Preparation method of cyanogen / acylamino double group modified carbon nitride photocatalytic material

Abstract

The application discloses a preparation method of cyanogroup / amidogroup dual-group modified carbon nitride photocatalytic material, and specifically comprises the following process: using original g-C3N4 obtained by heat polymerization of melamine as a starting material, using ionothermal reaction of a molten salt containing ammonium chloride to prepare a crystalline g-C3N4 photocatalyst with cyanogroup, and then using the characteristic that the cyanogroup can be hydrolyzed into amidogroup under acidic conditions, and treating the cyanogroup and amidogroup dual-group modified g-C3N4 photocatalytic material with a hydrochloric acid solution. The application solves the problems of low crystallinity, high photo-generated carrier recombination rate and poor solar light absorption and utilization rate of traditional photocatalytic materials using graphite phase carbon nitride.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photocatalytic materials technology, and relates to a method for preparing a carbon nitride photocatalytic material modified with cyano / amide dual groups. Background Technology

[0002] Photocatalysis, capable of reducing water to hydrogen and degrading pollutants, is considered one of the most promising "green" technologies for addressing rapidly growing energy demands and environmental problems. The key to this technology lies in designing and synthesizing photocatalysts that can absorb and utilize sunlight across a broad solar spectrum while simultaneously generating long-lived active electrons and holes for redox reactions. Over the past few decades, various semiconductor photocatalysts have been successfully developed, such as TiO2, WO3, CdS, BiVO4, and Ta3N5. Among these, graphitic carbon nitride (g-C3N4) with a triazine ring structure has attracted considerable attention as a non-metallic photocatalyst due to its suitable band gap (~2.70 eV), readily available and inexpensive raw materials (urea, melamine, or dicyandiamide, etc.), simple preparation method, and excellent physicochemical stability (Nat. Commun., 2019, 10, 2467). However, its low visible light absorption utilization rate and high photogenerated carrier recombination rate result in low photocatalytic performance (Chem.Eng.J.,2021,410,127791). Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing carbon nitride photocatalytic materials modified with cyano / amide dual groups. The catalytic materials prepared by this method solve the problems of low crystallinity, high recombination rate of photogenerated carriers, and poor absorption and utilization rate of sunlight in traditional catalytic materials using graphite phase carbon nitride.

[0004] The technical solution adopted in this invention is a method for preparing cyano / amide bifunctional modified carbon nitride photocatalytic materials. The method involves uniformly mixing the g-C3N4 sample obtained by thermal polymerization of melamine in a muffle furnace with KCl, LiCl, and NH4Cl. A ceramic boat containing the mixture is placed in a tube furnace and heat-treated under a N2 atmosphere. After removing the sample and cooling it to room temperature, the sample is washed several times with deionized water and anhydrous ethanol, then dried and collected. The collected sample is added to a hydrochloric acid solution and stirred. After centrifugation, the sample is washed with deionized water and dried to obtain the final product.

[0005] The invention is further characterized by:

[0006] The dosage of g-C3N4 is 400mg to 600mg.

[0007] The heat treatment time in the tubular furnace is 2 to 4 hours.

[0008] The treatment conditions for adding the collected samples to the hydrochloric acid solution were as follows: 100 mg to 300 mg of g-C3N4 was added to the hydrochloric acid solution and stirred for 3 to 6 hours.

[0009] The preparation method of cyano / amide bifunctional modified carbon nitride photocatalytic material and its application in enhancing the degradation performance of ciprofloxacin and oxytetracycline.

[0010] The beneficial effects of this invention are that it improves the crystallinity of g-C3N4 and forms cyano groups through a thermally induced reaction between pristine g-C3N4 and a molten salt containing ammonium chloride. Then, it utilizes the easy hydrolysis of cyano groups in acidic conditions to modify the crystalline carbon nitride. The modified carbon nitride obtained by this method possesses both cyano and amide groups. The synergistic effect of these two groups generates more photogenerated electrons and effectively enhances the migration and separation of photogenerated charges, thereby greatly improving the photocatalytic performance of g-C3N4. Catalytic performance tests show that the obtained photocatalytic material exhibits excellent photocatalytic activity in the photocatalytic degradation of high concentrations of ciprofloxacin (CIP) and oxytetracycline (OTC), with removal rates reaching 86% and 85%, respectively. Attached Figure Description

[0011] Figure 1 The XRD patterns of Comparative Example 1, Comparative Example 2 and Example 1 in the preparation method of the cyano / amide bigroup modified carbon nitride photocatalyst material of the present invention are shown. The horizontal axis represents the angle and the vertical axis represents the intensity.

[0012] Figure 2 The images show the FT-IR spectra of Comparative Example 1, Comparative Example 2, and Example 1 in the preparation method of the cyano / amide bifunctional modified carbon nitride photocatalyst material of the present invention. The horizontal axis represents wavenumber, and the vertical axis represents transmittance.

[0013] Figure 3 The UV-Vis diffuse reflectance spectra of Comparative Example 1, Comparative Example 2, and Example 1 in the preparation method of the cyano / amide bifunctional modified carbon nitride photocatalytic material of the present invention are shown. The horizontal axis represents wavelength and the vertical axis represents absorbance.

[0014] Figure 4 The above are the Tauc curves of Comparative Example 1, Comparative Example 2, and Example 1 in the preparation method of the cyano / amide bifunctional modified carbon nitride photocatalyst material of the present invention. The horizontal axis is hv, and the vertical axis is ahv. (1 / 2) ;

[0015] Figure 5 The graphs are Mott-Schottky curves of Comparative Example 1 and Example 1 in the preparation method of the cyano / amide bi-group modified carbon nitride photocatalyst material of the present invention. The horizontal axis is the potential and the vertical axis is Cs-2 / uF-2.

[0016] Figure 6 The steady-state fluorescence spectra of Comparative Example 1, Comparative Example 2 and Example 1 in the preparation method of the cyano / amide bifunctional modified carbon nitride photocatalytic material of the present invention are shown. The horizontal axis represents wavelength and the vertical axis represents intensity.

[0017] Figure 7 The electrochemical impedance spectroscopy diagrams of Comparative Example 1, Comparative Example 2 and Example 1 in the preparation method of the cyano / amide bigroup modified carbon nitride photocatalytic material of the present invention are shown. The horizontal axis is the real part impedance and the vertical axis is the imaginary part impedance.

[0018] Figure 8 The linear sweep voltammetry curves of Comparative Example 1, Comparative Example 2 and Example 1 in the preparation method of the cyano / amide bigroup modified carbon nitride photocatalyst material of the present invention are shown. The horizontal axis is voltage and the vertical axis is current density.

[0019] Figure 9 The graphs show the degradation performance of ciprofloxacin on Comparative Example 1, Comparative Example 2, blank, and Example 1 in the preparation method of the cyano / amide bifunctional modified carbon nitride photocatalyst material of the present invention. The horizontal axis represents time, and the vertical axis represents the change in concentration.

[0020] Figure 10 The graphs show the degradation performance of oxytetracycline by Comparative Example 1, Comparative Example 2, blank, and Example 1 in the preparation method of the cyano / amide dual-group modified carbon nitride photocatalyst material of the present invention. The horizontal axis represents time, and the vertical axis represents the change in concentration. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0022] This invention relates to the design and synthesis of cyano / amide-modified carbon nitride photocatalytic materials. The process involves obtaining pristine g-C3N4 through melamine thermal polymerization, followed by ionothermal synthesis using a molten salt containing ammonium chloride as a high-temperature solvent to obtain cyano-modified, highly crystalline g-C3N4. Finally, taking advantage of the easy hydrolysis of cyano groups under acidic conditions, the cyano / amide-modified g-C3N4 is obtained by stirring in hydrochloric acid solution for several hours. The process is simple and yields significant results.

[0023] Specifically, 5g of melamine was placed in a covered alumina crucible and heated in a muffle furnace at 550℃ for 2 hours at a heating rate of 5℃ / min. The resulting pale yellow sample (original carbon nitride) was ground into powder for later use. Then, 400mg–600mg of the above sample was ground and mixed with 2.8g KCl, 2.2g LiCl, and 0.5g NH4Cl until homogeneous, and then placed in a porcelain boat. Subsequently, the mixture was heated in a tube furnace at 550℃ for 2–4 hours under a N2 atmosphere at a heating rate of 5℃ / min. After cooling to room temperature, the resulting sample was washed with deionized water and anhydrous ethanol, then dried and collected. Finally, 100mg–300mg of the collected sample was added to a hydrochloric acid solution (30mL, 2mol / L), stirred for 3–6 hours, centrifuged, washed with deionized water until neutral, and then dried at 60℃ for further use.

[0024] The preparation method of the cyano / amide dual-group modified carbon nitride photocatalyst of the present invention is characterized by: (1) using the original g-C3N4 obtained by thermal polymerization of melamine as the starting material, and preparing a highly crystalline g-C3N4 photocatalyst with cyano modification by using an ionothermal reaction containing ammonium chloride molten salt. Then, taking advantage of the characteristic of cyano hydrolysis to amide under acidic conditions, the g-C3N4 photocatalyst modified with cyano and amide dual groups is obtained by treatment with hydrochloric acid solution; (2) the method of the present invention is simple and the raw materials are cheap and readily available, the photocatalytic performance is greatly improved, and the application prospects are good; (3) the prepared cyano / amide dual-group modified carbon nitride photocatalyst can greatly improve the photogenerated charge separation efficiency, and the obtained catalyst has excellent photocatalytic performance. The removal rates of ciprofloxacin and oxytetracycline reach 86% and 85%, respectively, and the degradation rates are 17 times and 8 times that of pure carbon nitride, respectively.

[0025] This invention utilizes the property that cyano groups hydrolyze into amide groups under acidic conditions. By treating cyano-modified crystalline carbon nitride with hydrochloric acid solution, amide groups are successfully introduced into cyano-modified carbon nitride, resulting in a carbon nitride photocatalytic material modified with cyano / amide dual groups.

[0026] Example 1

[0027] 5g of melamine was placed in a covered alumina crucible and heated in a muffle furnace at 550℃ for 2 hours at a heating rate of 5℃ / min. The prepared pale yellow sample (original carbon nitride) was ground into powder for later use. Then, 500mg of the prepared original carbon nitride sample was uniformly mixed with KCl (2.8g), LiCl (2.2g), and NH4Cl (0.5g) and placed in a porcelain boat. Subsequently, the porcelain boat containing the mixture was placed in a tube furnace and heated at 550℃ for 4 hours under a N2 atmosphere at a heating rate of 5℃ / min. After removing the sample and cooling it to room temperature, the sample was washed several times with deionized water and anhydrous ethanol, then dried (at 60℃) and collected. Finally, hydrochloric acid solution (30mL, 2mol / L) was added to 300mg of the collected sample. The yellow solid immediately turned white. After stirring for 6 hours, the sample was separated by centrifugation, repeatedly washed with deionized water until neutral, and then dried at 60℃ to obtain the final product.

[0028] Comparative Example 1

[0029] Melamine (5g) was placed in a covered alumina crucible and heated in a muffle furnace at 550°C for 2 hours at a heating rate of 5°C / min. The resulting pale yellow sample (original carbon nitride) was ground into powder for further use.

[0030] Comparative Example 2

[0031] 500 mg of Comparative Example 1 sample was uniformly mixed with KCl (2.8 g), LiCl (2.2 g), and NH4Cl (0.5 g) and placed in a porcelain boat. The boat containing the mixture was then placed in a tube furnace and heated at 550 °C for 4 h under a N2 atmosphere with a heating rate of 5 °C / min. After removing the sample and cooling it to room temperature, the sample was washed several times with deionized water and anhydrous ethanol, then dried (at 60 °C) and collected. This sample was identified as cyano-modified crystalline g-C3N4 and named Comparative Example 2.

[0032] The photocatalytic performance of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 was determined by photocatalytic degradation of high-concentration ciprofloxacin and oxytetracycline solutions. The specific testing process is as follows:

[0033] The photocatalytic degradation process of ciprofloxacin according to the present invention is as follows: 10 mg of sample is ultrasonically dispersed in 80 mL (30 mg / L) of ciprofloxacin solution. A 500 W xenon lamp is used as the light source system to provide visible light. The resulting suspension is magnetically stirred in a dark room for 30 min to ensure that it reaches adsorption-desorption equilibrium, and 4 mL of the reaction solution is taken and placed in a centrifuge tube. Subsequently, the xenon lamp is turned on for photocatalytic testing, and 4 mL of the suspension is taken and placed in centrifuge tubes at 15 min, 30 min, 45 min, and 60 min of illumination, respectively. The resulting suspension is centrifuged, and the supernatant is collected. The concentration of ciprofloxacin at each stage of the degradation process is determined using a UV-Vis-NIR spectrophotometer (Purkinje General, TU-1900). The test without the addition of any catalyst is a blank experiment.

[0034] The photocatalytic degradation process of oxytetracycline according to the present invention is as follows: 10 mg of sample is ultrasonically dispersed in 80 mL (80 mg / L) of oxytetracycline solution. A 500 W xenon lamp is used as the light source system to provide visible light. The resulting suspension is magnetically stirred in a dark room for 30 min to ensure that it reaches adsorption-desorption equilibrium, and 4 mL of the reaction solution is taken and placed in a centrifuge tube. Subsequently, the xenon lamp is turned on for photocatalytic testing, and 4 mL of the suspension is taken and placed in centrifuge tubes at 10 min, 20 min, 30 min, 40 min, and 50 min of illumination, respectively. The resulting suspension is centrifuged, and the supernatant is collected. The concentration of oxytetracycline at each stage of the degradation process is determined using a UV-Vis-NIR spectrophotometer (Purkinje General, TU-1900). The test without the addition of any catalyst is a blank experiment.

[0035] Figure 1 The XRD patterns of Comparative Example 1, Comparative Example 2, and Example 1 are shown. The results indicate that the molten salt was completely removed after washing with deionized water. The XRD patterns of the samples obtained after hydrochloric acid treatment were not significantly different from those before treatment, indicating that hydrochloric acid hydrolysis does not change the basic structure of g-C3N4.

[0036] Figure 2 The FT-IR spectra of Comparative Example 1, Comparative Example 2, and Example 1 show that the hydrolysis treatment with molten salt and hydrochloric acid does not change the original core chemical structure of g-C3N4, and the vibrational peaks of cyano and amide groups in the infrared spectra confirm the successful synthesis of g-C3N4 modified with two groups.

[0037] Figure 3The UV-Vis diffuse reflectance spectra of Comparative Example 1, Comparative Example 2, and Example 1 are shown. All samples exhibit typical visible light absorption characteristics. Compared with the original g-C3N4, Comparative Example 2 and Example 1 show a significant increase in light absorption intensity, and their fundamental absorption edges also show a slight red shift. However, compared with Comparative Example 2, the fundamental absorption edge of Example 1 obtained after hydrolysis shows a blue shift.

[0038] Figure 4 The corresponding Tauc curves for Comparative Example 1, Comparative Example 2, and Example 1 are shown in the figures. It can be seen from the figures that the band gap values ​​of Comparative Example 1 and Example 1 are 2.66 eV and 2.59 eV, respectively.

[0039] Figure 5 The graphs show the Mott-Schottky curves for Comparative Example 1 and Example 1. From the graphs, we can see that the conduction band (CB) potentials of Comparative Example 1 and Example 1 relative to the standard hydrogen electrode are -0.85V and -0.96V, respectively.

[0040] Figure 6 The steady-state fluorescence spectra of Comparative Example 1, Comparative Example 2 and Example 1 are shown. The fluorescence quenching intensities of Comparative Example 2 and Example 1 are much lower than those of Comparative Example 1, which indicates that the samples of Comparative Example 2 and Example 1 have lower photogenerated charge carrier recombination rates.

[0041] Figure 7 The electrochemical impedance spectroscopy diagrams for Comparative Example 1, Comparative Example 2, and Example 1 show smaller arc radii compared to Comparative Example 1. The Nyquist radius of the sample in Example 1 is the smallest, indicating that the sample has the smallest charge transfer impedance and the fastest charge carrier transfer.

[0042] Figure 8 The figure shows linear sweep voltammetry curves for Comparative Example 1, Comparative Example 2, and Example 1. The figure shows that the overpotentials of the samples of Comparative Example 2 and Example 1 are lower than those of Comparative Example 1 over the entire potential range. The sample of Example 1 has the lowest overpotential, indicating that Example 1 has fast charge transport efficiency.

[0043] Figure 9 The degradation performance curves of ciprofloxacin for Comparative Examples 1, 2, blank, and Example 1 are shown. Without the addition of any photocatalyst, the concentration of ciprofloxacin in the solution remained essentially unchanged. For Comparative Examples 1 and 2, only approximately 10% and 50% of the ciprofloxacin were degraded after 60 minutes of illumination, respectively, while the maximum photocatalytic degradation rate of the sample in Example 1 reached 86%.

[0044] Figure 10The performance curves of oxytetracycline for Comparative Example 1, Comparative Example 2, blank, and Example 1 are shown. In the absence of a photocatalyst, the concentration of oxytetracycline in the solution did not change significantly after 50 minutes of light irradiation. Comparative Example 1 and Comparative Example 2 could only degrade about 20% and 55% of oxytetracycline, respectively, while the sample of Example 1 could degrade about 85% of oxytetracycline.

[0045] Example 2

[0046] 5g of melamine was placed in a covered alumina crucible and heated in a muffle furnace at 550℃ for 2 hours at a heating rate of 5℃ / min. The prepared pale yellow sample (original carbon nitride) was ground into powder for later use. Then, 400mg of the prepared original carbon nitride sample was uniformly mixed with KCl (2.8g), LiCl (2.2g), and NH4Cl (0.5g) and placed in a porcelain boat. Subsequently, the porcelain boat containing the mixture was placed in a tube furnace and heated at 550℃ for 4 hours under a N2 atmosphere at a heating rate of 5℃ / min. After removing the sample and cooling it to room temperature, the sample was washed several times with deionized water and anhydrous ethanol, then dried (at 60℃) and collected. Finally, hydrochloric acid solution (30mL, 2mol / L) was added to 100mg of the collected sample. The yellow solid immediately turned white. After stirring for 3 hours, the sample was separated by centrifugation, repeatedly washed with deionized water until neutral, and then dried at 60℃ to obtain the final product.

[0047] Example 3

[0048] 5g of melamine was placed in a covered alumina crucible and heated in a muffle furnace at 550℃ for 2 hours at a heating rate of 5℃ / min. The prepared pale yellow sample (original carbon nitride) was ground into powder for later use. Then, 600mg of the prepared original carbon nitride sample was uniformly mixed with KCl (2.8g), LiCl (2.7g), and NH4Cl (0.5g) and placed in a porcelain boat. Subsequently, the porcelain boat containing the mixture was placed in a tube furnace and heated at 550℃ for 4 hours under a N2 atmosphere at a heating rate of 5℃ / min. After removing the sample and cooling it to room temperature, the sample was washed several times with deionized water and anhydrous ethanol, then dried (at 60℃) and collected. Finally, hydrochloric acid solution (30mL, 2mol / L) was added to 200mg of the collected sample. The yellow solid immediately turned white. After stirring for 5 hours, the sample was separated by centrifugation, repeatedly washed with deionized water until neutral, and then dried at 60℃ to obtain the final product.

Claims

1. A method for preparing cyanogroup / amidogroup dual group modified carbon nitride photocatalytic material, characterized in that: The obtained g-C3N4 sample is uniformly mixed with KCl, LiCl and NH4Cl in a muffle furnace, a porcelain boat containing the mixture is placed in a tube furnace for heat treatment under N2 atmosphere, the sample is taken out and cooled to room temperature, the sample is washed several times with deionized water and anhydrous ethanol, and then dried and collected, the collected sample is added to a hydrochloric acid solution for stirring, separated by centrifugation, washed with deionized water, and dried to obtain; The amount of g-C3N4 is 400 mg to 600 mg; The heat treatment time in the tube furnace is 2 h to 4 h; When the collected sample is added to the hydrochloric acid solution, the treatment condition is that 100 mg to 300 mg of g-C3N4 is added to 30 mL of a 2 mol / L hydrochloric acid solution for stirring for 3 h to 6 h.

2. Use of the photocatalytic material prepared by the method for preparing a cyanogroup / amidogroup double-group modified carbon nitride photocatalytic material according to claim 1 for enhancing the degradation performance of ciprofloxacin and terramycin.

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