A Ni-Co-S material for electrochemically recovering formate from the hydrolysis product of PET waste plastics

Abstract

The present invention discloses a preparation method and electrocatalytic application of a metal organic framework compound (Co-MOF NSAs) and its derivative (Ni-Co-S NSAs) based on nickel foam. The preparation of the material includes the following steps: (1) cleaning of nickel foam; (2) preparation of Co-MOF NSAs: adding cobalt nitrate hexahydrate and 2-methylimidazole to deionized water, stirring and placing them in a 100mL autoclave with nickel foam for hydrothermal reaction at 70°C for 4 hours, taking them out and cleaning and drying them. (3) preparation of Ni-Co-S NSAs: using Co-MOF NSAs as a precursor, adding thioacetamide to deionized water, ultrasonically mixing them, placing them in a 100mL autoclave for hydrothermal reaction at 120°C for 4 hours, taking them out and cleaning and drying them to obtain Ni-Co-S NSAs. The electrocatalytic material is used for electrocatalytic oxidation of ethylene glycol (EG), a hydrolysis product of polyethylene terephthalate (PET), and can generate about 130mA cm at the positive terminal. ‑2 The current density of 1.5 V vs RHE was achieved, and the formate Faradaic efficiency exceeded 90%.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials, and specifically relates to the preparation of a non-precious metal electrocatalytic material and the application research of the material in electrochemically oxidizing PET hydrolysis products to formate. Background Art

[0002] Plastics are increasingly used in our daily lives. Polyethylene terephthalate (PET), a key plastic, has been widely used in industries such as packaging, automotive, and textiles due to its excellent properties. However, PET plastic products are often discarded, resulting in a large amount of plastic waste each year. Due to its slow natural degradation, large amounts of PET waste accumulate in the environment, eroding and fragmenting into smaller plastic particles, posing a serious threat to the ecosystem.

[0003] Therefore, upgrading PET plastics into valuable chemicals is of great significance from both economic and environmental perspectives. Currently, typical methods for treating plastics include separation and degradation. Plastic separation technologies involve adsorption, coagulation / flocculation, and filtration, while plastic degradation technologies primarily include biodegradation, advanced oxidative degradation, electrochemical degradation, and photocatalytic degradation. Separation technologies struggle to completely remove microplastics, while degradation technologies are energy-intensive and prone to producing byproducts that cannot be recycled, leading to secondary pollution.

[0004] In contrast, electrochemical plastic reforming promises to provide a green, convenient, and efficient plastic recycling pathway. In recent years, research on the electrochemical upcycling of PET has been increasing. This method is based on the catalytic hydrolysis of PET, followed by electrochemical oxidation of ethylene glycol (EG) and purified terephthalic acid (PTA) in aqueous solution. Further electrochemical catalytic EG oxidation reaction (EGOR) yields valuable chemicals such as formic acid, glycolic acid, and green hydrogen energy.

[0005] This approach offers a sustainable and compelling pathway for the direct upcycling of PET-derived EG into high-value chemicals under alkaline conditions. On the one hand, the reaction conditions are relatively mild and the experimental setup is simple. On the other hand, the production of high-value-added chemicals from plastic upgrading at the anode can be carried out simultaneously with hydrogen production (hydrogen evolution reaction, HER) at the cathode. This approach, by converting PET into PTA and other readily separable valuable products (such as formic acid), is a highly promising recycling strategy.

[0006] According to previous reports, some electrocatalysts have shown remarkable performance in the ethylene glycol oxidation reaction (EGOR). For example, Wang et al. demonstrated the use of CuO nanowires to oxidize PET hydrolyzates, selectively converting ethylene glycol to formate with a Faradaic efficiency (FE) of 86.5%. In a similar study, a nickel-modified cobalt phosphide (CoNi 0.25 P) can electrochemically convert PET-derived ethylene glycol into formic acid and acetic acid with a FE exceeding 80%, but the selectivity for formic acid is relatively low. Recently, Liu et al. demonstrated that PET-derived ethylene glycol can be efficiently converted into acetic acid in Pd-Ni(OH)2 at 300 mA cm -2 The selectivity exceeds 90% at a current density of 1.5 Å. However, the use of Pd reduces the cost-effectiveness of the process. In general, the development of efficient non-precious metal electrocatalysts that can achieve high formate selectivity at high current density is a major research direction.

[0007] Therefore, we used a simple hydrothermal method to prepare non-precious metal organic framework compounds (Co-MOF) and their derivatives (Ni-Co-S) materials with nanosheet array morphology (NSAs) that can convert PET hydrolysis products into formate at the cathode. As a preferred catalyst, Ni-Co-S can generate about 130 mA cm -2 A high formate Faradaic efficiency exceeding 90% was achieved at an applied potential of 1.5 V vs RHE. Summary of the Invention

[0008] To address the low Faradaic efficiency of electrocatalytic conversion of PET waste plastics into formate and the high cost of noble metal-based electrocatalytic materials, the present invention provides electrocatalytic materials based on non-noble metal organic frameworks (Co-MOF NSAs) and their derivatives (Ni-Co-S NSAs), as well as their preparation methods and applications. These electrocatalytic materials are grown directly on nickel foam (NF), facilitating contact between the active material and charged species, thereby reducing charge transfer paths and improving electrochemical performance.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0010] (1) Nickel foam treatment: Nickel foam was continuously sonicated in hydrochloric acid solution, anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60 °C to obtain blank NF.

[0011] (2) Preparation of Co-MOF NSAs: Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in 40 mL of deionized water and stirred. After complete dissolution, they were added together with the treated nickel foam into a stainless steel autoclave and then heated in an electric oven at 70°C for 4 hours. After cooling, the autoclave was removed, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 hours to obtain Co-MOF NSAs.

[0012] (3) Preparation of Ni-Co-S NSAs: Using Co-MOF NSAs as precursors, thioacetamide (TAA) was dissolved in 60 mL of deionized water and stirred. After complete dissolution by ultrasonication, the precursors were added to a stainless steel autoclave and then heated in an electric oven at 120°C for 4 h. After cooling, the mixture was removed, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 h to obtain Ni-Co-S NSAs.

[0013] Preferably, in step (1), the size of the nickel foam is 2cm*4cm, the concentration of hydrochloric acid is 3mol / L aqueous solution, and the concentration of anhydrous ethanol is 95%.

[0014] In step (2), the mass of cobalt nitrate hexahydrate in solution 1 is 291.5 mg, the amount of deionized water is 40 mL, and the stirring time is 10 minutes. The mass of 2-methylimidazole in solution 2 is 1250.3 mg, the amount of deionized water is 40 mL, and the stirring time is 10 minutes.

[0015] Preferably, in step (2), the hydrothermal reaction temperature is 70° C. and the reaction time is 4 hours.

[0016] Preferably, in step (3), the amount of TAA is 202.3 mg, the total amount of deionized water is 60 mL, the ultrasonic time is 5 min, the hydrothermal reaction temperature is 120° C., and the reaction time is 4 hours.

[0017] The aforementioned NF, Co-MOF, and Ni-Co-S NSAs electrocatalytic materials were used as working electrodes. In summary, a two-step hydrothermal generation method was used to in situ form Ni-Co-S NSAs nanosheet arrays with spherical particles on nickel foam. These nanosheets exhibited excellent EGOR performance, capable of oxidizing ethylene glycol and increasing its added value to produce formic acid. Using PET alkaline hydrolysis products as the electrolyte, the positive terminal was able to achieve a charge of ~130 mA cm at an applied voltage of 1.5 V vs RHE. -2 Highly selective conversion of FE formate (>90%) was achieved at a current density of 1.5 Å. This study reveals a synthetic strategy for transition metal sulfides, providing a new, efficient and sustainable route for the value-added conversion of PET. DETAILED DESCRIPTION

[0018] For the convenience of comparison and analysis, the present invention uses the following three examples to illustrate the advantages of Ni-Co-S NSAs in detail:

[0019] Example 1. A method for preparing a blank NF catalytic material comprises the following steps: continuously sonicating nickel foam in a hydrochloric acid solution, anhydrous ethanol, and deionized water, and then drying in a vacuum drying oven at 60° C. to obtain a blank NF.

[0020] Example 2. A method for preparing a Co-MOF NSAs catalytic material comprises the following steps: dissolving cobalt nitrate hexahydrate and 2-methylimidazole in 40 mL of deionized water and stirring. After complete dissolution, the cobalt nitrate hexahydrate and 2-methylimidazole are added together with the treated nickel foam (Example 1) into a stainless steel autoclave, followed by heating in an electric oven at 70°C for 4 hours. After cooling, the autoclave is removed, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 hours to produce Ni-Co NSAs.

[0021] Example 3. A method for preparing a Ni-Co-S NSAs catalytic material comprises the following steps: using Co-MOF NSAs (Example 2) as a precursor, dissolving thioacetamide (TAA) in 60 mL of deionized water and stirring. After complete dissolution by ultrasonication, the precursor and the precursor are added to a stainless steel autoclave, and then heated in an electric oven at 120°C for 4 hours. After cooling, the mixture is removed, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 hours to obtain Ni-Co-SNSAs.

[0022] The NF, Co-MOF NSAs and Ni-Co-S NSAs materials obtained in steps (1)(2)(3) were first analyzed for their microstructure and morphology.

[0023] Figure 1 The following is a flow chart of the preparation process of the present invention. Nickel and cobalt salts and a piece of treated NF were added to an autoclave via a simple hydrothermal method and placed at 70°C for 4 hours, followed by washing and drying to obtain a precursor. The precursor was then hydrothermally treated with TAA at 120°C, followed by washing and drying to obtain Ni-Co-S NSAs.

[0024] Figure 2This is the XRD diagram of the present invention. As shown in the figure, in addition to the three diffraction peaks of the nickel foam substrate, the XRD spectrum of Ni-Co NSAs shows four obvious diffraction peaks at (12.5°, 16°, 18° and 27.5°), and the diffraction peak positions are the same as those of CO-MOF reported in the literature, indicating that Ni-Co NSAs are successfully synthesized on nickel foam. After sulfurization, we can see that the sulfurized catalyst has diffraction peaks at (29°, 31°, 41° and 48°), which are basically consistent with the diffraction peak positions of the Co9S8 standard card, corresponding to (311)(222)(420)(511) crystal planes respectively. The results show that Co9S8 is successfully grown on nickel foam.

[0025] Figure 3 The SEM images of Examples 2 and 3 of the present invention are shown in FIG. Figure 3 As shown in a, the nanosheet arrays are uniformly grown on the nickel foam skeleton. Figure 3 As shown in (b), the nanosheet array gradually becomes thinner, and nanospheres are attached to the surface of the nanosheets. This Ni-Co-S NSAs / NF morphology exposes a larger contact area, thereby increasing the number of electrochemically active sites and electrolyte absorption.

[0026] Figure 4 : -EDS diagram of Example 2 and Example 3 of the present invention. Figure 4 As shown in a, Ni and Co elements exist in the Ni-Co NSAs sample; Figure 4 As shown in b, Ni, Co and S exist in the Ni-Co-S NSAs sample, and the atomic ratios of the elements are 15.68%, 44.38% and 36.54%, respectively.

[0027] Taking the electrocatalytic materials of Examples 1, 2 and 3 as examples, performance tests were conducted. The test process was as follows: electrochemical tests were performed on the electrocatalytic materials using a three-electrode system in 1M KOH and 1M KOH+1M EG electrolytes prepared with deionized water.

[0028] The specific operation of the electrochemical test is as follows: 1M KOH and 1M KOH+1M EG electrolytes prepared with an appropriate amount of deionized water are placed in the electrolytic cell, NF, Co-MOF NSAs and Ni-Co-SNSAs electrocatalytic materials are used as working electrodes, saturated Hg / HgO electrode is used as reference electrode, platinum wire is used as counter electrode, and electrochemical testing of the electrocatalytic materials is carried out at room temperature using a Coster electrochemical workstation.

[0029] Figure 5a is the LSV polarization curve of the electrocatalytic materials of Examples 1, 2 and 3 of the present invention in an alkaline environment. It can be seen from the figure that at the same current density, the OER overpotential of the Ni-Co-S NSAs catalyst is much lower than that of the Co-MOF NSAs and NF catalysts, and the catalyst performance is significantly improved after sulfurization. Figure 5 b It can be seen that the Ni-Co-S NSAs catalyst exhibits the best electrocatalytic performance after adding 1MEG. Specifically, Figure 5 c, at 50 and 100 mA cm -2 The overpotential of Ni-Co-S NSAs is lower than that of other catalysts at a current density of 100 mA cm -2 When the overpotential of Ni-Co-S NSAs (1.28 V) is much lower than that of Co-MOF NSAs (1.33 V) and NF (1.42 V).

[0030] Figure 6 This is a schematic diagram of the hydrolysis process of PET under alkaline conditions. The polyester structure of PET readily hydrolyzes into PTA and EG in alkaline aqueous solutions. Therefore, EG monomer is obtained by heating in an alkaline environment. Under experimental conditions, PET powders of varying masses were hydrolyzed in 100 mL of 1M KOH solution at 60°C for 24 hours to produce varying amounts of ethylene glycol monomer.

[0031] Figure 7 The figure shows the hydrolysis effect of PET of different masses in 100 mL 1 M KOH solution of the present invention. Figure 7 a and Figure 7 b are the EG detection curve of the standard solution in liquid chromatography and the standard curve drawn with different concentrations of ethylene glycol, the purpose of which is to facilitate the investigation of the EG yield after PET hydrolysis. Figure 7 As can be seen in c, the curve shows a clear peak at 15.8min, which is consistent with the peak of standard ethylene glycol, indicating that PET produces a large amount of EG under alkaline hydrolysis. In order to study the relationship between the amount of PET used and the amount of EG hydrolysis, PET of different masses were hydrolyzed under the same conditions, and then the amount of EG hydrolysis was calculated according to the standard curve. Figure 7 d It can be seen that in 100 mL of 1 M KOH, about 1.0 g of PET can be hydrolyzed to 0.35 M EG.

[0032] Figure 8 The electrochemical performance test of Example 3 of the present invention was carried out in an alkaline environment and 1.0g PET hydrolyzate environment. Figure 8 In a, we can see that at the same current density (10 mA cm -2), it takes 1.34V to drive OER in an alkaline environment, while only 1.24V is required in a PET hydrolyzate environment. This indicates that in the presence of EG, the starting voltage of Ni-Co-SNSAs / NF is much lower than the starting voltage required to drive OER, which can simultaneously promote more efficient hydrogen production at the cathode. In addition, Figure 8 b The optimal EG concentration of the catalyst was also explored. Figure 8 As shown in Figure b, the anodic oxidation potential gradually decreases with the increase of EG concentration. When 1M EG is added to the electrolyte aqueous solution, the oxidation potential is only 1.33V and the current density is 100mA cm -2 However, as the EG concentration further increases, the oxidation potential slowly moves toward the negative direction. Therefore, the optimal EGOH concentration is 1 M. Figure 8 As shown in Figure c, the catalytic performance of Ni-Co-SNSAs / NF catalyst when the EG concentration of PET hydrolyzate is 1.0 g is very close to the catalytic performance at the optimal EG concentration.

[0033] Figure 9 This is the stability test of Example 3 under the hydrolysis conditions of 1.0g PET. Figure 9 As shown in a, the initial current density can reach 130 mA cm -2 About, after 24 hours of CA testing, the current density can be maintained at more than half. Figure 9 b is the analysis after stability testing. After IC testing, the product is basically formic acid, and the Faradaic efficiency is calculated to be around 91%.

[0034] The experimental results show that PET is hydrolyzed to produce ethylene glycol under alkaline conditions. The catalytic performance of the catalyst is well enhanced in the presence of PET hydrolysis products, generating valuable formic acid and promoting hydrogen evolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of the product obtained in Example 3 of the present invention;

[0036] Figure 2 XRD patterns of the materials in Examples 2 and 3 of the present invention;

[0037] Figure 3 are SEM images of the materials in Examples 2 and 3 of the present invention;

[0038] Figure 4 These are the EDS images of the materials in Examples 2 and 3 of the present invention;

[0039] Figure 5a is the LSV polarization curve of Examples 1, 2, and 3 of the present invention in an alkaline environment; b is the LSV polarization curve of Examples 1, 2, and 3 in an ethylene glycol environment; c is the LSV polarization curve of Examples 1, 2, and 3 in an alkaline medium containing and not containing ethylene glycol, maintaining 50 and 100 mA cm -2 Comparison of the potential required for current density.

[0040] Figure 6 Schematic diagram of the electrocatalytic hydrolysis of PET to produce hydrogen and formic acid according to the present invention.

[0041] Figure 7 The present invention aims to explore the optimal hydrolysis quality of PET in 100 ml LM KOH solution. Figure 7 a is the EG detection curve of the standard solution in liquid chromatography; Figure 7 b is the standard curve drawn for different concentrations of ethylene glycol; Figure 7 c is the liquid phase detection diagram of EG produced by hydrolysis of PET of different masses under the same conditions; Figure 7 d is the actual EG concentration measured according to the standard curve.

[0042] Figure 8 a is the LSV polarization curve of Example 3 of the present invention under alkaline and PET hydrolysis environment; Figure 8 b is the LSV polarization curve of Example 3 at different EG concentrations; Figure 8 c Comparison of the catalytic performance of Example 3 in 1.0 g PET hydrolysate with different EG concentrations.

[0043] Figure 9 a is a 24-h stability test of Example 3 of the present invention with 1.0 g of PET hydrolysate; Figure 9 b IC analysis after stability test.

Claims

1. Preparation of an electrocatalytic material for producing formic acid by electrocatalytic oxidation of ethylene glycol, a hydrolysis product of PET waste plastics, characterized in that The following steps are involved: (1) Preparation of blank nickel foam (NF): Nickel foam was treated with hydrochloric acid solution and then ultrasonically cleaned with anhydrous ethanol and deionized water, respectively, and then dried in a vacuum drying oven at 60°C to obtain blank NF. (2) Preparation of Co-MOF NSAs: Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in 40 mL of deionized water and stirred. After complete dissolution, they were added together with the treated nickel foam into a stainless steel autoclave and then heated in an electric oven at 70°C for 4 hours. After cooling, the autoclave was taken out, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 hours to obtain Co-MOF NSAs. (3) Preparation of Ni-Co-S NSAs: Using Co-MOF NSAs as precursors, TAA (thioacetamide) was dissolved in 60 mL of deionized water and stirred. After complete dissolution by ultrasonication, they were added together with the precursor into a stainless steel autoclave and then heated in an electric oven at 120°C for 4 h. After cooling, the mixture was taken out, rinsed with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 4 h to obtain Ni-Co-S NSAs.

2. The method for preparing NF, Co-MOF NSAs, or Ni-Co-S NSAs according to claim 1, wherein: In the step (1), the thickness of the nickel foam is 1 mm, the length and width are 2 cm*4 cm, the hydrochloric acid concentration is 3 mol / L aqueous solution, and the ultrasonic cleaning time is 30 minutes.

3. The method for preparing an electrocatalytic material of Co-MOF NSAs according to claim 2, characterized in that: In the step (2), the mass of cobalt nitrate hexahydrate in solution 1 is 291.5 mg, the amount of deionized water is 40 mL, and the stirring time is 10 minutes; the mass of 2-methylimidazole in solution 2 is 1250.3 mg, the amount of deionized water is 40 mL, and the stirring time is 10 minutes.

4. The method for preparing Co-MOF NSAs according to claim 3, wherein: In the step (2), the hydrothermal reaction temperature is 70° C. and the reaction time is 4 hours.

5. The method for preparing Ni-Co-S NSAs according to claim 4, wherein: In the step (3), the amount of TAA is 202.3 mg, the total amount of deionized water is 60 mL, the ultrasonic time is 5 min, the hydrothermal reaction temperature is 120° C., and the reaction time is 4 hours.

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