Method for preparing photocatalytic material by modifying silver iodide / bismuth oxyiodide n-n type heterojunction with carbon quantum dots

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a method for preparing a photocatalytic material by modifying a silver iodide / bismuth oxyiodide n-n type heterojunction with carbon quantum dots. The preparation method comprises the following steps: firstly, taking pure natural bamboo cellulose as a carbon source, preparing carbon quantum dot powder by a mild hydrothermal method, and preparing the carbon quantum dot powder into a carbon quantum dot solution; then adding the carbon quantum dot solution into a solution for preparing bismuth oxyiodide, and drying to obtain a bismuth oxyiodide / carbon quantum dot composite material; and uniformly dispersing the composite material, silver nitrate and a surfactant in water, and adding a potassium iodide aqueous solution for reaction to finally obtain the carbon quantum dot modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material. The preparation method is simple, environment-friendly and economical; the prepared photocatalytic material has excellent photocatalytic performance, and the degradation rate of RhB can reach 99%.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a method for preparing a photocatalytic material by modifying silver iodide / bi-iodate n-n type heterojunction with carbon quantum dots. Background Art

[0002] As an advanced oxidation technology, semiconductor photocatalytic technology has the advantages of strong oxidation ability, fast reaction rate, simple operation, less secondary pollution, etc., and can effectively degrade refractory organic pollutants. Photocatalytic materials have many advantages among numerous pollutant degradation materials. First, the reaction conditions are mild. Using sunlight at room temperature to convert solar energy into chemical energy can carry out degradation. Second, during the photocatalytic degradation process, photocatalytic materials directly degrade pollutants into carbon dioxide, water and inorganic salts, without the problem of secondary pollution. In addition, photocatalytic materials usually have the characteristics of being cheap, environmentally friendly and recyclable, which reduces their cost in practical applications and improves economic benefits. However, photocatalytic materials still have disadvantages in application, such as narrow spectral response range, decline in photocatalytic performance caused by fast electron-hole recombination rate, and insufficient material stability and durability. To solve the above problems, a simple, economical and green photocatalytic material preparation process needs to be developed.

[0003] As a photocatalytic material, silver iodide can carry out photocatalytic reactions under visible light conditions. However, due to problems such as weak separation ability of photo-generated carriers and easy photocorrosion, the reaction is hindered. Bismuth iodate is a visible light-responsive photocatalytic material. When constructing a heterojunction with silver iodide, the valence band and conduction band match, which can maximize the reaction rate. Carbon quantum dots are composed of ultra-fine, dispersed carbon nanoparticles with a size below 10 nm. They are a new type of "zero-dimensional" carbon-based nanomaterial. Due to their inherent properties such as up-conversion photoluminescence, excellent electron transfer ability and good biocompatibility, they are considered excellent candidates for interface regulation and have a very broad prospect in the field of photocatalysis. At the same time, they also have high stability and environmental friendliness. They are not easily affected by environmental factors and change in performance, and are pollution-free to the environment, meeting the requirements of green chemistry and sustainable development. By modifying the heterojunction with carbon quantum dots, a channel for electron transfer can be provided, the recombination of electron-hole pairs can be slowed down, the absorption ability of the material to visible light can be enhanced, and the photocatalytic efficiency can be effectively improved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a photocatalytic material by modifying a heterojunction with carbon quantum dots. The present invention selects natural bamboo cellulose as the carbon source and prepares carbon quantum dots by a mild hydrothermal method to effectively improve the performance of the photocatalytic material through carbon quantum dots. The preparation method of the present invention is simple, environmentally friendly and economical; the prepared photocatalytic material has excellent photocatalytic performance, and the degradation rate of RhB can reach 99%.

[0005] To achieve the above object, the technical solution of the present invention is as follows.

[0006] The present invention provides a method for preparing a photocatalytic material by using carbon quantum dots to modify an AgI / BiOI n-n type heterojunction, comprising the following steps:

[0007] (1) Preparation of BiOI / carbon quantum dots

[0008] First, weigh the bismuth salt and dissolve it in an organic solvent, then add the carbon quantum dot solution to obtain a mixed solution; then add an aqueous potassium iodide solution to the mixed solution and continuously stir and react. After the reaction is completed, perform solid-liquid separation, washing, and drying to obtain BiOI / carbon quantum dots;

[0009] (2) After the BiOI / carbon quantum dot powder, surfactant, and silver nitrate are fully dispersed and homogenized in water, add a potassium iodide solution thereto. After adding, continuously stir and react. After the reaction is completed, perform solid-liquid separation, washing, and drying to obtain a carbon quantum dot-modified AgI / BiOI n-n type heterojunction photocatalytic material.

[0010] In the present invention, in step (1), the carbon quantum dot solution is prepared by the following method:

[0011] Disperse bamboo cellulose powder into pure water to obtain a uniform bamboo cellulose dispersion; then transfer the bamboo cellulose dispersion to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, perform solid-liquid separation to obtain a carbon quantum dot solution, and then perform freeze-drying to obtain carbon quantum dot powder; dissolve the carbon quantum dot powder in deionized water to obtain a carbon quantum dot solution.

[0012] In the present invention, the concentration of the bamboo cellulose dispersion is 10-50 mg / mL, the hydrothermal reaction temperature is 200-220 °C, and the hydrothermal reaction time is 3-4 h.

[0013] In the present invention, filtration or centrifugation is used for solid-liquid separation.

[0014] In the present invention, in step (1), the bismuth salt is bismuth nitrate pentahydrate, the organic solvent is ethylene glycol, the feeding ratio of the bismuth salt to the organic solvent is 1:10-1:50 mmol / mL, the concentration of the carbon quantum dot solution is 0.1-1 mg / mL, and the concentration of the aqueous potassium iodide solution is 1:15-1:30 mmol / mL; the molar ratio of the bismuth salt to potassium iodide is 1:0.9-1:1.1, and the feeding ratio of the bismuth salt to the carbon quantum dot solution is 2:0.5-2:0.75 mmol / mL; continuously stir and react for 3-5 h.

[0015] In the present invention, in step (2), the surfactant is polyvinylpyrrolidone PVP; the feeding ratio of bismuth oxyiodide / carbon quantum dot powder, surfactant and water is (10 - 30) mg : (30 - 100) mg : (20 - 60) mL; the molar ratio of silver nitrate to potassium iodide is 1:0.9 to 1:1.1; the reaction is continuously stirred for 3 - 5 h.

[0016] In the present invention, in step (2), the feeding ratio of bismuth oxyiodide / carbon quantum dot powder, silver nitrate and potassium iodide satisfies that the mass ratio of bismuth oxyiodide / carbon quantum dot powder to the silver iodide theoretically formed by silver nitrate and potassium iodide is 1:15 to 1:25.

[0017] In the present invention, in steps (1) and (2), the drying conditions are as follows: drying at a temperature of 60 - 80 °C for 6 - 18 h.

[0018] The present invention also provides a photocatalytic material prepared by the above method.

[0019] Furthermore, the present invention also provides an application of the above photocatalyst material in catalyzing organic pollutants in water under visible light conditions.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The preparation process of the present invention is simple. The carbon quantum dot solution is prepared by a simple hydrothermal method, and the photocatalytic material is prepared by a coprecipitation method;

[0022] (2) The present invention is green and pollution-free, with low cost and high economic value.

[0023] (3) The photocatalytic material prepared by the present invention has better performance than silver iodide and silver iodide / bismuth oxyiodide materials. The carbon quantum dots in the present invention provide a channel for the transfer of electrons in the composite material, slow down the rate of electron-hole recombination, enhance the light response and absorption ability of the material, reduce the energy required for electron transition, and thus improve the photocatalytic performance. Description of the Drawings

[0024] Figure 1 It is a preparation flow chart of a carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material.

[0025] Figure 2 It is a scanning electron microscope image of a carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material prepared in Example 2.

[0026] Figure 3 It is a transient photocurrent diagram of a carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material.

[0027] Figure 4UV-Vis diffuse reflectance spectrum of the carbon quantum dot modified AgI / BiOI n-n type heterojunction photocatalytic material.

[0028] Figure 5 Degradation performance diagram of the carbon quantum dot modified AgI / BiOI n-n type heterojunction photocatalytic material. Detailed implementation mode

[0029] The technical solution of the present invention will be introduced in detail below with reference to the drawings and embodiments.

[0030] In the embodiment, the raw material reagents include: bismuth nitrate pentahydrate; silver nitrate; potassium iodide; ethylene glycol; bamboo cellulose; polyvinylpyrrolidone.

[0031] The bamboo cellulose is sourced from moso bamboo and is prepared by alkali treatment of bamboo powder; the specific preparation process is as follows:

[0032] Put 10 g of bamboo powder into a beaker with a suitable capacity, and then add 4 g of NaOH and 196 g of distilled water to it respectively. Stir for 4 hours under the condition of water bath heating at 90 °C. After filtering once, repeat the above steps. Then take out the beaker from the water bath, let it stand, filter the mixture with a vacuum filter, and wash it several times with distilled water until it is neutral. Finally, put it into an oven at 60 °C for drying. After drying, add 8.5 g of NaClO 2 and 491.5 g of distilled water, and adjust the overall pH value to 4. Under the condition of water bath heating at 80 °C, stir for 6 hours. After filtering once, repeat the above steps until the material shows a milky white color. Finally, dry the purified material in an oven at 60 °C to obtain bamboo cellulose.

[0033] Figure 1 Flow chart for the preparation of the carbon quantum dot modified AgI / BiOI n-n type heterojunction photocatalytic material in the embodiment.

[0034] Example 1

[0035] First, dissolve the weighed bismuth nitrate pentahydrate in ethylene glycol without adding the carbon quantum dot solution, and then add potassium iodide. After continuously stirring for 3 h, precipitate and centrifuge, wash the powder, and put it into an oven at 60 °C for 12 h for drying. After drying, weigh an appropriate amount of the powder, put it into deionized water and ultrasonically disperse it evenly. Then add polyvinylpyrrolidone and silver nitrate respectively. After complete dissolution, slowly dropwise add the potassium iodide solution while stirring. After the addition is complete, continuously stir for 3 h. Finally, precipitate and centrifuge, wash the powder, and put it into an oven at 60 °C for 12 h for drying. The finally prepared sample is called the first photocatalytic material.

[0036] Testing of the degradation rate of the catalytic material:

[0037] Put the first photocatalytic material into a mortar and grind it into a powder with a smaller particle size. Weigh 50 mg and put it into a photocatalytic glass reactor. Add 100 mL of 1×10 -5 mol / L rhodamine B solution. First, perform adsorption for 1 h under dark conditions until adsorption equilibrium is reached. Subsequently, turn on a 300 W xenon lamp (λ>420 nm) and carry out a 1 h photocatalytic reaction. Take 3 mL of the mixed solution every 10 min and transfer it to a centrifuge tube. Place the centrifuge tube in a centrifuge and centrifuge for 5 min (rotation speed is 5000 rpm), then take the supernatant. Measure the concentration of RhB in the supernatant with a UV-visible spectrophotometer at 554 nm. After measurement, the degradation rate of the first photocatalytic material for RhB within 1 h is 76%.

[0038] Example 2

[0039] 1) Preparation of carbon quantum dots

[0040] Disperse 0.5 g of bamboo cellulose powder into 50 mL of pure water, and quickly stir for 30 min to make it evenly dispersed. Subsequently, pour it into a 100 mL high-pressure reactor lined with polytetrafluoroethylene and heat it at 200 °C for 3 h. After cooling to room temperature, centrifuge at 3000 rpm for 30 min and collect the light yellow supernatant. Freeze-dry the collected CQDs solution to obtain 15 mg of CQDs powder, and then disperse it in 30 mL of pure water. Store the obtained CQDs solution in the dark at 4 °C.

[0041] 2) Preparation of carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction catalytic material

[0042] First, dissolve the weighed bismuth nitrate pentahydrate in ethylene glycol, add 0.5 mL of carbon quantum dot solution, and then add potassium iodide. After continuously stirring for 3 h, precipitate and centrifuge, wash the powder, and put it in an oven at 60 °C for 12 h to dry. After drying, weigh an appropriate amount of powder, put it into deionized water and ultrasonically disperse it evenly. Subsequently, add polyvinylpyrrolidone and silver nitrate respectively. After complete dissolution, slowly dropwise add potassium iodide solution while stirring. After dropping, continuously stir for 3 h. Finally, precipitate and centrifuge, wash the powder, and put it in an oven at 60 °C for 12 h to dry. The finally prepared sample is called the second photocatalytic material.

[0043] Figure 2 Figure 21 is a scanning electron microscope image of the carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material prepared in Example 2. The morphologies of silver iodide and bismuth oxyiodide can be clearly seen, indicating that the two are composite and the silver iodide-bismuth oxyiodide heterojunction photocatalytic material is successfully prepared.

[0044] 3) Test of the degradation rate of the catalytic material

[0045] Put the second photocatalytic material into a mortar and grind it into a powder with a smaller particle size. Weigh 50 mg and put it into a photocatalytic glass reactor. Add 100 mL of 1×10-5 A rhodamine B solution with a concentration of 1 mol / L was first adsorbed for 1 h under dark conditions until the adsorption equilibrium was reached. Subsequently, a 300 W xenon lamp (λ>420 nm) was turned on for a 1 h photocatalytic reaction. Every 10 min, 3 mL of the mixed solution was taken and transferred to a centrifuge tube. The centrifuge tube was placed in a centrifuge and centrifuged for 5 min (at a rotation speed of 5000 rpm), and then the supernatant was taken. The concentration of RhB in the supernatant was measured at 554 nm using a UV-visible spectrophotometer. After measurement, the degradation rate of RhB by the second photocatalytic material within 1 h was 90%.

[0046] Example 3

[0047] 1) The preparation of carbon quantum dots was the same as in Example 2.

[0048] 2) Preparation of a carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction catalytic material

[0049] First, the weighed bismuth nitrate pentahydrate was dissolved in ethylene glycol, and 0.75 mL of the carbon quantum dot solution was added. Subsequently, potassium iodide was added, and after continuous stirring for 3 h, the precipitate was centrifuged, the powder was washed, and then placed in an oven at 60 °C for 12 h to dry. After drying, an appropriate amount of the powder was weighed, dispersed evenly by ultrasonic treatment in deionized water, and then polyvinylpyrrolidone and silver nitrate were added respectively. After complete dissolution, the potassium iodide solution was slowly added dropwise with stirring. After the addition was completed, stirring was continued for 3 h. Finally, the precipitate was centrifuged, the powder was washed, and then placed in an oven at 60 °C for 12 h to dry. The finally prepared sample was called the third photocatalytic material.

[0050] 3) Testing the degradation rate of the catalytic material

[0051] The third photocatalytic material was ground into a powder with a smaller particle size in a mortar. 50 mg was weighed and placed in a photocatalytic glass reactor, and 100 mL of a 1×10 -5 mol / L rhodamine B solution was added. First, adsorption was carried out for 1 h under dark conditions until the adsorption equilibrium was reached. Subsequently, a 300 W xenon lamp (λ>420 nm) was turned on for a 1 h photocatalytic reaction. Every 10 min, 3 mL of the mixed solution was taken and transferred to a centrifuge tube. The centrifuge tube was placed in a centrifuge and centrifuged for 5 min (at a rotation speed of 5000 rpm), and then the supernatant was taken. The concentration of RhB in the supernatant was measured at 554 nm using a UV-visible spectrophotometer. After measurement, the degradation rate of RhB by the third photocatalytic material within 1 h was 99%.

[0052] Table 1 shows the degradation rate results of the carbon quantum dot-modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic materials in the examples.

[0053] Table 1 Degradation rate table of carbon quantum dot-modified silver iodide / bismuth oxyiodide n-type heterojunction photocatalytic materials

[0054] Addition amount of carbon quantum dots Degradation rate of RhB Photocatalytic material of Example 1 0 76％ Photocatalytic material of Example 2 0.5 mL 90％ Photocatalytic material of Example 3 0.75 mL 99％

[0055] Figure 3 Transient photocurrent diagram of the carbon quantum dot modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material.

[0056] Transient photocurrent refers to the current generated due to photoexcitation within a very short period of time. When light irradiates certain dielectric materials, photons are absorbed by the materials, and then electrons are excited to jump from the valence band to the conduction band, forming electron-hole pairs. To a certain extent, the magnitude of the transient photocurrent can reflect the catalytic performance of the photocatalyst, and there is a positive correlation between the two. As can be seen from Figure 3 it, the third photocatalytic material has the strongest response ability, so its photocatalytic performance is the strongest.

[0057] Figure 4 UV-visible diffuse reflectance spectrum diagram of the carbon quantum dot modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material.

[0058] The UV-visible diffuse reflectance spectrum diagram can be used to study the light absorption performance of photocatalytic materials. Through the spectrum diagram, the light absorption situation of the material at different wavelengths can be understood, so as to judge its absorption ability of ultraviolet light and visible light. This is of great significance for evaluating the catalytic efficiency of photocatalytic materials under sunlight. As can be seen from Figure 4 it, within the visible light range, the third photocatalytic material has the strongest absorption ability.

[0059] Figure 5 Degradation performance diagram of the carbon quantum dot modified silver iodide / bismuth oxyiodide n-n type heterojunction photocatalytic material.

Claims

1. A method for preparing a photocatalytic material by using carbon quantum dots to modify silver iodide / bismuth iodide nn-type heterojunction, characterized in that: The following steps are involved: (1) First, the weighed bismuth salt is dissolved in an organic solvent, and then the carbon quantum dot solution is added to obtain a mixed solution; then, a potassium iodide aqueous solution is added to the mixed solution, and the mixture is continuously stirred for reaction. After the reaction is completed, the solid-liquid separation, washing, and drying are performed to obtain iodine oxybismuth / carbon quantum dots; (2) After the bismuth iodide / carbon quantum dot powder, surfactant and silver nitrate are fully and evenly dispersed in water, potassium iodide solution is added thereto and the reaction is continuously stirred after the addition. After the reaction is completed, the solid-liquid separation, washing and drying are performed to obtain a carbon quantum dot-modified silver iodide / bismuth iodide nn-type heterojunction photocatalytic material.

2. The method according to claim 1, characterized in that In step (1), the carbon quantum dot solution is prepared by the following method: The bamboo cellulose powder is dispersed in pure water to obtain a uniform bamboo cellulose dispersion; the bamboo cellulose dispersion is then transferred to a hydrothermal kettle for a hydrothermal reaction. After the reaction is completed, the solid and liquid are separated to obtain a carbon quantum dot solution, which is then freeze-dried to obtain a carbon quantum dot powder; the carbon quantum dot powder is dissolved in deionized water to obtain a carbon quantum dot solution.

3. The method according to claim 2, characterized in that The concentration of the bamboo cellulose dispersion is 10-50 mg / mL, the hydrothermal reaction temperature is 200-220° C., and the hydrothermal reaction time is 3-4 h.

4. The method according to claim 1 or 2, characterized in that: Solid-liquid separation is done by filtration or centrifugation.

5. The method according to claim 1, characterized in that In step (1), the bismuth salt is bismuth nitrate pentahydrate, the organic solvent is ethylene glycol, the feed ratio of the bismuth salt to the organic solvent is 1:10-1:50 mmol / mL, the concentration of the carbon quantum dot solution is 0.1-1 mg / mL, and the concentration of the potassium iodide aqueous solution is 1:15-1:30 mmol / mL; the molar ratio of the bismuth salt to potassium iodide is 1:0.9-1:1.1, and the feed ratio of the bismuth salt to the carbon quantum dot solution is 2:0.5-2:0.75 mmol / mL; and the reaction is stirred continuously for 3-5 hours.

6. The method according to claim 1, characterized in that In step (2), the surfactant is polyvinyl pyrrolidone (PVP); the feed ratio of bismuth oxyiodide / carbon quantum dot powder, surfactant and water is (10-30) mg: (30-50) mg: (20-60) mL; the molar ratio of silver nitrate to potassium iodide is 1:0.9~1:1.1; and the reaction is stirred continuously for 3-5 hours.

7. The method according to claim 1, characterized in that In step (2), the feed ratio of bismuth oxyiodide / carbon quantum dot powder to silver nitrate and potassium iodide satisfies the mass ratio of the bismuth oxyiodide / carbon quantum dot powder to the theoretical mass ratio of silver iodide generated by silver nitrate and potassium iodide is 1:15-1:

25.

8. The method according to claim 1, characterized in that In step (1) and step (2), the drying conditions are as follows: drying at a temperature of 60-80°C for 6-18 hours.

9. A photocatalytic material prepared according to the method of any one of claims 1 to 8.

10. Use of the photocatalyst material according to claim 9 to catalyze organic pollutants in water under visible light conditions.

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