A porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate and a preparation method and application thereof

Abstract

The application provides a kind of porous carbon nitride photocatalyst with double defect modification prepared by iron molybdate in one step and its preparation method and application.The catalyst 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 is significantly enhanced. The defects formed by the presence of surface N vacancies and the doping of metal oxides help to enhance the effective charge separation, and the ability of photogenerated carrier separation and transfer under visible light irradiation is stronger, and the catalytic activity is significantly improved. The application of the photocatalyst in degrading tetracycline antibiotic pollutants only needs to achieve photocatalytic degradation of tetracycline under the condition of low-power 5 W LED visible light, and the preparation process is simple and the cost is lower.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photocatalysis, and particularly relates to a porous carbon nitride photocatalyst with double defects prepared by one step of iron molybdate and application of the photocatalyst in degradation of tetracycline antibiotic pollutants. BACKGROUND

[0002] Tetracycline antibiotics are the most widely used and frequently used antibiotics, and are widely used in medicine, livestock and aquaculture industries. Tetracycline molecules contain four parallel rings, have complex and stable structures, and are difficult to be completely absorbed and degraded. The large-scale use and improper discharge of tetracycline antibiotics will lead to the increasingly serious problem of tetracycline residues in the environment, and pose multiple threats to the ecological system and human health. Photocatalytic degradation of tetracycline antibiotics is a kind of advanced oxidation technology that uses active substances such as hydroxyl radicals ·OH, superoxide radicals ·O2 - , and holes h + generated by semiconductor materials under light to oxidize and decompose tetracycline antibiotic pollutants, and is an efficient and environmentally friendly wastewater treatment technology.

[0003] Graphitic carbon nitride (g-C3N4) is a new type of polymer semiconductor photocatalytic material, which has good visible light response, high stability and easy preparation, and is one of the commonly used catalysts for photocatalytic degradation of tetracycline. However, for pure g-C3N4, there are problems such as limited visible light absorption range, small specific surface area (usually less than 10 m 2 ·g -1 ), and easy recombination of photo-generated electrons and holes, which seriously limit the adsorption capacity and photocatalytic performance of pollutants. At present, the improvement strategies for pure g-C3N4 include: morphology control to form a porous structure, increase the specific surface area, and accelerate the transmission rate of pollutants and products; introducing defects such as vacancies or doping, generating defect energy levels, and promoting the separation of photo-generated carriers; and constructing heterojunctions to promote the separation of photo-generated electrons and holes.

[0004] Polyoxometalates (POMs) are a class of polynuclear metal clusters, which have nearly two hundred years of development history, and have become an important research field in inorganic chemistry. Polyoxometalates have a clear molecular structure, adjustable composition, nanoscale size, strong acidity and excellent redox ability. The prior art CN114192102B discloses a kind of graphite phase carbon nitride material modified by polyoxometalate prepared by one step of Anderson type cobalt molybdate, a porous structure is manufactured by polyoxometalate etching technology, nitrogen vacancies are introduced at the same time, polyoxometalate derived metal oxide is embedded into the structure of g-C3N4, the process is simple, the morphology control and double defect control of g-C3N4 are realized in one step, the absorption range and intensity of visible light are widened, the specific surface area is increased, and the separation efficiency of photo-generated carriers is enhanced, and the mass transfer rate of pollutants and products is accelerated, but the prepared cobalt molybdate modified graphite phase carbon nitride material has weak oxidation ability on the one hand, and on the other hand, the cobalt molybdate modified carbon nitride has strong adsorption capacity for cationic dyes, which leads to the aggregation of dyes on the surface of carbon nitride, affects the optical density, and has adverse effects on photocatalytic degradation, so in the experimental process, the photocatalytic activity of cobalt molybdate modified carbon nitride for antibiotics such as tetracycline hydrochloride and gold chloroform hydrochloride is poor.

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

[0006] Therefore, how to improve the efficiency of g-C3N4 photocatalytic degradation of tetracycline class pollutants and improve its catalytic performance, while the method is simple and conducive to industrial production, is still a technical problem to be solved in the art.

[0007] The information disclosed in this Background section is intended only to increase an understanding of the general background of the application, and is not admitted to be prior art against anyone except the patentee, nor does it constitute an admission that the information forms any part of the prior art. SUMMARY

[0008] In order to improve the deficiency of existing graphite carbon nitride (g-C3N4) in photocatalytic degradation of tetracycline antibiotic pollutants, the application provides a kind of porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate, compared with other kinds of polyacid modified graphite phase carbon nitride materials or the way of loading polyacid on the surface of graphite phase carbon nitride material to form heterojunction, the prepared iron molybdate modified double defect carbon nitride material has stronger oxidation capacity and higher catalytic activity, and can more efficiently catalyze and degrade tetracycline pollutants.

[0009] Specifically, the technical scheme of the application is as follows:

[0010] A kind of porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate, comprising the following steps:

[0011] (1) mix dicyandiamide and polyacid uniformly, the polyacid is Anderson type iron molybdate, and the chemical formula is (NH4)3[FeMo6O 18 (OH)6]·6H2O;

[0012] (2) calcine in a muffle furnace, and keep at 500 DEG C for 4 hours, to finally obtain a porous carbon nitride photocatalyst with nitrogen defects and metal oxide doping.

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

[0014] In some embodiments, the specific steps of mixing dicyandiamide and iron molybdate uniformly in step (1) are as follows: dissolve dicyandiamide in water, continuously stir at a temperature of 50 DEG C to form a transparent solution, then add iron molybdate, stir and mix uniformly, continue to stir at a temperature of 60-70 DEG C until all the water evaporates completely to obtain a solid, and grind into powder; preferably, the dicyandiamide and iron molybdate aqueous solution is continuously stirred at 65 DEG C until all the water evaporates completely to obtain a solid.

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

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

[0017] The application of a porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate in photocatalytic degradation of tetracycline, wherein the degradation rate of tetracycline is greater than 95.3% after visible light irradiation for 60 min.

[0018] The application has the following beneficial effects:

[0019] (1) The porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate has a conduction band potential of-0.66 eV and a valence band potential of 2.06 eV, and the oxidation ability of holes on the valence band is improved, so that the holes can oxidize pollutants, and the valence band potential is more positive than OH - / ·OH (1.99 V relative to the standard hydrogen electrode), and the holes can oxidize OH - into ·OH which can efficiently oxidize organic pollutants, so that the tetracycline pollutants can be efficiently oxidized by superoxide radicals, hydroxyl radicals and holes.

[0020] (2) The porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate 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 is obviously enhanced, and the defects formed by the existence of surface N vacancies and the doping of metal oxides help to enhance the effective charge separation, so that the recombination rate of photo-generated electron-hole pairs is lower, and the separation and transfer ability of photo-generated carriers is stronger under visible light irradiation, and the catalytic activity is obviously improved.

[0021] (3) The porous carbon nitride photocatalyst with double defect modification prepared by one step of iron molybdate has a low dosage of iron molybdate, and only one third of the dosage of cobalt molybdate in the prior research is needed to form a porous structure on the surface of carbon nitride, and the catalytic performance is improved, so that the photocatalytic degradation of tetracycline can be realized under the condition of low-power 5 W LED visible light, the preparation process is simple, and the cost is lower. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a scanning electron microscope image of the porous carbon nitride photocatalyst (20-FeMoO-CN) with double defect modification prepared by one step of iron molybdate according to example 1 of the application;

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

[0024] Figure 3 is an electron paramagnetic resonance spectrum of 20-FeMoO-CN and pure g-C3N4 (CN) prepared in example 1 of the application;

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

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

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

[0028] Figure 7 Photocatalytic degradation of tetracycline curves of 20-FeMoO-CN and pure g-C3N4(CN) prepared in Example 1 of the present application. DETAILED DESCRIPTION

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

[0030] The embodiments of the present application are described below by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. The present application can also be implemented or applied by other different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application.

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

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

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

[0034] Example 1

[0035] (1) First, take 2 g of dicyandiamide (C2H4N4) dissolved in 30 mL of deionized water, continuously stir at 50 °C to form a transparent solution, then add 20 mg of iron molybdate (NH4)3[FeMo6O 18 (OH)6]·6H2O, stir and mix evenly; continue to stir at 65 °C until all the water evaporates completely to obtain a solid, grind to form a mixed powder;

[0036] (2) Put the mixed powder in a covered crucible, heat in a muffle furnace at 500 °C for 4 h, the initial temperature is 25 °C, the heating rate is 5 °C / min, the obtained sample is a double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN.

[0037] Example 2

[0038] (1) First, take 2 g of dicyandiamide (C2H4N4) dissolved in 30 mL of deionized water, continuously stir at 50 °C to form a transparent solution, then add 10 mg of iron molybdate (NH4)3[FeMo6O 18 (OH)6]·6H2O, stir and mix evenly; continue to stir at 60 °C until all the water evaporates completely to obtain a solid, grind to form a mixed powder;

[0039] (2) Put the mixed powder in a covered crucible, heat in a muffle furnace at 500 °C for 4 h, the initial temperature is 25 °C, the heating rate is 5 °C / min, the obtained sample is a double-defect modified porous carbon nitride photocatalyst 10-FeMoO-CN.

[0040] Example 3

[0041] (1) First, take 2 g of dicyandiamide (C2H4N4) dissolved in 30 mL of deionized water, continuously stir at 50 °C to form a transparent solution, then add 30 mg of iron molybdate (NH4)3[FeMo6O 18 (OH)6]·6H2O, stir and mix evenly; continue to stir at 70 °C until all the water evaporates completely to obtain a solid, grind to form a mixed powder;

[0042] (2) Put the mixed powder in a covered crucible, heat in a muffle furnace at 500 °C for 4 h, the initial temperature is 25 °C, the heating rate is 5 °C / min, the obtained sample is a double-defect modified porous carbon nitride photocatalyst 30-FeMoO-CN.

[0043] Comparative Example 1

[0044] Prepare a double-defect modified porous carbon nitride photocatalyst according to the method of Example 1, except that 60 mg of iron molybdate is 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 iron molybdate does not destroy the original crystal phase structure of carbon nitride. However, the peak intensity decreases, and the (100) crystal plane peak decreases, due to the etching of iron molybdate, which reduces the plane size. The peak value of the (002) crystal plane moves from 27.5° to 27.6°, indicating that the distance between the layers is reduced, which is beneficial to light absorption and photo-generated carrier transport. No signal of FeMoO is observed in the XRD spectrum, indicating that FeMoO is embedded in the carbon nitride skeleton.

[0058] 3. Electron paramagnetic resonance

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

[0060] 4. UV-Vis diffuse reflectance spectrum

[0061] The UV-Vis diffuse reflectance spectrum of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN prepared in Example 1 and pure g-C3N4 (CN) was tested, as shown in the figure. 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 to 800 nm.

[0062] 5. Fluorescence emission spectrum

[0063] Figure 5 The fluorescence emission spectrum of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN prepared in Example 1 and pure g-C3N4 (CN) is shown in the figure. As can be seen from the figure, compared with pure g-C3N4 (CN), the peak intensity of 20-FeMoO-CN is significantly weakened, indicating that the recombination rate of photo-generated electron-hole pairs of 20-FeMoO-CN is lower, i.e. the charge separation effect is higher.

[0064] 6. Photocurrent test

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

[0066] 7. Photocatalytic degradation of tetracycline

[0067] In an open reactor, 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 tetracycline hydrochloride solution with a concentration of 20 mg / L were added, stirred for 30 min in the dark to reach adsorption equilibrium, then a 5 W LED lamp (wavelength range 380-780 nm) was used as a light source to irradiate the mixed solution, then 5 mL of the solution was taken from the reaction system every 5 min, the catalyst was removed after high-speed centrifugation, and the upper clear liquid was taken for ultraviolet-visible spectrophotometer test to evaluate the catalytic performance. The photocatalytic degradation of tetracycline curves of the double-defect modified porous carbon nitride photocatalyst 20-FeMoO-CN of Example 1 and pure g-C3N4 (CN) are shown in 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 visible light irradiation for 60 min are shown in Table 1.

[0068] Table 1.

[0069]

[0070] The experimental results show that the degradation rates of tetracycline of the catalyst polyacid modified graphite phase carbon nitride materials prepared in Examples 1-3 are 95.3%, 71.2%, and 88.4% respectively after visible light irradiation for 60 min. The photocatalytic degradation efficiency of the photocatalysts prepared in Examples 1-3 is higher than that of other kinds of polyacid prepared graphite phase carbon nitride materials, higher than that of the material formed by loading polyacid on the surface of graphite phase carbon nitride material to form a heterojunction, and higher than that of pure g-C3N4 material.

[0071] Due to different amounts of polyacid, the etching degree of carbon nitride is different. The amount of polyacid in Comparative Example 1 is too much, which increases the amount of nitrogen vacancies and metal oxide doping, forms trap centers, increases the defect concentration, forms new charge recombination centers, reduces the charge separation efficiency, and reduces the oxidation ability.

[0072] The composite photocatalyst prepared in Comparative Example 2 has iron-molybdenum acid supported on the surface of g-C3N4 to form a heterojunction, resulting in a small specific surface area. In contrast, the porous carbon nitride photocatalyst 20-FeMoO-CN prepared in this application, which is modified with dual defects, has a larger specific surface area, more exposed adsorption and reaction active sites, and stronger oxidation capacity due to the simultaneous regulation of morphology and structure and defects.

[0073] Comparative Examples 3-5, respectively, utilized cobalt molybdic acid (NH4)4[Co(II)Mo6O 24 H6], Nickelmolybdic acid (NH4)4[NiMo6O 18 [(OH)6]·7H2O, manganomolybdic acid (NH4)3[MnMo6O] 18 The preparation of dual-defect porous carbon nitride photocatalysts using [OH)6·6H2O presents several challenges. Firstly, the different heteroatoms at the polyacid centers result in varying redox capabilities and etching degrees on the carbon nitride, leading to differences in pore structure morphology and nitrogen vacancy concentration. Secondly, the different types of metal oxides derived from the polyacids result in variations in the band gap structure, visible light absorption intensity, and other physicochemical properties of the modified carbon nitride. These combined factors contribute to the different photocatalytic performances of the carbon nitride, with iron-molybdenum acid-modified carbon nitride exhibiting the best performance in the visible light degradation of tetracycline pollutants.

Claims

1. The use of a double-defect modified porous carbon nitride photocatalyst prepared in one step with iron molybdate in the photocatalytic degradation of tetracycline, characterized in that, The preparation method of the porous carbon nitride photocatalyst with double defects modified by one step of iron molybdate preparation comprises the following steps: (1) mixing dicyandiamide and polyacid uniformly; the polyacid is Anderson type iron molybdenum acid, and its chemical formula is: (NH4)3[FeMo6O 18 (OH)6]·6H2O; (2) calcination in a muffle furnace, heat preservation at 500 DEG C for 4 hours, finally obtain nitrogen defect, metal oxide doped porous carbon nitride photocatalyst, namely double defect modified porous carbon nitride photocatalyst; The mass ratio of iron molybdate to dicyandiamide in step (1) is 0.01:1; The specific steps of mixing dicyandiamide and iron molybdate uniformly in step (1) are as follows: dissolve dicyandiamide in water, continuously stir at 50 DEG C to form a transparent solution, then add iron molybdate, stir and mix uniformly, continue to stir at 60-70 DEG C until all the water is completely evaporated to obtain a solid, and grind into powder; In step (2), the muffle furnace is heated to 500 DEG C at a heating rate of 5 DEG C / min.

2. Use according to claim 1, characterized in that, In step (1), continue to stir at 65 DEG C until all the water is completely evaporated to obtain a solid.

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