Photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater and preparation method thereof

Abstract

The present invention discloses a photothermal conversion composite material suitable for purifying oil-containing wastewater and organic sewage and a preparation method thereof. On the basis of retaining the special light-absorbing structure of reduced graphene oxide nanotubes, hydrazine hydrate is successively dropped in the edge region and the bottom of the film to promote its foaming to form an aerogel structure, and a reduced graphene oxide material with a tube array and an aerogel composite structure is obtained after cutting. The present invention also endows the material with hydrophilic and oleophobic properties by coating a poly(diallyldimethylammonium chloride)-sodium perfluorooctanoate polymer film on the outer surface, making it perfectly suitable for the purification of oil-containing wastewater and organic sewage. The test results show that the composite material prepared by the present invention has a light absorption rate higher than 98% in the wavelength range of 200-2500 nm, and can reach a water evaporation rate of 1.28 kg·m-2·h-1 and an energy conversion efficiency of 81.95% under the light intensity of 1 kW·m-2.

Description

Technical Field

[0001] The present invention relates to the field of photothermal materials, and in particular to a photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater and a preparation method thereof. Background Art

[0002] Solar water evaporation systems are an emerging photothermal evaporation technology that converts solar energy into heat to evaporate the water around the photothermal material. In interfacial solar evaporation systems, the photothermal conversion material needs to float on the water surface. Aerogel materials have good thermal insulation and self-floating capabilities, making them excellent photothermal conversion materials. The surface of aerogel materials does not have special light-absorbing structures or light-absorbing substances, which leads to low aerogel absorbance and reduced photothermal efficiency, which is not conducive to the solar water evaporation process. Researchers use smearing, spraying, deposition, and loading of light-absorbing materials on the surface of aerogels to increase the aerogel's absorbance. However, the light-absorbing material of the photothermal conversion material prepared by this method is not the same substance as the aerogel material, and has disadvantages such as poor stability during long-term use. In long-term and complex use environments, the light-absorbing material may separate from the thermal insulation and water supply material, which not only makes it difficult to achieve long-term water evaporation performance, but also brings certain pollution emission problems.

[0003] Patent CN115403093A discloses a SMNG evaporator for solar thermal steam conversion. The SMNG evaporator is prepared by dispersing silver-doped manganese dioxide nanoparticles in water to prepare a suspension, then dropping the suspension into a graphene aerogel and allowing it to settle and dry. Patent CN112898627A discloses a polydopamine / tea polyphenol / cellulose composite photothermal gel. This gel is prepared by first immersing a cellulose aerogel in an ammonia solution, then in a dopamine hydrochloride / tea polyphenol solution, in situ coating the cellulose aerogel with a polydopamine / tea polyphenol film, and then freeze-drying it. These two methods of preparing photothermal conversion materials are composed of two different materials, combined only by deposition and drying. This results in poor material stability. During long-term photothermal water evaporation, the light-absorbing material may separate from the aerogel, affecting the material's absorbance and solar water evaporation performance, while also leading to new pollution and material waste.

[0004] At the same time, most researchers focus only on improving the evaporation rate and efficiency of photothermal materials and increasing their salt tolerance. However, in actual application environments, organic pollutants, oily wastewater, seawater, etc. are ubiquitous, and most photothermal conversion materials are hydrophilic and lipophilic. The pores of photothermal conversion materials are extremely easily clogged by oil, which makes it difficult for water molecules to be transported to the sample surface for water evaporation, thus seriously affecting the photothermal conversion efficiency of the interfacial solar evaporation system. In some extreme cases, it can even cause the photothermal conversion material to completely fail or even be scrapped. Summary of the Invention

[0005] In order to solve the shortcomings that the light-absorbing layer and the heat-insulating layer are not made of the same material and the interface bonding is unstable and easy to separate, the present invention provides a photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater and a preparation method thereof.

[0006] The present invention adopts the following technical solution: a photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater and a preparation method thereof, comprising the following steps:

[0007] S1 Preparation of Reduced Graphene Oxide Tube Array-Aerogel Material

[0008] S11 uses nanoimprinting to imprint densely packed nanotube structures in the center of a graphene film.

[0009] S12: Add hydrazine hydrate dropwise to the other areas except the nanotubes in the central area, let it stand for a while, and repeat the addition several times until the added area is obviously foamed and an aerogel structure is formed;

[0010] S13: adding hydrazine hydrate dropwise to the other side of the graphene film, letting it stand for a while, and repeating the addition several times until the added area is obviously foamed and an aerogel structure is formed;

[0011] S14 cutting excess areas of the aerogel, retaining areas where the nanotube structure is located, and allowing the material to stand until a dry and hardened reduced graphene oxide tube array-aerogel material is obtained;

[0012] Preparation of S2 photothermal conversion composite materials

[0013] S21: soaking the reduced graphene oxide tube array-aerogel material in a positively charged polydiallyldimethylammonium chloride (PDDA) solution for a period of time, and then soaking it in a negatively charged sodium perfluorooctanoate (PFO) solution for a period of time;

[0014] S22 repeats step S21 multiple times to obtain a light-to-heat conversion composite material after drying.

[0015] Furthermore, in step S11, the graphene film has a thickness of 10-100 μm and a diameter of 10-50 mm.

[0016] Furthermore, in step S12 and step S13, the concentration of hydrazine hydrate is 50-85 wt %, the dropping rate is 2-5 μL / 30 min, and the number of dropping times is 10-30 times.

[0017] Furthermore, in step S12 and step S13, the mixture is allowed to stand for more than 30 minutes.

[0018] Furthermore, in step S14, the mixture is allowed to stand for more than 12 hours.

[0019] Furthermore, in step S21, the molecular weight of PDDA is 10,000-20,000, and the concentration of the PDDA solution is 35-55 wt%.

[0020] Furthermore, in step S21, the PFO concentration is 0.1-1.0 mol / L.

[0021] Furthermore, in step S21, the soaking time is 10 to 30 minutes.

[0022] Further, in step S22, step S21 is repeated three to five times.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] (1) Compared with traditional photothermal conversion materials with poor stability, the present invention, while retaining ultra-black reduced graphene oxide nanotubes, prepares an integrated double-layer graphene material with a tube array upper layer and an aerogel base by partially foaming a thin film, thereby effectively improving the photothermal conversion efficiency and structural interface stability of the material, while significantly improving the service life of the material;

[0025] (2) A layer of hydrophilic and oleophobic PDDA-PFO polymer membrane is loaded on the surface of the base by the immersion method, which gives the material excellent anti-oil and anti-organic solution pollution properties, making it perfectly suitable for the wastewater purification process containing oil and organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Characterization image of the prepared reduced graphene oxide tube array-aerogel RGOTAAC, (a) digital photo of the upper surface of the composite material, (b) SEM characterization image of the nanotube array on the upper surface, (c) digital photo of the composite material aerogel base, and (d) SEM characterization image of the aerogel base.

[0027] Figure 2 Water contact angle (a) and oil contact angle (b) of ROGTAAC / PDDA-PFO composite materials.

[0028] Figure 3RGOTAAC water evaporation performance test, (a) RGOTAAC-1 water mass loss over time under 1 times the sunlight, (b) RGOTAAC-2 water mass loss over time under 1 times the sunlight, (c) water temperature over time during evaporation, (d) sample surface temperature over time during evaporation (taking the highest point).

[0029] Figure 4 The graph shows the evaporation rate and evaporation efficiency of RGOTAAC at different heights.

[0030] Figure 5 This is the infrared thermal imaging image of RGOTAAC water evaporation.

[0031] Figure 6 Water evaporation performance test of RGOTAAC / PDDA-PFO composite material in 10 wt% hexadecane (CN), (a) the trend of water mass loss over time, (b) the trend of temperature over time. DETAILED DESCRIPTION

[0032] The following examples are provided to facilitate a better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples, unless otherwise specified, are conventional methods. The experimental materials used in the following examples, unless otherwise specified, are commercially available.

[0033] The present invention discloses a method for preparing a reduced graphene oxide tube array-aerogel / PDDA-PFO composite material that can efficiently generate solar steam and can be used to purify oily wastewater. The present invention partially foams an ultra-black reduced graphene oxide nanotube film to prepare an aerogel to retain its unique light-absorbing structure, thereby obtaining a tube array / aerogel composite reduced graphene oxide material with a light absorptivity exceeding 98% within a wavelength range of 200-2500nm. Furthermore, the present invention further prepares a photothermal conversion composite material (PDDA-PFO / RGOTAAC) having a three-dimensional structural feature of a tube array upper layer, an aerogel base, and a PDDA-PFO coating layer by surface-loading a hydrophilic and oleophobic PDDA-PFO polymer film, thereby broadening its application in the purification of wastewater containing oil, organic matter, and the like.

[0034] The specific steps are as follows:

[0035] (1) Preparation of reduced graphene oxide tube array-aerogel material: At room temperature, a closely arranged nanotube structure is imprinted on the graphene film by nanoimprinting. Subsequently, hydrazine hydrate is added dropwise to other areas except the central nanotube area, and the film is allowed to foam on its own. This is repeated three times until the added area foams significantly and forms an aerogel structure. The foamed film is turned over with tweezers, and hydrazine hydrate is repeatedly added to the reverse side several times, and each time it is allowed to stand for 30 minutes to adjust the thickness of the aerogel structure. Finally, the excess area of ​​the aerogel is cut and allowed to stand for 12 hours to obtain a dried and hardened reduced graphene oxide material having a tube array and aerogel composite structure (hereinafter referred to as RGOTAAC).

[0036] (2) Preparation of photothermal conversion composite material, i.e., PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material: the prepared double-layer composite structure aerogel part was immersed in PDDA solution for 30 minutes to fully contact with PDDA. After the sample surface was coated with a layer of positively charged PDDA, it was immersed in negatively charged PFO solution for 30 minutes. After repeating three times, a layer of PDDA-PFO film was covered on the sample surface with the help of the chemical reaction between PDDA and PFO, thereby preparing a hydrophilic and oleophobic composite material with the structural characteristics of the tube array upper layer, the aerogel base and the PDDA-PFO coating layer, hereinafter referred to as PDDA-PFO / RGOTAAC.

[0037] Implementation Case 1

[0038] (1) Preparation of reduced graphene oxide tube array-aerogel material: At room temperature, a densely arranged nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. Subsequently, hydrazine hydrate with a concentration of 85% was added to other areas except the central nanotube area at a rate of 2 μl / 30 min, and then the film was allowed to stand and wait for self-foaming. This was repeated 3 times until the added area was obviously foamed and an aerogel structure was formed. The foamed film was turned over with tweezers, and hydrazine hydrate was repeatedly added to the reverse side at the same rate for 10 times, and each time it was allowed to stand for 30 minutes, thereby adjusting the thickness of the aerogel structure. Finally, the excess area of ​​the aerogel was cut, and after standing for 12 hours, as shown in FIG. Figure 1 As shown in FIG, a reduced graphene oxide tube array-aerogel material RGOTAAC-1 with a dry and hardened structure and a special light-absorbing structure was prepared. Figure 3-4 Shown at 1kW·m -2 The light intensity reached 1.048 kg·m -2 ·h -1 The water evaporation efficiency is 67.03% with an energy conversion efficiency of 67.03%.

[0039] (2) Preparation of PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material: The prepared double-layer structure material aerogel part was immersed in a PDDA solution with a molecular weight of 10,000 for 30 minutes, so that the aerogel foaming structure below was fully in contact with PDDA. After the sample surface was coated with a layer of positively charged PDDA, it was immersed in a negatively charged 0.1 mol / L PFO solution for 30 minutes. After repeating three times, a layer of PDDA-PFO film was covered on the sample surface with the help of the chemical reaction between PDDA and PFO, and a hydrophilic and oleophobic PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material was prepared. Figure 2 Test the hydrophilic and oleophobic properties of the sample.

[0040] Implementation Case 2

[0041] (1) Preparation of reduced graphene oxide tube array-aerogel material: At room temperature, a densely arranged nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. Subsequently, hydrazine hydrate with a concentration of 85% was added to other areas except the central nanotube area at a rate of 2 μl / 30 min, and then the film was allowed to stand and wait for self-foaming. This was repeated 3 times until the added area was obviously foamed and an aerogel structure was formed. The foamed film was turned over with tweezers, and hydrazine hydrate was repeatedly added to the reverse side at the same rate for 20 times, and each time it was allowed to stand for 30 minutes, thereby adjusting the thickness of the aerogel structure. Finally, the excess area of ​​the aerogel was cut, and after standing for 12 hours, a reduced graphene oxide tube array-aerogel material RGOTAAC-2 that was dried and hardened and had a special light absorption structure was obtained, such as Figure 3-4 Shown at 1kW·m -2 The water evaporation rates and efficiencies of RGOTAAC-1 and RGOTAAC-2 were tested under a light intensity of 1.336 kg·m -2 ·h -1 The water evaporation rate and energy conversion efficiency of 87.12% are much higher than that of Example 1 (RGOTAAC-1) (1.048 kg·m -2 ·h -1 The water evaporation rate is 67.03% with an energy conversion efficiency of 67.03%. Figure 5 The sample is at 1kW·m -2 Infrared thermal imaging under light intensity.

[0042] (2) Preparation of PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material: The prepared double-layer structure material aerogel part was immersed in a PDDA solution with a molecular weight of 10,000 for 30 minutes, so that the aerogel foaming structure below was fully in contact with PDDA. After the sample surface was coated with a layer of positively charged PDDA, it was immersed in a negatively charged 0.1 mol / L PFO solution for 30 minutes. After repeating three times, a layer of PDDA-PFO film was covered on the sample surface by the chemical reaction between PDDA and PFO, thereby preparing a hydrophilic and oleophobic PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material, as shown in FIG. Figure 6 Shown at 1kW·m -2 The light intensity reached 1.28 kg·m in 10% hexadecane (CN) solution. -2 ·h -1 The water evaporation rate is 81.95% with an energy conversion efficiency of 81.95%.

[0043] Comparative Case 2-1

[0044] (1) At room temperature, a densely packed nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. The film was then immersed in 85% hydrazine hydrate for 30 min. The film foamed and turned into aerogel, and the ultra-black tube array completely disappeared.

[0045] Comparative Case 2-2

[0046] (1) At room temperature, a densely packed nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. Subsequently, 85% hydrazine hydrate was added dropwise at a rate of 2 mL / 30 min to the other regions except the central nanotube region. After the addition was completed, the film was allowed to foam on its own. The film foamed completely into an aerogel, and the ultra-black tube array disappeared completely.

[0047] Implementation Case 3

[0048] (1) Preparation of reduced graphene oxide tube array-aerogel material: At room temperature, a densely arranged nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. Subsequently, hydrazine hydrate with a concentration of 50% was added to other areas except the central nanotube area at a rate of 2 μl / 30 min, and then the film was allowed to stand and wait for self-foaming. This was repeated 3 times until the added area was obviously foamed and an aerogel structure was formed. The foamed film was turned over with tweezers, and hydrazine hydrate was repeatedly added to the reverse side at the same rate 20 times, and each time it was allowed to stand for 30 minutes, thereby adjusting the thickness of the aerogel structure. Finally, the excess area of ​​the aerogel was cut, and after standing for 12 hours, a reduced graphene oxide tube array-aerogel material with a dry and hardened special light absorption structure was obtained.

[0049] (2) Preparation of PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material: The prepared double-layer structure material aerogel part was immersed in a PDDA solution with a molecular weight of 10,000 for 30 minutes, so that the aerogel foaming structure below was fully in contact with PDDA. After the sample surface was coated with a layer of positively charged PDDA, it was immersed in a negatively charged 0.1 mol / L PFO solution for 30 minutes. After repeating three times, a layer of PDDA-PFO film was covered on the sample surface with the help of the chemical reaction between PDDA and PFO, thereby preparing a hydrophilic and oleophobic, PDDA-PFO coated reduced graphene oxide tube array-aerogel composite material.

[0050] Comparative Case 3-1

[0051] (1) At room temperature, a densely packed nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. The film was then immersed in 50% hydrazine hydrate for 30 min. The film foamed and turned into aerogel, and the ultra-black tube array completely disappeared.

[0052] Comparative Case 3-2

[0053] (1) At room temperature, a densely packed nanotube structure was imprinted on a graphene film with a diameter of 20 mm and a thickness of 60 μm by nanoimprinting. Subsequently, 50% hydrazine hydrate was added dropwise at a rate of 2 mL / 30 min to the other regions except the central nanotube region. After the addition was completed, the film was allowed to foam on its own. The film foamed completely and turned into aerogel, and the ultra-black tube array disappeared completely.

Claims

1. A method for preparing a photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater, characterized in that: The steps include: S1 Preparation of reduced graphene oxide tube array-aerogel material S11 uses nanoimprinting to imprint a densely packed nanotube structure in the center of a graphene film; S12: except for the nanotubes in the central area, hydrazine hydrate is added dropwise to other areas, left to stand for a period of time, and the addition is repeated several times until the added area is obviously foamed and an aerogel structure is formed; S13: adding hydrazine hydrate to the other side of the graphene film, leaving it to stand for a while, and repeating the adding several times until the adding area is obviously foamed and an aerogel structure is formed; S14 cutting the redundant area of ​​the aerogel, retaining the area where the nanotube structure is located, and standing still until a dry and hardened reduced graphene oxide tube array-aerogel material is obtained; Preparation of S2 photothermal conversion composite materials S21: soaking the reduced graphene oxide tube array-aerogel material in a positively charged polydiallyldimethylammonium chloride (PDDA) solution for a period of time, and then soaking it in a negatively charged sodium perfluorooctanoate (PFO) solution for a period of time; S22 repeats step S21 multiple times, and obtains the light-to-heat conversion composite material after drying.

2. The method according to claim 1, characterized in that In step S11, the graphene film has a thickness of 10-100 um and a diameter of 10-50 mm.

3. The method according to claim 1, characterized in that In step S12 and step S13, the concentration of hydrazine hydrate is 50-85 wt %, the dropping rate is 2-5 μL / 30 min, and the number of dropping times is 10-30 times.

4. The method according to claim 1, characterized in that In step S12 and step S13, the mixture is allowed to stand for more than 30 minutes.

5. The method according to claim 1, characterized in that In step S14, the mixture is left to stand for more than 12 hours.

6. The method according to claim 1, wherein: In step S21, the molecular weight of PDDA is 10000-20000, and the concentration of PDDA solution is 35-55 wt%.

7. The method according to claim 1, characterized in that In step S21, the concentration of PFO is 0.1-1.0 mol / L.

8. The method according to claim 1, wherein In step S21, the soaking time is 10-30 min.

9. The method according to claim 1, characterized in that In step S22, step S21 is repeated three to five times.

10. A photothermal conversion composite material suitable for purifying oily wastewater and organic wastewater, prepared by the method according to any one of claims 1 to 9.

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