CN110756168A

CN110756168A - Preparation method and application of modified biochar for adsorbing tetracycline in wastewater

Info

Publication number: CN110756168A
Application number: CN201911224068.7A
Authority: CN
Inventors: 张鑫; 李亚茹; 吴梦茹; 庞瑶; 郝振冰; 陈治华; 曹治国; 张永晖
Original assignee: Henan Normal University
Current assignee: Henan Normal University
Priority date: 2019-12-04
Filing date: 2019-12-04
Publication date: 2020-02-07

Abstract

The invention belongs to the technical field of biomass application, and particularly relates to a preparation method and application of modified biochar for adsorbing tetracycline in wastewater. The method comprises soaking the treated biomass in KMnO₄And FeCl₂ ^.4H₂Modifying in O solution, and pyrolyzing in a tubular furnace to obtain charcoal with good magnetism, recoverability and high-efficiency adsorption of tetracyclineAnd the whole pyrolysis process has short time, simple procedure, high efficiency and high speed, and has better use value.

Description

Preparation method and application of modified biochar for adsorbing tetracycline in wastewater

Technical Field

The invention belongs to the technical field of biomass application, and particularly relates to a preparation method and application of modified biochar for adsorbing tetracycline in wastewater.

Background

Biomass is a renewable energy resource with huge natural reserves, and only agricultural waste and forestry waste in China can respectively produce 7.3 million tons and 0.37 billion cubic meters every year. Henan is used as a big province of agriculture, and generates a large amount of agricultural wastes in the agricultural production and processing process every year, so that a part of resources are changed into pollution sources because the agricultural wastes are not effectively utilized, and the ecological environment is greatly influenced. Therefore, the method realizes that the agricultural wastes are changed into wastes and improves the ecological environment in rural areas, and has great significance for realizing the sustainable development of agriculture.

Pyrolysis is one of the major pathways for energy conversion of biomass. The biomass raw materials (including agricultural and forestry wastes) are pyrolyzed and converted in inert gas to generate biochar, the biochar has a huge specific surface area and a certain micropore, mesopore and macropore amorphous structure, the surface contains rich carboxyl, hydroxyl, carbonyl and other oxygen-containing active functional groups, the physicochemical characteristics enable the biochar to show stronger chemical affinity, the biochar can be used as a cheap and efficient adsorbent after being properly modified to remove pollutants in wastewater, the reasonable treatment and recycling of the biomass can be realized, and the purpose of treating wastes with processes of wastes can be achieved.

Antibiotics have been widely used in medical health, breeding industry and the like since the discovery, but the problem of antibiotic contamination is becoming more serious due to human abuse and limited antibiotic absorption capacity of human and livestock. Tetracycline (TET) is a common antibiotic that is not metabolically absorbed by humans and animals, excreted and accumulated with the feces and urine into the environment, affects plant growth, is transported and enriched through the food chain, and also can be detrimental to human health. At present, methods for removing antibiotics mainly include a photolysis method, an ozone oxidation method, a Fenton method, a photocatalytic method, a microbiological treatment method, an electrochemical method, an adsorption method and the like. Compared with other methods, the adsorption method has simpler and more convenient engineering operation, the adsorption reactors are easy to realize series and parallel work, and the treatment capacity is improved; and the adsorbent can be prepared from different wastes, and has low raw material price and low cost. Due to the facts that the biochar is derived from biomass pyrolysis, is cheap and easy to obtain, and has the potential of energy and solid waste resource utilization, a plurality of researchers adopt the biochar to research the adsorption and removal of antibiotics, however, although the biochar prepared at present can adsorb the antibiotics, the adsorption effect and the removal efficiency are difficult to meet the requirements.

Disclosure of Invention

Aiming at the defects and problems of the existing biochar in adsorbing antibiotic substances, the invention provides a preparation method and application of modified biochar for adsorbing tetracycline in wastewater.

The technical scheme adopted by the invention for solving the technical problems is as follows: a preparation method of modified biochar for adsorbing tetracycline in wastewater comprises the following steps:

cleaning and cutting biomass, placing the biomass in a blast drying oven, drying for 10 hours at 105 ℃, screening, and reserving sawdust biomass not smaller than 100 meshes;

step two, soaking the biomass treated in the step one in KMnO with the molar ratio of iron to manganese of 3:1₄And FeCl₂.4H₂Mixing and stirring the solution O for 12 hours, drying the solution O in an oven at the temperature of 80 ℃ until the supernatant disappears, then putting the solution O in a tube furnace, heating the solution O to the temperature of 500 ℃ at the heating rate of 10 ℃/min, then pyrolyzing the solution O for 40min, and continuously introducing N into the tube furnace in the heating process₂，N₂The flow rate is 80-120ml/min, and the material is cooled to room temperature and taken out after pyrolysis;

and step three, soaking the pyrolyzed biochar in absolute ethyl alcohol for 3 hours, and performing suction filtration and drying to obtain the modified biochar.

According to the preparation method of the modified biochar for adsorbing tetracycline in wastewater, the biomass is sawdust biomass.

The biomass and KMnO are used for adsorbing tetracycline in the wastewater, and the preparation method of the modified biochar is characterized in that₄And FeCl₂.4H₂The ratio of the O mixed solution is 1: 10.

The biochar prepared by the preparation method is applied to the aspect of adsorbing tetracycline in wastewater.

The optimal pH value of the biochar prepared by the invention for removing tetracycline in wastewater is 11.

The invention has the beneficial effects that: the preparation method for preparing the biochar has the advantages of high temperature rise speed, short pyrolysis time and simple pyrolysis procedure, and can efficiently and quickly complete the pyrolysis procedure. And two metal oxides are formed on the surface of the biochar prepared by the method, so that the biochar has good magnetism, is beneficial to recovery and reuse, can realize high-efficiency adsorption of tetracycline, and has a good using effect.

Drawings

FIG. 1 is an SEM image of biochar prepared by the present invention; in the figure, a is unmodified biochar, b is biochar prepared by the method of the invention, and BC-500 is biochar prepared by comparative example 1.

FIG. 2 is a graph comparing FTIR before and after modification and before and after adsorption; wherein (a) is a FTIR comparison before and after modification; (b) FTIR contrast before and after adsorption.

FIG. 3 is a comparison FTIR before and after adsorption of biochar prepared in comparative example 1.

FIG. 4 is a Raman spectrum of the biochar of the present invention.

FIG. 5 is an XRD data pattern of a blank biochar and a modified biochar of the present invention.

FIG. 6 is a graph of XPS data for the interaction of biochar composites with tetracycline; wherein panels (e1) and (e3) represent the modified biochar O1s peaks of the present invention; FIGS. (e2) and (e4) show peaks for modified biochar C1s of the present invention; FIGS. (e5) and (e6) show the iron and manganese peaks before adsorption of the modified biochar of the invention; FIG. e7 shows the nitrogen peak of the biochar after adsorption by the modified biochar of the present invention.

FIG. 7 is a graph showing the results of adsorption kinetics curves for modified biochar according to the present invention.

FIG. 8 is a graph of the results of a kinetic fit of biochar of the invention to the initial concentrations of four tetracyclines.

FIG. 9 is an adsorption isotherm diagram of biochar of the present invention.

FIG. 10 is a graph showing the effect of pH on the adsorption results of the biochar of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Example 1: the embodiment provides a preparation method of modified biochar for adsorbing tetracycline in wastewater, which comprises the following steps:

cleaning and shearing sawdust biomass, placing the sawdust biomass in a blast drying oven, drying for 10 hours at 105 ℃, screening, and reserving the sawdust biomass with the mesh size not smaller than 100 meshes;

step two, dipping the sawdust biomass processed in the step one in KMnO with the molar ratio of iron to manganese of 2:1₄And FeCl₂.4H₂Mixing O solution at a solid-to-liquid ratio of 1:10, stirring for 12h, oven drying at 80 deg.C until the supernatant disappears, placing in a tubular furnace, heating to 500 deg.C at a heating rate of 10 deg.C/min, pyrolyzing for 40min, and introducing N into the tubular furnace continuously during heating₂，N₂The flow rate is 80-120ml/min, and the material is cooled to room temperature and taken out after pyrolysis;

and step three, soaking the pyrolyzed biochar in absolute ethyl alcohol for 3 hours, and then carrying out suction filtration and drying to obtain biochar, which is marked as FeMn-BC.

Comparative example 1: the comparative example 1 is different from the example 1 in that: the biochar of comparative example 1 was directly pyrolyzed without treatment in the manner of example 1, with a pyrolysis temperature of 500 ℃, a pyrolysis process with a temperature rise rate of 5 ℃/min, a pyrolysis time of 2h, and is noted BC-500.

Experimental example 1: biochar characterization verification

The biochar prepared by the method and the biochar of the comparative example are verified in the aspects of characterization structure, adsorption kinetics experiment, adsorption isotherm experiment and tetracycline adsorption effect of the biochar by pH, and the method is concretely as follows.

1. Biochar characterization structure

Some characteristics of the biochar, including SEM, FTIR, XRD, XPS and Raman, are analyzed and processed on a data line, and some changes occurring on the surface of the modified biochar and the adsorption mechanism of tetracycline are researched.

(1) The morphological structures of the unmodified biochar (Bulk-BC), the biochar (FeMn-BC) prepared according to the method of example 1 and the biochar (BC-500) prepared according to the method of comparative example 1 were respectively subjected to characterization tests by using a field emission Scanning Electron Microscope (SEM), and the results are shown in FIG. 1.

As can be seen from FIG. 1, the biochar (Bulk-BC) before modification has a smooth surface and a uniform pore structure; the modified biochar (FeMn-BC) has a rough surface, tiny crystals and a large and uneven pore structure; the biochar (BC-500) in comparative example 1 has a slightly smooth surface and no obvious pore structure is seen, which is not beneficial to the absorption of tetracycline; the phenomenon is probably caused by the fact that the iron-manganese oxide is successfully attached to the surface of the biochar, the rough surface can provide more adsorption sites for the tetracycline, the adsorption performance of the tetracycline is enhanced, and the tetracycline is favorably absorbed.

From the view point of the adsorption quantity of the tetracycline, the rough surface of the modified biochar can provide more adsorption sites for the tetracycline, and the adsorption performance of the tetracycline is enhanced. The surface of the biochar in the comparative example is slightly smooth, no obvious pore structure is seen, and the adsorption of tetracycline is not facilitated, so that the adsorption effect is poor.

(2) Fourier infrared spectrum analysis of change of different biochar functional groups

The results of this experiment are shown in fig. 2 by analyzing the change in the biochar before and after modification, and in the functional groups and chemical bonds of the biochar before and after adsorption using fourier-infrared spectroscopy.

For comparison of biochar before and after modification, see fig. 2 (a), it can be clearly seen that the modified biochar (FeMn-BC) is 3440cm^-1Has obvious reduction of-OHWeak, 1583cm^-1、1186cm^-1And 873cm^-1All the peaks have obvious enhancement. At 500-^-1Meanwhile, the modified biochar has many peaks compared with the unmodified biochar, because oxides of iron and manganese are attached to the surface of the biochar to form Fe-O (581 cm)^-1)，MnO₂The results were consistent with the SEM of biochar.

Comparing FTIR patterns of biochar before and after adsorption, see FIG. 2 (b), it can be seen that-OH of biochar after adsorption has a tendency to decrease and is 1000cm at 500-^-1The peak between the two phases is enhanced and weakened to different degrees, which shows that the iron and manganese substances loaded on the surface of the biochar play a certain role in the tetracycline adsorption process, and the modified biochar is also the reason of large tetracycline adsorption capacity and accords with the experimental results.

FIG. 3 is an infrared spectrum before and after adsorption of contaminants by the BC-500 raw material in comparative example 1. From FIG. 3, it can be seen that the infrared spectrum of BC-500 has no significant difference after adsorbing TC, which indicates that the adsorption of TC by the biochar mainly occurs in the pore filling, and no interaction with the surface functional group occurs, so that the adsorption amount of tetracycline is small.

(3) Raman spectrum analysis of carbonization degree of biomass

The Raman spectrum determines the charring degree of the biochar by the area and ratio of the D peak and the G peak, see fig. 4 in particular. From FIG. 4, at 1353cm^-1And 1591cm^-1The bond at the position has two obvious absorption peaks respectively corresponding to a D peak and a G peak, and represents the graphitization degree of the biomass and the defect degree in the graphitization structure. The degree of graphitization of carbon materials is generally evaluated by the intensity ratio of the G peak to the D peak, which is compared to I_G/I_DIs in direct proportion. The Roman graph shows that the carbonization degrees of the biomass of the blank biochar and the biomass of the modified biochar are different, which indicates that the loading of the iron-manganese oxide can have a certain influence on the graphitization degree of the material.

(4) XRD (X-ray diffraction) determination of existence forms of Fe and Mn on the surface of the biochar

The XRD data patterns of the blank biochar and the modified biochar are shown in figure 5; by analysis, it was found thatSurface of charcoal, initial soaked KMnO₄And FeCl₂.4H₂The O solution is converted into gamma-Fe on the surface of the sawdust biomass through pyrolysis₂O₃And MnO₂The successful loading of iron and manganese on the surface of the biochar is proved, while the blank biochar does not have any characteristic peaks related to iron and manganese, and the result is also consistent with FTIR.

(5) XPS analysis of changes in main functional groups of biochar before and after adsorption experiments

XPS characterization can be used for qualitative and quantitative analysis of elements, and can be used for analyzing the structure of chemical substances, and mainly for judging various forms of C and O and valence states of Fe and Mn. XPS analysis was used to identify the interaction of the biochar composite with tetracycline, and the results are shown in FIG. 6.

See peaks (e1) and (e3) of modified biochar O1s in fig. 6, wherein (e1) XPS spectra before adsorption of modified biochar and (e3) XPS spectra after adsorption of modified biochar. It can be seen that the peaks are divided into five peaks before and after the adsorption, namely 530.1eV, 531.6eV, 532,3eV, 533.1eV and 534.0eV, but the peaks after the adsorption are weakened, which indicates that the oxygen-containing functional group plays a certain role in the adsorption process of tetracycline.

See peaks (e2) and (e4) of modified biochar C1s in fig. 6, wherein (e2) XPS spectra before adsorption of modified biochar and (e4) XPS spectra after adsorption of modified biochar. It can be seen that the C1s peak is divided into four peaks before and after adsorption, namely 284.7eV, 286.1eV, 288.8eV and 293.3eV, the peak C1s of the modified biochar after tetracycline adsorption is weakened, but the peak at 293.3eV is obviously weakened after adsorption, which indicates that the biochar has pi-pi interaction with tetracycline adsorption.

See (e5) and (e6) in fig. 6 for iron and manganese peaks before adsorption of the modified biochar. The valence states of iron and manganese are respectively Fe2p through the peaks of iron and manganese^1/2，Fe2p^3/2；Mn2p^1/2，Mn2p^3/2This result is consistent with XRD results; XPS analysis can prove that ferro-manganese is successfully loaded on the biochar and the corresponding oxide valence state, and can also obtain that the adsorption of tetracycline is related to oxygen-containing functional groups and pi-pi interaction and electrostatic adsorptionIt is related.

Referring to the nitrogen peak of the biochar after adsorption in fig. 6 (e7), the nitrogen peaks were measured for both before and after adsorption when the XPS test was performed, and no nitrogen peak was detected before adsorption of the modified biochar and a nitrogen peak was detected after adsorption, and (e7) was the nitrogen peak after adsorption of the modified biochar. As the tetracycline contains nitrogen elements, the detection of a nitrogen peak proves that the tetracycline is successfully adsorbed on the surface of the biochar, so that the effect of removing the tetracycline in the solution is achieved.

Example 2 application of prepared biochar in adsorption of tetracycline in wastewater

In order to verify the effect of the biochar prepared by the method of the invention on adsorbing tetracycline in wastewater, an adsorption test is carried out, which is specifically as follows.

(1) Adsorption kinetics experiment

Adsorption kinetics were performed with modified charcoal at initial tetracycline concentrations of 5, 10, 15, 20, 30, 40, 50, 80mg/L and the results are shown in FIG. 7, where (a) is a first order kinetics Phantom (PFO), (b) is a second order kinetics Phantom (PSO), and (c) is an Elovich kinetics phantom.

From fig. 7, it can be seen that the adsorption amount of the modified biochar increases with the increase of the initial concentration of tetracycline, the adsorption rate is high in the initial stage of adsorption, and the adsorption rate is gradually gentle after 90min and tends to the adsorption equilibrium. When the initial concentration of tetracycline was 80mg/L, the adsorption capacity at which adsorption equilibrium was reached was 16.3 mg/g.

Three kinetic curves, first order Pseudo (PFO), second order Pseudo (PSO) and Elovich, were fitted to the initial tetracycline adsorption process at 5, 10, 15, 20mg/L, and the results are shown in Table 1 and FIG. 8.

TABLE 1 kinetic parameters Table

By fitting a data map and fitting a parameter R²It can be seen that the adsorption process of tetracycline conforms to quasi-first and quasi-second order kinetic models. The magnitude of the RSS and AIC values may also be used to determine fourWhether the adsorption process of the cyclic element conforms to the model. Comparing the RSS and AIC values of each model shows that the pseudo-second order (PSO) model is the most suitable for the tetracycline adsorption process in the three fitting models, the experimental data are within the confidence interval, and the experimental data have the confidence level.

(2) Adsorption isotherm

The modified charcoal was subjected to adsorption experiments under conditions of initial tetracycline concentrations of 5, 10, 20, 30, 40, 50, 80mg/L, and absorbance at adsorption equilibrium was measured to obtain adsorption isotherms, and the results are shown in FIG. 9.

As can be seen from FIG. 9, the adsorption amount of tetracycline by the modified biochar increases with the initial concentration and then gradually reaches equilibrium. The experimental data were fitted with five isotherm models of Langmuir, Sims, Redlich-Peterson, Freundlich and Temkin. As can be seen from the fitted curves, the adsorption process was in accordance with Langmuir, Sips, Redlich-Peterson isotherm model, and the results are shown in Table 2.

TABLE 2 isotherm model fitting results

It can be known that the fitting coefficient R²The adsorption model is compared by RSS, AIC, delta AICu and other parameters, and the isotherm model which is most consistent with the tetracycline adsorption process is the Sips model, and for the Sips model, the fitting parameter is R²＝0.997，RSS＝0.888,AIC＝-14.85,ΔAICu＝0。

(3) Influence of pH on adsorption experiments

The initial pH affects the existing form of tetracycline, and has an important effect on tetracycline removal. Wherein the effect of pH on the form of tetracycline present is as follows:

at pH<3.3 the tetracycline is present in aqueous solution in the form of TETH³⁺；

At 3.3<pH<7.7 the tetracycline is present in aqueous solution in the form of TETH₂ ⁰；

At 7.7<pH<9.7 the tetracycline is present in aqueous solution in the form of TETH^-；

At pH>9.7 the tetracycline is present in aqueous solution in the form of TET^2-。

The adsorption experiments were carried out by adjusting the initial pH of tetracycline to 2,3, 5, 7, 9, 11, 12 with HCl (0.1mol/L) and NaOH (0.1mol/L), respectively, and the results are shown in FIG. 10. The initial pH value influences the existence form of tetracycline, and further influences the adsorption quantity of the FeMn-BC to the tetracycline. The tetracycline molecules have different existing forms under different pH conditions, so that the binding force between FeMn-BC and tetracycline is different.

It can be seen from FIG. 10 that the tetracycline removal rate increases with increasing pH at pH 2-3. Mainly because the positively charged biochar adsorbs a great deal of TCH in the form of ion exchange³⁺. When the pH value is increased from 3 to 5, the adsorption amount of tetracycline on FeMn-BC is obviously reduced. And pH is>At 5, the adsorption capacity increased with increasing pH. At this time, the form of tetracycline present in the solution is converted to TETH^-And TET^2-The tetracycline in the solution can be removed by sharing an electron pair with metal oxide on the surface of the biochar or through electrostatic adsorption, so that the effect of treating antibiotic wastewater is achieved.

From the fitting results, the optimum pH for tetracycline removal was 11. This result is consistent with the physicochemical properties of tetracycline (tetracycline is poorly soluble in water and readily soluble in weak acids and bases, and the experimental tetracycline is formulated under conditions such that the tetracycline is dissolved in an aqueous solution at a pH of 11 and the initial pH of the solution is 6.86 after the tetracycline is dissolved (C0. about.40 mg/L). The adsorption effect is better than that before and after the initial pH value under the acidic or alkaline condition, which proves that the modification of the biochar can lead the surface of the biochar to have positive charges, and the H and the TETH in the biochar are mainly subjected to deprotonation under the acidic condition³⁺Ion exchange occurs to reduce the concentration of tetracycline in solution; under alkaline conditions, tetracycline exists in solution in a form predominantly of TET^2-The tetracycline in the solution is removed by sharing an electron pair with the metal oxide on the surface of the biochar or enhancing the electrostatic adsorption between the biochar and the tetracycline, and the optimal adsorption pH is 11. In the adsorption test, the initial concentration of tetracycline is 40mg/L, and the pH is 11The adsorption capacity at the adsorption equilibrium can reach 13.70 mg/g.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and scope of the present invention are intended to be covered thereby.

Claims

1. A preparation method of modified biochar for adsorbing tetracycline in wastewater is characterized by comprising the following steps: the method comprises the following steps:

step two, soaking the biomass treated in the step one in KMnO with the molar ratio of iron to manganese of 3:1₄And FeCl₂ ^.4H₂Mixing and stirring the solution O for 12 hours, drying the solution O in an oven at the temperature of 80 ℃ until the supernatant disappears, then putting the solution O in a tube furnace, heating the solution O to the temperature of 500 ℃ at the heating rate of 10 ℃/min for pyrolysis for 40min, and continuously introducing N into the tube furnace in the heating process₂，N₂The flow rate is 80-120ml/min, and the material is cooled to room temperature and taken out after pyrolysis;

and step three, soaking the pyrolyzed biochar in ethanol, performing suction filtration, and drying to obtain the biochar.

2. The preparation method of the modified biochar for adsorbing tetracycline in wastewater as claimed in claim 1, wherein the method comprises the following steps: the biomass is sawdust biomass.

3. The preparation method of the modified biochar for adsorbing tetracycline in wastewater as claimed in claim 1, wherein the method comprises the following steps: the biomass is reacted with KMnO₄And FeCl₂ ^.4H₂The solid-liquid ratio of the O solution is 1: 10.

4. Use of the biochar prepared by the preparation method according to any one of claims 1 to 3 for adsorbing tetracycline in wastewater.

5. Use according to claim 4, characterized in that: the optimum pH for tetracycline removal from the wastewater was 11.