Double-defect modified porous carbon nitride photocatalyst prepared by utilizing iron molybdic acid in one step as well as preparation method and application of double-defect modified porous carbon nitride photocatalyst

Abstract

The invention provides a double-defect-modified porous carbon nitride photocatalyst prepared by one step from ferromolybdic acid as well as a preparation method and application of the double-defect-modified porous carbon nitride photocatalyst. The catalyst is of a thin-layer porous structure, so that the specific surface area of the catalyst is increased, and more surface active sites are provided for adsorption and reaction; compared with pure g-C3N4, the visible light absorption intensity of the catalyst is obviously enhanced, due to the existence of surface N vacancies and defects formed by doping of metal oxides, effective charge separation is enhanced, the photon-generated carrier separation and transfer capacity is higher under visible light irradiation, and the catalytic activity is remarkably improved. When the photocatalyst is applied to degradation of tetracycline antibiotic pollutants, photocatalytic degradation of tetracycline can be realized only under the condition of low-power 5W LED visible light, the preparation process is simple, and the cost is lower.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and in particular to a method for preparing a double-defect modified porous carbon nitride photocatalyst by using ferromolybdic acid in one step, and an application of the method in photocatalytic degradation of tetracycline antibiotic pollutants. Background Art

[0002] Tetracycline antibiotics are the most widely used and frequently used class of antibiotics, and are widely used in the pharmaceutical, animal husbandry, and aquaculture industries. Tetracycline molecules contain four parallel rings, which are complex and stable, making them difficult to be completely absorbed and degraded. Their large-scale use and improper discharge will lead to increasingly serious tetracycline residue problems in the environment, posing multiple threats to ecosystems and human health. Photocatalytic degradation of tetracycline is the use of active substances generated by semiconductor materials under light conditions, such as hydroxyl radicals · OH and superoxide radicals · O2 - 、H + It is an advanced oxidation technology that can oxidize and decompose tetracycline antibiotic pollutants. It is an efficient and environmentally friendly wastewater treatment technology.

[0003] Graphitic carbon nitride (g-C3N4) is a new type of polymer semiconductor photocatalytic material. It is one of the commonly used catalysts for photocatalytic degradation of tetracycline due to its good visible light response, high stability and easy preparation. However, for pure g-C3N4, there are limited visible light absorption range and small specific surface area (usually around 10 m 2 ·g -1 The photogenerated electrons and holes easily recombine, thus affecting carrier transport and severely limiting their adsorption capacity for pollutants and photocatalytic performance. Current strategies for improving pure g-C3N4 include: morphological manipulation to create a porous structure, increasing the specific surface area and accelerating the transport rate of pollutants and products; introducing defects such as vacancies or doping to generate defect levels and promote the separation of photogenerated carriers; and constructing heterojunctions to promote the separation of photogenerated electrons and holes.

[0004] Polyoxometalates (POMs) are a class of polynuclear metal clusters with nearly 200 years of development history. They have become a key research area in inorganic chemistry. These metal clusters possess well-defined molecular structures, tunable compositions, nanoscale sizes, strong acidity, and excellent redox properties. The prior art CN114192102B discloses a method for preparing a polyacid-modified graphite-phase carbon nitride material using Anderson-type cobalt molybdate in one step. A porous structure is manufactured by polyacid etching technology, and nitrogen vacancies are introduced at the same time. The polyacid-derived metal oxide is embedded in the structure of g-C3N4. The process is simple, and the morphology control and double-defect control of g-C3N4 are achieved in one step, which broadens the absorption range and intensity of visible light, increases the specific surface area, and enhances the separation efficiency of photogenerated carriers, while accelerating the mass transfer rate of pollutants and products. However, the prepared cobalt molybdate-modified graphite-phase carbon nitride material has a weak oxidation ability on the one hand, and on the other hand, due to the strong adsorption ability of cobalt molybdate-modified carbon nitride for cationic dyes, the dyes accumulate on the carbon nitride surface, affecting the optical density and having an adverse effect on photocatalytic degradation. Therefore, during the experiment, the cobalt molybdate-modified carbon nitride has poor photocatalytic activity for antibiotics such as tetracycline hydrochloride and gold chloride hydrochloride.

[0005] In addition, patent CN112007679A synthesizes a Co / V bimetallic-doped g-C3N4 photocatalyst in one step by thermal polymerization. The degradation rate of tetracycline hydrochloride catalytically degraded under visible light is about 68%, which fails to reach the ideal state. Patent CN110756215A recrystallizes dicyandiamide and fixes it on nickel foam, obtains highly crystalline g-C3N4 through annealing and acidification, and then composites it with CoP to prepare a photocatalyst. The degradation rate of tetracycline hydrochloride can reach 95%, but the preparation method is complicated and not conducive to industrial production.

[0006] Therefore, how to improve the efficiency of g-C3N4 photocatalytic degradation of tetracycline pollutants and enhance its catalytic performance while making the method simple and conducive to industrial production remains a technical problem to be solved in this field.

[0007] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0008] In order to improve the shortcomings of existing graphitic carbon nitride (g-C3N4) in photocatalytic degradation of tetracycline antibiotic pollutants, the present invention provides a one-step preparation of a double-defect modified porous carbon nitride photocatalyst using ferromolybdic acid. Compared with other types of polyacid-modified graphitic carbon nitride materials or the method of loading polyacids on the surface of graphitic carbon nitride materials to form a heterojunction, the prepared ferromolybdic acid-modified double-defect carbon nitride material has stronger oxidation ability and higher catalytic activity, and can catalytically degrade tetracycline pollutants more efficiently.

[0009] Specifically, the technical solution of the present invention is as follows:

[0010] A method for preparing a double-defect modified porous carbon nitride photocatalyst using ferromolybdic acid in one step comprises the following steps:

[0011] (1) Dicyandiamide and polyacid are mixed evenly; the polyacid is Anderson type ferromolybdic acid, and its chemical formula is: (NH4)3[FeMo6O 18 (OH)6]·6H2O;

[0012] (2) Calcination in a muffle furnace at 500 °C for 4 hours finally yielded a nitrogen-deficient, metal oxide-doped porous carbon nitride photocatalyst.

[0013] In some embodiments, the mass ratio of ferromolybdic acid to dicyandiamide in step (1) is 0.005-0.015:1; preferably, the mass ratio of ferromolybdic acid to dicyandiamide is 0.01:1.

[0014] In some embodiments, the specific steps of uniformly mixing dicyandiamide and ferromolybdic acid in step (1) are as follows: dissolving dicyandiamide in water, continuously stirring at 50°C to form a transparent solution, then adding ferromolybdic acid, stirring and mixing uniformly, continuing stirring at 60-70°C until all water evaporates to obtain a solid, and grinding into powder; preferably, the uniformly mixed dicyandiamide ferromolybdic acid aqueous solution is continuously stirred at 65°C until all water evaporates to obtain a solid.

[0015] In some embodiments, in step (2), the muffle furnace is heated to 500° C. at a heating rate of 5° C. / min.

[0016] In some embodiments, the prepared double-defect modified porous carbon nitride photocatalyst is a porous layered graphite phase carbon nitride material, which is stacked in layers, and has a large number of pores with a size of 10-60 nm distributed on the surface of the layers, and its specific surface area is 53.605 m 2 / g, which is 8 times that of the product without polyacid modification.

[0017] A double-defect modified porous carbon nitride photocatalyst prepared in one step using ferromolybdic acid is used in the photocatalytic degradation of tetracycline. After 60 minutes of visible light irradiation, the tetracycline degradation rate is greater than 95.3%.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention uses a double-defect modified porous carbon nitride photocatalyst prepared in one step using ferromolybdic acid. The conduction band potential is -0.66 eV and the valence band potential is 2.06 eV. The oxidation ability of the holes in the valence band is improved, which can oxidize pollutants. At the same time, the valence band potential is higher than that of OH - / ·OH (1.99 V relative to standard hydrogen electrode), the hole can convert OH - It is oxidized into ·OH which can efficiently oxidize organic pollutants, and realize the efficient oxidation of tetracycline pollutants by multiple active species such as superoxide radicals, hydroxyl radicals, and holes.

[0020] (2) The double-defect modified porous carbon nitride photocatalyst prepared in one step using ferromolybdic acid in the present invention has a thin-layer porous structure, which increases the specific surface area of ​​the catalyst and provides more surface active sites for adsorption and reaction. Compared with pure g-C3N4, the visible light absorption intensity of the catalyst of the present invention is significantly enhanced. At the same time, due to the presence of surface N vacancies and defects formed by the doping of metal oxides, it helps to enhance effective charge separation, and the recombination rate of photogenerated electron-hole pairs is lower. Under visible light irradiation, the ability of photogenerated carrier separation and transfer is stronger, and the catalytic activity is significantly improved.

[0021] (3) The present invention uses ferromolybdic acid to prepare a double-defect modified porous carbon nitride photocatalyst in one step. The amount of ferromolybdic acid used is low, and only one-third of the amount of cobalt molybdic acid used in previous studies is needed to form a porous structure on the carbon nitride surface, and the catalytic performance is improved. It only needs to be under low-power 5 W LED visible light conditions to achieve photocatalytic degradation of tetracycline. The preparation process is simple and the cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope image of a double-defect modified porous carbon nitride photocatalyst (20-FeMoO-CN) prepared in one step using ferromolybdic acid in Example 1 of the present invention;

[0023] Figure 2 is the X-ray diffraction pattern of 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention;

[0024] Figure 3 1 is the electron paramagnetic resonance image of 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention;

[0025] Figure 4 is the UV-visible diffuse reflectance spectra of 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention;

[0026] Figure 5 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention are fluorescence emission spectra;

[0027] Figure 6 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention are photocurrent response graphs;

[0028] Figure 7 This is the photocatalytic degradation curve of tetracycline by 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0030] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] The sources of the instruments and reagents used in the examples are as follows:

[0032] Reagents: Dicyandiamide, ammonium molybdate, ferric sulfate, and tetracycline hydrochloride were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0033] Instruments included a muffle furnace (B410, Nabertherm, Germany); an X-ray powder diffractometer (SmartLab SE, Rigaku, Japan); an ultraviolet-visible spectrophotometer (UV-2700, Shimadzu, Japan); a scanning electron microscope (SU8010, HITACHI); a solid-state ultraviolet diffuse reflectance spectrometer (Cary 5000, Agilent Technologies, USA); nitrogen adsorption-desorption spectrometer (Mini X, Microtrac BEL, Japan); a fluorescence spectrometer (F97, Shanghai Lingguang Technology Co., Ltd.); an electrochemical workstation (Squidstat Plus, Advantec, USA); and a photocatalytic device (PCX-50C Discover, Beijing Perfect).

[0034] Example 1

[0035] (1) First, weigh 2 g of dicyandiamide (C2H4N4) and dissolve it in 30 mL of deionized water. Stir continuously at 50 °C to form a transparent solution. Then add 20 mg of ferromolybdic acid (NH4)3 [FeMo6O 18 (OH)6]·6H2O, stirring and mixing evenly; continuing stirring at 65 °C until all water evaporates completely to obtain a solid, and grinding to form a mixed powder;

[0036] (2) The mixed powder was placed in a crucible with a lid and calcined at 500 °C in a muffle furnace for 4 h. The starting temperature was 25 °C and the heating rate was 5 °C / min. The obtained sample was a double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN.

[0037] Example 2

[0038] (1) First, weigh 2 g of dicyandiamide (C2H4N4) and dissolve it in 30 mL of deionized water. Stir continuously at 50 °C to form a transparent solution. Then add 10 mg of ferromolybdic acid (NH4)3 [FeMo6O 18 (OH)6]·6H2O, stirring and mixing evenly; continuing stirring at 60°C until all water evaporates completely to obtain a solid, and grinding to form a mixed powder;

[0039] (2) The mixed powder was placed in a crucible with a lid and calcined at 500 °C in a muffle furnace for 4 h. The starting temperature was 25 °C and the heating rate was 5 °C / min. The obtained sample was a double-defect modified porous carbon nitride photocatalyst 10-FeMoO-CN.

[0040] Example 3

[0041] (1) First, weigh 2 g of dicyandiamide (C2H4N4) and dissolve it in 30 mL of deionized water. Stir continuously at 50 °C to form a transparent solution. Then add 30 mg of ferromolybdic acid (NH4)3 [FeMo6O 18 (OH)6]·6H2O, stirring and mixing evenly; continuing stirring at 70 °C until all water evaporates completely to obtain a solid, and grinding to form a mixed powder;

[0042] (2) The mixed powder was placed in a crucible with a lid and calcined at 500 °C in a muffle furnace for 4 h. The starting temperature was 25 °C and the heating rate was 5 °C / min. The obtained sample was a double-defect modified porous carbon nitride photocatalyst 30-FeMoO-CN.

[0043] Comparative Example 1

[0044] A double-defect modified porous carbon nitride photocatalyst was prepared according to the method of Example 1, except that 60 mg of ferromolybdic acid was added in step (1).

[0045] Comparative Example 2

[0046] Take 30 mg iron molybdate (NH4) 3[FeMo6O 18 (OH)6]·6H2O, 1g g-C3N4 is placed in a mortar and ground for 20 min to mix well, forming a mixture powder, and the mixture powder is placed in a covered crucible and calcined at 200-300℃ in a muffle furnace for 1-2h, with an initial temperature of 25℃ and a heating rate of 2-5 ℃ / min. The obtained sample is a composite photocatalyst with iron molybdate loaded on the surface of g-C3N4.

[0047] Comparative Example 3

[0048] The cobalt molybdate modified graphite phase carbon nitride material is prepared according to the method disclosed in the prior research content patent CN114192102B of the present inventors.

[0049] Comparative Example 4

[0050] The double-defect modified porous carbon nitride photocatalyst is prepared according to the method of Example 1, except that 20 mg nickel molybdate (NH4) 4[NiMo6O 18 (OH)6]·7H2O is added in step (1).

[0051] Comparative Example 5

[0052] The double-defect modified porous carbon nitride photocatalyst is prepared according to the method of Example 1, except that 20 mg manganese molybdate (NH4) 3[MnMo6O 18 (OH)6]·6H2O is added in step (1).

[0053] Verification Example

[0054] 1. Scanning electron microscopy characterization

[0055] The double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN prepared in Example 1 is subjected to scanning electron microscopy test, Figure 1 is its scanning electron microscopy image. As can be seen from the image, the prepared double-defect modified porous carbon nitride photocatalyst presents a thin-layer porous structure, with many pores of 10-60 μm in size on the surface. The porous layered structure increases the specific surface area of the catalyst, provides more surface active sites for adsorption and reaction, and improves the mass transfer rate.

[0056] 2. X-ray diffraction test

[0057] The double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN prepared in Example 1 and pure g-C3N4 (CN) are subjected to X-ray diffraction test, and the test results are as followsFigure 2 As shown in the figure, the diffraction peaks at 13.1° and 27.5° correspond to the (100) and (002) crystal planes of g-C3N4, respectively. The XRD spectrum of 20-FeMoO-CN is similar to that of pure g-C3N4 (CN), indicating that the introduction of ferromolybdic acid did not destroy the original crystal structure of carbon nitride. However, the peak intensity decreased, and the (100) crystal plane peak decreased, which was attributed to the reduction of the plane size by ferromolybdic acid etching. The peak of the (002) crystal plane moved from 27.5° to 27.6°, indicating that the distance between the layers was reduced, which is conducive to light absorption and photogenerated carrier transport. No FeMoO signal was observed in the XRD spectrum, indicating that FeMoO is embedded in the carbon nitride skeleton.

[0058] 3. Electron Paramagnetic Resonance

[0059] Electron paramagnetic resonance (EPR) tests were performed on the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN and pure g-C3N4 (CN) prepared in Example 1 to analyze whether there were nitrogen defects in the catalysts. The test results are as follows: Figure 3 As shown in Figure 3, 20-FeMoO-CN shows a stronger electron paramagnetic resonance signal than pure g-C3N4(CN) when the g value is close to 2.003. This is because there are more unpaired electrons on the carbon atoms in the π-conjugated aromatic ring due to the presence of N defects. The presence of nitrogen defects in 20-FeMoO-CN helps to enhance the effective charge separation.

[0060] 4. UV-visible diffuse reflectance spectrum

[0061] The UV-visible diffuse reflectance spectra of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN and pure g-C3N4 (CN) prepared in Test Implementation 1 are as follows: Figure 4 As shown in the figure, compared with pure g-C3N4(CN), the visible light absorption intensity of 20-FeMoO-CN is significantly enhanced, and the absorption edge is significantly red-shifted, extending to 800 nm.

[0062] 5. Fluorescence emission spectrum

[0063] Figure 5 Figure 1 is the fluorescence emission spectra of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN and pure g-C3N4 (CN) prepared by implementation 1. It can be seen from the figure that compared with pure g-C3N4 (CN), the peak intensity of 20-FeMoO-CN is significantly weakened, indicating that the recombination rate of photogenerated electron-hole pairs in 20-FeMoO-CN is lower, that is, the charge separation effect is higher.

[0064] 6. Photocurrent test

[0065] Figure 6The photocurrent test of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN and pure g-C3N4 (CN) prepared in Implementation 1 is shown. As can be seen from the figure, the photocurrent intensity of 20-FeMoO-CN is significantly improved compared with pure g-C3N4 (CN), indicating that under visible light irradiation, 20-FeMoO-CN has a stronger ability to separate and transfer photogenerated carriers.

[0066] 7. Photocatalytic degradation of tetracycline

[0067] 40 mg of the modified carbon nitride photocatalyst prepared in Examples 1-3 and Comparative Examples 1-5, pure g-C3N4, and 100 mL of a 20 mg / L tetracycline hydrochloride solution were added to an open reactor. After stirring for 30 minutes in the dark to reach adsorption equilibrium, the mixed solution was irradiated with a 5 W LED lamp (wavelength range 380-780 nm) as a light source. Then, 5 mL of the solution was taken from the reaction system every 5 minutes, the catalyst was removed after high-speed centrifugation, and the supernatant was taken and tested with a UV-visible spectrophotometer to evaluate the catalytic performance. The photocatalytic degradation curve of tetracycline by the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN and pure g-C3N4 (CN) in Example 1 is shown in FIG. Figure 7 The degradation rates of tetracycline of the modified carbon nitride photocatalysts prepared in Examples 1-3 and Comparative Examples 1-5 and pure g-C3N4 after irradiation with visible light for 60 minutes are shown in Table 1.

[0068] Table 1.

[0069]

[0070] The experimental results show that the catalyst polyacid-modified graphite-phase carbon nitride materials prepared in Examples 1-3 can achieve tetracycline degradation rates of 95.3%, 71.2%, and 88.4%, respectively, after irradiation with visible light for 60 minutes. The efficiency of the photocatalysts prepared in Examples 1-3 in photocatalytic degradation of tetracycline is higher than that of graphite-phase carbon nitride materials prepared with other types of polyacids, higher than that of materials in which polyacids are loaded on the surface of graphite-phase carbon nitride materials to form heterojunctions, and higher than that of pure g-C3N4 materials.

[0071] Due to the different amounts of polyacid used, the degree of etching of carbon nitride is different. The amount of polyacid used in comparative example 1 is too much, resulting in an increase in nitrogen vacancies and metal oxide doping, defects forming trap centers, and an increase in defect concentration, resulting in the formation of new charge recombination centers in the trap centers, a decrease in charge separation efficiency, and a decrease in oxidation ability.

[0072] In the composite photocatalyst prepared in Comparative Example 2, ferromolybdic acid is loaded on the surface of g-C3N4 to form a heterojunction, and the specific surface area is small; while the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN prepared in the present application adopts simultaneous morphology structure regulation and defect regulation, with a larger specific surface area, more exposed adsorption and reaction active sites, and stronger oxidation ability.

[0073] Comparative Examples 3-5, respectively using cobalt molybdate (NH4)4[Co(II)Mo6O 24 H6], nickel molybdate (NH4)4[NiMo6O 18 (OH)6]·7H2O, manganese molybdate (NH4)3[MnMo6O 18 The preparation of a double-defect porous carbon nitride photocatalyst using [(OH)6]·6H2O reveals that, due to the varying redox abilities of the polyacids' central heteroatoms, the extent of their etching of the carbon nitride varies, leading to varying pore structures and nitrogen vacancy concentrations. Furthermore, the varying types of metal oxides derived from the polyacids lead to varying physicochemical properties of the modified carbon nitride, including band gap structure and visible light absorption intensity. This combination of factors results in varying photocatalytic performance, with ferromolybdic acid-modified carbon nitride performing best under visible light for tetracycline degradation.

Claims

1. A method for preparing a double-defect modified porous carbon nitride photocatalyst using ferromolybdic acid in one step, characterized in that: The following steps are involved: (1) Dicyandiamide and polyacid are mixed evenly; the polyacid is Anderson type ferromolybdic acid, and its chemical formula is: (NH4)3[FeMo6O 18 (OH)6]·6H2O; (2) Calcination in a muffle furnace at 500 °C for 4 hours finally yielded a nitrogen-deficient, metal oxide-doped porous carbon nitride photocatalyst.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of ferromolybdic acid to dicyandiamide is 0.005-0.015:

1.

3. The preparation method according to claim 2, characterized in that In step (1), the mass ratio of ferromolybdic acid to dicyandiamide is 0.01-0.015:

1.

4. The preparation method according to claim 1, characterized in that The specific steps of step (1) uniformly mixing dicyandiamide and ferromolybdic acid are as follows: dissolve dicyandiamide in water, continuously stir at 50°C to form a transparent solution, then add ferromolybdic acid, stir and mix evenly, continue stirring at 60-70°C until all water evaporates completely to obtain a solid, and grind into powder.

5. The preparation method according to claim 4, characterized in that The dicyandiamide and the ferromolybdic acid aqueous solution were stirred and mixed uniformly, and then continued to be stirred at 65° C. until all the water was completely evaporated to obtain a solid.

6. The preparation method according to claim 1, characterized in that In step (2), the muffle furnace is heated to 500°C at a heating rate of 5°C / min.

7. The double-defect modified porous carbon nitride photocatalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: It is a porous layered graphite phase carbon nitride material, which is stacked in layers, and has a large number of 10-60 nm pores distributed on the surface of the layers.

8. Use of the double-defect modified porous carbon nitride photocatalyst according to claim 7 in photocatalytic degradation of tetracycline.

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