Iron-cobalt modified biochar as well as preparation method and application thereof

Abstract

The invention discloses iron-cobalt modified biochar as well as a preparation method and application thereof, and belongs to the technical field of organic pollutant treatment, the iron-cobalt modified biochar can remove norfloxacin through an adsorption effect, and can activate peroxymonosulfate to generate sulfate free radicals, so that the norfloxacin is degraded through an advanced oxidation process. Fe and Co on the surface of Co-Fe-BC are used as catalysts, the energy threshold of sulfate free radicals generated by persulfate decomposition can be reduced, and the activation rate of persulfate is increased. The generated sulfate free radicals have high oxidation-reduction potential, can attack norfloxacin molecules in a non-selective manner, and initiate free radical chain reaction through hydrogen atom picking or an electron transfer mechanism, and finally, norfloxacin is mineralized into harmless small molecular substances, such as carbon dioxide and water. The process not only effectively removes norfloxacin, but also reduces the generation of disinfection by-products, and improves the safety of water quality.

Description

Technical Field

[0001] The present invention relates to the technical field of organic pollutant treatment, and particularly relates to an iron-cobalt modified biochar, a preparation method thereof, and an application thereof. Background Art

[0002] Norfloxacin, denoted as NOR, as a broad-spectrum antibiotic, has been widely used in the fields of healthcare and aquaculture. However, it is worth noting that due to the excessive use of NOR and its incomplete metabolic process in organisms, a large amount of NOR enters the environmental medium in the form of the original form or metabolites through excretion, which not only poses a potential threat to human health but also affects the balance of the ecosystem. In view of this, it is particularly urgent to develop effective NOR environmental removal technologies. Recent studies have explored various NOR removal technologies, including advanced oxidation processes, i.e., AOPs, biological treatment technologies, and adsorption technologies. Among these methods, advanced oxidation processes are generally regarded as the preferred strategy for treating emerging pollutants in NOR-containing wastewater due to their high removal efficiency and economic cost-effectiveness.

[0003] Advanced oxidation technology is a class of technologies that utilize strong oxidants to generate highly reactive free radicals to degrade organic pollutants that are difficult to remove in water. These technologies can effectively mineralize or partially oxidize organic pollutants, including drug residues, pesticides, dyes, and other persistent organic pollutants. Among AOPs, sulfate radical-based technologies have received attention due to their strong oxidation ability and relatively low environmental impact. Peroxymonosulfate, also known as persulfate, i.e., PMS, is a compound containing sulfate radicals, which can generate sulfate radicals in the activated state, and these sulfate radicals can rapidly react with organic pollutants to achieve the degradation of organic pollutants. PMS itself is a stable compound, relatively safe and easy to store in water treatment. PMS needs to be activated to release sulfate radicals. In the prior art, the activation process is mainly achieved through heat, light, metal ions, or catalytic reactions with transition metal ions. However, the existing activation methods have a low activation rate for PMS, and simply relying on the activation to generate sulfate radicals to degrade and remove organic pollutants has poor treatment effects. Summary of the Invention

[0004] The present invention provides an iron-cobalt modified biochar, its preparation method and application, effectively solving the technical problems of low activation rate of persulfate to generate sulfate radicals by existing activation methods and poor removal effect of organic pollutants solely relying on sulfate radicals. The present invention introduces Fe and Co into biochar by the eutectic solvent method. On the one hand, it endows biochar with a high specific surface area and porous structure, providing abundant adsorption sites for norfloxacin, and removing norfloxacin through adsorption. On the other hand, introducing Fe and Co into biochar increases the surface functional groups of biochar. The Fe and Co elements form stable complexes with the carboxyl and keto groups of norfloxacin through metal coordination bonds. As catalysts, Fe and Co lower the energy threshold for the decomposition of persulfate to generate sulfate radicals, improve the activation rate of persulfate, and achieve the efficient degradation of norfloxacin.

[0005] The first object of the present invention is to provide a preparation method of an iron-cobalt modified biochar, comprising the following steps: Air-dry and crush the biomass material to obtain biomass powder.

[0006] Under stirring, add Fe 3+ source and Co 2+ source and the eutectic solvent, deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat up to 120°C - 150°C for carbonization reaction, convert the biomass powder into biochar, and at the same time convert Fe 3+ and Co 2+ into iron oxide and cobalt oxide and load them on the biochar to obtain the iron-cobalt modified biochar.

[0007] As a preferred embodiment, the molar ratio of Fe 3+ to Co 2+ is 1.5 - 2.5:1.

[0008] As a preferred embodiment, the dosage ratio of Fe 3+ and Co 2+ to the eutectic solvent is 0.25g - 3.5g:75mL.

[0009] As a preferred embodiment, the eutectic solvent is: mix choline chloride and oxalic acid dihydrate according to a molar ratio of 1:1 - 1.1, stir at 75°C - 80°C to obtain a transparent liquid, and cool to room temperature to obtain it.

[0010] As a preferred embodiment, the time of the carbonization reaction is 4h - 5h.

[0011] As a preferred embodiment, the heating rate is 5°C / min - 6°C / min.

[0012] As a preferred embodiment, after the carbonization reaction is completed, a primary product is obtained, rinsed, filtered to obtain a black solid, and the black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar.

[0013] As a preferred embodiment, the biomass powder passes through a 60-mesh sieve.

[0014] The second object of the present invention is to provide an iron-cobalt modified biochar prepared by the above preparation method.

[0015] The third object of the present invention is to provide an application of iron-cobalt modified biochar in removing norfloxacin, which is characterized in that the application includes the following steps: adding iron-cobalt modified biochar into a solution containing norfloxacin for adsorption, and adding a persulfate solution for degradation and removal.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The iron-cobalt modified biochar prepared by the present invention has a high specific surface area and a porous structure, providing abundant adsorption sites for norfloxacin. The introduction of Fe and Co not only increases the surface functional groups of the biochar but also enhances its chemical affinity for norfloxacin. The presence of Fe and Co elements can form a complexation effect with specific functional groups in the norfloxacin molecule, forming stable complexes with the carboxyl and ketone groups of norfloxacin through metal coordination bonds. In addition, the reducibility of Fe and Co enables Co-Fe-BC to destroy the aromatic ring structure of norfloxacin through reduction, further improving the degradation effect of norfloxacin. Under acidic conditions, the functional groups on the surface of Co-Fe-BC will be protonated, enhancing the electrostatic attraction to norfloxacin and thus improving the adsorption efficiency. The iron-cobalt modified biochar can not only remove norfloxacin through adsorption but also activate persulfate to generate sulfate radicals, and then degrade norfloxacin through an advanced oxidation process. Fe and Co on the surface of Co-Fe-BC act as catalysts, which can lower the energy threshold for the decomposition of persulfate to generate sulfate radicals and accelerate the activation rate of persulfate. Under the catalytic action of Co-Fe-BC, the reaction of persulfate decomposition to generate sulfate radicals is as follows:

[0017] The generated sulfate radicals have a high redox potential, can attack norfloxacin molecules non-selectively, initiate a radical chain reaction through a hydrogen atom abstraction or electron transfer mechanism, and finally mineralize norfloxacin into harmless small molecule substances such as carbon dioxide and water. This process not only effectively removes norfloxacin but also reduces the generation of disinfection by-products and improves the water quality safety. Description of the Drawings

[0018] Figure 1 Removal effect diagrams of norfloxacin by activating persulfate with iron-cobalt modified biochar with different contents prepared by the present invention.

[0019] Figure 2 pH change diagrams when removing norfloxacin by activating persulfate with iron-cobalt modified biochar with different contents prepared in the examples of the present invention.

[0020] Figure 3 Adsorption kinetics diagrams of the iron-cobalt modified biochar of the present invention.

[0021] Figure 4 Fitting diagrams of the adsorption isotherm Langmuir model of the iron-cobalt modified biochar of the present invention.

[0022] Figure 5 Fitting diagrams of the adsorption isotherm Freundlich model of the iron-cobalt modified biochar of the present invention.

[0023] Figure 6 Fitting diagrams of the adsorption isotherm Temkin model of the iron-cobalt modified biochar of the present invention.

[0024] Figure 7 SEM diagrams of the iron-cobalt modified biochar of the present invention. Among them, figure (a) is the iron-cobalt modified biochar prepared by the conventional pyrolysis method in Comparative Example 1, figure (b) is the unmodified biochar prepared by the eutectic solvent method in Comparative Example 2, and figure (c) is the iron-cobalt modified biochar prepared in Example 4.

[0025] Figure 8 SEM diagrams and element distribution MAPPING diagrams of the iron-cobalt modified biochar in Example 4 of the present invention. Among them, figure (a) is the SEM diagram, figure (b) is the element distribution MAPPING diagram, and figures (c)-(e) are the distribution diagrams of C element, Co element and Fe element respectively.

[0026] Figure 9 FTIR diagrams of the iron-cobalt modified biochar of the present invention. Among them, 0% is Comparative Example 2, 5% is Example 1, 30% is Example 2, 50% is Example 3, and 70% is Example 4.

[0027] Figure 10 XRD diagrams of the iron-cobalt modified biochar of the present invention.

[0028] Figure 11 N2 adsorption-desorption isotherm diagrams of different biochars Figure 11 The small diagrams in are the comparison diagrams of the BET specific surface areas of different biochars.

[0029] Figure 12 BJH desorption pore size distribution diagrams of different biochars.

[0030] Figure 13 Elemental analysis results of iron-cobalt modified biochar with different contents prepared for the present invention. Detailed implementation manners

[0031] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the specific embodiments cited shall not be construed as limiting the present invention. The following test methods and detection methods are all conventional methods unless otherwise specified; the reagents and raw materials are all commercially available unless otherwise specified.

[0032] Regarding the low activation rate of PMS by the existing activation methods mentioned in the background art of the present invention, and the treatment effect is not good for the degradation and removal of organic pollutants by simply relying on the activation to generate sulfate radicals. Based on the above technical problems, the present invention provides an iron-cobalt modified biochar, its preparation method and application.

[0033] The technical solutions of the present invention will be described in detail below.

[0034] The present invention first provides a preparation method of an iron-cobalt modified biochar, comprising the following steps: Air-dry, crush and sieve the biomass material through a 60-mesh sieve to obtain biomass powder.

[0035] Under stirring, add Fe 3+ source and Co 2+ source and eutectic solvent, deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat up to 120 °C - 150 °C, and carry out carbonization reaction for 4 h - 5 h to convert the biomass powder into biochar, and at the same time convert Fe 3+ and Co 2+ into iron oxides and cobalt oxides and load them on the biochar to obtain iron-cobalt modified biochar.

[0036] In the above technical solution, introducing Fe and Co into the biochar endows the biochar with a high specific surface area and a porous structure, provides rich adsorption sites for norfloxacin, and removes norfloxacin through adsorption; introducing Fe and Co into the biochar increases the surface functional groups of the biochar. Fe and Co elements form stable complexes with the carboxyl group and ketone group of norfloxacin through metal coordination bonds. Fe and Co act as catalysts, reducing the energy threshold for the decomposition of persulfate to generate sulfate radicals, improving the activation rate of persulfate, and realizing the efficient degradation of norfloxacin. The present invention greatly improves the removal effect of norfloxacin through the combined action of biochar adsorption and sulfate radical degradation.

[0037] For the temperature of the above carbonization reaction, which is 120°C to 150°C, and the carbonization reaction time, which is 4h to 5h, if the carbonization temperature is lower than 120°C and the time is less than 4h, the carbonization effect will be poor, and biochar with a better pore structure cannot be formed, thus affecting the adsorption capacity of organic pollutants; if the carbonization temperature is higher than 150°C and the time exceeds 5h, the microporous structure may collapse and the total pore volume may decrease, which is instead unfavorable for adsorption.

[0038] To increase the activation rate of peroxymonosulfate, the molar ratio of the Fe 3+ to Co 2+ is 1.5 to 2.5:1. The synergistic effect of iron and cobalt is the key to its activation of peroxymonosulfate. If the molar ratio is 1:1, the iron content decreases, which destroys the effect of the synergistic activation of peroxymonosulfate by Fe 3+ and Co 2+ and leads to a decrease in the radical generation rate. If the molar ratio is 1:3, the excessive cobalt covers the iron active sites, resulting in metal agglomeration and the formation of an inert complex of Co-Fe oxide, which instead inhibits the catalytic activity.

[0039] As a preferred embodiment, the dosage ratio of the Fe 3+ and Co 2+ to the eutectic solvent is 0.25g to 3.5g:75mL. Excessive eutectic solvent will cause excessive deposition of iron and cobalt metals on the surface of the biochar, forming metal particle agglomeration, which will not only cover the active sites of the biochar but also reduce the specific surface area and porosity. When the eutectic solvent is insufficient, the synergistic effect of the bimetal will be destroyed, resulting in a decrease in the generation efficiency of sulfate radicals.

[0040] It should be emphasized that the eutectic solvent used in the present invention is obtained by mixing choline chloride and oxalic acid dihydrate in a molar ratio of 1:1 to 1.1, stirring at 80°C to obtain a transparent liquid, and cooling to room temperature. This eutectic solvent can deconstruct the porous matrix of the biomass powder. The eutectic solvent can act as a "dynamic template" during the pyrolysis process, guiding the formation of pores through hydrogen bond networks and solvent volatilization: the hydrogen bond donors in the eutectic solvent decompose at high temperatures, releasing gases and promoting the formation of a hierarchical pore structure in the biochar. The micropores with a size of <2 nm and mesopores with a size of 2nm to 50nm in it are beneficial for adsorbing small molecule pollutants such as heavy metal ions. The ash residue of some eutectic solvents remaining after carbonization can act as a pore-forming agent to form through pores with a size of >50 nm, improving the mass transfer efficiency.

[0041] To avoid the influence of a large temperature difference on the pore structure of the biochar, resulting in uneven pore distribution, the present invention controls the heating rate at 5°C / min to 6°C / min during the carbonization reaction.

[0042] It should be noted that in order to improve the purity of the final iron-cobalt modified biochar, after the carbonization reaction is completed, a primary product is obtained, which is rinsed and filtered to obtain a black solid. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain the iron-cobalt modified biochar.

[0043] The following specifically describes the content of the present invention through the following examples and comparative examples.

[0044] Example 1 A preparation method of iron-cobalt modified biochar includes the following steps: S1. Air-dry, pulverize the biomass material, and pass it through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate according to a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0045] S2. Under stirring conditions, add 0.25 g of Fe 3+ source and Co 2+ source with a molar ratio of 2:1 to 5 g of the biomass powder, then add 75 mL of the eutectic solvent. Deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat it to 140 °C at a rate of 5 °C / min, and carry out a carbonization reaction for 4 h to convert the biomass powder into biochar. At the same time, convert Fe 3+ and Co 2+ into iron oxide and cobalt oxide and load them on the biochar. After the carbonization reaction is completed, a primary product is obtained, which is rinsed and filtered to obtain a black solid. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain the iron-cobalt modified biochar, denoted as D-140-Co-Fe-5%.

[0046] Example 2 A preparation method of iron-cobalt modified biochar includes the following steps: S1. Air-dry, pulverize the biomass material, and pass it through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate according to a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0047] S2. Under stirring conditions, add 1.5 g of Fe 3+ source and Co 2+ source with a molar ratio of 2:1 to 5 g of the biomass powder, then add 75 mL of the eutectic solvent. Deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat it to 140 °C at a rate of 5 °C / min, and carry out a carbonization reaction for 4 h to convert the biomass powder into biochar. At the same time, convert Fe 3+and Co 2+ It is converted into iron oxide and cobalt oxide and loaded on the biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, filtered, and a black solid is obtained. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar, D-140-Co-Fe-30%.

[0048] Example 3 A preparation method of iron-cobalt modified biochar includes the following steps: S1, Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate in a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0049] S2, Under stirring, add 2.5 g of Fe with a molar ratio of 2:1 to 5 g of the biomass powder 3+ source and Co 2+ source, then add 75 mL of the eutectic solvent. Deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat up to 140 °C at a rate of 5 °C / min, and carry out a carbonization reaction for 4 h to convert the biomass powder into biochar. At the same time, convert Fe 3+ and Co 2+ into iron oxide and cobalt oxide and load them on the biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, filtered, and a black solid is obtained. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar, D-140-Co-Fe-50%.

[0050] Example 4 A preparation method of iron-cobalt modified biochar includes the following steps: S1, Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate in a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0051] S2, Under stirring, add Fe with a molar ratio of 2:1 to 5 g of the biomass powder 3+ source and Co 2+ source, then add the eutectic solvent, Fe 3+ and Co 2+The dosage ratio with the eutectic solvent is 3.5 g:75 mL. The porous matrix of the biomass powder is deconstructed by the eutectic solvent, heated to 140 °C at a rate of 5 °C / min, and carbonized for 4 h to convert the biomass powder into biochar. At the same time, Fe 3+ and Co 2+ are converted into iron oxide and cobalt oxide and loaded on the biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, and filtered to obtain a black solid. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar, D-140-Co-Fe-70%.

[0052] Example 5 A preparation method of iron-cobalt modified biochar includes the following steps: S1. Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate in a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0053] S2. Under stirring, add 0.25 g of Fe 3+ source and Co 2+ source with a molar ratio of 1.5:1 to 5 g of the biomass powder, then add 75 mL of the eutectic solvent. The porous matrix of the biomass powder is deconstructed by the eutectic solvent, heated to 120 °C at a rate of 5 °C / min, and carbonized for 5 h to convert the biomass powder into biochar. At the same time, Fe 3+ and Co 2+ are converted into iron oxide and cobalt oxide and loaded on the biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, and filtered to obtain a black solid. The black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar.

[0054] Example 6 A preparation method of iron-cobalt modified biochar includes the following steps: S1. Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate in a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0055] S2. Under stirring, add 0.25 g of Fe 3+ source and Co 2+Source, then add 75 mL of the eutectic solvent. The porous matrix of the biomass powder is deconstructed by the eutectic solvent, heated to 150 °C at a rate of 5 °C / min, and carbonized for 4 h to convert the biomass powder into biochar. At the same time, Fe 3+ and Co 2+ are converted into iron oxides and cobalt oxides and loaded on the biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, filtered to obtain a black solid, and the black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain iron-cobalt modified biochar.

[0056] To further illustrate the effects of the present invention, a comparative example is also set in the present invention as follows: Comparative Example 1 Compared with Example 1, the difference is that biochar is prepared by a conventional pyrolysis method.

[0057] A method for preparing biochar includes the following steps: S1. Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder.

[0058] S2. Under stirring conditions, add 75 mL of ultrapure water to 5 g of the biomass powder, heat to 140 °C at a rate of 5 °C / min, and carbonize for 4 h to convert the biomass powder into biochar. After the carbonization reaction is completed, a primary product is obtained, rinsed, filtered to obtain a black solid, and the black solid is washed with ultrapure water until the washing liquid is neutral to obtain a secondary product. The secondary product is dispersed in absolute ethanol, dried, and ground to obtain unmodified biochar, denoted as H-140.

[0059] Comparative Example 2 Compared with Example 1, the difference is that iron and cobalt are not used for modification.

[0060] A method for preparing biochar includes the following steps: S1. Air-dry, crush, and sieve the biomass material through a 60-mesh sieve to obtain biomass powder. Mix choline chloride and oxalic acid dihydrate in a molar ratio of 1:1, stir at 80 °C to obtain a transparent liquid, and cool to room temperature to obtain a eutectic solvent.

[0061] S2. Under stirring, add 75 mL of the eutectic solvent to 5 g of the biomass powder. Deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat it to 140 °C at a rate of 5 °C / min, carry out carbonization reaction for 4 h to convert the biomass powder into biochar. After the carbonization reaction is completed, obtain the primary product, rinse and filter to obtain a black solid. Wash the black solid with ultrapure water until the washing liquid is neutral to obtain the secondary product. Disperse the secondary product in absolute ethanol, dry and grind to obtain biochar, denoted as D-140.

[0062] Detect the performance of the iron-cobalt modified biochars provided in Examples 1 to 6 above, the biochar prepared by the conventional pyrolysis method in Comparative Example 1, and the biochar provided in Comparative Example 2, and use the biochars prepared in the above examples and comparative examples to remove norfloxacin. The process and results are as follows.

[0063] Adsorption + activation degradation of persulfate process: Adsorption: The biochar concentration is 0.5 g / L, 100 mL of 100 mg / L NOR solution. Set the temperature at 25 °C in a constant temperature shaker. In the adsorption experiment, use 150 mL conical flasks and seal them with a film. Set the rotation speed of the constant temperature shaker at 200 r / min. Take samples of the NOR solution at regular intervals, filter them with a 0.22 μm filter membrane, and then measure the solution concentration by HPLC and calculate the adsorption capacity.

[0064] Activation: After 24 h of adsorption, add 0.5 mL of 0.1 M PMS solution to the conical flask, seal it with a film, keep the temperature at 25 °C, set the rotation speed of the shaker at 200 r / min, and carry out the reaction. Take samples of the NOR solution at regular intervals and add an equal amount of methanol, filter them with a 0.22 μm filter membrane, and then measure the solution concentration by HPLC and calculate the adsorption capacity.

[0065] It can be seen from Figure 1 that the unmodified biochar in Comparative Example 2 precipitated the previously adsorbed norfloxacin after adding persulfate, indicating that relying solely on adsorption to remove NOR is unreliable and norfloxacin may also precipitate during actual application, resulting in environmental pollution again. For the iron-cobalt modified biochars prepared in Examples 1 to 4, with the increase of the content of iron and cobalt, the removal effect on NOR is better, but when the addition amount exceeds 70% of the weight of the biochar raw material, it will also affect the adsorption of NOR. Therefore, the iron-cobalt modified biochar with a maximum addition amount of 70% of the weight of the biochar raw material powder.

[0066] When the biochar prepared by the eutectic solvent method simulates pseudo-first-order and pseudo-second-order kinetics, as Figure 3As shown, the correlation coefficients R² are 0.65 and 0.86 respectively, indicating that its adsorption of NOR is more in line with the pseudo-second-order kinetic model, which implies that the adsorption process may be chemisorption. The adsorption of norfloxacin by the eutectic solvent carbon shows a large adsorption rate within 500 min and still has an upward trend in the subsequent time.

[0067] The Langmuir isotherm fitting, Freundlich isotherm fitting and Temkin isotherm fitting of the adsorption of norfloxacin by the iron-cobalt modified biochar prepared by the eutectic solvent method of the present invention are as Figure 4 , Figure 5 and Figure 6 shown. The fitting results show that there are both monolayer adsorption and multilayer adsorption in the adsorption of the iron-cobalt modified biochar prepared by the eutectic solvent under these conditions; the fitting parameter B of the Temkin model is greater than 0, indicating that all adsorptions belong to exothermic processes. The best fitting result of the Freundlich isotherm indicates that the surface adsorption sites of the biochar prepared by the eutectic solvent are different and there is multimolecular layer adsorption.

[0068] Figure 7 is the micrograph of the iron-cobalt modified biochar prepared by the eutectic solvent method. It can be seen from Figure 7 that the biomass structure of the farmland tailings is gradually destroyed, forming many irregular pore structures and a large number of spherical microspheres. These microspheres are very likely biochar microspheres synthesized by the biomass through a series of condensation polymerization reactions. The microstructures of biochars synthesized by the hydrothermal method reported previously are also similar to this. It can be seen from Figure 8 that both iron and cobalt elements are evenly distributed and the content of Fe(III):Co is approximately 2, meeting the initial expected value

[0069] Figure 9 is the FTIR diagram of the iron-cobalt modified biochar of the present invention. It can be seen from Figure 9 that the iron-cobalt modified biochar has rich functional groups and the types of functional groups are the same. The positions and types of vibration peaks of each functional group have been marked in Figure 9 . For the iron-cobalt modified biochar prepared by the eutectic solvent, the -OH vibration peak appearing near 3351 cm -1 , and the -CHX vibration peaks near 2924 cm -1 and 2860 cm -1 show a trend of decreasing spectral intensity with the increase of temperature. This is because with the increase of temperature, the degree of carbonization gradually deepens, resulting in dehydration and dehydroxylation; the C=C vibration peak near 1623 cm -1 and the intensity of the C=O vibration peak near 1554 cm -1 gradually become stronger, indicating that one or more sugar molecules dehydrogenate and aromatize with themselves to form an aromatic ring during the reaction process. The 778 cm -1The vibration peak that appears nearby is aromatic C-H, which also indicates that an aromatization reaction has occurred.

[0070] According to Figure 10 The results show that the XRD patterns of the iron-cobalt modified biochar have many amorphous broad peaks, indicating that the iron-cobalt modified biochar belongs to amorphous substances; the differences in the broad peaks of the XRD analysis results of each iron-cobalt modified biochar are mainly manifested at 18.8°, 22.9° and 28.14°. Using jade 6.0 for analysis, the diffraction peak at 18.8° may represent the characteristic peak of iron oxalate, and the standard card number is PDF#23-0293. Moreover, the peak intensity at this point becomes stronger and stronger from high to low iron-cobalt content, indicating that oxalic acid in the DES participates in the reaction and forms iron oxalate with the iron mineral elements in the agricultural tail vegetables; the diffraction peaks at 22.9° and 28.14° can be identified as carbon in jade 6.0, and the standard card is PDF#50-0926. The XRD analysis results are in good agreement with the XRD analysis in the previous related research on biochar, indicating that the biomass carbonization of agricultural tail vegetables can be achieved by using DES at 140°C. According to the XRD analysis results, the standard card numbers corresponding to the diffraction peaks of iron and cobalt elements are PDF#34-1266, PDF#23-0293, PDF#21-0920, PDF#50-1674, PDF#48-1069 respectively, indicating that iron exists in the form of Fe+3O(OH), C2Fe+2O4·2H2O, Fe2O3, and cobalt exists in the form of (Co(NH3)4CO3)·0.5H2O, C2CoO4 in the modified biochar.

[0071] Figure 11 and Figure 12 show the N2 adsorption-desorption isotherms and BJH desorption pore size distribution diagrams of the biochar prepared at different temperatures. According to the IUPAC classification, the adsorption-desorption isotherm of the biochar prepared by the eutectic solvent at 140°C can be classified as type Ⅳ, indicating that the prepared biochar has a certain mesoporous structure. Due to capillary condensation occurring in the mesoporous channels, the adsorption and desorption isotherms do not coincide, resulting in a hysteresis loop. The hysteresis loop belongs to the H3 type. The characteristic of the H3 type hysteresis loop is that the isotherm does not show a plateau when the relative pressure approaches the saturated vapor pressure, indicating that the synthetic material has a flat slit structure, crack or wedge-shaped pore structure, etc., and at the same time it also shows that the pore structure is irregular, which is consistent with the results of the biochar scanning electron microscope. The relevant data of the biochar specific surface area and pore structure can be combined with Figure 12 and Table 1 to obtain. According to the BJH desorption pore size distribution Figure 12It can be seen that the pore size of the iron-cobalt modified biochar prepared by the eutectic solvent is below 60 nm, and the pore size of the biochar prepared by hydrothermal method is below 50 nm. According to the IUPAC pore size classification, pores larger than 50 nm are macropores, pores between 2 nm and 50 nm are mesopores, and pores smaller than 2 nm are micropores. This indicates that the biochar prepared by the eutectic solvent has a macroporous structure compared to the hydrothermally prepared biochar, but the main pores are still concentrated in the mesoporous structure of 5 nm - 25 nm.

[0072] Table 1 Elemental analysis results of biochar in the examples and comparative examples of the present invention As can be seen from Table 1, the biochar H-140 prepared by the conventional hydrothermal method exhibits the lowest specific surface area of 4.72 m 2 / g. The specific surface areas of the biochars prepared by the eutectic solvent are all better than that of H-140. Moreover, it can be seen that the specific surface area of the biochar prepared by the eutectic solvent method is significantly better than that of the conventional pyrolysis method. The specific surface area of D-140 prepared at 140 °C is 15.94 m 2 / g, which is 3.38 times that of H-140; the total pore volume and the specific surface area show the same pattern. The lowest of H-140 is 0.018 cm 3 / g, while that of D-140 is 0.066 cm 3 / g, which is 3.67 times that of H-140; the average pore size results calculated from the mesopore size analysis of the biochars do not differ much, and all show mesoporous properties.

[0073] Figure 13 Figure for the elemental analysis results of different contents of iron-cobalt modified biochars prepared in the present invention. Among them, 5% FeCo is Example 1, 30% FeCo is Example 2, 50% FeCo is Example 3, 70% FeCo is Example 4, and non-modified is Comparative Example 2. From Figure 13 It can be seen that: Fe / Co content gradient: As the Fe-Co addition ratio increases from 5% to 70%, the bar chart shows that the proportions of Fe and Co increase significantly. The metals are evenly dispersed, forming effective Fe 2+ / Co 3+The redox cycle has the highest efficiency in activating PMS to generate sulfate radicals. The unmodified biochar has the highest carbon content, which is the main basic adsorption component. With the addition of Fe-Co, the carbon content gradually decreases but still remains dominant. The key turning point is at the 30% addition amount: when C ≥ 50%, enough carbon skeletons are retained to support π-π interactions, and the ability to adsorb norfloxacin is stable. When C < 50%, such as in the 70% addition group, the carbon skeleton is covered by metals, and the adsorption capacity may decrease. The unmodified group has the highest O / C ratio, rich in hydroxyl / carboxyl groups. With the addition of metals, the O / C ratio gradually decreases; with the addition of metals, the H / C ratio gradually decreases, indicating a reduction in aliphatic structures and an increase in aromatization degree. The ASH content is < 20%, the pore structure is intact, and the adsorption-catalysis synergistic effect is significant.

[0074] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A preparation method of iron-cobalt modified biochar, characterized in that, It includes the following steps: Air-dry and pulverize the biomass material to obtain biomass powder; While stirring, add Fe to the biomass powder 3+ source and Co 2+ source and eutectic solvent. Deconstruct the porous matrix of the biomass powder through the eutectic solvent, heat up to 120 °C to 150 °C, and carry out a carbonization reaction to convert the biomass powder into biochar. At the same time, convert Fe 3+ and Co 2+ into iron oxides and cobalt oxides and load them on the biochar to obtain iron-cobalt modified biochar.

2. The preparation method of the iron-cobalt modified biochar according to claim 1, wherein, The Fe 3+ and Co 2+ have a molar ratio of 1.5 to 2.5:

1.

3. The preparation method of the iron-cobalt modified biochar according to claim 1, wherein, The Fe 3+ and Co 2+ and the dosage ratio of the eutectic solvent is 0.25 g to 3.5 g: 75 mL.

4. The preparation method of the iron-cobalt modified biochar according to claim 3, characterized in that, The eutectic solvent is obtained by mixing choline chloride and oxalic acid dihydrate in a molar ratio of 1:1 to 1.1, stirring at 75°C to 80°C to obtain a transparent liquid, and cooling to room temperature; 5. The preparation method of the iron-cobalt modified biochar according to claim 1, wherein The time of the carbonization reaction is 4h to 5h; 6. The preparation method of the iron-cobalt modified biochar according to claim 1, wherein The heating rate is 5°C / min to 6°C / min; 7. The preparation method of the iron-cobalt modified biochar according to claim 1, characterized in that, After the carbonization reaction, a primary product is obtained, rinsed and filtered to obtain a black solid. Wash the black solid with ultrapure water until the washing liquid is neutral to obtain a secondary product. Disperse the secondary product in absolute ethanol, dry and grind to obtain iron-cobalt modified biochar; 8. The preparation method of the iron-cobalt modified biochar according to claim 1, characterized in that, The biomass powder passes through a 60-mesh sieve; 9. Iron-cobalt modified biochar prepared by the preparation method according to any one of claims 1 to 8; 10. Use of the iron-cobalt modified biochar according to claim 9 in removing norfloxacin, characterized in that, The application includes the following steps: adding the iron-cobalt modified biochar into a solution containing norfloxacin for adsorption, and adding a persulfate solution for degradation and removal.

Images