CN115321497B - Carbon nitride material modified by thermal stripping and double covalent bond grafting and preparation method thereof - Google Patents
Carbon nitride material modified by thermal stripping and double covalent bond grafting and preparation method thereof Download PDFInfo
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Abstract
A carbon nitride material modified by thermal stripping and double covalent bond grafting and a preparation method thereof relate to the technical field of new material preparation, and adopt sodium potassium nitrate molten salt as a heat treatment medium and adopt ammonium salt to cooperate with sodium potassium nitrate molten saltThe salt can effectively reduce the heat treatment temperature of the molten salt, and further, the carbon nitride-NH can be fully utilized 2 Functional groups such as carbon-nitrogen double bonds exist in (or-NH) and a main structure to react with aldehyde-containing organic functional molecules, and the obtained material has controllable double covalent bond coupling modified carbon nitride composite material of the aldehyde-containing organic functional molecules. The invention has the beneficial effects that: the material obtained by the invention has strong visible light absorptivity, good ultraviolet and visible light excitation catalysis effect, good dispersibility and stability, and greatly improved catalysis efficiency.
Description
Technical Field
The invention relates to the technical field of new material preparation, in particular to a carbon nitride material modified by thermal stripping and double covalent bond grafting and a preparation method thereof.
Background
g-C 3 N 4 The porous ceramic material has excellent wear resistance, chemical stability and thermal stability, and has the porosity of a lamellar structure, so that the porous ceramic material can be used as a good membrane material, an adsorption material, a biological material, a sensing material and the like, and the special semiconductor property plays an important role in the catalysis field and the semiconductor related field, for example, the porous ceramic material can be widely used as a catalyst, a photoelectric material, an electrode material, a semiconductor material and the like.
However, pure g-C 3 N 4 The problems of small surface area, large surface defects, serious agglomeration, poor dispersibility in aqueous phase and organic solvent, narrow light absorption range and the like exist, and the modified water-based polyurethane foam is required to be subjected to modification treatment in the actual use process. The common modification method mainly comprises strategies such as element doping, morphology regulation, heat stripping, surface functionalization and the like. Wherein the heat stripping treatment is to raise the purity of g-C 3 N 4 The performance and the effective means for reducing the defects are another very effective strategy, and organic or inorganic target functional groups and compounds can be introduced according to the needs to realize the further G-C 3 N 4 Functional regulation and performance optimization of (c).
However, in general for g-C 3 N 4 The heat stripping treatment requires a high treatment temperature (the temperature is generally above 500 ℃), and has the disadvantages of high control difficulty, high energy consumption and low yield. The molten salt method is a new method, at present, the existing molten salt method for preparing or for heat treatment of carbon nitride has partial reports,such as LiCl/KCl, liCl/NaCl, liCl/KCl/NaCl, liBr/KBr, liCl/ZnCl 2 The molten salt system is required to use lithium-containing salts for lowering the melting point, and the presence of lithium salts lowers the heat treatment temperature of these molten salts to some extent, but lithium salts also cause carbon nitrides prepared or obtained by heat treatment by these types of molten salt methods to change the structural units thereof and generate Polytriazineimine (PTI) structures, which have low thermal stability and poor catalytic performance. To avoid PTI-like structure formation, there is a need to find and develop new low melting point molten salt systems that do not contain lithium salts.
In addition to the above, the carbon nitride needs to be further modified. The organic group, organic functional molecule or cluster has the advantages of strong structural adjustability, good structural designability, low cost, easy availability and the like, and plays an important role in a surface functionalization strategy. Coupling target organic groups or functional molecules to g-C using covalent bonds 3 N 4 The surface can obviously improve the structural stability and target performance of the modified functional compound, and is a very effective strategy.
The modification of carbon nitride with reactive groups represented by aldehyde groups is advantageous because, if an organic functional molecule containing aldehyde groups is used, not only the amine groups (-NH) remaining in carbon nitride can be used 2 Less content) is used as active site modification, more importantly, functional groups such as-C=N-and the like existing in a large amount in the main structure of the carbon nitride can be used as active sites for full grafting modification, the modified covalent bond types and optional structures are greatly enriched, and double covalent bond grafting modification of the carbon nitride can be realized by using aldehyde group-containing functional molecules, so that the method is very significant.
However, since the reactivity of the molecule containing aldehyde functional group is generally lower than that of the conventional carboxyl group, and since carbon nitride is obtained by high-temperature polymerization, amine groups (-NH) remain on the surface 2 ) The reactivity with the-C=N-functional groups existing in the main structure is low, and the carbon nitride is hardly dissolved in any solvent, so that the aldehyde group-containing functional molecules and the carbon nitride are difficult to effectively react and modify under the conventional conditions, and the aldehyde is effectively promotedThe reactivity between the groups and the carbon nitride and the realization of effective covalent bond grafting modification of various types of carbon nitride based on aldehyde group-containing organic molecules are the challenges to be solved.
Disclosure of Invention
Aiming at the problems, limitations and difficulties existing in the prior heat treatment preparation method and modified functional groups, the invention provides a new way, and provides a simple and efficient nitrate molten salt heat treatment and preparation of aldehyde group-containing organic functional molecule covalent bond coupling modified g-C 3 N 4 Firstly, adopting nitrate salt to carry out heat treatment modification on carbon nitride; then, a solvothermal method is adopted to realize the reaction of amino (-NH) in the carbon nitride 2 ) And the functional groups such as-C=N-and the like which are present in a large amount in the main structure are subjected to simultaneous double covalent bond grafting modification.
The invention provides a preparation method of a thermal stripping and double covalent bond grafting modified carbon nitride material, which comprises the following specific steps:
(1) Firstly, performing thermal polymerization reaction on a nitrogen-containing carbon precursor raw material I and an ammonium salt additive II under a certain condition, and controlling polymerization temperature and time to prepare a bulk phase carbon nitride sample;
(2) Grinding and mixing the bulk phase carbon nitride obtained in the step (1) with molten nitrate salt III uniformly, and carrying out secondary heat treatment on the mixture in air or nitrogen atmosphere;
(3) Removing molten salt in the molten salt heat-treated carbon nitride obtained in the step (2) to obtain heat-treated modified carbon nitride;
(4) Dispersing the heat-treated modified carbon nitride obtained in the step (3) in a proper hydrophobic solvent IV, placing the solvent IV in a reaction kettle, adding a certain amount of organic molecules V containing target functional groups and additives VI, introducing a protective gas VII, controlling a certain temperature or pressure and time, and performing solvothermal covalent bond coupling grafting reaction;
(5) After the reaction in the step (4) is finished, carrying out suction filtration or centrifugal separation to obtain a solid-phase primary product, and then repeatedly washing in a solvent VIII;
(6) And (3) carrying out vacuum drying on the product obtained in the step (5) to obtain the target organic molecule covalent bond coupling modified carbon nitride material.
The nitrogen-containing carbon precursor raw material I is one or a mixture of more than two of melamine, urea, cyanamide, dicyandiamide and ammonium chloride;
the ammonium salt II is one or a mixture of ammonium chloride and hydroxylamine hydrochloride; in the mixed ammonium salt, ammonium chloride or hydroxylamine hydrochloride occupies 0 to 100 percent (100 to 0 percent) of the mass fraction of the mixed salt of the ammonium chloride and the hydroxylamine hydrochloride; the mass ratio of the nitrogen-containing carbon precursor raw material I to the ammonium salt additive II is as follows: 1:0.2-50.
The molten salt III is sodium nitrate or potassium nitrate or a mixture of the sodium nitrate and the potassium nitrate; or a mixture of one of the two with sodium chloride or potassium chloride; in the mixed molten salt, the proportion of the mixed salt is generally proportioned according to the composition corresponding to the lowest eutectic point temperature in the two molten salt phase diagrams, or the mass ratio of the mixed salt to the mixed salt is controlled as follows: 40-60:40-60;
in the step (2), the mass ratio of the carbon nitride to the nitrate salt is as follows: 1:2-100;
the hydrophobic solvent IV is one or more than two of benzene, toluene, xylene, mesitylene, monohalogenated benzene, polyhalogenated substituted benzene, nitrobenzene, tetrahydronaphthalene and diphenylmethane;
the organic molecule V containing target functional groups is aliphatic organic molecules or aromatic organic molecules containing aldehyde groups (-CHO) or compounds or complexes composed of the aliphatic organic molecules or aromatic organic molecules or the aliphatic organic molecules;
the additive VI is glycine substituted by N-aliphatic group; the additive VI is N-methylglycine, N-ethylglycine or N-propylglycine.
The solvent VIII is one or more than two of N, N-dimethylformamide, N-dimethylacetamide, tetrahydrofuran, dimethyl sulfoxide, methanol, ethanol and isopropanol; .
The mass-to-volume ratio of the heat treatment modified carbon nitride (m, mass) to the solvent IV (v, volume) is 1g: 10-100 mL; the mass ratio of the heat-treated modified carbon nitride (m, mass) to the target organic molecule V (m, mass) was 1:0.01 to 1; the molar ratio of organic molecule V to additive IV is 1:0.01 to 2.
The reaction condition of the thermal polymerization is 450-650 ℃ for 1-6 h; the secondary heat treatment condition of the nitrate salt is 300-500 ℃ for 2-6 h; the solvothermal condition is 100-300 ℃ for 1-48 h; the vacuum drying process is that the drying is carried out for 2 to 24 hours under the condition of 50 to 90 ℃ in a vacuum state.
The reaction system shielding gas is as follows: nitrogen, argon, etc.; the heating equipment is an oven, a muffle furnace and the like, and the reaction vessel is a stainless steel water heating reaction kettle (polytetrafluoroethylene liner) or other material reaction kettles and reaction devices capable of bearing pressure.
The carbon nitride material with heat stripping and double covalent bond grafting modification is obtained by adopting the heat stripping modification and covalent bond coupling modification of organic functional molecules.
The invention has the beneficial effects that:
the invention develops a novel low-melting-point molten salt system without lithium salt, adopts a sodium potassium nitrate molten salt system with lower overall melting point, and can realize the pure phase g-C of the nitrate molten salt 3 N 4 The lower temperature heat treatment does not use lithium-containing salts, so that the PTI structure problem caused by the use of lithium salts can be effectively avoided. Further, further researches show that the effect of heat stripping treatment of carbon nitride by sodium potassium nitrate molten salt can be effectively improved by adding ammonium salt, the heat treatment temperature is greatly reduced, the performance is improved, and few related researches are reported. Wherein, the carbon nitride is modified by utilizing the addition of ammonium salt to cooperate with the heat stripping treatment of sodium potassium nitrate molten salt, which is not reported, and belongs to the first original innovation point of the patent core of the invention.
The selected target organic functional molecule containing aldehyde group is subjected to nitrate molten salt heat treatment to prepare g-C 3 N 4 Under the special reaction condition of solvothermal, g-C is fully utilized by selecting proper raw materials containing aldehyde groups and auxiliary amino acid 3 N 4 self-existing-NH in structure 2 Functional groups such as-C=N-exist in the (or-NH) and main structures as active sites for covalent bond coupling reaction with aldehyde group-containing organic functional molecules, so that double covalent bond grafting modification is realized. Greatly enriches grafting sites and grafting types, improves grafting modification efficiency, and can also haveThe method effectively avoids using high-temperature solid-phase reaction, avoids using acidic carboxyl, anhydride or acyl chloride and other strong acid functional groups, and does not need to use any additional noble metal or organic catalyst, thereby effectively simplifying the synthesis experimental conditions of the composite material, improving the preparation efficiency of the material and effectively expanding the method and the way of modifying carbon nitride by using aldehyde-based organic functional molecules.
The hydrophobic solvent is used as a dehydration medium and a reaction solvent, and the solvent polarity difference is used for carrying out in-situ physical separation on the reaction byproduct water and the target product, so that the forward reaction is effectively promoted, liquid solvothermal is provided, the heat transfer and mass transfer of a reaction system are promoted, and further, the organic functional molecules containing aldehyde groups are grafted and modified on the carbon nitride material in a plurality of covalent bond coupling modes. The design has the advantage that the target aldehyde group-containing organic functional molecule is in molecular form and g-C under solvothermal conditions 3 N 4 The contact reaction can efficiently carry out mass transfer and heat transfer, and the polarity, the temperature, the pressure and the like of the solvent of the reaction system can be conveniently regulated and controlled by selecting a proper solvent, so that the reaction dehydration and the separation of byproduct water and a target product can be effectively promoted, and the reaction is accelerated.
Drawings
FIG. 1 is a flow chart of the nitrate salt heat treatment and the preparation of an organic functional molecule modified carbon nitride material;
FIG. 2 is an XRD pattern of unmodified bulk carbon nitride, comparative example 1 direct heat treated carbon nitride, comparative example 2 molten salt treated carbon nitride, and modified carbon nitride prepared in example 1 by double covalent bond coupling of molten salt treatment with organic molecule TPA-CAAH;
FIG. 3 is a TEM image of unmodified bulk carbon nitride, comparative example 1 direct heat treated carbon nitride, comparative example 2 molten salt treated carbon nitride, and modified carbon nitride prepared by double covalent bond coupling of molten salt treatment prepared in example 1 with an organic molecule TPA-CAAH;
FIG. 4 is a graph corresponding to C, N showing the correlation between the original unmodified bulk carbon nitride and the molten salt treatment prepared in example 1 and the organic molecule TPA-CAAH coupled with modified carbon nitride XPS by double covalent bonds;
FIG. 5 is a UV-Vis absorption spectrum of the molten salt treatment prepared in example 1 and organic molecule TPA-CAAH coupled with double covalent bonds to modify carbon nitride material, comparative example 2 molten salt treatment carbon nitride and bulk carbon nitride;
FIG. 6 is a PL spectrum of the molten salt treated carbon nitride prepared in example 1 and the organic molecule TPA-CAAH coupled by double covalent bonds to modify the carbon nitride material, comparative example 2 molten salt treated carbon nitride and bulk carbon nitride;
FIG. 7 is a graph showing the comparison of photocatalytic hydrogen production rates for the modified carbon nitride material prepared in example 1 by coupling the molten salt treatment and the organic molecule TPA-CAAH with double covalent bonds, the carbon nitride physically adsorbed by the molten salt treatment and the organic molecule in comparative example 3, the carbon nitride treated with the molten salt in comparative example 2, the carbon nitride directly heat-treated in comparative example 1, and the bulk carbon nitride;
FIG. 8 is a graph showing the stability test of photocatalytic hydrogen production cycle of the modified carbon nitride material by double covalent bond coupling between the molten salt treatment and the organic molecule TPA-CAAH prepared in example 1.
Detailed Description
Example 1
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 20.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium-potassium nitrate is 45:55), grinding and mixing the two, placing the mixture into a 50mL corundum crucible, covering, placing the crucible into a muffle furnace, performing heat treatment at 325 ℃ for 4 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 0.6g of carbon nitride obtained in the step (4) through molten salt heat treatment, dispersing in 60mL of solvent toluene, placing in a 100mL reaction kettle, adding 0.6g of organic molecule (Z) -3- (10-ethyl-10H-phenothiazin-3-yl) -2-formylacrylonitrile (abbreviated as PTZ-CAAH) containing target functional groups, adding 0.35g of azoylglycine as a reaction additive, introducing protective gas nitrogen, replacing for 5min, sealing the reaction kettle, placing in an oven, controlling the reaction condition to be 190 ℃ for reaction for 24H, and performing Schiff base and cycloaddition double coupling grafting reaction on PTZ-CAAH and carbon nitride through a solvothermal method;
(6) After the reaction in (5) is finished, carrying out centrifugal separation to obtain a solid-phase primary product, and then repeatedly and alternately washing in a solvent N, N-dimethylformamide and ethanol until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) for 8 hours at the temperature of 80 ℃ in a vacuum drying oven to obtain the organic molecule PTZ-CAAH, and coupling and grafting the modified carbon nitride material through double covalent bonds of imine bonds and azomethine rings.
Example 2
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 20.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium-potassium nitrate is 45:55), grinding and mixing the two, placing the mixture into a 50mL corundum crucible, covering, placing the crucible into a muffle furnace, performing heat treatment at 325 ℃ for 4 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 1.2g of molten salt heat-treated carbon nitride obtained in the step (4), dispersing in 60mL of solvent diphenylmethane, placing in a 100mL reaction kettle, adding 0.6g of organic molecule (Z) -3- (3- (diphenylamino) phenyl) -2-formylacrylonitrile (abbreviated as TPA-CAAH) containing target functional groups, introducing protective gas nitrogen without additional additives, replacing for 5min, sealing the reaction kettle, placing in an oven, controlling the reaction condition to be 240 ℃ for 15h, and performing Schiff base coupling grafting reaction on TPA-CAAH and carbon nitride by a solvothermal method;
(6) After the reaction in step (5) is finished, performing centrifugal separation to obtain a solid-phase primary product, and then repeatedly washing in ethanol solvent until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) for 12 hours at 60 ℃ in a vacuum drying oven to obtain the organic molecule TPA-CAAH modified carbon nitride material through imine covalent bond coupling.
Example 3
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 20.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium-potassium nitrate is 45:55), grinding and mixing the two, placing the mixture into a 50mL corundum crucible, covering, placing the crucible into a muffle furnace, performing heat treatment at 325 ℃ for 4 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 0.6g of carbon nitride obtained in the step (4) through molten salt heat treatment, dispersing in 60mL of solvent toluene, placing in a 100mL reaction kettle, adding 0.4g of organic molecule (Z) -3- (10-ethyl-10H-phenothiazin-3-yl) -2-formylacrylonitrile (abbreviated as PTZ-CAAH) containing target functional groups, adding 0.35g of azoylglycine as a reaction additive, introducing protective gas nitrogen, replacing for 5min, sealing the reaction kettle, placing in an oven, controlling the reaction condition to be 180 ℃ for reaction for 24H, and performing cycloaddition coupling grafting reaction between PTZ-CAAH and carbon nitride through a solvothermal method;
(6) After the reaction in (5) is finished, carrying out centrifugal separation to obtain a solid-phase primary product, and then repeatedly and alternately washing in a solvent N, N-dimethylformamide and ethanol until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) for 8 hours at 80 ℃ in a vacuum drying oven to obtain the organic molecule PTZ-CAAH, and coupling the modified carbon nitride material by azomethine ring covalent bonds.
Example 4
(1) Grinding and mixing 6g melamine and 1.2g hydroxylamine hydrochloride uniformly, placing into a crucible, heating to 450 ℃ in a muffle furnace at a heating rate of 5 ℃/min, maintaining for 6h, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 4.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium nitrate to potassium nitrate is 40:60), grinding and mixing the two uniformly, placing the mixture into a 10mL corundum crucible, covering the corundum crucible, placing the corundum crucible into a muffle furnace, performing heat treatment at 300 ℃ for 6 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 1.2g of molten salt heat-treated carbon nitride obtained in the step (4), dispersing in 12mL of solvent diphenylmethane, placing in a 30mL reaction kettle, adding 0.012g of organic molecule (Z) -3- (3- (diphenylamino) phenyl) -2-formylacrylonitrile (abbreviated as TPA-CAAH) containing target functional groups, introducing protective gas nitrogen without additional additives, replacing for 5min, sealing the reaction kettle, placing in an oven, controlling the reaction condition to be 100 ℃ for 48h, and performing Schiff base coupling grafting reaction on TPA-CAAH and carbon nitride by a solvothermal method;
(6) After the reaction in step (5) is finished, performing centrifugal separation to obtain a solid-phase primary product, and then repeatedly washing in ethanol solvent until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) for 12 hours at 60 ℃ in a vacuum drying oven to obtain the organic molecule TPA-CAAH modified carbon nitride material through imine covalent bond coupling.
Example 5
(1) Grinding and mixing a mixture of 6g of melamine, 300g of ammonium chloride and hydroxylamine hydrochloride (1:1), placing the mixture into a crucible, heating to 650 ℃ in a muffle furnace at a heating rate of 5 ℃/min, maintaining for 1h, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and 200.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium nitrate to potassium nitrate is 60:40), grinding and mixing the two, placing the mixture into a 300mL corundum crucible, covering the crucible, placing the crucible into a muffle furnace, and performing heat treatment at 500 ℃ for 2 hours and a heating rate of 5 ℃/min under an air atmosphere to perform fused salt secondary heat treatment;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 0.6g of carbon nitride obtained in the step (4) through molten salt heat treatment, dispersing in 60mL of solvent toluene, placing in a 100mL reaction kettle, adding 0.6g of organic molecule (Z) -3- (10-ethyl-10H-phenothiazin-3-yl) -2-formylacrylonitrile (abbreviated as PTZ-CAAH) containing target functional groups, adding 1.2g of azoylglycine as a reaction additive, introducing protective gas nitrogen, replacing for 5min, sealing the reaction kettle, placing in an oven, controlling the reaction condition to be 300 ℃ for reaction for 1H, and performing cycloaddition coupling grafting reaction between PTZ-CAAH and carbon nitride through a solvothermal method;
(6) After the reaction in (5) is finished, carrying out centrifugal separation to obtain a solid-phase primary product, and then repeatedly and alternately washing in a solvent N, N-dimethylformamide and ethanol until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) for 8 hours at 80 ℃ in a vacuum drying oven to obtain the organic molecule PTZ-CAAH, and coupling the modified carbon nitride material by azomethine ring covalent bonds.
Comparative example 1
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), directly placing the bulk phase carbon nitride into a 50mL corundum crucible without adding molten salt, covering, placing the crucible into a muffle furnace, performing heat treatment for 4 hours at 325 ℃ in an air atmosphere, and performing direct secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, performing suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the direct heat treatment carbon nitride material serving as a control sample 1.
Comparative example 2
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 20.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium-potassium nitrate is 45:55), grinding and mixing the two, placing the mixture into a 50mL corundum crucible, covering, placing the crucible into a muffle furnace, performing heat treatment at 325 ℃ for 4 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride material serving as a control sample 2.
Comparative example 3
(1) Grinding and mixing 6g melamine and 12g ammonium chloride uniformly, placing the mixture in a crucible, heating to 550 ℃ in a muffle furnace at a heating rate of 5 ℃/min, keeping for 4 hours, and naturally cooling to room temperature to obtain the bulk phase carbon nitride (g-C) 3 N 4 ) A sample;
(2) Weighing 2.0g of bulk phase carbon nitride obtained in the step (1), and weighing 20.0g of mixed fused salt of sodium nitrate and potassium nitrate (the mass ratio of sodium-potassium nitrate is 45:55), grinding and mixing the two, placing the mixture into a 50mL corundum crucible, covering, placing the crucible into a muffle furnace, performing heat treatment at 325 ℃ for 4 hours under an air atmosphere, and performing fused salt secondary heat treatment at a heating rate of 5 ℃/min;
(3) After the reaction in the step (2) is finished, dispersing the product into deionized water, soaking for 12 hours, carrying out suction filtration and separation to obtain a solid-phase product, and repeatedly washing with the deionized water until the supernatant is neutral;
(4) And (3) repeatedly washing the product in the step (3), and drying the product in a vacuum drying oven at 70 ℃ for 4 hours to obtain the nitrate molten salt heat treatment carbon nitride sample.
(5) Weighing 0.6g of carbon nitride obtained in the step (4) through molten salt heat treatment, dispersing in 30mL of carbon tetrachloride, placing in a 50mL reaction kettle, adding 0.3g of organic molecule 2-cyano-3- (4- (diphenylamino) phenyl) acrylic acid (abbreviated as TPA-CAAH) containing target functional groups, introducing protective gas nitrogen without additional additives, replacing for 5min, sealing the reaction kettle, heating without heating, and carrying out stirring reaction for 24h under the condition of keeping away from light at room temperature, wherein TPA-CAAH and carbon nitride are subjected to weak interaction bonding reaction;
(6) After the reaction in step (5) is finished, carrying out suction filtration and separation to obtain a solid-phase primary product, and then repeatedly washing in tetrahydrofuran solvent until the supernatant is colorless;
(7) And (3) drying the product obtained in the step (6) in a vacuum drying oven at 70 ℃ for 4 hours to obtain the simple heat treatment and organic molecule TPA-CAAH modified carbon nitride material with weak interaction, wherein the modified carbon nitride material is used as a control sample 3.
The method is simple and convenient to operate, high in practicability and unique in method, firstly, sodium potassium nitrate molten salt is adopted as a heat treatment medium, the use of lithium salt is avoided, and the heat treatment temperature of the molten salt can be effectively reduced by adopting ammonium salt to cooperate with the sodium potassium nitrate molten salt, so that the PTI phase problem caused by the use of the lithium salt is avoided; further, carbon nitride-NH can be fully utilized 2 The (or-NH) and main structure have-C=N-functional groups as the functional groups to react with aldehyde-containing organic functional molecules, the obtained material has controllable double covalent bond coupling modified carbon nitride composite material of the aldehyde-containing organic functional molecules, and the obtained material has strong visible light absorptivity, good ultraviolet and visible light excitation catalysis effect, good dispersibility and stability, and the catalysis efficiency is greatly improved.
Claims (7)
1. The preparation method of the heat stripping and double covalent bond grafting modified carbon nitride material is characterized by comprising the following specific steps of:
(1) Firstly, performing thermal polymerization reaction on a nitrogen-containing carbon precursor raw material I and an ammonium salt additive II, and controlling polymerization temperature and time to prepare a bulk phase carbon nitride sample;
(2) Grinding and mixing the bulk phase carbon nitride obtained in the step (1) with molten nitrate salt III uniformly, and carrying out secondary heat treatment on the mixture in air or nitrogen atmosphere;
(3) Removing molten salt in the molten salt heat-treated carbon nitride obtained in the step (2) to obtain heat-treated modified carbon nitride;
(4) Dispersing the heat-treated modified carbon nitride obtained in the step (3) in a hydrophobic solvent IV, placing the hydrophobic solvent IV in a reaction kettle, adding a certain amount of organic molecules V containing target functional groups and additives VI, introducing a protective gas VII, and controlling the temperature, the pressure and the time to carry out solvothermal covalent bond coupling grafting reaction;
(5) After the reaction in the step (4) is finished, carrying out suction filtration or centrifugal separation to obtain a solid-phase primary product, and then repeatedly washing in a solvent VIII;
(6) Vacuum drying the product obtained in the step (5) to obtain the target organic molecule covalent bond coupling modified carbon nitride material;
the ammonium salt additive II is one or a mixture of ammonium chloride and hydroxylamine hydrochloride;
the nitrate salt III does not use lithium-containing salts;
the hydrophobic solvent IV is one or more than two of benzene, toluene, xylene, mesitylene, monohalogenated benzene, polyhalogenated substituted benzene, nitrobenzene, tetrahydronaphthalene and diphenylmethane; the organic molecule V containing the target functional group is an aliphatic organic molecule or an aromatic organic molecule containing an aldehyde group or a compound or a complex formed by the molecules of the aliphatic organic molecule or the aromatic organic molecule;
the additive VI is glycine substituted by N-aliphatic group;
the solvent VIII is one or more than two of N, N-dimethylformamide, N-dimethylacetamide, tetrahydrofuran, dimethyl sulfoxide, methanol, ethanol and isopropanol.
2. The preparation method of the heat stripping and double covalent bond grafting modified carbon nitride material according to claim 1, wherein the mass ratio of the nitrogen-containing carbon precursor raw material I to the ammonium salt additive II is as follows: 1:0.2-50.
3. The method for preparing the heat-stripping and double covalent bond grafting modified carbon nitride material according to claim 2, wherein the molten nitrate salt III is sodium nitrate or potassium nitrate or a mixture of the two; or a mixture of one of the two with sodium chloride or potassium chloride; in the mixture, the proportion of the mixed salt is proportioned according to the composition corresponding to the lowest eutectic point temperature in the molten salt phase diagram of the two, or the mass ratio of the mixed salt to the mixed salt is controlled as follows: 40-60:40-60.
4. The method for preparing the thermally stripped and double covalent bond grafted modified carbon nitride material according to claim 3, wherein the mass ratio of carbon nitride to molten nitrate salt in the step (2) is as follows: 1:2-100.
5. The method for preparing the heat-stripping and double covalent bond grafting modified carbon nitride material according to claim 4, wherein the mass-volume ratio of the heat treatment modified carbon nitride to the solvent IV is 1g: 10-100 mL; the mass ratio of the heat treatment modified carbon nitride to the target organic molecule V is 1:0.01 to 1; the molar ratio of organic molecule V to additive IV is 1:0.01 to 2.
6. The method for preparing a thermally stripped and double covalent bond grafted modified carbon nitride material according to claim 5, wherein the reaction condition of thermal polymerization is 450-650 ℃ for 1-6 h; the secondary heat treatment is carried out at 300-500 ℃ for 2-6 h; the solvothermal condition is 100-300 ℃ for 1-48 h; the vacuum drying process is that the drying is carried out for 2 to 24 hours under the condition of 50 to 90 ℃ in a vacuum state.
7. A thermally stripped and double covalent bond grafted modified carbon nitride material characterized in that it is prepared by the method of any one of claims 1-6.
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