Photo-thermal composite film based on cobalt porphyrin and graphene as well as preparation method and application of photo-thermal composite film

Abstract

The invention discloses a photo-thermal composite film based on cobalt porphyrin and graphene and a preparation method and application thereof.The photo-thermal composite film comprises a substrate layer, a photo-thermal active layer loaded on the substrate layer and a sealing layer wrapping the surface of the photo-thermal active layer, and the photo-thermal active layer is a composite material of a cobalt porphyrin covalent organic framework material and reduced graphene oxide; and the sealing layer is made of polydimethylsiloxane. The flexible PVDF microporous membrane is used as a mechanical support substrate, the COF-rGO photo-thermal active layer is loaded through a vacuum filtration method, surface sealing and hydrophobic strengthening are achieved through impregnation and curing of the PDMS solution, the whole preparation process is simple, conditions are mild, and the obtained membrane material is stable in structure and firm in combination and has good application prospects. The material has high-efficiency photo-thermal conversion performance, stable super-hydrophobic property and excellent oil-water separation capability, can effectively adsorb high-viscosity oil in a severe environment, and provides a feasible technical path for developing a high-efficiency and durable solar-driven oil-water separation material.

Description

Technical Field

[0001] This invention relates to the field of separation membrane material preparation, specifically to a photothermal composite membrane based on cobalt porphyrin and graphene, its preparation method, and its application. Background Technology

[0002] With the rapid development of offshore oil extraction and the petrochemical industry, oil spills and oily wastewater discharge have become serious global environmental problems. High-viscosity crude oil, due to its poor fluidity and tendency to adhere, is extremely inefficient when separated using traditional physical adsorption or gravity methods. In recent years, solar-driven photothermal conversion technology has provided a new approach to the recovery of high-viscosity oils: by converting solar energy into heat energy through photothermal materials, localized heating is used to reduce the viscosity of the crude oil, thereby significantly improving its fluidity and separation efficiency. However, existing photothermal materials still suffer from problems such as narrow light absorption range, limited photothermal conversion efficiency, and insufficient cycle stability.

[0003] Covalent organic frameworks (COFs), as a new type of porous crystalline material, have attracted widespread attention due to their high specific surface area, tunable pore structure, and good stability. Among them, metalloporphyrin-based COFs have garnered significant interest due to their broad-spectrum light absorption and excellent photothermal potential. However, the photothermal conversion efficiency of single COF materials is limited by their high carrier recombination rate and poor thermal conductivity.

[0004] Reduced graphene oxide (rGO) has excellent light absorption and photothermal conversion capabilities as well as good thermal conductivity. However, rGO sheets tend to stack, which reduces the number of effective adsorption sites, and its hydrophilic properties are not conducive to the selective adsorption of oil.

[0005] How to combine covalent organic frameworks (COF) and reduced graphene oxide (rGO) with a separation membrane through reasonable structural design to develop a composite photothermal separation membrane with high photothermal conversion efficiency, stable hydrophobic properties, simple preparation and good cycle durability is an urgent problem to be solved in this field. Summary of the Invention

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a photothermal composite film based on cobalt porphyrin and graphene, and its preparation method. This photothermal composite film possesses high-efficiency photothermal conversion performance, stable superhydrophobic properties, and excellent oil-water separation capability, enabling effective adsorption of high-viscosity oils in harsh environments.

[0007] A first aspect of the present invention is to provide a photothermal composite film based on cobalt porphyrin and graphene, comprising a substrate layer, a photothermal active layer loaded on the substrate layer, and a sealing layer wrapped around the surface of the photothermal active layer, wherein the photothermal active layer is a composite material of cobalt porphyrin covalent organic framework material and reduced graphene oxide, and the sealing layer is polydimethylsiloxane.

[0008] A second aspect of the present invention is to provide a method for preparing a photothermal composite film based on cobalt porphyrin and graphene, comprising the following steps: (1) Preparation of cobalt porphyrin-based covalent organic framework (COF) materials Co-5,10,15,20-tetra(4-aminophenyl)porphyrin and thieno[3,2-b]thiophene-2,5-dicarboxaldehyde were dissolved in a mixed solvent, ultrasonicated to homogenize, and then a catalyst was added. After a freezing-pumping-thawing degassing process, the mixture was reacted under vacuum to obtain a cobalt porphyrin-based covalent organic framework material. (2) Preparation of composite material COF-rGO The cobalt porphyrin-based covalent organic framework material obtained in step (1) was dispersed in an ethanol solution to obtain a dispersion. Ascorbic acid, a reducing agent, was added to the dispersion, and the composite material COF-rGO was obtained by high-temperature reduction reaction. (3) Preparation of composite membrane COF-rGO-PVDF The COF-rGO composite material obtained in step (2) was added to an ethanol solution and ultrasonically dispersed. It was then loaded onto the substrate surface by vacuum filtration to obtain the composite membrane COF-rGO-PVDF. (4) Preparation of photothermal composite film PDMS@COF-rGO-PVDF The COF-rGO-PVDF composite membrane obtained in step (3) was impregnated with polydimethylsiloxane PDMS solution and cured to obtain the photothermal composite membrane PDMS@COF-rGO-PVDF.

[0009] In an optional embodiment, in step (1), the molar ratio of Co-5,10,15,20-tetra(4-aminophenyl)porphyrin to thieno[3,2-b]thiophene-2,5-dicarboxaldehyde is 1:(1.5-2.5).

[0010] In an optional embodiment, in step (1), the mixed solvent is a mixture of benzyl alcohol and mesitylene, wherein the volume ratio of benzyl alcohol to mesitylene is 1:(1-2); the catalyst is an acetic acid solution, wherein the concentration of the acetic acid solution is 6M.

[0011] In one alternative embodiment, in step (1), the reaction temperature is 110–130°C and the time is 48–72 h.

[0012] In an optional embodiment, in step (2), the mass ratio of cobalt porphyrin-based covalent organic framework material to graphene oxide is 1:1; the ascorbic acid concentration is 0.5-2 wt%; the reduction reaction temperature is 70-90°C, and the time is 2-4 h.

[0013] In one alternative embodiment, the vacuum level in step (3) is 5 to 10 Mbar.

[0014] In an optional embodiment, in step (4), the concentration of the PDMS solution is 0.5-2 wt%, and the immersion time is 2-10 min.

[0015] In one alternative embodiment, in step (4), the curing temperature is 80-100°C and the time is 2-4 hours.

[0016] A third aspect of the present invention is to provide the application of a photothermal composite membrane based on cobalt porphyrin and graphene in oil-water separation.

[0017] Compared with the prior art, the technical solution of the present invention has the following advantages: (1) The present invention combines the COF-rGO functional layer constructed by vacuum filtration with PDMS surface modification to give the composite membrane superhydrophobic properties, so that the water contact angle is greater than 153.3° and maintains stable hydrophobic performance in complex environments; the membrane has a separation efficiency of more than 98% for oil-water mixtures and is suitable for efficient oil-water separation in complex chemical environments.

[0018] (2) The photothermal composite membrane of the present invention can be rapidly heated to above 63.5°C under one solar irradiance, effectively reducing the viscosity of high-viscosity crude oil and improving its fluidity, thereby enabling better adsorption; and after five cycles of heating and cooling tests, the photothermal performance did not show significant attenuation, demonstrating good stability for repeated use.

[0019] (3) The present invention uses a flexible PVDF microporous membrane as a mechanical support substrate, loads a COF-rGO photothermal active layer by vacuum filtration, and then achieves surface sealing and hydrophobic enhancement by PDMS solution impregnation and curing. The entire preparation process is simple and mild, and the obtained membrane material has a stable structure and strong bonding, providing a feasible technical path for developing efficient and durable solar-driven oil-water separation materials. Attached Figure Description

[0020] Figure 1 The images show SEM images of the PDMS@COF-rGO-PVDF photothermal composite film and the unmodified PVDF film from Example 1 of this invention. Figure 2 This is a water contact angle test diagram of the PDMS@COF-rGO-PVDF photothermal composite film of Embodiment 1 of the present invention; Figure 3 This is an experimental diagram of oil-water separation performed on the PDMS@COF-rGO-PVDF photothermal composite membrane of Embodiment 1 of the present invention in a gravity-driven device; Figure 4This is a graph showing the oil-water separation efficiency of the PDMS@COF-rGO-PVDF photothermal composite membrane after 10 cycles of use in Example 1 of the present invention. Figure 5 This is a photothermal temperature rise curve of the PDMS@COF-rGO-PVDF photothermal composite film of Embodiment 1 of the present invention under one solar intensity. Figure 6 The graph shows the photothermal stability test results of the PDMS@COF-rGO-PVDF photothermal composite film in Example 1 of this invention after 5 temperature increases and decreases. Figure 7 This is a schematic diagram of the adsorption process of high-viscosity crude oil by the PDMS@COF-rGO-PVDF photothermal composite film in Example 1 of the present invention under light irradiation. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0022] Example 1 A photothermal composite film based on cobalt porphyrin and graphene is prepared by the following steps: (1) Preparation of cobalt porphyrin-based covalent organic framework (COF) materials 1 mol of Co-5,10,15,20-tetra(4-aminophenyl)porphyrin and 2 mol of thieno[3,2-b]thiophene-2,5-dicarboxaldehyde were dissolved in a mixed solvent of benzyl alcohol and mesitylene (v / v=1:2). After ultrasonic homogenization, 6M acetic acid solution was added. After freezing-pumping-thawing degassing treatment, the mixture was reacted under vacuum at 120℃ for 72 h to obtain a cobalt porphyrin-based covalent organic framework material. (2) Preparation of composite material COF-rGO 5 mg of the cobalt porphyrin-based covalent organic framework material obtained in step (1) and 5 mg of graphene oxide were dispersed in an ethanol solution to obtain a dispersion. 1.5 wt% ascorbic acid was added to the dispersion, and the reduction reaction was carried out at 80 °C for 3 h to obtain the composite material COF-rGO. (3) Preparation of composite membrane COF-rGO-PVDF The COF-rGO composite material obtained in step (2) was added to an ethanol solution and ultrasonically dispersed. It was then loaded onto the surface of a polyvinylidene fluoride membrane by vacuum filtration at a vacuum degree of 8 Mbar to obtain the composite membrane COF-rGO-PVDF. (4) Preparation of photothermal composite film PDMS@COF-rGO-PVDF The COF-rGO-PVDF composite film obtained in step (3) was impregnated with a 1.5wt% polydimethylsiloxane PDMS solution for 6 min, and then cured at 90℃ for 3 h to obtain the photothermal composite film PDMS@COF-rGO-PVDF.

[0023] Example 2 A photothermal composite film based on cobalt porphyrin and graphene is prepared by the following steps: (1) Preparation of cobalt porphyrin-based covalent organic framework materials 1 mol of Co-5,10,15,20-tetra(4-aminophenyl)porphyrin and 1.5 mol of thieno[3,2-b]thiophene-2,5-dicarboxaldehyde were dissolved in a mixed solvent of benzyl alcohol and mesitylene (v / v=1:2). After ultrasonic homogenization, 4M acetic acid solution was added. After freezing-pumping-thawing degassing treatment, the mixture was reacted under vacuum at 110℃ for 72 h to obtain a cobalt porphyrin-based covalent organic framework material. (2) Preparation of composite materials 5 mg of the cobalt porphyrin-based covalent organic framework material obtained in step (1) was dispersed in an ethanol solution at a mass ratio of 1:1 to obtain a dispersion. 0.5 wt% ascorbic acid was added to the dispersion, and the reduction reaction was carried out at a temperature of 70 °C for 4 h to obtain the composite material. (3) Preparation of composite membrane The COF-rGO composite material obtained in step (2) was added to an ethanol solution and ultrasonically dispersed. It was then loaded onto the surface of a polyvinylidene fluoride membrane by vacuum filtration at a vacuum degree of 6 Mbar to obtain a composite membrane. (4) Preparation of photothermal composite film The composite film obtained in step (3) was immersed in a 0.5 wt% polydimethylsiloxane PDMS solution for 9 min, and then cured at 80 °C for 4 h to obtain a photothermal composite film.

[0024] Example 3 A photothermal composite film based on cobalt porphyrin and graphene is prepared by the following steps: (1) Preparation of cobalt porphyrin-based covalent organic framework materials 1 mol of Co-5,10,15,20-tetra(4-aminophenyl)porphyrin and 2.5 mol of thieno[3,2-b]thiophene-2,5-dicarboxaldehyde were dissolved in a mixed solvent of benzyl alcohol and mesitylene (v / v=1:2). After ultrasonic homogenization, 8M acetic acid solution was added. After freezing-pumping-thawing degassing treatment, the mixture was reacted under vacuum at 130℃ for 48 h to obtain a cobalt porphyrin-based covalent organic framework material. (2) Preparation of composite materials 5 mg of the cobalt porphyrin-based covalent organic framework material obtained in step (1) and 5 mg of graphene oxide were dispersed in an ethanol solution to obtain a dispersion. 2 wt% ascorbic acid was added to the dispersion, and the reduction reaction was carried out at 90 °C for 2 h to obtain the composite material. (3) Preparation of composite membrane The composite material obtained in step (2) was added to an ethanol solution and ultrasonically dispersed. It was then loaded onto the surface of a polyvinylidene fluoride membrane by vacuum filtration at a vacuum degree of 10 Mbar to obtain a composite membrane. (4) Preparation of photothermal composite film The COF-rGO-PVDF composite film obtained in step (3) was impregnated with a 2wt% polydimethylsiloxane PDMS solution for 3 min, and then cured at 80℃ for 4 h to obtain a photothermal composite film.

[0025] Test Example 1 The structure of the photothermal composite film PDMS@COF-rGO-PVDF was observed using scanning electron microscopy. The results are as follows: Figure 1 As shown. Figure 1 a represents the structure of the PVDF membrane (polyvinylidene fluoride membrane). Figure 1 b represents the structure of a photothermal composite film based on cobalt porphyrin and graphene. From... Figure 1 As can be seen in image a, the original PVDF membrane has a loose, three-dimensional interconnected porous network structure with a relatively uniform pore distribution. High-magnification images show that the pore wall surfaces are relatively smooth, providing good channels for fluid transport.

[0026] from Figure 1As shown in image b, after constructing the COF-rGO functional layer through vacuum filtration and supplementing it with PDMS surface modification, the surface and some pores of the composite membrane are covered with a composite coating of nanometer to micrometer scale. The original macroporous structure is partially filled, and the surface morphology is significantly roughened. Local high-magnification images further reveal that the composite membrane surface is uniformly distributed with a composite structure of sheet-like (corresponding to the typical two-dimensional morphology of reduced graphene oxide rGO) and granular (corresponding to the typical morphology of COF microcrystals) structures. PDMS acts as a binder and coating phase, enabling the aforementioned functional components to adhere firmly and uniformly to the pore walls and surface of the PVDF membrane, thereby forming a continuous and stable functionalized modified layer.

[0027] Test Example 2 The wettability of the photothermal composite membrane PDMS@COF-rGO-PVDF was characterized by water contact angle testing. The tests were conducted at room temperature using a contact angle meter. First, the prepared PDMS@COF-rGO-PVDF composite membrane sample was flattened and fixed on the sample stage. 5 μL of deionized water was drawn as a test droplet using a microsyringe and slowly and gently deposited onto the membrane surface. The results are shown below. Figure 2 As shown, from Figure 2 As can be seen, the water contact angle of the composite membrane reaches 153.3°, indicating that the prepared PDMS@COF-rGO-PVDF composite membrane possesses typical superhydrophobic properties. This superhydrophobic property is a key foundation for achieving efficient and selective oil-water separation. It is worth noting that the composite membrane maintains stable superhydrophobic performance in different pH environments, salt solutions, and copper ion-containing solutions, demonstrating good environmental adaptability.

[0028] Test Example 3 The oil-water separation process of the PDMS@COF-rGO-PVDF photothermal composite membrane was visually demonstrated using a simple gravity-driven device. The prepared PDMS@COF-rGO-PVDF composite membrane was cut into circles approximately 3 cm in diameter and fixed in the intermediate filter membrane interlayer of a self-made gravity-driven separation device (mainly composed of two nested glass funnels). Carbon tetrachloride was selected as the model oil phase and mixed with deionized water at a volume ratio of 1:2 (v / v). The oil and water phases were stained with Sudan III and methylene blue, respectively, for observation. The results are as follows: Figure 3 As shown, from Figure 3 As can be seen, during the separation process, the oil phase can quickly permeate through the membrane layer, while the aqueous phase is effectively blocked, achieving efficient separation of the oil and water phases. The separation efficiency of the photothermal composite membrane PDMS@COF-rGO-PVDF was tested after 10 consecutive cycles of use, and the results are as follows: Figure 4 As shown, from Figure 4As can be seen from the data, after 10 consecutive cycles of use, the oil-water separation efficiency of the photothermal composite membrane can still be stably maintained at over 98%, which fully demonstrates that the photothermal composite membrane prepared by the present invention not only has high separation efficiency, but also excellent operational stability and cyclic durability, and can meet the requirements for material life in practical applications.

[0029] Test Example 4 The photothermal performance and stability of the PDMS@COF-rGO-PVDF composite film were investigated. A xenon lamp was used to simulate one solar radiation intensity. The PDMS@COF-rGO-PVDF composite film sample was laid flat on an insulating foam substrate and fixed in the center of the light path, ensuring the light spot completely covered the sample surface. Infrared thermal imagers were used to record the film surface temperature changes in real time, with an illumination duration of 3 minutes. Five "light-cooling" cycles were performed on the same film sample. Each cycle consisted of 1 minute of illumination under one solar light, followed by turning off the light source and allowing it to cool naturally to room temperature. Temperature-time curves were recorded throughout the cycle using infrared thermal imagers, and performance stability was evaluated by comparing the steady-state temperature and heating rate of each cycle. The results are shown below. Figure 5 and Figure 6 As shown.

[0030] from Figure 5 As can be seen, under one solar irradiance, the surface temperature of the PDMS@COF-rGO-PVDF composite film can rapidly rise to above 63.5℃, which significantly confirms the synergistic photothermal effect generated by the composite of cobalt porphyrin-based COF and reduced graphene oxide.

[0031] from Figure 6 As can be seen from the data, after five complete heating and cooling cycles, the final equilibrium temperature of the photothermal composite membrane did not decrease significantly, indicating that its photothermal performance is stable and has good reusability. This provides a core performance guarantee for its application in solar-driven continuous oil-water separation processes.

[0032] Test Example 5 The effect of the photothermal composite membrane PDMS@COF-rGO-PVDF on high-viscosity crude oil was investigated. The PDMS@COF-rGO-PVDF composite membrane sample was spread evenly in a petri dish, and approximately 0.2 g of high-viscosity crude oil was dropped onto the center of the membrane surface. Subsequently, a xenon lamp (sunlight) was turned on and vertically irradiated the sample area. The entire process of crude oil spreading and permeation on the membrane surface was recorded using a camera, and the time required for the oil droplet to be completely adsorbed was accurately measured. The results are as follows: Figure 7 As shown, from Figure 7As can be seen from the image, under illumination, the photothermal effect of the composite membrane locally heats the crude oil at its contact points, leading to a significant decrease in crude oil viscosity and increased fluidity, thus enabling rapid adsorption by the composite membrane. This indicates that the photothermal composite membrane provided by this invention can actively reduce the viscosity of high-viscosity crude oil using solar energy, effectively overcoming the technical bottleneck of low recovery efficiency of traditional adsorption materials when dealing with high-viscosity oils.

[0033] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by those skilled in the art to the above embodiments without departing from the spirit and scope of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A photothermal composite film based on cobalt porphyrin groups and graphene, characterized in that, It comprises a substrate layer, a photo-thermal active layer loaded on the substrate layer, and a sealing layer wrapped on the surface of the photo-thermal active layer, wherein the photo-thermal active layer is a composite material of cobalt porphyrin-based covalent organic framework and reduced graphene oxide, and the sealing layer is polydimethylsiloxane.

2. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 1, characterized in that, It comprises the following steps: (1) Preparation of cobalt porphyrin-based covalent organic framework material COF Co-5,10,15,20-tetra(4-aminophenyl) porphyrin and thieno[3,2-b]thiophene-2,5-diformaldehyde are dissolved in a mixed solvent, and a catalyst is added after ultrasonic homogenization. After freeze-pump-thaw degassing treatment, the reaction is carried out under vacuum conditions to obtain a cobalt porphyrin-based covalent organic framework material; (2) Preparation of composite material COF-rGO The cobalt porphyrin-based covalent organic framework material obtained in step (1) and graphene oxide are dispersed in an ethanol solution to obtain a dispersion liquid, and a reducing agent ascorbic acid is added to the dispersion liquid. After high-temperature reduction reaction, a composite material COF-rGO is obtained; (3) Preparation of composite film COF-rGO-PVDF The COF-rGO composite material prepared in step (2) is added to an ethanol solution and ultrasonically dispersed, and is loaded on the surface of the substrate layer by vacuum filtration to obtain a composite film COF-rGO-PVDF; (4) Preparation of photo-thermal composite film PDMS@COF-rGO-PVDF The composite film COF-rGO-PVDF obtained in step (3) is immersed in a polydimethylsiloxane PDMS solution and solidified to obtain a photo-thermal composite film PDMS@COF-rGO-PVDF.

3. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (1), the molar ratio of Co-5,10,15,20-tetra(4-aminophenyl) porphyrin to thieno[3,2-b]thiophene-2,5-diformaldehyde is 1:(1.5-2.5).

4. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (1), the mixed solvent is a mixture of benzyl alcohol and mesitylene, and the volume ratio of benzyl alcohol to mesitylene is 1:(1-2); the catalyst is an acetic acid solution, and the concentration of the acetic acid solution is 3-8 M.

5. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (1), the reaction temperature is 110-130℃, and the reaction time is 48-72h.

6. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (2), the mass ratio of cobalt porphyrin-based covalent organic framework material to graphene oxide is 1:1; the concentration of ascorbic acid is 0.5-2wt%; the reduction reaction temperature is 70-90℃, and the reaction time is 2-4h.

7. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (3), the vacuum degree is 5-10 Mbar.

8. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (4), the concentration of the PDMS solution is 0.5-2wt%, and the immersion time is 2-10min.

9. The method for preparing a cobalt-porphyrin-based and graphene-based photothermal composite film according to claim 2, characterized in that, In step (4), the solidification temperature is 80-100℃, and the solidification time is 2-4h.

10. The application of the cobalt porphyrin-based and graphene-based photo-thermal composite film in oil-water separation according to claim 1.

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