CN114160180A - Microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4Method for compounding materials - Google Patents
Microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4Method for compounding materials Download PDFInfo
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/344—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy
- B01J37/346—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy of microwave energy
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- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
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- B82Y40/00—Manufacture or treatment of nanostructures
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- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/30—Treatment of water, waste water, or sewage by irradiation
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C—CHEMISTRY; METALLURGY
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- C—CHEMISTRY; METALLURGY
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- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2305/00—Use of specific compounds during water treatment
- C02F2305/10—Photocatalysts
Abstract
The invention discloses a microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4CompoundingA method of making a material comprising the steps of: (1) under the microwave radiation power of 600-700W, reacting the precursor citric acid of the CNQDs with thiourea for 5-7 min in a bulk phase heating mode according to the molar ratio of 1 (0.9-1.1) to obtain the graphite Carbon Nitride Quantum Dots (CNQDs); (2) g to C3N4Adding the precursor substance into water, stirring until the precursor substance is dissolved, adding the CNQDs prepared in the step, and continuously stirring for 0.5-1h to obtain CNQDs and g-C3N4The mixture of precursor substances is irradiated by microwave for 2-6min at 14-16 deg.C for min‑1The temperature is raised to 550 ℃, the calcination is carried out for 1 to 1.5 hours, then the temperature is lowered to the room temperature at the speed of 10 to 12 ℃/min, and the CNQDs/g-C are obtained after the washing with water and the washing with ethanol in sequence and the drying at the temperature of 50 to 70 DEG C3N4A composite material. The method is simple to operate, low in cost, green and environment-friendly, and easy for large-scale production; preparing to obtain CNQDs/g-C3N4The composite material has good crystallinity, the particle size is less than 20nm, the distribution is uniform, the specific surface area is large, the photoelectric property is good, and the photocatalysis performance is better.
Description
Technical Field
The invention relates to a microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4A method for compounding materials belongs to the technical field of clean and efficient material synthesis.
Background
The development of a semiconductor photocatalyst with excellent catalytic performance and good stability under visible light is an important subject in the field of photocatalysis, and has important significance for solving the current energy and environmental problems. Carbon nitride graphite (g-C)3N4) As a metal-free photocatalyst, people have attracted great attention because of its advantages such as appropriate band gap (2.7eV), high stability, easy synthesis, and low cost of raw materials. However, the strong recombination of carriers still limits g-C due to the weak van der Waals interactions between adjacent CN layers3N4Photocatalytic activity of (1). Although coupling to other semiconductors has proven effective in suppressing charge recombination, the currently available metal-free materials are very limited.
In recent years, the synthesis of Quantum Dot (QDs) -based composites has become a focus of research. Quantum dots can be used to generate multiple quantum dots using thermionic electrons or using a single high-energy photonA carrier. The design of QDs-Based composite materials is an effective strategy for improving the photodegradation efficiency of the photocatalyst under the irradiation of visible light. At the same time, QDs-based materials offer a unique opportunity: by researching a theoretical model, the mechanism path of the catalytic reaction is rationalized, so that the precision is higher than that of a bulk material. Finally, the process of catalytic reaction is deeply understood at the atomic level, and the correlation between the structure of the material and the corresponding performance of the material is researched. Novel g-C3N4Quantum Dot (CNQDs) materials are receiving much attention due to their special optical properties. The CNQDs have up-conversion PL characteristics and quantum effects irrelevant to excitation, and unique photoelectric characteristics of the CNQDs endow visible light and long-wavelength broadband optical absorption, so that near infrared light can be converted into visible light, and the collection of solar energy is promoted; in addition, it is also possible to construct homoheterojunctions with semiconductors by forming them in g-C3N4CNQDs are modified on the surface, so that the photocatalytic degradation performance of the composite material is enhanced. In the prior art, melamine and thiourea are used as raw materials, sulfur-doped carbon nitride quantum dots (S-CNQDs) are prepared by a single-pot copolymerization method, and g-C with larger specific surface area is prepared by a one-step in-situ polymerization method3N4(S-CNQDs); however, it is prepared by first mixing g-C3N4Dissolving in dimethyl sulfoxide, adding CNQDs precursor solution, heating to 180 deg.C, and refluxing for 2, 6, and 10 hr respectively; after cooling to room temperature, the crude product was collected by centrifugation, washed sequentially with tetrahydrofuran, dichloromethane and acetone and dried under vacuum for 24 h. The preparation method has certain defects: (1) the reaction time is long and the process is complex; (2) the energy consumption is large; (3) organic solvents such as tetrahydrofuran, dichloromethane and the like are adopted in the experimental process, so that the method is not green and environment-friendly.
Disclosure of Invention
The invention provides a microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4The method for preparing the composite material is simple, green and environment-friendly, and easy for large-scale production, and the obtained CNQDs/g-C3N4The composite material has the characteristics of rich pore structure, better photocatalytic performance and the like, and has application value in the fields of photocatalysis, wastewater treatment and the like.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4A method of compounding a material comprising the steps of:
(1) under the microwave radiation power of 600-700W, reacting the precursor citric acid of the CNQDs with thiourea for 5-7 min in a bulk phase heating mode according to the molar ratio of 1 (0.9-1.1) to obtain the graphite Carbon Nitride Quantum Dots (CNQDs);
(2) g to C3N4Adding the precursor substance into water, stirring until the precursor substance is dissolved, adding the CNQDs prepared in the step, and continuously stirring for 0.5-1h to obtain CNQDs and g-C3N4The mixture of precursor substances is irradiated by microwave for 2-6min at 14-16 deg.C for min-1The temperature is raised to 550 ℃, the calcination is carried out for 1 to 1.5 hours, then the temperature is lowered to the room temperature at the speed of 10 to 12 ℃/min, and the CNQDs/g-C are obtained after the washing with water and the washing with ethanol in sequence and the drying at the temperature of 50 to 70 DEG C3N4A composite material.
The method can obtain CNQDs/g-C with high specific surface area, lamella morphology and abundant pore structures3N4A composite material. The method obviously overcomes the defects of long time consumption and low yield of the traditional synthetic method, is simple to operate, environment-friendly and green, and is easy for large-scale production, and meanwhile, the synthesized material can keep a higher photocatalytic degradation effect, so that an effective way is provided for the synthesis of the composite photocatalyst, and the method has application values in the fields of photocatalysis, wastewater treatment and the like. Compared with the drying process of 12-24h in the traditional method, the microwave treatment before calcination greatly reduces the drying time of the calcined precursor, reduces the raw material loss in the drying process, improves the yield of the carbon nitride prepared from urea, improves the yield by 10 times compared with direct calcination, and improves the 120min photocatalytic degradation effect by 25 percent compared with the traditional method.
In order to ensure the catalytic performance of the composite material, in step (2), CNQDs/g-C are obtained3N4In the composite material, the content of CNQDs is 0.5-7 wt%, and more preferably, the content of CNQDs is 4-6 wt%.
In the above step (2), g to C3N4The precursor is urea, and the concentration of the dissolved urea is 0.4-0.6 g/ml.
In the step (2), the power of microwave irradiation is 600-700W.
In the step (2), the calcining atmosphere is air or nitrogen, and the drying is vacuum drying at 50-55 ℃.
The traditional thermal copolymerization method is adopted to prepare CNQDs/g-C3N4The composite material is long in time consumption and complex in process. The microwave-assisted thermal copolymerization method can be adopted to rapidly polymerize Carbon Nitride Quantum Dots (CNQDs) and g-C3N4The mixed precursor substances are calcined, so that the efficiency is greatly improved, and the loss of urea is reduced. The method reduces the sample synthesis time and unnecessary raw material waste through the microwave-assisted heating process, is simple to operate, is environment-friendly, green and efficient, and is a rapid, clean and efficient material synthesis method. Simultaneously, CNQDs/g-C prepared by microwave-assisted thermal copolymerization3N4The composite material has excellent photocatalytic performance.
The microwave-assisted thermal copolymerization method is used for preparing CNQDs/g-C3N4Composite material prepared by mixing at g-C3N4CNQDs are modified on the surface, so that the transport of photon-generated carriers is accelerated, the separation efficiency of electron holes is improved, and the photocatalytic performance of the electron holes is improved. In addition, CNQDs are of interest because of their unique upconversion properties, which convert near infrared light into visible light, thereby facilitating the collection of solar energy.
Microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4The composite material is applied, is prepared by the method, is used as a photocatalyst, and has the dosage of 100-200 mg/L in photocatalytic degradation of pollutants.
CNQDs/g-C prepared by the application3N4The composite material has high activity and low consumption. The dosage of the existing similar materials in photocatalytic degradation of pollutants is 1 g/L.
CNQDs/g-C prepared by the application3N4The composite material can be recycled after being washed and dried by ethanol for five timesThe photocatalytic performance of the photocatalyst can still keep more than 90 percent of the original activity after being recycled.
The prior art is referred to in the art for techniques not mentioned in the present invention.
The invention relates to a microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4The method for preparing the composite material is simple to operate, low in cost, green and environment-friendly, and easy for large-scale production; preparing to obtain CNQDs/g-C3N4The composite material has good crystallinity, the particle size is less than 20nm, the distribution is uniform, the specific surface area is large, the photoelectric property is good, the photocatalytic property is good, and the composite material has application value in the fields of photocatalysis, wastewater treatment and the like.
Drawings
FIG. 1 shows CNQDs/g-C of the present invention3N4Composite material synthesis flow chart;
FIG. 2 shows the conventional and microwave-assisted methods for preparing CNQDs/g-C3N4Composite time versus time plot;
FIG. 3 shows 5% CNQDs/g-C prepared in example 1 of the present invention3N4SEM images of the composite;
FIG. 4 shows CNQDs/g-C doped with different amounts of CNQDs prepared in example 1 of the present invention3N4XRD pattern of the composite;
FIG. 5 shows CNQDs/g-C doped with different amounts of CNQDs prepared in example 1 of the present invention3N4UV-vis DRS profile of the composite;
FIG. 6 shows CNQDs/g-C prepared in example 1 of the present invention3N4An apparent rate constant graph of the degradation of NOF (norfloxacin) by the composite material;
FIG. 7 shows 5% CNQDs/g-C prepared in example 1 of the present invention3N4A recycling graph of the composite;
FIG. 8 shows 5% CNQDs/g-C prepared in example 1 of the present invention3N4SEM images of direct polymerization (left panel) and microwave-assisted polymerization (right panel);
FIG. 9 shows 5% CNQDs/g-C prepared in example 1 of the present invention3N4Photocatalytic degradation profiles of direct polymerization and microwave-assisted polymerization;
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the following examples.
Example 1 CNQDs/g-C3N4Preparation of composite photocatalytic material
Preparation of CNQDs by modified Rapid microwave method: under the microwave radiation power of 600W, the precursor citric acid of the CNQDs reacts with thiourea for 7min according to the molar ratio of 1:1 by a bulk phase heating mode to obtain the CNQDs.
Adding 10g of urea into 20ml of water, stirring for dissolving, mixing the prepared CNQDs stock solution with the urea, and continuously stirring for 0.5h to form a transparent solution; transferring the solution into a 40ml crucible, heating in a 600W household microwave oven for 3min, calcining at 550 deg.C for 1h in air atmosphere, and heating at 15 deg.C for min-1(ii) a After calcination, the mixture is heated at 10 ℃ for min-1The temperature is reduced to room temperature, and the mixture is dried in vacuum at 50 ℃ to constant weight after being washed by water and ethanol in sequence. Composites with different CNQDs contents (0.5 wt%, 1 wt%, 2 wt%, 5 wt% and 8 wt%) were prepared. Furthermore, pure g-C was prepared by the same method except adding CNQDs3N4(CNQDs content 0 wt%).
FIG. 3 shows CNQDs/g-C3N4SEM image of the composite material (CNQDs content 5 wt%), confirming that the composite material prepared above has an ultra-thin 2D folded laminar structure; figure 4 is an XRD pattern of the composite material showing two typical g-C at 27.74 ° and 12.9 ° 2 θ3N4Diffraction peaks of g-C, respectively3N4(002) And (100) a crystal plane; after the CNQDs were introduced, the position of the (002) peak was slightly shifted from 27.74 ° to 27.46 °, which may be related to the compression of CNQDs nanoparticles; the final material prepared in this example is shown as CNQDs/g-C3N4A composite material. The ultraviolet-visible DRS analysis method is adopted to research CNQDs/g-C3N4As shown in FIG. 5, it can be seen that pure g-C3N4Has a basic absorption at 460nmThe edge is narrowed, almost no absorption is generated in the range of 400-800nm, and after CNQDs are modified, CNQDs/g-C3N4The light trapping ability of the composite material in the visible light region gradually increases.
As can be seen from FIG. 6, CNQDs/g-C obtained in example 13N4The composite material has better photocatalytic degradation performance under visible light, the dosage of the composite material in a photocatalytic pollutant degradation experiment is 200mg/L, and the quasi-first-order reaction kinetic constant is 0.023min-1Is pure g-C3N4And (k is about 2.3 times of 0.01).
To evaluate the recyclability of the composite, a recycling experiment was carried out: after each NOR degradation experiment, the powder catalyst was filtered and recovered and washed with ethanol 3 times, and then dried in an oven for the next use. As shown in FIG. 7, after 5 cycles, the photocatalytic performance of the photocatalyst still maintains more than 90% of the original activity. The result shows that the prepared photocatalytic composite membrane has stable NOR removal performance and recycling performance.
Example 2 CNQDs/g-C3N4Preparation of composite photocatalytic material
The microwave heating time before calcination was 5min, and the other steps and parameters were the same as in example 1.
The inventor finds that microwave radiation can promote material densification, promote grain growth and accelerate chemical reaction, and in the microwave process, the microwave not only serves as a heating energy source, but also has the function of catalyzing, activating and sintering. In this example, after 5min of microwave, a uniform lamellar microstructure was obtained, which was more ductile and tough.
Example 3 CNQDs/g-C3N4Preparation of composite photocatalytic material
After adding CNQDs, the mixture is stirred at a speed of 500r/min for 1 h. The other steps and parameters were the same as in example 1.
Stirring is an important step in the material synthesis process, in order to obtain a uniform mixture, and in this embodiment, the quantum dots are more uniformly attached to g-C through 1h of stirring process3N42D sheet structureIn (1).
Example 4 CNQDs/g-C3N4Preparation of composite photocatalytic material
The difference from example 1 is: the drying temperature is 65 ℃. The other steps and parameters were the same as in example 1. Increasing the temperature accelerates the drying process of the material, but increasing the drying temperature also has a slight effect on the morphology of the material.
Comparative example 1
Different from the embodiment 1, the microwave irradiation step before calcination does not exist, and specifically comprises the following steps: adding 10g of urea into 20ml of water, stirring for dissolving, mixing the prepared CNQDs stock solution with the urea, and continuously stirring for 1 hour to form a transparent solution; transferring the solution into a forced air drying oven, drying overnight, calcining at 550 deg.C for 1h at a heating rate of 15 deg.C for min-1(ii) a After calcination, the mixture is heated at 10 ℃ for min-1The temperature is reduced to room temperature, and the mixture is dried in vacuum at 60 ℃ to constant weight after being washed by water and ethanol in sequence.
As can be seen from fig. 8, the microwave-assisted polymerization method significantly improved the agglomeration phenomenon as compared to the direct polymerization method. Furthermore, as can be seen from FIG. 9, CNQDs/g-C synthesized in comparative example 1 was used3N4The degradation efficiency of NOR is about 70% at 120min, and 5 wt% CNQDs/g-C synthesized by microwave-assisted thermal copolymerization method3N4The photocatalytic degradation efficiency of the composite material can reach more than 95% within 120min, and the photocatalytic performance of the composite material is obviously improved. In addition, the CNQDs/g-C is also obviously improved in the example 13N4The yield of the composite material was increased by 10 times compared to comparative example 1. Meanwhile, as shown in fig. 2, example 1 improves the reaction speed and the reaction selectivity, thereby rapidly synthesizing the nanomaterial in a short time.
Claims (8)
1. Microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4A method of compounding a material, characterized by: the method comprises the following steps:
(1) under the microwave radiation power of 600-700W, reacting the precursor citric acid of the CNQDs with thiourea for 5-7 min in a bulk phase heating mode according to the molar ratio of 1 (0.9-1.1) to obtain the graphite Carbon Nitride Quantum Dots (CNQDs);
(2) g to C3N4Adding the precursor substance into water, stirring until the precursor substance is dissolved, adding the CNQDs prepared in the step, and continuously stirring for 0.5-1h to obtain CNQDs and g-C3N4The mixture of precursor substances is irradiated by microwave for 2-6min at 14-16 deg.C for min-1The temperature is raised to 550 ℃, the calcination is carried out for 1 to 1.5 hours, then the temperature is lowered to the room temperature at the speed of 10 to 12 ℃/min, and the CNQDs/g-C are obtained after the washing with water and the washing with ethanol in sequence and the drying at the temperature of 50 to 70 DEG C3N4A composite material.
2. The method of claim 1, wherein: the CNQDs/g-C obtained in step (2)3N4In the composite material, the content of CNQDs is 0.5-8 wt%.
3. The method of claim 2, wherein: the CNQDs/g-C obtained in step (2)3N4In the composite material, the content of CNQDs is 4-6 wt%.
4. A method according to any one of claims 1-3, characterized by: in step (2), g to C3N4The precursor is urea, and the concentration of the dissolved urea is 0.4-0.6 g/ml.
5. A method according to any one of claims 1-3, characterized by: in the step (2), the power of microwave irradiation is 600-700W.
6. A method according to any one of claims 1-3, characterized by: in the step (2), the calcining atmosphere is air or nitrogen, and the drying is vacuum drying at 50-55 ℃.
7. Microwave-assisted thermal copolymerization method for preparing CNQDs/g-C3N4Use of a composite material obtainable by the process of any one of claims 1 to 6, wherein: the dosage is 100-200 mg/LContaminants。
8. The use of claim 7, wherein: washed by ethanol, dried and recycled.
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