CN113307262B - Preparation method and application of highly graphitized biochar-based material - Google Patents

Abstract

The present invention provides a preparation method and application of a highly graphitized biochar-based material. The preparation method includes the following steps: step S1, crushing and screening the biochar, cleaning and drying; step S2, cleaning and drying the biochar The carbon is added to the acid solution, washed with water to make it neutral after stirring, and dried to obtain acid-modified bio-char; step S3, the acid-modified bio-char obtained in step S2 is blended with K ₂ FeO ₄ , after grinding, under N ₂ High temperature pyrolysis is carried out in the atmosphere, and the obtained carbonized product is a highly graphitized biochar-based material. By adopting the technical scheme of the present invention, a graphene nanosheet structure can be formed on the surface of the biochar material by exfoliation to enhance the electron transport performance; at the same time, the surface is endowed with abundant oxygen-containing functional groups to enhance the decomplexing ability of the heavy metal complex, which can be used as a particle electrode The efficient removal of heavy metal complexes, especially the deep mineralization of organic ligands, is achieved in a three-dimensional particle electrode reaction system.

Description

A kind of preparation method and application of highly graphitized biochar-based material

technical field

The invention belongs to the technical field of biomass resource utilization technology and environmental water pollution control technology, and particularly relates to a preparation method and application of a highly graphitized biochar-based material.

Background technique

Affected by the complexation effect, it is difficult to remove heavy metal complexes in electroplating wastewater by conventional methods such as chemical precipitation, physical adsorption, and membrane separation. The use of advanced oxidation technologies such as Fenton and photocatalysis to destroy the coordination bonds in the complex molecular structure in advance releases free heavy metals while oxidatively degrading organic ligands. Preferred strategy for wastewater treatment. However, how to achieve efficient removal of heavy metals in the treatment process, especially the deep mineralization of organic complexes, still faces many challenges.

Adding carbonaceous materials (such as activated carbon, etc.) as particle electrodes in a traditional two-dimensional electrode reactor, and then constructing a three-dimensional electrode reaction system, helps to enhance the mass transfer effect, improve the current utilization rate, and strengthen the oxidative degradation of organic matter. It is generally applicable to the mineralization treatment of refractory pollutants such as dye wastewater, phenol-containing wastewater, pesticide wastewater, etc. It can provide solutions for the simultaneous and efficient removal of heavy metals and organic complexes in electroplating wastewater. In the three-dimensional electrode reaction system, the physicochemical properties of the carbonaceous particle electrode are the key to the operation of the system. Efficient and stable carbonaceous particle electrodes have requirements on the microstructure, surface physicochemical properties, electron transport ability, and bonding strength of metal active components and supports of carbonaceous materials. How to explore carbonaceous particle electrodes suitable for their treatment and their controllable preparation methods based on the reaction characteristics of heavy metal complexes needs to be solved urgently.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention discloses a preparation method and application of a highly graphitized biochar-based material, and the obtained highly graphitized biochar-based material can be used as a particle electrode to construct a three-dimensional electrode system, and efficiently treat electroplating wastewater. heavy metal complexes.

To this, the technical scheme of the present invention is:

A preparation method of a highly graphitized biochar-based material, comprising the steps of:

Step S1, crushing and screening the biochar, cleaning and drying;

In step S2, the cleaned and dried biochar is added to the acid solution, washed with water to be neutral after stirring, and dried to obtain acid-modified biochar;

In step S3, the acid-modified biochar obtained in step S2 is blended with K ₂ FeO ₄ , and after grinding, high temperature pyrolysis is performed under N ₂ atmosphere, and the obtained carbonized product is a highly graphitized biochar-based material.

Using this technical solution, biochar is used as the base material to prepare highly graphitized biochar-based materials with specific structures and functions through processes such as acidizing treatment, grinding and blending, and high-temperature pyrolysis. The obtained highly graphitized biochar-based material possesses a highly dispersed graphene nanosheet structure, abundant surface oxygen-containing functional groups and a low dissolution rate of metal components, and can be used as a particle electrode to realize the removal of heavy metals in a three-dimensional electrode reaction system. Efficient removal and deep mineralization of organic ligands.

As a further improvement of the present invention, the biochar is derived from nutshell biomass solid waste. Preferably, it is derived from almond shell, coconut shell and the like. Using this technical solution, it is easy to control, and after being activated by carbonization, it can endow the biochar with specific morphological structure and surface chemical properties.

As a further improvement of the present invention, the acid is an inorganic acid. Further preferably, the acid is hydrochloric acid, sulfuric acid or nitric acid. The adoption of this technical solution helps to improve the reduction potential of the Fe element valence state conversion process.

As a further improvement of the present invention, in step S3, the mass percentage of K ₂ FeO ₄ in the blend is 1-10%. Further, the blending is carried out by means of ball milling.

As a further improvement of the present invention, in step S3, before the high-temperature pyrolysis, the tube furnace is pre-passed with N ₂ for 30 minutes to maintain an oxygen-free environment in the tube; during the high-temperature pyrolysis, the N ₂ flow rate is controlled to be 50 mL/cm ³ , and the temperature is increased. The speed is 2-5 °C/min, and the pyrolysis temperature is 700-800 °C.

As a further improvement of the present invention, in step S1, the filtrate is repeatedly washed with deionized water until the filtrate is clear, and then dried at 105°C.

As a further improvement of the present invention, in step S2, after continuous stirring by a magnetic stirrer, the filtrate is repeatedly washed with deionized water until the filtrate is neutral, and dried at 105 °C to obtain acid-modified biochar.

The invention also discloses the application of a highly graphitized biochar-based material, which is used in the treatment of wastewater containing heavy metal complexes, including:

The highly graphitized biochar-based material is added to the two-dimensional electrode reaction system containing heavy metal complex wastewater, stirred and mixed; then the reaction is carried out under the condition of applying electric current, and the precipitation separation is carried out after the reaction;

The highly graphitized biochar-based material is prepared by the method for preparing a highly graphitized biochar-based material as described in any one of the above.

As a further improvement of the present invention, the cathode and anode sheets in the two-dimensional electrode reaction system are graphite electrodes and BDD electrodes respectively, the electrodes are fixed by two clips, and the panel of the fixed clips is marked with a scale, and the clips are adjusted according to the experimental requirements. , to determine the target plate spacing and height.

As a further improvement of the present invention, before adding the highly graphitized biochar-based material, the pH value of the wastewater is pre-adjusted to 4-6, and the cathode and anode plates are connected to a DC voltage stabilized power supply.

As a further improvement of the present invention, the heavy metal complex is an EDTA complex of copper, nickel and the like.

As a further improvement of the present invention, the three-dimensional electrode reactor composed of a two-dimensional electrode reaction system and a highly graphitized biochar-based material adopts the form of a fluidized bed, and the relative position of the particle electrodes changes continuously under the action of external force. The particle electrodes collide with each other to ensure sufficient contact between the particle electrodes and the pollutants during the reaction.

Compared with the prior art, the beneficial effects of the present invention are:

By adopting the technical scheme of the present invention, combined with acidification and K ₂ FeO ₄ modification comprehensive treatment, the graphitization degree of the biochar material is improved, and the graphene nano-sheet structure is further exfoliated on the surface thereof to enhance the electron transport performance; The abundant oxygen-containing functional groups on the surface of biochar materials enhance the ability of heavy metal complexes to break complex. The prepared highly graphitized biochar-based material has a mesoporous structure, the surface is rich in graphene nanosheet structure and organic oxygen-containing functional groups, and the dissolution rate of metal components is low. Efficient removal of compounds, especially deep mineralization of organic ligands.

Description of drawings

Figure 1 is a SEM comparison diagram of the highly graphitized biochar-based material prepared in Example 1 of the present invention; wherein, (a) is the highly graphitized biochar-based material under the acidification and K ₂ FeO ₄ modification conditions in Example 1, (b) is the K ₂ FeO ₄ modified biochar-based material without acid treatment.

Figure 2 is an XPS diagram of the highly graphitized biochar-based material prepared in Example 1 of the present invention; wherein (a) is the full spectrum of O1s, and (b) is the fine spectrum of Fe2p.

Figure 3 shows the treatment effect of Cu-EDTA by the three-dimensional electrode system in Example 1 of the present invention; wherein (a) is the removal effect of Cu ²⁺ , and (b) is the removal effect of COD.

FIG. 4 is a diagram showing the dissolution effect of metal active components in the cycle test in Example 1 of the present invention.

Detailed ways

The preferred embodiments of the present invention will be further described in detail below.

Example 1

A preparation method of a highly graphitized biochar-based material, comprising the steps of:

In step S1, the biochar is crushed and sieved, repeatedly washed with deionized water until the filtrate is clear, and then dried at 105°C.

In step S2, the obtained biochar is put into an acid solution, continuously stirred by a magnetic stirrer, rinsed repeatedly with deionized water until the filtrate is neutral, and dried at 105°C to obtain acid-modified biochar.

In step S3, a certain amount of acid-modified biochar is weighed, blended with 5% K ₂ FeO ₄ , ground in a ball mill, and then pyrolyzed at high temperature in a tube furnace under N ₂ atmosphere, and the obtained carbonized product is highly graphitized Biochar based materials.

Through acidizing treatment, grinding and blending, potassium ferrate co-pyrolysis and other processes, highly graphitized biochar-based materials with specific structures and functions are prepared. As shown, it has a mesoporous structure with a large number of graphene nanosheet structures dispersed on the surface, and the H ⁺ introduced by pre-acid treatment is crucial for the improvement of the degree of graphitization and the formation of the graphene nanosheet structure. In the absence of acid treatment, no graphene nanosheet structure was formed on the surface of biochar. The surface composition of the highly graphitized biochar-based material is shown in Figure 2. XPS O1s analysis shows that there are a large number of oxygen-containing functional groups on the surface of the highly graphitized biochar-based material, mainly in the form of hydroxyl, carboxyl, and lattice oxygen. Fe It exists in the form of Fe ⁰ , Fe ²⁺ and Fe ³⁺ .

The embodiment of the present invention also discloses the application of the highly graphitized biochar-based material prepared by the above method in the oxidative degradation of heavy metal complexes in a three-dimensional electrode system, including:

(1) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater into the two-dimensional electrode reactor, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to about 5, and the cathode and anode plates are connected to a DC stabilizer. Press the power source to adjust the magnetic stirrer to the target speed. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(2) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater in a two-dimensional electrode reactor, connect the cathode and anode plates with a DC voltage stabilized power supply, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to 5 or so, add a certain amount of particle electrodes, adjust the magnetic stirrer to the target speed, so that the particle electrodes are evenly dispersed in the three-dimensional electrode system. The particle electrode is a highly graphitized biochar-based material prepared by processes such as acidizing treatment, grinding and blending, and co-pyrolysis of potassium ferrate. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(3) After 3 h of treatment, as shown in Figure 3, the removal efficiencies of Cu ²⁺ and COD in the three-dimensional electrode system reached 96.8% and 92.5%, respectively, and the TOC removal rate was 86.2%. Compared with the two-dimensional electrode oxidation system, its performance is significantly improved. After 5 cycles, the removal rate of Cu ²⁺ and COD decreased by 10%, but it was still higher than that of the two-dimensional electrode system. After regeneration treatment with hydrochloric acid, the treatment effect of Cu ²⁺ and COD recovered to 95.3% and 93.7% of the first use. As shown in Figure 4, the iron ion dissolution rate was always lower than 1 mg/L during the reaction.

Example 2

A preparation method of a highly graphitized biochar-based material, comprising the steps of:

In step S1, the biochar is crushed and sieved, washed repeatedly with deionized water until the filtrate is clear, and then dried at 105°C.

In step S2, the obtained biochar is put into an acid solution, continuously stirred by a magnetic stirrer, repeatedly washed with deionized water until the filtrate is neutral, and dried at 105 °C to obtain acid-modified biochar.

In step S3, a certain amount of acid-modified biochar and 5% K ₂ FeO ₄ are weighed, and 5% K ₂ FeO ₄ is loaded on the acid-modified bio _- char by direct blending and ultrasonic blending respectively. High temperature pyrolysis in a tube furnace, the resulting carbonized product is a highly graphitized biochar-based material.

The embodiment of the present invention also discloses the application of the highly graphitized biochar-based material prepared by the above method in the oxidative degradation of heavy metal complexes in a three-dimensional electrode system, including:

(1) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater into the two-dimensional electrode reactor, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to about 5, and the cathode and anode plates are connected to a DC stabilizer. Press the power source to adjust the magnetic stirrer to the target speed. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(2) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater in a two-dimensional electrode reactor, connect the cathode and anode plates with a DC voltage stabilized power supply, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to 5 or so, add a certain amount of particle electrodes, adjust the magnetic stirrer to the target speed, so that the particle electrodes are evenly dispersed in the three-dimensional electrode system. The particle electrode is a highly graphitized biochar-based material prepared by processes such as direct blending, ultrasonic blending, and co-pyrolysis of potassium ferrate. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(3) After 3 h treatment, the removal efficiency of Cu ²⁺ in the three-dimensional electrode system of the highly graphitized biochar-based materials prepared by direct blending and ultrasonic blending reached 93.4% and 94.5%, respectively, and the removal rate of COD was 83.3%, respectively. and 82.8%.

Example 3

A preparation method of a highly graphitized biochar-based material, comprising the steps of:

In step S1, the biochar is crushed and sieved, washed repeatedly with deionized water until the filtrate is clear, and then dried at 105°C.

In step S2, the obtained biochar is put into an acid solution, continuously stirred by a magnetic stirrer, repeatedly washed with deionized water until the filtrate is neutral, and dried at 105 °C to obtain acid-modified biochar.

In step S3, a certain amount of acid-modified biochar and K ₂ FeO ₄ in different mass ratios are weighed, grinded by a ball mill, and then pyrolyzed at high temperature in a tube furnace under N ₂ atmosphere, and the obtained carbonized product is highly graphitized biochar base material.

The embodiment of the present invention also discloses the application of the highly graphitized biochar-based material prepared by the above method in the oxidative degradation of heavy metal complexes in a three-dimensional electrode system, including:

(1) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater into the three-dimensional electrode reactor, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to about 5, and connect the cathode and anode plates to DC voltage stabilizer Power on and adjust the magnetic stirrer to the target speed. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(2) Take 250 mL of 50 mg/L Cu-EDTA simulated wastewater into the three-dimensional electrode reactor, connect the cathode and anode plates with a DC voltage stabilized power supply, add a certain concentration of sodium sulfate electrolyte solution, and pre-adjust the pH value of the wastewater to 5 Left and right, add a certain amount of particle electrodes, adjust the magnetic stirrer to the target speed, so that the particle electrodes are evenly dispersed in the three-dimensional electrode system. The particle electrode is a highly graphitized biochar-based material prepared by acidizing treatment, grinding and blending of K ₂ FeO ₄ with different mass ratios, and co-pyrolysis of potassium ferrate. After each reaction period, a small amount of supernatant was taken, and the pH was adjusted to 11.0 with NaOH solution. After the samples were fully precipitated, the concentrations of Cu ²⁺ and COD were measured after passing through a 0.45 μm pinhole filter.

(3) After 3 h treatment, the highly graphitized biochar-based materials prepared by grinding with 1%, 10% and 20% K ₂ FeO ₄ achieved Cu ²⁺ removal efficiencies of 95.4%, 81.1% and 95.4% in the three-dimensional electrode system, respectively. 64.5%, and the COD removal rates were 85.2%, 84.4% and 36.2%, respectively.

It can be seen from the above examples that using the highly graphitized biochar-based material of the present invention as a particle electrode can effectively remove heavy metal complexes in electroplating wastewater in a three-dimensional electrode reaction system, especially the deep mineralization of organic ligands. .

The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (9)

1. a preparation method of highly graphitized biochar-based material, is characterized in that: it comprises the steps: Step S1, crushing and screening the biochar, cleaning and drying; In step S2, the cleaned and dried biochar is added to the acid solution, washed with water to be neutral after stirring, and dried to obtain acid-modified biochar; In step S3, the acid-modified biochar obtained in step S2 is blended with K ₂ FeO ₄ , and after grinding, high-temperature pyrolysis is performed in an N ₂ atmosphere, and the obtained carbonized product is a highly graphitized biochar-based material; In step S3, in the blend, the mass percentage of K ₂ FeO ₄ is 1-10%; The surface of the highly graphitized biochar-based material is rich in graphene nanosheet structure and organic oxygen-containing functional groups. 2 . The method for preparing a highly graphitized biochar-based material according to claim 1 , wherein the biochar is derived from nutshell biomass solid waste. 3 . 3. The method for preparing a highly graphitized biochar-based material according to claim 1, wherein the acid is hydrochloric acid, sulfuric acid or nitric acid. 4. The method for preparing a highly graphitized biochar-based material according to claim 1, characterized in that: in step S3, before the high-temperature pyrolysis, the tube furnace is pre-passed with N ₂ to maintain an oxygen-free environment in the tube; the high-temperature pyrolysis During the process, the flow rate of N ₂ was controlled to be 30-70 mL/cm ³ , the heating rate was 2-5 °C/min, and the pyrolysis temperature was 700-800 °C. 5. The method for preparing a highly graphitized biochar-based material according to any one of claims 1 to 4, characterized in that: in step S1, after repeated cleaning with deionized water until the filtrate is clear, drying at 105°C . 6. The preparation method of highly graphitized biochar-based material according to claim 5, characterized in that: in step S2, after continuous stirring by a magnetic stirrer, repeatedly rinsed with deionized water until the filtrate is neutral, and at 105 drying at ℃ to obtain acid-modified biochar. 7. An application of a highly graphitized biochar-based material, characterized in that: it is used in the treatment of heavy metal complex waste water, comprising: The highly graphitized biochar-based material is added to the two-dimensional electrode reaction system containing heavy metal complex wastewater, stirred and mixed; then the reaction is carried out under the condition of applying electric current, and the precipitation separation is carried out after the reaction; The highly graphitized biochar-based material is prepared by the method for preparing a highly graphitized biochar-based material according to any one of claims 1 to 6. 8. The application of the highly graphitized biochar-based material according to claim 7, wherein the cathode and anode sheets are respectively graphite electrodes and BDD electrodes in the two-dimensional electrode reaction system, and the electrodes are fixed by two clips, The panels that hold the clips are marked with graduations. 9 . The application of the highly graphitized biochar-based material according to claim 7 , wherein the pH value of the wastewater is pre-adjusted to 4-6 before adding the highly graphitized biochar-based material. 10 .

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