Potassium, chlorine and iodine co-doped carbon nitride, preparation method thereof and method for preparing hydrogen peroxide through photocatalysis
阅读说明：本技术 一种钾、氯、碘共掺杂氮化碳及其制备方法、光催化制备过氧化氢的方法 (Potassium, chlorine and iodine co-doped carbon nitride, preparation method thereof and method for preparing hydrogen peroxide through photocatalysis ) 是由 陈洁洁 刘练练 陈飞 俞汉青 于 2021-07-02 设计创作，主要内容包括：本发明提供了一种共掺杂氮化碳,其特征在于,所述共掺杂氮化碳为K、Cl和I共掺杂的石墨相氮化碳。本发明结合了非金属掺杂和金属掺杂的优点,对氮化碳进行多种杂原子的共掺杂改性,改善其电子结构,提高电荷分离性能,K、Cl、I三者的协同作用提升了改性后氮化碳的光催化活性。本发明采用共掺杂氮化碳作为光催化剂的主体材料,可见光驱动下催化合成过氧化氢的速率快,并且光催化性能稳定,能够可持续和重复使用。本发明仅通过三聚氰胺在KCl/KI熔融盐辅助下的热聚合,就可以得到共掺杂的氮化碳材料,方法简便,操作流程简单,易拓展,可大规模制备。(The invention provides co-doped carbon nitride which is characterized by being K, Cl and I co-doped graphite phase carbon nitride. The invention combines the advantages of nonmetal doping and metal doping, co-doping modification of various heteroatoms is carried out on carbon nitride, the electronic structure of the carbon nitride is improved, the charge separation performance is improved, and the photocatalytic activity of the modified carbon nitride is improved by the synergistic effect of K, Cl and I. According to the invention, the co-doped carbon nitride is used as a main material of the photocatalyst, the speed of catalytically synthesizing hydrogen peroxide under the drive of visible light is high, the photocatalytic performance is stable, and the catalyst can be continuously and repeatedly used. According to the invention, the co-doped carbon nitride material can be obtained only by thermal polymerization of melamine under the assistance of KCl/KI molten salt, the method is simple and convenient, the operation flow is simple, the expansion is easy, and the large-scale preparation can be realized.)
1. The co-doped carbon nitride is K, Cl and I co-doped graphite-phase carbon nitride.
2. The co-doped carbon nitride according to claim 1, wherein the graphite phase carbon nitride is a graphite phase carbon nitride in which an amorphous form and a crystalline form coexist;
the co-doped carbon nitride is a photocatalyst for photocatalytic reaction;
the particle size of the co-doped carbon nitride is 1-20 mu m;
the codoped carbon nitride comprises codoped carbon nitride with a laminated structure formed by stacking codoped carbon nitride nanosheets.
3. The codoped carbon nitride as claimed in claim 1, wherein the doping amount of K atoms in the codoped carbon nitride is 3-7%;
in the co-doped carbon nitride, the doping amount of Cl atoms is less than or equal to 0.2%;
in the co-doped carbon nitride, the doping amount of I atoms is 0.1-0.5%;
the co-doped carbon nitride is obtained by thermal polycondensation of melamine under the assistance of KCl/KI molten salt.
4. The co-doped carbon nitride according to claim 1, wherein the co-doped carbon nitride comprises co-doped carbon nitride with lattice stripes;
the width of the lattice fringes is 0.25-0.30 nm;
the length of the lattice fringes is 10-20 nm;
the co-doped carbon nitride is a photocatalyst for the reaction of preparing hydrogen peroxide by photocatalysis;
the rate of preparing hydrogen peroxide by photocatalysis is 138-13100μmol·gCatalyst and process for preparing same -1·h-1。
5. A preparation method of co-doped carbon nitride is characterized by comprising the following steps:
1) mixing melamine, potassium chloride and potassium iodide to obtain a solid phase mixture;
2) calcining the solid phase mixture obtained in the step to obtain a one-step product;
3) and calcining the product obtained in the previous step again to obtain the co-doped carbon nitride.
6. The preparation method according to claim 5, wherein the molar ratio of the melamine to the potassium chloride is (2-8): 1;
the molar ratio of the melamine to the potassium iodide is (2-8): 1;
the mixing mode comprises grinding and mixing;
the temperature rise rate of the calcination is 2-10 ℃/min;
the calcining temperature is 500-600 ℃;
and the calcining time is 4-8 h.
7. The method of claim 5, further comprising a regrinding step after the calcining;
the temperature rise rate of the secondary calcination is 2-10 ℃/min;
the temperature for secondary calcination is 500-600 ℃;
and the secondary calcination time is 4-8 h.
8. Application of the co-doped carbon nitride according to any one of claims 1 to 4 or the co-doped carbon nitride prepared by the preparation method according to any one of claims 5 to 7 in photocatalytic preparation of hydrogen peroxide.
9. A method for preparing hydrogen peroxide by photocatalysis is characterized by comprising the following steps:
(1) mixing the co-doped carbon nitride photocatalyst with an aqueous solution containing a sacrificial agent, and carrying out a photocatalytic reaction under the irradiation of a xenon lamp to obtain hydrogen peroxide;
the co-doped carbon nitride photocatalyst comprises the co-doped carbon nitride of any one of claims 1 to 4 or the co-doped carbon nitride prepared by the preparation method of any one of claims 5 to 7.
10. The method according to claim 9, wherein the volume fraction of ethanol in the aqueous solution containing ethanol is between 5% and 20%;
the sacrificial agent comprises one or more of ethanol, methanol, isopropanol, formic acid and lactic acid;
the addition amount of the co-doped carbon nitride is 0.2-1 g/L;
the light intensity of the xenon lamp is 60-450 mW/cm2；
The wavelength of the light irradiated by the xenon lamp is more than 400 nm;
the temperature of the photocatalytic reaction is 20-30 ℃;
the time of the photocatalytic reaction is 0.5-7 h.
Technical Field
The invention relates to the technical field of graphite-phase carbon nitride photocatalysts, in particular to co-doped carbon nitride and a preparation method thereof, and a method for preparing hydrogen peroxide through photocatalysis, and in particular relates to potassium, chlorine and iodine co-doped carbon nitride and a preparation method thereof, and a method for preparing hydrogen peroxide through photocatalysis.
Background
Hydrogen peroxide is widely used in our production and life. The anthraquinone process is a general method for industrially preparing hydrogen peroxide, but the method has many defects, such as high energy consumption, complex process flow, serious pollution and the like. The photocatalytic hydrogen peroxide production method can avoid the problems and is an economic, green and sustainable hydrogen peroxide production method. Firstly, the photocatalysis can utilize solar energy, and other energy input is not needed, so that the energy is saved and the economy is realized. Secondly, the photo-generated electrons excited by light are used for producing hydrogen peroxide by reducing oxygen, and the process is simple and pollution-free. However, the current photocatalytic production of hydrogen peroxide is mainly limited by the low activity of the photocatalyst and the slow rate of hydrogen peroxide generation.
The graphite phase carbon nitride semiconductor photocatalyst draws wide attention because of the advantages of visible light response, easily-adjusted energy band structure, two-dimensional conjugated structure, no toxicity, no pollution, low price, easy preparation and the like. However, carbon nitride has many inherent disadvantages, such as small specific surface area, insufficient visible light absorption capability, poor photo-generated charge separation performance, etc., which result in low photocatalytic efficiency of bulk phase carbon nitride. Hetero atoms are introduced into the carbon nitride framework, so that the electronic structure of the carbon nitride can be effectively changed, and the photoelectric property of the carbon nitride is improved. However, although the conventional heteroatom doping has certain advantages and certain effects, the conventional heteroatom doping also has corresponding limitations.
Therefore, how to find a suitable way to solve the defects existing in the current application of carbon nitride, improve the photocatalytic efficiency of carbon nitride, and further widen the application field and the application depth of carbon nitride has become one of the problems to be solved by many researchers.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a co-doped carbon nitride, a preparation method thereof, and a method for preparing hydrogen peroxide by photocatalysis, wherein the co-doped carbon nitride provided by the present invention combines the advantages of non-metal doping and metal doping, and the synergistic effect of the two improves the photocatalytic activity of the modified carbon nitride, and has good stability, and particularly, hydrogen peroxide can be produced by photocatalysis; and the preparation method is simple, easy to operate and low in cost, and is suitable for industrial popularization and application.
The invention provides co-doped carbon nitride, which is K, Cl and I co-doped graphite-phase carbon nitride.
Preferably, the graphite phase carbon nitride is amorphous and crystalline graphite phase carbon nitride;
the co-doped carbon nitride is a photocatalyst for photocatalytic reaction;
the particle size of the co-doped carbon nitride is 1-20 mu m;
the codoped carbon nitride comprises codoped carbon nitride with a laminated structure formed by stacking codoped carbon nitride nanosheets.
Preferably, in the co-doped carbon nitride, the doping amount of K atoms is 3% -7%;
in the co-doped carbon nitride, the doping amount of Cl atoms is less than or equal to 0.2%;
in the co-doped carbon nitride, the doping amount of I atoms is 0.1-0.5%;
the co-doped carbon nitride is obtained by thermal polycondensation of melamine under the assistance of KCl/KI molten salt.
Preferably, the codoped carbon nitride comprises codoped carbon nitride with lattice stripes;
the width of the lattice fringes is 0.25-0.30 nm;
the length of the lattice fringes is 10-20 nm;
the co-doped carbon nitride is a photocatalyst for the reaction of preparing hydrogen peroxide by photocatalysis;
the rate of preparing hydrogen peroxide by photocatalysis is 138-13100 mu mol gCatalyst and process for preparing same -1·h-1。
The invention provides a preparation method of codoped carbon nitride, which comprises the following steps:
1) mixing melamine, potassium chloride and potassium iodide to obtain a solid phase mixture;
2) calcining the solid phase mixture obtained in the step to obtain a one-step product;
3) and calcining the product obtained in the previous step again to obtain the co-doped carbon nitride.
Preferably, the molar ratio of the melamine to the potassium chloride is (2-8): 1;
the molar ratio of the melamine to the potassium iodide is (2-8): 1;
the mixing mode comprises grinding and mixing;
the temperature rise rate of the calcination is 2-10 ℃/min;
the calcining temperature is 500-600 ℃;
and the calcining time is 4-8 h.
Preferably, the calcination further comprises a regrinding step;
the temperature rise rate of the secondary calcination is 2-10 ℃/min;
the temperature for secondary calcination is 500-600 ℃;
and the secondary calcination time is 4-8 h.
The invention provides application of the codoped carbon nitride in any one of the technical schemes or the codoped carbon nitride prepared by the preparation method in any one of the technical schemes in photocatalytic preparation of hydrogen peroxide.
The invention also provides a method for preparing hydrogen peroxide by photocatalysis, which comprises the following steps:
(1) mixing the co-doped carbon nitride photocatalyst with an aqueous solution containing a sacrificial agent, and carrying out a photocatalytic reaction under the irradiation of a xenon lamp to obtain hydrogen peroxide;
the codoped carbon nitride photocatalyst comprises codoped carbon nitride prepared by the codoped carbon nitride or the preparation method of any one of the above technical schemes.
Preferably, the volume fraction of ethanol in the ethanol-containing aqueous solution is 5-20%;
the sacrificial agent comprises one or more of ethanol, methanol, isopropanol, formic acid and lactic acid;
the addition amount of the co-doped carbon nitride is 0.2-1 g/L;
the light intensity of the xenon lamp is 60-450mW/cm2；
The wavelength of the light irradiated by the xenon lamp is more than 400 nm;
the temperature of the photocatalytic reaction is 20-30 ℃;
the time of the photocatalytic reaction is 0.5-7 h.
The invention provides co-doped carbon nitride which is characterized by being K, Cl and I co-doped graphite phase carbon nitride. Compared with the prior art, the invention aims at the existing g-C3N4The photocatalytic efficiency of (A) is still low, although there are many ways to increase g-C3N4Such as heteroatom doping. However, the present invention is researched and recognized that the existing heteroatom doping has corresponding limitations, and the doping of carbon nitride can be divided into metal doping and non-metal doping according to the type of the heteroatom, and the advantages and the limitations of the existing heteroatom doping are respectively provided. In the case of metal doping, for example, Na, K, Fe, Co, Ni, Pt, Au and the like, although the transfer of photogenerated carriers can be accelerated, these metal elements have limited ability to adjust the electronic structure of carbon nitride, and the light absorption ability is not improved. The nonmetal doping, such as O, S, P, Cl, can form a firm covalent bond with C or N atoms of carbon nitride, has good stability, can significantly adjust the electronic structure of carbon nitride, and enhance light absorption, but the nonmetal doping still cannot reduce the charge transfer resistance of carbon nitride, and excessive defects may cause the formation of new charge recombination centers, but rather unfavorable for photocatalytic reaction.
The invention creatively obtains a specific three-element co-doped carbon nitride material, adopts K, Cl and I co-doped carbon nitride as a main material of the photocatalyst, and combines the advantages of non-metal doping and metal doping. The doping of K reduces the charge transfer resistance and improves the separation performance of photon-generated carriers. The Cl and I doping changes the electronic structure of the carbon nitride, and enhances the light trapping capacity. K. Cl, I three's synergistic action carries out the co-doping of multiple heteroatom to the carbon nitride and modifies, improves its electronic structure, improves charge separation performance, has promoted the photocatalysis activity of modified carbon nitride. The co-doped carbon nitride provided by the invention also has a specific microstructure and morphology, and the catalytic activity and the stability are further improved. According to the invention, the co-doped carbon nitride is used as a main material of the photocatalyst, the speed of catalytically synthesizing hydrogen peroxide under the drive of visible light is high, the photocatalytic performance is stable, and the catalyst can be continuously and repeatedly used.
The K, Cl and I co-doped carbon nitride material can be obtained only by thermal polymerization of melamine under the assistance of KCl/KI molten salt, the method is simple and convenient, the operation flow is simple, the expansion is easy, the large-scale preparation can be realized, the catalyst is used as a photocatalyst in the process of producing hydrogen peroxide by photocatalysis, the photocatalytic activity is high, the stability is good, the catalyst can be applied to preparing low-concentration hydrogen peroxide on site, and the catalyst can also be applied to preparing hydrogen peroxide by sunlight under simple conditions.
Experimental results show that the K, Cl and I co-doped carbon nitride material provided by the invention is used as a photocatalyst to produce hydrogen peroxide under the drive of visible light at a rate of 13.1 mmol/gCatalyst and process for preparing same -1·h-1。
Drawings
FIG. 1 is a scanning electron microscope image of K, Cl and I co-doped carbon nitride prepared in example 1 of the present invention;
FIG. 2 is a high-resolution transmission electron microscope image of K, Cl and I co-doped carbon nitride prepared in example 1 of the present invention;
FIG. 3 is a partial enlarged view of the high resolution TEM image of FIG. 2;
FIG. 4 is an infrared spectrum of the K, Cl and I codoped carbon nitride and carbon nitride prepared in example 1 of the present invention;
FIG. 5 is a graph showing the relationship between the concentration of hydrogen peroxide produced by co-doping carbon nitride and carbon nitride with K, Cl and I under the drive of visible light, which is prepared in example 1 of the present invention, and the change with time of light irradiation;
FIG. 6 is a graph showing the cycle stability of hydrogen peroxide photocatalytic production by K, Cl and I co-doped carbon nitride prepared in example 1 of the present invention;
FIG. 7 is a graph showing the change of the concentration of hydrogen peroxide produced by photocatalysis of K, Cl and I three-element co-doped carbon nitride obtained by changing the precursor in example 2 of the present invention with time;
FIG. 8 is a graph showing the change of hydrogen peroxide concentration over time in the photocatalytic production of K-doped carbon nitride according to comparative example 1 of the present invention;
FIG. 9 is a graph showing the change of hydrogen peroxide concentration over time in the photocatalytic production of Cl-doped carbon nitride according to comparative example 2 of the present invention;
FIG. 10 is a graph showing the change of hydrogen peroxide concentration over time in photocatalytic production of I-doped carbon nitride according to comparative example 3 of the present invention;
FIG. 11 is a graph showing the change of the concentration of hydrogen peroxide produced by the photo-catalysis of K, Cl co-doped carbon nitride according to comparative example 4 of the present invention with time;
fig. 12 is a graph showing the change of the concentration of hydrogen peroxide produced by the photo-catalysis of K, I co-doped carbon nitride according to comparative example 5 of the present invention with time.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
All the raw materials of the present invention are not particularly limited in their purity, and the present invention preferably employs a purity which is conventional in the field of analytical purification or photocatalyst preparation.
The invention provides co-doped carbon nitride, which is K, Cl and I co-doped graphite-phase carbon nitride.
In the co-doped carbon nitride, the doping amount of K atoms is preferably 3% to 7%, more preferably 3.5% to 6.5%, more preferably 4% to 6%, and more preferably 4.5% to 5.5%. The doping amount of the invention is specifically the atomic doping amount of the doping atoms, namely the atomic concentration.
In the present invention, the doping amount of Cl atoms in the co-doped carbon nitride is preferably equal to or less than 0.2%, more preferably equal to or less than 0.18%, and still more preferably equal to or less than 0.16%. The doping amount of the invention is specifically the atomic doping amount of the doping atoms, namely the atomic concentration.
In the co-doped carbon nitride, the doping amount of the I atom is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, and more preferably 0.25% to 0.35%. The doping amount of the invention is specifically the atomic doping amount of the doping atoms, namely the atomic concentration.
In the present invention, the graphite phase carbon nitride is preferably a graphite phase carbon nitride in which an amorphous form and a crystalline form coexist.
In the invention, the particle size of the co-doped carbon nitride is preferably 1-20 μm, more preferably 5-16 μm, and more preferably 9-12 μm.
In the present invention, the co-doped carbon nitride preferably includes co-doped carbon nitride having a laminated structure formed by stacking co-doped carbon nitride nanosheets.
In the present invention, the co-doped carbon nitride preferably includes co-doped carbon nitride having lattice stripes.
In the present invention, the width of the lattice stripe is preferably 0.25 to 0.30nm, more preferably 0.26 to 0.29nm, and still more preferably 0.27 to 0.28 nm.
In the invention, the length of the lattice fringes is preferably 10-20 nm, more preferably 12-18 nm, and more preferably 14-16 nm.
In the present invention, the co-doped carbon nitride is preferably a photocatalyst for photocatalytic reaction. Specifically, the co-doped carbon nitride is preferably a photocatalyst used for a reaction of preparing hydrogen peroxide through photocatalysis.
In the invention, the rate of preparing hydrogen peroxide by photocatalysis is preferably 138-13100 mu mol-gCatalyst and process for preparing same -1·h-1More preferably 2138 to 11100. mu. mol/gCatalyst and process for preparing same -1·h-1More preferably 4138 to 9100. mu. mol. gCatalyst and process for preparing same -1·h-1More preferably 6138 to 7100. mu. mol/gCatalyst and process for preparing same -1·h-1。
In the invention, the codoped carbon nitride is preferably obtained by thermal polycondensation of melamine with the aid of a KCl/KI molten salt.
The invention provides a preparation method of codoped carbon nitride, which comprises the following steps:
1) mixing melamine, potassium chloride and potassium iodide to obtain a solid phase mixture;
2) calcining the solid phase mixture obtained in the step to obtain a one-step product;
3) and calcining the product obtained in the previous step again to obtain the co-doped carbon nitride.
The invention firstly mixes the melamine, the potassium chloride and the potassium iodide to obtain a solid phase mixture.
In the present invention, the molar ratio of the melamine to the potassium chloride is preferably (2 to 8): 1, more preferably (3-6): 1, more preferably (4-5): 1.
in the invention, the molar ratio of the melamine to the potassium iodide is preferably (2-8): 1, more preferably (3-6): 1, more preferably (4-5): 1.
in the present invention, the mixing means preferably includes a grinding mixing.
The solid phase mixture obtained in the step is calcined to obtain a one-step product.
In the invention, the heating rate of the calcination is preferably 2-10 ℃/min, more preferably 3-9 ℃/min, more preferably 4-8 ℃/min, and more preferably 5-7 ℃/min.
In the invention, the calcination temperature is preferably 500-600 ℃, more preferably 520-580 ℃, and more preferably 540-560 ℃.
In the invention, the calcination time is preferably 4-8 h, more preferably 4.5-7.5 h, more preferably 5-7 h, and more preferably 5.5-6.5 h.
In the present invention, the calcination preferably further includes a regrinding step.
Finally, calcining the product obtained in the previous step again to obtain the co-doped carbon nitride.
In the invention, the temperature rise rate of the re-calcination is preferably 2-10 ℃/min, more preferably 3-9 ℃/min, more preferably 4-8 ℃/min, and more preferably 5-7 ℃/min.
In the invention, the temperature of the secondary calcination is preferably 500-600 ℃, more preferably 520-580 ℃, and more preferably 540-560 ℃.
In the invention, the time for the secondary calcination is preferably 4 to 8 hours, more preferably 4.5 to 7.5 hours, more preferably 5 to 7 hours, and more preferably 5.5 to 6.5 hours.
The preparation method of the potassium, chlorine and iodine co-doped carbon nitride provided by the steps can specifically comprise the following steps:
s1, weighing melamine, KCl and KI, fully grinding in a mortar, and uniformly mixing;
s2: placing the mixture in a covered crucible, then placing the crucible in a muffle furnace, heating to a temperature, keeping for a period of time, naturally cooling to room temperature, and grinding to obtain co-doped carbon nitride;
s3: placing the obtained co-doped carbon nitride in a covered crucible again, then placing the crucible in a muffle furnace, calcining again under the same conditions to improve the polymerization degree of the co-doped carbon nitride, and grinding to obtain a yellow co-doped carbon nitride product;
post-treatment: and cleaning the obtained co-doped carbon nitride with ultrapure water, repeatedly washing and centrifuging, and drying in a vacuum drying oven to obtain the co-doped carbon nitride product.
The invention also provides a method for preparing hydrogen peroxide by photocatalysis, which comprises the following steps:
(1) and mixing the co-doped carbon nitride photocatalyst with an aqueous solution containing a sacrificial agent, and carrying out a photocatalytic reaction under the irradiation of a xenon lamp to obtain the hydrogen peroxide.
The codoped carbon nitride photocatalyst comprises codoped carbon nitride prepared by the codoped carbon nitride or the preparation method of any one of the above technical schemes.
In the present invention, the volume fraction of ethanol in the ethanol-containing aqueous solution is preferably 5% to 20%, more preferably 8% to 17%, and still more preferably 11% to 14%.
In the present invention, the sacrificial agent preferably includes one or more of ethanol, methanol, isopropanol, formic acid, and lactic acid, and more preferably ethanol, methanol, isopropanol, formic acid, or lactic acid.
In the invention, the addition amount of the co-doped carbon nitride is preferably 0.2-1 g/L, more preferably 0.3-0.9 g/L, more preferably 0.4-0.8 g/L, and more preferably 0.5-0.7 g/L.
In the invention, the light intensity of the xenon lamp is preferably 60-450 mW/cm2More preferably 100-400 mW/cm2More preferably 150-350 mW/cm2More preferably 200-300 mW/cm2。
In the present invention, the wavelength of the light irradiated by the xenon lamp is preferably more than 400nm, more preferably more than 500nm, and still more preferably more than 600 nm.
In the invention, the temperature of the photocatalytic reaction is preferably 20-30 ℃, more preferably 22-28 ℃, and more preferably 24-26 ℃.
In the invention, the time of the photocatalytic reaction is preferably 0.5-7 h, more preferably 1.5-6 h, more preferably 2.5-5 h, and more preferably 3.5-4 h.
The invention is a complete and refined integral technical scheme, better ensures the photocatalysis effect of co-doped carbon nitride, and the method for preparing hydrogen peroxide by photocatalysis provided by the steps can specifically comprise the following steps:
and dispersing the co-doped carbon nitride into deionized water, adding ethanol as a sacrificial agent, magnetically stirring, irradiating by using a xenon lamp as a light source, controlling the temperature by using external circulating water, sampling at intervals, and measuring the concentration of the produced hydrogen peroxide by an iodometry method. Specifically, the adding amount of the co-doped carbon nitride can be 0.2 g/L; the volume fraction of the added ethanol can be 10 percent; the power of the xenon lamp can be 300W, and a 400nm cut-off filter is assembled; and the reaction temperature can be kept at 25 ℃ by using external circulating water.
The invention provides potassium, chlorine and iodine co-doped carbon nitride, a preparation method thereof and a method for preparing hydrogen peroxide through photocatalysis. The invention adopts K, Cl and I co-doped carbon nitride as the main material of the photocatalyst, and combines the advantages of non-metal doping and metal doping. The doping of K reduces the charge transfer resistance and improves the separation performance of photon-generated carriers. The Cl and I doping changes the electronic structure of the carbon nitride, and enhances the light trapping capacity. K. Cl, I three's synergistic action carries out the co-doping of multiple heteroatom to the carbon nitride and modifies, improves its electronic structure, improves charge separation performance, has promoted the photocatalytic activity of modified carbon nitride to accelerate photocatalytic speed. The co-doped carbon nitride provided by the invention also has a specific microstructure and morphology, and the catalytic activity and the stability are further improved. According to the invention, the co-doped carbon nitride is used as a main material of the photocatalyst, the speed of catalytically synthesizing hydrogen peroxide under the drive of visible light is high, the photocatalytic performance is stable, and the catalyst can be continuously and repeatedly used.
The K, Cl and I co-doped carbon nitride material can be obtained only by thermal polymerization of melamine under the assistance of KCl/KI molten salt, the method is simple and convenient, the operation flow is simple, the expansion is easy, the large-scale preparation can be realized, the catalyst is used as a photocatalyst in the process of producing hydrogen peroxide by photocatalysis, the photocatalytic activity is high, the stability is good, the catalyst can be applied to preparing low-concentration hydrogen peroxide on site, and the catalyst can also be applied to preparing hydrogen peroxide by sunlight under simple conditions.
Experimental results show that the K, Cl and I co-doped carbon nitride material provided by the invention is used as a photocatalyst to produce hydrogen peroxide under the drive of visible light at a rate of 13.1 mmol/gCatalyst and process for preparing same -1·h-1。
In order to further illustrate the present invention, the co-doped carbon nitride and the preparation method thereof, and the method for preparing hydrogen peroxide by photocatalysis provided in the present invention are described in detail with reference to the following examples, but it should be understood that the examples are carried out on the premise of the technical solution of the present invention, and the detailed embodiments and the specific operation procedures are given, only for further illustrating the features and advantages of the present invention, but not for limiting the claims of the present invention, and the scope of the present invention is not limited to the following examples.
The materials and equipment used in the following examples are commercially available; wherein the light source system is PLS-SXE300 xenon lamp, available from Beijing Pofely Tech Co.
Example 1
K. The preparation method of the Cl and I co-doped carbon nitride specifically comprises the following steps:
s1, weighing 5g of melamine, 10mmol of KCl and 10mmol of KI, fully grinding in a mortar, and uniformly mixing;
s2: placing the mixture in a covered crucible, then placing the crucible in a muffle furnace, heating to 550 ℃ at the speed of 2.5 ℃/min, keeping for 4h, naturally cooling to room temperature, and grinding to obtain co-doped carbon nitride;
s3: placing the obtained co-doped carbon nitride in a covered crucible again, then placing the crucible in a muffle furnace, calcining again under the same conditions to improve the polymerization degree, and grinding to obtain a yellow co-doped carbon nitride product;
the preparation method also comprises the following post-treatment steps: and cleaning the co-doped carbon nitride with ultrapure water, repeatedly washing and centrifuging for 3 times, and drying in a vacuum drying oven at 60 ℃ to obtain a co-doped carbon nitride product.
In order to facilitate the distinction between the different catalysts, unmodified carbon nitride is denoted CN and K, Cl, I co-doped carbon nitride is denoted CN-KCl/KI.
The co-doped carbon nitride prepared in example 1 has K, Cl and I heteroatoms introduced into the carbon nitride by thermal polymerization of melamine with the aid of KCl/KI mixed salt.
The appearance of the co-doped carbon nitride prepared in the embodiment 1 of the invention is represented by a scanning electron microscope.
Referring to fig. 1, fig. 1 is a scanning electron microscope image of the co-doped carbon nitride prepared in example 1 of the present invention.
As can be seen from fig. 1, the co-doped carbon nitride has a random morphology and non-uniform size.
The codoped carbon nitride prepared in the embodiment 1 of the invention is characterized by a high transmission electron microscope.
Referring to fig. 2, fig. 2 is a high-resolution transmission electron microscope image of the co-doped carbon nitride prepared in example 1 of the present invention.
As can be seen from fig. 2, the codoped carbon nitride prepared by the invention has the appearance of a laminated structure formed by stacking codoped carbon nitride nanosheets, and the prepared K/Cl/I codoped carbon nitride is partially crystalline and has lattice stripes, i.e., amorphous and crystalline coexist.
Referring to fig. 3, fig. 3 is a partially enlarged view of the high-resolution tem image of fig. 2.
As can be clearly seen from FIG. 3, the co-doped carbon nitride prepared by the method has lattice stripes, the width of the lattice stripes is 0.257nm, and the length of the lattice stripes is 10-20 nm as can be seen by combining FIG. 2.
Infrared spectroscopic analysis was performed on the co-doped carbon nitride prepared in example 1 of the present invention.
Referring to fig. 4, fig. 4 is an infrared spectrum of the co-doped carbon nitride and carbon nitride prepared in example 1 of the present invention.
From the IR spectrum of FIG. 4, it is found that the intensity is 800cm-1The characteristic peak of the compound is attributed to the in-plane bending vibration of the tris-s-triazine and is 1200-1800 cm-1Characteristic peaks of the range due to stretching vibration of the C-N heterocycle, 3300cm-1The characteristic peak at the left and right sides is the stretching vibration of unpolymerized N-H bond, 2150cm-1The characteristic peak of (A) is C [ identical to ] N stretching vibration. The appearance of these characteristic peaks indicates the successful synthesis of carbon nitride, consisting of tris-s-triazine units.
K. The application of Cl and I co-doped carbon nitride in the photocatalytic production of hydrogen peroxide:
(1) the performance of the K, Cl and I co-doped carbon nitride for producing hydrogen peroxide through photocatalysis is tested, and the specific steps are as follows:
pouring 45mL of deionized water into a 100mL double-layer glass beaker, adding 5mL of ethanol as a cavity sacrificial agent, adding 10mg of the prepared codoped carbon nitride, magnetically stirring, and then carrying out simulated sunlight irradiation, wherein a light source system adopts a 300W xenon lamp (the wavelength is more than 400nm) provided with an ultraviolet cut-off filter, circulating water is externally connected into the double-layer glass beaker to keep the reaction temperature at 25 ℃, the sampling time is 0, 10, 20 and 30min, and the catalyst is removed by filtering with a 0.22 mu m PTFE filter after sampling. 1mL of 0.1M potassium hydrogen phthalate solution and 1mL of 0.4M potassium iodide solution were added to 1mL of the filtrate, and after a sufficient reaction for 30min, I was measured by an ultraviolet-visible spectrophotometer3-ultraviolet absorption intensity at 350nm, thereby indirectly determining the concentration of hydrogen peroxide.
The results of the above experiments were processed and the results are shown in fig. 5. Fig. 5 is a graph showing the relationship between the concentration of hydrogen peroxide produced by co-doped carbon nitride and carbon nitride driven by visible light according to the embodiment 1 of the present invention and the change of the light irradiation time.
As shown in FIG. 5, under the irradiation of visible light, the concentration of hydrogen peroxide gradually increases with time, and after normalization, the rate of producing hydrogen peroxide by photocatalysis of K, Cl and I co-doped carbon nitride can reach 13.1 mmol-g-1·h-1The modified carbon nitride is 95 times of the modified carbon nitride, and the co-doping of the hetero atoms greatly improves the photocatalytic activity of the carbon nitride.
(2) The K, Cl and I co-doped carbon nitride catalyst for the experiment of producing hydrogen peroxide by photocatalysis is centrifugally recovered, washed and dried by deionized water, and then is subjected to the experiment of producing hydrogen peroxide by photocatalysis again, and other experiment conditions are kept consistent and are repeatedly utilized for 5 times.
The results of the experiment are shown in FIG. 6. Fig. 6 is a graph showing the cycle stability of hydrogen peroxide photocatalytic production of co-doped carbon nitride prepared in example 1 of the present invention.
As can be seen from FIG. 6, the K, Cl and I co-doped carbon nitride has good recycling performance and strong photocatalytic stability, and can still maintain the initial photocatalytic activity after 5 cycles of experiments.
Example 2
The precursor was replaced to prepare K, Cl and I co-doped carbon nitride, and "KCl and KI" in step S1 in example 1 was changed to "NH4Cl, KI' or "KCl, NH4I', the rest of the synthesis steps are not changed, and the prepared samples are respectively marked as CN-NH4Cl/KI and CN-KCl/NH4I。
Testing of prepared CN-NH4Cl/KI and CN-KCl/NH4Properties for photocatalytic production of hydrogen peroxide: the test method was the same as in example 1.
Referring to fig. 7, fig. 7 is a graph showing the change of the concentration of hydrogen peroxide produced by photocatalysis of the K, Cl and I three-element co-doped carbon nitride prepared by changing the precursor in example 2 of the present invention with time.
CN-NH as shown in FIG. 74Cl/KI and CN-KCl/NH4The rate of photocatalytic hydrogen peroxide production of I is 9.40 and 10.3 mmol-g-1·h-1The photocatalytic performance of the compounds is slightly lower than that of CN-KCl/KI prepared by KCl/KI serving as a doping agent, but is obviously higher than that of original CN, single-doped or double-doped carbon nitride. This shows that the photocatalytic activity of carbon nitride is synergistically improved by the doping of the three elements of K, Cl and I.
Comparative example 1
The preparation of the K-doped carbon nitride photocatalyst comprises the following steps:
s1 weighing melamine 5g and KHCO310mmol, and fully grinding in a mortar;
s2: placing the mixture in a covered crucible, then placing the crucible in a muffle furnace, heating to 550 ℃ at the speed of 2.5 ℃/min, keeping for 4h, naturally cooling to room temperature, and grinding;
s3: placing the obtained sample in a covered crucible again, then placing the crucible in a muffle furnace, and calcining again under the same conditions;
the preparation method also comprises the following post-treatment steps: and cleaning the prepared K-doped carbon nitride with ultrapure water, repeatedly washing, centrifuging for 3 times, and drying in a vacuum drying oven at 60 ℃ to obtain the K-doped carbon nitride photocatalyst, which is marked as CN-K.
The performance of the prepared K-doped carbon nitride for producing hydrogen peroxide through photocatalysis is tested, and the method comprises the following specific steps:
pouring 45mL of deionized water into a 100mL double-layer glass beaker, adding 5mL of ethanol as a cavity sacrificial agent, adding 10mg of the prepared catalyst, magnetically stirring, and then carrying out simulated solar radiation, wherein a light source system adopts a 300W xenon lamp (the wavelength is more than 400nm) additionally provided with an ultraviolet cut-off filter, circulating water is externally connected into the double-layer glass beaker to keep the reaction temperature at 25 ℃, the sampling time is 0, 10, 20 and 30min, and the catalyst is removed by filtering with a 0.22 mu m PTFE filter after sampling. 1mL of 0.1M potassium hydrogen phthalate solution and 1mL of 0.4M potassium iodide solution were added to 1mL of the filtrate, and after a sufficient reaction for 30min, I was measured by an ultraviolet-visible spectrophotometer3-ultraviolet absorption intensity at 350nm, thereby indirectly determining the concentration of hydrogen peroxide.
Referring to fig. 8, fig. 8 is a graph showing the change of the concentration of hydrogen peroxide produced by K-doped carbon nitride photocatalysis according to comparative example 1 of the present invention with time.
As shown in FIG. 8, the rate of hydrogen peroxide production by CN-K photocatalysis under visible light irradiation is 2.3 mmol-g-1·h-1. The photocatalytic activity of CN-K is higher than that of original CN, which reflects the function of doped K. The doped K accelerates the migration of photo-generated charges, thereby improving the photocatalytic performance.
Comparative example 2
Preparation of the Cl-doped carbon nitride photocatalyst: except that KHCO at step S1 in comparative example 1 was added3By NH4Except for Cl, the remaining steps were the same as in comparative example 1. The Cl-doped carbon nitride prepared is denoted as CN-Cl.
The prepared Cl-doped carbon nitride was tested for its performance in photocatalytic production of hydrogen peroxide: the test method was the same as in comparative example 1.
Referring to fig. 9, fig. 9 is a graph showing the change of the concentration of hydrogen peroxide produced by the Cl-doped carbon nitride photocatalyst prepared in comparative example 2 according to the present invention with time.
As shown in FIG. 9, the rate of photocatalytic production of hydrogen peroxide by CN-Cl was 2.65 mmol.g-1·h-1. The photocatalytic activity of CN-Cl is higher than that of original CN, and the effect of doped Cl is reflected. The doping of Cl optimizes the electronic structure of carbon nitride, improves the absorption capacity of the carbon nitride to visible light, and accelerates the separation of photo-generated electron hole pairs, so that CN-Cl shows better photocatalytic performance than CN.
Comparative example 3
I, preparation of a doped carbon nitride photocatalyst: except that KHCO at step S1 in comparative example 1 was added3By NH4Except for I, the remaining steps were the same as in comparative example 1. The prepared I-doped carbon nitride is marked as CN-I.
The prepared I-doped carbon nitride was tested for its performance in photocatalytic production of hydrogen peroxide: the test method was the same as in example 1.
Referring to fig. 10, fig. 10 is a graph showing the change of the concentration of hydrogen peroxide produced by photocatalysis of I-doped carbon nitride according to comparative example 3 of the present invention with time.
As shown in FIG. 10, the rate of photocatalytic production of hydrogen peroxide by CN-I was 1.52mmol g-1·h-1. The photocatalytic activity of CN-I is also superior to that of original CN, and the doped I function is embodied. Doping I enhances the absorption of visible light by carbon nitride.
Comparative example 4
K. Preparation of a Cl-codoped carbon nitride photocatalyst: except that KHCO at step S1 in comparative example 1 was added3The remaining steps were the same as in comparative example 1 except for the change to KCl. The K, Cl codoped carbon nitride prepared was designated as CN-KCl.
The prepared K, Cl co-doped carbon nitride was tested for its performance in photocatalytic production of hydrogen peroxide: the test method was the same as in comparative example 1.
Referring to fig. 11, fig. 11 is a graph showing the change of the concentration of hydrogen peroxide produced by the photocatalysis of K, Cl co-doped carbon nitride according to comparative example 4 of the present invention with time.
As shown in FIG. 11, the rate of photocatalytic production of hydrogen peroxide by CN-KCl was 4.41mmol g-1·h-1. The photocatalytic activity of CN-KCl is better than that of original CN and singly doped carbon nitride (CN-K, CN-Cl and CN-I) but is inferior to that of K, Cl and I three-element co-doped carbon nitride. This bodyThe doping of K and Cl synergistically improves the photocatalytic performance of carbon nitride.
Comparative example 5
K. I, preparation of co-doped carbon nitride photocatalyst: except that KHCO at step S1 in comparative example 1 was added3The procedure was the same as in comparative example 1 except for changing to KI. The K, I co-doped carbon nitride prepared was designated CN-KI.
The prepared K, I co-doped carbon nitride was tested for its performance in photocatalytic production of hydrogen peroxide: the test method was the same as in comparative example 1.
Referring to fig. 12, fig. 12 is a graph showing the change of the concentration of hydrogen peroxide produced by the photocatalysis of K, I co-doped carbon nitride according to comparative example 5 of the present invention with time.
As shown in FIG. 12, the rate of hydrogen peroxide production by photocatalysis of CN-KI was 5.53mmol g-1·h-1. Similarly, CN-KI has photocatalytic activity superior to that of the original CN and singly doped carbon nitride (CN-K, CN-Cl, CN-I) but inferior to that of K, Cl and I doped carbon nitride. This shows that the doping of K and I synergistically improves the photocatalytic performance of carbon nitride.
The present invention provides a potassium, chlorine and iodine co-doped carbon nitride, a method for preparing the same, and a method for preparing hydrogen peroxide by photocatalysis, which are described in detail above, and the principles and embodiments of the present invention are explained herein by using specific examples, and the above description of the examples is only provided to help understanding the method of the present invention and its core ideas, including the best mode, and also to enable any person skilled in the art to practice the present invention, including making and using any devices or systems, and implementing any combination of the methods. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.