A method for preparing a chromium dioxide nanowire array

Abstract

The application relates to a preparation method of a chromium dioxide nanowire array, and belongs to the technical field of inorganic nonmetal material preparation. The steps comprise the following: filling a chromium trioxide aqueous solution into nanopores of a porous alumina template by a vacuum impregnation method; drying the chromium trioxide aqueous solution in the nanopores of the template by a vacuum drying method; placing the dried template into an autoclave, sealing the autoclave after high-pressure pure oxygen with a pressure of 10-15 Mpa is filled into the autoclave; and heating the autoclave to 390-400 DEG C for 30 minutes, so that the chromium dioxide nanowire array is obtained. The preparation process is simple and easy to operate, and long chromium dioxide nanowire arrays can be prepared in porous alumina templates with various pore diameters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inorganic non-metallic material, and particularly relates to a preparation method of a chromium dioxide nanowire array. BACKGROUND

[0002] The porous alumina template has a regularly arranged nano-pore structure, and the nano-pores are straight and vertical to the template surface. The magnetic material is grown in the nano-pores of the porous alumina template, and thus a magnetic nanowire array is prepared. The magnetic nanowire array includes iron nanowire array, cobalt nanowire array, and magnetite nanowire array. The magnetic nanowire array has high coercivity caused by great shape anisotropy, and has potential application in high-density magnetic storage field, and can also be applied to nanowire to construct nanodevices. Chromium dioxide is an important conductive ferromagnetic metal oxide, and has a Curie temperature of 392-396K and a theoretical saturation magnetization of 133emu / g. The commercially produced chromium dioxide nanorod has strong shape anisotropy, and has a coercivity of about 500-600Oe. In recent years, it is found that chromium dioxide is also an important half-metallic ferromagnet, and has a spin polarization rate very close to 100%. These excellent magnetic and electrical properties make it have important potential application value in spintronic devices. Therefore, it is of great significance to develop a method for synthesizing a chromium dioxide nanowire array. However, chromium dioxide is a metastable oxide, and is difficult to synthesize. At present, only the method of atmospheric pressure chemical vapor deposition is used to grow a chromium dioxide nanowire array in the porous alumina template. However, the method of atmospheric pressure chemical vapor deposition can only grow a chromium dioxide nanowire array of several microns long in the porous alumina template with a pore diameter of 40nm or less, and can only grow a chromium dioxide nanorod of several hundred nanometers long in the porous alumina template with a pore diameter of more than 75nm. SUMMARY

[0003] The present application aims at overcoming the defects of the prior art, and provides a method for preparing a chromium dioxide nanowire array, which can grow a long chromium dioxide nanowire in a porous alumina template with different pore diameters.

[0004] To achieve the object of the present application, the following technical scheme is adopted:

[0005] A preparation method of a chromium dioxide nanowire array, which fills a chromium trioxide aqueous solution into nano-pores of a porous alumina template by using a vacuum impregnation method; dries the chromium trioxide aqueous solution in the nano-pores of the template by using a vacuum drying method; puts the dried template into an autoclave, fills high-pressure pure oxygen of 10-15Mpa into the autoclave, and then seals the autoclave; heats the autoclave to 390-400℃, and reacts for 30 minutes, so as to obtain a chromium dioxide nanowire array.

[0006] Further, the vacuum impregnation refers to cooling the chromium trioxide aqueous solution to below -15℃, and then injecting it into the bottom of a vertically fixed test tube; fixing a magnet on the outer wall of the upper part of the test tube, gluing an iron sheet on the back of a porous alumina template, and using the magnetic force of the magnet to adsorb the porous alumina template on the inner wall of the upper part of the test tube, and keeping a distance of 5-10 cm from the liquid surface; connecting the test tube with a mechanical pump through a vacuum rubber tube, and vacuumizing for 30 minutes; then moving the magnet to move the porous alumina template on the inner wall of the upper part of the test tube into the lower chromium trioxide aqueous solution by the magnetic force, and continuing to vacuumize for 30 minutes; closing the mechanical pump, and disconnecting the vacuum rubber tube from the test tube, taking out the porous alumina template, and scraping the excess liquid adsorbed on the surface of the template with a soft silica gel sheet.

[0007] Further, the vacuum drying refers to placing the porous alumina template impregnated with the chromium trioxide aqueous solution into a horizontally fixed clean and dry test tube with the surface upward, connecting the test tube with a mechanical pump through a vacuum rubber tube, and vacuumizing for 5 hours to dry the solution impregnated into the nanopores of the template.

[0008] Further, the heating process of the autoclave is to first increase the temperature from room temperature to 250℃ at a speed of 1-2℃ per minute, and keep the temperature for 12 hours, and then increase the temperature to the reaction temperature at a speed of 2℃ per minute.

[0009] As preferred, the porous alumina template is a single-pass porous alumina template prepared by anodizing a high-purity aluminum sheet in an acidic electrolyte, and composed of a porous alumina layer and a residual aluminum layer.

[0010] The above technical solution can be summarized as follows:

[0011] Step one, preparing a chromium trioxide aqueous solution with a concentration of 40%-50%, and cooling the chromium trioxide aqueous solution to below -15℃;

[0012] Step two, injecting the chromium trioxide aqueous solution into the bottom of a vertically fixed test tube; fixing a magnet on the outer wall of the upper part of the test tube, gluing an iron sheet on the back of a porous alumina template, and using the magnetic force of the magnet to adsorb the porous alumina template on the inner wall of the upper part of the test tube, and keeping a distance of 5-10 cm from the liquid surface; connecting the test tube with a mechanical pump through a vacuum rubber tube, and vacuumizing for 30 minutes; moving the magnet to move the porous alumina template on the inner wall of the upper part of the test tube into the lower chromium trioxide aqueous solution by the magnetic force, and continuing to vacuumize for 30 minutes; closing the mechanical pump, and disconnecting the vacuum rubber tube from the test tube, taking out the porous alumina template, and scraping the excess liquid adsorbed on the surface of the template with a soft silica gel sheet;

[0013] Step three, put the porous alumina template surface immersed with the chromium trioxide aqueous solution upward into a horizontal fixed clean dry test tube, connect the test tube with a mechanical pump through a vacuum rubber tube, and dry the solution immersed into the nano-pores of the template by vacuum for five hours;

[0014] Step four, put the dried template into an autoclave, seal the autoclave after filling with 10-15 MPa high-pressure pure oxygen, and heat the autoclave from room temperature to 250 degrees Celsius at a rate of 1-2 degrees per minute, and then heat to the reaction temperature at a rate of 2 degrees per minute, and keep for 30 minutes; the reaction temperature is 390-400 degrees Celsius; after natural cooling of the reaction kettle, the product is taken out after pressure relief, and the chromium dioxide nanowire array grown in the porous alumina template is obtained.

[0015] Due to the above technical scheme, compared with the prior art, the present application has the following beneficial effects: 1. The preparation process is simple and easy to operate; 2. The chromium dioxide nanowire array with a relatively long length can be prepared in a porous alumina template with various hole diameters. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 SEM morphology of the partially exposed chromium dioxide nanowire array in Example 1 of the present application.

[0017] Figure 2 SEM morphology of the fully exposed chromium dioxide nanowire array in Example 1 of the present application.

[0018] Figure 3 Magnetic hysteresis loop of the chromium dioxide nanowire array in the porous alumina template in Example 1 of the present application.

[0019] Figure 4 X-ray diffraction pattern of the chromium dioxide nanowire array in the porous alumina template in Example 1 of the present application. DETAILED DESCRIPTION

[0020] The present application will be further described in detail by the following examples. The protection scope of the present application is not limited to the description of the following contents.

[0021] Example 1:

[0022] Firstly, a 50% chromium trioxide aqueous solution was prepared and cooled to -20℃. The cooled chromium trioxide aqueous solution was injected into the bottom of a vertically fixed test tube. A magnet was fixed to the outer wall of the upper part of the test tube. A piece of iron was glued to the back of a porous alumina template with an average pore size of 80 nm, and the porous alumina template was adsorbed to the inner wall of the upper part of the test tube by the magnetic force of the magnet, with a distance of 7 cm from the liquid surface. The test tube was connected to a mechanical pump through a vacuum rubber tube, and vacuum was applied for 30 minutes. The magnet was moved to move the porous alumina template in the upper part of the test tube into the chromium trioxide aqueous solution in the lower part by magnetic force, and vacuum was continued for 30 minutes. The mechanical pump was turned off, and the vacuum rubber tube was disconnected from the test tube. The porous alumina template was removed, and the excess liquid adsorbed on the surface of the template was scraped off with a soft silicone rubber sheet. The porous alumina template immersed in the chromium trioxide aqueous solution was placed in a horizontally fixed clean and dry test tube with the surface facing upwards, and the test tube was connected to a mechanical pump through a vacuum rubber tube, and vacuum was applied for 5 hours to dry the solution immersed in the pores of the template. The vacuum-dried template was placed in an autoclave, and 10 MPa of high-pressure pure oxygen was filled and sealed. The autoclave was heated from room temperature to 250℃ at a rate of 1°C per minute, and then heated to 390℃ at a rate of 2°C per minute, and kept for 30 minutes. After the reaction kettle was naturally cooled, the product was removed after pressure relief, and a chromium dioxide nanowire array grown in the porous alumina template was obtained. The porous alumina template with the grown chromium dioxide nanowire array was placed on a glass slide with the back facing upwards, and the gap between the two was sealed by coating the edges with transparent universal glue. After the transparent universal glue was cured, the glass slide with the porous alumina template was placed in a mixture of 5% dilute hydrochloric acid and 5% copper chloride solution to completely remove the aluminum layer in the porous alumina template. Then the glass slide with the porous alumina template was washed with deionized water, and then placed in a 1% sodium hydroxide solution to gradually etch the aluminum oxide in the template to expose the chromium dioxide nanowire array. Figure 1 SEM morphology of the chromium dioxide nanowire array exposed in the template after etching with sodium hydroxide solution for 10 minutes;

[0023] Figure 2 SEM morphology of the chromium dioxide nanowire array exposed after the template was completely etched, with an average diameter of 80 nm. Figure 3 Magnetic hysteresis loop of the chromium dioxide nanowire array in the porous alumina template, when the magnetic field is parallel to the chromium dioxide nanowire array, the chromium dioxide nanowire array is more easily magnetized and has a larger remanence, indicating that the direction parallel to the chromium dioxide nanowire is the easy magnetization axis. Figure 4 X-ray diffraction pattern of the chromium dioxide nanowire array in the porous alumina template, mainly chromium dioxide diffraction peaks, in addition to only weak chromium trioxide (012) diffraction peaks.

[0024] Example 2:

[0025] First, a 50% concentration of chromium trioxide aqueous solution was prepared and cooled to minus eighteen degrees Celsius. The cooled chromium trioxide aqueous solution was injected into the bottom of a vertically fixed test tube. A magnet was fixed to the outer wall of the upper portion of the test tube. A piece of iron was glued to the back of a piece of porous alumina template with an average pore size of 40 nm, and the porous alumina template was adsorbed to the inner wall of the upper portion of the test tube using the magnetic force of the magnet, maintaining a distance of 8 cm from the liquid surface. The test tube was connected to a mechanical pump through a vacuum rubber tube, and vacuum was applied for 30 minutes. The magnet was moved to use the magnetic force to move the porous alumina template in the upper portion of the test tube into the lower chromium trioxide aqueous solution, and vacuum was continued for 30 minutes. The mechanical pump was turned off, and the vacuum rubber tube was disconnected from the test tube. The porous alumina template was removed, and the excess liquid adsorbed on the surface of the template was scraped off with a soft silicone sheet. The porous alumina template immersed in the chromium trioxide aqueous solution was placed with the surface facing upwards into a horizontally fixed clean and dry test tube, and the test tube was connected to a mechanical pump through a vacuum rubber tube, and vacuum was applied for 5 hours to dry the solution immersed in the nanopores of the template. The vacuum-dried template was placed in an autoclave, sealed after filling with 12 MPa of high-pressure pure oxygen. The autoclave was heated from room temperature to 250 degrees Celsius at a rate of 1 degree per minute, and then heated to 400 degrees Celsius at a rate of 2 degrees per minute, and held for 30 minutes. After the reaction kettle was naturally cooled, the product was removed after pressure relief, and a chromium dioxide nanowire array grown in the porous alumina template was obtained.

Claims

1. A method for preparing a chromium dioxide nanowire array, comprising: filling a chromium trioxide aqueous solution into nanopores of a porous alumina template by a vacuum impregnation method; drying the chromium trioxide aqueous solution in the nanopores of the template by a vacuum drying method; placing the dried template into an autoclave, sealing the autoclave after filling the autoclave with high-pressure pure oxygen at 10-15 MPa; and heating the autoclave to 390 o C-400 ℃ for 30 minutes to obtain the chromium dioxide nanowire array.

2. The method according to claim 1, wherein the porous alumina template is prepared by a method comprising: preparing an alumina sol by mixing alumina powder with deionized water; stirring the alumina sol at 200-300 rpm for 1-2 hours; placing the alumina sol into a Teflon beaker; placing the Teflon beaker into a water bath; and heating the water bath to 80-90 ℃ for 1-2 hours.

3. The method according to claim 1, wherein the porous alumina template is prepared by a method comprising: preparing an alumina sol by mixing alumina powder with deionized water; stirring the alumina sol at 200-300 rpm for 1-2 hours; placing the alumina sol into The vacuum impregnation refers to cooling the chromium trioxide aqueous solution to below -15℃, and then injecting it into the bottom of a vertically fixed test tube; fixing a magnet on the outer wall of the upper part of the test tube, gluing an iron sheet on the back of a porous alumina template, and using the magnetic force of the magnet to adsorb the porous alumina template on the inner wall of the upper part of the test tube, and keeping a distance of 5-10 cm from the liquid surface; connecting the test tube with a mechanical pump through a vacuum rubber tube, and vacuumizing for 30 minutes; then moving the magnet to use the magnetic force to move the porous alumina template on the inner wall of the upper part of the test tube into the lower chromium trioxide aqueous solution, and continuing to vacuumize for 30 minutes; closing the mechanical pump, and disconnecting the vacuum rubber tube from the test tube, taking out the porous alumina template, and scraping off the excess liquid adsorbed on the surface of the template with a soft silica gel sheet.

2. The method of claim 1, wherein the method further comprises the step of: The vacuum drying refers to placing the porous alumina template impregnated with the chromium trioxide aqueous solution with the surface upward into a horizontally fixed clean and dry test tube, connecting the test tube with a mechanical pump through a vacuum rubber tube, vacuumizing for 5 hours, and drying the solution impregnated into the nanopores of the template.

3. The method of claim 1, wherein the method further comprises the step of: The heating process of the autoclave is first heating from room temperature to 250℃ at a speed of 1-2℃ per minute, and keeping the temperature for 12 hours, and then heating to the reaction temperature at a speed of 2℃ per minute. ​ 4. The method of claim 1, wherein the method further comprises the step of: The porous alumina template is a single-pass porous alumina template prepared by anodizing a high-purity aluminum sheet in an acidic electrolyte, and composed of a porous alumina layer and a residual aluminum layer.

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