CN115814829B - Co and Mo2C-codoped biochar-based composite material and preparation method and application thereof - Google Patents

Abstract

The invention discloses a Co and Mo ₂ C Co-doped biochar-based composite material, a preparation method and application thereof, wherein the Co and Mo ₂ C Co-doped biochar-based composite material is obtained by crushing cattail biomass, immersing the cattail biomass in a mixed solution containing cobalt acetate and ammonium molybdate overnight, performing rotary evaporation and vacuum drying, and performing pyrolysis in an N ₂ atmosphere. The composite material obtained by the invention can activate Peroxomonosulfate (PMS) to oxidize and treat dye-containing wastewater, has excellent removal effect, and has the removal efficiency of more than 95% on Methylene Blue (MB) within 15 min.

Description

A Co and Mo2C co-doped biochar-based composite material and its preparation method and application

Technical Field

The invention belongs to the field of carbon material preparation, and particularly relates to an application of adsorption and advanced oxidation technology to catalyze the degradation of common dye methylene blue.

Background Art

my country is the world's largest dye producer and consumer. At present, my country's production of various dyes has reached 900,000 tons, accounting for about 70% of the world. In the field of environmental governance, dye molecules can be divided into cationic dyes, anionic dyes, and non-ionic dyes according to their ionic state in aqueous solution. Methylene blue (MB) is a typical cationic dye - alkaline dye. This type of dye is very bright in color. Even at a very low concentration, the chromaticity of the water body will be very high, which will affect the light penetration, thereby affecting the photosynthesis of underwater plants and the growth of aquatic animals. Its "three-hazard" effect will also cause potential harm to the human body. If it is not handled properly, it will cause serious environmental and health problems.

Traditional sewage treatment systems have a poor effect on dye removal, which has greatly stimulated the innovation of related water treatment technologies. Advanced oxidation treatments (AOPs) show great application potential here. They produce free radicals with strong oxidizing ability to oxidize large molecular refractory organic matter into low-toxic or non-toxic small molecules. In recent years, sulfate radical-based advanced oxidation technology (SR-AOPs) has attracted widespread attention.

Peroxymonosulfate (PMS) is a representative persulfate with an asymmetric structure (HO-SO ₄ ^- ) that can produce highly oxidizing SO ₄ ^- · and is widely used in SR-AOPs. The cleavage of the OO bond in its molecule is a necessary condition for the production of SO ₄ ^- · and ·OH. Ultraviolet light and high temperature are good methods for producing SO ₄ ^- ·, but they require high equipment investment and operating costs; transition metals (such as Co, Fe, Mn, etc.) and their oxides, sulfides, and carbides also have certain PMS activation abilities, but they have a series of problems such as metal ion leaching and limited stability. Therefore, it is urgent to develop a PMS activator with higher performance, lower cost, and environmental friendliness.

Compared with other transition metals, Mo has low toxicity and is relatively beneficial to human health and environmental protection. Its sulfide _MoS2 has been widely used in the study of activating PMS to degrade pollutants, while its carbide _Mo2C has been reported very little. However, _Mo2C has more exposed Mo sites than _MoS2 in structure, and studies have shown that ^Mo2+ active sites may have a higher potential for effectively activating PMS. In order to reduce metal ion leaching and improve the stability of materials in practical applications, it is a good solution strategy to load it on a solid carrier with high specific surface area, high mechanical strength and good chemical stability. Common carriers mainly include metal oxide carriers such as MgO, ZnO, _TiO2 , carbon-based carriers such as carbon nanotubes, _graphene , _gC3N4 , and other carriers such as metal-organic frameworks, zeolites, and molecular sieves. Among them, biochar (BC) is a new type of carbonaceous carrier with low cost, wide source and environmental friendliness. Therefore, it will be very meaningful to explore the heterogeneous catalyst composed of it for the activation of PMS.

Summary of the invention

The invention provides a method for preparing a biochar-based composite material co-doped with Co and Mo ₂ C, aiming to simultaneously meet the requirements of high performance and environmental friendliness of a PMS activator and broaden the application field of Mo ₂ C.

In order to solve the technical problem, the present invention adopts the following technical solution:

A method for preparing a biochar-based composite material co-doped with Co and Mo ₂ C comprises the following steps:

Step 1: After drying the cattail biomass, crush it with a crusher to obtain the original biomass material;

Step 2, weighing Co(CH ₃ COO) ₂ ·4H ₂ O and (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O, and dissolving them in deionized water under magnetic stirring to obtain a mixed solution; immersing the original biomass material obtained in step 1 in the mixed solution, and then dehydrating by rotary evaporation and vacuum drying to obtain a precursor material;

Step 3: Place the precursor material obtained in step 2 in a porcelain boat, put it into a tubular pyrolysis furnace, slowly pyrolyze it in a N ₂ atmosphere, and then grind it to obtain a biochar-based composite material doped with Co and Mo ₂ C.

Preferably, in step 1, the particle size of the raw biomass material is less than 100 mesh (<0.15 mm).

Preferably, in step 2, the total mass of Co(CH ₃ COO) ₂ ·4H ₂ O and (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O is 30%-30.5% of the mass of the original biomass material.

Preferably, in step 2, the mass ratio of Co(CH ₃ COO) ₂ ·4H ₂ O and (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O satisfies n(Co):n(Mo)=1:4.95-5.05 (ie, the molar ratio of Co element to Mo element satisfies 1:4.95-5.05).

Preferably, in step 2, the immersion time is 24 hours, and the temperatures of rotary evaporation and vacuum drying are both set to 60°C.

Preferably, in step 3, the conditions for slow pyrolysis of the obtained precursor material in a _N2 atmosphere are: at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min, first heating to 400°C and keeping warm for 2 hours, then continuing to heat to 800-900°C and annealing for 2 hours, and finally naturally cooling to room temperature.

The biochar-based composite material co-doped with Co and Mo ₂ C obtained in the present invention can be used to activate peroxymonosulfate (PMS) to increase the oxidation rate of PMS to methylene blue (MB). Based on this, the present invention provides a method for improving the efficiency of PMS oxidation of MB, comprising the following steps:

The biochar-based composite material co-doped with Co and Mo ₂ C is added to the MB solution to be treated, and fully adsorbed to make the reaction reach adsorption/desorption equilibrium; after the adsorption is completed, PMS is added for oxidation.

Preferably, the mass ratio of the dosage of the biochar-based composite material co-doped with Co and Mo ₂ C to MB is 5:1, and the mass ratio of the dosage of PMS to MB is 1:100.

Preferably, the adsorption time is 30 min and the oxidation time is 15 min.

The beneficial effects of the present invention are embodied in:

The present invention provides a preparation method of a biochar-based composite material co-doped with Co and _Mo2C , which can efficiently activate PMS to degrade pollutants. Mo has a large number of unoccupied d orbitals, while Co has abundant outer electrons. The method dopes a trace amount of Co and combines it with _Mo2C to form a good heterogeneous interface, increase active sites, and then use BC obtained by pyrolysis of cattail as a carrier and electron transport medium, which can not only realize the resource utilization of waste biomass, but also prevent the agglomeration of metal nanoparticles, protect Co and _Mo2C from corrosion in the working environment, reduce metal ion leaching, accelerate the cycle of gain and loss of electrons and the transfer of free electrons, and promote the activation of PMS and the degradation of pollutants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM image of the Co and Mo ₂ C co-doped biochar-based composite material obtained in Example 1 of the present invention.

FIG2 is an XRD diagram of the composite materials obtained in Examples 1-4 of the present invention, wherein the annealing temperatures are 600° C., 700° C., 800° C., and 900° C., respectively.

FIG. 3 is a graph showing MB degradation experiments of the composite materials obtained in Examples 1-4 of the present invention.

FIG. 4 is a graph showing MB degradation experiments of the materials obtained in Example 1 and Comparative Examples 1-3 of the present invention.

DETAILED DESCRIPTION

The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, without departing from the concept of the present invention, several variations and improvements may be made, which all belong to the protection scope of the present invention.

Example 1

1. Preparation of Co and Mo ₂ C co-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.2667 g Co(CH ₃ COO) ₂ ·4H ₂ O and 0.9451 g (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O were weighed and dissolved in 200 mL deionized water under magnetic stirring to obtain a mixed solution; 4 g original biomass material was placed in the mixed solution, immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60°C and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat, put into a tubular pyrolysis furnace, and heated to 400°C for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be raised to 800°C for annealing for 2 h. Finally, the material was naturally cooled to room temperature and ground with an agate mortar to obtain a Co and _Mo2C co-doped biochar-based composite material (Co, _Mo2C @BC).

2. Oxidative degradation of MB

Take 5 mg of the prepared Co,Mo ₂ C@BC and add it to 50 mL of 20 mg/L MB solution, adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

The SEM image of Co,Mo ₂ C@BC prepared in this example is shown in Figure 1. As can be seen from Figure 1, similar to typical pyrolysis biochar, the main body of the material is composed of rough carbon sheets with discontinuous jagged gaps, and metal nanoparticles are evenly distributed on the surface.

Example 2

1. Preparation of Co and Mo ₂ C co-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.2667 g Co(CH ₃ COO) ₂ ·4H ₂ O and 0.9451 g (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O were weighed and dissolved in 200 mL deionized water under magnetic stirring to obtain a mixed solution; 4 g original biomass material was placed in the mixed solution, immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60°C and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat, put into a tubular pyrolysis furnace, and heated to 400°C for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be raised to 900°C for annealing for 2 h. Finally, the material was naturally cooled to room temperature and ground with an agate mortar to obtain a biochar-based composite material co-doped with Co and _Mo2C (Co,Mo@BC-900).

2. Oxidative degradation of MB

Take 5 mg of the prepared Co,Mo@BC-900 and add it to 50 mL of 20 mg/L MB solution, and adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

Example 3

1. Preparation of Co and Mo ₂ C co-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.2667 g Co(CH ₃ COO) ₂ ·4H ₂ O and 0.9451 g (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O were weighed and dissolved in 200 mL deionized water under magnetic stirring to obtain a mixed solution; 4 g original biomass material was placed in the mixed solution, immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60°C and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat and put into a tubular pyrolysis furnace. The temperature was first increased to 400°C and kept for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be increased to 700°C and annealed for 2 h. Finally, the material was naturally cooled to room temperature and ground with an agate mortar to obtain a biochar-based composite material co-doped with Co and _Mo2C (Co,Mo@BC-700).

2. Oxidative degradation of MB

Take 5 mg of the prepared Co,Mo@BC-700 and add it to 50 mL of 20 mg/L MB solution, and adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

Example 4

1. Preparation of Co and Mo ₂ C co-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.2667 g Co(CH ₃ COO) ₂ ·4H ₂ O and 0.9451 g (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O were weighed and dissolved in 200 mL deionized water under magnetic stirring to obtain a mixed solution; 4 g original biomass material was placed in the mixed solution, immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60°C and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat, put into a tubular pyrolysis furnace, and heated to 400°C for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be raised to 600°C for annealing for 2 h. Finally, the material was naturally cooled to room temperature and ground with an agate mortar to obtain a biochar-based composite material co-doped with Co and _Mo2C (Co,Mo@BC-600).

2. Oxidative degradation of MB

Take 5 mg of the prepared Co,Mo@BC-600 and add it to 50 mL of 20 mg/L MB solution, and adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

The XRD patterns of the composite materials prepared in Examples 1-4 are shown in FIG2 . As can be seen from FIG2 , the samples of Examples 1-4 all have diffraction peaks at 44.3°, corresponding to the (111) crystal plane of Co nanoparticles (JCPDS15-0806), indicating that Co is successfully incorporated. The samples of Examples 1 and 2 have diffraction peaks at 34.47°, 38.06°, 39.54°, 52.31°, 61.76°, 74.98°, and 75.41°, corresponding to the standard diffraction peaks of Mo ₂ C (JCPDS35-0787). The diffraction peaks of the samples of Examples 3 and 4 mainly correspond to MoO _x and MoC, indicating that as the annealing temperature gradually increases, MoO _x is gradually reduced to Mo ₂ C by the reducing gas generated by the pyrolysis of biochar, and the valence state of Mo gradually decreases. When the annealing temperature is ≥800°C, Mo ₂ C can be formed.

The MB degradation effect diagram of the materials prepared in Examples 1-4 is shown in Figure 3. As can be seen from Figure 3, the MB removal rates of the samples of Examples 1-4 above within 15 minutes by activating PMS are 97.52%, 97.12%, 86.13%, and 70.78%, respectively, among which the effects of Example 1 (Co, Mo ₂ C@BC) and Example 2 (Co, Mo@BC-900) are almost the same, which indicates that with the increase of annealing temperature, the MB removal rate of the material is higher.

Comparative Example 1

1. Preparation of Co-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.2667 g of Co(CH ₃ COO) ₂ ·4H ₂ was weighed and dissolved in 200 mL of deionized water under magnetic stirring to obtain a cobalt acetate solution; 4 g of the original biomass material was placed in the cobalt acetate solution and immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60° C. and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat and put into a tubular pyrolysis furnace. The temperature was first increased to 400°C and kept for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be increased to 800°C and annealed for 2 h. Finally, the mixture was naturally cooled to room temperature and ground with an agate mortar to obtain a Co-doped biochar-based composite material (Co@BC).

2. Oxidative degradation of MB

Take 5 mg of the prepared Co@BC and add it to 50 mL of 20 mg/L MB solution, and adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

Comparative Example 2

1. Preparation of Mo ₂ C-doped biochar-based composite materials:

After the cattail biomass is dried, it is crushed by a crusher to obtain the original biomass material with a particle size of less than 100 meshes.

0.9451 g (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O was weighed and dissolved in 200 mL of deionized water under magnetic stirring to obtain an ammonium molybdate solution; 4 g of the original biomass material was placed in the ammonium molybdate solution, immersed for 24 h under magnetic stirring, and then dehydrated by rotary evaporation at 60° C. and vacuum drying to obtain a precursor material.

The precursor material obtained in step 2 was placed in a porcelain boat, put into a tubular pyrolysis furnace, and heated to 400°C for 2 h at a heating rate of 2°C/min and a _N2 flow rate of 60 mL/min. The temperature was then continued to be raised to 800°C for annealing for 2 h. Finally, the material was naturally cooled to room temperature and ground with an agate mortar to obtain a _Mo2C -doped biochar-based composite material ( _Mo2C @BC).

2. Oxidative degradation of MB

Take 5 mg of the prepared Mo ₂ C@BC and add it to 50 mL of 20 mg/L MB solution. Adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

Comparative Example 3

1. Preparation of biochar materials:

Weigh 4 g of cattail biomass and place it in a porcelain boat, then put it into a tubular pyrolysis furnace. At a heating rate of 2 °C/min and a _N2 flow rate of 60 mL/min, first heat it to 400 °C and keep it for 2 h, then continue to heat it to 800 °C and anneal it for 2 h. Finally, cool it naturally to room temperature and grind it with an agate mortar to obtain biochar material (BC).

2. Oxidative degradation of MB

Take 5 mg of the prepared BC and add it to 50 mL of 20 mg/L MB solution, and adsorb for 30 minutes to allow the reaction to reach adsorption/desorption equilibrium. After the adsorption is completed, add 1 mL of 10 g/L peroxymonosulfate (PMS) and start timing. Take out 1 mL of the reaction solution at regular intervals, dilute it by half, and filter it with a 0.22 μm organic filter. Use a UV spectrophotometer to detect the remaining MB concentration in the reaction solution.

See Figure 4 for the MB degradation effect diagram of the materials prepared in Example 1 and Comparative Examples 1-3. As can be seen from Figure 4, the removal rates of MB by the samples of Example 1 and Comparative Examples 1-3 within 15 minutes through activation of PMS are 97.52%, 65.43%, 32.56%, and 9.3%, respectively, which indicates that the activation ability of the biochar-based composite material co-doped with Co and Mo ₂ C (Example 1) for PMS is better than that of the biochar doped with Co only (Comparative Example 1), Mo ₂ C only (Comparative Example 2), and undoped biochar (Comparative Example 3). This shows that the material prepared in Example 1 has outstanding effects, and there is a good synergistic effect between Co, Mo ₂ C, and BC, which is conducive to the cycle of gain and loss of electrons and the transfer of free electrons, thereby effectively activating PMS.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. An application of a biochar-based composite material co-doped with Co and Mo ₂ C for activation of peroxymonosulfate, characterized in that: it is used to activate peroxymonosulfate PMS to increase the oxidation rate of PMS to methylene blue MB; The method for preparing the Co and Mo ₂ C co-doped biochar-based composite material comprises the following steps: Step 1: After drying the cattail biomass, crush it with a crusher to obtain the original biomass material; Step 2, weighing Co(CH ₃ COO) ₂ ·4H ₂ O and (NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O, and dissolving them in deionized water under magnetic stirring to obtain a mixed solution; immersing the original biomass material obtained in step 1 in the mixed solution, and then dehydrating by rotary evaporation and vacuum drying to obtain a precursor material; Step 3: Place the precursor material obtained in step 2 in a porcelain boat, put it into a tubular pyrolysis furnace, slowly pyrolyze it in a N ₂ atmosphere, and then grind it to obtain a biochar-based composite material doped with Co and Mo ₂ C. 2. The activation application according to claim 1, characterized in that: the biochar-based composite material co-doped with Co and Mo ₂ C is added to the methylene blue solution to be treated, and fully adsorbed to make the reaction reach adsorption/desorption equilibrium; after the adsorption is completed, PMS is added for oxidation. 3. The activation application according to claim 1 or 2, characterized in that the mass ratio of the dosage of the biochar-based composite material co-doped with Co and _Mo2C to MB is 5:1, and the mass ratio of the dosage of PMS to MB is 1:100. 4. The activation application according to claim 1 is characterized in that: in step 1, the particle size of the original biomass material is less than 100 mesh. 5. The activation application according to claim 1, characterized in that: in step 2, the total mass of the Co( _CH3COO ) ₂ · _4H2O and ( _NH4 ) _6Mo7O24 · _4H2O is 30 _{% -30.5} % of the mass of the original biomass material. 6. The activation application according to claim 1, characterized in that: in step 2, the mass ratio of Co( _CH3COO ) ₂ · _4H2O and ( _NH4 ) _6Mo7O24 · _4H2O satisfies n(Co):n(Mo) _{= 1} :4.95-5.05. 7. The activation application according to claim 1, characterized in that: in step 2, the immersion time is 24 hours, and the temperature of rotary evaporation and vacuum drying are both set to 60°C. 8. The activation application according to claim 1 is characterized in that: in step 3, the conditions for slow pyrolysis of the obtained precursor material in a _N2 atmosphere are: at a heating rate of 2°C/min and a _N2 flow rate of 60mL/min, first heating to 400°C and keeping it for 2h, then continuing to heat to 800-900°C and annealing for 2h, and finally naturally cooling to room temperature.