CN113460979B - Method for dissolving graphite phase carbon nitride - Google Patents
Method for dissolving graphite phase carbon nitride Download PDFInfo
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- CN113460979B CN113460979B CN202110665487.5A CN202110665487A CN113460979B CN 113460979 B CN113460979 B CN 113460979B CN 202110665487 A CN202110665487 A CN 202110665487A CN 113460979 B CN113460979 B CN 113460979B
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- 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
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Abstract
The invention relates to a dissolving method of graphite phase carbon nitride, which comprises the steps of adding graphite phase carbon nitride (in a powder state) into a choline eutectic solvent, and heating, stirring and dissolving at 50-95 ℃; nitriding of choline eutectic solvent and graphite phaseThe mass ratio of carbon is 10-50: 1; the dissolution rate of the graphite phase carbon nitride is more than 52 percent. The invention adopts choline eutectic solvent to accelerate graphite-phase carbon nitride g-C 3 N 4 A large amount of positive and negative ions in the choline eutectic solvent can be adsorbed on the g-C through electrostatic interaction 3 N 4 The surface layer is beneficial to dissociating the lamella, and can ensure that the dissociated lamella keeps a free dispersion state, thereby avoiding agglomeration; choline eutectic solvent with freezing points lower than zero is selected, graphite phase carbon nitride is continuously separated out through gradual cooling, and the solvent can be recycled after filtration before the freezing point is reached.
Description
Technical Field
The invention belongs to the technical field and relates to a method for dissolving graphite-phase carbon nitride.
Background
Graphite phase carbon nitride (g-C) 3 N 4 ) The material can be obtained by simple one-step calcination as a typical two-dimensional material, is acid-resistant, alkali-resistant, corrosion-resistant, and stable in physical and chemical properties, and is widely applied to the fields of electro-catalysis, photoelectric detection and the like. But is difficult to be dissolved by common organic or inorganic solvents due to its chemical stability, and thus is difficult to be applied to homogeneous reaction systems. It is reported in the literature that dissolving graphite phase carbon nitride requires exfoliation and acidification, and that dissolution requires strong acid, high temperature and the ability to react with g-C 3 N 4 The N-hydrogen bond-forming solvent (A scalable chemical to soluble acidic carbon nitride: An ideal precorsor for isolated ultrathin g-C) 3 N 4 nanosheets&chem.Sci.,2018,9, 7912-. It has been reported that concentrated sulfuric acid, potassium permanganate and hydrogen peroxide solvent are used to dissolve Carbon Nitride (CN201611103718.9, CN201510031354.7, CN201610238941.8, Dissolution and Liquid Crystals Phase of 2D Polymeric Carbon Nitride) or methyl sulfonic acid group solvent&Chem.sci.,2018,9,7912- 3 N 4 The hydrolysis of the carbon nitride is accelerated, and the structure of the graphite phase carbon nitride is destroyed under the participation of oxidation or hydrolysis reaction, so that the application and popularization of the graphite phase carbon nitride are limited. Although there is literature on preventing g-C 3 N 4 Hydrolyzing by acidifying g-C with concentrated sulfuric acid and fuming sulfuric acid 3 N 4 And ion exchange to obtain carbon nitride with polyammonium salt property, which can be dissolved in various solvents (A scalable chemical to soluble acidic carbon nitride: An ideal precorsor for isolated ultrathin g-C) 3 N 4 nanosheets) but strong acid and high temperature (140-170 ℃) conditions and complex dissolution processes are still unavoidable.
Patent CN202010191097.4 reports a dissolving system and a dissolving method for dissolving graphite-phase carbon nitride, which adopts a solvent system consisting of halogenated salt, inorganic acid, graphite-phase carbon nitride and alcohol to dissolve g-C at the temperature of between room temperature and 200 DEG C 3 N 4 The solvent system used is a novel solvent system obtained by dissolving carbon nitride in sulfuric acid or methanesulfonic acid, but has the disadvantages of high dissolution temperature, long ultrasonic dispersion time, low yield and the like, and the post-treatment of a solvent containing a metal inorganic salt is difficult.
Patent CN201610658892.3 ionic liquid functionalized carbon nitride nanosheet modified electrode, preparation thereof and application thereof in chlorophenol detection 3 N 4 Protonating N in concentrated sulfuric acid, and performing substitution reaction with N-bromobutane under alkaline condition to realize quaternization to prepare functionalized g-C of ionic liquid 3 N 4 The nano-sheet increases catalytic active sites. The solvent used for dissolving still does not get rid of strong acid environment such as concentrated sulfuric acid, and g-C is changed by the ionic liquid functional treatment 3 N 4 The structure of (1) can only be used for catalysis, and has no universality.
Therefore, it is very important to research a method for effectively preventing the graphite phase carbon nitride from structural damage and efficiently dissolving the graphite phase carbon nitride in a high-temperature and strong-acid and strong-oxidizing-property dissolving environment.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides a method for dissolving graphite-phase carbon nitride.
In order to achieve the purpose, the invention adopts the following scheme:
a method for dissolving graphite-phase carbon nitride comprises adding graphite-phase carbon nitride (powder state) into choline eutectic solvent, and heating and stirring at 50-95 deg.C for dissolving; the invention adopts polar choline eutectic solvent, because the choline eutectic solvent has a large amount of anions and cations and hydrogen bond donors and hydrogen bond acceptors in the solvent, the choline eutectic solvent is different from common hydrogen bond action, the choline eutectic solvent can interact with graphite phase carbon nitride to form a new hydrogen bond network, the original inter-layer van der Waals force of the graphite phase carbon nitride is gradually replaced by the hydrogen bond action with the choline eutectic solvent, and choline cation [ HOC ] in the choline eutectic solvent 2 H 4 N(CH 3 ) 3 ] + The alkyl and hydroxyl in the solvent and the ligand in the choline eutectic solvent can form a large hydrogen bond network with N on a graphite-phase carbon nitride sheet layer, and in addition, a large amount of positive and negative charges in the choline eutectic solvent can also be adsorbed on the surface or between layers of the graphite-phase carbon nitride, and the positive and negative ions and g-C 3 N 4 An ion-dipole effect is formed, and the hydrogen bonding effect between the solvent and the solute and the ion-dipole effect are beneficial to dissolving the solute graphite phase carbon nitride. Under the electrostatic action of the anions and cations, the ion-dipole action and the hydrogen bond network action, Van der Waals acting force between graphite-phase carbon nitride layers is broken and dispersed, more N atoms capable of interacting with a solvent are exposed, and under the solvation surrounding of the choline eutectic solvent, the graphite-phase carbon nitride can be dissolved at a lower temperature without a particularly high temperature. That is, the choline eutectic solvent is more dependent on the presence of such a compound with g-C 3 N 4 The hydrogen bonding interaction of (a) is reduced with increasing temperature, and the solvent and g-C are correspondingly destroyed 3 N 4 The hydrogen bonding of (a) to (b),high temperatures can instead lead to a decrease in dissolution rate. In the prior art, the temperature range of the dissolved graphite phase carbon nitride is 140-200 ℃, and more energy is provided by heating to destroy g-C 3 N 4 Inter-layer van der waals force and the like.
The mass ratio of the choline eutectic solvent to the graphite-phase carbon nitride is 10-50: 1; the dissolution degree is basically unchanged above the ratio, the solubility is weakened below the ratio, only 10-30% of graphite-phase carbon nitride can be dissolved, and the choline eutectic solvent cannot be fully and uniformly mixed with the graphite-phase carbon nitride.
As a preferable technical scheme:
in the method for dissolving graphite-phase carbon nitride, the Choline eutectic solvent is [ Choline] + [Cl·2phenol] - 、[Choline] + [Cl·2ethanediol] - 、[Choline] + [Cl·2triethanolamine] - 、[Choline] + [Cl·2p-methyl phenol] - 、[Choline] + [Cl·2o-methyl phenol] - 、[Choline] + [Cl·2glycerol] - Or [ Choline] + [Cl·2trifluocoacetic acid] - . The solvents are required to be used independently, and because the freezing points of the solvents are different, the change of the freezing points after mixing can be large, and the recovery is difficult.
According to the method for dissolving the graphite-phase carbon nitride, the heating and stirring time is 1-8 hours. When the heating time is less than 1h, the dissolving effect is not ideal, and only 30-40% of the solution can be dissolved; the solution can be fully dissolved after being heated for more than 8 hours, and the dissolution rate is not improved any more after the heating is continued for a prolonged time.
According to the method for dissolving the graphite-phase carbon nitride, before the graphite-phase carbon nitride is added into the choline eutectic solvent, protonation treatment is carried out on the graphite-phase carbon nitride, and the specific process is as follows: adding graphite phase carbon nitride into an acid solution, carrying out acidification treatment under a stirring condition, washing with a solvent until the pH value is 5-6, and drying (the drying temperature is 30 ℃, and low-temperature drying is also used for preventing hydrolysis of the graphite phase carbon nitride);
the acid solution is prepared by stirring and mixing organic weak acid and/or strong acid and deionized water;
when the acid solution is prepared by stirring and mixing organic weak acid, strong acid and deionized water, the volume ratio of the organic weak acid to the strong acid to the deionized water is 0.5: 0.1-0.5: 7-15; the volume ratio is set in this range to control 0.5moL/L in the acid treatment<c(H + )<1.5moL/L, i.e. c (H) + ) Too large a dissolution rate decreases, c (H) + ) Too small a dissolution rate also decreases.
The organic weak acid is more than one of citric acid, malic acid, tartaric acid, succinic acid, acetic acid, oxalic acid and propionic acid;
the strong acid is hydrochloric acid (commercially available product) having a mass concentration of 37 wt.%.
According to the method for dissolving the graphite-phase carbon nitride, the volume mass ratio of the acid solution to the graphite-phase carbon nitride is (10-80) mL:1 g; the temperature of the acidification treatment under the stirring condition is 70-90 ℃. Temperature affects the protonation rate of the acid treated graphite phase carbon nitride. Below this temperature, the acidification effect is not ideal and the dissolution rate will be reduced by 20-50% over a certain period of time, above which the graphite phase carbon nitride will hydrolyze.
In general, the reaction formula for the acid hydrolysis of graphite phase carbon nitride is as follows:
if the graphite phase carbon nitride is hydrolyzed, an-OH functional group generated in the molecular structure due to the hydrolysis is shown as a formula (D), in the protonation treatment of the invention, namely mixed acid treatment, cleaning by solvents such as acetone and the like, drying the graphite phase carbon nitride, performing KBr tabletting test, and obtaining an infrared FTIR test result without-OH infrared peak (the general-OH peak appears in 3300 cm) -1 Nearby) of only 1250 to 1270cm -1 C-N absorption peak and 2210cm -1 C ═ absorption peak at N. The temperature (70-90 ℃) for acidizing the graphite-phase carbon nitride is lower than that of the prior art, so that the condition that the graphite-phase carbon nitride is easy to hydrolyze at high temperature (for example, more than 150 ℃) is greatly avoided, and the hydrolysis process can be effectively avoided. And as a result of the dissolution process of the present invention,only water is introduced during the protonation process, and the drying treatment is carried out after the protonation process. No water is introduced in the subsequent step, so if the protonation process is not hydrolyzed, it can be said that the hydrolysis can be avoided in the whole dissolution process in the present invention.
A method for dissolving graphite-phase carbon nitride as described above, the solvent is acetone, acetonitrile, Dimethylformamide (DMF) or Dimethylsulfoxide (DMSO), preferably acetone; polar aprotic solvents are all selected here because polar protic solvents are not easily separated and are difficult to recover.
The dissolving method of graphite-phase carbon nitride comprises the steps of heating and stirring at 50-95 ℃ to dissolve the graphite-phase carbon nitride, marking the system as a choline eutectic solvent system, keeping the temperature at 75-80 ℃, and sequentially adding NaF, NaCl, NaBr and NaI (all halogenated inorganic salts are selected, and halogenated inorganic salts are selected because halogen anions regularly increase in volume from top to bottom in the periodic variation of elements) into the choline eutectic solvent system to carry out intercalation treatment; the mass ratio of the added NaF to the graphite-phase carbon nitride is 0.5-5: 1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1, (1.01-1.05), (1.02-1.07), (1.03-1.08). When the halogenated inorganic salt is added, it is necessary to set a concentration gradient having a gradually increasing concentration, that is, to ensure that the concentration added in sequence is gradually increased, and generally, a large concentration tends to diffuse to a place having a small concentration, and the formation of the concentration gradient contributes to the diffusion effect.
Ion exchange is carried out through diffusion, intercalation treatment is carried out on graphite phase carbon nitride, and g-C is continuously enlarged 3 N 4 The interlayer distance of (a) is increased, so that more N-containing hydrogen bond receptors are exposed, and the N-containing hydrogen bond receptors can be dissolved with hydroxyl or amino in the choline eutectic solvent through forming strong hydrogen bond interaction. The volume size of the halogen anion is from F - To I - The ions are increased in turn, the concentration of the anions introduced in the sequence is increased gradually, the concentration gradient promotes the diffusion of halogen anions, the halogen anions are diffused into the interlayer or embedded holes of the graphite-phase carbon nitride, so that enough electrostatic repulsion action is provided between the layers, and the volume of the anions is increasedUnder the condition of gradual increase, the interlayer spacing of graphite phase carbon nitride is enlarged to lead g-C 3 N 4 More of the dispersion dissolved in the choline eutectic solvent.
According to the method for dissolving the graphite-phase carbon nitride, in the process of sequentially adding the NaF, the NaCl, the NaBr and the NaI, after each halogenated inorganic salt is added, the mixture is stirred for 0.5-3 hours at the keeping temperature, so that halogen anions are ensured to enter the interlayer of the graphite-phase carbon nitride to realize sufficient exchange.
The method for dissolving graphite-phase carbon nitride according to any one of the above embodiments, wherein the dissolution rate of graphite-phase carbon nitride is 52% or more (weighing a certain mass of graphite-phase carbon nitride (denoted as M1), stirring and dissolving by the above-mentioned dissolution method, filtering the insoluble substance, washing and drying with acetone to a constant weight, weighing the mass of the insoluble substance (denoted as M2), and the specific gravity of the insoluble substance to the mass of graphite-phase carbon nitride before dissolution, that is, the dissolution rate ω ═ M1/M2 × 100%).
The mechanism of the invention is as follows:
the dissolution of substances is usually based on polar (e.g., similar compatibility principles) or hydrogen bonding between the solute and the solvent. The carbon nitride has a layered aromatic conjugated heterocyclic material with a 3-s-triazine structure as a basic unit, belongs to a molecular crystal, has van der Waals force between layers, and has good chemical stability. Albeit g-C 3 N 4 The surface layer having N atoms capable of interacting with polar protic solvents, but g-C 3 N 4 The layers of (A) have van der Waals' force, and it is difficult for ordinary solvents to break the inter-layer interaction and dissolve it, so g-C 3 N 4 Is difficult to dissolve in water, ethanol, diethyl ether, tetrahydrofuran, toluene and other common solvents. Even at high temperatures and strong acids, the hydrogen bonding between the resulting sheets in the presence of large amounts of polar protic solvents can promote sheet recombination and agglomeration, and the reported dissolution methods tend to be less than ideal and are accompanied by graphite-phase carbon nitride hydrolysis. Hydrolysis of the graphite phase carbon nitride results in structural damage that can lead to changes in properties (e.g., reduced catalytic properties, increased hygroscopicity, etc.).
Low choline contentThe eutectic solvents (DESs) are formed from the anion (F) of choline salts - 、Cl - 、Br - 、I - 、BF 4 - 、NO 3 - ) And a complexing agent (such as polyols, organic carboxylic acids, amides, etc.) through hydrogen bonding, wherein the formation process of the hydrogen bonding is that the anion of choline salt is used as a hydrogen bonding acceptor, and the complexing agent is used as a hydrogen bonding donor to form the hydrogen bonding (for example, in a choline eutectic solvent formed by choline chloride and urea, the urea molecule and the chlorine atom in the choline chloride form hydrogen bonding action N-H … Cl).
The invention designs a method for preventing g-C from being dissolved in high-temperature and strong-acid strong-oxidation environment from the interaction of a solvent and graphite-phase carbon nitride 3 N 4 The method specifically comprises the following steps: firstly, acidizing graphite-phase carbon nitride by organic weak acid, then adding choline eutectic solvent and halogenated inorganic salt, heating and dissolving, carrying out ion exchange in the choline eutectic solvent according to the anion volume from small to large by the diffusion principle, thereby sequentially introducing anions to carry out layer treatment on the graphite-phase carbon nitride, and slowly expanding the interlayer spacing by the ion exchange to ensure that g-C 3 N 4 Can be exposed in a solvent capable of forming hydrogen bonds or electrostatic interaction with the choline eutectic solvent in a sheet form, can be completely dissolved in the choline eutectic solvent, and can be recycled by filtration. The choline eutectic solvent does not contain proton polar solvents such as water and the like, so that the hydrolysis of graphite-phase carbon nitride can be effectively avoided.
The invention selects choline eutectic solvent containing different ligands such as hydroxyl or amino, and the like, wherein the ligands can be used as hydrogen bond donors, and graphite phase carbon nitride g-C 3 N 4 The N atom containing lone pair electrons can be used as a hydrogen bond acceptor, a large number of hydrogen bonds (N.H-O, N. H-N) are formed between the hydrogen bond donor and the hydrogen bond acceptor, and the solute g-C 3 N 4 Hydrogen bonds are formed between the polar choline eutectic solvent and the polar choline eutectic solvent, different from the common hydrogen bond action, the choline eutectic solvent can interact with graphite-phase carbon nitride to form a new hydrogen bond network, and the original inter-layer van der Waals force of the graphite-phase carbon nitride is gradually replaced by the hydrogen bond network between the choline eutectic solvent and the graphite-phase carbon nitrideHydrogen bonding of choline, choline cation [ HOC ] in choline eutectic solvent 2 H 4 N(CH 3 ) 3 ] + The alkyl and hydroxyl in the solvent and the ligand in the choline eutectic solvent can form a large hydrogen bond network with N on a graphite-phase carbon nitride sheet layer, and in addition, a large amount of positive and negative ions in the choline eutectic solvent can also be adsorbed on the surface or between layers of the graphite-phase carbon nitride, and the positive and negative charges and g-C 3 N 4 Ion-dipole interactions are formed, which are hydrogen bonding interactions between the solvent and solute, as well as ion-dipole interactions, that facilitate dissolution of the solute graphite phase carbon nitride. Thus, solutes g to C 3 N 4 The solubility of (a) increases. Meanwhile, the charges of the choline eutectic solvent can be adsorbed to g-C through electrostatic interaction 3 N 4 The surface of the lamella is beneficial to dissociating the lamella and promoting the g-C 3 N 4 The dissolution can ensure that the dissociated lamella keeps a free dispersion state, and the agglomeration is avoided. The freezing point of the choline eutectic solvent is lower than zero, the graphite-phase carbon nitride is continuously separated out through gradual cooling, and the choline eutectic solvent is filtered before reaching the freezing point, so that the solvent can be recycled. The choline eutectic solvent has strong dissolving capacity, is green and environment-friendly, does not pollute the environment, and is expected to realize large-scale popularization and application.
Firstly, treating g-C with mixed acid consisting of strong acid and organic weak acid 3 N 4 The polar choline eutectic solvent and the g-C can be prepared by regulating the experimental conditions such as acidification temperature, acidification time, pH and the like under the conditions of lower temperature and weaker acidity 3 N 4 Further increase the g-C of the graphite phase carbon nitride 3 N 4 The dissolution of the sodium-ferric phosphate overcomes the defect that g-C is caused by strong acid, concentrated acid, high temperature and strong oxidation conditions in the traditional dissolution method 3 N 4 Hydrolysis of (3). The present invention attenuates g-C by protonation 3 N 4 Van der Waals forces between layers, i.e. H ionized by acid + Ion exchange of g-C 3 N 4 N atom in (1) is protonated, H + Ions can enter g-C by diffusion 3 N 4 Interlayer of (2) protonated N or adsorbed H + Between the N atoms of the ionThere is a repulsion of positive charges, and the repulsion between the positive charges gradually weakens the van der Waals forces between the graphite phase carbon nitride layers, so that g-C 3 N 4 The layers are gradually propped apart due to electrostatic repulsion, so that the structure of the layer becomes loose, and the g-C is dissolved by the choline eutectic solvent in the next step 3 N 4 Provides favorable conditions for accelerating g-C 3 N 4 Dissolving. Meanwhile, the weak organic acid can also play a role in continuously supplementing the strong acid, namely the strong acid can inhibit the ionization of the weak acid at the initial stage of protonation, the ionization of the weak organic acid is gradually enhanced along with the consumption of the strong acid, and the weak organic acid can be continuously supplemented for g-C in a certain range 3 N 4 Protonated H + And hydroxyl groups in the weak acid can form hydrogen bond with N atoms of graphite-phase carbon nitride to further accelerate g-C 3 N 4 Dissolving.
Further, the invention introduces F according to the anion volume from small to large in sequence - 、Cl - 、Br - 、I - Halogen ions and anions are subjected to anion exchange continuously through diffusion, the interlayer spacing of graphite-phase carbon nitride is further gradually enlarged under the electrostatic repulsion action and the ion exchange, so that more and more N atoms between the layers are exposed on the surface layer originally, more and more of N atoms are combined with hydroxyl and amino in the choline eutectic solvent to form a hydrogen bond network, and the introduced halogen anions also play a role in supplementing the part of the choline eutectic solvent, in which the anions are reduced due to adsorption. Finally, under the combined action of electrostatic repulsion, ion-dipole action, hydrogen bond network action and ion exchange, the g-C is greatly improved 3 N 4 The dissolving capacity of (c). g-C 3 N 4 Forming a uniform light yellow solution with the choline eutectic solvent and the halogenated inorganic salt to achieve the purpose of dissolution.
The dissolution temperature required in the whole dissolution process is lower (50-95 ℃), the acidity required by protonation is not strong, and the choline eutectic solvent avoids graphite-phase carbon nitride g-C caused by polar protic solvent 3 N 4 Is broken down by hydrolysis. The freezing point of the choline eutectic solvent is mostly-66-150 ℃, and the choline eutectic solvent with the freezing point lower than 0 ℃ is selected by the inventionFreezing, cooling, filtering, and recovering solvent.
Advantageous effects
(1) The invention relates to a method for dissolving graphite-phase carbon nitride, which adopts mixed acid to treat graphite-phase carbon nitride g-C 3 N 4 The mixed acid consists of organic weak acid and strong acid, the organic weak acid plays a role in continuously supplementing the strong acid, namely the strong acid can inhibit the ionization of the organic weak acid at the initial stage of protonation, the ionization of the organic weak acid is gradually enhanced along with the consumption of the strong acid, and the organic weak acid can be continuously supplemented for g-C 3 N 4 Protonated H + (ii) a In addition, the hydroxyl group of the weak organic acid may be reacted with g-C 3 N 4 The N atom forms an N.H-O hydrogen bond, and g-C can be accelerated under the action of the hydrogen bond 3 N 4 Dissolving.
(2) The invention relates to a method for dissolving graphite-phase carbon nitride, which adopts a choline eutectic solvent to further accelerate g-C 3 N 4 Dissolving. g-C 3 N 4 N atoms with lone pair electrons can be used as a hydrogen bond acceptor to form a large number of hydrogen bonds N.H-O and N.H-N between choline cation in the choline eutectic solvent and hydroxyl, amino or alkyl in the ligand which can be used as a hydrogen bond donor, the choline eutectic solvent and graphite-phase carbon nitride form a new hydrogen bond network, and the graphite-phase carbon nitride is surrounded by the choline eutectic solvent to be 'solvated' under the action of the hydrogen bond network, thereby being beneficial to g-C 3 N 4 Dissolving; in addition, a large amount of positive and negative ions in the choline eutectic solvent can be adsorbed to g-C through electrostatic interaction 3 N 4 Surface layer, positive and negative ions and g-C 3 N 4 The ion-dipole effect is formed, which is beneficial to the dissociation of the lamella, and can ensure that the dissociated lamella keeps a free dispersion state, thereby avoiding the occurrence of agglomeration.
(3) The invention relates to a method for dissolving graphite-phase carbon nitride, which introduces F from small to large according to the volume of anions - 、Cl - 、Br - 、I - Halogen ions, under a certain concentration gradient, the anions continuously exchange anions through diffusion, and the interlayer spacing of graphite-phase carbon nitride is continuously enlarged under the actions of electrostatic repulsion and ion exchange, so that the N atoms between the layers are more and moreThe more exposed on the surface layer, more hydroxyl and amino groups are combined to form hydrogen bonding interaction, and the introduced halogen anion also serves to supplement the portion of the choline eutectic solvent in which the anion is reduced by adsorption. Finally, g-C 3 N 4 Forming a uniform light yellow solution with the choline eutectic solvent and the halogenated inorganic salt to achieve the purpose of dissolution.
(4) The method for dissolving graphite-phase carbon nitride avoids g-C caused by high temperature, strong acid and strong oxidation solvent in the prior art 3 N 4 The method realizes dissolution in a mild environment at a low temperature, the dissolution temperature required in the dissolution process is low (50-95 ℃), the acidity required by protonation is not strong, and the choline eutectic solvent avoids graphite-phase carbon nitride g-C caused by polar protic solvents 3 N 4 Is broken down by hydrolysis. The freezing point of the choline eutectic solvent is mostly-66-150 ℃, the choline eutectic solvent with the freezing point lower than 0 ℃ is selected, the graphite phase carbon nitride is continuously separated out through gradual cooling, and the choline eutectic solvent is filtered before reaching the freezing point, so that the solvent can be recycled. The solvent used in the invention has the advantages of low cost, recyclable solvent and the like, and the solvent range of the graphite phase carbon nitride dissolved in a homogeneous system is enlarged.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The graphite-phase carbon nitride is self-made, and the self-making process comprises the following steps:
preparing graphite phase carbon nitride: adding a precursor raw material into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, synthesizing graphite phase carbon nitride by a high-temperature calcination method, and grinding and crushing the graphite phase carbon nitride to obtain powdery graphite phase carbon nitride;
the precursor raw materials are melamine, cyanuric acid, cyanuric chloride, dicyanodiamide, cyanamide, urea or melamine cyanuric acid, and the high-temperature calcination condition is that the temperature is raised to 550-600 ℃ in a muffle furnace at the temperature rise rate of 2-3 ℃/min, the calcination is carried out for 2-4 h at constant temperature, and the calcination is naturally cooled to the room temperature; the size of the powdered graphite-phase carbon nitride is 50 nm-5 μm.
The choline eutectic solvent is self-made, and the self-made process comprises the following steps:
preparation of a choline eutectic solvent: mixing [ Choline] + [Cl] - Mixing the Choline cation with ligand Y according to the mass ratio of 1:2, heating and stirring at 90-95 ℃ until the Choline cation is clear to obtain Choline cation [ Choline [ ]] + With choline anions [ X.zY ]] - Composition of Choline eutectic solvent [ Choline] + [X·zY] - I.e., [ HOC 2 H 4 N(CH 3 ) 3 ] + [X·zY] - ；
When the ligand Y is phenol (phenol), the number of the ligands z is 2, and the Choline eutectic solvent is recorded as [ Choline] + [Cl·2phenol] - The freezing point is-30 ℃;
when the ligand Y is ethylene glycol (ethandiol), the number z of the ligand is 2, and the Choline eutectic solvent is recorded as [ Choline] + [Cl·2ethanediol] - The freezing point is-20 ℃;
when the ligand Y is triethanolamine (triethanolamine), the number z of the ligand is 2, and the Choline eutectic solvent is recorded as [ Choline] + [Cl·2triethanolamine] - The freezing point is-24 ℃;
when the ligand Y is p-methyl phenol (p-methyl phenol), the number z of the ligand is 2, and the Choline eutectic solvent is recorded as [ Choline [ ]] + [Cl·2p-methyl phenol] - The freezing point is-10 ℃;
when the ligand Y is o-methyl phenol (o-methyl phenol), the number z of the ligand is 2, and the Choline eutectic solvent is recorded as [ Choline] + [Cl·2o-methyl phenol] - The freezing point is-8 ℃;
when the ligand Y is glycerol, the number of ligands z is 2, and the Choline eutectic solvent is recorded as [ Choline [ ]] + [Cl·2glycerol] - The freezing point is-35 ℃;
when the ligand Y is trifluoroacetic acid (trifluococcoic acid), the number z of the ligand is 2, and the Choline eutectic solvent is recorded as [ Choline [ ]] + [Cl·2trifluocoacetic acid] - The freezing point is-40 ℃;
the formation of the choline hypo-eutectic solvent of the present invention can be described as: cl - And the ligand phenol (phenol), ethylene glycol (ethylene glycol), triethanolamine (triethanolamine), p-methyl phenol (p-methyl phenol), o-methyl phenol (o-methyl phenol), glycerol (glycerol) or trifluoroacetic acid (trifluococcoic acid) form an integral anion through hydrogen bonding, and form a choline chloride eutectic solvent with choline cation, as shown in the following reaction formula:
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(phenol)→(phenol) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(ethanediol)→(ethanediol) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(triethanolamine)→(triethanolamine) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(p-methyl phenol)→(p-methyl phenol) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(o-methyl phenol)→(o-methyl phenol) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(glycerol)→(glycerol) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
[HOC 2 H 4 N(CH 3 ) 3 ] + [Cl] - +2(trifluocoacetic acid)→(trifluocoacetic acid) 2 [Cl] - +[HOC 2 H 4 N(CH 3 ) 3 ] + ；
the method for testing the dissolution rate of the graphite-phase carbon nitride comprises the following steps: weighing a certain mass of graphite-phase carbon nitride (recorded as M1), stirring and dissolving by the dissolving method, filtering insoluble substances, washing and drying by acetone to constant weight, and weighing the mass of the insoluble substances (recorded as M2), wherein the specific gravity of the insoluble substances in the mass of the graphite-phase carbon nitride before dissolving is that the dissolution rate omega is (M1/M2) 100%.
Example 1
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding cyanuric acid, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, synthesizing graphite-phase carbon nitride by a high-temperature calcination method, heating the graphite-phase carbon nitride to 550 ℃ at a heating rate of 2 ℃/min in the muffle furnace, calcining the graphite-phase carbon nitride for 4 hours at constant temperature, naturally cooling the graphite-phase carbon nitride to room temperature, and grinding and crushing the graphite-phase carbon nitride; the prepared graphite-phase carbon nitride is powdery and has the size of 50 nm;
the Choline eutectic solvent is [ Choline] + [Cl·2phenol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to the volume mass ratio of 60mL:1g, stirring at 85 ℃ for acidification treatment for 4 hours, washing with a solvent (acetonitrile) until the pH value is 5 after the acidification treatment, and drying;
the acid solution is prepared by mixing organic weak acid (citric acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.5:7 through stirring;
(3) according to the mass ratio of 30:1, in a Choline eutectic solvent ([ Choline] + [Cl·2phenol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 90 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 5 hours;
(4) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.01:1.05: 1.08.
The graphite phase carbon nitride is completely dissolved.
Example 2
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 100 nm;
the deep eutectic solvent of Choline is [ Choline] + [Cl·2ethanediol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to the volume mass ratio of 50mL:1g, stirring at 90 ℃ for acidification treatment for 6h, cleaning with a solvent (acetone) until the pH value is 6 after acidification treatment, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (malic acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.3: 10;
(3) according to the mass ratio of 50:1, in a Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 95 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 3 hours;
(4) under the condition of keeping the temperature at 80 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 1h at the kept temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 0.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.05:1.06: 1.08.
The graphite phase carbon nitride is completely dissolved.
Comparative example 1
A method for dissolving graphite-phase carbon nitride, which is substantially the same as in example 2, except that the choline eutectic solvent in the step (3) is replaced by acetone, and the volume mass ratio of the acetone to the graphite-phase carbon nitride is 100mL:1 g.
The dissolution rate of graphite-phase carbon nitride was 20%.
The dissolution rate of comparative example 1 is much lower than example 2 compared to example 2, because the choline eutectic solvent can protonate g-C in mixed acid 3 N 4 Further dissolving and dispersing graphite phase carbon nitride, wherein the graphite phase carbon nitride is formed by sp 2 The choline eutectic solvent is characterized in that the triazine ring comprises a large number of N atoms, the N atoms with lone pair electrons can be used as a hydrogen bond acceptor to form a large number of hydrogen bonds (N.H-O, N. H-N) with hydroxyl or amino which can be used as a hydrogen bond donor in a choline eutectic solvent ligand, a large number of positive and negative ions of the choline eutectic solvent can be adsorbed on the surface layer of graphite phase carbon nitride through electrostatic interaction, and interlayer ions can also form electrostatic repulsion, so that the sheet layer can be favorably dissociated, the sheet layer is fully exposed to form more hydrogen bond interactions with the solvent ligand, more graphite phase carbon nitride is dissolved, the dissociated sheet layer can be kept in a free dispersion state, and agglomeration is avoided. The choline eutectic solvent treatment step was absent in comparative example 1, and thus the graphite phase carbon nitride was not as soluble in comparative example 1 as in example 2.
Example 3
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding a precursor cyanuric chloride for preparing the graphite phase carbon nitride into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite phase carbon nitride by a high-temperature calcination method. Heating to 580 ℃ at the heating rate of 3 ℃/min in a muffle furnace, calcining for 3 hours at constant temperature, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 300 nm;
the Choline eutectic solvent is [ Choline] + [Cl·2triethanolamine] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to a volume-mass ratio of 80mL:1g, stirring at 80 ℃ for acidification treatment for 3h, washing with a solvent (dimethylformamide) until the pH value is 5 after acidification treatment, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (tartaric acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.1: 7;
(3) according to the mass ratio of 10:1, in a Choline eutectic solvent ([ Choline] + [Cl·2triethanolamine] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 60 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 4 hours;
(4) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF) and n (NaCl) and n (NaBr) respectively, wherein n (NaI) is 1:1.02:1.03: 1.05.
The graphite phase carbon nitride is completely dissolved.
Example 4
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding dicyandiamide used as a precursor for preparing graphite-phase carbon nitride into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 3 ℃/min, calcining at constant temperature for 2h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 500 nm;
the deep eutectic solvent of Choline is [ Choline] + [Cl·2p-methyl phenol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite phase carbon nitride into an acid solution according to the volume mass ratio of 10mL to 1g, stirring at 70 ℃ for acidification treatment for 2h, cleaning with a solvent (dimethyl sulfoxide) until the pH value is 6 after acidification treatment, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (succinic acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.5: 10;
(3) according to the mass ratio of 20:1, in a Choline eutectic solvent ([ Choline] + [Cl·2p-methyl phenol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 50 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 1 h;
(4) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 0.5h at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 2:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.01:1.02: 1.03.
The graphite phase carbon nitride is completely dissolved.
Example 5
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding a precursor cyanamide for preparing graphite-phase carbon nitride into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 550 ℃ in a muffle furnace at the heating rate of 3 ℃/min, calcining at constant temperature for 3h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 1 mu m;
the Choline eutectic solvent is [ Choline] + [Cl·2o-methyl phenol] - ；
(2) Protonating graphite phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to the volume mass ratio of 40mL:1g, stirring at 90 ℃ for acidification for 5 hours, cleaning with a solvent (acetone) until the pH value is 6 after acidification, and drying;
the acid solution is prepared by mixing organic weak acid (oxalic acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.5:12 through stirring;
(3) according to the mass ratio of 40:1, in a Choline eutectic solvent ([ Choline] + [Cl·2o-methyl phenol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 70 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 6 hours;
(4) under the condition of keeping the temperature at 80 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 1.5 hours at the kept temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 3:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.04:1.05: 1.07.
The graphite phase carbon nitride is completely dissolved.
Example 6
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding a precursor urea for preparing graphite-phase carbon nitride into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 550 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 2.5h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 3 mu m;
the Choline eutectic solvent is [ Choline] + [Cl·2glycerol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to a volume-mass ratio of 70mL:1g, stirring at 85 ℃ for acidification treatment for 6h, cleaning with a solvent (acetone) until the pH value is 5 after acidification treatment, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (acetic acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.3: 15;
(3) according to the mass ratio of 45:1, in a Choline eutectic solvent ([ Choline] + [Cl·2glycerol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 80 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 7 hours;
(4) under the condition of keeping the temperature at 80 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 2.5 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 4:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.02:1.05: 1.08.
The graphite phase carbon nitride is completely dissolved.
Example 7
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine cyanuric acid serving as a precursor for preparing the graphite-phase carbon nitride into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 590 ℃ at the heating rate of 3 ℃/min in a muffle furnace, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite phase carbon nitride is powder, and the size of the graphite phase carbon nitride is 5 mu m;
the Choline eutectic solvent is [ Choline] + [Cl·2trifluocoacetic acid] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to a volume-mass ratio of 80mL:1g, stirring at 90 ℃ for acidification for 4 hours, washing with a solvent (dimethylformamide) until the pH value is 5 after acidification, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (propionic acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.4: 15;
(3) according to the mass ratio of 25:1, in a Choline eutectic solvent ([ Choline] + [Cl·2trifluocoacetic acid] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 95 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 8 hours;
(4) under the condition of keeping the temperature at 80 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF) and n (NaCl) and n (NaBr) respectively represent (1: 1.02:1.07: 1.08).
The graphite phase carbon nitride is completely dissolved.
Example 8
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powder with the size of 100 nm;
the Choline eutectic solvent is [ Choline] + [Cl·2ethanediol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into a strong acid solution according to the volume mass ratio of 50mL:1g, stirring at 85 ℃ for acidification treatment for 6h, cleaning with a solvent (acetone) until the pH value is 5 after acidification treatment, and drying;
the strong acid solution is prepared by stirring and mixing 0.8:10 volume ratio of strong acid (hydrochloric acid with the mass concentration of 37 wt.%) and deionized water;
(3) according to the mass ratio of 50:1, in a Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 90 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 6 hours;
(4) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.05:1.06: 1.08.
The dissolution rate of the graphite phase carbon nitride was 90%.
The graphite phase carbon nitride in example 8 is not dissolved as well as in example 2, except that example 8 lacks weak organic acids to participate in the dissolution process, for the following reasons: example 2 weak organic acids play an important role, and weak organic acids serve to continuously supplement strong acids with H + The strong acid can inhibit the ionization of the weak acid in the initial stage of protonation, the ionization of the organic weak acid is gradually enhanced along with the consumption of the strong acid, and H used for protonation of the graphite-phase carbon nitride can be continuously supplemented + Ensuring that the graphite phase carbon nitride is fully acidified and the hydroxyl of the organic weak acid can be reacted with the N atom of the carbon nitrideHydrogen bonds are formed, and the dissolving capacity of the graphite phase carbon nitride can be improved under the combined action of the electrostatic acting force and the hydrogen bonds. Thus, the lack of an organic weak acid results in a lack of hydrogen bonding with the graphite phase carbon nitride, which reduces solubility to some extent.
Example 9
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 100 nm;
the Choline eutectic solvent is [ Choline] + [Cl·2ethanediol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite phase carbon nitride into an organic weak acid solution according to the volume mass ratio of 50mL:1g, stirring at 85 ℃ for acidification treatment for 6h, cleaning with a solvent (acetone) until the pH value is 5 after acidification treatment, and drying;
the organic weak acid solution is prepared by stirring and mixing organic weak acid (a mixture of citric acid and propionic acid with a mass ratio of 1: 1) with deionized water in a volume ratio of 0.8: 10;
(3) according to the mass ratio of 50:1, in a Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (2), heating, stirring and dissolving at 90 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 6 hours;
(4) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the keeping temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.05:1.06: 1.08.
The dissolution rate of graphite-phase carbon nitride was 75%.
The graphite phase carbon nitride in example 9 is not dissolved as well as in example 2, except that example 9 lacks strong acid to participate in the dissolution process, for the following reasons: in example 2, the weak organic acid serves to continuously supplement the strong acid with H + And the effect of forming hydrogen bonds with carbon nitride, but weak organic acids are weak acids and cannot be ionized sufficiently and release H sufficiently + Ion, H + The low ion concentration results in a much lower concentration of protonation of the energy and graphite phase carbon nitride. The strong acid can fully ionize more positive and negative ions and H + Can be adsorbed on the surface and between layers of the graphite phase carbon nitride and can form electrostatic acting force with the graphite phase carbon nitride. Thus, the lack of strong acid, and hence the lack of electrostatic interaction with the graphite phase carbon nitride, reduces solubility to some extent.
Example 10
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining for 4 hours at constant temperature, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powder with the size of 100 nm;
the Choline eutectic solvent is [ Choline] + [Cl·2ethanediol] - ；
(2) According to the mass ratio of 50:1, in a Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) Adding graphite phase carbon nitride, heating and stirring at 90 ℃ to dissolve the mixture to obtain a choline eutectic solvent system, wherein the heating and stirring time is 6 hours;
(3) under the condition of keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI into a choline eutectic solvent system for intercalation treatment, and stirring for 3 hours at the kept temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.05:1.06: 1.08.
The dissolution rate of graphite-phase carbon nitride was 52%.
The graphite phase carbon nitride in example 10 is not dissolved as much as in example 2, but in example 10, a mixed acid treatment step of weak organic acid and strong organic acid is omitted, because: example 2 weak organic acids play an important role, and weak organic acids serve as a continuous H supplement to strong acids + The strong acid can inhibit the ionization of the weak acid in the initial stage of protonation, the ionization of the organic weak acid is gradually enhanced along with the consumption of the strong acid, and H used for protonation of the graphite-phase carbon nitride can be continuously supplemented + The graphite phase carbon nitride is fully acidified, and the hydroxyl of the organic weak acid can form a hydrogen bond with the N atom of the carbon nitride, so that the lack of the organic weak acid can lack the hydrogen bond action with the graphite phase carbon nitride. The strong acid can fully ionize more positive and negative ions and H + The carbon nitride can be adsorbed on the surface and between layers of graphite phase carbon nitride and can form electrostatic repulsion force with the graphite phase carbon nitride. Under the combined action of electrostatic acting force and hydrogen bonds, the dissolving capacity of graphite-phase carbon nitride can be improved. Therefore, the lack of acid treatment steps of strong acid and organic weak acid cannot pull the interlayer spacing of graphite-phase carbon nitride to a certain extent, and the subsequent choline eutectic solvent cannot enter the interlayer to be laid, so that the dissolution rate is greatly reduced.
Example 11
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 100 nm;
the deep eutectic solvent of Choline is [ Choline] + [Cl·2ethanediol] - ；
(2) Protonating graphite-phase carbon nitride;
adding graphite-phase carbon nitride into an acid solution according to the volume mass ratio of 50mL:1g, stirring at 85 ℃ for acidification treatment for 6h, cleaning with a solvent (acetone) until the pH value is 5 after acidification treatment, and drying;
the acid solution is prepared by stirring and mixing organic weak acid (citric acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.3: 10;
(3) according to the mass ratio of 50:1, in a Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) Adding the graphite-phase carbon nitride obtained after drying in the step (1), heating, stirring and dissolving at 90 ℃ to obtain a choline eutectic solvent system, wherein the heating and stirring time is 6 hours.
The dissolution rate of graphite-phase carbon nitride was 86%.
The graphite phase carbon nitride in example 11 is not as soluble as in example 2, except that example 11 lacks the halogenated inorganic salt treatment step, for the specific reason: the halogenated inorganic salt has the function of fully stripping the graphite-phase carbon nitride lamella by the ion exchange effect of gradually increasing the ion volume on the basis of the choline eutectic solvent treatment, thereby achieving the purpose of dissolution. Example 11 lacks the ion exchange step of the halogenated inorganic salt, and thus the graphite phase carbon nitride is only partially dissolved, not as well as example 2.
Example 12
A method for dissolving graphite-phase carbon nitride comprises the following specific steps:
(1) preparing raw materials;
preparing graphite phase carbon nitride: adding melamine, a precursor for preparing graphite-phase carbon nitride, into a ceramic crucible, then placing the ceramic crucible into a muffle furnace, and synthesizing the graphite-phase carbon nitride by a high-temperature calcination method. Heating to 600 ℃ in a muffle furnace at the heating rate of 2 ℃/min, calcining at constant temperature for 4h, naturally cooling to room temperature, and grinding and crushing; the prepared graphite-phase carbon nitride is powdery and has the size of 100 nm;
the deep eutectic solvent of Choline is [ Choline] + [Cl·2ethanediol] - ；
(2) Adding graphite-phase carbon nitride into acetone according to the mass-volume ratio of 1g to 100mL, keeping the temperature at 75 ℃, sequentially adding NaF, NaCl, NaBr and NaI for intercalation treatment, and stirring for 3 hours at the kept temperature after each addition; the mass ratio of the added NaF to the graphite-phase carbon nitride is 1.5:1, and the mass ratio of the added NaF, NaCl, NaBr and NaI is as follows: n (NaF), n (NaCl), n (NaBr), n (NaI) 1:1.05:1.06: 1.08.
(3) Adding a Choline eutectic solvent ([ Choline) into the solution obtained in the step (2)] + [Cl·2ethanediol] - ) And Choline eutectic solvent ([ Choline] + [Cl·2ethanediol] - ) The mass ratio of the graphite phase carbon nitride to the graphite phase carbon nitride is 50:1, and the graphite phase carbon nitride is heated, stirred and dissolved at the temperature of 90 ℃ for 6 hours;
(4) adding an acid solution into the solution obtained in the step (3), wherein the volume mass ratio of the acid solution to the graphite-phase carbon nitride is 50mL:1g, and stirring at 85 ℃ for acidification treatment for 6 h;
the acid solution is prepared by mixing organic weak acid (citric acid), strong acid (hydrochloric acid with the mass concentration of 37 wt.%), and deionized water in a volume ratio of 0.5:0.3:10 through stirring.
The dissolution rate of graphite-phase carbon nitride was 60%.
The graphite phase carbon nitride is not as soluble as in example 2 in example 12 because: van der Waals force exists between graphite-phase carbon nitride layers which are not protonated by mixed acid, most of the graphite-phase carbon nitride layers are always in a reaction inert state under the condition of no protonation, positive charge is not electrostatically attracted between the unprotonated graphite-phase carbon nitride layers, and anions and nitrogen-containing g-C with lone pair electrons 3 N 4 Has ion-dipole electric repulsion, even the anion with small volume in the inorganic sodium halide salt is difficult to diffuse into the interlayer in a large amount. And the surface layer of graphite phase carbon nitride can be partially mixed with inorganic sodium halide salt and linerThe alkali eutectic solvent is partially dissolved by electrostatic interaction or hydrogen bonding. However, the dissolution effect was not good and was far from the good dissolution effect of example 2.
Claims (7)
1. A method for dissolving graphite-phase carbon nitride is characterized in that: adding graphite-phase carbon nitride into a choline eutectic solvent, heating and stirring at 50-95 ℃ to dissolve the carbon nitride, recording a system which is heated, stirred and dissolved at 50-95 ℃ as a choline eutectic solvent system, keeping the temperature at 75-80 ℃, and sequentially adding NaF, NaCl, NaBr and NaI into the choline eutectic solvent system to perform intercalation treatment;
the mass ratio of the choline eutectic solvent to the graphite-phase carbon nitride is 10-50: 1;
before adding graphite-phase carbon nitride into the choline eutectic solvent, protonating the graphite-phase carbon nitride, wherein the specific process comprises the following steps of: adding graphite-phase carbon nitride into an acid solution, carrying out acidification treatment under a stirring condition, washing with a solvent until the pH value is 5-6, and drying;
the acid solution is prepared by stirring and mixing organic weak acid, strong acid and deionized water;
the deep eutectic solvent of Choline is [ Choline] + [Cl∙2phenol] - 、[Choline] + [Cl∙2ethanediol] - 、[Choline] + [Cl∙2triethanolamine] - 、[Choline] + [Cl∙2p-methyl phenol] - 、[Choline] + [Cl∙2o-methyl phenol] - 、[Choline] + [Cl∙2glycerol] - Or [ Choline] + [Cl∙2trifluocoacetic acid] - ；
The graphite phase carbon nitride is completely dissolved.
2. The method for dissolving graphite-phase carbon nitride according to claim 1, wherein the heating and stirring time is 1 to 8 hours.
3. The method for dissolving graphite-phase carbon nitride according to claim 1, wherein the volume ratio of the weak organic acid to the strong acid to the deionized water is 0.5: 0.1-0.5: 7-15;
the organic weak acid is more than one of citric acid, malic acid, tartaric acid, succinic acid, acetic acid, oxalic acid and propionic acid;
the strong acid is hydrochloric acid with a mass concentration of 37 wt.%.
4. The method for dissolving graphite-phase carbon nitride according to claim 3, wherein the volume-to-mass ratio of the acid solution to the graphite-phase carbon nitride is (10-80) mL:1 g; the temperature of the acidification treatment under the stirring condition is 70-90 ℃.
5. The method for dissolving graphite-phase carbon nitride according to claim 3, wherein the solvent is acetone, acetonitrile, dimethylformamide or dimethylsulfoxide.
6. The method for dissolving graphite-phase carbon nitride according to claim 1, wherein the mass ratio of the added NaF to the graphite-phase carbon nitride is 0.5-5: 1, and the ratio of the added NaF, NaCl, NaBr and NaI is: n (NaF), n (NaCl), n (NaBr), n (NaI) =1 (1.01-1.05), 1.02-1.07, and 1.03-1.08.
7. The method for dissolving graphite-phase carbon nitride according to claim 6, wherein each halogenated inorganic salt is added and stirred at the holding temperature for 0.5 to 3 hours during the sequential addition of NaF, NaCl, NaBr and NaI.
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