Metal-lignin composite material and preparation method and application thereof

Abstract

The invention discloses a metal-lignin composite material and a preparation method and application thereof, and belongs to the technical field of photothermal conversion materials. The metal-lignin composite material provided by the invention is obtained by reacting lignin with metal ions in an ammonia water system; at least a part of the metal ions are chemically bonded to the lignin, and at least a part of the metal ions chemically bonded to the lignin form metal / ammonia coordination; the metal ions are one of copper ions, iron ions, cobalt ions, nickel ions and chromium ions. According to the invention, through the synergistic effect of each coordination, the composite material can be endowed with excellent ultraviolet-visible light-near infrared light absorption capacity, the light absorption and photothermal conversion performance, stability and durability of the composite material are greatly improved, and the composite material has wide market application prospects in the technical field of solar water evaporation and water treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photothermal conversion materials, and particularly relates to a metal-lignin composite material and a preparation method and application thereof. BACKGROUND

[0002] How to effectively develop the utilization technology of unconventional water resources such as wastewater and seawater has become a key path to alleviate water resource shortage. Solar water evaporation technology is a method for obtaining fresh water based on the use of renewable solar energy resources. As a sustainable method for water treatment, it is becoming a more practical choice. Among them, a solar evaporator can achieve high solar evaporation efficiency by placing a series of photothermal conversion materials at the gas-liquid evaporation interface. Therefore, it is urgent to develop photothermal conversion materials with excellent comprehensive performance to expand their application in practice.

[0003] The core working mechanism of a solar evaporator is to convert solar energy into heat energy to drive water evaporation by arranging photothermal conversion materials at the gas-liquid evaporation interface. In recent years, researchers have developed new photothermal conversion systems such as graphene-based composite membranes, carbon nanotube arrays, and MXene materials. Some laboratory achievements have achieved high solar-heat conversion efficiency. However, there are still many challenges in the process of industrialization: existing photothermal conversion materials are easily deactivated by chemical corrosion, biological attachment and other problems in complex water quality environments such as high salt, acid and alkali, resulting in a significant reduction in evaporation efficiency and a shortening of equipment service life; at the same time, the preparation cost of high-end carbon-based materials and noble metal nanostructures is high, for example, the production cost per unit area of graphene membrane material is 5-8 times that of traditional evaporation materials, which seriously limits large-scale application.

[0004] Therefore, developing photothermal conversion materials with high stability, low cost and high conversion efficiency has become a core breakthrough to promote the commercialization of solar water evaporation technology. SUMMARY

[0005] The application discloses a metal-lignin composite material and a preparation method and application thereof, and aims to solve the technical problems of low photothermal conversion efficiency, insufficient stability and high cost of existing photothermal conversion materials.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the application is:

[0007] The first aspect of the application provides a metal-lignin composite material obtained by reacting lignin and metal ions in an ammonia system.

[0008] At least a part of the metal ions is chemically bonded to the lignin, and at least a part of the metal ions chemically bonded to the lignin forms a metal / ammonia coordination.

[0009] The metal ion is one of a copper ion, an iron ion, a cobalt ion, a nickel ion, and a chromium ion.

[0010] In combination with the first aspect, preferably, the metal ion is one of a copper ion, an iron ion, and a cobalt ion.

[0011] At least a part of the metal ions form metal oxide nanoparticles and are compounded in the metal-lignin composite material.

[0012] In combination with the first aspect, preferably, the metal ion is a copper ion.

[0013] The second aspect of the present application provides a preparation method of the metal-lignin composite material according to the first aspect, and the preparation method comprises the following steps:

[0014] After the lignin and the metal source are dissolved in water, ammonia water is added to adjust the pH value for reaction, and then the metal-lignin composite material is obtained after separation, collection, and drying.

[0015] In combination with the second aspect, preferably, the metal source is one of a copper salt, an iron salt, a cobalt salt, a nickel salt, and a chromium salt.

[0016] In combination with the second aspect, preferably, the molar ratio of one monomer unit in the lignin to the metal ion is (8-1):(1-2).

[0017] In combination with the second aspect, preferably, the molar ratio of one monomer unit in the lignin to the metal ion is (2-1):1.

[0018] In combination with the second aspect, preferably, the pH value is adjusted to 6-9.

[0019] In combination with the second aspect, preferably, the pH value is adjusted to 8-9.

[0020] The third aspect of the present application provides an application of the metal-lignin composite material according to the second aspect in solar water evaporation water treatment.

[0021] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application at least include:

[0022] The metal-lignin composite material provided by the present application is obtained by reacting lignin and metal ions in an ammonia water system. On the one hand, the coordination of part of the metal ions, lignin, and ammonia, and the coordination of the three, endow the composite material with excellent ultraviolet-visible-near infrared light absorption capacity. On the other hand, the composite material can greatly improve the light absorption and light-heat conversion performance, stability, and durability, and has a wide market application prospect in the field of solar water evaporation water treatment technology. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0024] Figure 1 The blackness value of A1-metal-lignin composite material, A2-metal-lignin composite material, A3-metal-lignin composite material, A4-metal-lignin composite material, A5-metal-lignin composite material, B1-lignin prepared for the embodiments of the present application;

[0025] Figure 2 The Raman spectrum of A3-metal-lignin composite material and B1-lignin prepared for the embodiments of the present application;

[0026] Figure 3 The absorption spectrum of A3-metal-lignin composite material and B1-lignin prepared for the embodiments of the present application;

[0027] Figure 4 The transmission electron microscope (TEM) image of A1-metal-lignin composite material, A2-metal-lignin composite material, A3-metal-lignin composite material, A4-metal-lignin composite material, A5-metal-lignin composite material prepared for the embodiments of the present application;

[0028] Figure 5 The scanning electron microscope (SEM) image of B1-copper oxide, B2-copper oxide, B3-copper oxide prepared for the embodiments of the present application;

[0029] Figure 6 The light absorption performance diagram of copper oxide 1, copper oxide 2, copper oxide 3 prepared for the embodiments of the present application;

[0030] Figure 7 The ultraviolet / visible / near-infrared diffuse reflectance test diagram of A1-metal-lignin composite material, A2-metal-lignin composite material, A3-metal-lignin composite material, A4-metal-lignin composite material, A5-metal-lignin composite material, B1-lignin prepared for the embodiments of the present application;

[0031] Figure 8 The photothermal performance diagram of A1-metal-lignin composite material, A2-metal-lignin composite material, A3-metal-lignin composite material, A4-metal-lignin composite material, A5-metal-lignin composite material, B1-lignin prepared for the embodiments of the present application;

[0032] Figure 9A10-metal-lignin composite material, A11-metal-lignin composite material, and A12-metal-lignin composite material prepared in the embodiments of the present application, and the photothermal performance diagram of the A10-metal-lignin composite material, the A11-metal-lignin composite material, and the A12-metal-lignin composite material;

[0033] Figure 10 The evaporation performance of the device made of the A3-metal-lignin composite material prepared in the embodiments of the present application;

[0034] Figure 11 The wastewater treatment stability performance diagram of the device made of the A3-metal-lignin composite material prepared in the embodiments of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0036] In the following description of the embodiments of the present application, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can mean that A exists alone, B exists alone, and A and B exist simultaneously. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0037] In the following description of the embodiments of the present application, the term "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0038] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of the serial numbers does not mean the order of execution, and some or all steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0039] The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the embodiments of the present application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0040] It should be noted that all raw reagents in the embodiments of the present application are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0041] In a first aspect, the embodiments of the present application provide a metal-lignin composite material, which is obtained by reacting lignin and metal ions in an ammonia system.

[0042] At least a part of the metal ions is chemically bonded to the lignin, and at least a part of the metal ions chemically bonded to the lignin forms a metal / ammonia coordination.

[0043] The metal ions are one of copper ions, iron ions, cobalt ions, nickel ions and chromium ions.

[0044] On the one hand, the coordination of part of the metal ions with the lignin, the coordination of the ammonia and the coordination of the metal oxide nanoparticles endow the composite material with excellent ultraviolet-visible-near infrared light absorption capacity; on the other hand, the composite material can greatly improve the light absorption and light-heat conversion performance, stability and durability, and has a wide market application prospect in the field of solar water evaporation water treatment technology.

[0045] It should be noted that the type of lignin is not particularly limited in the present application. In order to illustrate the actual effect, the most common alkali lignin is used for specific exploration, and other types of lignin (such as sodium lignosulfonate, calcium lignosulfonate, and dealkali lignin) are also applicable. Metal ions can form coordination with these lignins, thereby endowing them with excellent light-heat conversion performance.

[0046] In the embodiments of the present application, the metal ions are preferably one of copper ions, iron ions and cobalt ions, and more preferably copper ions; at least a part of the metal ions forms metal oxide nanoparticles and is compounded in the metal-lignin composite material. For example, copper ions can form coordination with lignin (taking the most common monomer unit as an example), Cu 2+ exist in the following forms: Cu-O coordination, Cu-NH3 coordination, and CuO nanoparticle action.

[0047]

[0048] In a second aspect, the embodiments of the present application also provide a preparation method of the metal-lignin composite material of the first aspect, which comprises:

[0049] After dissolving the lignin and the metal source in water, adjusting the pH value for reaction, and then separating, collecting and drying, the metal-lignin composite material is obtained.

[0050] In the embodiments of the present application, the metal source is preferably one of copper salt, iron salt, cobalt salt, nickel salt and chromium salt. In theory, the metal source used in the present application is not particularly limited, i.e., any salt that can generate metal ions in an aqueous solution, such as copper acetate, copper sulfate, copper chloride, copper bromide, etc., iron sulfate, iron chloride, etc., cobalt chloride, cobalt sulfate, cobalt nitrate, etc., nickel nitrate, nickel chloride, nickel sulfate, nickel carbonate, nickel acetate, etc., chromium nitrate, chromium chloride, chromium sulfate, etc. These metal salts can generate metal ions in an aqueous solution, build a multi-raw material basis, and optimize the optical absorption properties of the light-heat conversion material.

[0051] In the embodiments of the present application, the molar ratio of one monomer unit in the lignin to the metal ion is (8-1):(1-2), and more preferably (2-1):1. In order to obtain the optimal effect, a series of explorations are carried out according to the different molar ratios of the selected basic unit of lignin to the metal ion by controlling other reaction conditions, and the material with better performance is further applied to solar evaporation water treatment.

[0052] In the embodiments of the present application, the pH value is adjusted to 6-9, and more preferably 8-9. By controlling the pH value of the reaction system, the generation of metal oxide nanoparticles can be controlled. When the pH value is 8-9, the generation of metal oxide nanoparticles is more likely to occur, thereby improving the light-heat conversion performance. Moreover, as the pH value increases, the particle size of the metal oxide nanoparticles will gradually increase due to agglomeration.

[0053] It should be noted that, by the coordination between alkaline lignin and heavy metal ions, the present application introduces new copper-ammonia coordination and promotes the formation of metal oxides, thereby realizing the deep integration of light-heat function and wastewater treatment. This strategy not only significantly improves the stability of the material in heavy metal wastewater, but also improves the light absorption and light-heat conversion performance of the lignin material through coordination and the action of metal oxides, so that it can become a more efficient light-heat conversion material and be further applied to the field of water treatment.

[0054] In a third aspect, the embodiments of the present application also provide the use of the metal-lignin composite material in solar water evaporation water treatment. Based on the excellent light absorption and light-heat conversion performance, stability and durability of the prepared metal-lignin composite material, it has a wide market application prospect in the field of solar water evaporation water treatment.

[0055] The technical solutions of the present application will be further described below with reference to specific embodiments.

[0056] Example 1

[0057] This example provides a preparation method of A1-metal-lignin composite material (sample 1), which specifically comprises:

[0058] Under mechanical stirring, 2 g of alkali lignin was dissolved in 200-300 mL of deionized water to form a lignin solution. Then a metal ion solution containing 0.24 g of copper acetate was added, and the two were uniformly dispersed by stirring for 10 minutes. A 10% ammonia solution was added dropwise and the pH was adjusted to alkaline (8-9), then stirred at room temperature for 12 h, the unreacted molecules were removed by centrifugal separation, and dried in a vacuum oven at 40°C for 12 h to obtain A1-metal-lignin composite material (sample 1).

[0059] Example 2

[0060] This example provides a preparation method of A2-metal-lignin composite material, and the component ratio, preparation operation and process parameters are basically the same as those of Example 1, and the difference lies in that the mass of copper acetate added in this example is 0.48 g, 0.95 g, 1.90 g, 3.80 g, respectively, and the corresponding A2-metal-lignin composite material (sample 2), A3-metal-lignin composite material (sample 3), A4-metal-lignin composite material (sample 4), A5-metal-lignin composite material (sample 5) are obtained.

[0061] Example 3

[0062] This example provides a preparation method of A6-metal-lignin composite material (sample 6), which specifically comprises:

[0063] Under mechanical stirring, 2 g of alkali lignin was dissolved in 200-300 mL of deionized water to form a lignin solution. Then a metal ion solution containing 0.81 g of iron chloride was added, and the two were uniformly dispersed by stirring for 10 minutes. A 10% ammonia solution was added dropwise and the pH was adjusted to alkaline (8-9), then stirred at room temperature for 12 h, the unreacted molecules were removed by centrifugal separation, and dried in a vacuum oven at 40°C for 12 h to obtain A6-metal-lignin composite material (sample 6).

[0064] Example 4

[0065] This example provides a preparation method of A7-metal-lignin composite material (sample 7), which specifically comprises:

[0066] Dissolve 2 g of alkali lignin in 200-300 mL of deionized water under mechanical stirring to form a lignin solution. Then add a metal ion solution containing 1.36 g of cobalt nitrate, and stir for 10 minutes to disperse them uniformly. Add a 10% ammonia solution drop by drop and adjust the pH to alkaline (8-9), then stir for 12 h at room temperature, remove the unreacted molecules by centrifugal separation, and dry in a vacuum oven at 40°C for 12 h to obtain the A7-metal-lignin composite material (sample 7).

[0067] Example 5

[0068] This example provides a preparation method of A8-metal-lignin composite material (sample 8), which specifically comprises:

[0069] Dissolve 2 g of lignin in 200-300 mL of deionized water under mechanical stirring to form a lignin solution. Then add a metal ion solution containing 0.83 g of nickel acetate, and stir for 10 minutes to disperse them uniformly. Add a 10% ammonia solution drop by drop and adjust the pH to alkaline (8-9), then stir for 12 h at room temperature, remove the unreacted molecules by centrifugal separation, and dry in a vacuum oven at 40°C for 12 h to obtain the A8-metal-lignin composite material (sample 8).

[0070] Example 6

[0071] This example provides a preparation method of A9-metal-lignin composite material (sample 9), which specifically comprises:

[0072] Dissolve 2 g of alkali lignin in 200-300 mL of deionized water under mechanical stirring to form a lignin solution. Then add a metal ion solution containing 0.84 g of chromium chloride, and stir for 10 minutes to disperse them uniformly. Add a 10% ammonia solution drop by drop and adjust the pH to alkaline (8-9), then stir for 12 h at room temperature, remove the unreacted molecules by centrifugal separation, and dry in a vacuum oven at 40°C for 12 h to obtain the A9-metal-lignin composite material (sample 9).

[0073] Example 7

[0074] This example provides a preparation method of A10-12-metal-lignin composite material, which has basically the same component ratio, preparation operation, and process parameters as those of Example 1. The difference is that the mass of copper acetate added in this example is 0.42 g, 0.42 g, and 0.95 g, respectively, and the lignin is replaced by sodium lignosulfonate, calcium lignosulfonate, and dealkali lignin, respectively, to obtain A10-metal-lignin composite material (sample 10), A11-metal-lignin composite material (sample 11), and A12-metal-lignin composite material (sample 12).

[0075] The reaction conditions in the examples are shown in Table 1.

[0076] Table 1 Summary of reaction conditions of examples

[0077]

[0078] Meanwhile, in order to verify the comprehensive performance of the metal-lignin composite material prepared in the above examples, the following comparative examples are provided for detailed description.

[0079] Comparative Example 1

[0080] In this comparative example, the lignin without any modification in Example 1 is taken as Comparative Example 1, denoted as B1-lignin.

[0081] Comparative Example 2

[0082] In this comparative example, the preparation method of the material, the component ratio, the preparation operation and the process parameters are basically the same as those in Example 1, the difference lies in that no lignin is added in this example, and 10% ammonia solution is added and the pH value is adjusted to 6-7, 8-9 and 10-11 respectively, and B1-copper oxide, B2-copper oxide and B3-copper oxide are obtained accordingly.

[0083] In order to verify the appearance performance of the metal-lignin composite material, the blackness instrument is used to test the blackness value, and the test results are shown in Table 3. Figure 1 The metal-lignin composite material sample is fully ground and tested for sample blackness under the blackness instrument.

[0084] According to the knowledge that Figure 1 the metal ion concentration results of several samples prepared in the examples prove the successful incorporation of Cu 2+ , and compared with the unmodified lignin, all samples can have a significantly reduced blackness value, and different ratios can also achieve the adjustment of different blackness values, and with the increase of Cu 2+ content, the blackness value gradually decreases, and when the Cu 2+ content continues to increase, the blackness value shows a certain rise (this may be due to the excessive Cu 2+ converted into copper oxide and the phenomenon of aggregation), indicating that the addition amount of A3-metal-lignin composite material (sample 3) is optimal.

[0085] In order to verify the structural characteristics of the metal-lignin composite material, the test results are shown in Table 4. Figures 2-6

[0086] According to the knowledge that Figure 2 ​It can be seen that the method of using the Raman spectrometer to characterize B1-lignin and sample 3 can see that the sample 3 has obvious Cu-O and Cu-N coordination peaks, which further proves the successful preparation of the material and explains the coordination effect existing in the metal-lignin composite material, thereby facilitating the improvement of light absorption.

[0087] According to Figure 3 It can be seen that the calculated molecular light absorption ability can be greatly improved after the innovative introduction of Cu-NH3 coordination, which further proves the contribution of Cu-O and Cu-NH3 coordination to the light absorption of the material.

[0088] According to Figure 4 It can be seen that the method of using the transmission electron microscope to characterize several samples can see that Cu 2+ After doping, lignin promotes the formation of CuO nanoparticles with a particle size of about 10 nm, and they are all independent and uniformly dispersed in the lignin matrix. With the increase of the ratio, CuO gradually aggregates and the size gradually increases. Such CuO nanoparticles have strong near-infrared band light absorption ability, which mainly contributes to the short-wave infrared region light absorption of the metal-lignin composite material, thereby making the short-wave infrared light absorption of the material much higher than that of the previous lignin material, indicating that CuO nanoparticles are successfully introduced. And the particle size of CuO nanoparticles in sample 1, sample 2 and sample 3 is about 10 nm, and the particle size of CuO nanoparticles in sample 4 and sample 5 increases greatly. The present application can obtain materials with different light absorption abilities by different ratios, and the higher the ratio, the larger the size of the introduced CuO nanoparticles.

[0089] According to Figure 5 It can be seen that without lignin (pH = 6-9), CuO will aggregate and form larger particle size (>200nm), and CuO is more likely to be generated under the condition of pH = 8-9, while under the condition of higher pH, it is not conducive to the generation of CuO. Compared with Figure 5 It can be proved that lignin plays a role in uniformly dispersing and isolating CuO nanoparticles, thereby obtaining some CuO nanoparticles with very small size and monodisperse (~10nm) in sample 1-3. With the increase of the ratio, CuO tends to aggregate to form larger agglomerates. Figure 6The copper oxide 1 (40nm), copper oxide 2 (100nm) and copper oxide 3 (200nm) were directly purchased. It can be clearly found that the light absorption capacity of CuO with different particle sizes was characterized by UV-visible absorption spectroscopy. As the particle size of copper oxide 1-3 gradually increased, its light absorption capacity gradually decreased, further illustrating that compared with previously reported materials without CuO effect or materials directly introducing ordinary large-particle CuO, this innovative introduction of CuO nanoparticles with a size of about 10nm and uniform dispersion can qualitatively improve the light absorption capacity of the material.

[0090] In order to verify the photothermal performance of metal-lignin composite materials, the test results are as follows Figures 7-8 shown.

[0091] according to Figure 7 It can be seen that the UV absorption of the samples in the wavelength range of 200-2500nm was measured by UV / visible / near-infrared diffuse reflectance test. As can be seen from the figure, compared with unmodified lignin, all metal-lignin composite materials have good absorption within the solar radiation range, indicating that they can fully utilize the energy of sunlight to convert into heat energy. At the same time, as the ratio increases, the short-wave infrared absorption capacity of the material decreases to a certain extent, which also confirms that Figure 5 The influence of CuO particle size mentioned in (due to the aggregation of CuO) can also be achieved by regulating this ratio to obtain materials with different light absorption.

[0092] according to Figure 8 It can be seen that the photothermal performance diagrams of A1-metal-lignin composite material, A2-metal-lignin composite material, A3-metal-lignin composite material, A4-metal-lignin composite material, A5-metal-lignin composite material and B1-lignin were prepared. A xenon lamp was used to simulate the sun, and the temperature rise changes on the surface of the metal-lignin composite material were recorded with an infrared camera under one sunlight intensity. It can be seen that compared with the unmodified alkali lignin, the surface temperatures of the five samples after stabilization are higher, and they have better photothermal conversion capabilities.

[0093] according to Figure 9 It can be seen that the photothermal performance diagrams of A10-metal-lignin composite material, A11-metal-lignin composite material, A12-metal-lignin composite material, pure sodium lignin sulfonate, pure calcium lignin sulfonate, and pure dealkalized lignin were prepared. A xenon lamp was used to simulate the sun, and the temperature rise changes on the surface of the metal-lignin composite material were recorded with an infrared camera under one sunlight intensity. It can be seen that compared with the unmodified lignin, the surface temperature of the three different lignin materials after modification is higher, and they have better photothermal conversion capabilities, which verifies the feasibility of other types of lignin.

[0094] In order to further verify the performance of the prepared metal-lignin composite material in the solar evaporator, the metal-lignin composite material is prepared into a solar evaporator for testing. The wastewater is purchased from Kehaisi (Beijing) Technology Co., Ltd., and the seawater is sea salt purchased from Guangdong Salt Industry General Co., Ltd.

[0095] According to Figure 10 It can be known that the resin, lignin and A3-metal-lignin composite material with the best performance are prepared into a solar evaporation device with a porous channel by 3D printing (resin device: pure resin, lignin device: lignin and resin, metal-lignin device: resin and A3-metal-lignin composite material), and the quality change of the wastewater or seawater is monitored in real time by using an electronic analytical balance under the treatment of pure water, seawater and heavy metal wastewater under the same sunlight intensity by using a xenon lamp. The results show that the device prepared by the metal-lignin composite material has a higher water evaporation rate compared with the devices prepared by the resin and lignin. Meanwhile, the device also has excellent evaporation rate in seawater and wastewater, and the evaporation rate in wastewater can reach 2.58 kg m -2 h -1 , which shows that the device prepared by the metal-lignin composite material has excellent water treatment capacity.

[0096] According to Figure 11 It can be known that the wastewater treatment stability of the metal-lignin composite material device is tested, and the stability is tested under the same sunlight by using a xenon lamp. It can be seen that the evaporation rate of the evaporator can be stabilized at about 2.6 kg m -2 h -1 per hour in 14 cycles of heavy metal wastewater, which proves that the device can stably treat heavy metal wastewater and has excellent cycle stability.

[0097] Therefore, the metal-lignin composite material provided in the application is obtained by reacting lignin and metal ions in an ammonia system; at least a part of the metal ions is chemically bonded to the lignin, and at least a part of the metal ions chemically bonded to the lignin forms metal / ammonia coordination; the metal ions are one of copper ions, iron ions, cobalt ions, nickel ions and chromium ions. Through the synergistic effect of various coordinations, excellent ultraviolet-visible-near infrared light absorption capacity can be given, and the light absorption and light-heat conversion performance, stability and durability of the composite material are greatly improved, which has wide market application prospect in the field of solar water evaporation and water treatment technology.

[0098] Each embodiment in the specification is described in a progressive manner, and the same or similar parts between each embodiment can be referred to each other, and each embodiment mainly explains the difference from other embodiments.

[0099] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some or all of the technical features thereof can be replaced by equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A metal-lignin composite material, characterized in that: It is obtained by reacting lignin with metal ions in an ammonia system; At least a portion of the metal ions are chemically bonded to the lignin, and at least a portion of the metal ions chemically bonded to the lignin form metal / ammonia coordination; The metal ion is one of copper ion, iron ion, cobalt ion, nickel ion and chromium ion.

2. The metal-lignin composite material according to claim 1, characterized in that The metal ion is one of copper ion, iron ion and cobalt ion; At least a portion of the metal ions form metal oxide nanoparticles and are composited in the metal-lignin composite material.

3. The metal-lignin composite material according to claim 2, characterized in that The metal ions are copper ions.

4. A method for preparing the metal-lignin composite material according to any one of claims 1 to 3, characterized in that: The preparation method comprises: After dissolving lignin and metal source in water, adding ammonia water to adjust pH and react, the reaction is carried out, and then the metal-lignin composite material is obtained by separation, collection and drying.

5. The method for preparing the metal-lignin composite material according to claim 4, characterized in that: The metal source is one of copper salt, iron salt, cobalt salt, nickel salt and chromium salt.

6. The method for preparing the metal-lignin composite material according to claim 4, characterized in that: The molar ratio of one monomer unit in the lignin to the metal ion is (8-1):(1-2).

7. The method for preparing the metal-lignin composite material according to claim 6, characterized in that: The molar ratio of one monomer unit in the lignin to the metal ion is (2-1):

1.

8. The method for preparing the metal-lignin composite material according to claim 4, characterized in that: The adjusted pH value is 6-9.

9. The method for preparing the metal-lignin composite material according to claim 8, characterized in that: The adjusted pH value is 8-9.

10. Use of the metal-lignin composite material according to claim 7 in solar water evaporation water treatment.

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