Preparation method of ferroelectric nanometer PbTiO3 semiconductor material based on positive electrode polarization and application in photoelectrochemical cathodic protection

Abstract

The application discloses a preparation method of a ferroelectric nano PbTiO3 semiconductor material based on positive electrode polarization and application of the ferroelectric nano PbTiO3 semiconductor material in photoelectrochemical cathodic protection. The preparation method of the ferroelectric nano PbTiO3 semiconductor material comprises the following steps: (1) mixing TiO2, PbNO3 and an aqueous KOH solution to obtain a suspension, and then performing a hydrothermal reaction to obtain single-domain ferroelectric PbTiO3; (2) dispersing the single-domain ferroelectric PbTiO3 in ethanol to form a suspension; dropping the suspension on FTO glass, drying, and then performing first calcination; then dropping anhydrous alcohol solution of TiCl4, drying again, and then performing second calcination to obtain PTO after necking treatment; and finally performing positive electrode polarization in a saturated potassium chloride solution to obtain the ferroelectric nano PbTiO3 semiconductor material. The hydrothermal method is used to synthesize the ferroelectric nano material PbTiO3 which has a relatively negative conduction band potential, a large self-polarization intensity and a high Curie temperature; the internal electric field of the ferroelectric material effectively separates charges and holes, and promotes the ability of photoelectrochemical cathodic protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ferroelectric materials, in particular to a preparation method of ferroelectric nanometer PbTiO3 semiconductor material based on positive polarization and application thereof in photoelectrochemical cathodic protection. BACKGROUND

[0002] At present, cathodic protection technology has been widely used in the field of marine metal corrosion. Traditional cathodic protection technology is divided into impressed current cathodic protection and sacrificial anode cathodic protection. However, these technologies have disadvantages such as high energy consumption and potential environmental pollution. Therefore, photoelectrochemical cathodic protection technology with energy saving, environmental protection and economic advantages has attracted widespread attention. The principle of photoelectrochemical cathodic protection is as follows: coupling a semiconductor material with photoelectric effect with the metal to be protected. Under light conditions, the semiconductor material generates electrons and holes, inducing the flow of electrons to the metal to be protected, causing it to produce cathodic polarization, thereby preventing its corrosion. In order to enhance the protection effect of semiconductor materials on metals, how to improve the charge separation rate has been widely studied. Building heterojunctions between different semiconductor materials is one of the mainstream research methods. The principle is to effectively combine semiconductor materials with matching band gaps and interface structures to form built-in electric fields between different semiconductor materials to promote carrier separation. However, traditional heterojunctions also have their defects. Although the built-in electric field between semiconductor materials can promote carrier separation to some extent, due to the fact that the built-in electric field only exists at the surface, it can only promote carrier separation between interfaces, but not within the same material. In view of this problem, ferroelectric materials with inherent built-in electric fields have important research potential in this direction.

[0003] Lei et al. prepared TiO2 with a thickness of 800 nm on ITO conductive glass by liquid deposition method. After heat treatment at 300℃ and 500℃, the preferential orientation of the TiO2 thin film decreased, the optical band gap widened, and the crystal phase changed to anatase phase. The photoelectrochemical cathodic protection performance of the heat-treated TiO2 on 304 stainless steel (304SS) can reach a protection of 0.50V; In 2002, Ohko et al. deposited SrTiO3 on ITO conductive glass to study its protection performance on carbon steel. Under the irradiation of ultraviolet light, the SrTiO3 coating showed a more negative potential than the carbon steel. However, the existing photoanode itself has the shortcomings of too large band gap and positive bias of conduction band potential.

[0004] At present, ferroelectric materials are widely used in the field of photocatalysis to promote the separation of electrons and holes. Researchers have found that ferroelectric materials are a kind of pyroelectric materials with spontaneous polarization characteristics, and the polarization direction can be changed by an external electric field. In the ferroelectric lattice, the positive and negative charge centers do not coincide, which can generate an electric dipole moment, resulting in spontaneous polarization, forming different polarization surfaces, and promoting the directional migration of the corresponding carriers to the polarization surface. At present, due to similar principles, ferroelectric materials also have great application prospects in photoelectrode protection. However, there is still a lack of research on ferroelectric materials in photoelectrochemical cathodic protection technology. In 1950, Shirane et al. first developed and researched PbTiO3 materials. PbTiO3 material is a very typical ferroelectric material, which belongs to perovskite structure. PbTiO3 with perovskite phase hierarchical structure is an oxide functional material with special surface ferroelectric chemical effect. It has strong spontaneous polarization characteristics, stable crystal structure, easy to control morphology, large specific surface area, and its unique built-in electric field and surface electrostatic shielding effect can bring more surface active sites. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the ferroelectric nanomaterial PbTiO3 with a relatively negative conduction band potential, a large spontaneous polarization intensity and a high Curie temperature is synthesized by a hydrothermal method, and is coated on FTO to prepare a PbTiO3 photoanode (PTO). The PbTiO3 photoanode is polarized to obtain a forward polarization PbTiO3 photoanode (FP-PTO). The internal electric field of the ferroelectric material effectively separates the charges and holes, and promotes the ability of photoelectrode protection.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0007] The first aspect of the present application provides a preparation method of ferroelectric nanometer PbTiO3 semiconductor material, comprising the following steps:

[0008] (1) mixing TiO2, PbNO3 and KOH aqueous solution, stirring to obtain a suspension, and then performing a hydrothermal reaction; after the reaction, adjusting the pH of the suspension and centrifuging, washing the precipitate with deionized water, and drying to obtain single-domain ferroelectric PbTiO3;

[0009] (2) dispersing the single-domain ferroelectric PbTiO3 in ethanol, ultrasonic treatment to form a suspension; dropping the suspension on FTO glass, drying and performing first calcination, then adding TiCl4 anhydrous alcohol solution, drying again and performing second calcination, completing necking treatment to obtain PTO; finally, performing positive polarization in saturated potassium chloride solution to obtain ferroelectric nanometer PbTiO3 semiconductor material.

[0010] Preferably, the molar mass ratio of the TiO2 and PbNO3 is 1:(1.2-1.3); more preferably, the molar mass ratio of the TiO2 and PbNO3 is 1:1.25.

[0011] Preferably, in step (1), the pH of the suspension is adjusted to 6.5-7.5, close to neutral.

[0012] Preferably, in step (1), the temperature of the hydrothermal reaction is 180-220℃, and the time is 10-14h.

[0013] Preferably, in step (2), the concentration of the single-domain ferroelectric PbTiO3 in the suspension is 18-22mg / mL; and the drop-casting amount of the single-domain ferroelectric PbTiO3 suspension on the FTO glass per square centimeter area is 35-45μL.

[0014] Preferably, in step (2), the temperature of the first calcination is 400-500℃, and the time is 0.8-1.2h.

[0015] Preferably, in step (2), the concentration of the anhydrous alcohol solution of TiCl4 is 15-25mM; and the drop-casting amount of the anhydrous alcohol solution of TiCl4 on the FTO glass per square centimeter area is 20-30μL.

[0016] Preferably, in step (2), the temperature of the second calcination is 500-600℃, and the time is 0.8-1.2h.

[0017] Preferably, in step (2), the voltage of the positive electrode polarization is -0.7 to -1V.

[0018] The second aspect of the present application provides a ferroelectric nano PbTiO3 semiconductor material, which is prepared by the preparation method of the ferroelectric nano PbTiO3 semiconductor material.

[0019] The third aspect of the present application provides the application of the ferroelectric nano PbTiO3 semiconductor material in photoelectrochemical cathodic protection.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The positive polarization strategy is applied to the ferroelectric material with a relatively negative conduction band potential to construct FP-PTO, which can delay the irradiation recombination of electrons and holes, promote the consumption of photo-generated holes, and significantly improve the photoelectric conversion efficiency. Compared with other electrochemical methods and continuous ion layer adsorption reaction methods, the present application is easier to control and scale up.

[0022] The FP-PTO for photocathode protection of the present application can realize the absorption and utilization of visible light, and the photocathode protection performance in 3.5% NaCl solution is obviously improved compared with PTO. In 3.5wt% NaCl solution without adding hole trapping agent and under open light irradiation, the transient current of FP-PTO is 1.28μA / cm 2 , the transient current of PTO is 0.85μA / cm 2 , the photocurrent density is increased by 113%; the transient current of FP-PTO is 22μA / cm 2 , the transient current of PTO is 13μA / cm 2 , the photocurrent density is increased by 69.2%. The results show that the forward polarization has a promoting effect on the photoelectrochemical conversion efficiency of the photoanode. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a scanning electron microscope image of PTO;

[0024] Figure 2 is an XRD spectrum of PTO;

[0025] Figure 3 is the photocurrent density-time curve of PTO and FP-PTO without hole trapping agent and under intermittent light;

[0026] Figure 4 is the linear sweep voltammetry curve of PTO and FP-PTO without hole trapping agent and under intermittent light. DETAILED DESCRIPTION

[0027] The specific embodiments of the present application will be further described below. It should be noted that the description of the embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as there is no conflict.

[0028] The experimental methods in the following examples are all conventional methods unless otherwise specified, and the experimental materials used in the following examples are all commercially available unless otherwise specified.

[0029] Example 1

[0030] Monodomain ferroelectric PbTiO3 was prepared by hydrothermal method. Briefly, 1.600 g of TiO2 and 8.280 g of PbNO3 were added to 50 mL of 6 M KOH aqueous solution successively and stirred for 0.5 h. Then, the suspension was sealed in a stainless steel autoclave lined with polytetrafluoroethylene and heated at 200 °C for 12 h. The product suspension was neutralized to pH close to 7 with 1 M HNO3 solution, followed by centrifugation. The precipitate was washed with deionized water, followed by drying in an oven at 60 °C for 12 h to obtain monodomain ferroelectric PbTiO3.

[0031] The following procedure was used to prepare PTO-loaded FTO glass electrodes: An ethanol dispersion of monodomain ferroelectric PbTiO3 (20 mg / mL) was treated under ultrasonic conditions (20 min, 20 kHz, 500 W) to form a homogeneous suspension. Then, 80 μL of the above suspension was drop-casted onto FTO glass (10 mm x 20 mm). After drying at room temperature, the sample was calcined at 450 °C for 1 h. For electrodes used in PEC and PCP tests, PTO was completed by drop-casting 5 x 10 μL of 20 mM TiCl4 in anhydrous methanol, followed by drying in air for 30 min, and finally by necking treatment at 550 °C for 60 min with a ramping rate of 5 °C / min. FP-PTO was obtained by polarization in a saturated KCl solution at -1 V.

[0032] The micro-morphology of PTO was observed by scanning electron microscopy, as shown in Figure 1 PTO presented a dense distribution of a large number of nano-block structures.

[0033] The phase composition of PTO was tested by XRD, as shown in the XRD pattern of Figure 2 The peaks of PTO can be well corresponded to the standard card of PbTiO3, proving the existence of PbTiO3 in the prepared material. The diffraction peaks appearing at 21.36, 22.77, 31.42, 32.42, 39.15, 43.51, 46.50, 49.66, 51.71, 52.38, 55.29, 57.20, 65.58, 67.56 in the figure correspond to (001), (100), (101), (110), (111), (002), (200), (102), (201), (210), (112), (211), (202) and (003) of tetragonal PbTiO3 (JCPDS 78-0298). The XRD results show that PTO is successfully synthesized.

[0034] Effect test of photoelectrochemical cathodic protection technology of PTO and FP-PTO

[0035] PTO was tested using an electrochemical workstation for photocurrent density-time curves. The three-electrode method was used, with a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and PTO and FP-PTO as the working electrodes. Intermittent light irradiation was used to measure the photoinduced open-circuit potential change, demonstrating the photoelectrochemical cathodic protection performance of the materials. The intermittent light cycle was 25 seconds on and 25 seconds off in a 3.5wt% NaCl solution without a hole trap. A xenon lamp was used as the light source to simulate sunlight.

[0036] like Figure 3 As shown in Figure 2, in a 3.5 wt% NaCl solution without a hole trap and under light irradiation, the transient current of FP-PTO is 1.28 μA / cm 2 , the transient current of PTO is 0.85μA / cm 2 , and its photocurrent density increased by 51%. The results show that positive polarization has a promoting effect on the photoelectrochemical conversion efficiency of the photoanode.

[0037] PTO was tested using a three-electrode electrochemical workstation with a linear sweep voltammetry method using a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and PTO and FP-PTO as the working electrodes. Intermittent light irradiation was used to measure the photoinduced open-circuit potential change, demonstrating the photoelectrochemical cathodic protection performance of the material. The intermittent light cycle was 1s on and 1s off in a 3.5wt% NaCl solution without a hole trap. A xenon lamp was used as the light source to simulate sunlight.

[0038] like Figure 4 As shown in Figure 2, in a 3.5 wt% NaCl solution without a hole trap and under light irradiation, the transient current of FP-PTO is 22 μA / cm at a voltage of 1 V. 2 , the transient current of PTO is 13μA / cm 2 , and its photocurrent density increased by 69.2%.The results show that positive polarization has a promoting effect on the photoelectrochemical conversion efficiency of the photoanode.

[0039] As can be seen, the present invention utilizes a forward polarization method to construct an FP-PTO. Under light excitation, the material generates photogenerated electron-hole pairs due to the photovoltaic effect. The entire process achieves effective separation of the photogenerated electron-hole pairs, resulting in excellent photocathodic protection performance. Therefore, the FP-PTO constructed by the present invention offers the dual advantages of a simple method and high photoelectric separation efficiency. The photoanode material of the present invention can effectively solve the recombination of electrons and holes, laying the foundation for future industrialization.

[0040] The embodiments of the present application are described in detail above, but the present application is not limited to the described embodiments. Various changes, modifications, replacements, and variations of the embodiments can be made by those skilled in the art without departing from the principles and spirit of the present application, and still fall within the scope of the present application.

Claims

1. A method for preparing ferroelectric nano PbTiO3 semiconductor material, characterized in that: The following steps are involved: (1) TiO2, PbNO3 and KOH aqueous solution are mixed and stirred to obtain a suspension, and then subjected to a hydrothermal reaction; after the reaction, the pH of the suspension is adjusted and centrifuged, and the precipitate is washed with deionized water and dried to obtain a single-domain ferroelectric PbTiO3; (2) Dispersing single-domain ferroelectric PbTiO3 in ethanol and ultrasonically treating it to form a suspension; The suspension was drop-coated onto FTO glass, dried, and then calcined for the first time. Then, an anhydrous alcohol solution of TiCl4 was added, dried again, and calcined for the second time. After necking, the PbTiO3 photoanode was obtained. Finally, the ferroelectric nano-PbTiO3 semiconductor material was obtained by positive polarization in a saturated potassium chloride solution. In step (2), the concentration of the single-domain ferroelectric PbTiO3 in the suspension is 18-22 mg / mL; the drop coating amount of the single-domain ferroelectric PbTiO3 suspension per square centimeter area on the FTO glass is 35-45 μL; In step (2), the concentration of the anhydrous alcohol solution of TiCl4 is 15-25 mM; the drop amount of the anhydrous alcohol solution of TiCl4 per square centimeter area on the FTO glass is 20-30 μL; In step (2), the positive polarization voltage is -0.7 to -1 V; The ferroelectric nano PbTiO3 semiconductor material is used in photoelectrochemical cathode protection.

2. The method for preparing the ferroelectric nano PbTiO3 semiconductor material according to claim 1, characterized in that: The molar mass ratio of TiO2 and PbNO3 is 1:(1.2-1.3).

3. The method for preparing the ferroelectric nano PbTiO3 semiconductor material according to claim 1, characterized in that: In step (1), the temperature of the hydrothermal reaction is 180-220°C and the time is 10-14 h.

4. The method for preparing the ferroelectric nano PbTiO3 semiconductor material according to claim 1, characterized in that: In step (2), the temperature of the first calcination is 400-500°C and the time is 0.8-1.2 h.

5. The method for preparing the ferroelectric nano PbTiO3 semiconductor material according to claim 1, characterized in that: In step (2), the heating rate of the second calcination is 4-6 °C / min, the calcination temperature is 500-600 °C, and the calcination time is 0.8-1.2 h.

6. A ferroelectric nano PbTiO3 semiconductor material, characterized in that: The ferroelectric nano PbTiO3 semiconductor material is prepared by the preparation method of any one of claims 1 to 5.

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