CN101214928A - Method for Synthesizing Ordered Mesoporous Metal Oxide with High Specific Surface Area Using Hard Template - Google Patents

Abstract

A method for synthesizing ordered mesoporous metal oxides with high specific surface area by using a hard template belongs to the field of preparation of solid mesoporous materials. The existing methods are difficult to control the hydrolysis rate of the metal salt, the pores are easy to collapse when the template is removed by calcination, and the universality is poor. In the present invention, the hard template agent cubic phase mesoporous silica powder is first synthesized; the silica powder is added to a metal salt with a concentration of 0.12-0.40mol/L in a 50-95wt% ethanol solution to form a mixed solution, and ultrasonically dispersed for 90-120 minutes Afterwards, stir again and evaporate to dryness at 40-50°C, then raise the temperature to 400-850°C in a nitrogen atmosphere at a rate of 1°C/min, and keep the temperature at this temperature for 4 hours to obtain the mesoporous oxide precursor powder; The molar ratio of cubic phase mesoporous silicon oxide powder to metal salt is 7-14; it is washed with 10wt% HF solution to remove cubic phase mesoporous silicon oxide template agent, and then dried at 60-70°C for 20-24 hours. The mesoporous metal oxide of the present invention is suitable for use as an adsorbent, a catalyst, a carrier, etc., and can be used in dyes, magnetism, photoelectric materials, and the like.

Description

Method for Synthesizing Ordered Mesoporous Metal Oxide with High Specific Surface Area Using Hard Template

technical field

The invention relates to a preparation technology of solid mesoporous materials, in particular to a method for synthesizing ordered mesoporous metal oxides with high specific surface area by using cubic phase mesoporous silicon oxide (KIT-6) powder as a hard template.

Background technique

In recent years, the preparation technology of nanoparticles and ordered porous materials has been developed rapidly, making it possible to controlly synthesize such materials. Due to the high specific surface area and pore volume of mesoporous oxide materials, it has become an important research object in surface structure and heterogeneous catalysis, and is widely used in gas separation, heterogeneous catalysis, energy storage, printing and dyeing, Electromagnetic, optoelectronic and many other fields. Therefore, it is of great practical value to develop a method for preparing mesoporous metal oxides with high specific surface area.

The usual preparation method of mesoporous metal oxides is the sol-gel method using soft templates, that is, using the required inorganic salt precursors and soft templates to form a sol, activating the precursors at a certain temperature, and then activating the precursors under certain conditions. After removing the organic soft template, the target product with mesoporous structure can be obtained finally. For example, Sinha et al. used F127, ethylene glycol and propanol as a mixed template, and chromium nitrate as a chromium source, through a sol-gel process, and then burned at 400 ° C to synthesize a specific surface area of 96m ² /g and Mesoporous chromium oxide with a pore size of 7.9 nm (AK Sinha, et al. Angew. Chem. Int. Ed. 2005, 44: 271; AK Sinha, et al. Appl. Catal. B, 2007, 70: 417). Yan et al. used solid sols of citric acid and chromium nitrate mixtures in different molar ratios to prepare chromium oxides with different shapes, sizes, and pore structures by thermal decomposition under closed conditions (ZF Yan, et al.J.Phys . Chem. B, 2006, 110: 178). Guzman et al. used amino acid-modified yttrium oxide sol and P123 as a template to prepare mesoporous yttrium oxide with a specific surface area of 90m ² /g and a pore diameter of 6.5nm (J.Guzman, et al.Chem.Commun.2005, 743) , Wang et al., under the assistance of ultrasound, used sodium dodecyl sulfate as template agent, nitrate as metal source, and urea as precipitant to prepare mesoporous samarium oxide and erbium oxide with pore diameters of 4.7nm and 4.2nm, respectively. (Y. Wang, et al. Ultrasonics Sonochem. 2002, 9: 285). However, the above method also has some limitations, such as difficulty in controlling the hydrolysis rate of the metal salt, easy collapse of the pores when the template is removed by calcination, and poor universality of the method. Thus, the applications of the obtained mesoporous metal oxides are greatly limited.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of poor sample pore structure regularity, easy collapse of channels and poor universality of the method obtained by other organic template methods in the past. Using ordered mesoporous molecular sieves as hard templates, metal salt molecules can be effectively dispersed into the pores of mesoporous molecular sieves by means of ultrasonic waves, and then the target product can be obtained through calcination, washing, drying and other processes.

In the present invention, tetraethyl orthosilicate (TEOS) is used as raw material, triblock copolymer (EO) ₂₀ (PO) ₇₀ (EO) ₂₀ (Pluronic P123) is used as template, and n-butanol is used as auxiliary solvent. Cubic phase mesoporous silica was synthesized by hydrothermal reaction, and then used as a hard template and inorganic metal salt as a precursor to obtain a mesoporous metal oxide with a highly ordered pore structure and a high specific surface area.

Specific steps are as follows:

(1) Referring to the literature (Freddy K. et al. Chem. Commun. 2003, 2136) method, the cubic phase mesoporous silica (KIT-6) powder was first synthesized. The synthesis process is: at room temperature, add triblock copolymer (EO) ₂₀ (PO) ₇₀ (EO) ₂₀ (Pluronic P123) and n-butanol to 0.5-0.8 mol/L hydrochloric acid solution, stir to dissolve , to obtain a mixed solution of P123 and n-butanol with 2 to 5 wt%, keep it warm at 35°C for 1 hour, then add tetraethyl orthosilicate (TEOS) or sodium silicate as a silicon source to make the silicon content reach 4 to 10 wt %. Stirring was continued at 35°C for 24 hours. The resulting mixture was transferred to an autoclave, placed in a constant temperature box, and subjected to constant temperature hydrothermal treatment at 100°C for 24 hours, filtered, washed with deionized water and ethanol, and dried at 60-70°C for 20-24 hours to obtain a white solid powder. The resulting white solid powder was raised from room temperature to 550°C at a rate of 1°C/min in a muffle furnace and burned at a constant temperature of 550°C for 4 hours to obtain a cubic phase mesoporous silica (KIT-6) white powder.

(2) Add the above-mentioned cubic phase mesoporous silica powder to a 50-95wt% ethanol solution of a metal salt with a concentration of 0.12-0.40mol/L to form a mixed solution, and after ultrasonic dispersion for 90-120 minutes, stir again to make the mixture The liquid is evaporated to dryness at 40-50°C, then placed in a tube furnace and heated to 400-850°C in a nitrogen atmosphere at a rate of 1°C/min, and kept at this temperature for 4 hours to obtain a mesoporous oxide precursor Bulk powder; wherein the molar ratio of cubic phase mesoporous silica powder to metal salt is 7-14;

(3) Wash the obtained mesoporous oxide precursor powder with 10wt% HF solution to remove the cubic phase mesoporous silica template, and then dry it at 60-70°C for 20-24 hours to obtain the mesoporous metal oxide powder .

The physical properties of the obtained mesoporous metal oxides were characterized by X-ray diffractometer (XRD), N ₂ adsorption-desorption, transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results show that the sample prepared by this method is a mesoporous metal oxide with ordered pore structure and high specific surface area, the specific surface area is 120-280m ² /g, and the pore diameter is 3-20nm.

The present invention uses cubic phase mesoporous silicon oxide (KIT-6) powder as a hard template, can effectively overcome the shortcomings of the prior art, and obtain mesoporous metal oxides with a high specific surface area and an ordered pore structure. The method of the invention has low preparation cost, simple and convenient operation process, narrow pore size distribution of the target product, large specific surface area, and can adjust the metal salt type to obtain metal oxides with different compositions. There are no documents and patents to report the method of the present invention.

Description of drawings

In order to further understand the present invention, the following examples are described in detail, and the accompanying drawings are given to describe the high specific surface area mesoporous metal oxide obtained by the present invention, wherein:

Figures 1(a) and 1(b) are the XRD spectra of samples KIT-6 pure silicon molecular sieve and mesoporous chromium oxide in Example 1, respectively, and the insets are their corresponding small-angle XRD spectra.

Fig. 2 (a), 2 (b), 2 (c) are respectively the TEM photo of embodiment 1 sample KIT-6 pure silicon molecular sieve and mesoporous chromium oxide and the HRTEM photo of mesoporous chromium oxide sample, and the illustration wherein is this SAED pattern of the samples.

3(a) and 3(b) are the TEM photo and HRTEM photo of the sample mesoporous chromium oxide in Example 2, respectively.

Figures 4(a) and 4(b) are the TEM photo and HRTEM photo of the sample mesoporous chromium oxide in Example 3, respectively.

Fig. 5 (a), 5 (b), 5 (c), 5 (d) are embodiment 4 mesoporous samarium oxide respectively XRD spectrogram, N _Adsorption -desorption isotherm, TEM photograph and HRTEM photograph, wherein The insets in 5(a), 5(b) and 5(d) are the small-angle XRD spectrum, pore size distribution curve and SAED pattern of this sample, respectively.

Fig. 6 (a), 6 (b), 6 (c) are the XRD spectrogram, N of embodiment ₅ mesoporous europium oxide respectively Adsorption-desorption isotherm, and TEM photo, wherein 6 (a), 6 ( The insets in b) and 6(c) are the small-angle XRD spectrum, pore size distribution curve, and SAED pattern of the sample, respectively.

Detailed ways

Concrete implementation steps of the present invention are as follows:

Example 1: At room temperature, add 2.7g triblock copolymer (EO) ₂₀ (PO) ₇₀ (EO) ₂₀ (Pluronic P123) to 100mL 0.5mol/L hydrochloric acid solution, stir until dissolved, slowly (2°C /min) to heat up to 35°C, add 2.8g n-butanol while stirring, and keep stirring at 35°C for 1 hour, then add 5.8g tetraethyl orthosilicate to the above solution (the molar ratio of each substance is: orthosilicon ethyl acetate: triblock copolymer (EO) ₂₀ (PO) ₇₀ (EO) ₂₀ : hydrochloric acid: deionized water: n-butanol = 1: 0.017: 1.83: 195: 1.31), kept stirring at 35°C for 24 hours, Transfer to an autoclave and heat at 100°C for 24 hours, filter, wash with deionized water and ethanol, and dry at 60°C, then program the temperature in a muffle furnace (1°C/min) to 550°C and heat at 550°C Burning at low temperature for 4 hours, the cubic phase mesoporous silica (KIT-6) white powder was obtained. The obtained KIT-6 had a specific surface area of 780 m ² /g and an average pore diameter of 3 nm.

Add 1.0g of chromium nitrate to 10mL of absolute ethanol, stir to dissolve, add 0.5g of KIT-6 white powder to the above solution, ultrasonically disperse for 100 minutes, then evaporate the mixture to dryness at 40°C under magnetic stirring, The obtained solid was heated up to 400° C. at a rate of 1° C./min in a nitrogen atmosphere (nitrogen flow rate of 30 mL/min) and kept at 400° C. for 4 hours. Finally, the silicon template was removed by washing with 10 wt % HF solution, and then at 60 After drying at ℃ for 24 hours, the mesoporous polycrystalline chromium oxide powder was obtained, with a specific surface area of 124m ² /g and an average pore diameter of 13nm.

Example 2: The synthesis of hard template KIT-6 is the same as that in Example 1. Add 0.5g of ammonium dichromate to 10mL of 50wt% ethanol solution, stir to dissolve, add 0.5g of KIT-6 white powder to the above solution, ultrasonically disperse for 100 minutes, and then place the mixture at 40°C under magnetic stirring Evaporated until the obtained solid was heated to 400°C at a rate of 1°C/min in a nitrogen atmosphere (nitrogen flow rate of 30mL/min) and kept at 400°C for 4 hours, and finally washed with 10wt% HF solution to remove the silicon template. After drying at 60°C for 24 hours, the mesoporous polycrystalline chromium oxide powder was obtained, with a specific surface area of 167m ² /g and an average pore diameter of 7nm.

Example 3: The synthesis of hard template KIT-6 is the same as that in Example 1. Add 1.2g of chromium oxalate to 10mL of absolute ethanol, stir to dissolve, add 0.5g of KIT-6 white powder to the above solution, ultrasonically disperse for 100 minutes, then evaporate the mixture to dryness at 40°C under magnetic stirring, The obtained solid was heated up to 400° C. at a rate of 1° C./min in a nitrogen atmosphere (nitrogen flow rate of 30 mL/min) and kept at 400° C. for 4 hours. Finally, the silicon template was removed by washing with 10 wt % HF solution, and then at 60 After drying at ℃ for 24 hours, the mesoporous polycrystalline chromium oxide powder was obtained, with a specific surface area of 125m ² /g and an average pore diameter of 15nm.

Example 4: The synthesis of hard template KIT-6 is the same as that in Example 1. Add 1.1g of samarium nitrate to 10mL of absolute ethanol, stir to dissolve, add 0.5g of KIT-6 white powder to the above solution, ultrasonically disperse for 100 minutes, then evaporate the mixture to dryness at 40°C under magnetic stirring, The obtained solid was heated up to 850° C. at a rate of 1° C./min in a nitrogen atmosphere (nitrogen flow rate of 30 mL/min) and kept at 850° C. for 4 hours. Finally, the silicon template was removed by washing with 10 wt % HF solution, and then at 60 After drying at ℃ for 24 hours, the ordered mesoporous polycrystalline samarium oxide was obtained, with a specific surface area of 280m ² /g and an average pore diameter of 3nm. It can be seen from Figure 5 that the sample has a narrow pore size distribution, and the adsorption-desorption curve has obvious hysteresis loops characteristic of mesoporous materials, and the pore distribution is highly ordered.

Example 5: The synthesis of hard template KIT-6 is the same as that in Example 1. Add 1.1g of europium nitrate to 10mL of deionized water, stir to dissolve, add 0.5g of KIT-6 white powder to the above solution, ultrasonically disperse for 100 minutes, and then evaporate the mixture to dryness at 40°C under magnetic stirring to obtain The solid was heated up to 750°C at a rate of 1°C/min in a nitrogen atmosphere (nitrogen flow rate of 30mL/min) and kept at 750°C for 4 hours, and finally washed with 10wt% HF solution to remove the silicon template, and then heated at 60°C After drying for 24 hours, ordered mesoporous polycrystalline europium oxide was obtained, with a specific surface area of 144 m ² /g and an average pore diameter of 19 nm. It can be seen from Figure 6 that the hysteresis loop of the adsorption-desorption curve of this sample is obvious, the pore size distribution is concentrated around 19nm, and the order of the pores is good.

Claims (2)

1. Utilize the method for synthesizing the ordered mesoporous metal oxide of high specific surface area by hard template agent, it is characterized in that, concrete synthesis process is as follows: (1) first synthesize the hard template agent cubic phase mesoporous silica powder; (2) Add the above-mentioned cubic phase mesoporous silica powder to a 50-95wt% ethanol solution of a metal salt with a concentration of 0.12-0.40mol/L to form a mixed solution, and after ultrasonic dispersion for 90-120 minutes, stir again to make the mixture The liquid is evaporated to dryness at 40-50°C, then placed in a tube furnace and heated to 400-850°C in a nitrogen atmosphere at a rate of 1°C/min, and kept at this temperature for 4 hours to obtain a mesoporous oxide precursor Bulk powder; wherein the molar ratio of cubic phase mesoporous silica powder to metal salt is 7-14; (3) Wash the obtained mesoporous oxide precursor powder with 10wt% HF solution to remove the cubic phase mesoporous silica template, and then dry it at 60-70°C for 20-24 hours to obtain the mesoporous metal oxide powder . 2. The method according to claim 1, wherein the metal salt is one of chromium nitrate, ammonium dichromate, chromium oxalate, samarium nitrate and europium nitrate.

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