in the solid product after subsequent treatment even without complexation elution treatment. This result shows that conventional hot pure water washing processes are insufficient to completely remove copper species that are strongly bound to the support surface or embedded in the solid structure, resulting in some copper residue within the material framework. In actual water treatment projects, the adsorbent material itself carrying and potentially releasing heavy metal components is a secondary pollution risk that needs to be addressed at the source.

[0200] Taking advantage of the strong coordination affinity of free ammonia molecules in aqueous solution, a competitive displacement reaction was incorporated into the subsequent separation process. The test results of the example samples reflect the effectiveness of this displacement process. After the introduction of dilute ammonia, the copper residue in the solid powder decreased significantly, with the content in Example 1 dropping to 0.0416%. During the mass exchange process at the liquid-solid interface, free ammonia in the system can form soluble copper-ammonia complexes with copper ions, allowing some copper ions originally bound to the amino regions on the carrier surface to enter the liquid phase. This significantly reduces the copper residue in the solid product and facilitates the release of surface coordination sites.

[0201] Assessing the rationality of this impurity removal process requires examining its degree of disturbance to the structure of the active component. Comparing the zirconium content (8.083% and 8.115%) of Example 1 and Comparative Example 5 in Table 3, it can be seen that the zirconium content in the solid changes little before and after the complexation copper removal treatment, indicating that the target supported phase has high stability in this alkaline complexation environment. The amorphous zirconium oxide has a low dissolution rate under complexation elution conditions at around pH 9.5, and its tendency to form soluble complexes with ammonia is significantly weaker than that of copper ions. The difference in thermodynamic and kinetic properties between the precursor directing agent and the target supported phase constitutes the basis for the selectivity of the targeted impurity removal process. This complexation elution method targeting nucleation inducing agents significantly reduces copper residue in the final product, reduces the risk of secondary pollution caused by nucleation directing agent residue, and basically preserves the zirconium-based active layer structure formed by controlled growth, supporting the closed-loop process of this preparation scheme from the perspective of composition control.

[0202] Test Example 4:

[0203] This test case mainly evaluates the actual impact of different preparation routes on the exposure of active sites and interfacial mass transfer performance of composite materials through equilibrium adsorption experiments of the target pollutant (phosphate).

[0204] A phosphate stock solution was prepared using potassium dihydrogen phosphate, and after dilution, a series of test solutions with initial phosphorus concentrations of 10.5, 25.2, 51.8, 103.6, 205.1, and 308.5 mg / L were obtained. The phosphorus concentrations were all expressed as P. The initial pH of each solution was finely adjusted to 6.0 by adding dilute hydrochloric acid or sodium hydroxide solution dropwise using a microsyringe.

[0205] Accurately weigh 0.0500 g of each sample powder that has been ground and sieved. The experimental subjects include the products of Examples 1, 2, and 3, as well as Comparative Examples 1, 2, and 6. Add the powder to stoppered conical flasks containing 50 mL of the above-mentioned phosphate solutions of different initial concentrations.

[0206] Place the conical flask in a constant temperature water bath shaker, set the water bath temperature to 25℃ and the rotation speed to 150 r / min, and shake continuously for 24 hours to ensure that the solid and liquid phases fully reach thermodynamic adsorption equilibrium.

[0207] After adsorption, a portion of the suspension was filtered through a 0.22 μm pore size polyethersulfone aqueous microporous membrane to remove solid particles. The remaining phosphorus concentration in the filtrate was determined at 700 nm using the molybdenum-antimony spectrophotometric method, expressed as P. The solid-phase adsorption capacity under each equilibrium state was calculated based on the difference in liquid phase concentration before and after the experiment. The theoretical maximum monolayer equilibrium adsorption capacity was determined by nonlinear fitting of the experimentally measured discrete data using the Langmuir isotherm model.

[0208] Table 4. Langmuir isotherm adsorption fitting parameters for phosphate in water for each sample

[0209]

[0210] Experimental Conclusions: According to the data in Table 4, there are significant differences in the affinity and saturation adsorption limit of different material configurations for phosphate in the aqueous phase. In conventional adsorption material preparation systems, the pursuit of high metal loading often results in severe agglomeration and deactivation of the active phase. Comparative Example 6, using the traditional direct impregnation and drying process, even with the addition of an equal amount of zirconium precursor, only achieved a maximum fitted adsorption capacity of 15.42 mg P / g. This crude physical deposition approach easily leads to non-uniform enrichment of zirconium species on the outer surface or pores of the support, and the formation of large zirconium oxide agglomerates during drying and calcination. This not only blocks the abundant mesoporous channels inside the diatomaceous earth, but also causes most of the surface hydroxyl groups that should participate in coordination exchange reactions to be buried deep inside the bulk. The sharp increase in mass transfer resistance makes it difficult for liquid contaminants to penetrate, and the actual surface sites that can effectively contact phosphate are extremely few.

[0211] When a partial stepwise modification process is introduced but the core control link is removed, the improvement in material adsorption efficiency is still limited. In Comparative Example 1, due to the lack of an underlying covalent silanization network, some zirconium species may struggle to form stable and uniform interfacial bonds on the support surface, leading to some loss or aggregation during washing, solid-liquid separation, or heat treatment. Its adsorption capacity remained at 23.18 mg P / g. In Comparative Example 2, due to the lack of surface cation modification and electrostatic attraction and nucleation guidance, the zirconium complexes in solution are more likely to detach from the support interface. This may result in homogeneous nucleation in the liquid phase or relatively disordered deposition on the diatomaceous earth surface, forming relatively large particles. The maximum adsorption capacity measured was 25.86 mg P / g.

[0212] Based on the above pore structure and adsorption capacity results, it can be inferred that materials with insufficiently developed internal pores and uneven surface component distribution are more prone to mass transfer hindrance when dealing with high pollution loads, making it difficult for internal active sites to be utilized efficiently.

[0213] This invention presents a preparation pathway that utilizes interface-induced nucleation and controlled-release crystallization kinetics. The theoretical maximum adsorption capacity of Example 1 increased to 46.85 mg P / g, approximately three times that of Comparative Example 6. Within the same reaction vessel, pre-placed coordination islands constrained the free diffusion of newly formed crystal nuclei. Subsequently, the gentle alkalinization environment provided by the thermal decomposition of urea forced the hydrolysis reaction to proceed in sterically hindered, in-situ controlled-release growth centered on these discrete sites. This constrained growth mode facilitates the dispersion of active zirconium species at the nanoscale within the carrier network, expanding the solid-liquid contact boundary and allowing for more complete exposure of surface-active hydroxyl groups.

[0214] The test data show that the adsorption capacity of Examples 1 to 3 exhibits a stable positive correlation with the increase of the zirconium source addition ratio, with Example 3 reaching a high of 59.27 mg P / g. This indicates that within the established interface-induced and spatially controlled release framework, the increase of the active metal phase does not show a significant agglomeration and decay trend, and the material as a whole possesses engineering operability for adjusting the adsorption capacity according to specific operating conditions and loads.

[0215] Test Example 5:

[0216] This test case mainly examines the influence of the unobstructedness of the internal pores of the composite material and the spatial distribution of active sites on the liquid phase mass transfer kinetics by monitoring the adsorption amount of the solid-liquid contact over time.

[0217] Prepare a phosphate test solution with an initial phosphorus concentration of 50.0 mg / L (P). Use a microsyringe to fine-tune the pH of the system and maintain it at 6.0 ± 0.1 as the kinetic adsorption base solution.

[0218] Accurately weigh 0.1000g of the sample powder from Examples 1, Comparative Example 2, and Comparative Example 6, which has been ground and uniformly sieved to 100-200 mesh. Quickly add each group of powder into a conical flask containing 100mL of the above-mentioned base liquid, and immediately place the conical flask in a constant temperature water bath shaker at 25°C and start continuous shaking at a speed of 200r / min.

[0219] Sampling time points were set at 5, 15, 30, 60, 120, 240, 480, 720, and 1440 minutes. At each set time point, 1.0 mL of the suspension was rapidly drawn and filtered using a syringe equipped with a 0.45 μm polyethersulfone filter membrane. The sampling process was completed within 30 seconds to minimize time errors. No original solution was added after sampling, and the cumulative sampling volume was used to correct for the adsorption capacity at different time points.

[0220] The phosphorus concentration in the filtrate at each time point was determined by the molybdenum-antimony spectrophotometric method, expressed as P. The instantaneous adsorption capacity at different contact times was calculated using the material balance equation, and nonlinear fitting analysis of the discrete time-concentration data was performed using pseudo-first-order and pseudo-second-order kinetic models to evaluate the rate-determining step and mass transfer rate constant.

[0221] Table 5. Kinetic fitting parameters of phosphate in water for each sample

[0222]

[0223] Experimental Conclusions: According to the data in Table 5, the adsorption rates of the various samples after contact with the phosphate solution exhibited orders-of-magnitude differentiation, indicating that the internal texture properties of the material had a controlling influence on the liquid-phase mass transfer process. The coefficients of determination for the kinetic data of the three samples in the pseudo-second-order model were all higher than those in the corresponding pseudo-first-order model, suggesting that the phosphate removal process within the system is limited by the chemisorption steps at the solid-liquid interface. Specifically, this manifests as coordination exchange between phosphate ions in the solution and zirconium hydroxyl groups on the support surface, forming an inner-layer complex. In this type of chemically bond-dependent reaction, the ability of reactants to reach the effective active sites rapidly and without hindrance becomes crucial in determining the overall macroscopic rate.

[0224] An examination of the pseudo-second-order kinetic constant revealed that Comparative Example 6, using the direct impregnation-drying method, not only had a low equilibrium capacity but also an adsorption rate constant of only 0.00115 g / (mg·min). In continuous flow adsorption bed applications, pore blockage within the material typically increases the risk of premature breakthrough. Due to the lack of nucleation growth regulation, the zirconia aggregates formed on the surface of Comparative Example 6 easily blocked some of the originally open mesoporous channels of diatomaceous earth. Phosphate ions in the aqueous phase needed to overcome significant intraparticle diffusion resistance to reach available zirconium hydroxyl sites. This mass transfer limitation resulted in a slow ramp-up of adsorption capacity over a prolonged period; the macroscopic test data for this material did not fully stabilize even after more than 720 minutes.

[0225] Although the reaction rate of Comparative Example 2, which had its underlying silane network anchored, increased to 0.00287 g / (mg·min), the aggregates formed by homogeneous crystallization still retained a considerable portion of the pore volume in the absence of electrostatic induction sites, and the liquid-phase mass transfer channels were not completely opened. Example 1, which constructed a complete interface-induced nucleation and steric hindrance-controlled pathway, saw its kinetic constant jump to 0.01043 g / (mg·min), approximately nine times that of Comparative Example 6. Under this controlled growth mechanism, nanoscale amorphous zirconium species could be dispersed relatively uniformly at the carrier interface and within the pores, and the main mesoporous channels of the diatomaceous earth maintained good connectivity. Pollutant molecules in the liquid phase could diffuse along the concentration gradient into the deeper layers of the particles and rapidly undergo coordination exchange reactions with the exposed active sites on the inner wall.

[0226] Observing the reaction time span, Example 1 shows a steep increase in adsorption capacity in the initial contact stage, and rapidly approaches the kinetic equilibrium adsorption capacity in about 120 minutes. In actual water treatment engineering selection, this adsorbent material with high initial mass transfer flux is beneficial to reducing the contact residence time requirement and provides a material basis for reactor miniaturization design.

[0227] Test Example 6:

[0228] This test case mainly evaluates the structural stability of the composite material under alkaline elution environment and the resistance to loss of the active supported phase through continuous adsorption-desorption cycle regeneration experiments, and verifies the stabilizing effect of silanization-induced confined supported structure and Zr-O-Si interface bonding on the amorphous zirconium phase.

[0229] Prepare at least 4.0 L of phosphate test solution with an initial phosphorus concentration of 20.0 mg / L (calculated as P), and adjust the pH to 6.0. Accurately weigh 0.1000 g of sample powder from Example 1, Comparative Example 1, and Comparative Example 6, and place them in separate 500 mL blue-capped reagent bottles, adding 250 mL of phosphate test solution to each. Place the reagent bottles in a 25°C constant-temperature shaker and shake at 180 rpm for 12 hours.

[0230] After solid-liquid separation, a suitable amount of the supernatant was taken and the phosphate concentration was determined using the molybdenum-antimony spectrophotometric method. The unit adsorption capacity for that cycle was calculated based on the actual mass of the dried solid before the adsorption cycle. The remaining solid-liquid mixture was centrifuged at high speed to collect the bottom solid powder, and then rinsed once with a small amount of deionized water to remove any residual free waste liquid on the surface.

[0231] The collected solid powder was transferred to a new conical flask, and 100 mL of 0.5 mol / L sodium hydroxide solution was added as the desorbent. Desorption was carried out by shaking for 4 hours under the same temperature and rotation speed. After desorption, the supernatant was collected by centrifugation, and the bottom layer of regenerated solid powder was repeatedly washed with deionized water until the pH of the eluent was neutral. The eluent was then placed in a 60℃ vacuum drying oven to constant weight, reserved for the next round of phosphate adsorption. The above adsorption-desorption process was repeated a total of 5 times, with 250 mL of fresh phosphate test solution added in each round.

[0232] The alkaline supernatant generated from each desorption step of each sample was collected, filtered through a 0.22 μm filter membrane, and then acidified with an appropriate amount of nitric acid. The concentration of free zirconium (Zr) in the desorption solution of each cycle was determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the cumulative Zr concentration in the desorption solution of each cycle was calculated over five cycles. If it is necessary to calculate the total zirconium loss, the concentration of each cycle was further multiplied by the corresponding desorption solution volume before conversion.

[0233] Table 6. Capacity decay and elemental leakage analysis of each sample during 5 adsorption-desorption cycles.

[0234]

[0235] Experimental Conclusion: According to the data in Table 6, different preparation routes directly determine the service life of the composite material under strong alkaline regeneration conditions. In actual industrial wastewater treatment systems, the regeneration frequency of the adsorption bed and the replacement cycle of the packing material are the core parameters for calculating operating costs. The shedding of active components not only leads to an irreversible decrease in adsorption performance but also causes secondary pollution as it enters downstream processes with the effluent.

[0236] Comparative Example 6, prepared by the physical impregnation method, showed a significant decline in capacity after the first desorption, with a capacity retention of only 25.18% by the fifth cycle. Combined with the desorption solution test results, it was found that the cumulative Zr concentration in the desorption solution over the five cycles reached a high of 12.834 mg / L. Since bulk zirconium oxide may primarily adhere to the diatomaceous earth surface through relatively weak physical interfacial interactions, the oscillating shearing action during desorption and the chemical action of high-concentration hydroxide ions easily disrupt these interfacial bonds, leading to a significant loss of the active phase.

[0237] Comparative Example 1, which employed stepwise precipitation but stripped the underlying APTES silanization reaction, showed improved initial adsorption capacity. However, under continuous cyclic shock, the material still exhibited significant fatigue degradation, with a retention rate of less than 50% in the fifth cycle, and a cumulative Zr concentration of 7.412 mg / L in the desorption solution after five cycles.

[0238] The lack of a covalently bonded network means that the assembly of precursors on the carrier surface largely depends on electrostatic adsorption or non-directional local precipitation. This relatively unstable bonding mode is unable to withstand repeated liquid-phase ion diffusion and the scouring effect of alkaline desorption solutions. As a result, zirconium species that are not effectively anchored on the surface gradually migrate into the liquid phase with each cycle, manifested as an increase in the cumulative Zr concentration in the desorption solution.

[0239] In contrast, Example 1 exhibited superior structural stability. After five rounds of strong alkali desorption and regeneration, the adsorption capacity of the composite material showed only a slight decrease, with the final adsorption retention rate maintained at 91.86%. The accompanying filtrate analysis showed that the cumulative Zr concentration in the five desorption cycles was as low as 0.193 mg / L, close to the instrument's lower limit of quantitation. This phase stability under strong alkali conditions is mainly related to the interfacial localization and nucleation constraint provided by the silanization modification in the early stages of preparation.

[0240] The Si-O-Si linkage structure formed by the silane coupling agent on the diatomite surface and its amino end group act as acceptors to fix transition metal directing agents during the nucleation stage, thereby inducing the confined growth of zirconium species. After air calcination, the organic aminopropyl chain segment decomposes significantly, but the zirconium species may be fixed on the carrier surface and in the pores through the combined effects of Zr-O-Si interface interaction, pore confinement, and amorphous zirconium oxide network.

[0241] The confined loading structure, formed by pre-preparation substrate covalent bonding, interfacial coordination induction, and in-situ controlled hydrolysis, effectively confines amorphous zirconium nanoparticles within the carrier channels and surface, thereby reducing their migration and loss in the external chemical environment. This ensures that the reaction sites within the material can be continuously utilized in multiple cycles, indicating that the material has good potential for recycling and regeneration applications.

Claims

1. A zirconium-based adsorption composite material, characterized in that, It is prepared from raw materials comprising the following parts by weight: Based on 100.0 parts by weight of diatomaceous earth, 3-Aminopropyltriethoxysilane: 2.0-6.0 parts by weight; Copper sulfate pentahydrate: 1.57-2.70 parts by weight; Zirconium oxychloride octahydrate: 20.0-50.0 parts by weight; Citric acid monohydrate, wherein the molar ratio of citric acid monohydrate to zirconium in zirconium oxychloride octahydrate is 1.29:1 to 1.50:1; Urea, wherein the molar ratio of urea to zirconium in the zirconium oxychloride octahydrate is 8.4:1 to 12.1:

1.

2. The zirconium-based adsorption composite material according to claim 1, characterized in that, The weight ratio of the raw materials is as follows: Based on 100.0 parts by weight of diatomaceous earth, the amount of 3-aminopropyltriethoxysilane is 4.0 parts by weight, the amount of copper sulfate pentahydrate is 1.57 parts by weight, and the amount of zirconium oxychloride octahydrate is 35.0 parts by weight.

3. The zirconium-based adsorption composite material according to claim 1, characterized in that, The specific physicochemical parameters of the diatomaceous earth in the raw material are: silica mass fraction not less than 85%, and BET specific surface area of ​​10-25 m². 2 / g, with a median particle size D50 of 10-50μm.

4. The zirconium-based adsorption composite material according to claim 1, characterized in that, In the components constituting the composite material, the 3-aminopropyltriethoxysilane is pre-combined with diatomaceous earth and introduced in the form of amino-functionalized diatomaceous earth. The specific preparation method of the amino-functionalized diatomaceous earth is as follows: the dried and activated diatomaceous earth is dispersed in anhydrous toluene, and after reflux azeotropic dehydration, the 3-aminopropyltriethoxysilane is slowly added dropwise under nitrogen protection and the reaction continues. The product is then washed and dried to constant weight in a vacuum oven.

5. A method for preparing a zirconium-based adsorption composite material as described in any one of claims 1-4, characterized in that, The process includes the following: Aminofunctionalized diatomaceous earth with 3-aminopropyltriethoxysilane bonded to its surface was dispersed in a buffer solution, and an aqueous solution of copper sulfate pentahydrate was slowly added dropwise while stirring to obtain a slurry with cation-modified surface. Zirconium oxychloride octahydrate and citric acid monohydrate were dissolved in water, and the pH of the solution was adjusted after stirring to form a clear complex solution. The surface-cation-modified slurry was pumped into the complex solution, stirred and mixed, and then urea was added to carry out a urea slow-release hydrolysis reaction, using a two-stage programmed temperature rise. After the reaction was completed, the solid product was separated, washed with hot water, and then added with dilute ammonia to perform a complexation and copper removal operation. The solid product after copper removal is washed with water until neutral, then dried and calcined in sequence, and finally cooled to obtain the final product.

6. The preparation method according to claim 5, characterized in that, The buffer solution is an acetate-sodium acetate buffer solution with a pH of 5.8; when forming a clear complex solution, the pH of the system is pre-adjusted to 5.0 using ammonia.

7. The preparation method according to claim 5, characterized in that, The specific process parameters for the two-stage temperature program are as follows: first, the temperature is increased to 70°C at a rate of 3°C / min and stirred at a constant temperature for 1 hour, and then the temperature is increased to 95°C at a rate of 1°C / min and reacted at a constant temperature for 8 hours.

8. The preparation method according to claim 5, characterized in that, The specific implementation method of the complexation copper removal operation is as follows: The washed solid product was redispersed in deionized water at a solid-liquid ratio of 1g:5-10mL. Dilute ammonia was added dropwise to adjust the pH of the slurry to 9.5 while stirring continuously. The complexed eluent was collected by centrifugation. Repeat the complexation copper removal operation until the copper ion concentration in the final complexation eluent is below 1.0 mg / L.

9. The preparation method according to claim 5, characterized in that, The process parameters for the drying process are: drying at 105°C for 12 hours; The process parameters for the calcination process are as follows: heating to 450-500℃ in air at a heating rate of 5℃ / min, and calcining at a constant temperature for 2.5-3 hours.

10. The preparation method according to claim 5, characterized in that, Before preparing the surface-cation-modified slurry, the amino-functionalized diatomaceous earth needs to be prepared in advance; The preparation parameters for the amino-functionalized diatomaceous earth are as follows: The raw diatomaceous earth was activated and dried at 150°C for 2-4 hours, and then transferred to a reactor containing 800-1500 mL of anhydrous toluene for dehydration. After cooling the system to 80-90℃, add the corresponding amount of 3-aminopropyltriethoxysilane dropwise under a protective atmosphere, react continuously for 4-6 hours, and then dry under vacuum to constant weight.

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