Carbon nitride-based chromium monatomic catalyst as well as preparation method and application thereof

Abstract

The invention provides a carbon nitride-based chromium monatomic catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out water bath on a melamine solution, a cyanuric acid solution and a chromium salt solution at 50-60 DEG C to obtain a carbon nitride-based chromium monatomic catalyst precursor; the carbon nitride-based chromium monatomic catalyst precursor is washed and dried and then calcined at the high temperature of 500-600 DEG C for 5-8 h, and the carbon nitride-based chromium monatomic catalyst is obtained. The hydrogen peroxide generation capacity of the carbon nitride-based chromium monatomic catalyst system can resist interference of environmental influences, and the carbon nitride-based chromium monatomic catalyst system has excellent performance in the aspect of hydrogen peroxide production in a high-salt system.

Description

Technical Field

[0001] The invention belongs to the field of carbon nitride-based catalysts for photo-Fenton reactions, and specifically relates to a carbon nitride-based chromium single-atom catalyst, a preparation method thereof, and an application in producing hydrogen peroxide in a high-salt wastewater environment. Background Art

[0002] Chloride is the main inorganic salt in high-salinity organic wastewater. High-chloride organic wastewater has complex composition, high concentration of difficult-to-degrade organic matter, and poor biodegradability, which is a "chronic disease" in industrial wastewater treatment. Currently, the resource utilization of high-salinity wastewater to produce hydrogen peroxide has attracted much attention, but the complex water quality and many side reactions have seriously restricted the efficiency of hydrogen peroxide production.

[0003] Since single-atom catalysis was jointly proposed by Professors Zhang Tao, Li Jun and Liu Jingyue, the number of related articles published has increased year by year, and it has become a very popular frontier field of catalysis. Single-atom catalysis means that the active metal is loaded on the surface of the carrier in the form of a single atom, and is mainly connected to the surface of the carrier by bonding with heteroatoms. The coordination environment of the metal atom may not be completely consistent (A region); a single-atom catalyst does not mean that a single zero-valent metal atom is the active center. The single atom also undergoes coordination effects such as electron transfer with other atoms of the carrier, and often exhibits a certain charge. The synergistic effect of metal atoms and surrounding coordinated atoms is the main reason for the high activity of the catalyst. The synthesis methods of single-atom catalysts are becoming more and more abundant, and their applications are becoming more and more extensive. However, highly stable, highly active, and highly loaded single-atom catalysts still need to be explored before they can be truly applied in industry. Summary of the invention

[0004] The purpose of the present invention is to provide a carbon nitride-based chromium single-atom catalyst (Cr / CN), including carbon nitride with a single-atom structure, and Cr atoms on the surface of the carbon nitride. The carbon nitride-based Cr single-atom catalytic system has excellent performance in resource-based production of hydrogen peroxide from bisphenol A (BPA) and other different organic pollutants.

[0005] The object of the present invention is achieved through the following technical solutions.

[0006] A method for preparing a carbon nitride-based chromium single-atom catalyst comprises the following steps: Melamine, cyanuric acid and chromium salt are dissolved in dimethyl sulfoxide to prepare melamine solution, cyanuric acid solution and chromium salt solution respectively; the melamine solution and the chromium salt solution are mixed and magnetically stirred, and cyanuric acid solution is added dropwise during the magnetic stirring process, and the temperature is 50-60° C. to react for 10-14 hours, and then cooled to room temperature, washed and dried to obtain a Cr / CN precursor; the Cr / CN precursor is calcined at a high temperature of 500-600° C. for 5-8 hours in a nitrogen atmosphere to obtain Cr / CN.

[0007] As a more optimal technical solution of the present invention, the chromium salt is chromium nitrate nonahydrate.

[0008] As a more preferred technical solution of the present invention, the mass ratio of melamine, cyanuric acid and chromium nitrate nonahydrate is 1: (1-1.02): (0.0057-0.0171) As a more optimal technical solution of the present invention, the calcination temperature of the Cr / CN precursor is 550°C.

[0009] As a more optimal technical solution of the present invention, the melamine solution, cyanuric acid solution and chromium salt solution are reacted at 60° C. for 12 hours.

[0010] As a more optimal technical solution of the present invention, the mass ratio of melamine, cyanuric acid and chromium nitrate is 1:1.02:0.0114.

[0011] Another object of the present invention is to add the carbon nitride-based chromium single atom catalyst into the treatment of high-salinity wastewater to achieve efficient resource production of hydrogen peroxide from different organic pollutants in the high-salinity wastewater.

[0012] As a more preferred technical solution of the present invention, the organic pollutants are one or more of BPA, 3-AP, 3-BP, 4-CP and DCP.

[0013] As a more optimal technical solution of the present invention, the dosage is 0.5~1 mg / mL Beneficial effects: The carbon nitride-based chromium single-atom catalyst prepared by the present invention exhibits excellent hydrogen peroxide production efficiency and can be mass-produced to provide method support for the subsequent large-scale preparation of efficient resource-based treatment of high-salt organic wastewater; hydrogen peroxide can be produced from complex wastewater, and it has good anti-interference performance for anions (SO42− and NO3−, etc.) and water matrices (tap water and secondary effluent, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The morphology of Cr / CN in Example 1 is characterized. The left picture is the spherical aberration correction-high-angle annular dark field scanning transmission electron microscope (AC-STEM) picture of Cr / CN in Example 1, and the right picture is the mapping picture of Cr / CN in Example 1; Figure 2 is the transmission electron microscope (TEM) spectrum of Cr / CN of Example 1; Figure 3 X-ray diffraction (XRD) patterns of Cr / CN of Example 1 and CN of Comparative Example 4; Figure 4 The Fourier transform infrared (FT-IR) spectra of Cr / CN of Example 1 and CN of Comparative Example 4; Figure 5 X-ray photoelectron spectroscopy (XPS) of Cr / CN of Example 1; Figure 6 The amount of hydrogen peroxide produced in BPA is CN of Comparative Example 1, Cr / CN of Example 1, 0.5Cr / CN of Example 2, and 1.5Cr / CN of Example 3; Figure 7 The amount of hydrogen peroxide produced by Cr / CN in Example 1 in the BPA-high salt system at different pollutant concentrations; Figure 8 The amount of hydrogen peroxide produced by Cr / CN in Example 1 in different salt concentrations and BPA-high salt system; Fig. 9 The amount of hydrogen peroxide produced by Cr / CN in Example 1 in different pollutant-high salt systems. DETAILED DESCRIPTION

[0015] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0016] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0017] Comparative Example 1 5mmol melamine was dissolved in 80ml dimethyl sulfoxide, stirred at room temperature for 30min, and continuously stirred magnetically at 60℃. Subsequently, 5mmol cyanuric acid was dissolved in 50ml dimethyl sulfoxide, and dimethyl sulfoxide was slowly added to the hot solution with a dropper. The obtained sample was washed with ethanol and centrifuged 6 times, vacuum dried at 60℃ for 12h, and the obtained sample was heated to 550℃ at a rate of 5℃ / min under nitrogen atmosphere, calcined at 550℃ for 8h, and ground to obtain a yellow sample, which was recorded as CN.

[0018] Example 1 5mmol melamine was dissolved in 80ml dimethyl sulfoxide to obtain a melamine solution, which was stirred at room temperature for 30min, and then chromium nitrate nonahydrate was dissolved in 5ml dimethyl sulfoxide to obtain a chromium nitrate solution, and the above melamine solution was slowly added, and then the obtained mixture was continuously magnetically stirred at 60℃ for 12 hours. Subsequently, 5mmol cyanuric acid was dissolved in 50ml dimethyl sulfoxide to obtain a cyanuric acid solution, and dimethyl sulfoxide was added to the hot solution at a rate of 2 drops per second using a syringe or dropper. The total volume was close to 60ml. The stirring time was up to the situation, washed with ethanol, and centrifuged. The Cr / CN precursor obtained by vacuum drying for 12h was heated to 550℃ at a rate of 5℃ / min under N2 atmosphere and calcined for 8h to obtain a yellow-brown sample. The mass ratio of melamine, cyanuric acid and chromium nitrate was 1:1.02:0.0.0114, recorded as Cr / CN.

[0019] Example 2 The difference between this embodiment and embodiment 1 is that the mass ratio of melamine, cyanuric acid and chromium nitrate is 1:1.02:0.0057, denoted as 0.5Cr / CN.

[0020] Example 3 The difference between this embodiment and embodiment 1 is that the mass ratio of melamine, cyanuric acid and chromium nitrate is 1:1.02:0.0171, which is recorded as 1.5Cr / CN.

[0021] Example 4 The difference between this embodiment and embodiment 1 is that the Cr / CN precursor is calcined at 500° C. for 8 h in a nitrogen atmosphere.

[0022] Example 5 The difference between this embodiment and embodiment 1 is that the Cr / CN precursor is calcined at 600° C. for 8 h in a nitrogen atmosphere.

[0023] Example 6 The difference between this embodiment and embodiment 1 is that the melamine solution, cyanuric acid solution and chromium salt solution are reacted at 50° C. for 12 hours.

[0024] Example 7 The difference between this embodiment and embodiment 1 is that the melamine solution, cyanuric acid solution and chromium salt solution are reacted at a temperature of 55° C. for 12 hours.

[0025] Example 8 The difference between this embodiment and embodiment 1 is that the mass ratio of melamine, cyanuric acid and chromium nitrate is 1:1.02:0.1.

[0026] AC-STEM of Cr / CN of Example 1 is as follows Figure 1As shown in the left figure, it can be seen that uniform white bright spots appear in the Cr / CN of Example 1, proving the existence of single atoms. Uniform white bright spots appear in Examples 3 to 7, but no uniform white bright spots appear in Example 8. The element mapping of the AC-STEM of Cr / CN of Example 1 is shown in Figure 1 As shown in the right figure, it is shown that the Cr / CN of Example 1 is composed of Cr, O, C and N elements. The XRD results of the Cr / CN of Example 1 and the CN of Comparative Example 1 are as follows: Figure 2 The FT-IR results of Cr / CN of Example 1 and CN of Comparative Example 1 are shown in Figure 3 As shown in the figure, since the effects of Examples 1 to 3 are good, Examples 1 to 3 are used for the next step of application verification.

[0027] Application Example 1 The Cr / CN of Example 1, the 0.5Cr / CN of Example 2, the 1.5Cr / CN of Example 3, and the CN of Comparative Example 1 were used to produce hydrogen peroxide in BPA in a high-salt environment.

[0028] First, 25 mg of Cr / CN, Cr / CN-1:0.5, Cr / CN-1:1.5 and CN prepared in Examples 1 to 3 and Comparative Example 1 were placed in 25 mL of 10 mg / L BPA and stirred for 30 min in the dark to reach adsorption-desorption equilibrium. Then, 0.2060 g of sodium chloride was used to create a high salt environment and visible light to stimulate the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a wavelength less than 420 nm. The light intensity was 134.73 mW / cm 2 (Illuminated area = 3.34 cm 2 During the reaction, 1.0 mL of sample was collected every 3 minutes and filtered through a 0.22 μm filter membrane, and 500 μL of sample was added to a mixture consisting of 2 mL of potassium iodide (100 mM) and 50 μL of ammonium molybdate tetrahydrate (10 mM). After four minutes of reaction, the mixture was detected at 352 nm using a UV-visible spectrophotometer, and the amount of hydrogen peroxide produced was determined by the hydrogen peroxide mark.

[0029] Application Example 2 Application of Cr / CN in Example 1 to produce hydrogen peroxide in environments with different BPA concentrations and different salt concentrations.

[0030] First, 25 mg of Cr / CN from Example 1 was placed in 25 mL of 10 mg / L, 15 mg / L, 20 mg / L, and 30 mg / L BPA and stirred for 30 min in the dark to reach adsorption-desorption equilibrium. Then, 0.2060 g of sodium chloride was used to create a high salt environment and visible light to stimulate the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a wavelength less than 420 nm filter. The light intensity was 134.73 mW / cm 2 (Illuminated area = 3.34 cm 2 During the reaction, 1.0 mL of sample was collected every 3 minutes and filtered through a 0.22 μm filter membrane, and 500 μL of sample was added to a mixture consisting of 2 mL of potassium iodide (100 mM) and 50 μL of ammonium molybdate tetrahydrate (10 mM). After four minutes of reaction, the mixture was detected at 352 nm using a UV-visible spectrophotometer, and the amount of hydrogen peroxide produced was determined by the hydrogen peroxide mark.

[0031] Application Example 3 Application of Cr / CN in Example 1 to produce hydrogen peroxide in environments with different BPA concentrations and different salt concentrations.

[0032] First, 25 mg of Cr / CN from Example 1 was placed in 25 mL of 10 mg / L BPA and stirred for 30 min in the dark to reach adsorption-desorption equilibrium. Then, 0.2060 g, 0.4120 g, 0.6180 g, and 8240 g of sodium chloride were used to create a high salt environment and visible light excitation reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a wavelength less than 420 nm filter. The light intensity was 134.73 mW / cm 2 (Illuminated area = 3.34 cm 2 During the reaction, 1.0 mL of sample was collected every 3 minutes and filtered through a 0.22 μm filter membrane, and 500 μL of sample was added to a mixture consisting of 2 mL of potassium iodide (100 mM) and 50 μL of ammonium molybdate tetrahydrate (10 mM). After four minutes of reaction, the mixture was detected at 352 nm using a UV-visible spectrophotometer, and the amount of hydrogen peroxide produced was determined by the hydrogen peroxide mark.

[0033] Application Example 4 Application of Cr / CN in Example 1 to produce hydrogen peroxide in different organic pollutants.

[0034] First, 25 mg of Cr / CN from Example 1 was placed in 25 mL of 10 mg / L BPA, 4-chlorophenol (4-CP, 10 mg / L), 3-aminophenol (3-AP, 10 mg / L), m-bromophenol (3-BP, 10 mg / L) and 2,4-dichlorophenol (DCP, 10 mg / L), and stirred for 30 min in the dark to reach adsorption-desorption equilibrium. Then, 0.2060 g of sodium chloride was used to create a high salt environment and visible light to excite the reaction. Visible light was provided by a 300.0 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) with a wavelength filter less than 420 nm. The light intensity was 134.73 mW / cm 2 (Illuminated area = 3.34 cm 2 During the reaction, 1.0 mL of sample was collected every 3 minutes and filtered through a 0.22 μm filter membrane, and 500 μL of sample was added to a mixture consisting of 2 mL of potassium iodide (100 mM) and 50 μL of ammonium molybdate tetrahydrate (10 mM). After four minutes of reaction, the mixture was detected at 352 nm using a UV-visible spectrophotometer, and the amount of hydrogen peroxide produced was determined by the hydrogen peroxide mark.

[0035] The CN of Comparative Example 1, the Cr / CN of Example 1, the 0.5Cr / CN of Example 2, and the 1.5Cr / CN of Example 3, the hydrogen peroxide production is as follows: Figure 6 As shown in the figure, the hydrogen peroxide production of Cr / CN in Example 1 in pollutants is higher than that of the comparative example, and the Cr / CN in Example 1 is least affected in the presence or absence of salt environment, and the hydrogen peroxide production can reach 1.76 mM L -1 ·h -1 , indicating that the Cr / CN of Example 1 has excellent hydrogen peroxide production ability in a high-salt environment.

[0036] The efficiency of Cr / CN in Example 1 in producing hydrogen peroxide in different concentrations of BPA-high salt system and different pollutants-high salt system is as follows: Figure 7 , 8 As shown in Figure 2, under high-concentration pollutant environmental conditions, the amount of hydrogen peroxide produced by Cr / CN in Example 1 increases with the increase of pollutant concentration, and can reach a maximum of 2.6 mM L -1 ·h -1 Under high-salinity conditions, the amount of hydrogen peroxide produced by Cr / CN in Example 1 first increases and then decreases slightly as the salinity concentration increases. In a high-salinity environment of 564 mM, the amount of hydrogen peroxide produced by Cr / CN in Example 1 can also reach 1.8 mM L -1 ·h -1 , indicating that the hydrogen peroxide production ability of Cr / CN in Example 1 is resistant to the interference of environmental influences.

[0037] like Fig. 9As shown, the amount of hydrogen peroxide produced in 15 minutes in the system of Cr / CN in Example 1 for removing typical pollutants BPA, 3-AP, 3-BP, 4-CP and DCP in different fields is higher than that in the pure water system, indicating that Cr / CN in Example 1 has excellent hydrogen peroxide production ability under different environments.

[0038] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a carbon nitride-based chromium single-atom catalyst, characterized in that: The method comprises the following steps: dissolving melamine, cyanuric acid and chromium salt in dimethyl sulfoxide respectively to prepare melamine solution, cyanuric acid solution and chromium salt solution; mixing the melamine solution and the chromium salt solution and then stirring them magnetically, adding cyanuric acid solution dropwise during the magnetic stirring process, reacting at a temperature of 50-60° C. for 10-14 hours, cooling to room temperature, washing and drying to obtain a Cr / CN precursor; and calcining the Cr / CN precursor at a high temperature of 500-600° C. for 5-8 hours in a nitrogen atmosphere to obtain Cr / CN.

2. The method for preparing the carbon nitride-based chromium single-atom catalyst according to claim 1, characterized in that: The chromium salt is chromium nitrate nonahydrate.

3. The method for preparing the carbon nitride-based chromium single-atom catalyst according to claim 1, characterized in that: The mass ratio of melamine, cyanuric acid and chromium nitrate nonahydrate is 1:(1-1.02):(0.0057-0.0171).

4. The method for preparing the carbon nitride-based chromium single-atom catalyst according to claim 1, characterized in that: The calcination temperature of the Cr / CN precursor is 550°C.

5. The method for preparing the carbon nitride-based chromium single-atom catalyst according to claim 1, characterized in that: The melamine solution, cyanuric acid solution and chromium salt solution are reacted at 60° C. for 12 hours.

6. The method for preparing the carbon nitride-based chromium single-atom catalyst according to claim 1, characterized in that: The mass ratio of melamine, cyanuric acid and chromium nitrate is 1:1.02:0.0114.

7. A carbon nitride-based chromium single-atom catalyst, characterized in that: The catalyst is obtained by the method for preparing the carbon nitride-based chromium single-atom catalyst as described in any one of claims 1 to 6.

8. The carbon nitride-based chromium single-atom catalyst according to claim 7, characterized in that: It is added into high-salt wastewater environment to treat organic pollutants.

9. The carbon nitride-based chromium single-atom catalyst according to claim 7, characterized in that: The organic pollutants are one or more of BPA, 3-AP, 3-BP, 4-CP and DCP.

10. The carbon nitride-based chromium single-atom catalyst according to claim 7, characterized in that: The dosage is 0.5~1mg / mL.

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