TiO2 film with lotus leaf surface structure and preparation method thereof

Abstract

The application belongs to the field of inorganic functional materials, and particularly relates to a TiO2 film with lotus leaf surface structure and a preparation method thereof. The TiO2 film with lotus leaf surface structure is composed of dispersed sub-micron-sized TiO2 microspheres and a continuous film matrix, and the dispersed TiO2 microspheres are locally inlaid in the film matrix; the TiO2 microspheres are composed of nano-sized TiO2 particles. The TiO2 film with lotus leaf surface structure is prepared by using a sol containing tetra-n-butyl titanate complex and TiO2 colloidal particles as a precursor, and through phase separation of a sol liquid film formed by one-step dip-coating in a solvent evaporation process. The size and distribution density of the TiO2 microspheres on the hierarchical structure surface can be conveniently controlled by controlling the content of the TiO2 colloidal particles in the sol system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inorganic functional material preparation, and particularly relates to a TiO2 film with a lotus leaf surface structure and a preparation method thereof. BACKGROUND

[0002] Super-hydrophobic surfaces have wide application prospects in self-cleaning, anti-fogging and anti-icing, fluid drag reduction and material surface corrosion prevention. For example, water droplets on a super-hydrophobic lotus leaf surface are spherical, and the water droplets carry away the dust on the surface while rolling on the surface, so that the lotus leaf surface has self-cleaning ability. When the lotus leaf surface is observed by using an electron microscope, it is found that the super-hydrophobicity of the lotus leaf surface is closely related to the rough microstructure of the lotus leaf surface in addition to the low surface energy wax layer on the surface. The microstructure is characterized in that: the surface is distributed with dispersed micrometer-scale papillae, and the entire surface including the surface of the papillae is further distributed with nanometer-scale particles. The water droplets form liquid-solid and liquid-gas interfaces on the rough micro-nano structure surface, and the greater the area fraction of the liquid-gas interface, the greater the apparent contact angle of the water droplets. Therefore, the micro-nano hierarchical structure of the lotus leaf, which is composed of micrometer and nanometer scales, is very beneficial to reducing the area fraction of the liquid-solid interface, thereby greatly increasing the water contact angle of the water droplets on the lotus leaf surface.

[0003] Inspired by the super-hydrophobic mechanism of the lotus leaf surface, various rough structure surfaces have been synthesized at present. These rough structures can be summarized into two categories: pore modification and particle modification. The surface modified by pores can usually be synthesized by using polymer templates, water droplet templates and the like; and the preparation of the micro-nano hierarchical structure surface of the lotus leaf usually needs to synthesize the dispersed phase (particles) and the continuous phase (thin film matrix) in steps. The synthesized thin film is difficult to achieve the effect of integration of the dispersed phase and the continuous phase like the lotus leaf surface, and this method has problems of uneven distribution of the dispersed phase and unstable structure. By using a chemical bath deposition method, various morphologies of micro-nano hierarchical structures of ZnO, Co(OH)2 and the like crystals can be grown on the surface of a substrate. These micro-nano hierarchical structures can effectively improve the super-hydrophobic properties of the surface of the thin film, but the hierarchical structure units obtained by the chemical bath deposition are relatively fragile and lack the fixation of the continuous thin film matrix, so they are easy to fall off and break when subjected to external force. SUMMARY

[0004] The present application provides a TiO2 film with a lotus leaf surface structure. The film is composed of dispersed sub-micron-sized TiO2 microspheres and a continuous matrix, and the dispersed TiO2 microspheres are locally embedded in the thin film matrix, forming a continuous whole like the lotus leaf surface, so that the prepared film has high mechanical strength and good structural stability.

[0005] Further, the TiO2 microspheres are composed of nano-sized TiO2 particles; the nano-sized TiO2 particles are 10-30 nm.

[0006] The application also provides a preparation method of the TiO2 film with the lotus leaf surface structure, which uses a sol containing a tetra-n-butyl titanate complex and TiO2 colloidal particles as a precursor, and synthesizes a hierarchical structure surface with dispersed phase and continuous phase integrated by a one-step dip-coating process; the specific steps are as follows:

[0007] (1) Preparation of the TiO2 sol for dip-coating: tetra-n-butyl titanate and acetylacetone are added into a beaker, the beaker is sealed with a preservative film, and magnetic stirring is performed for 30 min, so that the tetra-n-butyl titanate complex is generated; some small holes are punched on the preservative film to make the air in and out of the beaker, and the tetra-n-butyl titanate complex system is aged for 4-5 days at room temperature; under stirring, ethanol and water are sequentially added into the tetra-n-butyl titanate complex system, and the obtained mixture system is used as the TiO2 sol for dip-coating;

[0008] If the aging time is too short, there are too few TiO2 colloidal particles in the system; if the aging time is too long, the system will be turbid when water is added subsequently, the turbid system is unstable, and a precipitate is generated after standing.

[0009] (2) Preparation of the TiO2 film: the dip-coating technology is used to prepare a film on a glass slide substrate, and the drawing speed is 28 cm / min; after drying, the sample obtained by dip-coating is subjected to heat treatment in a muffle furnace, so that the TiO2 film with the lotus leaf surface structure is obtained.

[0010] Further, in step (1), the volume ratio of tetra-n-butyl titanate, acetylacetone, ethanol and water is 2.5:0.67:9-11:9-11.

[0011] Further, the drying condition of step (2) is that the sample is dried at room temperature for 5 min, and then dried at 100°C in an oven for 1 h.

[0012] Further, the heat treatment temperature of step (2) is 550°C, and the heat treatment time is 2 h.

[0013] In the application, the aging time of the tetra-n-butyl titanate complex system is controlled to be 4-5 days, so that the tetra-n-butyl titanate complex is not completely hydrolyzed, the Ti-OH bond generated by the hydrolysis reaction forms a Ti-O-Ti bond through a polycondensation reaction, TiO2 colloidal particles are generated in the system, and then the ratio of the TiO2 colloidal particles and the partially hydrolyzed tetra-n-butyl titanate complex in the sol system is controlled, that is, the sol system contains two solutes, i.e., the unhydrolyzed tetra-n-butyl titanate complex and the TiO2 colloidal particles.

[0014] The TiO2 sol is prepared by sequentially adding ethanol and water into the system. At this time, the tetra-n-butyl titanate complex cannot be completely converted into TiO2 because only partial hydrolysis of the organic groups occurs. The prepared TiO2 sol is used as a precursor to form a sol liquid film on the surface of a glass slide substrate. With the evaporation of the solvent, the ethanol / water ratio in the liquid film decreases, the TiO2 colloidal particles in the liquid film aggregate due to the increase of the interfacial tension and phase separation in the form of microspheres occurs, and finally the TiO2 colloidal particles become the dispersed phase on the surface of the film, while the partially hydrolyzed tetra-n-butyl titanate complex forms a continuous film matrix. By controlling the aging time of the system and the ratio of the added ethanol and water, the ratio of the TiO2 colloidal particles and the partially hydrolyzed tetra-n-butyl titanate complex in the sol system can be controlled, thereby controlling the size and distribution density of the TiO2 microspheres on the surface of the hierarchical structure.

[0015] The TiO2 film with a lotus leaf-like surface structure prepared in the present application does not show phenomena such as collapse, damage or shedding of the microspheres due to external pressure after the pressure test, and the surface film coating has good structural stability. After the adhesion test, the edges of the film cutouts are smooth, and no peeling occurs at the edges of the lattices. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The SEM images of the film prepared in Example 1 of the present application at small magnification (a), large magnification (b) and larger magnification (d), and the size distribution of the microspheres (c) are shown.

[0017] Figure 2 The SEM images of the film prepared in Example 2 of the present application at small magnification (a) and large magnification (b), and the size distribution of the microspheres (c) are shown.

[0018] Figure 3 The SEM images of the film prepared in Example 3 of the present application at small magnification (a) and large magnification (b), and the size distribution of the microspheres (c) are shown.

[0019] Figure 4 The SEM image of the film prepared in Comparative Example 1 of the present application is shown.

[0020] Figure 5 The EDS elemental composition analysis results of the film prepared in Example 1 of the present application are shown.

[0021] Figure 6 The XRD pattern of the film prepared in Example 1 of the present application is shown.

[0022] Figure 7 The SEM photograph of the film prepared in Example 1 of the present application after the pressure resistance test is shown.

[0023] Figure 8Optical microscope photos of the surface grid (left) and grid intersection (right) of the thin film prepared in Example 1 of the present application after adhesion test. Embodiment

[0024] The present application is further illustrated in the following specific examples.

[0025] Example 1

[0026] (1) In a 50 mL beaker, 2.5 mL of tetra-n-butyl titanate and 0.67 mL of acetylacetone were added, the mouth of the beaker was sealed with a plastic wrap, and the system was magnetically stirred for 30 min, during which the complex of tetra-n-butyl titanate was generated in the system;

[0027] (2) Some small holes were punched on the plastic wrap to allow air communication between the inside and outside of the beaker, and the tetra-n-butyl titanate complex system was aged at room temperature for 4 days, during which the liquid viscosity slowly increased, but the system remained transparent;

[0028] (3) Under stirring, 10 mL of ethanol was added to the system, followed by the addition of 10 mL of water, and the obtained mixture system was used as a TiO2sol for dip-coating;

[0029] (4) Then, a thin film was prepared on a glass slide substrate by using the dip-coating technique, and the pulling speed was 28 cm / min;

[0030] (5) The sample obtained by dip-coating was dried at room temperature for 5 min, and then dried in an oven under the conditions of 100°C for 1 h;

[0031] (6) The sample obtained after drying was heat-treated in a muffle furnace, and a TiO2thin film with a lotus leaf-like surface structure was obtained, and the heat treatment conditions were 550°C for 2 h.

[0032] From Figure 1 (a) The small-magnification SEM image shows that the prepared thin film surface is densely distributed with microspheres, and the distribution of the microspheres is uniform as a whole; Figure 1 (b) The large-magnification SEM image shows that the microspheres are locally embedded in the matrix, which is similar to the papillae on the lotus leaf surface and is integrated with the matrix; Figure 1 (c) The average size of the microspheres is 407.5 nm, the distribution width is 200-650 nm, and the distribution density of the microspheres is 0.79 / μm 2 ; from Figure 1 (d) The larger-magnification SEM image shows that the microspheres are composed of nano-sized particles, and the surface of the microspheres is also similar to the papillae on the lotus leaf surface in microstructure, and is also distributed with nano-sized particles.

[0033] Figure 5The EDS element composition analysis results of the thin film prepared in this example are shown. The thin film surface contains titanium, oxygen and carbon three elements; the titanium element content is obviously higher at the position of TiO2 microspheres Figure 5 (b), indicating that the microspheres are aggregated by TiO2 colloidal particles, and the matrix with lower titanium element content is formed by the partially hydrolyzed tetra-n-butyl titanate complex; the oxygen element content difference between the microspheres and the matrix is not large Figure 5 (c); the existence of relatively low content of carbon element indicates that the carbonization phenomenon of residual organic groups occurs during the heat treatment process, and the overall uniform distribution of carbon element indicates that the microspheres do not completely separate from the matrix when phase separation occurs in the sol Figure 5 (d).

[0034] Figure 6 The XRD pattern of the prepared thin film shows that the prepared thin film is amorphous before and after heat treatment, and the reason may be that the doping of residual carbon atoms after carbonization of organic groups inhibits the crystallization of the thin film.

[0035] The test method for pressure resistance is that a weighing paper is covered on the surface of the thin film, and then 100g of weight is placed on it and rolled 100 times. Figure 7 The SEM photos of the thin film surface after the pressure test are shown. The surface of the thin film coating has good structural stability without the phenomenon of microsphere collapse, damage or falling off due to external pressure.

[0036] The test method for adhesion is that a crosscut knife with a blade spacing of 1mm is used to cut a 10x10 grid array on the thin film coating by crosscut method, and 3M No. 600 test tape is pasted on the surface of the cut grid, and the surface of the tape is wiped with a rubber eraser to ensure that the tape is in complete contact with the grid. Grasp one end of the tape and tear it off quickly at a 90° direction. According to the number of grid adhered on the tape, the adhesion between the thin film coating and the substrate is evaluated. Figure 8 The optical microscope photos of the grid (left) and the grid intersection (right) on the surface of the thin film after the adhesion test are shown. After the test, the edges of the cutouts are smooth, and no peeling occurs at the edges of the grid, reaching the highest level of 5B in the six levels of 0B-5B.

[0037] Example 2

[0038] (1) 2.5mL of tetra-n-butyl titanate and 0.67mL of acetylacetone were added into a 50mL beaker, the cup opening was sealed with plastic wrap, and the system was magnetically stirred for 30min. The complex of tetra-n-butyl titanate was generated in the system;

[0039] (2) Some small holes were punched on the plastic wrap to connect the air inside and outside the beaker. The tetra-n-butyl titanate complex system was aged at room temperature for 4 days. During this period, the liquid viscosity slowly increased, but the system remained transparent;

[0040] (3) Under stirring conditions, 11 mL of ethanol was added to the system, followed by 9 mL of water. The resulting mixture was used as a TiO2 sol for impregnation-lifting.

[0041] (4) Next, a thin film was prepared on the glass slide substrate using the dip-coating technique at a speed of 28 cm / min;

[0042] (5) The sample obtained by impregnation-lifting was dried at room temperature for 5 min and then dried in an oven at 100℃ for 1 h.

[0043] (6) The dried sample is heat-treated in a muffle furnace to obtain a TiO2 film with a surface structure similar to that of a lotus leaf. The heat treatment conditions are: 550℃, 2h.

[0044] from Figure 2 (a) Low-magnification SEM images show that the prepared film surface has a dense distribution of microspheres, but the distribution of microspheres is not uniform overall; from Figure 2 (b) High-magnification SEM images show that, as in Example 1, the microspheres are locally embedded in the matrix, similar to the papillae on the surface of a lotus leaf, and are integrated with the matrix. Figure 2 (c) The average size of the microspheres is 508.5 nm, the distribution width is 100-900 nm, and the distribution density of the microspheres is 0.65 per μm. 2 Compared with the microspheres of Example 1, the average size is increased, the size distribution is widened, and the distribution density is reduced.

[0045] Example 3

[0046] (1) Add 2.5 mL of tetrabutyl titanate and 0.67 mL of acetylacetone to a 50 mL beaker, seal the mouth of the beaker with plastic wrap, and stir magnetically for 30 min. The system will then react to produce a complex of tetrabutyl titanate.

[0047] (2) Make some small holes in the plastic wrap to allow air to pass through the inside and outside of the beaker. Let the tetrabutyl titanate complex system age at room temperature for 4 days. During this period, the viscosity of the liquid increases slowly, but it remains transparent.

[0048] (3) Under stirring conditions, add 9 mL of ethanol to the system, followed by 11 mL of water. The resulting mixture is used as a TiO2 sol for impregnation-lifting.

[0049] (4) Next, a thin film was prepared on the glass slide substrate using the dip-coating technique at a speed of 28 cm / min;

[0050] (5) The sample obtained by impregnation-lifting was dried at room temperature for 5 min and then dried in an oven at 100℃ for 1 h.

[0051] (6) The dried sample is heat-treated in a muffle furnace to obtain a TiO2 film with a surface structure similar to that of a lotus leaf. The heat treatment conditions are: 550℃, 2h.

[0052] from Figure 3 (a) Low-magnification SEM images show that the prepared film surface has a dense distribution of microspheres, but the distribution of microspheres is not uniform overall; from Figure 3 (b) High-magnification SEM images show that, as in Example 1, the microspheres are locally embedded in the matrix, similar to the papillae on the surface of a lotus leaf, and are integrated with the matrix. Figure 3 (c) The average size of the microspheres is 1110 nm, the distribution width is 200-1600 nm, and the distribution density of the microspheres is 0.073 per μm. 2 Compared with the microspheres of Example 1, the average size is significantly increased, the size distribution is significantly widened, and the distribution density is significantly reduced.

[0053] Example 4

[0054] (1) Add 2.5 mL of tetrabutyl titanate and 0.67 mL of acetylacetone to a 50 mL beaker, seal the mouth of the beaker with plastic wrap, and stir magnetically for 30 min. The system will then react to produce a complex of tetrabutyl titanate.

[0055] (2) Make some small holes in the plastic wrap to allow air to pass through the inside and outside of the beaker. Let the tetrabutyl titanate complex system age at room temperature for 5 days. During this period, the viscosity of the liquid increases slowly, but it remains transparent.

[0056] (3) Under stirring conditions, add 10 mL of ethanol to the system, followed by 10 mL of water. The resulting mixture is used as a TiO2 sol for impregnation-lifting.

[0057] (4) Next, a thin film was prepared on the glass slide substrate using the dip-coating technique at a speed of 28 cm / min;

[0058] (5) The sample obtained by impregnation-lifting was dried at room temperature for 5 min and then dried in an oven at 100℃ for 1 h.

[0059] (6) The dried sample is heat-treated in a muffle furnace to obtain a TiO2 film with a surface structure similar to that of a lotus leaf. The heat treatment conditions are: 550℃, 2h.

[0060] Comparative Example 1

[0061] (1) Add 2.5 mL of tetrabutyl titanate and 0.67 mL of acetylacetone to a 50 mL beaker, seal the mouth of the beaker with plastic wrap, and stir magnetically for 30 min. The system will then react to produce a complex of tetrabutyl titanate.

[0062] (2) Under stirring conditions, 10 mL of ethanol was added to the system, followed by 10 mL of water. The resulting mixture was used as a TiO2 sol for impregnation-lifting.

[0063] (3) Next, a thin film was prepared on the glass slide substrate using the dip-coating technique at a speed of 28 cm / min;

[0064] (4) The sample obtained by impregnation-lifting was dried at room temperature for 5 min, and then dried in an oven at 100℃ for 1 h;

[0065] (5) The dried sample is heat-treated in a muffle furnace to obtain a TiO2 film with a surface structure similar to that of a lotus leaf. The heat treatment conditions are: 550℃, 2h.

[0066] The main difference compared to Example 1 is that the aging step has been removed.

[0067] Figure 4 The SEM images show that the film prepared in Comparative Example 1 did not form a micro-nano hierarchical structure, and dense cracks appeared on the film, which also shows the key role of the aging step in preparing TiO2 films with a lotus leaf-like surface structure.

[0068] Comparative Example 2

[0069] (1) Add 2.5 mL of tetrabutyl titanate and 0.67 mL of acetylacetone to a 50 mL beaker, seal the mouth of the beaker with plastic wrap, and stir magnetically for 30 min. The system will then react to produce a complex of tetrabutyl titanate.

[0070] (2) Open the plastic wrap, add 10 mL of ethanol to the system while stirring, then add 10 mL of water, and seal the cup with plastic wrap again.

[0071] (3) Make some small holes in the plastic wrap to allow air to pass through the inside and outside of the beaker. Let the tetrabutyl titanate complex solution system age at room temperature for 4 days. The resulting mixture system is used as TiO2 sol for impregnation-lifting.

[0072] (4) Next, a thin film was prepared on the glass slide substrate using the dip-coating technique at a speed of 28 cm / min;

[0073] (5) The sample obtained by impregnation-lifting was dried at room temperature for 5 min and then dried in an oven at 100℃ for 1 h.

[0074] (6) The dried sample is heat-treated in a muffle furnace to obtain a TiO2 film with a surface structure similar to that of a lotus leaf. The heat treatment conditions are: 550℃, 2h.

[0075] Compared with Example 1, the main difference is that the order of steps (2) and (3) has been changed.

[0076] The thin film prepared in Comparative Example 2 did not form a micro-nano hierarchical structure, which shows that the order of steps (2) and (3) is important for preparing TiO2 thin films with a lotus leaf-like surface structure.

Claims

1. A method for preparing a TiO2 thin film with a lotus leaf-like surface structure, characterized in that, Using a sol containing tetrabutyl titanate complex and TiO2 particles as a precursor, a hierarchical structure surface resembling the integrated dispersed and continuous phases of a lotus leaf is synthesized through a one-step dip-coating process; the process includes the following steps: (1) Preparation of TiO2 sol for impregnation-lifting: Tetrabutyl titanate and acetylacetone were added to a beaker, the mouth of the beaker was sealed with plastic wrap, and the reaction was carried out under magnetic stirring to produce a complex of tetrabutyl titanate; some small holes were punched in the plastic wrap to allow air to circulate inside and outside the beaker, and the tetrabutyl titanate complex system was aged at room temperature for 4-5 days; under stirring, ethanol and water were added to the tetrabutyl titanate complex system in sequence, and the resulting mixture system was used as TiO2 sol for impregnation-lifting. (2) Preparation of TiO2 thin film: Thin film was prepared on glass slide substrate by dip-coating technique at a speed of 28 cm / min; After drying, the sample obtained by dip-coating is heat-treated to obtain a TiO2 film with a surface structure similar to that of a lotus leaf.

2. The method for preparing a TiO2 thin film with a lotus leaf-like surface structure according to claim 1, characterized in that, In step (1), the volume ratio of tetrabutyl titanate, acetylacetone, ethanol and water is 2.5:0.67:9-11:9-11.

3. The method for preparing a TiO2 thin film with a lotus leaf-like surface structure according to claim 1, characterized in that, The drying conditions for step (2) are: dry at room temperature for 5 minutes, and then dry in an oven at 100°C for 1 hour.

4. The method for preparing a TiO2 thin film with a lotus leaf-like surface structure according to claim 1, characterized in that, The heat treatment temperature in step (2) is 550℃ and the heat treatment time is 2h.

5. The TiO2 thin film with a lotus leaf-like surface structure prepared by the method according to any one of claims 1-4, characterized in that, The TiO2 film with a lotus leaf-like surface structure is composed of dispersed submicron-sized TiO2 microspheres and a continuous film substrate, with the dispersed TiO2 microspheres partially embedded in the film substrate; the TiO2 microspheres are composed of nano-sized TiO2 particles; the nano-size of the TiO2 particles is 10-30 nm.

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