Magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent as well as preparation method and application thereof

Abstract

The invention provides a magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent as well as a preparation method and application thereof, and relates to the technical field of adsorbents. According to the adsorbent prepared by the method, magnetic Fe3O4 nanoparticles are taken as an inner core, a layer of mesoporous SiO2 is coated outside the inner core, and an oxide / hydroxide composite layer of zinc (Zn) and lanthanum (La) is loaded on the surface through a coprecipitation technology, so that the magnetic mesoporous Zn-La bimetallic phosphate adsorbent is formed, and phosphorus in a water body can be efficiently and selectively adsorbed. The preparation process of the adsorbent is simple and efficient, and the obtained adsorbent has high adsorption capacity, rapid removal efficiency and excellent anti-interference performance, supports magnetic separation recovery and reutilization, and has significant application potential in the field of phosphorus-containing wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbents, and particularly relates to a magnetic mesoporous zinc lanthanum bimetallic phosphate adsorbent, a preparation method thereof, and an application thereof. Background Art

[0002] Water eutrophication is a global environmental problem, mainly caused by excessive input of phosphates. Traditional phosphorus removal technologies such as chemical precipitation and biological methods have limitations in the treatment of low-concentration phosphorus and resource recovery. The use of the adsorption method to remove phosphorus pollutants in water has the advantages of flexible operation and controllable cost, but traditional adsorbents often face problems such as low adsorption capacity, poor cycle stability, and difficulty in solid-liquid separation. Studies have found that the adsorption ability of adsorbents for phosphates is affected by their adsorption mechanisms, mainly including processes such as ion exchange, ligand exchange, hydrogen bonding, surface precipitation, and diffusion into the internal structure of the adsorbent. Lanthanum and zinc both have strong complexation abilities with phosphates and are considered ideal active components for constructing highly efficient phosphate adsorbents. In addition, existing studies have proved that bimetallic doping can enhance internal electron transfer, thereby enhancing the adsorption process of phosphates and showing potential in the field of pollutant adsorption. However, the difficult recovery of powdered adsorbent materials limits their application. Therefore, further improving the recyclability and reusability of adsorbents is a current research hotspot. Summary of the Invention

[0003] Based on this, the present invention provides a magnetic mesoporous zinc lanthanum bimetallic phosphate adsorbent, a preparation method thereof, and an application thereof. The adsorbent prepared by the present invention has a core-shell structure of Fe3O4@SiO2@mSiO2. This novel adsorbent has a high specific surface area and also has excellent magnetism, which is convenient for the magnetic recovery of the adsorbent. At the same time, the adsorbent of the present invention enhances the adsorption performance through the synergistic effect of lanthanum bimetals, and also improves the adsorption stability of the adsorbent, facilitating repeated use.

[0004] The preparation method of the magnetic mesoporous zinc lanthanum bimetallic phosphate adsorbent of the present invention includes the following steps:

[0005] S1: Dispersing nano Fe3O4 particles in isopropanol, and then sequentially dropping ammonia water, deionized water, and tetraethyl orthosilicate under heating and mechanical stirring conditions. After the dropping is complete and the stirring reaction is complete, the product is collected by magnetic separation, and the product is obtained after washing and drying to obtain Fe3O4@SiO2 nano particles;

[0006] S2: Dispersing the Fe3O4@SiO2 nano particles in deionized water, adding cetyltrimethylammonium bromide and triethanolamine, ultrasonic treatment, heating and stirring, then adding a mixed solution of cyclohexane and ethyl orthosilicate, continuing the stirring reaction, collecting the product by magnetic separation, washing the collected product, and then calcining to remove organic residues to obtain Fe3O4@SiO2@mSiO2 nano particles;

[0007] S3: Disperse the Fe3O4@SiO2@mSiO2 nanoparticles, zinc salt and lanthanum salt in an ethanol-water mixed solvent, perform ultrasonic treatment, then mechanically stir under constant temperature conditions, and then add an alkali solution dropwise to adjust the pH to 10 - 11. After aging, obtain the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent through magnetic separation, washing and drying.

[0008] Preferably, in step S1, the solid-liquid ratio of the nano Fe3O4 particles to isopropanol is 1:(100 - 200) g / mL; the heating temperature is 35 - 45 °C; the volume ratio of ammonia water, deionized water to tetraethyl orthosilicate is (20 - 24):(32 - 36):1. In the present invention, in step S1, the nano Fe3O4 particles are ultrasonically dispersed in isopropanol, and the ultrasonic treatment time is 25 - 35 min. The mechanical stirring rate in step S1 of the present invention is 600 - 700 rpm.

[0009] Preferably, in step S1 of the present invention, the solid-liquid ratio of the nano Fe3O4 particles to isopropanol is 1:150 - 180 (g / mL).

[0010] In step S1 of the present invention, the volume ratio of ammonia water, deionized water, tetraethyl orthosilicate (TEOS) is 20:(38 - 39.2):1; the dropping rate of tetraethyl orthosilicate (TEOS) is 0.5 - 1.0 mL / min; the stirring reaction time after complete dropping in the present invention is 2 - 5 h

[0011] Preferably, in step S2, the mass-volume ratio of the Fe3O4@SiO2 nanoparticles to deionized water is 1:(500 - 600) g / mL; the mass ratio of cetyltrimethylammonium bromide to the Fe3O4@SiO2 nanoparticles is (50 - 70):1; the mass-volume ratio of the Fe3O4@SiO2 nanoparticles to triethanolamine is 1:(0.1 - 0.3) g / mL; the heating temperature in step S2 is 55 - 65 °C. The calcination temperature in step S2 is 550 - 650 °C, and the calcination time is 5 - 10 h.

[0012] As a further improvement of the solution, the mass of cetyltrimethylammonium bromide to the Fe3O4@SiO2 nanoparticles is preferably 55 - 65:1, the mass-volume ratio of the Fe3O4@SiO2 nanoparticles to triethanolamine is 1:(0.15 - 0.25) mL / g, the calcination temperature is preferably 580 - 620 °C, and the calcination time is 5 - 7 h to improve the orderliness of the mesoporous structure.

[0013] Preferably, in the ethanol-water mixed solvent in step S3, the volume ratio of ethanol to water is (0.8 - 1.2):1; the aging time is 3 - 5 h; the molar ratio of the zinc salt to the lanthanum salt is (0.5 - 2):1; the mass ratio of the Fe3O4@SiO2@mSiO2 nanoparticles to the zinc salt is 0.2:(0.05 - 0.15).

[0014] As a further improvement of the solution, the volume ratio of ethanol to deionized water is preferably 1:1, the amount of the mixed solvent is 50 - 80 times the mass of the carrier, and the ultrasonic treatment time is 25 - 35 min to ensure that the carrier and the metal salt are fully dispersed.

[0015] As a further improvement of the solution, the mechanical stirring rate in step S3 is preferably 280 - 320 rpm, the pH is adjusted to 10.0 - 10.2 by dropping an alkali solution, and the aging time is preferably 4 h.

[0016] Preferably, the zinc salt is selected from zinc chloride or zinc nitrate, and the lanthanum salt is selected from lanthanum chloride or lanthanum nitrate.

[0017] Another object of the present invention is to provide a magnetic mesoporous zinc lanthanum bimetallic phosphate adsorbent, which is specifically prepared by the above method of the present invention. The adsorbent of the present invention has a magnetic nano-ferroferric oxide as the core, a mesoporous SiO2 layer coated on the surface of Fe3O4, and the surface is modified with oxides and hydroxides of zinc metal and lanthanum metal.

[0018] Preferably, the thickness of the mesoporous SiO2 layer of the present invention is 20 - 50 nm.

[0019] The present invention also provides the application of the magnetic mesoporous zinc lanthanum bimetallic phosphate adsorbent, specifically using the adsorbent to adsorb and remove phosphorus in water.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The adsorbent prepared by the present invention combines a magnetic core with a mesoporous structure, avoiding agglomeration and sedimentation and improving the recovery rate. It has high mechanical strength and good chemical stability, and does not collapse or lose active components during long-term use. It has a high magnetic saturation intensity and supports rapid magnetic separation.

[0022] The adsorbent of the present invention is prepared by a solvothermal-codeposition method. The process of uniformly loading zinc lanthanum bimetallic hydroxide in the mesopores is simple, and it has a high adsorption capacity for phosphates and can quickly remove phosphates in water.

[0023] The adsorbent prepared by the present invention has a wide pH application range and is affected by Cl - , SO4 2- , CO3 2-, with little influence from interfering substances such as humic acid, is suitable for complex water quality, still maintains a high adsorption capacity after 5 cycles, and has no secondary pollution. Description of the Drawings

[0024] Figure 1 It is the macroscopic morphology diagram of the adsorption material prepared in Example 1.

[0025] Figure 2 It is the scanning electron microscope diagram of the adsorption material prepared in Example 1.

[0026] Figure 3 It is the transmission electron microscope diagram of the adsorption material prepared in Example 1.

[0027] Figure 4 It is the energy-dispersive X-ray spectroscopy analysis diagram of the phosphorus removal adsorbent prepared in Comparative Example 1.

[0028] Figure 5 It is the adsorption isotherm fitting diagram of the adsorption materials prepared in Examples 1, 2, and 3.

[0029] Figure 6 It is the adsorption isotherm fitting diagram of the adsorption materials prepared in Comparative Examples 1 and 2.

[0030] Figure 7 It is the kinetic curve diagram of the adsorption of phosphorus by the adsorption materials prepared in Examples 1, 2, and 3.

[0031] Figure 8 It is the kinetic curve diagram of the adsorption of phosphorus by the adsorption materials prepared in Comparative Examples 1 and 2.

[0032] Figure 9 It is the X-ray diffraction analysis diagram of the material before and after the adsorption of phosphate by the material prepared in Example 1.

[0033] Figure 10 It is the adsorption capacity diagram of the adsorption material prepared in Example 1 for phosphorus at different pH values.

[0034] Figure 11 It is the adsorption capacity diagram of the adsorption material prepared in Example 1 for phosphorus under the influence of coexisting ions.

[0035] Figure 12 It is the magnetic separation performance diagram of the adsorption material prepared in Example 1.

[0036] Figure 13 It is the five-time adsorption and desorption cycle performance diagram of the adsorption material prepared in Example 1. Detailed Implementation Modes

[0037] To help readers understand the present invention more comprehensively, the following will be elaborated in detail through specific embodiments. It should be noted that these embodiments are only used to illustrate the principles and characteristics of the present invention, but the present invention is not limited to these embodiments.

[0038] Example 1: Preparation of Zn / La-0.5MMS composite material (Zn 2+ :La 3+ = 1:2)

[0039] Step 1: Weigh 150 mg of Fe3O4, add it to 180 mL of absolute ethanol, ultrasonically disperse for 30 min, dropwise add 10 mL of 28 wt% concentrated ammonia water and 18 mL of deionized water, stir at 40 °C and 600 rpm for 30 minutes, then inject 0.5 mL of TEOS, continue to stir for 2 h to form a Fe3O4@SiO2 core-shell structure. After magnetic separation, collect the product, wash it three times with ethanol and then dry it;

[0040] Step 2: Weigh 0.12 g of Fe3O4@SiO2, add it to a mixed solution of 112 mL of deionized water, 1.2 mL of ammonia water and 0.4 g of CTAB, add 28 mL of n-hexane, stir at 400 rpm for 10 min, dropwise add 0.8 mL of TEOS, stir and react at 30 °C and 400 rpm for 12 h. After magnetic separation, wash it three times with deionized water and ethanol, dry it and place it in the air, heat it to 500 °C at a rate of 1 °C / min, and calcine for 6 h to obtain Fe3O4@SiO2@mSiO2 (MMS);

[0041] Step 3: Weigh 0.2 g of MMS, 0.0613 g of ZnCl2 (0.45 mmol of Zn 2+ ) and 0.3898 g of La(NO3)3·6H2O (0.90 mmol of La 3+ ), ultrasonically disperse it in a mixed solvent of 40 mL of ethanol and 40 mL of deionized water for 30 min, stir at 25 °C and 300 rpm, dropwise add 0.1 M NaOH to adjust the pH to 10 ± 0.5, and vacuum dry overnight to obtain Zn / La-0.5MMS.

[0042] Example 2: Preparation of Zn / La-1 MMS composite material (Zn 2+ :La 3+ = 1:1)

[0043] Steps 1-2: The same as the preparation process of the Fe3O4@SiO2@mSiO2 carrier in Example 1.

[0044] Step 3: Weigh 0.2 g of MMS, 0.0926 g of ZnCl2 (0.68 mmol of Zn 2+) and 0.2934 g La(NO3)3·6H2O (0.68 mmol La 3+ ), and added them into a mixed solvent of 40 mL ethanol and 40 mL deionized water. The final product was labeled as Zn / La-1MMS.

[0045] Example 3: Preparation of Zn / La-2 MMS composite material (Zn 2+ :La 3+ = 2:1)

[0046] Step 1-2: The same preparation process of Fe3O4@SiO2@mSiO2 carrier as in Example 1.

[0047] Step 3: Weigh 0.2 g MMS, 0.1227 g ZnCl2 (0.90 mmol Zn 2+ ), and 0.1949 g La(NO3)3·6H2O (0.45 mmol La 3+ ), and added them into a mixed solvent of 40 mL ethanol and 40 mL deionized water. The final product was labeled as Zn / La-2MMS.

[0048] Comparative Example 1: Preparation of Zn-MMS composite material

[0049] Step 1-2: The same preparation process of Fe3O4@SiO2@mSiO2 carrier as in Example 1.

[0050] Step 3: Weigh 0.2 g MMS, 0.1227 g ZnCl2 (0.90 mmol Zn 2+ ), and added them into a mixed solvent of 40 mL ethanol and 40 mL deionized water. The final product was labeled as Zn-MMS.

[0051] Comparative Example 2: Preparation of La-MMS composite material

[0052] Step 1-2: The same preparation process of Fe3O4@SiO2@mSiO2 carrier as in Example 1.

[0053] Step 3: Weigh 0.2 g MMS, 0.3898 g La(NO3)3·6H2O (0.90 mmol La 3+ ), and added them into a mixed solvent of 40 mL ethanol and 40 mL deionized water. The final product was labeled as La-MMS.

[0054] Performance test

[0055] 1. Comprehensive performance characterization was carried out on the mesoporous magnetic zinc lanthanum composite materials prepared in each example. Figure 1 The macroscopic morphology of the sample in Example 1 was presented, and the material was in the form of uniform powder. Microscopic morphology analysis (seeFigures 2 - 4 ) The results show that the material has a porous spherical structure with good dispersibility. The surface of the spheres is relatively rough, and the particle size is about 300 - 350 nm. In addition, the core - shell structure is obvious and the metal is evenly distributed on the surface of the carrier. The high - specific - surface - area characteristic significantly improves the adsorption performance.

[0056] 2. Experiments on the adsorption and removal of inorganic phosphorus in water were carried out on the materials prepared in Examples 1 - 3 and Comparative Examples 1 - 2. In the experiment, 10 mg of the adsorbent material was added to 50 mL of phosphate solutions with concentrations of 3, 7, 11, 15, 19, 23, 27, and 30 mg P / L respectively, and shaken at a speed of 260 rpm / min for 24 h at room temperature. Samples were taken at different time intervals when the concentration was 11 mg P / L. The remaining phosphorus in the solution was analyzed by the molybdenum blue method combined with an ultraviolet spectrophotometer. The results of the inorganic phosphorus adsorption capacity and adsorption kinetic curves are as Figures 5 - 8 shown.

[0057] It can be seen from the experimental results that the composite materials in Examples 1 - 3 show high inorganic phosphorus adsorption efficiency, and the adsorption amounts all reach more than 110 mg P / g. Among them, the adsorption capacity of the Zn / La - 0.5MMS composite material in Example 1 is the largest, reaching 140.9 mg P / g. The materials in the other comparative examples have low adsorption efficiency for inorganic phosphorus in water. The adsorption rate of the Zn / La - x MMS composite material rises rapidly within the first 20 min and then basically reaches adsorption equilibrium within 1 h. And the adsorption behavior of Zn / La - x MMS for phosphate conforms more to the pseudo - second - order kinetic model, indicating that the adsorption process is mainly controlled by chemical adsorption.

[0058] 3. The materials before and after phosphate adsorption in Example 1 were subjected to X - ray diffraction analysis. The results show that ( Figure 9 ) the materials in each example exhibit characteristic diffraction peaks of zinc, lanthanum, and magnetite. The representative diffraction peak of Fe3O4 (JCPDS#99 - 000 - 2246), the characteristic peak of La(OH)3 (JCPDS#83 - 2034), and the characteristic diffraction peak of ZnO (JCPDS#5 - 0664) all appear in the XRD pattern of Zn / La - 0.5MMS, indicating that Zn / La is successfully loaded onto MMS. In addition, after phosphate adsorption, the main diffraction peak of the original La(OH)3 significantly weakens and new peaks appear, indicating that La(OH)3 is transformed into La - P complex through inner - sphere complexation. In addition, the characteristic diffraction peak corresponding to Zn3(PO4)2 is also observed, which indicates that ligand exchange occurs between the metal hydroxide and phosphate to form a phosphate compound, thus promoting the adsorption and removal of phosphate.

[0059] 4. In the adsorption performance test ( Figure 10) Based on an adsorbent dosage of 0.2 g / L and an initial phosphate concentration of 11 mg P / L, the effect of pH value (3.0 - 11.0) on the adsorption performance was investigated. The results showed that the material exhibited good adsorption performance in the pH range of 3.0 - 9.0, with an adsorption capacity of up to 54.25 mg P / g, and the adsorption demand could be met under neutral conditions. The change in the pH of the actual water body had little effect on the adsorption performance of the material.

[0060] 5. Further anti-interference tests ( Figure 11 ) simulated the actual wastewater environment, and common anions with concentrations of 200 mg / L, 500 mg / L, and 1 g / L were added to the phosphate solution. Adsorption experiments were carried out under the conditions of an adsorbent dosage of 0.2 g / L and an initial phosphate concentration of 11 mg P / L. The results showed that when the concentration was lower than 200 mg / L, the interference of HCO3 - and HA on phosphate adsorption was limited. When the concentration exceeded 500 mg / L, their interference effects began to appear, resulting in a decrease in the phosphate adsorption capacity. However, in any case, the decrease in the phosphate adsorption capacity was less than 20%, indicating that the material had good anti-interference ability against common ions.

[0061] 6. The magnetic strength performance test ( Figure 12 ) showed that the material had superparamagnetism, could be quickly separated under the action of a magnetic field, and could be evenly dispersed in the solution without a magnetic field. This characteristic greatly improved the recycling efficiency of the material and enhanced its practical application value.

[0062] 7. The adsorption-desorption cycle test ( Figure 13 ) evaluated the regeneration performance of the material. Five adsorption-desorption experiments on phosphate in water were carried out with a dosage of 0.2 g / L. The adsorption conditions were 25 °C, 260 rpm, an initial phosphate concentration of 11 mg P / L, and a reaction time of 6 h. The desorption conditions were 25 °C and 300 rpm for 4 h. The test results showed that after five cycles, the material still maintained a desorption capacity of more than 78% (44.99 mg P / g). The decrease in the adsorption capacity might be due to the permanent occupation of some active sites and the inability to recover through elution. Although the adsorption capacity decreased slightly over time, the overall regeneration performance of the material was still relatively ideal.

[0063] In summary, the mesoporous magnetic zinc lanthanum composite material of the present invention has excellent adsorption performance, anti-interference ability, magnetic separation performance, and regeneration performance, and has broad application prospects.

[0064] The embodiments of the present invention are only used to illustrate its basic principles, and can be adjusted and optimized according to requirements in actual applications. The protection scope of the present invention shall be subject to the appended claims and their equivalents.

Claims

1. A method for preparing a magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent, characterized in that: The following steps are involved: S1: Disperse nano-Fe3O4 particles in isopropanol, then add ammonia water, deionized water and tetraethyl orthosilicate dropwise in sequence under heating and mechanical stirring conditions, continue stirring until the addition is complete, and collect the product by magnetic separation after the reaction is complete, and obtain Fe3O4@SiO2 nano-particles after washing and drying; S2: dispersing the Fe3O4@SiO2 nanoparticles in deionized water, adding hexadecyltrimethylammonium bromide and triethanolamine, heating and stirring after ultrasonic treatment, then adding a mixed solution of cyclohexane and tetraethyl orthosilicate, continuing to stir the reaction, collecting the product by magnetic separation, washing the collected product, and calcining it to remove organic residues, thereby obtaining Fe3O4@SiO2@mSiO2 nanoparticles; S3: The Fe3O4@SiO2@mSiO2 nanoparticles, zinc salt and lanthanum salt are dispersed in an ethanol-water mixed solvent, and mechanically stirred under constant temperature after ultrasonic treatment, and then alkaline solution is added dropwise to adjust the pH to 10-11. After aging, a magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent is obtained by magnetic separation, washing and drying.

2. The method for preparing the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 1, characterized in that: The solid-liquid ratio of the nano-Fe3O4 particles to isopropanol in step S1 is 1:(100-200) g / mL; The heating temperature is 35-45°C; The volume ratio of ammonia water, deionized water and tetraethyl orthosilicate is (20-24):(32-36):

1.

3. The method for preparing the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 1, characterized in that: The mass volume ratio of the Fe3O4@SiO2 nanoparticles to deionized water in step S2 is 1:(500-600) g / mL; The mass ratio of the hexadecyltrimethylammonium bromide to the Fe3O4@SiO2 nanoparticles is (50-70):1; The mass volume ratio of the Fe3O4@SiO2 nanoparticles to the triethanolamine is 1:(0.1-0.3) g / mL; The heating temperature in step S2 is 55-65°C.

4. The method for preparing the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 1, characterized in that: In step S2, the calcination temperature is 550-650° C., and the calcination time is 5-10 hours.

5. The method for preparing the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 1, characterized in that: The volume ratio of ethanol to water in the ethanol-water mixed solvent in step S3 is (0.8-1.2):1; Aging time is 3 to 5 hours; The molar ratio of the zinc salt to the lanthanum salt is (0.5-2):1; The mass ratio of the Fe3O4@SiO2@mSiO2 nanoparticles to the zinc salt is 0.2:(0.05-0.15).

6. The method for preparing the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 1, characterized in that: The zinc salt is selected from zinc chloride or zinc nitrate, and the lanthanum salt is selected from lanthanum chloride or lanthanum nitrate.

7. A magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent, characterized in that: The method is prepared by any one of claims 1 to 6.

8. The magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 7, characterized in that: The adsorbent has magnetic nano-ferroferric oxide as the core, and is coated with a mesoporous SiO2 layer on the surface of Fe3O4, and the surface is modified with oxides and hydroxides of zinc metal and lanthanum metal.

9. The magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to claim 8, characterized in that: The thickness of the mesoporous SiO2 layer is 20-50nm.

10. Use of the magnetic mesoporous zinc-lanthanum bimetallic phosphate adsorbent according to any one of claims 7 to 9, characterized in that: The adsorbent is used to adsorb and remove phosphorus in water.

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