Modified iron-phosphorus doped titanium-based composite material with high selectivity for removing thallium and preparation method thereof

Abstract

This invention discloses a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal and its preparation method, relating to the field of water treatment technology. The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal comprises the following components by weight: 100 parts titanium source, 10-25 parts iron source, 1-10 parts phosphorus source, 30-60 parts composite chelating agent, and 0-50 parts functional adjustment precursor. The titanium and iron sources form a primary porous framework, and the phosphorus source is doped and modified on the surface and within the pores of the primary porous framework. The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal provided by this invention significantly enhances surface activity through the co-doping of iron and phosphorus elements; and the introduction of the composite chelating agent effectively solves the problem of excessively rapid hydrolysis of the titanium source, enabling the material to form a structurally stable porous framework at a lower temperature, while also exhibiting excellent versatility and scalability.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal and its preparation method. Background Technology

[0002] Thallium (Tl) is a highly toxic heavy metal, even more so than mercury and lead, which are known to cause significant cumulative damage to living organisms. In industrial wastewater from non-ferrous metal smelting, mining, and sulfuric acid production, thallium typically exists as monovalent thallium ions (Tl). + It exists in the form of ).

[0003] Due to Tl + The hydration radius (approximately 0.160 nm) and potassium ion (K) + The wavelength (approximately 0.133 nm) is very close to that of traditional inorganic adsorbents (such as pure titanium dioxide and manganese oxide), which are effective against high background concentrations of K. + Ca 2+ Mg 2+ In such cases, adsorption sites are easily preempted, leading to low thallium removal efficiency. Therefore, there is an urgent need for a new type of composite material that possesses both the high strength and chemical stability of an inorganic framework and precise recognition capabilities to address the current pain points in the field of industrial wastewater purification. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal and its preparation method. The specific technical solution is as follows: A modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal, comprising the following components by weight: 100 parts titanium source, 10-25 parts iron source, 1-10 parts phosphorus source, 30-60 parts composite chelating agent, and 0-50 parts functional regulating precursor. The titanium source and iron source form a primary porous framework, and the phosphorus source is doped and modified on the surface and in the pores of the primary porous framework.

[0005] Preferably: The titanium source is selected from at least one of tetrabutyl titanate, tetraisopropyl titanate, and titanium tetrachloride. The iron source is ferric nitrate; The phosphorus source is diammonium hydrogen phosphate; The composite chelating agent includes citric acid and acetylacetone.

[0006] Preferably: The functional regulating precursor is 0.8 to 50 parts by weight; The functional regulating precursor is selected from at least one of cyclic polyhydroxy thiorecognition monomers and guanidine precursors.

[0007] Preferably: The cyclic polyhydroxy thiorecognition monomer is a thiomodified β-cyclodextrin; The guanidino precursor is selected from at least one of cyanamide, dicyandiamide, guanidine, and guanidine nitrate; The present invention also provides a method for preparing a modified iron-phosphorus-doped titanium-based composite material with high selectivity for thallium removal as described in any one of the above claims, comprising the following steps: S1. Preparation of the mixed solution: The titanium source, iron source and composite chelating agent are mixed in an alcohol solvent to prepare a precursor mixed solution; S2. Controlled hydrolysis: Under stirring conditions, an alcohol-water mixture is added dropwise to the precursor mixture as a hydrolysis initiator to construct a Ti-O-Ti primary framework; S3. Doping and functionalization: Add a phosphorus source to the system obtained in step S2; S4. In-situ reaction: The system is heated to 70~90℃ to carry out an in-situ crosslinking reaction; S5. Post-processing: The product is obtained after centrifugation, drying, grinding and heat treatment; When the weight part of the functional regulating precursor is 0, the heat treatment is calcination at 300~500℃; When the weight percentage of the functional adjustment precursor is not 0, the heat treatment is constant temperature curing at 60~120℃.

[0008] Preferably, the method further includes a step of introducing a functionally modulating precursor, wherein the functionally modulating precursor is a cyclic polyhydroxy thiorecognition monomer and / or a guanidine precursor; When a cyclic polyhydroxy thiorecognition monomer is introduced, in step S3, the pH value of the system obtained in step S2 is adjusted to 3-5 before the cyclic polyhydroxy thiorecognition monomer is added. When a guanidine precursor is introduced, the guanidine precursor is added in step S1, and a multifunctional crosslinking agent is added in step S3.

[0009] Preferably: The multifunctional crosslinking agent is glutaraldehyde; The cyclic polyhydroxy thiorecognition monomer is a thiomodified β-cyclodextrin, which is prepared by the following steps: β-cyclodextrin is dissolved in an alkaline solution, epichlorohydrin is added dropwise at 30~60℃ for cross-linking pretreatment, then thiourea is added, and the temperature is raised to 60~90℃ for thiolation reaction. After purification and drying, the product is obtained.

[0010] Preferably: The alkaline solution is a sodium hydroxide or potassium hydroxide solution; The molar ratio of β-cyclodextrin to epichlorohydrin is 1:(5~15); The dropping rate of epichlorohydrin was 0.5~2.0 mL / min, and the pretreatment time was 2~4 h; The molar ratio of thiourea to β-cyclodextrin was (8~12):1, and the thiolation reaction time was 4~12h.

[0011] Preferably: In step S1, the composite chelating agent includes citric acid and acetylacetone, wherein the molar ratio of acetylacetone to titanium source is (0.2~0.5):1; and the molar ratio of citric acid to iron source is (4~6):1. In step S2, the system temperature is controlled at 0~10℃, and the dropping rate of the hydrolysis initiator is 0.5~2.0mL / min; In step S4, the heating reaction time is not less than 2 hours.

[0012] The present invention also provides a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal as described in any one of the above claims, or the application of the modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal prepared by any one of the above claims in the treatment of thallium-containing industrial wastewater.

[0013] The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal provided by this invention has the following beneficial effects: 1. Significantly enhanced surface activity: Through co-doping with iron and phosphorus, a large number of defect sites and phosphate active groups are introduced into the titanium dioxide lattice, which enhances the framework's initial capture ability of metal ions.

[0014] 2. Precise framework control: The introduction of composite chelating agents effectively solves the problem of excessively rapid hydrolysis of titanium sources, enabling the material to form a structurally stable porous framework at a lower temperature, avoiding pore closure caused by traditional high-temperature calcination.

[0015] 3. Excellent versatility and scalability: The constructed inorganic porous framework has good hydrophilicity and chemical stability, which can not only be used directly for preliminary thallium removal, but also provide an ideal physical carrier for subsequent chemical modification. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0017] Figure 1 This is a scanning electron microscope (SEM) morphology characterization image of the composite material prepared in Example 1 of the present invention; Figure 2 The graph shows the effect of the composite material prepared in Example 1 of this invention on the removal rate of thallium ions under different pH conditions. Figure 3 The adsorption isotherm and fitting diagram of thallium ions on the composite material prepared in Example 1 of this invention are shown. Figure 4 The adsorption kinetics and fitting diagram of thallium ions on the composite material prepared in Example 1 of this invention are shown. Figure 5 These are test images of the anti-interference performance of the composite material prepared in Example 1 of the present invention under different cation coexistence environments; Figure 6 The X-ray photoelectron spectroscopy (XPS) full spectrum comparison of the composite material prepared in Example 1 of this invention before and after adsorption; Figure 7 The XPS fine spectra of each element (Tl, Ti, O, P, Fe) before and after adsorption are shown for the composite material prepared in Example 1 of this invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0019] This embodiment provides a modified iron-phosphorus doped titanium-based composite material for highly selective thallium removal, which is made of the following components by weight: 100 parts of titanium source, 10-25 parts of iron source, 1-10 parts of phosphorus source, 30-60 parts of composite chelating agent, and 0-50 parts of functional regulating precursor.

[0020] Among them, titanium and iron sources form a primary porous framework, and phosphorus source is doped and modified on the surface and in the pores of the primary porous framework.

[0021] Specifically, the composite material provided in this embodiment achieves a synergistic effect through "rigid skeleton support + flexible network capture": 1. Iron source (Fe) 3+ Phosphorus source (PO4) and titanium source co-hydrolyze in an alcohol-water system, integrating into the amorphous titanium oxide gel network. Due to differences in ionic radius and valence state, abundant localized charge imbalance centers and structural defects are formed in the short-range ordered porous framework of Ti-O-Ti, altering the isoelectric point of the framework surface. 3- A phosphate-modified layer is formed on the TiO2 surface, which significantly increases the number of surface hydroxyl groups and provides initial electrostatic adsorption sites for thallium ions.

[0022] 2. Through the synergistic effect of composite chelating agents (citric acid and acetylacetone), the hydrolysis and polycondensation rate of titanium source can be controlled at the molecular level, enabling the material to self-assemble into a porous framework with a high specific surface area at low temperature, providing sufficient "carrier space" for the subsequent anchoring of organic functional components.

[0023] 3. The number of precursor components for functional regulation ranges from 0 to 50. When the number of components is 0, an iron-phosphorus-doped titanium substrate material with excellent hydrophilicity is constructed. When the number of components is not 0, the in-situ transformation of the precursor on the inner wall of the framework is utilized to achieve a qualitative upgrade from "physical adsorption" to "specific chemical recognition".

[0024] The modified iron-phosphorus-doped titanium-based composite material with high selectivity for thallium removal provided in this embodiment has the following beneficial effects: 1. Significantly enhanced surface activity: Through co-doping with iron and phosphorus, a large number of defect sites and phosphate active groups are introduced into the titanium dioxide lattice, which enhances the framework's initial capture ability of metal ions.

[0025] 2. Precise framework control: The introduction of composite chelating agents effectively solves the problem of excessively rapid hydrolysis of titanium sources, enabling the material to form a structurally stable porous framework at a lower temperature, avoiding pore closure caused by traditional high-temperature calcination.

[0026] 3. Excellent versatility and scalability: The constructed inorganic porous framework has good hydrophilicity and chemical stability, which can not only be used directly for preliminary thallium removal, but also provide an ideal physical carrier for subsequent chemical modification.

[0027] Furthermore: The titanium source is selected from at least one of tetrabutyl titanate, tetraisopropyl titanate, and titanium tetrachloride.

[0028] The iron source is ferric nitrate.

[0029] The phosphorus source is diammonium hydrogen phosphate.

[0030] The complex chelating agents include citric acid and acetylacetone.

[0031] Specifically, these liquid or highly volatile titanium sources are chosen because they exhibit good solubility and dispersibility in alcohol-based solvents, making them ideal precursors for constructing homogeneous TiO2 sol-gel networks. These liquid precursors enable a uniform distribution of titanium atoms at the molecular level, laying the foundation for subsequent doping.

[0032] Ferric nitrate, as an iron source, has extremely high water solubility, and nitrate ions are easily decomposed and removed during subsequent heat treatment, without introducing residual impurity anions. Meanwhile, Fe... 3+ The radius and Ti 4+ Proximity facilitates lattice substitution. Diammonium hydrogen phosphate not only provides a phosphorus source to increase the hydroxyl active sites on the material surface, but its dissociated ammonium ions can also play a certain pH buffering role during hydrolysis, helping to regulate the stability of the sol.

[0033] Acetylacetone (AcAc) can undergo a strong chelation reaction with titanium sources (such as tetrabutyl titanate) to form stable chelates. Because the chelating force of AcAc is stronger than the hydrolytic attack force of water molecules, it can significantly inhibit the "explosive polymerization" of titanium sources, ensuring that the Ti-O-Ti framework grows slowly and uniformly.

[0034] Citric acid (CA) contains multiple carboxyl and hydroxyl groups, which can form stable soluble complexes with iron ions. During hydrolysis, as pH fluctuates, CA can effectively prevent iron ions from prematurely forming hydroxide precipitates, thus ensuring that iron can be "embedded" into the titanium oxide framework in an atomically dispersed state.

[0035] Furthermore: The functional regulating precursor is 0.8 to 50 parts by weight.

[0036] The functional regulatory precursor is selected from at least one of cyclic polyhydroxy thiorecognition monomers and guanidine precursors.

[0037] Specifically, regarding the dosage limit of the functional modulation precursor, when its content is below 0.8 parts, the density of specific recognition sites formed by organic functional groups on the inner wall of the porous titanium dioxide framework is too low due to the large specific surface area of ​​the titanium dioxide porous framework. This results in the material failing to exhibit a significantly superior selective adsorption advantage compared to basic iron-phosphorus doped materials at the macroscopic level. Therefore, 0.8 parts is defined as the minimum effective loading threshold for this invention to achieve the qualitative transformation from "general electrostatic adsorption" to "spatial-chemical specific recognition".

[0038] On the other hand, considering that the pore size of the titanium dioxide porous framework constructed in this embodiment is usually at the nanoscale, if the loading of the organic precursor is too high (more than 50 parts), the excessively thick organic functional layer is very likely to cause micropore blockage during the in-situ reaction. This will not only cause a sharp shrinkage of the effective specific surface area of ​​the material, but also seriously hinder the diffusion mass transfer rate of thallium ions inside the pores. Therefore, the upper limit is limited to 50 parts to ensure that the optimal ratio balance is maintained between the organic functional network and the inorganic porous structure, thereby ensuring high selectivity while taking into account the kinetic adsorption performance of the material.

[0039] Within the aforementioned effective load range, this embodiment constructs a dual cooperative recognition mode by introducing a specific precursor. Specifically, the cyclic polyhydroxy thiorecognition monomer utilizes its unique spatial configuration to interact with monovalent thallium ions (Tl) through its cavity size. + The precise matching of the radius creates a "spatial confinement" effect; while the guanidinium precursor enhances chemical affinity through its abundant electron cloud distribution. This synergistic effect of "spatial inclusion" and "chemical coordination" enables the material to exhibit extremely high thallium recognition specificity even in complex water environments containing high concentrations of interfering ions such as potassium and calcium.

[0040] Furthermore: The cyclic polyhydroxy thiorecognition monomer is a thiomodified β-cyclodextrin.

[0041] The guanidino precursor is selected from at least one of cyanamide, dicyandiamide, guanidine, and guanidine nitrate.

[0042] Among them, the cyclic polyhydroxy thiorecognition monomer selected is thiomodified β-cyclodextrin, which is based on the construction of a synergistic capture mechanism of "microenvironment dehydration-soft and hard acid-base coordination". The unique internal hydrophobic cone cavity of β-cyclodextrin provides a microenvironment with a low dielectric constant, when hydrated monovalent thallium ions (Tl... + When approached, this microenvironment can significantly reduce its dehydration energy, promoting Tl + The hydration shell is peeled off; subsequently, the exposed Tl, possessing "soft acid" properties, is revealed. + It rapidly and specifically coordinates with the "soft base" sulfur atoms grafted onto the cyclodextrin backbone. This mechanism of "dehydration" followed by "coordination" effectively shields against interference from hard acid ions (such as K+) that have high hydration energy and are difficult to dehydrate. + Ca 2+ The sulfur atoms are introduced into the cyclodextrin framework through thiolation modification, utilizing their strong coordination affinity as a "soft base" and thallium ions as a "soft acid" to construct a dual capture mechanism of "spatial recognition + chemical locking". Furthermore, at least one of cyanamide, dicyandiamide, guanidine, or guanidine nitrate is selected as the guanidine precursor, aiming to utilize the abundant high electron cloud density and multi-site coordination ability of the guanidine group to weave a high-density capture network within the porous channels of titanium dioxide. In practical applications, by adjusting the mass ratio of thiolated β-cyclodextrin to the guanidine precursor, the selectivity coefficient of the material can be dynamically optimized based on the initial concentration of thallium ions and the types of coexisting ions in the wastewater. When the wastewater contains a high concentration of potassium ions, the proportion of thiolated β-cyclodextrin can be appropriately increased to enhance the spatial size recognition effect, thereby ensuring robust thallium removal performance even under complex water quality conditions.

[0043] Benefically, by selecting bio-based β-cyclodextrin and its derivatives as the core recognition monomer, the raw material cost of functionalization modification is significantly reduced, enabling it to maintain crown ether-level specific recognition performance while possessing broader prospects for industrial applications. Simultaneously, the introduction of these specific components not only enhances the static adsorption capacity of the composite material for thallium ions, but also, due to the abundant hydroxyl and amino functional groups in its molecular structure, strengthens the wettability and diffusion rate of the material in aqueous systems, effectively shortening the adsorption equilibrium time and greatly improving the treatment efficiency of industrial wastewater.

[0044] This embodiment also provides a method for preparing a modified iron-phosphorus-doped titanium-based composite material with high selectivity for thallium removal as described in any one of the above embodiments, comprising the following steps: S1. Preparation of the mixed solution: The titanium source, iron source and composite chelating agent are mixed in an alcohol solvent to prepare a precursor mixed solution.

[0045] S2. Controlled hydrolysis: Under stirring conditions, an alcohol-water mixture is added dropwise to the precursor mixture as a hydrolysis initiator to construct a Ti-O-Ti primary framework.

[0046] S3. Doping and functionalization: Add a phosphorus source to the system obtained in step S2.

[0047] S4. In-situ reaction: Heat the system to 70~90℃ to carry out in-situ crosslinking reaction.

[0048] S5. Post-processing: The product is obtained after centrifugation, drying, grinding and heat treatment.

[0049] When the weight percentage of the functional regulating precursor is 0, the heat treatment is calcination at 300~500℃.

[0050] When the weight percentage of the functional adjustment precursor is not 0, the heat treatment is constant temperature curing at 60~120℃.

[0051] In step S1, the alcohol solvent is preferably anhydrous ethanol or anhydrous isopropanol. Specifically, this embodiment preferably uses an iron source with water of crystallization (such as ferric nitrate nonahydrate). The trace amount of water of crystallization introduced by the iron source, bound by the strong hydrogen bonds and chelate network of citric acid and acetylacetone, will not trigger macroscopic explosive polymerization of the titanium source. Instead, it acts as a microscopically localized 'slow-release hydrolysis initiator,' assisting the titanium and iron sources to undergo extremely mild pre-condensation polymerization at the atomic scale. This lays the foundation for homogeneous doping in the controlled hydrolysis of the subsequent step S2. The hydrolysis initiator used in step S2 can be an alcohol-water mixture, wherein the volume ratio of alcohol to water is controlled between 5:1 and 1:1. By synergistically controlling the dropping rate (preferably 0.5~2.0 mL / min) and ambient temperature (preferably 0~10℃), the hydrolysis kinetics process can be suppressed to the maximum extent, allowing for the orderly growth of the Ti-O-Ti primary framework. In step S3, to prevent localized agglomeration of the solid and ensure the uniformity of doping, the phosphorus source is pre-dissolved in a small amount of water or an alcohol-water mixture to prepare a solution, which is then slowly added dropwise to the system in liquid form. The post-processing stage in step S5 introduces heat treatment to drive the complete formation of chemical bonds without damaging the sensitive organic functional groups.

[0052] For basic framework schemes without organic components, post-treatment can be low-temperature calcination at 300~500℃. During calcination, it is recommended to use a heating rate of 2~5℃ / min and hold at the highest temperature for 2~4 hours to promote the transformation of amorphous titanium oxide components to crystalline state and improve the mechanical strength of the material.

[0053] To ensure the purity and structural stability of the product, the specific process details are as follows: 1. Centrifugal separation: A speed of 4000~8000 rpm and a centrifugation time of 5~15 min can be used to achieve efficient sedimentation of solid products and separation of mother liquor.

[0054] 2. Washing and purification: The solid after centrifugation can be washed 3 to 5 times with deionized water and anhydrous ethanol alternately until the pH value of the washing solution is close to neutral and there are no excess impurity ions remaining.

[0055] 3. Drying control: After washing, the sample is dried at a constant temperature of 60~100℃ for 6~12 hours. This gentle drying method can avoid capillary forces caused by rapid evaporation of moisture, which could lead to pore collapse.

[0056] 4. Grinding and shaping: The dried solid is ground and then passed through a 100-300 mesh sieve to obtain powder material with uniform particle size distribution.

[0057] Furthermore, it also includes a step of introducing a functionally modulating precursor, which is a cyclic polyhydroxy thiorecognition monomer and / or a guanidine precursor.

[0058] When a cyclic polyhydroxy thiorecognition monomer is introduced, in step S3, the pH of the system obtained in step S2 is adjusted to 3-5 before the cyclic polyhydroxy thiorecognition monomer is added.

[0059] When a guanidine precursor is introduced, the guanidine precursor is added in step S1, and a multifunctional crosslinking agent is added in step S3.

[0060] The differentiated introduction strategy of functionally modulating precursors is key to achieving the material's specific recognition function. For cyclic polyhydroxy thiorecognition monomers, their addition is scheduled for step S3, with the pH adjusted to 3-5. In practice, dilute nitric acid or ammonia is typically used as the pH adjuster. This weakly acidic range not only protects the cyclodextrin structure from damage but also stimulates the active hydroxyl groups on the backbone surface to generate stronger condensation activity. For guanidine precursors, the multifunctional crosslinking agent (such as glutaraldehyde) introduced in step S3 can be added at 0.5%-2% of the total precursor mass. Through the in-situ reaction process at 70-90℃ in step S4, a thermodynamically driven in-situ condensation reaction is initiated. The aldehyde group of glutaraldehyde undergoes a highly efficient Schiff base reaction with the amino group of the guanidine precursor (such as dicyandiamide), forming a nitrogen-rich polymer network through in-situ crosslinking on the inner wall of the titanium dioxide inorganic backbone. Meanwhile, the large-molecule, thiomodified β-cyclodextrin is firmly physically embedded and spatially interpenetrating between the cross-linked network and the inorganic porous framework, forming an "organic-inorganic semi-interpenetrating network structure." This avoids chemical damage to the active cavity structure of cyclodextrin and, through the "locking" effect of the cross-linked network, completely solves the problem of easy loss of organic recognition monomers in the aqueous phase.

[0061] Furthermore: The multifunctional crosslinking agent is glutaraldehyde.

[0062] The cyclic polyhydroxy thiorecognition monomer is thiomodified β-cyclodextrin, which is prepared by the following steps: β-cyclodextrin is dissolved in an alkaline solution, and epichlorohydrin is added dropwise at 30~60℃ for crosslinking pretreatment. Then, thiourea is added, and the temperature is raised to 60~90℃ for thiolation reaction. After purification and drying, the product is obtained.

[0063] Furthermore: The alkaline solution is a sodium hydroxide or potassium hydroxide solution.

[0064] The molar ratio of β-cyclodextrin to epichlorohydrin is 1:(5~15).

[0065] The epichlorohydrin was added at a rate of 0.5–2.0 mL / min, and the pretreatment time was 2–4 h.

[0066] The molar ratio of thiourea to β-cyclodextrin was (8~12):1, and the thiolation reaction time was 4~12h.

[0067] Specifically, the preparation of thiomodified β-cyclodextrin employs a two-step process: crosslinking pretreatment and thiolation modification. First, β-cyclodextrin is moderately crosslinked using epichlorohydrin under an alkaline environment, preferably provided by a 0.5–2.0 mol / L sodium hydroxide or potassium hydroxide solution. In the specific process implementation, the molar ratio of epichlorohydrin to β-cyclodextrin is maintained between 5:1 and 15:1. During the crosslinking pretreatment stage, the dropping rate of epichlorohydrin (0.5–2.0 mL / min) and the reaction time (2–4 h) are strictly controlled to ensure moderate single-end grafting and partial crosslinking. This control of process parameters prevents the complete consumption of the hydroxyl groups in β-cyclodextrin, thus retaining free chloroalkyl or terminal epoxy active sites on the backbone. These retained active sites provide a basis for subsequent nucleophilic substitution reactions of thiourea or thiocyanate, ensuring successful grafting of sulfur atoms. The subsequent thiolation process involves introducing thiocyanate or thiourea and grafting sulfur atoms onto the framework within a reaction time of 4–12 hours. After the reaction, the solution is purified by adjusting the pH to neutral, dialysis, or recrystallization, and finally dried under vacuum at 60°C for later use.

[0068] Furthermore: In step S1, the composite chelating agent includes citric acid and acetylacetone, with the molar ratio of acetylacetone to titanium source being (0.2~0.5):1; and the molar ratio of citric acid to iron source being (4~6):1.

[0069] In step S2, the system temperature is controlled at 0~10℃, and the dropping rate of the hydrolysis initiator is 0.5~2.0mL / min.

[0070] In step S4, the heating reaction time is not less than 2 hours.

[0071] In step S1, the molar ratio of acetylacetone to titanium source is controlled at (0.2~0.5):1, and the molar ratio of citric acid to iron source is controlled at (4~6):1, in order to construct a stable dual chelation system and utilize the different coordination strengths of the two chelating agents to lock the hydrolysis rate of different metal ions respectively.

[0072] This embodiment also provides a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal as described in any of the above embodiments, or the application of the modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal prepared by any of the above preparation methods in the treatment of thallium-containing industrial wastewater.

[0073] Specifically, the composite material provided in this embodiment exhibits excellent adaptability and process flexibility in treating thallium-containing industrial wastewater. In practical industrial applications, this material can be used in different treatment modes depending on the wastewater flow rate and site conditions: 1. Fixed-bed adsorption mode: The material is processed into granules and filled into the adsorption column. During application, the wastewater space velocity can be controlled between 2 and 10 h⁻¹. -1 The empty bed contact time is maintained between 10 and 30 minutes. This mode is particularly suitable for the deep purification of large-volume wastewater in the non-ferrous metal smelting or mining industries. Relying on the dual specific capture mechanism of internal spatial inclusion and coordination of soft and hard acids and bases, this material can effectively overcome the competitive interference of high concentrations of alkaline earth metal ions in complex water bodies, achieving deep interception of trace thallium ions and meeting the stringent environmental protection requirements for industrial wastewater discharge.

[0074] 2. Continuous stirring reaction mode: In intermittent wastewater treatment, powdered materials are directly added to the reaction tank, with the dosage controlled between 0.1 and 2.0 g / L. The stirring equipment maintains the material in suspension in the water, and after reacting for 30 to 120 minutes, solid-liquid separation is achieved through sedimentation or membrane filtration.

[0075] In terms of water quality adaptability, this material maintains a high efficiency in thallium capture within a wide pH range of 2 to 11. Particularly in wastewater containing high concentrations of potassium ions (up to 1000 times higher than thallium ions) or extremely high calcium and magnesium hardness, the material's internal thiomodified cyclodextrin specific recognition sites enable precise extraction of thallium ions from complex backgrounds.

[0076] Furthermore, this material exhibits excellent regeneration performance. Once adsorption reaches saturation, it can be regenerated using 0.1–1.0 mol / L dilute nitric acid or sulfuric acid as a desorbent. The thallium concentration in the regenerated solution can be concentrated to 50–100 times that of the original wastewater, facilitating subsequent resource recovery. Verification has shown that after more than 50 adsorption-desorption cycles, the material's thallium removal efficiency declines by less than 5%, demonstrating an extremely long industrial service life.

[0077] In terms of horizontal expansion in the technical field, based on the abundant soft base coordination groups (thiolated groups) and cross-linking network on the material surface, this composite material, in addition to treating thallium-containing wastewater, can also treat lead (Pb) in industrial wastewater. 2+ ), cadmium (Cd 2+ ), mercury (Hg) 2+ Soft acids or interface acids also have a significant synergistic removal effect on heavy metal ions and can be used as a deep purification agent for multi-metal polluted wastewater.

[0078] Benefically, the material of this embodiment exhibits significant advantages in reducing reagent and sludge volume during application. Compared with traditional chemical precipitation methods, this material operates through a physicochemical capture mechanism, avoiding the generation of large amounts of thallium-containing hazardous waste sludge and greatly reducing subsequent disposal costs. Simultaneously, the material's high selectivity avoids the ineffective interception of harmless mineral ions in wastewater, maximizing the utilization of effective active sites. Its excellent cycle stability and high concentration factor provide a highly efficient technological path for the treatment of thallium-containing wastewater, shifting from "end-of-pipe treatment" to "resource recovery," resulting in extremely high environmental, social, and economic benefits.

[0079] To fully verify the selectivity of the composite material under different water quality conditions, this embodiment employs a gradient evaluation strategy in its testing scheme. First, the initial anti-interference performance of the basic inorganic framework is evaluated under low background interference intensity (K:Tl=10:1); then, the specific recognition limit of the organic-inorganic hybrid material is further evaluated under extreme industrial wastewater environment with high background interference (K:Tl=1000:1). In practical engineering applications, the series of composite materials provided in this embodiment can be applied in stages according to the different concentrations of interfering ions in the wastewater: for wastewater with low background interference, the iron-phosphorus doped material of Example 1 can meet the discharge requirements; for extremely complex industrial wastewater with high potassium and high calcium content, the hybrid material with specific recognition function of Example 2 can be used.

[0080] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. Example 1

[0081] Weigh 5.82 g of citric acid and 2.5 g of ferric nitrate nonahydrate and dissolve them in 20 mL of anhydrous ethanol. Stir at room temperature for 25 min to obtain a mixed iron source precursor solution.

[0082] Measure 15g of tetrabutyl titanate into a dry beaker, add 1.51g of acetylacetone, stir for 15min under anhydrous conditions to allow it to fully chelate, and then add 30mL of anhydrous ethanol to dilute and obtain a titanium source solution.

[0083] The titanium source solution was transferred to the iron source precursor solution, and controlled hydrolysis was induced by slowly adding a mixture of ethanol and water (volume ratio of 2:1, totaling 15 mL) at a rate of 1.0 mL / min in an 8°C constant temperature water bath to obtain Ti-Fe primary framework sol.

[0084] 0.5 g of diammonium hydrogen phosphate was pre-dissolved in 2 mL of deionized water to prepare a solution, which was then added dropwise to the above Ti-Fe sol system while continuously stirring until homogeneous. The system was placed in an 80 °C oil bath and refluxed for 2 h to induce phosphorylation doping. After the reaction was completed, the mixture was centrifuged at 7500 rpm and washed three times alternately with deionized water and anhydrous ethanol. The product was dried at 105 °C for 10 h, ground, and then placed in a tube furnace. It was calcined at 450 °C for 2 h in air at a heating rate of 5 °C / min. After cooling, it was passed through a 200-mesh sieve to obtain the modified iron-phosphorus doped titanium-based inorganic material.

[0085] The microstructure of the prepared powder was observed, such as... Figure 1 As shown, the material exhibits an irregular layered morphology and abundant nanoporous structure. XPS full-spectrum analysis (such as...) further confirms this. Figure 6 (as shown) and detailed spectral analysis of each element (such as) Figure 7 As shown in the figure, it is confirmed that iron and phosphorus elements were successfully doped into the titanium dioxide framework, and the surface is rich in Ti-OH, Fe-OH and P=O active groups.

[0086] Adsorption isotherm and maximum adsorption capacity determination: 5 mg of the prepared powder was weighed and added to a series of 50 mL Tl(I) solutions with different initial concentrations (10–200 mg / L). The pH of the system was adjusted to 7.0, and the mixture was shaken at 250 rpm for 24 h to reach adsorption equilibrium. After filtration, the residual thallium concentration was measured, and the maximum adsorption capacity q of the material was calculated using the Langmuir isotherm adsorption model. max .

[0087] Selectivity and anti-interference adsorption test: 10 mg of the prepared powder was added to 50 mL of Tl(I) solution with an initial concentration of 20 mg / L. The pH was adjusted to 7.0, and the mixture was shaken at 250 rpm for 6 h for adsorption. After filtration, the residual thallium concentration was measured, and the equilibrium adsorption capacity q was calculated. e and removal rate.

[0088] During the adsorption process, the effect of different pH environments on the removal rate was investigated (e.g., Figure 2 As shown), and perform adsorption isotherm fitting (as shown). Figure 3 (as shown) and adsorption kinetics fitting (as shown) Figure 4 (As shown). The competitive adsorption test results for different cations are as follows: Figure 5 As shown. After adsorption, the sample was filtered through a 0.45µm filter membrane, and the residual thallium concentration was determined using ICP-OES to calculate the equilibrium adsorption capacity q. e The relevant performance test data are shown in Table 1 below: Table 1: Test Data Table for Example 1 Example 2

[0089] 11.35 g of β-cyclodextrin was dissolved in 100 mL of 1.5 mol / L sodium hydroxide solution and stirred at 40 °C for 1 h to fully activate it. Then, 9.25 g of epichlorohydrin was slowly added dropwise to the system, and the reaction was continued at 60 °C for 4 h to obtain a pre-crosslinked cyclodextrin system. 7.61 g of thiourea was added to the above reaction solution, and the temperature was raised to 80 °C for another 6 h. After the reaction was complete, the resulting product was precipitated in excess anhydrous ethanol, filtered, and repeatedly washed with deionized water and anhydrous ethanol until neutral. Finally, the product was vacuum dried at 60 °C for 12 h and ground to obtain powdered thiomodified β-cyclodextrin.

[0090] Weigh 5.82 g of citric acid and 2.5 g of ferric nitrate nonahydrate and dissolve them in 20 mL of anhydrous ethanol. Then add 0.51 g of dicyandiamide (guanidinium precursor) and stir at room temperature for 30 min to obtain a mixed precursor solution.

[0091] Measure 15g of tetrabutyl titanate, add 1.51g of acetylacetone and stir for 15min to fully chelate, then dilute with 30mL of anhydrous ethanol.

[0092] Under constant temperature water bath of 8℃, the titanium source solution was transferred to the mixed precursor, and hydrolysis was induced by adding 15 mL of alcohol-water mixture (volume ratio 2:1) dropwise at 0.8 mL / min.

[0093] 0.5 g of diammonium hydrogen phosphate was dissolved in 2 mL of deionized water to prepare an aqueous solution, which was then added to the obtained Ti-Fe sol and stirred until homogeneous. Subsequently, 1.53 g of the previously prepared thiomodified β-cyclodextrin was added, and the pH of the system was adjusted to 4.2 using 0.1 mol / L nitric acid solution. 40.5 mg of glutaraldehyde was added as a crosslinking agent, and the mixture was stirred continuously for 45 min. The mixture was heated to 85 °C and reacted in situ under reflux for 2.5 h. After centrifugation and washing, the mixture was dried at 85 °C for 12 h. Finally, it was placed in a tube furnace and heated to 100 °C at a rate of 3 °C / min under a nitrogen atmosphere, and cured at this temperature for 3 h. After cooling, it was ground and passed through a 200-mesh sieve to obtain the final product.

[0094] The adsorption performance of the material prepared in this embodiment was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 1. To further investigate its adaptability under extreme environments, a high-intensity interference test group with K(I):Tl(I) = 1000:1 and Ca(II):Tl(I) = 100:1 was added. After adsorption, the thallium was filtered through a 0.45µm filter membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 2 below: Table 2: Test Data Table for Example 2 As shown in Table 2, the modified material prepared in this embodiment exhibits significantly improved adsorption performance compared to Example 1, with a maximum adsorption capacity of 289.50 mg / g. Its equilibrium adsorption capacity reached 91.25 mg / g, demonstrating that the introduction of organic functional components effectively increased the density of active sites on the material surface. More significantly, even under strong interference from 1000 times the potassium ion concentration and 100 times the calcium ion concentration, the material's removal rate of thallium ions remained above 90%. This indicates that the microenvironmental dehydration effect of the thiomodified β-cyclodextrin and the specific chelating effect of sulfur atoms in soft and hard acids and bases form a strong synergistic effect, endowing the material with excellent selective capture capabilities. Furthermore, the high cycle retention rate of 96.34% confirms the crucial role of the glutaraldehyde crosslinking network in locking organic recognition molecules and enhancing the chemical stability of the material. Example 3

[0095] This embodiment aims to investigate the effect of a single thiolated modified β-cyclodextrin on the material properties.

[0096] The steps are the same as in Example 2. The only difference is that dicyandiamide and crosslinking agent are not added when preparing the precursor solution. After hydrolysis and addition of 0.5g of diammonium hydrogen phosphate, 2.01g of thiomodified β-cyclodextrin is added, and the pH is adjusted to 4.2. Subsequent reflux, drying, and curing at 100°C are the same as in Example 2.

[0097] The adsorption performance of the material prepared in this embodiment was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 3 below: Table 3: Test Data Table for Example 3 Table 3 shows that even with only the introduction of thiomodified β-cyclodextrin, the removal rate of the material remained at 89.12% under a 1000-fold potassium ion background. This strongly demonstrates that the cavity structure of thiomodified β-cyclodextrin and the sulfur atoms on its surface have a significant specific recognition and chelating effect on thallium ions. However, since dicyandiamide and glutaraldehyde crosslinking agents were not added in this example, the binding between the organic components and the inorganic framework mainly relied on physical adsorption or weak hydrogen bonding, leading to easy loss of organic components during recycling. Its retention rate after 50 cycles was only 65.32%, significantly lower than that of Example 2. This comparative result fully illustrates the necessity of in-situ crosslinking technology for improving the structural stability of the material. Example 4

[0098] This embodiment aims to investigate the effect of a single guanidine crosslinking network on material properties.

[0099] The steps are the same as in Example 2. The only difference is that: 1.02g of dicyandiamide is added beforehand; after hydrolysis and the addition of 0.5g of diammonium hydrogen phosphate, thiomodified β-cyclodextrin is not added, the pH is directly adjusted to 4.2, and 20.5mg of glutaraldehyde is added for cross-linking. Subsequent steps are the same as in Example 2.

[0100] The adsorption performance of the material prepared in this embodiment was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 4 below: Table 4: Test Data Table for Example 4 As shown in Table 4, the material prepared in this embodiment, through the introduction of dicyandiamide and in-situ crosslinking using glutaraldehyde, achieved a maximum adsorption capacity of 285.27 mg / g, slightly higher than that of Example 3. This indicates that the nitrogen-rich guanidine crosslinking network can provide a large number of chelating sites, significantly enhancing the material's ability to capture heavy metal ions. However, in the anti-interference test, due to the lack of cavity size recognition effect of thiomodified β-cyclodextrin, the removal rate of this material decreased significantly under interference from 1000 times potassium ions and 100 times calcium ions (reduced to 43.15% and 56.82%, respectively). Furthermore, due to the presence of the crosslinking network, its cycle retention rate (82.16%) was better than that of Example 3 without crosslinking agent, but it was still lower than that of the fully functional modified Example 2 due to the lack of support from the cyclodextrin backbone. This result further confirms the crucial role of thiomodified β-cyclodextrin in achieving specific recognition of thallium ions and the superiority of the synergistic effect of multiple components. Example 5

[0101] This embodiment aims to investigate the effect of high loading on the balance between selectivity and adsorption capacity.

[0102] The steps are the same as in Example 2. The difference lies in increasing the amount of organic matter: 1.01 g of dicyandiamide was added when preparing the precursor; the rate of hydrolysis and addition of the alcohol-water mixture was reduced to 0.6 mL / min; after adding 0.5 g of diammonium hydrogen phosphate, 4.51 g of thiomodified β-cyclodextrin was added, the pH was adjusted to 4.2, and 100.5 mg of glutaraldehyde was added. The reflux reaction at 85°C was extended to 3 h. After subsequent drying, the curing time at 100°C was extended to 5 h to ensure that the high-loading organic components were fully crosslinked.

[0103] The adsorption performance of the material prepared in this embodiment was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 5 below: Table 5: Test Data Table for Example 5 Table 5 shows that the material exhibits excellent selective capture ability and structural stability under a very high proportion of organic functional component loading. Its removal rates reached 93.21% and 91.45% respectively under interference from 1000 times potassium ions and 100 times calcium ions, the highest values ​​among all examples; simultaneously, its cycle retention rate was as high as 98.12%, demonstrating the stable anchoring effect of the dense cross-linked network on functional molecules. However, compared with Example 2, it can be found that the equilibrium adsorption capacity q of this material... e and maximum adsorption capacity q max A significant decrease was observed (reduced to 84.23 mg / g and 235.48 mg / g, respectively, even slightly lower than in the unmodified Example 1). This result indicates that although a high loading can maximize the selectivity of the material, in practical applications, it is necessary to find the optimal balance between adsorption capacity and selectivity based on the complexity of the water being treated. It also verifies the rationality of the range defined in this embodiment.

[0104] Comparative Example 1 This comparative example uses commercially available conventional nano-titanium dioxide (P25) as the adsorbent material to verify the adsorption effect of unmodified conventional titanium-based materials on thallium ions, serving as the performance baseline of this invention.

[0105] The adsorption performance of the material prepared in this comparative example was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 1. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 6 below: Table 6: Test Data Table for Comparative Example 1 Table 6 clearly shows that the unmodified conventional nano-titanium dioxide exhibits extremely low adsorption capacity for thallium ions, with an equilibrium adsorption capacity of only 12.45 mg / g, less than 15% of that in Example 1. In the presence of small amounts of potassium or calcium ions, its removal rate rapidly drops below 10%, essentially losing its ability to capture thallium ions. This indicates that the surface of pure titanium dioxide lacks active sites capable of strong complexation with thallium ions. Comparison with Example 1 demonstrates that this invention, through the synergistic doping of iron and phosphorus, successfully constructs a porous framework rich in Ti-OH, Fe-OH, and P=O active groups, thereby fundamentally improving the material's adsorption capacity and basic selectivity. Furthermore, the low cycle retention rate of conventional materials also reflects the instability of their surface physisorption.

[0106] Comparative Example 2 This comparative example aims to verify the importance of the composite chelating agent (acetylacetone and citric acid) in controlling the hydrolysis rate and constructing a porous structure during the preparation process.

[0107] Weigh 2.5 g of ferric nitrate nonahydrate and dissolve it in 20 mL of deionized water. Separately, dissolve 15 g of tetrabutyl titanate in 30 mL of anhydrous ethanol, without adding acetylacetone or citric acid. At room temperature, rapidly pour the titanium source solution into the iron source aqueous solution; the system instantly produces a large amount of coarse precipitate. Add 0.5 g of diammonium hydrogen phosphate, pre-dissolved in 2 mL of deionized water, to the hydrolysis system and stir until homogeneous. Reflux at 80 °C for 2 h. After washing and drying, calcine at 450 °C for 2 h to obtain the product.

[0108] The adsorption performance of the material prepared in this comparative example was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 1. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 7 below: Table 7: Test Data Table for Comparative Example 2 Table 7 shows that, without the use of a composite chelating agent, the equilibrium adsorption capacity q of the material is... eThe concentration (38.45 mg / g) was significantly lower than that in Example 1 (88.98 mg / g). The reason for this is that the absence of acetylacetone and citric acid led to an excessively rapid hydrolysis rate of the titanium and iron sources upon contact with the aqueous phase, preventing the formation of a uniform sol-gel system. This resulted in severe "agglomeration" of the product, causing collapse or blockage of internal pores. Due to the drastically reduced specific surface area, the effective adsorption sites on the material surface could not be fully exposed. Even though the total amounts of iron and phosphorus were the same as in Example 1, the macroscopic adsorption performance was significantly reduced. This comparative result fully confirms that the "controlled hydrolysis process" achieved through the composite chelating agent in this embodiment is a prerequisite for constructing a highly efficient porous framework structure.

[0109] Comparative Example 3 This comparative example aims to verify the necessity of thiolation modification process for improving the selective capture capability of thallium ions.

[0110] The steps are the same as in Example 2. The only difference is that after hydrolysis and the addition of 0.5g of diammonium hydrogen phosphate, the added organic monomer is replaced with 1.53g of unmodified ordinary β-cyclodextrin, which is then used in conjunction with glutaraldehyde for in-situ crosslinking and curing at 100°C.

[0111] The adsorption performance of the material prepared in this comparative example was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 8 below: Table 8: Test Data Table for Comparative Example 3 As shown in Table 8, the adsorption performance of the material significantly declined when ordinary β-cyclodextrin was used instead of thiomodified β-cyclodextrin. Its maximum adsorption capacity dropped drastically from 289.50 mg / g in Example 2 to 218.35 mg / g, and the removal rate under 1000 times potassium ion interference further decreased to 28.45%. This result strongly demonstrates the core role of thiomodification in thallium ion capture. 1) Enhanced coordination ability: thallium ions (Tl) + It has a strong affinity for sulfur. As a coordinating atom that is softer than an oxygen atom, the sulfur atom can form a more stable coordinate bond with the thallium ion.

[0112] 2) Enhanced selective recognition: While ordinary cyclodextrin cavities have some size recognition capabilities, their surface hydroxyl groups are highly polar and easily interfered with by competition from large amounts of alkaline earth metal ions such as potassium and calcium in water. Thio-modified cyclodextrins, through the specific chelation of sulfur atoms, enable the cavity to more accurately "position" thallium ions.

[0113] 3) Synergistic effect: Although this comparative example retains the guanidine crosslinking network (the cycle retention rate is still maintained at 87.52%), the overall "selective capture" logic cannot be closed due to the lack of sulfur atoms, which further highlights the criticality of the thiolation process.

[0114] Comparative Example 4 This comparative example aims to verify the crucial role of the crosslinking agent (glutaraldehyde) in immobilizing organic functional components and constructing a robust organic-inorganic hybrid network. The procedures are the same as in Example 2. The only difference is that after hydrolysis and the addition of 0.5 g of diammonium hydrogen phosphate, 1.53 g of thiomodified β-cyclodextrin, and adjustment of the pH to 4.2, the glutaraldehyde crosslinking agent was not added. The mixture was directly heated to reflux, washed, dried, and treated at 100°C.

[0115] The adsorption performance of the material prepared in this comparative example was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm filter membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 9 below: Table 9: Test Data Table for Comparative Example 4 As can be seen from Table 9, the absence of the crosslinking agent glutaraldehyde has a serious negative impact on the performance of the material.

[0116] 1) Poor structural stability: The most significant change is the precipitous drop in cycle retention to 35.12%. This indicates that in the absence of a Schiff base crosslinking network constructed from glutaraldehyde, the thio-modified β-cyclodextrin and dicyandiamide adhere to the titanium dioxide framework only through weak physical adsorption or hydrogen bonding. During repeated washing and nitric acid desorption, these organic functional molecules are largely lost (dissolved), leading to a rapid loss of adsorption performance.

[0117] 2) Significantly reduced selectivity: Due to the partial shedding of organic recognition molecules during the initial experiment and washing process, the density of thiolated cavities on the material surface is insufficient, resulting in a removal rate of only 42.15% under 1000 times potassium ion interference, which is far lower than that in Example 2.

[0118] 3) Capacity limitation: Due to the lack of effective chemical bonding, the organic components cannot form a uniform and stable functional layer on the inner wall of the inorganic framework, and are prone to local aggregation or loss during centrifugation with the mother liquor. This results in a significant drop in the initial maximum adsorption capacity (118.25 mg / g) compared to Example 2, and even much lower than the basic inorganic framework without organic modification (Example 1). This confirms that the free, uncrosslinked polymers are not only severely lost during washing, but their incomplete flexible segments also disorderly block the primary nanopores of the titanium dioxide basic framework, leading to a significant reduction in effective adsorption sites.

[0119] This result strongly demonstrates that the "in-situ crosslinking" step is the key technical guarantee for achieving deep organic-inorganic fusion and ensuring long-term stable thallium removal in this invention.

[0120] Comparative Example 5 This comparative example aims to verify the necessity of the low-temperature cross-linking curing process used in this invention for protecting the activity of organic functional components and maintaining the integrity of the organic-inorganic hybrid structure.

[0121] The initial ingredient preparation, hydrolysis, addition of phosphorus source, addition of cyclodextrin, and in-situ crosslinking steps were completely consistent with those in Example 2. The only difference was the final post-treatment thermal regime: the washed and dried product was placed in a tube furnace and calcined at 450°C for 2 hours in air at a heating rate of 5°C / min (instead of curing at 100°C).

[0122] The adsorption performance of the material prepared in this comparative example was tested, and the adsorption isotherm and maximum adsorption capacity (q) were determined. max Determination conditions, selectivity, and anti-interference adsorption (q) e The test conditions for thallium removal rate were the same as in Example 2. After adsorption, the sample was filtered through a 0.45µm membrane, and the residual thallium concentration was determined using ICP-OES. The relevant performance test data are shown in Table 10 below: Table 10: Test Data Table for Comparative Example 5 As can be seen from Table 10, when the heat treatment temperature is increased from 100℃ to 450℃, the adsorption behavior of the material undergoes a qualitative change.

[0123] 1) Loss of selectivity: Under 1000 times potassium ion interference, its removal rate was only 18.24%. This indicates that at a high temperature of 450℃, the thiomodified β-cyclodextrin and dicyandiamide crosslinking network underwent thermal decomposition and carbonization, and the thioclast structure originally used for specific recognition of thallium ions was destroyed, resulting in the material losing its selective capture ability for thallium ions.

[0124] 2) Capacity regression baseline: Its equilibrium adsorption capacity (87.12 mg / g) fell back to the level of Example 1 (88.98 mg / g). This further demonstrates that high-temperature calcination caused the organic modified layer to disappear, and the material reverted to a pure iron-phosphorus doped inorganic framework.

[0125] 3) Insufficient stability: Because the organic cross-linking layer may form unstable residues on the inorganic surface after carbonization, the performance of the material fluctuates greatly during the cycle, and the cycle retention rate (65.38%) is much lower than that of Example 2.

[0126] This comparative result strongly demonstrates the crucial significance of the "low-temperature curing process" defined in this embodiment for preserving the activity of organic functional groups and realizing the hybrid advantages of "organic recognition + inorganic loading". Although high temperature can strengthen the inorganic lattice, it will destroy the core selectivity mechanism of this embodiment.

[0127] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.

Claims

1. A modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal, characterized in that, The product is made from the following components in parts by weight: 100 parts titanium source, 10-25 parts iron source, 1-10 parts phosphorus source, 30-60 parts composite chelating agent, and 0-50 parts functional regulating precursor. The titanium source and iron source form a primary porous framework, and the phosphorus source is doped and modified on the surface and in the pores of the primary porous framework.

2. The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal according to claim 1, characterized in that: The titanium source is selected from at least one of tetrabutyl titanate, tetraisopropyl titanate, and titanium tetrachloride. The iron source is ferric nitrate; The phosphorus source is diammonium hydrogen phosphate; The composite chelating agent includes citric acid and acetylacetone.

3. The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal according to claim 2, characterized in that: The functional regulating precursor is 0.8 to 50 parts by weight; The functional regulating precursor is selected from at least one of cyclic polyhydroxy thiorecognition monomers and guanidine precursors.

4. The modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal according to claim 3, characterized in that: The cyclic polyhydroxy thiorecognition monomer is a thiomodified β-cyclodextrin; The guanidino precursor is selected from at least one of cyanamide, dicyandiamide, guanidine, and guanidine nitrate; A method for preparing a highly selective thallium-removing modified iron-phosphorus-doped titanium-based composite material as described in any one of claims 1 to 4, characterized in that it comprises the following steps: S1. Preparation of the mixed solution: The titanium source, iron source and composite chelating agent are mixed in an alcohol solvent to prepare a precursor mixed solution; S2. Controlled hydrolysis: Under stirring conditions, an alcohol-water mixture is added dropwise to the precursor mixture as a hydrolysis initiator to construct a Ti-O-Ti primary framework; S3. Doping and functionalization: Add a phosphorus source to the system obtained in step S2; S4. In-situ reaction: The system is heated to 70~90℃ to carry out an in-situ crosslinking reaction; S5. Post-processing: The product is obtained after centrifugation, drying, grinding and heat treatment; When the weight part of the functional regulating precursor is 0, the heat treatment is calcination at 300~500℃; When the weight percentage of the functional adjustment precursor is not 0, the heat treatment is constant temperature curing at 60~120℃.

5. The preparation method according to claim 5, characterized in that, It also includes the step of introducing a functional regulation precursor, wherein the functional regulation precursor is a cyclic polyhydroxy thiorecognition monomer and / or a guanidine precursor; When a cyclic polyhydroxy thiorecognition monomer is introduced, in step S3, the pH value of the system obtained in step S2 is adjusted to 3-5 before the cyclic polyhydroxy thiorecognition monomer is added. When a guanidine precursor is introduced, the guanidine precursor is added in step S1, and a multifunctional crosslinking agent is added in step S3.

6. The preparation method according to claim 6, characterized in that: The multifunctional crosslinking agent is glutaraldehyde; The cyclic polyhydroxy thiorecognition monomer is a thiomodified β-cyclodextrin, which is prepared by the following steps: β-cyclodextrin is dissolved in an alkaline solution, epichlorohydrin is added dropwise at 30~60℃ for cross-linking pretreatment, then thiourea is added, and the temperature is raised to 60~90℃ for thiolation reaction. After purification and drying, the product is obtained.

7. The preparation method according to claim 7, characterized in that: The alkaline solution is a sodium hydroxide or potassium hydroxide solution; The molar ratio of β-cyclodextrin to epichlorohydrin is 1:(5~15); The dropping rate of epichlorohydrin was 0.5~2.0 mL / min, and the pretreatment time was 2~4 h; The molar ratio of thiourea to β-cyclodextrin was (8~12):1, and the thiolation reaction time was 4~12h.

8. The preparation method according to claim 6, characterized in that: In step S1, the composite chelating agent includes citric acid and acetylacetone, wherein the molar ratio of acetylacetone to titanium source is (0.2~0.5):1; and the molar ratio of citric acid to iron source is (4~6):

1. In step S2, the system temperature is controlled at 0~10℃, and the dropping rate of the hydrolysis initiator is 0.5~2.0mL / min; In step S4, the heating reaction time is not less than 2 hours.

9. The application of a modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal as described in any one of claims 1 to 4, or the modified iron-phosphorus-doped titanium-based composite material for highly selective thallium removal prepared by the preparation method described in any one of claims 5 to 9, in the treatment of thallium-containing industrial wastewater.

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