Preparation method of carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst

Abstract

The invention provides a preparation method of a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, and belongs to the technical field of photocatalytic degradation and water photolysis hydrogen production. Comprising the following steps: dissolving a cadmium source and a sulfur source in an ethylenediamine solution, stirring the mixture until the mixture is uniform, carrying out hydrothermal reaction, and treating a product to obtain cadmium sulfide solid powder; the preparation method comprises the following steps: adding a carbon source into deionized water, performing ultrasonic treatment, performing microwave reaction, and filtering, washing and drying a product to obtain carbon quantum dot solid powder; the preparation method comprises the following steps: mixing phosphotungstic acid, cadmium sulfide solid powder and carbon quantum dot solid powder in deionized water, uniformly stirring, carrying out hydrothermal reaction, and centrifuging, filtering and washing a product to obtain the carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst. The photocatalytic performance of cadmium sulfide is effectively improved, the degradation effect on organic pollutants is excellent, the strong water photolysis hydrogen evolution effect is achieved, the preparation technology is simple, cost is low, and industrial application and environment restoration are facilitated.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of photocatalytic degradation and hydrogen production by water photolysis, and particularly relates to a preparation method of a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst. BACKGROUND

[0002] With the rapid advancement of industrialization and urbanization, a large amount of toxic and harmful organic pollutants (such as dyes, antibiotics, etc.) are discharged into the environment, which not only causes serious environmental pollution, but also exacerbates the global energy shortage problem. Under this background, developing efficient and environmentally friendly energy conversion and pollutant treatment materials has become an urgent task to meet the needs of human sustainable development. Photocatalytic technology has become an important research direction to solve the above problems because it can utilize light energy to realize organic pollutant degradation and hydrogen production by water photolysis.

[0003] In the field of photocatalytic materials, cadmium sulfide (CdS) as a narrow-band-gap semiconductor is widely used in the field of photocatalysis because of its suitable energy band, matching of water photolysis thermodynamic conditions and good hydrogen production performance. However, the serious recombination of photo-generated carriers and photo-corrosion defects greatly limit its catalytic activity. Although polyoxometalates (POMs) have strong redox activity and good catalytic performance, they can effectively degrade organic dyes, but have the disadvantages of low hydrogen production rate and only responding to ultraviolet light. Although carbon quantum dots (CQDs) can capture photo-generated electrons, prolong the carrier lifetime and realize photon conversion to enhance the catalytic activity, they cannot meet the actual application requirements when used alone. The existing single or binary composite systems cannot simultaneously solve the problems of narrow light absorption range, low catalytic efficiency and poor stability. In addition, the defects of cadmium sulfide, polyoxometalates and carbon quantum dots in the prior art limit their further application in the field of photocatalysis, and there is no research on constructing a composite material with energy level matching by compounding the three to improve the performance synergistically.

[0004] Therefore, carbon quantum dots, phosphotungstic acid (H3PW 12 O 40 , abbreviated as PW 12 ) and cadmium sulfide are compounded to solve the inherent defects of single materials by utilizing the synergistic effect of the three, and a composite material with high efficient photocatalytic activity is prepared, which is of great significance to improve the efficiency of photocatalytic degradation of organic pollutants and hydrogen production by water photolysis. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, which effectively improves the photocatalytic performance of cadmium sulfide, has excellent degradation effect on organic pollutants, has strong hydrogen evolution effect by water photolysis, and has simple preparation process, low cost, which is conducive to industrial application and environmental remediation.

[0006] To achieve the above object, the present application provides the following scheme:

[0007] A preparation method of a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, comprising the following steps:

[0008] S1, dissolving a cadmium source and a sulfur source in an ethylenediamine solution and stirring the mixture until uniform, after hydrothermal reaction, centrifuging, washing and drying the product to obtain a cadmium sulfide solid powder;

[0009] S2, adding a carbon source to deionized water, adjusting the pH, ultrasonic treatment, stirring, then microwave reaction, filtering, washing and drying the product to obtain a carbon quantum dot solid powder;

[0010] S3, mixing phosphotungstic acid, the cadmium sulfide solid powder and the carbon quantum dot solid powder in deionized water, stirring until uniform, then hydrothermal reaction, centrifuging, filtering and washing the product to obtain a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst.

[0011] Preferably, in S1, the cadmium source is Cd(NO3)2·4H2O and the sulfur source is CS(NH2)2.

[0012] Preferably, in S1, the stirring time of the mixture is 30-40 min, the hydrothermal reaction is carried out in a stainless steel high-pressure reaction kettle, the reaction temperature is 180℃, and the reaction is naturally cooled to room temperature after reaction.

[0013] Preferably, the cadmium sulfide solid powder is in a nanorod structure.

[0014] Preferably, in S2, the carbon source is glucose.

[0015] Preferably, in S2, the ultrasonic treatment time is 10 min, the microwave reaction temperature is 150℃, the time is 35 min, and the power is 300W.

[0016] Preferably, the particle size of the carbon quantum dot solid powder is 5-8 nm.

[0017] Preferably, in S3, the mass fraction of the phosphotungstic acid is 20%.

[0018] Preferably, in S3, the stirring speed is 290-310 r / min and the stirring time is 20 min; the hydrothermal reaction temperature is 180℃.

[0019] The present application also provides a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst prepared by the above preparation method, which is applied to photocatalytic degradation and treatment of organic pollutants in water, wastewater, sewage or sludge and hydrogen production by water splitting.

[0020] According to the specific embodiments provided by the application, the following technical effects are disclosed:

[0021] (1) The carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst has excellent photocatalytic activity in photocatalytic performance. The introduction of carbon quantum dots widens the light absorption range of phosphotungstic acid / cadmium sulfide, improves the light utilization rate, and makes it have full-spectrum photocatalytic activity. The degradation effect on organic pollutants rhodamine B under simulated sunlight is remarkable, and the degradation efficiency is as high as 93.83% after 120 minutes of irradiation, which is much higher than that of monomer cadmium sulfide and phosphotungstic acid / cadmium sulfide binary composite material, and the degradation follows pseudo-first-order reaction kinetics; at the same time, the hydrogen production amount of carbon quantum dots / phosphotungstic acid / cadmium sulfide composite material in 8h is 12.34mmol / g, which is 6 times of that of monomer cadmium sulfide.

[0022] (2) The carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst with rod-like structure has excellent crystal structure and more uniform pore size distribution in material structure, and the carbon quantum dots, phosphotungstic acid and cadmium sulfide form an effective heterojunction with close contact, which improves the separation efficiency of photo-generated carriers and further enhances the photocatalytic performance.

[0023] (3) The microwave-assisted hydrothermal method is used in the preparation process, which is simple, easy to operate, has good repeatability and low cost. The reaction conditions are mild, and the reaction can be carried out at normal temperature and pressure. The purity and yield of the composite catalyst are high, the amount of chemical drugs used is saved, it meets the concept of "green chemistry", and it is convenient for industrial application.

[0024] (4) The application provides a new path for water treatment containing organic pollutants such as dye wastewater, which can effectively reduce the harm of organic pollutants in water body to the environment, is conducive to the transformation from laboratory research to large-scale practical application, has important significance in environmental remediation, and can create certain economic benefits and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The flow chart of the preparation method of the carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst of the application is shown in the figure.

[0027] Figure 2XRD pattern of the carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst provided by the present invention;

[0028] Figure 3 SEM surface morphology image of the carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst provided by the present invention;

[0029] Figure 4 HRTEM image of the carbon quantum dot photocatalyst provided by the present invention;

[0030] Figure 5 The effect of cadmium sulfide, phosphotungstic acid / cadmium sulfide and carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalysts provided by the present invention on photocatalytic water splitting to produce hydrogen in lactic acid solution is shown in the figure.

[0031] Figure 6 The experimental results of direct degradation, cadmium sulfide, phosphotungstic acid / cadmium sulfide and carbon quantum dot / phosphotungstic acid / cadmium sulfide catalytic degradation of Rhodamine B under simulated sunlight conditions provided by the present invention are shown in the figure.

[0032] Figure 7 The reaction kinetics curves of direct degradation, cadmium sulfide, phosphotungstic acid / cadmium sulfide, and different ratios of carbon quantum dots / phosphotungstic acid / cadmium sulfide catalytic degradation of Rhodamine B under simulated sunlight conditions provided by the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, this invention provides a method for preparing a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, comprising the following steps:

[0036] S1. Dissolve the cadmium source and sulfur source in ethylenediamine solution and stir the mixture until homogeneous. After hydrothermal reaction, centrifuge, wash and dry the product to obtain cadmium sulfide solid powder.

[0037] S2. Add the carbon source to deionized water, adjust the pH, sonicate, stir and then carry out microwave reaction. Filter, wash and dry the product to obtain carbon quantum dot solid powder.

[0038] S3, mixing phosphotungstic acid, the cadmium sulfide solid powder and carbon quantum dots solid powder in deionized water, after stirring uniformly, hydrothermal reaction, centrifugation, filtration, washing treatment to the product, obtaining carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst.

[0039] In S1, the cadmium source is Cd(NO3)2·4H2O, and the sulfur source is CS(NH2)2. The stirring time of the mixture is 30-40 min, the hydrothermal reaction is carried out in a stainless steel high-pressure reaction kettle, the reaction temperature is 180℃, and the reaction is naturally cooled to room temperature after reaction. In addition, the cadmium sulfide solid powder is nanorod structure.

[0040] In S2, the carbon source is glucose. The ultrasonic treatment time is 10 min, the microwave reaction temperature is 150℃, the time is 35 min, and the power is 300 W. In addition, the particle size of the prepared carbon quantum dots solid powder is 5-8 nm.

[0041] In S3, the mass fraction of phosphotungstic acid is 20%. The stirring speed is 290-310 r / min, and the stirring time is 20 min; the temperature of the hydrothermal reaction is 180℃.

[0042] The carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst prepared according to the preparation method of the carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst provided above can be widely applied to photocatalytic degradation treatment and photolysis water hydrogen production of organic pollutants in water, wastewater, sewage or sludge.

[0043] The above content will be further described through specific embodiments.

[0044] Example 1

[0045] The embodiment provides a preparation method of carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst, which comprises the following steps:

[0046] Step one, first, a certain amount of ethylenediamine solution is added with a certain mass of Cd(NO3)2·4H2O and CS(NH2)2, and the mixture is ensured to be completely dissolved in the ethylenediamine solution. Then, the mixed solution is stirred for one hour using a stirrer to obtain a uniform mixed solution. Subsequently, the uniformly mixed solution is loaded into a polytetrafluoroethylene liner, and the polytetrafluoroethylene liner is installed in a stainless steel high-pressure reaction kettle and ensured to be airtight; then the whole high-pressure reaction kettle is placed in an oven, and the high-temperature oven reaction temperature is set to 180℃, and the reaction is carried out for a certain time. After the reaction is completed, the stainless steel high-pressure reaction kettle is naturally cooled to room temperature, and then the yellow precipitate is centrifuged, washed and dried to obtain a cadmium sulfide solid powder, which is stored for later use.

[0047] Step two, a certain mass of glucose as carbon source is added to the beaker, 30 mL of deionized water is added to the beaker, and the solution in the beaker is ultrasonic for 10 min. After the ultrasonic is finished, it is stirred with a magnetic stirrer for 30 min. The uniformly stirred mixture solution is placed into a microwave reaction kettle, which is then placed into a microwave instrument, and the reaction temperature is set to 150℃ and the reaction time is set to 35 min. After the microwave reaction is finished, the obtained carbon quantum dot solution is filtered and washed, and finally it is placed into a vacuum drying box to dry to obtain carbon quantum dot solid powder and reserve for use;

[0048] Step three, first, a certain mass of phosphotungstic acid and cadmium sulfide solid powder are weighed respectively and added to the beaker. Then deionized water is added to the beaker and stirred with a magnetic stirrer for 20 min. The mixed solution is loaded into a polytetrafluoroethylene liner, and the polytetrafluoroethylene liner is installed in a stainless steel high-pressure reaction kettle and ensured to be airtight. Then the reaction kettle is placed into a high-temperature oven at 180℃. The reaction is carried out in the oven for a certain time. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the precipitate is centrifuged, filtered and washed to obtain a phosphotungstic acid / cadmium sulfide composite photocatalyst, which is stored for use;

[0049] Step four, first, a certain mass of phosphotungstic acid, cadmium sulfide solid powder and carbon quantum dot solid powder are weighed respectively and added to the beaker. Then deionized water is added to the beaker and stirred with a magnetic stirrer for 20 min. The mixed solution is loaded into a polytetrafluoroethylene liner, and the polytetrafluoroethylene liner is installed in a stainless steel high-pressure reaction kettle and ensured to be airtight. Then the reaction kettle is placed into a high-temperature oven at 180℃. The reaction is carried out in the oven for a certain time. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the precipitate is centrifuged, filtered and washed to obtain a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, which is stored for use;

[0050] The mass fraction of phosphotungstic acid in steps three and four is 20%.

[0051] Example 2

[0052] The difference from example 1 is that the average particle size of the carbon quantum dot solid powder in step two is 2-5 nm, and the rest of the steps and parameters are consistent with example 1.

[0053] Example 3

[0054] The difference from example 1 is that the magnetic stirring time in step two is 30-40 min, and the rest of the steps and parameters are consistent with example 1.

[0055] Example 4

[0056] The difference from Example 1 is that the stirring speed in step three is 290 r / min to 310 r / min, while the remaining steps and parameters are the same as in Example 1.

[0057] Example 5

[0058] The difference from Example 1 is that the Cd(NO3)2·4H2O solution mentioned in step one is 0.0875 mol·L. -1 The remaining steps and parameters are the same as in Example 1.

[0059] Example 6

[0060] The difference from Example 1 is that the microwave reaction temperature in step two is 150°C, the reaction time is 35 min, and the power is 300 W. The remaining steps and parameters are the same as in Example 1.

[0061] Example 7

[0062] The difference from Example 1 is that in step three, the reaction product is washed 3 to 5 times with deionized water and anhydrous ethanol respectively, and then kept at 55℃ to 65℃ for 45h to 50h to obtain carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst. The remaining steps and parameters are the same as in Example 1.

[0063] Furthermore, the surface morphology and microstructure of the carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst prepared according to Example 1 were analyzed using various characterization methods. Figure 2 The XRD test results show that "CQDs / PW" 12 " / CdS" is a composite photocatalyst sample, where CQDs represent carbon quantum dots and PW 12 Representing phosphotungstic acid, CdS represents cadmium sulfide; PDF#04-009-5178 represents the standard diffraction pattern of phosphotungstic acid; PDF#04-001-7806 represents the standard diffraction pattern of cadmium sulfide; through Figure 2 This demonstrates that the composite material consists of hexagonal wurtzite phases of CdS and PW. 12 Composed of CQDs, the crystal phase composition and crystal structure of the composite material are clearly presented; reference Figure 3 The SEM surface morphology images clearly show that the sample exhibits the morphological characteristics of nanorods; furthermore, according to... Figure 4 HRTEM images of carbon quantum dots further revealed the microstructure of the material. The (002) crystal plane of CQDs can be clearly seen from the HRTEM images, indicating that CQDs were successfully prepared.

[0064] To further evaluate the photocatalytic hydrogen production capability of this composite photocatalyst through water splitting, lactic acid was used as a sacrificial agent in the CQDs / PW... 12 An 8-hour hydrogen production experiment was conducted using / CdS, and the results are as follows:Figure 5 As shown, CQDs / PW 12 The hydrogen production rate of CQDs / PW was significantly higher than that of CdS, approximately six times higher, further indicating that CQDs / PW 12 / CdS exhibits high photocatalytic hydrogen production activity. Furthermore, to further evaluate other properties of this composite photocatalyst, photocatalytic experiments were conducted on the degradation of the organic pollutant Rhodamine B, comparing it with direct photodegradation (without catalyst), monomeric CdS (monomeric cadmium sulfide), and monomeric PW. 12 (monomer phosphotungstic acid), PW 12 / CdS and different ratios of CQDs / PW 12 Photocatalytic experimental results of / CdS (i.e., CQDs mass fractions of 1%, 5%, and 10%). Based on Figure 6 Experimental results show that 5% CQDs / PW 12 The / CdS composite material exhibited the highest photocatalytic activity for the degradation of Rhodamine B under simulated sunlight, and its degradation effect far exceeded that of monomeric cadmium sulfide.

[0065] Figure 7 Demonstrated direct photolysis (catalyst-free), monomeric CdS (monomeric cadmium sulfide), and monomeric PW 12 (monomer phosphotungstic acid), PW 12 / CdS and 5% CQDs / PW 12 The effect of CdS on the degradation rate of Rhodamine B was calculated based on experimental data using the formula: ln(C t / C0)=k t +b(where C) t The concentration of the dye at time t (mg·L) -1 C0 is the initial dye concentration (mg·L⁻¹). -1 k is the rate constant, with units of min. -1 (b is the intercept) Calculation shows that ln(C t The degradation of Rhodamine B under simulated sunlight was basically linear with the reaction time t, and the degradation efficiency was as high as 93.83% after 120 minutes of irradiation, which far exceeded that of cadmium sulfide monomer and phosphotungstic acid / cadmium sulfide binary composite material. Moreover, the degradation followed pseudo-first-order reaction kinetics.

[0066] Therefore, the above-mentioned method for preparing a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst effectively improves photocatalytic performance, has a good degradation effect on organic pollutants, and has a simple preparation process and low cost, which is conducive to industrial application and environmental remediation.

[0067] The various embodiments described in this specification are presented for the purpose of illustrating the principles of the present application and its best mode of operation. Each of the embodiments described in this specification has been provided for the purpose of illustration and is not intended to limit the application.

[0068] The principles and implementations of the present application have been described in the specification with specific examples. The above description of the embodiments is only for the purpose of helping to understand the method of the present application and its core idea. Meanwhile, for those skilled in the art, the specific implementation and application range of the present application can be changed according to the idea of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for preparing a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst, characterized in that, The method comprises the following steps: S1, dissolving a cadmium source and a sulfur source in an ethylenediamine solution and stirring the mixture until uniform, then performing a hydrothermal reaction, and performing centrifugation, washing, and drying treatment on the product to obtain a cadmium sulfide solid powder; S2, adding a carbon source to deionized water, adjusting the pH, performing ultrasonic treatment and stirring, then performing a microwave reaction, and performing filtration, washing, and drying treatment on the product to obtain a carbon quantum dot solid powder; S3, mixing phosphotungstic acid, the cadmium sulfide solid powder, and the carbon quantum dot solid powder in deionized water, stirring until uniform, then performing a hydrothermal reaction, and performing centrifugation, filtration, and washing treatment on the product to obtain a carbon quantum dot / phosphotungstic acid / cadmium sulfide composite photocatalyst. 2.The method for preparing carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S1, the cadmium source is Cd(NO3)2·4H2O, and the sulfur source is CS(NH2)2. 3.The method for preparing carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S1, the stirring time of the mixture is 30-40 min, the hydrothermal reaction is performed in a stainless steel high-pressure reaction kettle, the reaction temperature is 180°C, and the reaction is naturally cooled to room temperature after the reaction. 4.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, The cadmium sulfide solid powder is in a nanorod structure. 5.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S2, the carbon source is glucose. 6.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S2, the ultrasonic treatment time is 10 min, the microwave reaction temperature is 150°C, the time is 35 min, and the power is 300 W. 7.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, The particle size of the carbon quantum dot solid powder is 5-8 nm. 8.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S3, the mass fraction of the phosphotungstic acid is 20%. 9.The method for preparing a carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst according to claim 1, characterized in that, In S3, the stirring speed is 290-310 r / min, and the stirring time is 20 min; the hydrothermal reaction temperature is 180°C.

10. The carbon quantum dots / phosphotungstic acid / cadmium sulfide composite photocatalyst prepared by the method according to any one of claims 1-9, characterized in that, The application is used for photocatalytic degradation and treatment of organic pollutants in water, wastewater, sewage, or sludge and for hydrogen production by water splitting.

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