Preparation method and application of carbon nitride photocatalyst

Abstract

The application discloses a preparation method and application of a carbon nitride photocatalyst, and particularly relates to the technical field of photocatalyst functional materials. The preparation method of the carbon nitride photocatalyst comprises the following steps: S1, mixing and dispersing a carbon nitride precursor and a copper source on a carrier; S2, calcining the carrier obtained in S1 together with the carbon nitride precursor and the copper source to obtain the carbon nitride photocatalyst; and the molar ratio of the carbon nitride precursor and the copper source in step S1 is (12.5-100):1. The copper single atom and the nitrogen element of the carbon nitride form a covalent bond, the structure of the carbon nitride is changed, the surface active sites and the contact area of the carbon nitride are increased, the loading amount of the carbon nitride on the carrier is increased, and the carbon nitride anchored by the copper single atom has a unique flower-like structure and a large specific surface area, so that the photocatalytic efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocatalyst functional materials, in particular to a preparation method and application of a carbon nitride photocatalyst. BACKGROUND

[0002] With the development of society and the progress of industry, water pollution is threatening human health. If wastewater containing heavy metal ions such as chromium, cadmium, mercury, nickel and zinc is not treated before being discharged, it will enter human life through biological circulation, which will lead to some health problems such as human deformity, nervous disorder, cardiovascular and intestinal diseases. Since the discovery of Honda-Fujishima effect in 1972, the field of semiconductor photocatalysis has attracted extensive attention and rapid development, which provides an ideal method for energy utilization and environmental pollution control. The principle of photocatalysis is based on the oxidation-reduction ability of photocatalysts under light, so as to achieve the purpose of purifying pollutants, material synthesis and transformation.

[0003] In recent years, organic semiconductor polymer carbon nitride graphite (g-C3N4) has the characteristics of chemical stability, non-toxicity, easy preparation and unique electronic structure, and shows high reduction performance or oxidation performance on heavy metal ions such as Cr 6+ , Hg 2+ , and various dyes such as rhodamine B, methyl orange and methylene blue. Single-atom catalyst (SAC) has attracted great attention in the field of catalysis due to its 100% atom utilization efficiency, low coordination environment and confinement effect. Metal atom anchored carbon nitride can achieve 100% metal atom utilization, thereby promoting the migration of in-plane charges. As a high quantum efficiency visible light responsive photocatalyst, it is one of the ideal candidate materials in the field of photocatalysis, and has attracted widespread attention from researchers. Most of the current carbon nitride photocatalysts exist in powder state, which is difficult to recycle and reuse, and has poor recycling performance and stability in practical application, which hinders its large-scale application in the field of photocatalysis.

[0004] The prior art discloses a preparation method of carbon cloth / large-area two-dimensional graphite phase carbon nitride nanosheet hydrogen production photocatalytic film. The prior art loads two-dimensional graphite phase carbon nitride on pretreated carbon cloth by calcination, and the graphite phase carbon nitride is wrapped on the surface of carbon fibers of the carbon cloth with a thickness of 55-60 nm. The loading amount of the graphite phase carbon nitride on the carrier in the prior art is small, and the photocatalytic efficiency is low. SUMMARY

[0005] In order to solve the problems of low loading capacity, small specific surface area and low photocatalytic efficiency of the existing carbon nitride photocatalyst on the carrier, the application provides a preparation method of a carbon nitride photocatalyst. The copper monatomic atom and the nitrogen element of the carbon nitride form a covalent bond, the structure of the carbon nitride is changed, the surface active site and the contact area of the carbon nitride are increased, the loading capacity of the copper monatomic atom anchored carbon nitride on the carrier is increased, the copper monatomic atom anchored carbon nitride has a unique flower-shaped structure and a large specific surface area, and the photocatalytic efficiency is improved.

[0006] Another purpose of the application is to provide a carbon nitride photocatalyst.

[0007] Still another purpose of the application is to provide an application of the carbon nitride photocatalyst in photocatalytic heavy metal wastewater.

[0008] The above purposes of the application are achieved by the following technical solutions.

[0009] A preparation method of a carbon nitride photocatalyst comprises the following steps:

[0010] S1, mixing and dispersing a carbon nitride precursor and a copper source on a carrier;

[0011] S2, calcining the carrier obtained in S1 together with the carbon nitride precursor and the copper source to obtain a carbon nitride photocatalyst;

[0012] The molar ratio of the carbon nitride precursor to the copper source in step S1 is (12.5-100):1.

[0013] It should be noted that:

[0014] In the above preparation method, the mixture of the carbon nitride precursor and the copper source is dispersed on the carrier in step S1, which helps to provide a larger contact area and reaction opportunity for the preparation of the copper monatomic atom anchored carbon nitride photocatalyst on the carrier in the subsequent step S2.

[0015] In step S2, the carrier obtained in step S1 is calcined together with the carbon nitride precursor and the copper source, so that the copper monatomic atom and the carbon nitride form a Cu-N covalent bond, the copper monatomic atom also causes an additional charge effect, thereby changing the electronic structure of the carbon nitride, increasing the surface active site and the contact area of the carbon nitride, and strengthening the interaction force between the carbon nitride and the carrier, thereby promoting the loading of the copper monatomic atom anchored carbon nitride on the carrier, and the entanglement between the copper monatomic atom anchored carbon nitride and the carrier has a certain stability, the copper monatomic atom anchored carbon nitride on the carrier is not easy to fall off, so that the loading capacity of the copper monatomic atom anchored carbon nitride on the carrier is increased.

[0016] The addition of copper source, calcination temperature and calcination atmosphere can affect the crystal growth and arrangement of carbon nitride, resulting in differences in crystal morphology, size and growth orientation of copper single atom anchored carbon nitride, so that the copper single atom anchored carbon nitride has a unique flower-like structure and can increase the specific surface area.

[0017] The increase of the loading amount and specific surface area of the copper single atom anchored carbon nitride on the carrier can also improve the photocatalytic efficiency.

[0018] In step S1 of the present application, the molar ratio of carbon nitride precursor to copper source is (12.5-100):1. By changing the molar ratio of carbon nitride precursor to copper source, the loading amount of copper single atom on carbon nitride is controlled, and then the loading amount of copper single atom anchored carbon nitride on the carrier is controlled. Excessive addition of copper source beyond the range defined in the present application will result in a decrease in the loading amount of copper single atom anchored carbon nitride on the carrier, thereby adversely affecting the reduction of potassium dichromate. Less addition of copper source than the range defined in the present application will also result in a decrease in the loading amount of copper single atom anchored carbon nitride on the carrier, thereby adversely affecting the reduction of potassium dichromate.

[0019] Preferably, the molar ratio of carbon nitride precursor to copper source in step S1 is (33.3-62.5):1.

[0020] Under this condition, the copper single atom can be better anchored on the carbon nitride, so that the loading amount of copper single atom anchored carbon nitride on the carrier is increased, thereby facilitating the reduction of potassium dichromate.

[0021] More preferably, the molar ratio of carbon nitride precursor to copper source in step S1 is (45-55):1.

[0022] In the specific embodiment of the present application, step S1 can be:

[0023] Step S11, the carrier is washed with acetone, anhydrous ethanol and deionized water respectively, dried, then the washed carrier is soaked in nitric acid, and then the soaked carrier is dried and weighed.

[0024] Step S12, the mixture of carbon nitride precursor and copper source is dissolved in deionized water, and the mixed solution is obtained by stirring, and the carrier treated in step S11 is soaked in the mixed solution.

[0025] Step S13, the soaked carrier is taken out and dried with the mixed solution.

[0026] In step S11, the amount of carbon nitride precursor can be 0.05-0.1 mol; the amount of copper source can be 0.0005-0.002 mol; the carrier can be cleaned with acetone, anhydrous ethanol and deionized water for 15-25 min, and the concentration of nitric acid can be 60-65%, and the soaking time of the cleaned carrier can be 15-24 h;

[0027] In step S12, the stirring time can be 60 min, and the soaking time of each side of the carrier can be 30 min.

[0028] In step S13, the drying conditions of the carrier can be 80℃, and the drying time can be 8 h, and the drying conditions of the precursor mixture can be 80℃, and the drying time can be 8 h.

[0029] In the specific embodiment of the present application, step S2 can be:

[0030] In step S21, the block-shaped solid obtained by drying the mixture is ground into powder;

[0031] In step S22, the precursor powder obtained in step S21 and the carrier dried in step S13 are transferred into a crucible, the carrier is completely covered with the powder, a lid is put on, and the crucible is transferred into a muffle furnace for calcination;

[0032] In step S23, the calcined sample is taken out, cleaned with anhydrous ethanol by ultrasonic, and then cleaned with deionized water and dried to obtain a carbon nitride photocatalyst.

[0033] In step S21, the solid can be ground into powder with a mortar;

[0034] In step S22, a layer of precursor powder obtained in step S21 can be laid under the crucible, and then the carrier obtained in step S13 is placed above the precursor powder, and the carrier is completely covered with the precursor powder obtained in step S21;

[0035] In step S23, the anhydrous ethanol can be 20 mL, the ultrasonic time can be 20 min, and the drying conditions can be a drying temperature of 60℃ and a drying time of 4 h.

[0036] In step S1, the carrier is one or more of carbon cloth, spunlace cloth, metal sheet and ceramic sheet.

[0037] The above-mentioned preferred carriers have certain porosity and spatial structure, which can make the precursor penetrate into the internal pores of the carrier, which helps to uniformly disperse the precursor solution in the carrier, provides more contact area and reaction opportunity, and thus improves the loading amount of carbon nitride.

[0038] Preferably, in step S1, the carrier is carbon cloth.

[0039] The carbon cloth has the characteristics of fiber structure, corrosion resistance, flexibility and large surface area, and is a loading substrate for many nanomaterials, which can provide more contact area and solve the problem of difficult separation and recovery of powder catalyst.

[0040] The carbon nitride precursor in step S1 is one or more of melamine, dimelamine or urea;

[0041] The copper source in step S1 is one or more of copper chloride, copper nitrate or copper sulfate.

[0042] Preferably, the calcination temperature in step S2 is 540-560℃.

[0043] Too high calcination temperature will cause the crystallinity of carbon nitride to be destroyed and the nitrogen element to be reduced, and too low calcination temperature will cause incomplete crystallization of carbon nitride.

[0044] Preferably, the calcination time in step S2 is 3.5-4.5h.

[0045] Too long calcination time will cause the reduction of nitrogen element, and too short calcination time will cause incomplete crystallinity and incomplete thermal decomposition of melamine at high temperature.

[0046] The application also protects a carbon nitride photocatalyst prepared by the above-mentioned method for preparing a carbon nitride photocatalyst.

[0047] The application also protects the use of the above-mentioned carbon nitride photocatalyst in photocatalytic heavy metal wastewater.

[0048] The mechanism of photocatalytic treatment of heavy metal wastewater is that the photocatalytic material absorbs light energy, the semiconductor photocatalytic material is excited, the electrons on the valence band jump to the conduction band to form photo-generated electrons, these electrons have high reducing activity, and these active species are used to reduce heavy metal ions, the heavy metal ions are reduced by photo-generated electrons, and the heavy metal ions are precipitated from the solution or adsorbed on the surface of the photocatalytic material, and finally the removal of heavy metal ions is realized.

[0049] Preferably, the heavy metal wastewater is chromium-containing wastewater.

[0050] Preferably, the light application time is 15-90min.

[0051] Too short light application time will not reduce potassium dichromate sufficiently, and at 90min, almost all hexavalent chromium has been reduced, and there are few reactants in the solution, which is sufficient to achieve the predetermined catalytic effect.

[0052] Preferably, the wavelength of the light source used is 200-800nm.

[0053] In this wavelength range, the light energy is high enough to excite electron transition, and achieve the purpose of reducing potassium dichromate.

[0054] Compared with the prior art, the present application has the following beneficial effects:

[0055] In the present application, the loading amount of copper single atom-anchored carbon nitride on the carrier is improved compared with carbon nitride without adding copper source, reaching 88.4 mg. Under the same conditions of photocatalytic reduction of heavy metal wastewater, the photocatalytic efficiency of copper single atom-anchored carbon nitride is improved compared with carbon nitride without adding copper source, and the reduction rate of Cr 6+ reaches 94% after 90 min of illumination. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 It is an X-ray diffraction pattern of the carbon cloth loaded copper single atom-anchored carbon nitride photocatalyst in Example 1.

[0057] Figure 2 It is a scanning electron microscope image of the carbon cloth loaded copper single atom-anchored carbon nitride photocatalyst in Example 1, with a magnification of 1 thousand times.

[0058] Figure 3 It is a scanning electron microscope image of the carbon cloth loaded copper single atom-anchored carbon nitride photocatalyst in Example 1, with a magnification of 5 thousand times.

[0059] Figure 4 It is a scanning electron microscope image of the carbon cloth loaded copper single atom-anchored carbon nitride photocatalyst in Example 1, with a magnification of 20 thousand times.

[0060] Figure 5 It is a high-angle annular dark-field scanning transmission electron microscope image of the carbon cloth loaded copper single atom-anchored carbon nitride photocatalyst in Example 1, and an element distribution map of the corresponding area.

[0061] Figure 6 It is a catalytic activity graph of photocatalytic reduction of chromium-containing wastewater in Example 6 and Comparative Example 4. DETAILED DESCRIPTION

[0062] The present application will be further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0063] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0064] Example 1

[0065] A preparation method of a carbon nitride photocatalyst, comprising the following steps:

[0066] S1, mixing and dispersing the carbon nitride precursor and the copper source on a carrier;

[0067] S2, calcining the carrier obtained in S1 together with the carbon nitride precursor and the copper source to obtain a carbon nitride photocatalyst;

[0068] The molar ratio of the carbon nitride precursor to the copper source in step S1 is 50:1.

[0069] In example 1, steps S1 and S2 specifically include the following steps:

[0070] S11, washing the carbon cloth with 20 mL of acetone, 20 mL of anhydrous ethanol, and 20 mL of deionized water respectively for 20 min, drying in a dry box at 60°C for 2 h, then immersing the washed carbon cloth in 20 mL of nitric acid (concentration of 65%) for 24 h, and then drying the immersed carbon cloth in a dry box at 60°C for 2 h, and then weighing;

[0071] S12, dissolving 0.25 g of copper sulfate and 6.3 g of melamine mixture in 20 mL of deionized water, stirring for 1 h to obtain a mixed solution, immersing the carbon cloth treated in step S11 in the mixed solution, and immersing both sides of the carbon cloth for 30 min;

[0072] S13, taking out the immersed carbon cloth and drying it together with the mixed solution at 80°C for 8 h;

[0073] S21, grinding the block-shaped solid obtained by drying the mixed solution into a powder;

[0074] S22, first laying a layer of the precursor powder obtained in step S21 under the crucible, then placing the carbon cloth obtained in step S13 above the precursor powder, and completely covering the carbon cloth with the precursor powder obtained in step S21, covering the lid, and transferring it to a muffle furnace for calcination at 550°C for 4 h;

[0075] S23, taking out the calcined sample, cleaning it with 20 mL of anhydrous ethanol for 20 min, then cleaning it with deionized water, and drying it at 60°C for 4 h to obtain a carbon nitride photocatalyst.

[0076] Example 2

[0077] A method for preparing a carbon nitride photocatalyst, which is different from example 1 in that the molar ratio of the carbon nitride precursor to the copper source in step S1 is 12.5:1.

[0078] Example 3

[0079] A method for preparing a carbon nitride photocatalyst, which is different from example 1 in that the molar ratio of the carbon nitride precursor to the copper source in step S1 is 100:1.

[0080] Example 4

[0081] A preparation method of a carbon nitride photocatalyst, different from example 1 is that the molar ratio of carbon nitride precursor and copper source in step S1 is 33.3:1.

[0082] Example 5

[0083] A preparation method of a carbon nitride photocatalyst, different from example 1 is that the molar ratio of carbon nitride precursor and copper source in step S1 is 62.5:1.

[0084] Example 6

[0085] An application of a carbon nitride photocatalyst in photocatalytic heavy metal wastewater, comprising the following steps:

[0086] The carbon nitride photocatalyst prepared in example 1 was placed in chromium-containing wastewater, and its catalytic efficiency was measured under the conditions of light source wavelength of 540 nm, light irradiation time of 90 min, and pH = 1.

[0087] Comparative example 1

[0088] A preparation method of a carbon nitride photocatalyst, different from example 1 is that no copper source is added in step S1.

[0089] Comparative example 2

[0090] A preparation method of a carbon nitride photocatalyst, different from example 1 is that the molar ratio of carbon nitride precursor and copper source in step S1 is 6.25:1.

[0091] Comparative example 3

[0092] A preparation method of a carbon nitride photocatalyst, different from example 1 is that the molar ratio of carbon nitride precursor and copper source in step S1 is 200:1.

[0093] Comparative example 4

[0094] An application of a carbon nitride photocatalyst in photocatalytic heavy metal wastewater, different from example 6 is that the carbon nitride photocatalyst used is prepared by comparative example 1.

[0095] Test example performance determination

[0096] (1) Determination of the loading amount of carbon nitride on carbon cloth.

[0097] The difference between the weight of carbon nitride photocatalyst anchored by copper monatomic on carbon cloth and the initial carbon cloth weight is obtained.

[0098] (2) Determination of the catalytic efficiency of carbon nitride photocatalyst.

[0099] η = 1 - C t / C0

[0100] Wherein η is catalytic efficiency, C t is the concentration of hexavalent chromium in the original solution, C0 is the concentration of hexavalent chromium after photocatalysis. The higher the photocatalytic efficiency, the better the photocatalytic performance of the material.

[0101] Figure 1 X-ray diffraction pattern of the carbon cloth loaded copper monatomic-anchored carbon nitride photocatalyst material of Example 1. From Figure 1 It can be seen that the position of the peak at (002) crystal plane does not shift before and after loading, indicating that the structure of copper monatomic-anchored carbon nitride does not change after being loaded on the carbon cloth. The results of the remaining examples are comparable to those of Example 1.

[0102] Figures 2-4 Scanning electron microscope images of the carbon cloth loaded copper monatomic-anchored carbon nitride of Example 1 at 1 thousand magnification, 5 thousand magnification and 20 thousand magnification, respectively. From Figure 2 It can be seen that the copper monatomic-anchored carbon nitride has a flower-like structure and is loaded in large quantities on the surface of the carbon cloth. From Figure 3 It can be seen that the diameter of these flower-like copper monatomic-anchored carbon nitrides is 5-10 μm. From Figure 4 It can be seen that these copper monatomic-anchored carbon nitrides are irregularly aggregated together. The results of the remaining examples are comparable to those of Example 1.

[0103] Figure 5 It is shown that the copper element in the material of Example 1 is evenly distributed in the carbon nitride and does not form a cluster structure. The results of the remaining examples are comparable to those of Example 1.

[0104] Figure 6 Performance diagram of photocatalytic reduction of potassium dichromate of Example 6 and Comparative Example 4, from which it can be clearly seen that the reduction performance of the copper monatomic-anchored carbon nitride photocatalyst on potassium dichromate is significantly higher than that of the pure carbon nitride photocatalyst without adding copper source.

[0105] The loading amount of copper monatomic-anchored carbon nitride on the carbon cloth in the carbon nitride photocatalysts of Examples 1-5 and Comparative Examples 1-3 is shown in Table 1 below:

[0106] Table 1 Loading amount of copper monatomic-anchored carbon nitride in carbon nitride photocatalyst (mg)

[0107] Example Copper monatomic anchored carbon nitride loading Example 1 88.4 Example 2 48.5 Example 3 55.2 Example 4 58.3 Example 5 65.4 Comparative Example 1 42.4 Comparative Example 2 26.2 Comparative Example 3 38.7

[0108] The catalytic efficiency of the carbon cloth loaded copper monatomic-anchored carbon nitride photocatalyst of Example 6 and Comparative Example 4 is shown in Table 2 below:

[0109] Table 2 Catalytic efficiency (%) of carbon nitride photocatalyst

[0110] Time (min) 0 15 30 45 60 75 90 Example 6 0 39 67 77 86 91 94 Comparative Example 4 0 22 34 44 54 63 70

[0111] The carbon nitride photocatalysts prepared in Examples 2-5 have the same photocatalytic effect as that of Example 6 when used to catalyze heavy metal wastewater containing chromium.

[0112] As can be seen from Table 1, within a certain range, the addition of copper source can increase the loading of copper single-atom-anchored carbon nitride on the carrier. As can be seen from Examples 1-5 and Comparative Examples 2-3, when the molar ratio of carbon nitride precursor to copper source is (12.5-100): 1, the loading of copper single-atom-anchored carbon nitride on the carrier increases first and then decreases with the increase of the molar ratio of carbon nitride precursor to copper source. The data of Example 1 and Comparative Example 1 show that when the molar ratio of carbon nitride precursor to copper source is 50: 1, the loading of copper single-atom-anchored carbon nitride on the carrier is increased by 108.5%, reaching 88.4 mg, compared with the case where no copper source is added.

[0113] Examples 6 and Comparative Example 4 are the catalytic activity diagrams of copper single-atom-anchored carbon nitride photocatalysts and carbon nitride photocatalysts prepared in Example 1 and Comparative Example 1, respectively, when used to catalytically reduce heavy metal wastewater containing chromium. As can be seen from Table 2, the loading of copper single-atom-anchored carbon nitride on the carrier can improve the photocatalytic efficiency of carbon nitride, and the reduction rate reaches 94% at 90 min, which is increased by 24% compared with the case where no copper source is added in the carbon nitride photocatalyst of Comparative Example 4, indicating that the introduction of copper single atom is beneficial to the improvement of photocatalytic reduction performance.

[0114] As can be seen from the above data, the present application can increase the loading of copper single-atom-anchored carbon nitride on the carrier by adding copper source, and the specific surface area of the copper single-atom-anchored carbon nitride with flower-like structure is increased, which has excellent photocatalytic efficiency in photocatalytic heavy metal wastewater, and is convenient to recover, solving the problem of difficult separation and recovery of carbon nitride powder.

[0115] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. Use of a carbon nitride photocatalyst in photocatalytic treatment of wastewater containing chromium, characterized in that, The preparation method of the carbon nitride photocatalyst comprises the following steps: S1, mixing and dispersing carbon nitride precursors and copper sources on a carrier; S2, calcining the carrier obtained in S1 together with the carbon nitride precursors and the copper sources to obtain the carbon nitride photocatalyst; In the step S1, the molar ratio of the carbon nitride precursors to the copper sources is (12.5-100):

1. In the step S2, the calcination temperature is 540-560°C; in the carbon nitride photocatalyst, the copper single-atom-anchored carbon nitride is in a flower-shaped structure; and in the step S1, the carrier is carbon cloth or a spunlace cloth.

2. The use of the carbon nitride photocatalyst according to claim 1 in the photocatalytic treatment of wastewater containing chromium, characterized in that, In the step S1, the molar ratio of the carbon nitride precursors to the copper sources is (33.3-62.5):

1.

3. The use of the carbon nitride photocatalyst according to claim 1 in the photocatalytic treatment of wastewater containing chromium, characterized in that, In the step S1, the molar ratio of the carbon nitride precursors to the copper sources is (45-55):

1.

4. The use of the carbon nitride photocatalyst according to claim 1 in the photocatalytic treatment of wastewater containing chromium, characterized in that, In the step S2, the calcination time is 3.5-4.5h.

5. The use of the carbon nitride photocatalyst according to claim 1 in the photocatalytic treatment of wastewater containing chromium, characterized in that, The light irradiation time of the application is 15-90min.

6. The use of the carbon nitride photocatalyst according to claim 1 in the photocatalytic treatment of wastewater containing chromium, characterized in that, The wavelength of the light source of the application is 200-800nm.

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