CN117563645A - Composite photocatalyst based on surface aminated carbon nitride, preparation method and application - Google Patents
Composite photocatalyst based on surface aminated carbon nitride, preparation method and application Download PDFInfo
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- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical class N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 title claims abstract description 166
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- 238000002360 preparation method Methods 0.000 title claims abstract description 17
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- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 2
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- 239000011261 inert gas Substances 0.000 claims description 2
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- 238000000034 method Methods 0.000 claims 7
- 230000001699 photocatalysis Effects 0.000 abstract description 25
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- 239000003054 catalyst Substances 0.000 abstract description 2
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- 230000000052 comparative effect Effects 0.000 description 56
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 40
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 5
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- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 4
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine powder Natural products NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 description 4
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- GSEJCLTVZPLZKY-UHFFFAOYSA-N Triethanolamine Chemical compound OCCN(CCO)CCO GSEJCLTVZPLZKY-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
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- 238000001816 cooling Methods 0.000 description 1
- XTVVROIMIGLXTD-UHFFFAOYSA-N copper(II) nitrate Chemical compound [Cu+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O XTVVROIMIGLXTD-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
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- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- 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
- B01J27/24—Nitrogen compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/16—Reducing
- B01J37/18—Reducing with gases containing free hydrogen
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention belongs to the technical field of catalysts, and particularly relates to a composite photocatalyst based on surface aminated carbon nitride, and a preparation method and application thereof. The preparation method comprises the steps of firstly placing bulk phase carbon nitride into a tube furnace, performing heat treatment under the action of oxygen, stripping the bulk phase carbon nitride into single-layer or oligolayer carbon nitride nano-sheets, then ultrasonically dispersing the carbon nitride nano-sheets and urea into ethylene glycol, performing solvothermal reaction to obtain surface amino carbon nitride nano-sheets, and finally depositing a metal cocatalyst on the surface of the carbon nitride to obtain the composite photocatalyst based on the surface amino carbon nitride. The metal promoter obtained by the invention has strong interaction between the metal particles and the aminated carbon nitride nano-sheets on the surface of the carrier, can promote the separation and transmission of photon-generated carriers, can also improve the utilization rate of metal atoms in photocatalytic reaction, and shows extremely excellent photocatalytic performance under visible light.
Description
Technical Field
The invention relates to the technical field of catalyst preparation, in particular to a composite photocatalyst based on surface aminated carbon nitride, and a preparation method and application thereof.
Background
The photocatalysis technology has been widely researched and developed in recent years by virtue of the advantages of high efficiency, green and pollution-free properties, direct utilization of solar energy and the like, and is especially used in a series of environmental and energy fields such as pollutant degradation, hydrogen production by photocatalytic water splitting, oxygen production, carbon dioxide reduction, organic synthesis and the like. As a visible light responsive photocatalyst, graphite phase carbon nitride has the characteristics of high stability, simple synthesis method, two-dimensional layered structure and the like, and is widely paid attention to by researchers in the field of photocatalysis. The graphite-phase carbon nitrides, which are in a two-dimensional layered structure, are stacked together, known as "bulk" carbon nitrides. However, bulk carbon nitride photocatalysts have many defects, and the photo-generated carriers have high recombination probability under illumination, so that the photocatalysts have low photocatalytic performance, and the practical application of the bulk carbon nitride photocatalysts in the field of photocatalysis is limited.
In the photocatalytic reaction, the cocatalyst plays a vital role in improving the activity, stability and the like of the photocatalyst, such as improving the electron-hole separation efficiency at an interface, reducing the activation energy of surface reaction, providing reactive sites, inhibiting the occurrence of reverse reaction and the like. Thus, by loading the promoter, particularly a metal promoter (e.g., platinum, gold, copper, etc.), a substantial improvement in the photocatalytic performance of the carbon nitride can be achieved. Because the bulk phase carbon nitride surface lacks enough active sites, after the metal is deposited on the carbon nitride surface, the interaction between the metal and the carbon nitride is weaker, the transfer probability of photo-generated carriers is lower, and the advantages of the metal promoter are difficult to fully develop.
Therefore, the structural optimization is carried out on the bulk phase carbon nitride surface, the metal-carrier interaction is improved, and the design of the efficient carbon nitride-based composite photocatalyst has important significance.
Disclosure of Invention
The invention aims to provide a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which can greatly enhance the interaction between metal and a carrier, realize the effective separation and transmission of photo-generated carriers and improve the utilization rate of metal atoms in photocatalytic reaction, thereby obviously enhancing the performance of the carbon nitride photocatalyst.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a preparation method of a composite photocatalyst based on surface aminated carbon nitride comprises the following steps:
s1, placing bulk phase carbon nitride in a tube furnace, and performing heat treatment in high-purity oxygen at 480-580 ℃ to obtain a carbon nitride nano sheet with a single-layer or oligolayer structure;
s2, dispersing the carbon nitride nano-sheets prepared in the step S1 into ethylene glycol, and then adding urea for continuous and uniform dispersion, wherein the mass ratio of the urea to the carbon nitride nano-sheets is (0.1-2.0): 1, so as to obtain a mixed suspension; carrying out solvothermal reaction on the mixed suspension at 120-200 ℃, and centrifuging, washing and drying a product to obtain the surface aminated carbon nitride nano-sheet;
s3, dispersing the surface aminated carbon nitride nano-sheets into deionized water, and then mixing with a metal precursor aqueous solution, wherein the mass ratio of metal in the metal precursor aqueous solution to the surface aminated carbon nitride nano-sheets is (0.1-10): 100, stirring the mixed solution at 60-100 ℃ for reaction, freeze-drying, placing the dried powder into a tube furnace, and performing thermal reduction at 200-600 ℃ under the action of hydrogen to obtain the composite photocatalyst based on the surface aminated carbon nitride.
As a further improvement in the preparation of surface aminated carbon nitride based composite photocatalyst:
preferably, the purity of the high purity oxygen in step S1 is >99.99%, and the heat treatment time is 5-30min.
Preferably, the dispersion concentration of the carbon nitride nano-sheets in the ethylene glycol in the step S2 is 1-3mg/ml, and the solvothermal reaction time is 1-24h.
Preferably, the metal precursor in the metal precursor aqueous solution in step S3 is a single metal water-soluble salt or a combination of two or more metal water-soluble salts.
Preferably, the metal of the metal water-soluble salt is one of noble metal Au, pt, pd, ag or non-noble metal Fe, cu, co, ni, and the water-soluble salt is chloride, nitrate, sulfate or sulfite.
Preferably, the mixture in step S3 is stirred at 60-100deg.C for 2-12 hours.
Preferably, the time for thermal reduction in step S3 is 1-6 hours.
Preferably, the hydrogen gas in step S3 is used as a high-purity hydrogen gas atmosphere with a purity of >99.99%, or as a mixed atmosphere of hydrogen gas and inert gas.
The second object of the invention is to provide a composite photocatalyst based on surface aminated carbon nitride prepared by the preparation method of any one of the above.
It is still another object of the present invention to provide a use of the above-mentioned composite photocatalyst based on surface aminated carbon nitride in photocatalytic reactions such as decomposition of water and reduction of carbon dioxide.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which comprises the steps of firstly stripping bulk phase carbon nitride into single-layer or oligolayer carbon nitride nanosheets through heat treatment, then aminating the surface of carbon nitride through solvothermal reaction with urea, and finally depositing a metal promoter on the surface of carbon nitride, thereby obtaining the composite photocatalyst based on surface aminated carbon nitride. Compared with bulk carbon nitride, when single-layer or oligolayer carbon nitride and urea are subjected to solvothermal reaction, the degree of amination of the carbon nitride surface can be greatly improved. Compared with the non-aminated carbon nitride nano-sheet, the carbon nitride nano-sheet subjected to amination treatment has stronger interaction with metal and smaller particles of metal promoter, can effectively promote the separation and transmission of photogenerated carriers, and can fully exert the advantages of the metal promoter, thereby obviously enhancing the photocatalysis performance of carbon nitride.
The metal promoter obtained by the invention has strong interaction between the metal particles and the aminated carbon nitride nano-sheets on the surface of the carrier, can promote the separation and transmission of photon-generated carriers, can also improve the utilization rate of metal atoms in photocatalytic reaction, and shows extremely excellent photocatalytic performance under visible light.
Drawings
Fig. 1 is a transmission electron microscope image of the surface-aminated carbon nitride composite photocatalyst synthesized in example 1, comparative example 2 and comparative example 3.
Fig. 2 is an infrared spectrum of bulk carbon nitride, example 1, comparative example 1 and comparative example 2.
Fig. 3 is a high resolution XPS spectrum of the element Pt in example 1, comparative example 2 and comparative example 5.
Fig. 4 is a high resolution XPS spectrum of bulk carbon nitride, element N in example 1 and comparative example 2.
Fig. 5 is a graph showing the photocatalytic hydrogen production performance under visible light for bulk carbon nitride, surface aminated carbon nitride nanoplatelets, example 1, comparative example 2, comparative example 3, comparative example 4, and comparative example 5.
FIG. 6 shows the stability of the composite photocatalyst synthesized in example 1 to produce hydrogen by photocatalysis.
Fig. 7 is a high resolution transmission electron microscope image of the surface-aminated carbon nitride composite photocatalyst co-supported by Au and Cu metals synthesized in example 3.
Fig. 8 is the photocatalytic reduction performance of carbon dioxide under visible light for bulk carbon nitride, example 3, comparative example 6, and comparative example 7.
Detailed Description
The present invention will be further described in detail with reference to the following examples, in order to make the objects, technical solutions and advantages of the present invention more apparent, and all other examples obtained by those skilled in the art without making any inventive effort are within the scope of the present invention based on the examples in the present invention.
Example 1
The embodiment provides a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which specifically comprises the following steps:
example 1
The embodiment provides a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which specifically comprises the following steps:
s1, weighing 10g of melamine powder, putting the melamine powder into a 100mL ceramic crucible with a cover, moving the melamine powder into an air muffle furnace, heating the melamine powder from room temperature to 550 ℃ at a heating rate of 5 ℃/min, and preserving heat for 2 hours. After cooling to room temperature, the sintered product was sufficiently ground to give pale yellow bulk carbon nitride (abbreviated as g-C 3 N 4 )。
S2, weighing 0.2g of bulk phase carbon nitride powder (abbreviated as g-C 3 N 4 ) Placing in a tube furnace, and introducing high-purity oxygen (purity>99.99 percent) and annealing and heat treating for 10 minutes at 500 ℃ to obtain the carbon nitride nano-sheet with a single-layer or oligolayer structure, wherein the yield is about 30 percent;
s3, weighing 50mg of the carbon nitride nanosheets prepared in the step S2, dispersing the carbon nitride nanosheets into 30mL of ethylene glycol, and carrying out ultrasonic treatment for 30min; adding 20mg of urea, and continuing to ultrasonically disperse for 30min, wherein the mass ratio of the urea to the carbon nitride nanosheets is 0.4, so as to obtain a mixed suspension;
the mixed suspension was transferred to a stainless steel reaction vessel containing a 100mL polytetrafluoroethylene liner and reacted at 160℃for 6 hours. Centrifuging, washing, and drying the reacted product to obtain surface aminated carbon nitride nanosheets (abbreviated as C 3 N 4 -amino)。
S4, weighing 100mg of surface amino carbon nitride nano-sheets, and dispersing the carbon nitride nano-sheets into 60mL of deionized water by ultrasonic. Then adding a certain amount of chloroplatinic acid aqueous solution (the mass of Pt is 0.5 mg), stirring at 70 ℃ for reaction for 6 hours, freeze-drying the product, placing the dried powder into a tube furnace, and annealing for 2 hours at 200 ℃ under the action of high-purity hydrogen (the purity is more than 99.99%), thus obtaining the metal Pt-loaded surface aminated carbon nitride composite photocatalyst. Wherein the loading of Pt is 0.5wt%.
Example 2
The embodiment provides a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which specifically comprises the following steps:
s1, weighing 0.3g of bulk phase carbon nitride powder prepared in the step S1 of the example 1, placing the bulk phase carbon nitride powder in a tube furnace, introducing high-purity oxygen (purity is more than 99.99%), and carrying out annealing heat treatment at 480 ℃ for 15min to obtain carbon nitride nano-sheets with a single-layer or oligolayer structure, wherein the yield is about 25%;
s2, weighing 100mg of the carbon nitride nanosheets prepared in the step S1, dispersing the carbon nitride nanosheets into 60mL of ethylene glycol, and carrying out ultrasonic treatment for 45min; adding 100mg of urea, and continuing ultrasonic dispersion for 45min, wherein the mass ratio of the urea to the carbon nitride is 1.0, so as to obtain a mixed suspension;
the mixed suspension was transferred to a stainless steel reaction vessel containing a 100mL polytetrafluoroethylene liner and reacted at 180℃for 4 hours. Centrifuging, washing, and drying the reacted product to obtain surface aminated carbon nitride nanosheets (abbreviated as C 3 N 4 -amino)；
S3, weighing 100mg of surface aminated carbon nitride nano-sheets, and ultrasonically dispersing the nano-sheets into 45mL of deionized water. Then adding a certain amount of chloroauric acid aqueous solution (Au is 1.5mg in mass), stirring at 60 ℃ for reaction for 8 hours, freeze-drying the product, placing the dried powder in a tube furnace, and annealing for 1 hour at 300 ℃ under the action of high-purity hydrogen (purity is more than 99.99%), thereby obtaining the metal Au-loaded surface aminated carbon nitride composite photocatalyst. Wherein the Au loading is 1.5wt%.
Example 3
The embodiment provides a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which specifically comprises the following steps:
s1, weighing 0.1g of bulk phase carbon nitride powder prepared in the step S1 of the example 1, placing the bulk phase carbon nitride powder in a tube furnace, introducing high-purity oxygen (purity is more than 99.99%), and carrying out annealing heat treatment at 550 ℃ for 5min to obtain carbon nitride nano-sheets with a single-layer or oligolayer structure, wherein the yield is about 20%;
s2, weighing 60mg of the carbon nitride nanosheets prepared in the step S1, dispersing the carbon nitride nanosheets into 40mL of ethylene glycol, and carrying out ultrasonic treatment for 30min; adding 120mg of urea, and continuing ultrasonic dispersion for 45min, wherein the mass ratio of the urea to the carbon nitride is 2.0, so as to obtain a mixed suspension;
the mixed suspension was transferred to a stainless steel reactor containing a 100mL polytetrafluoroethylene liner, in whichThe reaction was carried out at 140℃for 9h. Centrifuging, washing, and drying the reacted product to obtain surface aminated carbon nitride nanosheets (abbreviated as C 3 N 4 -amino)；
S3, weighing 100mg of surface aminated carbon nitride nano-sheets, and ultrasonically dispersing the nano-sheets into 45mL of deionized water. Then adding a certain amount of copper nitrate and chloroauric acid aqueous solution (Au 0.3mg and Cu 0.6 mg), stirring at 80deg.C for 2 hr, freeze drying, placing the dried powder in a tube furnace, mixing with hydrogen/nitrogen gas (80% N) 2 /20％H 2 ) And (3) annealing for 2 hours at 500 ℃ to obtain the surface aminated carbon nitride composite photocatalyst jointly loaded by the metal Au and Cu. Wherein the loading of Au is 0.3wt% and the loading of Cu is 0.6wt%.
To better embody the advantages of the present invention, we compare with the samples synthesized in the following comparative examples.
Comparative example 1
This comparative example is referred to example 1, except that: bulk carbon nitride is not stripped into carbon nitride nano-sheets through the step S1, and the surface amination and the Pt nano-particle deposition are directly carried out through the step S2 and the step S3.
Comparative example 2
This comparative example is referred to example 1, except that: after bulk carbon nitride is stripped into carbon nitride nano-sheets in the step S1, pt nano-particles are directly deposited in the step S3 without amination treatment in the step S2.
Comparative example 3
This comparative example is referred to example 1, except that: bulk carbon nitride directly deposits Pt nanoparticles through step S3 without undergoing the processing of step S1 and step S2.
Comparative example 4
This comparative example is referred to example 1, except that: the bulk phase carbon nitride is firstly stripped into carbon nitride nano-sheets through the step S1, then the carbon nitride nano-sheets and urea are ultrasonically dispersed in glycol, and Pt nano-particles are directly deposited through the step S3 without solvent thermal reaction.
Comparative example 5
This comparative example is referred to example 1, except that: after the bulk carbon nitride is treated in step S1 and step S2, the Pt nanoparticles synthesized in step S3 are not subjected to hydrogen thermal reduction.
Comparative example 6
This comparative example is referred to example 3, except that: and step S3, only loading Pt nano particles to obtain the metal Pt-loaded surface aminated carbon nitride composite photocatalyst. Wherein the loading of Pt is 0.5wt%.
Comparative example 7
This comparative example is referred to example 3, except that: and S3, only loading Cu nano particles to obtain the metal Cu-loaded surface aminated carbon nitride composite photocatalyst. Wherein the Cu loading is 0.2wt%.
The photocatalytic decomposition of water and reduction of carbon dioxide were used to evaluate the performances under visible light of the photocatalysts obtained in the above examples and comparative examples. The light source was a PLS-SXE300D xenon lamp and a UV420 filter (Beijing Porphy technology Co., ltd.). The gas chromatograph is of the type 1690C of the Kekodak, a thermal conductivity detector, an FID detector and a methane reformer are configured, and the carrier gas is high-purity nitrogen. The photocatalytic water splitting hydrogen production reaction steps are as follows: 5mg of the photocatalyst powder was weighed, added to 100mL of an aqueous solution containing 10vol% of triethanolamine, stirred uniformly, and the photocatalytic reactor was sealed. High purity nitrogen was introduced to purge the reactor at a flow rate of 50 ml per minute to eliminate residual gases in the reactor, and then the photocatalytic reaction was started. The photocatalytic reduction of carbon dioxide is carried out as follows: 50mg of the photocatalyst powder was weighed into a quartz glass reactor filled with carbon dioxide, and 2mL of deionized water was injected, and then the photocatalytic reaction was started.
Fig. 1 is a transmission electron microscope image of the surface-aminated carbon nitride composite photocatalyst synthesized in example 1, comparative example 2 and comparative example 3. By statistics, the particle sizes of Pt nanoparticles supported on the surface of carbon nitride were 0.97, 1.76, 2.1 and 3.8nm, respectively. The smaller the particle size of the Pt nanoparticles, the stronger the interaction between Pt and the carbon nitride of the support. For comparative example 3, the supported Pt and bulk carbon nitride had very weak interactions, neither exfoliated into carbon nitride nanoplatelets nor surface amination modified. For example 1, the support-phase carbon nitride was first exfoliated into carbon nitride nanoplatelets and then modified by surface amination, with strong interactions between the supported Pt and the surface aminated carbon nitride nanoplatelets. For comparative example 2, although the support-phase carbon nitride was exfoliated into carbon nitride nanoplatelets, the interaction between the supported Pt and the support carbon nitride nanoplatelets was also weak since no surface amination modification was performed. For comparative example 1, although bulk carbon nitride was not exfoliated into carbon nitride nanoplatelets, the metal-support interaction was superior to comparative examples 2 and 3 after modification by surface amination. In addition, the smaller the particle diameter of the Pt nano particles is, the larger the specific surface area of the Pt nano particles is, and the utilization rate of Pt atoms on the surface in the photocatalytic reaction can be improved, so that the performance of the photocatalyst is enhanced.
Fig. 2 is an infrared spectrum of bulk carbon nitride, example 1, comparative example 1 and comparative example 2. 3000-3500cm -1 The broad peak at this point corresponds to the N-H bond vibration of the carbon nitride surface, i.e., the degree of surface amination. The transmittance of n—h bond vibration was 78.8%, 71.3%, 77.1% and 78.3%, respectively, for bulk carbon nitride, example 1, comparative example 1 and comparative example 2. The result shows that the carbon nitride nano-sheet is not subjected to surface amination modification, and the surface amination degree is weaker; bulk carbon nitride is subjected to surface amination modification, but the bulk carbon nitride is serious in agglomeration and weak in actual amination degree; only when bulk carbon nitride is stripped into carbon nitride nano-sheets and then surface amination modification is carried out, the surface amination degree can be greatly enhanced.
Fig. 3 and 4 are high resolution XPS spectra of the elements Pt and N in bulk carbon nitride, example 1, comparative example 2 and comparative example 5, respectively. According to FIG. 3, the Pt nanoparticles synthesized in comparative example 2 were synthesized as Pt 0 The metal state form is loaded on the surface of the carrier carbon nitride nano-sheet, and the 70.8eV characteristic peak corresponds to Pt 0 4f of (2) 7/2 Energy level. For example 1, the Pt nanoparticles were also Pt 0 The metal state form is loaded on the surface of the carrier surface aminated carbon nitride nano-sheet. Comparison ofProportion 2 Pt in example 1 0 4f of (2) 7/2 The energy level binding energy red shifted to 71.0 eV. Meanwhile, in comparative example 5, pt was mainly in the metallic state Pt 0 In the form of a surface-aminated carbon nitride, but with a certain amount of Pt in the oxidation state 2+ . Numerous documents indicate that Pt is compared with the oxidation state 2+ Pt in metallic state 0 The nanoparticle is an active site center in a photocatalytic hydrogen production reaction. Therefore, the comparative example 5 had to be subjected to hydrogen thermal reduction to eliminate Pt in the oxidized state as much as possible 2+ (corresponding to example 1). According to the XPS spectrum of the N element in FIG. 4, the binding energy of the N element in example 1 and comparative example 2 showed a red shift compared to bulk carbon nitride, and the magnitude of the red shift of the N element in example 1 was larger. In combination with the results of fig. 1, 2, 3 and 4, the interaction between the metal Pt and the carbon nitride as the carrier can be significantly improved only when bulk carbon nitride is exfoliated into carbon nitride nanoplatelets and then subjected to surface amination modification.
Fig. 5 is a graph showing the photocatalytic hydrogen production performance under visible light for bulk carbon nitride, surface aminated carbon nitride nanoplatelets, example 1, comparative example 2, comparative example 3, comparative example 4, and comparative example 5. The hydrogen production yield is only 18.2 mu mol/h for bulk carbon nitride. For the surface aminated carbon nitride nano-sheet, the hydrogen production yield is slightly improved to 20.8 mu mol/h. Because both bulk carbon nitride and surface aminated carbon nitride nanoplates lack active sites for hydrogen production, their photocatalytic hydrogen production efficiency is very low. When the metal Pt is loaded on the surface of the carbon nitride carrier, the hydrogen production yield is greatly enhanced. For example 1, the hydrogen production yield was increased to 1157.5. Mu. Mol/h, which is 63.6 times that of bulk carbon nitride. For comparative example 5, since there is a small amount of Pt in oxidation state in the supported Pt nanoparticles 2+ The hydrogen production product was 915.2. Mu. Mol/h, lower than example 1. For comparative example 1, the hydrogen production activity of bulk carbon nitride was reduced to 841.2 μmol/h by loading Pt nanoparticles after direct amination. For comparative example 2, the carbon nitride nanosheets were not surface aminated, and the hydrogen production yield of the prepared composite photocatalyst was further reduced to 720.1. Mu. Mol/h. When bulk carbon nitride is not exfoliated into carbon nitride nanoplatelets, and surface amino groups are not carried outAnd (3) modification, wherein the hydrogen production yield of the prepared composite photocatalyst is lowest and is only 681.4eV. In addition, for comparative example 4, the degree of surface amination was weak because the carbon nitride nanosheets were not reacted by solvothermal reaction after being mixed with urea, and the hydrogen production yield of the resulting composite photocatalyst was 807.6 μmol/h, which was significantly lower than that of example 1, as well as that of comparative examples 5 and 1. Therefore, the bulk carbon nitride can be stripped into carbon nitride nano-sheets, then subjected to surface amination modification, and finally subjected to hydrogen thermal reduction on Pt nano-particles to obtain the efficient photocatalytic hydrogen production material.
FIG. 6 shows the stability of the composite photocatalyst synthesized in example 1 to produce hydrogen by photocatalysis. After 4 rounds of 16h photocatalytic reaction, the speed of photocatalytic hydrogen production is not obviously reduced basically, which indicates that the composite photocatalyst synthesized in the embodiment 1 has good photocatalytic stability.
Fig. 7 is a high resolution transmission electron microscope image of the surface-aminated carbon nitride composite photocatalyst co-supported by Au and Cu metals synthesized in example 3. According to statistics, the average particle diameter of the nanoparticles was about 1.3nm, and the lattice fringes of 0.217nm corresponded to the structure of AuCu alloy (0.2355 ×1/3+0.2087×2/3=0.217), indicating that Au and Cu were supported on the surface of the surface-aminated carbon nitride nanoplatelets in the form of an alloy.
Fig. 8 is the photocatalytic reduction performance of carbon dioxide under visible light for bulk carbon nitride, example 3, comparative example 6, and comparative example 7. For bulk carbon nitride, the product was predominantly CO with a yield of 0.54. Mu. Mol/hg and CO selectivity of 94.7%. When the metal Cu is loaded on the surface of the surface aminated carbon nitride nano-sheet, the yield of CO is improved to 1.71 mu mol/hg, but the product CH is obtained at the same time 4 The yield of (2) was also increased from 0.03 to 0.15. Mu. Mol/hg, with a CO selectivity of 91.9%. The yield and selectivity of CO of the metal Au-supported composite photocatalyst are 1.27 mu mol/hg and 90.7%, respectively. When AuCu alloy is loaded on the surface of the surface aminated carbon nitride nano-sheet, the CO yield is greatly improved to 3.26 mu mol/hg, and simultaneously CH 4 The yield of (2) is suppressed to 0.04 mu mol/hg, the selectivity of CO is improved to 98.8%, and the surface amination carbon nitride composite photocatalyst jointly loaded by metal Au and Cu synthesized in example 3 has good photocatalytic reduction and oxidationCarbon properties.
Those skilled in the art will appreciate that the foregoing is merely a few, but not all, embodiments of the invention. It should be noted that many variations and modifications can be made by those skilled in the art, and all variations and modifications which do not depart from the scope of the invention as defined in the appended claims are intended to be protected.
Claims (10)
1. The preparation method of the composite photocatalyst based on the surface aminated carbon nitride is characterized by comprising the following steps of:
s1, placing bulk phase carbon nitride in a tube furnace, and performing heat treatment in high-purity oxygen at 480-580 ℃ to obtain a carbon nitride nano sheet with a single-layer or oligolayer structure;
s2, dispersing the carbon nitride nano-sheets prepared in the step S1 into ethylene glycol, and then adding urea for continuous and uniform dispersion, wherein the mass ratio of the urea to the carbon nitride nano-sheets is (0.1-2.0): 1, so as to obtain a mixed suspension; carrying out solvothermal reaction on the mixed suspension at 120-200 ℃, and centrifuging, washing and drying a product to obtain the surface aminated carbon nitride nano-sheet;
s3, dispersing the surface aminated carbon nitride nano-sheets into deionized water, and then mixing with a metal precursor aqueous solution, wherein the mass ratio of metal in the metal precursor aqueous solution to the surface aminated carbon nitride nano-sheets is (0.1-10): 100, stirring the mixed solution at 60-100 ℃ for reaction, freeze-drying, placing the dried powder into a tube furnace, and performing thermal reduction at 200-600 ℃ under the action of hydrogen to obtain the composite photocatalyst based on the surface aminated carbon nitride.
2. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 1, wherein the purity of high purity oxygen in step S1 is >99.99%, and the time of heat treatment is 5-30min.
3. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 1, wherein the dispersion concentration of the carbon nitride nano-sheet in ethylene glycol in the step S2 is 1-3mg/ml, and the solvothermal reaction time is 1-24h.
4. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 1, wherein the metal precursor in the aqueous solution of metal precursor in step S3 is a single metal water-soluble salt or a combination of two or more metal water-soluble salts.
5. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 4, wherein the metal of the metal water-soluble salt is one of noble metal Au, pt, pd, ag or non-noble metal Fe, cu, co, ni, and the water-soluble salt is chloride, nitrate, sulfate or sulfite.
6. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 1, wherein the mixed solution in step S3 is stirred at 60-100 ℃ for 2-12 hours.
7. The method for preparing a surface aminated carbon nitride based composite photocatalyst according to claim 1, wherein the time for thermal reduction in step S3 is 1 to 6 hours.
8. The method for preparing a composite photocatalyst based on surface aminated carbon nitride according to claim 1, wherein the hydrogen gas in step S3 acts as a high purity hydrogen gas atmosphere having a purity of >99.99%, or as a mixed atmosphere of hydrogen gas and inert gas.
9. A composite photocatalyst based on surface aminated carbon nitride prepared by the preparation method of any one of claims 1 to 8.
10. Use of the surface-aminated carbon nitride-based composite photocatalyst according to claim 9 in photocatalytic reactions.
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