Titanium-based lithium ion adsorbent, preparation method and application thereof

Abstract

This invention relates to the field of ion sieve technology, providing a titanium-based lithium-ion adsorbent, its preparation method, and its applications. The invention involves pyrolyzing NH2-MIL-125(Ti), then mixing it with lithium carbonate for calcination, granulating it using an ethylene-vinyl alcohol copolymer as a binder, and finally acid washing to obtain the titanium-based lithium-ion adsorbent. This invention integrates metal-organic framework (MOF)-derived carbon intercalation, nitrogen doping, and polymer-assisted granulation into a single process, preparing a particulate adsorbent with a hierarchical porous structure, strong hydrophilicity, and abundant active sites, showing great potential for industrial applications. Example results show that the adsorbent of this invention, under conditions of pH=12 and 25℃, exhibits a high Li-ion concentration of 24 h. + The adsorption capacity reached 33.95 mg / g. After five cycles of adsorption and desorption, the adsorption capacity could still reach 96.9% of the initial adsorption capacity, and the titanium dissolution loss in each cycle was only about 0.4%.

Description

Technical Field

[0001] This invention relates to the field of ion sieve technology, and in particular to a titanium-based lithium ion adsorbent, its preparation method, and its application. Background Technology

[0002] The rapid expansion of the electric vehicle industry has significantly increased global demand for lithium, highlighting the urgent need for efficient and sustainable lithium extraction technologies. Among various lithium resources, salt lake brines and underground brines have attracted considerable attention due to their abundant reserves and relatively low production costs. Several technologies have been developed for recovering lithium from aqueous resources, including solvent extraction, membrane separation, electrochemical methods, and adsorption. Among these, adsorption is considered one of the most promising lithium extraction technologies for industrial application due to its advantages of low energy consumption, environmental friendliness, ease of operation, and high selectivity.

[0003] Currently, common lithium-ion adsorbents include aluminum-based salts, manganese-based lithium ion sieves (HMO), and titanium-based lithium ion sieves (HTO). Aluminum-based salt adsorbents generally suffer from limited lithium-ion adsorption capacity, making them unsuitable for large-scale lithium extraction. While manganese-based lithium ion sieves (HMO) possess some adsorption capacity, repeated adsorption-desorption cycles lead to manganese dissolution and loss, as well as material structural instability, resulting in rapid adsorption performance degradation and severely impacting long-term stability. In contrast, titanium-based lithium ion sieves (HTO), with their robust and stable Ti-O chemical bonds, exhibit not only superior theoretical adsorption capacity but also excellent chemical stability, demonstrating unique advantages in aqueous lithium resource extraction and becoming a key research focus for inorganic lithium adsorbents. However, current HTO adsorbents are mostly in powder form, and their practical applications still suffer from slow adsorption kinetics, actual adsorption capacity far lower than theoretical values, and poor recyclability.

[0004] To address the aforementioned issues in the practical application of HTO, researchers have explored various modification strategies, primarily including morphology and porosity engineering, surface modification, elemental doping, and granulation. Among these, improving the hydrophilicity of the HTO surface can effectively promote the desolvation and diffusion of lithium ions in the aqueous system, accelerating the adsorption rate. Elemental doping modification can introduce oxygen vacancies into the HTO material, increasing the active sites for lithium ion adsorption, thereby enhancing adsorption capacity and accelerating adsorption kinetics. Studies have shown that cobalt and nitrogen co-doped HTO adsorbents can achieve an adsorption capacity of 46.17 mg / g within 10 hours, with the performance improvement attributed to the synergistic effect of heteroatom modification and oxygen vacancy formation. Granulation is a key technology for converting powdered HTO into macroscale particles, significantly improving the material's flowability and permeability, making it suitable for industrial column adsorption operations. Currently, various polymer binders such as polyvinyl chloride (PVC), polyacrylonitrile (PAN), polyacrylamide (PAM), and polyethersulfone (PES) are used for HTO granulation.

[0005] While the aforementioned modification strategies can improve some of the properties of HTO adsorbents to a certain extent, they still have significant limitations and cannot achieve a synergistic improvement in all key performance aspects. To date, developing a particulate HTO adsorbent that simultaneously possesses a hierarchical porous structure, high hydrophilicity, abundant adsorption active sites, and robust mechanical integrity remains a major technical challenge in this field. Summary of the Invention

[0006] In view of this, the present invention provides a titanium-based lithium-ion adsorbent, its preparation method, and its application. The titanium-based lithium-ion adsorbent prepared by the present invention has a hierarchical porous structure, good hydrophilicity, abundant adsorption active sites, and is a particulate adsorbent with good recyclability, enabling efficient recovery of lithium from brine.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing a titanium-based lithium-ion adsorbent includes the following steps: NH2-MIL-125(Ti) was calcined for the first time to obtain N-TiO2 / C; The N-TiO2 / C and Li2CO3 were mixed, ground, and then subjected to a second calcination to obtain N-LTO / C; The N-LTO / C and ethylene-vinyl alcohol copolymer solution are mixed and granulated. The resulting granulated product is then acid-washed to obtain the titanium-based lithium ion adsorbent.

[0008] Preferably, the first calcination temperature is 600~800℃, the holding time is 5~8h, and the first calcination is carried out in a protective atmosphere.

[0009] Preferably, the molar ratio of Li in Li2CO3 to Ti in N-TiO2 / C is 2:1.

[0010] Preferably, the second calcination temperature is 500~700℃, and the holding time is 4~6h; the second calcination is carried out in a protective atmosphere.

[0011] Preferably, the mass ratio of the N-LTO / C and ethylene-vinyl alcohol copolymer solution is 2~5:1.

[0012] Preferably, the solvent of the ethylene-vinyl alcohol copolymer solution is N,N-dimethylacetamide; and the concentration of the ethylene-vinyl alcohol copolymer solution is 5~15wt%.

[0013] Preferably, the granulation product is further washed with water before acid washing.

[0014] Preferably, the acid used for pickling is hydrochloric acid, and the concentration of the hydrochloric acid is 0.1~0.5 mol / L.

[0015] The present invention also provides a titanium-based lithium-ion adsorbent prepared by the preparation method described above.

[0016] This invention also provides the application of the titanium-based lithium-ion adsorbent described above in lithium-ion adsorption. This invention provides a method for preparing a titanium-based lithium-ion adsorbent, comprising the following steps: first calcining NH2-MIL-125(Ti) to obtain N-TiO2 / C; mixing and grinding the N-TiO2 / C with Li2CO3 followed by a second calcination to obtain N-LTO / C; mixing the N-LTO / C with an ethylene-vinyl alcohol copolymer solution for granulation; and acid washing the resulting granulated product to obtain the titanium-based lithium-ion adsorbent. This invention uses amine-functionalized Ti-MOF (NH2-MIL-125(Ti)) as raw material, and obtains the titanium-based lithium-ion adsorbent through pyrolysis, calcination with lithium carbonate, granulation, and acid washing. This invention integrates metal-organic framework (MOF)-derived carbon embedding, nitrogen doping, and polymer-assisted granulation into a single process, achieving a synergistic effect, overcoming the inherent limitations of materials and obstacles in practical applications, and preparing a particulate adsorbent with strong hydrophilicity, hierarchical porosity, and abundant active sites. Compared with existing technologies, the titanium-based lithium-ion adsorbent prepared by this invention has the following beneficial effects: (1) It has a hierarchical porous structure and a large specific surface area: In this invention, NH2-MIL-125(Ti) is used as a precursor for pyrolysis. The resulting N-TiO2 / C can inherit the overall morphological integrity of MOF. After lithiation, it forms N-LTO / C with a hierarchical porous structure and a specific surface area as high as 59.78 m². 2 / g, far exceeding that of conventional solid-phase LTO; it still maintains 24.43m after granulation.2 The high specific surface area of ​​ / g provides a large number of exposed active sites for lithium ions, significantly improving the adsorption capacity.

[0017] (2) Excellent hydrophilicity: This invention uses NH2-MIL-125(Ti) as a precursor for derivatization synthesis. During the conversion process, in-situ N doping can be formed, resulting in abundant nitrogen- and oxygen-containing functional groups on the adsorbent surface, which effectively improves the surface wettability of the material and provides favorable interface conditions for the rapid adsorption and transport of lithium ions. The results of the examples show that the N-LTO / C / EVAL surface prepared by this invention has a water contact angle of only 28°, exhibiting strong hydrophilicity.

[0018] (3) High adsorption capacity and good selectivity: This invention induces a large number of oxygen vacancies through interstitial nitrogen doping, increasing low-energy adsorption sites and optimizing the charge environment; the obtained N-HTO / C / EVAL, under pH=12 and 25℃ conditions, Li + It has an adsorption capacity of up to 33.95 mg / g and excellent separation factor for competing ions, exhibiting extremely strong lithium selectivity in high-salinity brine.

[0019] (4) Good recyclability: The present invention uses EVAL as a binder for granulation to form a fibrous network structure. The particles are uniform, have good flowability and permeability, and completely solve the problem of difficult recycling of powdered HTO. In addition, the carbon matrix can form a protective coating on the HTO crystals. Combined with the intrinsic stability of Ti-O bonds, the cycling stability of the adsorbent material is greatly improved. The results of the examples show that the adsorbent material of the present invention still has a capacity retention rate of up to 96.9% after 5 adsorption-desorption cycles, and the titanium dissolution loss in each cycle is only about 0.4%, which is much lower than that of ordinary titanium-based adsorbents. It has excellent long-term stability. Attached Figure Description

[0020] Figure 1 The images show the morphology characterization results of various materials in the embodiments of the present invention, wherein: a~c are scanning electron microscope images of NH2-MIL-125(Ti), N-TiO2 / C and N-LTO / C, respectively; d~e are the elemental distribution map and transmission electron microscope image of N-LTO / C, respectively; and f is the scanning electron microscope image of N-LTO / C / EVAL. Figure 2The figures below represent the pore structure and surface chemical characterization results of the materials in the embodiments of the present invention, wherein: a is the XRD pattern of N-TiO2 / C, N-LTO / C, and N-LTO / C / EVAL; b is the N2 adsorption-desorption isotherm and BJH pore size distribution of N-LTO / C and LTO-d; c is the N2 adsorption-desorption isotherm and BJH pore size distribution of N-LTO / C / EVAL and LTO-d / EVAL; d is the water contact angle of N-LTO / C / EVAL; e~i are the high-resolution C1s, Li 1s, O 1s, N 1s, and Ti 2p XPS spectra of N-LTO / C and LTO-d, respectively; Figure 3 Images and adsorption performance test results of N-HTO / C / EVAL are shown below, where: a) is an image of N-HTO / C / EVAL in the embodiments of the present invention; b) is the adsorption performance of N-HTO / C / EVAL under different pH conditions; c) is the adsorption kinetic curves of N-HTO / C / EVAL according to the pseudo-first-order model (dashed line) and pseudo-second-order model (solid line); d) is the intraparticle diffusion model; e) is the liquid film diffusion model; f) is the adsorption performance of N-HTO / C / EVAL at different temperatures; g) is the thermodynamic fitting curve of lithium ion adsorption; h) is the adsorption performance of N-HTO / C / EVAL at different solid-liquid ratios; and i) is the isotherm fitting curve of N-HTO / C / EVAL. Figure 4 The results show the cyclic adsorption performance and selectivity of N-HTO / C / EVAL, where: a and b are the adsorption-desorption cycle performance of N-HTO / C / EVAL and HTO-d / EVAL and the dissolution rate of titanium, respectively, after five consecutive adsorption-desorption cycles; c is the XRD pattern of N-LTO / C / EVAL, N-HTO / C / EVAL, N-HTO / C / EVAL after the first adsorption (N-LTO / C / EVAL(A)), and N-LTO / C / EVAL after five cycles (N-LTO / C / EVAL(C)); d is the selectivity of N-HTO / C / EVAL. Detailed Implementation

[0021] This invention provides a method for preparing a titanium-based lithium-ion adsorbent, comprising the following steps: NH2-MIL-125(Ti) was calcined for the first time to obtain N-TiO2 / C; The N-TiO2 / C and Li2CO3 were mixed, ground, and then subjected to a second calcination to obtain N-LTO / C; The N-LTO / C and ethylene-vinyl alcohol copolymer solution are mixed and granulated. The resulting granulated product is then acid-washed to obtain the titanium-based lithium ion adsorbent.

[0022] This invention involves the first calcination of NH2-MIL-125(Ti) (an amino-functionalized titanium-based MOF material) to obtain N-TiO2 / C, wherein N-TiO2 / C is a composite material of nitrogen-doped titanium dioxide and carbon. In this invention, the NH2-MIL-125(Ti) is preferably synthesized via a solvothermal method. The specific preparation method preferably includes: dissolving tetrabutyl titanate and 2-aminoterephthalic acid in a solvent, homogenizing by ultrasonication, and then performing a solvothermal reaction. The resulting suspension is centrifuged, washed, and dried to obtain the NH2-MIL-125(Ti). The volume ratio of tetrabutyl titanate to 2-aminoterephthalic acid is preferably 1:4. The solvent is preferably a mixed solvent of N,N-dimethylformamide and methanol, with the volume ratio of N,N-dimethylformamide to methanol preferably being 9:1. The temperature of the solvothermal reaction is preferably 150°C, and the reaction time is preferably 24 hours.

[0023] In this invention, the preferred temperature for the first calcination is 600~800℃, specifically 600℃, and the preferred holding time is 5~8h, specifically 5h. The first calcination is preferably carried out in a protective atmosphere; the protective atmosphere is preferably nitrogen. During the first calcination process, NH2-MIL-125(Ti) undergoes pyrolysis, carbonization, and crystallization to form a MOF-derived nitrogen-doped titanium dioxide and carbon composite material, namely N-TiO2 / C.

[0024] After obtaining N-TiO2 / C, the present invention mixes and grinds the N-TiO2 / C and Li2CO3, then performs a second calcination to obtain N-LTO / C, wherein the N-LTO / C is a composite material of nitrogen-doped lithium titanate and carbon. In this invention, the molar ratio of Li in Li2CO3 to Ti in N-TiO2 / C is preferably 2:1; the grinding and mixing are preferably carried out in an agate mortar, and the grinding and mixing time is preferably 20-40 min, specifically 30 min; the second calcination temperature is preferably 500-700℃, specifically 600℃, and the holding time is preferably 4-6 h, specifically 5 h; the second calcination is preferably carried out in a protective atmosphere, preferably nitrogen; the second calcination is preferably carried out in a tube furnace. During the second calcination process, nitrogen-doped titanium dioxide and lithium carbonate react to generate nitrogen-doped lithium titanate.

[0025] In this invention, the specific surface area of ​​the N-LTO / C is 55~65 m² / g, and in the embodiment it is 59.78 m² / g, and the mesopore volume accounts for 55%~60% of the total pore volume.

[0026] After obtaining N-LTO / C, the present invention mixes the N-LTO / C with an ethylene-vinyl alcohol copolymer (EVAL) solution for granulation, and then acid-washes the resulting granulated product to obtain the titanium-based lithium-ion adsorbent. In this invention, the mass ratio of the N-LTO / C to the ethylene-vinyl alcohol copolymer solution is preferably 2~4:1, specifically 3:1; the solvent of the ethylene-vinyl alcohol copolymer solution is preferably N,N-dimethylacetamide; the concentration of the ethylene-vinyl alcohol copolymer solution is preferably 5~15wt%, specifically 10wt%; the ethylene-vinyl alcohol copolymer solution is used as a binder.

[0027] In a specific embodiment of the present invention, preferably, the ethylene-vinyl alcohol copolymer is dissolved in N,N-dimethylacetamide at 60°C under stirring to prepare a homogeneous copolymer solution. Then, N-LTO / C is added to the ethylene-vinyl alcohol copolymer solution, and the mixture is stirred to form a slurry. The resulting slurry is then cooled to room temperature. In the present invention, the granulation preferably includes: dripping the slurry into deionized water to form spherical particles, collecting the spherical particles to obtain the granulated product, denoted as N-LTO / C / EVAL; the injection is preferably performed using a syringe.

[0028] In this invention, the acid washing process preferably includes washing the granulated product with water to remove residual DMAC solvent.

[0029] In this invention, the acid used for pickling is hydrochloric acid, and the concentration of the hydrochloric acid is preferably 0.1~0.5 mol / L, specifically 0.2 mol / L; during the pickling process, hydrogen ions and lithium ions in N-LTO / C / EVAL undergo ion exchange.

[0030] After acid washing, the present invention preferably filters the product particles, rinses them with deionized water, and dries them at 60°C for 12 hours to obtain a titanium-based lithium ion adsorbent, which is denoted as N-HTO / C / EVAL.

[0031] The present invention also provides a titanium-based lithium-ion adsorbent prepared by the preparation method described above.

[0032] The present invention also provides the application of the titanium-based lithium ion adsorbent described above in lithium ion adsorption; in the present invention, the lithium ion adsorption specifically refers to the adsorption of lithium ions from brine, which can be salt lake brine or underground brine; the adsorption temperature is preferably 25~55℃, the pH value is preferably 9~13, more preferably 12~13, and the solid-liquid ratio is preferably 1:10~200 (g / mL).

[0033] In this invention, the adsorbed titanium-based lithium ion adsorbent is preferably regenerated and recycled. The regeneration method is preferably to acid wash the adsorbed titanium-based lithium ion adsorbent. The reagent used for acid washing is preferably hydrochloric acid solution, and the concentration of the hydrochloric acid solution is preferably 0.1~0.5 mol / L, specifically 0.2 mol / L.

[0034] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] Example 1 (1) Synthesis of NH2-MIL-125(Ti): 3 mmol of tetrabutyl titanate ((TiOC4H9)4) and 12 mmol of 2-aminoterephthalic acid (NH2-BDC) were dissolved in a mixed solvent of 36 mL N,N-dimethylformamide (DMF) and 4 mL methanol. After sonication for 30 min, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and heated at 150 °C for 24 h. Subsequently, the resulting suspension was centrifuged and thoroughly washed repeatedly with DMF and methanol. The final product was dried in an oven at 60 °C for 12 h.

[0036] (2) Preparation of N-TiO2 / C composite material: Using the prepared NH2-MIL-125(Ti) as a precursor, N-doped TiO2 / carbon (N-TiO2 / C) composite material was prepared by pyrolysis under a nitrogen atmosphere. The temperature was raised to 600℃ at a heating rate of 5℃ / min and held for 5 hours to complete the carbonization and crystallization process. The resulting black N-TiO2 / C composite material powder was collected for subsequent use.

[0037] (3) Synthesis of N-LTO / C: The prepared N-TiO2 / C was mixed with lithium carbonate (Li2CO3) in an agate mortar at a Li / Ti molar ratio of 2:1. After grinding for 30 minutes, the mixture was transferred to a tube furnace and calcined at 600°C for 5 hours under a nitrogen atmosphere to obtain nitrogen-doped Li2TiO3 / carbon composite material (N-LTO / C).

[0038] (4) Preparation of N-LTO / C / EVAL particles: Ethylene-vinyl alcohol copolymer (EVAL) was dissolved in N,N-dimethylacetamide (10% by mass) under continuous stirring at 60°C to prepare a homogeneous polymer solution. Then, 20.0 g of N-LTO / C powder was added to the EVAL solution and stirred to form a slurry. After cooling to room temperature, the slurry was injected dropwise into deionized water at 25°C using a syringe to form spherical particles. These spherical particles were collected and repeatedly rinsed with deionized water.

[0039] (5) Preparation of N-HTO / C / EVAL: Spherical particles were subjected to ion exchange treatment with 0.2 M hydrochloric acid (HCl) solution at 25 °C. The particles were filtered, washed with deionized water, and dried at 60 °C for 12 hours to obtain N-HTO / C / EVAL.

[0040] Comparative Example 1 Lithium titanate was synthesized by conventional solid-state method: anatase TiO2 and lithium carbonate (Li2CO3) were weighed at a Li / Ti molar ratio of 2:1 and mixed and ground in an agate mortar for 30 minutes. The mixed powder was then placed in a crucible and heated to 600℃ in a muffle furnace at a heating rate of 5℃ / min. The mixture was then calcined for 5 hours to obtain white Li2TiO3 (LTO) powder, denoted as LTO-d.

[0041] Following the method in step (4) of Example 1, the obtained lithium titanate was used to replace the N-LTO / C powder for granulation to prepare LTO-d / EVAL.

[0042] Following the method in step (5) of Example 1, LTO-d / EVAL was subjected to ion exchange treatment with hydrochloric acid to obtain HTO-d / EVAL.

[0043] Characterization and performance testing: Figure 1 The images show the morphology characterization results of various materials in the embodiments of the present invention, wherein: a~c are scanning electron microscope images of NH2-MIL-125(Ti), N-TiO2 / C and N-LTO / C, respectively; d~e are the elemental distribution map and transmission electron microscope image of N-LTO / C, respectively; and f is the scanning electron microscope image of N-LTO / C / EVAL.

[0044] according to Figure 1 It can be seen that N-LTO / C is prepared from a well-defined NH2-MIL-125(Ti) precursor, exhibiting a uniform coin-like morphology and excellent dispersibility. Figure 1(a) A stepwise calcination strategy was adopted. First, the MOF template was converted into N-TiO2 / C under a nitrogen atmosphere, and then reacted with lithium carbonate in a solid phase to obtain the final N-LTO / C. Notably, this transformation process maintained the overall morphological integrity of the MOF precursor while gradually roughening the surface, indicating in-situ crystallization and the possible development of a porous structure. Figure 1 (b, c). Energy-dispersive X-ray spectroscopy (EDS) confirmed the uniform distribution of C, N, Ti, and O elements throughout the LTO crystal, verifying the successful and uniform doping of elements from NH2-MIL-125(Ti). Figure 1 (d). High-resolution transmission electron microscopy (HRTEM) further revealed clear lattice fringes with a spacing of 0.480 nm, corresponding to the (002) crystal plane of lithium titanate. Figure 1 (e). Crucially, the LTO crystals are embedded within a continuous amorphous carbon matrix, forming a robust N-LTO / C composite material. To enable the practical application of the powder adsorbent, N-LTO / C was granulated using an ethylene-vinyl alcohol (EVAL) copolymer binder. Scanning electron microscopy (SEM) observation of the resulting N-LTO / C / EVAL particles revealed that the N-LTO / C particles were effectively connected through a fibrous EVAL network, forming uniform interparticle channels. Figure 1 (f). This hierarchical pore structure is crucial for facilitating efficient mass transfer and improving accessibility to adsorption sites during lithium recovery.

[0045] Figure 2 The following are the pore structure and surface chemical characterization results of the materials in the embodiments of the present invention, wherein: a is the XRD pattern of N-TiO2 / C, N-LTO / C and N-LTO / C / EVAL; b is the N2 adsorption-desorption isotherm and BJH pore size distribution of N-LTO / C and LTO-d; c is the N2 adsorption-desorption isotherm and BJH pore size distribution of N-LTO / C / EVAL and LTO-d / EVAL; d is the water contact angle of N-LTO / C / EVAL; e~i are the high-resolution C1s, Li 1s, O 1s, N 1s and Ti 2p XPS spectra of N-LTO / C and LTO-d, respectively.

[0046] Throughout the synthesis process, the crystalline phases were identified using X-ray diffraction (XRD). Figure 2As shown in Figure a, the diffraction pattern of N-TiO2 / C matches well with that of anatase TiO2 (JCPDS No. 73-1764), while the diffraction pattern of N-LTO / C corresponds to that of Li2TiO3 (JCPDS No. 33-0813), indicating that complete lithiation was achieved after calcination of lithium carbonate. Notably, the XRD pattern of N-LTO / C / EVAL is consistent with that of N-LTO / C powder, indicating that the crystallinity was well maintained after granulation. In contrast, pristine LTO (labeled LTO-d) was synthesized from anatase powder and lithium carbonate using a conventional solid-state method. Nitrogen adsorption-desorption measurements showed that both N-LTO / C and LTO-d exhibited a type IV isotherm with a hysteresis loop, characteristic of mesoporous / macroporous structures. Figure 2 (b) The pore size distribution calculated using the Barrett–Joyner–Halenda (BJH) method further confirms the hierarchical pore structure. As summarized in Table 1, the specific surface area of ​​N-LTO / C (59.78 m² / g) is significantly greater than that of LTO-d (3.51 m² / g), and the average pore size is smaller (13.14 nm vs. 42.14 nm). This significant increase in surface area implies more exposed adsorption sites in N-LTO / C. Mesopores dominate in N-LTO / C, providing a high surface area to accommodate a large number of adsorption sites, while significant macroporosity (58.71% of total pore volume) ensures efficient mass transfer. This structural design effectively addresses the common trade-off between high adsorption capacity and rapid kinetics. After granulation, the surface area of ​​N-LTO / C / EVAL decreases to 24.43 m² / g, but it is still superior to its conventional counterpart LTO-d / EVAL (6.59 m² / g). Figure 2 (c)

[0047] Table 1. Test results of the hole structure

[0048] Surface wettability is a key factor affecting solid-liquid interaction during adsorption, and it was evaluated using contact angle measurements. The contact angle of N-LTO / C / EVAL was 28°. Figure 2 (d) indicates its good hydrophilicity. This improvement is attributed to the nitrogen- and oxygen-containing functional groups introduced during the MOF derivatization synthesis, which is beneficial to Li + Desolvation and diffusion.

[0049] X-ray photoelectron spectroscopy (XPS) analysis elucidated the surface chemical state and doping effects. High-resolution C 1s spectrum ( Figure 2(e) reveals characteristic peaks corresponding to the CC / C=C (284.8 eV), CO / N (285.6 eV), C=O (288.8 eV), and graphite π-π transition satellite peak (290.1 ​​eV). The presence of the C–O / N bond is consistent with nitrogen doping and contributes to improved hydrophilicity. The Li 1s peak at 55.05 eV confirms successful lithiation ( Figure 2 decomposition of the O 1s spectrum (f). Figure 2 (g) at 531.0 eV (lattice oxygen, O) Lat ), 532.0 eV (oxygen vacancy, O V ) and 532.8 eV (surface hydroxyl / adsorbed water, OH) - Three components are shown at (). O in N-LTO / C v The integrated peak area is 2.1 times that of LTO-d, indicating that oxygen vacancies are more abundant in N-LTO / C, which is more favorable for Li + Adsorption. The oxygen vacancy content is significantly higher in N-LTO / C, which is attributed to interstitial nitrogen doping and is expected to promote Li adsorption. + Diffusion and enhanced adsorption capacity. The N 1s spectrum shows peaks at 398.5 eV and 401.0 eV, which is attributed to interstitial nitrogen doping in the Ti–O lattice, as confirmed by the absence of N–Ti bonds near 397 eV. Figure 2 (h). This is also supported by the Ti 2p and O 1s spectra. The Ti 2p spectrum shows two characteristic Ti... 4+ The peaks are located at 458.6 eV (Ti2p3 / 2) and 464.35 eV (Ti2p1 / 2), respectively. Figure 2 (i). Compared to LTO-d, these two peaks were positively shifted by 0.2 eV and 0.25 eV, respectively, consistent with the combined effects of oxygen vacancy formation and lattice distortion. Therefore, the N-LTO / C composite successfully integrates a hierarchical porous structure, high specific surface area, enhanced hydrophilicity, and favorable surface chemistry. Crucially, interstitial nitrogen doping not only improves surface wettability by adding electron polarity but also induces a large number of oxygen vacancies. These oxygen vacancy sites create a favorable local charge environment and may serve as a low-energy pathway, thereby promoting Li… + This process diffuses and enhances adsorption capacity. This synergistic modification of physical structure (porosity, surface area) and chemical properties (wetting properties, defect chemistry) addresses the common trade-off between high capacity and rapid kinetics, demonstrating a rational material design strategy.

[0050] Figure 3Images and adsorption performance test results of N-HTO / C / EVAL are shown below, including: (a) an image of N-HTO / C / EVAL in the embodiments of the present invention; (b) the adsorption performance of N-HTO / C / EVAL under different pH conditions (test conditions: lithium chloride solution, initial lithium ion concentration of 600 mg / L, 25℃, solid-liquid ratio of 1:100); (c) adsorption kinetic curves of N-HTO / C / EVAL according to the pseudo-first-order model (dashed line) and pseudo-second-order model (solid line); (d) intraparticle diffusion model; (e) ... Liquid film diffusion model; (f) shows the adsorption performance of N-HTO / C / EVAL at different temperatures (test conditions: lithium chloride solution, initial lithium ion concentration of 600 mg / L, pH=12, solid-liquid ratio of 1:100); (g) shows the thermodynamic fitting curve of lithium ion adsorption; (h) shows the adsorption performance of N-HTO / C / EVAL at different solid-liquid ratios (test conditions: lithium chloride solution, initial lithium ion concentration of 600 mg / L, 25℃, pH value of 12); (i) shows the isotherm fitting curve of N-HTO / C / EVAL.

[0051] Due to its synergistic structure and surface design, the acid-washed particulate adsorbent (N-HTO / C / EVAL) achieved an adsorption capacity increase of 32.68 mg / g in a lithium chloride solution at pH 12 within 12 hours. Figure 3 (b) This performance is superior to its conventional reference standard LTO-d / EVAL (25.38 mg / g, 24 h). The enhanced adsorption capacity and shortened equilibrium time may be attributed to the hierarchical porous structure, high hydrophilicity, and increased adsorption sites of N-LTO / C / EVAL. To elucidate the adsorption behavior, the adsorption kinetics, thermodynamics, and performance in simulated brine were systematically studied. Figure 3 As shown in Figure b, Li under alkaline conditions (pH>11) + The adsorption capacity increased significantly, reaching a maximum of 39.76 mg / g at pH 13 within 12 hours, showing a clear pH dependence. Several kinetic models were used to analyze the experimental data, including pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models. The adsorption kinetics best fit the pseudo-second-order model, as evidenced by its high correlation coefficient (R²). 2 This is reflected in the close consistency between the calculated equilibrium adsorption capacity and the experimental value. Figure 3 (c). This strongly suggests that chemisorption, achieved through ion exchange between lithium and hydrogen ions, is the main mechanism controlling the lithium absorption process.

[0052] Further analysis using an intraparticle diffusion model revealed a multi-stage adsorption process. Figure 3(d). The initial stage (Stage I) is attributed to the rapid diffusion of lithium ions to the adsorbent surface via the liquid phase. The second stage involves intraparticle diffusion (Stage II), during which lithium ions gradually migrate into the porous network of N-HTO / C / EVAL. The third stage (Stage III) corresponds to the adsorption equilibrium stage. Notably, the fitted lines for these stages do not pass through the origin, indicating that intraparticle diffusion is not the sole factor controlling the rate step. The significant influence of boundary layer diffusion is further confirmed by the fitting results of the liquid film diffusion model, suggesting that surface diffusion and intraparticle diffusion jointly determine the overall adsorption kinetics. Figure 3 (e). This mechanism is consistent with the hierarchical porous structure of the adsorbent, which facilitates stepwise mass transfer.

[0053] The effect of temperature on adsorption performance, such as Figure 3 As shown in f, the adsorption capacity of N-HTO / C / EVAL gradually increases with increasing temperature, indicating that this is an endothermic process. This result is supported by thermodynamic analysis (…). Figure 3 The positive enthalpy change (ΔH) was quantitatively confirmed. 0 >0) confirms Li + -H + The endothermic property of heat exchange. Positive standard entropy change (ΔS) 0 A value >0 indicates an increase in disorder at the solid-liquid interface during adsorption. Crucially, the negative value of the standard Gibbs free energy change (ΔG) indicates an increase in disorder at the solid-liquid interface during adsorption. 0 The value <0 confirms that the adsorption process is spontaneous at all test temperatures. As temperature increases, |ΔG 0 The increasing value of | indicates that higher temperatures are more favorable for adsorption. The operating parameters were further optimized by examining the solid-liquid ratio (S / L) and the initial lithium-ion concentration. Figure 3 As shown in h, a lower S / L ratio can improve adsorption capacity because it provides more relative availability of adsorption sites. The adsorption equilibrium isotherm was analyzed using the Langmuir, Freundrich, and Sypsy models. Figure 3 (i). High and comparable correlation coefficients for all models (R² for all models). 2 The values ​​(all greater than 0.98) indicate complex adsorption behavior. The Sips model fits slightly better than other models, meaning that the adsorption phenomenon is best described as monolayer chemisorption occurring on the inhomogeneous N-HTO / C / EVAL surface. This phenomenon can be explained by the composite properties of the material, i.e., chemisorption occurs at various active sites with different energies.

[0054] Figure 4The results show the cyclic adsorption performance and selectivity of N-HTO / C / EVAL, where: (a) and (b) are the adsorption-desorption cycle performance of N-HTO / C / EVAL and HTO-d / EVAL for five consecutive cycles and the dissolution rate of titanium, respectively (test conditions: lithium chloride solution, initial lithium ion concentration of 600 mg / L, 25℃, pH=12, solid-liquid ratio of 1:100); (c) are the XRD patterns of N-LTO / C / EVAL, N-HTO / C / EVAL, N-HTO / C / EVAL after the first adsorption (N-LTO / C / EVAL(A)), and N-LTO / C / EVAL (N-LTO / C / EVAL(C)) after five cycles; (d) is the selectivity of N-HTO / C / EVAL (test conditions: 25℃, pH=9, solid-liquid ratio of 1:100, competing ions are K+, K+, and K+, C+, and E-C ... + Ca 2+ Mg 2+ and Na + ).

[0055] The cycling stability and structural integrity of adsorbents are crucial for practical applications. For example... Figure 4 As shown in Figure a, N-HTO / C / EVAL exhibits extremely high stability in five adsorption-desorption cycles, with an initial capacity retention of 96.9% and a titanium dissolution loss of approximately 0.4% per cycle. In contrast, conventional HTO-d / EVAL shows a more significant capacity loss (6.65%) and a higher titanium dissolution loss (approximately 0.5% per cycle). Figure 4 (b). The exceptional stability of N-HTO / C / EVAL is attributed to its robust Ti-O structure and protective carbon matrix derived from MOF precursors, which prevent structural degradation during acid washing.

[0056] The structural evolution during the entire adsorption-desorption cycle was monitored by XRD. The diffraction patterns of N-LTO / C / EVAL, acid-washed N-HTO / C / EVAL, adsorbed (N-LTO / C / EVAL(A)), and (N-LTO / C / EVAL(C)) after five cycles are shown below. Figure 4 As shown in c, the diffraction pattern of N-LTO / C / EVAL is observed to be a very good match with that of Li₂TiO₃ (JCPDS #33-0813). The conversion to N-HTO / C / EVAL by acid washing induced a significant structural change, manifested as the disappearance of the (-133) plane. Crucially, the diffraction pattern remained stable in subsequent cycles, indicating excellent structural reversibility. The shift of the systematic peaks to higher angles observed in all particulate samples is attributed to isotropic compressive stress caused by the shrinkage of the EVAL adhesive during drying, resulting in slight lattice shrinkage.

[0057] In simulated saline containing competing cations ( Figure 4 The selectivity of N-HTO / C / EVAL was evaluated in section d). N-HTO / C / EVAL exhibited excellent selectivity for lithium ions, with separation factors of 140.52, 76.98, 24.45, and 21.46 for α(Li / Na), α(Li / K), α(Li / Mg), and α(Li / Ca), respectively. This superior selectivity stems from the synergistic effect of the ion-sieving effect of the HTO crystal structure and the customized surface chemistry. In summary, the N-HTO / C / EVAL particles obtained from MOFs demonstrate excellent performance in efficient lithium extraction, which is attributed to their innovative structural and chemical design. The hierarchical porosity solves the mass transfer limitation problem, and the N-doping and O-doping... V The combination of these elements enhances the adsorption sites and kinetics, while the stable HTO crystal structure provides ion sieve selectivity. This comprehensive approach, through synergistic achievement of high capacity, rapid reaction rate, excellent selectivity, and robust cycling performance, successfully addresses key challenges and highlights its significant potential for industrial lithium extraction from brine resources.

[0058] In summary, this invention develops a multi-level design strategy to manufacture a novel, highly hydrophilic nitrogen-doped particulate HTO for efficient lithium recovery from brine. The method involves pyrolyzing amine-functionalized Ti-MOF (NH2-MIL-125(Ti)), followed by calcination with lithium carbonate, granulation using an ethylene-vinyl alcohol copolymer as a binder, and acid washing to obtain the target product. The titanium-based lithium-ion adsorbent prepared by this invention possesses a hierarchical porous structure, strong hydrophilicity, and abundant exposed adsorption sites; these characteristics collectively shorten the lithium recovery time. + The diffusion pathway is improved and the adsorption efficiency is enhanced. This invention combines the design concept of metal-organic framework (MOF) materials with the practical application needs of adsorption engineering, providing a high-performance particulate adsorbent for sustainable lithium extraction and opening up a completely new technical path.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a titanium-based lithium-ion adsorbent, characterized in that, Includes the following steps: NH2-MIL-125(Ti) was calcined for the first time to obtain N-TiO2 / C; The N-TiO2 / C and Li2CO3 were mixed, ground, and then subjected to a second calcination to obtain N-LTO / C; The N-LTO / C and ethylene-vinyl alcohol copolymer solution are mixed and granulated. The resulting granulated product is then acid-washed to obtain the titanium-based lithium ion adsorbent.

2. The preparation method according to claim 1, characterized in that, The first calcination temperature is 600~800℃, the holding time is 5~8h, and the first calcination is carried out in a protective atmosphere.

3. The preparation method according to claim 1, characterized in that, The molar ratio of Li in Li2CO3 to Ti in N-TiO2 / C is 2:

1.

4. The preparation method according to claim 1, characterized in that, The second calcination temperature is 500~700℃, and the holding time is 4~6h; the second calcination is carried out in a protective atmosphere.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the N-LTO / C and ethylene-vinyl alcohol copolymer solution is 2~5:

1.

6. The preparation method according to claim 1, characterized in that, The solvent for the ethylene-vinyl alcohol copolymer solution is N,N-dimethylacetamide; the concentration of the ethylene-vinyl alcohol copolymer solution is 5~15wt%.

7. The preparation method according to claim 1, characterized in that, The process before acid washing also includes washing the granulated product with water.

8. The preparation method according to claim 1, characterized in that, The acid used for pickling is hydrochloric acid, and the concentration of the hydrochloric acid is 0.1~0.5 mol / L.

9. The titanium-based lithium-ion adsorbent prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the titanium-based lithium-ion adsorbent according to claim 9 in lithium-ion adsorption.

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