CN107837816B - Fe2O3/g-C3N4 composite system and preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of photocatalyst synthesis, and particularly relates to Fe₂O₃/g‑C₃N₄The composite system, the preparation method and the application can be used for visible light catalytic degradation of tetracycline hydrochloride pollutants. P123 and hexamethyleneimine were accurately weighed, dissolved in a mixed solution of absolute ethanol and ethylene glycol, and stirred to obtain a solution A. Accurately weighing ferric chloride tetrahydrate, and adding the ferric chloride to the solution A to be ultrasonically dissolved to form a solution B. Adding mesoporous g-C into the solution B₃N₄A suspension C was formed. And carrying out ultrasonic dispersion and magnetic stirring on the suspension C to obtain a turbid liquid D. Transferring the turbid solution D into a reaction kettle, and reacting for 15h in an oven at 200 ℃. And after naturally cooling to room temperature, centrifuging, washing and drying to obtain solid F. And (4) putting the solid F into a crucible, and putting the crucible into a muffle furnace for calcining to obtain a sample.

Description

Fe2O3/g-C3N4 composite system and preparation method and application

technical field

_The invention belongs to the technical field of photocatalyst synthesis, and utilizes a simple and fast solvothermal method to synthesize mesoporous Fe ₂ O ₃ nanometer balls modified _{gC 3} N ₄ in one _{step .} The system can be used for visible light catalytic degradation of tetracycline hydrochloride pollutants.

Background technique

With the increasing global energy crisis and environmental pollution problems, it is imperative to develop and utilize clean and renewable energy. Solar energy is one of the cleanest, most realistic and most promising renewable energy sources in the world, suitable for large-scale development and utilization. The photocatalytic technology has the characteristics of energy saving, high efficiency and environmental protection, and is an ideal new method to use clean solar energy to control environmental pollution. However, the design and preparation of photocatalytic materials with efficient photocatalytic properties is still a huge challenge for researchers.

In recent years, conductive polymeric carbon nitride-based materials have attracted much attention because of their good optical properties and surface adsorption properties, and have become new targets for modifying semiconductor materials. Graphite phase carbon nitride (gC ₃ N ₄ for short) is a unique non-metallic semiconductor photocatalytic material, which not only has a narrow band gap (2.7 eV) and can respond to visible light, but also has acid resistance. It is one of the research hotspots in the field of photocatalytic degradation of organic pollutants. However, gC ₃ N ₄ still has some shortcomings, such as low specific surface area and high recombination rate of photogenerated electron-hole pairs, which lead to its low photocatalytic performance. The study found that the use of the superior adsorption performance of gC ₃ N ₄ and the synergistic effect between different energy levels with metal oxides can effectively achieve the efficient separation of electron-hole pairs and greatly improve the photocatalytic activity.

Iron oxide is nontoxic, cheap and abundant, and exhibits a relatively narrow band gap, enabling it to respond to a wide range of visible light. However, single iron oxide has low photocatalytic activity due to the high recombination rate of photogenerated carriers. Therefore, a "Z _- Scheme" type composite system was constructed with Fe ₂ O ₃ and gC ₃ N ₄ by using Fe ₂ O ₃ as the composite structural unit _. It will greatly improve the photocatalytic performance and be used to remove organic pollutants in water, opening up a new way for the construction of new composite visible photocatalytic materials.

In this work, mesoporous "Z _- Scheme"-type _{Fe2O3 / gC3N} was constructed in one step by a simple and fast solvothermal method by surface modification _{of gC3N4} using mesoporous _Fe2O3 nanospheres ₄ composite systems. Compared with pure gC ₃ N ₄ , the photocatalytic activity of the optimal mesoporous “Z-Scheme” type Fe ₂ O ₃ /gC ₃ N ₄ composite system can degrade tetracycline hydrochloride as high as 73.78% within 120 min, which is the highest for pure gC 3 N 4 . 2.63 times that of ₃ N ₄ (28.08%). The surface modification effect of mesoporous Fe ₂ O ₃ nanospheres on gC ₃ N ₄ significantly improves its light-collecting ability and carrier separation efficiency, while increasing the specific surface area and surface active sites, which ultimately greatly improves the Degradation efficiency of tetracycline hydrochloride contaminants. So far, a "Z _- Scheme"-type _{Fe2O3 / gC3N4} composite system for the synthesis _of mesoporous _Fe2O3 nanospheres modified _gC3N4 by a one-step solvothermal method has not been found _.

SUMMARY OF THE INVENTION

_The invention belongs to the technical field _of nanomaterial synthesis, and utilizes a simple and fast _solvothermal method to synthesize _{mesoporous Fe2O3 nanospheres} modified _gC3N4 in one step by a simple and fast solvothermal method _. The system can be used for visible light catalytic degradation of tetracycline hydrochloride pollutants.

The preparation method of the present invention features the following steps:

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and hexamethyleneimine, and dissolve them in a mixed solution of absolute ethanol and ethylene glycol , and stirred to obtain solution A.

2. Accurately weigh ferric chloride tetrahydrate, add it to solution A and dissolve by ultrasonic to form solution B.

_3. Add mesoporous _gC3N4 to solution B to form suspension C.

4. Perform ultrasonic dispersion and magnetic stirring on the suspension C to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged, washed and dried to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace for calcination to obtain a sample.

The mass volume ratio of P123, the mixed solution of hexamethyleneimine and absolute ethanol and ethylene glycol is 0.2g: 0.1g: 29.5ml, wherein in the mixed solution of absolute ethanol and ethylene glycol, absolute ethanol and The volume ratio of ethylene glycol is 16.5:13; the mass ratio of gC ₃ N ₄ and P123 and hexamethyleneimine is 3:2:1.

Wherein the amount of ferric chloride tetrahydrate was weighed according to the mass ratio _{of Fe2O3} and _gC3N4 from 0.003:0.3 to 0.045:0.3, mesoporous "Z _- Scheme" type _{Fe2O3 / gC3N4 composite} The mass percentages of Fe ₂ O ₃ to gC ₃ N ₄ in the system are respectively 1 wt % to 15 wt %, preferably 5 wt %.

In step (1), the stirring time was 30 min.

In step (4), the time of ultrasonic dispersion is 30min, and the time of magnetic stirring is 48h.

The drying temperature in step (6) is 80°C.

In step (7), the calcination temperature is 350° C., and the calcination time is 2h.

In the present invention, the mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N was analyzed by means of X-ray diffraction (XRD), transmission electron microscope (TEM), N ₂ adsorption-desorption isotherm and BJH pore size distribution. ₄ The composite system was characterized. As shown in Figure ₁ , the XRD diffraction peaks of _gC3N4 hardly changed after surface modification with _Fe2O3 , which may be due to the lower content _of mesoporous _{Fe2O3 nanospheres} . Figure 2(a,b) are the FESEM photographs and EDS spectra (inset) of pure gC ₃ N ₄ and mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system, as can be seen from the figure gC ₃ N ₄ has a sheet-like structure, and Fe ₂ O ₃ nanospheres are uniformly dispersed on the surface of gC ₃ N ₄ nanosheets. Meanwhile, Fig. ₂ (c) is the TEM image of pure _gC3N4 , and the nanosheet morphology of _gC3N4 can be clearly observed _. While Fig. 2(d,e) are TEM images of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ , it can be observed that Fe ₂ O ₃ nanospheres are uniformly decorated on the surface of gC ₃ N ₄ nanosheets , whose diameter is about 140 nm, and the _Fe2O3 nanospheres exhibit mesoporous structure features composed _of nanodots. Figure 2(f) is the HRTEM and SAED images (inset) of the mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ with a lattice spacing of 0.252 nm corresponding to the (110) plane of Fe ₂ O ₃ , and the nanodots are in a single crystal state. In addition, the N ₂ adsorption and desorption curves and pore size distribution in Fig. 3(a,b) further prove that the sample is a mesoporous structure with a pore size of about 35 nm. Figure 4(a,b) shows that the obtained mesoporous "Z-Scheme"-type Fe ₂ O ₃ /gC ₃ N ₄ composite system remarkably enhanced the photocatalytic performance for degrading tetracycline hydrochloride pollutants, and at the same time had high stability and reusability.

In the present invention, a mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system is constructed by precisely controlling the reaction conditions and the amount of reactants. The modification effect of mesoporous Fe ₂ O ₃ nanospheres on gC ₃ N ₄ significantly improves the carrier separation efficiency and light absorption capacity, and increases the specific surface area and surface active sites, which are the main reasons for improving the photocatalytic activity. The distinguishing technical feature of the present invention from the prior art is that this simple one _- step solvothermal method is used to synthesize mesoporous "Z _- Scheme" type _{Fe 2 O 3 /} gC ₃ N ₄ composite system, and the mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system solves the problem of low degradation efficiency of tetracycline hydrochloride pollutants by some photocatalysts under visible light.

The main purposes of the present invention: 1. Provide a typical example for constructing a "Z-Scheme" type composite system by controlling the surface microstructure of the heterojunction by a simple method; 2. Mesoporous Fe ₂ O ₃ nanospheres modify gC ₃ N ₄ The mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system can be used for photocatalytic degradation of tetracycline hydrochloride pollutants under visible light.

beneficial effect

_A mesoporous "Z _- Scheme"-type _Fe2O3 / _gC3N4 composite system _{of gC3N4} modified by mesoporous _Fe2O3 nanospheres was constructed by a simple and fast one _- step solvothermal method, which degrades hydrochloric acid under visible light Tetracycline shows excellent photocatalytic activity; the invention has simple process, convenient operation and short reaction time, thereby reducing energy consumption and production cost, facilitating mass production, being non-toxic and harmless, and meeting the requirements of environmental friendliness.

Description of drawings

Fig.1 XRD spectra of gC ₃ N ₄ and mesoporous “Z-Scheme” type Fe ₂ O ₃ /gC ₃ N ₄ composite system.

Fig. 2 FESEM images (a, b) and EDS spectra (inset b) of gC ₃ N ₄ and mesoporous “Z-Scheme” type Fe ₂ O ₃ /gC ₃ N ₄ composite system, gC ₃ N ₄ (c) and TEM images of the mesoporous “Z-Scheme” Fe ₂ O ₃ /gC ₃ N ₄ composite system (d, e) and HRTEM of the mesoporous “Z-Scheme” Fe ₂ O ₃ /gC ₃ N ₄ composite system Photo (f) and SAED (f inset).

Fig. 3 N ₂ adsorption-desorption isotherms (a) and pore size distributions (b) of gC ₃ N ₄ and mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system.

Figure 4. Kinetic curve (a) of sample degradation of tetracycline hydrochloride under visible light and degradation rate (b) of five cycles.

Detailed ways

Example 1: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2g of P123 and 0.1g of hexamethyleneimine, dissolve them in a mixed solution of 16.5ml of absolute ethanol and 13ml of ethylene glycol, and stir for 30min to obtain solution A.

2. Accurately weigh 0.0077g of ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

Example 2: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2 g of P123 and 0.1 g of hexamethyleneimine, dissolve them in a mixed solution of 16.5 ml of absolute ethanol and 13 ml of ethylene glycol, and stir for 30 minutes to obtain solution A.

2. Accurately weigh 0.0231g of ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

Example 3: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2 g of P123 and 0.1 g of hexamethyleneimine, dissolve them in a mixed solution of 16.5 ml of absolute ethanol and 13 ml of ethylene glycol, and stir for 30 minutes to obtain solution A.

2. Accurately weigh 0.0386g of ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

Example 4: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it and put it into a crucible, add a lid, and heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C/min for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2 g of P123 and 0.1 g of hexamethyleneimine, dissolve them in a mixed solution of 16.5 ml of absolute ethanol and 13 ml of ethylene glycol, and stir for 30 minutes to obtain solution A.

2. Accurately weigh 0.0540g ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

Example 5: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2 g of P123 and 0.1 g of hexamethyleneimine, dissolve them in a mixed solution of 16.5 ml of absolute ethanol and 13 ml of ethylene glycol, and stir for 30 minutes to obtain solution A.

2. Accurately weigh 0.077 1g ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

Example 6: Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Preparation of _{gC3N4 photocatalyst}

1. Weigh the urea, dry it in an oven at 80°C for 24h, grind it, put it into a crucible, add a lid, heat it from room temperature to 550°C in a muffle furnace at a heating rate of 2°C min ^-1 , and calcine for 4h.

2. After taking out, soak and stir with 1 mol L ^-1 nitric acid for 24 hours, filter, then wash with distilled water for 7-8 times until neutral, and dry in an oven at 80°C for 24 hours.

3. The sample was taken out and ground, placed in a crucible, and calcined in a muffle furnace at 500° C. for 4 hours without a cover to obtain a mesoporous gC ₃ N ₄ photocatalyst.

2. Preparation of mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system

1. Accurately weigh 0.2 g of P123 and 0.1 g of hexamethyleneimine, dissolve them in a mixed solution of 16.5 ml of absolute ethanol and 13 ml of ethylene glycol, and stir for 30 minutes to obtain solution A.

2. Accurately weigh 0.1157g of ferric chloride tetrahydrate, add it to solution A and dissolve it by ultrasonic to form solution B.

_3. Add 0.3 g of _gC3N4 to solution B to form suspension C.

4. After ultrasonically dispersing the suspension C for 30 min, magnetic stirring was performed for 48 h to obtain the turbid liquid D.

5. Transfer the turbid liquid D to the reaction kettle and react in an oven at 200°C for 15h.

6. After being naturally cooled to room temperature, centrifuged and washed three times with deionized water and ethanol, and dried in an oven at 80° C. to obtain solid F.

7. Put the solid F into a crucible, and put it into a muffle furnace at 350°C for 2h calcination to obtain a sample.

"Z-Scheme" type mesoporous Fe ₂ O ₃ /gC ₃ N ₄ with mesoporous Fe ₂ O ₃ nanospheres modified by gC ₃ N ₄ was prepared by one-step solvothermal method by controlling the mass of ferric chloride tetrahydrate added. composite system, the degradation effect of 50 mg of each sample on tetracycline hydrochloride solution (10 mg L ^-1 ) under visible light was investigated, and the results showed that this unique mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite The system significantly enhanced the photocatalytic activity. In addition, the 5 wt% mesoporous "Z-Scheme" type Fe ₂ O ₃ /gC ₃ N ₄ composite system has the best catalytic performance. After 120 min of visible light irradiation, the degradation rate of tetracycline hydrochloride reaches 73.78%, indicating that the The obtained mesoporous "Z-Scheme" Fe ₂ O ₃ /gC ₃ N ₄ composite system can be applied to the treatment of tetracycline hydrochloride pollutants.

Claims (9)

1.Fe₂O₃/g-C₃N₄A composite system of mesoporous Fe₂O₃Nanosphere-modified g-C₃N₄Mesoporous 'Z-Scheme' type Fe₂O₃/g-C₃N₄The composite system is characterized by being prepared by the following method:

(1) accurately weighing a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and hexamethyleneimine, dissolving in a mixed solution of absolute ethyl alcohol and ethylene glycol, and stirring to obtain a solution A;

(2) accurately weighing ferric chloride tetrahydrate, and adding the ferric chloride tetrahydrate into the solution A to be ultrasonically dissolved to form a solution B;

(3) adding mesoporous g-C into the solution B₃N₄Forming a suspension C;

(4) carrying out ultrasonic dispersion and magnetic stirring on the suspension C to obtain a turbid liquid D;

(5) transferring the turbid solution D into a reaction kettle, and reacting for 15h in an oven at 200 ℃;

(6) after naturally cooling to room temperature, centrifuging, washing and drying to obtain solid F;

(7) putting the solid F into a crucible, and putting the crucible into a muffle furnace for calcining to obtain a sample;

the mesoporous g-C₃N₄The preparation method comprises the following steps:

weighing urea, drying in an oven at 80 deg.C for 24h, grinding and loading into a crucible, adding a lid, and heating in a muffle furnace at 2 deg.C for 2 min^-1Heating rate of from room temperature toCalcining for 4h at 550 ℃;

taken out and then used for 1mol L^-1Soaking in nitric acid, stirring for 24h, filtering, washing with distilled water for 7-8 times to neutrality, and drying in an oven at 80 deg.C for 24 h;

taking out a sample, grinding, placing in a crucible, calcining in a muffle furnace at 500 ℃ for 4h without covering to obtain mesoporous g-C₃N₄A photocatalyst.

2. Fe as claimed in claim 1₂O₃/g-C₃N₄The composite system is characterized in that the mass volume ratio of the P123, the hexamethyleneimine to the mixed solution of the absolute ethyl alcohol and the ethylene glycol is 0.2 g: 0.1 g: 29.5ml, wherein in the mixed solution of the absolute ethyl alcohol and the glycol, the volume ratio of the absolute ethyl alcohol to the glycol is 16.5: 13; g-C₃N₄And the mass ratio of P123 to hexamethyleneimine is 3: 2: 1.

3. fe as claimed in claim 1₂O₃/g-C₃N₄Composite system, characterized in that the amount of iron dichloride tetrahydrate is in accordance with Fe₂O₃And g-C₃N₄0.003: 0.3 to 0.045: 0.3 weight of mesoporous 'Z-Scheme' type Fe₂O₃/g-C₃N₄Fe in composite system₂O₃For g-C₃N₄Is 1 wt% to 15 wt%.

4. Fe as claimed in claim 3₂O₃/g-C₃N₄A composite system characterized by mesoporous 'Z-Scheme' type Fe₂O₃/g-C₃N₄Fe in composite system₂O₃For g-C₃N₄Is 5 wt%.

5. Fe as claimed in claim 1₂O₃/g-C₃N₄The composite system is characterized in that in the step (1), the stirring time is 30 min.

6. Fe as claimed in claim 1₂O₃/g-C₃N₄The composite system is characterized in that in the step (4), the ultrasonic dispersion time is 30min, and the magnetic stirring time is 48 h.

7. Fe as claimed in claim 1₂O₃/g-C₃N₄The composite system is characterized in that the drying temperature in the step (6) is 80 ℃.

8. Fe as claimed in claim 1₂O₃/g-C₃N₄The composite system is characterized in that the calcination temperature in the step (7) is 350 ℃, and the calcination time is 2 hours.

9. Fe as claimed in any one of claims 1 to 8₂O₃/g-C₃N₄The application of the composite system is used for degrading tetracycline hydrochloride pollutants by visible light catalysis.

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