A photothermal material

Abstract

There is provided a photothermal material, comprising a plurality of layers of two-dimensional phyllosilicate intercalated with a liquid metal. In a particular embodiment, the phyllosilicate is mica and the liquid metal is gallium.

Description

[0001] A photothermal material

[0002] Technical Field

[0003] The present invention relates to a photothermal material.

[0004] Background

[0005] Solar energy is an attractive sustainable energy source. Efficient harvesting and conversion are critical. Photothermal conversion stands out for its high energy conversion efficiency and the wide range applications of the generated thermal energy, such as solar vapour generation, liquid-liquid phase separation, and localized water heating. However, current photothermal materials face challenges in limited spectral response, long-term stability, and efficiency.

[0006] Thus, there is a need for an improved photothermal material.

[0007] Summary of the invention

[0008] The present invention seeks to address these problems, and / or to provide an improved photothermal material.

[0009] According to a first aspect, there is provided a photothermal material, comprising a plurality of layers of two-dimensional phyllosilicate intercalated with a liquid metal.

[0010] According to a particular aspect, the phyllosilicate may be mica. According to a particular aspect, the liquid metal may be gallium.

[0011] According to a particular aspect, the weight ratio of phyllosilicate to liquid metal may be 1 :0.01 to 1:0.75.

[0012] According to a particular aspect, each of the plurality of layers may have an average thickness of 2-12 nm. The plurality of layers may have an average thickness of 10-300 nm.

[0013] The photothermal material may have full-solar-spectrum absorption.

[0014] According to a second aspect, there is provided a dispersion comprising a transparent fluid and the photothermal material according to the first aspect. The photothermal material may be comprised in the dispersion in an amount of 0.1-10 mg / mL.

[0015] According to a particular aspect, the photothermal material may increase solar thermal conversion in water by > 50%.

[0016] Brief Description of the Drawings

[0017] In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments, the description being with reference to the accompanying illustrative drawings. In the drawings:

[0018] Figure 1 shows a diagram of the set-up for photothermal conversion test;

[0019] Figure 2 shows photothermal conversion mechanics based on two phenomena; Figures 2(a) and 2(b) shows electron-hole generation and relaxation, similar to semiconductors; Figure 2(c) shows plasmonic localized heating of metals; and

[0020] Figure 3 shows the temperature variation over time with and without Ga / mica nanosheets under a one-sun solar simulator during the photothermal conversion test.

[0021] Detailed Description

[0022] As explained above, there is a need for an improved photothermal material.

[0023] In general terms, the present invention provides a photothermal material. The photothermal material may be used in solar heating devices without any conventional solar panels, and / or integrated with existing commercial liquid desiccant cooling systems to enhance the efficiency, sustainability, and operational lifespan of climate control solutions.

[0024] According to a first aspect, there is provided a photothermal material, comprising a plurality of layers of two-dimensional phyllosilicate intercalated with a liquid metal.

[0025] For the purposes of the present invention, the use of the singular includes the plural unless specifically stated otherwise. It should be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Further, the use of the term “including”, “comprising”, and “having” as well as other forms, such as “include”, “comprise”, “have’ are not considered limiting.

[0026] For the purposes of the present invention, references to a photothermal material refers to a material which converts light to heat.

[0027] The photothermal material may comprise any suitable number of layers of two- dimensional phyllosilicate, intercalated with a liquid metal. For example, the photothermal material may comprise up to 5 layers, up to 10 layers, up to 20 layers, up to 30 layers, up to 40 layers, up to 50 layers. In particular, the photothermal material may comprise up to 10 layers.

[0028] The two-dimensional phyllosilicate may be in any suitable two-dimensional form. The two-dimensional form may be in the form of nanosheets, nanoparticles, nanotubes, nanoflakes, nanoplatelets. In particular, the two-dimensional form may be in the form of nanosheets.

[0029] The phyllosilicate may be any suitable phyllosilicate. The phyllosilicate may be a nonvan der Waals material. Thus, the photothermal material may comprise two-dimensional non-van der Waals material, which overcomes technical prejudice against such material due to its strong bonding. For example, the phyllosilicate may be mica, serpentine, smectite, chlorite, vermiculite, talc, kaolinite, illite, or any combination thereof. In particular, the phyllosilicate may be mica.

[0030] The liquid metal may be any suitable liquid metal, and / or metals and alloys with a low melting temperature. The liquid metal may have a melting temperature < 300 °C. For example, the liquid metal may be mercury, caesium, gallium, rubidium, bismuth, indium, or any combination thereof. In particular, the liquid metal may be gallium.

[0031] The liquid metal may be any suitable liquid metal for intercalation within the plurality of layers. The degree of intercalation may be adjusted such that the ratio of phyllosilicate to liquid metal may be any suitable ratio. According to a particular aspect, the weight ratio of phyllosilicate to liquid metal may be 1 :0.01 to 1 :0.75. In particular, the weight ratio of phyllosilicate to liquid metal may be 1 :0.05 to 1 :0.7, 1 :0.1 to 1 :0.6, 1 :0.2 to 1 :0.5, 1 :0.3 to 1:0.4. Even more in particular, the weight ratio of phyllosilicate to liquid metal may be 1 :0.1 to 1 :0.5. According to a particular aspect, each of the plurality of layers may have an average thickness of 2-12 nm. In particular, each of the plurality of layers may have an average thickness of 3-11 nm, 4-10 nm, 5-9 nm, 6-8 nm. Even more in particular, each of the plurality of layers may have an average thickness of 4-6 nm.

[0032] The plurality of layers may have an average thickness of 10-300 nm. In particular, the plurality of layers may have an average thickness of 15-250 nm, 20-200 nm, 30-250 nm, 40-240 nm, 50-230 nm, 60-220 nm, 70-210 nm, 80-200 nm, 90-190 nm, 100-180 nm, 110-170 nm, 120-160 nm, 130-150 nm. Even more in particular, the plurality of layers may have an average thickness of 12-71 nm.

[0033] The photothermal material may have full-solar-spectrum absorption. For the purposes of the present invention, references to full-solar-spectrum absorption refers to the ability to absorb a wide range of wavelengths within the solar spectrum, spanning from ultraviolet (UV) to near-infrared (NIR) wavelengths. Thus, the photothermal material advantageously increases efficacy of capturing a broad spectrum when exposed to sunlight, and overcomes challenges associated with limited spectral responses.

[0034] The photothermal material may advantageously reach a higher temperature upon solar heating. For example, the photothermal material may reach a temperature of 40-60 °C upon solar heating. In particular, the photothermal material may reach a temperature of 42-58 °C, 45-55 °C, 47-53 °C upon solar heating. Even more in the photothermal material may reach a temperature of 50-60 °C upon solar heating.

[0035] According to a second aspect, there is provided a dispersion comprising a transparent fluid and the photothermal material according to the first aspect. The transparent fluid may be any suitable medium that allows light to pass through so that the photothermal material may convert the light to heat. For example, the transparent fluid may be water, organic solvents, oil, aqueous solutions, organic solutions, liquid crystals, molten materials, or any combination thereof.

[0036] The photothermal material may be comprised in the dispersion in an amount of 0.1 to 10 mg / mL. In particular, the photothermal material may be comprised in the dispersion in an amount of 0.2 to 9.5 mg / mL, 0.3 to 9.0 mg / mL, 0.4 to 8.5 mg / mL, 0.5 to 8.0 mg / mL, 0.6 to 7.5 mg / mL, 0.7 to 7.0 mg / mL, 0.8 to 6.5 mg / mL, 0.9 to 6.0 mg / mL, 1.0 to 5.5 mg / mL, 1.5 to 5.0 mg / mL, 2.0 to 4.5 mg / mL, 2.5 to 4.0 mg / mL, 3.0 to 3.5 mg / mL. Even more in particular, the photothermal material may be comprised in the dispersion in an amount of 5.0 mg / mL.

[0037] According to a particular aspect, the photothermal material may increase solar thermal conversion in water by > 50%, at a suitable loading. For example, the loading may be at least 5 g / L. The temperature of the dispersion may increase by a greater amount upon exposure to solar energy, as compared to the temperature increase in water alone at the same exposure to solar energy. The exposure may be at any suitable power for any suitable period of time. For example, the exposure may be one-sun to five-sun simulation. The exposure may be for 15-120 minutes. In particular, the exposure may be for 20-110 minutes, 30-100 minutes, 40-90 minutes, 50-80 minutes, 60-70 minutes.

[0038] Upon exposure to one-sun simulation for 15 minutes, the temperature increase in the dispersion comprising water and the photothermal material may be > 50% greater compared to the temperature increase in water. In particular, the photothermal material may increase solar thermal conversion in water by > 55%, > 60%, > 65%, > 70 %, > 75%, > 80%, > 85%, > 90%, > 100%, > 110%, > 120%, > 130%, > 140%, > 150%, > 160%, > 170%, > 180%, > 190%, > 200%. Even more in particular, the photothermal material may increase solar thermal conversion in water by > 200%. For example, at a loading of 5 g of photothermal material per litre of water, and starting at 25°C, upon 1 hour of one-sun simulation exposure, the temperature may increase by up to 32°C, as compared to other materials or pure water with a temperature increase of only up to 10°C. Thus, the photothermal material advantageously has greater efficiency of solar thermal conversion.

[0039] Having now generally described the invention, the same will be more readily understood through reference to the following example which is provided by way of illustration, and is not intended to be limiting.

[0040] Example

[0041] Materials and methods

[0042] Natural mica particles with hundreds of layers of alumina silicate were converted to Ga / mica nanosheets. Natural ground muscovite mica of 99.5% purity was obtained from Huajing mica Co. Ltd (Shijiazhuang City, China). Gallium ingot (99.9999%) was purchased from Fisher Scientific Pte Ltd.

[0043] For exfoliation of ground mica, 20 g of natural mica was first mixed with 10 g of gallium using a motor and pestle for 30 minutes. To keep gallium in the liquid state, the temperature of the motor was maintained at about 60 °C using a hot plate. The mixed sample was kept in the oven at 60 °C for 30 minutes. Then, the sample was divided into two equal weights and put into 100 ml zirconia grinding vessels with 90 g grinding balls of sizes 3, 5, 10 and 15 mm.

[0044] Grinding was performed in a ball milling machine. The spinning speed of the high energy planetary ball mill was maintained at 600 rpm for 30 minutes. The obtained powder was sonicated for one hour using a FB5061 Ultrasonic Unit with a vibration frequency of 37 kHz (Thermo Fisher Scientific Inc.). The mixture was centrifuged at 6000 rpm for 10 min to remove any unexfoliated mica.

[0045] The supernatant was freeze-dried to obtain the Ga-mica nanosheet products.

[0046] Characterization

[0047] Morphology

[0048] Mica sheet morphology was evaluated using scanning electron microscopy (SEM) JEOL JSM-7600F coupled with energy dispersive X-ray spectroscopy (EDS) and FEI Titan 80 / 300 Scanning / Transmission Electron Microscopy (TEM) (200 KV). The samples for TEM analysis were prepared by suspending the exfoliated mica nanosheets in ethanol using sonication. The suspended solution was then dropped onto a carbon coated copper grid and let dry in room temperature.

[0049] Evaluation of solar thermal conversion efficiency

[0050] The evaluation of solar thermal conversion efficiency was conducted using the experimental setup illustrated in Figure 1. 0.5 grams of Ga / mica nanoparticles were dispersed in 100 mL of water in a beaker. The beaker was then placed in a CEL-LB70 photochemical reactor equipped with a CEL-PE300L-3A solar simulator (Beijing China Education Au-light Co Ltd) and a magnetic stirring plate to ensure uniform heat distribution and consistent dispersion of the Ga / mica nanosheets. The simulator was activated with a current of 15 A, and the sample was exposed to one-sun illumination.

[0051] Temperature changes in the solution were monitored using an infrared (IR) camera.

[0052] Results and discussion

[0053] Morphology

[0054] Natural mica had an average particle diameter of 2.07 ± 0.70 pm. The magnified image of the natural mica showed an average thickness of 293.37 ± 164.20 nm.

[0055] Exfoliated Ga / mica nanoplatelets (Ga / mica nanosheets) composite exhibited a sheetlike structure with uniform size, having a width range of 100-300 nm.

[0056] TEM images were magnified to measure the thickness of single and few layer nanoplatelets. The average thickness was 4.93 nm ± 3.19 nm.

[0057] The utilization of EDS elemental mapping provided unequivocal evidence regarding the presence of Ga within the mica.

[0058] In the case of natural mica, the surface atomic composition is as follows: Ga=0%, Al=8.1 %, Si=9.5%, 0=79.9%, and K=2.5%.

[0059] Conversely, for the Ga / mica nanoplatelets, the surface atomic composition showed Ga=2.1%, Al=8.1 %, Si=9.5%, 0=79.9%, and K=3.0%. There was a discernible increase in Ga content in the exfoliated Ga / mica nanoplatelets.

[0060] Evaluation of solar thermal conversion efficiency

[0061] In the Ga / mica nanosheets, the presence of Ga-intercalated mica nanoplatelets with different bandgaps and metallic Ga on the surface allows for photothermal conversion mechanics based on two phenomena: (i) electron-hole generation and relaxation of semiconductors (Figures 2(a) and (b)), and (ii) plasmonic localized heating of metals (Figure 2(c)).

[0062] Upon interaction with light at suitable wavelengths, free electrons on the surfaces of metallic nanoparticles become energized, resulting in the collective, coherent oscillation of conduction-band electrons. This interaction is known as localized surface plasmon resonance (LSPR). LSPR experiences decay either radiatively, contributing to the enhanced electromagnetic field at close range, or non-radiatively, through intra band or inter band transitions. This non-radiative process results in the heating of the surface. The incorporation of Ga on the mica surface can induce LSPR, leading to the production of heat.

[0063] In semiconductors, the absorption of photons with energy at or exceeding the band gap leads to the generation of electron-hole pairs. Upon photoexcitation, electrons are promoted to the conduction band, creating holes in the valence band. The relaxation of these excited states electron can emit photons (radiative process) or transfer energy as heat to the lattice (non-radiative process), thereby increasing the thermal energy and temperature of the material. For the Ga / mica nanosheets samples, the existence of various narrow band gaps expands the spectrum of absorbable wavelengths, thereby enhancing solar thermal conversion efficiency.

[0064] As seen in Figure 3, the solar thermal conversion of a 1 mg / mL Ga / mica nanosheet dispersion demonstrated a 51 % increase in temperature compared to deionized water under a one-sun solar simulator for 15 minutes.

[0065] Whilst the foregoing description has described exemplary embodiments, it will be understood by those skilled in the technology concerned that many variations may be made without departing from the present invention.

Claims

Claims1. A photothermal material, comprising a plurality of layers of two-dimensional phyllosilicate intercalated with a liquid metal.

2. The photothermal material according to claim 1 , wherein the phyllosilicate is mica.

3. The photothermal material according to claim 1 or 2, wherein the liquid metal is gallium.

4. The photothermal material according to any preceding claim, wherein the weight ratio of phyllosilicate to liquid metal is 1 :0.01 o 1 :0.75.

5. The photothermal material according to any preceding claim, wherein each of the plurality of layers has an average thickness of 2-12 nm.

6. The photothermal material according to any preceding claim, wherein the plurality of layers have an average thickness of 100-300 nm.

7. The photothermal material according to any preceding claim, wherein the material has full-solar-spectrum absorption.

8. A dispersion comprising a transparent fluid and the photothermal material according to any preceding claim.

9. The dispersion according to claim 8, wherein the photothermal material is comprised in the dispersion in an amount of 0.1-10mg / mL.

10. The dispersion according to claim 8 or 9, wherein the photothermal material increases solar thermal conversion in water by > 50%.

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