A method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts and its application

Abstract

A method for preparing g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts using microwave-assisted hydrothermal methods and their applications are disclosed. The purpose of this invention is to address the shortcomings of g-C3N4, such as rapid recombination of photoinduced charge carriers, low visible light utilization, easy particle aggregation, and limited reactive sites. The preparation method includes: 1. Preparation of g-C3N4 precursor; 2. Preparation of carbon quantum dot powder from biomass using a microwave-assisted hydrothermal method; 3. Preparation of g-C3N4 / CQDs; 4. Preparation of g-C3N4 / CQDs / FeVO4. This invention provides a high-performance and low-cost g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst, as well as a highly efficient, environmentally friendly, simple, and low-cost g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst preparation technology.

Description

Technical Field

[0001] This invention relates to a method for preparing a photocatalyst and its application. Background Technology

[0002] With the continuous development of industrial society, environmental and energy problems are becoming increasingly severe. In the past few decades, many pollutants have been directly discharged into nature without thorough treatment, causing enormous pollution. The large-scale production and use of antibiotics has led to the enrichment of large amounts of antibiotics in the environment, causing serious harm to aquatic environments and ecosystems. Because antibiotic pollution can potentially lead to the emergence and spread of antibiotic resistance genes (ARGs), it has become a significant environmental issue. Researching efficient, environmentally friendly, simple, and low-cost methods for treating organic pollutants in water bodies is now urgently needed.

[0003] Photocatalysis has become an effective technology for removing pollutants from water due to its simplicity, low cost, and environmental friendliness. Among these technologies, g-C3N4 is a polymer semiconductor material with excellent photocatalytic performance. Compared to traditional semiconductor photocatalysts, g-C3N4 possesses superior characteristics such as high chemical and thermal stability, a medium bandgap (2.7 eV), an ideal electronic structure, non-toxicity, and low density, making it one of the most popular photocatalytic materials in the field of environmental pollution control. However, several drawbacks severely limit its widespread application, including rapid recombination of photoinduced charge carriers, insufficient utilization of visible light, and difficulty in recycling. Solving these problems to achieve efficient photocatalysis remains a challenging task.

[0004] FeVO4 is a semiconductor with a low bandgap and is a highly stable and selective catalyst with various applications, including photocatalytic degradation of organic pollutants and catalytic dehydrogenation. Constructing heterojunctions using FeVO4 and g-C3N4 can effectively enhance the photocatalytic performance of g-C3N4. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of g-C3N4, such as rapid recombination of photoinduced charge carriers, low utilization of visible light, easy agglomeration of particles, and few reactive sites, and to provide a microwave-assisted hydrothermal method for preparing g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts.

[0006] A method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts is performed according to the following steps:

[0007] I. Preparation of g-C3N4 precursor:

[0008] ① Disperse melamine evenly in deionized water and place it in a beaker to obtain solution A. Similarly, disperse cyanuric acid in another beaker to obtain another solution B.

[0009] ② Mix solution A with solution B and stir vigorously for a certain period of time to obtain the suspension precursor product for preparing g-C3N4. After naturally cooling to room temperature, centrifuge to obtain a white powder of g-C3N4 precursor, wash with deionized water and ethanol, and finally dry in an oven.

[0010] II. Preparation of CQDs:

[0011] ① The biomass (roots, stems, and leaves) is first thoroughly washed several times with deionized water, then dried in a drying oven, and finally pulverized into powder using a pulverizer.

[0012] ② In a beaker, biomass (roots, stems, and leaves) powder, boric acid, and urea are stirred vigorously and gradually dispersed into deionized water. Then, the mixture is transferred to a polytetrafluoroethylene (PTFE) microwave reactor. The reactor is then sealed and reacted at a specific temperature for a specific time within the microwave reactor.

[0013] ③ After cooling to room temperature, filter the solution using a syringe to remove larger particles of residue, then transfer it to a dialysis bag with a molecular cutoff of 14000 Da and dialyze for a certain period of time.

[0014] ④ Finally, evaporate on a rotary evaporator, dry in a vacuum oven, and grind with an agate mortar to obtain CQDs powder.

[0015] III. Preparation of g-C3N4 / CQDs

[0016] ① Dissolve the prepared CQDs in deionized water to prepare CQDs stock solution.

[0017] ② Weigh a certain mass of g-C3N4 precursor, measure a certain amount of CQDs stock solution, mix the two together, add an appropriate amount of deionized water, ultrasonically disperse evenly, and then transfer to a rotary evaporator for evaporation.

[0018] ③ The collected powder was calcined under N2 atmosphere to obtain g-C3N4 / CQDs.

[0019] IV. Preparation of g-C3N4 / CQDs / FeVO4

[0020] ① First, FeCl3·6H2O is dissolved in deionized water to form a clear orange solution A. Then, NH4VO3 is dissolved in deionized water and heated, and this solution is denoted as solution B.

[0021] ② Add solution B from step ① to solution A under vigorous stirring to form a yellow solution, and then uniformly disperse the binary g-C3N4 / CQDs formed above into the precursor solution under ultrasonication and continue stirring.

[0022] ③ Transfer the mixed solution from step ② to a microwave reactor and react in the microwave reactor.

[0023] ④ Collect the obtained precipitate, wash it several times by centrifugation with deionized water and ethanol, then transfer it to an oven to dry and grind it with an agate mortar to obtain g-C3N4 / CQDs / FeVO4 photocatalyst.

[0024] Advantages of this invention:

[0025] I. This invention provides a method for preparing g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts using microwave-assisted hydrothermal methods. The preparation process is simple and easy to operate, low in cost, requires little equipment investment, and is suitable for widespread application.

[0026] II. This invention solves the problems of easy aggregation, small specific surface area, insufficient active sites, and low visible light utilization efficiency of pure g-C3N4 by CQDs induction.

[0027] Third, the g-C3N4 / CQDs / FeVO4 prepared by this invention has advantages such as good stability, low pollution, low energy consumption, short cycle and good product performance, and has important theoretical and practical significance;

[0028] IV. The microwave-assisted water technology used in this invention has the advantages of high controllability, low reaction temperature, small footprint and environmental friendliness.

[0029] V. This invention addresses the shortcomings of low visible light utilization, easy particle aggregation, and few reactive sites by inducing g-C3N4 with CQDs. Furthermore, by constructing a heterojunction with composite FeVO4, the electron-hole recombination rate is reduced, thereby improving photocatalytic performance. The degradation rate of levofloxacin reaches 95.8% within 180 minutes, which can significantly remove levofloxacin antibiotic contaminants.

[0030] This invention provides a microwave-assisted hydrothermal preparation method for g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts. Attached Figure Description

[0031] Figure 1 Scanning electron microscope image of g-C3N4;

[0032] Figure 2 Scanning electron microscope images of g-C3N4 / CQDs;

[0033] Figure 3Scanning electron microscope (SEM) image of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1;

[0034] Figure 4 Infrared spectra of g-C3N4, FeVO4, and g-C3N4 / CQDs / FeVO4;

[0035] Figure 5 XPS image of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1;

[0036] Figure 6 This is a comparison image showing the degradation curves of levofloxacin using the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1, as well as pure g-C3N4 and FeVO4, in Example 2. Detailed Implementation

[0037] Specific Implementation Method 1: A method for preparing g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts using microwave-assisted hydrothermal methods, comprising the following steps:

[0038] 1. A certain mass of FeCl3·6H2O is dissolved in deionized water to form a clear orange solution A. Then, a certain mass of NH4VO3 is dissolved in deionized water and heated, and this solution is denoted as solution B.

[0039] 2. Solution B is added to solution A under vigorous stirring to form a yellow solution, and a certain mass of the binary g-C3N4 / CQDs formed is uniformly dispersed into the above precursor solution under ultrasonic action and stirred continuously.

[0040] 3. Transfer the mixed solution to a microwave reactor and react it in the microwave reactor at a certain temperature range for a certain time;

[0041] IV. Collect the obtained precipitate, centrifuge and wash it several times with deionized water and ethanol, then transfer it to an oven to dry and grind it with an agate mortar to obtain g-C3N4 / CQDs / FeVO4;

[0042] This invention provides a microwave-assisted hydrothermal preparation method for g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the amounts of FeCl3·6H2O and NH4VO3 added in step one are both 1 mmol to 20 mmol, and the molar ratio of FeCl3·6H2O to NH4VO3 is (1:1). The other steps are the same as in Specific Implementation Method One.

[0044] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the amount of g-C3N4 / CQDs added in step two is 1.00 g to 5.00 g. The other steps are the same as in Specific Implementation Method One or Two.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the microwave reaction temperature in step three is 120℃~180℃. The other steps are the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the reaction time of the microwave reactor described in step three is 30 min to 180 min. The other steps are the same as in Specific Implementation Methods One to Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the drying temperature in step four is 50℃~90℃, and the drying time is 6~24 hours. The other steps are the same as in Specific Implementation Methods One to Five.

[0048] The beneficial effects of the present invention are verified using the following embodiments:

[0049] Example 1: A method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts is carried out according to the following steps:

[0050] 1. Dissolve 2.0 mmol FeCl3·6H2O in 50 mL of deionized water to form a clear orange solution A. Dissolve 2.0 mmol NH4VO3 in 50 mL of deionized water and heat to 80 °C. This solution is denoted as solution B.

[0051] II. Optimize and adjust the addition amounts of FeCl3·6H2O, NH4VO3 and g-C3N4 / CQDs to prepare g-C3N4 / CQDs / FeVO4 heterojunction photocatalysts by microwave-assisted hydrothermal treatment;

[0052] The amount of FeCl3·6H2O added in step two is 2.0 mmol;

[0053] The amount of NH4VO3 added in step two is 2.0 mmol;

[0054] The amount of g-C3N4 / CQDs added in step two is 2.00 g;

[0055] 3. Place the stirred mixture into a microwave reactor to carry out the reaction, and adjust the reaction temperature and reaction time.

[0056] The reaction temperature of the microwave reactor described in step three is 180°C;

[0057] The microwave reaction time mentioned in step three is 60 minutes;

[0058] 4. Remove the g-C3N4 / CQDs / FeVO4 obtained in step 3 above from the microwave reactor, dry it, bake it, and grind it.

[0059] The drying temperature described in step four is 60°C;

[0060] Figure 1 Scanning electron microscope image of pure g-C3N4;

[0061] Depend on Figure 1 It is known that pure g-C3N4 has a bulk aggregate morphology, which has a small specific surface area and few active sites, which is not conducive to the photoreaction.

[0062] Figure 2 Scanning electron microscope images of g-C3N4 / CQDs;

[0063] Depend on Figure 2 It can be seen that the introduction of CQDs into the g-C3N4 precursor can induce the growth of g-C3N4 crystals, and the aggregation of g-C3N4 is significantly improved.

[0064] Figure 3 Scanning electron microscope (SEM) image of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1;

[0065] Depend on Figure 3 It can be seen that FeVO4 attaches to the hollow tubular g-C3N4 / CQDs to form a heterojunction, which improves charge transport efficiency, increases specific surface area, and provides more active sites.

[0066] Figure 4 Infrared spectra of g-C3N4, FeVO4, and g-C3N4 / CQDs / FeVO4;

[0067] Depend on Figure 4 It can be seen that at 3404 cm -1 The infrared absorption peak at 2923 cm⁻¹ corresponds to the stretching vibration of the NH / OH bond. -1 and 2852 cm -1 The peak at 1629-1251 cm⁻¹ represents the stretching vibration of the CH bond. -1 The peaks within this range are attributed to the stretching vibrations of C=N / CN. 812 cm⁻¹ -1 The characteristic peak at this location is related to the vibrational mode of the triazine ring. The peak value is at 742 cm⁻¹. -1 and 595 cm -1The characteristic peaks are attributed to the bending vibrations of the VO and Fe-O bonds, respectively. The infrared spectrum confirms the successful preparation of the composite material g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst.

[0068] Figure 5 XPS image of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1;

[0069] Depend on Figure 5 It can be seen that the XPS spectra of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst show characteristic peaks of C 1s, O 1s, N 1s, Fe 2p, and V 2p, proving that the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst is composed of these elements, and also proving the successful preparation of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst.

[0070] Figure 6 This is a comparison of the degradation curves of levofloxacin by the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst prepared in Example 1, and pure g-C3N4 and FeVO4 in Example 2.

[0071] Depend on Figure 6 It can be seen that the prepared g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst achieved a 95.8% degradation rate of levofloxacin after 180 minutes, while pure g-C3N4 and g-C3N4 / CQDs only achieved 13.2% and 57.3%, respectively. This indicates that the construction of the g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst greatly improved the photocatalytic performance of g-C3N4.

[0072] Will Figure 6 The degradation rate of the medium at different times is shown in Table 1.

[0073] Table 1

[0074] Degradation time 30min 60min 90min 120min 150min 180min <![CDATA[g-C3N4]]> 3.1% 3.5% 7.2% 10.1% 11.3% 13.2% <![CDATA[g-C3N4 / CQDs]]> 21.3% 28.3% 39.0% 49.3% 55.2% 57.3% <![CDATA[g-C3N4 / CQDs / FeVO4]]> 51.9% 70.1% 81.8% 91.0% 93.7% 95.8%

Claims

1. A method for preparing a g-C 3 N 4 / CQDs / FeVO 4 heterojunction photocatalyst by microwave-assisted hydrothermal method, characterized in that Comprising the following steps: I. Preparation of g-C3N4 precursor: ①Under stirring conditions, melamine is uniformly dispersed into deionized water to obtain solution A; similarly, cyanuric acid is dissolved in deionized water to obtain another solution B; ②Under water bath conditions, solution A solution and solution B solution are mixed, and a precursor suspension is obtained by vigorous stirring; after natural cooling to room temperature, a white powder of the precursor is obtained by centrifugation, and then washed with deionized water and ethanol, and finally dried in an oven; II. Preparation of CQDs: After the cleaned biomass is dried in an oven, it is crushed into powder by a pulverizer; the biomass powder, boric acid and urea are successively stirred in a beaker, and then gradually dispersed into deionized water, and then transferred into a polytetrafluoroethylene microwave reaction kettle; then, the microwave reaction kettle is sealed, and hydrothermal reaction is carried out in a microwave reactor; after cooling to room temperature, a CQDs solution is obtained by filtering with a microporous filter membrane, and the residual particles are removed and transferred into a dialysis bag for dialysis; finally, the solvent is removed on a rotary evaporator, and dried in a vacuum oven, and then ground with a agate mortar to obtain CQDs powder; III. Preparation of g-C3N4 / CQDs: The prepared CQDs are dissolved in deionized water to prepare a CQDs stock solution; a certain amount of g-C3N4 precursor is weighed, a certain volume of CQDs stock solution is measured, and the two are mixed, and then a proper amount of deionized water is added, and then ultrasonic dispersion is carried out, and then transferred to a rotary evaporator for evaporation; the obtained powder is collected and calcined under N2 atmosphere to obtain g-C3N4 / CQDs; The concentration of the CQDs stock solution in step three is 1 g / L -1 5 g / L -1 The added mass of the g-C3N4 precursor is 1 g to 5 g, the added amount of the CQDs stock solution is 5 mL to 40 mL, and the added amount of deionized water is 10 mL to 100 mL. The calcination temperature in step three is 350℃-550℃, and the calcination time is 1-4 hours; IV. Preparation of g-C3N4 / CQDs / FeVO4: ①First, FeCl3·6H2O is dissolved in deionized water to form a clear orange solution A; NH4VO3 is dissolved in deionized water and heated, and is recorded as solution B; In step four ①, the addition amount of FeCl3·6H2O and NH4VO3 is 1mmol-20mmol, the molar ratio of FeCl3·6H2O and NH4VO3 is 1:1, and the addition amount of deionized water is 50mL-250mL; ②Solution B in step ① is slowly added to solution A under vigorous stirring to form a yellow solution, and the binary g-C3N4 / CQDs formed above is uniformly dispersed into the above solution under ultrasonic action and continues to be stirred; In step four ②, the addition amount of binary g-C3N4 / CQDs is 1g-5g; ③The mixed solution in step ② is transferred to a microwave digestion tank, and hydrothermal reaction is carried out in a microwave reactor; In step four ③, the temperature of the microwave reactor is 120℃-180℃, and the reaction time is 30min-180min; ④The obtained precipitate is washed several times with deionized water and ethanol, dried in an oven, and then ground with a agate mortar to obtain a g-C3N4 / CQDs / FeVO4 composite catalyst. In step one ①, the addition amount of melamine is 5g-20g, and the addition amount of cyanuric acid is 2g-8g.

2. The method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst according to claim 1, characterized in that... ​ 3. The method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst according to claim 1, characterized in that... The adding amount of the biomass in the step two is 0.4g-1.6g, the adding amount of the boric acid is 0.2g-0.8g, the adding amount of the urea is 0.1g-0.4g, the mass ratio of the boric acid and the urea is 2:1, and the volume of the deionized water is 15mL-60mL.

4. The method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst according to claim 1, characterized in that... The temperature of the microwave reactor in the step two is 120℃-180℃, and the reaction time is 30min-80min.

5. The method for microwave-assisted hydrothermal preparation of g-C3N4 / CQDs / FeVO4 heterojunction photocatalyst according to claim 1, characterized in that... The temperature of the drying in the step four ④ is 50℃-90℃, and the drying time is 6-24 hours.

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