A method for removing heavy metals and organic matter based on free radicals formed in situ on biochar

Abstract

The present invention provides a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar, and belongs to the technical field of solid free radicals. The method comprises the following steps: (1) preparation of tea residue biochar: drying the tea residue at 40-80°C to constant weight, grinding through an 80-mesh sieve, and then heating at a rate of 5-25°C / min under the protection of an inert gas atmosphere, with a pyrolysis temperature range of 200-600°C and a pyrolysis time of 1-6h. After the pyrolysis is completed, cooling is performed to obtain tea residue biochar; (2) constructing a catalytic system based on the in situ formation of free radicals on biochar: adding the tea residue biochar to an aqueous solution containing heavy metals and organic matter, adjusting the initial pH value, stirring, reacting at room temperature, and the adsorbed heavy metals in situ catalyze the biochar to form new solid free radicals, and these solid free radicals act as new active sites to promote the adsorption, degradation and stabilization of organic matter.

Description

Technical Field

[0001] The invention belongs to the technical field of solid free radicals, and in particular relates to a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar. Background Art

[0002] Organic micropollutants in the water environment, such as endocrine disruptors, antibiotics, and anti-inflammatory drugs, can all react with metal ions due to the presence of carboxyl, hydroxyl, amino, and heterocyclic groups. The resulting complexes may be more toxic to plants, animals, and microorganisms in the water environment. Therefore, it is necessary to develop an efficient and low-cost technology for the remediation of water bodies contaminated by heavy metals and organic matter.

[0003] At present, common treatment technologies include advanced oxidation processes (AOPs), adsorption, membrane filtration, chemical precipitation, etc. Among them, AOPs have attracted widespread attention due to their low cost, simple operation, and good removal effect on organic / inorganic pollutants. However, AOPs are usually accompanied by the addition of chemical oxidants, such as hydrogen peroxide, persulfate, periodate, etc. The activation of these oxidants may require harsh conditions, and may also form inorganic salt ions that are discharged into the treated water, thereby causing secondary pollution.

[0004] Therefore, technologies that use the redox properties of the catalytic material itself without adding an external oxidant have attracted attention. Biochar formed by pyrolysis of biomass is an emerging carbon-based catalyst. In addition to being green and environmentally friendly and having abundant raw material sources, the persistent free radicals it contains also give biochar a certain redox ability. Current research often uses complex chemical modifications to enhance the catalytic ability of free radicals on biochar, thereby improving the redox properties of biochar, but ignores the use of the characteristics of the pollutants themselves to in situ regulate the content and type of free radicals on biochar. Summary of the invention

[0005] The present invention is made to solve the above-mentioned problems, and aims to provide a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar.

[0006] The present invention provides a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar, which has the following characteristics and comprises the following steps: (1) preparing tea residue biochar: drying the tea residue at 40-80°C to constant weight, grinding and passing through an 80-mesh sieve, and then heating at a rate of 5-25°C / min under the protection of an inert gas atmosphere, with a pyrolysis temperature range of 200-600°C and a pyrolysis time of 1-6h. After the pyrolysis is completed, cooling is performed to obtain tea residue biochar; (2) constructing a catalytic system based on free radicals formed in situ on biochar: adding the tea residue biochar to an aqueous solution containing heavy metals and organic matter, adjusting the initial pH value, stirring, and reacting at room temperature, wherein the adsorbed heavy metals in situ catalyze the biochar to form new solid free radicals, and these solid free radicals serve as new active sites to promote the adsorption, degradation and stabilization of organic matter.

[0007] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (1), the tea residues are any one of green tea residues, black tea residues, and white tea residues, and the inert gas is nitrogen or argon.

[0008] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (2), the matrix of the aqueous solution is any one of laboratory ultrapure water, laboratory deionized water, tap water, river water, lake water, etc.

[0009] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (2), the heavy metal is any one or more of Cu(II), Zn(II), Fe(III), Ni(II), and the concentration of the heavy metal is 0.2-4.0 mmol / L.

[0010] In the method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention, it can also have the following characteristics: wherein, in step (2), the organic matter is any one of tetracycline, sulfamethoxazole, norfloxacin, estrone, atrazine, diclofenac, and caffeine, and the concentration of the organic matter is 0.1-2.0 mmol / L.

[0011] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (2), the amount of tea residue biochar used is 0.1-1.0 g / L.

[0012] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (2), the initial pH value is 2-6, the stirring speed is 100-200 r / min, and the reaction time is 120-420 min.

[0013] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics, and further include the following steps: (3) Regeneration of tea residue biochar: adding an ethanol solution with a concentration of 10-50% to the tea residue biochar to be regenerated, stirring at room temperature for 2-8 hours, rinsing multiple times until the ethanol concentration in the rinsing liquid is lower than 0.1%, then adding an EDTA-2Na solution with a concentration of 10-30%, stirring for 30-120 minutes, rinsing multiple times until the EDTA-2Na concentration in the rinsing liquid is lower than 0.1%, and drying the rinsed tea residue biochar at 40-80°C to constant weight to obtain regenerated tea residue biochar.

[0014] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (3), the tea residue biochar to be regenerated is the tea residue biochar taken out and dried from the system after the reaction in step (2) is completed, and the stirring speed is 50-100 r / min.

[0015] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar provided by the present invention may also have the following characteristics: wherein, in step (3), the ratio of ethanol to tea residue biochar to be regenerated is 1 mL:100 mg-1 mL:400 mg, and the ratio of EDTA-2Na to tea residue biochar is 1 mL:200 mg-1 mL:400 mg.

[0016] Functions and Effects of the Invention

[0017] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar involved in the present invention utilizes free radicals formed in situ by combining heavy metals, one of the pollutants, with tea residue biochar during the reaction process to achieve the enhancement of free radicals on the biochar, thereby achieving the simultaneous removal of heavy metals and organic matter.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The biochar of the present invention is derived from tea residues, which realizes the resource utilization of waste tea residues. In addition, when preparing tea residue biochar, no additional chemical modification is required, and the preparation method is simple.

[0020] (2) The reaction system of the present invention does not require the addition of additional chemical oxidants, which effectively avoids the risk of secondary pollution caused by chemical oxidants during the reaction process.

[0021] (3) The present invention cleverly utilizes the free radicals formed in situ after the biochar combines with heavy metals during the reaction process, thereby achieving in situ regulation of free radicals on the biochar.

[0022] (4) The present invention alleviates the competition of multiple pollutants in heterogeneous systems for effective active sites on catalytic materials.

[0023] (5) After 5 reaction cycles in a system where heavy metals and organic matter coexist, the tea residue biochar used in the present invention still maintains a high removal rate for heavy metals and organic matter, indicating that the catalytic system of the present invention has good stability and recyclability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The removal results of heavy metals and organic matter by tea residue biochar obtained at different pyrolysis temperatures in Example 1 of the present invention;

[0025] Figure 2 The removal results of heavy metals and organic matter by tea residue biochar obtained at different pyrolysis times in Example 2 of the present invention;

[0026] Figure 3 The effect of the initial pH value on the removal of organic matter in Example 3 of the present invention;

[0027] Figure 4 The effect of the initial pH value on the heavy metal removal effect in Example 3 of the present invention;

[0028] Figure 5 The influence of the types of heavy metals on the removal effect of heavy metals and organic matter in Example 4 of the present invention;

[0029] Figure 6 The TOC removal rates of the biochar + organic matter system and the biochar + heavy metal + organic matter system in Example 4 of the present invention are compared;

[0030] Figure 7 The changes of free radicals in tea residue biochar after removing different heavy metals in Example 4 of the present invention;

[0031] Figure 8 The free radical changes of tea residue biochar in Example 4 of the present invention after the heavy metals and organic matter are removed simultaneously;

[0032] Fig. 9 The effect of the type of organic matter on the removal of heavy metals and organic matter in Example 5 of the present invention;

[0033] Fig.10 The changes of free radicals in tea residue biochar after removing different kinds of organic matter in Example 5 of the present invention;

[0034] Fig.11 The effect of the initial concentration of organic matter on the removal of heavy metals and organic matter in Example 6 of the present invention;

[0035] Fig.12 The effect of the initial concentration of heavy metals on the removal of heavy metals and organic matter in Example 7 of the present invention; Fig.13 The total ion current diagrams of organic matter degradation products in the biochar + organic matter system and the biochar + heavy metal + organic matter system in Example 8 of the present invention are compared;

[0036] Fig.14 is a secondary mass spectrum of organic matter degradation products in the biochar+organic matter system in Example 8 of the present invention;

[0037] Fig.15 This is a secondary mass spectrum of organic matter degradation products in the biochar+heavy metal+organic matter system in Example 8 of the present invention;

[0038] Fig.16 The application of biochar to remove actual raw water in Example 9 of the present invention;

[0039] Fig.17 The recyclability of the biochar in Example 10 of the present invention when removing organic matter;

[0040] Fig.18 The recyclability of the biochar in Example 10 of the present invention in removing heavy metals;

[0041] Fig.19 This is the effect of removing heavy metals and organic matter after biochar regeneration after 10 cycles of cyclic reaction in Example 10 of the present invention. DETAILED DESCRIPTION

[0042] The present invention provides a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar, which is characterized by comprising the following steps:

[0043] (1) Preparation of tea residue biochar: Dry the tea residue at 40-80°C to constant weight, grind through an 80-mesh sieve, and then heat at a rate of 5-25°C / min under the protection of an inert gas atmosphere, with a pyrolysis temperature range of 200-600°C and a pyrolysis time of 1-6h. After pyrolysis is completed, cool the mixture to obtain tea residue biochar. The tea residue is green tea, black tea or white tea residue, and the inert gas is nitrogen or argon.

[0044] (2) Constructing a catalytic system based on the in-situ formation of free radicals on biochar: adding 0.1-1.0 g / L tea residue biochar to an aqueous solution containing heavy metals and organic matter, adjusting the initial pH value to 2-6, stirring at 100-200 r / min, reacting at room temperature for 120-420 min, and the adsorbed heavy metals in situ catalyze the biochar to form new solid free radicals, which serve as new active sites to promote the adsorption, degradation and stabilization of organic matter. Wherein, the matrix of the aqueous solution is any one of laboratory ultrapure water, laboratory deionized water, tap water, river water, lake water, etc.; the heavy metal is any one or more of Cu(II), Zn(II), Fe(III), Ni(II), and the concentration of the heavy metal is 0.2-4.0 mmol / L; the organic matter is any one of tetracycline, sulfamethoxazole, norfloxacin, estrone, atrazine, diclofenac, and caffeine, and the concentration of the organic matter is 0.1-2.0 mmol / L.

[0045] The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar of the present invention may also include the following steps:

[0046] (3) Regeneration of tea residue biochar: Add 10-50% ethanol solution to the tea residue biochar to be regenerated, stir at 50-100 r / min for 2-8 h at room temperature of 20-25°C, rinse several times until the ethanol concentration in the rinse liquid is lower than 0.1%, then add 10-30% EDTA-2Na solution, stir at 50-100 r / min for 30-120 min at room temperature of 20-25°C, rinse several times until the EDTA-2Na concentration in the rinse liquid is lower than 0.1%, and dry the rinsed tea residue biochar at 40-80°C to constant weight to obtain regenerated tea residue biochar. The tea residue biochar to be regenerated is the tea residue biochar taken out and dried after the reaction in step (2) is completed. The ratio of ethanol to the tea residue biochar to be regenerated is 1 mL: 100 mg-1 mL: 400 mg, and the ratio of EDTA-2Na to the tea residue biochar is 1 mL: 200 mg-1 mL: 400 mg.

[0047] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate the method of removing heavy metals and organic matter based on free radicals formed in situ on biochar.

[0048] Example 1

[0049] This embodiment provides a method for removing heavy metals and organic matter based on free radicals formed in situ on biochar, comprising the following steps:

[0050] (1) Preparation of tea residue biochar: Green tea residue was dried at 60°C to constant weight, ground through an 80-mesh sieve, and then heated at a rate of 20°C / min under nitrogen atmosphere. The pyrolysis temperatures were set at 200, 300, 400, 500, and 600°C, and the pyrolysis time was 2 h. After pyrolysis, the mixture was cooled to obtain 5 groups of tea residue biochar. In addition, the original green tea residue was used as a control for the degradation effect of pollutants.

[0051] (2) Construction of a catalytic system based on in situ formation of free radicals on biochar (i.e., pollutant degradation experiment):

[0052] 0.5 g / L original tea residue and the tea residue biochar prepared at the above five different pyrolysis temperatures were added with 0.1 mmol / L tetracycline, 0.6 mmol / L CuCl 2 The single and the mixture of the two were prepared with laboratory ultrapure water, the initial pH of the solution was adjusted to 5.0, the reaction was carried out for 420 minutes, and the content of heavy metals and organic matter in the solution was determined after the reaction.

[0053] Figure 1 The results of heavy metal and organic matter removal by tea residue biochar obtained at different pyrolysis temperatures in Example 1 of the present invention.

[0054] Depend on Figure 1 It can be seen that as the pyrolysis temperature increases in the range of 0-600℃, the removal of Cu(Ⅱ) and tetracycline by tea residue biochar first increases (0-400℃), then stabilizes (400-500℃), and then decreases (500-600℃). The temperature around 400℃ may be more conducive to the formation of functional groups with redox ability in biochar, so the optimal pyrolysis temperature is determined to be 400℃.

[0055] Example 2

[0056] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C, and the pyrolysis time was set to 1, 2, 4, and 6 h, respectively, to obtain 4 groups of tea residue biochars, and the original tea residue was also used as a control for the pollutant degradation effect. The steps of the pollutant degradation experiment (i.e., step (2)) were consistent with those in Example 1.

[0057] Figure 2 The removal results of heavy metals and organic matter by the tea residue biochar obtained at different pyrolysis times in Example 2 of the present invention.

[0058] like Figure 2 As shown in the figure, with the extension of pyrolysis time, the removal of Cu(II) and tetracycline by tea residue biochar first increased (0-2h), and then remained stable (2-6h). Considering the removal effect and energy consumption, 400℃ and 2h were determined to be the optimal pyrolysis conditions.

[0059] Example 3

[0060] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. In the pollutant degradation experiment, the initial pH range of the single tetracycline-containing water was controlled to be 3-11, and the single CuCl 2 With CuCl 2 , the initial pH range of the tetracycline coexistence system is 2-6, and the other steps of the pollutant degradation experiment are consistent with Example 1.

[0061] Figure 3 This is the effect of the initial pH value on the organic matter removal effect in Example 3 of the present invention. Figure 4 This is the effect of the initial pH value on the heavy metal removal effect in Example 3 of the present invention.

[0062] like Figure 3 As shown in the figure, when the pH increases from 3.0 to 7.0, the removal of single tetracycline increases, and when the pH further increases to 11.0, the removal decreases, which may be related to the dissociation form of tetracycline in the solution. The removal of single Cu(II) increases continuously with the increase of the initial pH in the range of 2.0-6.0 ( Figure 4 ).CuCl 2 , tetracycline coexistence system ( Figure 3 , Figure 4 ), the complex of Cu(II) and tetracycline will convert between cations and zwitterions, thereby alleviating the electrostatic repulsion between the complex and biochar, making the removal amount of Cu(II) and tetracycline continue to increase in the pH range of 2.0-6.0.

[0063] Example 4

[0064] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. In the pollutant degradation experiment, the organic matter was fixed to 0.1 mmol / L tetracycline, and the heavy metal type was changed to CuCl 2 、ZnCl 2 、FeCl 3 、NiCl 2 , the concentration was 0.6mmol / L, and the other steps of the pollutant degradation experiment were consistent with Example 1. 2 The system was used as a representative to analyze the TOC removal rate, and the tea residue biochar before and after the reaction of each system was tested by EPR to observe the changes in free radicals on the biochar.

[0065] Figure 5 This is the effect of heavy metal types on the removal of heavy metals and organic matter in Example 4 of the present invention. Figure 6The TOC removal rates of the biochar + organic matter system and the biochar + heavy metal + organic matter system in Example 4 of the present invention are compared.

[0066] Depend on Figure 5 It can be seen that biochar has the best removal effect on the single heavy metal system. After 420 minutes of reaction, the maximum removal of heavy metals is 1.156mmol / g. The presence of heavy metals significantly promoted the removal of tetracycline. When coexisting with 0.6mmol / L Cu(II), the removal of tetracycline increased from 0.0541mmol / g in the single system to 0.168mmol / g. The order of tetracycline removal in the presence of different heavy metals is: tetracycline [Cu(II)] ≈ tetracycline [Ni(II)] > tetracycline [Fe(III)] > tetracycline [Zn(II)]. Figure 6 Further analysis showed that at the end of the reaction, biochar + tetracycline + CuCl 2 The TOC removal rate of the system was 86.23%, which was much higher than the 16.75% of the biochar + tetracycline system, indicating that the presence of heavy metals increased the mineralization of organic matter.

[0067] Figure 7 This is the change of free radicals in tea residue biochar after removing different heavy metals in Example 4 of the present invention. Figure 8 This is the change of free radicals in the tea residue biochar after the heavy metals and organic matter are removed simultaneously in Example 4 of the present invention.

[0068] comprehensive Figure 5 , 7 8. Compared with the initial tea residue biochar, the characteristic peaks of free radicals on biochar were significantly enhanced and shifted to the left, whether it was the removal of a single heavy metal or the simultaneous removal of heavy metals and tetracycline. This indicates that the presence of heavy metals triggered the formation of new free radicals on biochar, and these new free radicals provided more effective sites for the adsorption and removal of organic matter. Heavy metals are not only a pollutant in the system, but also a trigger for the formation of in-situ free radicals. In the coexistence system of heavy metals and tetracycline, the order of free radical intensity on biochar after the reaction is: free radical [Cu(II)] ≈ free radical [Ni(II)] > free radical [Fe(III)] > free radical [Zn(II)], which is consistent with the removal amount of tetracycline in the coexistence system, indicating that the free radicals formed in situ play a key role in the removal of tetracycline.

[0069] Example 5

[0070] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. In the pollutant degradation experiment, the heavy metal was fixed to 0.6 mmol / L CuCl 2, the organic matter types were changed to tetracycline, sulfamethoxazole, norfloxacin, estrone, atrazine, diclofenac, and caffeine, and the organic matter concentration was 0.1 mmol / L. The other steps of the pollutant degradation experiment were consistent with Example 1. 2 The system was used as a representative to analyze the TOC removal rate, and the tea residue biochar before and after the reaction of each system was tested by EPR to observe the changes in free radicals on the biochar.

[0071] Fig. 9 This is the effect of the type of organic matter on the removal effect of heavy metals and organic matter in Example 5 of the present invention.

[0072] like Fig. 9 As shown in the figure, the removal effect of biochar on single organic matter is poor. In the system where single organic matter coexists with organic matter and Cu(II), the removal amount of organic matter is in the same order: caffeine > diclofenac > sulfamethoxazole > atrazine > estrone > tetracycline > norfloxacin. Among them, the sulfonamide group in sulfamethoxazole may hinder the combination of Cu(II) and biochar, resulting in a significant deterioration in the removal effect of Cu(II).

[0073] Fig.10 This is the change of free radicals in tea residue biochar after removing different types of organic matter in Example 5 of the present invention.

[0074] from Fig.10 It can be seen that when biochar removes a single organic matter, the intensity of the free radical decreases to varying degrees. After the reaction, the order of the intensity of the free radicals on the biochar is: free radical [estrone] > free radical [tetracycline] > free radical [diclofenac]. This shows that the removal of a single organic matter is a process of consuming the original persistent free radicals on the biochar. The stronger the ability of the organic matter to combine with the biochar, the greater the amount of the original free radicals on the biochar consumed.

[0075] Example 6

[0076] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. In the pollutant degradation experiment, the heavy metal was fixed to 0.6 mmol / L CuCl 2 The organic matter was tetracycline, and the initial concentration of tetracycline was changed to 0.1, 0.2, 0.4, 0.6, 1.0, and 2.0 mmol / L, respectively. The other steps of the pollutant degradation experiment were consistent with those in Example 1.

[0077] The heavy metal was fixed to 0.6mmol / L CuCl 2 , the organic matter was tetracycline, and the initial concentration of tetracycline was changed to 0.1, 0.2, 0.4, 0.6, 1.0, and 2.0 mmol / L respectively.

[0078] Fig.11 This is the effect of the initial concentration of organic matter on the removal effect of heavy metals and organic matter in Example 6 of the present invention.

[0079] like Fig.11 As shown in the figure, the increase in the initial concentration of tetracycline brought about a slow increase in tetracycline removal, and the inhibition of Cu(II) removal in the coexistence system was more obvious. This indicates that the increase in tetracycline in the system hindered the binding of Cu(II) with the effective active sites on the biochar, thereby affecting the formation of in-situ free radicals.

[0080] Example 7

[0081] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400°C and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. In the pollutant degradation experiment, the organic matter was fixed to 0.1 mmol / L tetracycline and the heavy metal was CuCl 2 , changing CuCl 2 The initial concentrations were 0.2, 0.4, 0.6, 1.0, 2.0, and 4.0 mmol / L, respectively. The other steps of the pollutant degradation experiment were consistent with Example 1.

[0082] Fig.12 This is the effect of the initial concentration of heavy metals on the removal of heavy metals and organic matter in Example 7 of the present invention.

[0083] like Fig.12 As shown, with CuCl 2 As the initial content continued to increase, the amount of Cu(II) removed in the single heavy metal system increased significantly, while the amount of Cu(II) removed in the coexistence system first increased significantly (0.2-0.6mmol / L) and then gradually leveled off (0.6-4.0mmol / L). This indicates that even though the formation of in-situ free radicals provides new sites for the binding of tetracycline and alleviates the competition between Cu(II) and tetracycline for effective sites in the coexistence system, the presence of tetracycline still affects the removal of Cu(II) to a certain extent.

[0084] Example 8

[0085] In order to explore the degradation products of organic matter, the biochar + tetracycline, biochar + tetracycline + CuCl 2 The initial solution in the system, the solution after the reaction, and the biochar extract after the reaction were analyzed by HPLC-MS / MS. The steps of extracting degradation products from biochar are as follows: taking a small amount of tea residue biochar after the pollutant degradation reaction, putting it into a 50% methanol solution, ultrasonically extracting it in a water bath at 37°C for 30 minutes, and then filtering it with a 0.22μm filter membrane before use.

[0086] Fig.13This is a comparison of the total ion currents of organic matter degradation products in the biochar + organic matter system and the biochar + heavy metal + organic matter system in Example 8 of the present invention. Fig.14 This is the secondary mass spectrum of the organic matter degradation products in the biochar + organic matter system in Example 8 of the present invention. Fig.15 This is the secondary mass spectrum of the organic matter degradation products in the biochar+heavy metal+organic matter system in Example 8 of the present invention.

[0087] Combination Figure 13-15 Analysis shows that after the reaction, there are obvious characteristic peaks of tetracycline and macromolecular degradation products in the solution of the biochar + tetracycline system, and products with molecular weight greater than the initial tetracycline also appear on the biochar, which indicates that the original free radicals on the biochar have a weak ability to adsorb and degrade organic matter. 2 The characteristic peak response in the solution after the reaction in the system was very weak, and obvious characteristic peaks of small molecule degradation products appeared on the biochar, which indicated that the free radicals formed in situ triggered by heavy metals enhanced the biochar's ability to adsorb, decompose and stabilize organic matter.

[0088] Example 9

[0089] The pyrolysis temperature in step (1) of Example 1 was adjusted to 400° C. and the pyrolysis time was adjusted to 2 h to obtain tea residue biochar. The tea residue biochar was applied to tap water, lake water, and river water containing heavy metals and organic matter.

[0090] Fig.16 This is the application of biochar in Example 9 of the present invention to remove actual raw water.

[0091] like Fig.16 As shown, the tea residue biochar still maintains a relatively high removal rate for tap water, lake water and river water containing heavy metals and organic matter, indicating that the present invention has certain practical applicability.

[0092] Example 10

[0093] After the reaction, the biochar + tetracycline, biochar + tetracycline + CuCl in Example 4 were taken out. 2 The tea residue biochar in the system was dried and repeated tests of pollutant degradation were carried out. The steps of the pollutant degradation experiment were consistent with step (2) in Example 1.

[0094] Fig.17 The recyclability of the biochar in Example 10 of the present invention in removing organic matter. Fig.18 This is the recyclability of the biochar in Example 10 of the present invention in removing heavy metals.

[0095] Depend on Fig.17It can be seen that in the single organic matter system, due to the consumption of the original persistent free radicals of biochar, after 5 consecutive reaction cycles, the removal effect of biochar on tetracycline became significantly worse. Fig.17 and Fig.18 When heavy metal Cu(II) was present, after 5 cycles of continuous reaction, the removal of tetracycline by tea residue biochar remained at 82.2% of the initial level, while the removal of Cu(II) was above 95% of the initial level, indicating that the free radicals formed in situ improved the stability and sustainability of the system. After 10 cycles of reaction, tea residue biochar could hardly remove single tetracycline, and the removal of Cu(II) also decreased significantly.

[0096] Fig.19 This is the effect of removing heavy metals and organic matter after biochar regeneration after 10 cycles of cyclic reaction in Example 10 of the present invention.

[0097] like Fig.19 As shown in the figure, after regeneration with 40% ethanol solution for 6h and 20% EDTA-2Na solution for 1h, the tea residue biochar recovered its removal capacity for heavy metals and organic matter after 10 cycles of reaction. The removal amount of heavy metals and organic matter by tea residue biochar accounted for more than 85% of the initial tea residue biochar removal amount.

[0098] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for removing heavy metals and organic matter based on free radicals formed in situ on biochar, characterized in that: The following steps are included: (1) Preparation of tea residue biochar: The tea residue is dried at 40-80°C to constant weight, ground through an 80-mesh sieve, and then heated at a rate of 5-25°C / min under an inert gas atmosphere. The pyrolysis temperature range is 200-600°C, and the pyrolysis time is 1-6h. After the pyrolysis is completed, the mixture is cooled to obtain tea residue biochar. (2) Constructing a catalytic system based on the in-situ formation of free radicals on biochar: adding the tea residue biochar to an aqueous solution containing heavy metals and organic matter, adjusting the initial pH value, stirring, and reacting at room temperature, so that the adsorbed heavy metals in situ catalyze the biochar to form new solid free radicals, and these solid free radicals serve as new active sites to promote the adsorption, degradation and stabilization of organic matter; (3) Regeneration of tea residue biochar: Add 10-50% ethanol solution to the tea residue biochar to be regenerated, stir for 2-8 hours at room temperature, rinse several times until the ethanol concentration in the rinse liquid is less than 0.1%, then add 10-30% EDTA-2Na solution, stir for 30-120 minutes, rinse several times until the EDTA-2Na concentration in the rinse liquid is less than 0.1%, dry the rinsed tea residue biochar at 40-80°C to constant weight to obtain regenerated tea residue biochar. In step (2), no additional chemical oxidant needs to be added.

2. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (1), the tea residue is any one of green tea residue, black tea residue and white tea residue. The inert gas is nitrogen or argon.

3. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (2), the matrix of the aqueous solution is any one of laboratory ultrapure water, laboratory deionized water, tap water, river water, and lake water.

4. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (2), the heavy metal is any one or more of Cu(II), Zn(II), Fe(III), Ni(II), and the concentration of the heavy metal is 0.2-4.0 mmol / L.

5. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (2), the organic matter is any one of tetracycline, sulfamethoxazole, norfloxacin, estrone, atrazine, diclofenac, and caffeine, and the concentration of the organic matter is 0.1-2.0 mmol / L.

6. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (2), the amount of tea residue biochar used is 0.1-1.0 g / L.

7. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (2), the initial pH value is 2-6, the stirring speed is 100-200 r / min, and the reaction time is 120-420 min.

8. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to claim 1, characterized in that: in, In step (3), the tea residue biochar to be regenerated is the tea residue biochar taken out and dried from the system after the reaction in step (2). The stirring speed is 50-100 r / min.

9. The method for removing heavy metals and organic matter based on free radicals formed in situ on biochar according to any one of claims 1 to 8, characterized in that: in, In step (3), the ratio of ethanol to tea residue biochar to be regenerated is 1 mL: 100 mg-1 mL: 400 mg, and the ratio of EDTA-2Na to tea residue biochar is 1 mL: 200 mg-1 mL: 400 mg.

Images