Preparation method of metal ion liquid modified co-doped biochar and application of metal ion liquid modified co-doped biochar in tetracycline removal

Abstract

The invention discloses a preparation method of metal ion liquid modified co-doped biochar and application of the metal ion liquid modified co-doped biochar in tetracycline removal, and belongs to the technical field of water pollution treatment and adsorption material preparation. The preparation method comprises the following steps: mixing a biochar precursor with a metal ion liquid containing transition metal and a heteroatom source, and carrying out high-temperature carbonization to obtain the metal ion liquid modified co-doped biochar. Multiple modification of the biochar is realized through one-time high-temperature carbonization (transition metal elements and heteroatoms are introduced into a biochar skeleton, abundant surface active sites are provided, and the specific surface area and pore volume of the biochar are improved), so that the adsorption performance of the biochar on tetracycline antibiotics is remarkably improved. The preparation method is simple in process, raw materials are easy to obtain, and the obtained metal ion liquid modified co-doped biochar has excellent adsorption performance on antibiotic pollutants such as tetracycline and is suitable for purification treatment of water polluted by antibiotics.

Description

Technical Field

[0001] The present invention relates to the technical field of water pollution control and adsorption material preparation, and in particular to a preparation method of metal ion liquid modified co-doped biochar and application thereof in removing tetracycline. Background Art

[0002] At present, the methods for removing antibiotic pollutants from water mainly include advanced oxidation technology, membrane separation technology, coagulation and sedimentation, and adsorption technology. Among them, the adsorption method has attracted widespread attention due to its simple operation, low cost and high removal efficiency for low-concentration pollutants. The development of efficient adsorbents to remove antibiotics in water is an important research direction in the field of environmental remediation. Biochar is a carbon-rich material obtained by high-temperature cracking and carbonization of biomass. It is considered to be a very promising antibiotic adsorbent due to its advantages such as a wide source of raw materials (agricultural waste, forestry waste, etc.), low price, developed pore structure and rich surface functional groups. However, ordinary biochar often has disadvantages such as insufficient specific surface area, insufficient functional groups and active sites, and strong hydrophobicity, resulting in limited adsorption capacity for polar organic pollutants such as tetracycline. How to improve the porosity and surface chemical properties of biochar through modification methods, thereby improving its adsorption performance for antibiotics, is a technical problem that needs to be solved urgently.

[0003] In order to improve the adsorption effect of biochar on pollutants, researchers have proposed a variety of modification strategies. For example, chemical activation (acid modification, alkali modification) can significantly increase the porosity and specific surface area of biochar and introduce additional surface functional groups; heteroatom doping can change the surface chemical composition of biochar, increase polar functional groups and enhance the interaction with pollutant molecules. At the same time, metal loading or metal doping is also an effective modification method. The common practice is to introduce metal salt precursors into biochar, and then carbonize them at high temperature to form metal oxides or zero-valent metal particles in order to provide additional active sites and special surface effects. However, traditional heteroatom doping and metal loading usually require multi-step processing, the preparation process is relatively complicated, and the adsorption performance of the obtained product still needs to be improved. Therefore, it is very necessary to develop a preparation method for high-performance doped modified biochar with a simple preparation process. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing metal ion liquid modified co-doped biochar and its application in removing tetracycline, so as to solve the problems existing in the above-mentioned prior art. The present invention simultaneously realizes multiple modifications of biochar through a single high-temperature carbonization to significantly improve its adsorption performance for tetracycline antibiotics. The present invention also provides the application of the modified co-doped biochar obtained by this method in removing tetracycline antibiotic pollutants in water. The modified co-doped biochar prepared by the method of the present invention has a higher specific surface area and more surface active sites, and exhibits excellent adsorption and removal effects on tetracycline antibiotics.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing metal ion liquid modified co-doped biochar, comprising the following steps:

[0007] A biochar precursor (i.e., preliminarily carbonized biochar) is mixed with a metal ion liquid containing a transition metal and a heteroatom source, and carbonized at high temperature to obtain the metal ion liquid-modified co-doped biochar.

[0008] The present invention uses metal ionic liquids to modify biochar. Metal ionic liquids are a special type of ionic liquid whose cations or anions contain metal complexes. On the one hand, they can decompose at high temperatures and act as pore-forming agents for the biochar, improving its pore structure. On the other hand, the transition metals and heteroatoms contained in the ionic liquids can be simultaneously incorporated into the biochar skeleton, achieving co-doping modification of the heteroatoms and metals and providing abundant surface active sites. Furthermore, using metal ionic liquids as modifiers can effectively increase the specific surface area and pore volume of the biochar while achieving co-doping modification of the heteroatoms and transition metals. Therefore, the method of the present invention can effectively improve the adsorption performance of biochar for tetracycline antibiotics.

[0009] The present invention simultaneously achieves multiple modifications of biochar through one high-temperature carbonization to significantly improve its adsorption performance for tetracycline antibiotics, and the preparation process is simple.

[0010] Furthermore, the transition metal contained in the metal ion liquid is manganese, the heteroatom source is a nitrogen atom source, and the obtained metal ion liquid modified co-doped biochar is manganese / nitrogen co-doped modified biochar (abbreviated as Mn / N-BC).

[0011] More preferably, the metal ionic liquid is 1-ethyl-3-methylimidazolium tetrachloromanganate.

[0012] The cation of 1-ethyl-3-methylimidazolium tetrachloromanganate ([Emim]2[MnCl4]) is 1-ethyl-3-methylimidazolium ion ([Emim] +), the anion is the tetrachloro complex anion of divalent manganese ([MnCl4] 2- ). Through a high-temperature pyrolysis reaction, the ionic liquid decomposes and introduces manganese and nitrogen elements into the biochar matrix, achieving manganese / nitrogen co-doping modification and generating a developed pore structure. After the carbonization and heat preservation is completed, it is naturally cooled to room temperature to obtain metal ion liquid modified and co-doped biochar. Among them, nitrogen doping can increase the π-π interaction and hydrogen bonding of aromatic ring-containing pollutants by introducing nitrogen-containing functional groups on the surface of biochar, which is beneficial to the adsorption of multi-functional group molecules such as tetracycline. Manganese doping can introduce more active sites. The synergistic effect of manganese and nitrogen can effectively improve the adsorption performance of tetracycline antibiotics.

[0013] Furthermore, the biochar precursor is an activated biochar precursor.

[0014] Furthermore, the preparation step of the activated biochar precursor includes:

[0015] The biomass raw material is activated by immersion in an alkaline solution and pre-carbonized at a medium temperature to obtain the activated biochar precursor.

[0016] Furthermore, the alkaline solution impregnation activation comprises: mixing the biomass raw material and the alkaline solution, stirring evenly, and then standing for activation for 0.5-3 hours, preferably 1-2 hours.

[0017] Alkali activation pretreatment can promote the carbonization reaction of biomass and increase the porosity and surface functional group content of the product biochar.

[0018] Furthermore, the alkaline solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, preferably a potassium hydroxide aqueous solution.

[0019] Furthermore, the concentration of the alkaline solution is 20-40 wt%, preferably 30 wt%.

[0020] Furthermore, the biomass raw material is biomass waste rich in carbon.

[0021] Optionally, the biomass raw material includes wood chips, straw or fruit shells, preferably wood chips of lignocellulosic material, such as poplar wood chips.

[0022] Optionally, the biomass raw materials are further crushed and screened before the alkaline solution soaking and activation.

[0023] The purpose of crushing and sieving the biomass raw materials is to refine the particle size of the biomass raw materials. The use of biomass powder with smaller particle size (for example, 200 mesh sieve) is conducive to the infiltration and full activation of the alkaline solution, thereby improving the subsequent carbonization effect.

[0024] Furthermore, the medium-temperature pre-carbonization temperature is 400-600° C., and the time is 1-4 hours.

[0025] By controlling the appropriate medium-temperature pre-carbonization temperature and time, we can ensure that the biomass is fully carbonized to form primary biochar (i.e., biochar precursor), while avoiding excessively high temperatures that may cause the pore structure to collapse or the ash content to increase.

[0026] Furthermore, the medium-temperature pre-stage carbonization is carried out in an inert atmosphere or under vacuum conditions, and the heating rate of the medium-temperature pre-carbonization is 3-10°C / min.

[0027] Further preferably, the medium-temperature pre-carbonization is carried out at a heating rate of 5°C / min, a temperature of 500°C, and a time of 2 hours.

[0028] Optionally, after the medium-temperature pre-carbonization, the method further comprises grinding and sieving the obtained carbonized product, washing it to neutrality, and then drying it.

[0029] Furthermore, the mass ratio of the biochar precursor to the metal ionic liquid containing transition metals and heteroatom sources is 1:1-20, preferably 1:10-15.

[0030] By controlling the amount of ionic liquid, the doping level and pore structure of the biochar can be adjusted: too little can lead to insufficient doping and pore formation, while excessive amounts exceeding the optimal value can slow the doping efficiency increase and potentially waste resources. The optimal ratio yields modified biochar with the best overall performance.

[0031] Furthermore, the high-temperature carbonization temperature is 700-900° C., and the time is 1-3 hours.

[0032] Furthermore, the high-temperature carbonization is carried out in an inert atmosphere, and the heating rate of the high-temperature carbonization is 3-10°C / min.

[0033] Further preferably, the high-temperature carbonization is carried out at a heating rate of 5°C / min, a temperature of 800°C, and a time of 2 hours.

[0034] High temperature conditions are conducive to the decomposition of ionic liquids and element doping, but too high a temperature may cause the biochar skeleton to burn out or the pore structure to shrink. A temperature of around 700-900°C can balance the biochar structural stability and doping effect, with a temperature of around 800°C being the best.

[0035] Optionally, after the high-temperature carbonization, the process further includes grinding and screening the carbonized product to obtain metal ion liquid modified co-doped biochar with uniform particles.

[0036] The second technical solution of the present invention: a metal ion liquid modified co-doped biochar prepared by the above preparation method.

[0037] Furthermore, the metal ion liquid modified co-doped biochar contains manganese elements in the form of manganese oxide and nitrogen elements doped in the form of nitrogen functional groups.

[0038] Furthermore, the specific surface area of the metal ion liquid modified co-doped biochar is greater than 400m 2 / g.

[0039] The third technical solution of the present invention: an application of the above-mentioned metal ion liquid modified co-doped biochar in the adsorption of tetracycline antibiotics.

[0040] Furthermore, the application step includes: adding the metal ion liquid modified co-doped biochar to a water body containing tetracycline antibiotics, and adsorbing the tetracycline antibiotics under room temperature oscillation conditions.

[0041] The present invention discloses the following technical effects:

[0042] (1) The present invention introduces metal ionic liquid modification, achieves the co-doping of transition metal elements and heteroatoms on biochar, and the development of biochar pore structure in a high-temperature carbonization process, which greatly improves the adsorption performance of biochar for tetracycline antibiotics. On the one hand, the specific surface area of the modified biochar is significantly improved, reaching 435-653m 2 / g, the specific surface area of the Mn / N co-doped modified biochar obtained under the optimal preparation conditions increased to about 2.5 times that of the unmodified biochar, and the pore volume also increased to about 2.4 times that of the unmodified biochar. The rich micropore and mesoporous structure is conducive to the entry and filling of tetracycline antibiotic molecules; on the other hand, the introduction of transition metals formed dispersed transition metal oxide nanoparticles or coordination structures, and the introduction of heteroatoms formed heteroatom-containing functional groups on the biochar surface (when the heteroatom is a N atom, specifically pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen functional groups). These new active sites can form coordination bonds, hydrogen bonds and π-π interactions with tetracycline antibiotic molecules.

[0043] (2) The present invention uses waste biomass such as waste poplar as raw materials, which has the advantages of easy availability of raw materials and low cost, realizes waste recycling, and has environmental protection significance.

[0044] (3) The Mn / N co-doped modified biochar obtained in the present invention exhibits excellent adsorption capacity for tetracycline: at 25°C, its maximum adsorption capacity for tetracycline can reach about 201.5 mg / g, which is nearly 2.8 times higher than that of the unmodified biochar (about 72.2 mg / g).

[0045] (4) The Mn / N co-doped modified biochar obtained by the present invention has the best adsorption effect in a water environment near neutrality (pH about 7), has a certain adaptability to the initial pH of the solution (pH 3-11 can effectively remove tetracycline), and has a good adsorption effect in a water environment with common coexisting ions (such as Na + , Ca 2+ 、Cl - 、SO4 2- ) and natural organic matter (such as humic acid and fulvic acid), it still maintains high adsorption performance and good anti-interference ability.

[0046] In summary, the preparation method provided by the present invention is simple and feasible. It uses cheap and readily available biomass and ionic liquid as raw materials. The prepared biochar adsorbent has a high efficiency in removing antibiotic pollutants such as tetracycline, is suitable for the purification of water bodies contaminated by antibiotics, and has broad application prospects in the field of water environment management. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 Scanning electron microscope photographs of the unmodified biochar (BC) prepared in Comparative Example 1 and the manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared in Examples 1-4, wherein a and f are the morphologies of BC at 5,000 times and 20,000 times magnification; b and g are the morphologies of Mn / N-BC-1 at 5,000 times and 20,000 times magnification; c and h are the morphologies of Mn / N-BC-2 at 5,000 times and 20,000 times magnification; d and i are the morphologies of Mn / N-BC-3 at 5,000 times and 20,000 times magnification; e and j are the morphologies of Mn / N-BC-4 at 5,000 times and 20,000 times magnification.

[0049] Figure 2This is a comprehensive characterization result diagram of the unmodified biochar (BC) prepared in comparative example 1 and the manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared in Examples 1-4, wherein a is the nitrogen adsorption-desorption isotherm of BC and Mn / N-BC materials; b is the pore size distribution curve corresponding to the nitrogen adsorption-desorption isotherm; c is the X-ray diffraction pattern of BC and Mn / N-BC-3; d is the Raman spectrum of BC and Mn / N-BC-3; e is the Fourier transform infrared spectrum of BC and Mn / N-BC-3; f is the full X-ray photoelectron energy spectrum of BC and Mn / N-BC-3; g and h are the XPS high-resolution spectra of Mn 2p and N1s elements of Mn / N-BC-3 samples, respectively.

[0050] Figure 3 The figures show the adsorption kinetics and isotherm results of tetracycline on the unmodified biochar (BC) prepared in comparative example 1 and the manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared in examples 1-4, wherein ae are the tetracycline adsorption kinetic fitting curves of BC, Mn / N-BC-1, Mn / N-BC-2, Mn / N-BC-3, and Mn / N-BC-4 samples, respectively, comparing the pseudo-first-order kinetic model and the pseudo-second-order kinetic model; fj are the tetracycline adsorption isotherm fitting curves of the above five samples at 25°C, comparing the Langmuir model and the Freundlich model.

[0051] Figure 4 Figure 3 is the effect curve of coexisting inorganic ions and dissolved organic matter on the tetracycline adsorption capacity of Mn / N-BC-3 (a) and the effect curve of initial pH of the solution on the tetracycline adsorption capacity of Mn / N-BC-3 (b). DETAILED DESCRIPTION

[0052] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0053] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0054] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0055] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0056] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0057] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0058] As a first aspect of the present invention, the present invention provides a method for preparing metal ion liquid modified co-doped biochar, comprising the following steps:

[0059] The biochar precursor is mixed with a metal ion liquid containing a transition metal and a heteroatom source, and carbonized at high temperature to obtain the metal ion liquid modified co-doped biochar.

[0060] As a preferred embodiment of the present invention, the transition metal contained in the metal ionic liquid is manganese, and the heteroatom source is a nitrogen atom source.

[0061] As a preferred embodiment of the present invention, the biochar precursor is an activated biochar precursor.

[0062] As a preferred embodiment of the present invention, the steps of preparing the activated biochar precursor include:

[0063] The biomass raw material is activated by immersion in an alkaline solution and pre-carbonized at a medium temperature to obtain the activated biochar precursor.

[0064] As a preferred embodiment of the present invention, the preparation method of the metal ion liquid modified co-doped biochar has the following more specific steps:

[0065] (1) Biomass activation and pre-carbonization: The biomass raw materials (wood chips, straw or fruit shells, preferably wood chips of lignocellulosic materials, such as poplar wood chips) are crushed and sieved and then mixed with an alkaline solution (a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution with a concentration of 20-40 wt%, preferably a potassium hydroxide aqueous solution with a concentration of 30 wt%), stirred evenly and then allowed to stand for activation for 0.5-3 hours (preferably 1-2 hours); after the end of the standing activation, the biomass raw materials are taken out and heated at 3-10 ° C / min under inert atmosphere or vacuum conditions. The temperature is raised to a medium-temperature pre-carbonization temperature (400-600°C, preferably 500°C) at a heating rate (preferably 5°C / min) and kept at this temperature for 1-4 hours (preferably 2 hours) to perform medium-temperature pre-carbonization (which may be referred to as the first stage carbonization). After the carbonization is completed, the product is cooled, ground and sieved (for example, a 200-mesh sieve), and then washed alternately with an acid solution (such as 1 mol / L hydrochloric acid) and deionized water until neutral to remove residual inorganic salts and impurities, and then dried at 70-80°C to obtain an activated biochar precursor;

[0066] (2) Ionic liquid modified co-doping: The activated biochar precursor obtained in step (1) is mixed evenly with a metal ionic liquid (preferably 1-ethyl-3-methylimidazolium tetrachloromanganate) in a mass ratio of 1:1-20 (preferably 1:10-15), placed in an inert atmosphere, heated at a heating rate of 3-10°C / min (preferably 5°C / min) to a high-temperature carbonization temperature (700-900°C, preferably 800°C) and kept warm for 1-3 hours (preferably 2 hours) to perform high-temperature carbonization (which can be referred to as the second stage carbonization); after cooling, the product is ground and sieved to obtain metal ionic liquid modified co-doped biochar (i.e., manganese / nitrogen co-doped modified biochar).

[0067] As a preferred embodiment of the present invention, the synthesis steps of the metal ionic liquid [Emim]2[MnCl4] include: mixing 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) and manganese chloride (MnCl2) in a molar ratio of 2:1, heating and stirring at 90°C for 24 hours to obtain a stable dark liquid product [Emim]2[MnCl4]. This ionic liquid is stable at room temperature and decomposes when heated to several hundred degrees Celsius, releasing the manganese and nitrogen source.

[0068] As a second aspect of the present invention, the present invention provides a metal ion liquid modified co-doped biochar prepared by the above preparation method.

[0069] As a preferred embodiment of the present invention, the metal ion liquid modified co-doped biochar contains manganese elements in the form of manganese oxide and nitrogen elements doped in the form of nitrogen functional groups.

[0070] As a preferred embodiment of the present invention, the specific surface area of the metal ion liquid modified co-doped biochar is greater than 400m 2 / g.

[0071] As a third aspect of the present invention, the present invention provides an application of the above-mentioned metal ion liquid modified co-doped biochar in the adsorption of tetracycline antibiotics.

[0072] As a preferred embodiment of the present invention, the application step includes: adding the metal ion liquid modified co-doped biochar to a water body containing tetracycline antibiotics, and adsorbing the tetracycline antibiotics under room temperature oscillation conditions.

[0073] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0074] When referring to room temperature or normal temperature in the specific embodiments of the present invention, it specifically refers to 20-30°C.

[0075] Unless otherwise specified, all raw materials used in the embodiments of the present invention are common commercial products.

[0076] The synthesis steps of the metal ionic liquid [Emim]2[MnCl4] used in the following examples are as follows: 146.62g (1 mol) of 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) is placed in a flask and heated in an oil bath at 90°C to melt it into a transparent liquid; 62.92g (0.5 mol) of anhydrous manganese chloride (MnCl2) is slowly added thereto, mechanically stirred while heating, and the temperature is maintained at 90°C and stirred for 24 hours. After the reaction is completed, the resulting product is cooled to room temperature to obtain a dark brown metal ionic liquid [Emim]2[MnCl4]. The ionic liquid is a stable liquid at room temperature and pressure and is stored in a dry and sealed container for future use. The synthesis method of the metal ionic liquid [Emim]2[MnCl4] provided by the present invention is simple and easy, and the resulting [Emim]2[MnCl4] can be used in subsequent biochar modification steps without further purification.

[0077] Example 1

[0078] A metal ion liquid modified co-doped biochar (i.e., manganese / nitrogen co-doped modified biochar) adsorbent is prepared by the following steps:

[0079] (1) Biomass activation and pre-carbonization: Poplar wood sawdust waste (i.e., poplar sawdust) was selected, dried, crushed, and passed through a 200-mesh sieve. The fine powder was collected as the biomass raw material. 50 g of poplar wood biomass powder was weighed and 100 g of a 30 wt% KOH aqueous solution was added. The mixture was stirred evenly at room temperature and then left to activate for 2 hours to allow the KOH to fully penetrate the biomass pores. The activated biomass was then placed in a vacuum drying oven and dried at 80°C for 12 hours to remove moisture.

[0080] The dried alkali-activated biomass was moved into a vacuum tube furnace, heated to 500°C at a rate of 5°C / min under a nitrogen atmosphere, and pre-carbonized at a constant temperature of 500°C for 2 hours. After the carbonization was completed, the heating was turned off and the furnace was allowed to cool naturally to room temperature. The carbonized product (i.e., the activated preliminary carbonized biochar) was taken out, ground finely, passed through a 200-mesh sieve, and the powder under the sieve was collected. The biochar was then washed alternately with 1 mol / L hydrochloric acid solution and deionized water several times until the pH of the washing solution was close to neutral to fully remove the residual inorganic salts. The washed biochar was placed in a vacuum drying oven and dried at 70°C for 12 hours to obtain an activated biochar precursor sample, recorded as PBC (Poplar Biochar).

[0081] (2) Ionic liquid modified carbonization: Take 10g of the activated biochar precursor (PBC) obtained in step (1) and add 150g of metal ionic liquid [Emim]2[MnCl4] (i.e., the mass ratio of the activated biochar precursor to the metal ionic liquid is 1:15). Stir the mixture evenly so that the activated biochar precursor is fully immersed in the ionic liquid. Then place the mixture in a tube furnace under nitrogen protection, heat it to 800℃ at a rate of 5℃ / min, and further carbonize it at 800℃ for 2 hours. The ionic liquid gradually decomposes during the high temperature process: the organic imidazole cation decomposes to produce nitrogen-containing free radicals and combines with the carbon skeleton to form nitrogen functional groups, and the tetrachloromanganate anion decomposes to generate manganese chloride intermediates and further converts them into manganese oxide nanoparticles embedded in the pore structure of the biochar. After the carbonization is completed, stop heating and let the furnace cool to room temperature, take out the product, and obtain manganese / nitrogen co-doped modified biochar. This is the target adsorbent prepared in this example, recorded as Mn / N-BC-3, and stored in a desiccator for future use.

[0082] Example 2

[0083] The same as Example 1, except that in step (2), the mass ratio of the activated biochar precursor to the metal ionic liquid [Emim]2[MnCl4] is adjusted to 1:5. The manganese / nitrogen co-doped modified biochar finally obtained is recorded as Mn / N-BC-1 and stored in a desiccator for later use.

[0084] Example 3

[0085] The same as Example 1, except that in step (2), the mass ratio of the activated biochar precursor to the metal ionic liquid [Emim]2[MnCl4] is adjusted to 1:10. The manganese / nitrogen co-doped modified biochar finally obtained is recorded as Mn / N-BC-2 and stored in a desiccator for future use.

[0086] Example 4

[0087] The same as Example 1, except that in step (2), the mass ratio of the activated biochar precursor to the metal ionic liquid [Emim]2[MnCl4] is adjusted to 1:20. The manganese / nitrogen co-doped modified biochar finally obtained is recorded as Mn / N-BC-4 and stored in a desiccator for future use.

[0088] Comparative Example 1

[0089] The same as Example 1, except that the addition of the metal ionic liquid [Emim]2[MnCl4] was omitted in step (2), and the activated biochar precursor (PBC) was further carbonized at 800°C for 2 hours. The final product was unmodified biochar, recorded as BC, which was stored in a desiccator for later use.

[0090] Comparative Example 2

[0091] The same as Example 1, except that the addition of the alkaline solution is omitted in step (1) (i.e., the activation step is omitted), the poplar biomass powder is directly pre-carbonized at a constant temperature of 500°C for 2 hours, and ground, sieved, washed, and dried to obtain a biochar precursor, and then the obtained biochar precursor and the metal ion liquid [Emim]2[MnCl4] are mixed in a mass ratio of 1:15, and further carbonized at a high temperature of 800°C for 2 hours. The final alkali solution-free activated manganese / nitrogen co-doped modified biochar is recorded as NK-Mn / N-BC and stored in a desiccator for later use.

[0092] Comparative Example 3

[0093] The same as Example 1, except that in step (2), 150 g of the metal ionic liquid [Emim]2[MnCl4] is replaced with a MnCl2 aqueous solution (the molar amount of the Mn element contained in the MnCl2 aqueous solution is the same as the molar amount of the Mn element contained in 150 g of the metal ionic liquid [Emim]2[MnCl4]). The mixture is then placed in a tube furnace under nitrogen protection, heated to 800°C at a rate of 5°C / min, and further carbonized at 800°C for 2 hours. The final product is MnCl2-modified biochar, recorded as Mn-BC, which is stored in a desiccator for later use.

[0094] Comparative Example 4

[0095] The same as Example 1, except that in step (2), 150 g of the metal ionic liquid [Emim]2[MnCl4] is replaced with a mixed aqueous solution of MnCl2 and urea (the molar amounts of Mn and N elements contained in the mixed aqueous solution of MnCl2 and urea are the same as the molar amounts of Mn and N elements contained in 150 g of the metal ionic liquid [Emim]2[MnCl4]). The mixture is then placed in a tube furnace under nitrogen protection, heated to 800°C at a rate of 5°C / min, and further carbonized at 800°C for 2 hours. The final product is MnCl2 and urea-modified biochar, recorded as Mn-N-BC, which is stored in a desiccator for later use.

[0096] Test Example 1

[0097] Morphology, structure, and composition characterization

[0098] Figure 1 Scanning electron microscope (SEM) images of the unmodified biochar (BC) prepared in Comparative Example 1 and the manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared in Examples 1-4. Figures a and f show the morphology of BC at 5,000x and 20,000x magnifications; b and g show the morphology of Mn / N-BC-1 at 5,000x and 20,000x magnifications; c and h show the morphology of Mn / N-BC-2 at 5,000x and 20,000x magnifications; d and i show the morphology of Mn / N-BC-3 at 5,000x and 20,000x magnifications; and e and j show the morphology of Mn / N-BC-4 at 5,000x and 20,000x magnifications. The comparison reveals the differences in micromorphology and pore structure between the unmodified and modified biochars. Specifically, it can be seen that with the increase of [Emim]2[MnCl4] modifier, a hierarchical pore structure is formed on the surface of biochar, and the more [Emim]2[MnCl4] modifier is used, the richer the pore structure is.

[0099] Figure 2 This is a comprehensive characterization result diagram of the unmodified biochar (BC) prepared in comparative example 1 and the manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared in Examples 1-4, wherein a is the nitrogen adsorption-desorption isotherm of BC and Mn / N-BC materials; b is the pore size distribution curve corresponding to the nitrogen adsorption-desorption isotherm; c is the X-ray diffraction (XRD) pattern of BC and Mn / N-BC-3; d is the Raman spectrum of BC and Mn / N-BC-3; e is the Fourier transform infrared (FT-IR) spectrum of BC and Mn / N-BC-3; f is the full X-ray photoelectron spectroscopy (XPS) spectrum of BC and Mn / N-BC-3; g and h are the XPS high-resolution spectra of Mn 2p and N1s elements of Mn / N-BC-3 samples, respectively. Figure 2The changes in the pore structure, crystal phase composition, and surface functional groups of biochar before and after modification were revealed. Specifically, it can be seen that the N2 adsorption-desorption isotherms of the materials exhibit the characteristics of type I and type IV isotherms, indicating that the pore structure is mainly composed of micropores and mesopores. With the increase of the [Emim]2[MnCl4] modification ratio (i.e., dosage), the biochar materials show more obvious type IV isotherm characteristics. In terms of crystal phase composition, after [Emim]2[MnCl4] modification, new diffraction peaks appear at 2θ=34.2°, 50.6°, and 50.1°, which are attributed to the (311), (105), and (204) crystal planes of Mn3O4, respectively (PDF 33-0900 / 24-0734). The peaks at 26.8°, 42.1°, 46.0°, 55.7°, and 57.0° are attributed to the (201), (211), (210), (212), and (402) crystal planes of MnO2, respectively (PDF 44-0143 / 43-1445), indicating that Mn is embedded in the pore structure of biochar in the form of metal oxide nanoparticles. Raman spectroscopy results show that with the increase of [Emim]2[MnCl4] dosage, the intensity ratio of D peak and G peak also increases, indicating that the degree of surface defects of biochar increases due to the doping of manganese and nitrogen. FT-IR and XPS show that Mn-O is generated on the surface of the material after [Emim]2[MnCl4] modification, and the introduction of nitrogen forms functional groups such as pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen on the surface of biochar.

[0100] Test Example 2

[0101] Specific surface area and pore volume test of materials

[0102] The specific surface area and pore volume of the adsorption materials prepared in Examples 1-4 and Comparative Examples 1-4 were tested using the nitrogen adsorption-desorption method (BET method). The results are shown in Table 1.

[0103] Table 1 Specific surface area and pore volume data of 8 adsorption materials

[0104]

[0105] As shown in Table 1, after the activated biochar precursor was subjected to secondary high-temperature carbonization, the specific surface area of the unmodified sample BC was 260.98 m 2 / g, pore volume is 0.082cm 3 / g; with the increase of [Emim]2[MnCl4] modifier dosage, the specific surface area of modified biochar increased significantly. Among them, the specific surface area of Mn / N-BC-1 was 435.66m 2 / g, and the specific surface area of Mn / N-BC-2 is 550.02m 2 / g, and the specific surface area of Mn / N-BC-3 is 637.33m2 / g, the specific surface area of Mn / N-BC-4 reaches 652.67m 2 / g; the total pore volume also increases from about 0.08cm 3 / g increased to 0.15~0.20cm 3 / g. This shows that the metal ionic liquid has a good pore-forming effect, which is beneficial to the adsorption of pollutants by modified biochar. At the same time, the specific surface area of the material NK-Mn / N-BC without KOH activation is 352.63m 2 / g, and the specific surface area and pore volume of the material modified with [Emim]2[MnCl4] after KOH activation were significantly improved. Mn / N-BC-3 exhibited a larger specific surface area and pore volume than Mn-BC activated with MnCl2 at the same Mn content, and Mn-N-BC activated with MnCl2 and urea at the same Mn and N contents.

[0106] Application Example 1

[0107] Adsorption performance test of tetracycline on manganese / nitrogen co-doped modified biochar

[0108] (1) Enhanced adsorption of tetracycline by manganese / nitrogen co-doped modified biochar

[0109] The adsorption conditions were as follows: tetracycline was added to 10 mL of distilled water to a solution concentration of 200 mg / L (pH = 7), the adsorption temperature was 25°C, 10 mg of adsorbent material was added, and the mixture was shaken at 180 rpm in a thermostatic oscillator. Samples were taken after 12 hours and filtered through a 0.22 μm water filter. The tetracycline concentration was determined by LC-MS / MS, and the adsorption capacity was calculated. The experiment was repeated three times, and the average value was taken. The adsorption effects of the adsorbents prepared in Examples 1-4 and Comparative Examples 1-4 on tetracycline are shown in Table 2.

[0110] Table 2 Adsorption capacity of 8 adsorption materials for tetracycline

[0111]

[0112]

[0113] The adsorption test results in Table 2 show that manganese / nitrogen co-doped modified biochar can improve the adsorption capacity of biochar for tetracycline. The adsorption capacities of the unmodified sample BC, the non-KOH activated sample NK-Mn / N-BC, the MnCl2 activated sample Mn-BC, the MnCl2 activated sample, and the urea activated sample Mn-N-BC for tetracycline are only 69.2, 113.7, 147.8, and 161.7 mg / g, respectively. However, when the modified ionic liquid dosage is 1:15 (Mn / N-BC-3), its adsorption capacity for tetracycline can reach 186.6 mg / g. This shows that the modification method of the present invention can greatly improve the adsorption effect of biochar on tetracycline in the environment.

[0114] (2) Adsorption kinetics

[0115] The adsorption conditions were as follows: tetracycline was added to 10 mL of distilled water to a concentration of 200 mg / L (pH = 7), the adsorption temperature was 25°C, 10 mg of adsorbent material was added thereto, the mixture was shaken at 180 r / min in a constant temperature oscillator, samples were taken regularly from 0 to 540 minutes, and then filtered through a 0.22 μm water filter membrane. The tetracycline concentration was determined by LC-MS / MS and the adsorption capacity was calculated. The experiment was repeated three times and the average value was taken.

[0116] The results are as follows Figure 3 As shown in Figures ae and b: the adsorption of tetracycline by each material increases rapidly with time, rising rapidly in the first 120 minutes, and then the adsorption rate gradually slows down and approaches equilibrium in about 8 hours. For the kinetic data, the pseudo-first-order kinetic model (pseudo-first-order) and pseudo-second-order kinetic model (pseudo-second-order) were used for fitting analysis. The curve shows that the pseudo-second-order model has a good correlation coefficient R for all sample data. 2 All were above 0.99, significantly better than the pseudo-first-order model. This indicates that the adsorption process is primarily controlled by a chemical adsorption mechanism, i.e., the adsorption step involves valence bonds or electron sharing between tetracycline molecules and active sites on the adsorbent surface. In particular, the Mn / N-BC-3 sample, due to its abundant surface active sites, reacted more quickly with tetracycline, removing over 70% of tetracycline within the first 30 minutes; whereas the unmodified BC only removed approximately 40% in the same time, verifying the improvement in adsorption rate achieved by modification.

[0117] (3) Adsorption isotherm and thermodynamics

[0118] The adsorption conditions are as follows: tetracycline is added to 10 mL of distilled water to a concentration of 50-300 mg / L (pH = 7), the adsorption temperature is 25-45°C (i.e., the adsorption test is carried out at different temperatures), 10 mg of adsorption material is added thereto, and the mixture is shaken at 180 r / min in a constant temperature oscillator. A sample is taken after 540 minutes, and then filtered through a 0.22 μm water filter membrane. The tetracycline concentration is determined by LC-MS / MS and the adsorption capacity is calculated. The experiment is repeated three times and the average value is taken.

[0119] The results are as follows Figure 3 As shown in fj: the adsorption capacity of each material for tetracycline increases with the increase of equilibrium concentration and tends to saturation. The Langmuir model and Freundlich model were used to fit the data, and it was found that the Langmuir model had a higher correlation (R 2 close to 1), indicating that the adsorption of tetracycline on the biochar surface tends to occur with monolayer coverage and the surface active sites are relatively uniform. According to the Langmuir model, the maximum adsorption capacity of BC for tetracycline at 25°C was calculated to be only 72.2 mg / g, while the maximum adsorption capacity of Mn / N-BC-3 reached 201.5 mg / g, which is 2.8 times that of the former. This result clearly demonstrates the effectiveness of the modification method of the present invention: by co-doping with manganese / nitrogen, the adsorption capacity of biochar for tetracycline was greatly improved. In addition, the capacities of other samples in the Mn / N-BC series were also higher than those of BC, for example, Mn / N-BC-1 was approximately 120 mg / g, Mn / N-BC-2 was approximately 170 mg / g, and Mn / N-BC-4 was slightly higher than 200 mg / g but comparable to Mn / N-BC-3. It can be seen that when the dosage of ionic liquid reaches a certain level (the mass ratio of activated biochar precursor to metal ionic liquid is 1:15), the adsorption performance has reached its maximum, and further increasing the dosage will not significantly improve it.

[0120] In order to further study the thermodynamic behavior of adsorption, isothermal adsorption experiments were carried out at different temperatures. Taking Mn / N-BC-3 as an example, the tetracycline adsorption isotherms were measured at 25℃ (298K), 35℃ (308K), and 45℃ (318K). Figure 3 The results show that increasing the temperature is beneficial to improving the equilibrium adsorption capacity: at 45°C, the Langmuir saturation adsorption capacity of Mn / N-BC-3 increases to about 230 mg / g. The thermodynamic parameters are calculated according to the van't Hoff equation to obtain the standard Gibbs free energy change Δ for tetracycline adsorption. r G m θ At all three temperatures, the values are negative (about -20 kJ / mol), which proves that the adsorption process occurs spontaneously at ambient temperature; the standard enthalpy change Δ r Hm θ is positive (about +35 kJ / mol), indicating that the adsorption is an endothermic reaction and increasing the temperature is conducive to adsorption; standard entropy change Δ r S m θ is also positive, indicating that adsorption increases the disorder of the solid-liquid interface system. These thermodynamic results are consistent with the typical physical-chemical mixed adsorption characteristics.

[0121] Application Example 2

[0122] Effects of different environmental factors on the adsorption of tetracycline by manganese / nitrogen co-doped modified biochar

[0123] Taking into account the complexity of the actual water environment, the present invention also investigates the effects of coexisting inorganic ions, solution pH, and dissolved organic matter on the tetracycline adsorption performance of modified biochar to reflect the influence of the solution chemical environment on the adsorption process.

[0124] (1) Effects of inorganic ions or dissolved organic matter on the adsorption of tetracycline by manganese / nitrogen co-doped modified biochar

[0125] The adsorption conditions are as follows: tetracycline is added to 10 mL of distilled water to a solution concentration of 200 mg / L (pH = 7), and different concentrations of different inorganic ions or soluble organic matter (NaCl, CaCl2, NaSO4, humic acid or fulvic acid) are added respectively. The adsorption temperature is 25°C, 10 mg of adsorption material is added thereto, and the mixture is oscillated at 180 r / min in a constant temperature oscillator. Samples are taken at regular intervals from 0 to 540 minutes, and then filtered through a 0.22 μm water filter membrane. The tetracycline concentration is determined by LC-MS / MS and the adsorption capacity is calculated. The experiment is repeated three times and the average value is taken.

[0126] The results are as follows Figure 4 Figure (a) shows the changes in the adsorption capacity of tetracycline by Mn / N-BC-3 in the presence of different inorganic ions. As can be seen, the adsorption of tetracycline by Mn / N-BC-3 decreases slightly with increasing ionic strength in the solution. This suggests that common inorganic salt ions in water have a certain, but not significant, effect on adsorption, indicating that the modified biochar still exhibits good adsorption properties in saline environments.

[0127] Natural water bodies often contain a certain concentration of dissolved organic matter (DOM), such as fulvic acid (FA) and humic acid (HA), which may affect the removal of target pollutants by competing for adsorption or occupying active sites. Figure 4Figure a shows the adsorption of tetracycline by Mn / N-BC-3 in the presence of different concentrations of HA and FA. It can be seen that when the concentration of HA or FA increases from 0 to 10 mg / L, the adsorption capacity of tetracycline decreases slightly, but the decrease (<10%) is relatively limited. FA has a slightly greater impact than HA. For example, at 10 mg / L FA, the adsorption capacity decreases by approximately 9%, while at the same HA concentration, it decreases by approximately 6%. This is because FA molecules contain a large number of functional groups, such as carboxyl and phenolic hydroxyl groups, which are highly negatively charged in water and easily attract and compete for adsorption to the positive sites on the biochar surface. HA, on the other hand, has a larger molecular weight and fewer functional groups, making it less susceptible to adsorption. Despite this, in the presence of typical environmentally relevant concentrations of DOM (e.g., ≤5 mg / L), the tetracycline removal efficiency of Mn / N-BC-3 remains above 80%, demonstrating the excellent performance of this adsorbent in natural waters containing fulvic or humic acids.

[0128] (2) Effect of solution pH on tetracycline adsorption by manganese / nitrogen co-doped modified biochar

[0129] The adsorption conditions are as follows: tetracycline is added to 10 mL of distilled water to a solution concentration of 200 mg / L, and the pH of the solution is adjusted to 3-11, the adsorption temperature is 25°C, 10 mg of adsorption material is added thereto, and the solution is oscillated at 180 r / min in a constant temperature oscillator. Samples are taken after 12 hours, and then filtered through a 0.22 μm water filter membrane. The tetracycline concentration is determined by LC-MS / MS and the adsorption capacity is calculated. The experiment is repeated three times and the average value is taken.

[0130] The results are as follows Figure 4 Figure (b) shows the trend of the equilibrium adsorption capacity of tetracycline by Mn / N-BC-3 over the pH range of 3-11. It can be seen that the adsorption capacity gradually increases from the acidic to neutral range, reaching a maximum at pH ≈ 7, and then significantly decreases under alkaline conditions. Therefore, the modified biochar of the present invention is suitable for use under neutral conditions and can effectively remove tetracycline in weakly acidic or weakly alkaline environments. However, the adsorption effect is affected under strong alkaline conditions.

[0131] The Mn / N co-doped modified biochar prepared by this invention exhibits stable and excellent tetracycline removal performance under a variety of environmental conditions. It can effectively purify tetracycline solutions contaminated with varying concentrations. This makes the material highly suitable for the treatment of antibiotic contamination in real-world water bodies.

[0132] In summary, this invention, through the use of metal ionic liquids to modify biochar, has achieved the preparation of a simple, highly effective manganese / nitrogen co-doped biochar adsorbent. This adsorbent exhibits excellent performance and broad adaptability in the treatment of tetracycline wastewater, and can be used to treat antibiotic-contaminated wastewater in real-world settings.

[0133] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing metal ion liquid modified co-doped biochar, characterized in that: The following steps are involved: The biochar precursor is mixed with a metal ion liquid containing a transition metal and a heteroatom source, and carbonized at high temperature to obtain the metal ion liquid modified co-doped biochar.

2. The preparation method according to claim 1, wherein The transition metal contained in the metal ion liquid is manganese, and the heteroatom source is a nitrogen atom source.

3. The preparation method according to claim 2, wherein The metal ion liquid is 1-ethyl-3-methylimidazolium tetrachloromanganate.

4. The preparation method according to claim 1, wherein The biochar precursor is an activated biochar precursor.

5. The preparation method according to claim 4, wherein The steps of preparing the activated biochar precursor include: The biomass raw material is activated by immersion in an alkaline solution and pre-carbonized at a medium temperature to obtain the activated biochar precursor.

6. The preparation method according to claim 5, wherein The alkaline solution impregnation activation comprises: mixing the biomass raw material and the alkaline solution, stirring evenly, and then standing for activation for 0.5-3 hours; And / or, the alkaline solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution; and / or, the concentration of the alkaline solution is 20-40 wt%; And / or, the medium-temperature pre-carbonization temperature is 400-600° C., and the time is 1-4 hours.

7. The preparation method according to claim 1, wherein The mass ratio of the activated biochar precursor to the metal ionic liquid containing a transition metal and a heteroatom source is 1:1-20; And / or, the high-temperature carbonization temperature is 700-900° C., and the time is 1-3 hours.

8. A metal ion liquid modified co-doped biochar prepared by the preparation method according to any one of claims 1 to 7.

9. The metal ion liquid modified co-doped biochar according to claim 8, characterized in that: The metal ion liquid modified co-doped biochar contains manganese in the form of manganese oxide and nitrogen doped in the form of nitrogen functional groups; And / or, the specific surface area of the metal ion liquid modified co-doped biochar is greater than 400m 2 / g.

10. Use of the metal ion liquid modified co-doped biochar according to any one of claims 8 to 9 in the adsorption of tetracycline antibiotics.

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