S-type BiOI / g-C3N4 heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses an S-type BiOI / g-C3N4 heterojunction photocatalyst and a preparation method thereof. The preparation method specifically comprises the following steps: preparing three-dimensional porous g-C3N4 by adopting an alkali-assisted thermal polymerization method; biOI is grown on the surface of the three-dimensional porous g-C3N4 in situ, and the S-type BiOI / g-C3N4 heterojunction photocatalyst is obtained. The invention also discloses an application of the S type BiOI / g-C3N4 heterojunction photocatalyst in degradation of pollutants. According to the method, three-dimensional porous g-C3N4 is prepared through alkali-assisted thermal polymerization, and two-dimensional flaky BiOI is grown on the surface of the g-C3N4 through an in-situ microwave method, so that the S-type BiOI / g-C3N4 heterojunction photocatalyst is prepared, separation of photo-excitation electron-hole pairs is remarkably accelerated, photocatalytic degradation performance is improved, and the degradation rates of methylene blue, tetracycline and methyl orange can reach 91.7%, 91.9% and 97.7% respectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalyst preparation, and specifically relates to S-type BiOI / gC 3 N 4 Preparation method of heterojunction photocatalyst, also involving S-type BiOI / gC 3 N 4 Heterojunction photocatalysts and their applications. Background Art

[0002] The photocatalytic performance mainly depends on the photocatalyst. For the photocatalyst, the high utilization rate of solar energy and the photogenerated electron holes (e - -h + ) can promote the generation of more and more efficient photogenerated electron holes. In addition, photocatalysts with abundant active sites can promote light absorption and contact with pollutants, thus facilitating photocatalytic degradation reactions. Among many semiconductor photocatalysts, BiOI has a narrow band gap width (1.6-1.9 eV) and a high 4 cm -1 BiOI is one of the most promising photocatalysts due to its high absorption coefficient and excellent chemical stability, which results in excellent visible light response. However, BiOI is still affected by electron-hole pairs (e - -h + ) rapid recombination, which seriously limits its photocatalytic performance and practical application.

[0003] Constructing heterojunctions is considered to be an effective strategy to effectively promote the transfer and separation of photogenerated carriers. In particular, the S-type heterojunction composed of an oxidizing photocatalyst and a reducing photocatalyst can not only achieve rapid separation of photogenerated carriers, but also maintain strong redox activity of each component. Based on its high redox potential, BiOI plays the role of an oxidizing photocatalyst in the heterojunction, so a reducing photocatalyst with a matching band gap is essential for the successful construction of an S-type heterojunction. At the same time, constructing a heterojunction by in situ growing BiOI on another photocatalyst may be a better strategy to establish a uniform and tightly bound composite photocatalyst. Therefore, a photocatalyst with a matching band gap and capable of serving as a carrier is needed.

[0004] C 3 N 4 With suitable energy band, reduction potential and excellent photocatalytic performance, it is a suitable choice for constructing S-type heterojunction with BiOI. However, gC prepared by direct thermal polymerization 3 N 4 It is a block structure and is not a suitable carrier. 3 N 4, exposing more surface active sites, which is beneficial to the loading growth of BiOI and the construction of closely contacted BiOI / gC 3 N 4 S-type heterojunction photocatalyst. Summary of the invention

[0005] The object of the present invention is to provide S-type BiOI / gC 3 N 4 The preparation method of heterojunction photocatalyst significantly improves the separation of photoexcited electron-hole pairs and improves the photocatalytic degradation performance.

[0006] The technical solution adopted by the present invention is that S-type BiOI / gC 3 N 4 The preparation method of the heterojunction photocatalyst is specifically implemented according to the following steps: Step 1: Preparation of three-dimensional porous gC by base-assisted thermal polymerization 3 N 4 , denoted as CNx; Step 2: In the three-dimensional porous gC 3 N 4 In situ growth of BiOI on the surface to obtain S-type BiOI / gC 3 N 4 Heterojunction photocatalyst; specifically: Under stirring conditions, Bi(NO 3 ) 3 ·5H 2 O aqueous solution was added to CNx, KI aqueous solution was slowly added, stirred, and then transferred to a reactor for microwave treatment to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, namely S-type BiOI / gC 3 N 4 Heterojunction photocatalysts.

[0007] The present invention is also characterized in that: In step 1, specifically: Melamine and KOH were dissolved in deionized water and stirred for 2-5 hours, then the mixture was placed in an oven to dry, and the dried mixture was heated to 550°C at a rate of 2-5°C / min in an air atmosphere for 3-5 hours to obtain an alkali-etched three-dimensional porous gC 3 N 4 , denoted as CNx.

[0008] The drying temperature is 70~90℃ and the drying time is 8-12h.

[0009] The mass ratio of melamine to KOH is 15:1.

[0010] In step 2, the stirring time is 20-40 min; the microwave treatment temperature is 100° C., and the microwave treatment time is 20-40 min.

[0011] In step 2, Bi(NO 3 ) 3 ·5H 2 The concentrations of O aqueous solution and KI aqueous solution were both 0.9~1.2 mol / L; CNx, Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI is 72-434:485.07:166.

[0012] Another object of the present invention is to provide S-type BiOI / gC 3 N 4 S-type BiOI / gC prepared by the preparation method of heterojunction photocatalyst 3 N 4 Heterojunction photocatalysts.

[0013] The third object of the present invention is to provide S-type BiOI / gC 3 N 4 Application of heterojunction photocatalysts in pollutant degradation.

[0014] The beneficial effects of the present invention are: 1) The method of the present invention is to prepare three-dimensional porous gC by base-assisted thermal polymerization 3 N 4 , and two-dimensional BiOI flakes were grown on its surface by in-situ microwave method to prepare S-type BiOI / gC 3 N 4 Heterojunction photocatalyst significantly accelerates the separation of photoexcited electron-hole pairs, improves photocatalytic degradation performance, and the degradation rates of methylene blue, tetracycline and methyl orange can reach 91.7%, 91.9% and 97.7% respectively; 2) The CNx prepared by the present invention has a three-dimensional porous structure, which is convenient for serving as a carrier to in-situ grow BiOI on its surface and to contact with pollutants; 3) gC 3 N 4 It is a reducing photocatalyst. The N defects introduced by base-assisted thermal polymerization will adjust the electronic structure and reduce the band gap of CNx, making it more suitable for matching with the oxidized photocatalyst BiOI to construct an S-type heterojunction. 3 N 4 The zeta potential is negative, which is beneficial to the adsorption of Bi ions and the growth of BiOI; 4) The present invention adopts a microwave-assisted synthesis method for BiOI, which has the advantages of fast reaction rate, uniform reaction, and high product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a SEM image of the BiOI photocatalyst prepared in Comparative Example 1; Figure 2 This is the SEM image of the CNx photocatalyst prepared in Comparative Example 2; Figure 3 This is a SEM image of the BC-3 photocatalyst prepared in Example 3; Figure 4 EPR graphs of the photocatalysts prepared in Comparative Example and Example 3; Figure 5 UV–Vis / DRS graphs of the photocatalysts prepared in the comparative example and examples 1-4; Figure 6 Photocurrent diagram of the photocatalyst prepared in the comparative example and Example 3; Figure 7 Photodegradation performance of methylene blue by photocatalysts prepared in comparative example and examples 1-4; Figure 8 Photocatalyst photodegradation performance of tetracycline prepared in comparative example and examples 1-4; Fig. 9 Photodegradation diagram of methyl orange by the photocatalysts prepared in Comparative Example and Example 3. DETAILED DESCRIPTION

[0016] The present invention is described in detail below in conjunction with specific implementation modes and accompanying drawings.

[0017] The S-type BiOI / gC of the present invention 3 N 4 The preparation method of the heterojunction photocatalyst is specifically implemented according to the following steps: Step 1: Preparation of three-dimensional porous gC by base-assisted thermal polymerization 3 N 4 ; Specifically: Melamine and KOH were dissolved in deionized water and stirred for 2-5 hours. Then, the mixture was placed in an oven for drying at a temperature of 70-90°C for 8-12 hours. The dried mixture was heated to 550°C at a rate of 2-5°C / min in an air atmosphere for thermal polymerization for 3-5 hours to obtain an alkali-etched three-dimensional porous gC 3 N 4 , denoted as CNx; The mass ratio of melamine to KOH is 15:1; Step 2: In the three-dimensional porous gC 3 N 4 In situ growth of BiOI on the surface to obtain S-type BiOI / gC 3 N4 Heterojunction photocatalysts; Under stirring conditions, Bi(NO 3 ) 3 ·5H 2 O aqueous solution was added to CNx, KI aqueous solution was slowly added, stirred for 20-40 min, and then transferred to the reactor and microwaved at 100 ° C for 20-40 min to obtain 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, namely S-type BiOI / gC 3 N 4 Heterojunction photocatalysts; Bi(NO 3 ) 3 ·5H 2 The concentrations of O aqueous solution and KI aqueous solution were both 0.9~1.2 mol / L; CNx、Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI is 72-434:485.07:166; The preparation method of the present invention aims to solve the technical problems of the rapid recombination of photogenerated electrons and holes and poor photocatalytic performance of existing photocatalysts. The CNx prepared by alkali etching assisted thermal polymerization presents a three-dimensional structure, which is conducive to the in-situ growth of BiOI and contact with pollutants. At the same time, N defects are introduced to reduce the band gap of CNx, making it more suitable for matching with BiOI to construct an S-type heterojunction, thereby significantly accelerating the separation of photoexcited electron-hole pairs and improving the photocatalytic degradation performance.

[0018] Comparative Example 1 The preparation method of BiOI photocatalyst is as follows: 30 ml of Bi(NO 3 ) 3 ·5H 2 O aqueous solution and KI aqueous solution, and then to Bi(NO 3 ) 3 ·5H 2 The KI aqueous solution was slowly added to the O aqueous solution, stirred for 30 min, and then transferred to the reactor. The mixture was microwaved at 100 ° C for 30 min to obtain the BiOI photocatalyst. The SEM image of the BiOI photocatalyst prepared in Comparative Example 1 is as follows: Figure 1 As shown, BiOI is assembled from 40 nm thick sheets into a nanoflower-like morphology.

[0019] Comparative Example 2 Three-dimensional porous gC with nitrogen defects 3 N 4The preparation method is as follows: 15g melamine and 1g KOH are dissolved in 50ml deionized water, stirred for 2h, and then the mixture is placed in an oven at 80℃ for 10h. The dried mixture is heated to 550℃ at a rate of 3℃ / min for 4h in an air atmosphere to obtain alkaline-etched gC 3 N 4 , denoted as CNx. The SEM image of the CNx photocatalyst prepared in Comparative Example 2 is as follows Figure 2 As shown, thanks to the etching effect of KOH, CNx presents a three-dimensional porous structure, which is beneficial to the loading of BiOI, as well as the contact with pollutants and photocatalytic reaction during the photocatalytic process.

[0020] Example 1 15 g of melamine and 1 g of KOH were dissolved in 50 ml of deionized water and stirred for 4 h. Then, the mixture was placed in an oven and dried at 70 °C for 12 h. The temperature was raised to 550 °C at a rate of 5 °C / min for 5 h under air atmosphere to obtain alkaline-etched gC 3 N 4 , denoted as CNx. Prepare 30 ml of Bi(NO 3 ) 3 ·5H 2 O aqueous solution and KI aqueous solution, and then to Bi(NO 3 ) 3 ·5H 2 O aqueous solution was added with CNx, CNx, Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI was 72: 485.07: 166. The KI aqueous solution was slowly added and stirred for 30 min, then transferred to the reactor, and the mixture was microwaved at 100 °C for 20 min to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, which was recorded as BC-1.

[0021] Example 2 15 g of melamine and 1 g of KOH were dissolved in 50 ml of deionized water and stirred for 5 h. Then, the mixture was placed in an oven and dried at 90 °C for 8 h. The mixture was heated to 550 °C at a rate of 2 °C / min for 3 h under air atmosphere to obtain alkaline-etched gC 3 N 4 , denoted as CNx. Prepare 30 ml of 1.1 mol / L Bi(NO 3 ) 3 ·5H 2 O aqueous solution and KI aqueous solution, and then to Bi(NO 3 )3 ·5H 2 O aqueous solution was added with CNx, CNx, Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI was 163:485.07:166. The KI aqueous solution was slowly added, stirred for 30 min, and then transferred to the reactor. The mixture was microwaved at 100 °C for 40 min to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, which was recorded as BC-2.

[0022] Example 3 15 g of melamine and 1 g of KOH were dissolved in 50 ml of deionized water and stirred for 5 h. Then, the mixture was placed in an oven and dried at 80 °C for 9 h. The mixture was heated to 550 °C at a rate of 4 °C / min for 4 h under air atmosphere to obtain alkaline-etched gC 3 N 4 , denoted as CNx. Prepare 30 ml of 1 mol / L Bi(NO 3 ) 3 ·5H 2 O aqueous solution and KI aqueous solution, and then to Bi(NO 3 ) 3 ·5H 2 O aqueous solution was added with CNx, CNx, Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI was 279:485.07:166. The KI aqueous solution was slowly added, stirred for 30 min, and then transferred to the reactor. The mixture was microwaved at 100 °C for 30 min to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, which was recorded as BC-3.

[0023] SEM image of BC-3, such as Figure 3 As shown, it can be seen that the flake BiOI is loaded on the three-dimensional porous CNx surface, indicating the successful preparation of the BiOI / CNx S-type heterojunction photocatalyst. Figure 4 gC 3 N 4 , CNx and BC-3 EPR diagrams, it can be seen that relative to gC 3 N 4 , CNx and BC-3 have stronger peaks, and the weaker peak of BC-3 relative to CNx is due to the presence of BiOI in the composite photocatalyst, proving that KOH etching introduces nitrogen defects, which adjusts the electronic structure of CNx to make it more compatible with BiOI to construct an S-type heterojunction.

[0024] Example 4 15 g of melamine and 1 g of KOH were dissolved in 50 ml of deionized water and stirred for 4 h. Then, the mixture was placed in an oven and dried at 80 °C for 10 h. The temperature was raised to 550 °C at a rate of 3 °C / min for 4 h under air atmosphere to obtain alkaline-etched gC 3 N 4 , denoted as CNx. Prepare 30 ml of 1.2 mol / L Bi(NO 3 ) 3 ·5H 2 O aqueous solution and KI aqueous solution, and then to Bi(NO 3 ) 3 ·5H 2 O aqueous solution was added with CNx, CNx, Bi(NO 3 ) 3 ·5H 2 The mass ratio of O and KI was 434:485.07:166. The KI aqueous solution was slowly added, stirred for 30 min, and then transferred to the reactor. The mixture was microwaved at 100 °C for 30 min to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, which was recorded as BC-4.

[0025] Example 5 Figure 5 The DRS diagrams of the photocatalysts prepared in the comparative example and the example show that compared with comparative examples 1 and 2, the example has both the wide light response range of the BiOI photocatalyst prepared in comparative example 1 and the strong light absorption intensity of the CNx photocatalyst prepared in comparative example 2, among which BC-3 has the strongest light absorption intensity. Figure 6 The photocurrent diagrams of the photocatalysts prepared in Comparative Examples 1, 2 and Example 3 show that the photocurrent of BC-3 prepared in Example 3 is significantly enhanced compared with Comparative Examples 1 and 2. This is because the photogenerated carriers are effectively transferred and retained in the S-type heterojunction photocatalyst, which also indicates better photocatalytic degradation performance.

[0026] Example 6 In order to verify the gC prepared in the embodiment of the present invention 3 N 4 The degradation performance of the gC prepared in the embodiment of the present invention is investigated. 3 N 4 / BiOI heterojunction photocatalyst and the photocatalyst prepared in the comparative example were used to evaluate the degradation performance of the prepared materials against methylene blue, tetracycline and methyl orange. Weigh 20 mg of the photocatalyst respectively and add it to 50 mL of 20 mg / L methylene blue, tetracycline and methyl orange solution, put it into the photocatalytic test device, start stirring to make it act evenly, maintain the dark reaction for about 20 min until the adsorption and degradation equilibrium is reached, extract 3 mL of solution and record it as the test solution No. 0, then turn on the PLS-SXE300 / 300UV xenon light source to carry out the light reaction, and extract 3 mL of the solution at fixed intervals for absorbance data testing. Figure 7-9 The photodegradation performance graphs of methylene blue, tetracycline and methyl orange for the photocatalysts prepared in the comparative example and the embodiment respectively show that the pollutants are continuously degraded over time. It can be seen that compared with comparative examples 1 and 2, the BiOI / CNx S-type heterojunction photocatalysts prepared in the embodiments all show faster degradation rates, among which BC-3 has the best degradation performance, and the photodegradation rates of methylene blue, tetracycline and methyl orange at 60, 100 and 100 min can reach 91.7%, 91.9% and 97.7%, respectively.

Claims

1. A method for preparing an S-type BiOI / g-C3N4 heterojunction photocatalyst, characterized in that: Follow the steps below to implement it: Step 1: Prepare three-dimensional porous g-C3N4 by base-assisted thermal polymerization, denoted as CNx; Step 2: In-situ growth of BiOI on the three-dimensional porous g-C3N4 surface to obtain an S-type BiOI / g-C3N4 heterojunction photocatalyst; specifically: Under stirring conditions, Bi(NO3)3·5H2O aqueous solution was added to CNx, KI aqueous solution was slowly added, stirred, and then transferred to a reactor for microwave treatment to obtain a 2D / 3D BiOI / CNx S-type heterojunction photocatalyst, that is, an S-type BiOI / g-C3N4 heterojunction photocatalyst.

2. The method for preparing the S-type BiOI / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that: In the step 1, specifically: Melamine and KOH were dissolved in deionized water and stirred for 2-5 h, then the mixture was placed in an oven to dry, and the dried mixture was heated to 550 °C at a rate of 2-5 °C / min in an air atmosphere for thermal polymerization for 3-5 h to obtain alkali-etched three-dimensional porous g-C3N4, denoted as CNx.

3. The method for preparing the S-type BiOI / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that: The drying temperature is 70~90℃ and the drying time is 8-12h.

4. The method for preparing the S-type BiOI / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that: The mass ratio of melamine to KOH is 15:

1.

5. The method for preparing the S-type BiOI / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that: In the step 2, the stirring time is 20-40 min; the microwave treatment temperature is 100° C., and the microwave treatment time is 20-40 min.

6. The method for preparing the S-type BiOI / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that: In step 2, the concentrations of the Bi(NO3)3·5H2O aqueous solution and the KI aqueous solution are both 0.9-1.2 mol / L; the mass ratio of CNx, Bi(NO3)3·5H2O, and KI is 72-434:485.07:

166.

7. The S-type BiOI / g-C3N4 heterojunction photocatalyst prepared by the preparation method of the S-type BiOI / g-C3N4 heterojunction photocatalyst according to any one of claims 1 to 6.

8. Use of the S-type BiOI / g-C3N4 heterojunction photocatalyst according to any one of claims 1 to 6 in the degradation of pollutants.

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