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

Abstract

The application discloses a preparation method of metal ionic liquid modified co-doped biochar and application of the biochar in removal of tetracycline, and belongs to the technical field of water pollution treatment and preparation of adsorbing materials. The preparation method comprises the following steps: mixing biochar precursors with metal ionic liquid containing transition metal and heteroatom sources, and performing high-temperature carbonization to obtain the metal ionic liquid modified co-doped biochar. The multiple modifications of the biochar (introducing transition metal elements and heteroatoms into the biochar skeleton, providing rich surface active sites, and improving the specific surface area and pore volume of the biochar) are simultaneously realized through one-time high-temperature carbonization, so that the adsorption performance of the biochar on tetracycline antibiotics is significantly improved. The preparation method is simple in process, raw materials are easy to obtain, the obtained metal ionic liquid modified co-doped biochar has excellent adsorption performance on antibiotic pollutants such as tetracycline, and is suitable for purification treatment of water bodies polluted by antibiotics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water pollution treatment and adsorption material preparation, in particular to a preparation method of metal ionic liquid modified co-doped biochar and application thereof in removal of tetracycline. BACKGROUND

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

[0003] In order to improve the adsorption effect of biochar on pollutants, researchers have proposed various modification strategies. For example, chemical activation (acid modification, alkali modification) can significantly improve 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 the 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, and the common practice is to introduce the precursor of metal salt into biochar, and then carbonize at high temperature to form metal oxide or zero-valent metal particles, so as to provide additional active sites and special surface action. However, traditional heteroatom doping and metal loading usually need multiple steps of processing, and the preparation process is relatively complex, and the adsorption performance of the obtained product still needs to be improved. Therefore, it is necessary to develop a preparation method of high-performance doped modified biochar with simple preparation process. SUMMARY

[0004] The application aims to provide a preparation method of metal ionic liquid modified co-doped biochar and application thereof in removing tetracycline, so as to solve the problems in the prior art. The multiple modification of biochar is realized by one-time high-temperature carbonization, so as to significantly improve the adsorption performance of the biochar on tetracycline antibiotics. The application also provides application of the modified co-doped biochar obtained by the method in removing tetracycline antibiotic pollutants in water. The modified co-doped biochar prepared by the method of the application has a higher specific surface area and more surface active sites, and exhibits excellent adsorption and removal effect on tetracycline antibiotics.

[0005] To achieve the above-mentioned object, the application provides the following solutions.

[0006] One of the technical solutions of the application is a preparation method of metal ionic liquid modified co-doped biochar, comprising the following steps.

[0007] The biochar precursor (i.e. the biochar after preliminary carbonization) is mixed with a metal ionic liquid containing a transition metal and a heteroatom source, and high-temperature carbonization is performed to obtain the metal ionic liquid modified co-doped biochar.

[0008] The application adopts metal ionic liquid to modify the biochar. The metal ionic liquid is a special kind of ionic liquid, which contains a metal complex in the cation or anion. On the one hand, it can be decomposed at high temperature and act as a pore former of the biochar, so as to improve the pore structure. On the other hand, the transition metal and the heteroatom contained in the ionic liquid can be simultaneously doped into the biochar skeleton, so as to realize the co-doping modification of the heteroatom and the metal and provide abundant surface active sites. Moreover, the metal ionic liquid as the modifier can effectively improve the specific surface area and the pore volume of the biochar while realizing the co-doping modification of the heteroatom and the transition metal. Therefore, the method of the application can effectively improve the adsorption performance of the biochar on tetracycline antibiotics.

[0009] The application realizes the multiple modification of the biochar by one-time high-temperature carbonization, so as to significantly improve the adsorption performance of the biochar on tetracycline antibiotics. The preparation process is simple.

[0010] Further, the transition metal contained in the metal ionic liquid is manganese, and the heteroatom source is a nitrogen atom source, so as to obtain a manganese / nitrogen co-doped modified biochar (referred to as Mn / N-BC).

[0011] Further preferably, the metal ionic liquid is 1-ethyl-3-methyl imidazole tetrachloromanganate.

[0012] The cation of 1-ethyl-3-methyl imidazole tetrachloromanganate ([Emim]2[MnCl4]) is 1-ethyl-3-methyl imidazole ion ([Emim] +), the anion is a tetrachloro complex anion of divalent manganese ([MnCl4] 2- ) is decomposed and manganese and nitrogen elements are introduced into the biochar matrix through a high-temperature pyrolysis reaction, achieving manganese / nitrogen co-doped modification, and at the same time, a developed pore structure is generated. After the carbonization holding is completed, natural cooling to room temperature is performed, and a metal ionic liquid modified co-doped biochar is obtained. Among them, nitrogen doping can improve the π-π interaction force and hydrogen bond interaction with aromatic ring-containing pollutants by introducing nitrogen-containing functional groups on the surface of the biochar, which is beneficial to the adsorption of tetracycline and other multi-functional group molecules, and manganese doping can introduce more active sites. The synergistic effect of manganese and nitrogen can effectively improve the adsorption performance of tetracycline antibiotics.

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

[0014] Further, the preparation step of the activated biochar precursor comprises:

[0015] The biomass raw material is subjected to alkali solution impregnation activation and medium-temperature pre-carbonization to obtain the activated biochar precursor.

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

[0017] Through alkali activation pretreatment, the carbonization reaction of the biomass can be promoted, and the porosity and surface functional group content of the product biochar can be increased.

[0018] Further, the alkali solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, and preferably a potassium hydroxide aqueous solution.

[0019] Further, the concentration of the alkali solution is 20-40wt%, and preferably 30wt%.

[0020] Further, the biomass raw material is a biomass waste rich in carbon elements.

[0021] Optionally, the biomass raw material comprises sawdust, straw or fruit shells, and preferably is a lignocellulose material such as poplar sawdust.

[0022] Optionally, the alkali solution impregnation activation further comprises a crushing and sieving step of the biomass raw material.

[0023] The biomass raw material is crushed and sieved to refine the particle size of the biomass raw material. The use of biomass powder with a smaller particle size (for example, passing through a 200-mesh sieve) is beneficial to the impregnation and activation of the alkali solution, thereby improving the subsequent carbonization effect.

[0024] Further, the temperature of the medium-temperature pre-carbonization is 400-600℃, and the time is 1-4 hours.

[0025] By controlling the appropriate medium-temperature pre-carbonization temperature and time, both the sufficient carbonization of the biomass to form the primary biochar (i.e. biochar precursor) and the avoidance of the collapse of the pore structure or the increase of the ash content caused by the excessively high temperature can be ensured.

[0026] Further, the medium-temperature pre-carbonization is carried out under an inert atmosphere or vacuum condition, and the heating rate of the medium-temperature pre-carbonization is 3-10℃ / min.

[0027] Further preferably, the heating rate of the medium-temperature pre-carbonization is 5℃ / min, the temperature is 500℃, and the time is 2 hours.

[0028] Optionally, the medium-temperature pre-carbonization further comprises the steps of grinding and sieving the obtained carbonization product, and washing to neutral and drying.

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

[0030] By controlling the amount of the ionic liquid, the doping degree and the pore structure of the biochar can be adjusted: too little amount may result in insufficient doping and pore-forming effect, and too much amount exceeding the optimal value may result in slow increase of the doping efficiency and waste of resources. The modified biochar with the optimal comprehensive performance can be obtained at the preferred ratio.

[0031] Further, the temperature of the high-temperature carbonization is 700-900℃, and the time is 1-3 hours.

[0032] Further, the high-temperature carbonization is carried out under an inert atmosphere, and the heating rate of the high-temperature carbonization is 3-10℃ / min.

[0033] Further preferably, the heating rate of the high-temperature carbonization is 5℃ / min, the temperature is 800℃, and the time is 2 hours.

[0034] The high-temperature condition is conducive to the decomposition of the ionic liquid and the element doping, but excessively high temperature may cause the loss of the biochar skeleton or the shrinkage of the pore structure, and the temperature of about 700-900℃ can balance the stability of the biochar structure and the doping effect, and the temperature of about 800℃ is optimal.

[0035] Optionally, the high-temperature carbonization further comprises the steps of grinding and sieving the carbonization product to obtain the metal ionic liquid modified co-doped biochar with uniform particles.

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

[0037] Further, the metal ionic 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] Further, the specific surface area of the metal ionic liquid modified co-doped biochar is greater than 400 m 2 / g.

[0039] The third technical solution of the present application is the application of the above-mentioned metal ionic liquid modified co-doped biochar in adsorbing tetracycline antibiotics.

[0040] Further, the step of the application comprises: adding the metal ionic liquid modified co-doped biochar to a water body containing tetracycline antibiotics, and performing adsorption of tetracycline antibiotics under room temperature oscillation conditions.

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

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

[0043] (2) The present application uses discarded poplar and other discarded biomass as raw materials, 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 by the present application shows excellent adsorption capacity to tetracycline: under the condition of 25 DEG C, the maximum adsorption capacity of tetracycline can reach about 201.5 mg / g, which is about 2.8 times that of the unmodified biochar (about 72.2 mg / g).

[0045] (4) The Mn / N co-doped modified biochar obtained by the method has the best adsorption effect in a water environment near neutral (pH is about 7), has a certain adaptive range for the initial pH of a solution (pH is 3-11, and tetracycline can be effectively removed), and still has high adsorption performance in the presence of common coexisting ions (such as Na + , Ca 2+ , Cl - , SO4 2- ) and natural organic matters (such as humic acid and fulvic acid), and has good anti-interference ability.

[0046] In conclusion, the preparation method is simple and feasible, and the prepared biochar adsorbent has high removal effect on antibiotic pollutants such as tetracycline, is suitable for purification treatment of water bodies polluted by antibiotics, and has wide application prospect in the field of water environment treatment. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

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

[0049] Figure 2The comprehensive characterization results of unmodified biochar (BC) prepared for Comparative Example 1 and manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared for 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 X-ray photoelectron spectroscopy full spectrum of BC and Mn / N-BC-3; g and h are the XPS high-resolution spectra of Mn 2p and N 1s elements of the Mn / N-BC-3 sample, respectively.

[0050] Figure 3 The results of adsorption kinetics and isotherm of tetracycline of unmodified biochar (BC) prepared for Comparative Example 1 and manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared for Examples 1-4, wherein a-e are the tetracycline adsorption kinetics 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; f-j are the tetracycline adsorption isotherm fitting curves of the above five kinds of samples at 25°C, comparing the Langmuir model and the Freundlich model.

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

[0052] The various illustrative embodiments of the present application will now be described in detail below. This description is not to be considered limiting in scope, but rather as being illustrative of certain aspects of the present application. Various examples of the present application are described in detail below.

[0053] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a numerical range recited in this disclosure, it is contemplated that each intervening value, to the upper and lower limits of the ranges is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the application. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0054] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as those of ordinary skill in the art to which the application relates. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described therein. In case of conflict, the content of the present specification will control.

[0055] Many modifications and variations of the present application described in the specific embodiments of the application can be made by those skilled in the art without departing from the spirit or scope of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0056] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean inclusion, but not limited to, the listed material or step.

[0057] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

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

[0059] Mixing the biochar precursor with the metal ionic liquid containing transition metal and heteroatom source, and carrying out high-temperature carbonization to obtain the metal ionic liquid modified co-doped biochar.

[0060] As a preferred embodiment of the present application, 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 application, the biochar precursor is an activated biochar precursor.

[0062] As a preferred embodiment of the present application, the preparation step of the activated biochar precursor comprises:

[0063] Impregnating and activating the biomass raw material with an alkali solution and pre-carbonizing at a medium temperature to obtain the activated biochar precursor.

[0064] As a preferred embodiment of the present application, the method for preparing the metal ionic liquid modified co-doped biochar, more specifically, comprises the following steps:

[0065] (1) Biomass activation and pre-carbonization: Biomass raw material (wood chips, straw or fruit shells, preferably wood fiber material wood chips such as poplar wood chips) is crushed and sieved, then mixed with an alkali solution (20-40wt% sodium hydroxide solution or potassium hydroxide solution, preferably 30wt% potassium hydroxide solution), stirred evenly, and then activated for 0.5-3 hours (preferably 1-2 hours). After the activation is completed, the biomass raw material is removed, heated to a medium temperature pre-carbonization temperature (400-600°C, preferably 500°C) at a heating rate of 3-10°C / min (preferably 5°C / min) in an inert atmosphere or vacuum, and held for 1-4 hours (preferably 2 hours) to perform medium temperature pre-carbonization (which can be referred to as the first stage of carbonization). After carbonization is completed, the product is cooled, ground and sieved (for example, 200 mesh sieve), then washed with acid solution (such as 1 mol / L hydrochloric acid) and deionized water alternately until neutral, to remove residual inorganic salts and impurities, 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 with a metal ionic liquid (preferably 1-ethyl-3-methyl imidazole tetrachloromanganate) in a mass ratio of 1:1-20 (preferably 1:10-15), heated to a high temperature carbonization temperature (700-900°C, preferably 800°C) at a heating rate of 3-10°C / min (preferably 5°C / min) in an inert atmosphere, and held for 1-3 hours (preferably 2 hours) to perform high temperature carbonization (which can be referred to as the second stage of carbonization). After cooling, the product is ground and sieved to obtain a metal ionic liquid modified co-doped biochar (i.e. manganese / nitrogen co-doped modified biochar).

[0067] As a preferred embodiment of the present application, the synthesis steps of the metal ionic liquid [Emim]2[MnCl4] include: mixing 1-ethyl-3-methyl imidazole chloride salt ([Emim]Cl) with 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 a stable liquid at room temperature, and when heated to several hundred degrees Celsius, it will decompose and release manganese and nitrogen sources.

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

[0069] As a preferred embodiment of the present application, the metal ionic 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 application, the specific surface area of the metal ionic liquid modified co-doped biochar is greater than 400 m 2 / g.

[0071] As a third aspect of the present application, the present application provides a use of the above-mentioned metal ionic liquid modified co-doped biochar in adsorbing tetracycline antibiotics.

[0072] As a preferred embodiment of the present application, the step of the use comprises: adding the metal ionic liquid modified co-doped biochar into a water body containing tetracycline antibiotics, and performing adsorption of tetracycline antibiotics under room temperature oscillation conditions.

[0073] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0074] If room temperature or normal temperature is mentioned in the specific embodiments of the present application, it specifically refers to 20-30℃.

[0075] If no special description is made, each raw material used in the specific embodiments of the present application is a common commercially available product.

[0076] The synthesis steps of the metal ionic liquid [Emim]2[MnCl4] used in the following examples are as follows: 1-ethyl-3-methyl imidazole chloride salt ([Emim]Cl) 146.62 g (1 mol) is placed in a flask, and is heated to melt into a transparent liquid at 90℃ oil bath; anhydrous manganese chloride (MnCl2) 62.92 g (0.5 mol) is slowly added thereto, and mechanical stirring is performed while heating, the temperature is maintained at 90℃ and stirring is performed for 24 hours. After the reaction is completed, the obtained product is cooled to room temperature, and a dark brown metal ionic liquid [Emim]2[MnCl4] is obtained. The ionic liquid is a stable liquid at normal temperature and pressure, and is stored in a dry and airtight container for standby. The synthesis method of the metal ionic liquid [Emim]2[MnCl4] provided by the present application is simple and easy to operate, and the generated [Emim]2[MnCl4] can be used in the subsequent biochar modification step without further purification.

[0077] Example 1

[0078] A metal ionic liquid modified co-doped biochar (i.e. manganese / nitrogen co-doped modified biochar) adsorbent is prepared, and the steps are as follows:

[0079] (1) Biomass activation and pre-carbonization: Poplar sawdust waste (i.e., poplar wood chips) was selected as the biomass raw material. After drying, the sawdust was ground and sieved through a 200-mesh screen to collect fine powder. 50 g of poplar biomass powder was weighed and mixed with 100 g of 30 wt% KOH aqueous solution. The mixture was stirred uniformly at room temperature and then left to stand for 2 hours to allow the KOH to fully penetrate the biomass pores. Subsequently, the activated biomass was placed in a vacuum drying oven and dried at 80°C for 12 hours to remove water.

[0080] The dried alkali-activated biomass was transferred to a vacuum tube furnace and heated to 500°C at a rate of 5°C / min under nitrogen atmosphere. The temperature was held at 500°C for 2 hours for pre-carbonization. After carbonization, the heating was turned off and the furnace was allowed to cool naturally to room temperature. The carbonized product (i.e., activated primary carbonized biochar) was removed, ground into fine powder, and sieved through a 200-mesh screen to collect the undersize powder. The biochar was then washed repeatedly with 1 mol / L hydrochloric acid solution and deionized water until the wash water pH approached neutrality to fully remove residual inorganic salts. The washed biochar was placed in a vacuum drying oven and dried at 70°C for 12 hours to obtain the activated biochar precursor sample, which was labeled as PBC (Poplar Biochar).

[0081] (2) Ionic liquid modified carbonization: 10 g of the activated biochar precursor (PBC) obtained in step (1) was mixed with 150 g of metal ionic liquid [Emim]2[MnCl4] (i.e., the mass ratio of activated biochar precursor to metal ionic liquid was 1:15). The mixture was stirred uniformly to allow the activated biochar precursor to fully soak in the ionic liquid. The mixture was then placed in a tube furnace under nitrogen protection and heated to 800°C at a rate of 5°C / min. The temperature was held at 800°C for 2 hours for further carbonization. During the high-temperature process, the ionic liquid gradually decomposed: the organic imidazole cation cracked to produce nitrogen-containing radicals and combined with the carbon skeleton to form nitrogen functional groups, and the tetrachloromanganate anion decomposed to generate manganese chloride intermediates and further transformed into manganese oxide nanoparticles embedded in the biochar pore structure. After carbonization, the heating was stopped and the furnace was allowed to cool to room temperature. The product was removed, and a manganese / nitrogen co-doped modified biochar was obtained. This is the target adsorbent prepared in this example, labeled 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 activated biochar precursor to metal ionic liquid [Emim]2[MnCl4] was adjusted to 1:5. The final manganese / nitrogen co-doped modified biochar was labeled as Mn / N-BC-1 and stored in a desiccator for future use.

[0084] Example 3

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

[0086] Example 4

[0087] The same as Example 1, the only difference is that the mass ratio of activated biochar precursor to metal ionic liquid [Emim]2[MnCl4] in step (2) is adjusted to 1:20, and the final manganese / nitrogen co-doped modified biochar 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, the only difference is that the addition of metal ionic liquid [Emim]2[MnCl4] in step (2) is omitted, and the activated biochar precursor (PBC) is further carbonized at 800°C for 2 hours alone, and the final product is unmodified biochar, recorded as BC, and stored in a desiccator for future use.

[0090] Comparative Example 2

[0091] The same as Example 1, the only difference is that the addition of alkali solution in step (1) is omitted (i.e., the activation step is omitted), and the poplar biomass powder is directly pre-carbonized at 500°C for 2 hours, and then ground, sieved, washed, and dried to obtain a biochar precursor. Then, the biochar precursor and metal ionic liquid [Emim]2[MnCl4] are mixed at a mass ratio of 1:15, and further carbonized at 800°C for 2 hours. The final product is a manganese / nitrogen co-doped modified biochar without alkali solution activation, recorded as NK-Mn / N-BC, and stored in a desiccator for future use.

[0092] Comparative Example 3

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

[0094] Comparative Example 4

[0095] The same as Example 1, except that in step (2), 150 g of metal ionic liquid [Emim]2[MnCl4] is replaced by a mixed aqueous solution of MnCl2 and urea (the mixed aqueous solution of MnCl2 and urea contains the same molar amount of Mn and N elements as the 150 g of metal ionic liquid [Emim]2[MnCl4]). Then the mixture is placed in a tube furnace under nitrogen protection, heated to 800℃ at a rate of 5℃ / min, and further carbonized at 800℃ for 2 hours. The final product is MnCl2 and urea modified biochar, denoted 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) photos of unmodified biochar (BC) prepared for Comparative Example 1 and manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared for Examples 1-4, wherein a and f are the morphology of BC at magnifications of 5,000 times and 20,000 times; b and g are the morphology of Mn / N-BC-1 at magnifications of 5,000 times and 20,000 times; c and h are the morphology of Mn / N-BC-2 at magnifications of 5,000 times and 20,000 times; d and i are the morphology of Mn / N-BC-3 at magnifications of 5,000 times and 20,000 times; e and j are the morphology of Mn / N-BC-4 at magnifications of 5,000 times and 20,000 times. By comparison, the differences in micro-morphology and pore structure between unmodified and modified biochar can be observed. Specifically, it can be seen that with the increase of [Emim]2[MnCl4] modifier, a layered pore structure is formed on the surface of the biochar, and the more the amount of [Emim]2[MnCl4] modifier, the more abundant the pore structure.

[0099] Figure 2 Graphs of comprehensive characterization results of unmodified biochar (BC) prepared for Comparative Example 1 and manganese / nitrogen co-doped modified biochar (Mn / N-BC) prepared for 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 X-ray photoelectron spectroscopy (XPS) full spectrum of BC and Mn / N-BC-3; g and h are the XPS high-resolution spectra of Mn 2p and N1s elements of the Mn / N-BC-3 sample, respectively. Figure 2The changes of the modified and unmodified biochar in pore structure, crystal phase composition and surface functional groups are disclosed. Specifically, it can be seen that the N2 adsorption-desorption isotherm of the material shows the characteristics of type I and type IV isotherm, indicating that the pore structure is mainly microporous and mesoporous. With the increase of the modification ratio (i.e. the amount) of [Emim]2[MnCl4], the biochar material shows more obvious characteristics of type IV isotherm. In terms of crystal phase composition, after modification by [Emim]2[MnCl4], the material appears new diffraction peaks at 2θ = 34.2°, 50.6° and 50.1°, which are respectively attributed to the (311), (105) and (204) crystal planes of Mn3O4 (PDF 33-0900 / 24-0734). The peaks at 26.8°, 42.1°, 46.0°, 55.7° and 57.0° are respectively attributed to the (201), (211), (210), (212) and (402) crystal planes of MnO2 (PDF 44-0143 / 43-1445), indicating that Mn is embedded in the pore structure of biochar in the form of metal oxide nanoparticles. The Raman spectrum results show that with the increase of the amount of [Emim]2[MnCl4], the intensity ratio of D peak and G peak also increases, which indicates that due to the doping of manganese and nitrogen, the degree of defects on the surface of biochar has increased. It can be seen from FT-IR and XPS that after modification by [Emim]2[MnCl4], Mn-O is generated on the surface of the material, and the introduction of nitrogen forms functional groups such as pyridine nitrogen, pyrrole nitrogen and graphite nitrogen on the surface of biochar.

[0100] Test Example 2

[0101] Specific surface area and pore volume test of the material

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

[0103] Table 18 specific surface area and pore volume data of 8 adsorption materials

[0104]

[0105] As can be seen from Table 1, after the activated biochar precursor is carbonized at high temperature for the second time, the specific surface area of the unmodified sample BC is 260.98 m 2 / g, and the pore volume is 0.082 cm 3 / g; with the increase of the amount of [Emim]2[MnCl4] modifier, the specific surface area of the modified biochar is significantly improved. Among them, the specific surface area of Mn / N-BC-1 is 435.66 m 2 / g, the specific surface area of Mn / N-BC-2 is 550.02 m 2 / g, and the specific surface area of Mn / N-BC-3 is 637.33 m2 / g, the specific surface area of Mn / N-BC-4 reached 652.67 m 2 / g; the total pore volume also increased from about 0.08 cm 3 / g to 0.15-0.20 cm 3 / g or so. This shows that the metal ionic liquid has good pore-forming effect, which is conducive to the adsorption of pollutants by the modified biochar. At the same time, the specific surface area of the material NK-Mn / N-BC without KOH activation is 352.63 m 2 / g, and the specific surface area and pore volume of the material modified by first using KOH activation and then using [Emim]2[MnCl4] are obviously improved. Compared with Mn-BC activated by MnCl2 with the same Mn content and Mn-N-BC activated by MnCl2 and urea with the same Mn and N content, Mn / N-BC-3 shows greater specific surface area and pore volume.

[0106] Application Example 1

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

[0108] (I) Adsorption promotion of manganese / nitrogen co-doped modified biochar on tetracycline

[0109] The adsorption conditions are as follows: 10 mL of distilled water is added with tetracycline to make the solution concentration 200 mg / L (pH = 7), the adsorption temperature is 25°C, 10 mg of adsorption material is added, oscillation is carried out in a constant temperature oscillator at 180 r / min, sampling is taken at 12 hours, 0.22 μm water filter membrane is used for filtration, LC-MS / MS is used for tetracycline concentration determination and adsorption capacity calculation, the experiment is repeated three times, and the average value is taken. The adsorption effect of several adsorption materials prepared in Examples 1-4 and Comparative Examples 1-4 on tetracycline is shown in Table 2.

[0110] Table 2: Adsorption capacity of several adsorption materials on tetracycline

[0111]

[0112]

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

[0114] (ii) Adsorption kinetics

[0115] The adsorption conditions are: adding tetracycline in 10 mL distilled water to make the concentration 200 mg / L (pH = 7), the adsorption temperature is 25°C, adding 10 mg of adsorbent material into it, oscillating in a constant temperature oscillator at 180 r / min, sampling at 0-540 minutes, passing through a 0.22 μm water filter membrane, using LC-MS / MS to determine the tetracycline concentration and calculate the adsorption capacity, the experiment is repeated three times, and the average value is taken.

[0116] The results are shown as a-e in Table 2: Figure 3 The adsorption amount of each material for tetracycline increases rapidly with time, and rises faster in the first 120 minutes, and then the adsorption rate gradually slows down, and approaches equilibrium at about 8 hours. For the kinetic data, the pseudo-first-order kinetic model and the pseudo-second-order kinetic model are used for fitting analysis, and the curve shows that the correlation coefficient R 2 of the pseudo-second-order model for the data of all samples is higher than 0.99, which is significantly better than the pseudo-first-order model. This shows that the adsorption process is mainly controlled by the chemical adsorption mechanism, that is, the adsorption step involves the valence bond or electron sharing action between the tetracycline molecules and the active sites on the surface of the adsorbent. In particular, the Mn / N-BC-3 sample has a large number of active sites on the surface, and reacts faster with tetracycline, and more than 70% of tetracycline can be removed within the first 30 minutes; while the unmodified BC only removes about 40% in the same time, which verifies the improvement of the modification on the adsorption rate.

[0117] (iii) Adsorption isotherm and thermodynamics

[0118] Adsorption conditions: add tetracycline in 10 mL distilled water to make its concentration 50-300 mg / L (pH = 7), adsorption temperature is 25-45 ℃ (namely, respectively, carry out adsorption test at different temperatures), add 10 mg adsorption material to it, oscillate in constant temperature oscillator at 180 r / min, take sample at 540 min, pass through 0.22 μm water filter membrane, use LC-MS / MS to carry out tetracycline concentration determination and calculate adsorption capacity, repeat experiment three times, take average value.

[0119] Results are shown as f-j in Figure 3 : the adsorption capacity of each material to tetracycline increases with the increase of equilibrium concentration, and tends to saturation. Adopt Langmuir model and Freundlich model to fit data, find that Langmuir model has higher correlation degree (R 2 close to 1), which indicates that tetracycline adsorption on the surface of biochar tends to occur monolayer coverage, and the surface active site is relatively uniform. According to Langmuir model, calculate the maximum adsorption capacity of BC to tetracycline at 25 ℃ to be only 72.2 mg / g, while the maximum adsorption capacity of Mn / N-BC-3 reaches 201.5 mg / g, which is 2.8 times of the former. This result clearly reflects the effectiveness of the modification method of the application: by manganese / nitrogen co-doping, the adsorption capacity of biochar to tetracycline is greatly improved. In addition, the capacities of other samples in the Mn / N-BC series are also higher than that of BC, for example, Mn / N-BC-1 is about 120 mg / g, Mn / N-BC-2 is about 170 mg / g, and Mn / N-BC-4 is slightly higher than 200 mg / g but comparable to Mn / N-BC-3. As can be seen, when the amount of ionic liquid reaches a certain degree (the mass ratio of activated biochar precursor to metal ionic liquid is 1:15), the adsorption performance tends to be maximum, and further increasing the amount does not improve significantly.

[0120] In order to further study the thermodynamic behavior of adsorption, isothermal adsorption experiment was carried out at different temperatures. Take Mn / N-BC-3 as an example, its tetracycline adsorption isotherm was determined at 25 ℃ (298 K), 35 ℃ (308 K) and 45 ℃ (318 K) respectively (as shown in f-j of Figure 3 ). The results show that the increase of temperature is conducive to improving the equilibrium adsorption capacity: at 45 ℃, the Langmuir saturated adsorption capacity of Mn / N-BC-3 increases to about 230 mg / g. According to Van't Hoff equation, calculate the thermodynamic parameters, and obtain the standard Gibbs free energy change Δ r G m θ of tetracycline adsorption is negative (about-20 kJ / mol order) at three temperatures, which proves that the adsorption process is spontaneous at ambient temperature; the standard enthalpy change Δ r Hm θ A positive value (approximately +35 kJ / mol) indicates that the adsorption is an endothermic reaction, and increasing the temperature favors adsorption; the standard entropy change Δ r S m θ The positive value indicates that adsorption increases the disorder of the solid-liquid interface system. These thermodynamic results are consistent with typical physicochemical mixed adsorption characteristics.

[0121] Application Example 2

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

[0123] Considering the complexity of actual aquatic environments, this invention also investigated the effects of coexisting inorganic ions, solution pH, and dissolved organic matter on the tetracycline adsorption performance of modified biochar, in order to reflect the influence of the solution chemical environment on the adsorption process.

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

[0125] The adsorption conditions were as follows: tetracycline was added to 10 mL of distilled water to make the solution concentration 200 mg / L (pH = 7), and different concentrations of inorganic ions or dissolved organic matter (NaCl, CaCl2, NaSO4, humic acid or fulvic acid) were added. The adsorption temperature was 25℃. 10 mg of adsorbent material was added, and the solution was shaken at 180 r / min in a constant temperature shaker. Samples were taken at regular intervals from 0 to 540 minutes, and then filtered through a 0.22 μm aqueous 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.

[0126] The results are as follows Figure 4 Figure a shows the change in the adsorption capacity of Mn / N-BC-3 for tetracycline in the presence of different inorganic ions. It can be seen that the adsorption capacity of Mn / N-BC-3 for tetracycline decreases slightly with increasing ionic strength in the solution. This indicates that common inorganic salt ions in water have some influence on the adsorption effect, but it is not significant; the modified biochar still exhibits good adsorption performance 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 competitive 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 observed 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. The effect of FA is slightly greater than that of HA; for example, at 10 mg / L FA, the adsorption capacity decreases by about 9%, while at the same concentration of HA it decreases by about 6%. This is because FA molecules contain more functional groups such as carboxyl and phenolic hydroxyl groups, exhibiting a strong negative charge in water, and are easily attracted by positive sites on the biochar surface, resulting in competitive adsorption. HA, with its larger molecular weight and fewer functional groups, has a relatively smaller impact. Nevertheless, in the presence of typical environmentally relevant concentrations (e.g., ≤5 mg / L) of DOM, the removal rate of tetracycline by Mn / N-BC-3 can still remain above 80%, indicating that this adsorbent still has good application effects in natural water bodies containing fulvic acid or humic acid.

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

[0129] The adsorption conditions were as follows: tetracycline was added to 10 mL of distilled water to make the solution concentration 200 mg / L, and the pH of the solution was adjusted to 3-11. The adsorption temperature was 25℃, 10 mg of adsorbent material was added, and the solution was shaken at 180 r / min in a constant temperature shaker. Samples were taken after 12 hours and filtered through a 0.22 μm aqueous 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.

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

[0131] The Mn / N co-doped modified biochar prepared in this invention exhibits stable and excellent tetracycline removal performance under various environmental conditions. It can still achieve efficient purification of tetracycline solutions with different concentrations of contamination. This makes the material highly suitable for the treatment of antibiotic pollutants in real-world water bodies.

[0132] In summary, the application realizes preparation of a manganese / nitrogen co-doped modified biochar adsorbent with simple preparation and remarkable modification effect by using metal ionic liquid to modify biochar. The adsorbent exhibits excellent performance and wide adaptability in tetracycline wastewater treatment and can be used for treatment of antibiotic pollution wastewater in actual environment.

[0133] The above-described embodiments are only used to describe the preferred modes of the present application, and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope of the present application defined by the claims.

Claims

1. The application of metal ion liquid-modified co-doped biochar in the adsorption of tetracycline antibiotics, characterized in that, The preparation steps of the metal ion liquid modified co-doped biochar include: The activated biochar precursor was mixed with a metal ionic liquid containing transition metals and heteroatom sources and then carbonized at high temperature to obtain the metal ionic liquid modified co-doped biochar. The transition metal contained in the metal ionic liquid is manganese, and the heteroatom source is a nitrogen atom source; The preparation steps of the activated biochar precursor include: The activated biochar precursor is obtained by alkaline solution impregnation activation and medium-temperature pre-carbonization of biomass raw materials.

2. The application as described in claim 1, characterized in that, The metal ionic liquid is 1-ethyl-3-methylimidazolium tetrachloromanganate.

3. The application as described in claim 1, characterized in that, The alkaline solution impregnation activation includes: mixing biomass raw materials and alkaline solution, stirring evenly, and then allowing it to stand for activation for 0.5-3 hours; And / or, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide; And / or, the concentration of the alkaline solution is 20-40 wt%; And / or, the temperature of the intermediate-temperature pre-carbonization is 400-600℃, and the time is 1-4 hours.

4. The application as described in claim 1, characterized in that, The mass ratio of the activated biochar precursor to the metal ionic liquid containing transition metals and heteroatom sources is 1:1-20. And / or, the high-temperature carbonization is carried out at a temperature of 700-900°C for 1-3 hours.

5. The application as described in claim 1, 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 400 m². 2 / g.

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