A composite photocatalyst and preparation method thereof

Abstract

The present invention relates to the field of photocatalysis technology, and in particular to a composite photocatalyst and a preparation method thereof. 3 N 4 ) surface by in-situ conversion reaction 2 Se 3 A simple method for nanodots, the reaction is carried out by pre-preparing Bi 2 O 3 / g‑C 3 N 4 Precursor, and then through in-situ selenization reaction, Bi 2 O 3 Convert to Bi 2 Se 3 Nanodots, get Bi 2 Se 3 / g‑C 3 N 4 Composite photocatalyst. In the experiment of photocatalytic degradation of phenol, Bi 2 Se 3 / g‑C 3 N 4 The composite photocatalyst performs significantly better than Bi 2 O 3 / g‑C 3 N 4 Precursors, and single Bi 2 Se 3 and g‑C 3 N 4 . It also has good stability in N 2 When photoreduction is performed in the environment, Bi 2 Se 3 Shows good light corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and in particular to a composite photocatalyst and a preparation method thereof. Background Art

[0002] Graphitic carbon nitride (g-C3N4) is an important semiconductor visible light photocatalytic material. It has the characteristics of simple preparation, low cost, abundant raw material sources and good stability. It has received extensive attention in the field of photocatalysis. It also has good application prospects in photocatalytic fuel cells using it to prepare photoelectrodes. However, g-C3N4 has poor electrical conductivity and its photogenerated carriers are easy to recombine, resulting in poor photocatalytic performance when used alone.

[0003] Bi2Se3 can absorb visible light in the entire wavelength range, has good photoresponse activity, and has strong reduction ability. It is one of the few reduced semiconductors. However, its valence band position is relatively high, and its oxidation ability is very weak, so it is rarely used in the field of photocatalysis. If its advantages of strong reduction ability and strong light absorption ability can be fully utilized, it can have good application potential in the field of photocatalysis.

[0004] One of the effective methods to improve its photocatalytic performance is to use Bi2Se3, which can absorb all visible light, to construct a trapezoidal (S-type) heterojunction to effectively separate photogenerated carriers with strong redox ability. The existing preparation of Bi2Se3 / g-C3N4 heterojunctions is rarely reported. It is mainly prepared by physical methods, in which Bi2Se3 particles and g-C3N4 are mixed and ultrasonically treated. Only a part of Bi2Se3 is combined with g-C3N4, and the Bi2Se3 particles are large in size and have a small contact surface, so that the combination of the two semiconductors is not sufficient and tight. At the same time, since the trapezoidal heterojunction is not formed, the photogenerated holes on Bi2Se3 are still not consumed, and the photogenerated electrons on its conduction band cannot be effectively retained, and the enhancement effect of the heterojunction is insufficient. It is very difficult to prepare a composite catalyst with an S-type electron transport mode and Bi2Se3 and g-C3N4 fully and tightly combined. Summary of the invention

[0005] The purpose of the present invention is to provide a composite photocatalyst and a preparation method thereof, so as to solve the problem of insufficient and loose combination of two semiconductors in the existing g-C3N4 composite preparation technology.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a composite photocatalyst, comprising the following steps:

[0008] (1) g-C3N4, Bi(NO3)3 solution, ethanol, ethylene glycol and water are mixed, and the resulting mixture is subjected to light treatment under sealed conditions;

[0009] (2) After the light treatment, an oxidation reaction is carried out under air conditions to form a complex;

[0010] (3) Under a protective atmosphere, the obtained composite and selenium powder are subjected to heat treatment to generate a composite photocatalyst.

[0011] Preferably, in step (1), the dosage ratio of g-C3N4, Bi(NO3)3 solution, ethanol, ethylene glycol and water is 0.5g:(0.3-2.5)mL:1mL:(10-50)mL:(10-40)mL;

[0012] The concentration of the Bi(NO3)3 solution is 0.01-0.03 g / mL.

[0013] Preferably, the time of the light treatment in step (1) is 0.5 to 2 hours.

[0014] Preferably, the oxidation reaction time in step (2) is 1 to 3 hours.

[0015] Preferably, the mass ratio of g-C3N4 in step (1) to selenium powder in step (3) is 0.5:(0.1-0.5).

[0016] Preferably, the heat treatment temperature in step (3) is 240-360° C. and the time is 30-150 min.

[0017] The present invention also provides a composite photocatalyst obtained by the preparation method, wherein the composite photocatalyst is a Bi2Se3 / g-C3N4 photocatalyst.

[0018] The present invention provides a simple method for in-situ deposition of Bi2Se3 nanodots on the surface of g-C3N4, which has a simple operation method and is easy to control. In the obtained Bi2Se3 / g-C3N4 composite, the particle size of Bi2Se3 is in the nanoscale range (less than 100nm), and the size can be reduced to the quantum scale by changing the amount of Bi added. The Bi2Se3 nanodots are evenly distributed on the surface of g-C3N4 and tightly combined, and the bonding surface is the (003) dominant crystal plane of Bi2Se3, and the loading amount is adjustable below 10wt%. At the same time, through the full contact of the interface, a heterojunction of an S-type charge transfer mode is formed, so that carriers with strong redox ability can be retained. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1XRD spectra of Bi2Se3, g-C3N4 and Bi2Se3 / g-C3N4 obtained in Example 2;

[0020] Figure 2 TEM image of Bi2Se3 / g-C3N4 obtained in Example 2;

[0021] Figure 3 Visible light (λ>400nm) photocatalytic degradation curves of phenol when Bi2Se3, g-C3N4 and Bi2Se3 / g-C3N4 of Example 2 are used respectively;

[0022] Figure 4 This is the experimental situation of photoreduction comparison. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing a composite photocatalyst, comprising the following steps:

[0024] (1) g-C3N4, Bi(NO3)3 solution, ethanol, ethylene glycol and water are mixed, and the resulting mixture is subjected to light treatment under sealed conditions;

[0025] (2) After the light treatment, an oxidation reaction is carried out under air conditions to generate a composite (Bi2O3 / g-C3N4 precursor);

[0026] (3) Under a protective atmosphere, the obtained composite and selenium powder are subjected to heat treatment to generate a composite photocatalyst.

[0027] In the present invention, the dosage ratio of g-C3N4, Bi(NO3)3, ethanol glycol and water in the step (1) is 0.5g:(0.3-2.5)mL:1mL:(10-50)mL:(10-40)mL, preferably 0.5g:(1-2)mL:1mL:(20-40)mL:(15-30)mL; the concentration of the Bi(NO3)3 solution is 0.01-0.03g / mL, preferably 0.02g / mL.

[0028] In the present invention, the time of the light treatment in step (1) is 0.5 to 2 hours, preferably 1 to 1.5 hours.

[0029] In the present invention, the oxidation reaction time in step (2) is 1 to 3 hours, preferably 2 hours.

[0030] In the present invention, the mass ratio of g-C3N4 in step (1) to selenium powder in step (3) is 0.5:(0.1-0.5), preferably 0.5:(0.2-0.4).

[0031] In the present invention, the temperature of the heat treatment in step (3) is 240-360° C., preferably 260-290° C.; the time is 30-150 min, preferably 50-100 min, and more preferably 60-80 min.

[0032] The present invention also provides a composite photocatalyst obtained by the preparation method, wherein the composite photocatalyst is a Bi2Se3 / g-C3N4 photocatalyst.

[0033] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0034] Example 1

[0035] Add 0.5g g-C3N4 to a mixture of 10mL water and 50mL ethylene glycol, and ultrasonicate for 30min to obtain a light yellow suspension; dissolve Bi(NO3)3.5H2O in water to prepare a 0.02g / mL solution; add 0.3ml of the prepared Bi(NO3)3 aqueous solution and 1ml of ethanol to the g-C3N4 suspension, stir evenly, pour into a glass reaction bottle, cover with a lid and seal, irradiate with a xenon lamp for 1h under constant stirring until the color of the mixture changes to gray-black; stop irradiation, open the sealed lid of the glass reaction bottle, and continue stirring for 2h until the color of the mixture changes from gray-black to light yellow; centrifuge, wash, and dry the prepared powder, then put it into a tubular furnace together with 0.1g of selenium powder, and heat treat at 250℃ for 30min under N2 protection to obtain the final product.

[0036] Example 2

[0037] Add 0.5g g-C3N4 to a mixture of 10mL water and 50mL ethylene glycol, ultrasonicate for 30min, and obtain a light yellow suspension; add 1mL Bi(NO3)3 aqueous solution (0.02gl / mL) and 1ml ethanol, stir evenly; pour into a glass reaction bottle, cover with a lid and seal, irradiate with a xenon lamp for 1h under constant stirring until the color of the mixture changes from gray to black; stop irradiation, open the sealed lid of the glass reaction bottle, continue stirring for 2h, and wait until the color of the mixture changes from gray to yellow. Centrifuge, wash, and dry the prepared powder, then put it into a tube furnace together with 0.2g selenium powder, and heat treat at 350℃ for 60min under N2 protection to obtain the final product.

[0038] Example 3

[0039] Add 0.5g g-C3N4 to a mixture of 10mL water and 50mL ethylene glycol, ultrasonicate for 30min, and obtain a light yellow suspension; add 2.5mL Bi(NO3)3 aqueous solution (0.02g / mL) and 1ml ethanol, stir evenly; pour into a glass reaction bottle, cover with a lid and seal, irradiate with a xenon lamp for 1h under constant stirring until the color of the mixture changes from gray to black; stop irradiation, open the sealed lid of the glass reaction bottle, continue stirring for 2h, and wait until the color of the mixture changes from gray to yellow. Centrifuge, wash, and dry the prepared powder, then put it into a tube furnace together with 0.5g selenium powder, and heat treat at 300℃ for 120min under N2 protection to obtain the final product.

[0040] Example 4

[0041] Add 0.5g g-C3N4 to a mixture of 40mL water and 20mL ethylene glycol, ultrasonicate for 30min, and obtain a light yellow suspension; add 1mL Bi(NO3)3 aqueous solution (0.02g / mL) and 1ml ethanol, stir evenly; pour into a glass reaction bottle, cover with a lid and seal, irradiate with a xenon lamp for 1h under constant stirring until the color of the mixture changes from gray to black; stop irradiation, open the sealed lid of the glass reaction bottle, continue stirring for 2h, and wait until the color of the mixture changes from gray to yellow. Centrifuge, wash, and dry the prepared powder, then put it into a tube furnace together with 0.5g selenium powder, and heat treat at 300℃ for 30min under N2 protection to obtain the final product.

[0042] Example 5

[0043] Add 0.5g g-C3N4 to a mixture of 30mL water and 30mL ethylene glycol, ultrasonicate for 30min to obtain a light yellow suspension; add 1mL Bi(NO3)3 aqueous solution (0.02g / mL) and 1ml ethanol, stir evenly; pour into a glass reaction bottle, cover with a lid and seal, irradiate with a xenon lamp for 1h under constant stirring until the color of the mixture changes to gray-black; stop irradiation, open the sealed lid of the glass reaction bottle, continue stirring for 2h, and wait until the color of the mixture changes from gray-black to light yellow. Centrifuge, wash, and dry the prepared powder, then put it into a tube furnace together with 0.1g selenium powder, and heat treat at 250℃ for 120min under N2 protection to obtain the final product.

[0044] The products of each embodiment are tested, wherein:

[0045] Figure 1 XRD spectra of Bi2Se3, g-C3N4 and Bi2Se3 / g-C3N4 obtained in Example 2, Figure 1 This indicates that the Bi2Se in the sample is at nanoscale.

[0046] Figure 2TEM image of Bi2Se3 / g-C3N4 obtained in Example 2, Figure 2 This indicates that the sample is Bi2Se3 / g-C3N4, and the Bi2O3 in the precursor has been completely converted into Bi2Se3.

[0047] Figure 3 The visible light (λ>400nm) photocatalytic degradation curves of phenol using Bi2Se3, g-C3N4 and Example 2 Bi2Se3 / g-C3N4, respectively, Figure 3 This indicates that the sample has higher photocatalytic activity. In the figure, Bi2Se3 is a commercial product, and carbon nitride is homemade.

[0048] Figure 4 In order to compare the photoreduction experiments using the composite photocatalyst obtained in Example 2, a photocatalytic degradation experiment was conducted: a 0.1 mg / L phenol solution was used as the target, 50 mg of the sample was added to 15 ml of the phenol solution, and a photocatalytic degradation experiment was conducted under 60 W visible light LED irradiation. The solution was taken at regular intervals to measure the ultraviolet spectrum, and the change in phenol concentration was monitored by the intensity of the characteristic peak (269 nm) of phenol.

[0049] Figure 4 This indicates that the sample has high stability. Usually, the bismuth in bismuth-based photocatalysts is easily reduced and oxidized to form bismuth oxide in the absence of oxygen, which destroys the original composition of the bismuth-based photocatalyst.

[0050] In the stability experiment, the prepared Bi2O3 / g-C3N4 precursor and Bi2Se3 / g-C3N4 samples were placed in sealed bottles containing 20ml of ethylene glycol, 20ml of water and 1ml of ethanol mixed solvent, filled with nitrogen, and then irradiated with a xenon lamp for 1 hour. Then, the xenon lamp was turned off, the sealed cover was opened, and the samples were exposed to air for 3 hours. It can be seen that Bi2O3 / g-C3N4 first turned black and then turned white, indicating that Bi2O3 was reduced to metallic bismuth during the light exposure process, and then oxidized when exposed to air. However, Bi2Se3 / g-C3N4 did not turn white after being exposed to air, indicating that Bi2Se3 was not reduced to metallic bismuth under light, showing good stability.

[0051] The present invention can prepare a tightly bound Bi2Se3 / g-C3N4 complex with significantly enhanced photocatalytic activity and stability, thus overcoming the photocorrosion that is prone to occur in general bismuth-based photocatalysts.

[0052] The present invention uses a Bi2O3 / g-C3N4 complex as a precursor, and can effectively control the size of Bi2O3 by controlling the amount of bismuth nitrate added, so that it can be completely converted into Bi2Se3 (if commercially available bismuth oxide is used, it cannot be completely converted into Bi2Se3 due to its large particles). At the same time, since it is an in-situ conversion, the full and tight combination of Bi2Se3 and g-C3N4 is guaranteed. The currently reported Bi2Se3 / g-C3N4 uses a mixed ultrasonic method, which cannot achieve a full and tight combination of the two.

[0053] The present invention controls the temperature range to be 240-360° C., at which time the selenium powder does not react with g-C 3 N 4 .

[0054] As can be seen from the above embodiments, the present invention provides a simple method for in-situ deposition of Bi2Se3 nanodots on the surface of g-C3N4, which has a simple operation method and is easy to control. In the obtained Bi2Se3 / g-C3N4 composite, the Bi2Se3 particle size is in the nanoscale range (less than 100nm in size), and the size can be reduced to the quantum scale by changing the amount of Bi added. The Bi2Se3 nanodots are evenly distributed on the surface of g-C3N4 and tightly combined. The bonding surface is the (003) dominant crystal plane of Bi2Se3, and the loading amount is adjustable below 10wt%. At the same time, through the full contact of the interface, a heterojunction with an S-type charge transfer mode is formed, so that carriers with strong redox ability are retained. In the experiment of photocatalytic degradation of phenol, the performance of the Bi2Se3 / g-C3N4 composite photocatalyst is significantly better than that of the Bi2O3 / g-C3N4 precursor, as well as single Bi2Se3 and g-C3N4. At the same time, it has good stability. When photoreduced in a N2 environment, Bi2Se3 exhibits good light corrosion resistance.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a composite photocatalyst, characterized in that: The following steps are included: (1) g-C3N4, Bi(NO3)3 solution, ethanol, ethylene glycol and water are mixed, and the resulting mixture is subjected to light treatment under sealed conditions; (2) After the light treatment, an oxidation reaction is carried out under air conditions to form a complex; (3) heat-treating the obtained composite and selenium powder under a protective atmosphere to generate a composite photocatalyst; The mass ratio of g-C3N4 in step (1) to selenium powder in step (3) is 0.5:(0.1-0.5); The heat treatment temperature in step (3) is 240-360°C and the time is 30-150 min; The composite photocatalyst is a Bi2Se3 / g-C3N4 photocatalyst.

2. The preparation method according to claim 1, characterized in that: In the step (1), the usage ratio of g-C3N4, Bi(NO3)3 solution, ethanol, ethylene glycol and water is 0.5g:(0.3-2.5)mL:1mL:(10-50)mL:(10-40)mL; The concentration of the Bi(NO3)3 solution is 0.01~0.03g / mL.

3. The preparation method according to claim 1 or 2, characterized in that: The time of the light treatment in step (1) is 0.5 to 2 hours.

4. The preparation method according to claim 3, characterized in that: The oxidation reaction time in step (2) is 1 to 3 hours.

5. The composite photocatalyst obtained by the preparation method according to any one of claims 1 to 4.

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