CN114669289A - A kind of synthetic method of carbon quantum dot/ZnO composite photocatalyst - Google Patents

Abstract

A synthetic method of a carbon quantum dot/ZnO composite photocatalyst comprises the following steps: adding the air-dried sugarcane peel into distilled water, and carrying out ultrasonic crushing; transferring all the solution into a reaction container, placing the reaction container into an oven for reaction, transferring the solution in the reaction container into a dialysis bag, and dialyzing to obtain a carbon quantum dot solution; adding 2-methylimidazole into distilled water, magnetically stirring, and adding Zn (NO) dropwise₃)₂·6H₂O water solution, continuing magnetic stirring, ultrasonic treating, centrifuging, and addingWashing with anhydrous methanol for more than 5 times, and drying the solid collected after washing in an oven to obtain ZIF-8; heating ZIF-8, calcining and pyrolyzing to obtain a ZnO nano material; dispersing the ZnO nano material in a carbon quantum dot solution, adding absolute ethyl alcohol and distilled water, carrying out magnetic stirring reaction, centrifuging and washing in sequence, and finally placing in an oven for drying to obtain the carbon quantum dot/ZnO composite photocatalyst. The carbon quantum dots are uniformly distributed on the surfaces of the ZnO nanoparticles, so that the dispersibility of the ZnO nanoparticles is improved, and the increase of the specific surface area of the catalyst is facilitated.

Description

A kind of synthesis method of carbon quantum dot/ZnO composite photocatalyst

technical field

The invention relates to the technical field of preparation of photocatalytic materials, in particular to a method for synthesizing carbon quantum dots/ZnO composite photocatalysts.

Background technique

In today's rapid development, environmental pollution, especially water pollution, has become a difficult problem that people must face. The rapid development of chemical, textile, dye, pharmaceutical, leather and other industries has resulted in the emergence of a large number of harmful substances in the water body, which has seriously damaged human beings and the ocean. The living environment of aquatic organisms. How to deal with the negative impact brought by the extensive economic development model and adopt effective methods to deal with water pollution is a problem that people urgently need to solve.

ZnO is an important semiconductor material, and nano-ZnO materials have been widely used in many technical fields. Because ZnO has the advantages of high surface activity, stable chemical properties, and abundant content in nature, it shows potential application value in the field of photocatalysis. However, the photocatalytic efficiency of ZnO is reduced due to the rapidly recombined photogenerated electrons and holes, and the wide band gap makes it almost unresponsive to visible light, which limit the further application of ZnO. Researchers have modified ZnO to broaden its photoresponse range and inhibit the recombination of photogenerated electrons and holes, thereby helping to improve the photocatalytic performance of ZnO. For example, Wang J et al. believed that oxygen vacancy was a self-doping method without introducing any impurity elements, and successfully introduced a high concentration of oxygen vacancies into ZnO. The photocurrent response of ZnO is enhanced under visible light irradiation (Wang J, et al., ACS Applied Materials & Interfaces, 2012, 4(8), 4024-4030.). Sin JC et al. synthesized rare-earth-doped nano-ZnO microspheres by liquid-phase precipitation. Compared with pure ZnO and commercial _TiO2 , the absorption spectrum showed a red shift, showing better photocatalytic activity, and photocatalytic degradation of phenol under visible light irradiation. , exhibiting good photocatalytic activity (Sin JC, et al., Ceramics International, 2014, 40(4), 5431-5440.). Rajbongshi BM et al. synthesized Co-doped ZnO nanorods by hydrothermal method, which catalyzed the degradation of methylene blue and phenol under visible light, red-shifted the absorption spectrum, and exhibited high photocatalytic activity (Rajbongshi BM, et al., Materials Science and Engineering). :B, 2014, 182, 21-28.).

In addition, as a new type of carbon material, carbon quantum dots have rapidly attracted extensive research due to their excellent optical properties and good chemical inertness. Carbon quantum dots have no dependence on the wavelength of light excitation, and have the ability to transfer fast photogenerated electrons and control the functionalized surface, which can greatly improve the photocatalytic performance of the material. How to easily and efficiently prepare composites composed of carbon quantum dots and nano-ZnO materials with good visible light catalytic performance is an important topic of current research.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems existing in the prior art, the present invention provides a method for synthesizing carbon quantum dots/ZnO composite photocatalysts. The carbon quantum dots/ZnO composite photocatalyst synthesized by the method has carbon quantum dots evenly distributed on ZnO nanometers. The particle surface improves the dispersibility of ZnO nanoparticles, which helps to increase the specific surface area of the catalyst; and provides more active sites, and the photocatalytic effect of the carbon quantum dot/ZnO composite photocatalyst is significantly higher than that of the single photocatalyst. ZnO catalyst material.

To achieve the above object, the present invention provides a method for synthesizing carbon quantum dots/ZnO composite photocatalyst, which comprises the following steps:

(1) get air-dried sugar cane husks and join in distilled water, ultrasonically crush, obtain suspension;

(2) Transfer all the suspension in step (1) into the reaction vessel, place it in an oven to react at 180-220° C. for 4-8 hours, cool down to room temperature naturally after the reaction is completed, and then transfer the solution in the reaction vessel Dialyze in a dialysis bag for 24-48h to obtain a carbon quantum dot solution;

(3) Take 2-methylimidazole in distilled water, stir evenly with magnetic force, add Zn(NO ₃ ) ₂ ·6H ₂ O aqueous solution dropwise to it, continue magnetic stirring for 5-10min, sonicate for 0.5-1h, and the solution after sonication Centrifuge first, then wash with anhydrous methanol for more than 5 times, and place the solid collected after washing in an oven to dry at 60-75°C for 6-8h to obtain ZIF-8;

(4) heating the ZIF-8 obtained in step (3) to 500-600°C at a heating rate of 4-6°C/min, calcining for 3-5h, and pyrolyzing to obtain a white solid product as a ZnO nanomaterial;

(5) disperse the ZnO nanomaterial obtained in step (4) in the carbon quantum dot solution obtained in step (2), add absolute ethanol and distilled water to it, and stir magnetically for 3-5h;

(6) The solution obtained by magnetic stirring in step (5) was reacted at 120-160 ° C for 2-8 h, and after the reaction was completed, it was cooled to normal temperature, and then the cooled product was subjected to centrifugation and washing in sequence, and finally placed at 50 The carbon quantum dots/ZnO composite photocatalyst was obtained by drying in an oven at -80°C for 6-8 hours.

As a further preferred technical solution of the present invention, in step (1), according to the consumption of every 25-200mg of air-dried sugar cane peel, the consumption of corresponding distilled water is 40mL, and the time of ultrasonic crushing is 30-90min.

As a further preferred technical scheme of the present invention, in step (3), according to the consumption of every 2.000g 2-methylimidazole, the consumption of corresponding distilled water is 90mL, and the concentration is the Zn(NO) of ^50-200mg ·mL ₃ ) The amount of ₂ ·6H ₂ O aqueous solution is 10 mL.

As a further preferred technical solution of the present invention, in step (5), according to the consumption of each 0.075g ZnO nanomaterial, the corresponding carbon quantum dot solution is 5-20mL, the consumption of absolute ethanol is 6mL, and the consumption of distilled water to 10mL.

As a further preferred technical solution of the present invention, the reaction vessel in step (1) is a stainless steel autoclave lined with polytetrafluoroethylene.

As a further preferred technical solution of the present invention, in step (4), the ZIF-8 is heated to 500-600°C at a heating rate of 4-6°C/min through a muffle furnace, and then calcined for 3-5h.

As a further preferred technical solution of the present invention, in step (6), the solution obtained by magnetic stirring is reacted at 120-160° C. for 2-8 hours in a high-pressure reactor.

The synthetic method of the carbon quantum dot/ZnO composite photocatalyst of the present invention can achieve the following beneficial effects by adopting the above-mentioned technical scheme:

1) The present invention prepares carbon quantum dots by using air-dried sugarcane peel as a precursor, which well realizes the resource utilization of biomass and reduces the production cost of materials;

2) the synthetic method of the present invention is simple and easy to operate, and has good repeatability;

3) the carbon quantum dots/ZnO composite photocatalyst synthesized by the present invention, the carbon quantum dots are evenly distributed on the surface of the ZnO nanoparticles, which improves the dispersibility of the ZnO nanoparticles, thereby helping to increase the specific surface area of the catalyst; With more active sites, the photocatalytic effect of carbon quantum dots/ZnO composite photocatalyst is significantly higher than that of single ZnO catalyst material;

4) In the carbon quantum dot/ZnO composite photocatalyst synthesized by the present invention, the addition of carbon quantum dots can inhibit the recombination of ZnO photogenerated electrons and holes, and the up-conversion effect of carbon quantum dots is used to broaden the light response range, thereby greatly improving the performance of the photocatalyst. Properties of carbon quantum dots/ZnO composite photocatalysts.

Description of drawings

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

1 is a high-resolution transmission electron microscope (HRTEM) photo of the product in Example 1;

Fig. 2 is the X-ray diffraction pattern (XRD) of product in embodiment 1;

Fig. 3 is the infrared spectrogram of carbon quantum dot/ZnO composite;

FIG. 4 is a comparison diagram of the photocatalytic performance of rhodamine B by carbon quantum dots/ZnO composites.

The object realization, functional features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Terms such as "up", "down", "left", "right", "middle" and "one" quoted in the preferred embodiment are only for the convenience of description and clarity, and are not intended to limit the scope of the present invention. The scope of implementation, the change or adjustment of the relative relationship, and the technical content without substantial change, shall also be regarded as the scope of the present invention.

Example 1

Weigh 25 mg of air-dried sugar cane peel in 40 mL of distilled water, and ultrasonically crush for 60 min to obtain a clear solution;

All the above-mentioned clear solutions were transferred to a stainless steel autoclave lined with polytetrafluoroethylene (volume filling rate was 80%), and the autoclave was placed in an oven at 200°C for 4 hours of reaction. The solution was transferred to a dialysis bag for 48h dialysis to obtain a carbon quantum dot solution;

Accurately weigh 2.000g of 2-methylimidazole in 90mL of distilled water, stir magnetically to obtain a uniform solution, add 10mL of 75mg·mL ^-1 Zn(NO ₃ ) ₂ ·6H ₂ O aqueous solution dropwise thereto, stir magnetically for 10min, then Sonicate for 1 h, centrifuge the sonicated solution, wash it with anhydrous methanol for more than 5 times, and place the collected solid in an oven at 70°C for 8 h to obtain ZIF-8;

The ZIF-8 was put into a muffle furnace and heated to 550°C at 5°C/min, calcined for 4h, and pyrolyzed to obtain a white solid product ZnO nanomaterial;

Accurately weigh the 0.075g ZnO nanomaterial prepared above and disperse it in 12.5mL carbon quantum dot solution, then add 6mL absolute ethanol and 10mL distilled water to it in turn, stir magnetically for 4h, after the end of magnetic stirring, transfer all the solution to high pressure reaction In the kettle, the reaction was carried out at 140 °C for 4 hours. The cooled product was centrifuged, washed, and finally dried in an oven at 70 °C for 8 hours. Finally, carbon quantum dots/ZnO composites were prepared, that is, carbon quantum dots/ZnO composite photocatalysts.

The product prepared in this example was tested by scanning electron microscope, X-ray diffraction and infrared spectrum, as shown in Figures 1-3.

Figure 1 is the HRTEM image of the carbon quantum dot/ZnO composite. It can be seen from the figure that the carbon quantum dots with a size of 2-5 nm are evenly distributed on the surface of the ZnO nanoparticles, and the small-sized carbon quantum dots are effectively loaded on the surface of the ZnO nanoparticles. It helps to inhibit the agglomeration of ZnO nanoparticles, increases the specific surface area of ZnO nanoparticles, provides more active sites, and is expected to obtain better photocatalytic effects. Figure 2 is the XRD pattern of carbon quantum dots/ZnO composites. The composites have diffraction peaks at 31.73°, 34.36°, 36.21°, 47.47°, 56.53°, 62.75°, 66.29°, 67.85° and 68.99°, respectively. Corresponding to the (100), (002), (101), (102), (110), (103), (200), (112) and (201) facets of ZnO, consistent with hexagonal wurtzite ZnO (JCPDSNo.36-1451), indicating that the ZnO in the product has a hexagonal wurtzite structure. No significant diffraction peaks were found in the range of 2θ=20-30°, which may be caused by the fact that the amount of carbon quantum dots was too small, and the diffraction peaks of carbon were not detected by XRD. To confirm the existence of carbon quantum dots, the FT-IR spectra of carbon quantum dots/ZnO composites were studied, as shown in Figure 3. The diffraction peak at the wavenumber of 430cm ^-1 in the FT-IR image corresponds to the characteristic absorption peak of Zn-O, the weak _-CH2 characteristic absorption peak at 2850cm ^{- 1} , and the characteristic absorption peak of CO at 1260cm-1, which proves the complex The presence of carbon quantum dots and the shift of characteristic peaks indicate an interaction between ZnO and carbon quantum dots.

In order to study the adsorption properties of the products prepared by the present invention, 10 mg·L ^-1 Rhodamine B (RhB, purchased from Sinopharm Chemical Reagent Co., Ltd.) was used as the photocatalytic degradation target, and a 300W xenon lamp was used as the light source (with a filter to make λ>420 nm), to explore the catalytic degradation effect of carbon quantum dots/ZnO composites. Figure 4 is a comparison diagram of the photocatalytic performance of rhodamine B by two catalysts of purchased ZnO powder (denoted as ZnO) and carbon quantum dots/ZnO composite (denoted as CQDs/ZnO). The degradation of rhodamine B showed a trend of rapid first and then gentle; when the light was illuminated for 20 min, the degradation rate of rhodamine B by the purchased ZnO powder was 42%, and the degradation rate of rhodamine B by carbon quantum dots/ZnO composites was 42%. More than 95%; when irradiated for 30 min, the degradation rates of rhodamine B by the purchased ZnO powder and carbon quantum dots/ZnO composites were 43% and 99%, respectively. The above results show that the photocatalytic effect of carbon quantum dots/ZnO composites is significantly higher than that of purchased ZnO powders.

Example 2-33

Using the amount of carbon quantum dot solution and other experimental conditions in Table 1, the carbon quantum dot/ZnO composite photocatalyst was prepared according to the preparation process described in Example 1.

Table 1. Comparison of various experimental conditions and photocatalytic degradation of RhB in Examples 2-33

According to the experimental data in Table 1, it can be known that:

(1) When the amount of air-dried sugarcane peel is low (such as 25 mg) and the solvothermal time is short (such as 4 h), the carbon quantum dot solution can be synthesized, and it can be combined with the lower concentration Zn(NO ₃ ) ₂ ·6H ₂ O solution (50mg·mL ^-1 ) composite, the prepared carbon quantum dot/ZnO composite photocatalyst, the photocatalytic RhB degradation rate is not less than 95%.

(2) When the amount of air-dried sugarcane peel is large (such as 200mg), a longer solvothermal time (such as 8h) is required, and the concentration of the Zn(NO ₃ ) ₂ ·6H ₂ O solution involved in the compounding is also high (such as 200mg· mL ^-1 ), the prepared carbon quantum dots/ZnO composite photocatalyst showed a slight increase in the photocatalytic RhB degradation rate, reaching 98%.

To sum up, in order to degrade more Rhodamine B, it is necessary to increase the amount of air-dried sugarcane peel, increase the solvothermal time and a higher concentration of Zn(NO ₃ ) ₂ ·6H ₂ O solution.

Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to the embodiments without departing from the principle and essence of the present invention. The scope of protection is limited only by the appended claims.

Claims (7)

1. a synthetic method of carbon quantum dot/ZnO composite photocatalyst, is characterized in that, comprises the following steps: (1) get air-dried sugar cane husks and join in distilled water, ultrasonically crush, obtain suspension; (2) Transfer all the suspension in step (1) into the reaction vessel, place it in an oven to react at 180-220° C. for 4-8 hours, cool down to room temperature naturally after the reaction is completed, and then transfer the solution in the reaction vessel Dialyze in a dialysis bag for 24-48h to obtain a carbon quantum dot solution; (3) Take 2-methylimidazole in distilled water, stir evenly with magnetic force, add Zn(NO ₃ ) ₂ ·6H ₂ O aqueous solution dropwise to it, continue magnetic stirring for 5-10min, sonicate for 0.5-1h, and the solution after sonication Centrifuge first, then wash with anhydrous methanol for more than 5 times, and place the solid collected after washing in an oven to dry at 60-75°C for 6-8h to obtain ZIF-8; (4) heating the ZIF-8 obtained in step (3) to 500-600°C at a heating rate of 4-6°C/min, calcining for 3-5h, and pyrolyzing to obtain a white solid product as a ZnO nanomaterial; (5) disperse the ZnO nanomaterial obtained in step (4) in the carbon quantum dot solution obtained in step (2), add absolute ethanol and distilled water to it, and stir magnetically for 3-5h; (6) The solution obtained by magnetic stirring in step (5) was reacted at 120-160 ° C for 2-8 h, and after the reaction was completed, it was cooled to normal temperature, and then the cooled product was subjected to centrifugation and washing in sequence, and finally placed at 50 The carbon quantum dots/ZnO composite photocatalyst was obtained by drying in an oven at -80°C for 6-8 hours. 2. the synthetic method of carbon quantum dots/ZnO composite photocatalyst according to claim 1, is characterized in that, in step (1), by the consumption of every 25-200mg air-dried sugarcane peel, the consumption of corresponding distilled water is 40mL, And the time of ultrasonic fragmentation is 30-90min. 3. the synthetic method of carbon quantum dots/ZnO composite photocatalyst according to claim 2, is characterized in that, in step (3), by the consumption of every 2.000g 2-methylimidazole as benchmark, the consumption of corresponding distilled water It is 90 mL, and the dosage of the Zn(NO ₃ ) ₂ .6H ₂ O aqueous solution with a concentration of 50-200 mg·mL ^-1 is 10 mL. 4. the synthetic method of carbon quantum dots/ZnO composite photocatalyst according to claim 3, is characterized in that, in step (5), according to the consumption of every 0.075g ZnO nanomaterial as benchmark, corresponding carbon quantum dot solution is 5-20mL, the amount of absolute ethanol is 6mL, and the amount of distilled water is 10mL. 5. the synthetic method of carbon quantum dots/ZnO composite photocatalyst according to claim 1, is characterized in that, the reaction vessel in step (1) is the stainless steel autoclave whose inner lining is polytetrafluoroethylene. 6. the synthetic method of carbon quantum dot/ZnO composite photocatalyst according to claim 1, is characterized in that, in step (4), ZIF-8 is heated up to 500 with 4-6 ℃/min heating rate by muffle furnace -600℃, then calcined for 3-5h. 7. the synthetic method of carbon quantum dots/ZnO composite photocatalyst according to any one of claim 1 to 6, is characterized in that, in step (6), by autoclave by the solution obtained after magnetic stirring at 120- 160 ℃ reaction 2-8h.

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