La-Ca-Fe compound adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of environmental protection, in particular to a La-Ca-Fe-MOF core-shell composite adsorbent which is characterized in that the adsorbent is of a core-shell structure; the inner core of the core-shell structure is La-Ca-Fe ternary metal oxide, the shell of the core-shell structure is a ZIF-8 type MOF shell layer modified by a sulfonic group, and the MOF shell layer is provided with a mesoporous-microporous hierarchical pore network. According to the core-shell structure adsorption material, the specific surface area can reach 350-400 m < 2 > / g to the maximum, the mesopore proportion can reach 68% to the maximum, the mass transfer resistance for adsorbing phosphorus in a water body is reduced by 30%, the adsorption equilibrium time is shortened to 1 h, and the performance is greatly broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental protection, in particular to a La-Ca-Fe@MOF core-shell composite adsorbent with a hierarchical mesopore-micropore structure, a low-temperature microwave-assisted preparation method thereof, and a wastewater phosphorus removal-phosphorus recovery-material regeneration integrated application process. In particular, it can be used as an environmental functional material and is suitable for water pollution control technology. BACKGROUND

[0002] In the prior art, La-Ca-Fe composite adsorbents are used for water phosphorus pollution control, and three major technical bottlenecks are often encountered: (1) The adsorption efficiency of traditional La-based adsorbents significantly decreases under neutral-alkaline conditions, and the adsorption capacity decreases by more than 40% when the solution pH is greater than 7, resulting in the need for pH adjustment before application of La-based adsorbents, otherwise the adsorption stability cannot be guaranteed.

[0003] (2) The regeneration energy consumption of saturated adsorbents is high, and traditional thermal regeneration requires heating the adsorbent at a temperature of more than 400℃, resulting in high energy consumption per unit of phosphorus recovery. If the thermal regeneration temperature is reduced, the adsorbent cannot be fully regenerated, and the saturated adsorption volume of the adsorbent is greatly reduced. At the same time, the purity of the phosphorus recovery product is low.

[0004] (3) There are problems such as slow adsorption kinetics and large mass transfer resistance in large-scale applications. In laboratory small-scale research, new adsorbents perform well, but in actual applications, they often cannot achieve ideal results.

[0005] Therefore, although the existing La-Ca-Fe composite material has certain phosphorus removal capacity, it lacks adaptability design for complex water quality conditions, and a sustainable "adsorption-regeneration-resource recovery" closed-loop system has not been established. The adsorption performance of oxygen vacancy-containing metal oxides in the composite material is significantly affected by pH, while the porous structure of the MOF material can regulate the diffusion path of the adsorbate.

[0006] The composite material prepared by traditional mechanical mixing method has problems such as weak interface bonding and insufficient exposure of active sites, and it is difficult to be used in the granulation and molding process of La-Ca-Fe composite material.

[0007] In addition, although the electrochemical regeneration technology can realize in-situ activation of the adsorbent, the existing system has defects such as high energy consumption (electric potential > 1.5V) and multiple side reactions. SUMMARY

[0008] The present application aims to overcome the problems of pH limited application, high regeneration energy consumption, and incomplete resource recovery of the existing La-Ca-Fe composite adsorbent in the prior art, and provides a La-Ca-Fe composite adsorbent, a preparation method thereof, and an application thereof.

[0009] In a first aspect, the present application provides an adsorption material.

[0010] A La-Ca-Fe@MOF core-shell composite adsorbent, the adsorbent has a core-shell structure; The inner core of the core-shell structure is a La-Ca-Fe ternary metal oxide, The shell of the core-shell structure is a ZIF-8 type MOF shell layer modified by a sulfonic group, and the MOF shell layer has a mesopore-micropore hierarchical pore network.

[0011] The ZIF-8 type MOF shell layer modified by a sulfonic group is a ZIF-8-SO3H structure shell layer.

[0012] Further, the molar ratio of the three metal elements in the La-Ca-Fe ternary metal oxide is La:Ca:Fe = 1:2-4:3-6.

[0013] Further, the surface of the inner core has a 5-20 nm thick hydroxyapatite transition layer.

[0014] Further, the surface of the inner core has a 5-15 nm thick hydroxyapatite transition layer.

[0015] The shell is a ZIF-8 type MOF shell layer modified by a sulfonic group.

[0016] Further, the inner core is doped with 0.2-1.1 wt% of a nano-conductive material.

[0017] In a second aspect, the present application provides a preparation method of the above adsorption material.

[0018] A preparation method of a La-Ca-Fe@MOF core-shell composite adsorbent, comprising the following steps: S1, prepare salts of lanthanum, calcium and iron according to the molar ratio of La-Ca-Fe ternary metal in the inner core, dissolve in a solution; then, add 0.2-1.1 wt% of graphene nanoribbons, disperse uniformly, adjust the pH to alkaline, and form a sol.

[0019] S2, to the sol, add ammonium dihydrogen phosphate, and hydrothermally react at 50-95℃ for 1-4 hours to form a La-Ca-Fe / GNRs-HAP inner core.

[0020] S3, disperse the inner core obtained in S2 in a small molecular alcohol solution of 2-methylimidazole and zinc nitrate, add p-toluene sulfonic acid, and microwave react for 10-40 minutes to grow a ZIF-8 type MOF shell layer modified by a sulfonic group, i.e. a ZIF-8-SO3H shell layer, on the surface of the inner core in situ.

[0021] In S1, the amount of graphene nanoribbons is calculated relative to the total weight of La-Ca-Fe metal elements in the core.

[0022] In S3, a ZIF-8-SO3H shell layer, i.e., a ZIF-8 type MOF shell layer modified by a sulfonic acid group, is grown in situ on the surface of the core.

[0023] Further, S4 is further included, wherein the core-shell structure composite adsorbent obtained in S3 is filtered, washed, and dried.

[0024] Further, after drying is completed, the composite adsorbent is reduced by hydrogen for 10-60 minutes, so that the oxygen vacancy concentration of the composite adsorbent reaches 7-15%.

[0025] In a third aspect, the application provides an application of the above-mentioned adsorbent material.

[0026] An application of the above-mentioned La-Ca-Fe@MOF core-shell composite adsorbent, wherein the adsorbent is applied to adsorb phosphorus in wastewater.

[0027] A regeneration method of the above-mentioned La-Ca-Fe@MOF core-shell composite adsorbent, wherein a three-electrode system is adopted, the adsorbent is connected to a working electrode, a Pt sheet is used as a counter electrode, and Ag / AgCl is used as a reference electrode; and the composite adsorbent is regenerated by electrolysis at a potential of 0.7-0.9 V for 5-30 minutes.

[0028] Compared with the prior art, the application has the following beneficial effects: 1. The application provides a core-shell structure adsorbent material, wherein a ZIF-8 type MOF shell is combined on the surface of a La-Ca-Fe ternary metal oxide core, and the specific surface area of the composite adsorbent can reach 350-400 m 2 / g at most, the mesopore ratio can reach 68% at most, the mass transfer resistance of phosphorus in water is reduced by 30%, the adsorption equilibrium time is shortened to 1 h, and the performance is greatly improved.

[0029] 2. The preparation method of the core-shell structure adsorbent material provided by the application adopts a microwave-assisted synthesis process to realize controllable synthesis of the material, form a HAP transition layer on the surface of the core to enhance the interfacial bonding force of the core-shell structure, and the actual shear strength is more than 1.2 MPa at most. Moreover, after the composite adsorbent adsorbs phosphorus, the composite adsorbent can be regenerated by an electrochemical method, and the energy consumption is reduced by more than 70% compared with a thermal regeneration technology, and the energy-saving advantage is significant.

[0030] 3. The core-shell structured adsorbent material has excellent performance, and can be used to construct a closed-loop system of "wastewater phosphorus removal-zinc phosphate preparation-adsorbent regeneration". 0.8 kg of zinc phosphate (worth about 2.4 yuan) can be recovered from 1 ton of wastewater containing phosphorus (50 mg / L), which can offset 30% of the wastewater treatment cost according to the current market value of phosphorus. DETAILED DESCRIPTION

[0031] In order to more clearly analyze and illustrate the La-Ca-Fe@MOF core-shell composite adsorbent of the present application, the following preferred embodiments of the present application are described in detail. In order to better help the technical personnel understand the core idea and implementation method of the present application, some specific parameter preferred cases are also provided. These are the innovative content of the present application and should be included in the protection scope of the present application, and should not be regarded as ordinary technical knowledge in the art.

[0032] The La-Ca-Fe@MOF core-shell composite adsorbent of the present application is an adsorbent material with a core-shell structure. The inner core is a La-Ca-Fe ternary metal oxide. In some specific embodiments of the present application, the molar ratio of the three metal elements in the inner core can be La:Ca:Fe=1:2.5-3.5:3.5-5.0. The molar ratio here is calculated based on the atomic number of the three metal elements, and the corresponding weight used is slightly different for different salt raw materials. The calculation should be based on the atomic weight of the metal elements.

[0033] Preferably, the molar ratio of the three metal elements is La:Ca:Fe=1:3:4.

[0034] The shell of the La-Ca-Fe@MOF core-shell composite adsorbent of the present application is a ZIF-8 type MOF shell layer, and the MOF shell layer has a hierarchical pore network of mesopores and micropores. This unique pore network structure allows the La-Ca-Fe ternary metal oxide in the inner core to better selectively contact the target adsorbent, and the hierarchical pore structure can increase the adsorption rate by 1-2 orders of magnitude, which is particularly advantageous for dynamic adsorption in water. The hierarchical pore network of mesopores and micropores greatly increases the specific surface area, ensuring the capture ability of the target adsorbent. In addition, the hierarchical pore network of mesopores and micropores also forms a buffer zone, avoiding the breakage of the inner core ternary metal adsorbent when the adsorbent is put into water, and improving the service life of the material.

[0035] In some specific embodiments of the present application, the surface of the inner core has a 5-15 nm thick hydroxyapatite transition layer.

[0036] Hydroxyapatite is widely used in the field of biological medicine, and the application of the hydroxyapatite in the modification of the core-shell structure is innovative, the HAP is used as a transition layer to relieve the mismatching problem of the thermal expansion coefficient or elastic modulus between the core and the shell layer, and the interface stress is reduced, so that the composite adsorbent is less likely to be broken and invalid in the recycling process.

[0037] Preferably, the thickness of the hydroxyapatite transition layer is 5-10 nm. 2+ -PO4 3- The coordination bond enhances the core-shell binding force, and a double active center of 'oxygen vacancy-HAP' is constructed.

[0038] In some specific embodiments of the application, the shell is a MOF shell layer, and a sulfonic acid group is introduced into the MOF shell layer to construct a sulfonic acid group modified ZIF-8 type MOF shell layer. When the pH of the solution changes, the surface functional groups of the adsorbent will dissociate or protonate, resulting in a change in the surface charge property, thereby affecting the adsorption capacity for charged ions (such as phosphate). Under acidic conditions of pH < 6, the sulfonic acid group dissociates into -SO 3⁻ ⁻, and the positive charge of the inner core La 3 ⁺ and Fe 3 ⁺ is electrostatically attracted to strengthen the capture of H2PO 4⁻ ⁻; under alkaline conditions of pH > 7, the surface hydroxyl groups of the inner core metal oxide are deprotonated, and the MOF shell layer releases Zn 2 ⁺ to form Zn3(PO4)2 precipitate with PO4 3⁻ ⁻, realizing the dual-mechanism of 'electrostatic attraction + chemical precipitation' for phosphorus removal.

[0039] In addition, the change in pH will also change the existing form of phosphate in the solution, such as H2PO4 ⁻ ⁻, HPO4 2⁻ ⁻ and PO4 3⁻ ⁻, and the mesoporous and microporous MOF shell of the adsorbent can also assist the entry of phosphate into the interior of the adsorbent, so as to adapt to the adsorption requirements of different forms of phosphate.

[0040] In short, at low pH, the phosphorus element in the water body is mainly H2PO4⁻, which is captured by the composite adsorbent through inner sphere complexation (such as La-O-P bond) and electrostatic attraction; at high pH, the phosphorus element in the water body is mainly HPO4 2⁻ ⁻ and PO4 3⁻ ⁻, in addition to the complexation effect, the released Zn 2 ⁺ of the MOF can form a difficult-to-dissolve salt precipitate, thereby improving the removal efficiency.

[0041] Therefore, the application is a pH-responsive La-Ca-Fe@MOF core-shell composite adsorbent.

[0042] Preferably, the La-Ca-Fe@MOF core-shell composite adsorbent is a pH-responsive La-Ca-Fe@MOF core-shell composite adsorbent.

[0043] By introducing sulfonic acid groups (-SO3H) modification in the MOF shell layer, a pH-responsive site is realized, and the problem that the adsorption performance of traditional adsorbents is easily affected by changes in pH is overcome.

[0044] In some specific embodiments of the present application, the core is doped with 0.2-1.1 wt% of a nano-conductive material.

[0045] Preferably, the nano-conductive material is a graphene nanoribbon.

[0046] More specifically, in one embodiment of the present application, the core is doped with 0.2-1.1 wt% of graphene nanoribbons (GNRs) to form a La-Ca-Fe / GNRs@MOF composite structure, and the electronic conductivity is increased by 3 times to provide a conductive channel for electrochemical regeneration. The comprehensive performance of the composite material is greatly improved by using graphene nanoribbons to construct a conductive network.

[0047] Preferably, the core is doped with 0.5 wt% of graphene nanoribbons.

[0048] Therefore, the La-Ca-Fe@MOF core-shell composite adsorbent of the present application is an intelligent adsorbent material with a core-shell hierarchical structure, which realizes the integrated application of efficient phosphorus removal in a wide pH range, low-energy-consumption electrochemical regeneration, and high-purity phosphorus recovery through interface engineering and field effect regulation.

[0049] In order to obtain the above-mentioned La-Ca-Fe@MOF core-shell composite adsorbent, the following preparation method is provided in some specific embodiments of the present application.

[0050] A method for preparing a La-Ca-Fe@MOF core-shell composite adsorbent by microwave assistance, comprising the following steps: S1. Dissolve lanthanum nitrate, calcium nitrate, and iron nitrate in a first solvent according to a molar ratio of 1:2.5-3.5:3.5-4.9, add graphene nanoribbons, and ultrasonically disperse for 10-60 minutes. Drop 2 mol / L NaOH solution to pH=10 to form a sol.

[0051] Preferably, the first solvent is a small molecular alcohol and / or an aqueous solution, and more preferably, the first solvent is an ethylene glycol-water mixed solvent, and the volume ratio of ethylene glycol to water is 2-4:1. Preferably, the volume ratio of ethylene glycol to water is 3:1.

[0052] Preferably, the amount of graphene nanoribbons is m1, the total weight of La-Ca-Fe metal elements in the core is m2, and m1 / m2 = 0.2-1.1%, preferably 0.3-0.7%, for example 0.4%, 0.5%, or 0.6%, calculated with respect to the total weight of La-Ca-Fe metal elements in the core.

[0053] Preferably, the ultrasonic dispersion is performed for 20-30 minutes.

[0054] Preferably, the graphene nanoribbons of the present application improve the electronic conductivity by introducing GNRs, construct a metal oxide-HAP-MOF core-shell structure, solve the core-shell interface bonding problem through the HAP transition layer, and improve the electronic conductivity through GNRs, so that the electrostatic adsorption capacity is particularly excellent.

[0055] S2, ammonium dihydrogen phosphate is added to the sol obtained in S1, and a hydrothermal reaction is performed to form a La-Ca-Fe / GNRs-HAP core. The core structure thus constructed has a HAP transition layer, which can better combine with the shell structure.

[0056] Preferably, the amount of ammonium dihydrogen phosphate is calculated based on the calcium ions in the core, and the molar ratio of ammonium dihydrogen phosphate to calcium ions (Ca 2+ ) in the core is 1:1.1-1.4, preferably 1:1.2.

[0057] Preferably, the hydrothermal reaction temperature is 70-90°C.

[0058] Preferably, the hydrothermal reaction time is 1-4 hours, preferably 1-3 hours, for example 2 hours or 2.5 hours.

[0059] S3, 2-methylimidazole and zinc nitrate are added to a second solvent and dissolved uniformly; the core obtained in S2 is added, a pH response modifier is added, and a ZIF-8-SO3H shell layer is in-situ grown under microwave irradiation for 10-40 minutes to obtain a core-shell structured composite adsorbent.

[0060] Preferably, the second solvent is methanol and / or water, preferably a methanol solution with a concentration of 70-90%.

[0061] The ratio of 2-methylimidazole to zinc nitrate added to the second solvent is as follows: the molar ratio of 2-MI:Zn 2 ⁺ = 8-13:1, preferably 10:1. Zinc is calculated as zinc ions, and other zinc salts can be used instead of zinc nitrate. Zinc nitrate has the best stability and solubility, so it is usually selected.

[0062] Preferably, the pH response modifier is p-toluenesulfonic acid. Preferably, the concentration of p-toluenesulfonic acid is 5-20 mmol / L, preferably 8-12 mmol / L, for example 10 mmol / L.

[0063] Preferably, the frequency of the microwave is 2450 MHz.

[0064] Preferably, the microwave power is 200-400 W. It has been verified through experiments that the microwave reaction is best at this power.

[0065] Preferably, the temperature of the microwave irradiation reaction is controlled at 50-68℃. Preferably, the medium-low temperature is 55-65℃, for example 60℃.

[0066] Preferably, the microwave irradiation reaction is 12-25 minutes, preferably 10-20 minutes, for example 15 minutes.

[0067] In addition, S4 can also be included, which reduces the product in an inert atmosphere containing hydrogen at 80-120℃ for 10-50 minutes, to regulate the oxygen vacancy concentration to 8-14%. Interface activation treatment Preferably, the inert atmosphere containing hydrogen is 5v% H2 / Ar.

[0068] Preferably, the reduction in the inert atmosphere containing hydrogen is 20-40 minutes, for example 30 minutes.

[0069] After hydrogen reduction, the oxygen vacancy concentration of the product is 10-14%, preferably 12.5%.

[0070] The above preparation method of the present application innovatively uses microwave-induced interface reaction (MIIR) technology, which utilizes the selective heating effect of microwave field on polar molecules to make the MOF shell grow directionally on the surface of the core, which shortens the reaction time by 80% compared with the traditional hydrothermal method, and reduces the energy consumption by 40%. Through precise control of energy input position by microwave, local activation is realized on the surface of the core, which promotes the heterogeneous directional growth of MOF crystals and constructs a controllable core-shell composite material. The obtained MOF shell usually retains microporous characteristics, so that the adsorption performance of the composite adsorbent is much better than that of conventional adsorbent materials.

[0071] Further, S4 is further included, which filters, washes and dries the core-shell structure composite adsorbent obtained in S3; and then reduces the composite adsorbent with hydrogen for 10-60 minutes, so that the oxygen vacancy concentration of the composite adsorbent is 7-15%.

[0072] In another specific embodiment of the present application, application examples of the above La-Ca-Fe@MOF core-shell composite adsorbent are also provided.

[0073] The application of the La-Ca-Fe@MOF core-shell composite adsorbent, which is applied to the adsorption treatment of phosphorus in wastewater, has the following performance advantages.

[0074] The equilibrium adsorption capacity of the core-shell composite adsorbent of the application to phosphate is greater than or equal to 95 mg P / g in the pH range of 3-11, wherein the equilibrium adsorption capacity is as high as 132 mg P / g at pH = 3 (calculated based on the Langmuir fitting function), and the equilibrium adsorption capacity is still 87 mg P / g at pH = 9, which is 50% higher than that of the unmodified material. Therefore, the application can meet the requirements of phosphorus removal in a wide pH range, and greatly expand the application scenarios of the composite adsorbent.

[0075] Moreover, after the core-shell composite adsorbent of the application fully adsorbs phosphorus in water, the regenerated waste liquid can be treated by electrodeposition (current density 10 mA / cm 2 , 2h) to prepare zinc phosphate crystals Zn3(PO4)2·2H2O with a purity of more than 99%, realizing high-value utilization of phosphorus.

[0076] In addition, the La-Ca-Fe@MOF core-shell composite adsorbent of the application can be regenerated by in-situ electrochemistry. The specific regeneration method is as follows: a three-electrode system (the adsorbent as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode) is used, and the electrolysis is carried out at a constant potential of 0.8 V for 10 min, and the regeneration efficiency is greater than 90%, and the energy consumption of a single cycle is only 0.12 kWh / kg adsorbent.

[0077] The La-Ca-Fe@MOF core-shell composite adsorbent of the application is innovatively optimized from multiple dimensions of structure design, preparation process, and application of the adsorbent, realizing comprehensive innovation of the whole chain of "adsorption-electrochemical regeneration-phosphorus electrodeposition". In addition, it can be designed into an integrated device, and the integrated device comprises: (1) a multi-stage pore adsorption column (filled with adsorbent, flow rate 5-10 BV / h).

[0078] (2) a pulse electrochemical regeneration unit (pulse voltage 0.5-1.0 V, frequency 50 Hz).

[0079] (2) a phosphorus resource electrodeposition tank (pH = 4-5, temperature 40℃), realizing continuous operation of wastewater treatment and resource recovery.

[0080] The integrated device forms a closed-loop water phosphorus adsorption and recovery device system, which turns waste into treasure.

[0081] The application will be further described in detail below with reference to specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the application is limited to the following embodiments, and any technology realized based on the content of the application falls within the scope of the application.

[0082] Example 1 Composite adsorbent preparation Step 1: Inner core synthesis: 4.8 mmol of lanthanum nitrate, 14.4 mmol of calcium nitrate, and 19.2 mmol of iron nitrate were dissolved in 60 mL of an ethylene glycol-water mixed solution (volume ratio of ethylene glycol to water 3:1), 20 mg of graphene nanoribbons (0.5wt% relative to the total mass of La-Ca-Fe metal) were added, and ultrasonic dispersion was performed for 30 min. Then, NaOH solution was added dropwise to adjust the pH to 10, and a sol was formed.

[0083] Step 2: HAP transition layer: 17.3 mmol of ammonium dihydrogen phosphate was added, and hydrothermal reaction was performed at 80°C for 2 h. After centrifugal washing, the La-Ca-Fe / GNRs-HAP inner core was obtained.

[0084] Step 3: MOF shell growth: a 100 mL methanol solution containing 24 mmol of 2-methylimidazole, 2.4 mmol of zinc nitrate, and 10 mmol of p-toluenesulfonic acid was prepared, and the inner core was dispersed in the methanol solution. Microwave (2450 MHz, 300 W) irradiation was performed for 15 min, followed by filtration and drying in a hot air oven at 90°C.

[0085] Step 4: Interface activation: the product was reduced in 5% H2 / Ar at 100°C for 30 min to obtain the target adsorbent, i.e., La-Ca-Fe@MOF core-shell composite adsorbent. The specific surface area was determined by the BET method, and the results were 382 m 2 / g, and the mesopore ratio was 65%.

[0086] Example 2 Phosphorus removal performance test 100 mL of a phosphate solution with pH=6 and a concentration of 50 mg / L was taken, 0.1 g of the adsorbent of Example 1 was added, and oscillation was performed at 25°C for 1 h. The residual phosphorus concentration was 0.5 mg / L, and the adsorption capacity was 49.5 mgP / g. When pH=9, the residual phosphorus concentration was 1.3 mg / L, and the adsorption capacity was 48.7 mgP / g.

[0087] Example 3 Electrochemical regeneration and phosphorus recovery The saturated adsorbent in Example 2 was loaded into an electrochemical regeneration column (diameter 1 cm, column height 10 cm), and constant potential electrolysis was performed at 0.8 V for 10 min. The phosphorus concentration in the regeneration solution (10 mL) was 45 mg / L. 0.1 mol / L of ZnSO4 solution was added to the regeneration solution, the pH was adjusted to 4.5, and white crystals were obtained by electrodeposition at a current density of 10 mA / cm 2 X-ray diffraction confirmed that the white crystals were Zn3(PO4)2・2H2O, and the purity was 99.2%.

[0088] Comparative Example 1 Adsorbent without HAP transition layer.

[0089] La-Ca-Fe / GNRs@ZIF-8-SO3H without HAP transition layer was prepared by the same procedure as Example 1. The interface bonding force between the core and shell was weak, and the MOF shell layer was detached at a rate of 40% after 5 min of ultrasonic treatment. The adsorption capacity was reduced by 25% compared with Example 1.

[0090] Comparative Example 2 Prepared by a traditional hydrothermal method.

[0091] The same composition of adsorbent was prepared by a hydrothermal method (120°C, 12h). The specific surface area was 280m 2 / g, the mesoporous proportion was 52%, the adsorption equilibrium time was extended to 3h, and the energy consumption of electrochemical regeneration was increased to 0.25kWh / kg.

[0092] Example 4 Compared with Example 1, the amount of calcium nitrate was increased by 10% Step 1. Core synthesis: 4.8mmol of lanthanum nitrate, 15.8mmol of calcium nitrate, and 19.2mmol of iron nitrate were dissolved in 60mL of ethylene glycol-water (volume ratio 3:1) mixed solvent, 20mg of graphene nanoribbons (GNRs) were added, and ultrasonic dispersion was performed for 30min. Then NaOH solution was added dropwise until the pH of the system was 10, and a uniform sol was formed.

[0093] The subsequent steps were the same as Example 1.

[0094] Example 5 Compared with Example 1, the amount of calcium nitrate was reduced by 10%.

[0095] Step 1. Core synthesis: 4.8mmol of lanthanum nitrate, 15.8mmol of calcium nitrate, and 19.2mmol of iron nitrate were dissolved in 60mL of ethylene glycol-water (volume ratio 3:1) mixed solvent, 20mg of graphene nanoribbons (GNRs) were added, and ultrasonic dispersion was performed for 30min. Then NaOH solution was added dropwise until the pH of the system was 10, and a uniform sol was formed.

[0096] The subsequent steps were the same as Example 1.

[0097] Example 6 Compared with Example 1, the amount of iron nitrate was increased by 30%.

[0098] Step 1. Core synthesis: 4.8mmol of lanthanum nitrate, 15.8mmol of calcium nitrate, and 19.2mmol of iron nitrate were dissolved in 60mL of ethylene glycol-water (volume ratio 3:1) mixed solvent, 20mg of graphene nanoribbons (GNRs) were added, and ultrasonic dispersion was performed for 30min. Then NaOH solution was added dropwise until the pH of the system was 10, and a uniform sol was formed.

[0099] The subsequent steps are the same as in Example 1.

[0100] Example 7 Compared with Example 1, the amount of iron nitrate is reduced by 30%.

[0101] Step 1. Core synthesis: 4.8 mmol of lanthanum nitrate, 14.4 mmol of calcium nitrate, and 13.4 mmol of iron nitrate were dissolved in 60 mL of ethylene glycol-water (volume ratio 3:1) mixed solvent, 20 mg of graphene nanoribbons (GNRs) was added, and after ultrasonic dispersion for 30 min, NaOH solution was added dropwise to the system until pH=10, forming a uniform sol.

[0102] The subsequent steps are the same as in Example 1.

[0103] Example 8 Compared with Example 1, 10 mmol of ammonium dihydrogen phosphate was added in step 2.

[0104] Step 2. HAP transition layer construction: 10 mmol of ammonium dihydrogen phosphate was added to the product of step 1, and transferred to a polytetrafluoroethylene reaction kettle, and hydrothermal reaction was carried out at 80°C for 2h. After the reaction was completed, centrifugal separation was carried out, and deionized water was used for washing 3 times, to obtain La-Ca-Fe / GNRs-HAP core material.

[0105] The remaining steps are the same as in Example 1.

[0106] Example 9 Compared with Example 1, the product obtained in step 3 was directly filtered and dried for use. There is no interface activation treatment in step 4.

[0107] Example 10 Compared with Example 1, the only difference is that in step 1, the pH is adjusted to 8 by dropwise addition of NaOH solution. The remaining steps are unchanged.

[0108] Example 11 Compared with Example 1, the only difference is that in step 1, the pH is adjusted to 11 by dropwise addition of NaOH solution. The remaining steps are unchanged.

[0109] Example 12 Compared with Example 1, the only difference is that in step 1, the pH is adjusted to 12 by dropwise addition of NaOH solution. The remaining steps are unchanged.

[0110] Example 13 Compared with Example 1, the only difference is that in step 1, the pH is adjusted to 13 by dropwise addition of NaOH solution. The remaining steps are unchanged.

[0111] Test Example The adsorbent materials prepared from the foregoing examples 1 to 13 and comparative examples 1 to 2 were subjected to performance testing, and the testing method adopted the method for determining the residual phosphorus concentration in a solution according to the national standard GB / T 11893-1989 “Water quality-Determination of total phosphorus-Ammonium molybdate spectrophotometric method”, and the test results were as follows.

[0112] Table 1: Adsorbent performance test results

[0113] As can be seen from the foregoing examples and comparative examples, the composite adsorbent material of the present application has the characteristic of wide pH adaptability, and the adsorption capacity of the traditional La-based adsorbent significantly decreases (decreases by more than 40% at pH>7) under alkaline conditions. The adsorption capacity of the composite adsorbent of each embodiment of the present application is ≥95mgP / g in the pH range of 3-11, and still maintains 87mgP / g at pH=9, which is suitable for different water quality conditions (such as domestic sewage, industrial wastewater, and natural water bodies).

[0114] The adsorbent of the present application can trigger the desorption behavior of the adsorbent (such as the competition of OH⁻ and PO4 3 ⁻ active sites under alkaline conditions) through pH change, combined with electrochemical regeneration technology, to realize low-energy in-situ activation, and the regeneration efficiency is >90%, and the energy consumption per cycle is only 0.12kWh / kg, solving the problem of difficult regeneration of traditional adsorbents.

[0115] As can be seen from the foregoing experimental records, the present application breaks through the performance bottleneck of traditional adsorbents through triple innovation of material design, preparation process and application mode, and constructs a phosphorus pollution control and resource recovery technology system with engineering application prospect. Compared with the prior art, the pH adaptability, regeneration energy consumption and resource recovery rate are significantly improved, the adsorbent is endowed with the sensing and feedback ability to the environmental pH, and it can automatically adjust the adsorption mechanism under different acid-base conditions, thereby improving the phosphorus removal efficiency, widening the application scenarios, breaking through the limitation of traditional adsorbent to pH conditions, and realizing the intelligent design and application of environmental functional materials.

[0116] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

[0117] In the description of the specific embodiments of the present application, the terms of orientation or position relationship such as "upper", "lower", "left", "right", "center", "inner", "outer" and the like are used without special indication, which are expressions of orientation or position relationship or the orientation or position relationship of the product / device / apparatus of the present application when it is usually used. These terms of orientation or position relationship are only used for the convenience of describing the present application or simplifying the description of the specific embodiments, so as to facilitate the quick understanding of the scheme by the skilled in the art, and are not intended to indicate or imply that a specific device / component / element must have a specific orientation or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation of the present application.

[0118] In addition, the terms "first", "second", "third" and the like appearing in the description of the present application are only used to distinguish the same or similar components for description, and should not be understood as emphasizing or implying the relative importance of the specific components.

[0119] In addition, in the description of the embodiments of the present application, "several", "a plurality of", "several" represent at least 2. It can be 2, 3, 4, 5, 6, 7, 8, 9, etc. in any case, and even more than 9.

[0120] In addition, in the description of the technical scheme of the present application, unless otherwise specified / limited / limited, the terms "set", "install", "connect", "connect", "set", "lay", "arrange" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected, which can be welding, riveting, bolting, screwing and other commonly used connection means in the art. The connection can be mechanical connection, electrical connection or communication connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the communication between two elements. In addition, in the description of the technical scheme of the present application, unless otherwise specified / limited / limited, the terms "set", "install", "connect", "connect", "set", "lay", "arrange" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected, which can be welding, riveting, bolting, screwing and other commonly used connection means in the art. The connection can be mechanical connection, electrical connection or communication connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the communication between two elements.

Claims

1. A La-Ca-Fe@MOF core-shell composite adsorbent, characterized in that, The adsorbent has a core-shell structure; The inner core of the core-shell structure is a La-Ca-Fe ternary metal oxide, The shell of the core-shell structure is a ZIF-8 type MOF shell layer modified by a sulfonic group, and the MOF shell layer has a mesopore-micropore hierarchical pore network.

2. The La-Ca-Fe@MOF core-shell composite adsorbent according to claim 1, characterized in that, The molar ratio of the three metal elements in the La-Ca-Fe ternary metal oxide is La:Ca:Fe = 1:2-4:3-6.

3. The La-Ca-Fe@MOF core-shell composite adsorbent according to claim 1, wherein, The surface of the inner core has a 5-20 nm thick hydroxyapatite transition layer.

4. The La-Ca-Fe@MOF core-shell composite adsorbent according to claim 3, characterized in that, The shell is a ZIF-8 type MOF shell layer modified by a sulfonic group.

5. The La-Ca-Fe@MOF core-shell composite adsorbent according to claim 4, characterized in that, The inner core is doped with 0.2-1.1 wt% of a nano-conductive material.

6. The method of claim 5, wherein the composite adsorbent is prepared by the steps of: The method comprises the following steps: S1, prepare the salts of lanthanum, calcium and iron according to the molar ratio of La-Ca-Fe ternary metal in the inner core, and dissolve them in a solution; Then, add 0.2-1.1 wt% of graphene nanoribbons, disperse uniformly, adjust the pH to alkaline, and form a sol; S2, add ammonium dihydrogen phosphate to the sol, and hydrothermally react at 50-95°C for 1-4 hours to form a La-Ca-Fe / GNRs-HAP inner core; S3, disperse the inner core obtained in S2 in a small molecular alcohol solution of 2-methyl imidazole and zinc nitrate, add p-toluene sulfonic acid, and microwave react for 10-40 minutes to grow a ZIF-8 type MOF shell layer modified by a sulfonic group on the surface of the inner core in situ.

7. The method of claim 6, wherein the composite adsorbent is prepared by the steps of: Further comprising S4, filter, wash and dry the core-shell composite adsorbent obtained in S3.

8. The method of claim 7, wherein the composite adsorbent is prepared by the steps of: After drying, reduce the composite adsorbent with hydrogen for 10-60 minutes to make the oxygen vacancy concentration of the composite adsorbent reach 7-15%.

9. Use of the La-Ca-Fe@MOF core-shell composite adsorbent according to any one of claims 1-5 for phosphorus adsorption treatment in wastewater.

10. A regeneration method of the La-Ca-Fe@MOF core-shell composite adsorbent according to any one of claims 1-5, which adopts a three-electrode system, connects the adsorbent to a working electrode, uses a Pt sheet as a counter electrode, and uses Ag / AgCl as a reference electrode; electrolyze at a potential of 0.7-0.9V for 5-30 minutes to regenerate the composite adsorbent.

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