An organic small molecule-modified nano-carbon nitride, preparation method thereof and application thereof

Abstract

The present invention relates to the technical field of material preparation, and particularly relates to an organic small molecule-modified nano-carbon nitride, a preparation method thereof and an application thereof. According to the easily modifiable characteristics of the carbon nitride molecular structure, the organic small molecule is coupled with the carbon nitride by ball milling, effectively enhancing the light response ability of the functionalized carbon nitride material and delaying the recombination time of photo-generated electron-hole pairs, thereby improving its photocatalytic performance. The present invention aims to solve the problem that the photocatalytic performance of the single-phase carbon nitride as a catalyst is not ideal due to its low quantum efficiency. Moreover, the preparation method is simple, the raw materials are cheap and easily available, the environmental pollution is low, and it is conducive to large-scale industrial production, having significant economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and particularly relates to an organic small molecule-modified nano-carbon nitride, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its economy and environmental friendliness, semiconductor photocatalysis can degrade organic pollutants into carbon dioxide and water under natural conditions and has been widely used in the field of environmental cleaning. However, there are still some defects, such as limited light response ability and low photogenerated charge transfer rate, which limit their further application. Therefore, it is necessary to find a suitable semiconductor as a photocatalyst.

[0003] The first synthesis of polymeric carbon nitride was reported in 1834. Subsequent in-depth studies found that it has a series of excellent physical and chemical properties, such as high hardness, high melting point, high chemical stability, high thermal conductivity, low density, acid and alkali resistance, and oxidation and corrosion resistance, etc. Carbon nitride has five structures, such as alpha phase, beta phase, graphite phase, cubic phase, quasi-cubic phase, etc. Among them, graphite-phase carbon nitride is the most widely reported metal-free polymer photocatalyst due to its large conjugated structure, stable chemical properties, and simple preparation method. Professor Wang Xinchen and his research team, as early experts in the research direction of carbon nitride photocatalysis, have made extensive attempts on the modification and application direction of carbon nitride and achieved a large number of research results. For example, using modified carbon nitride photocatalysis to remove refractory organic pollutants in the environment and prepare clean energy (oxygen, hydrogen, carbon monoxide). At the same time, the photocatalytic activity of graphite-phase carbon nitride is limited because the charges generated by its light are easily recombined, the sample size is large, and the low specific surface area leads to low photocatalytic efficiency. Therefore, it is necessary to modify and decorate the original carbon nitride. To solve the above problems, researchers have explored many new synthesis techniques and modification methods to improve the photocatalytic activity of carbon nitride. Among them, element doping or constructing heterostructures has been proven to be an effective method. These methods generally improve the migration efficiency of photogenerated charges of photocatalysts by changing the band gap and delaying photogenerated electron-hole pairs. However, most of the materials and methods used for modification have limited improvement in the photocatalytic performance of carbon nitride, or the preparation process is relatively cumbersome, costly, and even has a certain degree of danger, which is not conducive to production applications. Therefore, it is of important research and application value to develop an economically efficient and environmentally friendly functionalized carbon nitride.

[0004] In view of the above defects, the creator of the present invention finally obtained the present invention after long-term research and practice. Summary of the Invention

[0005] The object of the present invention is to solve the problem of how to effectively improve the photocatalytic performance of modified graphitic carbon nitride and reduce the production cost, and provides an organic small molecule-modified nano carbon nitride, a preparation method thereof and an application thereof.

[0006] In order to achieve the above object, the present invention discloses a preparation method of an organic small molecule-modified nano carbon nitride, comprising the following steps:

[0007] S1, preparing bulk carbon nitride: calcining melamine in an air atmosphere and waiting for natural cooling to room temperature to obtain bulk carbon nitride;

[0008] S2, preparing functionalized carbon nitride: grinding the bulk carbon nitride solid obtained in step S1 into a uniformly textured powder, mixing the powder with an organic solvent solution and then placing it in a ball mill jar for ball milling to obtain a mixture of functionalized carbon nitride and the organic solvent;

[0009] S3, drying the dispersion obtained in step S2 to obtain a carbon nitride powder.

[0010] The amount of melamine added in step S1 is 1-20.0 g.

[0011] In step S1, the calcination heating rate is 2.5-3.5 °C / min, the calcination temperature is 500-600 °C, and the constant temperature time is 1-2 h.

[0012] In step S2, the organic solvent is any one of a methanol solution, an ethanol solution, a dimethyl sulfoxide solution, an N,N-dimethylformamide solution, and a tetrahydrofuran solution.

[0013] In step S2, the ratio of bulk carbon nitride to the organic solvent is 1 g:1-10 mL.

[0014] In step S2, the ball milling speed is 100-500 rpm, and the ball milling time is 2-20 h.

[0015] In step S3, a water bath heating method is used for drying, and the temperature of the water bath heating is 40-95 °C.

[0016] The present invention also discloses an organic small molecule-modified nano carbon nitride prepared by the above preparation method and an application of this organic small molecule-modified nano carbon nitride in photocatalytic removal of pollutants in water.

[0017] The pollutants in the water include organic dyes and heavy metal ions.

[0018] The preparation method of the nano-carbon nitride modified by organic small molecules effectively enhances the light response ability of the functionalized carbon nitride material and delays the recombination time of photo-generated electron-hole pairs according to the characteristics of the easy modification of the carbon nitride molecular structure, thereby improving its photocatalytic performance by coupling organic small molecules with carbon nitride through ball milling.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The present invention uses cheap and easily available melamine as a raw material to prepare nano-carbon nitride modified by organic small molecules. After simply soaking and mixing with a tetrahydrofuran solution, functionalized carbon nitride is prepared through ball milling. This method has good controllability and repeatability, a simple preparation process, and low environmental pollution, which is conducive to large-scale industrial production.

[0021] 2. The powder prepared by this method can be stored for a long time and has good stability in acidic and high-temperature environments.

[0022] 3. The material of the present invention is a two-dimensional nano-material modified by organic small molecules, which has good photocatalytic performance and has a wide range of application directions in the research of the photocatalytic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the preparation principle diagram of the nano-carbon nitride modified by organic small molecules of the present invention;

[0024] Figure 2 It is the degradation effect diagram of rhodamine B dye by carbon nitride modified with different organic solvent molecules;

[0025] Figure 3 It is the degradation effect diagram of rhodamine B dye by carbon nitride modified with organic small molecules under different rotation speed conditions;

[0026] Figure 4 It is the crystal form diagram (XRD) and infrared spectrum diagram (FTIR) of bulk carbon nitride and nano-carbon nitride modified by tetrahydrofuran organic small molecules. (a) is the XRD diagram, and (b) is the infrared spectrum diagram;

[0027] Figure 5 It is the contact angle (CA) of bulk carbon nitride and nano-carbon nitride modified by tetrahydrofuran organic small molecules. (a) is the contact angle of bulk carbon nitride, and (b) is the contact angle of nano-carbon nitride modified by tetrahydrofuran organic small molecules;

[0028] Figure 6 It is the transmission electron microscope diagram (TEM) of bulk carbon nitride and nano-carbon nitride modified by tetrahydrofuran organic small molecules. (a) is bulk carbon nitride, and (b) is a carbon nitride nanosheet modified by tetrahydrofuran;

[0029] Figure 7Scanning electron microscopy (SEM) images of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules. (a) shows bulk-phase carbon nitride, and (b) shows carbon nitride nanosheets modified with tetrahydrofuran.

[0030] Figure 8 X-ray photoelectron spectroscopy (XPS) spectra of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules. (a) is the survey spectrum, (b) is the carbon spectrum, (c) is the nitrogen spectrum, and (d) is the oxygen spectrum.

[0031] Figure 9 Solid-state nuclear magnetic resonance (NMR) spectra of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules.

[0032] Figure 10 Diffuse reflectance spectroscopy (DRS) spectra of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules.

[0033] Figure 11 To test the effect of carbon nitride modified with tetrahydrofuran organic small molecules on the degradation of Rhodamine B dye in acidic and alkaline environments.

[0034] Figure 12 Photocatalytic degradation effect diagrams of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules on Rhodamine B dye. (a) shows bulk-phase carbon nitride, and (b) shows carbon nitride nanosheets modified with tetrahydrofuran organic small molecules.

[0035] Figure 13 Photocatalytic degradation effect diagrams of carbon nitride nanosheets modified with tetrahydrofuran organic small molecules on different organic dyes in aqueous environments. (a) is Evans Blue (aqueous system), (b) is Crystal Violet (aqueous system), and (c) is Methylene Blue (aqueous system).

[0036] Figure 14 Photocatalytic degradation effect diagrams of carbon nitride nanosheets modified with tetrahydrofuran organic small molecules on different organic dyes in organic environments (methanol system). (a) is Evans Blue (methanol solution), (b) is Crystal Violet (methanol solution), and (c) is Methylene Blue (methanol solution).

[0037] Figure 15 Photocatalytic degradation effect diagrams of carbon nitride nanosheets modified with tetrahydrofuran organic small molecules on different organic dyes in organic environments (ethanol system). (a) is Methylene Blue (ethanol solution), and (b) is Fast Green (ethanol solution).

[0038] Figure 16 Photocatalytic reduction effect diagrams of bulk-phase carbon nitride and carbon nitride nanosheets modified with tetrahydrofuran organic small molecules on hexavalent chromium ions. (a) shows bulk-phase carbon nitride, and (b) shows carbon nitride nanosheets modified with tetrahydrofuran organic small molecules. Detailed implementation methods

[0039] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with the accompanying drawings.

[0040] Example 1

[0041] (1) Preparation of bulk carbon nitride:

[0042] Weigh 10.0 g of melamine powder into a crucible and place it in a muffle furnace. In an air atmosphere, heat it to 550°C at a rate of 2.5°C / min and keep it for 2 hours. After cooling to room temperature, take out the blocky carbon nitride sample and grind it evenly to obtain bulk carbon nitride.

[0043] (2) Preparation of nano carbon nitride modified with small molecules of different organic solvents:

[0044] The carbon nitride powder was mixed with different organic solutions (methanol, dimethyl sulfoxide, N,N-dimethylformamide) at a ratio of 1g:2mL and stirred evenly; the mixed samples were placed in different ball milling jars, and then placed in a ball mill at a speed of 400rpm and ball milled for 10 hours; the samples were taken out, dried, and ground to obtain carbon nitride powder functionalized with different organic solvents.

[0045] (3) Testing the photocatalytic performance of nano-carbon nitride modified with different organic solvent molecules:

[0046] Rhodamine B dye was selected as the probe dye molecule. 100 mL of Rhodamine B (about 4.5 ppm) was added to 50 mg of carbon nitride functionalized with different organic solvents and reacted under photocatalytic conditions for a certain period of time. The concentration of the original solution and the absorbance intensity of the solution after the reaction were tested using an ultraviolet spectrophotometer. Figure 2 As shown in the figure, it can be seen that when methanol solution, ethanol solution, dimethyl sulfoxide solution, N,N-dimethylformamide solution and tetrahydrofuran solution are used as grinding solvents respectively, the photocatalytic performance of carbon nitride nanosheets modified with tetrahydrofuran molecules is significantly improved.

[0047] Example 2

[0048] (1) Preparation of bulk carbon nitride:

[0049] Weigh 10.0 g of melamine powder into a crucible and place it in a muffle furnace. In an air atmosphere, heat it to 550°C at a rate of 2.5°C / min and keep it for 2 hours. After cooling to room temperature, take out the blocky carbon nitride sample and grind it evenly to obtain bulk carbon nitride.

[0050] (2) Preparation of nano carbon nitride modified with tetrahydrofuran organic small molecules under different rotation speed conditions:

[0051] Mix carbon nitride powder and tetrahydrofuran solution at a ratio of 1 g:5 mL to ensure that the carbon nitride powder can be fully wetted in the tetrahydrofuran solution, and stir evenly after mixing; place the mixed sample in a ball milling jar, and then place it in a ball mill and treat it at different rotation speeds (100, 200, 300, 400, 500 rpm) for 10 h; take out the sample, dry and grind it to obtain the functionalized light yellow carbon nitride powder.

[0052] (3) Test the photocatalytic performance of nano-carbon nitride modified by tetrahydrofuran organic small molecules under different rotation speed conditions:

[0053] Select rhodamine B dye as the probe dye molecule, take 100 mL of rhodamine B (about 4.5 ppm), add 50 mg of the prepared functionalized carbon nitride and react for a certain time under photocatalytic conditions, and use an ultraviolet spectrophotometer to measure the concentration of the original solution and the absorbance intensity of the solution after the reaction. As Figure 3 shown in the figure, the data shows that as the ball milling speed increases, the energy provided to the material is also higher. At low rotation speed conditions (100 - 300 rpm), the energy is too low to allow the organic small molecules to bind well with the carbon nitride molecules; while at high rotation speed conditions (500 rpm), the excessive energy will damage the molecular structure of the material and lead to a decrease in photocatalytic performance; while when the rotation speed reaches 400 rpm, the energy provided to the material can fully functionalize the organic small molecules onto the carbon nitride structure, and the catalyst shows the optimal photocatalytic performance.

[0054] Example 3

[0055] (1) Prepare bulk carbon nitride:

[0056] Weigh 10.0 g of melamine powder in a crucible and place it in a muffle furnace. Under an air atmosphere, heat it to 550 °C at a rate of 2.5 °C / min and hold for 2 h; after cooling to room temperature, take out the bulk carbon nitride sample, grind it evenly to obtain bulk carbon nitride.

[0057] (2) Prepare carbon nitride modified by tetrahydrofuran organic small molecules (functionalized carbon nitride):

[0058] Mix carbon nitride powder and tetrahydrofuran solution at a ratio of 1 g:2 mL to ensure that the tetrahydrofuran solution just wets the carbon nitride powder, stir evenly after mixing; place the mixed sample in a ball milling jar, and then place it in a ball mill at a rotation speed of 400 rpm for 10 h; take out the sample, dry and grind it to obtain the functionalized carbon nitride powder.

[0059] (3) Test the photocatalytic performance of carbon nitride modified by tetrahydrofuran organic small molecules:

[0060] Rhodamine B dye was selected as the probe dye molecule. 100 mL of Rhodamine B (about 4.5 ppm) was taken, and 50 mg of the prepared organic small molecule-modified nano-carbon nitride was added and reacted for a certain time under photocatalytic conditions. The concentration of the original solution and the absorbance intensity of the solution after the reaction were measured using a UV spectrophotometer. The crystal structure and infrared spectrum of the organic molecule-modified carbon nitride are respectively as Figure 4 shown, and the organic small molecule-modified nano-carbon nitride belongs to a multi-layer flake structure as Figure 6 , 7 shown; its solid-state nuclear magnetic resonance carbon spectrum and elemental composition are respectively as Figure 8 , 9 shown; its diffuse reflection spectrum and photocatalytic performance applications are respectively as Figure 10 , 12 , 13, 14, 15, 16 shown. It can be seen from the figure that the tetrahydrofuran molecule was successfully introduced into the carbon nitride structure, effectively enhancing the light response ability of the functionalized carbon nitride nanosheet material, delaying the recombination time of photogenerated electron-hole pairs, and thus improving its photocatalytic performance.

[0061] Example 4

[0062] (1) Preparation of bulk carbon nitride:

[0063] Weigh 10.0 g of melamine powder into a crucible and place it in a muffle furnace. Under an air atmosphere, heat it to 550 °C at a rate of 2.5 °C / min and hold for 2 h; after cooling to room temperature, take out the bulk carbon nitride sample, grind it evenly to obtain bulk carbon nitride.

[0064] (2) Preparation of tetrahydrofuran organic small molecule-modified nano-carbon nitride:

[0065] Subsequently, the carbon nitride powder and the tetrahydrofuran solution were mixed at a ratio of 1 g: 2 mL and stirred evenly; the mixed sample was placed in a ball milling tank and then placed in a ball mill at a rotation speed of 400 rpm for ball milling for 10 h; the sample was taken out for drying and grinding to obtain the functionalized carbon nitride powder.

[0066] (3) Testing the photocatalytic performance of tetrahydrofuran organic small molecule-modified nano-carbon nitride under acidic and basic conditions:

[0067] First, the functionalized carbon nitride was immersed in a strong acid (hydrochloric acid solution with pH = 1) and a strong base (sodium hydroxide solution with pH = 14) environment overnight. Rhodamine B dye was selected as the probe dye molecule. 100 mL of Rhodamine B (about 4.5 ppm) was taken, and 50 mg of the functionalized carbon nitride eroded by the strong acid and strong base environments was added respectively and reacted for a certain time under photocatalytic conditions. The concentration of the original solution and the absorbance intensity of the solution after the reaction were measured using a UV spectrophotometer. As Figure 11As shown in the figure, it can be seen from the figure that the carbon nitride modified by tetrahydrofuran molecules has good acid resistance and can have stable catalytic performance in an acidic environment.

[0068] Example 5

[0069] (1) Preparation of bulk carbon nitride:

[0070] Weigh 10.0 g of melamine powder into a crucible and then place it in a muffle furnace. Under an air atmosphere, heat it to 550 °C at a rate of 2.5 °C / min and hold for 2 h; after cooling to room temperature, take out the bulk carbon nitride sample, grind it evenly to obtain bulk carbon nitride.

[0071] (2) Preparation of nano-carbon nitride modified by tetrahydrofuran organic small molecules:

[0072] Subsequently, mix the carbon nitride powder and the tetrahydrofuran solution in a ratio of 1 g:10 mL and stir evenly; place the mixed sample in a ball milling tank, and then place it in a ball mill and ball mill at a speed of 400 rpm for 10 h; take out the sample, dry it and grind it to obtain the functionalized carbon nitride powder.

[0073] (3) Test the performance of nano-carbon nitride modified by tetrahydrofuran organic small molecules in photocatalytic reduction of potassium dichromate:

[0074] In an acidic environment, take 100 mL of potassium dichromate solution (5 ppm), add a trace amount (0.01 - 0.1 mmol) of hole scavenger, and then add 50 mg of the prepared nano-carbon nitride modified by tetrahydrofuran organic small molecules and react for a certain time under photocatalytic conditions. Use the diphenylcarbamide colorimetric method to measure the concentration of the original solution and the absorbance intensity of the solution after the reaction with a UV spectrophotometer. As Figure 16 shown, the carbon nitride nanosheets modified by tetrahydrofuran molecules have excellent reduction effect on heavy metal chromium ions in aqueous solution.

[0075] The nano-carbon nitride powder modified by tetrahydrofuran molecules prepared in this invention was characterized by X-ray diffraction ( Figure 4 ) and the characteristic peaks were at 12.9° and 27.5°, which respectively corresponded to the (100) crystal surface from the interlayer stacking of the aromatic system and the (002) diffraction plane of the interlayer reflection of the graphite-like structure. As shown by infrared spectroscopy ( Figure 4 ), the peak at about 1068 cm -1 represented the asymmetric stretching vibration of the ether group, indicating the successful introduction of oxygen-containing groups, presumably belonging to the five-membered single oxygen ring structure of the tetrahydrofuran molecule. As shown by solid-state nuclear magnetic resonance carbon spectrum ( Figure 9 ), it could further confirm that the tetrahydrofuran molecule was successfully introduced into the carbon nitride structure, indicating that the carbon nitride was successfully functionalized by organic small molecules. The X-ray photoelectron spectroscopy of the functionalized carbon nitride (Figure 8 ) and diffuse reflection spectroscopy ( Figure 10 ) respectively illustrate the elemental composition and band gap change of functionalized carbon nitride. The photocatalytic performance of functionalized carbon nitride was evaluated through the removal experiments of organic dyes ( Figure 12 , Figure 13 , Figure 14 , Figure 15 ) and heavy metal ions (hexavalent chromium ions) ( Figure 16 ).

[0076] This preparation method of nano-carbon nitride modified by organic small molecules, according to the easily modified characteristics of the carbon nitride molecular structure, couples organic small molecules with carbon nitride through ball milling, effectively enhancing the light response ability of the functionalized carbon nitride material, delaying the recombination time of photo-generated electron-hole pairs, and thus improving its photocatalytic performance. Subsequently, the photocatalytic performance of the functionalized carbon nitride was evaluated through the photocatalytic degradation experiment of Rhodamine B. By comparing the absorbance after degradation (as shown in Figure 2 ), it was found that when the organic solvent used was tetrahydrofuran, the nano-carbon nitride modified by tetrahydrofuran small molecules had the optimal photocatalytic performance. This was probably because the tetrahydrofuran molecule had the same elemental composition and similar molecular structure as carbon nitride, making it easier to combine with carbon nitride molecules (as shown in Figure 9 ), strengthening the conjugation effect, and improving the migration rate of photo-generated carriers, thereby improving the photocatalytic performance.

[0077] The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A preparation method of organic small molecule modified nano-carbon nitride, characterized in that, It includes the following steps: S1. Prepare bulk carbon nitride: Calcinate melamine in an air atmosphere and wait for it to cool naturally to room temperature to obtain bulk carbon nitride; S2. Prepare functionalized carbon nitride: Mix the bulk carbon nitride obtained in step S1 with an organic solvent solution, place it in a ball milling jar, and ball mill to obtain a carbon nitride mixture modified with organic molecules; S3. Dry the mixture obtained in step S2 to obtain an organic molecule-modified nano carbon nitride powder; The organic solvent in step S2 is a tetrahydrofuran solution; the ratio of bulk carbon nitride to the organic solvent in step S2 is 1 g: 5 mL; The ball milling speed in step S2 is 400 rpm, and the ball milling time is 10 h; The amount of melamine added in step S1 is 10.0 g.

2. The preparation method of organic small molecule modified nano-carbon nitride according to claim 1, characterized in that, In step S1, the calcination heating rate is 2.5 °C / min, the calcination temperature is 550 °C, and the constant temperature time is 2 h.

3. The preparation method of organic small molecule modified nano-carbon nitride according to claim 1, characterized in that, In step S3, a water bath heating method is used for drying, and the temperature of the water bath heating is 40-95 °C.

4. An organic small molecule modified nano-carbon nitride prepared by the preparation method according to claim 1 or 2.

5. An application of the organic small molecule modified nano-carbon nitride according to claim 4 in photocatalytic removal of pollutants in water.

6. The application of the organic small molecule modified nano-carbon nitride according to claim 5 in photocatalytic removal of pollutants in water, characterized in that, The pollutants in the water body include organic dyes and heavy metal ions.

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