Preparation method of monodisperse nano carbon nitride material

Abstract

The invention discloses a preparation method of monodisperse nano carbon nitride, which comprises the following steps: (1) carrying out prepolymerization treatment on a polymer carbon nitride (PCN) precursor to obtain a prepolymerized PCN intermediate; and (2) uniformly mixing the prepolymerized PCN intermediate and a template agent, carrying out roasting treatment in an inert atmosphere, and then removing the template agent to obtain the monodisperse nano carbon nitride. The monodisperse nano carbon nitride is prepared by adopting a step-by-step pyrolysis and mechanical ball milling method and regulating and controlling the polymerization degree of a precursor and the use amount of a template agent. The preparation method is simple and low in raw material cost, and has a certain application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic material preparation, and specifically relates to a method for preparing a monodisperse nano carbon nitride material. Background Art

[0002] In the past few decades, the research hotspots in the field of photocatalysis have mainly focused on traditional inorganic semiconductor photocatalysts (TiO2, CdS, etc.). A large number of basic studies based on these photocatalysts have laid a solid foundation for the exploration of photocatalytic reaction mechanisms (light absorption, charge separation and transfer, surface reaction) and the design of high-performance photocatalysts. However, the problems of inorganic semiconductor photocatalysts in terms of light absorption efficiency, toxicity and photocorrosion have restricted their further development. In 2009, Wang et al. [Nat. Mater., 2008, 8, 76-80] first reported that graphite phase carbon nitride has visible light photocatalytic activity for hydrogen production from water, opening a new chapter in the field of carbon nitride materials in the field of photocatalysis. Carbon nitride has the advantages of high nitrogen content, good physical and chemical stability, and suitable band gap. It can be widely used in various photocatalytic reactions and as a metal catalyst carrier. The preparation method of carbon nitride is very simple, and it can be prepared on a large scale by pyrolysis of high nitrogen-containing organic small molecule precursors. However, the carbon nitride synthesized by this traditional pyrolysis method is usually in bulk form, with low specific surface area, low light absorption and carrier separation efficiency, resulting in very limited photocatalytic activity, which greatly restricts its practical application.

[0003] As an organic semiconductor material, carbon nitride has good tunability in structure, and the regulation of carbon nitride nanostructure plays an important role in enhancing light absorption and photogenerated carrier separation efficiency, and can provide more reactive sites. The hard template method is one of the effective means to prepare carbon nitride with special nanostructure or special morphology. This method usually uses nitrogen-rich organic matter with high solubility as a precursor (such as monocyanamide, dicyandiamide, etc.), which is dissolved in a solvent and then pre-cast with a template. The precursor is converted into carbon nitride through thermal decomposition and polymerization, and then the template is removed to obtain a carbon nitride material with a specific morphology. For example, Zhang et al. [Adv. Mater., 2014, 26, 4121-4126] reported a method for preparing carbon nitride nanospheres, which was obtained by pre-casting the precursor and silica spheres, and then undergoing thermal decomposition and polymerization and template removal to obtain carbon nitride nanospheres with a particle size of about 300nm, which improved its optical properties and photocatalytic performance. However, this method has strict requirements on the solubility of the precursor, and the subsequent preparation process is complicated and cumbersome. The subsequent removal of the template will use fluorine-containing toxic substances, which will cause environmental pollution. Therefore, it is of great research significance to develop simple and green synthesis methods to prepare carbon nitride photocatalytic materials with special morphology. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing monodisperse nano carbon nitride, which adopts a step-by-step pyrolysis and mechanical ball milling method, and prepares monodisperse nano carbon nitride by regulating the degree of polymerization of the precursor and the amount of the template agent. The preparation method is simple, has low raw material cost, and has certain application prospects.

[0005] The method for preparing monodisperse nano carbon nitride of the present invention comprises the following contents:

[0006] (1) prepolymerizing a polymer carbon nitride (PCN) precursor to obtain a prepolymerized PCN intermediate; (2) uniformly mixing the prepolymerized PCN intermediate and a template, calcining the mixture under an inert atmosphere, and then removing the template to obtain monodispersed nano carbon nitride.

[0007] In the method of the present invention, the PCN precursor in step (1) is selected from one or more of melamine, dicyandiamide, monocyanamide, urea and thiourea.

[0008] In the method of the present invention, the prepolymerization treatment temperature in step (1) is 250-550° C., and the prepolymerization treatment time is 1-5 hours.

[0009] In the method of the present invention, the template described in step (2) is a soluble metal salt, which can be one or more of NaCl, LiCl, KCl, CsCl, ZnCl2, MgCl2, GaCl2, BaCl2, preferably one or more of NaCl, LiCl, KCl and ZnCl2.

[0010] In the method of the present invention, the mass ratio of the prepolymerized PCN intermediate to the template agent in step (2) is 1:1-20, preferably 5-10.

[0011] In the method of the present invention, the mixing method in step (2) is mechanical ball milling, and the mixing time is generally 1 to 5 hours.

[0012] In the method of the present invention, the roasting temperature in step (2) is 480-620° C., and the roasting time is 1-5 hours.

[0013] In the method of the present invention, the method of removing the template agent in step (2) is generally to wash with water, and the metal salt is dissolved and removed by washing with a solvent, and the solvent can be water and / or an alcohol solvent. For example, the monodispersed nano-carbon nitride can be obtained by centrifugation after washing with water and then drying. The drying temperature is 60 to 120° C., and the drying time is 4 to 12 hours.

[0014] The particle size of the nano carbon nitride prepared by the method of the present invention is 10 to 800 nm, preferably 30 to 400 nm. The nano carbon nitride prepared by the method of the present invention is used in biological phototherapy and photocatalytic reaction.

[0015] The present invention constructs a step-by-step pyrolysis strategy, in which a PCN precursor is prepolymerized at a certain temperature to obtain a prepolymerized PCN intermediate, the prepolymerized PCN intermediate and a water-washable template are fully mixed, and the uniformly mixed mixture is then placed in a tubular furnace for calcination, so that the polymer intermediate is further fully polymerized in the presence of the template to obtain a solid powder, and then the template is removed by washing with water to obtain monodisperse nano carbon nitride.

[0016] The beneficial effects of the present invention are as follows: the step-by-step pyrolysis strategy includes two processes: PCN precursor prepolymerization and high-temperature pyrolysis. The prepolymerization stage mainly causes the nitrogen-containing small molecule precursor to undergo a preliminary polymerization reaction to form a PCN intermediate with a certain degree of polymerization. The PCN intermediate and the template agent mixture are further polymerized at high temperature to obtain a higher yield of nano-carbon nitride. If the nitrogen-containing small molecule precursor and the template agent mixture are directly calcined at high temperature, no nitride will be generated or the amount generated will be too low. And this method uses a water-washable metal salt as a template, avoiding the problem that the subsequent template removal process of the hard template method uses fluorine-containing toxic substances to cause environmental pollution. The preparation method of the present invention is simple, the raw material cost is low, and the synthesized nano-carbon nitride particles have good dispersibility, and are expected to be used in biophototherapy, various high-efficiency photocatalytic reactions, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image of carbon nitride A prepared in Example 1 of the present invention.

[0018] Figure 2 This is a SEM image of carbon nitride E prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in more detail below through specific embodiments, but the present invention is not limited to these embodiments.

[0020] Monodisperse nano-carbon nitride characterization experiment: Scanning electron microscopy (SEM) SEM was used to observe the dispersibility of nano-carbon nitride. The scanning electron microscope models were SU8200 cold field electron microscope and S-5500 scanning electron microscope of Hitachi Company of Japan. The accelerating voltages were 5KV and 3KV respectively. The sample preparation method was as follows: the sample powder was dispersed in ethanol, and then a proper amount of suspension was sucked and dropped onto the silicon wafer with a capillary. After the ethanol was completely evaporated, the silicon wafer was glued to the conductive glue for later use.

[0021] Example 1

[0022] Carbon nitride A is synthesized by the preparation method of the present invention: 10 g of PCN precursor (melamine) is put into a muffle furnace, pre-baked at 400° C. for 3 h, and naturally cooled to obtain a PCN intermediate; 2 g of the PCN intermediate and 12 g of NaCl are weighed, ball-milled in a ball mill for 2 h, and then put into a tubular furnace, and calcined at 550° C. for 5 h (heating rate of 5° C. / min) under an argon atmosphere, and naturally cooled to obtain a solid powder; the solid powder is ultrasonically washed with water for 2 hours, and centrifugally washed with water 4 times to obtain carbon nitride A.

[0023] Example 2

[0024] The preparation method of carbon nitride B is the same as that of Example 1, except that 10 g of PCN precursor (melamine) is replaced by 20 g of PCN precursor (dicyandiamide), and 12 g of NaCl is replaced by 12 g of KCl to obtain carbon nitride B.

[0025] Example 3

[0026] The preparation method of carbon nitride C is the same as that of Example 1, except that 12 g of NaCl is replaced by 8 g of NaCl to obtain carbon nitride C.

[0027] Example 4

[0028] The preparation method of carbon nitride D is the same as that of Example 1, except that the pre-calcination at 400°C for 3h is changed to the pre-calcination at 300°C for 3h, and 12g NaCl is changed to 8g ZnCl2 to obtain carbon nitride D.

[0029] Comparative Example 1

[0030] The preparation method of carbon nitride E is the same as that of Example 1, except that 12 g of NaCl is replaced by 0 g of NaCl to obtain carbon nitride E.

[0031] Comparative Example 2

[0032] The preparation method of carbon nitride F is the same as that of Example 1, except that the pre-baking at 400° C. for 3 h is changed to the pre-baking at 150° C. for 3 h, to obtain carbon nitride F.

[0033] Comparative Example 3

[0034] Preparation of carbon nitride G: Take 2g PCN precursor (monocyanamide) and 12g NaCl, ball mill in a ball mill for 1h, then put into a tubular furnace, calcine at 600℃ for 5h (heating rate 5℃ / min) under argon atmosphere, cool naturally to obtain solid powder, and no carbon nitride product is obtained after washing with water.

[0035] Table 1 Average particle size of nano carbon nitride particles

[0036] catalyst Average particle size range (nm) Carbon Nitride A 55-140 Carbon Nitride B 33-90 Carbon Nitride C 100-180 Carbon Nitride D 150-400 Carbon Nitride E Irregular blocks Carbon Nitride F Irregular blocks Carbon Nitride G －

[0037] As attached Figure 1 As shown in Table 1, the average particle size of the nano carbon nitride particles prepared by the step-by-step pyrolysis strategy combined with the mechanical ball milling method of Example 1 is in the range of 55 to 140 nm, and the nanoparticles are highly dispersed. Figure 2 As shown, in Comparative Example 1, no water-washable metal salt template is added. Even if the PCN intermediate is ball-milled and then pyrolyzed, only irregular bulk carbon nitride of micrometer size can be obtained. As described in Comparative Example 2, if the step-by-step pyrolysis strategy is not adopted, and the nitrogen-containing small molecule precursor is directly mixed with the template agent and then pyrolyzed at high temperature, no carbon nitride product is formed. This is mainly due to the fact that the nitrogen-containing small molecule precursor is easily decomposed / volatized at high temperature. This shows that the preparation method of the present invention can successfully prepare monodisperse nano carbon nitride particles.

Claims

1. A method for preparing monodisperse nanocarbon nitride, characterized in that The method comprises the following contents: (1) prepolymerizing a polymer carbon nitride (PCN) precursor to obtain a prepolymerized PCN intermediate; (2) uniformly mixing the prepolymerized PCN intermediate and a template agent, calcining the mixture under an inert atmosphere, and then removing the template agent to obtain monodispersed nano carbon nitride.

2. The method according to claim 1, characterized in that: The PCN precursor described in step (1) is selected from one or more of melamine, dicyandiamide, monocyanamide, urea and thiourea.

3. The method according to claim 1, characterized in that: The prepolymerization treatment temperature in step (1) is 250-550° C., and the prepolymerization treatment time is 1-5 hours.

4. The method according to claim 1, characterized in that: The template described in step (2) is a soluble metal salt, which can be one or more of NaCl, LiCl, KCl, CsCl, ZnCl2, MgCl2, GaCl2, BaCl2, preferably one or more of NaCl, LiCl, KCl and ZnCl2.

5. The method according to claim 1, characterized in that: The mass ratio of the prepolymerized PCN intermediate to the template agent in step (2) is 1:1-20, preferably 5-10.

6. The method according to claim 1, characterized in that: The mixing method in step (2) is mechanical ball milling, and the mixing time is 1 to 5 hours.

7. The method according to claim 1, characterized in that: The calcination temperature in step (2) is 480-620° C., and the calcination time is 1-5 hours.

8. The method according to claim 1, characterized in that: The method of removing the template in step (2) is a solvent washing method, and the solvent is water and / or alcohol solvent.

9. A monodisperse nanocarbon nitride prepared by any method of claims 1 to 8, characterized in that: The particle size is 10 to 800 nm, preferably 30 to 400 nm.

10. Use of monodisperse nanocarbon nitride prepared by the method of any one of claims 1 to 8 in biophototherapy and photocatalytic reaction.

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