A cysteine-modified iron-oxygen coordination polymer catalyst and a preparation method and application thereof

Abstract

This invention discloses a cysteine-modified iron-oxygen coordination polymer (NIC-Cys), its preparation method, and its applications. By biomimetic design of the NIC catalyst and cysteine ​​modification, a catalyst with a wider applicable pH range for electrocatalytic oxygen activation is obtained, showing promising applications in the synthesis of electrode materials and electrocatalytic water treatment. Compared with NIC catalysts, the cysteine-modified NIC catalyst provided in this invention exhibits faster bisphenol A removal kinetics and a higher concentration of hydroxyl radical generation. It maintains a high bisphenol A removal rate within a pH range of 3-8.5, demonstrating good pH adaptability and meeting the needs of practical wastewater treatment.

Description

Technical Field

[0001] This invention relates to an iron-oxygen coordination polymer catalyst, its preparation method and application, and more particularly to a cysteine-modified iron-oxygen coordination polymer catalyst (NIC-Cys), its preparation method and application. Background Technology

[0002] Electrocatalytic oxygen reduction (OR) technology is an effective method for removing recalcitrant organic pollutants such as bisphenol A from water. It converts oxygen into reactive oxygen species through reduction and activation, thereby mineralizing organic pollutants. The main reactive oxygen species involved in the OR process are hydroxyl radicals, singlet oxygen, and superoxide radicals. While singlet oxygen and superoxide radicals have limited oxidizing power and therefore limited ability to remove stable, recalcitrant pollutants, hydroxyl radicals possess strong oxidizing power and can be used to mineralize most stubborn organic pollutants. Currently, the most common method for generating hydroxyl radicals is the electro-Fenton method, which involves the two-electron reduction of oxygen to produce hydrogen peroxide, followed by activation of the hydrogen peroxide to generate hydroxyl radicals. However, improving the efficiency of hydroxyl radical generation is a key challenge in electrocatalytic OR water treatment technology. Non-heme iron catalysts are important mediators for the efficient activation of oxygen in biological processes, and the iron-oxygen coordination unit is a key active structure, providing a reference for designing electrocatalysts to activate oxygen and generate hydroxyl radicals.

[0003] The pH of aqueous solutions is a crucial factor affecting the oxygen reduction reaction. For example, graphite electrodes can electrocatalyze the production of hydrogen peroxide under acidic conditions, but their ability to produce hydrogen peroxide is weaker under alkaline and neutral conditions. Patent application CN119977089A discloses an electrode material based on a non-heme iron catalyst, its preparation method, and its application. This material mainly relies on the formation of coordination bonds between an inner auxiliary ligand layer and an outer non-heme iron layer to enhance the activation efficiency of oxygen. However, this technology is primarily applicable to conditions with pH ≤ 6. Under neutral and alkaline conditions, the precipitation of iron ions limits the activation rate of hydrogen peroxide, causing a rapid decline in the electrocatalytic performance of existing electro-Fenton technologies. However, the pH of municipal wastewater is often neutral or weakly alkaline. Therefore, existing catalysts are insufficient to meet the requirements of practical applications. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a cysteine-modified iron-oxygen coordination polymer catalyst with a wider pH range in electrocatalytic oxygen activation technology, as well as its preparation method and application.

[0005] Technical solution: The structure of the cysteine-modified iron-oxygen coordination polymer catalyst is as follows: the inner layer is a polydopamine structure, and the outer layer is a chelate of polydopamine and iron grafted with cysteine.

[0006] Cysteine ​​possesses proton-exchangeable groups such as carboxyl, thiol, and amino groups, which can be used to modify iron-oxygen coordination polymers, thus demonstrating the potential to construct pH buffer bands on electrode surfaces. Since electrocatalytic reactions often occur at the electrode surface, constructing a buffer band on the electrode surface, causing a difference in proton concentration between the electrode surface and the bulk solution, can enable iron-oxygen coordination polymer catalysts to maintain high electrocatalytic efficiency in neutral or alkaline aqueous environments.

[0007] Furthermore, referencing bio-enzymatic reactions that exhibit ultra-high reaction efficiency using organic ligands as proton sources, this invention, through the design of a biomimetic iron-oxygen coordination polymer catalyst, enables the transformation of the proton source from water to organic ligands, thereby improving the efficiency of electrocatalytic oxygen reduction activation.

[0008] The method for preparing the catalyst includes the following steps:

[0009] (1) Dissolve cysteine ​​and dopamine in ultrapure water, keep the solution continuously exposed to oxygen, and after the reaction is complete, cysteine-modified dopamine is obtained;

[0010] (2) Adjust the pH of the solution obtained in step 1 to acidic, evaporate the water to dryness using a rotary evaporator, add methanol and dissolve it completely. The cysteine ​​residue is solid. Filter and take the filtrate for rotary evaporation again. Retain the solid product. Wash the product thoroughly with a mixed solution of acetonitrile and methanol. After filtration, dry the filter residue in a vacuum drying oven.

[0011] (3) Dissolve the filter residue in water, adjust the pH to acidic, add ferrous ions to react; after the reaction is complete, adjust the pH of the system to neutral or weakly alkaline, add phosphate buffer, so that the cysteine-modified dopamine is chelated with iron to form a cysteine-modified iron-oxygen coordination monomer.

[0012] (4) Dissolve dopamine hydrochloride in phosphate buffer solution, and electrodeposit a polydopamine film on the surface of the electrode substrate material in a three-electrode system by cyclic voltammetry. Then, deposit the cysteine-modified iron-oxygen coordination polymer precursor on the surface of the polydopamine film by cyclic voltammetry and wash it thoroughly in ultrapure water.

[0013] In step (1), the preferred molar ratio of cysteine ​​to dopamine is 0.4-4:1, the solution pH is 5-8, and the reaction temperature is 20-40℃. The preferred reaction time is 6-24 h. The preferred oxygen flow rate per liter of solution is 5-2000 mL / min.

[0014] In step (2), the ratio of acetonitrile to methanol is preferably 50-5:1, and the drying temperature is 30-60℃.

[0015] In step (3), the preferred amount of ferrous ions added is a molar ratio of ferrous ions to dopamine of 0.14-2:1. The preferred concentration of the phosphate buffer solution is 0.01-0.1 M.

[0016] This invention also provides the application of the catalyst in electrocatalytic water treatment. The application method is as follows: in a three-electrode system, using the electrode material made of the catalyst as the working electrode and the water to be treated as the electrolyte, an electrocatalytic degradation reaction is carried out; the pH of the water to be treated is 3-8.5.

[0017] Preferably, a constant potential is applied to the working electrode, with the voltage set to -0.4V to -1.5V.

[0018] Beneficial Effects: Compared with existing technologies, the present invention has the following significant advantages: 1. Compared with iron-oxygen coordination polymer catalysts (NIC), cysteine-modified iron-oxygen coordination polymer catalysts (NIC-Cys) exhibit faster bisphenol A removal kinetics and higher concentrations of hydroxyl radical generation. 2. Cysteine-modified iron-oxygen coordination polymer catalysts (NIC-Cys) can maintain a high bisphenol A removal rate at pH 3-8.5, demonstrating good pH adaptability and meeting the needs of practical wastewater treatment. Attached Figure Description

[0019] Figure 1 Mass spectrometry analysis of dopamine grafted with cysteine ​​and dopamine;

[0020] Figure 2 The diagram shows the electrocatalytic kinetics of bisphenol A removal.

[0021] Figure 3 To detect hydroxyl radicals generated in an electrocatalytic system using electron spin resonance;

[0022] Figure 4 The effect of pH on the removal kinetics of bisphenol A during the reaction of cysteine ​​and dopamine in the preparation process;

[0023] Figure 5 The effect of temperature on the kinetics of bisphenol A removal during the preparation process of cysteine ​​and dopamine reactions;

[0024] Figure 6 The removal rate of bisphenol A by NIC-Cys in different wastewater pH systems is shown. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0026] Example 1

[0027] This embodiment provides a cysteine-modified iron-oxygen coordination polymer catalyst with the following structure: an inner layer of polydopamine and an outer layer of cysteine-branched polydopamine-iron chelate. The preparation method of the cysteine-modified iron-oxygen coordination polymer catalyst is as follows.

[0028] (1) Cysteine ​​modification reaction. Cysteine ​​and dopamine hydrochloride monomer were weighed in a molar ratio of 1:1, dissolved in ultrapure water, and the pH of the solution was adjusted to 8. The reaction was carried out at 30°C for 6 h. The solution was continuously aerated with oxygen, and the required oxygen flow rate was 400 mL / min per liter of solution, so that cysteine ​​and dopamine monomer could react fully.

[0029] (2) Adjust the pH of the solution obtained in step 1 to 3, evaporate the water to dryness using a rotary evaporator, add methanol and dissolve completely. The remaining cysteine ​​is solid. Filter and collect the filtrate for rotary evaporation again, retaining the solid product. Wash the product thoroughly with a mixed solution of acetonitrile:methanol (15:1), filter, and dry the filter residue at 40°C in a vacuum drying oven. Mass spectrometry analysis of the product is shown in [reference needed]. Figure 1 .

[0030] (3) Dissolve the product in step 2 in water, adjust the pH to below 6, add ferrous ions according to the molar ratio of ferrous ions to dopamine of 0.2:1, after the reaction is complete, adjust the pH of the system to neutral or weakly alkaline, the solution color changes from light green to dark purple, add 0.02 M phosphate buffer, cysteine-modified dopamine chelates with iron to form cysteine-modified iron-oxygen coordination monomer.

[0031] (4) Dissolve dopamine hydrochloride in phosphate buffer solution, and electrodeposit a polydopamine film on the surface of the electrode substrate material in a three-electrode system by cyclic voltammetry. Then, deposit cysteine-modified iron-oxygen coordination monomers on the surface of the polydopamine film by cyclic voltammetry to form an iron-oxygen coordination polymer, and wash thoroughly in ultrapure water.

[0032] Example 2

[0033] This embodiment provides an application of the cysteine-modified iron-oxygen coordination polymer catalyst described in Example 1 in electrocatalytic water treatment. 5 mg / L bisphenol A (pH=3) was used as the water to be treated. Hydroxyl radicals in the electrocatalytic system were detected by electron spin resonance.

[0034] Application Method: Electrode materials were prepared according to Example 1 and used as the working electrode in an electrocatalytic degradation experiment in a three-electrode system. The electrochemical reactor was a 100 mL cylindrical reactor, with a platinum sheet (10×10×0.1 mm) as the counter electrode and Ag / AgCl as the reference electrode; all electrodes were spaced 2 cm apart. The temperature was controlled at 30℃, the stirring speed at 500 rpm, the oxygen aeration flow rate at 20 mL / min, and the electrolyte as sodium sulfate. A constant potential was applied to the working electrode using an electrochemical workstation, with the voltage set to -1 V. The treatment effect was compared with that of an electrode material prepared using an unmodified iron-oxygen coordination polymer iron catalyst.

[0035] Test results: such as Figure 2 , Figure 3 As shown, compared to the unmodified cysteine-based iron-oxygen coordination polymer catalyst, the cysteine-modified iron-oxygen coordination polymer catalyst exhibits faster bisphenol A removal kinetics and can catalyze the generation of higher concentrations of hydroxyl radicals. Figure 5 As shown, after 1 h of energization, the cysteine-modified iron-oxygen coordination polymer catalyst achieved a 99% removal rate of bisphenol A.

[0036] Example 3

[0037] Based on Example 1, this example illustrates the effect of pH on the removal kinetics of bisphenol A during the reaction of cysteine ​​and dopamine in the synthesis process.

[0038] Experimental method: The pH of the solution in step (1) of Example 1 was adjusted to 3, 5, 7, 8 and 9 respectively to prepare cysteine-modified iron-oxygen coordination polymer catalysts. The bisphenol A removal effect was tested according to Example 2.

[0039] Test results: such as Figure 4 As shown, under the synthesis conditions of pH 5-8, the cysteine-modified non-heme iron catalyst exhibits faster bisphenol A removal kinetics.

[0040] Example 4

[0041] Based on Example 1, this example investigates the effect of the temperature of the cysteine ​​and dopamine reaction during synthesis on the removal kinetics of bisphenol A.

[0042] Experimental method: The reaction temperature in step (1) of Example 1 was adjusted to 10, 20, 30, 40 and 50 °C respectively to prepare cysteine-modified iron-oxygen coordination polymer catalysts. The bisphenol A removal effect was tested according to Example 2.

[0043] Test results: such as Figure 5As shown, under the synthesis conditions of 20-40℃, the cysteine-modified iron-oxygen coordination polymer catalyst exhibits faster bisphenol A removal kinetics.

[0044] Example 5

[0045] Based on Example 2, this example explores the applicable pH of the wastewater to be treated when the cysteine-modified iron-oxygen coordination polymer catalyst is applied to electrocatalytic water treatment.

[0046] Experimental method: Following the application method in Example 3, the pH of the wastewater to be treated was adjusted to 3, 5, 7, 7.5, 8, and 8.5, respectively. The bisphenol A removal efficiency was then tested.

[0047] Test results: such as Figure 6 As shown, the cysteine-modified iron-oxygen coordination polymer catalyst (NIC-Cys) can maintain a high bisphenol A removal rate at pH 3-8.5, that is, it has a wide pH adaptability, especially maintaining a high bisphenol A removal rate under neutral conditions.

Claims

1. A cysteine-modified iron-oxygen coordination polymer catalyst, characterized in that, The inner layer is a polydopamine structure, and the outer layer is a chelate of cysteine-branched polydopamine and iron. The preparation method of the catalyst includes the following steps: (1) Synthesis of cysteine-modified dopamine: Cysteine ​​and dopamine were dissolved in ultrapure water, and oxygen was continuously aerated in the solution. After the reaction was complete, cysteine-modified dopamine was obtained. (2) Purification of cysteine-modified dopamine: Adjust the pH of the solution obtained in step (1) to acidic, then evaporate the water to dryness, add methanol and dissolve it completely. The cysteine ​​residue is solid. Filter and take the filtrate to evaporate again. Retain the solid product. Wash the product thoroughly with a mixture of acetonitrile and methanol. After filtration, dry the filter residue in a vacuum drying oven. (3) Synthesis of cysteine-modified iron-oxygen coordination polymer precursor: Dissolve the filter residue from step (2) in water, adjust the pH to acidic, add ferrous ions to react; after the reaction is complete, adjust the pH of the system to neutral or weakly alkaline, add phosphate buffer, so that the cysteine-modified dopamine chelates with iron to form cysteine-modified iron-oxygen coordination polymer precursor; (4) Catalytic electrode synthesis: Dopamine hydrochloride was dissolved in phosphate buffer and a polydopamine film was electrodeposited on the surface of the electrode substrate material by cyclic voltammetry in a three-electrode system. Then, cysteine-modified iron-oxygen coordination polymer precursor was deposited on the surface of the polydopamine film by cyclic voltammetry and thoroughly washed in ultrapure water.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of cysteine ​​to dopamine is 0.4-4:1, the solution pH is 5-8, and the reaction temperature is 20-40℃.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of ferrous ions added is 0.14-2:1, which is the molar ratio of ferrous ions to dopamine.

4. The method of claim 1, wherein, The ratio of acetonitrile to methanol is 50-5:1, and the drying temperature is 30-60℃.

5. The catalyst as set forth in claim 1, which is mainly used for the treatment of municipal waste water or industrial waste water, characterized by, Suitable for treating wastewater with a wider pH range (pH=3-8.5), especially for the efficient treatment of wastewater under neutral conditions.

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