Photocatalyst based on carbon nitride covalent grafted ionic liquid and preparation method thereof

Abstract

The invention discloses a photocatalyst based on carbon nitride covalent grafted ionic liquid and a preparation method thereof, and belongs to the technical field of photocatalyst preparation, the preparation method comprises the following steps: mixing carbon nitride and NH4Cl, and calcining to obtain polyamino carbon nitride; the preparation method comprises the following steps: co-grinding the polyamino carbon nitride and the carboxyl-containing ionic liquid, adding a solvent into the ground powder, and heating until the solvent is evaporated, thereby obtaining the product. According to the photocatalyst, the electron transfer capability of imidazolium ionic liquid is utilized, separation of photo-generated charge carriers is promoted, compounding is inhibited, a stable chemical bonding interface is constructed through condensation of amine functionalized carbon nitride free-NH2 groups and carboxyl-OH groups of the ionic liquid, and the problems existing in the prior art are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and in particular relates to a photocatalyst based on carbon nitride covalently grafted ionic liquid and a preparation method thereof. Background Art

[0002] With the rapid advancement of industrialization and urbanization and the continuous growth of the global population, environmental pollution and resource shortages have become key bottlenecks restricting sustainable development. In this context, the development of new clean and renewable energy systems is particularly urgent. Photocatalytic technology is considered to be one of the effective ways to solve the above problems because it can directly use solar energy for environmental governance and energy conversion, and has significant advantages such as simple operation, environmental friendliness, and low cost. Among the many semiconductor photocatalysts, non-metallic graphite phase carbon nitride (g-C3N4) has attracted much attention due to its suitable band gap structure (about 2.7eV), good visible light response characteristics, excellent chemical stability and environmental friendliness. However, this material still has inherent defects such as insufficient light absorption efficiency, fast photogenerated carrier recombination rate, and low quantum efficiency, which seriously restrict its practical application performance. Summary of the Invention

[0003] In response to the above-mentioned deficiencies in the prior art, the present invention provides a photocatalyst based on covalently grafted carbon nitride ionic liquid and a preparation method thereof. The photocatalyst utilizes the ability of imidazolium ionic liquid to transfer electrons to promote the separation of photogenerated charge carriers and inhibit recombination. By condensing the free -NH2 groups of amine-functionalized carbon nitride with the carboxyl -OH groups of the ionic liquid, a stable chemical bonding interface is constructed, which effectively solves the problems existing in the prior art.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0005] A method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid comprises the following steps:

[0006] (1) Mixing carbon nitride with NH4Cl and calcining to obtain polyamino carbon nitride;

[0007] (2) Grinding polyamino carbon nitride with carboxyl-containing ionic liquid, adding solvent to the ground powder and heating until the solvent evaporates to obtain the product.

[0008] Furthermore, the carbon nitride preparation method in step (1) is as follows: melamine and urea are ground and mixed, and then heated to 200-600°C at a rate of 2-10°C / min under an inert atmosphere, and calcined for 2-5h to obtain the carbon nitride.

[0009] Furthermore, in step (1), the mass ratio of carbon nitride to NH4Cl is 1:1-8.

[0010] Furthermore, in step (1), the calcination temperature is 200-600° C., the heating rate is 2-10° C. / min, and the calcination time is 1-5 h.

[0011] Furthermore, in step (2), the mass molar ratio of polyamino carbon nitride to carboxyl-containing ionic liquid is 0.1 g:0.01-0.1 mmol, and the grinding time is 20-120 min.

[0012] Furthermore, the heating temperature in step (2) is 60-120°C.

[0013] Furthermore, in step (2), the solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol or ethylene glycol.

[0014] Furthermore, the carboxyl-containing ionic liquid in step (2) is an imidazolium ionic liquid.

[0015] A photocatalyst based on carbon nitride covalently grafted ionic liquid is prepared by the above method.

[0016] 1. In step (1) of the present invention, carbon nitride is calcined twice with NH4Cl. The thermal decomposition of the ammonium salt produces reactive NH3 and HCl vapors. This gas phase treatment induces the rupture of the interlayer N-ridge bond and introduces terminal amino groups (-NH2), thereby producing amine-functionalized carbon nitride with enhanced surface reactivity, preparing for subsequent ionic liquid grafting; in step (2), the free -NH2 group of the amine-functionalized carbon nitride condenses with the carboxyl -OH group of the imidazolium ionic liquid to finally produce a photocatalyst. Imidazolium ionic liquid is grafted on the edge of g-C3N4, and the ability of imidazolium ionic liquid to transfer electrons is utilized to promote the separation of photogenerated charge carriers and inhibit recombination. A stable chemical bonding interface is constructed through condensation of the free -NH2 groups of amine-functionalized carbon nitride with the carboxyl -OH groups of the ionic liquid. This not only solves the problem of ionic liquid leaching in traditional modifications, but also provides an efficient directional transmission channel for photogenerated carriers, better solving the problems of poor visible light response of graphitic carbon nitride and easy recombination of photogenerated electrons and holes.

[0017] 2. The preparation method of the photocatalyst of the present invention has the advantages of simple synthesis steps, short reaction time, mild conditions and convenient operation; the prepared photocatalyst has a high conversion rate and production rate for the oxidative dehydrogenation reaction of imines. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FT-IR spectra of the sample obtained in Example 1 and the carboxyl-containing ionic liquid;

[0019] Figure 2 is the solid fluorescence spectrum of the sample obtained in Example 1;

[0020] Figure 3 is the transient photocurrent curve of the sample obtained in Example 1;

[0021] Figure 4 This is a diagram showing the experimental results of photocatalytic secondary amine oxidative dehydrogenation of the sample obtained in Example 1. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, rather than all embodiments.

[0023] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0024] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0025] The features and performance of the present invention are further described in detail below with reference to the embodiments and drawings.

[0026] Example 1

[0027] A photocatalyst based on carbon nitride covalently grafted ionic liquid, the preparation method of which comprises the following steps:

[0028] (1) 2.5 g of melamine and 2.5 g of urea were ground and mixed, and the mixture was placed in a porcelain boat, placed in a tube furnace, and then heated to 550 ° C at a rate of 5 ° C / min under a nitrogen atmosphere, calcined for 4 h, and cooled to room temperature to obtain carbon nitride (CN); 0.8 g of carbon nitride was mixed with 1.6 g of NH4Cl and ground and mixed, and placed in a porcelain boat, placed in a tube furnace, and heated to 480 ° C at a rate of 2 ° C / min, held for 2 h, and cooled to room temperature to obtain polyamino carbon nitride (ACN);

[0029] (2) 0.1 g of polyamino carbon nitride was mixed with 0.075 mmol of [PhCEIm][BPh4] ionic liquid and ground thoroughly in a mortar for 30 min. The mixture was then transferred to a round-bottom flask containing 15 ml of methanol. The mixture was continuously stirred at 90 °C until the solvent evaporated and cooled to room temperature to prepare a photocatalyst (ILCN).

[0030] Example 2

[0031] A photocatalyst based on carbon nitride covalently grafted ionic liquid, the preparation method of which comprises the following steps:

[0032] (1) 2.5 g of melamine and 2.5 g of urea were ground and mixed, and the mixture was placed in a porcelain boat, placed in a tube furnace, and then heated to 550 ° C at a rate of 5 ° C / min under a nitrogen atmosphere, calcined for 4 h, and cooled to room temperature to obtain carbon nitride (CN); 0.8 g of carbon nitride was mixed with 3.2 g of NH4Cl and ground and mixed, and placed in a porcelain boat, placed in a tube furnace, and heated to 420 ° C at a rate of 6 ° C / min, held for 2 h, and cooled to room temperature to obtain polyamino carbon nitride (ACN);

[0033] (2) 0.1 g of polyamino carbon nitride was mixed with 0.01 mmol of [PhCEIm][Br] ionic liquid and ground thoroughly in a mortar for 30 min. The mixture was then transferred to a round-bottom flask containing 15 ml of methanol. The mixture was continuously stirred at 60 °C until the solvent evaporated and cooled to room temperature to prepare the photocatalyst (ILCN-Br).

[0034] Example 3

[0035] A photocatalyst based on carbon nitride covalently grafted ionic liquid, the preparation method of which comprises the following steps:

[0036] (1) 2.5 g of melamine and 2.5 g of urea were ground and mixed, and the mixture was placed in a porcelain boat, placed in a tube furnace, and then heated to 550 ° C at a rate of 5 ° C / min under a nitrogen atmosphere, calcined for 4 h, and cooled to room temperature to obtain carbon nitride (CN); 0.8 g of carbon nitride was mixed with 6.4 g of NH4Cl and ground and mixed, and placed in a porcelain boat, placed in a tube furnace, and heated to 520 ° C at a rate of 8 ° C / min, held for 2 h, and cooled to room temperature to obtain polyamino carbon nitride (ACN);

[0037] (2) 0.1 g of polyamino carbon nitride was mixed with 0.1 mmol of [VCEIm][BPh4] ionic liquid and ground thoroughly in a mortar for 100 min. The mixture was then transferred to a round-bottom flask containing 15 ml of methanol. The mixture was continuously stirred at 100 °C until the solvent evaporated and cooled to room temperature to prepare the photocatalyst (ILCN-V).

[0038] Test example

[0039] Taking the product prepared in Example 1 as an example, the obtained ACN and ILCN samples were subjected to secondary amine oxidative dehydrogenation reaction to determine the photocatalytic performance of the prepared samples. The specific test process is as follows:

[0040] At room temperature, 10 mg of photocatalyst, 0.15 mmol of secondary amine and 10 ml of acetonitrile were mixed and sealed in a 20 mL quartz photoreactor. Initially, the mixture was stirred in the dark for 30 min to reach adsorption-desorption equilibrium. Subsequently, the reaction was carried out at 30°C, under a 300 W xenon lamp and an oxygen atmosphere. After the reaction, an internal standard substance (chlorobenzene) was added to the mixture, and the photocatalyst was separated by centrifugation. Finally, the filtrate was analyzed by gas chromatography (GC, Agilent 7890A), and the product was identified by comparing its retention time with that of the standard sample, and the yield of the product was determined. The specific results are shown in the accompanying drawings.

[0041] Figure 1 The Fourier transform infrared spectra of the obtained [PhCEIm][BPh4], ILCN, and ACN.

[0042] It can be seen that in [PhCEIm][BPh4] 744cm -1 and 711cm -1 The peaks at 3000-3500 cm correspond to the fingerprint peaks of monosubstituted benzene rings, and these characteristic peaks still exist in the newly formed ILCN. -1The vibration peaks in the range are weaker than those in ACN, indicating that the carboxyl groups on the ionic liquid condense with the amino groups on the ACN, resulting in a reduction in the amino groups (the mass of ACN is used as the basis for the quantitative analysis of ACN and ILCN). -1 The carboxyl C=O peak obviously disappeared in ILCN, and the peak at 1680 cm-1 corresponded to the amide bond, which coincided with the stretching vibration peak of the aromatic CN heterocycle of ACN, further confirming that [PhCEIm][BPh4] was successfully modified onto ACN by amidation.

[0043] Figure 2 Solid-state fluorescence spectra of ACN and ILCN photocatalysts; it can be seen that the fluorescence intensity of ILCN after ionic liquid grafting is significantly lower than that of ACN, indicating that the recombination rate of photogenerated electron-hole pairs is the lowest and the carrier separation is the most effective.

[0044] Figure 3 Figure 2 shows the transient photocurrent spectra of ACN and ILCN photocatalysts. It can be seen that the photocurrent intensity of the ILCN sample after ionic liquid grafting is higher than that of the original ACN, indicating that ILCN has faster charge carrier transfer and higher separation of photogenerated electron-hole pairs.

[0045] Figure 4 The results of the oxidative dehydrogenation reaction of secondary amines using ACN and ILCN photocatalysts are shown in the figure. It can be seen that the yield of the ILCN sample after ionic liquid grafting is significantly higher than that of ACN. This is because the ionic liquid grafting can accelerate the charge carrier transfer and inhibit the electron-hole recombination.

Claims

1. A method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid, characterized in that: The following steps are involved: (1) Mixing carbon nitride with NH4Cl and calcining to obtain polyamino carbon nitride; (2) Grinding polyamino carbon nitride with carboxyl-containing ionic liquid, adding solvent to the ground powder and heating until the solvent evaporates to obtain the product.

2. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, characterized in that: The carbon nitride preparation method in step (1) is as follows: melamine and urea are ground and mixed, and then heated to 200-600°C at a rate of 2-10°C / min under an inert atmosphere, and calcined for 2-5h to obtain the carbon nitride.

3. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: The mass ratio of carbon nitride to NH4Cl in step (1) is 1:1-8.

4. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: In step (1), the calcination temperature is 200-600° C., the heating rate is 2-10° C. / min, and the calcination time is 1-5 h.

5. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: In step (2), the mass molar ratio of polyamino carbon nitride to carboxyl-containing ionic liquid is 0.1 g:0.01-0.1 mmol, and the grinding time is 20-120 min.

6. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: The heating temperature in step (2) is 60-120°C.

7. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: The solvent in step (2) is methanol, ethanol, n-propanol, isopropanol, n-butanol or ethylene glycol.

8. The method for preparing a photocatalyst based on carbon nitride covalently grafted ionic liquid according to claim 1, wherein: The carboxyl-containing ionic liquid in step (2) is an imidazolium ionic liquid.

9. A photocatalyst based on carbon nitride covalently grafted ionic liquid, characterized in that: Prepared by the method according to any one of claims 1 to 8.

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