A nitrogen-doped magnetic biochar and its preparation method and application

Abstract

The present invention discloses a nitrogen-doped magnetic biochar and a preparation method thereof. A preparation method of nitrogen-doped magnetic biochar comprises the following steps: 1) adding agricultural and forestry wastes to a mixed solution of ferrous sulfate and urea, impregnating, centrifuging, and obtaining a solid mixture; 2) calcining the solid mixture to obtain the nitrogen-doped magnetic biochar. The present invention utilizes agricultural and forestry wastes to prepare nitrogen-doped magnetic biochar in one step, which is not only beneficial to cost control but also beneficial to environmental protection. The preparation method is simple, has few process steps, low energy consumption, and is easy to realize large-scale production. At the same time, no wastewater or sludge is generated during the preparation process, thereby avoiding secondary pollution or the generation of secondary waste.

Description

Technical Field

[0001] The present invention relates to the field of waste resource utilization, and in particular to nitrogen-doped magnetic biochar and a preparation method and application thereof. Background Art

[0002] In recent years, advanced oxidation processes (AOPs) have been widely used to degrade biorefractory pollutants in water due to their high efficiency and strong adaptability compared with traditional wastewater treatment technologies. Carbon-based materials have inherent advantages such as large specific surface area, good electron transfer capacity, good thermal stability and eco-friendliness, so their applicability in AOPs has been studied a lot. Studies have shown that nitrogen-doped magnetic biochar materials exhibit superior catalytic activity compared with undoped materials. This is because the doping of heteroatoms can adjust the electronic properties of the original Sp2 hybridized carbon, increase the specific surface area and generate new active sites. During the pyrolysis process, nitrogen atoms are trapped in the growing carbon network, resulting in the appearance of nitrogen-doped structures such as pyridinic-N and graphitic-N in biochar. These nitrogen-doped structures in biochar will lead to changes in the charge distribution, bond structure and Lewis base position in the carbon network, thereby improving the loading, distribution and catalytic activity of iron, accelerating the reduction ability of active sites and the electron transfer cycle between persulfate (PS) and the catalyst.

[0003] However, the existing preparation methods of nitrogen-doped magnetic biochar are complex and costly, and there is an urgent need for a simple and low-cost preparation method. Summary of the invention

[0004] In order to overcome the problems of complex preparation method and high preparation cost of nitrogen-doped magnetic biochar in the prior art, one of the objects of the present invention is to provide a preparation method of nitrogen-doped magnetic biochar, the second object of the present invention is to provide a nitrogen-doped magnetic biochar, the third object of the present invention is to provide the application of nitrogen-doped magnetic biochar, and the fourth object of the present invention is to provide a method for treating metronidazole-containing wastewater.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a method for preparing nitrogen-doped magnetic biochar, comprising the following steps:

[0007] 1) adding agricultural and forestry wastes to a mixed solution of ferrous sulfate and urea, immersing, and centrifuging to obtain a solid mixture;

[0008] 2) calcining the solid mixture to obtain the nitrogen-doped magnetic biochar.

[0009] Preferably, in this preparation method, the agricultural and forestry waste includes one of peanut shells and sawdust; further preferably, the agricultural and forestry waste is sawdust; in some preferred embodiments of the present invention, the particle size of the sawdust is 0.01-0.02 cm, and the moisture content of the sawdust is 15-20%.

[0010] Preferably, in this preparation method, in step 1), the mass percentage of iron in the mixed solution of ferrous sulfate and urea is 10-20%; further preferably, the mass percentage of iron in the mixed solution of ferrous sulfate and urea is 12-18%; in some preferred embodiments of the present invention, the mass percentage of iron in the mixed solution of ferrous sulfate and urea is 15%.

[0011] Preferably, in this preparation method, in step 1), the mass percentage of nitrogen in the mixed solution of ferrous sulfate and urea is 30-40%; further preferably, the mass percentage of nitrogen in the mixed solution of ferrous sulfate and urea is 32-38%; further preferably, the mass percentage of nitrogen in the mixed solution of ferrous sulfate and urea is 35%.

[0012] Preferably, in this preparation method, in step 1), the mass volume ratio of agricultural and forestry waste to the mixed solution of ferrous sulfate and urea is 1g: (35-50)mL; further preferably, the mass volume ratio of agricultural and forestry waste to the mixed solution of ferrous sulfate and urea is 1g: (35-45)mL; even more preferably, the mass volume ratio of agricultural and forestry waste to the mixed solution of ferrous sulfate and urea is 1g: (38-42)mL.

[0013] Preferably, in this preparation method, in step 1), the immersion time is 1.5-2.5 h; more preferably, the immersion time is 1.8-2.2 h; and even more preferably, the immersion time is 2 h.

[0014] Preferably, in this preparation method, the pH of the mixed solution of ferrous sulfate and urea is 6.0-7.0; further preferably, the pH of the mixed solution of ferrous sulfate and urea is 6.2-6.8; in some preferred embodiments of the present invention, the pH of the mixed solution of ferrous sulfate and urea is 6.5.

[0015] Preferably, in this preparation method, in step 2), the solid mixture is heated to 550-650°C at a heating rate of 15-25°C / min and calcined under a protective atmosphere; further preferably, the solid mixture is heated to 550-650°C at a heating rate of 18-22°C / min and calcined.

[0016] Preferably, in this preparation method, in step 2), the calcination temperature is 550-650°C; more preferably, the calcination temperature is 580-620°C; and even more preferably, the calcination temperature is 600°C.

[0017] Preferably, in this preparation method, in step 2), the calcination time is 1.5-2.5 h; more preferably, the calcination time is 1.8-2.2 h; and even more preferably, the calcination time is 2.0 h.

[0018] Preferably, in this preparation method, in step 2), after calcination, the product is cooled to room temperature, ground, and passed through a 100-mesh sieve to obtain nitrogen-doped magnetic biochar.

[0019] A second aspect of the present invention provides a nitrogen-doped magnetic biochar, which is prepared by the above-mentioned preparation method.

[0020] Preferably, the specific surface area of ​​the nitrogen-doped magnetic biochar is 300-450 m 2 / g; Further preferably, the specific surface area of ​​nitrogen-doped magnetic biochar is 310-400m 2 / g.

[0021] Preferably, the micropore volume (Vm) of the nitrogen-doped magnetic biochar is 65-85 cm 3 / g; Further preferably, the micropore volume of nitrogen-doped magnetic biochar is 70-80cm 3 / g.

[0022] Preferably, the pore volume (Vt) of the nitrogen-doped magnetic biochar is 0.15-0.22 cm 3 / g; Further preferably, the pore volume of nitrogen-doped magnetic biochar is 0.17-0.2cm 3 / g.

[0023] Preferably, the average micropore diameter (D) of the nitrogen-doped magnetic biochar is 2.0-2.5 nm; further preferably, the average micropore diameter of the nitrogen-doped magnetic biochar is 2.15-2.25 nm.

[0024] Preferably, the mass percentage of nitrogen in the nitrogen-doped magnetic biochar is 0.5-0.6%.

[0025] Preferably, the mass percentage of iron in the nitrogen-doped magnetic biochar is 0.2-0.25%.

[0026] The third aspect of the present invention provides the use of nitrogen-doped magnetic biochar prepared by the above preparation method in treating metronidazole-containing wastewater.

[0027] A fourth aspect of the present invention provides a method for treating metronidazole-containing wastewater, comprising adding nitrogen-doped magnetic biochar and persulfate prepared by the above preparation method into the metronidazole-containing wastewater.

[0028] Preferably, in this treatment method, the dosage of nitrogen-doped magnetic biochar is 0.3-1.2 g / L.

[0029] Preferably, in this treatment method, the dosage of persulfate is 3-9 mmoL / L; further preferably, the dosage of persulfate is 5-9 mmoL / L; further preferably, the dosage of persulfate is 7 mmoL / L.

[0030] Preferably, in this treatment method, the concentration of metronidazole in the wastewater is 1-50 mg / L; further preferably, the concentration of metronidazole in the wastewater is 10-30 mg / L.

[0031] The beneficial effects of the present invention are:

[0032] 1. The present invention utilizes agricultural and forestry waste to prepare nitrogen-doped magnetic biochar in one step, which is not only beneficial to cost control but also beneficial to environmental protection. The preparation method is simple, has few process steps, low energy consumption, and is easy to achieve large-scale production. At the same time, no wastewater or sludge is generated during the preparation process, thus avoiding secondary pollution or the generation of secondary waste.

[0033] 2. The present invention utilizes the magnetic biochar modified material prepared from agricultural and forestry wastes, and only needs to add a small amount of persulfate, which has a significant removal effect on metronidazole. The product has high added value, and the removal method is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the SEM image of the nitrogen-doped magnetic biochar prepared in Example 1.

[0035] Figure 2 This is the SEM-mapping image of the nitrogen-doped magnetic biochar prepared in Example 1.

[0036] Figure 3 This is the XRD pattern of the nitrogen-doped magnetic biochar prepared in Example 1-2.

[0037] Figure 4 This is the degradation kinetics diagram of MNZ in Example 3.

[0038] Figure 5 This is a graph showing the removal of metronidazole by nitrogen-doped magnetic biochar with different activator dosages in Example 4.

[0039] Figure 6 This is a graph showing the removal of metronidazole by nitrogen-doped magnetic biochar at different PS dosages in Example 5. DETAILED DESCRIPTION

[0040] The following examples are further listed to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific data exemplified below.

[0041] Example 1

[0042] This embodiment provides a method for preparing nitrogen-doped magnetic biochar, comprising the following steps:

[0043] 1) At room temperature, 0.17 mol / L of ferrous sulfate heptahydrate and 5.35 mol / L of urea were added to deionized water, so that the mass percentage of iron in the mixed solution of ferrous sulfate and urea was 15%, the mass percentage of nitrogen was 35%, and the pH was 6.5;

[0044] 2) adding 5 g of sawdust particles washed, crushed to a particle size of 0.015 cm, and air-dried to a moisture content of 15-20% to 200 mL of a mixed solution of ferrous sulfate and urea in step 1), soaking for 2 h at room temperature, centrifuging, and discarding the supernatant to obtain a solid mixture with a moisture content of 15%;

[0045] 3) The solid mixture in step 2) was heated to 600° C. at a heating rate of 20° C. / min in a nitrogen atmosphere and calcined for 2 h, cooled to room temperature, ground, and passed through a 100-mesh sieve to obtain nitrogen-doped magnetic biochar (NMBC).

[0046] Example 2

[0047] This embodiment provides a method for preparing magnetic biochar (MBC), which differs from that of Embodiment 1 in that urea is not used.

[0048] The SEM image of the nitrogen-doped magnetic biochar prepared in Example 1 is as follows: Figure 1 As shown; the SEM-mapping image of the nitrogen-doped magnetic biochar prepared in Example 1 is as shown Figure 2 The XRD patterns of the biochars prepared in Examples 1 and 2 are shown in Figure 3 shown.

[0049] Depend on Figure 1 It can be seen that the nitrogen-doped magnetic biochar has a rough surface, well-developed pores and a honeycomb shape. Figure 2 It can be seen that Fe and N elements are mainly distributed on the surface and pore wall of nitrogen-doped magnetic biochar.

[0050] Depend on Figure 3 It can be seen that the nitrogen-doped magnetic biochar (NMBC) has the characteristic peaks of the (002) crystal plane of graphite carbon and Fe3O4 (PDF#89-0950) (compared by software Jade6.0 and XRD standard card). Figure 3 Here, NMBC fresh is the unused material prepared in Example 1, and NMBC used is the material treated for 180 min with a dosage of PS=7 mM and nitrogen-doped magnetic biochar=0.7 g / L in Example 5 of the present application.

[0051] The above shows that the present invention successfully uses agricultural and forestry wastes to prepare nitrogen-doped magnetic biochar.

[0052] The BET data of the magnetic biochar prepared in Examples 1 and 2 are shown in Table 1:

[0053] Table 1

[0054] Material Type <![CDATA[SA(m 2 / g)]]> <![CDATA[Vm(cm 3 / g)]]> <![CDATA[Vt(cm 3 / g)]]> D(nm) MBC 344.6 79.1 0.2 2.2 NMBC 310.46 71.329 0.1721 2.2171

[0055] Note: SA: specific surface area, Vm: micropore volume, Vt: pore volume, D: average micropore diameter

[0056] Example 3

[0057] Degradation experiment of PS activated by nitrogen-doped magnetic biochar to remove metronidazole:

[0058] First, take 1mM PS, wait for it to be completely dissolved, then take 0.5g / L NMBC prepared in Example 1 and 0.5g / L prepared in Example 2.

[0059] MBC was added to 250 mL conical flasks, and 100 mL of 20 mg / L metronidazole solution was added in sequence. The mixture was shaken at 250 r / min in a constant temperature oscillator at 25 ° C and protected from light. Two parallel samples were set for each group. When the preset sampling time point was reached, the reaction solution was magnetically separated. After the supernatant was filtered through a 0.22 μm filter membrane, the concentration of metronidazole in the solution was determined by high performance liquid chromatography. The results are shown in Table 1. Figure 4 .

[0060] Example 4

[0061] Degradation experiment of PS removal of metronidazole by nitrogen-doped magnetic biochar catalyzed by nitrogen-doped magnetic biochar under different nitrogen-doped magnetic biochar dosage conditions:

[0062] First, 7 mM PS was taken, and after it was completely dissolved, 0.3 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, and 1.2 g / L of nitrogen-doped magnetic biochar prepared in Example 1 were taken and added to 250 mL conical flasks respectively, and 100 mL of an initial 20 mg / L metronidazole solution was added in sequence. The mixture was oscillated at 250 r / min in a constant temperature oscillator at 25 ° C and protected from light. Two parallel samples were set for each group. When the preset sampling time point was reached, the reaction solution was magnetically separated, and the supernatant was filtered through a 0.22 μm filter membrane. The concentration of metronidazole in the solution was determined by high performance liquid chromatography. The results are shown in Table 1. Figure 5 .

[0063] Depend on Figure 5 It can be seen that when the dosage of nitrogen-doped magnetic biochar increases from 0.3g / L to 1.2g / L, the degradation effect increases by 2.5 times, reaching a removal effect of nearly 100%. This shows that the increase in the amount of activator can increase the chance of collision between PS and the activator, promoting the activation of PS to produce free radicals. In addition, when the dosage of nitrogen-doped magnetic biochar increases from 0.8g / L to 1.2g / L, the effect of nearly 100% can be achieved within 180 minutes. Therefore, in general, the dosage of 0.08g of nitrogen-doped magnetic biochar is the best choice.

[0064] Example 5

[0065] Degradation experiment of PS removal by nitrogen-doped magnetic biochar catalyzed by PS under different PS dosage conditions:

[0066] First, 3mM, 5mM, 7mM, and 9mM PS were taken, and after they were completely dissolved, 0.7g / L of nitrogen-doped magnetic biochar was taken and added to 250mL conical flasks respectively, and 100mL of the initial 20mg / L metronidazole solution was added in sequence. The mixture was oscillated at 250r / min in a constant temperature oscillator at 25°C and protected from light. Two parallel samples were set for each group. When the preset sampling time point was reached, the reaction solution was magnetically separated, and the supernatant was filtered through a 0.22μm filter membrane. The concentration of metronidazole in the solution was determined by high performance liquid chromatography. The results are shown in Table 1. Figure 6 .

[0067] The experimental results of different PS dosages in nitrogen-doped magnetic biochar / PS system are shown in Figure 2. Figure 6 As shown in the figure, when the dosage of PS increased from 3mM to 7mM, the degradation rate of MNZ increased from 62.47% to 99.66%, but when the dosage of PS continued to increase to 9mM, the degradation rate of MNZ gradually decreased to 82.21%. This shows that there is self-consumption between PS and SO4· - reacts with each other to produce SO4· -Excessive consumption reduces free radicals. Therefore, in general, the optimal dosage in the nitrogen-doped magnetic biochar / PS system is PS = 7mM and nitrogen-doped magnetic biochar = 0.7g / L.

[0068] The above tests show that the nitrogen-doped magnetic biochar activated PS prepared by the present invention has an excellent removal effect on metronidazole, which means that the scheme of preparing magnetic biochar from agricultural and forestry waste and modifying it with urea is feasible and has outstanding effects.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating wastewater containing metronidazole, characterized in that: It involves dosing nitrogen-doped magnetic biochar and persulfate into wastewater containing metronidazole; The method for preparing nitrogen-doped magnetic biochar comprises the following steps: 1) Adding agricultural and forestry wastes to a mixed solution of ferrous sulfate and urea, immersing, and centrifuging to obtain a solid mixture; 2) calcining the solid mixture to obtain the nitrogen-doped magnetic biochar; In step 2), the calcination temperature is 550-650°C; The XRD pattern of the nitrogen-doped magnetic biochar contains the (002) crystal plane of graphite carbon and the characteristic peak of Fe3O4; In step 1), the mass percentage of iron in the mixed solution of ferrous sulfate and urea is 10-20%, and the mass percentage of nitrogen is 30-40%.

2. The method for treating metronidazole-containing wastewater according to claim 1, wherein: In step 1), the mass volume ratio of the agricultural and forestry waste to the mixed solution of ferrous sulfate and urea is 1 g: (35-50) mL.

3. The method for treating metronidazole-containing wastewater according to claim 1, wherein: In step 1), the immersion time is 1.5-2.5 hours.

4. The method for treating metronidazole-containing wastewater according to claim 1, wherein: The specific surface area of ​​the nitrogen-doped magnetic biochar is 300-450m 2 / g.

5. The method for treating metronidazole-containing wastewater according to claim 1, wherein: The dosage of the nitrogen-doped magnetic biochar is 0.3-1.2 g / L; the dosage of the persulfate is 3-9 mmoL / L.

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