A magnetically derived cobalt-nitrogen-doped carbon adsorption material and its preparation method and application

Abstract

The present invention provides a magnetic-derived cobalt-nitrogen-doped carbon adsorption material and a preparation method and application thereof. The invention comprises the following steps: utilizing an in-situ synthesis method, polymerizing cobalt nitrate hexahydrate and dimethylimidazole to obtain ZIF-67(Co), reacting ZIF-67(Co) with melamine to obtain ZIF-67(Co) / melamine, and grinding dried ZIF-67(Co) / melamine powder and then subjecting the powder to high-temperature calcination and carbonization to obtain a magnetic cobalt-nitrogen-doped carbon adsorption material. The invention has the advantages of simple preparation process, mild reaction conditions, cheap and readily available raw materials, low manufacturing cost, high specific surface area, large pores, high salt tolerance, high stability, high magnetism and excellent cyclic performance, and can effectively remove malachite green from sewage, thus providing new possibilities for the industrial application of dye wastewater purification. The invention belongs to the fields of magnetic carbon material preparation and environmental science and technology.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic carbon material preparation and environmental science technology, and particularly relates to a magnetic-derived cobalt-nitrogen-doped carbon adsorption material and a preparation method and application thereof. Background Art

[0002] In recent years, adsorbents such as carbon materials, mesoporous silica, graphene-based nanocomposites, metal organic frameworks (MOFs) and other adsorption materials have been widely used in the field of adsorption. Compared with other adsorbents, carbon materials have inherent properties such as large adsorption capacity, large surface area, large yield, easy synthesis, low cost, easy regeneration, and excellent thermal stability and mechanical stability. Therefore, carbon materials have received widespread attention. In order to improve the adsorption performance of carbon materials, researchers have prepared nitrogen-doped carbon materials by doping nitrogen atoms into carbon-based materials, which increases the active sites of the adsorbent and significantly improves its adsorption performance. However, the synthesis method of nitrogen-doped carbon materials is usually more complicated, resulting in a high cost of nitrogen-doped carbon materials, which hinders their large-scale production and application.

[0003] Therefore, it is very important to develop a preparation method for nitrogen-doped carbon materials with simple preparation process, low manufacturing cost, and variable production and application scale. Summary of the Invention

[0004] The purpose of the present invention is to provide a magnetic-derived cobalt-nitrogen-doped carbon adsorption material and its preparation method and application, aiming to solve the technical problems of existing nitrogen-doped carbon materials such as complex preparation process, high manufacturing cost, and small production and application scale.

[0005] The present invention provides a method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material, comprising the following steps:

[0006] (1) Add cobalt nitrate hexahydrate to methanol and stir vigorously until dissolved to obtain solution A;

[0007] (2) adding melamine to solution A and stirring vigorously until dispersed to obtain a mixed solution B;

[0008] (3) Add 2-methylimidazole to methanol and stir vigorously until dissolved to obtain solution C;

[0009] (4) Solution C was slowly added to Solution B with vigorous stirring to obtain Solution D. Solution D was centrifuged and washed multiple times and then dried to obtain ZIF-67(Co) / melamine powder;

[0010] (5) The ground ZIF-67(Co) / melamine powder was placed in a porcelain boat and calcined at high temperature in an Ar inert gas atmosphere to obtain a magnetically derived cobalt-nitrogen-doped carbon adsorption material.

[0011] Preferably, the mass ratio of cobalt nitrate hexahydrate to melamine is 1:(0-2).

[0012] Preferably, in steps (1) to (3), the reaction temperature is room temperature, the stirring speed is 180-220 r / min, and the stirring time is 15-20 min.

[0013] Preferably, in step (4), the reaction temperature is room temperature, the stirring speed is 180-220 r / min, and the stirring time is 22-26 h.

[0014] Preferably, in step (4), the centrifugal rate is 8000 r / min, the centrifugal time is 15-25 min; the washing solution is 20 mL of methanol, and the ultrasonic time is 10-15 min; the centrifugation and washing operations are repeated 2-3 times; the drying temperature is 55-65° C., and the drying time is 12 h.

[0015] Preferably, in step (5), the high-temperature calcination temperature is 425-925°C, the heating rate is 2-3°C / min, the target temperature calcination time is 3h, and the flow rate of Ar inert gas is 40mL / min.

[0016] In the magnetic-derived cobalt-nitrogen-doped carbon adsorption material prepared by any of the above preparation methods, cobalt metal particles are loaded on the nitrogen-doped carbon material, and the magnetic-derived cobalt-nitrogen-doped carbon adsorption material has a graphite-like carbon structure.

[0017] Application of the magnetically derived cobalt-nitrogen-doped carbon adsorption material prepared by any of the preparation methods described above in the adsorption of malachite green.

[0018] Compared with the prior art, the present invention has the following beneficial effects: the present invention utilizes an in-situ synthesis method to obtain ZIF-67(Co) through the polymerization reaction of cobalt nitrate hexahydrate and dimethylimidazole, ZIF-67(Co) then reacts with melamine to obtain ZIF-67(Co) / melamine, and the dried ZIF-67(Co) / melamine powder is ground and then subjected to high-temperature calcination and carbonization to obtain a magnetic cobalt-nitrogen-doped carbon adsorption material; the magnetic-derived cobalt-nitrogen-doped carbon adsorption material prepared by the present invention has a graphite-like carbon structure, and cobalt metal particles are loaded on the nitrogen-doped carbon material, so that the magnetic-derived cobalt-nitrogen-doped carbon adsorption material has a large specific surface area, exhibits excellent adsorption performance for malachite green, and achieves adsorption of malachite green. Green adsorption and recycling; in addition, the magnetic derivative cobalt nitrogen doped carbon adsorption material prepared by the present invention has high magnetism, can be separated by a magnet, can be recycled, and its adsorption performance is still high after multiple cycles; the present invention avoids the direct reaction of cobalt nitrate hexahydrate with melamine to form insoluble granular substances by adopting a step-by-step stirring and dissolving method, so that ZIF-67 (Co) can be evenly distributed on melamine; the present invention optimizes the pore size and specific surface area of ​​the magnetic derivative cobalt nitrogen doped carbon adsorption material by regulating the mass ratio of ZIF-67 (Co) to melamine, and optimizes the structure of the magnetic derivative cobalt nitrogen doped carbon adsorption material by regulating the calcination temperature, thereby optimizing the adsorption performance of malachite green. The preparation process of the present invention is simple, the reaction conditions are mild, the raw materials are cheap and easy to obtain, the manufacturing cost is low, the production and application scales are variable, and industrial production can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is a diagram of the preparation process of the magnetically derived cobalt-nitrogen-doped carbon adsorption material of the present invention;

[0021] Figure 2 This is a relationship diagram showing the effect of the magnetically derived cobalt-nitrogen doped carbon adsorbent material obtained at different ZIF-67(Co) and melamine mass ratios on the adsorption capacity of malachite green;

[0022] Figure 3 This is a relationship diagram showing the effect of magnetically derived cobalt-nitrogen-doped carbon adsorbents obtained at different calcination temperatures on the adsorption capacity of malachite green;

[0023] Figure 4Scanning electron microscopy images (SEM images) of magnetically derived cobalt-nitrogen-doped carbon adsorbents obtained at different calcination temperatures, including (a) CNT / Co@NC-425, (b) CNT / Co@NC-525, (c) CNT / Co@NC-625, (d) CNT / Co@NC-725, (e) CNT / Co@NC-825, and (f) CNT / Co@NC-925.

[0024] Figure 5 Transmission electron microscopy images (TEM images) of the magnetically derived cobalt-nitrogen-doped carbon adsorption material CNT / Co@NC-525, where (a) is the TEM image of CNT / Co@NC-525, and (b)-(d) are the element distribution maps of C, N, and Co, respectively;

[0025] Figure 6 X-ray diffraction patterns (XRD patterns) of magnetically derived cobalt-nitrogen-doped carbon adsorption materials Co@NC and CNT / Co@NC-1.5;

[0026] Figure 7 Fourier transform infrared spectra (FT-IR spectra) of ZIF-67(Co), ZIF-67(Co) / melamine, Co@NC and CNT / Co@NC-1.5;

[0027] Figure 8 Raman spectra of magnetically derived cobalt-nitrogen-doped carbon adsorption materials Co@NC and CNT / Co@NC-1.5;

[0028] Figure 9 This is the hysteresis loop of the magnetically derived cobalt-nitrogen doped carbon adsorption material CNT / Co@NC-1.5 (VSM diagram);

[0029] Figure 10 This is the relationship diagram of the effect of adsorbent dosage on the adsorption capacity and removal efficiency of malachite green;

[0030] Figure 11 This is the relationship diagram of the effect of adsorption time and adsorption temperature of the adsorbent on the adsorption capacity of malachite green;

[0031] Figure 12 This is the relationship diagram of the effect of solution pH value on the adsorption capacity of malachite green;

[0032] Figure 13 This is a graph showing the effect of solution salinity on the adsorption capacity of malachite green;

[0033] Figure 14 This is a relationship diagram showing the effect of the number of times the adsorbent is used on the adsorption capacity and removal efficiency of malachite green. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0035] Example 1

[0036] This embodiment provides a method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material, comprising the following steps:

[0037] (1) Add 0.249 g of cobalt nitrate hexahydrate to 25 mL of methanol and stir vigorously at room temperature at 200 r / min for 15 min until the cobalt nitrate hexahydrate is dissolved to obtain a pink solution A;

[0038] (2) adding 0.374 g of melamine (i.e., the mass ratio of cobalt nitrate hexahydrate to melamine is 1:1.5) to solution A, and vigorously stirring and dispersing the mixture at a speed of 200 r / min at room temperature for 15 min to obtain a mixed solution B;

[0039] (3) 0.328 g of 2-methylimidazole was added to 25 mL of methanol and stirred vigorously at 200 rpm for 15 min at room temperature until the 2-methylimidazole was dissolved to obtain a clear solution C;

[0040] (4) Solution C was slowly added to solution B, and the mixture was vigorously stirred at 200 r / min at room temperature for 24 h to obtain solution D. Solution D was then centrifuged at 8000 r / min for 20 min, and the precipitate was collected. 20 mL of methanol was added and ultrasonically washed for 10 min. The centrifugation and washing operations were repeated twice, and the precipitate was dried in an oven at 60 °C for 12 h to obtain ZIF-67(Co) / melamine powder.

[0041] (5) The ZIF-67(Co) / melamine powder was placed in a mortar and ground thoroughly. The ground ZIF-67(Co) / melamine powder was then placed in a porcelain boat and placed in a tube furnace for high-temperature calcination at 525°C for 3 h. The initial temperature of the heating program was set to 25°C, and the heating rate was 2°C / min. During the high-temperature calcination process, Ar inert gas was introduced at a flow rate of 40 mL / min for protection. Finally, a magnetic-derived cobalt-nitrogen-doped carbon adsorption material was obtained, which was named CNT / Co@NC-1.5 or CNT / Co@NC-525. The specific preparation process is as follows: Figure 1 shown.

[0042] Example 2

[0043] The present embodiment differs from Example 1 in that, in step (2), melamine is not added (i.e., the mass ratio of cobalt nitrate hexahydrate to melamine is 1:0), and the other steps are the same to obtain ZIF-67(Co) powder, and finally obtain a magnetic-derived cobalt-nitrogen-doped carbon adsorption material, named Co@NC.

[0044] Example 3

[0045] The difference between this embodiment and Example 1 is that in step (2), 0.1246 g of melamine is added (i.e., the mass ratio of cobalt nitrate hexahydrate to melamine is 1:0.5), and the other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-0.5.

[0046] Example 4

[0047] The difference between this embodiment and Example 1 is that in step (2), 0.249 g of melamine is added (i.e., the mass ratio of cobalt nitrate hexahydrate to melamine is 1:1), and the other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-1.

[0048] Example 5

[0049] The difference between this embodiment and Example 1 is that in step (2), 0.498 g of melamine is added (i.e., the mass ratio of cobalt nitrate hexahydrate to melamine is 1:2), and the other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-2.

[0050] Example 6

[0051] The difference between this embodiment and Example 1 is that in step (5), high-temperature calcination is performed at 425°C for 3 hours. The other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-425.

[0052] Example 7

[0053] The difference between this embodiment and Example 1 is that in step (5), high-temperature calcination is performed at 625°C for 3 hours. The other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-625.

[0054] Example 8

[0055] The difference between this embodiment and Example 1 is that in step (5), high-temperature calcination is performed at 725°C for 3 hours. The other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-725.

[0056] Example 9

[0057] The difference between this embodiment and Example 1 is that in step (5), high-temperature calcination is performed at 825°C for 3 hours. The other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-825.

[0058] Example 10

[0059] The difference between this embodiment and Example 1 is that in step (5), high-temperature calcination is performed at 925°C for 3 hours. The other steps are the same, and finally a magnetic-derived cobalt-nitrogen-doped carbon adsorption material is obtained, which is named CNT / Co@NC-925.

[0060] In order to verify the reliability of the effect of the present invention, the magnetic-derived cobalt-nitrogen-doped carbon adsorption materials prepared in Examples 1 to 10 were respectively applied to malachite green adsorption tests to test their adsorption performance for malachite green.

[0061] Accurately weigh 3.5 mg of magnetically derived cobalt-nitrogen-doped carbon adsorbent material and 10 mL of malachite green solution with a concentration of 1000 mg / L and add them to a polypropylene bottle with a cap. Then place the polypropylene bottle in a floor-standing refrigerated shaker, set the temperature to 30°C and the speed to 120 r / min, take a sample at 360 min, use a magnet to magnetically separate the magnetically derived cobalt-nitrogen-doped carbon adsorbent from the sample to obtain a solution, dilute the solution, and use a UV-visible spectrophotometer to measure the absorbance of the diluted solution at a scanning rate of 200 nm / min. Repeat the measurement three times and take the average value. Then use the standard curve based on the Lamber-Beer law to calculate the concentration of malachite green in the diluted solution. Then calculate the concentration of malachite green in the solution before dilution. Finally, calculate the adsorption capacity and removal efficiency of malachite green by the magnetically derived cobalt-nitrogen-doped carbon adsorbent material according to the following formula:

[0062] Adsorption capacity (Dye removal):

[0063] Removal efficiency:

[0064] Where, C0: initial concentration of malachite green in solution (mg / L); C t : the concentration of malachite green in the solution at time t (mg / L); C e : concentration of malachite green in the solution at adsorption equilibrium (mg / L); V: volume of malachite green solution (L); M: mass of adsorbent (g); q t : adsorption capacity per unit weight of adsorbent at time t (mg / g); q e: adsorption capacity per unit weight of adsorbent at adsorption equilibrium (mg / g); Re: removal rate of malachite green.

[0065] According to the calculated adsorption capacity of the magnetic-derived cobalt-nitrogen-doped carbon adsorption material for malachite green prepared in Examples 1 to 10, a corresponding influence relationship diagram was drawn. The results are as follows: Figure 2-Figure 3 shown.

[0066] See also Figure 2 , is the relationship diagram of the effect of magnetic derivatized cobalt-nitrogen doped carbon adsorption material on the adsorption capacity of malachite green obtained at different ZIF-67(Co) and melamine mass ratios, Figure 2 It can be seen that the adsorption performance of magnetically derived cobalt-nitrogen doped carbon adsorbent material for malachite green increases significantly with the increase of the mass ratio of ZIF-67(Co) to melamine. When the mass ratio of ZIF-67(Co) to melamine is 1:1.5, CNT / Co@NC-1.5 has the best adsorption performance for malachite green. When the mass ratio of ZIF-67(Co) to melamine is 1:2, the adsorption performance of CNT / Co@NC-2 for malachite green decreases slightly. This is because after doping with melamine, the nitrogen element is introduced into the material, forming a highly dispersed stone. The ink-like carbon structure gives the material larger pores and higher specific surface area. The large specific surface area has more adsorption sites, which improves the material's adsorption performance for malachite green. However, when the amount of melamine used is too large, the excess melamine is carried away by argon during the calcination process and cannot form an effective load with ZIF-67(Co), so that the adsorption performance of CNT / Co@NC-2 no longer continues to improve. Therefore, the mass ratio of ZIF-67(Co) to melamine is preferably 1:1.5, that is, the mass ratio of cobalt nitrate hexahydrate to melamine is preferably 1:1.5.

[0067] See also Figure 3 , is the relationship diagram of the effect of magnetic derivative cobalt nitrogen doped carbon adsorption material obtained at different calcination temperatures on the adsorption capacity of malachite green, Figure 3 It can be seen that with the increase of calcination temperature, the adsorption performance of magnetic-derived cobalt-nitrogen-doped carbon adsorbent material for malachite green first increases and then decreases. When the calcination temperature is 525℃, the adsorption performance of CNT / Co@NC-525 for malachite green is the best. This is because the collapse degree of the adsorbent materials obtained at different calcination temperatures is different, resulting in different dispersion and surface roughness of the materials, which affects the adsorption active sites of the materials. Figure 4-Figure 5 shown.

[0068] See also Figure 4 , are scanning electron microscope images of magnetically derived cobalt-nitrogen-doped carbon adsorbents obtained at different calcination temperatures. Figure 4It can be seen that when the calcination temperature is 425℃, CNT / Co@NC-425 presents a better rhombic dodecahedron structure, with a smooth surface, complete structure and no large-scale collapse. It has a good degree of dispersion and can effectively adsorb malachite green. However, the color of the material is brown at this time and it has not reached the carbonization degree, so it has no magnetism. When the calcination temperature is increased to 525℃, the rhombic dodecahedron structure begins to collapse and the surface gradually becomes rough. A porous structure of carbon nanotubes entangled with each other is formed on the rough ZIF-67(Co) surface, thereby increasing the active adsorption sites and improving the adsorption capacity of the material. The color of the material is black and it has magnetism. , demonstrating carbonization. As the calcination temperature increases, the rhombic dodecahedron structure collapses dramatically, and the surface becomes rougher. Tentacle-like carbon nanotube structures appear in CNT / Co@NC-625 and CNT / Co@NC-725, resulting in a decrease in dispersion and poor contact with malachite green in solution. Consequently, the adsorption performance of the materials decreases sharply, with CNT / Co@NC-725 exhibiting the worst adsorption performance. Further increases in calcination temperature lead to agglomeration of CNT / Co@NC-825 and CNT / Co@NC-925, resulting in a decrease in specific surface area, which in turn reduces the number of active adsorption sites and the material's adsorption capacity. This suggests that the degree of dispersion and surface roughness of the magnetically derived cobalt-nitrogen-doped carbon adsorbent jointly determine its adsorption performance for malachite green, and therefore the optimal calcination temperature is 525°C.

[0069] See also Figure 5 , which is a transmission electron microscope image of the magnetically derived cobalt-nitrogen-doped carbon adsorption material CNT / Co@NC-525 and the element distribution map of C, N, and Co elements, Figure 5 It can be seen that CNT / Co@NC-525 contains uniformly distributed C, N and Co elements. The uniform distribution of N and Co elements will increase the defects of the carbon skeleton and produce more dipole centers and charge centers, which is conducive to the formation of a rich pore structure and the increase of active adsorption sites, making CNT / Co@NC-525 have excellent adsorption performance.

[0070] In summary, when the mass ratio of cobalt nitrate hexahydrate to melamine is 1:1.5 and the calcination temperature is 525℃, the prepared CNT / Co@NC-525 has the best adsorption performance for malachite green. Therefore, the optimal preparation conditions of magnetically derived cobalt-nitrogen-doped carbon adsorption material are: the mass ratio of cobalt nitrate hexahydrate to melamine is 1:1.5 and the calcination temperature is 525℃.

[0071] In order to further clarify the structure and properties of magnetically derived cobalt-nitrogen-doped carbon adsorbent materials, the magnetically derived cobalt-nitrogen-doped carbon adsorbent material CNT / Co@NC-1.5 (i.e., CNT / Co@NC-525) prepared under the optimal preparation conditions was subjected to X-ray diffraction test, Fourier transform infrared spectroscopy test, Raman spectroscopy test, and hysteresis loop test. The corresponding characterization diagrams are shown in FIG. Figure 6-Figure 9 shown.

[0072] See also Figure 6 , is the X-ray diffraction pattern of magnetically derived cobalt-nitrogen-doped carbon adsorption materials Co@NC and CNT / Co@NC-1.5, Figure 6 It can be seen that the peak of CNT / Co@NC-1.5 at 26.5C° is a typical peak of C(0 0 2), and the peak value is weak, indicating that the material has fewer carbon crystals. In addition, a series of diffraction peaks are shown at 44.1C°, 47.5C°, 51.6C° and 75.8C°, which are produced by Co(1 1 1), C(1 0 0), Co(2 0 0) and Co(2 2 0), respectively. The difference is that compared with Co@NC, the characteristic peaks of Co(1 1 1), Co(2 0 0) and Co(2 2 0) of CNT / Co@NC-1.5 are stronger, indicating that the degree of pyrolysis of CNT / Co@NC-1.5 is more severe.

[0073] See also Figure 7 , which are the Fourier transform infrared spectra of ZIF-67(Co), ZIF-67(Co) / melamine, Co@NC and CNT / Co@NC-1.5, as shown in Figure 7 As shown in the FT-IR of ZIF-67(Co), the -1 The absorption peaks at 1500-650 cm-1 are the CH stretching vibrations in the methyl and imidazole rings. -1 The absorption peak at 1583 cm is the characteristic peak of the imidazole ring. -1 The peak at 3466 cm is attributed to the stretching mode of C=N in imidazole. From the FT-IR of Co@NC, it can be seen that after calcination at 525 °C, the characteristic peak of ZIF-67(Co) disappears, indicating that the structure of ZIF-67(Co) is completely collapsed. From the FT-IR of ZIF-67(Co) / melamine, it can be seen that in addition to the characteristic peak of ZIF-67(Co), the peak at 3466 cm -1 、3413cm -1 and 3312cm -1 There is also NH stretching vibration from -NH2, and the CN bond in the melamine triazine ring at 1624cm -1 The stretching vibration of the triazine ring in melamine at 809 cm -1The out-of-plane bending mode at , the above results indicate the successful addition of melamine; from the FT-IR of CNT / Co@NC-1.5, it can be seen that the characteristic peak of ZIF-67(Co) / melamine weakens after pyrolysis at 525℃, indicating that the skeleton of ZIF-67(Co) / melamine is decomposed to form a carbon skeleton mainly composed of C=C double bonds and C=N double bonds.

[0074] See also Figure 8 , which is the Raman spectra of magnetically derived cobalt-nitrogen-doped carbon adsorption materials Co@NC and CNT / Co@NC-1.5. The Raman spectra can be used to study the degree of graphitization of Co@NC and CNT / Co@NC-1.5. Figure 8 It can be seen that both Co@NC and CNT / Co@NC-1.5 show two peaks centered at 1326 cm-1 and 1590 cm-1, corresponding to disordered carbon (D band) and graphitic carbon (G band), respectively. The relative intensity of the D band to the G band (ID / IG) can be used to evaluate the degree of graphitization of carbon-based materials. It can be seen that the ID / IG ratio of Co@NC is 0.88, and the ID / IG ratio of CNT / Co@NC-1.5 is 0.48, indicating that the degree of graphitization of CNT / Co@NC-1.5 is higher, that is, the degree of graphitization of ZIF-67(Co) doped with melamine is improved after pyrolysis.

[0075] See also Figure 9 , is the hysteresis loop of magnetically derived cobalt-nitrogen-doped carbon adsorption material CNT / Co@NC-1.5, Figure 9 It can be seen that the saturation magnetization intensity of CNT / Co@NC-1.5 is 82.59emu / g, indicating that CNT / Co@NC-1.5 has high magnetic properties, which is conducive to the separation and recycling of CNT / Co@NC-1.5 adsorption materials.

[0076] In order to further confirm the reliability of the effect of the present invention, the adsorption conditions of the magnetically derived cobalt-nitrogen-doped carbon adsorption material CNT / Co@NC-1.5 (i.e., CNT / Co@NC-525) prepared under the optimal preparation conditions were tested below.

[0077] (1) Effect of adsorbent dosage on adsorption effect

[0078] Accurately weigh 2.5 mg, 3 mg, 3.5 mg, and 4 mg of CNT / Co@NC-1.5 as adsorbents, respectively, and accurately measure 10 mL of 1000 mg / L malachite green solution as the dye solution. The adsorbent and dye solution were added to a polypropylene bottle with a cap, and then the polypropylene bottle was placed in a floor-standing refrigerated shaker. The temperature was set to 30 ° C and the speed was 120 r / min. Samples were taken at 360 min and magnetic separation was performed. The absorbance of the solution was measured using a UV-visible spectrophotometer. The adsorption capacity and removal efficiency of malachite green under different adsorbent dosages were calculated, and the corresponding influence relationship diagram was drawn. The results are shown in Figure 2. Figure 10 shown.

[0079] See also Figure 10 , is the relationship diagram of the effect of adsorbent dosage on malachite green adsorption capacity and removal efficiency, Figure 10 It can be seen that the removal efficiency of the adsorbent for malachite green increases significantly with the increase of the adsorbent dosage. When the adsorbent dosage is 3.5 mg, the removal efficiency of the adsorbent for malachite green reaches 98.89%. When the adsorbent dosage is 4 mg, the removal efficiency reaches 99.02%. The increase is not obvious, and the adsorption capacity of the adsorbent for malachite green decreases significantly with the increase of the adsorbent dosage. Therefore, considering the removal efficiency and adsorption capacity comprehensively, 3.5 mg is selected as the optimal dosage of the adsorbent CNT / Co@NC-1.5.

[0080] (2) Effect of adsorption time and adsorption temperature on adsorption effect

[0081] Accurately weigh 3.5 mg of CNT / Co@NC-1.5 as an adsorbent, accurately measure 10 mL of 1000 mg / L malachite green solution as a dye solution, add the adsorbent and dye solution into a polypropylene bottle with a cap, and place them in a floor-standing refrigerated shaker at 25°C, 30°C, and 35°C, respectively. Set the speed to 120 r / min, and take samples and perform magnetic separation at 10 min, 20 min, 30 min, 60 min, 90 min, 120 min, 180 min, 240 min, 360 min, 720 min, and 1400 min, respectively. Use a UV-visible spectrophotometer to measure the absorbance of the solution, calculate the adsorption capacity of the adsorbent for malachite green at different adsorption temperatures and adsorption times, and draw the corresponding influence relationship diagram. The results are shown in Figure 2. Figure 11 shown.

[0082] See also Figure 11 , is the relationship diagram of the effect of adsorption time and adsorption temperature on the adsorption capacity of malachite green, Figure 11It can be seen that with the increase of contact time, the adsorption capacity of the adsorbent for malachite green increases rapidly, and then the growth rate gradually slows down until it reaches equilibrium. When the adsorption time is about 360 minutes, the adsorbent reaches adsorption equilibrium for malachite green, so 360 minutes is selected as the optimal adsorption time of the adsorbent CNT / Co@NC-1.5; in addition, with the increase of adsorption temperature, the adsorption capacity of the adsorbent for malachite green also increases. This is because the adsorption process is an endothermic reaction, and the increase in temperature is conducive to the adsorption process. The increase in temperature helps the diffusion of malachite green and is more conducive to the interaction between malachite green and the adsorption site. Therefore, 35°C is selected as the optimal adsorption temperature of the adsorbent CNT / Co@NC-1.5.

[0083] (3) Effect of solution pH on adsorption effect

[0084] Use 0.1mol / L HCl and NaOH to adjust the pH value of the dye solution to pH=3, pH=4, pH=5, pH=6, pH=7, pH=8, pH=9, and pH=10, respectively. Accurately weigh 3.5mg of CNT / Co@NC-1.5 as an adsorbent, and accurately measure 10mL of 1000mg / L malachite green solution with different pH values ​​as dye solutions. Add the adsorbent and dye solution to a polypropylene bottle with a cap, and then place it in a floor-standing refrigerated shaker at 35°C. Set the speed to 120r / min, take samples at 360min, perform magnetic separation, and measure the absorbance of the solution using a UV-visible spectrophotometer. Calculate the adsorption capacity of the adsorbent for malachite green at different pH values, and draw the corresponding influence relationship diagram. The results are shown in Figure 2. Figure 12 shown.

[0085] See also Figure 12 , is the relationship diagram of the effect of solution pH value on the adsorption capacity of malachite green, Figure 12 It can be seen that when the pH of the dye solution is 3, the adsorption capacity of the adsorbent for malachite green is low. When the pH of the dye solution is 4, the adsorption capacity of the adsorbent increases. As the pH value continues to increase, the adsorption capacity of the adsorbent does not change significantly, which shows that the pH value has no obvious effect on the adsorption capacity of the adsorbent CNT / Co@NC-1.5. It can be concluded that the force between the adsorbent and malachite green is not electrostatic, but adsorption is achieved through other forces. The aromatic skeleton benzene ring of malachite green interacts with the adsorbent CNT / Co@NC-1.5 through π-π stacking. At the same time, it also proves the high stability of the adsorbent CNT / Co@NC-1.5, and it still maintains excellent adsorption performance under high alkali and high acid conditions, which is conducive to the industrial application and promotion of the adsorbent.

[0086] (IV) Effect of solution salinity on adsorption effect

[0087] Use 0.1mol / L NaCl to adjust the salinity of the dye solution to 0mg / L, 500mg / L, 1000mg / L, 1500mg / L, and 2000mg / L, respectively. Accurately weigh 3.5mg of CNT / Co@NC-1.5 as an adsorbent, and accurately measure 10mL of 1000mg / L malachite green solution with different salinities as dye solutions. Add the adsorbent and dye solution to a polypropylene bottle with a cap, and then place it in a floor-standing refrigerated shaker at 35°C. Set the speed to 120r / min, take samples at 360min, perform magnetic separation, and measure the absorbance of the solution using a UV-visible spectrophotometer. Calculate the adsorption capacity of the adsorbent for malachite green at different salinities, and draw the corresponding influence relationship diagram. The results are shown in Figure 2. Figure 13 shown.

[0088] See also Figure 13 , is the relationship diagram of the effect of solution salinity on the adsorption capacity of malachite green, Figure 13 It can be seen that under the salinity of 0-2000 mg / L, the adsorption performance of the adsorbent did not change at all, and the adsorbent still maintained a high activity, which showed that salinity had no effect on the adsorption process. + and Cl - It does not compete with malachite green for adsorption, which once again verifies that the adsorbent does not adsorb malachite green through an ionic action mechanism. The adsorbent CNT / Co@NC-1.5 exhibits excellent salt tolerance.

[0089] (5) The influence of the number of times the adsorbent is used on the adsorption effect

[0090] By studying the number of times the magnetic-derived cobalt-nitrogen-doped carbon adsorbent material can be reused in malachite green dye, the reusability of the adsorbent is verified, and then the practical applicability of the adsorbent is verified.

[0091] Accurately weigh 3.5 mg of CNT / Co@NC-1.5 as the adsorbent, and accurately measure 10 mL of 1000 mg / L malachite green solution as the dye solution. The adsorbent and dye solution were added to a polypropylene bottle with a cap and placed in a floor-standing refrigerated shaker at 35°C with a speed set at 120 r / min. Samples were taken at 360 min, and the adsorbent was magnetically separated from the sample using a magnet to obtain the solution and adsorbent. The absorbance of the solution was measured using a UV-visible spectrophotometer, and the adsorption capacity and removal efficiency of the adsorbent for malachite green were calculated. The adsorbent was washed with anhydrous ethanol as the desorption solvent to elute the malachite green until the anhydrous ethanol flowing down was colorless. The adsorbent was then washed with deionized water and dried at 60°C. After drying, the adsorbent was added to a new malachite green solution for a second adsorption test. This cycle was repeated until the adsorbent underwent four consecutive cycles. Each adsorption, desorption, and measurement were performed under the same conditions.

[0092] According to the calculated adsorption capacity and removal efficiency of the adsorbent in each adsorption test, the corresponding influence relationship diagram is drawn. The results are as follows: Figure 14 shown.

[0093] See also Figure 14 , which is the relationship between the number of times the adsorbent is used and the adsorption capacity and removal efficiency of malachite green, as shown in Figure 14 As shown in the figure, after four cycles of adsorption and desorption tests, the adsorption capacity and removal efficiency of malachite green by the adsorbent CNT / Co@NC-1.5 decreased significantly with the increase in the number of cycles. The reason may be that the amount of adsorbent used is too small, and a part of the adsorbent is lost during the elution and desorption process. In addition, during the adsorption process, the malachite green on the active sites of some adsorbents is not eluted, which leads to a decrease in the adsorption performance of the adsorbent. In the fourth adsorption test, the removal efficiency of malachite green by the adsorbent CNT / Co@NC-1.5 was about 72.87%, indicating that the adsorbent CNT / Co@NC-1.5 has good regeneration performance and stability.

[0094] In summary, the adsorption performance of adsorbent CNT / Co@NC-1.5 is best when the adsorbent dosage is 3.5 mg, the adsorption temperature is 35 °C, and the adsorption time is 360 min. Therefore, the optimal adsorption conditions of adsorbent CNT / Co@NC-1.5 are: dosage 3.5 mg, adsorption temperature 35 °C, and adsorption time 360 ​​min.

[0095] The invention discloses an application of the magnetically derived cobalt-nitrogen-doped carbon adsorption material prepared by the invention in adsorbing malachite green.

[0096] The present invention provides a magnetic-derived cobalt-nitrogen-doped carbon adsorption material, a preparation method and application thereof. The preparation process is simple, the reaction conditions are mild, the raw materials are cheap and easily available, and the manufacturing cost is low. The prepared magnetic-derived cobalt-nitrogen-doped carbon adsorption material has a high specific surface area, large pores, high salt tolerance, high stability, high magnetism and excellent circulation performance, and can be used for the treatment of malachite green wastewater, providing new possibilities for the industrial application of dye wastewater purification.

[0097] It should be noted that the raw materials, devices and instruments used in the present invention are conventional commercially available products unless otherwise specified.

[0098] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material for adsorbing malachite green, characterized in that: The following steps are involved: (1) Add cobalt nitrate hexahydrate to methanol and stir vigorously until dissolved to obtain solution A; (2) Add melamine to solution A and stir vigorously until dispersed to obtain a mixed solution B; (3) Add 2-methylimidazole to methanol and stir vigorously until dissolved to obtain solution C; (4) Solution C was slowly added to solution B with vigorous stirring to obtain solution D. Solution D was centrifuged and washed several times and then dried to obtain ZIF-67(Co) / melamine powder; (5) The ground ZIF-67(Co) / melamine powder was placed in a porcelain boat and calcined at high temperature in an Ar inert gas atmosphere to obtain a magnetically derived cobalt-nitrogen-doped carbon adsorption material; In step (1) to step (2), the mass ratio of cobalt nitrate hexahydrate to melamine is 1:(1-2); In step (5), the high-temperature calcination temperature is 525°C, the heating rate is 2-3°C / min, the calcination time is 3h, and the flow rate of Ar inert gas is 40mL / min; The magnetically derived cobalt-nitrogen-doped carbon adsorption material has a graphite-like carbon structure, and cobalt metal particles are loaded on the nitrogen-doped carbon material.

2. The method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material for adsorbing malachite green according to claim 1, characterized in that: In steps (1) to (3), the reaction temperature is room temperature, the stirring speed is 180-220 r / min, and the stirring time is 15-20 min.

3. The method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material for adsorbing malachite green according to claim 1, characterized in that: In step (4), the reaction temperature is room temperature, the stirring speed is 180-220 r / min, and the stirring time is 22-26 h.

4. The method for preparing a magnetically derived cobalt-nitrogen-doped carbon adsorption material for adsorbing malachite green according to claim 1, characterized in that: In step (4), the centrifugal speed is 8000 r / min, the centrifugal time is 15-25 min; the washing solution is 20 mL of methanol, and the ultrasonic time is 10-15 min; the centrifugation and washing operations are repeated 2-3 times; the drying temperature is 55-65°C, and the drying time is 12 h.

5. A magnetically derived cobalt-nitrogen-doped carbon adsorption material prepared by the preparation method according to any one of claims 1 to 4, characterized in that: Cobalt metal particles are loaded on the nitrogen-doped carbon material, and the magnetically derived cobalt nitrogen-doped carbon adsorption material has a graphite-like carbon structure.

6. Use of a magnetically derived cobalt-nitrogen-doped carbon adsorption material prepared by the preparation method according to any one of claims 1 to 4 in the adsorption of malachite green.

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