A method for preparing ultrathin layered composite metal hydroxide by using an atomically economic reaction

Abstract

The application discloses a method for preparing ultrathin layered composite metal hydroxide by using an atom economy reaction. The method uses divalent and trivalent metal hydroxide and an amide compound as raw materials, and through ultrasonic-assisted strengthening separation, ultrathin LDHs nanosheets with a c-axis direction size of only 2-3 nm are synthesized in one step. The amide compound raw material is hydrolyzed to generate formate, acetate and the like into the interlayer of the LDHs under a hydrothermal environment, the carboxyl group of the amide compound raw material is attached to the surface of the LDHs nanosheet, hydrogen bonds are formed between the carboxyl group and the hydroxyl group on the surface of the nanosheet, the hydrogen bonds between the hydroxyl group and the interlayer water molecules are prevented from being formed, the electrostatic attraction between the LDHs layers is reduced, the mutual accumulation between the layers is weakened, and the separation of the LDHs layers is further promoted under the high-frequency oscillation of the ultrasonic wave, the thickness of the layer accumulation is significantly reduced, and the ammonia water generated in the reaction can be recycled and reused, and the product can be obtained without washing.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of inorganic non-metallic functional materials, and specifically relates to a method for preparing ultrathin layered composite metal hydroxides using an atom-economic reaction. Background Technology

[0002] Layered double hydroxides (LDHs), also known as hydrotalcite, are a typical anionic layered material with the chemical formula [M... 2+ 1-x M 3+ x (OH)2]A n- x / n ·mH2O, where M 2+ M 3 + Representing divalent and trivalent metal cations respectively, A n- It is an interlayer anion, x is M 3+ The mole fraction of ions, where m is the amount of water of crystallization. The types and proportions of elements in the LDH layers, as well as the types and quantities of interlayer guests, can be controlled according to application requirements, thereby enabling the preparation of a series of materials with special structures and properties, which are widely used in adsorption, smoke suppression, and functional materials. As a layered functional material, its two-dimensional c-axis dimension, i.e., the stacking thickness, plays a crucial role in performance. By controlling the c-axis dimension, reducing the number of stacked layers, exposing more host layers, increasing the number of active sites in the layers, and increasing the specific surface area, the adsorption and catalytic properties of the material are significantly improved.

[0003] The preparation of LDHs often employs co-precipitation methods, generating numerous byproducts and requiring large amounts of water for washing, resulting in wasted water and materials. Patent (CN200710062650.9) proposes a method for preparing layered composite metal hydroxides using an atom-economic reaction. This method uses divalent and trivalent metal hydroxides as raw materials, preparing LDHs products through a hydrothermal reaction. This method is a typical heterogeneous (solid-liquid) nucleation reaction. Divalent metal hydroxides dissociate into metal ions at high temperatures, which then gradually migrate to the surface of trivalent metal hydroxides and instantaneously nucleate on that surface. The formed nuclei further diffuse and grow along the interface between LDHs and the raw materials to form LDHs. This method significantly improves the utilization rate of raw materials, but it suffers from problems such as difficulty in effectively controlling the two-dimensional size and morphology. As a phase interface chemical reaction between solid and liquid phases at high temperatures, the LDH nanosheets have high surface energy during formation, leading to a tendency for the synthesized LDH layers to stack and grow. The two-dimensional layered c-axis size is generally between tens of nanometers, and is difficult to control effectively. Severe stacking along the c-axis significantly reduces the number of active sites that LDHs can expose, thereby affecting their performance and limiting their application performance improvement and application scope expansion. Summary of the Invention

[0004] This invention provides an atom-economical method for preparing ultrathin LDH nanosheets. The method uses divalent and trivalent metal hydroxides and amide compounds as raw materials, employing ultrasound-assisted enhanced separation to synthesize ultrathin LDH nanosheets with a two-dimensional c-axis dimension of only 2–3 nm in one step. The amide compounds undergo hydrolysis under hydrothermal conditions to generate formate and acetate ions, which enter the LDH interlayer. Their carboxyl groups adhere to the surface of the LDH nanosheets, forming hydrogen bonds with the hydroxyl groups on the nanosheet surface. This prevents the formation of hydrogen bonds between hydroxyl groups and interlayer water molecules, reducing the electrostatic attraction between LDH layers and weakening the mutual stacking of layers. Furthermore, high-frequency ultrasonic oscillation promotes the separation of LDH layers, significantly reducing the stacking thickness. The ammonia water produced in the reaction can be recycled and reused, and the product can be obtained as a pure sample without washing, thus achieving atom-economical preparation of ultrathin LDHs.

[0005] The method for preparing ultrathin layered composite metal hydroxides using an atom-economic reaction is as follows: divalent metal hydroxide, trivalent metal hydroxide, amide compound, and deionized water are ultrasonically mixed to obtain a suspension; the suspension is added to an ultrasonic reactor, and a hydrothermal reaction is carried out under ultrasonic stirring; after the reaction is completed, the mixture is cooled to 80-100°C, the reactor is opened to release carbon dioxide gas, and the mixture is filtered to obtain ultrathin layered composite metal hydroxides, with the filtrate being ammonia water.

[0006] The divalent metal is one or more of Mg, Zn, Ca, Ni, Cu, and Co, preferably one or two of Mg, Ni, and Ca.

[0007] The trivalent metal is one or more of Al, Cr, Fe, Mn, and Ti, preferably one or two of Al, Cr, and Fe.

[0008] The amide compounds are one or more of formamide, acetamide, propionamide, and butyramide.

[0009] The molar ratio of the divalent metal to the trivalent metal is 2-4, and the molar ratio of the amide compound to the trivalent metal is 1-3.

[0010] The solid content of the suspension is 0.5-20 wt%, preferably 5-10%.

[0011] The temperature of the hydrothermal reaction is 100-200℃, preferably 120-160℃; the hydrothermal reaction time is 1-24h, preferably 3-8h.

[0012] The stirring speed is 100-800 rpm, preferably 500-700 rpm.

[0013] The power of the ultrasound is 100-1000W, preferably 500-700W.

[0014] The beneficial effects of this invention are as follows:

[0015] (1) This invention uses hydroxide and formamide as raw materials. Taking advantage of the fact that formamide hydrolyzes into ammonium formate at a certain temperature, formate ions are introduced into the interlayer of LDHs. During the synthesis of LDHs, the electrostatic attraction between LDHs layers is weakened. Furthermore, ultrasonic oscillation is used to intensify the destruction of electrostatic attraction, hydrogen bonding and other interactions between the multilayer plates of LDHs, forcing the separation between the multilevel plates of LDHs, reducing the surface energy between DHs nanosheets, avoiding the stacking of LDHs, and achieving the c-axis size of LDHs in the range of 2-3 nm (single layer or 2-3 layers).

[0016] (2) This invention achieves the preparation of ultrathin LDHs using an atom-economic reaction. Using hydroxides and formamide as raw materials, this invention designs an atom-economic reaction route. During the reaction, formamide hydrolyzes to generate anionic formate, which enters the LDHs to facilitate intercalation and delamination. The cationic ammonium ions combine with hydroxide ions in the solution to generate ammonia. Ammonia, an indispensable raw material in the chemical industry, can be directly recycled through simple centrifugation, making the treatment method simple. This synthesis method does not require the introduction of substances such as NaOH, significantly improving atom utilization. The product can be obtained as a pure sample without water washing, saving resources and conforming to the principles of green chemistry and sustainable development.

[0017] (3) After the hydrothermal reaction, the carbon dioxide gas in the reactor is discharged at 80-100℃ to prevent the generation of carbonate intercalated hydrotalcite during the synthesis process. Since carbonate has a stronger binding ability with hydrotalcite layers, it will affect the hydrotalcite exfoliation effect and thus affect the synthesis of ultrathin hydrotalcite. Attached Figure Description

[0018] Figure 1 This is the XRD pattern of the ultrathin layered composite metal hydroxide obtained in Example 1;

[0019] Figure 2 This is the FT-IR spectrum of the ultrathin layered composite metal hydroxide obtained in Example 1;

[0020] Figure 3 This is a TEM spectrum of the ultrathin layered composite metal hydroxide obtained in Example 1;

[0021] Figure 4 This is the AFM spectrum of the ultrathin layered composite metal hydroxide obtained in Example 1. Detailed Implementation

[0022] Example 1:

[0023] 281.4 g of nickel hydroxide, aluminum hydroxide, and formamide were weighed out in a molar ratio of 2:1:1 and added to a beaker. 2127.6 g of deionized water was added to prepare a reaction suspension with a solid content of 10%. The suspension was sonicated for 10 min to ensure homogeneity. The mixture was placed in an ultrasonic reactor, and the stirring speed was set to 600 rpm, the ultrasonic power to 600 W, the reaction temperature to 140℃, and the reaction time to 8 h. When the reactor temperature reached 90℃, the vent was opened to release carbon dioxide from the system to avoid the introduction of carbonate ions. After cooling to room temperature, the product was removed and centrifuged once. The sample at the bottom of the centrifuge tube was the pure ultrathin NiAl LDHs. The filtrate was recovered, and its composition was tested. The results showed that it contained only ammonia.

[0024] The product gel was characterized using an XRD-6000 X-ray powder diffractometer manufactured by Shimadzu Corporation of Japan. Figure 1 The image shows the XRD pattern of the sample obtained in Example 1. As can be seen from the image, the diffraction peaks of the 003 and 006 crystal planes of the LDHs have basically disappeared, indicating that the exfoliation effect is obvious, which corresponds to the ultrathin state of the product.

[0025] The relevant functional groups of the product were characterized using a VECTOR-22 infrared spectrometer from Bruker GmbH, Germany. Figure 2This is the FT-IR spectrum of the sample obtained in Example 1. As can be seen from the figure, the synthesized LDHs show a peak density at 1390 cm⁻¹. -1 and 1570cm -1 The two peaks, corresponding to the symmetric and asymmetric stretching vibrations of -COO-, are characteristic absorption peaks of the formate ions in the NiAl LDHs interlayer. The figure also shows the presence of peaks without impurities (carbonate ions).

[0026] The morphology of the samples was characterized using a JEM-2100 transmission electron microscope manufactured by Shimadzu Corporation of Japan. Figure 3 The image shows the TEM spectrum of the sample obtained in Example 1. As can be seen from the image, the overall morphology of the synthesized LDHs exhibits a curved, clustered, flower-like structure.

[0027] The thickness of LDH single nanosheets was characterized using a Dimenson ICON type subforce microscope from Bruker GmbH, Germany. Figure 4 The image shows the AFM spectrum of the sample obtained in Example 1. As can be seen from the image, the average thickness of the synthesized LDHs single nanosheets is 2.30 nm.

[0028] Example 2:

[0029] 212.6 g of magnesium hydroxide, aluminum hydroxide, and formamide were weighed out in a molar ratio of 2:1:1 and added to a beaker. 3139.4 g of deionized water was added to prepare a reaction suspension with a solid content of 5%. The suspension was sonicated for 10 minutes to ensure homogeneity. The mixture was placed in a specially designed ultrasonic reactor, with the stirring speed set to 600 rpm, ultrasonic power to 600 W, reaction temperature to 140℃, and reaction time to 6 hours. When the reactor temperature reached 90℃, the vent was opened to release carbon dioxide from the system, preventing the introduction of carbonate ions. After cooling to room temperature, the product was removed, centrifuged once, and the ammonia in the filtrate was recovered. The sample at the bottom of the centrifuge tube was the pure ultrathin MgAl LDHs.

[0030] Example 3:

[0031] Weigh out 208g of calcium oxide, aluminum hydroxide, and formamide in a molar ratio of 2:1:1 and add them to a beaker. Add 1829.5g of deionized water to prepare a reaction suspension with a solid content of 8%. Sonicate for 10 minutes to ensure homogeneity. Place the mixture in a specially designed ultrasonic reactor, set the stirring speed to 600rpm, the ultrasonic power to 600W, the reaction temperature to 120℃, and the reaction time to 3 hours. When the reactor temperature reaches 90℃, open the vent to release carbon dioxide from the system to avoid the introduction of carbonate ions. After cooling to room temperature, remove the product, centrifuge once, and recover the ammonia from the filtrate. The sample at the bottom of the centrifuge tube is the pure ultrathin CaAl LDHs.

[0032] Example 4:

[0033] Calcium oxide, magnesium hydroxide, aluminum hydroxide, and formamide, weighed in a molar ratio of 1:1:1:1, totaling 210.3 g, were added to a beaker. 1442.7 g of deionized water was added to prepare a reaction suspension with a solid content of 10%. The suspension was sonicated for 10 min to ensure homogeneity. The mixture was placed in a specially designed ultrasonic reactor, with the stirring speed set to 600 rpm, ultrasonic power 600 W, reaction temperature 140℃, and reaction time 6 h. When the reactor temperature reached 90℃, the vent was opened to release carbon dioxide from the system, preventing the introduction of carbonate ions. After cooling to room temperature, the product was removed, centrifuged once, and the ammonia in the filtrate was recovered. The sample at the bottom of the centrifuge tube was the pure ultrathin MgCaAl LDHs.

Claims

1. A method for preparing ultrathin layered composite metal hydroxides using an atom-economical reaction, characterized in that, The specific operation of the method is as follows: a divalent metal hydroxide, a trivalent metal hydroxide, an amide compound, and deionized water are ultrasonically mixed to obtain a suspension; the suspension is added to an ultrasonic reactor and subjected to a hydrothermal reaction under ultrasonic stirring; after the reaction is completed, the mixture is cooled to 80-100°C, the reactor is opened to release carbon dioxide gas, and the mixture is filtered to obtain an ultrathin layered composite metal hydroxide, with the filtrate being ammonia water; the amide compound is one or more of formamide, acetamide, propionamide, and butyramide.

2. The method according to claim 1, characterized in that, The divalent metal mentioned is one or more of Mg, Zn, Ca, Ni, Cu, and Co.

3. The method according to claim 1, characterized in that, The trivalent metal mentioned is one or more of Al, Cr, Fe, Mn, and Ti.

4. The method according to claim 1, characterized in that, The molar ratio of the divalent metal to the trivalent metal is 2-4, and the molar ratio of the amide compound to the trivalent metal is 1-3.

5. The method according to claim 1, characterized in that, The solid content of the suspension is 0.5-20 wt%.

6. The method according to claim 1, characterized in that, The hydrothermal reaction temperature is 100-200℃; the hydrothermal reaction time is 1-24h.

7. The method according to claim 1, characterized in that, The stirring speed is 100-800 rpm.

8. The method according to claim 1, characterized in that, The power of the ultrasound is 100-1000W.

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