Preparation method and application of a material co-loaded with zero-valent iron particles by graphene and surface iron oxide

Abstract

The present invention provides a preparation method and application of a material with surface iron oxide graphene co-loaded zero-valent iron particles, belonging to the technical fields of environmental remediation and material preparation. The preparation method of this material is to first prepare a zero-valent iron particle material with a clean surface, then use a chemical oxidation method to prepare graphene oxide with a large number of oxygen-containing functional groups, and finally through a reduction reaction, co-load iron oxide and graphene on the surface of zero-valent iron to obtain a material with surface iron oxide graphene co-loaded zero-valent iron particles. The reduction loading method used in the present invention firmly binds graphene and iron oxide to the surface of zero-valent iron through covalent interaction, greatly improving the surface electrochemical activity and stability of the material, enabling the specific induction of iron oxide with high conductivity and magnetism to form on the material surface, improving the material activity, and prolonging the service life of the material. The material of the present invention is safe and non-toxic, and is suitable for the efficient and stable treatment of water bodies contaminated by nitrates.

Description

Technical Field

[0001] The present invention belongs to the technical fields of environmental remediation and material preparation, and particularly relates to a preparation method and application of a surface iron oxide graphene co-loaded zero-valent iron particle material. Background Art

[0002] With the continuous development of social economy, the nitrate pollution problem in different industrial and agricultural wastewaters has become increasingly serious. When it enters water bodies, it will not only cause water eutrophication, damage the aquatic ecosystem, lead to the formation of black and odorous water bodies, but also endanger human health, resulting in methemoglobinemia. At present, the problem of excessive nitrate concentration has seriously threatened the water quality safety of drinking water sources. Therefore, exploring an efficient means for nitrate removal has become the focus of increasing attention.

[0003] Zero-valent iron is an environmental functional material with the ability to treat various types of pollution. Due to its low-cost advantage, it has been widely used to construct permeable reactive walls for the treatment of different pollutants in groundwater. Zero-valent iron can remove nitrate pollution in water bodies through reduction. However, during the interfacial reaction between zero-valent iron and pollutants, different iron oxides will be generated on the surface according to different chemical microenvironments. Iron oxides without electron transfer performance may hinder the redox reaction between pollutants and zero-valent iron, reducing the surface reaction activity of the material. Therefore, it is necessary to modify its interfacial microenvironment to induce the formation of iron oxides with excellent electron transfer performance during the interfacial reaction, thereby improving the utilization rate of zero-valent iron.

[0004] Graphene is a single-layer carbon atom material formed by sp2 hybridized carbon atoms arranged in a honeycomb network structure in a two-dimensional plane. The unique structure of graphene endows it with special properties, such as high thermal conductivity, large specific surface area, high electron mobility, and high tensile strength. Therefore, since graphene was first discovered in 2004, it has been widely studied and applied in various fields such as energy, electrical appliances, sensing, wearables, anti-corrosion, and the environment. Enhancing the interfacial electron transfer process of zero-valent iron by graphene is a valuable research direction for solving the surface passivation problem of zero-valent iron. Therefore, exploring the stable fixation of graphene on the surface of zero-valent iron particle materials while realizing the stable induction of the formation of iron oxides with excellent electron transfer performance during the reduction of pollutants is very important for improving the stability and activity of zero-valent iron-based materials.

[0005] More of the related prior arts load nano zero-valent iron on the surface of graphene. For example, the patent application number CN202110995249.0 discloses an rGO-ZVI nanocomposite material, and the preparation method includes: dissolving graphene oxide powder in deionized water to obtain a first mixed solution after ultrasonic dispersion; adding tea polyphenols into the first mixed solution and stirring well to obtain a second mixed solution; adding ferrous sulfate into the second mixed solution and stirring for a certain time to obtain a third mixed solution; adding tea polyphenols into deionized water and stirring evenly to obtain a fourth mixed solution; finally, adding the fourth mixed solution into the third mixed solution, stirring for a certain time to obtain a fifth mixed solution, and washing and drying the fifth mixed solution in sequence to prepare the rGO-ZVI nanocomposite material. However, this synthesis method has the following defects: (1) Using externally added tea polyphenols as a reducing agent to reduce divalent iron ions to prepare the graphene-nano zero-valent iron composite material has a low yield, high cost, and is difficult to mass-produce; (2) Nano zero-valent iron is prone to agglomeration, the surface reduction reaction process is difficult to control, and the stability is poor. Therefore, a zero-valent iron-based material with low cost, stable and controllable structure is needed. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a material of graphene co-loaded with zero-valent iron particles on the surface of iron oxide, its preparation method and application. By covalently binding graphene to the iron oxide on the surface of zero-valent iron, graphene is fixed on the surface of zero-valent iron, realizing the efficient removal of nitrate pollution in water under different environmental conditions, and the activity of the material can be stably maintained for a long time.

[0007] To achieve the above purpose, the following technical solutions are adopted in the present invention:

[0008] A preparation method of a material of graphene co-loaded with zero-valent iron particles on the surface of iron oxide, which includes the following steps:

[0009] S1. Mix the reduced zero-valent iron powder with an acid solution and then perform ultrasonic treatment. After treatment, separate the liquid and solid, wash the solid product, and after drying, obtain zero-valent iron with a clean surface, and store it in vacuum or in an inert gas environment;

[0010] S2. Prepare or obtain graphene oxide;

[0011] S3. Add the graphene oxide obtained in step S2 and the zero-valent iron obtained in step S1 to water, mix and react under anaerobic conditions, then perform solid-liquid separation, wash the solid product, vacuum dry it, and then slowly introduce air into the container to atmospheric pressure to obtain the material of graphene co-loaded with zero-valent iron particles on the surface of iron oxide.

[0012] Among them, the order of steps S1 and S2 can be interchanged.

[0013] The preparation method as described above, preferably, in step S1, the acid solution is sulfuric acid or hydrochloric acid solution, the concentration of the acid solution is 1-5 mol / L, and the mass-volume ratio of zero-valent iron to hydrochloric acid solution in units of g / mL is 1:1-100.

[0014] The preparation method as described above, preferably, in step S1, the ultrasonic treatment is carried out under anaerobic conditions, the power of the ultrasonic is 250-500 W, and the time of the ultrasonic is 24-72 h.

[0015] According to the differences in the particle size of the zero-valent iron raw material particles and the types and thicknesses of the native iron oxide shells on the surface, hydrochloric acid with different concentrations is used, preferably 1-5 mol / L; the ratio of zero-valent iron to hydrochloric acid and the power of the ultrasonic ensure that the surface of the raw material is clean without excessive loss of the raw material, preferably carried out at a mass-volume ratio of zero-valent iron to hydrochloric acid solution in units of g / mL of 1:1-100.

[0016] The preparation method as described above, preferably, in step S2, the method for preparing graphene oxide is to add graphite powder and NaNO3 to concentrated H2SO4 at a temperature of 1-5 °C, carry out a stirring reaction, add KMnO4 and continue stirring, heat up to 25-40 °C and continue the reaction for 1-2 h, then add deoxygenated deionized water, continue heating up to 90-98 °C and continue stirring and reacting for 1-2 h, add hydrogen peroxide, and after no bubbles are generated, carry out solid-liquid separation. The obtained solid material is washed with deionized water until the washing liquid is neutral, and graphene oxide is obtained after drying.

[0017] The preparation method as described above, preferably, in step S2, the concentration of graphite powder in concentrated sulfuric acid is 40-60 g / L, the concentration of NaNO3 in concentrated sulfuric acid is 20-30 g / L, and the stirring reaction is carried out for 0.5-1 h after adding NaNO3; the dosage of KMnO4 is such that its concentration in concentrated sulfuric acid is 150 g / L, and stirring is carried out for 1-2 h after adding KMnO4; the dosage ratio of deionized water to concentrated sulfuric acid is 2:5; the dosage of hydrogen peroxide is such that its final concentration is 1-2% to terminate the oxidation reaction.

[0018] The preparation method as described above, preferably, in step S3, the mass ratio of graphene oxide to zero-valent iron is 1:1-100, and the concentration of zero-valent iron is 1-100 g / L. The temperature of the mixing reaction is 25-30 °C, and the reaction time is 1-20 h; under sealed conditions, constant-temperature oscillation culture is carried out at a speed of 150 rpm;

[0019] Washing is to wash the material with anaerobic deionized water until the pH of the washing liquid is neutral;

[0020] Drying is carried out by vacuum drying, and after vacuum drying, air is slowly introduced into the container at a flow rate of 1-100 mL / min.

[0021] A surface iron oxide graphene co-loaded zero-valent iron particle material is obtained by the above preparation method. Application of the surface iron oxide graphene co-loaded zero-valent iron particle material in removing nitrate.

[0022] For the application as described above, preferably, when the surface iron oxide graphene co-loaded zero-valent iron particle material is applied in removing nitrate-containing water bodies, its addition amount is 1-10 g / L, and magnetic separation is used after application to achieve rapid recovery and reuse of the material. The surface iron oxide graphene co-loaded zero-valent iron particle material can be reused.

[0023] The beneficial effects of the present invention are as follows:

[0024] The preparation method of a surface iron oxide graphene co-loaded zero-valent iron particle material provided by the present invention first prepares a surface-cleaned zero-valent iron particle material, then prepares graphene oxide with a large number of oxygen-containing functional groups by chemical oxidation method, and finally co-loads iron oxide and graphene on the surface of zero-valent iron through a reduction reaction to obtain a surface iron oxide graphene co-loaded zero-valent iron particle material. This method successfully prepares a surface iron oxide graphene co-loaded zero-valent iron particle material by an oxidation-reduction method. Since the graphene on the material surface forms a stable covalent bond with iron oxide during the oxidation-reduction process, the surface structure of the material is stable.

[0025] The graphene carbon material on the surface of the surface iron oxide graphene co-loaded zero-valent iron particle material prepared by the present invention and zero-valent iron constitute an iron / carbon micro-electrolysis structure, greatly improving the surface electrochemical activity of the material, increasing the surface active sites of the material, and improving the reaction efficiency of pollutants.

[0026] During the process of preparing the surface iron oxide graphene co-loaded zero-valent iron particle material of the present invention, the iron oxide on the material surface is formed by the reaction of zero-valent iron with the oxygen-containing functional groups on the surface of graphene oxide. During the formation process, the Fe-O-C hyperconjugation effect is strengthened, so that the iron oxide formed on the surface is specifically transformed into an iron oxide with good electrochemical activity. Under the induction of the Fe-O-C hyperconjugation effect, the newly formed iron oxide during the reaction process of the material with nitrate pollution also has good electrochemical activity, so that the reaction activity of the material under different conditions is good, and at the same time the service life is greatly extended.

[0027] The reduction loading method used in the present invention firmly binds graphene and iron oxide to the surface of zero-valent iron through covalent interaction, greatly improving the surface electrochemical activity and stability of the material, enabling the specific induction of iron oxide with high conductivity and magnetism to form on the material surface, improving the material activity, and extending the service life of the material. The material of the present invention is safe and non-toxic and is suitable for efficiently and stably treating water bodies polluted by nitrate.

[0028] Simple zero-valent iron-based materials are magnetic and can be conveniently applied in water treatment magnetic separation technology. However, due to the accumulation of surface pollutants and non-magnetic iron oxides during use, the magnetism of the materials decreases significantly with the increase in the number of uses. In the process of the reaction of the surface iron oxide graphene co-loaded zero-valent iron particle material of the present invention with nitrate, the newly formed surface iron oxide also maintains good magnetism under the induction of the Fe-O-C hyperconjugation effect. Therefore, the service life of the material as a magnetic separation material can be greatly extended. Description of the Drawings

[0029] Figure 1 SEM image of the material prepared in Example 1.

[0030] Figure 2 EDX spectrum of the material prepared in Example 1.

[0031] Figure 3 Infrared spectrum of the material prepared in Example 1.

[0032] Figure 4 XRD pattern of the surface iron oxide graphene co-loaded zero-valent iron particle material after repeated use for nitrate removal prepared in Example 1.

[0033] Figure 5 Efficiency graph of the surface iron oxide graphene co-loaded zero-valent iron particle material prepared in Example 1 of the present invention for repeated use in nitrate removal. Detailed Description of the Invention

[0034] The present invention provides a preparation method for a surface iron oxide graphene co-loaded zero-valent iron particle material, comprising the following steps:

[0035] S1. Mix zero-valent iron with an acid solution and perform ultrasonic treatment. After the reaction ends, separate the reactants in the solution by solid-liquid separation under the action of an external magnetic field, wash the solid product, and vacuum dry it to obtain surface-clean zero-valent iron, which is stored in vacuum or in an inert gas environment;

[0036] S2. Mix graphite powder, concentrated H2SO4, NaNO3, and KMnO4 for reaction to obtain graphene oxide;

[0037] S3. Mix graphene oxide and surface-clean zero-valent iron for reaction under anaerobic conditions. After the reaction ends, separate the reactants in the solution by solid-liquid separation under the action of an external magnetic field, wash the solid product, and vacuum dry it. After the material is vacuum dried, introduce air into the vacuum container at a flow rate of 1-100 mL / min until atmospheric pressure is reached to obtain a surface iron oxide graphene co-loaded zero-valent iron particle material, which is stored under dry conditions.

[0038] Further, in the step S1, the preferred concentration of the acid solution is hydrochloric acid with a concentration of 1-5 mol / L, the mass-volume ratio of zero-valent iron to the acid solution is 1:(1-100) (g / mL), the reaction is carried out under anaerobic conditions, the power of ultrasonic wave is 250-500 W, and the time of ultrasonic wave is 24-72 h. According to the differences in the particle size of the zero-valent iron raw material particles and the types and thicknesses of the native iron oxide shells on the surface, hydrochloric acid with different concentrations is used, preferably 1-5 mol / L; the ratio of zero-valent iron to hydrochloric acid and the power of ultrasonic wave ensure that the surface of the raw material is clean without excessive loss of raw material, and preferably the ratio of zero-valent iron to hydrochloric acid solution in terms of mass-volume ratio with the unit of g / mL is 1:1-100.

[0039] Further, in the step S2, first stir concentrated H2SO4 in a water bath at 1-5 °C, then slowly add graphite powder to concentrated H2SO4 to 40-60 g / L, then add NaNO3 to 20-30 g / L and react for 0.5-1 h, then add KMnO4 to 150 g / L and continue to react for 1-2 h, raise the water bath temperature to 25-40 °C and continue to react for 1-2 h, add deionized water and raise the water bath temperature to 90-98 °C and react for 1-2 h. During the reaction process, the addition of samples and the heating process in each step should be slow and fully stirred to ensure that the graphite carbon layers are in full contact with the oxidant and are fully oxidized, preventing overly intense local reactions. Finally, slowly add 30% hydrogen peroxide to a final concentration of 1-2% to terminate the oxidation reaction. After the reaction is completed, wash with deionized water until neutral, and dry to obtain graphene oxide.

[0040] Further, in the step S3, the mass ratio of graphene oxide to the surface-cleaned zero-valent iron is 1:(1-100), the reaction temperature during preparation is 25-30 °C, the reaction time is 1-20 h, and the reaction is carried out under anaerobic conditions. While reducing graphene oxide to graphene with excellent surface electrochemical properties through the reduction of zero-valent iron, the iron oxides generated by the oxidation of zero-valent iron form covalent bonds with the oxygen-containing functional groups on the surface of graphene oxide and are stably loaded on the surface of zero-valent iron. After the material is vacuum dried, slowly introduce air into the container at a flow rate of 1-100 mL / min. The ventilation process should not be too fast to prevent uneven formation of iron oxides on the material surface.

[0041] The following examples are used to further illustrate the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, any modification or replacement made to the present invention belongs to the scope of the present invention.

[0042] Unless otherwise specified, all technical and scientific terms used in the present invention, if not elaborated in detail, shall have the same meanings as those commonly understood by those skilled in the technical field of the present invention. The technical means used in the examples are conventional means well-known to those skilled in the art. Unless otherwise specified, the raw materials used are all ordinary commercially available products. The deoxygenated deionized water used in the following examples is obtained by charging high-purity nitrogen into deionized water for 1 h and then placing it in an anaerobic glove box for 24 h. The pH being neutral means pH = 7.

[0043] Example 1

[0044] (1) Weigh 1 g of commercially available 100-mesh reduced zero-valent iron powder. Dilute concentrated hydrochloric acid to 1 mol / L with deoxygenated deionized water. Mix zero-valent iron and 100 mL of diluted hydrochloric acid in an anaerobic glove box and ultrasonically treat for 24 h at a power of 250 W. After the ultrasonic treatment, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, and wash the zero-valent iron with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the clean zero-valent iron to a vacuum drying oven for drying and store it under vacuum conditions or in an inert gas environment to obtain clean zero-valent iron.

[0045] (2) Place 100 mL of 98% concentrated sulfuric acid in a beaker, continuously stir (300 rmp) under a water bath condition at 4°C, add 5 g of graphite powder and 2.5 g of NaNO3, after reacting for 0.5 h, add 15 g of KMnO4 and continue to stir for 1.5 h, raise the water bath temperature to 40°C and continue to stir for 1 h, then add 250 mL of deionized water and raise the water bath temperature to 95°C, continue to stir for 1 h and then add 20 mL of 30% hydrogen peroxide. After no bubbles are generated, obtain the solid by centrifugation (8000 rmp, 3 min), wash the material with deionized water until the washing solution is neutral, and dry to obtain graphene oxide.

[0046] (3) Weigh 0.2 g of the graphene oxide obtained in step (2) in an anaerobic glove box, suspend it in 100 mL of deoxygenated deionized water, weigh 5 g of the clean zero-valent iron obtained in step (1) into the solution, seal the reaction flask, and place it in a constant temperature shaking incubator at 30°C and shake and culture at a speed of 150 rpm for 16 h. After the reaction ends, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, and wash the material with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the material to a vacuum drying oven. After the material is vacuum dried, introduce dry air into the vacuum drying oven at a flow rate of 10 mL / min until the atmospheric pressure is reached, and store the material in dry air.

[0047] Example 2

[0048] This example is based on Example 1 and adjusts the following parameters.

[0049] Step (3) Weigh 0.01 g of graphene oxide in an anaerobic glove box, suspend it in 100 mL of deoxygenated deionized water, weigh 5 g of clean zero-valent iron into the solution, seal the reaction flask, place it in a constant temperature shaking incubator at 30 °C and shake it at a speed of 150 rpm for 16 h. After the reaction is completed, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, wash the material with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the material to a vacuum drying oven. After the material is vacuum dried, introduce dry air into the vacuum drying oven at a flow rate of 10 mL / min and store the material in dry air.

[0050] Example 3

[0051] This example is based on Example 1 and adjusts the following parameters.

[0052] Step (3) Weigh 0.05 g of graphene oxide in an anaerobic glove box, suspend it in 100 mL of deoxygenated deionized water, weigh 5 g of clean zero-valent iron into the solution, seal the reaction flask, place it in a constant temperature shaking incubator at 30 °C and shake it at a speed of 150 rpm for 16 h. After the reaction is completed, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, wash the material with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the material to a vacuum drying oven. After the material is vacuum dried, introduce dry air into the vacuum drying oven at a flow rate of 10 mL / min and store the material in dry air.

[0053] Example 4

[0054] This example is based on Example 1 and adjusts the following parameters.

[0055] Step (3) Weigh 0.5 g of graphene oxide in an anaerobic glove box, suspend it in 100 mL of deoxygenated deionized water, weigh 5 g of clean zero-valent iron into the solution, seal the reaction flask, place it in a constant temperature shaking incubator at 30 °C and shake it at a speed of 150 rpm for 16 h. After the reaction is completed, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, wash the material with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the material to a vacuum drying oven. After the material is vacuum dried, introduce dry air into the vacuum drying oven at a flow rate of 10 mL / min and store the material in dry air.

[0056] The materials prepared in the above embodiments were characterized by field emission scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results of field emission scanning electron microscopy (SEM) showed that there were irregular wrinkles formed by the overlapping of a large number of flake structures on the surface of the materials. By determining the surface element composition with energy dispersive X-ray spectroscopy (EDX), it was found that such surface flake structures were mainly composed of Fe, O, and C elements, which was in line with the characteristics of co-loading of surface iron oxide and graphene, that is, a material with co-loaded surface iron oxide and graphene on zero-valent iron particles was obtained. Taking the surface morphology characteristics of the surface iron oxide graphene co-loaded zero-valent iron particle material prepared in Example 1 as an example, the results of field emission scanning electron microscopy were as Figure 1 shown, where the magnification of the left figure was 1000 times and that of the right figure was 5000 times, and the scale bar in the figure was 10 μm; the energy dispersive X-ray spectrogram was as Figure 2 shown.

[0057] The surface functional groups of the surface iron oxide graphene co-loaded zero-valent iron particle material were determined by Fourier transform infrared spectrometer (FTIR), and the X-ray diffractometer (XRD) was used to determine the changes in the crystal phase structure of the surface iron oxide graphene co-loaded zero-valent iron particle material and after being used multiple times for nitrate pollution removal.

[0058] The results of Fourier transform infrared spectrometer (FTIR) showed that there were three main functional groups on the surface of the surface iron oxide graphene co-loaded zero-valent iron particle material, namely -OH at about 3400 cm -1 -1, C=C at about 1550 cm -1 -1, and Fe-O-C at about 565 cm -1 -1. The main source of -OH was the residual iron oxide on the material surface and the incomplete reduction of graphene oxide; C=C came from the interaction of sp2 carbon atoms in the graphene plane. Compared with the infrared peak of sp2 carbon in pure graphene (at about 1600 cm -1 -1), the infrared peak of C=C on the surface of the surface iron oxide graphene co-loaded zero-valent iron particle material had a large shift, which was one of the main evidences of its strong interaction with Fe atoms; the high-intensity Fe-O-C peak on the surface of the surface iron oxide graphene co-loaded zero-valent iron particle material was one of the main evidences of the covalent binding between graphene and iron oxide. Taking the surface morphology characteristics of the surface iron oxide graphene co-loaded zero-valent iron particle material prepared in Example 1 as an example, it was specifically as Figure 3 shown.

[0059] The X-ray diffractometer (XRD) only detected the zero-valent iron crystal peaks at 44.7°, 65.1° and 82.5° in the surface iron oxide graphene co-loaded zero-valent iron particle material, indicating that the surface iron oxide graphene only existed in a small amount on the material surface. After using this material multiple times for nitrate removal from water, Fe3O4 appeared on the material surface, indicating that the iron oxide graphene co-loading present on the material surface could specifically induce the formation of Fe3O4 on the material surface during the nitrate removal process. Fe3O4 has high conductivity and magnetism and does not hinder the electrochemical reaction process between zero-valent iron and pollutants, which can effectively ensure the service life of the material. Taking the surface morphology characteristics of the surface iron oxide graphene co-loaded zero-valent iron particle material prepared in Example 1 as an example, specifically as Figure 4 . The characterization results of other examples are not much different from those of Example 1.

[0060] Comparative Example 1

[0061] Weigh 5 g of commercially available 100-mesh reduced zero-valent iron powder, dilute concentrated hydrochloric acid to 1 mol / L with deoxygenated deionized water, mix zero-valent iron and 100 mL of diluted hydrochloric acid in an anaerobic glove box, ultrasonically treat for 24 h at a power of 250 W. After the ultrasonic treatment, fix the zero-valent iron in the solution at the bottom of the reaction vessel under the action of an external magnetic field, discard the supernatant, and wash the zero-valent iron with anaerobic deionized water until the pH of the washing solution is neutral. Transfer the material to a vacuum drying oven for drying. After the material is vacuum dried, introduce dry air into the vacuum drying oven at a flow rate of 10 mL / min and store the material in dry air.

[0062] Comparative Example 2

[0063] Weigh 0.2 g of commercially available graphene oxide and suspend it in 100 mL of deionized water. Weigh 5 g of commercially available 100-mesh zero-valent iron and add it to the solution. After sealing the reaction flask, place it in a constant temperature shaking incubator at 30 °C and shake it at a speed of 150 rpm for 16 h. After the reaction is completed, wash the material with deionized water until the pH of the washing solution is neutral. Store the material in dry air after drying. Performance test for nitrate reduction

[0064] Apply the materials prepared in the above examples and comparative examples to the treatment of nitrate-polluted water bodies. The specific experimental process is as follows: The following processes are all carried out in an anaerobic glove box. Put 50 mL of anaerobic deionized water in a 100 mL reaction flask, add nitrate to make its concentration 200 mg / L, and then add 0.3 g of the material prepared in the example or comparative example. After sealing the reaction flask, place it in a constant temperature oscillator at 25 °C and continuously shake and react at a speed of 180 rpm. Measure the content of nitrate in the solution after 25 h and 50 h of reaction, and use ultraviolet-visible spectrophotometry to measure the nitrate removal rate. The experimental results are shown in Table 1.

[0065] Table 1 Removal rates of nitrates by the materials prepared in each example and comparative example

[0066]

[0067] It can be seen from the experimental results that compared with the material of Comparative Example 1 without graphene on the surface, which can only remove 7.8% of nitrates in 50 h, the removal performance of nitrates in Experimental Example 2 with even a small amount of graphene on the surface is greatly improved, and the nitrate removal rate can reach 60.3% in 50 h. With the increase of the amount of graphene on the material surface, the nitrate removal rate in 50 h can increase to more than 85%. Among all experimental examples, the graphene loading amount is Example 4 > Example 1 > Example 3 > Example 2, but the nitrate removal rate in 50 h is the highest in Example 1, indicating that the amount of graphene on the surface is not the more the better, but the ratio of graphene and surface iron oxide should be considered. And Comparative Example 2 directly uses commercially available zero-valent iron and graphene oxide as raw materials, and its nitrate removal rate in 25 h is much lower than that of Example 4 with the same ratio of zero-valent iron and graphene oxide, indicating that directly using commercially available finished products reduces the loading efficiency of graphene. At the same time, the nitrate removal rate in 50 h of Comparative Example 2 is significantly lower than that of the examples, indicating that there is a problem of uncontrollable surface composition in commercially available raw materials, and it is difficult to maintain the long-term stable high activity of the finished material.

[0068] The material prepared in Example 1 after the above experiment was separated by applying an external magnetic field and vacuum dried, and the dried material was reused in the above experiment. The nitrate content was measured every 10 hours, and the nitrate removal rate was calculated. The experimental results are as follows Figure 5 , where 1st is the result of the first use test of the new material, 2nd is the material obtained after separating and vacuum drying the material obtained after the first use and then treating the 200 mg / L nitrate solution again, and the nitrate content was measured every 10 hours, and the nitrate removal rate was calculated. 3rd, 4th, and 5th are the results obtained by continuing the above experiment with the material after the previous test in turn. The results show that the experimental results of reusing the material prepared in Example 1 5 times prove that during multiple repeated uses, the nitrate removal rate of the material has been maintained at about 80%. It shows that the material prepared by the present invention has high utilization rate and long service life.

Claims

1. A preparation method of a surface iron oxide graphene co-loaded zero-valent iron particle material, characterized in that, It includes the following steps: S1. Mix the reduced zero-valent iron powder with an acid solution and then perform ultrasonic treatment. After treatment, perform solid-liquid separation, wash the solid product, and after drying, obtain zero-valent iron with a clean surface, and store it under vacuum or in an inert gas environment. The ultrasonic treatment is carried out under anaerobic conditions; S2. Prepare or obtain graphene oxide; S3. Add the graphene oxide obtained in step S2 and the zero-valent iron obtained in step S1 to anaerobic deionized water, and carry out a mixing reaction under anaerobic conditions. Then perform solid-liquid separation, wash the solid product, and after vacuum drying, slowly introduce air into the container until the atmospheric pressure is reached to obtain a zero-valent iron particle material co-loaded with iron oxide and graphene on the surface, The order of steps S1 and S2 can be interchanged with each other.

2. The preparation method according to claim 1, characterized in that, In step S1, the acid solution is sulfuric acid or hydrochloric acid solution, the concentration of the acid solution is 1-5 mol / L, and the mass-volume ratio of zero-valent iron to hydrochloric acid solution in units of g / mL is 1:1-100.

3. The preparation method according to claim 1, wherein In step S1, the power of the ultrasonic wave is 250-500 W, and the time of the ultrasonic wave is 24-72 h.

4. The preparation method according to claim 1, wherein, In step S2, the method for preparing graphene oxide is to add graphite powder and NaNO3 to concentrated H2SO4 at a temperature of 1-5 °C, carry out a stirring reaction, add KMnO4 and continue stirring, heat up to 25-40 °C and continue the reaction for 1-2 h, then add deoxygenated deionized water, continue to heat up to 90-98 °C and continue stirring and reacting for 1-2 h, add hydrogen peroxide, and after no bubbles are generated, perform solid-liquid separation. For the obtained solid material, wash the material with deionized water until the washing liquid is neutral, and after drying, obtain graphene oxide.

5. The preparation method according to claim 4, characterized in that, The concentration of graphite powder in concentrated sulfuric acid is 40-60 g / L, the concentration of NaNO3 in concentrated sulfuric acid is 20-30 g / L, and the stirring reaction is carried out for 0.5-1 h after adding NaNO3; the dosage of KMnO4 is such that its concentration in concentrated sulfuric acid is 150 g / L, and stir for 1-2 h after adding KMnO4; the dosage ratio of deionized water to concentrated sulfuric acid is 2:5; the dosage of hydrogen peroxide is such that its final concentration is 1-2% to terminate the oxidation reaction.

6. The preparation method according to claim 1, wherein In step S3, the mass ratio of graphene oxide to zero-valent iron is 1:1-100, and the concentration of zero-valent iron is 1-100 g / L.

7. The preparation method according to claim 1, wherein In step S3, the temperature of the mixing reaction is 25-30 °C, and the reaction time is 1-20 h; under sealed conditions, perform constant-temperature oscillation cultivation at a speed of 150 rpm; The washing is to wash the material with anaerobic deionized water until the pH of the washing liquid is neutral; After vacuum drying, slowly introduce air into the container at a flow rate of 1-100 mL / min.

8. A surface iron oxide graphene co-loaded zero-valent iron particle material, characterized in that, Prepared according to the preparation method described in claim 1.

9. Application of the zero-valent iron particle material co-loaded with iron oxide and graphene on the surface described in claim 8 in removing nitrates.

10. The application according to claim 9, characterized in that, When the zero-valent iron particle material co-loaded with iron oxide and graphene on the surface is applied to remove nitrate-containing water bodies, its addition amount is 1-10 g / L, and after application, magnetic separation is used to achieve rapid recovery and reuse of the material.

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