A zif-8 derived photothermal material, and a preparation method and application thereof

Abstract

The application provides a ZIF-8 derived photothermal material and a preparation method and application thereof. The preparation method of the ZIF-8 derived photothermal material comprises the following steps: carbonizing 2-methyl imidazole zinc salt to obtain ZIF-C powder, adsorbing Cu on the ZIF-C powder 2+ , and finally synthesizing Cu particles through high-temperature carbon reduction to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C. The ZIF-8 derived photothermal material prepared by the application has more excellent water evaporation performance, greatly improves the thermal energy conversion capacity of the material, improves the photothermal conversion efficiency of the material, and realizes efficient thermal energy water evaporation. Moreover, the preparation method is simple and practical.

Description

Technical Field

[0001] This invention relates to the field of photothermal materials, and in particular to a ZIF-8 derived photothermal material, its preparation method, and its application. Background Technology

[0002] In thermally localized solar evaporation systems, heat is generated by solar absorbers through solar energy absorption and subsequent photothermal processes. Many photothermal materials have been developed as solar energy absorption materials due to their high solar absorptivity. Photothermal materials absorb light energy in the form of photons and convert this absorbed energy into heat. The heat generation of photothermal materials depends on the material's inherent physical properties. Different photothermal materials can convert energy into heat in different forms due to their different physical properties, but it is impossible for any photothermal material to convert 100% of solar energy into heat. Currently, among the many types of photothermal conversion materials, those with relatively high conversion efficiency include metallic materials, semiconductor materials, and carbon-based materials, which are particularly common in the field of solar thermal energy conversion. These three types of materials all possess unique photothermal conversion mechanisms: the local resonance effect of metallic plasma particles; the non-radiative relaxation process of semiconductors; and the molecular thermal vibration of carbon materials.

[0003] Most photothermal materials show strong application prospects in the field of solar water evaporation, aiming to address the real scarcity of clean freshwater resources in daily life. Numerous research efforts have yielded diverse and distinctive designs and synthesizations of various materials, offering many solutions to the freshwater problem. However, the synthesis of most photothermal particulate materials is more complex, and their structures are not conducive to constructing more fundamental hydrothermal energy transfer interfaces. Currently, common photothermal materials suffer from problems such as complex synthesis, high cost, and low designability. Therefore, researching derivative materials with functionalized synergistic photothermal processes is of great significance. Summary of the Invention

[0004] In view of this, the present invention proposes a ZIF-8 derived photothermal material, its preparation method and application.

[0005] The technical solution of this invention is implemented as follows:

[0006] A method for preparing a ZIF-8 derived photothermal material includes the following steps: carbonizing ZIF-8 (2-methylimidazolium zinc salt) to obtain ZIF-C powder, thereby allowing the ZIF-C powder to adsorb Cu. 2+， Finally, Cu particles were synthesized by high-temperature carbon reduction to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C.

[0007] A further technical solution is that the preparation method of the ZIF-8 derived photothermal material includes the following steps:

[0008] (1) ZIF-8 powder is pretreated by carbonization under nitrogen or inert gas protection. The carbonization temperature is 890-910℃ and the carbonization is maintained at the temperature to obtain ZIF-C powder.

[0009] (2) Add the ZIF-C powder obtained in step (1) to the copper nitrate trihydrate solution, disperse and stir by ultrasonication to obtain a suspension, evaporate to dryness, and dry;

[0010] (3) After grinding the sample obtained from drying in step (2), high-temperature carbon reduction is carried out under nitrogen or inert gas protection. The carbon reduction temperature is 900-1200℃. After cooling to room temperature, the sample is taken out, washed, and dried to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C.

[0011] A further technical solution is that, in step (1), the copper nitrate solution is prepared by copper nitrate trihydrate and ethanol at a molar volume ratio of 0.8-1.2:40-50 mol / L.

[0012] A further technical solution is that, in step (1), the molar mass ratio of the copper nitrate trihydrate and the ZIF-C powder is 0.8-1.2 mmol / g: 0.4-0.6.

[0013] A further technical solution is,

[0014] In step (2), the specific operation of evaporation is as follows: the suspension is repeatedly evaporated by heating in an oil bath, and a solvent is added during the repeated evaporation process. The oil bath heating temperature is 75-85℃, and the number of repeated evaporation cycles is 2-4.

[0015] In step (3), the specific washing operation is as follows: after taking out the sample, ultrasonically wash it with 0.4-0.6M H2SO4 for 30-50 minutes, centrifuge, and wash it with deionized water.

[0016] A further technical solution is,

[0017] In step (1), the carbonization pretreatment temperature is 890-910℃, and the holding time is more than 1 hour, preferably 1-3 hours;

[0018] In step (2), the ultrasonic dispersion time is more than 30 minutes and the stirring time is more than 24 hours, preferably 24 to 30 hours;

[0019] In step (3), the heat preservation time for high-temperature carbon reduction is more than 2 hours, preferably 2 to 3 hours.

[0020] A further technical solution is,

[0021] In steps (1) and (3), the heating rate before heat preservation is 4-6℃ / min;

[0022] Step (2), the drying is vacuum drying, the drying temperature is 75-85℃, and the drying time is 7-9h;

[0023] Step (3) The drying is performed by forced air drying at a temperature of 75-85°C for 5-7 hours.

[0024] A further technical solution is to introduce water vapor for etching for 20 to 240 minutes during the heat preservation stage in step (1), and after the sample cools to room temperature, take out the sample for acid washing and drying.

[0025] A further technical solution is to introduce water vapor at a flow rate of 140–160 sccm.

[0026] A further technical solution is as follows: The preparation method of the ZIF-8 derived photothermal material includes the following steps:

[0027] (1) The ZIF-8 powder was loaded into a quartz boat and transferred into a tube furnace. Under nitrogen protection at a flow rate of 90-110 ml / min, the air in the tube was first purged for more than 20 minutes. Then, it was heated to 890-910℃ at a heating rate of 4-6℃ / min and held for more than 1 hour. After the temperature in the furnace cooled to room temperature, the black powder ZIF-C was obtained.

[0028] (2) Weigh 0.8–1.2 mmol of copper nitrate trihydrate and disperse it in 40–50 ml of ethanol solution to form a light blue solution. Then add 0.4–0.6 g of ZIF-C powder and sonicate for at least 30 minutes to disperse it evenly. Stir at room temperature for at least 24 hours to allow Cu to precipitate. 2+ The ethanol suspension is fully diffused into the ZIF-C channels through the concentration gradient difference. The resulting ethanol suspension is transferred to an oil bath stirred pot and heated at 75-85°C until the ethanol content in the beaker is close to dry. Then a small amount of ethanol is added and the process is repeated 2-4 times. Finally, the beaker is placed in a vacuum drying oven and vacuum dried at 75-85°C for 7-9 hours.

[0029] (3) After grinding the black sample obtained by vacuum drying, place it in a quartz boat, transfer it to a tube furnace, pre-pass it under a nitrogen atmosphere for 15-25 min, and then heat it to 900-1200℃ at a heating rate of 4-6℃ / min. Keep it at this temperature for 2 h. After the sample cools to room temperature, take out the sample and ultrasonically wash it with 30-50 ml of 0.4-0.6 M H2SO4 for 30-50 min. Centrifuge 2-4 times and wash with deionized water. After extracting the sample, dry it in a forced-air drying oven at 75-85℃ for 5-7 h. The material obtained is ZIF-8 derived copper-carbon composite photothermal particle Cu@ZIF-C.

[0030] The present invention relates to the application of ZIF-8 derived photothermal material in a photothermal evaporator.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) This invention uses ZIF-8 as the initial template to introduce and synthesize plasma metal copper particles, forming a copper-carbon coated composite material structure inside. It adopts simple high-temperature carbon reduction to achieve better water evaporation performance, greatly improving the material's thermal energy conversion capability and photothermal conversion efficiency, and realizing efficient thermal energy water evaporation.

[0033] (2) This invention also utilizes a water-gas reaction to control the aperture of carbon dots through etching with steam. The etching process not only modifies the collapsed channels but also thins the framework, achieving multi-level scattering and absorption limitation of the optical path. The aperture control of this invention makes the heat transfer process more efficient, and the additional specific surface area can promote the increase of thermal interfaces, making the heat transfer process more rapid.

[0034] (3) The ZIF-8 derivative photothermal material prepared in this invention is used in a photothermal evaporator, which enables the evaporation system to achieve a more efficient steam escape rate.

[0035] (4) The preparation method of the present invention is simpler, more practical and more designable.

[0036] (5) Utilizing the site characteristics of nitrogen elements within the ZIF-8 organic ligand, the nitrogen particles are anchored to the graphite plane in a doped form after carbonization. By leveraging the defect characteristics of different doped nitrogen sites, the connection structure between the metal particles and the conjugated nitrogen sites is designed to be adjustable. By controlling the close connection between the metal particles and the graphite plane, the energy release process of the plasma resonance effect is regulated by the change in nitrogen content. As the content of conjugated nitrogen gradually decreases, the overall photothermal conversion effect of the material is weakened. Regulating the Cu-N structure is beneficial for achieving efficient thermal water evaporation. Attached Figure Description

[0037] Figure 1 SEM images of ZIF-8 and its derivatives. (a, d) ZIF-8; (b, e) ZIF-C900; (c, f) Cu@ZIF-C.

[0038] Figure 2 TEM images of ZIF-8 and its derivatives. (a) TEM image of ZIF-C900, (b) TEM image of Cu@ZIF-C, (c) magnified TEM image of Cu@ZIF-C, (d) HRTEM image of Cu@ZIF-C.

[0039] Figure 3 EDX plot of Cu@ZIF-C. (a) HAADF plot, (b) Cu elemental distribution, (c) C elemental distribution, (d) N elemental distribution.

[0040] Figure 4 XRD patterns of ZIF-8 and its derivatives. (a) ZIF-8, (b) ZIF-C900 and Cu@ZIF-C. Figure 4 b, from top to bottom, the curves correspond to Cu@ZIF-C and ZIF-C900 respectively.

[0041] Figure 5 N2 adsorption-desorption curves (a) and pore size distribution curves (b) of ZIF-8 and Cu@ZIF-C.

[0042] Figure 6 UV spectra of ZIF-8 derivatives. (a) UV absorption spectrum, (b) UV reflectance spectrum.

[0043] Figure 7 The heating curve (a) and liquid UV absorption spectrum (b) of the ZIF-8 derivative are shown. Figure 7 a, Figure 7 b, from top to bottom, the curves correspond to Cu@ZIF-C and ZIF-C900 respectively.

[0044] Figure 8 The mass loss curve (a) of the ZIF-8 derivative and the comparison graph of evaporation rate and evaporation efficiency are shown. Figure 8 a, from top to bottom, the curves correspond to pure water, ZIF-C900, and Cu@ZIF-C, respectively.

[0045] Figure 9 Distribution of different nitrogen sites in the carbon plane (a); N1s XPS spectra of Cu@ZIF-C at different temperatures (b).

[0046] Figure 10 Raman spectra of Cu@ZIF-C after treatment at different temperatures.

[0047] Figure 11 N2 adsorption-desorption curves (a) and pore size distribution curves of Cu@ZIF-C after treatment at different temperatures.

[0048] Figure 12 Light absorption rate of Cu@ZIF-C materials at different carbonization temperatures.

[0049] Figure 13 (a) Heating curves of Cu@ZIF-C at different temperatures; (b) Line graph of nitrogen content change versus final stable temperature.

[0050] in, Figure 13 a, from top to bottom, the curves correspond to Cu@ZIF-C900, Cu@ZIF-C1000, Cu@ZIF-C1100, Cu@ZIF-C1200, and ZIF-C900 respectively.

[0051] Figure 14 (a) Schematic diagram of the evaporation structure of Cu@ZIF-C thin film; (b) Real-time infrared images of Cu@ZIF-C900 thin film (top) and Cu@ZIF-C1200 thin film (bottom) evaporating over time.

[0052] Figure 15 (a) Weight loss curves of different materials over time; (b) Scatter plots of evaporation efficiency and water evaporation rate. Figure 15 a. From bottom to top, the curves correspond to Cu@ZIF-C900, Cu@ZIF-C1000, Cu@ZIF-C1100, Cu@ZIF-C1200, ZIF-C900, and pure water, respectively.

[0053] Figure 16 SEM images of ZIF-C900 samples at different etching times: (a) no etching, (b) etched for 20 min, (c) etched for 80 min, (d) etched for 240 min.

[0054] Figure 17 N2 adsorption-desorption curves (a) and pore size distribution curves at different etching times.

[0055] Figure 18 The light reflectance curves (a) and light transmittance curves (b) of samples with different etching times. Among them, Figure 18 a. The curves from bottom to top correspond to etching at 240 min, 20 min, and 80 min, respectively. There is no difference in light reflectance between 20 min and 80 min.

[0056] Figure 19 Weight loss curves of samples with different etching times. Detailed Implementation

[0057] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0058] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0059] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0060] Example 1

[0061] 1. Experimental Materials and Methods

[0062] 1.1 Experimental Materials and Equipment

[0063] 1.1.1 Experimental reagents

[0064] All the chemical reagents used in the experiments described in this paper are shown in Table 1 below. Unless otherwise specified, all reagents were used directly without purification.

[0065] Table 1 Chemical Reagents

[0066]

[0067] 1.1.2 Instruments and Equipment

[0068] The instruments and equipment involved in the experiment are shown in Table 2.

[0069] Table 2 Main Test Instruments and Equipment

[0070]

[0071] 1.2 Synthesis and Preparation of ZIF-8 Based Photothermal Particles

[0072] 1.2.1 Synthesis of ZIF-8

[0073] Weigh 5.16g of Zn(NO3)2 and dissolve it in 400ml of anhydrous methanol to form a homogeneous solution. Then, slowly add 5.26g of 2-methylimidazole white granules while stirring. After mixing thoroughly, continue stirring until a milky white precipitate appears in the beaker and becomes opaque. Then, let it stand at room temperature for 12 hours until the white solid precipitate is formed. Discard the supernatant and transfer the white precipitate to a centrifuge bottle. Centrifuge using a benchtop centrifuge, washing with anhydrous methanol during centrifugation three times. Collect the precipitate in a beaker and dry it overnight in a 70℃ forced-air drying oven to obtain the dried ZIF-8 white block.

[0074] 1.2.2 Preparation of Cu@ZIF-C photothermal material

[0075] The synthesis of Cu@ZIF-C mainly consists of three steps: (1) the pretreatment and carbonization process of ZIF-8, i.e., the synthesis of ZIF-C; (2) the adsorption process of Cu2+; and (3) the synthesis of Cu particles by high-temperature carbon reduction. The specific operations are as follows:

[0076] (1) The dried white ZIF-8 lumps were pounded into powder using a mortar and pestle to obtain ZIF-C powder. The ZIF-8 powder was placed in a quartz boat and transferred to a tube furnace. Under nitrogen protection at a flow rate of 100 ml / min, the air inside the tube was first purged for 20 min, and then heated to 900℃ at a heating rate of 5℃ / min and held for 1 h. After the furnace temperature cooled to room temperature, the resulting black powder was named ZIF-C. The black powder synthesized by holding at 900℃ for 3 h in the same manner was named ZIF-C900.

[0077] (2) Weigh 1 mmol of copper nitrate trihydrate and disperse it in 40 ml of ethanol solution to form a light blue solution. Then add 0.5 g of ZIF-C powder and sonicate for 30 min to disperse evenly. Stir at room temperature for 24 h to allow Cu to precipitate. 2+ The ethanol suspension is fully diffused into the ZIF-C channels by the concentration gradient difference. The resulting ethanol suspension is transferred to an oil bath and heated at 80°C until the ethanol content in the beaker is almost evaporated. Then a small amount of ethanol is added, and the evaporation is repeated three times. Finally, the beaker is placed in a vacuum drying oven and dried under vacuum at 80°C for 8 hours.

[0078] (3) The black sample obtained by vacuum drying was ground and placed in a quartz boat, then transferred to a tube furnace. It was pre-purified under a nitrogen atmosphere for 20 min, then heated to 900℃ at a heating rate of 5℃ / min and held at this temperature for 2 h. After the sample cooled to room temperature, it was removed and ultrasonically washed with 40 ml of 0.5 M H₂SO₄ for 40 min. It was centrifuged twice and washed with deionized water. The extracted sample was then dried in an 80℃ forced-air drying oven for later use. The resulting material is ZIF-8 derived copper-carbon composite photothermal particle Cu@ZIF-C. 1.2.3 Preparation of Cu@ZIF-C at Different Carbonization Temperatures

[0079] The effects of different carbonization temperatures on the Cu@ZIF-C copper-carbon composite material were investigated.

[0080] Adsorbed Cu 2+ The black samples were placed in a corundum boat and transferred to a tube furnace. Nitrogen gas was first purged for 20 minutes to remove air from the furnace. The furnace was then heated to 900℃, 1000℃, 1100℃, and 1200℃ at a heating rate of 5℃ / min, and held at these temperatures for 2 hours. After the samples cooled to room temperature, they were removed and ultrasonically washed with 40 ml of 0.5 M H2SO4 for 40 minutes. The samples were centrifuged twice and washed with deionized water. After extraction, the samples were dried in an 80℃ forced-air drying oven for later use. The samples were named Cu@ZIF-C900, Cu@ZIF-C1000, Cu@ZIF-C1100, and Cu@ZIF-C1200, respectively.

[0081] 1.2.4 Preparation of Cu@ZIF-C with different pore sizes

[0082] Based on ZIF-C900 material, etching and pore-expanding designs were performed on carbon dots using the water-gas shift reaction equations C + H₂O = CO + H₂ or C + 2H₂O = CO₂ + 2H₂. A certain amount of ZIF-C was placed in a corundum boat and transferred to a tube furnace. Argon gas was pre-purged for 20 minutes to purge the air from the gas path. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 4 hours. During the holding period, water vapor was introduced for etching for 20 minutes, 80 minutes, and 240 minutes respectively. After the sample cooled to room temperature, it was removed, washed with 0.5M H₂SO₄, and dried in an 80℃ forced-air drying oven for 6 hours for later use. The sample products were named ZIF-S20, ZIF-S80, and ZIF-S240.

[0083] When connecting the gas path to the device, a sealed container filled with deionized water should be placed before the gas inlet of the tube. At the start of the etching reaction, the vent tube is introduced into the deionized water body to blow out water vapor (150 sccm) and add it to the reaction. During the etching reaction or when no etching reaction is being carried out, the vent tube is removed from the water body to maintain a pure Ar atmosphere path until the experiment is completed.

[0084] 1.3 Water Evaporation Framework and Water Evaporation Test

[0085] 20 mg of sample was weighed and dissolved in 40 ml of water. After ultrasonic dispersion for 30 min, the mixture was filtered through a water-based vacuum filtration membrane to form a homogeneous spherical membrane. ZIF-8-based photothermal particles were then deposited onto the membrane. The deposited membrane was cut into 2*2 cm squares and isolated from the water using a polylactic acid support frame. Non-woven fabric was then inserted into the water through slits on both sides for interfacial water supply, achieving efficient utilization of thermal energy. The non-woven fabric was cut into 2 cm wide strips, and the square membrane was placed on top of it. This simple placement allowed the membrane to be observed to be wetted by the water-transferring non-woven fabric. This structure is a typical two-dimensional interfacial evaporation framework.

[0086] The laboratory used a xenon lamp light source system to simulate sunlight, illuminating the light across the full spectrum. The intensity of the light source was calibrated using a high-intensity optical power meter, with values ​​ranging from 100 mW / cm². -2The direct sunlight conditions are equivalent to sunlight. The light source requires stability; to ensure data reliability, it needs to be stabilized for 30 minutes before testing. The light intensity is typically adjusted by changing the voltage and the distance between the light source and the sample. Using filters with different luminous flux can also quickly change the light intensity, generally used to mitigate the harmful effects of prolonged use at excessively high voltages or distances. After adjusting the light intensity to match sunlight, the entire experiment uses an electronic balance to record the overall mass loss of the container on the balance in real time during the evaporation process. The mass loss value is output as document data via connected computer software. The measurement time is generally greater than 1 hour. The obtained data is analyzed to calculate and evaluate the water evaporation performance; the evaporation rate is the mass loss per unit time.

[0087] 2.1 Material Characterization of ZIF-8 and its Derivative Cu@ZIF-C

[0088] ZIF-8 is a porous metal-organic framework material. Its material characterization includes microstructure, elemental composition, phase analysis, and pore size and specific surface area determination. As a material characterization method, the shape of the material can be visually observed, the composition of the material can be analyzed, and the structure of the pore surface can be measured.

[0089] 2.1.1 Microstructure characterization of ZIF-8 and its derivative Cu@ZIF-C

[0090] like Figure 1 As shown, Figure 1 a and 1d clearly show the basic microstructure of ZIF-8. Overall, the particles appear to be relatively uniform, with a particle size of approximately 400nm. All particles are regular dodecahedrons, with each face being rhomboid and having a smooth surface. Figure 1 Images b and e show the morphology of ZIF-8 after high-temperature carbonization at 900℃ for three hours. The overall shape remains largely unchanged, maintaining its dodecahedral shape, and the particles are relatively uniform. However, the particle surface has become rougher, showing obvious calcination marks, and the particle size has also decreased to some extent. This is due to the carbonization of the organic ligands and the stripping of the metal sites at high temperatures. Figure 1 c and Figure 1 f is the SEM image of Cu@ZIF-C. The image shows that the shape remains intact and the particles are uniform, with overall dimensions almost identical to ZIF-C900. However, the Cu@ZIF-C particles have many pores on their surface. These pores are caused by the reduction of copper ions by carbon at high temperatures, resulting in the loss of some of the skeletal structure. The presence of these pores and the roughened surface better promote diffuse light reflection, enhancing the material's ability to capture and convert light energy, thus providing a fundamental basis for the material's photothermal properties.

[0091] like Figure 2 As shown, by Figure 2 It can be seen that ZIF-C900 has a pure amorphous carbon structure inside, and is a homogeneous material when no other substances are introduced; on the contrary, Figure 2 The internal structure of Cu@ZIF-C shown in b reveals clearly visible nanoparticles within the carbon shell, all maintaining a size of approximately 30 nm. This suggests that copper ions underwent in-situ carbon reduction and aggregated into particles under internal adsorption. From Figure 2 As can be seen from c and d, the particles possess relatively obvious lattice fringes, and the lattice fringes spacing on the particle surface was measured to be 0.209 nm, which corresponds exactly to the interplanar spacing of Cu(111). Related simulations show that the 30-50 nm plasma particles have a good plasma resonance photothermal effect, which corresponds well with the metal particles inside the material in this paper. At this size, the photothermal conversion process can be promoted as much as possible.

[0092] like Figure 3 As shown, by Figure 3 High-angle annular dark field (HAADF) transmission maps can provide a very comparative view of particle distribution. Figure 3 EDX images b, c, and d show that Cu is concentrated at the particle sites, while C and N are distributed throughout the entire Cu@ZIF-C photothermal material. This indicates that the material's outer shell framework is a nitrogen-doped porous carbon structure. This is the result of designing carbon materials using ZIF-8 as a sacrificial template, resulting in a photothermal carbon material with a high proportion of nitrogen-doped sites.

[0093] 2.1.2 Phase characterization of ZIF-8 and its derivative Cu@ZIF-C

[0094] like Figure 4 As shown in the XRD pattern of ZIF-8, numerous peaks exist at relatively small derivation angles, and the peak shapes are sufficiently sharp, indicating that the dodecahedral structure of ZIF-8 has good crystallinity. The peak positions obtained from simulating its structure also show a very high degree of agreement with the measured peak positions. Subsequently, phase characterization was performed on related ZIF-8 derivatives, such as... Figure 4 As shown in b, the XRD pattern of ZIF-C900 has no peaks, only a large bulge-shaped curve structure, representing an amorphous carbon structure; while the phase of Cu@ZIF-C material clearly has three characteristic peaks of copper particles, located at 43.3°, 50.5° and 74.1°, respectively, corresponding to the three crystal planes of Cu (111), (200) and (220), which are completely matched with the standard card of Cu, further demonstrating the successful synthesis of copper particles.

[0095] 2.1.3 Specific surface area and pore size distribution of ZIF-8 and its derivative Cu@ZIF-C

[0096] like Figure 5 As shown. From Figure 5 The BET results for a show that the specific surface area of ​​the copper-containing material after high-temperature annealing is 745 m². 2 The pore size is slightly smaller than that of the original ZIF-8. This is because the Zn metal nodes in ZIF-8 detach at temperatures exceeding their boiling points, the organic ligands may partially collapse during high-temperature annealing, and some carbon sites may be eliminated during the reduction of copper ions. In contrast, the pore size distribution... Figure 5 b. Both ZIF-8 and its derivative Cu@ZIF-C have micropores. The original pore size of ZIF-8 is approximately 0.52 nm, while the pore size of Cu@ZIF-C shrinks to 0.35 nm after calcination. Although the specific surface area and pore size decrease to some extent after high-temperature calcination, they are still maintained to a certain degree. This provides a more direct utilization for subsequent heat energy transfer and lays the foundation for a highly efficient solar water evaporation process.

[0097] 2.2 Performance Testing of ZIF-8 and its Derivative Cu@ZIF-C

[0098] 2.2.1 Light absorption properties of ZIF-8 and its derivative Cu@ZIF-C

[0099] Depend on Figure 6 As shown, both derived carbon materials after ZIF-8 calcination exhibit high light absorption rates. The light absorption rate of Cu@ZIF-C is higher than that of ZIF-C900 in the 1200nm-2200nm range. Figure 6 The reflectance of the two materials is approximately 1-2% higher. There is also virtually no difference in reflectance between the two materials. This suggests that the introduction of copper particles did not improve the light absorption performance of the material; the light absorption performance of the copper particles may be masked by the broad-spectrum, strong absorption of the carbon shell material. Furthermore, the pore structure's light-restriction effect also contributes to the light absorption process to some extent.

[0100] 2.2.2 Photothermal heating effect of ZIF-8 and its derivative Cu@ZIF-C

[0101] like Figure 7 As shown. Figure 7 The heating results show that Cu@ZIF-C and ZIF-C900 stabilized after 15 minutes of simulated sunlight irradiation under a xenon lamp. The former achieved a temperature stability value approximately 12°C higher than the latter. Under the same annealing time, the material containing copper nanoparticles exhibited superior photothermal conversion performance. Copper metal particles possess a localized plasmon resonance effect, enabling some of the energy-acquired free electrons to collectively oscillate within an electromagnetic field, thus promoting the conversion of light into heat. Figure 7The liquid UV spectrum shown in b clearly demonstrates the plasma absorption peak (approximately 610 nm) of copper particles in the visible light range, while ZIF-C900 porous carbon does not have a corresponding peak, which is sufficient to show that the copper-carbon composite material has better photothermal performance than the single carbon material.

[0102] 2.2.3 Analysis of the water evaporation performance of ZIF-8 and its derivative Cu@ZIF-C

[0103] To investigate the impact of heat energy generated by photothermal processes on water evaporation performance and to analyze the evaporation efficiency of heat energy utilization during water evaporation, real-time mass loss of the evaporation system was analyzed under simulated sunlight. Figure 8 As shown in Figure a, it can be seen that Cu@ZIF-C has the highest evaporation rate, which is 1.94 kg / m³. -2 h -1 The evaporation rate of ZIF-C900 is 1.49 kg / m³. -2 h -1 Both are significantly higher than the evaporation rate of pure water (0.414 kg / m³). -2 h -1 Compared to ZIF-C900, Cu@ZIF-C exhibits superior water evaporation performance, primarily attributed to the enhanced photothermal conversion capability resulting from the embedding of copper metal particles. The energy boost from Cu's localized plasmon resonance is utilized for the phase transition of more water molecules, thus achieving the desired effect. Figure 8 The high evaporation efficiency shown in b is achieved by the material itself having a high specific surface area, which exchanges energy with water cluster molecules in the micropores at a faster transfer speed, thereby achieving high efficiency through high heat.

[0104] 2.2.4 Summary

[0105] In this invention, carbon-based photothermal particles are synthesized and designed using the MOF template method with high-temperature calcination. Using ZIF-8 as the initial template, a porous carbon shell obtained through high-temperature annealing is used to confine the synthesis of copper metal nanoparticles within it. Simple high-temperature carbon reduction is employed to achieve ZIF-8-based photothermal particles with superior water evaporation performance. ZIF-8 was chosen as the template due to its numerous micropores, large surface area, and simple and stable synthesis. The presence of these pores facilitates the adsorption and diffusion of copper ions, and the large surface area promotes heat transfer. Cu@ZIF-C particles, based on the original broad-spectrum absorbing carbon structure, introduce copper metal nanoparticles to broaden the photothermal conversion pathway and improve the overall photothermal conversion efficiency of the material. Compared to ZIF-C900 light-absorbing particles, Cu@ZIF-C achieves approximately a 12°C increase in photothermal temperature rise without improving the light absorption rate. This more efficient heat output can be used in the water evaporation process, and it is foreseeable that the constructed interfacial evaporation system can achieve a higher performance water evaporation process, increasing the water evaporation rate (1.94 kg / m³).-2 h -1 ).

[0106] 3. Study on the effect of carbonization temperature on the photothermal evaporation performance of Cu@ZIF-C particles

[0107] 3.1 Composition and structural analysis of Cu@ZIF-C under different carbonization conditions

[0108] 3.1.1 Nitrogen content analysis of Cu@ZIF-C at different carbonization temperatures

[0109] After high-temperature treatment, the nitrogen element in the 2-methylimidazolium ligand of ZIF-8 is distributed in a doped form throughout the porous carbon network. Nitrogen substitution types in graphite lattices can generally be classified into three categories: graphitic nitrogen, pyridine nitrogen, and pyrrole nitrogen. To investigate the existence forms of nitrogen at different sites, X-ray photoelectron spectroscopy (XPS) was used to determine the chemical state and coordination environment of nitrogen atoms in the sample. Figure 9 The three peaks at 398.6 eV, 400.3 eV, and 401.4 eV in the N1s spectrum shown in b are attributed to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, respectively. In the presence of all forms of nitrogen, pyridine nitrogen replaces one carbon atom on the six-membered carbon ring and bonds with two carbon atoms; graphitic nitrogen forms sp2 hybrid bonds with three carbon atoms on the graphite plane; and pyrrole nitrogen is a doping site within the five-membered ring, bonding with two carbon atoms. Figure 9 a). From Figure 9 As can be seen from b, the concentrations of pyridine nitrogen and pyrrole nitrogen gradually decrease with increasing calcination temperature, while the effect on graphitic nitrogen is minimal. This result is mainly determined by the coordination environment of the nitrogen sites in the carbon plane. Breaking bonds in pyridine nitrogen and pyrrole nitrogen, which are bonded to two carbon atoms within a carbon ring, requires less energy input than breaking bonds in graphitic nitrogen, which is located at the center of a three-carbon ring and forms a three-coordinate system with adjacent carbon atoms. It can be seen that when the processing temperature reaches 1200℃, the pyridine nitrogen and pyrrole nitrogen sites are essentially eliminated, while graphitic nitrogen is preserved as much as possible.

[0110] 3.1.2 Raman characterization of Cu@ZIF-C at different carbonization temperatures

[0111] To fully investigate the effects of in-plane graphitization and changes in structural sites, Raman spectroscopy was used to further characterize the material. Figure 10 The Raman spectra shown further confirm the structural compositional changes of Cu@ZIF-C, with the D band (1339 cm⁻¹) being particularly prominent. -1 The number represents the defect content; G-band (1594cm) -1 The π indicates the degree of graphite ordering, while the 2D bands indicate the degree of graphite coating; the sharper the band, the shallower the graphite layer. As the carbonization temperature increases, the graphite planes maintain a high degree of order, but I... D / IG The ratio monotonically decreased from 1.05 to 0.96, indicating a higher proportion of doping defects in the synthesized sample at the lower processing temperature. This confirms that increasing the temperature leads to the detachment of some nitrogen sites. Cu@ZIF-C at approximately 2707 cm⁻¹... -1 The presence of a relatively wide 2D band indicates the formation of a thick graphite layer in Cu@ZIF-C, which is attributed to the copper nanoparticles being encapsulated within nitrogen-doped carbon. The flattening of the 2D band remains essentially constant across all curves, indicating that the thickness of the graphite layer encapsulating the copper particles varies uniformly.

[0112] 3.1.3 Specific surface area and pore size distribution of Cu@ZIF-C at different carbonization temperatures

[0113] Cu@ZIF-C, as a MOF-derived nitrogen-doped porous carbon material, can have its micropore size and specific surface area characterized by nitrogen adsorption-desorption experiments. For example... Figure 11 As shown in figure a, these curves are highly similar to the Type I isotherms. The curves show the change in specific surface area of ​​the prepared samples with carbonization temperature, with an increasing tendency for the surface area to shift downwards as the temperature increases. However, the change process of all curves with relative pressure is consistent; they increase sharply at low relative pressures, confirming that the material's interior is mainly characterized by micropores. Analysis of the measured BET data revealed that the specific surface areas of ZIF-8, Cu@ZIF-C900, Cu@ZIF-C1000, Cu@ZIF-C1100, and Cu@ZIF-C1200 are 1268, 745, 787, 812, and 820 m², respectively. 2 / g; and by Figure 11 Figure b shows the pore size distributions for each material, which are 0.52, 0.35, 0.35, 0.36, and 0.37, respectively. This demonstrates that changing the carbonization temperature does not affect the high specific surface area of ​​the material, but it does produce different values ​​for the specific surface area. Pore size analysis verifies the microporous characteristics of the material, and the distribution is a concentrated, narrow range. The specific surface area of ​​Cu@ZIF-C900 in the figure is approximately 480 m² less than that of pure ZIF-8. 2 The pore size decreased by 0.17 nm / g, mainly due to the shrinkage and collapse of the structural framework caused by the volatilization of the metal nodes of the zinc clusters after elementalization at high temperatures. However, with increasing calcination temperature, there was a small positive correlation between specific surface area and micropore size. This is because the high-temperature carbonization reaction exacerbated the reduction in the number of nitrogen sites, and the slight increase in carbon structure pore size may be due to the formation of n-side rings (n>8) after the removal of dual-coordinated nitrogen sites. This also proves to some extent that changes in calcination temperature affect the nitrogen content of ZIF-8 derived nitrogen-doped porous carbon, especially the effects on pyridine nitrogen and pyrrole nitrogen.

[0114] 3.2 Performance Testing of Cu@ZIF-C under Different Carbonization Conditions

[0115] 3.2.1 Light absorption properties of ZIF-8 and its derivative Cu@ZIF-C

[0116] To reveal the sample's ability to absorb sunlight, the absorbance of the sample was measured using a UV-Vis-NIR spectrometer in the range of 250-2500 nm. Figure 12 As shown, the light absorption of Cu@ZIF-C900 encapsulated copper particles is 2% (90%) higher than that of ZIF-C900. The light absorption shows a slight decreasing trend with increasing carbonization temperature, but the overall change is not significant. It can be seen that all samples exhibit high light absorption performance, but changing the nitrogen doping content in the carbon layer and embedding copper particles does not contribute to achieving the expected higher light absorption rate.

[0117] 3.2.2 Photothermal heating performance of ZIF-8 and its derivative Cu@ZIF-C

[0118] To investigate the local heating effect during photothermal conversion after embedding Cu nanoparticles and altering the nitrogen content of their carbon layers, the surface temperature changes of ZIF-C900 and Cu@ZIF-C under one day of sunlight were carefully measured using an infrared camera. Figure 13 After 15 minutes of illumination, the surface temperature of ZIF-C900 remained stable at around 63℃. In comparison, the surface temperature of Cu@ZIF-C900 (74℃) was 11℃ higher than that of ZIF-C900. This result clearly demonstrates that the effective localized heating effect of Cu nanoparticles absorbed through LSPR conversion can significantly increase the surface temperature of the material, laying the foundation for effectively promoting the aqueous phase transition process. However, as the carbonization temperature increases, the plateau value of the heating curve decreases, mainly due to the reduction in nitrogen content and the altered relationship between different types of nitrogen sites and copper nanoparticles. Figure 13 As shown in b, the reduction in pyridine and pyrrole nitrogen sites due to temperature increase leads to a gradual decrease in the heating effect from 74℃ to 67℃. The doping content of graphitic nitrogen remained almost constant when the photoinduced temperature rise of the samples varied. Clearly, the effect of temperature difference is independent of the graphitic nitrogen content. The nitrogen content distribution histogram clearly shows that the column heights of pyridine and pyrrole nitrogen continuously decrease, while the height of the graphitic nitrogen portion remains constant. However, compared to ZIF-C900, Cu nanoparticles exhibit a positive feedback effect in photothermal conversion in all samples, enhancing the absorption effect of plasmon resonance under the broad spectral absorption of porous carbon. This enhanced photothermal conversion originates from the utilization of light by the LSPR of Cu particles. The key to improving the Cu particle LSPR photothermal conversion process lies in the interaction between the copper particles and the nitrogen sites.

[0119] 3.2.3 Water evaporation performance of ZIF-8 and its derivative Cu@ZIF-C

[0120] The prepared material is filtered into a membrane, cut, and placed on a support frame of the cup. Water is supplied to the interface using a suitable water-transfer cloth to achieve a relatively complete two-dimensional interface evaporation system, such as... Figure 14 As shown in figure a, the photothermal evaporation process of the material was studied under a corresponding simulated light source. The temperature of the film material was recorded in real time immediately after the light source was turned on using an infrared thermal imager. The infrared images obtained at several time points are shown in figure a. Figure 14 As shown in b, the surface temperature of the membranes of both materials eventually remained at around 33℃. From the top row of images, it can be seen that the real-time surface temperature of the Cu@ZIF-C900 membrane material reached 33.1℃ in 220s, while the Cu@ZIF-C1200 material took 330s to reach this temperature. This is because during the evaporation process, the real-time water supply and heating process occur simultaneously, resulting in a harmonic stabilization of the temperature at a certain point. In terms of the time taken, Cu@ZIF-C900 exhibits better membrane material heating performance.

[0121] To quantitatively evaluate the performance of Cu@ZIF-C, the solar evaporation rate of the square thin film was measured, and the mass loss under simulated sunlight irradiation (one sun) was recorded, such as... Figure 15 As shown in Figure a. Although pure water has a very low ability to absorb sunlight, its evaporation rate was measured to be 0.414 kg / m³. -2 h -1 Due to the unique three-dimensional porous confined channel structure of ZIF-C900, its evaporation rate is increased to 1.488 kg / m³. -2 h -1 The concentration of Cu@ZIF-C1200 is significantly higher than that of pure water. After introducing plasmonic Cu nanoparticles, Cu@ZIF-C1200 achieved a concentration of 1.666 kgm³ within 1 hour. -2 h -1 The improved evaporation rate and water evaporation performance are attributed to the enhancement of Cu particle plasma. However, as the carbonization temperature decreases to 900℃, this rate increases to 1.94 kg / m³. -2 h -1 This is attributed to the intermediate π state of the PN structure modulating the heat release pathway. The introduction of Cu nanoparticles into ZIF-C900 porous carbon also significantly improves the water evaporation rate, and high PN doping content in porous carbon also enhances water evaporation. Compared to the evaporation rate of pure water, the evaporation rate of Cu@ZIF-C900 is increased by 4.73 times. These results demonstrate the key role of PN in inducing enhanced plasma-excited carrier relaxation processes during effective water evaporation. The calculated solar vapor generation efficiency and evaporation rate of the sample under one solar radiation are as follows: Figure 15 As shown in b. The detailed calculation formula is as follows:

[0122]

[0123] Where η is the evaporation efficiency. The net evaporation rate, h LV Total enthalpy change, including sensible heat (23.52 Jg). -1 The specific heat is 4.2 J / kg K from 27.5℃ to 33.1℃. -1 ) and the heat of phase change of liquid water (2013Jg) -1 P is the optical power density of the incident light. The value is obtained by subtracting the dark evaporation rate under no xenon lamp illumination from the water evaporation rate under one sun. Calculations show that the solar evaporation system efficiency of ZIF-C900 is 64%. It is worth noting that under the same conditions, the evaporation efficiencies of Cu@ZIF-C900, Cu@ZIF-C1000, Cu@ZIF-C1100, and Cu@ZIF-C1200 are 89.3%, 83.7%, 77.9%, and 74.1%, respectively. The excellent evaporation efficiency and rate are mainly attributed to the large heat transfer surface and three-dimensional micropores of ZIF-8 derived carbon, which promote rapid energy exchange among water molecule clusters. Increasing the PN content also lowers the energy barrier required for heat conduction, which is key to improving evaporation efficiency and rate. The evaporation layer is then completely separated from the bulk water, effectively confining heat to the material layer at the interface to achieve high thermal steam generation efficiency.

[0124] 3.3 Summary

[0125] In summary, a Cu@ZIF-C photothermal evaporator was successfully assembled by pyrolysis of ZIF-8 with a Cu NPs embedded core structure. Cu@ZIF-C exhibits broad light absorption across the entire solar spectrum, while the microporous channels of ZIF-8 facilitate steam generation, mass transfer, and heat transfer. In particular, the significant LSPR absorption of Cu NPs generates a localized thermal effect, which is manifested by modulating the relaxation process of photogenerated carriers in the plasma plume by varying the ratio of pyridine and pyrrole nitrogen (p-type doping) and graphite nitrogen (n-type doping) in the carbon layer. Under one solar radiation, a vapor density of 1.94 kgm³ was achieved. -2 h -1 It boasts a remarkable solar steam generation rate and a solar thermal efficiency of up to 89.3%.

[0126] 4. Study on the effect of ZIF-8 derived porous carbon pore size on water evaporation performance

[0127] 4.1 Microscopic characterization of ZIF-8 derived porous carbon materials

[0128] 4.1.1 Microstructure of ZIF-8 derived porous carbon materials

[0129] Depend on Figure 16 As shown, the microstructure of the ZIF-8 derived porous carbon material remains intact after etching to varying degrees, with the overall structure still exhibiting a regular dodecahedral shape and uniform particle size. All samples maintain a certain degree of roughness; however, with prolonged water vapor etching, the surface roughness of the dodecahedral carbon material noticeably increases. This is because some surface carbon reacts with water vapor and is etched away, and the surface shrinks and depressions with increasing etching time. The particle size change is significant from Figure a to Figure d, gradually decreasing from approximately 200 nm to approximately 100 nm. Continuous etching under prolonged water vapor heating may remove the outer carbon framework, causing the particles to be thinned under the vapor atmosphere. This also preliminarily demonstrates that the etching method is quite effective in the experimental process and can effectively address the adjustment of pore size.

[0130] 4.2.2 Different pore sizes of ZIF-8 derived porous carbon materials

[0131] To determine the specific conditions after etching within the material bulk, BET characterization was used to test its specific surface area and pore size. The specific test results are as follows: Figure 17 As shown in Figure a, which is the isothermal adsorption curve of N2 at 200℃, the adsorption and desorption processes can be more complete at higher temperatures. Solid dots in the figure represent the adsorption process, which is relatively slow; hollow dots represent the desorption curve, which shows a slight lag. The plotted curves are quite similar to Type I isotherms, exhibiting a good adsorption and desorption process. The results show that the specific surface area of ​​the unetched material is 773 m². 2 / g; The specific surface area of ​​the material after 20 minutes of etching is 1214m². 2 / g; The specific surface area of ​​the material after 80 min etching is 1423m². 2 / g; The specific surface area of ​​the material after etching for 240 min is 2467m². 2 / g. As etching time increases, the specific surface area of ​​the material gradually increases. Short-term water vapor etching away the previously collapsed pores exposes their surfaces. When etching time accumulates sufficiently, it leads to a decrease in the overall mass of individual ZIF-C particles, resulting in an increase in the specific surface area ratio. And from... Figure 17 As can be seen from b, the pore diameter gradually increases after etching. The pore diameters of the four samples from unetched to 240-minute etched samples are 0.38 nm, 0.40 nm, 0.44 nm, and 0.49 nm, respectively. There is a noticeable increase in pore size, and the pore size distribution gradually widens. This explains why the specific surface area doubles after 240-minute water vapor etching. It can be seen that etching porous materials using this method can indeed expand the micropore size to a certain extent, which is beneficial for preparing more efficient water-evaporation porous carbon materials.

[0132] 4.2 Effect of different pore sizes on the properties of ZIF-8 derived porous carbon

[0133] 4.2.1 Effect of different pore sizes on the light absorption properties of ZIF-8 derived porous carbon

[0134] To investigate the effect of etching on the light absorption performance of the sample, the results are as follows: Figure 18 As shown in Figure a, the reflectance curves of different etched samples reveal a further decrease in light reflectance after etching. This is due to increased surface roughness and a certain degree of pore enlargement, which further restricts diffuse emission and absorption in the light path. The rough surface facilitates multi-level reflection processes under light irradiation, promoting higher light absorption. Shorter etching times are less effective for etching the porous carbon surface and pore size, resulting in no difference in light reflectance between 20 min and 80 min. The light absorption rate of the material is generally expressed as A = 1 - RT, where A is the light absorption rate, R is the reflectance, and T is the transmittance. Therefore, the transmittance of the material was tested again. It can be seen that the transmittance of the material is essentially zero. The small step at 850 nm in the spectrum is due to the instrument itself and can be ignored. Simple calculations show that the material etched for 240 min can achieve a light absorption rate as high as 95%, which can further provide a better water evaporation process.

[0135] 4.2.2 Effect of different pore sizes on the water evaporation performance of ZIF-8 derived porous carbon

[0136] To verify the water evaporation performance of the etched sample, a xenon lamp light source system was used to simulate sunlight irradiation, and the real-time weight loss process of the system was recorded using a balance. A computer connected to the balance in real time allowed software to measure the weight change of the entire evaporation system at specific time points, down to the second. The obtained data were plotted as follows: Figure 19 As shown, the slope of the curve gradually increases with the extension of etching time, and the slope represents the evaporation rate of the sample. After 20 minutes of etching, the water evaporation rate of the material is 1.33 kg / m³. -2 h -1 After 240 minutes of etching, the evaporation rate of the material increased to 1.58 kg / m³. -2 h -1 It is evident that the actual water evaporation process is significantly improved by pore expansion and increased specific surface area, which is more conducive to the preparation of highly efficient water-evaporating porous carbon materials.

[0137] 4.3 Summary

[0138] This invention utilizes a water-gas reaction to etch the internal carbon network of a carbonaceous material under high-temperature conditions using a steam flow, achieving a carbonaceous structure with adjustable pore size. After a prolonged etching process, the internal carbon dots of the ZIF-8-based derived carbon material are etched, resulting in increased pore size and a significantly increased specific surface area. The extended etching process not only thins the material's framework but also removes collapsed internal channels, leading to a wider pore size distribution. The etched material exhibits significant improvements in water evaporation applications; the increased pore size and specific surface area also enhance the water evaporation rate, indicating that etching further improves the material's water evaporation performance.

[0139] Example 2

[0140] (1) The ZIF-8 powder was loaded into a quartz boat and transferred into a tube furnace. Under nitrogen protection at a flow rate of 100 ml / min, the air in the tube was first pre-purged for 20 min to remove the original air. Then, it was heated to 890℃ at a heating rate of 4℃ / min and held for 3 h. After the temperature in the furnace cooled to room temperature, the black powder ZIF-C was obtained.

[0141] (2) Weigh 1.2 mmol of copper nitrate trihydrate and disperse it in 60 ml of ethanol solution to form a light blue solution. Then add 0.6 g of ZIF-C powder and sonicate for 30 min to disperse evenly. Stir at room temperature for 30 h to allow Cu to settle. 2+ The ethanol suspension was fully diffused into the ZIF-C channels by the concentration gradient difference. The resulting ethanol suspension was transferred to an oil bath stirred pot and heated at 80°C until the ethanol content in the beaker was almost evaporated. Then a small amount of ethanol was added and the evaporation was repeated 3 times. Finally, the beaker was placed in a vacuum drying oven and dried under vacuum at 75°C for 9 hours.

[0142] (3) The black sample obtained by vacuum drying was ground and placed in a quartz boat, then transferred to a tube furnace. It was pre-ventilated under a nitrogen atmosphere for 20 min, then heated to 900℃ at a heating rate of 6℃ / min and held at this temperature for 1 h. After the sample cooled to room temperature, it was removed and ultrasonically washed with 40 ml of 0.5 M H₂SO₄ for 40 min, centrifuged twice, and washed with deionized water. The extracted sample was then dried in a 75℃ forced-air drying oven for 6 h to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C. The properties of this material are comparable to those of the ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C prepared in Example 1.

[0143] Example 3

[0144] (1) The ZIF-8 powder was loaded into a quartz boat and transferred into a tube furnace. Under nitrogen protection at a flow rate of 100 ml / min, the air in the tube was first pre-purged for 20 min to remove the original air. Then, it was heated to 910℃ at a heating rate of 6℃ / min and held for 3 h. After the temperature in the furnace cooled to room temperature, the black powder ZIF-C was obtained.

[0145] (2) Weigh 0.8 mmol of copper nitrate trihydrate and disperse it in 40 ml of ethanol solution to form a light blue solution. Then add 0.4 g of ZIF-C powder and sonicate for 40 min to disperse it evenly. Stir at room temperature for 24 h to allow Cu to precipitate. 2+ The ethanol suspension was fully diffused into the ZIF-C channels by the concentration gradient difference. The resulting ethanol suspension was transferred to an oil bath stirred pot and heated at 80°C until the ethanol content in the beaker was almost evaporated. Then a small amount of ethanol was added and the evaporation was repeated 3 times. Finally, the beaker was placed in a vacuum drying oven and dried under vacuum at 85°C for 7 hours.

[0146] (3) The black sample obtained by vacuum drying was ground and placed in a quartz boat, then transferred to a tube furnace. It was pre-ventilated under a nitrogen atmosphere for 20 min, then heated to 900℃ at a heating rate of 6℃ / min and held at this temperature for 3 h. After the sample cooled to room temperature, it was removed and ultrasonically washed with 40 ml of 0.5 M H₂SO₄ for 40 min. It was centrifuged twice and washed with deionized water. The extracted sample was then dried in an 85℃ forced-air drying oven for 6 h to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C. The properties of this material are comparable to those of the ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C prepared in Example 1.

[0147] Comparative Example 1

[0148] Based on Example 1, the carbonization pretreatment temperature was increased. Specifically, the dried white ZIF-8 lumps were pounded into powder using a mortar and pestle to obtain ZIF-C powder. The ZIF-8 powder was placed in a quartz boat and transferred to a tube furnace. Under nitrogen protection at a flow rate of 100 ml / min, the furnace was first pre-purged for 20 minutes to remove the existing air, and then heated to 950°C at a heating rate of 5°C / min and held for 3 hours. After the furnace temperature cooled to room temperature, black ZIF-C powder was obtained. Other treatments were the same as in Example 1. As a result, the properties of the prepared material decreased.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a ZIF-8 derived photothermal material, characterized in that, ZIF-C powder was prepared by carbonization pretreatment with 2-methylimidazolium zinc salt. The ZIF-C powder was then added to a copper ion solution to adsorb Cu. 2+ Finally, Cu particles are synthesized by carbon reduction to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C; including the following steps: (1) 2-methylimidazolium zinc salt was carbonized under nitrogen or inert gas protection, and then carbonized at a constant temperature to obtain ZIF-C powder; (2) Add the ZIF-C powder obtained in step (1) to a copper nitrate solution, disperse and stir by ultrasonication to obtain a suspension, evaporate to dryness, and dry; (3) After grinding the sample obtained by drying in step (2), high-temperature carbon reduction is carried out under nitrogen or inert gas protection. The carbon reduction temperature is 900~1200℃. After cooling to room temperature, the sample is taken out, washed and dried to obtain ZIF-8 derived copper-carbon composite photothermal particles Cu@ZIF-C. In step (2), the copper nitrate solution is prepared by copper nitrate trihydrate and ethanol at a molar volume ratio of 0.8~1.2:40~50 mol / L; the molar mass ratio of copper nitrate trihydrate and ZIF-C powder is 0.8~1.2:0.4~0.6 mmol / g. In step (1), the carbonization pretreatment temperature is 890~910℃; In step (1), during the carbonization pretreatment and heat preservation stage, water vapor is introduced for etching for 80~240 minutes. After the sample cools to room temperature, the sample is taken out for acid washing and drying.

2. The method for preparing ZIF-8 derived photothermal material according to claim 1, characterized in that, In step (2), the specific operation of evaporation is as follows: the suspension is repeatedly evaporated by heating in an oil bath, and a solvent is added during the repeated evaporation process. The oil bath heating temperature is 75~85℃, and the number of repeated evaporation cycles is 2~4. In step (3), the specific washing operation is as follows: after taking out the sample, ultrasonically wash it with 0.4~0.6M H2SO4 for 30~50 min, centrifuge, and wash it with deionized water.

3. The method for preparing ZIF-8 derived photothermal material according to claim 1, characterized in that, In step (1), the heat preservation time is more than 1 hour; In step (2), the ultrasonic dispersion time is more than 30 minutes and the stirring time is more than 24 hours; In step (3), the heat preservation time for high-temperature carbon reduction is more than 2 hours.

4. The method for preparing ZIF-8 derived photothermal material according to claim 1, characterized in that, Step (1): The heating rate before heat preservation is 4~6℃ / min; Step (2), the drying is vacuum drying, the drying temperature is 75~85℃, and the drying time is 7~9h; Step (3) The drying is performed by forced air drying at a temperature of 75-85°C for 5-7 hours.

5. A ZIF-8 derived photothermal material, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. The application of the ZIF-8 derived photothermal material according to claim 5 in the preparation of a photothermal evaporator.

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