COMPOSITE PHOTOCATALYST OF CLAY BASED BISMUTH PHOSPHATE HOMOJUNCTIONS, PREPARATION METHOD AND APPLICATION THEREOF

Abstract

The invention discloses a composite photocatalyst of clay based bismuth phosphate homojunctions, preparation method and application thereof. The preparation method includes the following steps: S1, preparing a bismuth nitrate solution, sodium dihydrogen phosphate solution, and rectorite suspension; S2, adding bismuth nitrate solution into sodium dihydrogen phosphate solution, stirring thoroughly, then adding rectorite suspension for hydrothermal reaction, and finally separation, washing, and drying. This invention loads BiPO.sub.4 onto the rectorite while preparing BiPO.sub.4 through a one-step hydrothermal method. Due to the addition of rectorite, it can induce the BiPO.sub.4 heterophase homojunction structure composed of hexagonal phase and monazite monoclinic phase, improving the separation ability of electrons and holes. In addition, composite rectorite can enhance the adsorption performance of the catalyst, reduce the recombination rate of electron-hole pairs, and significantly improve the photocatalytic performance of the catalyst through the synergistic effect of the two aspects.

Claims

1. A preparation method of a composite photocatalyst of clay based bismuth phosphate homojunctions, including the following steps: S1, dissolving bismuth nitrate in a mixture of ethanol, ethylene glycol, and glycerol to obtain a bismuth nitrate solution; dissolving sodium dihydrogen phosphate in deionized water to obtain a sodium dihydrogen phosphate solution; dispersing rectorite in deionized water to obtain a rectorite suspension; S2, adding the bismuth nitrate solution obtained in step S1 dropwise to the sodium dihydrogen phosphate solution, stirring thoroughly, and then adding the rectorite suspension for hydrothermal reaction; finally, after separation, washing, and drying, the composite photocatalyst of clay based bismuth phosphate homojunctions is obtained.

2. The preparation method of claim 1, in the step S1, the rectorite includes at least one of organic pillared rectorite, Na-rectorite, and inorganic pillared rectorite.

3. The preparation method of claim 1, in the step S2, the temperature of the hydrothermal reaction is 155-165? C., and the reaction time is 2.5-3.5 h.

4. The preparation method of claim 1, in the step S2, the temperature of the hydrothermal reaction is 160? C., and the reaction time is 3 h.

5. The preparation method of claim 1, in the step S2, the molar ratio of bismuth nitrate to sodium dihydrogen phosphate is 1:(1-1.2); the mass of the rectorite is 30-50% of the mass of the bismuth phosphate BiPO.sub.4.

6. The preparation method of claim 1, in the step S1, the concentration of bismuth nitrate in the bismuth nitrate solution is 0.15-0.17 mol/L; the concentration of sodium dihydrogen phosphate in the sodium dihydrogen phosphate solution is 0.30-0.35 mol/L; the concentration of rectorite in the rectorite suspension is 0.01-0.02 g/m L.

7. The preparation method of claim 1, in the step S1, the volume ratio of ethanol, ethylene glycol, and glycerol is 5:3:2.

8. The preparation method of claim 1, in the step S2, after the reaction is completed, collecting the reaction sediment and washing it separately with anhydrous ethanol and deionized water.

9. A composite photocatalyst of clay based bismuth phosphate homojunctions obtainable by the preparation method of claim 1, wherein the bismuth phosphate BiPO.sub.4 has a heterophase homojunction structure composed of hexagonal phase and monazite monoclinic phase.

10. An application of the composite photocatalyst of clay based bismuth phosphate homojunctions according to claim 1, the composite photocatalyst of clay based bismuth phosphate homojunctions is applied to photocatalytic degradation of organic pollutants.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Accompanying drawings are for providing further understanding of embodiments of the disclosure. The drawings form a part of the disclosure and illustrate the principle of the embodiments of the disclosure along with the literal description. The drawings in the description below are merely some embodiments of the disclosure; a person skilled in the art can obtain other drawings according to these drawings without creative efforts. In the figures:

[0022] FIG. 1 shows the X-ray diffraction patterns of Na-rectorite, and samples prepared in Example 1-3 and Comparative Example 1, wherein the R in the figure represents Na-rectorite;

[0023] FIG. 2 shows the SEM image of samples, wherein FIG. 2(a) shows the SEM image of Na-rectorite, FIG. 2(b) shows the SEM image of samples prepared in Comparative Example 1, and FIG. 2(c) shows the SEM image of samples prepared in Example 2;

[0024] FIG. 3 shows the degradation efficiency image of Na-rectorite and samples prepared in Example 1-3 and Comparative Example 1 on tetracycline and Rhodamine B, wherein FIG. 3(a) shows the degradation efficiency image of tetracycline, and FIG. 3(b) shows the degradation efficiency image of Rhodamine B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] The following is a clear and complete description of the technical solution in conjunction with some embodiments of the present invention. Obviously, the following embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technical personnel in the art without creative labor fall within the scope of protection of the present invention.

Example 1

[0026] In this example, the preparation method of a composite photocatalyst of clay based bismuth phosphate homojunctions includes the following steps:

[0027] S1, dissolving 1.5960 g Bi(NO.sub.3).sub.3.Math.5H.sub.2O in a mixture of 10 mL ethanol, 6 mL ethylene glycol, and 4 mL glycerol to obtain a bismuth nitrate solution by sonicate for 10 min; dissolving 0.5133 g NaH.sub.2PO.sub.4.Math.2H.sub.2O in 10 mL deionized water, and stirring for 10 min to obtain a sodium dihydrogen phosphate solution; dispersing 0.3 g Na-rectorite in 30 mL deionized water, and stirring for 40 min to obtain a rectorite suspension.

[0028] S2, adding the bismuth nitrate solution obtained in step S1 dropwise to the sodium dihydrogen phosphate solution, stirring thoroughly, and then adding the rectorite suspension; then stirring at a speed of 500 r/min for 2 h and transfer the reaction liquid to a hydrothermal reactor; the hydrothermal condition is at 160? C. for 3 h; after the hydrothermal reaction is completed, cooling down and separating the gray precipitate; finally, washing the gray precipitate alternately with ethanol absolute and deionized water three times, and drying at 60? C. to obtain the composite photocatalyst of BiPO.sub.4/rectorite homojunctions, denoted as BiPO.sub.4/R-30% (the mass of Na-rectorite is 30% of the mass of BiPO.sub.4).

Example 2

[0029] The preparation method in Example 2 is basically the same as Example 1, except that in Step S1, the mass of Na-rectorite is 0.4 g, and the obtained composite photocatalyst of BiPO.sub.4/rectorite homojunctions is denoted as BiPO.sub.4/R-40% (the mass of Na-rectorite is 40% of the mass of BiPO.sub.4).

Example 3

[0030] The preparation method in Example 3 is basically the same as Example 1, except that in Step S1, the mass of Na-rectorite is 0.5 g, and the obtained composite photocatalyst of BiPO.sub.4/rectorite homojunctions is denoted as BiPO.sub.4/R-50% (the mass of Na-rectorite is 50% of the mass of BiPO.sub.4).

Example 4

[0031] In this example, the preparation method of a composite photocatalyst of clay based bismuth phosphate homojunctions includes the following steps:

[0032] S1, dissolving 1.5960 g Bi(NO.sub.3).sub.3.Math.5H.sub.2O in a mixture of 10 mL ethanol, 6 mL ethylene glycol, and 4 mL glycerol to obtain a bismuth nitrate solution by sonicate for 20 min; dissolving 0.5133 g NaH.sub.2PO.sub.4.Math.2H.sub.2O in 10 mL deionized water, and stirring for 5 min to obtain a sodium dihydrogen phosphate solution; dispersing 0.3 g organic pillared rectorite in 30 mL deionized water, and stirring for 30 min to obtain a rectorite suspension.

[0033] S2, adding the bismuth nitrate solution obtained in step S1 dropwise to the sodium dihydrogen phosphate solution, stirring thoroughly, and then adding the rectorite suspension; then stirring at a speed of 600 r/min for 2.5 h and transfer the reaction liquid to a hydrothermal reactor; the hydrothermal condition is at 165? C. for 2.5 h; after the hydrothermal reaction is completed, cooling down and separating the gray precipitate; finally, washing the gray precipitate alternately with ethanol absolute and deionized water three times, and drying at 60? C. to obtain the composite photocatalyst of BiPO.sub.4/rectorite homojunctions, denoted as BiPO.sub.4/R-30%.

Comparative Example 1

[0034] In this comparative example, the preparation method of a composite photocatalyst of clay based bismuth phosphate homojunctions includes the following steps:

[0035] S1, dissolving 1.5960 g Bi(NO.sub.3).sub.3.Math.5H.sub.2O in a mixture of 10 mL ethanol, 6 mL ethylene glycol, and 4 mL glycerol to obtain a bismuth nitrate solution by sonicate for 20 min; dissolving 0.5133 g NaH.sub.2PO.sub.4.Math.2H.sub.2O in 10 mL deionized water, and stirring for 5 min to obtain a sodium dihydrogen phosphate solution.

[0036] S2, adding the bismuth nitrate solution obtained in step S1 dropwise to the sodium dihydrogen phosphate solution, stirring thoroughly at a speed of 500 r/min for 2 h and transfer the reaction liquid to a hydrothermal reactor; the hydrothermal condition is at 160? C. for 3 h; after the hydrothermal reaction is completed, cooling down and separating the gray precipitate; finally, washing the precipitate alternately with ethanol absolute and deionized water three times, and drying at 60? C. to obtain the BiPO.sub.4 photocatalyst, denoted as BiPO.sub.4.

[0037] Compared with Example 1, the preparation method for this comparative example did not add Na-rectorite.

[0038] FIG. 1 shows the X-ray diffraction patterns of Na-rectorite, and samples prepared in Example 1-3 and Comparative Example 1, wherein the R in the figure represents Na-rectorite. From FIG. 1, it can be seen that the BiPO.sub.4 prepared in comparative Example 1 only has monazite monoclinic phase. The composite photocatalyts prepared in Examples 1-3 all contain two crystal phases: hexagonal phase and monazite monoclinic phase. With the increase of Na-rectorite addition, the diffraction peak intensity of the hexagonal phase increases. The reason is that BiPO.sub.4 is a hexagonal phase at room temperature, and the hexagonal phase will transform into monazite monoclinic phase at high temperature. The addition of rectorite inhibits the transformation process, so the prepared composite photocatalysts all contain two crystal phases, which form a heterophase homojunction structure. The characteristic diffraction peak of the rectorite in the composite photocatalysts prepared in Examples 1-3 disappears, indicating that the layered structure of the rectorite has been destroyed.

[0039] FIG. 2 shows the SEM image of samples, wherein FIG. 2(a) shows the SEM image of Na-rectorite, FIG. 2(b) shows the SEM image of BiPO.sub.4 prepared in Comparative Example 1, and FIG. 2(c) shows the SEM image of the composite photocatalyst of BiPO.sub.4/rectorite homojunctions prepared in Example 2. From the figure, it can be seen that the rectorite has a layered structure, while BiPO.sub.4 has a rod-shaped structure. After the combination of the two, the structure changed. The layered structure of rectorite was destroyed, and a spherical hexagonal phase BiPO.sub.4 was appeared, consistent with the XRD results.

[0040] Test 1

[0041] The composite photocatalyst of BiPO.sub.4/rectorite homojunctions prepared in Examples 1-3 and the BiPO.sub.4 photocatalyst prepared in Comparative Example 1 are used for photocatalytic degradation of tetracycline (TC) and Rhodamine B (RhB) to evaluate the photocatalytic activity of photocatalysts.

[0042] The process of TC degradation is as follows: the initial concentration of TC is 10 mg/L, the amount of photocatalyst used is 0.05 g, and a 420 nm visible light LED lamp is used as the light source. After adding the photocatalyst, it is first stirred under dark conditions until the photocatalyst reaches adsorption saturation on TC; Then turn on the light source, absorb a small amount of reaction solution at a certain interval. After centrifugation at 4000 r/min for 5 min, the absorbance of the reaction solution was measured by using a UV visible spectrophotometer to calculate the degradation rate of TC over a certain period of time, which can then evaluate the photocatalytic activity of the photocatalyst.

[0043] The process of RhB degradation is as follows: the initial concentration of TC is 10 mg/L, the amount of photocatalyst used is 0.05 g, and a 420 nm visible light LED lamp is used as the light source. After adding the photocatalyst, it is first stirred under dark conditions until the photocatalyst reaches adsorption saturation on RhB; Then turn on the light source, absorb a small amount of reaction solution at a certain interval. After centrifugation at 4000 r/min for 5 min, the absorbance of the reaction solution was measured by using a UV visible spectrophotometer to calculate the degradation rate of RhB over a certain period of time, which can then evaluate the photocatalytic activity of the photocatalyst.

[0044] FIG. 3 shows the degradation efficiency image of Na-rectorite and samples prepared in Example 1-3 and Comparative Example 1 on tetracycline and Rhodamine B, wherein FIG. 3(a) shows the degradation efficiency image of tetracycline, and FIG. 3(b) shows the degradation efficiency image of Rhodamine B. From FIG. 3, it can be seen that a single rectorite or BiPO.sub.4 has low degradation rates for tetracycline and Rhodamine B, while the BiPO.sub.4/R-40% prepared in Example 2 of the present invention has degradation rates of 84% and 86% for tetracycline and rhodamine B, respectively. This indicates that the composite photocatalyst of BiPO.sub.4/rectorite homojunctions prepared by the method of the present invention has excellent photocatalytic activity.

[0045] The reason why the photocatalytic activity of the composite photocatalyst of BiPO.sub.4/rectorite homojunctions prepared by the present invention is significantly improved is: the addition of rectorite induces the formation of BiPO.sub.4 heterophase homojunction structure. This charge transfer mechanism not only effectively separates photo-generated carriers, but also ensures their strong redox ability; secondly, the combination of BiPO.sub.4 and rectorite enhances the adsorption capacity of the photocatalyst, reduces the electron-hole recombination rate, and significantly improves the photocatalytic performance of the material through the synergistic effect of the two aspects.

[0046] The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the present invention shall be included in the protection of the present invention.