CN105032342A - Preparation method of stratiform bimetallic oxide sorbent capable of effectively removing low-concentrated phosphate radical - Google Patents

Abstract

The invention discloses a preparation method and application of a layered double metal oxide adsorbent for effectively removing low-concentration phosphate radicals. In the present invention, the BmimPF ₆ /DMF/H ₂ O ionic liquid water-in-water reversed phase without surfactant is firstly used as the oil phase of the hydrophobic ionic liquid BmimPF ₆ and N,N-dimethylformamide (DMF) as the co-solvent In the microemulsion system, the double microemulsion co-precipitation method is used to prepare the small particle size ultra-thin layered double metal hydroxide nanosheet precursor, and then it is calcined at a high temperature of 500 ° C in the air atmosphere to prepare the layered double metal oxide Adsorbent. The specific surface area of the obtained layered double metal oxide is 107.36-158.46m ² /g, the pore diameter is 8.56-11.17nm, and the pore volume is 0.358-0.468cm ³ /g; it can be recovered in an aqueous medium to form a particle size of 150-200nm , layered double metal hydroxide nanosheets with a thickness of about 5nm and uniform particle size distribution; its adsorption rate for low-concentration phosphate is much higher than that prepared by its precursor layered double hydroxide and traditional co-precipitation method Large particle hydrotalcite.

Description

A preparation method of layered double metal oxide adsorbent for effectively removing low-concentration phosphate

Technical field:

The invention relates to a method for preparing a layered double metal oxide adsorbent that can effectively remove low-concentration phosphate radicals, and the application of the layered double metal oxide adsorbent obtained by the preparation method to adsorb low-concentration phosphate radicals in water bodies, belonging to field of nanomaterials.

Background technique:

With the development of industrial and agricultural modernization, a large amount of nutrients such as nitrogen and phosphorus enter the water body with the sewage, causing eutrophication in the water body of the coastal waters and lakes, causing the rapid reproduction of algae and other plankton, resulting in the deterioration of the water quality and the death of a large number of aquatic organisms. Not only will it destroy the ecosystem, but the toxins produced will threaten human health through the food chain. Studies have shown that phosphorus is the key controlling factor of water eutrophication. When its concentration is higher than 0.03mg/L, the eutrophication of water body will lead to red tide or algal bloom. Therefore, it is of great significance to effectively reduce the phosphorus content in the discharged wastewater to inhibit the eutrophication of the water body and prevent the occurrence of red tide or algal bloom. Domestic and foreign wastewater phosphorus removal methods mainly include biological methods, adsorption methods, chemical precipitation methods, crystallization methods, ion exchange methods, and ecological methods, among which the adsorption method has the advantages of simple equipment, easy operation, and no secondary pollution. , is very popular, and clay minerals have been used as a new type because of their unique layered structure, large specific surface area, good adsorption and ion exchange properties, abundant reserves, low price, non-toxic and harmless to the environment, and easy regeneration. Efficient adsorbent materials have been widely used in the field of phosphorus removal from wastewater [ZhouJ, YangS, YuJ, ShuZ.

Layered double hydroxides (Layered Double Hydroxides, LDH) is a kind of anionic clay, its general formula is [M _1-x ²⁺ M _x ³⁺ (OH) ₂ ] ^x+ (A ^n- ) _x/n mH ₂ O, where the M(OH) ₆ octahedra share edges and present an open sheet-packed structure, and each octahedral unit is formed by a six-coordinated central metal ion M and OH- at the apex. Since part of M ²⁺ is replaced by M ³⁺ , the sheet will be positively charged, and there are exchangeable anions between the layers to balance the charge. LDH has weak bonding force between layers, elastic interlayer space, large surface area, high ion exchange capacity and excellent thermal stability, and shows strong capture ability for organic and inorganic anions. However, LDH can produce non-stoichiometric layered double metal oxide (LDO) after calcination at 400-800 ° C. Due to the "memory effect" of LDH, the calcined product LDO will be hydrated in the aqueous solution containing pollutants, and the LDH will be restored. During the process, anionic pollutants are intercalated between layers, thus having a higher adsorption capacity [CaiP, ZhengH, WangC, MaH, HuJ, _PuY , LiangP. 214, 100-108.]. At present, LDH and LDO have been successfully used for the removal of silver phosphate in wastewater and seawater. However, the LDH prepared by the conventional method has a large particle size and uncontrollable shape, and is prone to aggregation during use, and the obtained calcined product LDO has not fully exerted its adsorption performance on pollutants. Therefore, increasing the surface area of the precursor LDH, Increasing the adsorption sites and adsorption capacity is of great significance for the development of efficient LDO adsorbents.

Inverse microemulsion is usually an isotropic, transparent and thermodynamically stable dispersion system formed by numerous "tiny water droplets" dispersed in the continuous oil phase. Appropriate proportion composition. Each of these stable and separated "tiny water droplets" is a microreactor with a large interface, and its adjustable size can not only control the nucleation and growth of nanoparticles, but also control the particle size, which is It is considered to be an excellent medium for the controllable preparation of inorganic nanoparticles. Traditional inverse microemulsions contain surfactants, and the inorganic nanoparticles prepared by them are all mixed with surfactants without exception, especially when LDH is prepared by inverse microemulsions, the surfactants will intercalate in the form of anions Between layers, or adsorbed on the surface of layered materials [HuG, O'HareD. Uniquelayereddoublehydroxidemorphologiesusingreversemicroemulsionsynthesis, J.Am.Chem.Soc.2005, 127, 17808-17813.], so that the resulting adsorption material will cause secondary pollution, and the regeneration process of the adsorption material is extremely cumbersome and costly.

Studies have shown that in the absence of surfactants, some three-component systems can also form microemulsions, which are called surfactant-free microemulsions (SFME). Using the SFME system to prepare LDH can not only control the size of nanoparticles, narrow the particle size distribution range, improve dispersibility, and obtain LDH particles without impurity pollution, but also has simple components and easy operation, which fundamentally solves the problem of traditional microemulsion preparation of LDH. At the same time, it also provides a new idea for the preparation of high-efficiency LDO adsorbents. However, in the BmimPF ₆ /DMF/H ₂ O ionic liquid water-in-water reversed-phase SFME system with the hydrophobic ionic liquid BmimPF ₆ as the oil phase and N,N-dimethylformamide (DMF) as the co-solvent There are no reports on the preparation of LDO by ultrathin LDH nanosheets with small particle size, followed by high-temperature calcination, and its use in the adsorption of low-concentration phosphate in water.

Invention content:

In view of the deficiencies of the prior art and the needs of research and application in this field, the purpose of the present invention is to provide a preparation method for a layered double metal oxide adsorbent that can effectively remove low-concentration phosphate. First, in the BmimPF ₆ /DMF/H ₂ O ionic liquid water-in-water reversed-phase SFME system with the hydrophobic ionic liquid BmimPF ₆ as the oil phase and N,N-dimethylformamide (DMF) as the co-solvent, the bis The microemulsion co-precipitation method is used to prepare ultra-thin LDH nanosheets with small particle size, and then calcined at 500 ° C to prepare a layered bimetallic oxide adsorbent with large specific surface area and high adsorption performance.

The preparation method of a layered double metal oxide adsorbent provided by the present invention is to prepare its precursor layered double metal hydroxide by double microemulsion co-precipitation method, and then perform high-temperature calcination to prepare layered double metal oxide adsorbent. Metal oxides, specifically comprising the following steps:

1) Weigh MgCl ₂ 6H ₂ O and AlCl ₃ 9H ₂ O respectively, add deionized water to prepare a mixed salt solution of MgCl ₂ and AlCl ₃ with a total metal ion concentration of 0.05-3.0 mol/L; Add N,N-dimethylformamide DMF and hydrophobic ionic liquid BmimPF ₆ into the salt solution, wherein the volume ratio of the mixed salt solution, DMF and BmimPF ₆ is 2-15:30-50:40-70, and the magnetic force at room temperature Stir for 30-60 minutes, wait until the solution turns from turbid to transparent, and prepare the inverse microemulsion A;

2) Take ammonia water with a certain volume concentration of 25%, add DMF and BmimPF ₆ into it, wherein the volume ratio of 25% ammonia water, DMF and BmimPF ₆ is 2-15:30-50:40-70, stir magnetically at room temperature 30-60min, when the solution turns from cloudy to transparent, the inverse microemulsion B is prepared;

3) Under the condition of magnetic stirring, titrate the inverse microemulsion A and the inverse microemulsion B at the same time, control the pH between 9.0 and 10.0, stir and react at room temperature for 12 hours, and then age at 25 to 75°C for 10 to 24 hours, The resulting slurry was centrifuged at 10,000 rpm for 10 min, washed twice with DMF, absolute ethanol and deionized water in sequence, and dried under vacuum at 60°C for 12 hours to obtain the precursor small particle size ultra-thin layered double metal oxide nanosheets;

4) Put the small particle size ultra-thin layered bimetallic hydroxide nanosheet dry powder of the precursor obtained in step 3) into a muffle furnace, and calcinate for 3 to 8 hours at 500°C in an air atmosphere to obtain a layered Bimetallic oxide adsorbents.

In step 1) MgCl ₂ and AlCl ₃ The total concentration of metal ions in the mixed salt solution is 0.45mol/L, and the mol ratio of MgCl ₂ and AlCl ₃ is 2:1; the water phase is the inverse microemulsion of the mixed salt solution The volume ratio of aqueous solution, DMF and BmimPF ₆ in the inverse microemulsion B that A and aqueous phase are ammonia solution are completely equal; Step 3) the transverse dimension of the precursor small particle diameter ultrathin layered double metal hydroxide nanosheet of gained It is 10-35nm, with an average thickness of 0.71nm, and is composed of single-layer layered double metal hydroxide sheets.

The specific surface area of the layered double metal oxide prepared by the above preparation method is 107.36-158.46m ² /g, the pore diameter is 8.56-11.17nm, and the pore volume is 0.358-0.468cm ³ /g.

The layered double metal oxide adsorbent prepared by the above preparation method can restore and form layered double metal hydroxide nanosheets with a particle size of 150-200 nm, a thickness of about 5 nm, and a uniform particle size distribution in an aqueous medium.

The layered double metal oxide adsorbent prepared by the above preparation method is suitable for the adsorption application of low-concentration phosphate radicals in water bodies. L in aqueous solution, and shaken at room temperature for 5 hours.

Compared with the prior art, the present invention has main beneficial effects and advantages in that:

1) The preparation method of the layered double metal oxide adsorbent that effectively removes low-concentration phosphate radicals of the present invention solves the problems of aggregation, large particle size, and wide particle size distribution range when the traditional co-precipitation method is used to prepare the precursor LDH. Defects such as small specific surface area show the characteristics of small particle size, narrow particle size distribution range, large specific surface area, thin sheet, and small pore volume. Correspondingly, the high-temperature calcined product layered bimetallic oxide has a large specific surface area, The advantage of high adsorption performance.

2) In the preparation method of the present invention, the components of the three-component inverse microemulsion system used in the preparation of the precursor LDH are simple, do not contain surfactants, and there is no cumbersome process of removing surfactants during product purification; Layered bimetallic oxide adsorbents can be prepared after bulk LDH is calcined at high temperature, so the preparation of high-efficiency layered bimetallic oxide adsorbents is simpler and more environmentally friendly.

3) The inverse microemulsion system used in the present invention is water-in-ionic liquid inverse microemulsion, which is more in line with the requirements of green chemistry than the existing microemulsion system.

4) The layered bimetallic oxide adsorbent obtained by the preparation method of the present invention has much better adsorption performance on low-concentration phosphate in water than LDH, and the preparation method is simple in operation, mild in conditions and low in cost.

Description of drawings:

Fig. 1 is the XRD diffractogram of the samples obtained in Example 2 and Comparative Examples 1-3.

Fig. 2 is the _N2 adsorption-desorption isotherm and pore size distribution diagram of samples obtained in Example 2 and Comparative Examples 1-2.

Fig. 3 is the scanning electron micrograph of the samples obtained in Example 2 and Comparative Examples 1-3.

Figure 4 is the atomic force microscope photo (a) of the layered double metal oxide adsorbent obtained in Example 2 and the cross-sectional analysis (b) along the red straight line in the figure a.

Detailed ways:

In order to further understand the present invention, the present invention will be further described below in conjunction with the accompanying drawings and examples, but the present invention is not limited in any way.

Example 1:

1) Weigh MgCl ₂ 6H ₂ O and AlCl ₃ 9H ₂ O respectively, add deionized water to prepare a total metal ion concentration of 0.45mol/L, and a molar concentration ratio of MgCl ₂ and AlCl ₃ of 2:1; Add N,N-dimethylformamide (DMF) and hydrophobic ionic liquid BmimPF ₆ to the mixed salt solution, wherein the volume ratio of the mixed salt solution, DMF and BmimPF ₆ is 4:48:48, and stir magnetically for 40 minutes at room temperature , when the solution turns from cloudy to transparent, an inverse microemulsion A is prepared;

2) Take a certain volume concentration of 25% ammonia water, add DMF and BmimPF ₆ to it, make the volume ratio of 25% ammonia water, DMF and BmimPF ₆ be 4:48:48, stir magnetically at room temperature for 40min, and wait until the solution becomes cloudy Become transparent, and the inverse microemulsion B has been prepared;

3) Under the condition of magnetic stirring, titrate the inverse microemulsion A and the inverse microemulsion B at the same time, control the pH between 9.0 and 10.0, stir and react at room temperature for 12 hours, and then age at 75°C for 24 hours, and the obtained slurry is heated at 10000rpm Centrifuge at rotational speed for 10 min, wash with DMF, absolute ethanol and deionized water twice respectively, and dry under vacuum at 60°C for 12 hours to obtain the precursor small particle size ultrathin layered double metal oxide nanosheets.

4) Put the small particle size ultra-thin layered bimetallic hydroxide nanosheet dry powder of the precursor obtained in step 3) into a muffle furnace, and calcinate it in an air atmosphere at 500°C for 5 hours to obtain a layered bimetallic The oxide adsorbent is denoted as LDO _a .

Example 2:

1) Referring to the method and preparation conditions in step 1) of Example 1, only the volume ratio of the mixed salt solution, DMF and BmimPF ₆ was changed to 7:46.5:46.5, and an inverse microemulsion A was prepared;

2) With reference to the method and preparation conditions in step 2) of Example 1, only the volume ratio of the mixed salt solution, DMF and BmimPF ₆ was changed to 7:46.5:46.5, and an inverse microemulsion B was prepared;

3) Using the method and preparation conditions in step 3) of Example 1, the precursor small particle size ultra-thin hydrotalcite-like nanosheets are obtained;

4) Using the method and preparation conditions in Step 4) of Example 1, calcining the precursor small-size ultra-thin hydrotalcite-like nanosheets obtained in the previous step to obtain a layered bimetallic oxide adsorbent, denoted as LDO _b .

Example 3:

1) With reference to the method and preparation conditions in step 1) of Example 1, only the volume ratio of the mixed salt solution, DMF and BmimPF ₆ was changed to 7:31:62, and an inverse microemulsion A was prepared;

2) With reference to the method and preparation conditions in step 2) of Example 1, only the volume ratio of the mixed salt solution, DMF and BmimPF ₆ was changed to 7:31:62, and an inverse microemulsion B was prepared;

3) Using the method and preparation conditions in step 3) of Example 1, the precursor small particle size ultra-thin hydrotalcite-like nanosheets are obtained;

4) Using the method and preparation conditions in Step 4) of Example 1, calcining the precursor small-size ultra-thin hydrotalcite-like nanosheets obtained in the previous step to obtain a layered bimetallic oxide adsorbent, denoted as LDO _c .

Example 4:

1) The method and preparation conditions in Step 1) of Example 2 were adopted to prepare an inverse microemulsion A;

2) using the method and preparation conditions in step 2) of Example 2, an inverse microemulsion B was prepared;

3) Adopt the method and preparation conditions in step 3) of Example 1, but reduce the aging time to 12h, and obtain the ultra-thin hydrotalcite-like nanosheets with a small particle size of the precursor;

4) Using the method and preparation conditions in Step 4) of Example 1, calcining the precursor small-size ultra-thin hydrotalcite-like nanosheets obtained in the previous step to obtain a layered bimetallic oxide adsorbent, denoted as LDO _d .

Example 5:

1) The method and preparation conditions in Step 1) of Example 2 were adopted to prepare an inverse microemulsion A;

2) using the method and preparation conditions in step 2) of Example 2, an inverse microemulsion B was prepared;

3) Adopt the method and preparation conditions in Step 3) of Example 1, except that the reaction temperature is lowered to 25° C. to obtain ultrathin hydrotalcite-like nanosheets of the precursor with small particle size.

4) Using the method and preparation conditions in Step 4) of Example 1, calcining the precursor small-size ultra-thin hydrotalcite-like nanosheets obtained in the previous step to obtain a layered bimetallic oxide adsorbent, denoted as LDO _e .

Comparative example 1:

1) Weigh MgCl ₂ 6H ₂ O and AlCl ₃ 9H ₂ O respectively, add deionized water to prepare a total metal ion concentration of 0.45mol/L, and a molar concentration ratio of MgCl ₂ and AlCl ₃ of 2:1 to prepare Solution A is obtained;

2) Aqueous ammonia with a concentration of 25% (w/w) is solution B;

3) Under the condition of magnetic stirring, titrate solution A and solution B at the same time, control the pH between 9.0 and 10.0, stir and react at room temperature for 12 hours, and then age at 75°C for 24 hours, centrifuge the obtained slurry at 10000rpm for 10 minutes, and then Wash twice with DMF, absolute ethanol and deionized water, and dry under vacuum at 60°C for 12 hours to obtain LDH.

Comparative example 2:

According to the method and conditions of steps 1) to 3) in Implementation 2, the precursor small particle size ultra-thin hydrotalcite-like nanosheets were prepared, which was denoted as LDH-M.

Comparative example 3:

The sample LDH _b obtained in Example 2 was stirred and reacted in deionized water for 2 hours to obtain a recovered layered double metal hydroxide, which was denoted as LDH _r .

Fig. 1 is the XRD result chart of the samples obtained in Example 2 and Comparative Examples 1-3. In the figure, the three samples of LDH, LDH-M and LDH _r all have three characteristic diffraction peaks of hydrotalcite-like crystal planes 003, 006, and 009 at low 2θ, and LDH-M and LDH _r are similar to the characteristic peaks of the LDH sample. Ratio, its peak width obviously widens, and intensity obviously weakens, and the crystallinity of the precursor LDH nanosheet that adopts double microemulsion co-precipitation method of the present invention to prepare is lower, and its crystallization is recovered by double metal oxide hydration. degree becomes lower. The d ₀₀₃ values of the three samples are between 0.78 and 0.80nm, comparable to Cl-LDH, and their unit cell parameters a and b (a=b=2d ₁₁₀ ) are about consistent with literature values. The width and intensity of the diffraction peaks well reflect the crystallinity of the sample. The three samples also have 110 and 113 diffraction peaks at high 2θ, but it is obvious that compared with the characteristic peaks of LDH samples, the 110 and 113 diffraction peaks of LDH-M and LDH _r not only overlap, but also become weaker in intensity and wider in width. Broadly, it shows that the crystallinity of the precursor LDH nanosheets prepared by the double microemulsion co-precipitation method described in the present invention and the LDH recovered from the double metal oxide hydration are low, and the sheets are very thin. When LDH-M was calcined at 500°C for 5 hours, a layered double metal oxide was formed. XRD showed that the original sheet structure collapsed, the combined hydroxide and interlayer water molecules were lost, and new oxides appeared at the same time. phase diffraction peaks.

Fig. 2 is the _N2 adsorption-desorption isotherm and pore size distribution diagram of samples obtained in Example 2, Comparative Examples 1 and 2. Adsorption isotherms showed that all samples were typical IV isotherms with H3-type hysteresis curves (P/P ₀ >0.4), indicating mesoporous materials. Among them, the specific surface area of the LDH-M sample is 140.83m ² /g, which is higher than that of the LDH sample (53.28m ² /g) prepared by the traditional co-precipitation method, indicating that the microemulsion co-precipitation method without surfactant can prepare a layer with a large specific surface area double metal hydroxide nanosheets. The specific surface area of the calcined product LDO _b is 113.05m ² /g because of the loss of the original hydrotalcite-like sheet structure, but it is still much higher than that of the LDH sample prepared by the traditional co-precipitation method. The pore diameters of LDH-M and LDO _b are 3.83 and 10.94 nm, respectively, which are much smaller than the LDH sample (21.87 nm) prepared by the traditional co-precipitation method, which indicates that the first two samples lack an ordered lamellar structure. The specific results are shown in Table 1.

Table 1: BET specific surface and pore size results of LDH nanosheets.

Fig. 3 is the scanning electron micrograph of the samples obtained in Example 2 and Comparative Examples 1-3. Electron micrographs show that the LDH samples prepared by the traditional co-precipitation method have obvious layered structure, large particles and obvious aggregation. However, the precursor LDH-M prepared by the co-precipitation method of the surfactant-free microemulsion of the present invention has a smaller particle size, and is curved and uniformly dispersed due to the thin layer. The calcined product LDO _b presents an amorphous structure with small particles due to the collapse of the hydrotalcite-like sheet structure. When LDO _b was recovered in aqueous medium, due to the "memory effect" of LDH, LDH _r appeared a hydrotalcite-like sheet structure, and still had good dispersion, but its sheet became larger, and the sheet The layer also becomes thicker, because the hydrotalcite-like nanosheets can grow freely without the confinement of the "small pool" in the microemulsion system during this process.

Fig. 4 is the atomic force microscope photograph (a) of the sample obtained in Comparative Example 3 and the cross-sectional analysis (b) along the red straight line in the figure a. The atomic force microscope photos show that the prepared calcined product LDO _b shows obvious aggregation after being recovered in water, although the cross-sectional analysis results of the red line show that its particle size is between 20-60nm and the thickness is about 0.96-3.22nm , but it can be clearly seen that there are obvious aggregations in other regions, and the particle size and thickness should be larger, which is consistent with the results of scanning electron microscopy.

Embodiment 5 application effect test example

Test object: the product that embodiment 1-5 makes, comparative example 1 gained product;

Purpose of the test: To investigate the adsorption performance of the products obtained in Examples 1-5 of the present invention and LDH obtained in Comparative Example 1 on low-concentration phosphate radicals in water.

Test group:

Test 1 group: the product LDO _a that embodiment 1 makes;

Test 2 groups: the product LDO _b that embodiment 2 makes;

Test 3 groups: the product LDO _c that embodiment 3 makes;

Test 4 groups: the product LDO _d that embodiment 4 makes;

Test 5 groups: the product LDO _e that embodiment 5 makes;

Comparative test group: the products LDH and LDH-M prepared in Comparative Examples 1 and 2.

experiment method:

Add 50 mg of each test object of the present invention into 50 mL of potassium dihydrogen phosphate aqueous solution with a concentration of 2 mg/L, and stir and react for 5 hours. Every group of experiments is repeated six times, and the concentration after its treatment is measured, and its removal rate is determined, and the average value is obtained, wherein the calculation formula of the removal rate is as follows:

test results:

Table 2: Adsorption test results of products of the present invention and comparative samples to low-concentration phosphate radicals in water bodies

group comparison group comparison group Test 1 group Test 2 groups Test 3 groups Test 4 groups Test 5 groups test product LDH LDH-M LDO _a LDO _b LDO _c LDO _d LDO _e Removal rate (%) 55.33 70.12 ^* 92.3 ^*# 92.6 ^*# 90.8 ^*# 91.8 ^*# 91.4 ^*#

Remarks: ^* Compared with the comparison group LDH, P<0.05;^#Compared with the comparison group LDH-M, P<0.05.

Summary: From the test results in Table 2, it can be seen that:

The result shows: under adding same mass adsorbent condition, each experimental group of the present invention (experiment 1,2,3,4 and 5 groups) compares contrast group LDH and LDH-M, they are to the phosphate radical of low concentration in water body The adsorption and removal rates all have significant differences. It can be seen that the layered double metal oxide adsorbent LDO obtained by the present invention has significantly better adsorption and removal effects on low-concentration phosphate radicals in water than those prepared by small particle size ultra-thin LDH nanosheets and traditional co-precipitation methods. This is mainly because the layered double metal oxide adsorbent LDO obtained in the present invention not only utilizes the large specific surface area for adsorption, but also when the structure is reconstructed to form LDO, the phosphate radical participates in the reconstruction of the hydrotalcite, Therefore, compared with ultra-thin LDH nanosheets with small particle size and large-particle hydrotalcites prepared by traditional co-precipitation method, they have achieved unexpected technical effects.

Claims (6)

1. the preparation method of a layered bi-metal oxide adsorbent, it is characterized in that first adopting two microemulsion coprecipitation to prepare its presoma layered double hydroxide, and then high-temperature calcination is carried out to it prepare layered bi-metal oxide, specifically comprise the following steps:

1) MgCl is taken respectively ₂6H ₂o and AlCl ₃9H ₂o, adds deionized water, prepares the MgCl that total concentration of metal ions is 0.05 ~ 3.0mol/L ₂and AlCl ₃mixed-salt aqueous solution; DMF DMF and hydrophobic ionic liquid BmimPF is added in this mixing salt solution ₆, wherein mixed-salt aqueous solution, DMF and BmimPF ₆volume ratio be 2 ~ 15:30 ~ 50:40 ~ 70, room temperature lower magnetic force stir 30 ~ 60min, treat that solution is become from muddiness transparent, prepared reverse micro emulsion A;

2) get the ammoniacal liquor that certain volume concentration is 25%, add DMF and BmimPF wherein ₆, wherein ammoniacal liquor, DMF and BmimPF of 25% ₆volume ratio be 2 ~ 15:30 ~ 50:40 ~ 70, room temperature lower magnetic force stir 30 ~ 60min, treat that solution is become from muddiness transparent, prepared reverse micro emulsion B;

3) under magnetic agitation condition, by reverse micro emulsion A and reverse micro emulsion B titration simultaneously, control pH is between 9.0 ~ 10.0, stirring at room temperature reaction 12h, aging 10 ~ 24h under 25 ~ 75 DEG C of conditions afterwards, gained slurries are centrifugal 10min under 10000rpm rotating speed, washs 2 times respectively successively by DMF, absolute ethyl alcohol and deionized water, under 60 DEG C of vacuum, drying 12 hours, obtains presoma small particle diameter ultra-thin stratiform bimetallic oxide nanometer sheet;

4) by step 3) the presoma small particle diameter ultra-thin layered duplex metal hydroxide nanometer sheet dry powder of gained puts into Muffle furnace, and calcine 3 ~ 8 hours under 500 DEG C of conditions in air atmosphere, obtain layered bi-metal oxide adsorbent.

2. the preparation method of a kind of layered bi-metal oxide adsorbent according to claim 1, is characterized in that step 1) middle MgCl ₂and AlCl ₃in mixing salt solution, the total concentration of metal ion is 0.45mol/L, MgCl ₂and AlCl ₃mol ratio be 2:1; Described aqueous phase is the reverse micro emulsion A of mixed-salt aqueous solution and aqueous phase is the aqueous solution, DMF and BmimPF in the reverse micro emulsion B of ammonia spirit ₆volume ratio completely equal; Step 3) lateral dimension of the ultra-thin layered duplex metal hydroxide nanometer sheet of presoma small particle diameter of gained is 10 ~ 35nm, average thickness is 0.71nm, is made up of individual layer layered double hydroxide sheet.

3. the preparation method of a kind of layered bi-metal oxide adsorbent according to claim 1, is characterized in that the layered bi-metal oxide specific area utilizing the preparation method described in claim 1 or 2 to prepare is 107.36 ~ 158.46m ²/ g, aperture is 8.56 ~ 11.17nm, and pore volume is 0.358 ~ 0.468cm ³/ g.

4. the preparation method of a kind of layered bi-metal oxide adsorbent according to claim 1 prepares the layered bi-metal oxide adsorbent of gained, it is characterized in that: can recover to form the layered duplex metal hydroxide nanometer sheet that particle diameter is 150 ~ 200nm, thickness is about 5nm, domain size distribution is homogeneous in aqueous medium.

5. layered bi-metal oxide adsorbent according to claim 4, is characterized in that gained adsorbent is suitable for the adsorption applications of low phosphorus acid group in water body.

6. adsorbent according to claim 5 is suitable for the adsorption applications of low phosphorus acid group in water body, it is characterized in that the phosphate concentration in water body is 2mg/L.