CN113600221A

CN113600221A - Au/g-C3N4Monoatomic photocatalyst, and preparation method and application thereof

Info

Publication number: CN113600221A
Application number: CN202110824870.0A
Authority: CN
Inventors: 董红军; 肖梦雅; 李春梅; 左延; 朱达强; 宋宁; 洪士欢
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2021-07-21
Filing date: 2021-07-21
Publication date: 2021-11-05
Anticipated expiration: 2041-07-21
Also published as: CN113600221B

Abstract

The invention provides an Au/g-C ₃ N ₄ single-atom photocatalyst and a preparation method and application thereof, belonging to the technical field of photocatalysts; in the present invention, based on Au chelate as a precursor, continuous stirring is simply used An Au/g-C ₃ N ₄ single-atom photocatalyst was prepared by a one-step calcination method, and the Au/g-C ₃ N ₄ single-atom photocatalyst showed excellent photocatalytic activity for reducing carbon dioxide under visible light.

Description

Au/g-C3N4Monoatomic photocatalyst, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of photocatalysts, and particularly relates to Au/g-C₃N₄A monatomic photocatalyst, a preparation method and application thereof.

Background

Solar energy is currently the cleanest, most abundant, most promising renewable resource, and it is well suited for large-scale utilization. Solar energy needs to be converted through a photocatalyst, so that effective utilization of energy is realized, and meanwhile, the problems of global warming and greenhouse effect and the like caused by continuous increase of carbon dioxide concentration in the atmosphere are increasingly serious, so that a novel and efficient photocatalytic material is designed to recycle carbon dioxide, and the novel and efficient photocatalytic material not only can solve the environmental problem caused by the greenhouse effect, but also can solve the problem of increasingly severe energy exhaustion.

At present, the photocatalytic carbon dioxide reduction technology mainly utilizes solar energy to excite a semiconductor photocatalytic material to generate photoproduction electrons and holes so as to induce oxidation-reduction reaction to synthesize carbon dioxide and water into hydrocarbon fuel. In recent years, a single photocatalytic material such as titanium dioxide has a small crystal size, a large specific surface area and uniformly dispersed crystal grains, and is beneficial to material adsorption reaction, but the limitation of the energy band position of the material is not beneficial to absorption of visible light. And graphite phase g-C₃N₄(abbreviation g-C₃N₄) Etc. has a narrow forbidden band width (2.7eV), can respond to visible light, has the advantages of acid resistance, alkali resistance, corrosion resistance and the like, can be used as a nonmetal semiconductor photocatalytic material, but g-C₃N₄Still has the defects of small specific surface area, easy recombination of electron hole pairs, low photocatalytic performance and the like. Meanwhile, the problems that the synthesis steps are complicated, the required materials are not easy to obtain, the reaction conditions are harsh and the like exist when a single photocatalytic material is compounded with the material.

4, 4-amino-2, 2-bipyridine (C)₁₀H₁₀N₄) The double-tooth chelate ligand can form chelate such as gold, ruthenium, palladium and the like with a plurality of metal ions, and simultaneously has more lone pair electrons due to the existence of amino functional groups, so that the nucleophilic reaction is easy to occur due to the high density of electron cloud.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides Au/g-C₃N₄A monatomic photocatalyst, a preparation method and application thereof. In the invention, based on Au chelate as a precursor, Au/g-C is prepared by simply utilizing a method of continuous stirring and one-step calcination₃N₄A monoatomic photocatalyst, said Au/g-C₃N₄The monatomic photocatalyst exhibits excellent photocatalytic activity in the reduction of carbon dioxide under visible light.

The invention firstly provides Au/g-C₃N₄The single-atom photocatalyst is of a 2D ultrathin nanosheet structure.

The invention also provides the Au/g-C₃N₄The preparation method of the monatomic photocatalyst specifically comprises the following steps:

（1）Au- (C₁₀H₁₀N₄)₃preparing a chelate precursor:

c is to be₁₀H₁₀N₄Dissolving in ethanol solution, performing ultrasonic treatment, continuously stirring until the solution is uniformly dispersed, and slowly dropwise adding Au³ ⁺Stirring the solution to obtain a mixed solution, and reacting to obtain Au- (C)₁₀H₁₀N₄)₃A chelate precursor solution;

（2）Au/g-C₃N₄preparation of monatomic photocatalyst:

dissolving melamine in Au- (C)₁₀H₁₀N₄)₃Ultrasonically stirring the chelate precursor solution, heating in a water bath until the chelate precursor solution is evaporated to dryness, grinding and drying the evaporated solid, then calcining at high temperature, washing, centrifuging and drying to obtain Au/g-C₃N₄A monatomic photocatalyst.

Further, in the step (1), C₁₀H₁₀N₄The dosage ratio of the alcohol to the ethanol is 0.035-0.175 g: 20 mL.

Further, in the step (1), the Au is³⁺The concentration of the mixed solution is 10-50 mg/mL.

Further, in the step (2), theMelamine and Au- (C)₁₀H₁₀N₄)₃The mass ratio of Au in the chelate precursor solution is 1: 100.

Further, in the step (2), the water bath heating is carried out at 40-75 ℃.

Further, in the step (2), the high-temperature calcination conditions are as follows: calcining for 6 hours at 550 ℃, wherein the temperature rise rate of the calcination is 5-6 ℃/min.

Further, the heating rate of the calcination is 5 ℃/min.

The invention also provides the Au/g-C₃N₄The application of the monatomic photocatalyst in photocatalytic carbon dioxide reduction.

Compared with the prior art, the invention has the beneficial effects that:

in the present invention, g-C is used₃N₄The excellent adsorption performance and the easy formation of chelate with noble metal lead the formed chelate system to have a multi-electron structure, thus forming a synergistic effect and greatly improving the occurrence of photocatalytic reduction reaction, thereby greatly improving the photocatalytic performance.

In the present invention, Au- (C) is used₁₀H₁₀N₄)₃Is used as a chelate precursor and is further calcined with melamine to prepare Au/g-C₃N₄A monatomic photocatalyst. Due to Au- (C)₁₀H₁₀N₄)₃Has chelating property, and can be in g-C₃N₄The surface has thermodynamic adsorption stability, so Au- (C)₁₀H₁₀N₄)₃Novel Au/g-C prepared by taking chelate as precursor₃N₄The monatomic photocatalyst increases the active sites of the photocatalyst prepared by the system, enhances the utilization rate of light energy, simultaneously improves the utilization rate of photon-generated carriers, obtains further application in photocatalytic carbon dioxide reduction, and opens up a new way for constructing a novel visible light catalytic material prepared by taking a noble metal chelate as a precursor.

In the present invention, Au- (C) is used₁₀H₁₀N₄)₃Preparing Au/g-C by continuously stirring chelate precursor and melamine in ethanol solution and simply calcining₃N₄A monatomic photocatalyst. The photocatalyst obtained by the experimental procedure and g-C obtained by calcining pure melamine in one step₃N₄Compared with the method for preparing Au/g-C based on Au chelate as precursor₃N₄The photo catalytic activity of the monatomic photocatalyst is to reduce carbon dioxide into carbon monoxide with the yield of 36.92 umol within 4h, and the carbon monoxide is monomer g-C₃N₄3.6 times of (10.28 umol).

Au/g-C prepared by taking Au chelate as precursor₃N₄The formation of the monatomic photocatalyst system obviously improves the capture capability of the monatomic photocatalyst system to light and the utilization rate of photon-generated carriers, and finally greatly improves the efficiency of carbon dioxide reduction. In addition, the method simply utilizes the Au chelate compound constructed by continuous stirring and one-step calcination as a precursor to prepare Au/g-C₃N₄The monatomic photocatalyst has simple process, convenient operation and short reaction time, thereby reducing the energy consumption and the production cost, being convenient for batch production, having no toxicity and harm and meeting the environment-friendly requirement.

Drawings

FIG. 1 shows Au-g-C₃N₄-1 microstructure composition diagram of catalyst, wherein a is Au/g-C₃N₄-1 transmission electron microscopy image of monatomic photocatalyst at 50nm on a scale; b is Au/g-C₃N₄-1 transmission electron microscopy imaging of a monatomic photocatalyst at 100nm on a scale; c is Au/g-C₃N₄-1 high angle spherical dark field image of a monatomic photocatalyst at 5nm on a scale; d is Au/g-C₃N₄1 high angle spherical dark field image of monoatomic photocatalyst at scale 10 nm.

FIG. 2 shows g-C₃N₄And Au/g-C₃N₄-1 XPS spectrum of the catalyst, in which a is the C spectrum of XPS, b is the N spectrum, C is the O spectrum and d is the Au spectrum.

FIG. 3 is g-C₃N₄And Au/g-C₃N₄-1 catalysisPL of the agent.

FIG. 4 shows g-C₃N₄And Au/g-C₃N₄-1 transient photocurrent test of the catalyst.

FIG. 5 is g-C₃N₄And Au/g-C₃N₄The energy diagrams of the catalysts under different proportions are shown in the figure, wherein a is a reaction kinetic diagram of different catalysts, and b is a chart of carbon monoxide yield per unit time of different catalysts.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.

Example 1:

（1）Au- (C₁₀H₁₀N₄)₃preparing a chelate precursor:

weigh 0.035 g C₁₀H₁₀N₄Dissolving in 20ml ethanol solution, ultrasonic treating for 30 min, and continuously stirring to obtain solution C₁₀H₁₀N₄The Au was dissolved sufficiently and 2 ml of 5 mg/ml was taken up³⁺Transferring the solution twice with 1000 μ l pipette, slowly dripping into the continuously stirred solution, and stirring for 24 hr to obtain Au- (C)₁₀H₁₀N₄)₃A chelate precursor solution;

（2）Au/g-C₃N₄preparation of monatomic photocatalyst:

2.0 g of melamine were accurately weighed and dissolved in Au- (C)₁₀H₁₀N₄)₃Performing ultrasonic treatment for 15min in the chelate precursor solution, stirring for 24 h, then performing water bath heating at 45 ℃ until the chelate precursor solution is dried to dryness, grinding the dried solid, drying, placing the obtained solid in a porcelain boat, wrapping the solid with tinfoil, tightly calcining at 550 ℃, keeping the temperature for 6h, increasing the temperature at the rate of 6 ℃/min, centrifuging, washing and drying to obtain Au/g-C₃N₄-0.5 monatomic photocatalyst.

FIG. 1 is Au-g-C₃N₄-1 microstructure composition diagram of photocatalyst, FIG. 1(a) (b) is complex sample Au-g-C₃N₄1 projection diagram, g-C observed in diagrams (a) (b)₃N₄The ultra-thin nanosheet structure, but the microstructure and local mapping of Au of the Au cannot be observed, which shows that Au-g-C₃N₄1 Au in the sample may be in the form of a single atom which cannot be observed at lower magnification, and (C) (d) is Au-g-C₃N₄-1 spherical aberration diagrams at different magnifications, from which it is clearly observed that Au particles with certain light spots are uniformly dispersed in g-C₃N₄In (1), Au/g-C is thus demonstrated by the above pictures₃N₄Successful synthesis of monatomic photocatalysts.

FIG. 2 is pure g-C₃N₄And Au/g-C₃N₄XPS spectra of photocatalysts, pure g-C was investigated with XPS₃N₄And Au/g-C₃N₄Chemical bond states of elements in the sample. Wherein FIG. 2(a) C1 s is in the monomers g-C₃N₄Two binding energy peaks at 284.6 eV and 287.9 eV, assigned to C = C/C-C and N-C = N, respectively, and Au/g-C are shown in₃N₄-1 shows a peak binding energy shift of 0.1 eV to lower levels on N-C = N structures, indicating a change in the chemical environment of C; FIG. 2 (b) N1 s in monomers g-C₃N₄Three binding energy peaks are shown at 398.4 eV, 400.0 eV, and 404.2 eV, respectively, due to C-N = C, N-C₃And C-NH_xAnd Au/g-C₃N₄-1 is located at a binding energy peak shifted towards high energy levels by 0.1 eV on N-C = N structure, Au/g-C₃N₄1, the energy levels of C and N elements in the sample are shifted to opposite directions, which shows that the introduction of Au changes the valence bond structure between the C and N elements, and a new acting force is formed between the Au and the N elements. FIG. 2 (C) O1 s spectrum at g-C₃N₄And Au/g-C₃N₄Little or no significant change in-1 occurred due to the binding energy at 531.8 eV coming from water molecules-OH in the air present at the sample surface; FIG. 2(d) Au 4f is Au/g-C₃N₄Spectra in the sample-1, 87.7 eV and 83.7 eV belonging to Au 4f 5/2 and Au 4f 7/2, respectively, to Au⁰The valence state. It was further demonstrated by XPS analysis that Au chelates based on the precursorsBulk preparation of Au/g-C₃N₄Successful synthesis of monatomic photocatalysts.

FIG. 3 is pure g-C₃N₄And Au/g-C₃N₄-1 PL profile of the monatomic photocatalyst, with PL being used to study the migration and separation of photogenerated electron-hole pairs in a sample. As can be seen, Au/g-C was prepared based on Au chelate as precursor₃N₄The fluorescence intensity of the-1 monatomic photocatalyst was significantly reduced relative to that of the carbon nitride monomer, indicating that Au/g-C₃N₄The synthesis of the-1 monatomic photocatalyst obviously improves the migration and separation efficiency of the photo-generated electron-hole pairs, greatly inhibits the recombination efficiency of photo-generated carriers, and is also the main reason for improving the photocatalytic reduction activity.

FIG. 4 is pure g-C₃N₄And Au/g-C₃N₄-1 instantaneous photocurrent test pattern of the monatomic photocatalyst (test method: the catalyst is formulated as ink spin-coated on conductive glass, under xenon lamp (420 nm) irradiation, the instantaneous photocurrent test is performed by using a three-electrode system through an electrochemical workstation, a shutter is used to block the light source during the test, and the switching interval is 30 s). As can be seen in FIG. 4, Au/g-C was prepared based on Au chelate as precursor₃N₄The photocurrent intensity of the-1 photocatalyst is obviously enhanced and is far higher than that of the monomer g-C₃N₄The photocurrent intensity of the photocatalyst material is that Au/g-C is prepared based on Au chelate as a precursor in photocatalysis₃N₄The capture capability of the-1 photocatalyst to a photo-generated carrier is obviously improved, and the preparation of Au/g-C based on Au chelate as a precursor is proved₃N₄The-1 photocatalyst can effectively inhibit the recombination of photo-generated electron-hole pairs, and the photocatalytic performance is improved.

Example 2:

（1）Au- (C₁₀H₁₀N₄)₃preparing a chelate precursor:

（2）Au/g-C₃N₄preparation of monatomic photocatalyst:

1.0g of melamine was accurately weighed and dissolved in Au- (C)₁₀H₁₀N₄)₃Performing ultrasonic treatment for 15min in the chelate precursor solution, stirring for 24 h, then performing water bath heating at 45 ℃ until the chelate precursor solution is dried to dryness, grinding the dried solid, drying, placing the obtained solid in a porcelain boat, wrapping the solid with tinfoil, tightly calcining at 550 ℃, keeping the temperature for 6h, increasing the temperature at the rate of 5 ℃/min, centrifuging, washing and drying to obtain Au/g-C₃N₄-1 monatomic photocatalyst.

Example 3:

（1）Au- (C₁₀H₁₀N₄)₃preparing a chelate precursor:

weigh 0.175 gC₁₀H₁₀N₄Dissolving in 20ml ethanol solution, ultrasonic treating for 30 min, and continuously stirring to obtain solution C₁₀H₁₀N₄Fully dissolved, and 10 ml of 5 mg/ml Au is absorbed³⁺Transferring the solution twice with 1000 μ l pipette, slowly dripping into the continuously stirred solution, and stirring for 24 hr to obtain Au- (C)₁₀H₁₀N₄)₃A chelate precursor solution;

（2）Au/g-C₃N₄preparation of monatomic photocatalyst:

1.665 g of melamine were accurately weighed and dissolved in the above Au- (C)₁₀H₁₀N₄)₃Performing ultrasonic treatment for 15min, stirring for 24 h, heating in water bath at 45 deg.C until it is evaporated to dryness, grinding the evaporated solid, oven drying, wrapping the obtained solid in porcelain boat with tinfoil, calcining at 550 deg.C, and keepingThe temperature is 6h, the heating rate is 5 ℃/min, then the Au/g-C is obtained by centrifugation, washing and drying₃N_4-3 a monatomic photocatalyst.

Example 4:

（1）Au- (C₁₀H₁₀N₄)₃preparing a chelate precursor:

weigh 0.175g C₁₀H₁₀N₄Dissolving in 20ml ethanol solution, ultrasonic treating for 30 min, and continuously stirring to obtain solution C₁₀H₁₀N₄Fully dissolved, and 10 ml of 5 mg/ml Au is absorbed³⁺Transferring the solution twice with 1000 μ l pipette, slowly dripping into the continuously stirred solution, and stirring for 24 hr to obtain Au- (C)₁₀H₁₀N₄)₃A chelate precursor solution;

（2）Au/g-C₃N₄preparation of monatomic photocatalyst:

1.0g of melamine was accurately weighed and dissolved in the above Au- (C)₁₀H₁₀N₄)₃Performing ultrasonic treatment for 15min in the chelate precursor solution, stirring for 24 h, then performing water bath heating at 45 ℃ until the chelate precursor solution is dried to dryness, grinding the dried solid, drying, placing the obtained solid in a porcelain boat, wrapping the solid with tinfoil, tightly calcining at 550 ℃, keeping the temperature for 6h, increasing the temperature at the rate of 5 ℃/min, centrifuging, washing and drying to obtain Au/g-C₃N₄-5 monatomic photocatalyst.

Example 5:

the photocatalytic carbon dioxide reduction test is respectively carried out on photocatalytic materials (50 mg) with different proportions in a pure water solution, 100 ml of deionized water is injected into a quartz glass reactor, 50mg of catalyst is added, the reactor is sealed and then exhausted, namely, carbon dioxide gas is introduced as a reactant in the photocatalytic reduction, air in the reactor is exhausted, the interference of external gas is eliminated, the exhaust lasts for 20min and then is finished, then a miniature ultraviolet lamp tube is used for irradiating the reactor for photocatalytic reaction, and the whole system is carried out at room temperature. And detecting the gas product and yield of the reaction by using gas chromatography.

FIG. 5(a) shows different ratios of the single atom Au/g-C₃N₄Kinetic curves of the reaction of the catalyst, from which the monoatomic Au/g-C can be obtained₃N₄The yield of carbon monoxide produced by photocatalytic carbon dioxide reduction of the catalyst is far higher than that of the monomer g-C₃N₄Yield of monoatomic Au/g-C₃N₄The catalytic reduction performance of-1 reaches the highest, and the monoatomic Au/g-C can be seen from a kinetic curve₃N₄0.5 to monoatomic Au/g-C₃N₄5 Monoatomic Au/g-C which still has a reducing potential after 4 hours of reaction₃N₄The reaction rate of-1 is highest, while the monomers g-C₃N₄There was almost no reduction performance after 4 hours of reaction. Thus, Au/g-C is prepared based on Au chelate as precursor₃N₄The carbon dioxide reduction performance of the photocatalyst is higher than that of the monomer g-C₃N₄Reduction performance of (1), optimum photocatalytic material Au/g-C₃N₄The photocatalytic performance of-1 tends to be stable in the trend of growth per unit time and also much higher per hour than that of the monomers g-C₃N₄And photocatalytic material at other ratios.

FIG. 5(b) is the reduction yield per unit time, monoatomic Au/g-C₃N₄0.5 to monoatomic Au/g-C₃N₄5 reduction performance is higher than that of the monomer g-C₃N₄Reduction performance of (2), and optimum ratio of Au/g-C₃N₄1 up to 9.23umol/g/h for the production of carbon monoxide is a monomer_、g-C₃N₄3.6 times of performance. The material Au/g-C can be seen₃N₄The reason why the performance of the photocatalytic reduction of the carbon dioxide is greatly improved can be attributed to that the Au single atom is in g-C₃N₄Is formed on the molecule. The result shows that Au/g-C is prepared based on Au chelate as a precursor₃N₄The-1 photocatalyst obviously enhances the photocatalytic carbon dioxide reduction performance.

Comparative example 1:

1.0g of melamine was dissolved in Au- (C)₁₀H₁₀N₄)₃Performing ultrasonic treatment for 15min in the chelate precursor solution, stirring for 24 h, then heating in water bath at 45 ℃ until the chelate precursor solution is evaporated to dryness, grinding and drying the evaporated solid, placing the obtained solid in a porcelain boat, wrapping the solid with tinfoil, tightly calcining at 550 ℃, keeping the temperature for 6h, increasing the temperature at the rate of 5 ℃/min, centrifuging, washing and drying to obtain Au/g-C₃N₄A monatomic photocatalyst.

The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.

Claims

1. a preparation method of Au/gC ₃ N ₄ single-atom photocatalyst, is characterized in that, comprises:

(1) Preparation of Au-(C ₁₀ H ₁₀ N ₄ ) ₃ chelate precursor:

Dissolve C ₁₀ H ₁₀ N ₄ in ethanol solution and sonicate, then continuously stir until the dispersion is uniform, slowly add Au ³⁺ solution dropwise, stir to obtain a mixed solution and react to obtain Au- (C ₁₀ H ₁₀ N ₄ ) ₃ chelate precursor solution;

(2) Preparation of Au/gC ₃ N ₄ single-atom photocatalyst:

Melamine is dissolved in Au-(C ₁₀ H ₁₀ N ₄ ) ₃ chelate precursor solution, ultrasonically stirred, then heated in a water bath until evaporated to dryness, the evaporated solid is ground and dried, followed by high temperature calcination, washing, Centrifuge and dry to obtain Au/gC ₃ N ₄ single-atom photocatalyst.

2. The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1, wherein in step (1), the consumption ratio of C ₁₀ H ₁₀ N ₄ and ethanol is 0.035~0.175g: 20mL.

3 . The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1, wherein in step (1), the concentration of the Au ³⁺ in the mixed solution is 10-50 mg/mL .

4. The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1, wherein in step (2), the melamine is chelated with Au-(C ₁₀ H ₁₀ N ₄ ) ₃ The mass ratio of Au in the precursor solution was 1:100.

5 . The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1 , wherein, in step (2), the heating in a water bath is heating in a water bath at 40-75° C. 6 .

6 . The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1 , wherein, in step (2), the high temperature calcination condition is: calcination at 550° C. for 6 hours. 7 .

7 . The method for preparing an Au/gC ₃ N ₄ single-atom photocatalyst according to claim 1 , wherein in step (2), the heating rate of the calcination is 5-6° C./min. 8 .

8 . The preparation method of Au/gC ₃ N ₄ single-atom photocatalyst according to claim 7 , wherein the heating rate of the calcination is 5° C./min. 9 .

9 . The Au/gC ₃ N ₄ single-atom photocatalyst prepared by the method according to any one of claims 1 to 8, wherein the photocatalyst has a 2D ultrathin nanosheet structure.

The application of the Au/gC ₃ N ₄ single-atom photocatalyst according to claim 9 in photocatalytic carbon dioxide reduction. 11 .