CN110711553B

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

Info

Publication number: CN110711553B
Application number: CN201911140925.5A
Authority: CN
Inventors: 蔡卫权; 陈依婷; 党成雄; 杨文文
Original assignee: Guangzhou University
Current assignee: Guangzhou University
Priority date: 2019-11-20
Filing date: 2019-11-20
Publication date: 2022-05-17
Anticipated expiration: 2039-11-20
Also published as: CN110711553A

Abstract

The invention provides a hydrotalcite-like pseudo-boehmite composite film and a preparation method and application thereof, wherein the hydrotalcite-like pseudo-boehmite composite film consists of a pseudo-boehmite film and hydrotalcite loaded on the surface of the pseudo-boehmite film; then adding the pseudo-boehmite film, and growing the hydrotalcite in situ on the pseudo-boehmite film by a hydrothermal method to obtain the nano-hydrotalcite. The invention makes hydrotalcite precursor alkaline by urea hydrolysis under hydrothermal condition, and contains abundant OH^‑. Divalent metal ions and aluminum ions liberated from the boehmite film pass through OH^‑And in-situ combination is carried out to form the composite film with rich hydroxyl on the surface. The existence of a large amount of hydroxyl can inhibit acidolysis of the pseudo-boehmite, and ensure that the hydrotalcite is firmly bonded to the surface of the pseudo-boehmite so as to avoid dispersion or breakage, and can also improve the adsorption effect on metal ions.

Description

Hydrotalcite-pseudo-boehmite composite film and preparation method and application thereof

Technical Field

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

Background

In recent years, with the rapid development of industrial production, heavy metal ion pollutants (such as Pb (ii), Cd (ii), Cu (ii), Zn (ii), Hg (i), etc.) generated in the fields of mining, metallurgical industry, chemical fertilizer and machinery manufacturing are discharged in large quantities into water, which poses a serious threat to water quality supplied in agriculture, industry and life. Heavy metal ions, because they are not biodegradable and highly toxic, can cause serious harm to the human body through the transfer and enrichment of the food chain. In which Pb (II) affects the intelligence and skeletal development of human body, and causes dyspepsia and endocrine dyscrasia, resulting in anemia, hypertension, and destruction of renal function and immune function. The existing technologies for treating heavy metal ion pollutants include adsorption methods, precipitation methods, membrane separation methods, electrodialysis methods, ion exchange methods, reverse osmosis methods, biological methods and the like. The adsorption method is considered to be one of the most suitable techniques in view of its advantages of simple preparation method, easy operation, and economical feasibility, compared with other methods.

Pseudo-boehmite (gamma-AlOOH), also called boehmite-like, is a thin wrinkled sheet layer with unstable composition and incomplete crystallization, has the characteristics of high specific surface area, high porosity, high interface Gibbs free energy, good dispersibility and peptization and the like, and is often applied to the field of wastewater treatment. For example, CN105107486A is precipitated in alkaline condition to obtain inorganic aluminium salt solution, the precipitate is centrifugally washed and separated, then concentrated hydrochloric acid, glacial acetic acid or nitric acid is added to peptize the precipitate, and film-forming assistant polyvinyl alcohol and structure regulator P123 or F127 are added at the same time, and the gamma-AlOOH film adsorbent is prepared after casting molding and drying, and the adsorption removal rate of the gamma-AlOOH film adsorbent on Cr (VI) with the concentration of 20mg/L can reach 99.4%. Wang et al (Wang Y Q, Wang G Z, Wang H Q, Cai W P, Liang C H, Zhang L. template-induced synthesis of theoretical SiO₂@γ-AlOOH spheres and their application in Cr(VI)removal[J]Nanotechnology, 2009, 20(15):155604.) SiO destruction using alkaline conditions₂Silicon-oxygen bond of colloid ball and inducing metaaluminate ion to hydrolyze on surface to generate unstable Al (OH)₃The colloid is gradually converted into gamma-AlOOH under the hydrothermal condition of 160 ℃ to synthesize SiO₂@ gamma-AlOOH sphere. The SiO modified by inorganic material₂The maximum adsorption capacity of the @ gamma-AlOOH spheres for Cr (VI) was 4.5mg/g, which is higher than that of gamma-AlOOH (about 2 mg/g). However, whether the pure gamma-AlOOH film or the SiO film is used₂The gamma-AlOOH film compounded by the colloid balls has the defect of poor acid resistance, and can be partially hydrolyzed when the pH value is 1-5, so that secondary pollution to a water body is easily caused.

Hydrotalcite, also known as Layered Double Hydroxide (LDH), is a new type of inorganic functional material with a Layered structure, in which exchangeable anions are present between layers and a large number of hydroxyl groups are present on the surface of the laminate. The chemical formula of hydrotalcite is

WhereinM²⁺Is Mg²⁺，Ni² ⁺，Co²⁺， Zn²⁺，Cu²⁺The divalent metal cation being Al³⁺，Cr³⁺，Fe³⁺An iso-trivalent metal cation, A^n-Being anions, e.g. CO₃ ^2-， NO₃ ^-，Cl^-，OH^-，SO₄ ^2-，PO₄ ^3-And inorganic and organic ions and complex ions. Wherein MgAl-LDH is a potential adsorption material, and the hydroxyl groups between layers can exchange with anions in water and can also carry out complex reaction or electrostatic attraction with cations. CN109012573A is dripped into a mixed solution of aluminum nitrate and magnesium nitrate by ammonia water at room temperature to obtain MgAl-LDH precipitate, the precipitate is centrifugally washed and separated, then citric acid is added to lead the precipitate to be peptized and simultaneously added with a film aid polyvinyl alcohol, after casting molding and drying, the adsorbent is prepared after roasting for 4h by a muffle furnace, and the adsorption removal rate of the adsorbent on Cr (VI) with the concentration of 20mg/L can reach 100%. However, the MgAl-LDH film prepared by CN109012573A is easy to be broken and is not beneficial to the adsorption operation. Lyu et al (Lyu F Y, Yu H Q, Hou T L, Yan L G, Zhang X H, Du B. effective and fast removal of Pb²⁺and Cd²⁺from an aqueous solution using a chitosan/Mg-Al-layered double hydroxide nanocomposite[J]Journal of Colloid and Interface Science, 2019, 539: 184-. However, the Lyu adsorbent is powder, and has the problems of difficult separation after adsorbing pollutants and easy secondary pollution caused by remaining in water.

Disclosure of Invention

The invention aims to provide a hydrotalcite-like pseudo-boehmite composite film and a preparation method and application thereof, overcomes the defect that the existing pseudo-boehmite film is easy to be subjected to acidolysis, and simultaneously solves the problem that the existing hydrotalcite material is difficult to form a film or is easy to break after the film is formed.

The hydrotalcite-like pseudo-boehmite composite film provided by the invention consists of a pseudo-boehmite film and hydrotalcite loaded 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-like pseudo-boehmite composite film comprises the steps of dissolving divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding the pseudo-boehmite film, and carrying out hydrothermal reaction to obtain the hydrotalcite pseudo-boehmite composite film.

Further, the hydrothermal reaction temperature is 90-150 ℃, and the reaction time is 10-12 h. Preferably, the hydrothermal reaction temperature is 90-110 ℃, the reaction time is 12 hours, the hydrotalcite has a good appearance on the pseudo-boehmite under the condition, and the whole composite film has 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 divalent metal salt in the precursor is 0.002-0.06 mol/L, and the concentration of 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 comprises the steps of adding ammonia water into an aluminum salt aqueous solution to obtain a precipitate; adding peptizing agent and film-forming assistant into the precipitate, and aging to obtain pseudo-boehmite sol; and carrying out tape casting on the pseudo-boehmite sol to obtain the pseudo-boehmite film.

Further, the aging temperature is 90-100 ℃, and the aging time is 20-24 hours.

Further, the peptizing agent is selected from acetic acid, and the film forming auxiliary agent is selected from polyvinyl alcohol.

The invention also provides a method for removing heavy metal ions in the aqueous solution, which comprises the steps of adjusting the pH value of the aqueous solution containing the heavy metal to be 5-6, adding the hydrotalcite and pseudo-boehmite composite film to adsorb the heavy metal ions, and removing the heavy metal ions.

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

Compared with the prior art, the method utilizes urea hydrolysis to make the hydrotalcite precursor alkaline and contain rich OH under the hydrothermal condition^-. Divalent metal ions and aluminum ions liberated from the boehmite film pass through OH^-And combining in situ to form the composite film with rich hydroxyl on the surface. The existence of a large number of hydroxyl groups inhibits the acidolysis of the pseudo-boehmite, and on the other hand, the hydrotalcite is firmly bonded to the surface of the pseudo-boehmite so as to avoid the dispersion or the fragmentation, and the adsorption effect on metal ions can be improved by enhancing the complexation reaction or the electrostatic attraction effect on the metal ions.

Drawings

FIG. 1 is an XRD pattern of a gamma-AlOOH thin film and an MgAl-LDH/gamma-AlOOH composite thin film;

FIG. 2 is an SEM photograph of a γ -AlOOH thin film and MgAl-LDH/γ -AlOOH composite thin films of examples 1 to 6, in which FIG. 2a shows a γ -AlOOH thin film of a comparative example, FIG. 2b shows example 1, FIG. 2c shows example 2, example 2d shows example 3, FIG. 2e shows example 4, FIGS. 2f and 2g show example 5, and FIG. 2h shows example 6;

FIG. 3 is a photomicrograph of the γ -AlOOH film (FIG. 3a) and the MgAl-LDH/γ -AlOOH composite film of example 4 (FIG. 3 b);

FIG. 4 is a graph showing the adsorption kinetics of the MgAl-LDH/gamma-AlOOH composite film for Pb (II).

Detailed Description

The technical solution of the present invention will be described in detail with reference to specific examples.

Examples 1 to 12

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

(1) preparing a pseudo-boehmite film (namely a gamma-AlOOH film): adding ammonia water into the aluminum salt aqueous solution to obtain a precipitate; adding peptizing agent and film-forming assistant into the precipitate to obtain pseudo-boehmite sol; and carrying out tape casting on the pseudo-boehmite sol to obtain the gamma-AlOOH film.

Specifically, 9g of aluminum nitrate nonahydrate was dissolved in 25mL of deionized water at room temperature, and 35mL of 5 wt% ammonia water was added dropwise under magnetic stirring at a rate of 500r/min to obtain a precipitate. The resulting precipitate was washed centrifugally with deionized water until the filtrate had a pH of about 7. The precipitate was then dispersed in 65mL of deionized water to form a suspension, 0.440mL of peptizing agent acetic acid was added and the temperature was raised to 90 ℃. Then 1.24g of film forming aid polyvinyl alcohol is added, stirred for 2h and aged for 24h at 90 ℃ to obtain the gamma-AlOOH sol. And finally, coating the gamma-AlOOH sol on a polytetrafluoroethylene plate with the thickness of 2cm multiplied by 4cm, carrying out tape casting, drying at room temperature for 48 hours, and then removing the film to obtain the gamma-AlOOH film.

(2) Preparing a hydrotalcite-like pseudo-boehmite composite film: dissolving divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding the pseudo-boehmite film, and growing hydrotalcite in situ on the pseudo-boehmite film by adopting a hydrothermal method to obtain the hydrotalcite-pseudo-boehmite composite film.

Specifically, the divalent metal salt and urea were completely dissolved in 50mL of deionized water at room temperature to prepare hydrotalcite precursors having the concentrations shown in table 1, and the hydrotalcite precursors were transferred to a 100mL hydrothermal reaction vessel lined with a polytetrafluoroethylene inner liner together with a 2cm × 4cm γ -AlOOH thin film. And sealing the hydrothermal reaction kettle, then carrying out hydrothermal reaction at a certain temperature, and growing hydrotalcite in situ on the gamma-AlOOH film. And after the reaction is finished, cooling to room temperature, washing with deionized water for several times, and drying at room temperature for 24 hours to obtain a film-shaped hydrotalcite-like pseudo-boehmite composite film which is marked as an MAL-LDH/gamma-AlOOH composite film, wherein M represents Mg, Ni or Co.

For comparison, a γ -AlOOH thin film was hydrothermally treated alone without a hydrotalcite precursor (comparative example). Namely, a 2cm x 4cm gamma-AlOOH film and 50mL deionized water are transferred into a 100mL hydrothermal reaction kettle with a polytetrafluoroethylene inner liner, the hydrothermal reaction kettle is sealed, and then the hydrothermal reaction kettle is heated in an oven at 110 ℃ for 12 hours. Finally, after cooling to room temperature, washing with deionized water for a plurality of times, and drying at room temperature for 24 hours.

TABLE 1 raw material consumption and reaction conditions of hydrotalcite-like pseudo-boehmite composite film

The MAL-LDH/gamma-AlOOH composite films obtained in the above examples and the gamma-AlOOH film of the comparative example were characterized, and the results were as follows:

XRD patterns of the gamma-AlOOH thin film of the comparative example, the MgAl-LDH/gamma-AlOOH composite thin films of examples 1 to 4, the NiAl-LDH/gamma-AlOOH composite thin film of example 11, and the CoAl-LDH/gamma-AlOOH composite thin film of example 12 are shown in FIG. 1. Fig. 1 shows new 2 θ values in XRD patterns of samples prepared by other examples, compared to γ -AlOOH thin films of comparative examples: the characteristic peaks of the hydrotalcite at the temperature of 11 degrees, 23 degrees and 48 degrees show that the method for growing the hydrotalcite on the gamma-AlOOH film in situ by a hydrothermal method is feasible.

FIG. 2 is SEM images of the gamma-AlOOH thin film of the comparative example and the MgAl-LDH/gamma-AlOOH composite thin films prepared in examples 1 to 6. As can be seen from FIG. 2a, the surface of the gamma-AlOOH film is flat and smooth. Example 1 after hydrothermal reaction of a γ -AlOOH thin film with a hydrotalcite precursor having a low concentration, a small amount of flaky hydrotalcite was present on the surface of the γ -AlOOH thin film, and the surface began to become rough, as shown in fig. 2 b. In examples 2 to 4, the concentration of magnesium sulfate is 0.006 to 0.02mol/L, the concentration of urea is 0.03 to 0.1mol/L, the number of hydrotalcite sheets on the surface of the gamma-AlOOH film increases with the increase of the concentration of the hydrotalcite precursor, the hydrotalcite sheets become dense gradually, staggered nets and abundant gaps are formed on the surface, and the specific surface area of the hydrotalcite-like pseudo-boehmite composite film is increased remarkably, as shown in FIGS. 2c to 2 e. However, when the concentration of magnesium sulfate is increased to 0.04mol/L or more and the concentration of urea is increased to 0.2mol/L, the voids on the surface of the hydrotalcite-like pseudo-boehmite composite film of example 5 in FIGS. 2f and 2g and example 6 in FIG. 2h are gradually filled with the newly deposited and grown hydrotalcite.

Meanwhile, the gamma-AlOOH thin film of the comparative example is semi-transparent in a macroscopic view, as shown in the macroscopic photograph of fig. 3 a. The film becomes white and non-transparent after growing hydrotalcite, as shown in figure 3b, the macrographic photograph of the MgAl-LDH/gamma-AlOOH composite film of example 4.

Therefore, the hydrotalcite can be successfully grown on the surface of the gamma-AlOOH film in situ by a hydrothermal method, and the growth morphology of the hydrotalcite on the surface of the gamma-AlOOH film can be effectively controlled by properly selecting the concentration of the precursor and the hydrothermal reaction temperature and time. The reaction mechanism of the process is mainly as follows: under hydrothermal conditions, urea is slowly hydrolyzed to release NH₃Then the reaction takes place: NH (NH)₃+H₂O→NH₄ ⁺+OH^-，OH^-The precursor is alkaline, and Al atoms released on the surface of the gamma-AlOOH film and Mg atoms in the solution synthesize MgAl-LDH in situ under alkaline conditions, so that the MgAl-LDH/gamma-AlOOH composite film is obtained. Mg capable of reacting with Al atoms on the gamma-AlOOH film in solution when the concentration of the precursor is lower²⁺Less hydrotalcite is grown on the surface of the film, and only a small part of hydrotalcite is grown and deposited on the surface of the film. When the precursor concentration is too high, the amount of hydrotalcite deposited increases, gradually filling the gaps between the hydrotalcites.

Example 13

The embodiment provides a method for removing heavy metal ions in an aqueous solution, in particular to a method for removing Pb (II), which comprises the steps of adjusting the pH value of the aqueous solution containing the heavy metal to be 5-6, and adding the MAl-LDH/gamma-AlOOH composite film described in the embodiment 1-12 to adsorb the heavy metal ions, so as to remove the heavy metal ions.

For example, 50mL of 50mg/L (or 100mg/L, 500mg/L) Pb (II) solution was added with 0.1mol/L NaOH solution, pH was adjusted to 5, 0.05g of the MAL-LDH/γ -AlOOH composite film described in examples 1 to 12 was added, and Pb (II) was adsorbed by the MAL-LDH/γ -AlOOH composite film at 25 ℃ under 150r/min shaking.

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

After the adsorption, it can be observed that the MAL-LDH/gamma-AlOOH composite film is hardly subjected to acidolysis or shedding, the adsorption results of each material on Pb (II) are shown in Table 2, and the adsorption kinetics curves of the MgAl-LDH/gamma-AlOOH composite films of examples 1-6 on Pb (II) in 50mg/L Pb (II) solution are shown in FIG. 4.

TABLE 2 adsorption results of hydrotalcite-like pseudo-boehmite composite film on Pb (II)

As can be seen from table 2, the removal rate of the MgAl-LDH/γ -AlOOH composite film of the present invention to Pb (ii) in 50mg/L Pb (ii) solution can reach as high as 99.99% (example 7), even if the hydrotalcite precursor with very low concentration is used in example 1, the removal rate of the obtained MgAl-LDH/γ -AlOOH composite film to Pb (ii) can still reach 86.34%, which is improved by 59.04% compared with the removal rate of the pure γ -AlOOH composite film of the comparative example; or in the case of using too high hydrothermal reaction temperature in example 8, the removal rate of Pb (II) by the MgAl-LDH/gamma-AlOOH composite film can still reach 83.72%, which is 56.42% higher than that of the gamma-AlOOH film. And the residual concentration of Pb (II) of 50mg/L and 100mg/L is respectively reduced to 0.16mg/L and 0.17mg/L, thereby reaching the discharge standard of Pb (II) content in the industrial wastewater regulated by the state. In addition, the NiAl-LDH/gamma-AlOOH composite film and the CoAl-LDH/gamma-AlOOH composite film also have a certain adsorption effect on Pb (II). Obviously, the adsorption removal capacity of the film to Pb (II) can be obviously improved by growing the hydrotalcite in situ on the gamma-AlOOH film.

As can be seen from the graph of FIG. 4, the MgAl-LDH/gamma-AlOOH composite film has a fast Pb (II) adsorption rate, the Pb (II) adsorption amount is almost linearly increased within 200min, and the adsorption can be completed within about 550 min.

The results and analysis show that the hydrotalcite is grown in situ on the pseudo-boehmite film to form the composite film with the surface rich in hydroxyl groups, and the existence of a large number of hydroxyl groups inhibits the acidolysis of the pseudo-boehmite, so that the hydrotalcite pseudo-boehmite film can effectively adsorb Pb (II) without acidolysis under the strong acid condition that the pH is about 5; on the other hand, the adsorption effect on metal ions can be improved by enhancing the complexation reaction or the electrostatic attraction effect on the metal ions, so that the removal rate of the hydrotalcite-like pseudo-boehmite film on Pb (II) is improved to be close to 100 percent, and the removal rate is improved by at least 56.42 percent compared with that of a pure boehmite film. In addition, the hydrotalcite can be firmly bonded to the surface of the pseudo-boehmite, and the MAL-LDH/gamma-AlOOH composite film still keeps a film state after being used for many times, so that the phenomenon of falling of the hydrotalcite is avoided.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A method for removing heavy metal ions in an aqueous solution is characterized by comprising the following steps: adjusting the pH value of a water solution containing heavy metals to 5-6, adding a hydrotalcite-like pseudo-boehmite composite film to adsorb heavy metal ions, wherein the preparation method of the hydrotalcite-like pseudo-boehmite composite film comprises the following steps: dissolving divalent metal salt and urea in water to obtain a hydrotalcite precursor; then adding a pseudo-boehmite film, and carrying out hydrothermal reaction to obtain the hydrotalcite pseudo-boehmite composite film, wherein the divalent metal salt is 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 ℃, and the reaction time is 10-12 h.

3. The method for removing heavy metal ions in an aqueous solution according to claim 1, wherein: the concentration of divalent metal salt in the precursor is 0.002-0.06 mol/L, and the concentration of 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 an aqueous solution according to claim 1, wherein: the preparation method of the pseudo-boehmite film comprises the following steps: adding ammonia water into the aluminum salt aqueous solution to obtain a precipitate; adding peptizing agent and film-forming assistant into the precipitate, and aging to obtain pseudo-boehmite sol; and carrying out tape casting on the pseudo-boehmite sol to obtain the pseudo-boehmite film.

6. The method for removing heavy metal ions in an aqueous solution according to claim 5, wherein: the aging temperature is 90-100 ℃, and the aging time is 20-24 hours.