Preparation method and application of CuGaS2 quantum dot photocatalyst

Abstract

The invention discloses a CuGaS2 quantum dot preparation method, which comprises: mixing a copper source, a gallium source, octadecene and oleylamine, heating to a temperature of 95-100 DEG C under a protective gas, and carrying out thermal insulation for 4-6 min; adding a sulfur precursor solution, heating to 180-260 DEG C, and reacting for 25-30 minutes; and quenching and purifying. The CuGaS2 quantum dot prepared by the method has a chalcopyrite structure, is uniform in particle size distribution, has better crystal quality, fewer defect modes and lower photoinduced electron-hole pair recombination rate, is used as a photocatalyst for treating water pollution, and can effectively degrade organic pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and in particular relates to a preparation method and application of a CuGaS2 quantum dot photocatalyst. Background Art

[0002] In recent years, organic pollutants, especially antibiotic pollution, have increasingly attracted global attention. The main sources are medical wastewater, animal husbandry and aquaculture emissions. Since antibiotics are not easily degraded in the environment, they accumulate in water and are taken by humans or livestock. Only 10%-70% can be absorbed and utilized. Residual antibiotics and their metabolites will enter the water environment with human and livestock excrement and accumulate, leading to the spread of antibiotic resistance genes in the environment. Long-term exposure to low-concentration antibiotics in the water environment may induce drug resistance in some pathogens, and may even lead to the emergence of "super-resistant bacteria" that are resistant to most drugs. This pollution not only threatens the health of aquatic ecosystems, but may also be transmitted to humans through the food chain, increasing the difficulty of medical treatment and posing a long-term threat to public health and safety.

[0003] Photocatalysis is known for its high efficiency and environmental protection. It is considered one of the most promising technologies for treating water pollution and has made significant progress in environmental remediation and energy conversion. In the photocatalytic process using traditional catalysts such as titanium dioxide (TiO2) and zinc oxide (ZnO), the high recombination rate of photogenerated electrons and holes hinders the photocatalytic efficiency. The degradation rate of TiO2 for tetracycline hydrochloride in 2h reported in existing literature is only about 40%. Quantum dot materials show great potential in the field of photocatalysis due to their high light absorption properties. Although traditional quantum dot materials such as Cd and Pb groups have excellent photoelectric properties, they are potentially toxic due to the presence of heavy metal ions, which limits their development. Commonly used quantum dot materials include CuInS2 (band gap 1.53eV) and CuInSe2 (band gap 1.04eV), but their narrow optical band gap limits their application range. It has been reported that the degradation rate of CuInS2QDs for tetracycline hydrochloride in 1h is only 74.7%, which cannot completely replace traditional quantum dot materials. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a novel non-toxic green material CuGaS2 quantum dots to enhance its application in the field of treating organic pollutants.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The invention provides a method for preparing CuGaS2 quantum dots, comprising the following steps: mixing a copper source, a gallium source, octadecene and oleylamine, heating the mixture to 95-100°C under a protective gas, and keeping the temperature for 4-6 minutes; adding a sulfur precursor solution, heating the mixture to 180-260°C, and reacting the mixture for 25-30 minutes; quenching and purifying the mixture; The amount ratio of the copper source, gallium source, octadecene, oleylamine and sulfur precursor solution is 0.3mmol:0.3mmol:10mL:3mL:1mL; the sulfur precursor solution is an oleylamine solution of sulfur powder, and the amount ratio of sulfur powder to oleylamine is 1mmol:1mL.

[0006] Preferably, the copper source is cuprous chloride, and the gallium source is gallium chloride.

[0007] Preferably, the quenching method is to rapidly cool in a 25°C cold water bath.

[0008] Preferably, the purification method is to first add acetone for extraction, centrifuge, take the supernatant and add anhydrous ethanol, centrifuge, take the precipitate and dry it to obtain the CuGaS2 quantum dots.

[0009] Preferably, after adding the sulfur precursor solution, the temperature is raised to 220° C. and the reaction is carried out for 25 minutes.

[0010] The present invention also provides a CuGaS2 quantum dot photocatalyst. The CuGaS2 quantum dots are prepared by the above-mentioned preparation method. The CuGaS2 quantum dots have a chalcopyrite structure, a particle size of 5-18 nm, and an optical band gap of 2.64-3.11 eV.

[0011] Preferably, the particle size of the CuGaS2 quantum dots is 8 nm and the optical band gap is 2.83 eV.

[0012] The present invention also provides the use of the CuGaS2 quantum dot photocatalyst in degrading organic pollutants.

[0013] Preferably, the organic pollutant is tetracycline hydrochloride or methyl orange.

[0014] The present invention also provides a method for treating wastewater containing organic pollutants, wherein the CuGaS2 quantum dot photocatalyst is added under illumination conditions for treatment.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The CuGaS2 quantum dots prepared by the preparation method of CuGaS2 quantum dots provided by the present invention have a chalcopyrite structure, uniform particle size distribution, better crystal quality, fewer defect states and lower photogenerated electron-hole pair recombination rate, and are used as photocatalysts for treating water pollution. They can effectively degrade organic pollutants, especially tetracycline hydrochloride, with a degradation rate of up to 93.76% within 1 hour. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD pattern of CuGaS2 quantum dots synthesized in Example 1; Figure 2 TEM image of CuGaS2 quantum dots synthesized in Example 1; Figure 3 This is the optical absorption diagram of the CuGaS2 quantum dots synthesized in Example 1; Figure 4 These are the test results of the degradation ability of the CuGaS2 quantum dots synthesized in Example 1 for TCH and MO. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can more clearly understand the present invention. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; unless otherwise specified, the technical means used are conventional means well known to those skilled in the art.

[0018] Example 1 Preparation of CuGaS2 quantum dots (CGS QDs) The method for preparing CuGaS2 quantum dots provided in this embodiment comprises the following steps: (1) Add 15 mL of oleylamine and 0.48 g of sulfur powder into a three-necked flask, perform triple degassing to remove moisture and other gas impurities, heat to 90 ° C under nitrogen protection and maintain for 5 minutes, and cool naturally to obtain a sulfur precursor solution; (2) In a three-necked flask, 29.7 mg of cuprous chloride, 52.8 mg of gallium chloride, 10 mL of octadecene, and 3 mL of oleylamine were mixed, and then subjected to triple degassing treatment to remove moisture and other gas impurities. The mixture was heated to 100 °C under nitrogen protection and maintained for 5 minutes to ensure that the mixture was repeatedly dissolved. The mixture was heated to a reaction temperature of 180-260 °C, 1 mL of sulfur precursor solution was injected, and the reaction was continued for 25 minutes. After the reaction, the three-necked flask was quickly cooled in a 25 °C cold water bath, 20 mL of acetone was added for extraction, separation and purification, and the centrifugal speed was 2500 r / min. The insoluble impurities were separated and the supernatant was retained. The CuGaS2 quantum dots were obtained after multiple washing with anhydrous ethanol and centrifugation (5000 r / min).

[0019] In this embodiment, five groups of CuGaS2 quantum dot samples were prepared, the difference being that the reaction temperatures in step (2) were 180°C, 200°C, 220°C, 240°C, and 260°C, respectively.

[0020] X-ray diffraction (XRD) analysis was used to characterize the crystal structure of CuGaS2 quantum dots synthesized at different reaction temperatures. Figure 1 As shown, the diffraction peaks of the CuGaS2 quantum dots synthesized at 180~260℃ completely correspond to the CuGaS2 standard card (PDF#00-025-0279), without any impurity peaks, and always show a single chalcopyrite phase structure, indicating that high-purity, single-phase structure CuGaS2 quantum dots were synthesized in this embodiment.

[0021] By comparing the (112) diffraction peaks of CuGaS2 quantum dots synthesized at different temperatures, it was found that with the increase of reaction temperature, the peak intensity of the diffraction peak gradually increased and the full width at half maximum (FWHM) gradually decreased, which means the improvement of crystal quality and the reduction of defect level, indicating that the structural order is enhanced and the grain size is increased. These observations were confirmed by transmission electron microscopy (TEM).

[0022] Figure 2 (a)~ Figure 2 (e) are TEM images of CuGaS2 quantum dots synthesized at reaction temperatures of 180~260℃. It can be seen that at 180℃, the particle size is mainly distributed around 5nm, at 200℃, the particle size is mainly distributed around 7nm, at 220℃, the particle size is mainly distributed around 8nm, at 240℃, the particle size is mainly distributed around 13nm, and at 260℃, the particle size is mainly distributed around 18nm. It can be clearly observed that as the reaction temperature increases, the average particle size of the quantum dots gradually increases. Figure 2 (f) shows the change of quantum dot size with reaction temperature. As the temperature increases, the growth rate of quantum dot grains becomes faster and faster.

[0023] The optical absorption of CuGaS2 quantum dots synthesized at a reaction temperature of 180~260℃ was analyzed by UV-Vis spectrophotometer. Figure 3 (a) As shown. It can be seen that with the increase of synthesis temperature, the absorption edge of quantum dots has a red shift, indicating that its optical band gap gradually decreases and the light absorption range gradually increases. The relationship between the light absorption coefficient of semiconductor materials and the optical band gap is (αhν) 1⁄n = A(hν-E g ), where α is the light absorption coefficient, E g is the optical band gap, hν is the photon energy, direct band gap semiconductor n=1 / 2, indirect band gap semiconductor n=2. Figure 3 (b) (αhν) of CuGaS2 quantum dots at different temperatures 2 The relationship diagram with hν is shown. By linearly fitting the straight line part of the figure, the optical band gap of the sample is obtained. As can be seen from the figure, the calculated optical band gap of CuGaS2 quantum dots gradually decreases from 3.11eV at 180°C to 2.64 eV at 260°C, gradually approaching the optical band gap of 2.4eV of CuGaS2 bulk material. This is due to the size effect of the quantum dot material. When the size of the quantum dot is reduced to the same as its bound wavelength, a quantum confinement effect will occur, that is, the discretization of the energy level. This discrete energy level distribution allows the optical band gap of the quantum dot material to increase as the size decreases. The increase in temperature causes the size of the CuGaS2 quantum dots to continue to approach that of the bulk material, resulting in a narrowing of the optical band gap.

[0024] Example 2 Application of CuGaS2 quantum dots (CGS QDs) photocatalyst in degradation of organic pollutants 100 mL of 30 mg / L tetracycline hydrochloride (TCH) solution or methyl orange (MO) solution was added to the reactor, and 10 mg of the photocatalyst prepared in Example 1 was added. The catalyst was kept in a suspended or floating state by magnetic stirring. After 20 minutes, a sample was taken for determination and recorded as the initial value C0. An 18 W UV-LED lamp was used for irradiation, and samples were taken for analysis at intervals of 10 minutes during the illumination process and recorded as C t After centrifugation, the supernatant was measured by spectrophotometer TCH =355nm,λ MO =455nm to measure the absorbance, and use the formula: ƞ=[(1-C t / C0)]*100% to calculate the degradation rate, where C0 is the absorbance of the solution when adsorption equilibrium is reached, C t The absorbance is measured by regular sampling.

[0025] Figure 4The degradation ability of CGS QDs synthesized at a reaction temperature of 220°C on two pollutants, tetracycline hydrochloride (TCH) and methyl orange (MO). Figure 4 (a) is the UV-VIS absorption spectrum of the solution after TCH degradation by CGS QDs. It can be seen that the adsorption-desorption equilibrium is reached under the condition of no light, and the concentration of the solution changes only slightly. The concentration of the solution decreases rapidly when irradiated with a UV-LED lamp with a wavelength of 365nm, and the characteristic peak of TCH disappears completely in about 1 hour. The formula η= (C0-C) / C0 can be used to calculate that the degradation is 93.76% in 1 hour. Figure 4 (b) is the UV-VIS absorption spectrum of the solution after CGS QDs degradation of MO. In comparison, the degradation rate of MO is lower, with a degradation of 22.45% in 1 hour. Figure 4 (c) is the relationship between -ln (C / C0) and illumination time (t) of CGS QDs degradation of TCH and MO. The results show that the two are linearly related. Due to the limitation of instrument testing accuracy, the characteristic peak disappears after 1 hour of illumination for degradation of TCH and the concentration of the solution hardly changes, so it is no longer linearly related. Using the Langmuir-Hinshelwood rate equation ln (C / C0) = k app t, where k app is the rate constant, C0 and C are the initial concentration and final concentration, respectively. The pseudo-first-order rate constants of CGS QDs degradation of TCH and MO are calculated to be 0.0477 min -1 and 0.0045 min -1 ,like Figure 4 (d) as shown.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A CuGaS 2 Method for preparing quantum dots, It is characterized in that The following steps are involved: After mixing the copper source, gallium source, octadecene and oleylamine, heat to 95-100°C under protective gas and keep warm for 4-6 minutes; add the sulfur precursor solution, heat to 180-260°C and react for 25-30 minutes; quench and purify; The amount ratio of the copper source, gallium source, octadecene, oleylamine and sulfur precursor solution is 0.3mmol:0.3mmol:10mL:3mL:1mL; the sulfur precursor solution is an oleylamine solution of sulfur powder, and the amount ratio of sulfur powder to oleylamine is 1mmol:1mL.

2. CuGaS according to claim 1 2 Method for preparing quantum dots, It is characterized in that The copper source is cuprous chloride, and the gallium source is gallium chloride.

3. CuGaS according to claim 1 2 Method for preparing quantum dots, It is characterized in that The quenching method is to rapidly cool in a 25° C. cold water bath.

4. The CuGaS according to claim 1 2 Method for preparing quantum dots, It is characterized in that The purification method is to first add acetone for extraction, centrifuge, take the supernatant and add anhydrous ethanol, centrifuge, take the precipitate and dry it to obtain the CuGaS 2 Quantum dots.

5. The CuGaS according to claim 1 2 Method for preparing quantum dots, It is characterized in that After adding the sulfur precursor solution, the temperature was raised to 220° C. and the reaction was carried out for 25 minutes.

6. A CuGaS 2 Quantum dot photocatalysts, It is characterized in that The CuGaS 2 The quantum dots have a chalcopyrite structure, a particle size of 5~18nm, and an optical band gap of 2.64~3.11eV.

7. The CuGaS according to claim 6 2 Quantum dot photocatalysts, It is characterized in that The CuGaS 2 The particle size of the quantum dots is 8nm and the optical band gap is 2.83eV.

8. CuGaS according to claim 6 or 7 2 Application of quantum dot photocatalysts in degradation of organic pollutants.

9. The CuGaS according to claim 8 2 Application of quantum dot photocatalysts in the degradation of organic pollutants, It is characterized in that The organic pollutant is tetracycline hydrochloride or methyl orange.

10. A method for treating wastewater containing organic pollutants, It is characterized in that Add the CuGaS according to claim 6 or 7 under light conditions 2 Quantum dot photocatalyst treatment.

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