A method for preparing a 2D evaporation film constructed by self-assembling a two-dimensional superlattice of molybdate-heterocyanate subnanowires and its application.

Abstract

A method for preparing a 2D evaporation membrane constructed from a self-assembled two-dimensional superlattice of molybdate-heteropolyblue subnanowires and its application are disclosed. The method involves dissolving phosphomolybdic acid and transition metal chlorides in a mixed solvent system of oleic acid, oleylamine, and ethanol, stirring at room temperature; then pouring the solution into a stainless steel high-pressure reactor lined with PTFE, reacting, cooling to room temperature, and collecting the solid product by centrifugation; washing, and vacuum drying overnight to obtain molybdate-heteropolyblue powder; dispersing the molybdate-heteropolyblue powder in a cyclohexane-ethanol mixed solution, heating the resulting dispersion, filtering it through a hydrophilic filter membrane to form a membrane, and air-drying it overnight to obtain the 2D evaporation membrane constructed from the molybdate-heteropolyblue two-dimensional superlattice. The advantages are: the nanowire structure of this evaporation membrane provides long-range ordered nanoscale water transport channels, and its internal hydrophilic and external hydrophobic properties enhance water management capabilities, thereby promoting efficient water transport and evaporation, enabling efficient and stable solar thermal seawater evaporation.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal seawater desalination, specifically relating to a method for preparing a 2D evaporation membrane constructed by self-assembly of molybdate-heterocyanate subnanowires in a two-dimensional superlattice and its application. Background Technology

[0002] Against the backdrop of increasingly severe global energy and water crises, sustainable access to clean freshwater has become a core issue of concern for the international community. Compared with traditional processes such as electrodialysis, reverse osmosis, and multi-stage flash evaporation, solar thermal steam generation technology has the advantages of being environmentally friendly and pollution-free, simple in equipment, cost-effective, and capable of decentralized purification, and is expected to become an effective solution to the global freshwater crisis.

[0003] In recent years, extensive research has been conducted on traditional photothermal materials based on carbon-based materials (such as carbon nanotubes, graphene, and amorphous carbon), organic polymers (such as porphyrin, polyaniline, and polypyrrole), semiconductors, and plasma-enhanced metal nanoparticles (such as Au, Ag, and Cu). However, all of these approaches have significant limitations. While carbon-based materials have a wide spectral absorption range, their insufficient hydrophilicity leads to low evaporation efficiency. Polymer materials can improve hydrophilicity through surface modification, but they are susceptible to photobleaching and decomposition, making continuous evaporation difficult. Semiconductor materials exhibit excellent stability, but their light absorption band is narrow in the 200-2500 nm solar spectrum. Plasma-enhanced metal nanoparticles are limited in practical applications due to their tendency to aggregate and high cost. Therefore, developing novel photothermal materials that combine broad-spectral absorption, high-efficiency photothermal conversion, controllable hydrophilic-hydrophobic surface structures, and high stability has become a key direction for promoting breakthroughs in solar photovoltaic water heating evaporation technology.

[0004] Polyoxometalates (POMs) and their reduced products—heteropolyblues (HPBs)—show promise in photothermal catalysis and photothermal therapy due to their excellent photosensitivity and photothermal conversion properties, and also provide new material options for solar-powered photothermal water evaporation. POMs / HPBs possess broad and strong light absorption characteristics across the solar spectrum, and their oxygen-rich surface structure endows them with good hydrophilicity, facilitating the construction of efficient water transport and evaporation interfaces. Furthermore, POMs / HPBs carry a high negative charge, allowing them to self-assemble with cationic semiconductors, polymers, and carbon materials through electrostatic interactions, thereby constructing composite functional materials. Through rational POM self-assembly, efficient and stable loading of POMs / HPBs can be achieved while preventing water leaching. Further regulation of the surface microenvironment of functional self-assembled materials can enable water transport management and localized thermal temperature management, potentially becoming a major research direction for efficient solar steam generation materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires in a two-dimensional superlattice and its application, which can realize efficient and stable solar thermal seawater evaporation.

[0006] The technical solution of this invention is: A method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice includes the following steps: Step 1: Preparation of molybdate-heteropolyblue powder First, phosphomolybdic acid (PMA) and transition metal chloride were dissolved in a mixed solvent system of oleic acid, oleylamine, and ethanol at a molar ratio of 1:(2.5–5) and stirred at room temperature for 5–30 min. Then, the mixture was poured into a stainless steel high-pressure reactor lined with PTFE and reacted at 120–200 °C for 0.5–4 h. After cooling to room temperature, the solid product was collected by centrifugation, washed, and then vacuum dried overnight at 50 °C to obtain molybdate-heteropolyblue powder. Step 2: Preparation of 2D evaporation membranes constructed from molybdate-heterocyanate-blue two-dimensional superlattice Molybdate-heteropolyblue powder was dispersed in a cyclohexane-ethanol mixed solution and heated to 20–60 °C. The dispersion solution was then filtered through a hydrophilic filter membrane to form a film, which was then air-dried overnight to obtain a 2D evaporation membrane constructed from a two-dimensional superlattice of molybdate-heteropolyblue.

[0007] Furthermore, the molar ratio of phosphomolybdic acid (PMA) to transition metal chloride is 1:2.5.

[0008] Furthermore, the transition metal chloride is an iron chloride, a cobalt chloride, a nickel chloride, or a copper chloride.

[0009] Furthermore, the volume ratio of oleylamine to oleic acid is 1:8; the volume ratio of oleylamine to ethanol is 1:5.4.

[0010] Furthermore, in step one, the stirring time is 15 min; the reaction temperature is 180℃; and the reaction time is 2 h. In step two, the heating temperature is 45℃.

[0011] Furthermore, in step two, the volume ratio of cyclohexane to ethanol in the cyclohexane-ethanol mixed solution is 1:1.

[0012] Furthermore, in step two, when the molybdate-heterocyanate powder is 0.08 g, the hydrophilic filter membrane used is a circular hydrophilic filter membrane with a diameter of 4.0 cm.

[0013] Furthermore, in step two, the volume of the molybdate-heterocyanate powder mixed with the cyclohexane-ethanol solution is 0.004 g / mL.

[0014] Furthermore, in step one, during washing, a mixed solution of ethanol and cyclohexane with a volume ratio of 3:1 is used.

[0015] Application of a 2D evaporation membrane constructed from a molybdate-heterocyanate two-dimensional superlattice prepared by the above method in solar steam generation and seawater desalination.

[0016] The principle of this invention is as follows: a two-dimensional (2D) superlattice self-assembled body, TMoO4-HPB-SL, is constructed by a simple one-step solubilization method using phosphomolybdic acid and transition metal chlorides. This assembly consists of ordered TMoO4-HPB subnanowires (T being Fe, Co, Ni, or Cu). In the TMoO4-HPB-SL composite material, the TMoO4-HPB nanowires possess the dual advantages of being hydrophilic on the inside and hydrophobic on the outside: on the one hand, TMoO4-HPB provides long-range ordered nanoscale water transport channels, promoting efficient water molecule transport; on the other hand, its hydrophobic outer layer can achieve thermal insulation regulation of bulk water, effectively suppressing heat loss. Under the synergistic effect of the binary photothermal components FeMoO4 and HTB with the long-range ordered structure of the nanowires, TMoO4-HPB significantly enhances light-harvesting ability and photothermal conversion efficiency. Furthermore, the hydrophobic modification of the TMoO4-HPB-SL surface provides a certain degree of self-cleaning ability, avoiding salt crystallization. Based on this unique structural advantage, TMoO4-HPB-SL-M exhibits excellent performance in solar steam generation and solar seawater desalination.

[0017] The hydrophilicity of phosphomolybdic acid (PMA) makes it readily soluble in aqueous systems, and its oxidized state exhibits weak light-harvesting and thermal conversion capabilities, while its powder form is unsuitable for direct practical applications. This study employs a co-assembly strategy of PMA clusters with transition metal salts within a hydrophobic oleic acid-oleylamine system. A small portion of the PMA clusters reacts with transition metal ions to form TMoO4 (FeMoO4, CoMoO4, NiMoO4, and CuMoO4) nanocrystals; the remaining PMA clusters are reduced to heteropolyblue (HPB) at high temperatures, subsequently undergoing cluster-nucleus interactions with the PMA nanocrystals with the aid of oleic acid and oleylamine, controlling the formation and ordered self-assembly of sub-nanoscale structural units. Notably, under this self-assembly strategy, the oxidized PMA is reduced to HPB, ensuring that the 2D TMoO4-HPB-SLs exhibit excellent light absorption and photothermal response under sunlight. The formation of semiconductor molybdates and the modification of surface oleic acid and oleamine molecules not only prevent heteropolyblue (HPB) from agglomerating and clustering during self-assembly, but also avoid the problem of HPB water leaching during solar water evaporation, thereby achieving high efficiency and stability of solar photothermal water evaporation.

[0018] The beneficial effects of this invention are: (1) Utilizing the nanoscale structural size effect of POM to guide the development of transition metal chlorides (TCl) n A two-dimensional superlattice self-assembled structure (labeled TMoO4-HPB-SL) composed of molybdate-heterocyanate sub-nanowires was synthesized by self-assembly in an ethanol-oleic acid and oleylamine solvent system. The TMoO4-HPB nanowire structure provides long-range ordered nanoscale water transport channels, and its internal hydrophilic and external hydrophobic properties enhance water management capabilities, thereby promoting efficient water transport and evaporation. Furthermore, its hydrophobic outer layer enables thermal insulation regulation of bulk water, effectively suppressing heat loss. Through the synergistic effect of the binary photothermal components and the long-range ordered structure, TMoO4-HPB significantly enhances light-harvesting ability and photothermal conversion efficiency.

[0019] (2) The TMoO4-HPB-SL-M of this invention can be directly used as an evaporator, exhibiting excellent solar steam generation and seawater desalination performance. Simulation experiments show that the solar water evaporation rate of the 2D TMoO4-HPB-SL-M of this invention reaches as high as 3.2 kg·m³. -2 ·h -1 It also boasts an energy efficiency of 94.3%. This efficiency figure indicates that most of the input solar energy is effectively utilized, preventing energy loss. Furthermore, the evaporator exhibits excellent seawater salinity adaptability, enabling it to accommodate seawater with varying salinity levels and improving resource utilization.

[0020] (3) Compared with traditional seawater evaporation processes, this invention uses solar energy as the core driving force, abandons the dependence on fossil fuels, fundamentally eliminates the emission of pollutants and greenhouse gases during use, effectively helps carbon emission reduction, and practices the green and low-carbon concept.

[0021] In summary, this material demonstrates outstanding performance in improving photothermal conversion efficiency, optimizing the evaporation process, enhancing energy and resource utilization efficiency, and promoting environmental protection and energy conservation. Its applications are wide-ranging, not only suitable for industrial wastewater evaporation treatment and indoor humidification, but also showing great potential in the field of solar seawater evaporation, with broad prospects for industrialization. Attached Figure Description

[0022] Figure 1The figures show transmission electron microscopy (TEM) images of FeMoO4 synthesized in Examples 1, 2, and Comparative Example 1 of this invention, prepared according to different doses of phosphomolybdic acid (PMA). In the figures, a. is the TEM image of FeMoO4 in the 0.05 mmol PMA synthesis system (corresponding to Example 1), b. is the high-resolution TEM image of FeMoO4 in the 0.05 mmol PMA synthesis system (corresponding to Example 1), c. is the TEM image of FeMoO4-HPB-SL in the 0.1 mmol PMA synthesis system (corresponding to Example 1), and d. is the TEM image of FeMoO4-HPB-SL in the 0.2 mmol PMA synthesis system (corresponding to Example 2). Figure 2 The figures show X-ray powder diffraction (XRD) characterization patterns of the different phosphomolybdic acid (PMA) dosages prepared in Examples 1, 2 and Comparative Example 1 of this invention. In the figures, a. wide-angle X-ray powder diffraction patterns of different PMA synthesis systems, and b. small-angle X-ray powder diffraction patterns of different PMA synthesis systems. Figure 3 The figures show the aberration-corrected high-resolution transmission electron microscopy (TEM) characterization of FeMoO4-HPB-SL prepared in Example 2 of this invention and the X-ray absorption near-edge structure (XANES) spectrum of FeMoO4-HPB-SL. In the figures, a. TEM characterization of FeMoO4-HPB-SL, b. TEM characterization of FeMoO4-HPB-SL, c. aberration-corrected TEM characterization of FeMoO4-HPB-SL, d and e. high-angle annular dark field and corresponding energy dispersive spectroscopy (EDS) line scan characterization of FeMoO4-HPB-SL, f. K-edge X-ray absorption near-edge structure (XANES) spectrum of P in FeMoO4-HPB-SL, and g. L-edge X-ray absorption near-edge structure spectrum of Mo in FeMoO4-HPB-SL. Figure 4 The images shown are transmission electron microscopy (TEM) images of TMoO4-HPB-SL prepared in Examples 2-5 of this invention: a. TEM image of FeMoO4-HPB-SL, b. TEM image of CoMoO4-HPB-SL, c. TEM image of NiMoO4-HPB-SL, d. TEM image of CuMoO4-HPB-SL, e. wide-angle X-ray powder diffraction pattern of TMoO4-HPB-SL, and f. small-angle X-ray powder diffraction pattern of TMoO4-HPB-SL. Figure 5 The infrared spectrum of FeMoO4-HPB-SL prepared in this invention is shown below. Yellow line: phosphomolybdic acid (PMA); blue line: heteropoly blue (HPB); green line: corresponding to Example 1; red line: corresponding to Example 2. Figure 6The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of FeMoO4-HPB-SL prepared in Example 2 of this invention; in the image, a. the 1s peak of C in FeMoO4-HPB-SL, b. the 1s peak of N in FeMoO4-HPB-SL, c. the 2s peak of O in FeMoO4-HPB-SL, d. the 2p peak of Fe in FeMoO4-HPB-SL, e. the 3d peak of Mo in FeMoO4-HPB-SL, and the 2p peak of P in FeMoO4-HPB-SL. Figure 7 The figure shows the solar photothermal evaporation performance of FeMoO4-HPB-SL-M in Example 2 of this invention; in the figure, a. scanning electron microscopy characterization of FeMoO4-HPB-SL-M, b. high-resolution scanning electron microscopy characterization of FeMoO4-HPB-SL-M, c. elemental mapping characterization of the cross section of FeMoO4-HPB-SL-M, and d. ultraviolet-visible-near-infrared absorption spectrum of FeMoO4-HPB-SL-M in the solar spectrum range of 200-2500 nm (UV- (VIS-NIR) diagram, e. Photothermal conversion performance of FeMoO4-HPB-SL-M under dry state under 1 Sun irradiation, f. Photothermal conversion performance of FeMoO4-HPB-SL-M at the beginning of evaporation under 1 Sun irradiation, g. Rate comparison diagram of FeMoO4-HPB-SL-M under 1 Sun irradiation, h. Evaporation rate and energy efficiency diagram of different evaporators, i. Evaporation rate diagram of FeMoO4-HPB-SL-M under 0-2 Sun irradiation; Figure 8 The figure shows the solar thermal desalination performance of FeMoO4-HPB-SL-M in Example 2 of this invention. In the figure, a. is a schematic diagram of the solar thermal desalination system structure of FeMoO4-HPB-SL-M, b. is the result of zero liquid discharge of FeMoO4-HPB-SL-M under 0.5 Sun irradiation, c. is the result of zero liquid discharge of FeMoO4-HPB-SL-M under 0.75 Sun irradiation, d. is the result of zero liquid discharge of FeMoO4-HPB-SL-M under 1.0 Sun irradiation, e. is the evaporation rate and energy efficiency of FeMoO4-HPB-SL-M with zero liquid discharge under different irradiation intensities, and g. is the durability test of FeMoO4-HPB-SL-M. Figure 9This invention demonstrates the solar thermal desalination performance of the FeMoO4-HPB-SL-M evaporator in Embodiment 2 of this invention, simulating the purification performance of nuclear wastewater and industrial wastewater. The figures show: a. Salinity comparison of FeMoO4-HPB-SL-M before and after solar desalination in simulated seawater and the Dead Sea system; b. Major ion concentrations in purified water obtained from FeMoO4-HPB-SL-M in simulated seawater; c. Major ion concentrations in purified water obtained from FeMoO4-HPB-SL-M in simulated nuclear wastewater; d. Purification performance of FeMoO4-HPB-SL-M in industrial wastewater; e. Purification performance of FeMoO4-HPB-SL-M in dye wastewater; f. Stability experiment of FeMoO4-HPB-SL-M in seawater desalination; g. Water quality assessment of purified water obtained from FeMoO4-HPB-SL-M in seawater desalination. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to the embodiments.

[0024] Example 1 Step 1: Preparation of FeMoO4-HPB-SL powder First, phosphomolybdic acid (PMA) (0.1 mmol) and FeCl3·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL), and stirred at room temperature for 15 minutes. Then, the entire solution was transferred to a sealed stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the solid product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (ethanol to cyclohexane volume ratio of 3:1), and then dried overnight under vacuum at 50 °C to obtain FeMoO4-HPB-SL powder. Step 2: Prepare the FeMoO4-HPB-SL-M membrane structure using a typical vacuum filtration method. First, 0.08 g of FeMoO4-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm covering the FeMoO4-HPB-SL area; after being air-dried overnight, a 2D ferric molybdate-heteropolyblue membrane evaporator (FeMoO4-HPB-SL-M) was obtained.

[0025] Example 2 Step 1: Preparation of FeMoO4-HPB-SL powder First, phosphomolybdic acid (PMA) (0.2 mmol) and FeCl3·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL), and stirred at room temperature for 15 minutes. Then, the entire solution was transferred to a sealed stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the blue-green product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (ethanol to cyclohexane volume ratio of 3:1), and then dried overnight under vacuum at 50 °C to obtain FeMoO4-HPB-SL powder. Step 2: Prepare the FeMoO4-HPB-SL-M membrane structure using a typical vacuum filtration method. First, 0.08 g of FeMoO4-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm covering the FeMoO4-HPB-SL area; after being air-dried overnight, a 2D ferric molybdate-heteropolyblue membrane evaporator (FeMoO4-HPB-SL-M) was obtained.

[0026] Example 3 Step 1: Preparation of CoMoO4-HPB-SL powder First, phosphomolybdic acid (PMA) (0.2 mmol) and CoCl3·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL). Then, 0.1 mL of concentrated hydrochloric acid was added, and the mixture was stirred at room temperature for 15 minutes. The entire solution was then transferred to a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the blue-green product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (ethanol to cyclohexane volume ratio of 3:1) and then dried overnight under vacuum at 50 °C to obtain CoMoO4-HPB-SL powder.

[0027] Step 2: CoMoO4-HPB-SL-M was prepared using a typical vacuum filtration method. First, 0.08 g of CoMoO4-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm covering the area of ​​CoMoO4-HPB-SL; after being air-dried overnight, a 2D iron molybdate-heteropolyblue membrane evaporator (CoMoO4-HPB-SL-M) was obtained.

[0028] Example 4 Step 1: Preparation of NiMoO4-HPB-SL powder First, phosphomolybdic acid (PMA) (0.2 mmol) and NiCl2·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL). Then, 0.1 mL of concentrated hydrochloric acid was added, and the mixture was stirred at room temperature for 15 minutes. The entire solution was then transferred to a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the blue-green product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (ethanol to cyclohexane volume ratio of 3:1) and then dried overnight under vacuum at 50 °C to obtain NiMoO4-HPB-SL powder.

[0029] Step 2: NiMoO4-HPB-SL-M was prepared using a typical vacuum filtration method. First, 0.08 g of NiMoO4-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm covering the NiMoO4-HPB-SL area; after being air-dried overnight, a 2D iron molybdate-heteropolyblue membrane evaporator (NiMoO4-HPB-SL-M) was obtained.

[0030] Example 5 Step 1: Preparation of CuMoO4-HPB-SL powder First, phosphomolybdic acid (PMA) (0.2 mmol) and CuCl2·2H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL). Then, 0.1 mL of concentrated hydrochloric acid was added, and the mixture was stirred at room temperature for 15 minutes. The entire solution was then transferred to a sealed stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the blue-green product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (ethanol to cyclohexane volume ratio of 3:1) and then dried overnight under vacuum at 50 °C to obtain CuMoO4-HPB-SL powder.

[0031] Step 2: CuMoO4-HPB-SL-M was prepared using a typical vacuum filtration method. First, 0.08 g of CuMoO4-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm covering the CuMoO4-HPB-SL area; after being air-dried overnight, a 2D ferric molybdate-heteropolyblue membrane evaporator (CuMoO4-HPB-SL-M) was obtained.

[0032] Comparative Example 1 Step 1: Preparation of FeMoO4 powder First, phosphomolybdic acid (PMA) (0.05 mmol) and FeCl3·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL), and stirred at room temperature for 15 minutes. Then, the entire solution was transferred to a sealed stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, ferric molybdate was collected by centrifugation, washed three times with an organic solution of ethanol and cyclohexane (volume ratio of ethanol to cyclohexane 3:1), and then dried overnight under vacuum at 50 °C to obtain FeMoO4 powder. Step 2: FeMoO4-M was prepared using a typical vacuum filtration method. First, 0.08 g of FeMoO4 powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm for the FeMoO4-M coverage area; after being air-dried overnight, a ferric molybdate membrane (FeMoO4-M) was obtained.

[0033] Comparative Example 2 Without adding phosphomolybdic acid (the dosage was adjusted to zero) as in Example 2, and otherwise the reaction was the same as in Example 2, a molybdate-heterocyanate self-assembled superlattice could not be obtained in the reaction system.

[0034] Comparative Example 3 Without adding FeCl3·6H2O chloride (the dosage was adjusted to zero) as in Example 2, and otherwise the reaction was the same as in Example 2, a molybdate-heterocyanate self-assembled superlattice could not be obtained in the reaction system.

[0035] Comparative Example 4 Replacing oleylamine with ethanol in Example 2, while keeping everything else the same as in Example 2, failed to synthesize molybdate-heterocyanate self-assembled superlattice.

[0036] Comparative Example 5 Replacing oleic acid with ethanol in Example 2, while keeping everything else the same as in Example 2, failed to synthesize molybdate-heterocyanate self-assembled superlattice.

[0037] Comparative Example 6 Replacing ethanol with methanol in Example 2, while otherwise remaining the same as in Example 2, failed to synthesize a highly ordered molybdate-heterocyanate self-assembled superlattice.

[0038] Comparative Example 7 Replacing ethanol with acetone in Example 2, while otherwise remaining the same as in Example 2, failed to synthesize a highly ordered molybdate-heterocyanate self-assembled superlattice.

[0039] Comparative Example 8 The phosphomolybdic acid in Example 2 was replaced with phosphotungstic acid, and the rest was the same as in Example 2. However, it was not possible to synthesize the molybdate-heteropolyblue self-assembled superlattice.

[0040] Comparative Example 9 In Example 2, phosphomolybdic acid was replaced with silicotungstic acid, and the rest was the same as in Example 2. However, it was not possible to synthesize molybdate-heteropolyblue self-assembled superlattice.

[0041] Comparative Example 10 Step 1: Preparation of Li-HPB-SL powder First, phosphomolybdic acid (PMA) (0.1 mmol) and LiCl3·6H2O (0.5 mmol) were dissolved in a mixed solvent system including oleic acid (6.67 mL), oleylamine (0.83 mL), and ethanol (4.5 mL), and stirred at room temperature for 15 minutes. Then, the entire solution was transferred to a sealed stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 2 hours. After cooling to room temperature, the blue-green product was collected by centrifugation. The product was washed three times with an organic solution of ethanol and cyclohexane (volume ratio of ethanol to cyclohexane 3:1), and then dried overnight under vacuum at 50 °C to obtain Li-HPB-SL powder. Step 2: Li-HPB-SL-M was prepared using a typical vacuum filtration method. First, 0.08 g of Li-HPB-SL powder was dispersed in 20 mL of a mixed solution of cyclohexane and ethanol (v / v = 1 / 1); then heated to 45 °C; subsequently, the dispersion was filtered through a hydrophilic filter membrane to form a membrane with a diameter of 4.0 cm for the Li-HPB-SL coverage area; after being air-dried overnight, a lithium-heteropoly blue membrane evaporator (Li-HPB-SL-M) was obtained.

[0042] The FeMoO4-HPB-SL prepared in Example 2 of this invention was characterized and its performance was tested. 1. The assembly process and structural morphology of FeMoO4-HPB-SL were observed using transmission electron microscopy (TEM). Figure 1 It can be seen that with the increase of phosphomolybdic acid (PMA) dosage (0.0-0.2 mmol), irregular FeMoO4 nanocrystals ( Figure 1a) and irregular FeMoO4 nanowires ( Figure 1 b) Finally, self-assembly yielded a perfect two-dimensional superlattice structure (named FeMoO4-HPB-SL), exhibiting highly ordered properties. Figure 1 d). Furthermore, this self-assembly process also reveals the crucial guiding role of phosphomolybdic acid (PMA) in the self-assembly process.

[0043] 2. Obvious sharp peaks were observed by X-ray powder diffraction (XRD). Figure 2 As can be seen from 'a' in the figure, the FeMoO4-HPB-SL phase contains components of FeMoO4 and heteropolyblue (HPB), indicating the successful preparation of FeMoO4-HPB-SL. Figure 2 As can be seen from b, the characteristic peaks in the small-angle range are obvious and sharp, which also proves the highly ordered result of FeMoO4-HPB-SL.

[0044] 3. FeMoO4-HPB-SL was observed using high-resolution transmission electron microscopy (TEM). Figure 3 As can be seen from a and b in the figure, FeMoO4-HPB-SL exhibits a 2D layered structure. From... Figure 3 As can be seen from c, FeMoO4-HPB-SL exhibits distinct FeMoO4 lattice fringes. From... Figure 3 The line scan results for d and e show that FeMoO4 and heteropolyblue (HPB) are assembled in an almost alternating pattern, consistent with the attraction characteristics of the positive charge of FeMoO4 and the anion of heteropolyblue (HPB). From Figure 3 As can be seen from f and g in the figure, the composition and structure of heteropolyblue (HPB) in FeMoO4-HPB-SL are well preserved.

[0045] 4. The morphology of FeMoO4-HPB-SL from Example 2, CoMoO4-HPB-SL from Example 3, NiMoO4-HPB-SL from Example 4, and CuMoO4-HPB-SL from Example 5 were further observed using high-resolution transmission electron microscopy (TEM). From Figure 4 As can be seen from a, b, c, and d, CoMoO4-HPB-SL, NiMoO4-HPB-SL, and CuMoO4-HPB-SL exhibit a highly ordered 2D structure, consistent with the observations of FeMoO4-HPB-SL. From... Figure 4 As can be seen from e and f in the figure, CoMoO4-HPB-SL, NiMoO4-HPB-SL and CuMoO4-HPB-SL also have the same 2D highly ordered structure.

[0046] 5. Observation using Fourier transform infrared spectroscopy, from Figure 5As can be seen from the data, FeMoO4-HPB-SL possesses the characteristic peaks (873-1064 cm⁻¹) of heteropoly blue (HPB) molecules. -1 In addition to ), oleic acid and oleylamine molecules were also observed. At 1650.43 cm⁻¹ -1 and 1703.21cm -1 The characteristic peaks at [location] are attributed to oleylamine (-NH) and oleic acid (-C=O), respectively. Also, at 2922.69 cm⁻¹... -1 and 2852.37cm -1 -CH3 and -CH2 groups were observed on the carbon chains of oleylamine / oleic acid molecules. Notably, at 1598.2 cm⁻¹... -1 and 3550cm -1 The strong absorption at approximately 100°C indicates that the heteropolyblue (HPB) molecules in the sample contain a large amount of free H2O molecules, which is attributed to the large number of water molecules adsorbed within the HPB molecular structure. This sub-nanowire structure also suggests that it can function as a water transport channel. In summary, all the above results demonstrate the internal hydrophilic and external hydrophobic properties of FeMO4-HPB-SL.

[0047] 6. FeMoO4-HPB-SL was characterized by X-ray photoelectron spectroscopy (XPS). Figure 6 It can be seen that C, N, O, Fe, Mo and P elements are all present, and Fe is in the +2 valence state, while Mo is in the +5 and +6 valence states, indicating the coexistence of FeMoO4 and heteropolyblue (HPB).

[0048] 7. The structure of the FeMoO4-HPB-SL film was analyzed by scanning electron microscopy (SEM). Figure 7 As can be seen from the illustration in section a, FeMoO4-HPB-SL-M exhibits good stability, which may be attributed to the flexibility of the 2D superlattice itself and the strong interactions between them. From Figure 7 As can be seen from a and b in the diagram, the FeMoO4-HPB-SL-M structure possesses a large number of micron and nanometer-sized pores, which facilitates the escape of water vapor. From Figure 7 As can be seen from 'c', the thickness of FeMoO4-HPB-SL-M is approximately 45 μm. The solar absorption capacity of FeMoO4-HPB-SL-M was observed using ultraviolet-visible-near-infrared absorption spectroscopy (UV-VIS-NIR). Figure 7As can be seen from d, the light absorption performance of FeMoO4-HPB-SL-M in the wavelength range of 200-2500 nm is significantly better than that of Comparative Example 1 FeMoO4-M and Comparative Example 10 Li-HPB-SL-M, demonstrating the advantages of the FeMoO4-HPB-SL-M composite structure. Subsequently, the solar evaporation performance of FeMoO4-HPB-SL-M was tested at 1 Sun. From... Figure 7 As can be seen from e and f, FeMoO4-HPB-SL-M can achieve solar thermal conversion, with most of the thermal energy used to drive water evaporation. From Figure 7 As can be seen from g and h, FeMoO4-HPB-SL-M achieved a high yield of 3.20 kg·m³ under one solar irradiation. -2 ·h -1 The water evaporation rate exhibits excellent performance in semiconductor materials. Figure 7 As can be seen from the i in the figure, FeMoO4-HPB-SL-M can exhibit a high evaporation rate under different irradiation conditions.

[0049] 8. The stability of FeMoO4-HPB-SL-M was analyzed using solar thermal seawater evaporation tests. Figure 8 As can be seen from 'a', the evaporation system consists of a top layer of FeMoO4-HPB-SL-M (as the evaporator), a middle layer of hydrophilic filter paper, and a bottom layer of foam and hydrophilic cotton core, forming a solar-powered seawater evaporation system. Here, a 10wt% high-salinity brine prepared with sodium chloride was selected as the evaluation sample. Considering the influence of region or season, outdoor solar irradiance is usually much lower than 1 Sun; therefore, solar irradiance was set at 0.5, 0.75, and 1 Sun. Figure 8 As shown in b, c, and d, FeMoO4-HPB-SL-M achieved complete separation of water and salt in a 10wt% salinity sample under solar irradiance of 0.5, 0.75, and 1, respectively. From... Figure 8 As can be seen from 'e', ​​their average evaporation rates are 1.62 kg·m³, respectively. -2 ·h -1 2.43 kg·m -2 ·h -1 and 3.23 kg·m -2 ·h -1 The salt recovery rates were as high as 94.24%, 93.52%, and 88.92%, respectively. Figure 8 As can be seen from f, at a salinity of 10 wt%, FeMoO4-HPB-SL-M has a salinity of 3.2 kg·m³. -2 ·h -1The water evaporation rate was stable and continuous for up to 48 hours. During this period, salt-free crystallization was observed on the surface, which further supports the excellent anti-salinization performance of FeMoO4-HPB-SL-M and makes it a promising candidate for practical outdoor seawater desalination applications.

[0050] 9. The water quality of the purified water was obtained through testing and analysis of FeMoO4-HPB-SL-M in solar photothermal evaporation; from Figure 9 As shown in figures a and b, FeMoO4-HPB-SL-M exhibits excellent purification capabilities. For seawater samples of 3.5 wt% and 100 wt%, the salinity of the purified water was significantly reduced by approximately 3-4 orders of magnitude, with a substantial decrease in K+ collected from the evaporated purified water. + Na + Ca 2+ Mg 2+ The concentrations of all four major ions decreased by 3-4 orders of magnitude. From Figure 9 As can be seen from samples c, d, and e, FeMoO4-HPB-SL-M also demonstrated excellent purification capabilities in solar energy purification tests of nuclear wastewater, dye wastewater, and industrial wastewater. From... Figure 9 As can be seen from f, FeMoO4-HPB-SL-M exhibits excellent cycle stability. From... Figure 9 As can be seen from the value of g, the quality of purified water obtained from seawater desalination is comparable to the standards for residential drinking water.

[0051] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a 2D evaporation film constructed by self-assembly of a two-dimensional superlattice of molybdate-heterocyanate subnanowires, characterized in that: Includes the following steps: Step 1: Preparation of molybdate-heteropolyblue powder First, phosphomolybdic acid and transition metal chloride were dissolved in a mixed solvent system of oleic acid, oleylamine and ethanol at a molar ratio of 1:(2.5-5) and stirred at room temperature for 5-30 minutes. Then, the mixture was poured into a stainless steel high-pressure reactor lined with PTFE and reacted at 120-200 °C for 0.5-4 hours. After cooling to room temperature, the solid product was collected by centrifugation, washed, and then vacuum dried overnight at 50 °C to obtain molybdate-heteropolyblue powder. Step 2: Preparation of 2D evaporation membranes constructed from molybdate-heterocyanate-blue two-dimensional superlattice Molybdate-heteropolyblue powder was dispersed in a cyclohexane-ethanol mixed solution and heated to 20–60 °C. The dispersion solution was then filtered through a hydrophilic filter membrane to form a film, which was then air-dried overnight to obtain a two-dimensional superlattice evaporation membrane of molybdate-heteropolyblue.

2. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: The molar ratio of phosphomolybdic acid to transition metal chloride is 1:2.

5.

3. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: The transition metal chloride is an iron chloride, a cobalt chloride, a nickel chloride, or a copper chloride.

4. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: The volume ratio of oleylamine to oleic acid is 1:8; the volume ratio of oleylamine to ethanol is 1:5.

4.

5. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: In step one, the stirring time is 15 min; the reaction temperature is 180℃ and the reaction time is 2 h. In step two, the heating temperature is 45℃.

6. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: In step two, the volume ratio of cyclohexane to ethanol in the cyclohexane-ethanol mixed solution is 1:

1.

7. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: When the molybdate-heterocyanate powder is 0.08 g, the hydrophilic filter membrane used is a circular hydrophilic filter membrane with a diameter of 4.0 cm.

8. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: In step two, the volume of the molybdate-heterocyanate powder mixed with the cyclohexane-ethanol solution is 0.004 g / mL.

9. The method for preparing a 2D evaporation film constructed by self-assembly of molybdate-heterocyanate subnanowires into a two-dimensional superlattice according to claim 1, characterized in that: In step one, the washing process uses a mixed solution of ethanol and cyclohexane with a volume ratio of 3:

1.

10. The application of a 2D evaporation membrane constructed from a molybdate-heterocyanate two-dimensional superlattice prepared by the method of claim 1 in solar steam generation and seawater desalination.

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