CN113086955A - Preparation method of carbon-deficient carbon nitride material for photocatalytic nitrogen fixation - Google Patents
Preparation method of carbon-deficient carbon nitride material for photocatalytic nitrogen fixation Download PDFInfo
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- 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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- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
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Abstract
The invention discloses a preparation method of a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation. The mesoporous carbon nitride with loose structure and more surface carbon defects is obtained by taking urea as a precursor through a high-temperature stripping method. The photocatalytic activity ratio of the carbon-defect carbon nitride prepared by controlling the atom scale structure and constructing the surface defect to the ammonia conversion is g-C3N4There is a great improvement. The invention can realize the enhancement of the light absorption capability of a visible light region and the improvement of the photo-generated charge separation efficiency by utilizing a thin layer structure and more surface carbon vacancies and mesoporous structures. Notably, the engineering carbon vacancies greatly promote the adsorption and activation of nitrogen molecules and improve the defect ultrathin g-C3N4Nitrogen fixation activity of-V (carbon-deficient carbon nitride) material, and production method thereofSimple and easy to operate, quick and convenient, and has universality.
Description
Technical Field
The invention relates to the field of preparation of inorganic functional materials, in particular to a preparation method of a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation.
Background
Nitrogen is the most abundant element in air and is one of the most important elements in the body of an organism. Nitrogen and its compounds have a wide range of applications in production and life.
Currently, the industrial synthesis of ammonia still relies on the Haber-Bosch reaction. As the Haber-Bosch reaction can not solve the defects of high energy consumption, high pollution and the like, the search for a green and sustainable ammonia synthesis technology is urgent. In contrast, photocatalytic nitrogen reduction is a process by which nitrogen can be reduced by solar drive to produce ammonia. The method can be carried out under normal temperature and pressure, so the photocatalysis nitrogen fixation technology is a very promising ammonia synthesis technology. As the core of the photocatalytic nitrogen reduction technology, the development of efficient photocatalysts is the focus of research at present.
Nitrogen fixation is a well known complex six-electron reduction process. The main factor affecting effective nitrogen fixation is the treatment of N2The high activation potential barrier improves the adsorption of nitrogen and obtains enough photoexcited electrons. Ultra-thin materials with appropriate band gaps may offer new opportunities. They exhibit strong quantum confinement effects and surface effects due to the anisotropy of crystals and ultra-thin structures at the atomic level. The low coordination and large specific surface area of the surface atoms make it possible to make full use of sunlight. However, the photogenerated carriers are easily recombined on the surface, resulting in low carrier utilization and slow redox reaction on the surface. For this reason, the construction of defects on the surface of the semiconductor will effectively solve this problem, and the generation of more electrons will facilitate the nitrogen fixation reaction.
The carbon nitride material has the characteristics of low cost, simple process, good light responsiveness, good stability and the like, and becomes a research hotspot of photocatalysis. However, carbon nitride (g-C)3N4) The low dispersibility, the low conductivity and the high recombination rate of the compound seriously affect the photocatalytic performance, but the conduction band potential ratio of the compound is N2/NH3The reduction potential is more negative, making N2Reduction of NH3It becomes possible. The method for improving the material performance comprises the following steps: heteroatom doping, heterojunction structures, structural and morphological engineering, and the like. In addition to the above strategies, defect engineering is also gaining high performanceg-C of energy3N4The catalyst aspect shows great potential. In fact, the defective carbon nitride significantly improves the photocatalytic activity by introducing defects into the carbon nitride polymer network to form intermediate energy gap states, thereby significantly broadening the visible light absorption range and accelerating the charge separation of the photo-redox catalysis. This provides a new strategy for improving the photocatalytic performance of the photocatalyst.
Thus, the bulk phase g-C3N4Heat-treated to produce defective porous ultra-thin g-C3N4After thermal stripping, an ultrathin porous structure can be formed, and the carbon defects increased greatly can promote nitrogen fixation in a pure water environment.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a preparation method of a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation.
The preparation method of the carbon-deficient carbon nitride material for photocatalytic nitrogen fixation provided by the invention is characterized in that urea is used as a precursor to obtain ultrathin carbon nitride with a loose structure and more surface carbon defects by a high-temperature stripping method. The invention prepares carbon defect type carbon nitride with photocatalytic activity specific volume g-C for ammonia conversion by controlling atom scale structure and constructing surface defect3N4There is a great improvement. The thin layer structure and more surface carbon vacancies are utilized to realize the enhancement of the light absorption capability of the visible light region and the improvement of the photo-generated charge separation efficiency. Notably, the engineered carbon vacancies greatly promote the adsorption and activation of nitrogen molecules, and improve the ultra-thin g-C of carbon defects3N4-nitrogen fixation activity of V material.
In order to achieve the above object, the present invention provides a method for preparing a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation, comprising: the ultrathin carbon nitride with a loose structure and more surface carbon defects is obtained by a high-temperature stripping method, which specifically comprises the following steps:
the precursor is calcined at high temperature for three times to obtain ultrathin carbon nitride with loose structure and more surface carbon defects; the temperature of each calcination is 520-550 ℃, and the heat preservation time is 2-4 hoursThe temperature rise rate is 2-5 ℃/min; wherein the precursor adopts urea with a chemical formula of CH4N2O。
Preferably, the first calcination is carried out in a 100ml quartz crucible with a cover to obtain bulk-phase carbon nitride;
the second calcination and the third calcination are carried out in a rectangular ceramic boat with the diameter of 90mm x 60mm x 15mm, and the carbon nitride with defects is obtained.
Further, the carbon nitride obtained by the first calcination is fully ground into fine powder to ensure that the next full calcination can be carried out;
the second calcination and the third calcination are to place the product obtained by the previous calcination into a porcelain boat for secondary calcination.
Furthermore, the carbon nitride is uniformly spread in the porcelain boat, and the thickness of the carbon nitride can not exceed 2 mm.
Further, the method comprises the following specific steps:
s1: placing 20g of urea into a 100ml quartz crucible with a cover, and placing the quartz crucible into a muffle furnace for calcination, wherein the calcination temperature is 520-550 ℃, the heat preservation time is 2-4 hours, and the heating rate is 2-5 ℃/min;
s2: grinding for 30min to obtain fine carbon nitride powder;
s3: and (3) second calcination: uniformly spreading the carbon nitride in a porcelain boat, wherein the thickness of the carbon nitride cannot exceed 2mm, putting the porcelain boat into a muffle furnace for calcination, wherein the calcination temperature is 520-550 ℃, the heat preservation time is 2-4 hours, and the heating rate is 2-5 ℃/min;
s4: and (3) third calcination: uniformly spreading the carbon nitride in a porcelain boat with the thickness not exceeding 2mm, putting the porcelain boat into a muffle furnace for calcination at the calcination temperature of 520 ℃ and 550 ℃, keeping the temperature for 2-4 hours and raising the temperature at the rate of 2-5 ℃/min.
The precursor adopted by the invention is urea, and the prepared carbon nitride has higher photocatalytic activity than carbon nitride prepared by other precursors. The defect carbon nitride prepared by the thermal oxygen etching method of multiple times of calcination has the following advantages: the introduction of defects will further destroy some in-plane triazine structures, forming holes, increasing photogenerated electrons. g-C3N4Can be made in an ultra-thin structureQuickly transferring carriers from the interior of the semiconductor to the surface of the semiconductor. Due to the heterogeneous coordination with high atomic activity, surface defects are generally used as active sites for activating reactant molecules and can inhibit the surface recombination of carriers, resulting in a greatly reduced recombination rate.
The invention has the following advantages and remarkable effects:
1. the precursor is urea, and the prepared carbon nitride has higher photocatalytic activity than carbon nitride prepared from other precursors.
2. g-C after three calcinations3N4Has an ultra-thin structure and carbon defects, and thus can rapidly transfer carriers from the inside of a semiconductor to the surface of the semiconductor.
3. Because the raw materials do not need to be subjected to a mixed grinding process, the production process is simple, the production period is short, and the production cost is favorably reduced;
4. the calcination is carried out only by using a muffle furnace under air separation, and the method is simple.
5. The carbon nitride prepared by the scheme also has a mesoporous structure, is universal and has high application and popularization values.
Drawings
FIG. 1 is an XRD pattern of bulk phase carbon nitride and carbon deficient carbon nitride obtained in example 1;
FIG. 2 is a scanning electron micrograph of bulk carbon nitride and carbon-deficient carbon nitride obtained in example 1;
FIG. 3 is a transmission electron micrograph of bulk carbon nitride and carbon-deficient carbon nitride obtained in example 1.
FIG. 4 is an infrared spectrum of bulk carbon nitride and carbon-deficient carbon nitride obtained in example 1;
FIG. 5 is an EPR chart of bulk-phase carbon nitride and carbon-deficient carbon nitride obtained in example 1;
FIG. 6 is a graph showing the impedance of bulk carbon nitride and carbon-deficient carbon nitride obtained in example 1;
FIG. 7 is a fluorescence spectrum of bulk-phase carbon nitride and carbon-deficient carbon nitride obtained in example 1.
Detailed Description
The salient features and significant improvements of the present invention are further clarified by the following examples, which are intended to be illustrative only and not limiting in any way.
Example 1
1. Placing 20g of urea into a 100ml quartz crucible with a cover, and calcining in a muffle furnace at 550 ℃ for 4 hours at a heating rate of 5 ℃/min;
2. grinding for 30min to obtain fine carbon nitride powder;
3. and (3) second calcination: uniformly spreading the carbon nitride in a porcelain boat, wherein the thickness of the carbon nitride cannot exceed 2mm, putting the porcelain boat into a muffle furnace for calcination, wherein the calcination temperature is 520 ℃, the heat preservation time is 2 hours, and the heating rate is 5 ℃/min;
4. and (3) third calcination: uniformly spreading the carbon nitride in a porcelain boat with the thickness not exceeding 2mm, putting the porcelain boat into a muffle furnace for calcining, wherein the calcining temperature is 520 ℃, the heat preservation time is 2 hours, and the heating rate is 5 ℃/min.
Example 2
1. Placing 20g of urea into a 100ml quartz crucible with a cover, and calcining in a muffle furnace at 530 ℃ for 2 hours at a heating rate of 2 ℃/min;
2. grinding for 30min to obtain fine carbon nitride powder;
3. and (3) second calcination: uniformly spreading the carbon nitride in a porcelain boat, wherein the thickness of the carbon nitride cannot exceed 2mm, putting the porcelain boat into a muffle furnace for calcination, wherein the calcination temperature is 550 ℃, the heat preservation time is 4 hours, and the heating rate is 2 ℃/min;
4. and (3) third calcination: uniformly spreading the carbon nitride in a porcelain boat with the thickness not exceeding 2mm, putting the porcelain boat into a muffle furnace for calcining, wherein the calcining temperature is 550 ℃, the heat preservation time is 4 hours, and the heating rate is 2 ℃/min.
Example 3
1. Placing 20g of urea into a 100ml quartz crucible with a cover, and calcining in a muffle furnace at 520 ℃ for 3 hours at a heating rate of 3 ℃/min;
2. grinding for 30min to obtain fine carbon nitride powder;
3. and (3) second calcination: uniformly spreading the carbon nitride in a porcelain boat, wherein the thickness of the carbon nitride cannot exceed 2mm, putting the porcelain boat into a muffle furnace for calcination, wherein the calcination temperature is 530 ℃, the heat preservation time is 3 hours, and the heating rate is 3 ℃/min;
4. and (3) third calcination: uniformly spreading the carbon nitride in a porcelain boat with the thickness not exceeding 2mm, putting the porcelain boat into a muffle furnace for calcining, wherein the calcining temperature is 530 ℃, the heat preservation time is 3 hours, and the heating rate is 3 ℃/min.
As shown in FIG. 1, g-C3N4Bulk phase carbon nitride, g-C3N4-V is a carbon deficient carbon nitride. At 2 θ ═ 13.4 ° and 27.4 °, corresponding to g-C3N4The (100) and (002) crystal planes of (a). A repeating structure of a triazine unit and an interlaminar stacking structure of a conjugated aromatic system are illustrated. g-C obtained by three calcinations3N4The XRD peak intensity of-V is obviously lower than that of C3N4It is stated that the crystallinity of carbon nitride is poor, probably due to C3N4Vacancies are present in the backbone.
As shown in fig. 2, the typical morphological features of intact CN can be clearly observed, showing that the lamellae are aggregated and interconnected. The prepared sample was confirmed to be a sheet-like structure (fig. 2a), and it can be seen that the sheet thickness was very thin, covered by holes (fig. 2 b).
As shown in fig. 3, TEM clearly characterizes the morphology of this invention. Corresponding to FIG. 3a confirms g-C3N4The form of the layer connection. g-C3N4After sufficient calcination in an air atmosphere, the resulting V-g-C3N4Sample size reduction from the original g-C3N4The curled edges of the sample are clearer, showing a loose lamellar morphology (fig. 3 b).
As shown in FIG. 4, g-C of comparative preparation3N4And C3N4-V infrared spectrum, peak at 810cm-1Corresponding to the respiratory vibrations of the triazine units. 1204 1639cm-1Is an aromatic CN heterocycle corresponding to bone vibration, bulk phase g-C3N4And g-C3N4The main characteristic peak between-V did not change, indicating that the triple calcination did not changeA skeleton of the material.
As shown in FIG. 5, at g-C3N4in-V, this line has considerable damping, which means that the number of unpaired electrons is reduced, possibly due to the formation of carbon vacancies.
Electrochemical Impedance Spectroscopy (EIS) further confirms the efficient separation of carriers, as shown in fig. 6. g-C3N4The arc radius on the EIS graph of-V is smaller than the arc radius of the original CN. The arc radius on the EIS spectrum reflects the rate of reaction occurring at the electrode surface; the results show that efficient electron-hole pair separation and rapid interface charge transfer occurs after the introduction of carbon vacancies in the CN.
As shown in FIG. 7, PL spectra for both samples are shown at 385nm excitation at room temperature. g-C3N4The strong emission peak around 480nm is caused by direct band transitions. In contrast, g-C3N4The photoluminescence intensity of-V was more than 50% lower, indicating g-C3N4The recombination of photo-generated charges in the-V material is effectively suppressed. g-C3N4The improved photoproduction charge separation efficiency of the V samples is attributed to the construction of carbon vaccines, which have the ability to capture electrons and inhibit the radiative recombination of the photoproduction charge.
When the carbon nitride regulated and controlled by the carbon defect is used for screening the precursor, the urea is considered to be easier to form a porous structure and a carbon defect site after being calcined for multiple times. The results of examples 1-3 and FIGS. 1-7 are combined to show that the carbon nitride produced is indeed a porous carbon defect carbon nitride. In addition: examples 2-3 gave results similar to example 1, with the difference that the content of voids and carbon defect sites formed was different.
Claims (5)
1. A preparation method of a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation is characterized by comprising the following steps: the ultrathin carbon nitride with a loose structure and more surface carbon defects is obtained by a high-temperature stripping method, which specifically comprises the following steps:
the precursor is calcined at high temperature for three times to obtain ultrathin carbon nitride with loose structure and more surface carbon defects; the temperature of each calcination was 52 deg.CThe temperature is kept at 0-550 ℃ for 2-4 hours, and the heating rate is 2-5 ℃/min; wherein the precursor adopts urea with a chemical formula of CH4N2O。
2. The method for preparing a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation according to claim 1, wherein:
the first calcination is carried out in a 100ml quartz crucible with a cover to obtain bulk-phase carbon nitride;
the second calcination and the third calcination are carried out in a rectangular ceramic boat with the diameter of 90mm x 60mm x 15mm, and the carbon nitride with defects is obtained.
3. The method for preparing a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation according to claim 2, wherein:
fully grinding the carbon nitride obtained by the first calcination into fine powder to ensure that the next full calcination can be carried out;
the second calcination and the third calcination are to place the product obtained by the previous calcination into a porcelain boat for secondary calcination.
4. The method for preparing a carbon-deficient carbon nitride material for photocatalytic nitrogen fixation according to claim 3, wherein: the carbon nitride is uniformly spread in the porcelain boat, and the thickness of the carbon nitride can not exceed 2 mm.
5. The method for preparing a carbon nitride material deficient in carbon for photocatalytic nitrogen fixation according to any one of claims 1 to 4, comprising: the method comprises the following specific steps:
s1: placing 20g of urea into a 100ml quartz crucible with a cover, and placing the quartz crucible into a muffle furnace for calcination, wherein the calcination temperature is 520-550 ℃, the heat preservation time is 2-4 hours, and the heating rate is 2-5 ℃/min;
s2: grinding for 30min to obtain fine carbon nitride powder;
s3: and (3) second calcination: uniformly spreading the carbon nitride in a porcelain boat, wherein the thickness of the carbon nitride cannot exceed 2mm, putting the porcelain boat into a muffle furnace for calcination, wherein the calcination temperature is 520-550 ℃, the heat preservation time is 2-4 hours, and the heating rate is 2-5 ℃/min;
s4: and (3) third calcination: uniformly spreading the carbon nitride in a porcelain boat with the thickness not exceeding 2mm, putting the porcelain boat into a muffle furnace for calcination at the calcination temperature of 520 ℃ and 550 ℃, keeping the temperature for 2-4 hours and raising the temperature at the rate of 2-5 ℃/min.
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Cited By (4)
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|---|---|---|---|---|
| CN113830742A (en) * | 2021-07-16 | 2021-12-24 | 中国科学技术大学 | Ultrathin carbon nitride nanosheet rich in nitrogen defects, preparation method of ultrathin carbon nitride nanosheet and method for preparing hydrogen peroxide through photocatalysis |
| CN114628651A (en) * | 2021-09-27 | 2022-06-14 | 万向一二三股份公司 | Preparation method and application of high-first-efficiency long-cycle SiO/C composite negative electrode material |
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