CN108031481B - A kind of ultra-thin bismuth oxyhalide nanosheet photocatalyst with silver intercalation exfoliation and preparation method thereof - Google Patents

Abstract

The invention discloses an ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst prepared by a silver intercalation stripping method and an application thereof, belonging to the field of photocatalysis. Taking advantage of the strong force between Ag ⁺ and ^Cl‑ , Ag ⁺ was inserted between the [Bi ₁₂ O ₁₇ ] ²⁺ and [Cl ₂ ] ^2‑ layers of bulk Bi ₁₂ O ₁₇ Cl ₂ through self-assembly in aqueous ethanol solution , and the photoreduction method is used to convert Ag ⁺ into Ag simple substance. As the Ag simple substance nucleates and grows in the interlayer, the bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets are gradually peeled off into ultrathin nanosheets. The preparation method has the advantages of simple operation, low cost of raw materials, less energy consumption, large-scale preparation, etc., and belongs to the green synthesis technology.

Description

A silver-intercalated and exfoliated ultrathin bismuth oxyhalide nanosheet photocatalyst and its preparation method

technical field

The invention belongs to the field of photocatalysis, and in particular relates to an ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst prepared by silver intercalation exfoliation, a preparation method and application thereof.

Background technique

With the rapid development of our country's economy, the problems of environmental degradation and energy shortage are becoming increasingly prominent. Solving these two problems is an urgent need for our country to achieve sustainable development, improve people's quality of life and ensure national security. Photocatalytic technology is considered to be one of the ideal solar energy conversion technologies, and it has potential advantages in the fields of water treatment, air purification, hydrogen production from water splitting, _CO2 reduction, and artificial photosynthesis.

Two-dimensional nanomaterials are a new class of materials with infinite planar dimensions, which can be considered as materials obtained by thinning three-dimensional crystals to a thickness of one or several atomic layers. Because of its unique thickness size and structural characteristics, it can not only enhance the intrinsic properties of the material, but also may produce some new features that are not available in bulk materials.

Photocatalytic redox reactions are carried out on the surface, so the exposed surface structure of semiconductor materials has a decisive effect on its photocatalytic activity. Two-dimensional nanomaterials have the characteristics of high specific surface area, high exposure ratio of active sites, and extremely small migration distance of bulk photogenerated carriers, all of which make two-dimensional materials have potential application prospects in photocatalytic applications.

The preparation methods of layered two-dimensional nanomaterials that have been reported so far mainly include mechanical exfoliation, liquid phase ultrasonic exfoliation, and intercalation exfoliation. Among them, the mechanical peeling method has low yield and difficult to control the size; the liquid phase peeling method also has the disadvantages of low peeling efficiency and difficult to control the thickness. However, the yield of the intercalation and exfoliation method is relatively high, and the thickness of the synthesized nanosheets is controllable. Li J, Zhan G, Yu Y, et al. Superior visible light hydrogen evolution of Janus bilayer junctions via atomic-level charge flow steering[J]. Nature communications, 2016, 7. ), but lithium intercalation reagents are usually metal-organic compounds, which are very active and easily react with water and oxygen, which makes the reaction conditions relatively harsh. Therefore, it is necessary to find more suitable intercalation species, and the silver intercalation stripping method can solve these problems well.

Contents of the invention

The purpose of the invention is to provide a method for preparing ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet material by silver intercalation to address the deficiencies in the prior art.

To solve the above object, the present invention adopts the following technical solutions:

(1) Preparation of bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets

Add _BiCl3 into weakly acidic ethanol aqueous solution at room temperature, then add polyethylene glycol 4000, and after complete dissolution, add strong alkaline ethanol aqueous solution drop by drop to obtain a mixed solution, stir evenly, transfer to a polytetrafluoroethylene reaction kettle, and heat up To 80 ℃ ~ 160 ℃, keep warm for 2 ~ 5 h; the obtained product is naturally cooled to room temperature, washed with deionized water and absolute ethanol several times respectively, collected by centrifugation, and dried in vacuum at 60 ~ 80 ℃;

(2) Preparation of ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets

The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in step (1) were ultrasonically dispersed in ethanol aqueous solution, and then AgNO ₃ ethanol aqueous solution was added dropwise under light-shielding conditions, stirred at room temperature for 0.5–2 h, and then illuminated (λ >= 420 nm) for 0.5~2 h, washed with deionized water after centrifugation, and dried in vacuum to prepare ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst;

The volume ratio of ethanol and water in the aqueous ethanol solution is 1:1;

The weakly acidic ethanol aqueous solution described in step (1) is an ethanol aqueous solution adjusted by dilute HCl, pH=4~6;

The strong alkaline ethanol aqueous solution described in step (1) is an ethanol aqueous solution adjusted by NaOH or KOH, pH=12~14.

The mass fraction of silver in the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets prepared in step (2) is 0.1 %~1 %.

The thickness of bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets is 20~40 nm.

The thickness of ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets is 3~4 nm.

The invention provides the application of the above-mentioned ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst and the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst prepared by the above preparation method in degrading rhodamine B. This application includes the following steps: the ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst and rhodamine B solution are mixed and adsorbed under light-proof conditions; the mixed solution is illuminated by a 300 W xenon lamp (λ>= 420 nm) under the photocatalytic reaction for 5 min to 60 min to complete the degradation of rhodamine B.

The innovation of the present invention lies in: the present invention proposes for the first time the preparation of ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheets by the method of silver intercalation and exfoliation. This method not only realizes the thickness control, but also successfully introduces simple silver between the nanosheets, Under the coupling effect of these two factors, the photocatalytic performance of ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets is greatly improved compared with that of bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets.

Compared with the prior art, the present invention has the advantages of:

(1) For the first time, the present invention uses the strong force between Ag ⁺ and Cl ^- to insert Ag ⁺ into bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets [Bi ₁₂ O ₁₇ ] ²⁺ and [Cl ₂ ] ^2- interlayer, and adopt photoreduction method to convert Ag ⁺ into Ag simple substance, as the Ag simple substance nucleates and grows in the interlayer, the interlayer spacing of Bi ₁₂ O ₁₇ Cl ₂ nanosheets becomes larger , the interlayer van der Waals force will also be weakened, thereby achieving the effect of peeling off Bi ₁₂ O ₁₇ Cl ₂ nanosheets. The preparation method has the advantages of simple operation, low raw material cost, less energy consumption, large-scale preparation, etc., and belongs to the green synthesis technology;

(2) The ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst of the present invention has an excellent photocatalytic effect. Under the same conditions, the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst degrades 87.2% rhodan within 20 minutes Ming B, while the bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst only catalytically degrades 38.0% within 20 min.

Description of drawings

Figure 1 is the field emission scanning electron microscope (FE-SEM) of the bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets (BOC) and ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets (U-BOC) synthesized in Example 1 .

Fig. 2 is an atomic force microscope (AFM) image of bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets (BOC) and ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets (U-BOC) synthesized in Example 1.

3 is the X-ray powder diffraction pattern (XRD) of the bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets (BOC) and ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets (U-BOC) synthesized in Example 1.

Fig. 4 is the photocatalytic degradation rate diagram of rhodamine B for bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets (BOC) and ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets (U-BOC) synthesized in Example 1.

Detailed ways

In order to describe the present invention more clearly and completely, some of the enumerated embodiments will be specifically described below in conjunction with the drawings of the invention.

Example 1

preparation:

Step 1: Preparation of Bulk Bi ₁₂ O ₁₇ Cl ₂ Nanosheets (BOC)

(1) Preparation of reaction precursor solution: Dissolve 2.5 mmol BiCl ₃ in 25 mL weakly acidic ethanol aqueous solution (pH=5) at room temperature, then add 1 g polyethylene glycol 4000, after complete dissolution, add 25 mL dropwise Strong alkaline ethanol aqueous solution (pH=13), fully stirred for 1 h to form a reaction precursor solution;

(2) Hydrothermal reaction: The obtained precursor solution was transferred to a 100 mL polytetrafluoroethylene reactor, heated to 120 °C, and kept for 3 h;

(4) Washing and collection of precipitates: naturally cool the obtained product to room temperature, wash several times with deionized water and absolute ethanol respectively, collect the precipitate by centrifugation, and vacuum dry at 60°C to obtain the block Bi ₁₂ O ₁₇ Cl ₂ Nanosheets.

Step 2: Preparation of Ag-intercalated ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets (U-BOC)

The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in the first step were ultrasonically dispersed in 50 mL ethanol aqueous solution, and 50 mL AgNO ₃ ethanol aqueous solution (90 mg/L) was added dropwise in the dark, and stirred for 2 h , placed under a xenon lamp equipped with a 420 nm filter to illuminate for 1 h, the obtained product was centrifuged, washed with deionized water, and dried in vacuum at 60°C to obtain Ag-intercalated ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets .

application:

Weigh 30 mg of ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst, add it to 60 mL, 5 mg/L Rhodamine B solution, stir and adsorb for 1 h under dark conditions, and use a filter equipped with 420 nm A xenon lamp was used to provide a visible light source to study the degradation of Rhodamine B. As shown in Figure 4, under the same conditions, the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst degraded 87.2% rhodamine B within 20 min, while the Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst degraded 87.2% of rhodamine B within 20 min. Only 38.0% of the catalyst was degraded.

Example 2

The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets and the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in Example 1 were characterized by field emission scanning electron microscopy, and the results are shown in Figure 1 . It can be seen that after the silver intercalation treatment, the thickness of the Bi ₁₂ O ₁₇ Cl ₂ nanosheets has changed significantly, and the thickness of the ultrathin nanosheets is within 10 nm.

Example 3

The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets and ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in Example 1 were characterized by atomic force microscopy, as shown in FIG. 2 . It can be seen from the figure that the thickness of bulk Bi ₁₂ O ₁₇ Cl ₂ thick nanosheets is between 20 and 40 nm, while the thickness of nanosheets obtained after silver intercalation treatment is about 3 to 4 nm. It proves that ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets can be prepared by silver intercalation exfoliation method.

Example 4

The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets and the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in Example 1 were analyzed by X-ray diffraction, and the results are shown in FIG. 3 . It proves that the silver intercalation stripping method proposed by the present invention does not change the crystal form of Bi ₁₂ O ₁₇ Cl ₂ , but the peak intensity of the {0012} plane is significantly enhanced, which may be due to more exposed {0012} planes during the thinning process of the nanosheets surface, resulting in a change in the orientation of the crystal plane.

The above descriptions are only preferred embodiments of the present invention, and are only used to illustrate the present invention, and are not intended to limit the scope of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention without any creative effort.

Claims (4)

1. a kind of silver intercalation exfoliation ultrathin Bi ₁₂ O ₁₇ Cl ₂ the preparation method of nanosheet photocatalyst, it is characterized in that: utilize the strong force between Ag ⁺ and ^Cl- , in aqueous ethanol by self-assembly Ag ⁺ is inserted between the [Bi ₁₂ O ₁₇ ] ²⁺ and [Cl ₂ ] ^2- layers of the bulk Bi ₁₂ O ₁₇ Cl ₂ , and the Ag ⁺ is converted into Ag simple substance by photoreduction method, with the Ag simple substance in the layer Inter-nucleation and growth, the bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets are gradually peeled off into ultrathin nanosheets; including the following two steps: (1) Preparation of bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets Add 2.5 mmol BiCl3 to ₂₅ mL of weakly acidic ethanol aqueous solution, then add 1 g of polyethylene glycol 4000, and after complete dissolution, add 25 mL of strong alkaline ethanol aqueous solution drop by drop to obtain a mixed solution, stir well, and transfer to polytetrafluoroethylene In an ethylene reactor, carry out hydrothermal reaction; the obtained product is naturally cooled to room temperature, washed several times with deionized water and absolute ethanol respectively, collected by centrifugal precipitation, and dried; (2) Preparation of ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets The bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheets obtained in step (1) were ultrasonically dispersed in 50 mL ethanol aqueous solution, and then AgNO ₃ ethanol aqueous solution was added dropwise under light-shielding conditions, and stirred and illuminated at room temperature to realize the peeling of the block into Nanosheets; after centrifugation, the product was washed with deionized water and dried in vacuum to obtain an ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst; The pH of the weak acid ethanol aqueous solution described in step (1) is 4～6; The pH of the strong alkaline ethanol aqueous solution described in step (1) is 12 to 14; The thickness of the ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheets is 3-4 nm; the hydrothermal reaction temperature in step (1) is 80°C-160°C, and the hydrothermal reaction time is 2-5 h; The mass fraction of silver in the thin Bi ₁₂ O ₁₇ Cl ₂ nanosheets is 0.1 %~1 %. 2. the ultrathin Bi of a kind of silver intercalation stripping according to claim 1 ₁₂ O ₁₇ Cl ₂ the preparation method of nanosheet photocatalyst, it is characterized in that: in the ethanol aqueous solution, the volume ratio of ethanol and water is 1: 1. 3. A method for preparing a silver intercalation stripped ultrathin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst according to claim 1, characterized in that: step (1) bulk Bi ₁₂ O ₁₇ Cl ₂ nanosheet The drying temperature is 60°C~100°C. 4. The preparation method of a silver intercalation stripped ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet photocatalyst according to claim 1, characterized in that: step (2) ultra-thin Bi ₁₂ O ₁₇ Cl ₂ nanosheet During the peeling operation, the light wavelength is 200 nm~700 nm, and the peeling time is 0.5-3 h.