A zinc oxide nanorod modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation and a preparation method thereof

Abstract

This invention provides a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation and its preparation method, belonging to the field of new materials technology. Polyacrylonitrile (PAN) is selected as the fiber substrate material. Anhydrous zinc acetate (Zn(Ac)2) and PAN are sequentially dissolved in N,N-dimethylformamide (DMF) to obtain a precursor solution. A PAN / Zn(Ac)2 fiber membrane is prepared by electrospinning. Then, a PAN fiber membrane with surface-modified zinc oxide (ZnO) nanorods is obtained through thermal decomposition and low-temperature hydrothermal synthesis. This fiber membrane, with its superhydrophilicity and underwater superoleophobicity, can effectively trap oil droplets in emulsions. Simultaneously, the membrane can convert pulsed water pressure into pulsed voltage. This piezoelectric effect not only promotes the deformation, collision, and aggregation of emulsified oil droplets, accelerating the demulsification process, but also generates electrostatic repulsion between the membrane surface charge and charged oil droplets, achieving dynamic antifouling. Therefore, this membrane can achieve efficient and long-lasting separation of oil-water emulsions. The preparation method of the present invention is low in cost and simple in process, and has good application prospects in the field of oily wastewater treatment.

Description

Technical Field

[0001] This invention relates to an oil-water separation membrane material, specifically to a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation and its preparation method, belonging to the field of new materials technology. Background Technology

[0002] With the acceleration of global industrialization, the discharge of oily wastewater from industries such as petroleum, metallurgy, food processing, and chemicals continues to rise, while frequent oil spills at sea pose a significant threat to marine ecosystems. If properly treated oily wastewater enters the natural environment, it will cause ecological imbalance, depletion of dissolved oxygen, and the death of organisms, as well as soil and groundwater pollution. Its harmful substances may also accumulate along the food chain, ultimately harming human health. Therefore, developing efficient and economical oily wastewater treatment technologies has become an urgent and crucial issue in the field of environmental science.

[0003] Compared to traditional oil-water separation technologies, membrane separation technology demonstrates significant potential in the field due to its core advantages such as low energy consumption, environmental friendliness, and operational flexibility, especially suitable for handling emulsified oils and finely dispersed oils that are difficult for traditional technologies to handle. However, traditional oil-water separation membranes often suffer from insufficient antifouling performance; oil droplets easily adsorb and deposit on the membrane surface, clogging the membrane pores and causing a sharp drop in membrane flux and reduced separation efficiency. This forces membrane modules to be cleaned and replaced frequently, resulting in shortened service life and increased maintenance costs, making it difficult to meet practical application requirements. Therefore, there is an urgent need to develop new membrane separation strategies to effectively solve the membrane fouling problem and achieve sustained separation of oil-water emulsions.

[0004] Piezoelectric materials can efficiently convert mechanical energy into electrical energy, and due to their excellent self-powered properties, they have been widely used in sensors, nanogenerators, and other fields. Introducing the piezoelectric effect into oil-water separation provides a new approach for developing novel separation technologies. Specifically, when a superhydrophilic separation membrane is endowed with piezoelectric properties, the membrane can convert pulsed water pressure into pulsed voltage, thereby autonomously activating the piezoelectric effect and enhancing its demulsification and antifouling capabilities.

[0005] This invention uses the piezoelectric polymer polyacrylonitrile (PAN) as the fiber substrate and modifies the surface in situ with zinc oxide (ZnO) nanorods. This structural design aims to enhance the piezoelectric properties of the material, thereby achieving efficient and durable separation of oil-water emulsions. Summary of the Invention

[0006] The purpose of this invention is to propose a new strategy to improve the demulsification and antifouling capabilities of superhydrophilic membrane materials, and to prepare a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation.

[0007] The implementation process of this invention is briefly explained below. First, PAN is selected as the fiber substrate material. Anhydrous zinc acetate (Zn(Ac)2) and PAN are sequentially dissolved in N,N-dimethylformamide (DMF) to prepare a precursor solution. Then, a PAN / Zn(Ac)2 fiber membrane is prepared by electrospinning. The membrane is then heat-treated in an oven to decompose Zn(Ac)2 into ZnO nanoparticle seeds. Subsequently, the heat-treated membrane is immersed in a growth solution, and ZnO nanorods are grown in situ on the fiber surface using a low-temperature hydrothermal synthesis technique to obtain the final sample. This fiber membrane, with its superhydrophilicity and underwater superoleophobicity, can effectively trap oil droplets in emulsions. Simultaneously, the membrane can convert pulsed water pressure into pulsed voltage. This piezoelectric effect not only promotes the deformation, collision, and aggregation of emulsified oil droplets, accelerating the demulsification process, but also generates electrostatic repulsion between the membrane surface charge and the charged oil droplets, achieving dynamic antifouling. Therefore, this membrane can efficiently and persistently separate oil-water emulsions.

[0008] This invention specifically relates to a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation and its preparation method, which is achieved through the following specific steps:

[0009] (1) Add Zn(Ac)2 (10% relative to PAN by mass) to DMF and stir magnetically at room temperature until completely dissolved. Then add PAN powder (12wt%) to the above solution to prepare a PAN / Zn(Ac)2 solution. Stir the mixture magnetically at 50°C for 10 h to obtain a homogeneous precursor solution.

[0010] (2) Fill the precursor solution into a syringe with a metal needle for electrospinning. Set the injection speed of the injection pump to 0.1 mm / min, adjust the distance between the syringe needle and the roller receiver to 10 cm, adjust the rotation speed of the roller receiver to 2800 r / min, connect the positive terminal of the high voltage power supply to the syringe needle and adjust the voltage to 9 kV, connect the negative terminal of the high voltage power supply to the roller receiver and adjust the voltage to -1.5 kV, and continue spinning for 4 hours. After spinning, remove the fiber membrane from the spinning machine and place it in a 40°C oven to dry thoroughly.

[0011] (3) The PAN / Zn(Ac)2 fiber membrane obtained in step (2) is placed in an oven at 130℃ for 24 hours to decompose Zn(Ac)2 into ZnO nanoparticle seeds.

[0012] (4) A growth solution was prepared by completely dissolving Zn(NO3)2·6H2O (30 mM), hexamethylenetetramine (10 mM), and NH3·H2O (3 mL) in 100 mL of deionized water. The heat-treated fiber membrane was immersed in the above growth solution, sealed, and heated in a 95°C oven for 3 h to allow ZnO nanoparticles to grow into nanorods. After the reaction was completed, the sample was removed, rinsed with a large amount of deionized water, and then ultrasonically cleaned for 10 min to remove residues. Finally, it was dried thoroughly in a 40°C oven to obtain a PAN fiber membrane with ZnO nanorods modified on the surface (hereinafter referred to as "PAN / ZnO fiber membrane").

[0013] This invention proposes a novel strategy to improve the demulsification and antifouling capabilities of superhydrophilic membrane materials, and uses this strategy to prepare a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation. The preparation method is low-cost and simple, and has good application prospects in the field of oily wastewater treatment. Attached Figure Description

[0014] Appendix Figure 1 These are scanning electron microscope images of the PAN fiber membrane with surface-modified ZnO nanorods in this invention. (a) is the intrinsic PAN fiber membrane, and (b) is the PAN / ZnO fiber membrane.

[0015] Appendix Figure 2 This is an image showing the change in the water contact angle between the intrinsic PAN fiber membrane and the PAN / ZnO fiber membrane over time in this invention.

[0016] Appendix Figure 3 Images showing the piezoelectric properties (output voltage) of intrinsic PAN fiber membrane and PAN / ZnO fiber membrane in this invention.

[0017] Appendix Figure 4 This is a schematic diagram of the pulse pressure and constant pressure driven oil-water separation device in this invention.

[0018] Appendix Figure 5 This refers to the separation flux of the intrinsic PAN fiber membrane and the PAN / ZnO fiber membrane under pulsed pressure and constant pressure in this invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] Example 1

[0021] 0.12 g Zn(Ac)₂ was added to 8.68 g DMF and magnetically stirred at room temperature until completely dissolved. Then, 1.2 g PAN powder was added to the above solution to prepare a PAN / Zn(Ac)₂ solution. The mixture was magnetically stirred at 50 °C for 10 h to obtain a homogeneous precursor solution.

[0022] The precursor solution was filled into a syringe with a metal needle for electrospinning. The injection speed of the injection pump was set to 0.1 mm / min, the distance between the syringe needle and the roller receiver was adjusted to 10 cm, and the rotation speed of the roller receiver was adjusted to 2800 r / min. The positive terminal of the high-voltage power supply was connected to the syringe needle and the voltage was adjusted to 9 kV. The negative terminal of the high-voltage power supply was connected to the roller receiver and the voltage was adjusted to -1.5 kV. The spinning time lasted for 4 hours. After spinning, the fiber membrane was removed from the spinning machine and placed in a 40℃ oven for thorough drying.

[0023] The PAN / Zn(Ac)2 fiber membrane was heat-treated in an oven at 130℃ for 24 hours to decompose Zn(Ac)2 into ZnO nanoparticle seeds.

[0024] A growth solution was prepared by completely dissolving 0.89 g Zn(NO3)2·6H2O, 0.14 g hexamethylenetetramine, and 3 mL NH3·H2O in 100 mL deionized water. The heat-treated fiber membrane was immersed in this growth solution, sealed, and heated in a 95°C oven for 3 hours to allow ZnO nanoparticles to grow into nanorods. After the reaction, the sample was removed, rinsed with plenty of deionized water, and then ultrasonically cleaned for 10 minutes to remove residues. Finally, it was thoroughly dried in a 40°C oven to obtain a PAN fiber membrane with surface-modified ZnO nanorods (PAN / ZnO fiber membrane).

[0025] Figure 1 Scanning electron microscope (SEM) images of PAN fiber films with surface-modified ZnO nanorods are presented. The images clearly show that the ZnO nanorods grow uniformly on the fiber surface, while the intrinsic PAN fiber surface is smooth and lacks any special structure.

[0026] Figure 2 The graphs showing the change of water contact angle over time for intrinsic PAN fiber membrane and PAN / ZnO fiber membrane are presented. Compared with intrinsic PAN fiber membrane, the surface modification with zinc oxide nanorods significantly improves hydrophilicity, and water droplets can be completely spread on the surface of PAN / ZnO fiber membrane in only 3.5s.

[0027] Figure 3 Images of the piezoelectric properties (output voltage) of intrinsic PAN fiber membrane and PAN / ZnO fiber membrane are presented. Compared with intrinsic PAN fiber membrane, PAN / ZnO fiber membrane has superior piezoelectric properties, with a piezoelectric voltage output of approximately 10V.

[0028] Figure 4A schematic diagram of a pulse pressure and constant pressure driven separation device for oil-in-water emulsions is provided. The entire system employs a cross-flow filtration device, with a peristaltic pump driving the feed and generating inherent pulse pressure during operation. To achieve constant pressure operation, a buffer bottle is installed between the pump and the membrane tank to mitigate pressure fluctuations caused by the pump, thereby maintaining a stable and uniform pressure environment on the membrane surface throughout the filtration process.

[0029] Figure 5 The separation fluxes of intrinsic PAN membranes and PAN / ZnO membranes under pulsed pressure and constant pressure are presented. Under pulsed pressure separation conditions, the permeation flux of the PAN / ZnO membrane stabilizes at approximately 7800 L·m⁻¹. −2 ·h −1 ·bar −1 The membrane maintains a high and stable filtration capacity throughout the process. In contrast, under constant pressure separation conditions, its separation flux decreases significantly. This is attributed to the fact that pulsed pressure effectively triggers the piezoelectric effect of the membrane, enhancing its demulsification and antifouling properties. For intrinsic PAN membranes with weaker piezoelectric properties, the separation flux decreases rapidly and remains at a low level under both constant and pulsed pressure conditions.

Claims

1. This invention specifically relates to a zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation and its preparation method, the method being: (1) Zn(Ac)2 (10% relative to PAN by mass) was added to N,N-dimethylformamide (DMF) and magnetically stirred at room temperature until completely dissolved. Then, PAN powder (12wt%) was added to the above solution to prepare a PAN / Zn(Ac)2 solution. The mixture was magnetically stirred at 50°C for 10 h to obtain a homogeneous precursor solution; (2) Fill the precursor solution into a syringe with a metal needle for electrospinning. Set the injection speed of the injection pump to 0.1 mm / min, adjust the distance between the syringe needle and the roller receiver to 10 cm, adjust the rotation speed of the roller receiver to 2800 r / min, connect the positive terminal of the high voltage power supply to the syringe needle and adjust the voltage to 9 kV, connect the negative terminal of the high voltage power supply to the roller receiver and adjust the voltage to -1.5 kV, and continue spinning for 4 hours. After spinning, remove the fiber membrane from the spinning machine and put it in a 40°C oven to dry thoroughly. (3) The PAN / Zn(Ac)2 fiber membrane was placed in an oven at 130℃ for 24 hours to decompose Zn(Ac)2 into ZnO nanoparticle seeds; (4) A growth solution was prepared by completely dissolving Zn(NO3)2·6H2O (30 mM), hexamethylenetetramine (10 mM), and NH3·H2O (3 mL) in 100 mL of deionized water. The heat-treated membrane was immersed in the above growth solution, sealed, and heated in a 95°C oven for 3 h to allow ZnO nanoparticles to grow into nanorods. After the reaction was completed, the sample was removed, rinsed with plenty of deionized water, and then ultrasonically cleaned for 10 min to remove residues. Finally, it was dried thoroughly in a 40°C oven to obtain a PAN fiber membrane with ZnO nanorods on the surface.

2. A zinc oxide nanorod-modified piezoelectric polyacrylonitrile fiber membrane for oil-water separation, prepared according to the method of claim 1, characterized in that... The uniform growth of ZnO nanorods on the surface of PAN fibers significantly enhances piezoelectricity and hydrophilicity, enabling efficient and long-lasting separation of oil-water emulsions.

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