CN111715267A - A kind of carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst and preparation method and application thereof - Google Patents

Abstract

The present invention is a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as well as a preparation method and application thereof. The method comprises step 1: g-C ₃ N _4-x powder containing nitrogen vacancies, WCl ₆ The powder and NaBiO ₃ powder were dispersed in absolute ethanol, and the precursor solution was subjected to an in-situ hydrothermal reaction, and the reaction system was deficient in oxygen, forming a reducing reaction atmosphere, resulting in the formation of oxygen vacancies in BiOCl and the formation of non-oxygen-containing vacancies. WO _2.92 in a stoichiometric ratio, and nitrogen vacancies in g-C ₃ N _4-x capture electrons to promote the reduction of WO ₃ to WO _2.92 in a non-stoichiometric ratio; step 2, the precipitate in the reaction solution is washed and dried to obtain nitrogen Carbonide/bismuth oxychloride/tungsten oxide heterojunction photocatalyst can realize photocatalytic deep oxidation of NO under visible light irradiation, and has a good application prospect.

Description

A kind of carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst and preparation method thereof and application

technical field

The invention belongs to the technical field of photocatalyst material preparation, in particular to a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst and a preparation method and application thereof.

Background technique

The rapid development of industry has led to more serious air pollution, which has seriously affected the sustainable development of human society and people's health. Photocatalytic technology can be used to control air pollution with good effect, and it has obvious advantages with low cost as the driving force of sunlight.

Photocatalytic NO removal, toxic _NO2 gas and _HNO2 are the main intermediate products during the reaction, which will produce secondary pollution. Therefore, there is a need to improve the conversion of NO to the final product _HNO3 . In addition, it is difficult for unactivated NO molecules to adsorb and activate on the surface of well-crystallized photocatalyst powders, which is unfavorable for the removal of ppb-level NO.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst and its preparation method and application, the operation is simple, and the prepared gC3N4 _{- x} /BiOCl/WO _2.92 heterojunction photocatalyst The catalyst contains a large number of nitrogen vacancies and oxygen vacancies, which can achieve deep oxidation of NO under visible light irradiation.

For achieving the above object, preparation method of the present invention is as follows:

A preparation method of carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst, comprising the following steps:

Step 1, disperse gC ₃ N _4-x powder, WCl ₆ powder and NaBiO ₃ powder containing nitrogen vacancies in absolute ethanol to obtain a precursor solution, and the precursor solution is subjected to a hydrothermal reaction. In the mol ratio of Bi element and Cl element is (0.15-0.5): 1, obtains reaction solution;

In step 2, the precipitate in the reaction solution is washed and then dried to obtain a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst.

Preferably, the mass ratio of the nitrogen vacancy-containing gC ₃ N _4-x powder to the WCl ₆ powder in step 1 is (0.50-1.33):1.

Preferably, in step 1, the gC ₃ N _4-x powder containing nitrogen vacancies and the WCl ₆ powder are dispersed into absolute ethanol, and then stirred and sonicated in sequence to obtain a blue suspension, and finally At the same time, the NaBiO ₃ powder is dispersed into the blue suspension, and the precursor solution is obtained after stirring.

Preferably, the filling ratio of the hydrothermal reaction in step 1 is 65%-80%.

Preferably, the hydrothermal reaction in step 1 is carried out at 140-180°C.

Further, the hydrothermal reaction in step 1 is carried out at the temperature for 10-18h.

A carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst is obtained by the preparation method of carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst according to any one of the above.

Further, nitrogen-containing vacancies in gC3N4 _{- x} , and oxygen-containing vacancies in BiOCl and WO _2.92 , this heterojunction photocatalyst exhibits light-absorbing properties in the visible and near-infrared light range.

Application of carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalysts for NO removal.

Compared with the prior art, the beneficial effects of the present invention are:

The present invention is a method for preparing a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst. The _{gC3N4 - x} , WCl6 and _NaBiO3 containing nitrogen vacancies are used as raw materials to be dispersed in anhydrous ethanol. In situ hydrothermal growth method, the reaction system is oxygen-deficient, forming a reducing reaction atmosphere, resulting in the formation of oxygen vacancies in BiOCl, while generating a non-stoichiometric WO _2.92 containing oxygen vacancies, and nitrogen vacancies in gC ₃ N _4-x are trapped The electrons promote the reduction of WO ₃ to non-stoichiometric WO _2.92 , and a double-defect-containing gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst was prepared, which can achieve photocatalytic NO deep oxidation under visible light irradiation, with good application prospects. Introducing defects into the catalyst powder can not only improve its adsorption and activation ability for NO molecules, but also improve the light absorption characteristics of the photocatalyst, thereby enhancing the photocatalytic activity.

The gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst of the present invention enhances light absorption due to the existence of nitrogen vacancies and oxygen vacancies, and the LSPR effect of oxygen vacancies makes gC ₃ N _4-x /BiOCl/WO _2.92 The light absorption of the heterojunction photocatalyst in the visible-near-infrared light range is obviously enhanced. The main oxidation product during the photocatalytic NO removal is HNO ₃ , only a trace amount of HNO ₂ is generated, and no toxic NO ₂ gas is generated. Has a good application prospect.

Description of drawings

FIG. 1 is the XRD pattern of the catalyst powder prepared by the present invention, and a-c in the figure are the XRD patterns of the powder prepared in Example 1-Example 3, respectively.

FIG. 2 is the EPR diagram of the catalyst powder prepared by the present invention, and b in the figure is the EPR diagram of the powder prepared in Example 2.

3 is a UV-vis-NIR DRS diagram of the catalyst powder prepared by the present invention, and a-c in the figure are the UV-vis-NIR DRS diagrams of the powder prepared in Example 1-Example 3, respectively.

FIG. 4 is the NO removal curve of the catalyst powder prepared by the present invention under visible light irradiation, and a-c in the figure are the NO removal curves of the powder prepared in Example 1-Example 3, respectively.

Fig. 5 is the real-time NO and NO ₂ concentrations during the removal of NO from the catalyst powder prepared by the present invention under the irradiation of visible light, and ac in the figure are the NO and NO ₂ during the photocatalytic NO removal of the powders prepared in Example 1-Example 3, respectively. real-time concentration.

FIG. 6 shows the concentrations of NO ₂ ^- and NO ₃ ^- ions in the supernatant after the powder prepared in Example 2 is ultrasonically washed and filtered with deionized water after photocatalytic NO removal.

Detailed ways

The present invention will be described in further detail below with reference to specific embodiments and accompanying drawings.

A preparation method of a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst of the present invention comprises the following steps:

Step 1: Put 30g of urea in a quartz crucible with a lid, place the crucible in a muffle furnace, and heat it up from room temperature to 550°C at a heating rate of 15°C/min. After holding for 4 hours, cool down to 50°C with the furnace. , to obtain gC ₃ N _4-x powder containing nitrogen vacancies;

Step 2: Disperse a certain amount of gC ₃ N _4-x and WCl ₆ powder into 40 mL of absolute ethanol, stir for 30 min, and ultrasonically treat for 60 min to obtain a blue suspension;

Step 3: Disperse a certain amount of NaBiO ₃ powder into the above suspension while magnetic stirring, and after stirring for 30min, obtain a light brown suspension, that is, the reaction precursor, the Bi element and Cl in the reaction precursor The molar ratio of elements is (0.15-0.5):1;

Step 4: Place the reaction precursor solution in a hydrothermal reaction kettle, the reaction filling ratio is 65%-80%, the temperature is raised from room temperature to 140-180°C in 60min, and the reaction is terminated after 10-18h of heat preservation. The reaction time is short and the reaction conditions are mild. .

Step 5: After the reaction is completed, it is naturally cooled to room temperature, and the obtained precipitate is washed three times with deionized water and absolute ethanol, and then dried at a constant temperature of 70 ° C for 12 h to obtain gC ₃ N _4-x /BiOCl/WO _{2.92 isoform} . Mass junction photocatalyst.

Among them, gC ₃ N _4-x contains nitrogen vacancies; BiOCl and non-stoichiometric WO _2.92 contain oxygen vacancies, and the reduction reaction atmosphere will inevitably form oxygen vacancies in BiOCl; WO _2.92 belongs to non-stoichiometric tungsten oxide, which is different from chemical Corresponding to the stoichiometric ratio of WO ₃ , it exhibits enhanced light absorption properties in the visible and near-infrared light range, the main product during photocatalytic NO removal is HNO ₃ , only a trace amount of HNO ₂ is produced, and no toxic of NO ₂ gas.

Example 1:

Step 1: Put 30g of urea in a quartz crucible with a lid, place the crucible in a muffle furnace, and heat it up from room temperature to 550°C at a heating rate of 15°C/min. After holding for 4 hours, cool down to 50°C with the furnace. , to obtain gC ₃ N _4-x powder containing nitrogen vacancies;

Step 2: Disperse 0.3 g of gC ₃ N _4-x and 0.225 g of WCl ₆ powder into 40 mL of absolute ethanol, stir for 30 min, and ultrasonically treat for 60 min to obtain a blue suspension;

Step 3: while magnetic stirring, disperse 0.238g of NaBiO ₃ powder into the above suspension, the molar ratio of Bi element to Cl element is 0.25:1, after stirring for 30min, a light brown suspension is obtained, That is, the reaction precursor;

Step 4: The reaction precursor solution is placed in a hydrothermal reactor, the reaction filling ratio is about 65%, the temperature is raised from room temperature to 140° C. in 60 minutes, and the reaction is terminated after 14 hours of heat preservation.

Step 5: After the reaction is completed, it is naturally cooled to room temperature, and the obtained precipitate is washed three times with deionized water and absolute ethanol, and then dried at a constant temperature of 70 ° C for 12 h to obtain gC ₃ N _4-x /BiOCl/WO _{2.92 isoform} . Mass junction photocatalyst.

Example 2:

Step 1: Put 30g of urea in a quartz crucible with a lid, place the crucible in a muffle furnace, and heat it up from room temperature to 550°C at a heating rate of 15°C/min. After holding for 4 hours, cool down to 50°C with the furnace. , to obtain gC ₃ N _4-x powder containing nitrogen vacancies;

Step 2: Disperse 0.3 g of gC ₃ N _4-x and 0.225 g of WCl ₆ powder into 40 mL of absolute ethanol, stir for 30 min, and ultrasonically treat for 60 min to obtain a blue suspension;

Step 3: while magnetic stirring, disperse 0.476g of NaBiO ₃ powder into the above suspension, the molar ratio of Bi element to Cl element is 0.5:1, and after stirring for 30min, a light brown suspension is obtained, That is, the reaction precursor;

Step 4: The reaction precursor solution is placed in a hydrothermal reaction kettle, the reaction filling ratio is about 80%, the temperature is raised from room temperature to 160° C. in 60 minutes, and the reaction is terminated after holding for 16 hours.

Step 5: After the reaction is completed, it is naturally cooled to room temperature, and the obtained precipitate is washed three times with deionized water and absolute ethanol, and then dried at a constant temperature of 70 ° C for 12 h to obtain gC ₃ N _4-x /BiOCl/WO _{2.92 isoform} . Mass junction photocatalyst.

Example 3:

Step 1: Put 30g of urea in a quartz crucible with a lid, place the crucible in a muffle furnace, and heat it up from room temperature to 550°C at a heating rate of 15°C/min. After holding for 4 hours, cool down to 50°C with the furnace. , to obtain gC ₃ N _4-x powder containing nitrogen vacancies;

Step 2: Disperse 0.3 g of gC ₃ N _4-x and 0.60 g of WCl ₆ powder into 40 mL of absolute ethanol, stir for 30 min, and ultrasonically treat for 60 min to obtain a blue suspension;

Step 3: while magnetic stirring, disperse 0.476g of NaBiO ₃ powder into the above suspension, the molar ratio of Bi element to Cl element is 0.19:1, after stirring for 30min, a light brown suspension is obtained, That is, the reaction precursor;

Step 4: The reaction precursor solution is placed in a hydrothermal reactor, the reaction filling ratio is about 75%, the temperature is raised from room temperature to 180° C. in 60 minutes, and the reaction is terminated after holding for 18 hours.

Step 5: After the reaction is completed, it is naturally cooled to room temperature, and the obtained precipitate is washed three times with deionized water and absolute ethanol, and then dried at a constant temperature of 70 ° C for 12 h to obtain gC ₃ N _4-x /BiOCl/WO _{2.92 isoform} . Mass junction photocatalyst.

Example 4:

Step 1: Put 30g of urea in a quartz crucible with a lid, place the crucible in a muffle furnace, and heat it up from room temperature to 550°C at a heating rate of 15°C/min. After holding for 4 hours, cool down to 50°C with the furnace. , to obtain gC ₃ N _4-x powder containing nitrogen vacancies;

Step 2: Disperse 0.6 g of gC ₃ N _4-x and 0.60 g of WCl ₆ powder into 40 mL of absolute ethanol, stir for 30 min, and ultrasonically treat for 60 min to obtain a blue suspension;

Step 3: while magnetic stirring, disperse 0.376g of NaBiO ₃ powder into the above suspension, the molar ratio of Bi element to Cl element is 0.15:1, after stirring for 30min, a light brown suspension is obtained, That is, the reaction precursor;

Step 4: The reaction precursor solution is placed in a hydrothermal reactor, the reaction filling ratio is about 70%, the temperature is raised from room temperature to 170° C. in 60 minutes, and the reaction is terminated after 10 hours of heat preservation.

Step 5: After the reaction is completed, it is naturally cooled to room temperature, and the obtained precipitate is washed three times with deionized water and absolute ethanol, and then dried at a constant temperature of 70 ° C for 12 h to obtain gC ₃ N _4-x /BiOCl/WO _{2.92 isoform} . Mass junction photocatalyst.

FIG. 1 is the XRD pattern of the powder, and ac in the figure is the XRD pattern of the powder prepared in Example 1-Example 3, respectively. The diffraction peaks of gC ₃ N _4-x , BiOCl and WO _2.92 can be observed in the XRD patterns of the powders prepared in Example 1-Example 3, which proves that three phases coexist in the samples. Among them, BiOCl belongs to the tetragonal crystal system, and the space point group is P4/nmm; WO _2.92 belongs to the monoclinic crystal system, and the space point group is P2/c.

Fig. 2 is an EPR chart of the powder. In the figure b is the EPR diagram of the powder prepared in Example 2. The weak EPR signals of gC ₃ N _4-x and BiOCl/WO _2.92 were attributed to the existence of nitrogen vacancies and oxygen vacancies, respectively. Both nitrogen vacancies and oxygen vacancies are positively charged centers, capturing electrons to balance the system charge; the single-electron paramagnetic resonance phenomenon at the defect site leads to the generation of EPR signals. The EPR signal of the gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst is significantly stronger than that of gC ₃ N _4-x and BiOCl/WO _2.92 , demonstrating the increased defect concentration. In the hydrothermal reaction with absolute ethanol as the reaction medium, the system is oxygen-deficient, forming a reducing reaction atmosphere, resulting in the formation of oxygen vacancies in BiOCl, and at the same time generating non-stoichiometric WO _2.92 containing oxygen vacancies, and gC ₃ N _4-x The electrons captured by the nitrogen vacancies promote the reduction of WO ₃ to non-stoichiometric WO _2.92 .

Fig. 3 is the UV-vis-NIR DRS diagram of the catalyst powder prepared by the present invention. In the figure, ac are the UV-vis-NIR DRS diagrams of the powders prepared in Example 1-Example 3, respectively. Since nitrogen vacancies and oxygen vacancies can form defect states between the forbidden bands of semiconductors, that is, the donor energy levels, leading to near absorption in the UV-vis-NIR DRS diagram of gC3N4 _{- x} /BiOCl/WO _2.92 heterojunction photocatalysts An obvious light absorption shoulder appears near the edge, and the LSPR effect of oxygen vacancies makes the light absorption of gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst significantly enhanced in the visible-NIR range.

4 is the NO removal curve of the catalyst powder prepared by the present invention under visible light irradiation, and ac in the figure is the NO removal curve of the powder prepared by Example 1 to Example 3, respectively. The C/C ₀ of the ordinate in Figure 4 is the ratio of the NO degraded concentration to its initial concentration. It can be seen from the figure that the prepared gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst exhibits significantly higher photocatalytic performance than gC ₃ N _4-x and BiOCl/WO _2.92 , Example 1 - Implementation The gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst prepared in Example 3 can achieve NO removal rates of 58.24%, 68.70% and 64.27% after being irradiated with visible light for 10 min.

Fig. 5 is the real-time NO and NO ₂ concentrations during the removal of NO from the catalyst powder prepared by the present invention under the irradiation of visible light, and ac in the figure are the NO and NO ₂ during the photocatalytic NO removal of the powders prepared in Example 1-Example 3, respectively. real-time concentration. It can be seen from the figure that during the photocatalytic reaction, with the gradual decrease of NO concentration, the concentration of NO ₂ did not increase significantly, and even showed a gradually decreasing trend, which proves that the prepared gC ₃ N _4-x /BiOCl/WO The _2.92 heterojunction photocatalyst did not generate a toxic intermediate product NO ₂ during the photocatalytic NO removal, and even could remove the original NO ₂ in the system.

FIG. 6 shows the concentrations of NO ₂ ^- and NO ₃ ^- ions in the supernatant after the powder prepared in Example 2 is ultrasonically washed and filtered with deionized water after photocatalytic NO removal. The NO ₂ ^- ion concentration is only 1.303 g/L, while the NO ₃ ^- ion concentration is as high as 41.442 g/L, which proves that the prepared gC ₃ N _4-x /BiOCl/WO _2.92 heterojunction photocatalyst performs well during photocatalytic NO removal. The main product is HNO ₃ , with only trace amounts of HNO ₂ produced.

Claims (9)

1. A preparation method of a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst is characterized by comprising the following steps:

step 1, adding g-C containing nitrogen vacancy₃N_4-xPowder, WCl₆Powder and NaBiO₃Dispersing the powder in absolute ethyl alcohol to obtain a precursor solution, and carrying out hydrothermal reaction on the precursor solution, wherein the molar ratio of Bi element to Cl element in the precursor solution is (0.15-0.5):1 to obtain a reaction solution;

and 2, washing and drying the precipitate in the reaction solution to obtain the carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst.

2. The method for preparing a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as claimed in claim 1, wherein g-C containing nitrogen vacancies in step 1₃N_4-xPowder and WCl₆The mass ratio of the powder is (0.50-1.33): 1.

3. the method for preparing a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as claimed in claim 1, wherein the nitrogen-containing vacancy is firstly generated in step 1g-C₃N_4-xPowder and WCl₆Dispersing the powder into absolute ethyl alcohol, sequentially stirring and ultrasonically treating to obtain blue turbid liquid, and finally stirring while adding NaBiO₃The powder is dispersed in blue suspension and stirred to obtain the precursor solution.

4. The method for preparing a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as claimed in claim 1, wherein the filling ratio of the hydrothermal reaction in the step 1 is 65-80%.

5. The method as claimed in claim 1, wherein the hydrothermal reaction in step 1 is carried out at 140-180 ℃.

6. The method for preparing a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as claimed in claim 5, wherein the hydrothermal reaction in the step 1 is carried out at the temperature for 10-18 h.

7. A carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst, which is characterized by being obtained by the preparation method of the carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst according to any one of claims 1 to 6.

8. The carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst of claim 7 wherein g-C₃N_4-xIn the nitrogen-containing vacancy, BiOCl and WO_2.92Containing oxygen vacancies, which has light absorption characteristics in the visible and near infrared light range.

9. Use of a carbon nitride/bismuth oxychloride/tungsten oxide heterojunction photocatalyst as claimed in claim 8 for the removal of NO.

Images