Method for removing nitro compounds in water through pyrite-mediated atomic hydrogen reduction

Abstract

The invention discloses a method for removing nitro compounds in water by pyrite-mediated atomic hydrogen reduction. The method comprises the following steps: (1) washing and drying natural pyrite, and grinding by using a ball mill to obtain a grey black powder catalyst; (2) placing the catalyst in an aqueous solution of nitroimidazole or nitrobenzene at normal temperature and normal pressure, then adding sodium borohydride, and continuously bubbling the solution with inert gas; (3) adding a low catalyst (0.8 g / L) and using amount (lt) of sodium borohydride; according to the method, under the condition that the initial concentration is 0.16 g / L, metronidazole, ornidazole and tinidazole with the initial concentration being 20 ppm are thoroughly removed within 1 min, the removal rate of 0.6 mM nitrobenzene within 20 min reaches 98.98%, and a main reduction product is a corresponding amino compound. Natural pyrite is used as a catalyst to generate atomic hydrogen through mediation, the process is simple, reagents are safe, and a practical strategy is provided for reducing nitro compound pollution in the water environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for activating sodium borohydride with pyrite to promote the reduction of atomic hydrogen to remove nitro compounds in water bodies. Background Art

[0002] The transformation of nitro compounds is an important class of chemical reactions in the fields of industrial production and environmental remediation. Among them, nitroaromatic compounds (NACs) and nitroimidazoles (NZs) have received more attention as typical nitro compounds. It is worth noting that the nitro group (─NO2) of NAC or NZ is always connected to the sp2 carbon on the benzene ring or imidazole ring. The N atom in ─NO2 has a tendency to draw electrons from surrounding atoms, and this electron-withdrawing effect makes the ring structure relatively stable, thus increasing the difficulty of mineralizing them. From this perspective, nitro compounds are easily reduced and transformed. In addition, NZ is widely used as a potent antibiotic, and its high solubility and low biodegradability can also have negative effects on various organisms and humans. Interestingly, many reduction products of NZ are less toxic and more easily degradable. Therefore, reduction strategies may be more suitable than oxidation for the transformation and removal of NACs and NZs in the water environment.

[0003] Regarding reduction strategies, catalytic H2 hydrogenation, electrochemical cathodic reactions, photocatalytic reduction, and some advanced reduction systems have been reported. Currently, most catalytic H2 hydrogenation technologies can reduce NACs in the liquid phase using single-atom catalysts under a stable H2 atmosphere, but the efficiency of related systems is usually limited by the dissociation rate and low solubility of H2 in the solution. At the same time, some electrochemical and photocatalytic methods usually require stable light or electrical energy, and even need additional salts as electrolytes. In contrast, advanced reduction technologies are based on the spontaneous interaction between catalysts and reductants, getting rid of the risk of H2 use and the dependence on external energy sources. In particular, a method of activating the green reductant sodium borohydride (NaBH4) to release atomic hydrogen (H*) at room temperature to reduce organic substrates. However, these methods have two problems: First, although the reduction and removal of NACs have been studied, the catalytic reduction of NZ for reduction and removal has rarely been reported. Second, the cost of current noble metal catalysts is usually high, and the design and preparation of single-atom catalysts are complex. The high cost of these synthetic materials is not conducive to large-scale popularization and application. Therefore, finding an appropriate method to meet the reduction and removal of NACs and NZs remains a challenge, and it would be more competitive if cheap but efficient natural materials could be used.

[0004] Pyrite (mainly FeS2) is the most abundant natural metal sulfide in the earth's crust and is an ideal catalyst for the above ideas. In FeS2, the Fe(II) sites not only have an electron-donating tendency but also carry a positive charge, which means that the pyrite surface can theoretically not only attract nitro compounds by the electrophilicity of ─NO2 but also attract negatively charged reducing agents (such as BH4 ─ ). However, at present, FeS2 is often used as a catalyst in oxidation systems, and the reduction system with pyrite as the catalytic core still needs to be explored and expanded. The use of pyrite avoids the cumbersome design and preparation process of synthetic catalysts, reduces the material usage cost, and conforms to the circular economy principle of wastewater treatment. The pyrite-mediated H* generation process achieves ultrafast pollutant removal by releasing active hydrogen species, providing a practical strategy for alleviating the stubborn nitro compound pollution in the water environment. Summary of the Invention

[0005] Based on the purpose of treating nitro compound pollution in water by reduction methods, the prior art faces limitations such as high catalyst acquisition cost, large energy demand, and complex processes. The present invention aims to provide a method for removing nitro compounds in water by pyrite-mediated atomic hydrogen reduction, which has the advantages of simple equipment, low cost, and environmental friendliness.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for removing nitro compounds in water by pyrite-mediated atomic hydrogen reduction, the specific steps are as follows:

[0008] (1) Initially crush natural pyrite to a particle size of about 1 - 3 mm, repeatedly wash it several times and drain it, and then place it in an oven at 60 °C for thorough drying;

[0009] (2) Put the dried pyrite obtained in step (1) into a ball mill, and obtain a gray-black solid powder after sufficient grinding, which is the target catalyst referred to in this method;

[0010] (3) At normal temperature and pressure, mix the catalyst obtained in step (2) with an aqueous solution of nitroimidazole or nitrobenzene in a reactor, where the catalyst dosage concentration is not less than 0.2 g / L;

[0011] (4) Add sodium borohydride to the reactor described in step (3) to initiate the reduction and conversion process of nitro compounds, and this process lasts for 1 - 20 min.

[0012] Preferably, in step (2), the ball milling parameters are set as ball volume: pyrite volume = 10:1, the rotation speed is 600 r / min, and the milling time is 6 h.

[0013] Preferably, the catalyst dosage concentration in step (3) is 0.2 - 0.4 g / L.

[0014] Preferably, the concentration of nitroimidazole drugs in step (3) is 20 ppm, and the concentration of nitrobenzene is 0.5 - 0.6 mM.

[0015] Preferably, the dosage concentration of sodium borohydride in step (4) is 0.04 - 0.20 g / L.

[0016] Preferably, the working state of the reactor in step (4) is set to continuous oxygen bubbling, with a flow rate of 100 mL / min - 200 mL / min.

[0017] The technical solution provided by this application has the following advantages compared with the known technology:

[0018] (1) Using natural and inexpensive pyrite with abundant reserves in nature as a catalyst to activate sodium borohydride, the reduction reaction of nitrobenzene can be initiated without the drive of light energy / electric energy, and the process flow is simple and fast;

[0019] (2) The reaction can be initiated at normal temperature and pressure, and the nitro compounds in wastewater can be efficiently reduced, removed, and converted into corresponding amino compounds in a short time;

[0020] (3) Using the main solid waste of mines as raw materials to obtain catalysts, avoiding the problems of the preparation and use costs of synthetic catalysts, which conforms to the strategy of finding new conversion and utilization scenarios for some low-value waste or resources.

[0021] (4) A simple H* utilization technology is realized, and only inexpensive natural minerals are required to efficiently mediate the release of H*, which has great potential for adaptation in solving the pollution problems of other organic substrates in the water environment. Description of the Drawings

[0022] Figure 1 The FeS2 catalyst processed from pyrite and its XRD pattern;

[0023] Figure 2 The performance of the FeS2 catalyst in activating sodium borohydride to reduce and remove metronidazole, ornidazole, and tinidazole;

[0024] Figure 3 The reduction, removal, and conversion performance of nitrobenzene under different dosing ratios of FeS2 and sodium borohydride;

[0025] Figure 4 The performance of FeS2 in activating sodium borohydride to catalyze the reduction, removal, and conversion of nitrobenzene under different oxygen-containing conditions;

[0026] Figure 5It is the EPR diagram of the reducing species H* generated in the FeS2-activated sodium borohydride system. The realization of the purpose, functional characteristics and advantages of this application will be further described with reference to the accompanying drawings in combination with the embodiments. Detailed Embodiments

[0027] The present invention will be described in detail below with reference to the accompanying drawings. It should be clear that the following embodiments give specific implementation manners and operation processes, but the protection scope of the present invention is not limited to the listed embodiments.

[0028] During the preliminary research process of this application, it was found that pyrite is the most abundant natural metal sulfide in the earth's crust, and it is often regarded as a by-product or solid waste with low utilization value in some mineral extraction processes. However, some studies have shown that FeS2, the main component of pyrite, has great potential for development in environmental catalysis and exhibits catalytic activity for certain reaction processes.

[0029] Therefore, this method provides a new application way for pyrite waste, and through simple pretreatment steps, it is transformed into a highly efficient catalyst for reduction reactions.

[0030] Example 1

[0031] Processing pyrite to obtain the FeS2 catalyst:

[0032] Crush natural pyrite and select particles with a particle size less than 3 mm through a sieve. Repeatedly wash the screened pyrite particles three times, drain them, and place them in a 60°C vacuum oven until completely dry. Load the dried pyrite and grinding balls into a sealed tank supporting a planetary ball mill at a volume ratio of 1:10, set the rotation speed at 600 rpm, and put pyrite: agate balls = 1:10 (volume) into the ball mill. After sufficient grinding, a gray-black solid powder is obtained, which is the target catalyst referred to in this method. The main component of this powdered catalyst is confirmed by the XRD results, as Figure 1 shown: The main component of the powder obtained by ball milling pyrite is FeS2, with a high purity.

[0033] Example 2

[0034] Determination of the ability of the catalyst to activate sodium borohydride for the reduction and removal of nitroimidazoles:

[0035] Step 1: Prepare an aqueous solution with a concentration of 20 ppm of metronidazole (MNZ), ornidazole (ONZ), and tinidazole (TNZ).

[0036] Step 2: Add 0.4 g / L of FeS2 catalyst into the solution of Step 1, and at the same time, use a flowmeter to control the flow rate of argon (or nitrogen) to bubble the solution. After bubbling for 20 min, add 0.1 g / L of sodium borohydride, and take samples at 0 s, 5 s, 10 s, 20 s, 30 s, 40 s, 50 s, and 60 s respectively. Take 2 mL of each sample and quickly filter it with a syringe filter to obtain water samples 1 - 8. At the same time, conduct the same sampling under the condition of only using FeS2 catalyst or only adding sodium borohydride for comparison.

[0037] Step 3: Detect the concentrations of MNZ, ONZ, and TNZ in the water samples 1 - 8 obtained in Step 2 by high performance liquid chromatography, and calculate the reduction and removal efficiency of nitroimidazoles in different reaction systems at different times.

[0038] The results are as Figure 2 shown, and it can be seen that:

[0039] Neither using FeS2 alone nor using sodium borohydride alone can significantly remove nitrobenzene, while the co - existence of FeS2 and sodium borohydride can quickly initiate the reduction and removal of nitroimidazoles. After 10 s of the start of the reaction, the concentrations of MNZ, ONZ, and TNZ decreased significantly ( Figure 2 a), and were completely removed at 1 min ( Figure 2 b). The kinetic fitting results showed that the degradation rates of the three nitroimidazoles in the system were TNZ > MNZ > ONZ.

[0040] Therefore, the above - mentioned method finds a new application scenario for natural pyrite solid waste, and when used together with the reducing agent sodium borohydride, it can form an advanced reduction system, which has a significant removal effect on nitroimidazole pollutants in the aqueous phase in a short time.

[0041] Example 3

[0042] Determine the reduction, removal, and conversion ability of FeS2 catalyst and sodium borohydride at different dosing ratios for nitrobenzene:

[0043] Step 1: Prepare an aqueous solution with a nitrobenzene concentration of 0.7 mM.

[0044] Step 2: The dosage of FeS2 catalyst added into the solution described in Step 1 is 0.8 g / L. Under the condition of continuous argon (or nitrogen) bubbling, add sodium borohydride to start the reaction after 20 min. Control the dosing ratios of sodium borohydride to FeS2 to be 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 1 respectively. Take samples when the reaction proceeds to 20 min, quickly filter them with a syringe filter, and the sampling volume is 2 mL. According to this sampling method, obtain specimens 1 - 7.

[0045] Step 3: Detect the concentrations of nitrobenzene and aniline in the sample by high performance liquid chromatography, and calculate the removal efficiency of nitrobenzene and the cumulative conversion percentage of aniline under different dosing ratios.

[0046] The results are as Figure 3 shown, and it can be seen that:

[0047] The system composed of FeS2 and sodium borohydride is also applicable to nitrobenzene, and sodium borohydride can be activated within a wide dosing range for the removal of nitrobenzene and its conversion to aniline. This greatly reduces the dependence on the usage amount of sodium borohydride and helps to further control the process and reagent costs. When sodium borohydride:FeS2 = 0.4, the removal efficiency of the system for nitrobenzene reaches 98.98% at 20 min, and 53.6% of it is converted to aniline.

[0048] Example 4

[0049] Determine the performance of FeS2 catalyst-activated sodium borohydride for the removal of nitrobenzene and the production of nitrobenzene without inert gas bubbling:

[0050] Step 1: Prepare an aqueous solution with a nitrobenzene concentration of 0.7 mM.

[0051] Step 2: Add 0.8 g / L of FeS2 catalyst to the solution in Step 1, and add 0.1 g / L of sodium borohydride under the conditions of being open to the environment and continuous oxygen bubbling respectively. Sampling is carried out at 0 min, 1 min, 3 min, 6 min, 10 min, and 20 min, 2 mL of each sample is taken, and it is quickly filtered with a syringe filter to obtain the third sample.

[0052] Step 3: Detect the cumulative conversion percentage and concentration of aniline in the third sample by high performance liquid chromatography.

[0053] The results are as Figure 4 shown, and it can be seen that:

[0054] The efficiency of obtaining aniline from the nitrobenzene solution when it is open to air is better than that under continuous oxygen bubbling. Therefore, the method of FeS2-activated sodium borohydride can avoid the use of flammable and explosive gases. This method obtains aniline from nitrobenzene waste liquid, which is beneficial to improving the product yield in the aniline production process.

[0055] Example 5

[0056] Determine the generation of free radicals when FeS2 catalyst activates sodium borohydride:

[0057] Step 1: Take 30 mL of ultrapure water, then add 200 μL of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and then add an FeS2 catalyst at a concentration of 0.8 g / L. Then, add 0.16 g / L under the condition of continuous bubbling of argon (or nitrogen) to obtain a liquid sample.

[0058] Step 2: At the 3rd minute of the reaction, quickly take the liquid sample described in Step 1 with a sampling capillary, and then use an electron paramagnetic resonance spectrometer (EPR) to detect the generation of free radicals in the solution.

[0059] The results are as Figure 5 shown, and it can be seen that:

[0060] The FeS2 catalyst in the method described in this application can generate an obvious nonet signal when activating sodium borohydride, indicating the existence of a large amount of atomic hydrogen (H*). H* is a strong reducing agent that can perform hydrogenation reduction on -NO2 on the benzene ring or imidazole ring and thus convert it into -NH2.

[0061] In summary, the method described in this application uses pyrite widely existing in nature as an efficient catalyst, mediates the generation of H* by activating sodium borohydride for the rapid reduction and transformation of nitro compounds. Different from the current electrochemical or photocatalytic methods, the strategy of H* generation mediated by natural and inexpensive minerals avoids the dependence of advanced reduction systems on external energy input, and the use of pyrite bypasses the cumbersome preparation process and high cost of artificially synthesized catalysts. The process of H* generation mediated by pyrite described in this application achieves rapid reduction of pollutants by releasing active hydrogen species, not only providing a practical strategy for the remediation of more nitro compound wastewater, but also having great adaptation potential in solving other water body organic substrate pollution problems.

[0062] For the field of chemical energy-driven reduction and transformation of compounds, various corresponding adjustments and deformations can be made with reference to the above technical solutions and concepts, and all relevant adjustments and deformations should be included within the protection scope of the claims of this invention.

Claims

1. A method for removing nitro compounds from water by pyrite-mediated atomic hydrogen reduction, the method steps are as follows: (1) The natural pyrite is initially crushed to a particle size of about 1 to 3 mm, washed repeatedly and drained, and then placed in a 60°C oven to dry thoroughly; (2) putting the dried pyrite obtained in step (1) into a ball mill, and after sufficient grinding, obtaining a gray-black solid powder, which is the target catalyst referred to in this method; (3) mixing the catalyst obtained in step (2) with an aqueous solution of a nitro compound in a reactor at room temperature and pressure, wherein the catalyst addition concentration is not less than 0.4 g / L; (4) Adding sodium borohydride to the reactor in step (3) initiates the reduction and conversion process of the nitro compound, and the duration of this process is 1 to 20 minutes.

2. A method for removing nitro compounds from water by pyrite-mediated atomic hydrogen reduction according to claim 1, characterized in that: In the step (2), the ball milling parameters are set as ball volume: pyrite volume = 10:1, the rotation speed is 600 r / min, and the grinding time is 6 h.

3. A method for obtaining aniline from nitrobenzene waste liquid by activating sodium borohydride with pyrite according to claim 1, characterized in that: In the step (3), the concentration of nitrobenzene is 0.5-0.6 mM, and the concentration of metronidazole, tinidazole and pyrrolidazole is 20 ppm.

4. A method for removing nitro compounds from water by pyrite-mediated atomic hydrogen reduction according to claim 1, characterized in that: The concentration of sodium borohydride added in step (4) is 0.04-0.20 g / L.

5. A method for removing nitro compounds from water by pyrite-mediated atomic hydrogen reduction according to claim 1, characterized in that: The working states of the reactor in step (4) are respectively set to continuous oxygen bubbling, open, and continuous inert gas bubbling.

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