AU2020102321A4 - Preparation for Alumina@Co Composite Film with Gradual Change Structural Color and Magnetism - Google Patents

Abstract

The alumina@Co composite film prepared by the existing electrochemical method has singular physical properties, and fine control of microstructure color and magnetism of the film cannot be realized. At first, the present invention aims to provide an electrolytic bath that can achieve deflection electric field assisted electrodeposition. By means of the electrolytic bath, an alumina@Co composite film and a preparation thereof are provided. The composite film has high saturation gradual change structure Co and magnetic gradual change along the radial direction of the alumina film, and fine regulation and control of the structure color and the magnetic property of the composite film micro-area can be realized by adjusting the size of the deflection electric field. The preparation method of the composite film is simple and can be applied to the fields of biomedicine, catalysis, anti-counterfeiting, decoration, imaging, dye sensitization, solar cells and the like. 1/4 8 12 9 -1 R 33 FIG, 1 500 400 U)200. 100 30 ; 40 60 70 BO 20( ) FIG, 2

Description

1/4

8

12

9

-1 R

33

FIG, 1

500

400

U)200.

100

30 ; 40 60 70 BO 20( )

FIG, 2

Preparation for Alumina@Co Composite Film with Gradual Change Structural Color and Magnetism

TECHNICAL FIELD

[01] The invention belongs to the technical field of electrochemical deposition. Specifically, the invention relates to an electrolytic bath for realizing deflection electric field assisted electrodeposition, and relates to an alumina@Co composite film with a gradual change structural color and magnetism and a preparation method.

BACKGROUND

[02] Porous Anodic Alumina (PAA) is a highly ordered nano-porous array structure with self-organization prepared through anodic oxidation of high-purity aluminum in an acidic electrolyte at a low temperature. It is composed of a barrier layer and a porous layer, wherein a thin and compact barrier layer is close to the surface of metallic aluminum; the membrane cells of porous layer are arranged in six-side tightly packed arrangement; and the center of each membrane cell is equipped with a nano scale micropore with a relatively uniform pore size, which is perpendicular to the surface of aluminum base body, and parallel to each other. The preparation process of the porous anodic alumina film is simple, and the shape and the size of pores can be regulated and controlled in a larger range under different electrolysis conditions; in addition, the porous anodic alumina film with nano pores is a wide-band gap metal oxide semiconductor material with thermal stability, corrosion resistance, chemical stability and high dielectric constant, and is widely applied to the synthesis of ordered nano structures.

[03] Structural colors are generated by polychromatic light (e.g., natural light) reflected by upper and lower surfaces of the film and then interfering with each other. The thickness of each part of the porous alumina film is the same, and the porous alumina film can exhibit a single structural color due to equal inclination interference. The color of the single structural color depends on the thickness of the porous alumina film, but the color saturation is low. With deepening of studies on photonic crystals, some researches have focused on structure colors of alumina films.

[04] In 1969, Diggle et al. reported that aluminum-based supported alumina films produced bright colors due to light interference when the thickness was less than 1 m in the visible light range. In 2007, Wang et al. from Tohoku University reported that, after deposition of carbon nanotubes on alumina films by CVD techniques, alumina films with high color saturation were produced. Subsequently, in 2010, Dr. Zhao Xianglong from the Solid Research Institute of Hefei Institute of Physical Science, Chinese Academy of Sciences, made great progress in the color control of carbon tube composite alumina composite films, and realized the fine control of the color of carbon tube composite alumina composite films. In 2011, the group of Profession Sun Huiyuan from Hebei Normal University prepared alumina composite films with the characteristics of changing color stripes by a multiple oxidation method. In 2015, Yang Shumin et al. from Hebei Normal University of Nationalities adopted the first oxidation technology to prepare the alumum thin film with gradual changes in pore depth and an iridescence annular structural color, but its structural color was low in saturation, and the thin film is singular in physical properties.

[05] In order to improve the saturation of the structural color of the porous alumina film and enrich its physical properties, in recent years, scholars have focused on using porous anodic alumina as a template and using electrodeposition to load magnetic metals in porous alumina nanopores to prepare composite materials. In 2006, Xu et al. used porous anodic aluminum oxide as a template, and used 50g/L CoSO4•7H20 and 30g/L H3B03 as the electrolyte. Under the voltage of 20V, pH of 3.0 4.0, and temperature of 30 °C, the PAA@Co nanowire composite material (Fabrication of amorphous Co and Co-P nanometer array with different shapes in alumina template by AC electrodeposition, Materials Letters, 2006, 60(17): 2069-2072) was prepared in minutes through AC electrodeposition. In 2014, Zhang Zhijun et al. prepared a PAA@M (M=Ag, Co) composite film. Experimental results show that the color saturation of the composite film structure was significantly improved, and the film was added with a new degree of freedom, that is, magnetism.

[06] The above research has effectively improved the optical and magnetic properties of alumina films, but the research on the different optical and magnetic properties of the same composite thin film in different micro-regions has not been reported yet, which is of great significance for enriching electrochemical theory and developing miniaturized devices integrating optical and magnetic properties.

SUMMARY

[07] The invention relates to an electrolytic bath for realizing deflection electric field assisted electrodeposition:

[08] An electrolytic bath for realizing deflection electric field application assisted electrodeposition is shown in FIG. 1. As shown in FIG. 1, names of all the components are as follows: 1. an annular rubber pad; 2. a circular aluminum foil; 3. a reducing copper electrode; 4. a hollow fastening screw buckle; 5. a small cylindrical hole; 6. a small cylindrical hole annular surrounding wall; 7. a large cylindrical hole; 8. an electrolytic bath wall; 9. a carbon sheet; 10. a carbon rod; 11. a deposition voltage source; and 12. a deflection voltage source."1" is on the innermost side inside "7"and fits "6", "2" and "1" fit, "3" fits "2" inside "7" and "4" is connected to "3" within "7". "8" is thewall of the cell,"11" is connected between "3" and "10", and "12" is connected between two "9".

[09] Further, preferably, the diameter of the large cylindrical hole is larger and the hole is longer, and the inner wall of the large cylindrical hole is internally screwed; the diameter of the small cylindrical hole is 4 mm smaller than the diameter of the large cylindrical hole, so that "6" is formed, the difference between the inner diameter and the outer diameter of the "6" is 4 mm, the thickness of the "6" is that the hole length of the small cylindrical hole is shorter and is 1 mm; the outer diameter of the "1" is equal to the diameter of the "7", and the inner diameter of the "1"is equal to the diameter of the "5"; the diamster of "2" is slightly smaller than the diameter of the "7", the maximum diameter of the "3" is slightly smaller than the diameter of the diameter of the "7", and the diameter of the middle part of the "3" is smaller than the inner diameter of the "4", and the minimum diameter of the "3" is connected to a conductive clip. Preferably, the diameter of the large cylindrical hole is 1.4 to 2.2 cm.

[010] By means of the electrolytic bath, an alumina@Co composite film and a preparation method thereof are provided, of which the technical scheme is as follows:

[011] The diameter of the circular porous alumina film is parallel to the direction of a deflection electric field. For convenience of explanation, the diameter direction is specified to point from the positive potential of the deflection electric field to the negative potential direction, which is called the radial direction for short.

[012] In one aspect, the invention provides an alumina@Co nanowire composite film. The composite film comprises Co nanowires and a porous alumina film, wherein the Co nanowires are positioned in nano holes of the porous alumina film, one part of the Co nanowires grow at the bottom of the porous alumina film, the density distribution of the Co nanowires increases along the radial direction, the other part of the Co nanowires grow at the top of the porous alumina film, and the density distribution of the Co nanowires decreases along the radial direction.

[013] The porous alumina film has a thickness of 1 m or less, such as 0.1m, 0.2m, 0.3[tm, 0.4[tm, 0.5[am, 0.6am, 0.7jam, 0.8tm or 0.9jam, and the like.

[014] The porous alumina film with the thickness below 1jm has a single structural color, and the Co nanowires are deposited into the pores of the porous alumina film with the single structural color, so that the refractive index of the porous alumina film is increased, and the reflection light intensity at the interface of aluminum and aluminum oxide is weakened, so that the color saturation of the film is improved; and because the density of the Co nanowires is gradually distributed along the diameter direction of the film, the composite film can show iridescent gradual change structural colors.

[015] The alumina@Co nanowire composite film provided by the invention comprises the Co nanowires, so that the film is magnetic. As the diameter Co nanowires deposited in each hole of the porous alumina film is the same, the density is gradually distributed along the radial direction of the film, and the magnetism of the composite film provided by the invention is gradually increased along the radial direction of the film.

[016] In a second aspect, the invention provides a preparation method of the alumina@Co nanowire composite film. The preparation method comprises the steps: the porous alumina film is placed in an electrolyte containing Co ions and is subjected alternating current electrodeposition under the application of a deflection electric field, and thus the alumina@Co nanowire composite film is obtained.

[017] The deflection electric field is obtained by adding DC voltage to two carbon sheets arranged in parallel. Two carbon sheets which are parallel to the central connecting line of the deposited counter electrode are subjected to direct current voltage to obtain an electric field which is perpendicular to the motion locus of the deposited Co ions, so that the two carbon sheets are deflected. The method is simple, and the carbon sheet is easy to obtain and low in cost.

[018] The preparation method of the Co nanowire porous alumina composite film provided by the invention is simple, the density of the Co nanowire can be gradually distributed along the radial direction of the film only by one time of alternating current electrodeposition, and the cost is lower.

[019] The voltage of the alternating current electrodeposition is 11-13 V, such as 1I V, 11.5 V, 12.0 V, 12.5 V, 13.0 V and the like.

[020] The voltage of the deflection electric field is 4-6 V, such as 4.1 V, 4.2 V, 4.3 V, 4.4 V, 4.5 V, 4.6 V, 4.7 V, 4.8 V, 4.9 V, 5.0 V and the like.

[021] Preferably, the distance between the counter electrodes of the deflection electric field is 6-9 cm, such as 6.5 cm, 7 cm or 7.5 cm, etc.

[022] The alternating current electrodeposition time is 30-60 s, such as 31 s, 32 s, 33 s,34s,35 s,36s,37s,38 sor39s.

[023] Preferably, the Co element-containing electrolyte is a CoSO4-containing solution. A CoSO4 solution a with a preferable concentration of 0.10 mol/L-0.14 mol/L is preferred, such as a CoSO4 solution with a concentration of 0.11 mol/L, 0.12 mol/L, 0.13 mol/L or 0.14 mol/L; and further preferably, the Co element-containing electrolyte further contains boric acid having a concentration of 0.37 mol/L-0.41 mol/L, such as boric acid having a concentration of 0.38 mol/L, 0.39 mol/L, 0.40 mol/L or 0.41 mol/L.

[024] The porous alumina film is obtained by the following method:

[025] (1) Pretreating the aluminum foil; and

[026] (2) Placing the pretreated aluminum foil as an anode and a cathode parallel to the anode into the electrolyte for electrochemical oxidation to obtain the porous alumina film.

[027] The pretreatment in step (1) t sequentially comprises cutting, cleaning, annealing and electrochemical polishing.

[028] Specifically, the pretreatment comprises: shearing a high-purity aluminum foil with the purity of 99.999% and the thickness of 0.3 mm into a round plate of about 2 cm, flattening, placing the round plate in an acetone solution for ultrasonic cleaning of 30 minutes, then placing the round plate in alcohol for ultrasonic cleaning of 30 minutes, finally repeatedly washing the round plate in deionized water, airing the round plate, placing the round plate in a quartz tube furnace, performing vacuum annealing at 400 °C for 2 hours, and cooling the round plate to a room temperature; and then carrying out electropolishing treatment on the annealed high-purity aluminum foil, wherein the electropolishing solution is a mixed solution of HClO4and absolute ethyl alcohol with the volume ratio of 1: 4, the aluminum foil is used as an anode, the carbon rod is used as a cathode, and electropolishing is carried out for 5min at the voltage of about 20 V.

[029] In step (2), the cathode is a carbon rod.

[030] Preferably, the distance between the cathode and the anode is 8-14 cm, such as 9 cm, 10 cm, 11 cm, 12 cm, 13 cm or 13.5 cm, etc.

[031] In step (2), the electrolyte is phosphoric acid of 4.75-5.25 wt%, such as phosphoric acid at a concentration of 4.8 wt%, 4.85 wt%, 4.9 wt%, 4.95 wt%, 5.0 wt%, 5.05 wt%, 5.1 wt%, 5.15 wt% or 5.2 wt%, etc. The phosphoric acid in the concentration range has a stable and controllable electrochemical reaction.

[032] Preferably, the electrochemical oxidation time is 10 to 14 min, such as 11 min, 12 min, 13 min or 14 min, etc., and the electrochemical oxidation voltage is 16-24 V, such as 17 V, 18 V, 19 V, 20 V, 21 V, 22 V or 23 V, etc.

[033] In step (2), proper oxidation time is selected to obtain the porous alumina film with a single structural color.

BRIEF DESCRIPTION OF THE FIGURES

[034] FIG. 1 is a schematic structural diagram showing a novel electrolytic bath for realizing deflection electric field application assisted electrodeposition. Where:

1. an annular rubber pad; 2. a circular aluminum foil; 3. a reducing copper electrode; 4. an inner space fastening screw buckle; 5. a small cylindrical hole; 6. a small cylindrical hole annular enclosing wall; 7. a large cylindrical hole; 8. an electrolytic bath wall; 9. a carbon sheet; 10. a carbon rod; 11. a deposition voltage source; and 12. a deflection voltage source.

[035] FIG. 2 is an XRD diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention.

[036] FIG. 3 is a cross section SEM diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention.

[037] FIG. 4 is a surface SEM diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention.

[038] FIG. 5 is a reflection spectrum diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention.

[039] FIG. 6 is a magnetizing curve of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention.

[040] FIG. 7 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 1-4 of the invention.

[041] FIG. 8 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 5, 6, 7 and 4 of the invention.

[042] FIG. 9 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 8, 4 and 9 of the invention.

[043] FIG. 10 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 10, 4 and 11 of the invention.

DESCRIPTION OF THE INVENTION

[044] This invention brings forth the technical effects described as below:

[045] 1. In the experiment of the novel electrolytic bath, the distance between the plane where the circular aluminum foil is positioned and the plane of the inner side wall of the cell is about 1 mm (namely, the thickness of "6", namely the hole length of the small cylindrical hole is short and equal to 1 mm), so that under the condition of the short distance, a deposition experiment under a deflection electric field can be carried out to prepare the alumina@Co nanowire composite film;

[046] 2. The alumina@Co nanowire composite film provided by the invention has a high-saturation iridescent gradual change structural color and magnetism changing gradually along the radial direction. The saturation magnetization intensities are successively 119, 147, 160 emu/ cm3 along the diameter direction of the cm film when the applied magnetic field is 6000oe.

[047] 3. The density distribution of Co nanowires in the alumina@Co nanowire composite film provided by the invention changes gradually along the radial direction of the film, wherein one part of Co nanowire grows at the bottom of the porous alumina film, the density distribution of the Co nanowire increases along the radial direction, the other part of Co nanowire grows at the top of the porous alumina film, and the density distribution of the Co nanowire decreases along the radial direction. The composite film can be prepared by one-time alternating current deposition process. The preparation method is simple and low in cost.

[048] 4. The alumina@Co nanowire composite film provided by the present invention presents saturated iridescent gradient structural colors and magnetism, and can be applied in the fields of biomedicine, catalysis, anti-counterfeiting, decoration, imaging, dye sensitization, solar cells and the like.

[049] The technical solution of the present invention will be described in further detail below with reference to specific embodiments.

[050] The equipment models and manufacturers used in the following examples are as follows:

[051] Ultrasonic cleaning machine (Model PS-08A, Shenzhen Permanent Ultrasonic Equipment Co., Ltd.);

[052] A quartz tube furnace (model number HTL1100-60, Hefei Kaiqin Material Technology Co., Ltd.);

[053] DC power supply (DC-1760, Hefei Dachun Electronics Co., Ltd.);

[054] Digital camera (model EOS 600D, Canon China Co., Ltd.);

[055] Scanning electron microscope (model S-4800, Hitachi Co., Japan);

[056] UV-Vis spectrophotometer (Hitachi U-3010, Hitachi Co., Japan);

[057] Physical property testing system (PPMS-6000, manufactured by Quantum Design Co., USA).

[058] In a specific application process of the electrolytic bath, before electrodeposition, according to the installation sequence of the arrow in FIG. 1, the "1" is firstly installed, then the "2" is installed, then the "3" is installed, finally the "4" is installed. External threads of the "4" and internal threads of the "7" are tightly buckled together, and meanwhile, the "1, 2, 3" are fixed and the "1"plays a role in preventing liquid leakage.

[059] Before electrodeposition, two pieces of "9" are placed as shown in FIG. 1, a proper deflection voltage source is applied while a deposition voltage source is applied, and the direction of a deposition electric field and the direction of the deflection electric field are vertical, so that an experiment of applying the deflection electric field to assist electrodeposition can be carried out, and an alumina composite film with saturated and gradual structure colors is prepared.

[060] Embodiment 1

[061] The Co nanowire porous alumina composite film is prepared according to the following steps:

[062] (1) Shearing a high-purity aluminum foil with h purity of 99.999% and the thickness of 0.3 mm into a round plate of about 1.8 cm, flattening, placing the round plate in acetone solution for ultrasonic cleaning of 30 minutes, then placing the round plate in alcohol for ultrasonic cleaning of 30 minutes, finally repeatedly washing the round plate in deionized water, airing the round plate, placing the round plate in a quartz tube furnace, performing vacuum annealing at 400 °C for 2 hours, and cooling the round plate to room temperature; then carrying out electropolishing treatment on the annealed high-purity aluminum foil, wherein the electropolishing solution is a mixed solution of HC104 and absolute ethyl alcohol with the volume ratio of 1:4, the aluminum foil is used as an anode, the carbon rod is used as a cathode, and electrooxidation is carried out for 5 min at the voltage of about 20 V;

[063] (2) Placing the polished high-purity aluminum foil in an electrolytic bath to serve as an anode, taking a carbon rod with the length of 8 cm and the diameter of 6 mm as a cathode, carrying out electrochemical oxidation on the carbon rod with the electrode spacing of 10 cm and the electrolyte of 5 wt% phosphoric acid solution under the voltage of20 V, and taking out and cleaning after the oxidation for 14 min to obtain a porous alumina film; and

[064] (3) Placing the porous alumina film into 0.12 mol/L CoSO4 electrosolution, wherein the voltage is 12 V, the electrodeposition time is 30 s, the electrode spacing is 6 cm; carrying out alternating current electrodeposition; and simultaneously adding a deflection electric field, wherein the deflection voltage is 6 V, so as to obtain the magnetic Co nanowire porous aluminum oxide composite film.

[065] Embodiment 2

[066] The other conditions were the same as in Embodiment 1 except that the deposition time in Step (3) was 40 s.

[067] Embodiment 3

[068] The other conditions were the same as in Embodiment 1 except that the deposition time in Step (3) was 50 s.

[069] Embodiment 4

[070] The other conditions were the same as in Embodiment 1 except that the deposition time in Step (3) was 60 s.

[071] Embodiment 5

[072] The other conditions were the same as in Embodiment 4 except that the oxidation time in Step (2) was 11 min.

[073] Embodiment 6

[074] The other conditions were the same as in Embodiment 4 except that the oxidation time in step (2) was 12 min.

[075] Embodiment 7

[076] The other conditions were the same as in Embodiment 4 except that the oxidation time in step (2) was 13 min.

[077] Embodiment 8

[078] The other conditions were the same as in Embodiment 4 except that the deflection voltage was 5 V in Step (3).

[079] Embodiment 9

[080] The other conditions were the same as in Embodiment 4 except that the deflection voltage was 7 V in Step (3).

[081] Embodiment 10

[082] The other conditions were the same as in Embodiment 4 except that the deposition voltage in step (3) was 11 V.

[083] Embodiment 11

[084] The other conditions were the same as in Example 4 except that the deposition voltage in step (3) was 13 V.

[085] Performance Test:

[086] A digital camera was used to take photos of the alumina@Co nanowire composite film prepared by the Embodiments 1-11. The surface and cross section morphology of the composite film prepared in Embodiment 5 were characterized by using a scanning electron microscope; the reflection spectrum of the composite film prepared in Embodiment 5 was measured by using an ultraviolet visible spectrophotometer; and the magnetic property of the composite film prepared in Embodiment 5 was measured by using a physical property test system.

[087] Test results:

[088] FIG. 2 is an XRD diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention. As observed in XRD results, the Co (101) hcp phase diffraction peak appears in the composite film, and the preferential growth in the direction of Co (101) is obviously observed.

[089] FIG. 3 is a cross section SEM diagram corresponding to an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention in different color areas along the diameter direction. FIG. 3(a), (b), and (c) are SEM cross sectional photographs corresponding to regions of different colors (corresponding to regions a, b, and c on the left side of FIG. 8) along the diameter, respectively. As can be seen from the figure, the thickness of the composite film is 280 nm, and the length of the Co nanowire at the bottom of the composite film is approximately the same, which is about 165 nm, but the density distribution of the Co nanowire increases along the radial direction. FIGs 3(a) and 3(b) show the presence of nanowires in the top nanopores thereof.

[090] FIG. 4 is a surface SEM diagram corresponding to an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention in different color areas along the diameter direction. FIG. 4(a), (b), and (c) are SEM surface photographs corresponding to regions of different colors (corresponding to regions a, b, and c on the left side of FIG. 8) along the diameter, respectively. It can be seen from the figure that (a) shows a larger nanowire density; (b) shows a smaller nanowire density (c) shows a nanowire density of almost zero. FIG. 4 and FIG. 5 combine to find that the Co nanowires are positioned in the nano holes of the porous alumina film, wherein one part of the Co nanowires grow at the bottom of the porous alumina film, and the distribution density of the Co nanowires increases along the radial direction; and the other part of the Co nanowires grow at the top of the porous alumina film, and the distribution density of the Co nanowires decreases along the radial direction.

[091] FIG. 5 is a reflection spectrum diagram of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention. As shown in the diagram, the wavelength corresponding to the peak position in the reflection spectrum is 365 nm and 581 nm, respectively, and the corresponding colors in the visible light range are purple and yellow, respectively. This is in accordance with the color shown in the digital photograph of Embodiment 5 of FIG. 8.

[092] FIG. 6 is a magnetizing curve of an alumina@Co nanowire composite film prepared according to the embodiment 5 of the invention, wherein a, b and c respectively correspond to the magnetization curves corresponding to the areas a, b and c of the left digital photograph of FIG. 8. When the direction of the applied magnetic field is parallel to the direction of the Co nanowire and the intensity of the applied magnetic field is 6000oe, saturation is achieved. As can be seen from the figure, the magnetic properties of the Co nanowire porous alumina composite film gradually increase along the radial direction, and the saturation magnetization values are 119, 147 and 160 emu/cm3 respectively, which are consistent with the increasing density of the bottom Co nanowire in FIG. 3.

[093] FIG. 7 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 1-4 of the invention. Embodiments 1, 2, 3 and 4 are shown in the figure in the order from left to right. As can be seen from the figure, when the same alumina template is used, the deposition voltage and the deflection voltage are the same, and the composite films with different iridescent gradual structure colors with high saturation are formed with the increase of the deposition time.

[094] FIG. 8 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 5, 6, 7 and 4 of the invention. Embodiments 5, 6, 7 and 4 are shown in the figure from the left in sequence. This figure shows that with the increase of oxidation time, the film thickness increases, and under the same deposition conditions and deflection conditions, the graded iridescent structure color composite films with different high saturation are formed.

[095] FIG. 9 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 8, 4 and 9 of the invention. Embodiments 8, 4 and 9 are shown from the left in the diagram. The graph shows that the deposition conditions of the porous alumina films prepared under the same oxidation conditions are the same, and different high-saturation iridescence gradient structure colors are formed along with the increase of the deflection voltage.

[096] FIG. 10 is a digital photo diagram of an alumina@Co nanowire composite film prepared according to the embodiments 10, 4 and 11 of the invention. Embodiments 10, 4 and 11 are shown from the left in the diagram. The graph shows that the deposition time and deflection electric field conditions of the porous alumina film prepared under the same oxidation condition are the same, and different high saturation iridescence gradual structure colors are formed along with the increase of the deposition voltage.

[097] As shown in above embodiments, the alumina@Co nanowire composite film provided by the invention has magnetism changing gradually along the diameter direction and a high-saturation iridescent gradual change structural color. The composite film has optical and magnetic properties at the same time, has great application prospects in the aspects Co anti-counterfeiting, painting, decoration, cosmetics, imaging technology, dye sensitization and solar cells, and also has important significance for opening up the application of the alumina film in other new fields.

[098] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

[099] The present invention and the described embodiments specifically include the best method known to the applicant of performing the invention. The present invention and the described preferred embodiments specifically include at least one feature that is industrially applicable

Claims (9)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An electrolytic bath for applying a deflection electric field to assist electrodeposition, wherein the names of the components in figure 1 are: 1. an annular rubber pad; 2. a circular aluminum foil; 3. a reducing copper electrode; 4. a hollow fastening screw; 5. a small cylindrical hole; 6. an annular wall of the small cylindrical hole; 7. a large cylindrical hole; 8. an electrolytic bath wall; 9. a carbon sheet; 10. a carbon rod; 11. a deposition voltage source; and 12. a deflection voltage source. When the electrolytic bath is installed, firstly, "1" is put into "7" and is tightly attached to "6", then "2" and "1" are tightly attached to each other, then "3" is put into "7" and is tightly attached to "2", finally "4" is screwed into "7" provided with a spiral buckle, and "1, 2, 3" are fixed at the same time, and "1"plays a role in preventing liquid leakage.

2. The electrolytic bath for deflection electric field application assisted electrodeposition according to claim 1, wherein the diameter of the large cylindrical hole is larger and the hole is longer, and the inner wall of the large cylindrical hole is provided with an inner thread; the diameter of the small cylindrical hole is 4 mm smaller than the diameter of the large cylindrical hole, so that "6", the difference between the inner diameter and the outer diameter of the "6" is 4 mm, the thickness of the "6", namely the hole length of the small cylindrical hole is shorter than 1 mm; the outer diameter of the "1" is equal to the diameter of the "7", the inner diameter of the "1" is equal to the diameter of the "5"; the diameter of the', Preferably, the diameter of the large cylindrical hole is 1.4-2.2 cm. Two pieces Co "9" are connected with "12" to form a deflection electric field, and "11" are connected with "10" and "3" to form an electrodeposition electric field, and the direction of the deposition electric field and the direction of the deflection electric field are vertical, so that experiments of applying the deflection electric field to assist electrodeposition can be carried out, namely, an alumina@Co nanowire composite film is prepared.

3. An alumina@Co nanowire composite film, wherein the film comprises Co nanowires and a porous alumina film, wherein the Co nanowires are positioned in nano holes of the porous alumina film, the density of the Co nanowires is gradually distributed along the radial direction, one part of the Co nanowires grows at the bottom of the porous alumina film, the density distribution of the Co nanowires is gradually increased along the radial direction, the other part of the Co nanowires grows at the top of the porous alumina film, and the density distribution of the Co nanowires is gradually reduced along the radial direction;

Co nanowires are deposited into the nano holes of the porous alumina film, so that the porous alumina film has magnetism; and due to the fact that the density of the Co nanowires deposited into the nano holes of the porous alumina film is gradually distributed along the radial direction, the magnetism is gradually increased along the radial direction of the porous alumina film.

4. The Co nanowire/porous aluminum oxide composite film according to claim 3, wherein the thickness and the length of the Co nanowire of the porous alumina film are both 0-1 [m, and the composite film show a saturated iridescent gradual structure color.

5. The preparation method of the Co nanowire/porous alumina composite film according to claim 3, wherein the preparation method comprises the following steps: taking a porous alumina film with a uniform microstructure as a template, taking a counter electrode as a carbon rod, placing the porous alumina film in parallel with the counter electrode, performing alternating current electrodeposition in a Co-containing solution, and simultaneously applying a deflection electric field to regulate and control the distribution of the density of the Co nanowire in the film.

6. The method for preparing the Co nanowire porous alumina composite film according to claim 5, wherein the alternating current deposition voltage is 11-13 V.

7. The method for preparing a Co nanowire porous alumina composite film according to claim 5, wherein the alternating current deposition time is 30-60 s.

8. The method for preparing a Co nanowire porous alumina composite film according to claim 5. Wherein the method for obtaining the deflection electric field comprises:

Obtaining the deflection electric field by applying direct current voltage to two carbon sheets which are arranged in parallel, wherein the carbon sheets are arranged in parallel with a connecting line of the centers of the two deposition counter electrodes, and the two carbon sheets which are arranged in parallel are applied with the direct current voltage to generate an electric field, so that Co ions are deflected in the deposition process; and the deflection electric field is vertical to the deposition electric field.

9. The preparation method of the Co nanowire porous alumina composite film according to claim 8, wherein the carbon sheet is 4-7 cm wide and 5-8 cm high, the deflection electric field voltage is 4-6 V, and the distance between the counter electrodes of the deflection electric field is 6-9 cm.