CN111646437A - Method for preparing white graphite phase carbon nitride by closed self-pressurization strategy - Google Patents
Method for preparing white graphite phase carbon nitride by closed self-pressurization strategy Download PDFInfo
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Images
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/0605—Binary compounds of nitrogen with carbon
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- 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
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- B01J35/39—
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- B01J35/613—
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- 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
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-like
- C01P2004/24—Nanoplates, i.e. plate-like particles with a thickness from 1-100 nanometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
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- 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 relates to a method for preparing white graphite phase carbon nitride by a closed self-pressurization strategy, in particular to the field of preparation methods of graphite phase carbon nitride. According to the method, the pressure in the tubular furnace can be increased under the action of gas and heat due to gas released in the process that the preset nitrogen-containing material generates a polymerization reaction after being heated, and then white graphite phase carbon nitride is obtained after cooling, and compared with yellow graphite phase carbon nitride obtained in the prior art, the white graphite phase carbon nitride obtained in the method has the specific surface area of 46.34m2g‑1Increased to 95.10m2g‑1The thickness of the white graphite phase carbon nitride is reduced to about 4.8nm on average, and the degradation rate is from 0.009min in the photocatalytic degradation of rhodamine B‑1Increased to 0.035min‑1The rate is improved by 3 times, and in the reaction of producing hydrogen by photocatalysis, the reaction rate is from 32.9 mu mol h‑1(1316μmol h‑1g‑1) Increased to 202.9. mu. mol h‑1(8116μmol h‑1g‑1) The catalyst is improved by 5 times, and the catalytic efficiency is greatly improved.
Description
Technical Field
The invention relates to the field of preparation methods of graphite-phase carbon nitride, and mainly relates to a method for preparing white graphite-phase carbon nitride by a closed self-pressurization strategy.
Background
With the development of global industrialization, the problem of environmental pollution, especially organic pollution of water bodies, is increasingly prominent, and the health and normal life of people are seriously harmed. Meanwhile, the current society is also troubled by the increasingly prominent energy shortage crisis, and the replacement of non-renewable fossil energy sources by clean energy sources and renewable energy sources becomes the focus of increasing attention of the current society. The method has important significance for effectively solving the problems of clean and renewable energy sources and environmental pollution control from the social and personal aspects. Semiconductor photocatalysis technology is an important approach for solving the problems and is an important research hotspot at present. At present, the development of efficient, economical and environmentally friendly solar-responsive photocatalysts remains a major challenge.
Graphite phase carbon nitride (g-C)3N4) As a metal-free photocatalytic material, the material has proper forbidden band width and valence band edge potential, visible light response, good stability, environmental friendliness and wide raw material source. Based on g-C3N4The development of photocatalytic materials has attracted extensive attention from various researchers in the world. g-C3N4The application of the method in the aspects of photocatalytic hydrogen production, photocatalytic degradation of organic pollutants, photocatalytic synthesis, photocatalytic disinfection and the like is widely researched.
For decades, the solvent thermal method, the solid-phase synthesis method, the electrochemical deposition method, the thermal polymerization method and other methods are adopted to synthesize the g-C with various shapes such as nano-sheets, hollow spheres, hollow nano-tubes, nano-rod structures, quantum dots and the like3N4. Wherein the thermal polymerization method has simple operation and short preparation periodAnd the like, and is widely applied to the synthesis of g-C by taking nitrogen-rich material as precursor3N4. However, despite g-C3N4Having a layered structure, but g-C3N4The specific surface area of the material is low, and a photon-generated carrier is easy to recombine, so that the application of the material as a photocatalytic material is limited. The problem can be solved to a certain extent by stripping the bulk carbon nitride into several layers of ultra-thin structures. Ultra-thin g-C3N4The nano-sheet has few or even single-layer structures, so that the specific surface area of the nano-sheet can be improved, more reactive active sites can be provided, photo-generated carriers can be transferred to the surface of a material more easily, the recombination probability of the photo-generated carriers is reduced, and the photocatalysis efficiency is improved. Generally, ultra-thin g-C3N4The nano-sheets are subjected to thermal oxygen etching, ultrasonic dispersion, acid-base etching and solvothermal stripping to form bulk g-C3N4And (4) stripping.
However, the method can cause extra environmental pollution and add other auxiliary materials when preparing the graphite phase carbon nitride, and the produced graphite phase carbon nitride is yellow graphite phase carbon nitride, the probability of photo-generated carrier recombination of the yellow graphite phase carbon nitride is higher, the service life of the photo-generated carrier is shorter, and the catalytic efficiency of the graphite phase carbon nitride is lower in the catalytic process.
Disclosure of Invention
The invention aims to provide a method for preparing white graphite-phase carbon nitride by a closed self-pressurization strategy, aiming at overcoming the defects in the prior art, and solving the problems that the prepared graphite-phase carbon nitride is yellow graphite-phase carbon nitride under the conditions of generating extra environmental pollution and adding other auxiliary materials during the preparation of the graphite-phase carbon nitride, the recombination probability of photo-generated carriers of the yellow graphite-phase carbon nitride is higher, the service life of the photo-generated carriers is shorter, and the catalytic efficiency of the graphite-phase carbon nitride is lower in the catalytic process.
In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:
the application provides a method for preparing white graphite phase carbon nitride by a closed self-pressurization strategy, which comprises the following steps:
putting a preset nitrogen-containing material into a closed heating vessel;
placing the closed heating vessel in a tube furnace, and sealing two ends of the tube furnace by using elastic pieces;
and heating the tubular furnace according to a preset heating method, and then cooling to obtain the white graphite phase carbon nitride.
Optionally, the step of heating the tube furnace according to a preset heating method and then cooling the tube furnace to obtain the white graphite-phase carbon nitride comprises:
heating the tube furnace to 520 ℃ at the temperature rising speed of 4 ℃ per minute, and preserving the heat for 120 minutes;
heating the tube furnace after heat preservation to 550 ℃, and preserving heat for 120 minutes;
and naturally cooling the closed heating vessel after heat preservation, and taking out the closed heating vessel from the tubular furnace to obtain the white graphite phase carbon nitride.
Optionally, the step of placing the preset nitrogen-containing material into the heating vessel further comprises:
a weight is arranged on the closed heating vessel.
Optionally, the closed heating vessel has a volume of 10 ml and the weight has a mass of not less than 50 g.
Optionally, the predetermined nitrogen-containing material comprises: at least one of urea, dicyandiamide, melamine and thiourea.
Optionally, the material of the elastic member is an elastic material.
Optionally, the material of the elastic member is a rubber balloon.
The invention has the beneficial effects that:
this application is through will predetermine nitrogenous material and put into confined heating household utensils to place confined heating household utensils in the tube furnace, and use elastic component closed tube furnace both ends, cool off the tube furnace after heating according to predetermineeing the heating method, obtain white graphite looks carbon nitride, because this predetermine nitrogenous material and produce the gas that polymerization reaction's in-process can release after the heating, the pressure in this tube furnace under the effect of gas and heatThe intensity is increased, and then white graphite phase carbon nitride is obtained after cooling, and the white graphite phase carbon nitride obtained by the application has the specific surface area of 46.34m compared with yellow graphite phase carbon nitride obtained by the prior art2g-1Increased to 95.10m2g-1The thickness of the white graphite phase carbon nitride is reduced to about 4.8nm on average, and the degradation rate is from 0.009min in the photocatalytic degradation of rhodamine B-1Increased to 0.035min-1The rate is improved by 3 times, and in the reaction of producing hydrogen by photocatalysis, the reaction rate is from 32.9 mu mol h-1(1316μmol h-1g-1) Increased to 202.9. mu. mol h-1(8116μmol h-1g-1) The catalyst is improved by 5 times, and the catalytic efficiency is greatly improved. And no extra environmental pollution is generated in the process of preparing the white graphite-phase carbon nitride, and no other auxiliary materials are needed to be added.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a flow chart of a process for preparing white graphite-phase carbon nitride by a closed self-pressurization strategy according to the present application;
FIG. 2 is a flow diagram of another closed self-pressurization strategy provided herein for preparing white graphite phase carbon nitride;
FIG. 3 is a graph of hydrogen production rates for white graphite phase carbon nitride (CN-PU) and yellow graphite phase carbon nitride (CN-U) under λ >400nm and λ >420nm irradiation;
FIG. 4 is a graph showing hydrogen production amounts of white graphite phase carbon nitride and yellow graphite phase carbon nitride within 6h at λ >400 nm;
FIG. 5 is a graph of the photocatalytic activity of white graphite phase carbon nitride and yellow graphite phase carbon nitride for degrading RhB;
FIG. 6 is a graph of the apparent rates of degradation of RhB by white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 7 is a graph of photocatalytic stability for three cycles of degradation of RhB by white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 8 is an XRD spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 9 is an FTIR spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 10 is an SEM image of yellow graphite phase carbon nitride;
FIG. 11 is an SEM image of white graphite phase carbon nitride;
FIG. 12 is another SEM image of white graphite phase carbon nitride;
FIG. 13 is an AFM image of white graphite phase carbon nitride;
FIG. 14 is an XPS C1s spectrum of white graphite phase carbon nitride;
FIG. 15 is a XPS N1s spectrum of white graphite phase carbon nitride;
FIG. 16 is a BET isotherm and pore size distribution plot of white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 17 is an ultraviolet DRS spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 18 shows [ F (R) for white graphite phase carbon nitride and yellow graphite phase carbon nitride∞)hν]1/2-a hv spectrogram;
FIG. 19 is a PL spectrum for white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 20 is a TRPL spectrum for white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 21 is a transient photocurrent diagram for white graphite phase carbon nitride and yellow graphite phase carbon nitride;
FIG. 22 is an impedance plot of white graphite phase carbon nitride and yellow graphite phase carbon nitride.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are one embodiment of the present invention, and not all embodiments. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In order to make the implementation of the present invention clearer, the following detailed description is made with reference to the accompanying drawings.
Fig. 1 is a flowchart of a method for preparing white graphite-phase carbon nitride by a closed self-pressurization strategy, as shown in fig. 1, the present application provides a method for preparing white graphite-phase carbon nitride by a closed self-pressurization strategy, the method includes:
s101, putting a preset nitrogen-containing material into a closed heating vessel.
In order to ensure the efficiency of the reaction of the predetermined nitrogen-containing material in the heating vessel, the heating vessel may be configured as a sealed heating vessel, and generally, the heating vessel may include two parts, namely a vessel and a lid, which are not limited herein.
And S102, placing the closed heating vessel in a tube furnace, and closing two ends of the tube furnace by using elastic pieces.
After the closed heating vessel is placed in the tube furnace, the two open ends of the tube furnace are closed by using the elastic member, so that a closed space is formed inside the tube furnace, the generated gas is prevented from leaking in the heating process, the pressure inside the tube furnace is further increased, and it needs to be noted that the elastic member is made of a high-temperature resistant material.
And S103, heating the tube furnace according to a preset heating method, and then cooling to obtain the white graphite phase carbon nitride.
And heating the tubular furnace by using a preset heating method, taking out the heating vessel in the tubular furnace after heating, and cooling, wherein the preset nitrogen-containing material in the heating vessel forms white graphite-phase carbon nitride after being heated and cooled by using the preset heating method.
In addition, since the graphite phase carbon nitride prepared in the prior art is in a block shape, the graphite phase carbon nitride prepared in the prior art can be called as bulk carbon nitride, yellow graphite phase carbon nitride and bulk graphite phase carbon nitride, that is, the bulk carbon nitride, the bulk graphite phase carbon nitride and the yellow graphite phase carbon nitride are all referred to as graphite phase carbon nitride prepared in the prior art, which shall be abbreviated as CN-U, and the white graphite phase carbon nitride prepared in the present application is abbreviated as CN-PU.
Fig. 2 is a flow chart of another closed self-pressurization strategy for preparing white graphite-phase carbon nitride provided by the present application, and as shown in fig. 2, optionally, the step of heating the tube furnace according to a preset heating method and then cooling the tube furnace to obtain white graphite-phase carbon nitride includes:
s201, heating the tube furnace to 520 ℃ at a heating rate of 4 ℃ per minute, and preserving heat for 120 minutes.
Set up heating device outside this tube furnace, general, this heating device can adjust the programming rate of tube furnace, when heating this tube furnace for this tube furnace heats 520 degrees centigrade from this tube furnace's initial temperature with the programming rate of 4 degrees centigrade per minute, and this heating device continues output heat and makes this tube furnace when 520 degrees centigrade, keeps warm for 120 minutes.
S202, heating the tube furnace with the heat preservation completed to 550 ℃, and preserving the heat for 120 minutes.
After the heat preservation is finished in the step S201, the heating device arranged outside the tube furnace continuously heats the tube furnace from 520 ℃ to 550 ℃, it is to be noted that the time for heating the tube furnace from 520 ℃ to 550 ℃ is as short as possible, the tube furnace needs to be rapidly heated from 520 ℃ to 550 ℃, the heating time is generally 1 minute, and the heating device continuously outputs heat so that the tube furnace is kept at 550 ℃ for 120 minutes.
And S203, naturally cooling the closed heating vessel after heat preservation, and taking out the closed heating vessel from the tubular furnace to obtain the white graphite phase carbon nitride.
After the heat preservation in the step S202 is finished, namely the tube furnace is heated to 550 ℃, and after the heat preservation is carried out for 120 minutes, the heating vessel is naturally cooled in the tube furnace and then taken out of the tube furnace, and the preset nitrogen-containing material in the heating vessel forms white graphite-phase carbon nitride after being processed in the step.
Optionally, the step of placing the preset nitrogen-containing material into the heating vessel further comprises:
a weight is arranged on the closed heating vessel.
To further increase the yield of white graphite phase carbon nitride, weights may be placed on the closed heating vessel.
Optionally, the closed heating vessel has a volume of 10 ml and the weight has a mass of not less than 50 g.
Optionally, the predetermined nitrogen-containing material comprises: at least one of urea, dicyandiamide, melamine and thiourea.
Optionally, the material of the elastic member is an elastic material.
Optionally, the material of the elastic member is a rubber balloon.
According to the method, the closed heating vessel is placed in the closed heating vessel by presetting the nitrogen-containing material, the closed heating vessel is placed in the tube furnace, the two ends of the tube furnace are closed by the elastic pieces, the tube furnace is cooled after being heated according to the preset heating method, white graphite phase carbon nitride is obtained, and due to the fact that the preset nitrogen-containing material generates gas released in the polymerization reaction process after being heated, the pressure in the tube furnace can be increased under the action of the gas and the heat, and then the pressure in the tube furnace can be increased after being cooledObtaining white graphite phase carbon nitride, wherein the surface area of the white graphite phase carbon nitride obtained by the method is 46.34m compared with that of yellow graphite phase carbon nitride obtained by the prior art2g-1Increased to 95.10m2g-1The thickness of the white graphite phase carbon nitride is reduced to about 4.8nm on average, and the degradation rate is from 0.009min in the photocatalytic degradation of rhodamine B-1Increased to 0.035min-1The rate is improved by 3 times, and in the reaction of producing hydrogen by photocatalysis, the reaction rate is from 32.9 mu mol h-1(1316μmol h-1g-1) Increased to 202.9. mu. mol h-1(8116μmol h-1g-1) The catalyst is improved by 5 times, and the catalytic efficiency is greatly improved. And no extra environmental pollution is generated in the process of preparing the white graphite-phase carbon nitride, and no other auxiliary materials are needed to be added.
To further illustrate the properties of the white graphite phase carbon nitride produced by the present application, the white graphite phase carbon nitride produced by the present application is compared with the yellow graphite phase carbon nitride produced by the prior art, and it should be noted that the yellow graphite phase carbon nitride produced by the prior art is generally blocky in shape, and the yellow graphite phase carbon nitride also becomes blocky graphite phase carbon nitride.
The difference between the white graphite phase carbon nitride and the yellow graphite phase carbon nitride can be mainly divided into: hydrogen production performance, degradation of organic dye rhodamine B (RhB) and other physical characteristics.
For convenience of explanation, the specific experimental procedures for comparing the hydrogen production performance of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride are as follows:
a. firstly, respectively putting prepared white graphite phase carbon nitride and yellow graphite phase carbon nitride into two agate mortars for grinding, filtering by using a 500-mesh sieve, respectively taking 25mg of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride to disperse in 45ml of deionized water, then respectively adding 3 wt% of chloroplatinic acid, using ultrasonic vibration for 60 minutes, irradiating by using a 300W Xe lamp to ensure that platinum atoms are photoprecipitated on the surface of an active material, respectively adding 5ml of triethanolamine as a sacrificial agent for absorbing cavities, and fully stirring by using a magnetic stirrer for 30 minutes to ensure that the platinum atoms and the yellow graphite phase carbon nitride are uniformly mixed;
b. the evaluation of hydrogen production activity is completed by a 7920 type gas chromatograph which is provided with a TCD detector, a TDX-01 chromatographic column and an automatic sample injection device, high-purity nitrogen is used as carrier gas, a hydrogen marking line is made in advance, the temperature of a tested material is controlled at 6 ℃ by a refrigerator, a 300W xenon lamp is used as a light source, the light source reaches a stable state after the xenon lamp is started for half an hour, the hydrogen production amount is measured, and the whole test is performed in a closed pipeline which is pumped into vacuum in advance;
c. the xenon lamp is provided with 400nm and 420nm cut-off filters, hydrogen production data is recorded every 30 minutes, and hydrogen production quantity is obtained through a hydrogen marking;
d. a400 nm band-pass filter is assembled on the xenon lamp, hydrogen production data are recorded every 30 minutes, and the passing optical power density is tested through a light intensity meter.
FIG. 3 is a graph at λ>400nm and lambda>A hydrogen production rate diagram of white graphite phase carbon nitride (CN-PU) and yellow graphite phase carbon nitride (CN-U) under 420nm irradiation; FIG. 4 is a graph at λ>A hydrogen production diagram of white graphite phase carbon nitride and yellow graphite phase carbon nitride within 6h at 400 nm; as shown in fig. 3 and 4, yellow graphite phase carbon nitride prepared by conventional thermal polymerization method, white graphite phase carbon nitride prepared by closed self-pressurization strategy in the present application, and photo-catalytic hydrogen production activity of the yellow graphite phase carbon nitride and white graphite phase carbon nitride are represented by the rate of hydrogen evolution of the yellow graphite phase carbon nitride and white graphite phase carbon nitride under the irradiation of light, wherein in fig. 3, the yellow graphite phase carbon nitride and the white graphite phase carbon nitride are placed in triethanolamine (10 vol%) aqueous solution and are respectively in lambda (lambda),>the hydrogen evolution rate of the white carbon nitride under the irradiation of 420nm reaches 43.9 mu mol h-1The hydrogen evolution rate of the yellow graphite phase carbon nitride reaches 28.8mmol h-1Compared with yellow graphite phase carbon nitride, the hydrogen evolution rate of the white carbon nitride is 52% higher than that of the yellow graphite phase carbon nitride; i.e. at λ>Under the irradiation of 400nm, the hydrogen precipitation rate of white carbon nitride is 6.2 times higher than that of yellow graphite phase carbon nitride, and the hydrogen precipitation rate is 32.9 mu mol h-1(1316μmol h-1g-1) To 202.9μmol h-1(8116μmol h-1g-1) The results show that the porous and few-layer structure of the white carbon nitride has better photocatalytic hydrogen production activity. In addition, as shown in fig. 4, the white carbon nitride still maintains good hydrogen production stability and photocatalytic activity after continuous hydrogen production for 6 hours.
To further illustrate, the performance of the degraded organic dye rhodamine b (rhb) of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride is compared here, and the specific experimental procedure is as follows:
a. the photocatalytic degradation of RhB is completed by a 300W xenon lamp equipped with an AM1.5 optical filter, 50mg of white graphite phase carbon nitride and yellow graphite phase carbon nitride are respectively added into two groups of 100ml of RhB solutions with concentration, and ultrasonic treatment is carried out for 30 minutes under dark conditions to carry out sufficient absorption and achieve absorption and desorption balance;
b. irradiating RhB added with active material by xenon lamp irradiation while stirring with a magnetic stirrer, taking 5ml of sample every 20 minutes, and removing the active material through a 0.45 μm filter membrane;
c. and (3) testing the concentration of the filtered RhB solution by using a Shimadzu UV-3600plus ultraviolet spectrophotometer, placing a sample to be tested in a quartz cuvette for measurement, and measuring the absorbance of the RhB solution corresponding to the characteristic peak value of 554 nm.
FIG. 5 is a graph of the photocatalytic activity of white graphite phase carbon nitride and yellow graphite phase carbon nitride for degrading RhB; FIG. 6 is a graph of the apparent rates of degradation of RhB by white graphite phase carbon nitride and yellow graphite phase carbon nitride; FIG. 7 is a graph of photocatalytic stability for three cycles of degradation of RhB by white graphite phase carbon nitride and yellow graphite phase carbon nitride; degradation of RhB aqueous solution was performed under simulated solar radiation (300WXe with AM1.5 filter); as shown in fig. 5, it is clear that RhB containing white graphite phase carbon nitride almost completely degraded in 80 minutes, whereas RhB containing yellow graphite phase carbon nitride only degraded by 40%. As can be seen from FIG. 6, the apparent degradation rate of the white graphite-phase carbon nitride was 0.035min-1The degradation rate of the yellow graphite phase carbon nitride is k 0.009min-1The degradation rate of white graphite phase carbon nitride is four times that of yellow graphite phase carbon nitride, as shown in the figure7, after 3 times of cyclic degradation, the white carbon nitride still maintains good stable photocatalytic degradation activity, which indicates that the rate of degrading RhB by the white carbon nitride is high and the service life is long.
To further illustrate, the physical properties of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride were analyzed herein, using the following experimental procedures:
FIG. 8 is an XRD spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride; as shown in fig. 8, the XRD diffraction patterns of white graphite phase carbon nitride and yellow graphite phase carbon nitride, which are abbreviated as CN-PU and CN-U, are compared, respectively, and fig. 7 shows that the XRD patterns of white graphite phase carbon nitride and yellow graphite phase carbon nitride both have two different diffraction peaks. The diffraction peak around 12.8 ℃ corresponds to g-C3N4The (100) crystal plane of (a), the interlayer spacing d ≈ 0.641nm, the stronger diffraction peak corresponding to the (002) crystal plane due to the in-plane repeating unit of tri-s-triazine, and belongs to the in-plane stacking peak of the conjugated aromatic ring. As can be seen from the inset of fig. 7, the stronger diffraction peak shifted from 27.3 ° for the yellow graphite phase carbon nitride to 27.6 ° for the white graphite phase carbon nitride, which corresponds to a decrease in lattice plane distance from 0.326 to 0.323nm, indicating a denser layer stack for the white carbon nitride. This is due to the disruption of interlayer hydrogen bonds and g-C during the closed self-pressurized synthesis3N4A reduction in the thickness of the nanoplatelets.
FIG. 9 is an FTIR spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride; as shown in fig. 9, comparing the FTIR spectra of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride, respectively, the FTIR spectra of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride are very similar, indicating that they have the same s-triazine/tri-s-triazine ring chemical group and structure. At 3500 and 3000cm-1The absorption peak in the range is due to-NH2And ═ NH group stretching vibration (incomplete crystallization) and — OH stretching vibration, and surface adsorption of water molecules; at 1200 and 1650cm-1The peak at (A) is mainly related to the C-N and C ═ N tensile vibrations of the aromatic heterocyclic units, 812cm-1The spike in (a) is due to the typical bending vibration of the s-triazine ring in the fingerprint region.
FIG. 10 is an SEM image of yellow graphite phase carbon nitride; FIG. 11 is an SEM image of white graphite phase carbon nitride; FIG. 12 is another SEM image of white graphite phase carbon nitride; FIG. 13 is an AFM image of white graphite phase carbon nitride; as shown in FIGS. 10, 11 and 12, it is apparent that the carbon nitride g-C phase with yellow graphite3N4The agglomerates of (a) are stacked differently, and the white graphite phase carbon nitride is composed of more curled and thinner nanosheets. White carbon nitride nanosheets have pores, which may be due to gaseous molecules (e.g., NH) upon polymerization by self-pressurization3，H2O and CO2) A circulating flow in the crucible. As shown in fig. 13, the AFM imaging further confirmed that the white graphitic carbon nitride was ultrathin nanoplatelets, and the AFM imaging indicated that the three cross-sectional profiles of the white graphitic carbon nitride were about 5.4nm, 4.7nm, and 4.4nm thick, respectively, with an average thickness of about 4.8nm, corresponding to the white graphitic carbon nitride being about 13-16 atomic layer nanoplatelets.
FIG. 14 is a XPS C1s spectrum of white graphite phase carbon nitride and FIG. 15 is a XPS N1s spectrum of white graphite phase carbon nitride; as shown in fig. 14 and 15, XPS C1s and N1s signals of white graphite-phase carbon nitride were measured with high resolution, and it can be seen that two peaks at 284.8eV and 288.2eV were observed in the C1s spectrum, which correspond to sp 2C-C/C ═ C bonds in the contaminated carbon structure and sp 2N-C ═ N bonds located at C in the s-triazine aromatic heterocycle; there are four peaks in the N1s spectrum, the peak at 398.6eV due to N (C-N ═ C) bonded in the triazine ring at sp2, and the peak at 399.9eV due to the bridge atom N of the N- (C)3 structure, the peak at 401.2eV being assigned to-NH/NH2The peak at 404.5eV results from pi excitation in a C ═ N conjugated structure. XPS spectra of C1s and N1s further confirmed the heterocyclic structure of the heptazine of the white graphite phase carbonitride.
FIG. 16 is a BET isotherm and pore size distribution plot of white graphite phase carbon nitride and yellow graphite phase carbon nitride, as shown in FIG. 16, the isotherm of the sample falls within the type IV curve and has a significant adsorption hysteresis loop over a relative pressure range of 0.7 to 1, indicating that white graphite phase carbon nitride is the same as yellow graphite phase carbon nitrideThe phase carbon nitride is a typical mesoporous material. The Specific Surface Area (SSA) of white carbon nitride is twice that of yellow graphite phase carbon nitride, from 46.34m2g-1Is lifted to 95.10m2g-1. As can be seen from the inset of fig. 15, the pore size distribution curve shows two peaks at 2.8nm and 3.8nm for both samples, the peaks for both samples corresponding to the diameter of the lumen. The white graphite phase carbon nitride has a broad peak of 20nm to 50nm compared to the yellow graphite phase carbon nitride, because a very small space of the curled nanosheets is formed. The larger SSA and wider pore size distribution of the white graphite phase carbon nitride may provide more adsorption sites and active sites as a catalyst, making the white graphite phase carbon nitride more beneficial for enhancing catalytic effect.
FIG. 17 is an ultraviolet DRS spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride; FIG. 18 shows [ F (R) for white graphite phase carbon nitride and yellow graphite phase carbon nitride∞)hν]1/2-a hv spectrogram; as shown in fig. 17 and 18, DRS spectra were used to study the light absorption characteristics of the materials, in fig. 16 the absorption edge of the white graphite phase carbon nitride was blue shifted from 445nm to 420nm compared to the yellow graphite phase carbon nitride, due to the quantum confinement effect of the ultra-thin white graphite phase carbon nitride nanosheets, and in fig. 17 it is shown that the bandgaps of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride are 2.96eV and 2.79eV, respectively.
FIG. 19 is a PL spectrum for white graphite phase carbon nitride and yellow graphite phase carbon nitride; FIG. 20 is a TRPL spectrum for white graphite phase carbon nitride and yellow graphite phase carbon nitride; as shown in fig. 19, under 325nm laser excitation, the blue of white carbon nitride PL shifts to 457nm due to quantum confinement effect. As shown in fig. 20, where fig. 20 shows time-resolved fluorescence decay spectra, two exponential decay fit results indicate that the short and long photon-generated carrier lifetimes for white graphite-phase carbon nitride are 1.357ns and 7.450ns, respectively, which are 17% and 13% higher for 1.159ns and 6.577ns, respectively, for yellow graphite-phase carbon nitride. Meanwhile, the proportion of the service life carriers of the white graphite phase carbon nitride is reduced to 77.43 percent from 86.27 percent compared with that of the yellow graphite phase carbon nitride, and the proportion of the service life carriers is increased to 22.57 percent from 13.73 percent. The corresponding average lifetime of the white graphite phase carbon nitride is increased by 37% compared with the average lifetime of the yellow graphite phase carbon nitride, and is increased from 3.731ns to 5.106ns, which means that photo-generated carriers generated by the white carbon nitride are easier to migrate to the surface and reduce the recombination of photo-generated electrons and holes in the photocatalysis process, and the photocatalysis activity is more favorably enhanced.
For convenience of explanation, the electrochemical performance of the white graphite phase carbon nitride and the yellow graphite phase carbon nitride is compared here, and the specific experimental procedures are as follows:
a. the photoelectrochemical properties of white graphite phase carbon nitride and yellow graphite phase carbon nitride were studied on a Bio-logic electrochemical workstation using a standard three-electrode system, a 2cm × 2cm platinum sheet as the counter electrode, Ag/AgCl (3M KCl solution) as the reference electrode, and 0.2M Na2SO4As an electrolyte;
b. the working electrode is prepared by coating a catalyst on the surface of ITO glass, 5mg of a sample is dispersed in an ethanol water solution containing 20 vol% nafion, ultrasonic treatment is carried out for 30min, then the sample is dripped on the ITO glass with the thickness of 1cm multiplied by 1cm, and the ITO glass is heated for 2 hours at 120 ℃ after being dried at room temperature;
c. the transient photocurrent response with time (I-t curve) -0.2V bias voltage is completed, and Electrochemical Impedance Spectroscopy (EIS) tests are carried out in the frequency range of 5mHz to 100kHz under the open circuit voltage.
FIG. 21 is a transient photocurrent diagram for white graphite phase carbon nitride and yellow graphite phase carbon nitride; fig. 22 is an impedance spectrum of white graphite phase carbon nitride and yellow graphite phase carbon nitride, as shown in fig. 21, under xenon lamp irradiation with an AM1.5 filter, and under-0.2V bias voltage to a reference electrode, the transient photocurrent of the white graphite phase carbon nitride is more than 2 times that of the yellow graphite phase carbon nitride. This indicates that the prepared CN-PU can effectively enhance the separation of photogenerated carriers. As shown in fig. 22, the nyquist plot of the material was measured at open circuit voltage. The radius of the nyquist curve for white graphite phase carbon nitride is smaller than that for yellow graphite phase carbon nitride, indicating that white graphite phase carbon nitride has less resistance to photon-generated carrier migration and is more likely to migrate to the surface of the material and to the surface.
By closingThe self-pressurization strategy successfully synthesizes the porous ultrathin white and yellow graphite-phase carbon nitride nanosheet in one step. The method is only carried out in a closed space without any other auxiliary materials, and is environment-friendly and simple and convenient to operate. The photocatalytic hydrogen production and RhB degradation of the synthesized white graphite-phase carbon nitride are both enhanced compared with bulk carbon nitride, and the synthesized white graphite-phase carbon nitride has twice specific surface area, wider pore size distribution, longer service life of a photogenerated carrier, lower charge transfer resistance, a porous structure and ultrathin thickness. The simple synthesis method is porous ultrathin g-C3N4Provides a simple way for the preparation and the scale production.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A method for preparing white graphite phase carbon nitride by a closed self-pressurization strategy, which is characterized by comprising the following steps:
putting a preset nitrogen-containing material into a closed heating vessel;
placing the closed heating vessel in a tube furnace, and sealing two ends of the tube furnace by using elastic pieces;
and heating the tubular furnace according to a preset heating method and then cooling to obtain the white graphite phase carbon nitride.
2. The method for preparing white graphite-phase carbon nitride according to the closed self-pressurization strategy of claim 1, wherein the step of heating the tube furnace according to a preset heating method and then cooling the tube furnace to obtain the white graphite-phase carbon nitride comprises the following steps:
heating the tube furnace to 520 ℃ at a heating rate of 4 ℃ per minute, and preserving heat for 120 minutes;
heating the tube furnace after heat preservation to 550 ℃, and preserving heat for 120 minutes;
and naturally cooling the closed heating vessel after heat preservation, and taking out the heating vessel from the tubular furnace to obtain the white graphite phase carbon nitride.
3. The method for preparing white graphite-phase carbon nitride according to the closed self-pressurization strategy of claim 1, wherein the step of placing the predetermined nitrogen-containing material into a heating vessel is further followed by:
and arranging a weight on the closed heating vessel.
4. The method for preparing white graphite-phase carbon nitride by the closed self-pressurization strategy according to claim 3, wherein the volume of the closed heating vessel is 10 ml, and the mass of the weight is not less than 50 g.
5. The method for preparing white graphite-phase carbon nitride according to the closed self-pressurization strategy of claim 1, wherein the preset nitrogen-containing material comprises: at least one of urea, dicyandiamide, melamine and thiourea.
6. The method for preparing white graphite-phase carbon nitride according to the closed self-pressurization strategy of claim 1, wherein the material of the elastic member is an elastic material.
7. The method for preparing white graphite-phase carbon nitride by adopting the closed self-pressurization strategy as claimed in claim 6, wherein the material of the elastic member is a rubber balloon.
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