Preparation method of BiOCl with chiral structure

Abstract

The present invention belongs to the technical field of photocatalytic materials, and relates to a photocatalyst material of BiOCl with a chiral structure and a preparation method thereof. The first object of the present invention is to design a BiOCl with a chiral structure and morphology that has not been reported before. The second object of the present invention is to improve the photocatalytic activity of the existing BiOCl photocatalytic material through morphology regulation. The yield under 4 hours of light irradiation is 1.8 times that of the generally (001)-plane-exposed BiOCl.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and relates to a photocatalyst material of BiOCl with a chiral structure and a preparation method thereof. Background Art

[0002] Since Fujishima and Honda discovered the photocatalytic water splitting using a TiO2 semiconductor electrode under ultraviolet light irradiation in 1972, photocatalytic technology and the corresponding photocatalytic materials have been attracting much attention for many years. Especially in recent years, with the aggravation of environmental pollution, the technology of degrading wastewater by semiconductor photocatalysts has higher application value and development prospects, also because photocatalysis has very good compatibility with modern technologies. In other words, photocatalysis can be applied to many fields, such as environmental control or remediation and energy-related fields. As many scientists have speculated, the future applications of photocatalysis still need to continue to be explored. In fact, exploring new photocatalysts is as important as developing photocatalytic applications. Therefore, it is still crucial to find new photocatalysts and improve the obtained photocatalysts in order to make better and greater contributions to their practical applications.

[0003] The earliest developed TiO2 photocatalyst has the advantages of simple production and environmental friendliness, but its bandgap is too wide to be excited by visible light, which has certain limitations for practical applications. Therefore, it is of great significance to prepare a heart-shaped semiconductor photocatalytic material with a wide bandgap width. In recent years, bismuth halide compounds BiOX (X = Cl, Br, I) have attracted the attention of researchers due to their unique layered structure. In particular, the layered structure of BiOX, which is composed of [Bi2O2] plates intertwined with double halogen plates, results in the formation of a self-built internal electrostatic field, thus inducing excellent photocatalytic activity. Among BiOX, BiOBr has received extensive research due to its suitable bandgap and excellent visible-light photocatalytic activity.

[0004] Different crystal planes of the same substance have different atomic arrangements and electronic structures. Therefore, it is of great significance to change the morphology structure and preferentially expose the crystallographic planes with high photocatalytic activity. During the photocatalytic process, the surface electron structure differences caused by the exposure of different crystal planes have different effects on the migration of carriers, the adsorption of reactants, and the desorption of products. The unique crystal structure of BiOCl results in a close atomic packing on the (001) plane; while the (010) crystal plane has open channels, so BiOCl crystals have a high degree of anisotropy. Therefore, it still has the value of further research to improve the photocatalytic performance of BiOCl by regulating its crystal planes. Summary of the Invention

[0005] The first object of the present invention is to design a BiOCl with a chiral structural morphology that has not been reported before. The second object of the present invention is to improve the photocatalytic activity of the existing BiOCl photocatalytic material through morphology regulation.

[0006] The method for preparing the BiOCl photocatalytic material with a chiral structure of the present invention is carried out according to the following steps:

[0007] Step S1: Weigh 0.706 mmol of Bi(NO3)3·5H2O and 1.755 mmol of KCl. Dissolve Bi(NO3)3·5H2O in 20 ml of absolute ethanol to form solution A, and dissolve KBr in 5 ml of deionized water to form solution B.

[0008] Step S2: After placing solutions A and B on a magnetic stirring table and stirring for 10 minutes respectively, slowly drip the transparent solution B into the white suspension A, and then stir vigorously for 25 - 35 minutes.

[0009] Step S3: Slowly drip 1.2 ml of 15 mol / L concentrated hydrochloric acid into the mixed solution until the white turbid liquid becomes a colorless transparent solution, and stir for 5 - 15 minutes.

[0010] Step S4: Seal the beaker containing the mixed solution and transfer it to an oil bath preheated to 140 °C, and heat for 3 hours.

[0011] Step S5: During the process of natural cooling to room temperature, place the transparent liquid under magnetic stirring and add 50 - 55 ml of deionized water, adjust the pH value to 1.5 - 2, observe the generation of white precipitate, and continue to stir for 2 - 3 hours for full reaction.

[0012] Step S6: After continuing to stir for 2 - 3 hours for full reaction, collect the precipitate, wash it with deionized water and absolute ethanol for multiple times, and obtain the BiOCl sample with a chiral structure by centrifugation, which is called S - BOC.

[0013] The present invention has the following beneficial effects:

[0014] 1. The raw material Bi(NO3)3·5H2O used in the present invention is inexpensive, the KBr raw material is easily available and the dosage is low, so the comprehensive cost is low, which is suitable for industrial production. Moreover, the preparation process of the method of the present invention is simple and the energy consumption is low;

[0015] 2. The S - BOC photocatalyst prepared by the present invention has a morphology with a chiral structure that has not been reported before. It is composed of bismuth oxychloride flakes with a tetragonal phase structure, 3 - 30 μm in length and 1 - 2 μm in thickness, stacked into a 40 - 95 μm terraced grain, growing in the structure of a right - hand helical molecule, and converging into 4 spiral flower - like structures of 18 - 35 μm at the top

[0016] 3. The S-BOC photocatalyst prepared by the present invention is formed by the structural stacking of chiral molecules, which highly exposes the (001) plane and has higher photocatalytic activity. The photocatalytic performance of S-BOC was tested by photocatalytic hydrogen evolution, and the yield in 4 hours was 0.035 mmol / g.

[0017] The basic invention principle proposed by this invention patent:

[0018] The present invention utilizes that Bi(NO3)3 and KCl are both insoluble in ethanol and it is difficult to directly react to form BiOCl at room temperature. By adding a certain amount of concentrated hydrochloric acid to the mixed solution, the solubility of Bi(NO3)3 and KCl in the solution is increased, and they are more likely to participate in the reaction in the liquid phase environment.

[0019] Bi(NO3)3 + 3HCl → BiCl3 + 3H2O

[0020] Subsequently, it is maintained at a high temperature of 160 °C for a period of time to completely react Bi3+ and Cl- in the solution to form BiCl3. At the same time, the water bath condition facilitates the sealing treatment of the reaction vessel, preventing impurities such as water vapor in the air from entering the reaction system, ensuring the complete reaction of Bi3+ and Cl- to form BiCl3, and inhibiting the hydrolysis of BiCl3 under a high H+ concentration. Then, during the cooling process, a certain amount of deionized water is added to increase the pH value of the system and promote the transformation of BiCl3 into BiOCl.

[0021] Bi3+ + Cl- + 2H2O → Bi(OH)2Cl + 2H+

[0022] Bi(OH)2Cl → BiOCl↓ + H2O

[0023] The (001) plane of BiOCl is closely packed with atoms and mainly composed of Bi-Cl bonds. During the hydrolysis of BiCl3 to form BiOCl, the Bi-Cl bonds are preferentially formed, and the bond energy of the Bi-Cl bonds is greater than other bonds, causing BiOCl to grow along the (001) plane. At the same time, under acidic conditions, the growth of BiOCl along the (010) plane is inhibited, generating BiOCl with the (001) plane exposed. The XRD characterization results also show that the (001) plane of BiOCl is almost completely exposed; on the other hand, the crystal size of BiOCl generated under acidic conditions is relatively large, and they will stack together during the growth process. And the crystals of BiOCl have high anisotropy, which will cause the crystals of BiOCl to stack in a way that can preferentially expose the (001) plane. Description of the Drawings

[0024] Figure 1 X-ray diffraction pattern of the S-BOC photocatalyst prepared for the example;

[0025] Figure 2 Scanning electron microscope image of the S-BOC photocatalyst prepared for the example;

[0026] Figure 3 Scanning electron microscope image of the S-BOC photocatalyst prepared for the example;

[0027] Figure 4 Scanning electron microscope image of the S-BOC photocatalyst prepared for the example;

[0028] Figure 5 Particle size distribution calculation of the S-BOC photocatalyst prepared for the example;

[0029] Figure 6 Photocatalytic hydrogen production test of the S-BOC photocatalyst prepared in the example;

[0030] Figure 7 Photocatalytic electrochemical impedance diagram of the S-BOC photocatalyst prepared in the example;

[0031] Figure 8 Photocatalytic Mott Schottky curve diagram of the S-BOC photocatalyst prepared for the example; Detailed implementation manners

[0032] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided.

[0033] It should be noted that, without conflict, the features in the embodiments of the present invention can be combined with each other. The meanings of the terms "comprising", "including", "containing", and "having" are non-limiting, that is, other steps and other components that do not affect the results can be added. The above terms cover the terms "consisting of" and "consisting essentially of". Unless otherwise specified, the materials, equipment, and reagents are commercially available.

[0034] Specific embodiment: The bismuth oxychloride with a chiral structural morphology prepared in this embodiment is denoted as S-BOC, and the following steps are carried out:

[0035] Step S1: Weigh 0.706 mmol of Bi(NO3)3·5H2O and 1.755 mmol of KCl. Dissolve Bi(NO3)3·5H2O in 20 ml of absolute ethanol to form solution A, and dissolve KBr in 5 ml of deionized water to form solution B.

[0036] Step S2: After stirring solutions A and B on a magnetic stirring platform for 10 minutes respectively, slowly add the transparent solution B to the white suspension A, and then stir vigorously for 25 - 35 minutes.

[0037] Step S3: Slowly add 1.2 ml of 15 mol / L concentrated hydrochloric acid to the mixed solution until the white turbid liquid becomes a colorless transparent solution, and stir for 5 - 15 minutes.

[0038] Step S4: Seal the beaker containing the mixed solution and transfer it to an oil bath preheated to 140 °C, and heat for 3 hours.

[0039] Step S5: While allowing it to cool naturally to room temperature, place the transparent liquid under magnetic stirring and add 50 - 55 ml of deionized water, adjust the pH value to 1.5 - 2, observe the formation of white precipitate, and continue stirring for 2 - 3 hours for full reaction.

[0040] Step S6: After continuing to stir for 2 - 3 hours for full reaction, collect the precipitate, wash it multiple times with deionized water and absolute ethanol, and obtain the BiOCl sample with chiral structure by centrifugation, which is called S - BOC.

[0041] Figure 1 XRD diffraction pattern of the S - BOC photocatalyst prepared in the example. From Figure 1 It can be observed that all the diffraction peaks of the S - BOC photocatalyst prepared in the example are completely matched with the standard card of its tetragonal phase structure, and no characteristic peaks of other impurities are observed. At the same time, it has a higher characteristic of preferred orientation along the (001) plane than the comparative example.

[0042] Figure 2 Electron scanning microscope image of the S - BOC photocatalyst prepared in the example at 500 μm. It can be observed that the grain size of the S - BOC photocatalyst prepared in the example is relatively uniform, and generally grows relatively completely.

[0043] Figure 3 Electron scanning microscope image of the S - BOC photocatalyst prepared in the example at 100 μm. It can be observed that generally 4 spiral flower - like structures will be formed at the top of the S - BOC photocatalyst prepared in the example.

[0044] Figure 4 Electron scanning microscope image of the S - BOC photocatalyst prepared in the example at 50 μm. It can be observed that the terraced grains of the S - BOC photocatalyst prepared in the example are stacked by typical tetragonal - shaped bismuth oxychloride, grow in the structure of a right - hand helix molecule, and converge into 4 spiral flower - like structures with a size of 18 - 35 μm at the top. Because the crystal of bismuth oxychloride has high anisotropy and is easy to grow on the (001) plane under the condition of high H+ concentration, and this chiral structure enhances the tendency of bismuth oxychloride to grow preferentially, making the (001) plane of bismuth oxychloride fully exposed.

[0045] Figure 5Calculation of the particle size distribution of the S-BOC photocatalyst prepared for the examples. The length of the typical tetragonal flake-like bismuth oxychloride thin sheet is 3 - 30 μm, the thickness is 1 - 2 μm, and the stacked terraced grains are 40 - 95 μm. The spiral flower-like structure formed by bismuth oxychloride at the top is 18 - 35 μm.

[0046] Figure 6 Photocatalytic hydrogen production test of the S-BOC photocatalyst prepared for the examples. Under 4 hours of light irradiation, the yield of the examples is 1.8 times that of the comparative examples.

[0047] Figure 7 Photocatalytic electrochemical impedance diagram of the S-BOC photocatalyst prepared for the examples. The examples have a smaller radius of curvature than the comparative examples, proving that the examples have a higher carrier separation efficiency.

[0048] Figure 8 Photocatalytic Mott - Schottky curve diagram of the S-BOC photocatalyst prepared for the examples. The examples have a more negative conduction band than the comparative examples, proving that the examples have a higher HER reaction potential

[0049] The above content is only a basic description under the concept of the present invention. Any equivalent transformation of the technical solution of the present invention adopted by reading the specification of the present invention, as long as it does not depart from the spirit and scope of the technical solution of the present invention, shall fall within the protection scope of the present invention.

Claims

1. A preparation method of BiOCl with a chiral structure, characterized in that The tetragonal-phase bismuth oxychloride flakes are stacked into table-like grains with a size of 40 - 95 μm, growing in the structure of a right-handed helical molecule and converging into 4 helical flower-like structures with a size of 18 - 35 μm at the top; the specific steps of the preparation method include: Step S1: Weigh 0.706 mmol of Bi(NO3)3·5H2O and 1.755 mmol of KCl. Dissolve Bi(NO3)3·5H2O in 20 ml of absolute ethanol to form solution A, and dissolve KCl in 5 ml of deionized water to form solution B; Step S2: After stirring solutions A and B on a magnetic stirring table for 10 minutes respectively, slowly add the transparent solution B to the white suspension A, and then stir vigorously for 25 - 35 minutes; Step S3: Slowly add 1.2 ml of 15 mol / L concentrated hydrochloric acid to the mixed solution until the white turbid liquid becomes a colorless transparent solution, and stir for 5 - 15 minutes; Step S4: Seal the beaker containing the mixed solution and transfer it to an oil bath preheated to 140 °C, and heat for 3 hours; Step S5: During the process of natural cooling to room temperature, place the transparent liquid under magnetic stirring and add 50 - 55 ml of deionized water to adjust the pH value to 1.5 - 2. Observe the generation of white precipitate, and continue to stir for 2 - 3 hours for full reaction; Step S6: After continuing to stir for 2 - 3 hours for full reaction, collect the precipitate, wash it with deionized water and absolute ethanol for multiple times, and obtain the chiral-structured BiOCl sample by centrifugation, which is called S-BOC.

2. The preparation method of a chiral-structured BiOCl according to claim 1, characterized in that, The sheet-like bismuth oxychloride has a high exposure of the (001) plane; the sheet-like bismuth oxychloride is 3 - 30 μm in length and 1 - 2 μm in thickness.

3. The preparation method of a BiOCl with a chiral structure according to any one of claims 1-2, characterized in that, The described BiOCl with a chiral structure is applied to photocatalytic hydrogen production.

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