CN115814808B - Iron-molybdenum doped hydrothermal carbon composite material and preparation method thereof, and wastewater degradation method - Google Patents

Abstract

The invention discloses an iron-molybdenum doped hydrothermal carbon composite material, a preparation method thereof and a wastewater degradation method, belongs to the technical field of water treatment, and solves the problems of narrow pH range and high persulfate consumption, which are applicable to an activating agent used for degrading organic matters in wastewater by the existing advanced oxidation technology. The preparation method comprises the following steps: step 1, dissolving a carbon source, ferric salt and molybdate in ultrapure water, and uniformly stirring to form a mixed solution; step 2, regulating the pH value of the mixed solution obtained in the step 1 to 7-8, and uniformly stirring; and 3, carrying out hydrothermal reaction on the mixed solution, and centrifuging, washing, drying and grinding after the reaction is finished to obtain the iron-molybdenum doped hydrothermal carbon composite material. The iron-molybdenum doped hydrothermal carbon composite material can be used for advanced treatment of organic pollutants in wastewater.

Description

Iron-molybdenum doped hydrothermal carbon composite material and preparation method thereof, and wastewater degradation method

Technical Field

The present invention belongs to the technical field of water treatment, and specifically relates to an iron-molybdenum-doped hydrothermal carbon composite material and a preparation method thereof, and a wastewater degradation method.

Background technique

With the rapid development of economy and the rapid rise of chemical-related industrial production, a large amount of organic wastewater is inevitably generated. Wastewater discharged from industries such as oil refining, coking, printing and dyeing, medicine, papermaking, pesticides, etc. often contains a large amount of "priority controlled pollutants" such as benzene, naphthalene, anthraquinone, phenols, nitrobenzene, polycyclic aromatic hydrocarbons, chlorobenzene and pesticides, which have obvious carcinogenic, teratogenic and mutagenic effects. At present, the main treatment methods for organic wastewater are biological, physical and chemical methods. Commonly used physical methods include adsorption and sedimentation, but this method cannot fundamentally remove pollutants and requires further treatment, and the material also faces the problem of regeneration; biological methods include aerobic biochemical degradation, anaerobic biochemical degradation, dominant bacteria treatment, etc., but their operating conditions are high, and the disturbance of environmental factors often causes the degradation bacteria to mutate, the number decreases, and the degradation rate of pollutants slows down; chemical methods include neutralization, oxidation-reduction, electrolysis, advanced oxidation technology, etc., which are widely used in the treatment of organic pollutants due to their simple operation and strong universality. Among them, advanced oxidation technology activates catalytic materials under high temperature, high pressure, electricity, sound, light irradiation and other reaction conditions to produce strong oxidizing free radicals, decomposing pollutants in organic wastewater into organic matter with low toxicity and small molecular chains, thereby achieving the purpose of purifying organic pollution. Persulfate oxidation is an advanced oxidation technology based on the production of sulfate free radicals (SO ₄ ^·- ) to activate persulfate to oxidize and degrade pollutants. Persulfate has the characteristics of low price, easy storage and transportation, and wide pH range of pollutant solutions, and has attracted more and more attention.

Transition metal ions can activate persulfate, so transition metal ion activation has been widely studied and applied. Currently, there are studies on using ferrous molybdate to activate H ₂ O ₂ or persulfate to degrade pollutants in water, but there are still many shortcomings.

Summary of the invention

In view of the above analysis, the present invention aims to provide an iron-molybdenum-doped hydrothermal carbon composite material and a preparation method thereof, and a wastewater degradation method, which can solve one of the following technical problems: (1) The applicable pH range of the activator used in the existing advanced oxidation technology to degrade organic matter in wastewater is narrow; (2) The consumption of persulfate is large; (3) The preparation process of the activator causes extremely high energy consumption.

The purpose of the present invention is mainly achieved through the following technical solutions:

In one aspect, the present invention provides a method for preparing an iron-molybdenum doped hydrothermal carbon composite material, comprising:

Step 1, dissolving the carbon source, iron salt and molybdate in ultrapure water, stirring evenly to form a mixed solution;

Step 2, adjusting the pH of the mixed solution obtained in step 1 to 7-8 and stirring evenly;

Step 3: subjecting the mixed solution to a hydrothermal reaction, and after the reaction is completed, centrifuging, washing, drying, and grinding to obtain an iron-molybdenum doped hydrothermal carbon composite material.

Furthermore, the carbon source in step 1 is glucose, sucrose, xylose or starch.

Furthermore, the iron salt in step 1 is ferrous sulfate, ferric nitrate, ferric chloride or ferric acetate.

Furthermore, the molybdate in step 1 may be sodium molybdate, potassium molybdate or ammonium molybdate.

Furthermore, in step 1, the molar ratio of the carbon source, the iron salt and the molybdate is 30-60:5-60:2-40.

Furthermore, in step 3, the hydrothermal reaction temperature is 160-200° C., and the reaction time is 18-26 h.

Furthermore, in step 3, the drying temperature is 40-80°C.

On the other hand, the present invention also provides an iron-molybdenum doped hydrothermal carbon composite material, which is prepared by the above-mentioned preparation method. In the iron-molybdenum doped hydrothermal carbon composite material, iron and molybdenum exist in an amorphous structure.

On the other hand, the present invention also provides a method for degrading wastewater using the above-mentioned iron-molybdenum doped hydrothermal carbon composite material, comprising:

S1. The iron-molybdenum doped hydrothermal carbon composite material and the oxidant are placed in wastewater at the same time, and react under light irradiation to generate activated free radicals, which oxidize and degrade organic pollutants in the wastewater.

Furthermore, in S1, the ratio of the iron-molybdenum doped hydrothermal carbon composite material to the oxidant is 1 g/L/0.5 mM to 5 g/L/100 mM.

Compared with the prior art, the present invention has the following beneficial effects:

1) The preparation method of the present invention utilizes glucose or sucrose or xylose or starch to be converted into hydrothermal carbon through hydrothermal reaction at a relatively low temperature, resulting in the presence of abundant pores and channel structures on the surface, and other materials are more easily doped on the surface, providing more reaction sites for the reaction; the iron-molybdenum-doped hydrothermal carbon composite material of the present invention has abundant oxygen-containing functional groups, lattice defects, amorphous oxyhydroxy iron, and Mo-Fe bimetallic structure, and the above structure of the iron-molybdenum-doped hydrothermal carbon composite material can activate the oxidant and improve the degradation effect of organic pollutants. Because the material exhibits excellent catalytic performance, the iron-molybdenum-doped hydrothermal carbon composite material can be used for deep treatment of organic pollutants in wastewater, and realize the removal of high-concentration organic matter in water, which is a green and environmentally friendly process technology.

(2) The method of the present invention is simple, easy to implement, safe and environmentally friendly, and can effectively remove high-concentration organic matter in water. It is a green and environmentally friendly process technology.

Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

FIG1 is an XRD diagram of the iron-molybdenum doped hydrothermal carbon composite material of Example 1;

FIG2 is an XRD diagram of the iron-molybdenum doped hydrothermal carbon composite material of Example 2;

FIG3 is an XRD diagram of the iron-molybdenum doped hydrothermal carbon composite material of Example 3;

FIG4 is an XRD diagram of the iron-molybdenum doped hydrothermal carbon composite material of Example 4.

Detailed ways

Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

After long-term research, the inventor found that the degradation rate of the existing persulfate activated by ferrous molybdate to degrade orange G dye wastewater is high, but the pH value of the solution needs to be adjusted to 3 in advance, and the strong acidity of the solution is not conducive to the subsequent recovery of the aqueous solution; and the consumption of persulfate in the treatment process is large, and the large amount of sulfate ions produced in the degradation process seriously restricts the reuse of organic wastewater. The biological carbon ball-loaded ferrous molybdate Fenton catalyst needs to be calcined at high temperature to show a high decolorization effect on methylene blue, and the preparation process causes extremely high energy consumption. Therefore, the inventor conducted in-depth research, aiming to provide a water treatment agent with good activation performance, less pollution in the reaction process and low energy consumption in the preparation process.

The present invention provides a method for preparing an iron-molybdenum doped hydrothermal carbon composite material, comprising:

Step 1, dissolve the carbon source, iron salt and molybdate in ultrapure water, stir evenly to form a light orange-red mixed solution;

Step 2: Using an alkaline solution, adjust the pH of the mixed solution obtained in step 1 to 7-8, and after stirring for 3-5 hours, the color of the mixed solution turns dark red;

Step 3: subjecting the mixed solution to a hydrothermal reaction, and after the reaction is completed, centrifuging, washing, drying, and grinding to obtain an iron-molybdenum doped hydrothermal carbon composite material.

Specifically, the carbon source in the above step 1 can be glucose, sucrose, xylose or starch.

Specifically, the iron salt in step 1 above may be ferrous sulfate, ferric nitrate, ferric chloride or ferric acetate.

Specifically, the molybdate in the above step 1 can be sodium molybdate, potassium molybdate or ammonium molybdate.

Specifically, in the above step 1, the molar ratio of the carbon source, the iron salt and the molybdate is 30-60:5-60:2-40. For example, the molar ratio of the carbon source, the iron salt and the molybdate is 30-60:10-40:5-10.

Specifically, in the above step 1, slowly dissolving means: using a rubber-tipped dropper, gradually and slowly dripping 50-80 mL of ultrapure water into the above three mixed substances within 15-30 minutes, using magnetic stirring in this process to accelerate the dissolution of the substances, and the stirring time is about 15-30 minutes.

Specifically, in the above step 2, the alkaline solution is a freshly prepared 2-4 mol/L aqueous solution of sodium hydroxide or potassium hydroxide.

Specifically, in the above step 2, since it is difficult to generate iron oxide under acidic conditions (Fe ³⁺ +OH ^- →Fe(OH) ₃ ), the pH of the mixed solution is adjusted to 7-8.

Specifically, in the above step 3, the hydrothermal reaction uses a hydrothermal kettle as a reaction vessel. Considering that it is difficult to generate carbon spheres if the temperature is too low or the time is too short, and the product obtained if the temperature is too high or the time is too long is not active. Therefore, the reaction temperature is set to 160-200°C (e.g., 160°C, 170°C, 180°C, 190°C), and the reaction time is 18-26h (e.g., 21h, 22h, 23h, 24h, 25h).

Specifically, in the above step 3, considering that too high a temperature may cause phase transition, the drying temperature is controlled to be 40-80°C (for example, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C), and the time is 12-24h (for example, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h).

Specifically, in the above step 3, in the obtained iron-molybdenum doped hydrothermal carbon composite material, iron and molybdenum both exist in an amorphous structure. On the one hand, the amorphous structure has a higher specific surface area to provide more active sites, and on the other hand, it is conducive to the dissolution of trace metals and improves the activation ability of the material.

Specifically, in the above step 3, considering that too large particles expose fewer active sites and too small particles are difficult to recycle, the ground iron-molybdenum-doped hydrothermal carbon composite material is finer than a 100-mesh sieve and is set aside.

Specifically, the route of the preparation method of the present invention is: the iron source, molybdenum source, and carbon source are dissolved to form an iron-molybdenum-carbon complex; when the pH is adjusted to neutral or weakly alkaline, the iron-molybdenum-carbon complex forms dark red hydroxy iron-molybdenum-carbon oxide and precipitate; during the hydrothermal reaction, the carbon source undergoes polymerization and dehydration, and iron and molybdenum enter the carbon skeleton, finally forming an amorphous iron-molybdenum-doped hydrothermal carbon composite material.

The present invention also provides a method for degrading polycyclic aromatic hydrocarbon wastewater using the above-mentioned iron-molybdenum doped hydrothermal carbon composite material. It includes:

S1. The above-mentioned iron-molybdenum doped hydrothermal carbon composite material and an oxidant (the oxidant includes persulfate or hydrogen peroxide) are placed in wastewater at the same time, and react under ultraviolet light, visible light or sunlight to generate activated free radicals, thereby oxidizing and degrading organic matter in the wastewater.

Specifically, in the above S1, too much amount of iron-molybdenum-doped hydrothermal carbon composite material will block light and affect the effect of activating persulfate, and too little amount will not be enough to activate persulfate to produce enough active free radicals to degrade organic pollutants. Therefore, the ratio of iron-molybdenum-doped hydrothermal carbon composite material to oxidant is controlled to be 1g/L/0.5mM~1g/L/20mM.

Specifically, the principle of the above-mentioned iron-molybdenum doped hydrothermal carbon composite material participating in the degradation of organic matter in wastewater is: the iron-molybdenum doped hydrothermal carbon composite material activates oxidants such as persulfate to produce active free radicals and degrade organic pollutants. There are three ways: first, the oxygen-containing organic functional groups and lattice defects in the iron-molybdenum doped hydrothermal carbon composite material act as electron donors, and under light excitation, they activate oxidants such as persulfate to produce active free radicals by providing electrons; second, the thermal protection of hydrothermal carbon in the iron-molybdenum doped hydrothermal carbon composite material maintains iron in a highly active amorphous hydroxyl iron form, which can provide electrons at a high speed to activate oxidants such as persulfate to produce active free radicals under light excitation; third, molybdenum in the iron-molybdenum doped hydrothermal carbon composite material is doped into the hydroxyl iron lattice. On the one hand, molybdenum itself can activate oxidants such as persulfate to produce active free radicals. On the other hand, the presence of molybdenum can accelerate the Fe(Ⅲ)/Fe(Ⅱ) cycle, promote the rate of iron activation of oxidants such as persulfate, and thus increase the yield of activated free radicals in the system.

Compared with the prior art, the preparation method of the present invention utilizes glucose or sucrose or xylose or starch to be converted into hydrothermal carbon through hydrothermal reaction at a lower temperature, resulting in rich pores and channel structures on the surface, and other materials are more easily doped on the surface, providing more reaction sites for the reaction; the iron-molybdenum-doped hydrothermal carbon composite material of the present invention has rich oxygen-containing functional groups, lattice defects, amorphous oxyhydroxide iron, and Mo-Fe bimetallic structure, and the above structure of the iron-molybdenum-doped hydrothermal carbon composite material can activate the oxidant and improve the degradation effect of organic pollutants. Because the material exhibits excellent catalytic performance, the method can be used for deep treatment of pollutants and removal of high-concentration organic matter in water, which is a green and environmentally friendly process technology.

The method of the invention is simple, easy to implement, safe and environmentally friendly, and can effectively remove high-concentration organic matter in water. It is a green and environmentally friendly process technology.

Example 1

This embodiment provides an iron-molybdenum doped hydrothermal carbon composite material, which is prepared by the following preparation method, including:

Step 1, weigh 6.005 g (30 mmol) of glucose, 4.123 g (10 mmol) of ferric nitrate nonahydrate, and 1.222 g (5 mmol) of sodium molybdate and mix to obtain a mixture, gradually and slowly drop 75 mL of ultrapure water into the mixture, stir for 20 min, and form a light orange-red mixed solution;

Step 2: Use 4 mol/L sodium hydroxide solution to adjust the pH of the mixed solution to about 7, stir for 4 hours, the alkaline solution is evenly dispersed, and the color of the mixed solution turns dark red;

Step 3, subjecting the mixed solution to a hydrothermal reaction at 180°C for 24 hours;

Step 4: After centrifuging the hydrothermal carbon mixed solution after the reaction and washing the hydrothermal carbon four times, the mixture was placed in an oven at 60° C. and dried for 24 hours, and then ground into powder in an agate mortar. After grinding, the mixture was sieved through a sieve of 200 mesh or above to obtain an iron-molybdenum doped hydrothermal carbon composite material.

The XRD characterization results of the iron-molybdenum doped hydrothermal carbon composite material prepared in this embodiment are shown in Figure 1. It can be seen that the iron-molybdenum doped hydrothermal carbon composite material in this embodiment does not form a crystalline structure, the carbon material exists in an amorphous state, and iron and molybdenum exist in the form of amorphous hydroxy oxides.

The XRD pattern of the iron-molybdenum doped hydrothermal carbon composite material prepared in this example is shown in FIG1 .

Example 2

This embodiment provides an iron-molybdenum doped hydrothermal carbon composite material, which is prepared by the following preparation method, including:

Step 1, weigh 17.1148 g (50 mmol) of sucrose, 8.245 g (20 mmol) of ferric nitrate nonahydrate, and 5.8195 g (5 mmol) of ammonium molybdate, mix to obtain a mixture, gradually and slowly drop 60 mL of ultrapure water into the mixture, stir for 20 min, and form a light orange-red mixed solution;

Step 2: Use 4 mol/L sodium hydroxide solution to adjust the pH of the mixed solution to about 7, stir for 4 hours, the alkaline solution is evenly dispersed, and the color of the mixed solution turns dark red;

Step 3, subjecting the mixed solution to a hydrothermal reaction at a temperature of 180°C for 25 hours;

Step 4: After centrifuging the hydrothermal carbon mixed solution after the reaction and washing the hydrothermal carbon four times, the mixture was placed in a 60° C. oven for 14 h, and then ground into powder in an agate mortar. After grinding, the mixture was sieved through a 200-mesh sieve to obtain an iron-molybdenum-doped hydrothermal carbon composite material.

The iron-molybdenum doped hydrothermal carbon composite material of this embodiment does not form a crystal structure, and the carbon material exists in an amorphous state.

The XRD pattern of the iron-molybdenum doped hydrothermal carbon composite material prepared in this example is shown in FIG. 2 .

Example 3

This embodiment provides an iron-molybdenum doped hydrothermal carbon composite material, which is prepared by the following preparation method, including:

Step 1, weigh 12.010 g (60 mmol) of glucose, 16.490 g (40 mmol) of ferric nitrate nonahydrate, and 2.3814 g (10 mmol) of potassium molybdate solution, and slowly drip 40 mL of ultrapure water into the mixture, and stir for 20 min to form a light orange-red mixed solution;

Step 2: Use 4 mol/L sodium hydroxide solution to adjust the pH of the mixed solution to about 7, stir for 4 hours, the alkaline solution is evenly dispersed, and the color of the mixed solution turns dark red;

Step 3, subjecting the mixed solution to a hydrothermal reaction at 180°C for 24 hours;

Step 4: After centrifuging the hydrothermal carbon mixed solution after the reaction and washing the hydrothermal carbon four times, the mixture was placed in an oven at 60° C. and dried for 23 hours, and then ground into powder in an agate mortar. After grinding, the mixture was sieved through a sieve of 200 mesh or above to obtain an iron-molybdenum doped hydrothermal carbon composite material.

The iron-molybdenum doped hydrothermal carbon composite material of this embodiment does not form a crystal structure, and the carbon, iron and molybdenum materials all exist in an amorphous state.

The XRD pattern of the iron-molybdenum doped hydrothermal carbon composite material prepared in this embodiment is shown in FIG3 .

Example 4

This embodiment provides an iron-molybdenum doped hydrothermal carbon composite material, which is prepared by the following preparation method, including:

Step 1, weigh 6.000 g (30 mmol) of glucose, 5.620 g (10 mmol) of ferrous sulfate nonahydrate, and 1.222 g (5 mmol) of sodium molybdate and mix to obtain a mixture, gradually and slowly drop 75 mL of ultrapure water into the mixture, and stir for 20 min to form a light orange-red mixed solution;

Step 2: Use 4 mol/L sodium hydroxide solution to adjust the pH of the mixed solution to about 7, stir for 4 hours, the alkaline solution is evenly dispersed, and the color of the mixed solution turns dark red;

Step 3, subjecting the mixed solution to a hydrothermal reaction at 180°C for 24 hours;

Step 4: After centrifuging the hydrothermal carbon mixed solution after the reaction and washing the hydrothermal carbon four times, the mixture was placed in an oven at 60° C. and dried for 24 hours, and then ground into powder in an agate mortar. After grinding, the mixture was sieved through a sieve of 200 mesh or above to obtain an iron-molybdenum doped hydrothermal carbon composite material.

The iron-molybdenum doped hydrothermal carbon composite material of this embodiment does not form a crystal structure, and the carbon, iron and molybdenum materials all exist in an amorphous state.

The XRD pattern of the iron-molybdenum doped hydrothermal carbon composite material prepared in this embodiment is shown in FIG. 4 .

Example 5

This embodiment provides a method for activating persulfate degradation wastewater using the iron-molybdenum doped hydrothermal carbon composite material of the above embodiment 1, comprising:

2 g/L of the iron-molybdenum-doped hydrothermal carbon composite material obtained in Example 1 was placed in wastewater containing 1 mM aniline, and then 5.0 mM sodium persulfate was added to the solution. The initial pH of the solution was not adjusted (the initial pH of the solution was about 6). The reaction was stirred under a xenon lamp for 120 minutes. After the reaction was completed, the pollutant removal effect was about 100%.

Example 6

This embodiment provides a method for using the above-mentioned iron-molybdenum doped hydrothermal carbon composite material to activate hydrogen peroxide to degrade wastewater, comprising:

1 g/L of the iron-molybdenum doped hydrothermal carbon composite material obtained in Example 2 was placed into wastewater containing 2 mM aniline at a pH of 3, and then 10.0 mM hydrogen peroxide was added to the solution. The reaction was stirred under xenon light for 120 minutes. After the reaction was completed, the pollutant removal effect was about 100%.

Example 7

This embodiment provides a method for using the above-mentioned iron-molybdenum doped hydrothermal carbon composite material to activate hydrogen peroxide to degrade wastewater, comprising:

1.5 g/L of the iron-molybdenum doped hydrothermal carbon composite material obtained in Example 3 was placed into wastewater containing 5 mM aniline with a pH of 11, and then 10.0 mM persulfate was added to the solution. The reaction was stirred under xenon light for 120 minutes. After the reaction was completed, the pollutant removal effect was about 100%.

Example 8

This embodiment provides a method for using the above-mentioned iron-molybdenum doped hydrothermal carbon composite material to activate hydrogen peroxide to degrade wastewater, comprising:

2 g/L of the iron-molybdenum doped hydrothermal carbon composite material obtained in Example 3 was placed in wastewater containing 2 mM aniline at a pH of 9, and then 6.0 mM hydrogen peroxide was added to the solution. The reaction was stirred under xenon light for 120 minutes. After the reaction was completed, the pollutant removal effect was about 99%.

Comparative Example 1

This comparative example provides a method for degrading wastewater by activating hydrogen peroxide using ferrous molybdate, comprising:

1.5 g/L ferrous molybdate was put into wastewater containing 5 mM aniline at a pH of 11, and then 10.0 mM persulfate was added to the solution. The reaction was stirred for 120 minutes. After the reaction was completed, the pollutant removal effect was about 50%.

Comparative Example 2

This comparative example provides a method for degrading wastewater by using iron-doped hydrothermal carbon to activate persulfate, comprising:

2 g/L iron-doped hydrothermal carbon was placed in wastewater containing 2 mM aniline at pH 9, and then 6.0 mM persulfate was added to the solution. The reaction was stirred for 120 minutes. After the reaction was completed, the pollutant removal effect was about 40%.

Comparative Example 3

This comparative example provides a method for degrading wastewater by using molybdenum-doped hydrothermal carbon to activate persulfate, comprising:

1 g/L molybdenum-doped hydrothermal carbon was placed in wastewater containing 2 mM aniline at pH 3, and then 10.0 mM hydrogen peroxide was added to the solution. The reaction was stirred for 120 minutes. After the reaction was completed, the pollutant removal effect was about 30%.

The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims (8)

1. A method for degrading aniline-containing wastewater using an iron-molybdenum doped hydrothermal carbon composite material, comprising: S1. Placing the iron-molybdenum doped hydrothermal carbon composite material and an oxidant in wastewater at the same time, reacting under light irradiation to generate activated free radicals, and oxidizing and degrading organic pollutants in the wastewater; The preparation method of the iron-molybdenum doped hydrothermal carbon composite material comprises: Step 1, dissolve the carbon source, iron salt and molybdate in ultrapure water, stir evenly to form a light orange-red mixed solution; Step 2: Adjust the pH of the mixed solution obtained in step 1 to 7-8, stir evenly, and the color of the mixed solution turns dark red; Step 3, subjecting the mixed solution to a hydrothermal reaction, and after the reaction is completed, centrifuging, washing, drying, and grinding to obtain an iron-molybdenum doped hydrothermal carbon composite material; In step 1, dissolving means: using a rubber-tipped dropper, gradually and slowly dripping 50-80 mL of ultrapure water into the mixed substance within 15-30 minutes; After the iron source, molybdenum source and carbon source are dissolved, an iron-molybdenum-carbon complex is formed. When the pH is adjusted to neutral or weakly alkaline, the iron-molybdenum-carbon complex forms dark red hydroxy iron-molybdenum-carbon oxide and precipitation. During the hydrothermal reaction, the carbon source undergoes polymerization and dehydration, and iron and molybdenum enter the carbon skeleton, and finally an amorphous iron-molybdenum-doped hydrothermal carbon composite material is formed. The iron-molybdenum-doped hydrothermal carbon composite material has rich oxygen-containing functional groups, lattice defects, amorphous hydroxy iron, and Mo-Fe bimetallic structure, and molybdenum is doped into the hydroxy iron oxylattice; The iron-molybdenum doped hydrothermal carbon composite material does not form a crystalline structure, the carbon material exists in an amorphous state, and the iron and molybdenum exist in the form of amorphous hydroxide oxides. 2. The method according to claim 1, characterized in that the carbon source in step 1 is glucose, sucrose, xylose or starch. 3. The method according to claim 1, characterized in that the iron salt in step 1 is ferric nitrate, ferric chloride or ferric acetate. 4. The method according to claim 1, characterized in that the molybdate in step 1 is sodium molybdate, potassium molybdate or ammonium molybdate. 5. The method according to claim 1, characterized in that in the step 1, the molar ratio of the carbon source, the iron salt and the molybdate is 30-60:5-60:2-40. 6. The method according to claim 1, characterized in that in the step 3, the hydrothermal reaction temperature is 160-200°C and the reaction time is 18-26 h. 7. The method according to claim 1, characterized in that in step 3, the drying temperature is 40-80°C. 8. The method according to claim 1, characterized in that in S1, the ratio of the iron-molybdenum doped hydrothermal carbon composite material to the oxidant is 1 g/L/0.5 mM ~ 5 g/L/100 mM.