KR20240007858A - Graphitized carbon nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation and method for synthesizing the same - Google Patents

Abstract

The present invention relates to a graphitic carbon nitride nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, characterized by high yield and photocatalytic efficiency using melamine and ammonium chloride, and a method for synthesizing the same. , When synthesizing graphitic carbon nitride using melamine, ammonium chloride (NH ₄ Cl) is used as a dynamic gas template in a solid process to form micropores in graphitic carbon nitride, which is synthesized by heat during polymerization of melamine. The graphite carbon nitride bulk is exfoliated into nanosheets by the gas generated by the decomposition of ammonium chloride (NH ₄ Cl) that has penetrated between the graphite carbon nitride bulk, making it possible to manufacture graphite carbon nitride nanosheets with high yield by a simple method. It is possible and has the effect of showing excellent photocatalytic performance for the decomposition of rhodamine B under visible light irradiation.

Description

Graphitized carbon nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation and method for synthesizing the same}

The present invention relates to a graphitic carbon nitride nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, characterized by high yield and photocatalytic efficiency using melamine and ammonium chloride, and a method for synthesizing the same. .

Today, the growth of industry and the improvement of people's living standards are causing problems such as lack of energy and polluting the environment, and photocatalyst technology is a potential technology for decomposing organic pollutants and generating hydrogen, and is a solution to many of these problems. It is attracting attention.

Since the production of hydrogen by decomposition of water using titanium dioxide (TiO ₂ ) was known in 1972 through a report by Fujishima and Honda, titanium dioxide (TiO ₂ ) has been used as a non-toxic and water _- soluble substance. Much research has been conducted to use titanium dioxide (TiO ₂ ) as a photocatalyst because it has many advantages such as insolubility, hydrophilicity, cheapness, and stability. However, titanium dioxide (TiO ₂ ) has the property of absorbing only ultraviolet rays, so it does not absorb visible light or solar radiation. There was a problem that limited the application of TiO ₂ to the actual environment under light irradiation.

Meanwhile, graphitic carbon nitride (gC ₃ N ₄ ), a compound that can replace the function of titanium dioxide (TiO ₂ ), is a photocatalyst material that has good thermal and chemical stability and a narrow band gap that can react even in visible light. However, the recombination rate of electron/hole pairs was large, limiting its use as a photocatalyst.

In particular, the photocatalytic activity of graphitic carbon nitride (gC ₃ N ₄ ) bulk has low photocatalytic efficiency due to its small surface area, fast electron-hole pair recombination rate, and low electrical conductivity. By overcoming these shortcomings, graphitic carbon nitride (gC ₃ N ₄ ), various studies are being attempted to increase the specific surface area of graphitic carbon nitride (gC ₃ N ₄ ) to improve the photocatalytic performance.

As known in Non-Patent Document 1, Zhang et al. successfully manufactured graphite carbon nitride nanosheets by water exfoliation of graphite carbon nitride bulk, but this manufacturing method involves manufacturing graphite carbon nitride in bulk and then There was a problem with the method of peeling it again and manufacturing it into nanosheets, which required a complicated process.

And Dong et al. manufactured graphitic carbon nitride nanosheets by directly heat-treating urea by extending the residence time, as known in Non-Patent Document 2. Although urea is a low-cost and active precursor for synthesizing graphitic carbon nitride nanosheets, the yield There was a problem that it could not be applied on a large scale due to its poor quality.

In addition, He et al., in Non-Patent Document 3, proposed a method of producing porous graphitic carbon nitride by heat condensation of melamine using sublimated sulfur as a soft template, and numerous methods were used to produce graphitic carbon nitride nanosheets. Although research has been used, most current methods often suffer from low yield and time consuming problems, and new methods to prepare graphitic carbon nitride nanosheets with high yield and high photocatalytic efficiency are still required.

In addition, Patent Document 1 proposes a method of manufacturing porous sulfur-doped graphitic carbon nitride nanosheets for use in the selective detection of silver ions and photocatalytic decomposition of organic materials using urea and thiourea. there is.

Accordingly, the present inventors completed the present invention by synthesizing graphitic carbon nitride nanosheets with high yield and high photocatalytic efficiency using melamine and ammonium chloride as a solution to the conventional problems described above.

Domestic Registered Patent Publication No. 10-2333766 (announced on November 30, 2021) Porous sulfur-doped graphite carbon nitride nanosheet for use in selective detection of silver ions and photocatalytic decomposition of organic materials and method for manufacturing the same

X. Zhang, X. Xie, H. Wang, J. Zhang, B. Pan, and Y. 135, no. 1, pp. 18-21, Jan. 2013, doi: 10.1021/ja308249k. F. Dong, Z. Wang, Y. Sun, W. K. Ho, and H. Zhang, "Engineering the nanoarchitecture and texture of polymeric carbon nitride semiconductor for enhanced visible light photocatalytic activity," Journal of Colloid and Interface Science, vol. 401, pp. 70-79, Jul. 2013, doi: 10.1016/j.jcis.2013.03.034. F. He, G. Chen, Y. Yu, Y. Zhou, Y. Zheng, and S. Hao, "The sulfur-bubble template-mediated synthesis of uniform porous g-C3N4 with superior photocatalytic performance," Chemical Communications, vol. . 51, no. 2, pp. 425-427, Jan. 2015, doi: 10.1039/c4cc07106a.

The present invention uses ammonium chloride (NH ₄ Cl) as a dynamic gas template in a solid process during the synthesis of graphitic carbon nitride using melamine to form fine pores in the graphitic carbon nitride, thereby forming the graphite carbon nitride by heat during polymerization of melamine. Visible light characterized in that the graphite carbon nitride bulk is exfoliated into nanosheets by the gas generated by decomposition of ammonium chloride (NH ₄ Cl) that penetrates between the synthesized graphite carbon nitride bulk, resulting in high yield and photocatalytic efficiency. The object is to provide graphitic carbon nitride nanosheets with excellent photocatalytic performance for rhodamine B decomposition under irradiation and a method for synthesizing the same.

In order to achieve the above problem, the method for synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation according to a preferred embodiment of the present invention is to pulverize the precursor compound and the template compound to obtain a mixture powder. Processing step (P100); Processing the mixture powder into a fired powder by heat treatment (P200); And, a post-processing step (P300) of cooling, grinding, washing, and drying the fired powder.

And the graphitic carbon nitride nanosheet according to another preferred embodiment of the present invention is characterized in that it is manufactured by the above method using a precursor compound and a template compound.

In addition, the present invention is characterized in that in the P100 step, 100 to 120 parts by weight of the template compound are mixed with 100 parts by weight of the precursor compound.

Meanwhile, in the above, the precursor compound is melamine (C ₃ N ₆ H ₆ ), and the template compound is ammonium chloride (NH ₄ Cl).

In the P200 step, heat treatment is performed at a temperature of 520 to 580 ℃ for 2.5 to 3.5 hours, and in the P300 step, drying is performed at 85 to 95 ℃ for 10 to 14 hours. .

Graphite carbon nitride (gC ₃ N ₄ ) nanosheets with improved photocatalytic performance for the decomposition of rhodamine B under visible light irradiation according to the present invention are ammonium chloride (NH ₄ Cl) during the synthesis of graphite carbon nitride using melamine. By using it as a dynamic gas template in the solid process to form fine pores in graphite carbon nitride, ammonium chloride (NH ₄ Cl) that penetrates between the bulk of graphite carbon nitride synthesized by heat decomposes during the polymerization of melamine. The graphite carbon nitride bulk is exfoliated into a nanosheet state by the gas, making it possible to produce graphite carbon nitride nanosheets with high yield by a simple method, and showing excellent photocatalytic performance for rhodamine B decomposition under visible light irradiation. It works.

1 is a process block diagram showing the manufacturing process of graphitic carbon nitride nanosheets according to a preferred embodiment of the present invention.
Figure 2 is a TEM image of a graphite carbon nitride nanosheet (ECN) according to a preferred embodiment of the present invention and a graphite carbon nitride bulk (BCN) as a comparative example.
Figure 3 (A) is a graph showing the XRD pattern of the example (ECN) and the comparative example (BCN), and (B) is a graph showing the FITR spectrum of the example (ECN) and the comparative example (BCN).
Figure 4 (A) is a graph showing the UV-visible absorption spectra of Example (ECN) and Comparative Example (BCN), and (B) the estimated band gap of Example (ECN) and Comparative Example (BCN).
Figure 5 is a graph showing the steady-state PL spectra of the example (ECN) and the comparative example (BCN).
In Figure 5, (A) is the photocatalyzed decomposition of RhB according to the example (ECN) and the comparative example (BCN), (B) is the primary kinetic curve for photodecomposition of RhB under visible light, and (C) is the decomposition at various times. This is a graph showing the UV-vis spectrum of the RhB solution decomposed by Example (ECN) at intervals.
Figure 7 (A) shows the effect of catalyst dosage on the removal efficiency RhB under visible light, (B) shows the effect of initial dye concentration on the removal efficiency RhB under visible light, and (C) shows the effect of pH on the removal efficiency under visible light. This graph shows each effect on RhB.
Figure 8 (A) is a graph showing the photodecomposition efficiency of the example (ECN) over 4 cycles, and (B) is a graph showing the XRD patterns of the example (ECN) before and after the above process.
Figure 9 (A) is a graph showing the photocatalytic decomposition efficiency of RhB for the example (ECN) by adding another reactive species remover under visible light irradiation, and (B) is a graph showing the preferred embodiment of the present invention when exposed to visible light. This is a diagram to explain the RhB decomposition mechanism using graphitic carbon nitride nanosheets.

Hereinafter, a graphitic carbon nitride nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation and a method for synthesizing the same according to a preferred embodiment of the present invention have been described in detail based on the attached drawings. Meanwhile, in each drawing and detailed description, illustrations and references to structures and operations that can be easily recognized by those in the field of general visible light-sensitive photocatalyst manufacturing are simplified or omitted.

Among the terms described in the specification of the present invention, the terms 'manufacture' and 'synthesis', which are used in the production of compounds, are terms used with the same meaning, and should be used interchangeably to ensure a natural flow of context in the description of the specification. shall.

The graphitic carbon nitride nanosheet (hereinafter referred to as 'graphitic carbon nitride nanosheet') with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation according to a preferred embodiment of the present invention is shown in FIG. 1. Likewise, it is manufactured by a heat treatment method, and specifically, the step of pulverizing the precursor compound and the template compound and processing it into a mixture powder (P100); Processing the mixture powder into a fired powder by heat treatment (P200); And, a post-processing step (P300) of cooling, grinding, washing, and drying the fired powder.

Hereinafter, the method of synthesizing graphitic carbon nitride (gC ₃ N ₄ ) nanosheets will be described in detail step by step as follows.

The mixture powder processing step (P100) is a step of pulverizing the mixture of the precursor compound (F1) and the template compound (F2) and processing it into a mixture powder. In this step, the mixture is crushed in an agate mortar for 10 to 20 minutes. Grind for minutes.

In this step, first, equal amounts of melamine, a precursor compound (F1), and ammonium chloride, a template compound (F2), are mixed in an agate mortar, and complete mixing of melamine and ammonium chloride is a very important process in the present invention.

The precursor compound (F1) is specifically melamine (C ₃ N ₆ H ₆ ), which is a compound for synthesizing graphitic carbon nitride (gC ₃ N ₄ ) as shown in Structural Formula 1 below.

And the template compound (F2) is specifically ammonium chloride (NH ₄ Cl), which exists as a white crystalline solid, decomposes at 350°C, sublimes at 520°C in a controlled environment, and is easily soluble in water. Therefore, it can be used as a dynamic gas mold in solid processes.

In other words, ammonia (NH ₃ ) is generated when ammonium chloride (NH ₄ Cl) penetrates into the bulk of graphite carbon nitride, which is synthesized by gas generated by decomposition of ammonium chloride (NH ₄ Cl) due to heat during polymerization of melamine. and hydrogen chloride (HCl) gas to exfoliate the graphite carbon nitride bulk into nanosheets, enabling the production of graphite carbon nitride nanosheets with high yield by a simple method.

The mixture preferably contains 100 to 120 parts by weight of the template compound (F2) based on 100 parts by weight of the precursor compound (F1). If the mixing amount of the template compound (F2) is less than 100 parts by weight, the bulk of the graphite carbon nitride is not sufficiently exfoliated, and there is a risk that the synthesis yield of the graphite carbon nitride nanosheet may decrease, and even if it exceeds 120 parts by weight, the graphite carbon nitride bulk is not sufficiently exfoliated. Since the synthesis yield of nanosheets is no longer high, an inefficient process may be performed.

In the above mixture, it is most preferable to mix melamine, which is the precursor compound (F1), and ammonium chloride, which is the template compound (F2), in the same amount, for example, mixing 100 parts by weight of ammonium chloride with 100 parts by weight of melamine.

The fired powder processing step (P200) is a step of synthesizing graphite carbon nitride in a fired state by heat-treating melamine, which is a precursor compound (F1). The mixture is placed in an aluminum crucible with a cover and heated in a heating furnace at 520 to 580°C. This is the step of cooling the product obtained by calcining at room temperature for 2.5 to 3.5 hours and then pulverizing it into powder.

If the firing conditions in this step are below the range of conditions limited above, graphitic carbon nitride is not sufficiently synthesized from melamine, the precursor compound (F1), or ammonium chloride (NH ₄ Cl), the template compound, is not properly sublimated. As a result, there is a risk that the synthesis yield of graphite carbon nitride nanosheets may decrease, and even if the range of conditions limited above is exceeded, the synthesis yield of graphite carbon nitride nanosheets does not increase any further, so an inefficient process may be performed.

The fired powder post-processing step (P300) is a processing step in which the fired powder goes through cooling, grinding, washing, and drying processes. After cooling the fired powder heated in the fired powder processing step (P200) to room temperature, , the cooled fired product powder is ground for 10 to 20 minutes using an agate mortar and processed into powder form.

The size of the powder particles processed in the mixture powder processing step (P100) and this step is not particularly limited, but is preferably 10 to 30 ㎛.

The pulverized fired powder is washed with distilled water several times to remove impurities contained in the graphite carbon nitride, and then dried in a vacuum dryer at 85 to 95°C for 10 to 14 hours to remove the remaining moisture in the graphite carbon nitride. It is preferable to do this, and the drying conditions are not particularly limited to the above conditions, and any condition that allows the moisture remaining in the graphite carbon nitride to be removed is possible.

The graphite carbon nitride in the form of a nanosheet manufactured through the process of steps P100 to P300 includes a structure shown in [Structural Formula 1] below, and has the characteristics of the graphite carbon nitride nanosheet manufactured according to a preferred embodiment of the present invention. This will be explained in detail in the examples below, and the description will be omitted here.

[Structural Formula 1]

The graphite carbon nitride nanosheet manufactured by the method described above uses melamine and ammonium chloride. When producing the graphite carbon nitride nanosheet, ammonium chloride (NH ₄ Cl) is used as a dynamic gas template in the solid process. By manufacturing, it is possible to manufacture graphitic carbon nitride nanosheets with high yield by a simple method, and is characterized by improved photocatalytic performance for rhodamine B decomposition under visible light irradiation.

Hereinafter, the method for synthesizing graphitic carbon nitride (gC ₃ N ₄ ) nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation according to the present invention is as follows, and the present invention is described in the examples below. It is not necessarily limited by .

1. Example: Synthesis of graphitic carbon nitride nanosheets

Add 100 g of melamine (C ₃ H ₆ N ₆ , 99.5%) and 100 g of ammonium chloride (NH ₄ Cl, 99.5%) into an agate mortar, grind for 10 minutes, place the mixture in an aluminum crucible with a cover, cover, and heat. It was placed in a furnace, raised at a temperature increase rate of 10°C min ^-1, heated to 550°C for 3 hours, and fired. After the fired product prepared by the above method was cooled to room temperature, the fired product was pulverized into powder using an agate mortar for 10 minutes. The ground powder was washed with distilled water several times and dried in a vacuum dryer at 90°C for 12 hours to synthesize graphitic carbon nitride nanosheets. In this example, the graphitic carbon nitride nanosheet is referred to as 'Example (ECN)'.

2. Comparative example: Synthesis of bulk graphitic carbon nitride (BCN)

Graphite carbon nitride bulk was synthesized using the same method as the synthesis method in 1 above, using only melamine (C ₃ H ₆ N ₆ , 99.5%) without using ammonium chloride. In this comparative example, the graphitic carbon nitride bulk is referred to as 'comparative example (BCN)'.

3. Characteristic test of graphitic carbon nitride

The properties of graphitic carbon nitride were determined using an X-ray diffractometer (XRD) [Rigaku (Ultima IV)] to determine the crystal structure of the sample. The morphology was measured using a transmission electron microscope [TEM, JEOL (JEM-F200)]. To investigate the chemical bonding state, a Fourier transform infrared spectrometer [Bruker (CARY 600)] was used, and the ultraviolet-visible (UV-vis) absorption spectrum of the sample was measured using a UV-visible spectrometer [JASCO (V-670)]. The photoluminescence spectrum (PL) was measured using a fluorescence spectrometer [Horiba (Fluorolog-QM)].

4. Photocatalytic activity test

To investigate the photocatalytic efficiency of all samples under visible light, the photodegradation of rhodamine B (RhB, 20 mg L1) was evaluated using a 300 W Xe-arc lamp and a 400 nm UV cutoff filter. Before turning on the light, 12.5 mg catalyst was dispersed in 25 ml RhB solution (20 mg L ^{- 1} ) and stirred magnetically. During the photocatalytic process, 1 ml of solution was taken at time intervals of (0, 15, 30, 60, 90, 150, and 210) min. The suspension was filtered using a 0.22 mm PTPE filter to remove solid particles. The decrease in concentration of the RhB solution at t was measured using a UV-vis spectrophotometer at a maximum wavelength of 554 nm, and the efficiency (H) of the organic dye was calculated by Equation 1 below.

here, is the initial concentration of RhB,

is the concentration of RhB at time t (min).

5. Active species capture experiment

The decomposition of rhodamine B [95%, Junsei Chemical Co., Ltd.] is produced in the photocatalytic process. and It is caused by active species such as, and can be detected by indirect chemical probe method. Isopropyl alcohol (IPA) [Shenzhen Dang Chemical Co., Ltd.], triethanolamine (TEA, C ₆ H ₁₅ NO ₃ , 98%, Sigma Aldrich) and p-benzoquinone (BQ, C ₆ H ₄ O ₂ , 98%) , Sigma Aldrich) and It was used as a scavenger. The experiment was performed with the same procedure as the photocatalyst experiment in the presence of chemicals. Chemical agents were added before the start of the photocatalysis experiment. Since the concentration of IPA and TEA was 0.1 M, while the concentration of BQ was 10 ^-3 M, the concentration of RhB may be difficult to determine by UV-vis spectrum where the concentration of BQ is higher.

6. Evaluation of examples (ECN) and comparative examples (BCN)

go. Characteristics of Examples (ECN) and Comparative Examples (BCN)

TEM was used to investigate the characteristics of the samples of Example (ECN) and Comparative Example (BCN). In Figure 2, (A) is a TEM (×500,000 times) of the example (ECN), and (B) is a TEM (×500,000 times) of the comparative example (BCN).

Figure 2 is a TEM image of a graphite carbon nitride nanosheet (ECN) according to a preferred embodiment of the present invention and a graphite carbon nitride bulk (BCN) as a comparative example.

The example (ECN) was found to be transparent to the electron beam due to the thinner layer than the comparative example (BCN), and it was also confirmed that the base sheet edges were rolled up to minimize the surface energy of the sheet. And the XRD pattern of the example (ECN) and the comparative example (BCN) showed two distinct diffraction peaks at about 13° and 27.4°, as shown in FIG. 3(A). These two peaks are compatible with the previously developed graphite-like hexagonal phase of graphitic carbon nitride. These peaks indicated for the as-prepared sample have the same crystal structure as graphitic carbon nitride. The lower peak corresponds to the (100) plane at approximately 13.0° and corresponds to structural stacking of tri-s-triazine units in the plane. The interlayer stacking of the conjugated aromatic system is responsible for the generally protruding peak at approximately 27.4°, which is attributed to the (002) plane. The (002) crystal plane corresponds to the sharp diffraction peak of the comparative example (BCN) at 27.45°, while the peak shifted to 27.49° in the example (ECN). This means that the gallery distance between base layer units is shortened, and it could be proven that graphitic carbon nitride nanosheets were formed during heat treatment of melamine and NH ₄ Cl.

The intensity of the peak decreases rapidly as shown in 3(A), indicating that the crystallinity of the example (ECN) is lower than that of the comparative example (BCN). In addition, the peak 100 moves downward from 12.9° to 12.7°, which is because flattening of the graphitic carbon nitride layer is promoted as the distance between holes in the plane increases. FTIR spectroscopy was performed in the range of 700-4000 cm ^-1 to investigate the surface functional groups of the examples (ECN) and comparative examples (BCN) prepared as above.

Figure 3 (A) is a graph showing the XRD pattern of the example (ECN) and the comparative example (BCN), and (B) is a graph showing the FITR spectrum of the example (ECN) and the comparative example (BCN).

In general, there is no significant difference between CN-bulk and CN-nanosheets in the characteristic FTIR spectra. These spectra confirmed that the CN-nanosheets still maintained the same chemical structure as the graphitic carbon nitride bulk. Specifically, the broad peak between 3000 cm ^-1 and 3500 cm ^-1 represents NH stretching. The set of peaks between 1200 cm ^-1 and 1600 cm ^-1 is the vibrational absorption of the aromatic CN heterocyclic unit. The sharp peak at 800 cm ^-1 is the characteristic peak of the tri-s-triazine unit, which was also confirmed in the XRD spectrum.

According to the above observations, the crystal structure and chemical composition of the synthesized graphitic carbon nitride nanosheets are generally similar to bulk graphitic carbon nitride. To study the optical performance of the examples (ECN) and comparative examples (BCN), UV-vis DRS was used. The absorption thresholds of the example (ECN) and comparative example (BCN) occur at 462 and 471 nm, as shown in Figure 4(A). This suggests that both CN bulk and CN nanosheets can be efficiently used under visible light. UV-vis DRS was used to test the optical performance of the examples (ECN) and comparative examples (BCN), and the absorption thresholds of the prepared samples (BCN and ECN) were 471 and 471, as shown in FIG. 4(A). Occurred at 462 nm. This suggests that both CN-bulk and CN-nanosheets can be used efficiently under visible light.

The band gap energy of the prepared sample was calculated based on UV-vis DRS data. The bandgap derived from the (Ahv) ^two versus photon energy plot is as shown in Figure 4(B). The band gap energies of CN-bulk and CN-nanosheets were estimated to be 2.68 eV and 2.78 eV. Different band gaps can result in different band gap levels, which can greatly affect the photooxidation and reduction abilities of graphitic carbon nitride. Although CN-nanosheets have a larger bandgap than CN-bulk, this means that CN-nanosheets have a stronger redox ability than CN-bulk.

For reference, Figure 4 (A) shows the UV-visible absorption spectrum of Example (ECN) and Comparative Example (BCN), and (B) shows the estimated band gap of Example (ECN) and Comparative Example (BCN), respectively. It's a graph.

Photoluminescence (PL) analysis was performed on the prepared samples to clarify the recombination of photogenerated electrons and holes, and the PL spectra of CN-bulk and CN-nanosheets were excited at 360 nm, as shown in Figure 5 .

For reference, Figure 5 is a graph showing the steady-state PL spectra of the example (ECN) and the comparative example (BCN).

The emission peaks of CN-bulk and CN-nanosheets are located at approximately 455 nm and 460 nm, which fit the results of DRS. Comparing the peak intensity of CN nanosheets with CN bulk, the peak intensity of CN nanosheets is much weaker, which indicates that the charge separation and transfer ability of CN nanosheets is quite good, while the radiation recombination rate of electron-hole pairs is reduced. it means.

me. Photocatalytic activity test

The photocatalytic performance of CN-nanosheets synthesized from ammonium chloride was evaluated by decomposition of rhodamine B under visible light irradiation. Figure 6(A) shows the photocatalytic activity of the prepared sample for the decomposition of Rhodamine B under visible light (≥400 nm). It can be seen that CN-nanosheets made of melamine and ammonium chloride have higher photocatalytic performance compared to bulk graphitic carbon nitride. The self-decomposition of rhodamine B in the absence of a photocatalyst is almost negligible.

After 210 min of irradiation, the decomposition percentage of rhodamine B is about 63% and 98% for graphitic carbon nitride bulk and CN-nanosheets. This means that CN-nanosheets have higher photocatalytic activity than bulk graphitic carbon nitride. UV-vis absorbance spectra were also used to show the degree of mineralization of rhodamine B during the photolysis reaction. It can be seen that under visible light irradiation, the absorption peak of rhodamine B moves from 554 nm to a shorter wavelength and the intensity decreases. In the case of CN-nanosheets, the change is much stronger than that of CN-bulk, which shows that the activity of graphitic carbon nitride nanosheets is higher, as shown in Figure 6(B).

The first-order kinetics of the photodegradation of RhB for both samples are shown in Figure 6(C). The decomposition rate constant of CN-nanosheets under visible light irradiation is 0.0211 min ^-1 , which is about 4.7 times that of CN-bulk. According to the RhB photodecomposition experiment, the photocatalytic oxidation ability of CN-nanosheets is much better than that of CN-bulk. This result is because CN-nanosheets have a larger specific surface area and longer visible light absorption range than CN-bulk.

For reference, Figure 6 (A) is the decomposition of RhB photocatalyzed by Example (ECN) and Comparative Example (BCN), (B) is the first kinetic curve for photodecomposition of RhB under visible light, (C) ) is a graph showing the UV-vis spectrum of the RhB solution decomposed by Example (ECN) at various time intervals.

(1) Effect of catalyst input

The effect of CN-nanosheets on rhodamine B decomposition was tested by adjusting the dosage of CN-nanosheets from 0.1 to 0.9 gL ^-1 in the photocatalytic reaction for 210 minutes, as shown in FIG. 7(A). The results show that as the amount of catalyst increases to 0.9 gL ^-1 , the decomposition efficiency of rhodamine B increases by almost 99%. The number of photon absorption sites increased with increasing amount of catalyst. This increased the photodegradation rate of rhodamine B.

(2) Effect of dye concentration

To find the optimal concentration (0.5 gL ^-1 used) for CN-nanosheets, the effect of initial concentration was evaluated at four concentrations: 10, 20, 30, and 40 mgL ^-1 . The results show that the percentage of photocatalytic degradation is highly dependent on the starting concentration of rhodamine B, as shown in Figure 7(B). The removal rates of rhodamine B after 210 minutes of visible light irradiation were 99.5%, 98.4%, 90.5%, and 78.1% for initial concentrations of rhodamine B of 10, 20, 30, and 40 mgL ^-1 , respectively. Meanwhile, at lower concentrations (10 mg L ^{- 1} ), the surface catalyst absorbs rhodamine B molecules and then superoxide radicals formed on the surface catalyst ( ) reacted with rhodamine B molecules. Because the concentration of rhodamine B is low, The number of is sufficient to effectively decompose the dye molecules. On the other hand, high rhodamine B concentration may lead to light shielding, ultimately limiting the generation of electron-hole pairs and the number of superoxide radicals. Additionally, at higher concentrations, dye molecules may block across the catalyst surface, reducing the photocatalytic decomposition rate.

(3) Effect of pH

The results of the experiment were investigated to determine the effect on the decomposition of rhodamine B by adjusting the pH of the dye solution, and the results are shown in Figure 7(C). The concentration of rhodamine B was maintained at 20 mgL ^-1 and the mass of the catalyst was 0.5g L ^-1 . The pH was changed to 3, 5, 7, 9 and other unadjusted values. Figure 7(C) shows the results of decomposition rate for all pH conditions. The order of removal efficiency is pH 3 > pH 5 > pH 7 > pH 9.

The reusability of catalysts is an important aspect in terms of efficiency in practical applications. Here, the reusability of CN-nanosheets was tested for 4 cycles as shown in Figure 8(A). After each experiment, the catalyst was centrifuged using a high-speed refrigerated centrifuge and washed several times with ethanol and distilled water for the next experiment. The results are as shown in Figure 8(A). As cycles were repeated, the photocatalytic efficiency of the photocatalyst decreased. The percentage removal of rhodamine B in each cycle was 98%, 95%, 88% and 84%. This result is because the catalyst is reduced during the centrifugation and washing process and the dye is absorbed onto the catalyst surface. Compared with the first cycle, the removal rate of rhodamine B in the second cycle decreased moderately and significantly in the third and fourth cycles.

To better understand the mechanism, scavenging experiments were conducted to discover the reactive species during the photocatalytic process. and For scavengers such as triethanolamine (TEA, C6H ₁₅ NO ₃ , 98%) ^, benzoquinone (BQ, C ₆ H ₄ O ₂ , 98%) and isopropyl alcohol [IPA, Samcheon Chemical Co., Ltd.] used. When the h+ scavenger TEA was added to the mixture, the decomposition efficiency of the photocatalyst decreased significantly, as shown in Figure 9(A). These changes indicate that the photogenerated hole plays an important role in the RhB degradation process. Additionally, adding BQ to the mixture significantly reduces the decomposition efficiency, Presence of reactive species is a photocatalyst for RhB degradation It shows that it is important for improving activity. Surprisingly, including IPA as a scavenger had only a slight effect on the degradation efficiency of CN-nanosheets. This result is Least active throughout the photoreaction I deduced that it was a bell.

In order to effectively remove organic pollutants in wastewater using a photocatalytic system, the concentration of scavengers such as TEA (amine-based) and IPA (hydroxyl-based) must be significantly reduced through physical or biological pretreatment. Based on trapping experiments, a mechanism for RhB decomposition in visible light using ECN was proposed, as shown in Figure 9(B). In general, the two possible pathways predicted for the degradation of RhB are the autologous photodye sensitization process and the semiconductor-mediated photodegradation process. As shown in Figure 9(B), during the photosensitization process, RhB molecules absorb visible light and undergo self-oxidative transformation to directly generate oxidized OH radicals. When RhB is irradiated with light, it emits electrons from the valence band to the conduction band, leaving RhB in an excited state (RhB*) that can be a singlet or triplet. This means that photoinduced electrons are injected into the conduction band of CN nanosheets and RhB* is converted to the radical cation RhB*+, and consequently, RhB acts as a photosensitizer. The RhB*+ radical is decomposed by itself or by the reactive oxygen species formed. The conduction band of CN nanosheets is only used at the electron acceptor level in this process, and the valence band is not used. In the semiconductor-mediated photolysis process, visible light is used to excite electrons from VB to CB of graphitic carbon nitride, leaving holes in VB. Electron-hole pairs are then created and used in oxidation and reduction processes. Peroxide radicals generated during reduction process and interacts with rhodamine B, an organic pollutant, and is converted into non-toxic compounds H ₂ O and CO ₂ .

As explained in the above embodiment, the present invention is a graphitic carbon nitride nanosheet synthesized by a thermal decomposition process of melamine and ammonium chloride, using ammonium chloride (NH ₄ Cl) in a solid state process to produce graphitic carbon nitride nanosheets. was used as a dynamic gas mold. The synthesized graphitic carbon nitride nanosheets showed excellent photocatalytic activity in the decomposition of RhB, which was 4.7 times higher than that of graphitic carbon nitride bulk. The significant improvement in the oxidation ability of Gwangi-like catalysts is attributed to the increased separation and transfer efficiency of the carrier and more reactive sites due to the nanosheet structure. In addition, graphite carbon nitride overcomes the limitations of the high recombination rate of light-generated electrons and holes and the low specific area of the graphite carbon nitride bulk, making it possible to produce graphite carbon nitride nanosheets with high yield and high photocatalytic activity.

As described above, the graphitic carbon nitride nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation and the method of synthesizing the same according to a preferred embodiment of the present invention have been described, but this is only an example. Those skilled in the art will be able to understand that various changes and modifications are possible without departing from the technical spirit of the present invention.

F1: precursor compound
F2: template compound
GC: Graphite carbon nitride nanosheet

Claims (7)

Grinding the precursor compound and the template compound and processing the mixture powder (P100);
Processing the mixture powder into a fired powder by heat treatment (P200); and,
A post-processing step (P300) of cooling, grinding, washing, and drying the fired powder;
A method for synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, comprising:
According to paragraph 1,
In the P100 step,
A method for synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, characterized in that the mixture is mixed with 100 to 120 parts by weight of the template compound with respect to 100 parts by weight of the precursor compound.
According to any one of paragraphs 1 and 2,
A method for synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, wherein the precursor compound is melamine (C ₃ N ₆ H ₆ ).
According to any one of paragraphs 1 and 2,
A method for synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, wherein the template compound is ammonium chloride (NH ₄ Cl).
In the P200 step,
A method of synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, wherein the heat treatment is performed at a temperature of 520 to 580 ° C. for 2.5 to 3.5 hours.
According to paragraph 1,
In the P300 step,
A method of synthesizing graphitic carbon nitride nanosheets with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, characterized in that drying is carried out at 85 to 95 ° C. for 10 to 14 hours.
A graphitic carbon nitride nanosheet with improved photocatalytic performance for rhodamine B decomposition under visible light irradiation, which is prepared by the method of any one of the methods of claims 1 to 6 using a precursor compound and a template compound. .