CN110711553B - Hydrotalcite-pseudo-boehmite composite film and preparation method and application thereof - Google Patents

Abstract

The invention provides a hydrotalcite pseudo-boehmite composite film, a preparation method and application thereof. The hydrotalcite pseudo-boehmite composite film is composed of a pseudo-boehmite film and water loaded on the surface of the pseudo-boehmite film. The composition of talc is prepared by dissolving a divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding a pseudo-boehmite film, and using a hydrothermal method to grow water on the pseudo-boehmite film in situ Talc is available. In the present invention, the hydrotalcite precursor is made alkaline by utilizing urea hydrolysis under hydrothermal conditions, and is rich in ^OH- . The divalent metal ions and the aluminum ions released from the diaspore film combine in situ through OH ^- to form a composite film with rich surface hydroxyl groups. The presence of a large number of hydroxyl groups can inhibit the acid hydrolysis of the pseudo-boehmite, and make the hydrotalcite firmly bond to the surface of the pseudo-boehmite to avoid scattering or breaking, and can also improve the adsorption of metal ions.

Description

A kind of hydrotalcite pseudo-boehmite composite film and its preparation method and application

technical field

The invention belongs to the technical field of composite material synthesis, and in particular relates to a hydrotalcite pseudo-boehmite composite film and a preparation method and application thereof.

Background technique

In recent years, with the rapid development of industrial production, heavy metal ion pollutants (such as Pb(II), Cd(II), Cu(II), Zn(II), etc.) , Hg(I), etc.) are discharged into water bodies in large quantities, posing a serious threat to the water quality of agriculture, industry and domestic supply. Because heavy metal ions cannot be biodegraded and are highly toxic, they will cause serious harm to the human body through the transmission and accumulation of food chains. Among them, Pb(II) will affect the development of human intelligence and bone, and at the same time cause indigestion and endocrine disorders, lead to anemia, high blood pressure, and also damage renal function and immune function. At present, the technologies used to treat heavy metal ion pollutants include adsorption method, precipitation method, membrane separation method, electrodialysis method, ion exchange method, reverse osmosis method and biological method. Compared with other methods, adsorption method is considered as one of the most suitable technologies due to its advantages of simple preparation method, simple operation and economic feasibility.

Pseudoboehmite (γ-AlOOH), also known as boehmite-like, is a class of thin wrinkled sheets with unstable composition and incomplete crystallization, with high specific surface area, large porosity, and interfacial Gibbs freedom. It has the characteristics of high energy, good dispersibility and peptization, and is often used in the field of wastewater treatment. For example, CN105107486A precipitates inorganic aluminum salt solution under alkaline conditions, separates the precipitate by centrifugal washing, and then adds concentrated hydrochloric acid, glacial acetic acid or nitric acid to make the precipitate peptized while adding film-forming aid polyvinyl alcohol and structural regulator P123 or F127, The γ-AlOOH thin film adsorbent was obtained after tape casting and drying, and its adsorption and removal rate for Cr(VI) with a concentration of 20 mg/L could reach as high as 99.4%. Wang et al. (Wang YQ, Wang GZ, Wang HQ, Cai WP, Liang CH, Zhang L. Template-induced synthesis of hierarchical SiO ₂ @γ-AlOOH spheres and their application in Cr(VI)removal[J]. Nanotechnology, 2009, 20(15): 155604.) Using alkaline conditions to break the silicon-oxygen bond of SiO ₂ colloidal spheres, and induce metaaluminate ions to hydrolyze on its surface, the resulting unstable Al(OH) ₃ colloids were heated at 160 °C It was gradually converted into γ-AlOOH under hydrothermal conditions, and _SiO2 @γ-AlOOH spheres were synthesized. The maximum adsorption capacity of Cr(VI) by the SiO ₂ @γ-AlOOH spheres modified with inorganic materials is 4.5 mg/g, which is higher than that of γ-AlOOH (about 2 mg/g). However, both the pure γ-AlOOH film and the γ-AlOOH film compounded with SiO ₂ colloidal spheres have the defect of poor acid resistance, partial hydrolysis occurs at pH=1-5, and it is easy to cause secondary pollution to the water body.

其中M²⁺为Mg²⁺，Ni^{2 +}，Co²⁺， Zn²⁺，Cu²⁺等二价金属阳离子，为Al³⁺，Cr³⁺，Fe³⁺等三价金属阳离子，A^n-为阴离子，如CO₃ ^2-， NO₃ ^-，Cl^-，OH^-，SO₄ ^2-，PO₄ ^3-等无机和有机离子以及络合离子。其中MgAl-LDH是具有潜力 的吸附材料，层间的羟基基团可以与水中的阴离子进行交换，也可以与阳离子发生络合反应 或静电吸引。CN109012573A在室温条件下利用氨水滴加到硝酸铝和硝酸镁的混合溶液中得 到MgAl-LDH沉淀物，对沉淀进行离心水洗分离，然后添加柠檬酸使沉淀胶溶的同时添加成 膜助剂聚乙烯醇，经流延成型和干燥后，经马弗炉焙烧4h后制得所述吸附剂，其对浓度为 20mg/L的Cr(Ⅵ)的吸附去除率可高达100％。但是CN109012573A制备的MgAl-LDH薄膜易 碎，不利于吸附操作。Lyu等人(Lyu F Y，Yu H Q，Hou T L，Yan L G，Zhang X H，DuB.Efficient and fast removal of Pb²⁺and Cd²⁺from an aqueous solution using achitosan/Mg-Al-layered double hydroxide nanocomposite[J].Journal of Colloidand Interface Science，2019，539:184-193.)报 道了一种壳聚糖/MgAl-LDH复合颗粒的制备方法，吸附材料对Pb(II)的最大吸附量为333.3 mg/g，去除率为99.59％。但是Lyu制备的吸附剂为粉体，在吸附污染物后存在分离困难且容 易在水体中残留造成二次污染的问题。Hydrotalcite, also known as Layered Double Hydroxide (LDH), is a new type of inorganic functional material with a layered structure. Lots of hydroxyl groups. The chemical formula of hydrotalcite is

M ²⁺ is Mg ²⁺ , Ni ²⁺ , Co ²⁺ , ^{Zn 2+ , Cu 2+ and other} divalent metal cations, Al ³⁺ , Cr ³⁺ , Fe ³⁺ and other trivalent metal cations, ^{An -} is an anion, such as CO ₃ ^2- , NO ₃ ^- , Cl ^- , OH ^- , SO ₄ ^2- , PO ₄ ^3- and other inorganic and organic ions and complex ions. Among them, MgAl-LDH is a potential adsorption material. The hydroxyl groups in the interlayer can be exchanged with anions in water, and can also undergo complex reaction or electrostatic attraction with cations. CN109012573A At room temperature, ammonia water is added dropwise to the mixed solution of aluminum nitrate and magnesium nitrate to obtain MgAl-LDH precipitate, the precipitate is subjected to centrifugal washing and separation, and then citric acid is added to make the precipitate peptized while adding film-forming aid polyethylene Alcohol, after tape casting and drying, and roasting in a muffle furnace for 4 hours to obtain the adsorbent, the adsorption and removal rate of Cr(VI) with a concentration of 20 mg/L can be as high as 100%. However, the MgAl-LDH film prepared by CN109012573A is fragile, which is not conducive to the adsorption operation. Lyu et al. (Lyu FY, Yu HQ, Hou TL, Yan LG, Zhang XH, DuB. Efficient and fast removal of Pb ²⁺ and Cd ²⁺ from an aqueous solution using achitosan/Mg-Al-layered double hydroxide nanocomposite[J ]. Journal of Colloid and Interface Science, 2019, 539: 184-193.) reported a preparation method of chitosan/MgAl-LDH composite particles, the maximum adsorption amount of Pb(II) by the adsorption material was 333.3 mg/g , the removal rate is 99.59%. However, the adsorbent prepared by Lyu is a powder, which is difficult to separate after adsorbing pollutants and easy to remain in the water body to cause secondary pollution.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a kind of hydrotalcite pseudo-boehmite composite film and its preparation method and application, overcome the defect that the existing pseudo-boehmite film is easy to be acidly hydrolyzed, and simultaneously solve the problem that the existing hydrotalcite material is not easy to form a film or The problem of easy breakage after film formation.

The hydrotalcite pseudo-boehmite composite film provided by the present invention is composed of a pseudo-boehmite film and a hydrotalcite supported on the surface of the pseudo-boehmite film.

Further, the hydrotalcite is selected from any one of magnesium-aluminum hydrotalcite, nickel-aluminum hydrotalcite, and cobalt-aluminum hydrotalcite.

The preparation method of the hydrotalcite pseudo-boehmite composite film of the present invention is as follows: dissolving a divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding a pseudo-boehmite film and performing a hydrothermal reaction to obtain the hydrotalcite Pseudo-boehmite composite film.

Further, the hydrothermal reaction temperature is 90-150° C., and the reaction time is 10-12 h. Preferably, the hydrothermal reaction temperature is 90-110°C, and the reaction time is 12 h. Under these conditions, the hydrotalcite has a good morphology on the pseudo-boehmite, and the whole composite film has a good adsorption performance.

Further, the divalent metal salt is selected from any one of magnesium sulfate, magnesium nitrate, magnesium chloride, nickel sulfate, and cobalt sulfate.

Further, the concentration of the divalent metal salt in the precursor is 0.002-0.06 mol/L, and the concentration of the urea is 0.01-0.2 mol/L.

Further, the ratio of the divalent metal salt to the pseudo-boehmite is (0.0001-0.3) mol: 0.12 g.

Further, the preparation method of the pseudo-boehmite film is as follows: adding ammonia water to the aluminum salt aqueous solution to obtain a precipitate; adding a peptizer and a film-forming aid to the precipitation, and obtaining a pseudo-boehmite sol after aging; A pseudo-boehmite film is obtained after the boehmite sol is cast and formed.

Further, the aging temperature is 90-100° C., and the aging time is 20-24 h.

Further, the peptizer is selected from acetic acid, and the film-forming aid is selected from polyvinyl alcohol.

The invention also provides a method for removing heavy metal ions in an aqueous solution. The pH of the aqueous solution containing heavy metals is adjusted to 5-6, and the heavy metal ions can be removed by adding a hydrotalcite pseudo-boehmite composite film to adsorb the heavy metal ions.

Preferably, the heavy metal ion is Pb(II).

Compared with the prior art, the present invention makes the hydrotalcite precursor alkaline and rich in OH ⁻ by utilizing urea hydrolysis under hydrothermal conditions. The divalent metal ions and the aluminum ions released from the diaspore film combine in situ through ^OH- to form a composite film with rich hydroxyl groups on the surface. The presence of a large number of hydroxyl groups, on the one hand, inhibits the acid hydrolysis of pseudo-boehmite, and on the other hand, makes the hydrotalcite firmly bound to the surface of pseudo-boehmite to avoid scattering or breaking, and can also enhance the resistance to metal ions. The complexation reaction or electrostatic attraction improves the adsorption of metal ions.

Description of drawings

Figure 1 shows the XRD patterns of γ-AlOOH thin films and MgAl-LDH/γ-AlOOH composite thin films;

Figure 2 is the SEM images of the γ-AlOOH thin film and the MgAl-LDH/γ-AlOOH composite thin films of Examples 1 to 6, wherein Figure 2a shows the γ-AlOOH thin film of the comparative example, Figure 2b shows Example 1, and Figure 2c shows the implementation Example 2, Example 2d represents Example 3, Figure 2e represents Example 4, Figure 2f and Figure 2g represent Example 5, and Figure 2h represents Example 6;

Fig. 3 is a macro photo of the γ-AlOOH thin film (Fig. 3a) and the MgAl-LDH/γ-AlOOH composite thin film (Fig. 3b) of Example 4;

Figure 4 shows the adsorption kinetics curve of Pb(II) by MgAl-LDH/γ-AlOOH composite film.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to specific embodiments.

Examples 1 to 12

The preparation method of the hydrotalcite pseudo-boehmite composite film of the present invention comprises the following steps:

(1) Preparation of pseudo-boehmite thin film (ie γ-AlOOH thin film): adding ammonia water to the aluminum salt aqueous solution to obtain a precipitate; adding a peptizer and a film-forming aid to the precipitate to obtain a pseudo-boehmite sol; The γ-AlOOH film is obtained after the pseudo-boehmite sol is cast and formed.

Specifically, 9 g of aluminum nitrate nonahydrate was dissolved in 25 mL of deionized water at room temperature, and 35 mL of 5wt% ammonia water was added dropwise under the condition of magnetic stirring at a rate of 500 r/min to obtain a precipitate. The obtained precipitate was centrifuged and washed with deionized water until the pH of the filtrate was ≈7. The precipitate was then dispersed in 65 mL of deionized water to form a suspension, 0.440 mL of peptizing agent acetic acid was added and the temperature was raised to 90°C. Then, 1.24 g of polyvinyl alcohol, a film-forming aid, was added, stirred for 2 h, and then aged at 90 °C for 24 h to obtain a γ-AlOOH sol. Finally, the γ-AlOOH sol was spread on a 2cm×4cm polytetrafluoroethylene plate to make it tape-cast, and dried at room temperature for 48 hours, and then the film was peeled off to obtain the γ-AlOOH film.

(2) Preparation of hydrotalcite pseudo-boehmite composite film: dissolving divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding pseudo-boehmite film, and using a hydrothermal method to prepare pseudo-boehmite In situ hydrotalcite is grown on the film to obtain a hydrotalcite pseudo-boehmite composite film.

Specifically, divalent metal salts and urea were completely dissolved in 50 mL of deionized water at room temperature to prepare a hydrotalcite precursor with the concentration shown in Table 1, and transferred to 100 mL together with a 2 cm × 4 cm γ-AlOOH film. In a hydrothermal reactor lined with a Teflon liner. After the hydrothermal reactor was sealed, the hydrothermal reaction was carried out at a certain temperature, and the hydrotalcite was grown in situ on the γ-AlOOH film. After the reaction, it was cooled to room temperature, washed with deionized water for several times, and dried at room temperature for 24 h to obtain a film-like hydrotalcite pseudo-boehmite composite film, which was marked as MAl-LDH/γ-AlOOH composite film, where M represents Mg, Ni or Co.

As a comparison, the γ-AlOOH films were hydrothermally treated alone without the hydrotalcite precursor (Comparative Example). That is, a 2cm×4cm γ-AlOOH film and 50mL of deionized water were transferred to a 100mL hydrothermal reactor lined with a PTFE liner, and the hydrothermal reactor was sealed and heated in an oven at 110°C for 12h . After finally cooling to room temperature, washed several times with deionized water and dried at room temperature for 24 h.

Table 1. Raw material dosage and reaction conditions of hydrotalcite pseudo-boehmite composite film

The MAl-LDH/γ-AlOOH composite films obtained in the above examples and the γ-AlOOH films of the comparative examples were characterized, and the results were as follows:

The γ-AlOOH film of the comparative example, the MgAl-LDH/γ-AlOOH composite film of Examples 1 to 4, the NiAl-LDH/γ-AlOOH composite film of Example 11, and the CoAl-LDH/γ-AlOOH composite film of Example 12 The XRD pattern of the film is shown in Figure 1. Figure 1 shows that, compared with the γ-AlOOH thin films of the comparative example, the newly added 2θ values in the XRD patterns of the samples prepared in other examples: 11°, 23°, and 48° are the characteristic peaks of hydrotalcite, which indicate that by hydrothermal The method of in situ growth of hydrotalcite on γ-AlOOH thin films is feasible.

Fig. 2 is the SEM image of the γ-AlOOH thin film of the comparative example and the MgAl-LDH/γ-AlOOH composite thin film prepared in Examples 1-6. It can be seen from Figure 2a that the surface of the γ-AlOOH film is flat and relatively smooth. Example 1 After the hydrothermal reaction of the γ-AlOOH film with a low concentration of hydrotalcite precursor, a small amount of flaky hydrotalcite appeared on the surface of the γ-AlOOH film, and the surface began to become rough, as shown in Figure 2b. In Examples 2-4, the magnesium sulfate concentration is 0.006-0.02 mol/L, and the urea concentration is 0.03-0.1 mol/L. With the increase of the concentration of the hydrotalcite precursor, the hydrotalcite flakes on the surface of the γ-AlOOH film As the number increases, it gradually becomes denser, and a staggered network and abundant voids are formed on the surface. However, when the concentration of magnesium sulfate increased to more than 0.04mol/L and the concentration of urea increased to 0.2mol/L, the voids on the surface of the hydrotalcite pseudo-boehmite composite films of Figure 2f, Figure 2g Example 5 and Figure 2h Example 6 gradually increased. Filled with newly deposited hydrotalcite.

Meanwhile, macroscopically, the γ-AlOOH film of the comparative example is translucent, as shown in the macrophotograph of Fig. 3a. However, after the hydrotalcite is grown, the film becomes white and non-transparent, as shown in the macrophotograph of the MgAl-LDH/γ-AlOOH composite film of Example 4 in Figure 3b.

It can be seen that hydrotalcite can be successfully grown in situ on the surface of γ-AlOOH thin film by the hydrothermal method, and the growth morphology of hydrotalcite on the surface of γ-AlOOH thin film can be effectively controlled by appropriate selection of precursor concentration and hydrothermal reaction temperature and time. . The main reaction mechanism of this process is: under hydrothermal conditions, urea is slowly hydrolyzed to release NH ₃ , and then the reaction occurs: NH ₃ +H ₂ O→NH ₄ ⁺ +OH ^- , the accumulation of OH ^- makes the precursor alkaline, At this time, the Al atoms released from the surface of the γ-AlOOH film and the Mg atoms in the solution synthesized MgAl-LDH in situ under alkaline conditions to obtain the MgAl-LDH/γ-AlOOH composite film. When the precursor concentration is low, the amount of Mg ²⁺ that can react with Al atoms on the γ-AlOOH thin film is less in solution, and only a small amount of hydrotalcite is grown and deposited on the surface of the thin film. When the precursor concentration is too high, the amount of hydrotalcite formed by deposition increases, which will gradually fill the gaps between the hydrotalcites.

Example 13

This embodiment provides a method for removing heavy metal ions in an aqueous solution, especially a method for removing Pb(II), by adjusting the pH of the aqueous solution containing heavy metals to 5-6, adding the MAl-LDH/γ- The AlOOH composite film can remove heavy metal ions by adsorbing heavy metal ions.

For example, add 0.1 mol/L NaOH solution to 50 mL of 50 mg/L (or 100 mg/L, 500 mg/L) Pb(II) solution, adjust the pH to 5, and add 0.05 g of MAl- LDH/γ-AlOOH composite film, the MAl-LDH/γ-AlOOH composite film was made to adsorb Pb(Ⅱ) at 25℃ and 150r/min shaking condition.

As a comparison, the same mass of the γ-AlOOH film of the comparative example was added to the Pb(II) solution, and Pb(II) was adsorbed under the same conditions.

After the adsorption is completed, it can be observed that the MAl-LDH/γ-AlOOH composite film hardly undergoes acidolysis or shedding. The adsorption results of Pb(II) by each material are shown in Table 2. The adsorption kinetics curve of γ-AlOOH composite film on Pb(II) in 50 mg/L Pb(II) solution is shown in Figure 4.

Table 2. Adsorption results of Pb(Ⅱ) by hydrotalcite pseudo-boehmite composite films

It can be seen from Table 2 that the removal rate of Pb(II) by the MgAl-LDH/γ-AlOOH composite film of the present invention in a 50 mg/L Pb(II) solution can reach up to 99.99% (Example 7). Example 1 In the case of using a very low concentration of hydrotalcite precursor, the obtained MgAl-LDH/γ-AlOOH composite film can still achieve a removal rate of 86.34% for Pb(II), compared with the removal rate of the simple γ-AlOOH film in the comparative example. The removal rate of Pb(II) by the MgAl-LDH/γ-AlOOH composite film can still reach 83.72% when the hydrothermal reaction temperature is too high in Example 8, which is higher than that of the γ-AlOOH film. The removal rate increased by 56.42%. And the residual concentration of Pb(II) of 50mg/L and 100mg/L was reduced to 0.16mg/L and 0.17mg/L respectively, which reached the discharge standard of Pb(II) content in industrial wastewater stipulated by the state. In addition, NiAl-LDH/γ-AlOOH composite films and CoAl-LDH/γ-AlOOH composite films also have a certain adsorption effect on Pb(Ⅱ). Apparently, by in-situ growth of hydrotalcite on γ-AlOOH films, the adsorption and removal ability of the films to Pb(II) can be significantly improved.

Combining with Figure 4, it can be seen that the adsorption rate of Pb(II) by the MgAl-LDH/γ-AlOOH composite film is relatively fast, and the adsorption amount of Pb(II) increases almost linearly within 200 min, and the adsorption can be completed in about 550 min.

From the above results and analysis, it is known that the present invention forms a composite film with a surface rich in hydroxyl groups by in-situ growth of hydrotalcite on the pseudo-boehmite film. On the one hand, the presence of a large number of hydroxyl groups inhibits the acidity of pseudo-boehmite. Therefore, the hydrotalcite pseudo-boehmite film can effectively adsorb Pb(II) without acid hydrolysis under the strong acid condition of pH 5; on the other hand, it can also enhance the complexation reaction of metal ions by or electrostatic attraction to improve the adsorption of metal ions, so that the removal rate of Pb(II) by the hydrotalcite pseudo-boehmite film is increased to nearly 100%, which is at least 56.42% higher than that of the pure diaspore film. %. In addition, the hydrotalcite can be firmly bonded to the surface of the pseudo-boehmite, and the MAl-LDH/γ-AlOOH composite film remains in a thin film state after multiple uses, and the hydrotalcite does not fall off.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (6)

1. a method for removing heavy metal ions in the aqueous solution is characterized in that: the pH of the aqueous solution containing heavy metals is adjusted to 5～6, adding a hydrotalcite pseudo-boehmite composite film to adsorb heavy metal ions, and the hydrotalcite pseudo-boehmite composite film is The preparation method of the diaspore composite film is as follows: dissolving a divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding a pseudo-boehmite film, and performing a hydrothermal reaction to obtain a hydrotalcite pseudo-boehmite composite film , the divalent metal salt is selected from any one of magnesium sulfate, magnesium nitrate, and magnesium chloride, and the heavy metal ion is Pb(II). 2 . The method for removing heavy metal ions in an aqueous solution according to claim 1 , wherein the hydrothermal reaction temperature is 90-150° C., and the reaction time is 10-12 h. 3 . 3. The method for removing heavy metal ions in an aqueous solution according to claim 1, wherein the concentration of the divalent metal salt in the precursor is 0.002-0.06 mol/L, and the concentration of the urea is 0.01-0.2 mol /L. 4. The method for removing heavy metal ions in an aqueous solution according to claim 1, wherein the ratio of the divalent metal salt to the pseudo-boehmite is 0.0001-0.3 mol:0.12 g. 5. the method for removing heavy metal ions in the aqueous solution according to claim 1, is characterized in that: the preparation method of described pseudo-boehmite film is: add ammoniacal liquor in aluminium salt aqueous solution, obtain precipitation; add glue in precipitation Solvents and film-forming aids are used to obtain pseudo-boehmite sol after aging; pseudo-boehmite thin films are obtained after casting the pseudo-boehmite sol. 6 . The method for removing heavy metal ions in an aqueous solution according to claim 5 , wherein the aging temperature is 90-100° C., and the aging time is 20-24 h. 7 .

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