Ferrocobalt spinel type oxide, preparation method thereof and application of ferrocobalt spinel type oxide in degradation of nitrogenous explosive wastewater

Abstract

The invention discloses an iron-cobalt spinel oxide, which is prepared by the following steps: with ferric salt and cobalt salt as raw materials, dissolving the ferric salt, the cobalt salt and sodium acetate in an ethanol aqueous solution to obtain a precursor solution, carrying out hydrothermal treatment on the precursor solution, and washing and drying a reaction product to obtain the iron-cobalt spinel oxide. The iron-cobalt spinel type oxide is stable in crystal structure, the leaching rate of metal ions is remarkably reduced due to existence of metal-oxygen bonds, the recycling rate is increased, and meanwhile the risk of secondary pollution of water is reduced. In the process of degrading nitrogen-containing organic wastewater by an advanced oxidation technology for generating sulfate free radicals based on peroxymonosulfate, the iron-cobalt spinel type oxide has good catalytic performance, and can basically complete degradation of multi-nitrogen organic pollutants in water; and the method has relatively strong capability of resisting interference of inorganic ions and organic matters, and has relatively great application potential in actual wastewater treatment. The invention also discloses a method for degrading the multi-nitrogen explosive wastewater by using the ferrocobalt spinel type oxide.

Description

Technical Field

[0001] The invention belongs to the field of resource utilization of materials and waste biomass, and particularly relates to an iron-cobalt spinel oxide and a preparation method thereof, as well as application of the cobalt-iron spinel oxide in degrading nitrogen-containing explosive wastewater. Background Art

[0002] Explosives, as high-energy organic compounds, can be used for both military and peaceful purposes, such as nuclear devices, solid rocket propellants, and artillery propellants. The production, transportation, and use of explosives can leave significant residues in water bodies. Some of these organic compounds are highly biotoxic, posing a potential threat to human health and ecological security. Hexanitrosilane (HNS, chemical name: 2,2′,4,4′,6,6′-hexanitrodiphenylethylene) is a heat-resistant, stun-resistant explosive widely used in aerospace and military applications. The HNS production process generates large amounts of explosive wastewater containing acutely toxic and mutagenic nitroaromatic compounds (NACs). These NACs are characterized by complex composition, high toxicity, high color, and high emission volumes. Therefore, appropriate treatment methods are required to meet national emission standards. Currently, methods for removing HNS include photocatalysis and biodegradation, but these methods suffer from low removal efficiency and incomplete degradation, preventing them from truly degrading into "green products."

[0003] Advanced oxidation technologies (AOPs) have shown great potential in degrading organic pollutants in wastewater. Traditional advanced oxidation technologies such as Fenton / Fenton-like oxidation, ozone (O3) oxidation, and photochemical catalytic oxidation have been used to remove organic pollutants. However, these methods also have some disadvantages, such as the Fenton / Fenton-like oxidation reaction conditions are acidic (pH is generally 3) and metal ions easily produce secondary pollutants, thus limiting the degradation liquid system; the ozone used in ozone oxidation is a highly selective oxidant with low solubility in water, thus limiting the ozonation process; photochemical catalytic oxidation is sensitive to turbidity and difficult to amplify. Studies have found that new advanced oxidation technologies based on PS (peroxydisulfate) and PMS (peroxymonosulfate) have high efficiency in degrading organic pollutants in wastewater, are highly durable and inexpensive. In addition, among the active oxygen produced by advanced oxidation technologies, SO4 ·-It possesses remarkable redox properties, with a standard redox potential (E°) ranging from 2.5 to 3.1 V. It exhibits high reactivity over a wide pH range (pH 2–8), a long half-life, and good oxidative selectivity. These properties enable it to exhibit efficient mineralization and rapid kinetics during the degradation of organic pollutants, enabling its efficient and rapid degradation. However, organic pollutants cannot be effectively degraded by either PS or PMS alone; a series of activation methods are required to promote the decomposition of organic pollutants. Compared to PS, PMS has a lower O-O bond energy (~377 kJ / mol) than PS (~140 kJ / mol), making it more susceptible to activation. Common activation methods include ultraviolet light, heating, ultrasound, and transition metals and their oxides. The high energy consumption and low energy conversion efficiency associated with UV, heating, and ultrasound activation of PMS limit its practical application in large-scale organic wastewater treatment. Furthermore, when transition metals and PMS degrade pollutants in a homogeneous system, the toxicity of the dissolved metals is high, making it unsuitable for practical organic wastewater treatment.

[0004] Transition metals such as cobalt, nickel, copper, and iron have been extensively studied in the degradation of organic pollutants due to their excellent catalytic activity. However, metal ion leaching is a common phenomenon during the catalytic degradation process, which not only reduces the stability of the catalyst but also may lead to excessive concentrations of heavy metal ions in water. Summary of the Invention

[0005] The purpose of the present invention is to address the problems of low removal efficiency and incomplete degradation of polynitrogen explosive wastewater, as well as the environmental pollution problem caused by ion leaching and strong biological toxicity of transition metal catalysts. The present invention provides a spinel-type oxide based on a cobalt-iron bimetallic and a preparation method. The cobalt-iron spinel-type oxide is used as a catalyst to degrade polynitrogen explosive wastewater, thereby solving the problems of environmental pollution and difficulty in degrading organic matter.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] An iron-cobalt spinel oxide is prepared by using iron salt and cobalt salt as raw materials. The iron salt, cobalt salt and sodium acetate are dissolved in an ethanol aqueous solution to obtain a precursor solution. The precursor solution is subjected to hydrothermal treatment, and the reaction product is washed and dried to obtain the iron-cobalt spinel oxide.

[0008] The iron salt is ferric nitrate or ferric chloride.

[0009] The cobalt salt is cobalt nitrate, cobalt chloride or cobalt acetate.

[0010] Another object of the present invention is to provide a method for preparing the iron-cobalt spinel oxide, comprising: dissolving ferric nitrate, cobalt nitrate and sodium acetate in an ethanol aqueous solution to obtain a precursor solution; subjecting the precursor solution to hydrothermal treatment, and washing and drying the reaction product to obtain the iron-cobalt spinel oxide.

[0011] The molar ratio of the iron salt to the cobalt salt is 1:2 to 1:3 or 2:1.

[0012] Preferably, the molar ratio of the iron salt to the cobalt salt is 1:3 or 2:1.

[0013] The molar ratio of the iron salt to the sodium acetate is 1:5 to 1:7.

[0014] Preferably, the molar ratio of the iron salt to sodium acetate is 1:6.74. Sodium acetate can promote the formation of a spinel structure. During the hydrothermal process, sodium acetate may decompose to form sodium carbonate or oxides. These alkaline substances help form a stable spinel structure.

[0015] The ethanol aqueous solution is a mixed solvent with anhydrous ethanol and deionized water in a volume ratio of 35:2.5 to 20:17.5.

[0016] The temperature of the hydrothermal treatment is 170-180° C., and the time of the hydrothermal treatment is 10-12 hours.

[0017] The hydrothermal treatment device is a hydrothermal synthesis reactor lined with polytetrafluoroethylene.

[0018] Preferably, after the hydrothermal treatment, the mixture is cooled to room temperature, filtered, and the solid is collected as the reaction product. The reaction product is repeatedly washed with deionized water and ethanol, filtered, and then dried to obtain an iron-cobalt spinel oxide.

[0019] The drying temperature is 50-60° C., and the drying time is 6-12 hours.

[0020] The drying process is normal pressure drying.

[0021] Another object of the present invention is to provide the use of the iron-cobalt spinel oxide in degrading polynitrogen explosive wastewater.

[0022] Another object of the present invention is to provide a method for degrading polynitrogenous explosive wastewater using the iron-cobalt spinel oxide, comprising: using the iron-cobalt spinel oxide as a catalyst, adding the iron-cobalt spinel oxide to the wastewater, first stirring to adsorption equilibrium, then adding peroxymonosulfate, and stirring at room temperature to degrade polynitrogenous organic pollutants.

[0023] The amount of the iron-cobalt spinel oxide is 50-450 mg / L, preferably 50-200 mg / L, more preferably 100 mg / L; the amount of the peroxymonosulfate is 0.30-0.81 mmol / L, preferably 0.48-0.60 mmol / L, more preferably 0.60 mmol / L; the pH is 5-9, preferably 5-7, more preferably 6.3.

[0024] The polynitrogen organic pollutant is at least one of hexanitropine, hexanitrobibenzyl, cyclotetramethylene tetranitramine, 2,4-dinitroanisole and trinitrotoluene.

[0025] The method for degrading nitrogen-rich explosive wastewater using iron-cobalt spinel oxides according to the present invention also includes: when the wastewater contains Cl - When adding silver nitrate, Cl - Convert it into silver chloride precipitate, then add iron-cobalt spinel oxide into the wastewater, stir it until adsorption equilibrium, then add peroxymonosulfate, and stir at room temperature to degrade organic pollutants.

[0026] Beneficial effects of the present invention:

[0027] The iron-cobalt spinel oxide of the present invention has a stable crystal structure, and the presence of metal-oxygen bonds in the iron-cobalt spinel oxide significantly reduces the leaching rate of metal ions, thereby improving the recycling rate of the iron-cobalt spinel oxide and reducing the risk of secondary pollution of water bodies.

[0028] The invention adopts a hydrothermal method to prepare the iron-cobalt spinel oxide, which has a simple preparation process, low preparation requirements, low cost, and is convenient for large-scale industrial application.

[0029] In the process of producing sulfate (SO4 - ) In the process of degrading nitrogen-containing organic wastewater by using the advanced oxidation technology of free radicals, iron-cobalt spinel oxide is used as a catalyst, which has good catalytic performance, mild reaction conditions, few by-products, clean and pollution-free; the degradation process steps are simple, the operation is simple, and the energy consumption is low; and it has a strong ability to resist interference from inorganic ions and organic matter, and has great application potential for actual wastewater treatment; compared with the conventional advanced oxidation technology for degrading this nitrogen-containing organic polluted wastewater, the iron-cobalt spinel oxide of this invention can basically degrade the multi-nitrogen organic pollutants in the water. At the same time, there is Co on the surface of the iron-cobalt spinel oxide. 2+ / Co 3+ and Fe 2+ / Fe 3+ The interaction between the two metal redox pairs can accelerate the kinetics of the surface redox reaction, which is beneficial to the oxidation reaction and further improves the removal rate of nitrogen-containing organic pollutants.

[0030] In addition, sulfate radicals (SO4 ·- ) can be flexibly used in conjunction with other pathways such as light and heat to trigger a series of redox reactions, generating reactive oxygen species (ROS) with strong oxidizing power. Through reactions such as addition, dehydrogenation, and electron transfer between the reactive species and the organic pollutants, large organic pollutants in the wastewater are converted into small organic molecules, which are ultimately mineralized into harmless molecules and some inorganic ions. Therefore, this invention not only develops green chemical technology, but also responds to the national call for green and environmentally friendly production concepts, and is of great significance to the development and construction of national ecological civilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the X-ray diffraction spectrum of the material CoFe2O4 before and after the reaction.

[0032] Figure 2 It is the element map of material CoFe2O4 under transmission electron microscope; among them, a and b are high-resolution transmission electron microscope images of material CoFe2O4 intercepted at different positions, c is the distribution map of all elements of material CoFe2O4, d is the Co element content map of material CoFe2O4 under transmission electron microscope, e is the Fe element content map of material CoFe2O4 under transmission electron microscope, f is the O element content map of material CoFe2O4 under transmission electron microscope, h is the EDS energy spectrum map of material CoFe2O4, Figure i is the lattice map of material CoFe2O4 at 20nm, and Figure j is the lattice map of material CoFe2O4 at 5nm.

[0033] Figure 3 The voltammogram (a) and impedance diagram (b) of the material CoFe2O4.

[0034] Figure 4 It is the degradation effect of Fe and different metal doping (Co, Mn) on HNS.

[0035] Figure 5 This is the XPS spectrum analysis of the surface element changes of the material CoFe2O4 before and after the reaction.

[0036] Figure 6 The purpose is to explore the optimal degradation system for the material CoFe2O4 to degrade HNS waste liquid; among them, (a) the amount of catalyst CoFe2O4, (b) the amount of permonosulfate, (c) the solution pH, and (d) the effects of anions in water.

[0037] Figure 7 This is the EPR spectrum in the CoFe2O4 / PMS system.

[0038] Figure 8The effect of humic acid on the degradation of HNS waste liquid by material CoFe2O4.

[0039] Figure 9 This is the degradation diagram of the material CoFe2O4 to other nitrogen-rich pollutants.

[0040] Figure 10 This is the performance diagram of the material CoFe2O4 cycle experiment. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods.

[0042] Example 1

[0043] A preparation method of iron-cobalt spinel oxide comprises the following steps:

[0044] Step (1), dissolving 2.039 g of ferric nitrate nonahydrate, 4.406 g of cobalt nitrate hexahydrate (the molar ratio of Fe to Co is 1:3), and 2.789 g of sodium acetate in a mixed solvent of 35 mL of anhydrous ethanol and 2.5 mL of deionized water, and stirring continuously for 1 h until dissolved to obtain a precursor solution;

[0045] Step (2): Transfer the precursor solution to a 50 mL polytetrafluoroethylene-lined hydrothermal synthesis reactor and perform hydrothermal treatment at 180° C. for 12 h.

[0046] After step (3), the reaction is completed, the reactor is cooled to room temperature, filtered, and the solid is collected. The solid is washed three times with deionized water and ethanol alternately to remove leached or unreacted Co and Fe ions. Each washing is: first washing once with deionized water and filtering, then washing once with ethanol and filtering, and then drying at 60° C. and normal pressure for 12 hours to obtain an iron-cobalt spinel oxide.

[0047] Figure 1 The X-ray diffraction spectrum of the iron-cobalt spinel oxide prepared in this example is shown. Seven diffraction peaks can be observed at 2θ = 18.13, 30.27, 35.74, 43.74, 53.89, 57.17 and 62.73°, corresponding to the (111), (220), (311), (400), (422), (511) and (440) crystal planes, respectively. All peaks can be indexed using the standard pattern of CoFe2O4 (PDF#22-1086), indicating that it has a typical spinel cobalt ferrite structure. The iron-cobalt spinel oxide prepared in this example is recorded as material CoFe2O4.

[0048] The structural characteristics of the material were investigated by high-resolution transmission electron microscopy (HRTEM). Figure 2 shown. Figure 2a and b are HRTEM images of CoFe2O4, a material of the present invention, taken at different positions. It can be seen that CoFe2O4 is evenly distributed without agglomeration. Figure 2 c, d are transmission electron microscopy and all element scanning images of CoFe2O4, respectively. Figure 2 e, f, g are the contents of Co, Fe, and O in CoFe2O4 under transmission electron microscopy, Figure 2 h is the EDS spectrum of Co, Fe, and O in the material CoFe2O4. Table 1 shows that the molar ratio of Fe / Co in the material CoFe2O4 is about 1:3, indicating that the material CoFe2O4 was successfully prepared.

[0049] Table 1. Contents of Co, Fe, and O in CoFe2O4

[0050]

[0051] The inventors tested the electrochemical characteristics of CoFe2O4, and the volt-ampere characteristic curve and impedance curve are shown in Figure 3 a and Figure 3 b, indicating that: compared with Fe2O3 (Comparative Example 1) and Co3O4 (Comparative Example 2), CoFe2O4 has a larger current area and a smaller curve radius, and has a faster electron transfer ability during the degradation process, which is beneficial to improving the degradation rate of organic pollutants.

[0052] Comparative Example 1

[0053] Preparation of Fe2O3: Dissolve 2.039g of ferric nitrate nonahydrate and 2.789g of sodium acetate in a mixture of 35mL of anhydrous ethanol and 2.5mL of deionized water. Stir continuously for 1 hour until dissolved to obtain a precursor solution. Transfer the precursor solution to a 50mL polytetrafluoroethylene-lined hydrothermal synthesis reactor and hydrothermally treat at 180°C for 12 hours. After the reaction, cool the reactor to room temperature, filter, and collect the solid. Wash the solid three times with deionized water and ethanol alternately, washing once with deionized water and filtering, then washing once with ethanol and filtering, and then drying at 60°C under atmospheric pressure for 12 hours to obtain Fe2O3.

[0054] Comparative Example 2

[0055] Preparation of Co₃O₄: Dissolve 4.406g of cobalt nitrate hexahydrate and 2.789g of sodium acetate in a mixture of 35mL of anhydrous ethanol and 2.5mL of deionized water. Stir continuously for 1 hour until dissolved to obtain a precursor solution. Transfer the precursor solution to a 50mL polytetrafluoroethylene-lined hydrothermal synthesis reactor and hydrothermally treat it at 180°C for 12 hours. After the reaction, cool the reactor to room temperature, filter, and collect the solid. Wash the solid three times with deionized water and ethanol alternately, washing once with deionized water and filtering, then washing once with ethanol and filtering, and then drying at 60°C and atmospheric pressure for 12 hours to obtain iron-cobalt Co₃O₄.

[0056] Example 2

[0057] Degradation effect of Fe and different metal doping (Co(NO3)3·6H2O, Mn(NO3)3·4H2O) on HNS

[0058] Referring to Example 1 "Preparation of Material CoFe2O4", the Fe(NO3)3·9H2O was fixed at 0.005 mol, and only the metals (Co, Mn) added later and their amounts were adjusted to obtain different iron-based materials.

[0059] Co and Fe were doped so that the molar ratios of Fe and Co were approximately 1:1, 1:2, 1:3, and 2:1, respectively. The rest were the same as in Example 1. The obtained materials were respectively recorded as Fe-Co-1:1, Fe-Co-1:2, Fe-Co-1:3 (i.e., the material CoFe2O4 prepared in Example 1), and Fe-Co-2:1.

[0060] Mn and Fe were doped so that the molar ratio of Fe to Mn was about 1:3. The rest was the same as in Example 1. The obtained material was recorded as Fe-Mn-1:3.

[0061] The catalytic degradation of organic pollutants was investigated using Fe-based materials prepared by doping with different metals as catalysts:

[0062] 40 mg of HNS was weighed into a 1 L volumetric flask and titrated to the mark with a mixture of deionized water and acetonitrile (water:acetonitrile volume ratio of 1:1) to obtain a 40 mg / L HNS solution. 50 mL of the HNS solution was added to a 100 mL beaker with an initial pH of 6.3. 5 mg of the iron-based material prepared in this example was added as a catalyst and stirred at room temperature for 25 min until adsorption equilibrium was reached. 0.6 mmol / L of peroxymonosulfate (PMS, 2KHSO5·KHSO4·K2SO4) was then added and stirred at room temperature. Approximately 2 mL of the solution was removed with a syringe every 25 min, filtered through a 0.22 μm polyethersulfone filter membrane, and the remaining free radicals were quenched with 0.5 mL of methanol. HNS concentration was determined using a high-performance liquid chromatography (HPLC) instrument with a UV-visible detector. HPLC conditions included a reverse-phase C18 column (5 μm, 4.6 mm × 250 mm), a mobile phase consisting of water and acetonitrile (40%:60%), a flow rate of 1 mL / min, and detection at a wavelength of 254 nm. The degradation rate of HNS was calculated by measuring the peak areas of the pre- and post-degradation solutions.

[0063] like Figure 4 As shown in the figure, the iron-based materials prepared according to the molar ratio of Fe to Co of 1:3 and 2:1 have good degradation effects on HNS, especially the material prepared according to the molar ratio of Fe to Co of 1:3, which has the best degradation effect.

[0064] The inventors tested the X-ray electron spectroscopy (XPS) of Co and Fe elements before and after the degradation of HNS by the material CoFe2O4 (Example 1). Figure 5 The results show that oxidation reactions occurred during the degradation process, with some Co(II) being oxidized to Co(III) and some Fe(II) being oxidized to Fe(III). Furthermore, the positions of the characteristic peaks of Co and Fe elements in the used catalyst remained almost unchanged, with no new peaks appearing. This change in the valence states of Co and Fe demonstrates the stability of CoFe2O4-activated PMS, which plays a dominant role in the degradation of HNS.

[0065] Example 3

[0066] After determining that the molar ratio of Fe and Co bimetallic was 1:3 for doping, referring to Example 2 "Investigation of catalytic degradation of organic pollutants", the dosage of catalyst CoFe2O4 (0, 0.05, 0.10, 0.15, 0.20 g / L), the dosage of peroxymonosulfate (0, 0.30, 0.48, 0.60, 0.81 mmol / L), the solution pH (pH was 3, 5, 6.3, 7, 9, 11, and the anion in water (HCO3 - 、Cl - 、NO3 -)) on the degradation of HNS (40 mg / L).

[0067] 1. Effect of the dosage of catalyst CoFe2O4 on the degradation of HNS

[0068] The concentration of peroxymonosulfate (2KHSO5·KHSO4·K2SO4) was fixed at 0.6 mmol / L, the initial pH was 6.3, and the amount of catalyst CoFe2O4 was adjusted to 0, 0.05, 0.10, 0.15, and 0.20 g / L, respectively. The rest was the same as in Example 2 "Investigation of catalytic degradation of organic pollutants".

[0069] 2. Effect of peroxymonosulfate dosage on HNS degradation

[0070] The fixed amount of CoFe2O4 was 0.10 g / L, the initial pH was 6.3, and the amounts of peroxymonosulfate were adjusted to 0, 0.30, 0.48, 0.60, and 0.81 mmol / L, respectively. The rest was the same as in Example 2 "Investigation of catalytic degradation of organic pollutants."

[0071] 3. Effect of solution pH on HNS degradation

[0072] The fixed amount of CoFe2O4 was 0.10 g / L, the concentration of peroxymonosulfate (2KHSO5·KHSO4·K2SO4) was 0.6 mmol / L, the initial pH of the HNS solution was 6.3, and 0.1 mmol / L sulfuric acid and 0.1 mmol / L sodium hydroxide solution were used to adjust the solution pH to 3, 5, 7, 9, and 11, respectively. The rest was the same as in Example 2 "Investigation of catalytic degradation of organic pollutants".

[0073] 4. Effect of anions in water on the degradation of HNS

[0074] Different anions (HCO3 - 、Cl - 、NO3 - , of which HCO3 - 、Cl - 、NO3 - By adding potassium bicarbonate, potassium chloride, and potassium nitrate, respectively), the amount of CoFe2O4 was fixed at 0.10 g / L, the concentration of peroxymonosulfate (2KHSO5·KHSO4·K2SO4) was 0.6 mmol / L, and no anion was added as a control (Control: CoFe2O4 amount = 0.10 g / L, PMS = 0.60 mmol / L initial pH = 6.3). The rest was the same as in Example 2 "Investigation of catalytic degradation of organic pollutants".

[0075] See the results Figure 6 The results showed that a catalyst dosage of 0.05-0.2 g / L, a peroxymonosulfate dosage of 0.48-0.60 mmol / L, and a pH of 5-9 exhibited excellent HNS degradation. In particular, a catalyst dosage of 0.10 g / L, a peroxymonosulfate dosage of 0.60 mmol / L, and a pH of 6.3 achieved a 96% HNS degradation rate after 150 minutes of reaction. Considering efficient resource utilization, the optimal conditions for HNS degradation were a catalyst dosage of 0.10 g / L, a peroxymonosulfate dosage of 0.60 mM, and a pH of 6.3.

[0076] Common anions HCO3 in actual water or wastewater - 、Cl - 、NO3 - , HCO3 was found - 、NO3 - The presence of Cl has little effect on degradation, but - It has a strong inhibitory effect on the degradation of HNS. The removal rate is only 79% after 150 minutes of reaction. Therefore, when the wastewater contains Cl - When Cl - Converted to silver chloride precipitate.

[0077] Example 4

[0078] Referring to Example 2 "Investigation of catalytic degradation of organic pollutants", a 40 mg / L HNS solution was degraded. Electron paramagnetic resonance (EPR) was used to determine the types of active oxygen species generated during the degradation process. The results are as follows: Figure 7 All relevant reactive oxygen species (·OH, O2 ·- and SO4 ·- and 1 O2 can be captured in EPR. Using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the capture agent, the 1:2:2:1 characteristic peak of DMPO-·OH and DMPO-SO4 ·- The weak response ( Figure 7 a) and DMPO-O2 ·- The characteristic peaks ( Figure 7 b) confirmed that OH, SO4 ·- and O2 ·- The formation of. Figure 7 Tetramethylpiperidinyl oxide (TEMP) can be observed in c, and TEMP- 1 The strong signal peak of O2 adducts indicates that 1 O2.

[0079] Example 5

[0080] Natural organic matter may compete with organic pollutants for SO4 ·- , ·OH, and other active oxygen species affect the degradation of organic pollutants. Therefore, humic acid (HA), a typical natural organic matter, was added to investigate its effect on the degradation of HNS.

[0081] Humic acid at different concentrations was added to a 40 mg / L HNS solution (initial pH 6.3). A solution without humic acid was used as a control (Control: CoFe2O4 dosage = 0.10 g / L, PMS = 0.60 mmol / L, initial pH = 6.3). Referring to Example 2 "Investigation of catalytic degradation of organic pollutants", the effect of humic acid on the degradation of HNS (40 mg / L) by peroxymonosulfate (PMS) activated by CoFe2O4 catalyst was investigated.

[0082] See the results Figure 8 After adding different concentrations of humic acid, the removal rate of HNS was between 56% and 64%, indicating that the organic matter in humic acid competed with HNS to consume active oxygen, resulting in a decrease in the removal rate of HNS.

[0083] Example 6

[0084] Take polynitrogen organic pollutants: hexanitrobibenzyl (HNBB), cyclotetramethylene tetranitramine (HMX), 2,4-dinitroanisole (DNAN), and trinitrotoluene (TNT). Deionized water was used to prepare hexanitrobibenzyl solution, cyclotetramethylene tetranitramine solution, 2,4-dinitroanisole solution, and trinitrotoluene solution with a concentration of 40 mg / L, respectively. The initial pH of the hexanitrobibenzyl solution, cyclotetramethylene tetranitramine solution, 2,4-dinitroanisole solution, and trinitrotoluene solution was adjusted to 6.3 with 0.1 mmol / L sulfuric acid and 0.1 mmol / L sodium hydroxide solution. Referring to Example 2 "Investigation of Catalytic Degradation of Organic Pollutants", the ability of CoFe2O4 to activate peroxymonosulfate (PMS) to degrade HNS (40 mg / L) was investigated.

[0085] The experimental results are as follows Figure 9 As shown, after 150 minutes of treatment, the degradation rates of hexanitropine, hexanitrobibenzyl, cyclotetramethylene tetranitramine, 2,4-dinitroanisole, and trinitrotoluene reached 96.3%, 93.1%, 81.4%, 88.2%, and 90.4%, respectively, and the total organic carbon (TOC) removal rates were 49.5%, 52.6%, 41.8%, 48.3%, and 46.7%, respectively. This indicates that the CoFe2O4 material of the present invention has good applicability in treating polynitrogen explosive wastewater.

[0086] Example 7

[0087] Referring to Example 2, "Investigation of Catalytic Degradation of Organic Pollutants," the ability of CoFe2O4 to cyclically catalyze the degradation of HNS (40 mg / L) using activated peroxymonosulfate (PMS) was tested. After each degradation cycle, the precipitate was centrifuged, washed multiple times with deionized water, and dried in an oven at 80°C for 3 h. The catalyst was recovered and the degradation of HNS (40 mg / L) was continued.

[0088] like Figure 10 As shown in FIG. 5 , after 5 uses, the degradation rate of CoFe2O4 for HNS solution (40 mg / L) decreased from 96% to 88%, indicating that the CoFe2O4 of the present invention has good stability and can maintain the degradation rate of HNS.

Claims

1. An iron-cobalt spinel oxide, characterized in that: The method uses iron salt and cobalt salt as raw materials, dissolves the iron salt, cobalt salt and sodium acetate in an ethanol aqueous solution to obtain a precursor solution, performs hydrothermal treatment on the precursor solution, and washes and dries the reaction product to obtain iron-cobalt spinel oxide.

2. The iron-cobalt spinel oxide according to claim 1, characterized in that: The iron salt is ferric nitrate or ferric chloride; the cobalt salt is cobalt nitrate, cobalt chloride or cobalt acetate; the molar ratio of the iron salt to the cobalt salt is 1:2 to 1:3 or 2:1, preferably 1:3 or 2:1; the molar ratio of the iron salt to sodium acetate is 1:5 to 1:7, preferably 1:6.

74.

3. The iron-cobalt spinel oxide according to claim 1, characterized in that: The ethanol aqueous solution is a mixed solvent with anhydrous ethanol and deionized water in a volume ratio of 35:2.5 to 20:17.

5.

4. A method for preparing the iron-cobalt spinel oxide according to claim 1, characterized in that: include: dissolving ferric nitrate, cobalt nitrate and sodium acetate in an ethanol aqueous solution to obtain a precursor solution; The precursor solution is subjected to hydrothermal treatment, and the reaction product is washed and dried to obtain the iron-cobalt spinel oxide.

5. The method for preparing the iron-cobalt spinel oxide according to claim 4, wherein: The temperature of the hydrothermal treatment is 170-180° C., and the time of the hydrothermal treatment is 10-12 hours.

6. The method for preparing the iron-cobalt spinel oxide according to claim 4, wherein: After the hydrothermal treatment, the mixture is cooled, filtered, and the reaction product is collected. The reaction product is repeatedly washed with deionized water and ethanol, filtered, and then dried to obtain an iron-cobalt spinel oxide.

7. A method for degrading nitrogen-rich explosive wastewater using the iron-cobalt spinel oxide according to claim 1, characterized in that: include: The iron-cobalt spinel oxide according to claim 1 is used as a catalyst, the iron-cobalt spinel oxide is added to wastewater, first stirred to adsorption equilibrium, then peroxymonosulfate is added, and the nitrogen-rich organic pollutants are degraded by stirring at room temperature.

8. A method for degrading nitrogen-rich explosive wastewater using the iron-cobalt spinel oxide according to claim 1, characterized in that: include: When the wastewater contains Cl - When adding silver nitrate, Cl - The wastewater is converted into silver chloride precipitate, and the iron-cobalt spinel oxide according to claim 1 is added into the wastewater, stirred to adsorption equilibrium, and then peroxymonosulfate is added and stirred at room temperature to degrade organic pollutants.

9. The method for degrading nitrogen-rich explosive wastewater using iron-cobalt spinel oxide according to claim 7 or 8, wherein: The amount of the iron-cobalt spinel oxide is 50-450 mg / L, preferably 50-200 mg / L, more preferably 100 mg / L; the amount of the peroxymonosulfate is 0.30-0.81 mmol / L, preferably 0.48-0.60 mmol / L, more preferably 0.60 mmol / L; the pH is 5-9, preferably 5-7, more preferably 6.

3.

10. The method for degrading nitrogen-rich explosive wastewater using iron-cobalt spinel oxide according to claim 7 or 8, characterized in that: The polynitrogen organic pollutant is at least one of hexanitropine, hexanitrobibenzyl, cyclotetramethylene tetranitramine, 2,4-dinitroanisole and trinitrotoluene.

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