Method for efficiently degrading nitrophenol wastewater by iron-zinc bimetallic catalytic system and catalyst recovery method

Abstract

The invention relates to a method for efficiently degrading nitrophenol wastewater by an iron-zinc bimetallic catalytic system and a catalyst recovery method, the method comprises the following steps: dissolving a zinc salt in pure water or deionized water to prepare a zinc salt solution, and the zinc salt solution is used as a cocatalyst; the method comprises the following steps: uniformly mixing wastewater containing the nitrophenol compound with a zinc salt solution, adding zero-valent iron particles to form an iron-zinc bimetallic catalytic system, and carrying out catalytic reduction reaction on the nitrophenol compound to realize wastewater treatment. Compared with a zero-valent iron reduction system, the method has the advantages of higher degradation efficiency, low catalytic reaction cost and no secondary pollution, has potential application prospects in utilization of zinc-containing wastewater generated in the industries of electroplating, metallurgy, chemical industry and the like, and can be used for treating nitrophenol-containing wastewater generated in the industries of military industry, chemical industry, dye, medicine and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and particularly relates to a method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system and a catalyst recovery method. Background Art

[0002] Nitrophenols are widely used in a wide range of fields, including synthetic dyes, plasticizers, pesticides, herbicides, coatings, pharmaceuticals, explosives, and wood and leather preservatives. However, nitrophenols and their derivatives are often highly toxic, carcinogenic, and bioaccumulative, and some nitrophenols have been listed as priority pollutants by the United States Environmental Protection Agency (USEPA). Direct discharge of wastewater containing nitrophenols and their derivatives into water bodies poses a threat to ecosystems and human health. Traditional biological wastewater treatment processes, such as activated sludge, are ineffective in treating these pollutants because the nitro group in nitrophenols is electron-absorbent, inhibiting electrophilic enzyme attack. However, the aminophenols produced by the reduction of nitrophenols exhibit significantly reduced biotoxicity. Therefore, there is a need to develop a simple and efficient catalytic reduction method for nitrophenols.

[0003] Currently, zero-valent iron (ZVI), a cost-effective, environmentally friendly functional material for water treatment, is considered a promising method for reducing nitrophenols. However, the formation of excess iron oxides from iron corrosion products coats the ZVI surface, limiting its catalytic performance. Adding promoter metals (such as Cu, Sn, In, and Zn) to the reducing agent surface can enhance the reactivity of the reducing agent. However, finding a cost-effective, environmentally friendly promoter to further enhance the degradation efficiency of nitrophenols remains an unmet challenge. Summary of the Invention

[0004] The present invention aims to address the aforementioned issues presented by the prior art by providing a method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system and a catalyst recovery method. This method utilizes zero-valent iron as a reducing agent and a zinc salt solution as a co-catalyst to achieve efficient degradation of nitrophenol compounds. For example, 500 mg / L of p-nitrophenol can be completely degraded within one hour using the iron-zinc bimetallic catalytic system. This system significantly improves degradation efficiency by accelerating electron transfer.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system, the method comprising the following steps:

[0007] Step 1: Dissolve zinc salt in pure water or deionized water to prepare a zinc salt solution, which serves as a co-catalyst;

[0008] Step 2: Evenly mix the wastewater containing nitrophenol compounds with the zinc salt solution, add zero-valent iron particles to form an iron-zinc bimetallic catalytic system, and carry out catalytic reduction reaction of nitrophenol compounds to achieve wastewater treatment. The catalyst of the iron-zinc bimetallic catalytic system is zero-valent iron particles, and the co-catalyst is Zn 2+ , forming zero-valent iron-Zn 2+ Solid-liquid two-phase system; During the degradation of nitrophenol in the iron-zinc bimetallic catalytic system, zinc is gradually adsorbed onto the surface of zero-valent iron and plays a catalytic role on the iron surface instead of being dispersed in the aqueous solution.

[0009] Furthermore, in step 1, the concentration of the zinc salt solution is 0.25-1.5 mmol / L; the zinc salt is one of zinc nitrate, zinc sulfate or zinc chloride; the resistivity of the pure water is 1-5 MΩ·cm, and the pH is 5.5-6.5.

[0010] Furthermore, in step 2, the nitrophenol compound is one or more of a p-nitrophenol compound, an o-nitrophenol compound or a m-nitrophenol compound; and the concentration of the nitrophenol compound in the wastewater containing the nitrophenol compound is 125-1000 mg / L.

[0011] Furthermore, in step 3, the volume ratio of the wastewater containing nitrophenol compounds to the zinc salt solution is 800:1~400:3; and the dosage of the zero-valent iron particles is 8~12 g / L.

[0012] Furthermore, in step 3, the zero-valent iron particles are sieved to obtain particles with a mesh size of 250-200.

[0013] Furthermore, in step 3, before mixing the wastewater containing nitrophenol compounds with the zinc salt solution, the initial pH of the wastewater needs to be adjusted to 3.0.

[0014] Furthermore, in step 3, the temperature of the catalytic reduction reaction is 20-30° C., and the time is 60 minutes.

[0015] A method for recovering the catalyst obtained by the above method is characterized by washing the reacted catalyst three times with clean water and drying it under vacuum at 40°C for four hours. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis of the recovered catalyst material revealed the presence of zinc on the surface of the zero-valent iron (ZVI) of the catalyst. X-ray diffraction (XRD) analysis revealed diffraction peaks associated with ZVI and ferroferric oxide, but no diffraction peaks associated with the crystalline structure of zinc. X-ray photoelectron spectroscopy analysis revealed that the zinc was divalent and existed in the Zn(II) form.

[0016] The beneficial effects of the present invention relative to the prior art are:

[0017] 1. The present invention uses an iron-zinc bimetallic catalytic system to degrade nitrophenol wastewater, which can not only effectively remove pollutants, but also overcome the problem of limited catalytic efficiency caused by the formation of excessive iron oxides in iron corrosion products covering the zero-valent iron surface. In the iron-zinc bimetallic catalytic system, Zn 2+ The presence of can accelerate the electron transfer on the surface of zero-valent iron, release more Fe(II), and thus enhance the reaction efficiency of zero-valent iron.

[0018] 2. The present invention has a higher degradation efficiency than zero-valent iron reduction systems, low catalytic reaction costs, and no secondary pollution. The present invention can utilize zinc from zinc-containing wastewater generated by industries such as electroplating, metallurgy, and chemical engineering as a source of zinc salts, achieving the goal of "treating waste with waste," thus possessing significant application prospects. The present invention can be used to treat nitrophenol-containing wastewater generated by industries such as military, chemical, dye, and pharmaceutical industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a comparison chart of the degradation efficiency of p-nitrophenol in Example 1 of the present invention;

[0020] Figure 2 This is a graph showing the change of Fe(II) content over time in the system of Example 1 of the present invention;

[0021] Figure 3 This is a comparison chart of the degradation efficiency of p-nitrophenol in Example 2 of the present invention;

[0022] Figure 4 This is a graph showing the change of Fe(II) content over time in the system of Example 2 of the present invention;

[0023] Figure 5 This is a comparison chart of the degradation efficiency of p-nitrophenol in Example 3 of the present invention;

[0024] Figure 6 is Zn in Example 4 of the present invention 2+ Concentration versus time graph;

[0025] Figure 7 This is a scanning electron microscope-energy spectrum analysis diagram of the catalyst after the reaction in Example 4 of the present invention;

[0026] Figure 8 This is the XPS fine spectrum fitting diagram of the zinc element of the catalyst after the reaction in Example 4 of the present invention;

[0027] Figure 9 This is the XRD spectrum of the catalyst after the reaction in Example 4 of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0029] This embodiment describes a method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system, the method comprising the following steps:

[0030] Step 1: dissolving zinc salt in pure water to prepare a zinc salt solution as a co-catalyst zinc salt solution;

[0031] The concentration of the zinc salt solution is 0.25~1.5mmol / L. The zinc salt can be zinc nitrate, zinc sulfate, or zinc chloride. When the zinc salt solution dosage is 0.25, 0.50, 1.00, and 1.50mmol / L, respectively, after 60 minutes of reaction, the degradation rates of p-nitrophenol (PNP) are 93.09%, 99.99%, 91.64%, and 78.26%, respectively, which are all higher than those without adding Zn. 2+ iron reduction system.

[0032] Step 2: After uniformly mixing the nitrophenol wastewater and the zinc salt solution in a volume ratio of 800:1 to 400:3, zero-valent iron particles are added to form an iron-zinc bimetallic catalyst system to perform a catalytic reduction reaction of the nitrophenol compound; the catalytic reduction reaction temperature is 20-30° C. and the time is 60 minutes;

[0033] In the iron-zinc bimetallic catalytic system, zero-valent iron is used as a catalyst, and the initial introduction form of the co-catalyst zinc is in the form of a divalent ion to form zero-valent iron-Zn 2+ Solid-liquid two-phase system.

[0034] When the dosage of the zero-valent iron particles is 8-12 g / L, the removal rate of p-nitrophenol can reach more than 95%. When the dosage is less than 8 g / L or greater than 12 g / L, the removal rate of nitrophenol is reduced to only about 85-88%.

[0035] The zero-valent iron particles are sieved to obtain particles with a mesh size of 250 to 200. The 250- to 200-mesh size of zero-valent iron has a large specific surface area, exposing more active sites to promote the degradation of nitrophenol. It is also easy to separate from the solution, overcoming the drawback of nano-zero-valent iron particles that are difficult to separate due to agglomeration. The synergistic effect of the iron-zinc bimetallic catalytic system can complete the rapid adsorption-electron transfer-reduction degradation process of nitrophenol within 60 minutes. Insufficient reaction time will result in incomplete degradation of nitrophenol pollutants, while excessive reaction time will lead to increased processing costs.

[0036] The removal of p-nitrophenol is most effective between 20°C and 30°C. Temperatures below 20°C impair mass transfer in the reduction system, hindering the reaction. Temperatures above 30°C intensify oxidation of the iron particles, reducing the efficiency of iron electron transfer. A temperature between 20°C and 30°C is close to room temperature, saving energy and making it suitable for treating most industrial wastewaters.

[0037] Furthermore, before mixing the nitrophenol wastewater with the zinc nitrate solution, the initial pH of the nitrophenol solution needs to be adjusted to 3.0. Adjusting the initial pH of the nitrophenol wastewater to 3.0 can effectively prevent iron surface passivation, enhance particle activity, and accelerate the corrosion of zero-valent iron for the reduction process of nitrophenol.

[0038] In the nitrophenol wastewater, the concentration of the nitrophenol compound is 125-1000 mg / L; the nitrophenol compound is a p-nitrophenol compound, an o-nitrophenol compound or a m-nitrophenol compound;

[0039] When using an iron-zinc bimetallic catalytic system for degradation, the removal rate for p-nitrophenol wastewater with a concentration between 125 and 1000 mg / L can reach over 85%. In particular, the removal rate can reach over 95% when the p-nitrophenol concentration is between 250 and 1000 mg / L.

[0040] Step 3: After the reaction is completed, the catalyst material is recovered (i.e., the zero-valent iron particles are recovered).

[0041] The catalyst material contains zinc on its surface after the reaction. The catalyst material is composed of zero-valent iron and ferroferric oxide, with no zinc crystal structure found. The zinc in the catalyst material exists in the form of Zn(II).

[0042] In the following examples, zero-valent iron was used as a catalyst and zinc ions as a co-catalyst to achieve efficient degradation of nitrophenol. Nitrophenol was taken as an example:

[0043] The preparation process of the p-nitrophenol solution used is as follows: 0.25g, 0.5g, 1.0g, 1.5g, and 2.0g of p-nitrophenol powder are dissolved in 2L of pure water to form 125mg / L, 250mg / L, 500mg / L, 750mg / L, and 1000mg / L p-nitrophenol solutions, respectively.

[0044] The zinc nitrate solution used was prepared by dissolving 1.894 g of zinc nitrate in 50 mL of pure water to form a 0.2 mol / L zinc nitrate solution.

[0045] The zero-valent iron particles used were: micron zero-valent iron particles were sieved, and particles between 250 and 200 meshes were used for subsequent experiments.

[0046] The ethanol used is: 99.5% pure anhydrous ethanol.

[0047] The acetic acid used was: glacial acetic acid with a purity of 99.5%.

[0048] Pb used 2+ The preparation process is as follows: 0.2399 g of lead nitrate is dissolved in 50 mL of pure water to form a lead nitrate solution.

[0049] The pure water used was Wahaha brand pure water for laboratory use, with a resistivity of 1–5 MΩ·cm and a pH of 5.5–6.5.

[0050] Recovery of zero-valent iron: After the reaction is completed, the zero-valent iron particles are collected by filtration and washed three times with clean water.

[0051] Example 1:

[0052] 300 mL of 500 mg / L p-nitrophenol wastewater and 0.375 mL, 0.75 mL, 1.50 mL, and 2.25 mL of 0.2 mol / L zinc nitrate solution were poured into four different beakers and mixed evenly to obtain a uniform mixed solution. The beakers were placed in a constant temperature water bath and heated to 25°C. The initial pH of the p-nitrophenol solution was adjusted to 3.0. 3.0 g of zero-valent iron particles were added to the mixed solution and stirred at a speed of 400 r / min to carry out the p-nitrophenol degradation reaction. 2 mL of sample was taken at 5, 10, 20, 30, 40, 50, and 60 min after the start of the reaction. The samples were immediately filtered through a 0.22 µm polytetrafluoroethylene (PTFE) filter membrane and the concentrations of p-nitrophenol and Fe(II) in the system were measured. The results are as follows: Figure 1 and Figure 2 shown.

[0053] The method of Example 1 of the present invention can improve the removal efficiency of p-nitrophenol in water. Figure 1 As shown, the removal efficiency of the method of the present invention is higher than that of the single zero-valent iron reduction system. At 25 ° C, the amount of zero-valent iron added to the iron-zinc reduction system is 3.0 g, and Zn 2+ Under the conditions of 0.25 mmol / L, 0.50 mmol / L, 1.00 mmol / L, and 1.50 mmol / L, after treating 500 mg / L p-nitrophenol solution for 60 minutes, the p-nitrophenol removal rates reached 93.09%, 99.98%, 91.64%, and 78.26%, respectively, which were all higher than the 76.88% of the zero-valent iron system alone. 2+ The increase in dosage indicates that the addition of Zn in the reduction system 2+It helps zero-valent iron transfer electrons for the reduction of p-nitrophenol.

[0054] Nitrophenol pollutants, such as p-nitrophenol, o-nitrophenol, and m-nitrophenol, have similar structures, all consisting of a benzene ring, a nitro group, and a hydroxyl group. The principle of the iron-zinc bimetallic catalytic system for the degradation of p-nitrophenol is that zero-valent iron reduces the nitro group (-NO2) in p-nitrophenol to an amino group (-NH2), while Zn 2+ It acts as a catalyst in the system, accelerating the reduction of p-nitrophenol by zero-valent iron. Therefore, the iron-zinc bimetallic catalytic system is suitable for the removal of nitrophenol pollutants.

[0055] Example 2:

[0056] 300 mL of 125 mg / L, 250 mg / L, 500 mg / L, 750 mg / L, and 1000 mg / L p-nitrophenol solutions and 0.75 mL of 0.2 mol / L zinc nitrate solution were poured into 5 different beakers, mixed evenly, and a uniform mixed solution was obtained. The beakers were placed in a constant temperature water bath, heated to 25°C, and the initial pH of p-nitrophenol was adjusted to 3.0. 3.0 g of zero-valent iron particles were added to the mixed solution in sequence, and stirred at a speed of 400 r / min to carry out the degradation reaction of p-nitrophenol. 2 mL of sample was taken at 5, 10, 20, 30, 40, 50, and 60 min after the start of the reaction, and immediately filtered through a 0.22µm polytetrafluoroethylene (PTFE) filter membrane. The concentrations of p-nitrophenol and Fe(II) in the system were measured. The results are as follows: Figure 3 and Figure 4 shown.

[0057] The method of Example 2 of the present invention has a good removal effect on different concentrations of p-nitrophenol in water. Figure 3 As shown in the figure, when the initial p-nitrophenol concentration is 125 mg / L, 250 mg / L, 500 mg / L, 750 mg / L, and 1000 mg / L, the pollutant degradation rates are 88.97%, 97.23%, 97.18%, 97.28%, and 95.70%, respectively, indicating that the iron-zinc bimetallic catalytic system has good removal efficiency for p-nitrophenol solutions of different concentrations. The change of ferrous ion concentration during the reaction is shown in the figure. Figure 4 As the concentration of p-nitrophenol increases, p-nitrophenol causes severe corrosion of zero-valent iron, which in turn promotes the reduction of p-nitrophenol.

[0058] In summary, the present invention sequentially dissolves p-nitrophenol and zinc nitrate in pure water to form a p-nitrophenol solution and a zinc nitrate solution, respectively; then, the p-nitrophenol solution is adjusted to an initial pH and mixed with the zinc nitrate solution, and then zero-valent iron particles are added to catalyze the degradation of p-nitrophenol.

[0059] Example 3:

[0060] In view of the complex composition of actual wastewater, this embodiment adds coexisting pollutants such as ethanol, acetic acid, and Pb 2+ To investigate the effect on the degradation efficiency of p-nitrophenol, ethanol, acetic acid, and lead nitrate solution were added to three beakers containing 300 mL of 500 mg / L p-nitrophenol and mixed evenly. 2+ The concentration of Pb is added according to the molar ratio of Pb to 4-nitrophenol in the actual water. The molar ratio of ethanol: acetic acid: nitrophenol in the actual nitrophenol production wastewater is 37.99:7.58:1. 2+ The maximum concentration is 5 mg / L. In this embodiment, ethanol, acetic acid, Pb 2+ The addition amounts were 136.3mmol / L, 27.2mmol / L, and 5mg / L, respectively. The beaker was placed in a constant temperature water bath, heated to 25°C, and the initial pH of p-nitrophenol was adjusted to 3.0. 0.75mL of 0.2mol / L zinc nitrate solution was added, and then 3.0g of zero-valent iron particles were added to the mixture in sequence. The mixture was stirred at a speed of 400r / min to degrade p-nitrophenol. 1mL of sample was taken at 5, 10, 20, 30, 40, 50, and 60min after the start of the reaction, and immediately filtered through a 0.22µm polytetrafluoroethylene (PTFE) filter membrane to determine the p-nitrophenol concentration. The results are as follows: Figure 5 shown.

[0061] The method of Example 3 of the present invention has a good effect on removing p-nitrophenol in the presence of coexisting pollutants in actual water bodies. Figure 5 As shown in the figure, in the process of degradation of p-nitrophenol by iron-zinc bimetallic catalytic system, ethanol, acetic acid, Pb 2+ After the treatment, the degradation rate of p-nitrophenol remained above 99.8%, which confirmed that the system has a high efficiency in removing p-nitrophenol in complex water environment.

[0062] Example 4:

[0063] Pour 300 mL of 500 mg / L p-nitrophenol solution and 0.75 mL of 0.2 mol / L zinc nitrate solution into a beaker in sequence and mix well to obtain a uniform mixed solution. Place the beaker in a constant temperature water bath and heat it to 25°C. Adjust the initial pH of the p-nitrophenol solution to 3.0. Add 3.0 g of zero-valent iron particles to the mixed solution in sequence and stir at 400 r / min to carry out the p-nitrophenol degradation reaction. Take 2 mL of sample at 5, 10, 20, 30, 40, 50, and 60 min after the start of the reaction. Immediately filter through a 0.22 µm polytetrafluoroethylene (PTFE) filter membrane and measure the zinc concentration in the solution. The results are as follows: Figure 6 After 60 minutes of reaction, the catalyst material was collected, washed with water three times, and dried at 40°C for 4 hours under vacuum conditions for characterization analysis. The results are shown in Figures 7 to 9 shown.

[0064] The materials recovered after the iron-zinc bimetallic catalytic system degraded p-nitrophenol were collected and characterized. Scanning electron microscopy-energy spectrum analysis observed the presence of zinc on the iron surface, indicating that zinc was adsorbed onto the zero-valent iron surface during the degradation of p-nitrophenol by the iron-zinc bimetallic catalytic system, rather than dispersed in the solution. The zinc concentration was less than 0.5 mg / L after 20 minutes of reaction, and less than 0.1 mg / L after 60 minutes of reaction, also confirming that zinc was not dispersed in the solution. During the degradation of p-nitrophenol by the iron-zinc bimetallic catalytic system, zinc first adsorbed onto the zero-valent iron surface, accelerating electron transfer, causing the zero-valent iron to release more electrons and convert into Fe(II). At the same time, electrons were transferred to p-nitrophenol, reducing it to p-aminophenol, completing the degradation process.

[0065] X-ray photoelectron spectroscopy analysis of the zinc speciation in the post-reaction catalyst revealed that the zinc was divalent and existed as Zn(II). X-ray diffraction (XRD) analysis of the post-reaction catalyst revealed diffraction peaks of zero-valent iron at 2θ=44.6°, 65.0°, and 82.3°, and peaks of Fe₃O₄ at 2θ=30.1°, 35.5°, and 43.2°. No diffraction peaks were observed for the crystalline structure of zinc, indicating that the post-reaction catalyst was composed of zero-valent iron and ferrosoferric oxide. No zinc crystal structure was observed, confirming that the zinc existed in an ionic form and that no form transformation occurred during the degradation of p-nitrophenol.

Claims

1. A method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system, characterized in that: The method comprises the following steps: Step 1: Dissolve zinc salt in pure water or deionized water to prepare a zinc salt solution; Step 2: Evenly mix the wastewater containing nitrophenol compounds with the zinc salt solution, add zero-valent iron particles to form an iron-zinc bimetallic catalytic system, and carry out a catalytic reduction reaction of the nitrophenol compounds to achieve wastewater treatment.

2. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system according to claim 1, wherein: In step 1, the concentration of the zinc salt solution is 0.25-1.5 mmol / L; the zinc salt is one of zinc nitrate, zinc sulfate or zinc chloride; the resistivity of the pure water is 1-5 MΩ·cm, and the pH is 5.5-6.

5.

3. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system according to claim 1, characterized in that: In step 2, the nitrophenol compound is one or more of a p-nitrophenol compound, an o-nitrophenol compound, or a m-nitrophenol compound; and the concentration of the nitrophenol compound in the wastewater containing the nitrophenol compound is 125 to 1000 mg / L.

4. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system according to claim 1, wherein: In step 3, the volume ratio of the wastewater containing nitrophenol compounds to the zinc salt solution is 800:1 to 400:3; and the dosage of the zero-valent iron particles is 8 to 12 g / L.

5. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system according to claim 1 or 4, characterized in that: In step 3, the zero-valent iron particles are sieved to obtain particles with a mesh size of 250-200.

6. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalyst system according to claim 1, characterized in that: In step 3, before mixing the wastewater containing nitrophenol compounds with the zinc salt solution, the initial pH of the wastewater needs to be adjusted to 3.

0.

7. The method for efficiently degrading nitrophenol wastewater using an iron-zinc bimetallic catalytic system according to claim 1, characterized in that: In step 3, the temperature of the catalytic reduction reaction is 20-30° C., and the time is 60 min.

8. A method for recovering the catalyst obtained by the method according to any one of claims 1 to 7, characterized in that: The reacted catalyst was washed with clean water three times and dried at 40°C under vacuum conditions for 4 hours.

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