Polydopamine modified metatitanic acid type lithium ion sieve and preparation method thereof

Abstract

The invention discloses a polydopamine modified metatitanic acid type lithium ion sieve and a preparation method thereof, and belongs to the technical field of lithium ion sieves, the preparation method comprises the following steps: grinding and uniformly mixing lithium acetate dihydrate and titanium dioxide in an organic solvent, and calcining the mixture at 650-800 DEG C for 3-5 hours to prepare a Li2TiO3 precursor; the preparation method comprises the following steps: putting dopamine hydrochloride, aminated crown ether and a Li2TiO3 precursor into a tris (hydroxymethyl) aminomethane solution with the pH value of 8-9, carrying out a constant-temperature oscillation reaction, carrying out suction filtration, and drying at low temperature, so as to obtain the polydopamine modified metatitanic acid type lithium ion sieve. According to the lithium ion sieve, the adsorption effect on lithium ions can be improved, the lithium extraction efficiency is improved, and the problem of low adsorption capacity of a lithium ion sieve in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion sieve technology, specifically relating to a polydopamine-modified metatitanic acid lithium-ion sieve and its preparation method. Background Technology

[0002] Lithium, as an important metallic element in the new energy field, has seen a gradual increase in demand due to the development and application of new energy technologies in recent years. Lithium-containing materials are widely used in aerospace, glass and battery, and metallurgy, with lithium being particularly prevalent in the battery industry. Compared to traditional lead-acid batteries, lithium-ion batteries have advantages such as higher specific energy, longer lifespan, and higher power, and are widely used in new energy vehicle production, electrical appliance manufacturing, and other related industries. Therefore, the demand for lithium is very high.

[0003] Lithium resources exist in nature as solid mineral resources and liquid mineral deposits, and the extraction methods differ depending on their form. Lithium-bearing ores such as spodumene and lepidolite are the main forms of solid lithium resources. Traditional ore-based lithium extraction technologies are costly and generate significant waste. Furthermore, due to the early development of ore-based lithium extraction technologies, long-term exploitation has led to the depletion of ore-based lithium resources. Besides solid lithium resources, lithium-containing salt lake brines and underground brines are also important liquid lithium resources.

[0004] Currently, the main processes for lithium extraction from salt lake brine include precipitation, extraction, membrane separation, adsorption, carbonization, calcination leaching, Schereschewsky process, and electrodialysis. Among these, adsorption offers advantages such as simplicity, high selectivity, high recovery rate, and environmental friendliness. In lithium extraction from salt lake brine, the core principle of lithium-ion adsorbents is based on the physical or chemical interaction between the target component and the adsorbent surface or pores, resulting in a significantly higher concentration of the target component in the adsorbent compared to other components. Lithium-ion sieves, as commonly used adsorption materials, are classified into aluminum-based, manganese-based, and titanium-based sieves according to their core elements. Titanium-based lithium-ion sieves exhibit higher ion selectivity and structural stability, along with advantages such as good acid resistance, low titanium dissolution loss, relatively stable adsorption performance, and the ability to be recycled multiple times. However, they still suffer from drawbacks such as high calcination temperature, large particle size, dense surface, poor hydrophilicity, long adsorption time, and low capacity. Summary of the Invention

[0005] To address the aforementioned shortcomings in the prior art, this invention provides a polydopamine-modified metatitanic acid lithium-ion sieve and its preparation method. This lithium-ion sieve can improve the adsorption effect of lithium ions, increase lithium extraction efficiency, and solve the problem of low capacity in existing lithium-ion sieves.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: A method for preparing a polydopamine-modified metatitanic acid type lithium-ion sieve includes the following steps: (1) Lithium acetate dihydrate and titanium dioxide are ground and mixed in an organic solvent, the mixture is dried, the mixture is heated to 650-800℃ at a uniform rate and calcined for 3-5 hours to obtain Li2TiO3 precursor; (2) Dopamine hydrochloride, amino crown ether and Li2TiO3 precursor were placed in a tris(hydroxymethyl)aminomethane solution with a pH of 8-9, stirred and mixed, and then reacted under constant temperature and shaking. After filtration, the mixture was dried at low temperature to obtain polydopamine-modified metatitanic acid lithium ion sieve.

[0007] Furthermore, in step (1), the mass ratio of lithium acetate dihydrate to titanium dioxide is 2-3:1.

[0008] Furthermore, the concentration of the tris(hydroxymethyl)aminomethane solution in step (2) is 9-11 mmol / L.

[0009] Furthermore, the mass ratio of dopamine hydrochloride to Li2TiO3 precursor is 0.05-0.3:1.

[0010] Furthermore, in step (2), the mass ratio of the aminated crown ether to the Li2TiO3 precursor is 0.05-1.5:1.

[0011] Furthermore, in step (2), the shaking reaction temperature is 35-45℃, the reaction time is 5-8h, and the shaking speed is 160-180 r / min.

[0012] A polydopamine-modified metatitanic acid type lithium-ion sieve is prepared by the above method.

[0013] The beneficial effects of this invention are as follows: In this application, polydopamine is modified on the surface of a lithium-ion sieve, which significantly reduces the contact angle of the sample surface and enhances the hydrophilicity of the lithium-ion sieve surface, thereby promoting the extraction of lithium ions. During the modification of polydopamine, an amino crown ether is added. The catechol / amino group of polydopamine undergoes a cross-linking reaction with the amino group of the crown ether, embedding the crown ether in the polydopamine network. The crown ether serves as a specific coordination site for lithium ions, thereby improving the recognition effect of lithium ions and enhancing the recognition of lithium ions. As a result, the maximum adsorption capacity of the lithium-ion sieve modified with polydopamine in this invention is increased to 50.65 mg / g, which is higher than that of the lithium-ion sieve without polydopamine modification.

[0014] Furthermore, the introduction of amino crown ethers during polydopamine modification enables strong binding between the crown ethers and polydopamine through amide bonds, making the crown ethers less prone to detachment, thus improving their stability and extending the service life of the lithium ion sieve. Attached Figure Description

[0015] Figure 1 A schematic diagram of the preparation process of lithium-ion sieve precursors; Figure 2 XRD patterns of samples with different dopamine dosages; Figure 3 XRD patterns of the modified samples after different mixing times; Figure 4 Contact angle test results of samples with different dopamine dosages; a is the contact angle of Li2TiO3 sample; b is the contact angle of PDA sample. 0.05 -Contact angle of Li2TiO3 sample; c is the PDA. 0.1 -Contact angle of the Li2TiO3 sample; d is the PDA. 0.2 -Contact angle of the Li2TiO3 sample; e is the PDA. 0.3 -Contact angle of the Li2TiO3 sample; Figure 5 Figure 1 shows the contact angle test results of samples after different mixing times; a represents the 2h PDA. 0.2 -Li2TiO3; b is 4hPDA 0.2 -Li2TiO3; c is 6h PDA 0.2 -Li2TiO3; d is 8h PDA 0.2 -Li2TiO3; e is 10h PDA 0.2 -Li2TiO3; f is 12h PDA 0.2 -Li2TiO3; Figure 6 SEM images of samples with different dopamine dosages; a is Li2TiO3; b is PDA. 0.05 -Li2TiO3; c is PDA 0.1 -Li2TiO3; d represents PDA 0.2 -Li2TiO3; e represents PDA 0.3 -Li2TiO3; Figure 7 SEM images of samples after different mixing times; a is 2h PDA. 0.2 -Li2TiO3; b is 4h PDA 0.2 -Li2TiO3; c is 6h PDA 0.2 -Li2TiO3; d is 8h PDA 0.2 -Li2TiO3; e is 10h PDA 0.2 -Li2TiO3; f is 12h PDA 0.2 -Li2TiO3; Figure 8 FTIR spectra of different samples; Figure 9Statistical curves of Li⁺ acid elution rate for unmodified and PDA-modified samples; Figure 10 The graphs show the adsorption capacity changes of the unmodified sample and the PDA-modified sample over time. Figure 11 The elution rate and adsorption capacity curves are shown for samples with different dopamine dosages, where a is the elution rate and b is the adsorption capacity. Figure 12 For PDA 0.2 -Li2TiO3, PDA after acid washing 0.2 -H2TiO3, PDA after adsorption 0.2 -Li x H (2-x) XRD pattern of TiO3; Figure 13 For Li2TiO3, PDA 0.2 -Li2TiO3, PDA after acid washing 0.2 -H2TiO3, PDA after adsorption 0.2 -Li x H (2-x) XPS images of TiO3: a is the full spectrum of the sample, b is the 1s spectrum of Li, c is the 1s spectrum of N, d is the 2p spectrum of Ti, e is the 1s spectrum of C, and f is the 1s spectrum of O. Figure 14 The curves are linear fitting curves, where a represents pseudo-first-order dynamics and b represents pseudo-second-order dynamics. Figure 15 For different concentrations of Li + Langmuir and Freundlich isotherms in solution. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0017] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0018] The features and performance of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0019] Example 1 A polydopamine-modified metatitanic acid lithium-ion sieve, the preparation method of which includes the following steps: (1) Grind 4.68g of lithium acetate dihydrate in 25ml of anhydrous ethanol for 20min, then heat the mixture to form a suspension, add 1.8g of titanium dioxide to it and continue grinding and mixing, dry the solvent of the mixture and grind it into powder, heat the powder to 750℃ at a rate of 4℃ / min and calcine for 4h to obtain Li2TiO3 precursor; (2) Dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor were placed in a 10 mmol / L tris(hydroxymethyl)aminomethane solution with a pH of 8.5. The mass ratio of dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor was 0.2:1:1. The reaction was carried out at 40°C with constant shaking for 6 h at a shaking speed of 170 r / min. After filtration, the mixture was dried at 60°C to obtain a polydopamine-modified metatitanic acid lithium ion sieve (PDA). 0.2 -Li2TiO3).

[0020] Example 2 A polydopamine-modified metatitanic acid lithium-ion sieve, the preparation method of which includes the following steps: (1) Grind 3.6g of lithium acetate dihydrate in 25ml of anhydrous ethanol for 20min, then heat the mixture to form a suspension, add 1.8g of titanium dioxide to it and continue grinding and mixing, dry the solvent of the mixture and grind it into powder, heat the powder to 650℃ at a rate of 4℃ / min and calcine for 5h to obtain Li2TiO3 precursor; (2) Dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor were placed in a 9 mmol / L tris(hydroxymethyl)aminomethane solution with a pH of 9. The mass ratio of dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor was 0.05:0.05:1. The mixture was reacted at 45°C with constant shaking for 5 h at a shaking speed of 160 r / min. After filtration, the mixture was dried at 60°C to obtain a polydopamine-modified metatitanic acid lithium ion sieve (PDA). 0.05 -Li2TiO3).

[0021] Example 3 A polydopamine-modified metatitanic acid lithium-ion sieve, the preparation method of which includes the following steps: (1) Grind 5.4g of lithium acetate dihydrate in 25ml of anhydrous ethanol for 20min, then heat the mixture to form a suspension, add 1.8g of titanium dioxide to it and continue grinding and mixing, dry the solvent of the mixture and grind it into powder, heat the powder to 800℃ at a rate of 4℃ / min and calcine for 3h to obtain Li2TiO3 precursor; (2) Dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor were placed in a tris(hydroxymethyl)aminomethane solution with a pH of 8 and a concentration of 11 mmol / L. The mass ratio of dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor was 0.1:1.5:1. The reaction was carried out at 35°C with constant shaking for 8 h at a shaking speed of 180 r / min. After filtration, the mixture was dried at 60°C to obtain a polydopamine-modified metatitanic acid lithium ion sieve (PDA). 0.1 -Li2TiO3).

[0022] Example 4 A polydopamine-modified metatitanic acid lithium-ion sieve, the preparation method of which includes the following steps: (1) Grind 4g of lithium acetate dihydrate in 25ml of anhydrous ethanol for 20min, then heat the mixture to form a suspension, add 1.8g of titanium dioxide to it and continue grinding and mixing, dry the solvent of the mixture and grind it into powder, heat the powder to 700℃ at a rate of 4℃ / min and calcine for 4h to obtain Li2TiO3 precursor; (2) Dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor were placed in a 10 mmol / L solution of tris(hydroxymethyl)aminomethane at pH 8. The mass ratio of dopamine hydrochloride, amino crown ether, and Li2TiO3 precursor was 0.3:0.8:1. The mixture was reacted at 38°C with constant shaking for 7 h at a shaking speed of 175 r / min. After filtration, the mixture was dried at 60°C to obtain a polydopamine-modified metatitanic acid lithium ion sieve (PDA). 0.3 -Li2TiO3).

[0023] Test case I. Characterization Test Crystal structure analysis: Different masses of dopamine hydrochloride were weighed and mixed with Li₂TiO₃ precursor, and labeled as PDA. 0.05 -Li2TiO3, PDA 0.1 -Li2TiO3, PDA 0.2 -Li2TiO3, PDA 0.3-Li₂TiO₃ was used to prepare hydrophilic polydopamine-modified titanium-based lithium-ion sieves. XRD tests were performed on different lithium-ion sieves, and XRD diffraction patterns were plotted. The unit cell parameters of the prepared samples were compared with the data from the ICDD PDF# 33-0831 standard card. The results are shown in [Figure number missing]. Figure 2 The results showed that as the amount of dopamine hydrochloride added gradually increased, the diffraction peak intensity of the (002) crystal plane of the sample exhibited a trend of first slightly increasing and then decreasing. Meanwhile, the diffraction peak intensities of the other two main crystal planes also showed a fluctuating pattern of first slightly increasing and then slowly decreasing, with a relatively small overall intensity change. No additional diffraction peaks of weak intensity were shown in the figure, indicating that polydopamine had undergone surface modification. With the increase of dopamine hydrochloride dosage, especially in PDA... 0.2 -Li2TiO3 exhibits the most significant sharpness in its diffraction peaks, while other proportions show no obvious changes compared to the unmodified form; With PDA 0.2 Taking Li₂TiO₃ as an example, the effect of different mixing times on the crystal structure of the sample is shown in the figure. Figure 3 The results showed that when the mixing time reached 6 hours, the sharpness of the diffraction peaks of the (002) crystal plane of the sample reached its maximum value, indicating that the crystallinity of the sample was at its highest level and the integrity of the crystal morphology was optimal at this mixing time.

[0024] Contact angle analysis: Precursor Li₂TiO₃ was added to materials modified with dopamine hydrochloride at different addition ratios and pressed into solids of a certain thickness. During the pressing process, uniform stress on the powder was ensured to guarantee the surface flatness of the sample for testing. Then, water droplets were precisely dropped at a rate of 5 µL / drop. Upon contact with the sample, the water droplets instantly spread out on the surface of the solid tablet. The angle formed between the water droplet and the surface is the contact angle. Specific results are shown in [link to results]. Figure 4 The results showed that the contact angle of unmodified Li₂TiO₃ was 17.324°. With the addition of dopamine hydrochloride, the contact angle of the sample gradually decreased and then increased. The increase in angle may be due to excessive polymerization of polydopamine, resulting in overly dense C-C bonds covering the surface and increasing the area of ​​hydrophobic groups, thus reducing hydrophilicity. When 0.2 g of PDA was added... 0.2 When using -Li2TiO3, the contact angle drops to 8.665°.

[0025] Regarding the optimal addition amount (PDA) 0.2 (Li2TiO3), to study the effect of mixing time of polydopamine with the sample on hydrophilicity, see details. Figure 5 The results showed that the contact angle reached 8.665° when the mixing time was 6 hours. Compared with the lithium-ion sieve without polydopamine modification, the contact angle was significantly reduced, indicating that polydopamine can effectively improve the hydrophilicity of the lithium-ion sieve precursor.

[0026] Crystal morphology analysis: SEM images of hydrophilic modified samples with different addition ratios of polydopamine are shown in the figure. Figure 6 At 5kx magnification, the surface of the unmodified Li₂TiO₃ precursor exhibited an irregular morphology, lacking a large pore structure, and showing signs of agglomeration, which is detrimental to elution and adsorption. With the addition of dopamine hydrochloride, the microstructure of the obtained sample changed significantly; the agglomeration effect initially weakened and then strengthened, possibly due to excessive polymerization of polydopamine. This indicates that polydopamine modification can improve the efficiency of Li₂TiO₃ during subsequent acid elution. + and H + The exchange rate.

[0027] Regarding the optimal addition amount (PDA) 0.2 (Li2TiO3), the effect of mixing time on morphology was studied, see details. Figure 7 The results showed that as time increased, the morphology of the sample gradually became more regular, but after 6 hours, agglomeration gradually appeared, which was speculated to be due to excessive polymerization time of polydopamine, resulting in overpolymerization.

[0028] Fourier Transform Infrared Spectroscopy Analysis: FTIR analysis was performed on different samples; see details below. Figure 8 Curve a represents Li₂TiO₃, and curve b represents PDA modified with polydopamine. 0.2 -Li2TiO3, curve c represents the result after acid washing (PDA) 0.2 -H2TiO3) and curve d represents the adsorption of (PDA) 0.2 -Li x H (2-x) TiO3). The results showed that curve c was at 3490 cm⁻¹. -1 A small diffraction peak appeared at 3210 cm⁻¹, possibly indicating that polydopamine reacted under acidic conditions, causing the hydroxyl groups on the benzene ring to detach and form hydroxyl groups. Compared with the infrared spectrum of the unmodified sample, the polydopamine-modified sample showed a higher peak at 3210 cm⁻¹. -1 and 960 cm -1 Two new characteristic absorption peaks were added at 3210 cm⁻¹. -1 The relatively broad peak at that location may be due to the stretching vibration of the hydroxyl group (-OH) on the benzene ring, or it may be due to the Li + and H + Caused by an exchange; 960 cm -1 The characteristic peak at 900 cm⁻¹ corresponds to the out-of-plane bending vibration of hydrogen (CH) on the benzene ring. This peak is strong and sharp. Both peaks are related to the added dopamine hydrochloride, indirectly confirming that polydopamine does indeed adhere to the sample surface and can effectively improve its hydrophilicity. This provides strong spectroscopic evidence for improving adsorption capacity and reducing contact angle. -1Vibrations of Ti-OH were observed on both sides. During the acid washing process, changes in the chemical environment caused the breaking of chemical bonds. After adsorption, the -OH groups carried by polydopamine formed new forms of bonds with Ti, thus generating vibrations. Furthermore, at 1530 cm⁻¹… -1 The absorption peaks observed at the observed wavelengths are consistent with the vibrational characteristics of the Li-O bond, strongly demonstrating the successful synthesis of lithium titanate crystals.

[0029] II. Study on Elution and Adsorption Performance Effect of polydopamine modification on the elution rate of Li₂TiO₃: A 0.20 mol / L HCl solution was prepared using concentrated hydrochloric acid (36%-38%). 1 g of PDA-modified Li₂TiO₃ powder and 1 g of unmodified powder were weighed separately using a graduated cylinder. The prepared hydrochloric acid was then poured into an Erlenmeyer flask at a solid-liquid ratio of 1 g:100 ml. The Erlenmeyer flask was then placed in a 60℃ water bath and eluted for 12 h. During the acid washing process, samples were taken at 2-h intervals, with 4 ml of the supernatant collected each time. The Erlenmeyer flask was shaken every 0.5 h to ensure sufficient contact between the eluent and the ion sieve. After 12 h of acid washing, the samples were filtered and dried. The resulting products were either a PDA-modified hydrophilic lithium ion sieve (PDA-H₂TiO₃) or an unmodified lithium ion sieve (H₂TiO₃).

[0030] The obtained supernatant was diluted 500 times to ensure that the solution concentration reached the detection limit of the atomic absorption spectrophotometer. The absorbance was preferably in the range of 0.2-0.8. The Li⁺ concentration in the solution was determined, and then the Li⁺ acid elution rate of the unmodified precursor and the polydopamine-modified precursor at the points on the time gradient was calculated according to the elution rate formula.

[0031] The change in elution rate over time is as follows: Figure 9 The results showed that both Li₂TiO₃ and PDA-Li₂TiO₃ samples reached their maximum lithium-ion elution rate after 8 hours, and their maximum elution rates were very close, basically between 94-95%. PDA-Li₂TiO₃ did not show an advantage in elution rate. We speculate that this may be because polydopamine and amino crown ethers in PDA-Li₂TiO₃ account for a certain mass in the sample, resulting in a lower effective Li₂TiO₃ mass in the modified sample compared to the control sample Li₂TiO₃. Therefore, the calculated Li⁺ elution rate would be lower.

[0032] Experiment on the increase of adsorption rate over time: Preparation of Li +A 2 g / L LiOH adsorption solution was prepared, and the water bath temperature was set to 25℃. Adsorption was performed using a 1 g solid sample to 50 ml adsorption solution ratio (solid-liquid ratio 1:50), mixing polydopamine-modified and unmodified powders with LiOH solution for eight time periods (2, 4, 6, 8, 10, 12, 14, and 24 h). Adsorption equilibrium was expected to be reached within 24 h. A 4 ml sample of the supernatant was taken; this supernatant needed to be diluted 500 times to reach the detection limit of the atomic absorption spectrophotometer. The measured data were used to calculate the remaining lithium ion concentration in the adsorption solution. These two sets of experiments clearly and intuitively demonstrate the difference in lithium adsorption capacity between PDA-H₂TiO₃ and H₂TiO₃, as well as the varying degrees of modification of lithium ion sieves by polydopamine.

[0033] Using formula (1) for Li adsorption kinetics + Calculation of equilibrium adsorption capacity.

[0034] (1) In Equation 1, Q e (mg / g) represents the adsorption capacity when adsorption reaches equilibrium; C 0 (mg / L) represents the initial concentration of lithium ions in the solution; C e (mg / L) refers to the concentration of residual lithium ions in the solution after adsorption equilibrium; V (L) represents the volume of the adsorbed liquid in the system; m (g) is the mass of the lithium-ion sieve adsorbent used in the experiment.

[0035] The adsorption capacity calculated according to formula (1) is used to obtain an adsorption curve showing the change of adsorption capacity with time. Figure 10 The adsorption capacity of both unmodified and modified Li increased with time, but the adsorption capacity of the modified Li was not significantly higher than that of the unmodified Li. The reason for this is speculated to be that Li... + At a concentration of 2 g / L, the pH of the lithium hydroxide adsorbent solution is around 13.5. Polydopamine is easily degraded under alkaline conditions with a pH greater than 11.0, and the stronger the alkalinity (pH 13.0), the faster the degradation rate is induced. Under a strongly alkaline environment of 13.5, the degradation of polydopamine will affect the hydrophilicity of the modified lithium ion sieve, thereby affecting the adsorption capacity. Figure 11The data pertains to the pickling rate and adsorption capacity at different dopamine addition levels. During pickling, the pickling rate of the unmodified sample is slightly higher than that of the polydopamine-modified sample. This may be due to polydopamine adhering to the sample, but the amount of adhering polydopamine cannot be calculated. The effective sample mass during pickling is relatively less than that of the unmodified sample, resulting in a slightly lower elution rate. The lithium-ion sieve adsorption capacity of the hydrophilically modified polydopamine is higher than that of the unmodified sample, and it can be seen that the sample with the highest adsorption capacity is PDA. 0.2 -H2TiO3.

[0036] Crystal structure analysis: Figure 12 The three curves correspond to the hydrophilic modified polydopamine sample, and curve a represents the PDA sample. 0.2 -Li2TiO3, curve b is PDA 0.2 -H2TiO3 and curve c represent PDA. 0.2 -Li x H (2-X) XRD pattern of TiO3. Comparison with the standard card shows that the diffraction peaks of curve a perfectly match those of the standard card, indicating that polydopamine did not alter the crystal structure of the lithium-ion sieve precursor. The diffraction peaks of curve b show... )and( The diffraction peaks on the crystal surface are weakened. Adsorbed Li + Afterwards, the weakened diffraction peaks did not recover, indicating that the changes in diffraction peaks after acid washing are irreversible. Comparing the XRD curves after acid washing and after adsorption, it can be observed that the (002) crystal plane and ( The diffraction peaks of the lithium ions shift to higher angles. This phenomenon indicates that the cell volume of the material shrinks after lithium ions are extracted. The main reason for this structural change is that the larger radius of the Li... + H with smaller radius + The ions are replaced, thus triggering an adjustment in the internal structure of the crystal. This ion substitution effect causes the interplanar spacing to shorten, and the unit cell to shrink accordingly.

[0037] Surface elemental composition analysis: Analysis of unmodified (Li2TiO3) and modified (PDA) materials was conducted separately. 0.2 -Li2TiO3), acid washing (PDA-H2TiO3) and adsorption (PDA-Li x H (2-x) XPS analysis was performed on four TiO3 samples. See attached results. Figure 13 Figure a shows the full spectrum of the sample, indicating the presence of C, O, Ti, and N elemental signals, with no other impurity peaks detected. Figure b shows the PDA. 0.2 After acid elution of Li₂TiO₃, the intensity of the Li 1s peak decreases. This is due to the decrease in H₂ concentration during the elution process. + and Li +A substitution occurs, and Li + The elution was successful, but the Li 1s peak signal was still present in the spectrum, indicating that H... + Cannot completely replace Li + This indicates that the elution was incomplete, and a small amount of Li remains. + The lithium ion sieve was present in the sample, and the peak intensity of Li increased after adsorption, but the increase was not significant. This indicates that the lithium ion sieve did not effectively sieve the Li ion during adsorption. + The adsorption capacity is limited. Figure c shows that the N 1s peak intensity decreases after adsorption, possibly due to the degradation of polydopamine under strong alkaline conditions, resulting in the release of amino groups and a reduction in the N content on the sample surface. Figure d shows two characteristic peaks in the Ti 2p energy level, located at 464 eV. 1 / 2 The peak and Ti 2p at 458.2 eV 3 / 2 The peaks, and both characteristic peaks, show a trend towards higher energies. This may be due to the influence of the charge compensation mechanism, thereby altering the binding energy and affecting the binding mode of Ti. Figure e shows the C 1s spectrum. The original sample contained C, and after testing, some more C was introduced. After modification with polydopamine, the 284.8 eV peak shifted towards lower energies. This may be because polydopamine contains hydroxyl and amino groups, forming hydrogen bonds that cause the peak to shift towards lower binding energies. After acid washing, the peak shifted towards lower energies again, possibly due to the degradation of polydopamine under acidic conditions, the breaking of old bonds, and the formation of new bonds, leading to charge transfer and a change in binding energy. Figure f shows that after acid washing, O shifted towards higher energies. This may be due to the change in the chemical environment during acid washing, causing the Ti-O bond to break and affecting its electron density, thus shifting the binding energy towards higher binding energies.

[0038] Table 1 shows the surface percentage of the corresponding elements for each sample. Compared with the unmodified sample, the Li content on the sample surface decreased from 26.67% to 1.41%, a decrease of 25.26%, while the Ti content decreased from 7.11% to 1.77%, a reduction of 5.34%. This is because polydopamine does not contain Li or Ti, but it adheres to the sample surface, significantly reducing the proportion of Li and Ti elements on the sample surface. Similarly, the O content on the sample surface decreased from 36.84% to 30.21% after modification, a reduction of 6.63%, because polydopamine itself has a low O content, and the O content is attached to the sample surface. On the surface, it occupies the original surface area of ​​Li₂TiO₃, reducing the proportion of O on the sample surface; while the N content on the sample surface increases from 2.87% to 4.76%, an increase of 1.89%. Unmodified Li₂TiO₃ contains no N, while polydopamine has the functional group -NH₂, thus increasing the N content on the surface; the C content increases from 29.38% to 45.55%, an increase of 16.17%. The original Li₂TiO₃ contains no C because C was introduced during XPS testing, while polydopamine contains a large number of benzene rings, and the adhesion of polydopamine introduces a large amount of C to the sample surface. The decrease in Li, Ti, and O and the increase in C and N indirectly confirm that polydopamine successfully adhered to the precursor surface.

[0039] After acid washing, the Li content was 0.41%, which was lower than the Li content before acid washing. + The content was 1.41%, and after acid elution, the content decreased by 1%. Based on the acid elution rate formula, the elution rate was 70.92%. This value is lower than the value calculated by atomic absorption spectrometry, possibly because XPS measures the elements on the sample surface, and the Li content decreased during the acid elution process. + Residue remained on the sample surface, while some Li... + The Li content was not eluted from the unit cell into the pickling solution, therefore the surface Li measured by XPS was... + The high content of certain elements resulted in a lower calculated elution rate. Simultaneously, the contents of Ti, C, O, and N all decreased, possibly due to acid washing altering the bonding between elements. After adsorption, the contents of Li, Ti, O, and N all increased to varying degrees, possibly due to changes in the chemical environment and the resulting alterations in elemental bonding. The decrease in C content is likely due to the degradation of polydopamine under acidic and alkaline conditions, leading to a reduction in C adhering to the sample surface.

[0040] Table 1: Elemental content of sample surface III. Adsorption Kinetics Study To deeply analyze the adsorption kinetics mechanism of polydopamine-modified lithium-ion sieves, pseudo-first-order and pseudo-second-order kinetic equations were fitted using measured data. These two adsorption kinetic models elucidate the kinetic behavior corresponding to different intrinsic adsorption mechanisms. A scatter plot was generated using Origin software, with the time gradient interval as the x-axis and the corresponding adsorption capacity as the y-axis. Linear fitting was then performed on the data. The goodness of agreement between the fitted curves of the pseudo-first-order and pseudo-second-order kinetic models and the experimental data was compared (primarily based on the coefficient of determination R0). 2 Statistical parameters (such as those used in the adsorption process) are then used to determine the dominant adsorption kinetics.

[0041] Pseudo-first-order dynamic equation: (2) Pseudo-second-order dynamic equation: (3) In equations (2) and (3), Q e (mg·g -1 This represents the amount of Li adsorbed per unit mass of adsorbent when adsorption reaches equilibrium. + This is called the equilibrium adsorption capacity, and Q t (mg·g -1 This represents the amount of adsorbent adsorbed per unit mass at any time t during the adsorption process. Where k1 (in hours) -1 ) is the adsorption rate constant of the pseudo-first-order kinetic model, k2(mg·h·g) -1 () is the adsorption rate constant of the pseudo-second-order kinetic model. It can be obtained from calculations using equations 2 and 3. Figure 14 , Figure 14 Table 2 shows the linear fitting curves of the pseudo-first-order and pseudo-second-order kinetic models with respect to the adsorption data. Details of the fitting parameters are shown in Table 2.

[0042] Depend on Figure 14 As shown in Table 2, the coefficient of determination (R²) for fitting the pseudo-second-order dynamics model is... 2 =0.9973) is significantly higher than that of the pseudo-first-order dynamics model (R 2 =0.83828). R 2 A value close to 1 indicates a higher degree of agreement between the model and experimental data. Therefore, the pseudo-second-order kinetic model of polydopamine-modified lithium-ion sieve better expresses the adsorption principle of adsorption kinetics, that is, the adsorption of Li by polydopamine-modified lithium-ion sieve. + The adsorption behavior is chemisorption.

[0043] Table 2: Li-ion adsorption of polydopamine-modified lithium ion sieves + Dynamic data IV. Adsorption Isotherm Study In the experiment studying adsorption isotherms, LiCl solutions with different concentration gradients were used as adsorption solutions to investigate the adsorption of LiCl. + Adsorption experiment, Li + The concentrations were 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 g / L, and the experimental data with the largest error were discarded. To ensure consistency of experimental conditions, after adding a certain amount of LiCl, the NaOH concentration in the solution was maintained at 0.285 mol / L, which is the same as the pH of the LiOH solution in the adsorption kinetics. The PDA-modified lithium-ion sieve and the LiCl solution with a concentration gradient were poured into a 50 ml Erlenmeyer flask and mixed (0.2 g: 20 ml), and adsorption was carried out at a constant temperature of 25 °C for 24 h. After adsorption, 4 ml of supernatant was taken from each sample at 24 h for subsequent operations. The adsorption solutions of 0.5, 1.0, and 1.5 g / L and the corresponding supernatants at 24 h were diluted 500 times, and the adsorption solutions of 2.0, 2.5, and 3.0 g / L and the corresponding supernatants at 24 h were diluted 1000 times. The concentration of lithium ions was then detected using an atomic absorption spectrophotometer and calculated according to the adsorption formula to explore the adsorption isotherm of the hydrophilic modified metatitanic acid type lithium ion sieve.

[0044] When describing the adsorption behavior of lithium-ion sieves, two conventional models, Langmuir and Freundlich, are commonly used, and their corresponding calculation formulas are: (4) (5) In equations (4) and (5), C e (g·L -1 This refers to the concentration of lithium ions remaining in the solution when adsorption reaches equilibrium. Q e (g·L -1 The value represents the amount of adsorption at equilibrium. Q m (g·L -1 K represents the theoretical maximum adsorption capacity calculated by the model. L It is the Langmuir adsorption constant, an exponent. n Correlation adsorption strength can be used to assess the ease or difficulty of the adsorption process; K F This is the Freundlich adsorption constant, which reflects the intrinsic relationship between relative adsorption capacity and adsorption rate. Figure 15 The linear fitting results of the adsorption isotherms are presented, based on which the adsorption of Li-ion sieves by polydopamine-modified lithium ions is evaluated. + Adsorption behavior.

[0045] Table 3: Isothermal Adsorption Types and Constants of Adsorbents Figure 15a shows the fitting results of the adsorption isotherm based on the Langmuir model. The experimental data were obtained by measuring the supernatant after the adsorption reaction reached equilibrium for 24 hours. Analysis shows that Li + equilibrium concentration C e Its corresponding adsorption capacity Q e ratio C e / Q e They exhibit a significant linear correlation, and their coefficient of determination for linear fit R0 is [value missing]. 2 The value reached as high as 0.99424. In contrast, when fitting the model using the Freundlich model, the logarithm of the equilibrium concentration was lg. C e Logarithm of adsorption capacity (lg) Q e It only exhibits an approximate linear relationship, and the fitted R... 2 The value is 0.89157. Comparing the fitting effects of the two models, the experimental data shows a higher agreement with the Langmuir model, indicating that the process conforms to the characteristics of the Langmuir model, that is, the adsorption of lithium ions on the surface of the modified ion sieve is mainly monolayer adsorption, and an adsorption-desorption dynamic equilibrium can be established under specific conditions.

Claims

1. A method for preparing a polydopamine-modified metatitanate type lithium ion sieve, characterized by, The method comprises the following steps: (1) grinding and mixing lithium acetate dihydrate and titanium dioxide in an organic solvent, drying the mixture, uniformly heating the mixture to 650-800 DEG C, and calcining for 3-5 h to obtain a Li2TiO3 precursor; (2) placing dopamine hydrochloride, amino-crown ether and the Li2TiO3 precursor in a tris(hydroxymethyl)aminomethane solution with a pH value of 8-9, stirring and mixing uniformly, constant-temperature oscillation reaction, suction filtration and low-temperature drying to obtain a polydopamine-modified metatitanate lithium ion sieve.

2. The preparation method of the polydopamine-modified metatitanic acid type lithium-ion sieve as described in claim 1, characterized in that, In step (1), the mass ratio of lithium acetate dihydrate to titanium dioxide is 2-3:

1.

3. The preparation method of the polydopamine-modified metatitanic acid type lithium-ion sieve as described in claim 1, characterized in that, In step (2), the concentration of the tris(hydroxymethyl)aminomethane solution is 9-11 mmol / L.

4. The preparation method of the polydopamine-modified metatitanic acid type lithium-ion sieve as described in claim 1, characterized in that, The mass ratio of dopamine hydrochloride to the Li2TiO3 precursor is 0.05-0.3:

1.

5. The preparation method of the polydopamine-modified metatitanic acid type lithium-ion sieve as described in claim 1, characterized in that, In step (2), the mass ratio of amino-crown ether to the Li2TiO3 precursor is 0.5-1.5:

1.

6. The preparation method of the polydopamine-modified metatitanic acid lithium-ion sieve as described in claim 1, characterized in that, In step (2), the oscillation reaction temperature is 35-45 DEG C, the reaction time is 5-8 h, and the oscillation rotation speed is 160-180 r / min.

7. A polydopamine-modified metatitanate type lithium ion sieve, characterized by, The polydopamine-modified metatitanate lithium ion sieve is prepared by the method of any one of claims 1-6.

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