阅读说明：本技术 一种具有铁电性的光催化剂及其制备方法 (Photocatalyst with ferroelectricity and preparation method thereof ) 是由 晏海学 章曼 王亚琼 晏忠钠 张斗 于 2020-06-10 设计创作，主要内容包括：本发明公开了一种具有铁电性的光催化剂及其制备方法,其结构通式为RbBi<Sub>n-1</Sub>B<Sub>n</Sub>O<Sub>3n+1</Sub>,其中金属B为Nb,或为Nb和Ti,2≤n≤4,通过简单的固相合成和球磨得到颗粒尺寸为纳米级的光催化剂。本发明的光催化剂为纳米级,能缩短载流子迁移到反应位点的时间,提高反应活性；而且具有铁电性,其自发极化产生的内电场可提高光生电子和空穴的分离,防止复合；可进一步通过高能球磨使其表面被助催化剂WC包裹,光催化效率高。(The invention discloses a photocatalyst with ferroelectricity and a preparation method thereof, and the general formula of the structure of the photocatalyst is RbBi n‑1 B n O 3n+1 Wherein the metal B is Nb or Nb and Ti, n is more than or equal to 2 and less than or equal to 4, and the metal B is obtained by simple solid phase synthesis and ball millingTo photocatalysts having a particle size on the order of nanometers. The photocatalyst is nano-scale, can shorten the time for a current carrier to migrate to a reaction site, and improves the reaction activity; the material has ferroelectricity, and an internal electric field generated by spontaneous polarization of the material can improve the separation of photo-generated electrons and holes and prevent recombination; the surface of the catalyst can be further coated by a cocatalyst WC through high-energy ball milling, and the photocatalysis efficiency is high.)

1. A photocatalyst having ferroelectricity, characterized in that: the structural general formula of the photocatalyst is RbBi_{n- 1}B_nO_3n+1Wherein the metal B is Nb or Nb and Ti, and n is more than or equal to 2 and less than or equal to 4.

2. The photocatalyst having ferroelectricity according to claim 1, characterized in that: the metal B is Nb and Ti, and the molar ratio of Nb to Ti is 1: 2, n is 3.

3. The photocatalyst having ferroelectricity according to claim 1, characterized in that: the surface of the photocatalyst is also wrapped with WC, and RbBi is obtained by_n-1B_nO_3n+1Placing the mixture in a WC tank for high-energy ball milling to obtain the product.

4. The method for preparing the photocatalyst having ferroelectricity according to any one of claims 1 to 3, comprising the steps of:

(1) will Rb₂CO₃、BiO₂And an oxide of metal B, wherein Rb is mixed according to a set molar ratio₂CO₃Excessive amount is 1-5 wt%, and the mixed powder is obtained by wet grinding and drying for later use;

(2) carrying out solid-phase synthesis on the mixed powder obtained in the step (1) at high temperature, then carrying out dry grinding, and repeating the solid-phase synthesis for 1-2 times to obtain synthetic powder for later use;

(3) and (3) performing ball milling on the synthetic powder obtained in the step (2) to obtain nanoscale sample powder.

5. The method for preparing a photocatalyst having ferroelectricity according to claim 4, wherein: in the step (1), the wet grinding process parameters are as follows: the ball milling tank is a nylon tank, the ball milling medium is alcohol, the rotating speed is 100-; the drying temperature is 80-100 deg.C, and the drying time is 8-12 h.

6. The method for preparing a photocatalyst having ferroelectricity according to claim 4, wherein: in the step (2), the temperature of solid phase synthesis is 850-1000 ℃, and the time is 4-24 h; the dry milling process parameters are as follows: the rotating speed is 50-100rmp, and the ball milling time is 2-6 h.

7. The method for preparing a photocatalyst having ferroelectricity according to claim 4, wherein: in the step (3), the ball milling mode is common ball milling, and the technological parameters are as follows: the ball milling tank is a nylon tank, and the grinding ball is ZrO₂Ball, the ball milling medium is alcohol, the rotating speed is 300-_n-1B_nO_3n+1；

Or the ball milling mode is high-energy ball milling, and the technological parameters are as follows: the ball milling tank is a WC tank, and the grinding balls are ZrO₂The ball milling medium is water, the rotating speed is 800-_{n- 1}B_nO_3n+1。

Technical Field

The invention belongs to the technical field of photocatalysts, and relates to a ferroelectric photocatalyst and a preparation method thereof.

Background

Photocatalytic materials have been studied for nearly fifty years, and titanium dioxide (TiO) was discovered and reported by Japanese researchers from the first 1972₂) Since photocatalytic materials are used for photolyzing water, researchers are constantly working on improving the light conversion efficiency of existing materials and searching for new high-performance materials. The commonly used photocatalysts at present comprise oxides such as titanium dioxide, zinc oxide, tin oxide, zirconium dioxide and the like, and sulfide semiconductors. However, the oxide catalyst material has a large forbidden band width, and the sulfide catalyst has a small forbidden band width but unstable chemical properties, which limits its application in the field of photocatalysis. Therefore, the modification of the photocatalyst and the development of new catalysts have become the hot directions for the research of the photocatalytic technology.

The photocatalysis process mainly comprises the following three steps: absorption of light energy, separation and migration of photo-generated electrons and holes, surface adsorption and reaction. In recent years, ferroelectric materials have attracted much attention as novel photocatalytic materials. On one hand, the ferroelectric material forms an internal electric field due to spontaneous polarization, thereby promoting the separation of electrons and holes in the photocatalytic reaction; on the other hand, a depolarization field inside the ferroelectric material can cause band bending, resulting in a spatially selective reaction. Ferroelectricity has been used to improve the photocatalytic properties of barium titanate (BaTiO)₃) Bismuth ferrite (BiFeO)₃) Lead zirconate titanate (Pb (Zr)_0.3Ti_0.7)O₃) Etc. were confirmed. The shape of the photocatalytic material is controlled, and the photocatalytic efficiency can be effectively improved by using the cocatalyst. Nano materialThe material has higher specific surface energy, more reaction sites and higher reaction activity; meanwhile, the nano material has small particle size, so that the path for a carrier to migrate to a particle surface is short, the recombination probability is low, and the nano material is favorable for obtaining high photocatalytic performance. On the other hand, the promoters commonly used at present are noble metals such as Pt, Rh and Ru, but these materials are expensive and cannot be widely used.

In summary, the existing photocatalytic materials have the disadvantage of low photocatalytic efficiency due to easy recombination of photo-generated electrons and holes, and therefore, it is very important to develop a catalyst with high catalytic activity and a preparation method thereof.

Disclosure of Invention

Aiming at the defect that the existing photocatalytic material is low in photocatalytic efficiency due to the fact that photo-generated electrons and holes are easy to combine, the invention aims to provide the photocatalyst with ferroelectricity and the preparation method thereof.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

a ferroelectric photocatalyst with a general structural formula of RbBi_n-1B_nO_3n+1Wherein the metal B is Nb or Nb and Ti, and n is more than or equal to 2 and less than or equal to 4.

Preferably, the metal B is Nb and Ti, and the molar ratio of Nb to Ti is 1: 2, n is 3.

Preferably, the surface of the photocatalyst is further coated with WC, and RbBi is obtained by coating RbBi_n-1B_nO_3n+1Placing the mixture in a WC tank for high-energy ball milling to obtain the product.

The invention also provides a preparation method of the photocatalyst, which comprises the following steps:

(1) will Rb₂CO₃、BiO₂And an oxide of metal B, wherein Rb is mixed according to a set molar ratio₂CO₃Excess of1-5 wt%, wet grinding and drying to obtain mixed powder for later use;

(2) carrying out solid-phase synthesis on the mixed powder obtained in the step (1) at high temperature, then carrying out dry grinding, and repeating the solid-phase synthesis for 1-2 times to obtain synthetic powder for later use;

(3) and (3) performing ball milling on the synthetic powder obtained in the step (2) to obtain nanoscale sample powder.

Preferably, in the step (1), the wet milling process parameters are as follows: the ball milling tank is a nylon tank, the ball milling medium is alcohol, the rotating speed is 100-; the drying temperature is 80-100 deg.C, and the drying time is 8-12 h.

In the preferable scheme, in the step (2), the temperature of solid phase synthesis is 850-1000 ℃, and the time is 4-24 h; the dry milling process parameters are as follows: the rotating speed is 50-100rmp, and the ball milling time is 2-6 h.

In the preferable scheme, in the step (3), the ball milling mode is common ball milling, and the technological parameters are as follows: the ball milling tank is a nylon tank, and the grinding ball is ZrO₂Ball, the ball milling medium is alcohol, the rotating speed is 300-_n-1B_nO_3n+1；

Or the ball milling mode is high-energy ball milling, and the technological parameters are as follows: the ball milling tank is a WC tank, and the grinding balls are ZrO₂The ball milling medium is water, the rotating speed is 800-_n-1B_nO_3n+1. The inventors surprisingly found that by placing the synthetic powder after solid phase synthesis in a WC tank for high-energy ball milling, the surface of the synthetic powder can be wrapped by WC, and the WC can be used as a cocatalyst, so that the composition of photo-generated electrons and holes is effectively prevented, and the photocatalytic performance of the catalyst is greatly improved.

Compared with the prior art, the invention has the advantages that:

(1) the photocatalyst has ferroelectricity, and an internal electric field generated by spontaneous polarization of the photocatalyst can improve the separation of photo-generated electrons and holes and prevent recombination.

(2) The invention adopts a simple solid phase reaction method to synthesize the powder, can inhibit the generation of impure phases and prepare pure-phase powder.

(3) The photocatalyst is nano-scale, can shorten the time for a current carrier to migrate to a reaction site, and improves the reaction activity.

(4) After the photocatalyst is subjected to high-energy ball milling through a WC tank, the surfaces of particles are wrapped by WC, and the WC serving as a cocatalyst can effectively prevent the recombination of photoproduction electrons and holes, so that the photocatalytic efficiency is further improved.

(5) The photocatalyst can be widely used in the fields of hydrogen production by photolysis of water, organic matter degradation and the like.

Drawings

FIG. 1 is an X-ray diffraction pattern of a sample prepared in example 1;

FIG. 2 is an X-ray diffraction pattern of a sample prepared in example 2;

FIG. 3 is an X-ray diffraction pattern of a sample prepared in example 3;

FIG. 4 is an X-ray diffraction pattern of the sample prepared in comparative example 1;

FIG. 5 is a transmission electron micrograph of a sample prepared in example 3;

FIG. 6 is T of a sample obtained in example 2_cA curve;

FIG. 7 is a PE-IE curve for the sample prepared in example 2;

fig. 8 shows the forbidden band widths of the samples prepared in example 1, example 2 and comparative example 1.

FIG. 9 is the light absorption spectra of RhB solutions of the samples prepared in example 3 under different illumination times.

Detailed description of the preferred embodiments

The invention is further illustrated by, but is not limited to, the following examples.

Rhodamine B (RhB) photocatalytic degradation rate: preparing 10ppm RhB solution, taking 50ml as experimental solution, adding 150mg sample, and stirring for 30min on a magnetic stirrer. Sampling at 30min intervals with 300W xenon lamp as light source, placing in dark, centrifuging after 8 times, collecting supernatant, and measuring absorbance.

Analysis of ferroelectricity: sintering the sample at 900-1000 ℃ to obtain the ceramic sample. After a ceramic sample is ground, polished and silvered, an LCR tester is adopted to measure the change of dielectric constant and loss along with temperature; and measuring the ferroelectric hysteresis loop of the material by adopting a ferroelectric tester.

Optical performance analysis: and measuring the light absorption curve of the sample by using a UV-Vis spectrometer, and calculating the bandwidth of the sample by using a Tauc formula.