A fully biomass-based fog water collection material and its application

Abstract

The present invention discloses a fully biomass-based efficient fog water collector and its preparation method and application. First, amphoteric nanofibers are dispersed in an ethanol / water solution to obtain an amphoteric nanofiber dispersion liquid, and then the above dispersion liquid is attached to the surface of a hydrophobic biomass-based polymer through coating and deposition to form a transition layer. Subsequently, negatively charged nanofibers and positively charged nanofibers on the surface are alternately coated on the above transition layer to construct a two-amphiphilic (hydrophilic and hydrophobic) fully biomass-based fog water collector film. The preparation method of the present invention avoids polluting chemical reactions and complex energy-consuming process operations; the prepared fog water collection film has the advantages of high efficiency, repeatability, biodegradability, etc., and has good application prospects in the field of fog water collection.

Description

Technical Field

[0001] The present invention relates to the technical field of polysaccharide materials and structural design applications, and particularly relates to a fully biomass-based fog water collection material, a preparation method thereof, and an application thereof. Background Technique

[0002] In semi-arid regions and countries with scarce land, water shortage has become a serious and long-term problem. According to a recent report by the Food and Agriculture Organization of the United Nations (FAO), by 2025, more than 1.8 billion people will face a global water crisis. Generally speaking, the most commonly used method for recovering fresh water is seawater desalination. However, this has made slow progress. In recent years, the method of extracting water by condensing in humid air has gradually matured and has become one of the important water production methods in arid regions. A fog water collector (FWC) can effectively collect clean water from the air in areas where fog water is the only water source. The FWC has relatively low requirements for the environment and aims to capture the tiny water droplets present in the fog. Generally speaking, most FWCs exist in the form of a membrane structure with two opposite wettabilities (hydrophilicity and hydrophobicity). However, due to the nature of this asymmetric interface, the process of achieving its compatible structure construction is relatively complex. Currently, the complex and energy-consuming preparation process and chemical reagent pollution have always been the resistance to the application of most FWCs. Therefore, seeking a fully biomass-based preparation technology with low energy consumption and environmental protection in the process is a key issue to break through the application resistance.

[0003] Since the early 1970s, the development of biodegradable polymers has been attracting the attention of researchers. Among biodegradable polymers, hydrophobic biomass-based materials such as polylactic acid, polybutylene succinate, poly(propylene carbonate), and polycaprolactone have the largest industrial demand applications. Their significant characteristics such as biodegradability, recyclability, and low carbon emissions make biomass-based composite materials have excellent market potential. Based on the previous research work of the team, we have prepared a series of biomass nanofiber materials with excellent hydrophilicity and water absorption, such as cellulose nanofibers, chitin nanofibers, and silk fibroin nanofibers. They are abundant in nature and have great potential in the development of a low-carbon economy. However, the compatibility and compatibility between hydrophilic biomass nanofibers and hydrophobic biomass-based materials are poor, and there is currently no research report on the composite preparation of FWCs from biomass nanofibers and hydrophobic biomass-based materials.

[0004] By changing the surface tension of amphoteric nanofibers, that is, nanofibers modified by esterification or acylation and carrying certain charges (such as oxalic acid hydrolyzed nanochitin (OAChN)), the wetting state of the droplets of the amphoteric nanofiber dispersion on the hydrophobic surface changes from the Cassie state to the Wenzel state, realizing the connection of the hydrophilic-hydrophobic interface between the hydrophilic nanofibers and the hydrophobic substrate. Subsequently, during the spin-coating process, the hydrophilic single-charged nanofibers promote the lap joint of the upper and lower layers through the electrostatic interaction of positive and negative charges (such as partially deacetylated chitin nanofibers (DEChN) with positive surface charge and TEMPO-oxidized cellulose nanofibers (TOCN) with negative charge) to achieve layer-by-layer self-assembly. Compared with the existing methods, the surface of the film prepared by the present invention is nearly flat and smooth, which promotes the water absorption and water flow of the film. Compared with other coating methods, the spin-coating method combined with layer-by-layer assembly has the advantages of simple process and high speed. The outstanding advantages of preparing the fog water collector in the present invention include low cost, nanoscale controllability, one-step preparation, environmental friendliness, simple process and high fog water collection efficiency. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a preparation technology and application of a highly efficient fog water collector based on all biomass, expanding the application research of hydrophobic biomass-based materials and polysaccharide nanofibers in the field of fog water collection.

[0006] To achieve the above object of the invention, the technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a method for preparing a fog water collector film based on all biomass is provided, including the following steps: (1) Coating an intermediate transition layer on a hydrophobic biomass-based polymer substrate, and the coating solution of the intermediate transition layer is an ethanol / water dispersion of amphoteric nanofibers, and the amphoteric nanofibers are nanofibers containing both positive and negative charges on the surface; (2) Continuing to alternately coat negatively charged nanofibers on the surface and positively charged nanofibers on the above transition layer, and curing in an oven at 20-40 °C for 6-24 h to construct an amphiphilic all-biomass-based fog water collector film containing both hydrophilic nanofibers and hydrophobic polymers.

[0008] Further, the source of the nanofibers is any one or a combination of at least two of chitin nanofibers, cellulose nanofibers and silk fibroin nanofibers.

[0009] Further, the length of the nanofibers is 50-5000 nm, and the width is 3-50 nm.

[0010] Further, the hydrophobic substrate can be any one of polylactic acid (PLA), polybutylene succinate (PBS), polypropylene carbonate, polycaprolactone, etc.

[0011] Further, the coating method is any one of spin coating, brushing, spraying, and dip coating.

[0012] Further, the preparation method of the nanofibers is to prepare nanofibers by mechanically treating or pre-treating and mechanically treating chitin or cellulose or silk fibroin raw materials; the pre-treatment method of chitin raw materials is at least one of partial deacetylation by alkali method, partial deacetylation by enzymatic method, TEMPO oxidation, DES treatment, and acid hydrolysis method; the pre-treatment method of cellulose raw materials is at least one of TEMPO oxidation, KMnO4 oxidation, laccase oxidation, DES treatment, and acid hydrolysis; the pre-treatment method of silk fibroin raw materials is at least one of laccase oxidation, alkali treatment, DES treatment, and acid hydrolysis method; the mechanical treatment method is at least one of homogenization treatment, ultrasonic treatment, colloid mill treatment, high-pressure homogenization treatment, ultrafine grinding treatment, stirring, and microfluidics.

[0013] Further, in step (1), the amphoteric nanofibers are at least one of oxalic acid hydrolyzed chitin nanofibers, formic acid modified chitin nanofibers, lactic acid modified chitin nanofibers, TEMPO oxidized chitin nanofibers, lactic acid modified cellulose nanofibers, formic acid modified cellulose nanofibers, and silk fibroin nanofibers.

[0014] Further, in order to reduce the surface tension of the dispersion liquid on the surface of the hydrophobic substrate, the concentration of the amphoteric nanofiber dispersion liquid in step (1) is 0.1 wt% - 5.0 wt%, and the concentration of the ethanol solvent is 50 - 80%, which can improve the affinity between the substance and the hydrophobic substrate.

[0015] Further, the hydrophobic substrate is fixed on a glass plate; the spin coating conditions of the transition layer are as follows: the deposition time of the ethanol dispersion liquid of amphoteric nanofibers is 20 - 60 s; the initial rotation speed is 200 - 1000 r / min; the acceleration of speed increase is 200 - 1000 r / min 2 , lasting for 5 - 30 s; the spin coating speed is 1000 - 4000 r / min, lasting for 30 - 60 s; the acceleration of speed decrease is 500 - 1000 r / min 2 , until it stops, and spin coat 5 - 30 layers to obtain a complete coating.

[0016] Further, the transition layer is oxalic acid hydrolyzed chitin nanofibers. In order to ensure the uniform deposition of each group of dispersion liquids during the spin coating process, in step (2), first coat the negatively charged oxidized cellulose nanofibers on the surface, and then coat the positively charged deacetylated chitin nanofibers on the surface. Subsequently, alternately spin coat the negatively charged oxidized cellulose nanofibers and the positively charged deacetylated chitin nanofibers on the transition layer in turn. Define one alternate spin coating as one layer, and spin coat a total of 5 - 100 layers.

[0017] Furthermore, the pH of the oxalic acid hydrolyzed chitin nanofiber dispersion is 3 - 5, making the OAChN nanofibers carry a trace amount of positive charge, which promotes the dispersion of the nanofibers in the ethanol solvent, and the zeta potential is 30 - 60 mV. The pH of the oxidized cellulose nanofiber dispersion is 6 - 8, and the zeta potential is - 30~- 80 mV; the pH of the deacetylated chitin nanofiber dispersion is 3 - 5, and the zeta potential is 30 - 80 mV. The concentration of the nanofibers is all within 0.1 wt% - 5.0 wt%.

[0018] According to another aspect of the present invention, there is provided a fully biomass-based fog water collector film, which is prepared by the preparation method of a fully biomass-based fog water collector described above.

[0019] Furthermore, the Young's modulus of the film is 1800 - 2300 MPa; the nanofiber coating thickness is 1.0 - 5.0 μm; the surface of the nanofiber coating tends to be smooth, and the roughness is 0.06 - 7.00 nm; the surface coating basically does not affect the light transmittance (>85%) and thermal stability (360 °C) of the film.

[0020] Furthermore, the film has wettability on both sides, the water contact angle of the hydrophilic surface is 35 - 60°, and the water contact angle of the hydrophobic surface is 90 - 110°.

[0021] Furthermore, the fog water collection efficiency of the film is 55.9 - 90.9 mg·cm -2 ·h -1 。

[0022] According to the third aspect of the present invention, there are provided a preparation method and applications of the fully biomass-based fog water collector film, such as the application of the fully biomass-based fog water collector film in fog water collection, and possible applications in the fields of medicine, optics, electricity, environmental protection, packaging, adsorption or composite materials.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The present invention innovatively designs a hydrophilic nanofiber transition layer material, which can connect the upper and lower hydrophilic nanofibers and the hydrophobic substrate material through simple physical deposition and adsorption, greatly saving the process cost and time.

[0025] (2) The fully biomass-based fog water collector film prepared by the present invention has good mechanical properties, and the fog water collection efficiency is as high as 90.9 mg·cm -2 ·h -1 , and at the same time has high light transmittance and thermal stability, expanding the preparation materials and technologies of fog water collectors.

[0026] (3) The present invention uses all biomass materials, which greatly guarantees the protection of the ecological environment. The entire preparation process has low energy consumption, a simple and rapid process, and no polluting chemical substances are generated. The Janus structure is constructed through simple physical deposition and self-assembly to realize the application of fog water collection.

[0027] (4) The present invention innovatively applies hydrophobic degradable plastics to the field of fog water collectors, and cleverly converts the weaknesses of hydrophobic degradable plastics (such as the heat intolerance, hardness, and hydrophobicity of PLA, etc.) into the advantages of fog water collectors. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic diagram of the structural composition of the fog water collector membrane of the present invention.

[0030] Figure 2 It is the influence of different ethanol concentrations on the dispersion performance and light transmittance performance of the OAChN dispersion.

[0031] Figure 3 It is the influence of different numbers of OAChN transition layers on the wetting performance of the surface of the polylactic acid film and on the mechanical properties of the film.

[0032] Figure 4 It is the infrared characterization of spin-coated nanofiber coatings with different numbers of layers.

[0033] Figure 5 It is the comparison of the cross-sectional microtopography and water contact angle of the coating SEM characterization.

[0034] Figure 6 It is the surface microtopography and roughness characterization of the coating AFM characterization.

[0035] Figure 7 It is the influence of nanofiber coatings with different numbers of layers on the optical properties and thermal stability properties of the PLA film.

[0036] Figure 8 It is the schematic diagram of the fog water collection device and the fog water collection efficiency characterization of the fog water collector membrane based on all biomass with different numbers of layers.

[0037] Figure 9 It is the measured values of the water contact angle hysteresis of the fog water collector film with different numbers of layers at different times.

[0038] Figure 10 Comparison graph of viscosities of OAChN dispersions dispersed in different ethanol concentrations with those of TOCN and DEChN aqueous dispersions.

[0039] Figure 11 Photographs of thin film coatings obtained with raw materials in different pH values.

[0040] Figure 12 Graph of linear fitting of coating thickness growth with the number of layers, and SEM surface morphology images of uncoated nanofibers (left) and coated nanofibers (right).

[0041] Figure 13 Photographs of the whole process of the comparative experiment on fog water collection of thin films with different numbers of layers. Specific implementation manners

[0042] The embodiments of the present invention will be described in detail below in combination with the implementation manners and examples. The described examples are only a part of the embodiments of the present invention, not all of them. The following implementation manners and examples are only used to illustrate the present invention and should not be regarded as the scope of the present invention. All other examples obtained by those of ordinary skill in the art based on the examples in the present invention without creative efforts belong to the scope protected by the present invention. Those not specified in specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer.

[0043] The present invention will be further described below. The all-biomass-based fog water collector film provided by the present invention can flexibly select the number of layers, thickness, and even modification and functionalization according to factors such as the use environment and demand conditions. As long as the nanofibers in the present invention meet the corresponding size and charge requirements, the present invention can be realized. The sources of the nanofibers are any one or at least two combinations of chitin nanofibers, cellulose nanofibers, and silk fibroin nanofibers. The size of the nanofibers is: the length is 50-5000 nm, and the width is 3-50 nm; the preparation method of the nanofibers is to mechanically process or pre-treat and mechanically process chitin or cellulose or silk fibroin raw materials to obtain nanofibers; amphoteric nanofibers are nanofibers that simultaneously contain positive and negative charges on the surface. The pretreatment methods of chitin raw materials are at least one of the following: partial deacetylation by the alkali method (reference: FANY. Carbohyd Polym, 2010, 79(4): 1046-51), partial deacetylation by the enzyme method (reference: BAI L. Chemical Reviews, 2022, 122(13): 11604-74), TEMPO oxidation (reference: FAN Y. Biomacromolecules, 2008, 9(1): 192-8), DES treatment (reference: BAI L. Chemical Reviews, 2022, 122(13): 11604-74), acid hydrolysis method (reference: FAN Y. Biomacromolecules, 2008, 9(7): 1919-23); the pretreatment methods of cellulose raw materials are at least one of the following: TEMPO oxidation, KMnO4 oxidation, laccase oxidation (reference: JIANG J. Journal of Agricultural and Food Chemistry, 2018, 66(43): 11372-9), DES treatment, acid hydrolysis; the pretreatment methods of silk fibroin raw materials are at least one of the following: laccase oxidation, alkali treatment, DES treatment, acid hydrolysis method; the mechanical treatment methods are at least one of the following: homogenization treatment, ultrasonic treatment, colloid mill treatment, high-pressure homogenization treatment, ultrafine grinding treatment, stirring, and microfluidics.

[0044] To complete the details of the entire invention, the present invention uses Examples 1-4 to illustrate the preparation of four raw materials respectively.

[0045] Example 1:

[0046] Preparation of amphoteric nanofibers: Hydrolysis of chitin nanocrystals with oxalic acid (OAChN): Oxalate groups are grafted onto the C6 hydroxyl group of chitin through an esterification reaction, and the degree of modification can be controlled by adjusting the solid-liquid ratio, acid concentration, reaction temperature, and reaction time.

[0047] The purified chitin from crab shells was obtained by alternately soaking it in 1M HCl and 1M NaOH solutions for 12 hours in three cycles and then washing it. The obtained clean and purified crab shell chitin was added to a 25wt% oxalic acid solution with a solid-liquid ratio (acid:crab shell = 100:1), and the reaction was carried out at 90 °C for 2 hours. The reaction solution was filtered and washed with hot water to obtain the reaction precipitate. Then, the precipitate was ultrasonically broken in 80% ethanol for 5 minutes to obtain a 0.2wt% OAChN dispersion in the ethanol phase. The pH of the dispersion was 3 - 5, and the zeta potential was 30 - 60 mV.

[0048] The stability of the OAChN ethanol dispersion prepared in the present invention can be achieved by adjusting the ethanol concentration as needed. The above-mentioned oxalic acid hydrolyzed chitin can be dispersed in an ethanol solution at a concentration of 0.1wt% - 5wt%. As the ethanol concentration increases, its stability gradually decreases, and it reaches the stability critical value in an ethanol environment with a concentration of 50 - 80% and can achieve its transition from the Cassie state to the Wenzel state.

[0049] Example 2:

[0050] Preparation of surface positively charged nanofibers: Partially deacetylated chitin nanofibers (DEChN): Partial deacetylation of chitin can be obtained under high-temperature and concentrated alkali conditions. The purified crab shell chitin in Example 1 was added to a sodium hydroxide solution containing 33%, and the reaction was carried out at 90 °C for 4 hours. The reaction precipitate was centrifuged and washed to neutrality, and the degree of deacetylation was measured to be 21%. The partially deacetylated chitin was ultrasonically dispersed in an aqueous solution with pH = 4 for 5 minutes to obtain a DEChN aqueous dispersion. The pH of the dispersion was 3 - 5, and the zeta potential was 30 - 80 mV.

[0051] Example 3:

[0052] Preparation of surface negatively charged nanofibers: TEMPO-oxidized cellulose nanofibers (TOCN): Oxidation of cellulose can be prepared by TEMPO oxidation under mild conditions. HBKP (purified hardwood pulp) was added to an aqueous solution containing a certain proportion of sodium bromide (NaBr), 2,2,6,6-tetramethylpiperidine oxide (TEMPO), and sodium hypochlorite (NaClO) at a solid-liquid ratio of 1:100 (0.1g:0.1g:0.016g:8 mmol), and the reaction was carried out at room temperature for 4 hours. The reaction precipitate was centrifuged and washed to neutrality, and the carboxyl content was measured to be 1.6 mmol / g. The oxidized cellulose was ultrasonically dispersed in an aqueous solution with pH 7 for 5 minutes to obtain a TOCN aqueous dispersion. The pH of the dispersion was 6 - 8, and the zeta potential was -30 to -80 mV.

[0053] Example 4:

[0054] Preparation of silk fibroin nanofibers: Using the degummed silk fibroin solution, place the degummed silk (1 g) in 25 ml of 2 wt% NaOH solution, incubate at 0 °C for 24 h, and dialyze until neutral. Then add the water-insoluble component to distilled water at a mass ratio of 0.1:100, perform high-pressure homogenization treatment at 800 bar for 5 min, and centrifuge the supernatant at 10,000 rpm to obtain top-down exfoliated silk fibroin nanofibers (SNF). SNF has both positive and negative charges and is an amphoteric nanofiber. The top-down method for obtaining SNF also includes the DES treatment method, including systems such as lactic acid / choline chloride, oxalic acid / choline chloride, and citric acid / choline chloride.

[0055] Example 5:

[0056] As Figure 1 shown, the fog water collector membrane of the present invention consists of a hydrophobic substrate, a transition layer, and a functional layer; raw material preparation and dispersion (amphoteric nanofiber OAChN as the transition layer; positively charged DEChN and negatively charged TOCN as the transition layer) → adjust the concentration (0.1 - 5.0 wt%) and pH value (3 - 5 or 6 - 8) to ensure the stable dispersion of nanofibers and maintain appropriate surface charges for subsequent electrostatic attraction → fix the hydrophobic substrate (such as polylactic acid, PLA) → coat the OAChN ethanol dispersion for transition → alternately spin-coat the DEChN and TOCN aqueous dispersions → cure in an oven at 20 - 40 °C for 6 - 24 h.

[0057] Example 6:

[0058] Take the raw material OAChN ethanol dispersion (0.2 wt%, 80% ethanol concentration) in Example 1 as the spin-coating adhesive solution. First, fix the PLA hydrophobic substrate on a 5 cm × 5 cm glass plate, which can be achieved by simple wetting and then removing the vacuum; adjust the spin-coating parameters, including: deposition time of OAChN ethanol dispersion 30 s; initial rotation speed 500 r / min; acceleration of speed increase 1000 r / min 2 , lasting for 5 s; spin-coating speed 2500 r / min, lasting for 40 s; deceleration acceleration 500 r / min 2 , lasting for 10 s until the speed becomes 0 r / min. Spin-coat 10 times and fix the obtained film at 30 °C for 12 h to obtain a PLA film with a transition layer.

[0059] Take the dispersion in Examples 2 - 3 as the spin-coating adhesive solution TOCN / DEChN (0.2 wt%). On the basis of the OAChN transition layer, first deposit the TOCN aqueous dispersion for 30 s, with an initial rotation speed of 500 r / min; acceleration of speed increase 1000 r / min 2 , lasting for 5 s; spin-coating speed 2500 r / min, lasting for 40 s; deceleration acceleration 500 r / min2 for 10 s until the rotational speed becomes 0 r / min; then deposit the DEChN aqueous dispersion for 30 s in the same steps, with an initial rotational speed of 500 r / min; the acceleration of speed increase is 1000 r / min 2 for 5 s; the rotational speed of spin coating is 2500 r / min for 40 s; the acceleration of speed decrease is 500 r / min 2 for 10 s until the rotational speed becomes 0 r / min, and alternate in turn. Each round of spin coating of TOCN and DEChN is recorded as 1 layer, and 10 layers are spin coated. The spin-coated film is fixed in an oven at 30 °C for 12 h to obtain a fully biomass-based fog water collector film.

[0060] Control the fog water collection conditions, fix the fog water collector film on a special bracket, place the beaker for collecting fog water directly below the test sample, and enclose all devices with an acrylic box to balance the humidity of the test environment. To promote the transportation of water droplets on the film, a small incision about 0.5 cm long was made under the sample film with a knife for drainage. The fog flow rate is controlled at 15 cm·s -1 for 1 h, measure the mass of water in the beaker, and calculate the efficiency of collecting fog water. In addition, the mass of water captured on the coating surface was weighted. Compared with the simple PLA film, the water collection efficiency of the nanofiber coating is greatly improved, from the original 32.96 mg·cm -2 ·h -1 to 84.69 mg·cm -2 ·h -1 and the fog water collection efficiency is increased by 257%.

[0061] Example 7:

[0062] The preparation process is the same as that of Example 6, except that the ethanol solvent concentration for dispersing oxalic acid hydrolyzed chitin is 0%, 20%, 40%, 60%, 80%, 100%. Similarly, 0.02 g of dry weight of chitin is added to 10 ml of ethanol solutions with different concentrations respectively, and the pH is adjusted to 4 with 0.1 M HCl. After 5 min of ultrasonic fragmentation, an OAChN ethanol dispersion with a concentration of 0.2 wt% is obtained. Compare the OAChN dispersions dispersed with different ethanol concentrations with the TOCN and DEChN aqueous dispersions with the same solid content. Investigate the influence of different ethanol concentrations on the optical properties of the prepared OAChN nanofiber coating, such as Figure 2 . At the same time, in order to obtain a uniform and flat coating, the viscosity relationship between the OAChN ethanol dispersion and the TOCN / DEChN aqueous dispersion was explored. Among them, the OAChN dispersion at 80% ethanol concentration has the most suitable viscosity with the TOCN / DEChN dispersion, which is more conducive to the uniformity and smoothness of spin coating, such as Figure 10 .

[0063] Example 8:

[0064] To ensure the smoothness and uniformity of the coating, it is necessary to prepare a spin-coating glue solution that is homogeneous, stable, and has complementary surface charge amounts. The preparation process is the same as that of Examples 1-3. 0.2 g of dry weight is dispersed in 10 ml of solvent. The feature is that the dispersion concentrations of the three raw materials are all diluted to 0.1 wt%, and at the same time, dispersions are prepared in two environments with pH 4 and pH 7 respectively, and ultrasonically treated for 2 min each. The resulting homogeneous systems are used for the determination of the zeta potential. The results show that OAChN and DEChN have electrokinetic potentials of +31 mV and +61 mV respectively at pH 4, and have good dispersion, while TOCN has an electrokinetic potential of -71 mV at pH 7 and can also be well dispersed. The two opposite charges can promote the overlap between fibers. However, if the absolute values of the electrokinetic potentials differ too much, it is easy to cause flocculation of the coating. Therefore, the purpose of this step is to determine a pair of matching electrokinetic potentials to ensure the uniformity and smoothness of the spin-coated coating, as Figure 2 .

[0065] Example 9:

[0066] To separately explore the performance of the transition layer coating, the OAChN ethanol dispersion in the raw materials of Example 1 is used as the spin-coating glue solution. The preparation process is the same as that of Example 6, except that only different numbers of layers of the transition layer are spin-coated. First, fix the PLA hydrophobic substrate on a 5 cm × 5 cm glass plate. This step can be achieved by simply wetting and then removing the vacuum; adjust the spin-coating parameters, including: deposition time of the OAChN ethanol dispersion of 30 s; initial rotation speed of 500 r / min; acceleration of the rising speed of 1000 r / min 2 , lasting for 5 s; spin-coating speed of 2500 r / min, lasting for 40 s; deceleration acceleration of 500 r / min 2 , lasting for 10 s until the rotation speed becomes 0 r / min. The films spin-coated with (1, 5, 10) layers are fixed in an oven at 30 °C for 12 h to obtain PLA films with different numbers of layers of the transition layer. Examine their mechanical properties and surface water contact angles. It shows that the extremely thin thickness of the coating basically does not affect the mechanical properties of the substrate, and the water contact angle decreases with the increase of the coating, as Figure 3 .

[0067] Example 10:

[0068] The preparation process is the same as that of Example 6, except that: adjust the dispersion concentration (0.1 wt%, 0.2 wt%, 0.3 wt%), the maximum spin-coating speed (1000 r / min, 2500 r / min, 4000 r / min), and the number of layers (1 layer, 5 layers, 10 layers), and test their light transmittance, water contact angle, and mechanical properties. The results are shown in Table 1.

[0069] Table 1. Light transmittance, water contact angle, and mechanical properties of OAChN-coated PLA films

[0070]

[0071] Example 11:

[0072] The preparation process is the same as that of Example 6, except that infrared characterization is carried out with different numbers of layers. The same spin-coating parameters as in Example 8 are adopted: depositing the nanofiber aqueous dispersion for 30 s, with an initial rotation speed of 500 r / min; the acceleration of speed increase is 1000 r / min 2 , lasting for 5 s; the spin-coating speed is 2500 r / min, lasting for 40 s; the deceleration acceleration is 500 r / min 2 , lasting for 10 s until the rotation speed becomes 0 r / min. Each round of spin-coating of TOCN and DEChN is recorded as 1 layer, and this cycle is repeated. The films obtained by spin-coating 1 layer, 10 layers, and 30 layers are fixed at 30 °C for 12 h to obtain PLA films with hydrophilic layers. The surface chemical structure of the above films is characterized by infrared spectroscopy. It shows that the increase of the coating can be manifested by the enhancement of infrared characteristic peaks, such as Figure 4 .

[0073] Example 12:

[0074] The preparation process is the same as that of Example 6, except that the number of spin-coated hydrophilic layers is changed to investigate the cross-sectional microstructure of the film. Spin-coating parameters: depositing the nanofiber aqueous dispersion for 30 s, with an initial rotation speed of 500 r / min; the acceleration of speed increase is 1000 r / min 2 , lasting for 5 s; the spin-coating speed is 2500 r / min, lasting for 40 s; the deceleration acceleration is 500 r / min 2 , lasting for 10 s until the rotation speed becomes 0 r / min. The cross-sectional microstructure and coating thickness of the film are characterized by SEM, such as Figure 5 .

[0075] Example 13:

[0076] The preparation process is the same as that of Example 6, except that the number of spin-coated hydrophilic layers is changed to investigate the surface roughness of the film. Spin-coating parameters: depositing the nanofiber aqueous dispersion for 30 s, with an initial rotation speed of 500 r / min; the acceleration of speed increase is 1000 r / min 2 , lasting for 5 s; the spin-coating speed is 2500 r / min, lasting for 40 s; the deceleration acceleration is 500 r / min 2 , lasting for 10 s until the rotation speed becomes 0 r / min. The surface microstructure of the film is characterized by AFM and the surface roughness is measured, such as Figure 6 .

[0077] Example 14:

[0078] The preparation process was the same as that of Example 6, except for the change in the number of spin-coated layers. The effects of different numbers of layers on the surface roughness, water contact angle, and mechanical properties of the film were investigated. Spin-coating parameters: depositing the nanofiber aqueous dispersion for 30 s, initial rotation speed 500 r / min; acceleration for speed increase 1000 r / min 2 , lasting for 5 s; spin-coating speed 2500 r / min, lasting for 40 s; deceleration acceleration 500 r / min 2 , lasting for 10 s until the speed became 0 r / min. The specific performance results are shown in Table 2. Meanwhile, SEM photos of the PLA film surface between nanofibers with and without a hydrophilic layer were compared, the relationship between the number of coating layers and the coating thickness (such as Figure 12 ) and the relationship between the coating thickness / layer number and the surface water contact angle (such as Figure 5 ). The results show that with the increase in the number of coatings, the coating thickness increases linearly, and the water contact angle on the coating surface gradually decreases, showing the hydrophilic property of TOCN, decreasing from the original water contact angle of 98° to 37°.

[0079] Table 2. Surface properties of PLA films with different numbers of hydrophilic nanofiber layers

[0080]

[0081] Example 15:

[0082] The preparation process was the same as that of Example 6, except for the change in the number of spin-coated layers. The effects of different numbers of layers on the light transmittance and thermal stability of the film were investigated. Spin-coating parameters: depositing the nanofiber aqueous dispersion for 30 s, initial rotation speed 500 r / min; acceleration for speed increase 1000 r / min 2 , lasting for 5 s; spin-coating speed 2500 r / min, lasting for 40 s; deceleration acceleration 500 r / min 2 , lasting for 10 s until the speed became 0 r / min. The prepared film was tested for its optical properties and thermal stability properties. As the number of coating layers increased, the light transmittance of the film remained above 80%, showing good light transmittance performance, and the thermal decomposition temperature did not decrease, indicating that the coating had basically no effect on the basic optical and thermal stability properties of PLA, as shown in Figure 7 .

[0083] Example 16:

[0084] Take the film in Example 6, with the difference that (5, 10, 30) layers of hydrophilic layers are set for comparison of the fog water collection performance. Control the fog water collection conditions, fix the fog water collector film on a special bracket, place the beaker for collecting fog water directly below the test sample, and enclose all devices with an acrylic plate box to balance the humidity of the test environment. To promote the transportation of water droplets on the film, a small incision about 0.5 cm long was made under the sample film with a knife for drainage. The fog flow rate was controlled at 15 cm·s -1 , collect fog water for 1 h, measure the water mass in the beaker, and calculate the efficiency of collecting fog water. In addition, the water mass captured on the coating surface was weighted. Compared with the simple PLA film, the water collection efficiency of the nanofiber coating was greatly improved, from the original 32.96 mg·cm -2 ·h -1 (0 layers) to 90.85 mg·cm -2 ·h -1 (30 layers), and the fog water collection efficiency increased by 276%, as shown in Figure 8 . Among them, the fog water collection efficiency at 5 layers was 55.91 mg·cm -2 ·h -1 , and the fog water collection efficiency at 10 layers was 84.69 mg·cm -2 ·h -1 . The whole process of the fog water collection comparison experiment is as shown in Figure 13 .

[0085] Example 17:

[0086] The contact angle hysteresis was measured during the process of Example 16. By regularly measuring the advancing angle and receding angle of water droplets on the surface of the fog water collector film, the absolute value of the difference between the two is the hysteresis angle. The fog water collector film was taken out regularly and placed vertically. Relying on the action of gravity, the retention of water droplets on the film was photographed through side focusing, and the sizes of the upper and lower water contact angles were calculated to obtain the size of the water contact angle hysteresis on the surface of the fog water collector film at that moment. As time goes by, the hydrophobic water contact angle hysteresis of the simple PLA film continuously increases, which hinders the flow of water droplets on the film and reduces the fog water collection efficiency. While the water contact angle hysteresis of the fog water collector film with a hydrophilic coating continuously decreases until it reaches 0°, enabling the water droplets to flow easily on the surface, as shown in Figure 9 .

[0087] Example 18:

[0088] Adopt the same process and raw materials as in Example 6, with the difference that the positively charged DEChN is replaced by the SNF in Example 4. The concentration of the SNF aqueous dispersion is 0.2 wt%, the spin-coating parameters remain unchanged, and 30 layers are spin-coated. The results show that the water contact angle of the obtained coating is 43.7° ± 2.13, the surface roughness is 3.62 ± 1.28 nm, and the fog water collection efficiency reaches 85.88 mg·cm-2·h-1 , good fog water collection effect can still be achieved.

[0089] Similarly, using the same process and raw materials as in Example 6, the difference is that the negatively charged TOCN is replaced with SNF in Example 4. The concentration of the SNF aqueous dispersion is 0.2 wt%, the spin-coating parameters remain unchanged, and 30 layers are spin-coated. The results show that the water contact angle of the obtained coating is 54.7° ± 1.53, the surface roughness is 2.64 ± 0.98 nm, and the fog water collection efficiency reaches 78.48 mg·cm-2·h -1 , and still has a good fog water collection effect.

[0090] Example 19:

[0091] The amphoteric nanofibers that can be used as the transition layer in the present invention can also be: esterified chitin nanofibers and esterified cellulose nanofibers: such as lactic acid-modified chitin nanofibers LA-ChN (preparation method reference: SARAVANA PS. Carbohyd Polym, 2018, 195: 622-30) and formic acid-modified chitin nanofibers FA-ChN (preparation method reference: CHEN H. Carbohyd Polym, 2022, 283: 119138), lactic acid-modified cellulose nanofibers LA-CNF (preparation method reference: LIU S. Carbohyd Polym, 2021, 251: 117018) and formic acid cellulose fibers FA-CNF (preparation method reference: SUN Y. Energy & Fuels, 2007, 21(4): 2386-9) and other esterified derivatives (preparation method reference: JIANG J. Journal of Agricultural and Food Chemistry, 2018, 66(43): 11372-9; WANG R. Cellulose, 2017, 24(12): 5443-54; MA H. Biomacromolecules, 2021, 22(10): 4373-82, etc.).

[0092] Using the method of Example 6, replacing the transition layer with the above esterified chitin nanofibers and esterified cellulose nanofibers, it was found that they could be dispersed in an 80% ethanol system and could be deposited on the PLA substrate. The water contact angle of the surface of the lactic acid-modified chitin nanofiber coating was 78°, the water contact angle of the surface of the formic acid-modified chitin nanofiber coating was 67°, the water contact angle of the surface of the lactic acid-modified cellulose nanofiber coating was 51°, and the water contact angle of the surface of the formic acid-modified cellulose nanofiber coating was 47°. This shows that the above lactic acid-modified chitin nanofibers, formic acid-modified chitin nanofibers, lactic acid-modified cellulose nanofibers, and formic acid-modified cellulose nanofibers can also successfully serve as transition layers and have good compatibility with hydrophobic PLA.

[0093] Using the SNF in Example 4, replacing the transition layer raw material with the amphoteric nanofiber SNF, and maintaining the same operating process as in Example 6, except that the SNF is dispersed in an aqueous phase system and the deposition time on the PLA substrate is increased to more than 3 min. The initial rotation speed is 500 r / min; the acceleration of speed increase is 1000 r / min 2 , lasting for 5 s; the spin coating speed is 2500 r / min, lasting for 40 s; the acceleration of speed decrease is 500 r / min 2 , lasting for 10 s until the speed becomes 0 r / min, and spin coating 10 layers. The result shows that the water contact angle changes from 98° to 61°, which is the surface wettability of the silk fibroin nanofiber film, indicating the feasibility of using SNF as a transition layer coating. In addition, the oxidized silk fibroin nanofibers and the silk fibroin nanofibers obtained by DES treatment can also achieve the above experiment.

[0094] Example 20:

[0095] The positively charged nanofibers of the functional layer can also be: polylysine-modified cellulose ε-PL-TOCN (prepared by the method of reference ZHANG S. Industrial Crops and Products, 2023, 194: 116288); the negatively charged nanofibers of the functional layer can also be: various oxidized celluloses such as laccase (TLO) / TEMPO (prepared by the method of reference JIANG J. ACS Publications. 2017: 191-201) or chitin nanofibers, oxalic acid (OA) / maleic acid (MA) and other binary acids (prepared by the method of reference MA H. Biomacromolecules, 2021, 22(10): 4373-82) and chitin or cellulose nanofibers treated with polybasic acids (prepared by reference CAMARERO ESPINOSA S. Biomacromolecules, 2013, 14(4): 1223-30); the hydrophobic substrate can also be: any one of polybutylene succinate (PBS), poly(propylene carbonate) (PPC) and polycaprolactone (PCL); the coating method is: spin coating, brush coating (prepared by the method of reference BUHL K B. Polymers, 2020, 12(7): 1475), spray coating (prepared by the method of reference AMINS. transfer, 2016, 2(4): 556-63), dip coating (prepared by the method of reference TANG X. Journal of Sol-Gel Science and Technology, 2017, 81: 378-404).

[0096] Consistent with Example 6, the difference is that different spin-coated nanofiber raw materials (nanofiber preparation methods are as described above), hydrophobic substrates and spin coating methods are changed, and different fog water collection effects as shown in Table 3 below are obtained through different combinations:

[0097] Table 3. Fog water collection effects of combinations between different substrates, raw materials and methods

[0098]

[0099] Comparative Example 1:

[0100] The experimental operation is the same as that of Example 8, the difference is that there is no connection of the OAChN intermediate layer. Coated 5 layers, 10 layers, and 30 layers respectively. As a result, hydrophilic TOCN and DEChN coatings cannot be deposited on the PLA surface, and the surface water contact angle is 95°, showing the original hydrophobic property of the PLA film. It shows that without a transition layer, it is very difficult to directly attach hydrophilic nanofibers to the PLA film surface, and a fog water collector cannot be prepared.

[0101] Comparative Example 2:

[0102] Replace the transition layer raw material with TOCN or DEChN aqueous dispersion, deposit for 30 s, 1 min, 5 min, the initial rotation speed of rotation is 500 r / min, and the acceleration of speed increase is 1000 r / min 2 , lasting for 5 s; the rotation speed of spin coating is 2500 r / min, lasting for 40 s; the acceleration of speed decrease is 500 r / min 2 , lasting for 10 s until the rotation speed becomes 0 r / min. The results show that deposition cannot occur on the surface of the hydrophobic PLA substrate. This is because there is a large surface tension between the hydrophilic nanofiber dispersion with a single charge on the surface and the hydrophobic PLA substrate surface, and the hydrophilic dispersion cannot fully contact the surface and deposit, resulting in the failure of spin coating.

[0103] Replace the transition layer raw material with TOCN or DEChN ethanol dispersion. When the ethanol concentration is 40 - 100%, both of them produce serious flocculation and cannot be dispersed. The flocculated nanocellulose cannot form a uniform and flat surface coating, and the result fails.

[0104] Comparative Example 3:

[0105] Dip coating comparison: Suspend PLA with a special device, place a 0.2 wt% OAChN dispersion dispersed in 80% ethanol below, immerse the suspended PLA film in the dispersion for 10 - 30 s, pull it out and dry it, then immerse it again, and cycle 10 times. The results show that OAChN nanofibers are successfully adsorbed on the surface of the PLA film.

[0106] According to the same steps above, alternately immerse the PLA film with an OAChN transition layer into 0.2 wt% TOCN and DEChN aqueous dispersions, the immersion time is 30 - 60 s, and cycle 30 - 50 times. The results show a significant thickening of the coating. However, the drying of the aqueous dispersion is extremely slow, the process takes a long time, and the immersion of the aqueous dispersion requires slow and strict control of time to avoid damage to the existing coating by water.

[0107] Comparative Example 4:

[0108] The influence of different pH on the spin - coating adhesive solution: During the spin - coating process, electrostatic interaction is considered to be the driving force for the deposition of nanofibrils in their dispersion. Use TOCN and DEChN dispersions with a larger pH span as the spin - coating adhesive solution, such as the combination of a TOCN dispersion with a pH of 8.5 and a DEChN dispersion with a pH of 2.5. Too large a surface charge difference will cause the dispersion to flocculate, resulting in a rough surface, as Figure 11 .

[0109] Legend analysis

[0110] Figure 1Structural composition diagram of the fog water collector membrane in Embodiment 5 of the present invention

[0111] Figure 2 Effect of different ethanol concentrations on the dispersibility and light transmittance of OAChN dispersion in Embodiment 8 of the present invention

[0112] It can be seen from the optical performance test data that OAChN is extremely unstable under 100% ethanol conditions and cannot be completely dispersed. While the ethanol solution with a concentration of 80% as the solvent not only has a high light transmittance (80%), the ability to maintain stable dispersion (+31 mV), but also can make the nanofibers in the transition layer carry a small amount of positive charge, which is conducive to the subsequent lamination and self-assembly with TOCN. Further, a high ethanol content helps the transformation from the Cassie state to the Wenzel state. The TOCN aqueous dispersion and the DEChN aqueous dispersion both show high surface potentials ( -70.9 and +60.5 respectively), which greatly promotes the layer-by-layer self-assembly between hydrophilic nanofibers.

[0113] Figure 3 Effect of different numbers of OAChN transition layers on the wetting performance of the film surface and the mechanical properties of the film in Embodiment 9 of the present invention

[0114] The results show that when spin-coating 5 layers, the water contact angle on the film surface is about 58°, and it basically remains unchanged above 5 layers, which is consistent with the hydrophilic nature of OAChN itself. Since the thickness of the nanofiber coating relative to the substrate is very small, the original mechanical properties of the PLA film are basically not affected.

[0115] Figure 4 Infrared characterization of different nanofiber coatings in Embodiment 11 of the present invention

[0116] The intermolecular interactions between coatings and between coatings and substrates were characterized by FITR. The absorption band around 3480 cm -1 is caused by the O-H stretching vibration, and the absorption band at 3400 - 3200 cm -1 is related to the symmetric and asymmetric stretching of -OH and -NH2 bonds in the chitin structure. Most hydroxyl groups form intermolecular hydrogen bonds and cooperate with electrostatic interactions to promote the self-assembly between layers. The vibration peak at 1745 cm -1 represents a large number of ester groups on the polylactic acid chain. The absorption peaks of the C=O stretching of the acetyl group (amide I) and the -NH bending and stretching (amide II) are detected at 1641 and 1550 cm -1 respectively. The superposition of the number of layers results in the appearance of nanofiber characteristic peaks, and the more the number of layers, the more obvious the nanofiber characteristic peaks.

[0117] Figure 5Comparison of the cross-sectional microtopography and water contact angle of the coatings in Examples 12 and 14 of the present invention.

[0118] The cross-sectional images of the scanning electron microscope (SEM) show the film thickness variation of each layer of the coating, and the evolution of the film thickness is obtained. As shown in the figure, within the experimental uncertainty range, with the increase in the number of deposition cycles, the coating thickness increases in a linear growth pattern, increasing by approximately 35.5 nm for each layer. Through the measurement of the water contact angle on the film surface, the water contact angle on the coating surface gradually decreases with the increase in the number of coating layers. Due to the connection of the transition layer OAChN, TOCN and DEChN dispersed in the aqueous phase can be deposited on the transition layer in the LBL manner, as shown in the figure. To verify that the nanofibers are indeed layer by layer, we specifically prepared the OAChN film by the suction filtration method, and then spin-coated the OAChN film with the TOCN and DEChN dispersions. Due to the uncut film, a clear layered structure can be seen. With the increase in the deposition thickness, the surface of the PLA film changes from hydrophobic (98°) to hydrophilic (37°). Finally, the wettability of the PLA film surface is consistent with that of the pure TOCN film (37°). On the other hand, the high water absorption of the nanofibers greatly improves the ability of the polylactic acid film to collect fog water.

[0119] Figure 6 Characterization of the microtopography and roughness of the coating surface in Example 13 of the present invention.

[0120] The AFM images show that the increase in the number of coating layers leads to a significant difference in the surface roughness RMS. The pure PLA film without the nanofiber coating is almost smooth, while the increase in the number of coating layers results in a smoother surface. Since the spin-coating method can maximize the uniformity and denseness of the coating, the obtained coating roughness difference is not large (RMS < 7 nm). With the increase in the number of spin-coating layers, the surface roughness of the coating decreases. The spin-coating process may be the reason for the continuous reduction of the surface roughness. The nanofibers can fill the pores layer by layer, improving the smoothness and denseness of the coating surface. The roughness of the spin-coated layer indicates that its surface can be considered smooth and uniform, which greatly improves the ability to collect fog water. It can also be seen from the images that the transition layer OAChN exists in the form of nanocrystalline rod-like structures, and both TOCN and DEChN spin-coated by electrostatic self-assembly exist in the form of nanofibers, which is related to the preparation method of the raw materials. The latter two treatments are relatively mild compared to the former, and the surface morphologies shown by the two coatings are significantly different, which also confirms the layer-by-layer stacking and covering of the coatings.

[0121] Figure 7 Effect of different numbers of layers on the optical properties and thermal stability of the PLA film in Example 15 of the present invention.

[0122] The PLA film is very transparent to visible light of 600 nm and above, with a transmittance as high as 91.2 ± 0.2%, as shown in the figure. On the other hand, in the entire wavelength range, the transmittance of the PLA film with a nanofiber coating is lower than that of the pure PLA film. The transmittances of the PLA-1L, PLA-10L, and PLA-30L films at 600 nm are 90.2 ± 0.5%, 89.2 ± 1.1%, and 86.5 ± 1.2% respectively. The transmittances are all above 85%, indicating that the surface coating has little effect on the transmittance of the substrate. The thermal stability of the sample films was evaluated by thermogravimetric analysis, and the obtained TGA and DTG temperature images are shown in the figure. The data show that the initial thermal decomposition temperature of the commercial polylactic acid film is 300 °C, which may be related to the molecular weight and the number of molecular chain end groups of the polylactic acid film. The thermal decomposition image of the PLA film after the nanofiber coating remains basically unchanged, proving that the coating basically does not affect the original thermal stability of the PLA film.

[0123] Figure 8 Schematic diagram of the fog water collection device and characterization of the fog water collection efficiency of the all-biomass-based fog water collector films with different numbers of layers in Example 16 of the present invention.

[0124] From the data of the fog water collection efficiency, it can be seen that the fog water collection efficiency of the polylactic acid film coated with 1 layer of nanofiber coating is 55.90 mg·cm -2 ·h -1 , the fog water collection efficiency of the polylactic acid film coated with 10 layers of nanofiber coating is 84.69 mg·cm -2 ·h -1 . The collection efficiency of the polylactic acid film coated with 30 layers of nanofiber coating reaches 90.85 mg·cm -2 ·h -1 , which is 276% higher than the fog water collection efficiency of the pure polylactic acid film (32.96 mg·cm -2 ·h -1 ). Due to the surface hydrophobicity, a large number of water droplets are formed on the surface of the uniform PLA film, resulting in the largest water storage capacity on the film (15.01 mg·cm -2 ·h -1 ). At the same time, due to the water storage effect of the hydrophilic nanofibers, the water storage capacity of 30 layers of nanofibers is (9.27 mg·cm -2 ·h -1 ), exceeding the water storage capacity of 1 layer (2.30 mg·cm -2 ·h -1 ) and the water storage capacity of 10 layers (4.15 mg·cm -2 ·h -1) It can be seen that the water storage capacity of the film is closely related to the coating thickness. From the photos of the fog water collection process in the figure, it can also be seen that there are obvious differences in the shape and size of the droplets on the film with the hydrophilic nanofiber coating and the film without the hydrophilic nanocellulose coating. It can be clearly seen that the nanofiber coating can completely absorb the moisture on the film surface, prevent the formation of water droplets on the film surface, and greatly reduce the retention of water droplets on the film.

[0125] Figure 9 This is the measurement of the water contact angle hysteresis at different times in Example 17 of the present invention.

[0126] A lower contact angle hysteresis promotes the water collection process; however, a higher contact angle also represents a higher contact angle hysteresis, causing the fog water to stay on the film surface in the form of water droplets, hindering the flow of humid air and resulting in a lower collection efficiency. For a uniform hydrophilic surface, once the water droplets aggregate, they will immediately spread to the hydrophilic surface and form a thin water film in a short time, which is called film-level condensation. This uniform surface water film reduces the hysteresis of the surface contact angle. On the contrary, the PLA film without the hydrophilic nanofiber coating cannot form a water film due to its hydrophobic surface, and the fog water can only continuously accumulate on the film surface to form water droplets. The larger the water droplets, the more obvious the contact angle hysteresis phenomenon. As shown in the figure, during the collection process, the contact angle hysteresis of our nanofiber coating continuously decreases, improving the efficiency of fog water collection.

[0127] Figure 10 This is the comparative characterization of the viscosities of the OAChN dispersion, TOCN, and DEChN aqueous dispersions dispersed in different ethanol concentrations in Example 7 of the present invention.

[0128] By comparing the effects of ethanol solvents with different concentrations on the viscosity of chitin oxalate and the viscosities of the TOCN and DEChN dispersions, it is concluded that the most suitable viscosity between TOCN and DEChN can ensure the uniformity of each coating.

[0129] Figure 11 This is the photo of the film obtained with different pH combinations in Comparative Example 4 of the present invention.

[0130] On the one hand, when depositing the coating using a spin coater, the nanofibers in the coating should be fully charged, otherwise the electrostatic bonds cannot be fully established; on the other hand, too large a surface charge difference will cause the dispersion to flocculate, resulting in a rough surface. Therefore, in order to ensure the surface charge and dispersibility of the two types of nanofibers, pH coordination was carried out, and it was found that DEChN pH = 4 and TOCN pH = 7 are optimal.

[0131] Figure 12 This is the supplementary data of Example 14 of the present invention.

[0132] One of them is the linear fitting growth diagram of the coating thickness with the number of layers.

[0133] Another group shows SEM surface morphology images of uncoated nanofibers and SEM surface morphology images of coated nanofibers.

[0134] Figure 13 These are the photos of the whole process of the fog water collection comparison test in Example 16 of the present invention.

Claims

1. A preparation method of a fully biomass-based fog water collector, characterized in that, It includes the following steps: (1) Coating an intermediate transition layer on a hydrophobic biomass-based polymer substrate, wherein the coating solution of the intermediate transition layer is an ethanol / water dispersion of amphoteric nanofibers, and the amphoteric nanofibers are nanofibers with both positive and negative charges on the surface; (2) Continuing to alternately coat negatively charged surface nanofibers and positively charged surface nanofibers on the above transition layer, and curing in an oven at 20-40 °C for 6-24 h to construct an amphiphilic all-biomass-based fog water collector film containing both hydrophilic nanofibers and hydrophobic polymers.

2. The preparation method of a fully biomass-based fog water collector according to claim 1, characterized in that, The source of the nanofibers is any one or a combination of at least two of chitin nanofibers, cellulose nanofibers, and silk fibroin nanofibers; the length of the nanofibers is 50-5000 nm, and the width is 3-50 nm; the hydrophobic biomass-based polymer is any one of polylactic acid, polybutylene succinate, poly(propylene carbonate), and polycaprolactone; the coating method is any one of spin coating, brush coating, spray coating, and dip coating.

3. The preparation method of a fully biomass-based fog water collector according to claim 2, characterized in that, The preparation method of the nanofibers is to prepare nanofibers by mechanical treatment or pretreatment and mechanical treatment of chitin or cellulose or silk fibroin raw materials; the pretreatment method of chitin raw materials is at least one of alkaline partial deacetylation, enzymatic partial deacetylation, TEMPO oxidation, DES treatment, and acid hydrolysis; the pretreatment method of cellulose raw materials is at least one of TEMPO oxidation, laccase oxidation, DES treatment, and acid hydrolysis; the pretreatment method of silk fibroin raw materials is at least one of laccase oxidation, alkali treatment, DES treatment, and acid hydrolysis; the mechanical treatment method is at least one of ultrasonic treatment, colloid mill treatment, high-pressure homogenization treatment, and ultrafine grinding treatment.

4. A preparation method of a fully biomass-based fog water collector according to claim 3, characterized in that, In step (1), the amphoteric nanofibers are at least one of lactic acid-modified chitin nanofibers, formic acid-modified chitin nanofibers, oxalic acid-modified chitin nanofibers, lactic acid-modified cellulose nanofibers, formic acid cellulose nanofibers, oxalic acid-modified cellulose nanofibers, and silk fibroin nanofibers.

5. A preparation method of a fully biomass-based fog water collector according to claim 4, characterized in that, In step (1), the concentration of the amphoteric nanofiber dispersion is 0.1 wt%-5.0 wt%, and the concentration of the ethanol solvent is 50-80%.

6. A method for preparing a fully biomass-based fog water collector according to claim 2, characterized in that, The hydrophobic substrate is fixed on the glass plate; the spin-coating conditions for the transition layer are as follows: the deposition time of the ethanol-water dispersion of amphoteric nanofibers is 20 - 60 s; the initial rotation speed is 200 - 1000 r / min; the acceleration of speed increase is 200 - 1000 r / min 2 , lasting for 5 - 30 s; the spin-coating speed is 1000 - 4000 r / min, lasting for 30 - 60 s; the acceleration of speed decrease is 500 - 1000 r / min 2 , until it stops, and 5 - 30 layers are spin-coated.

7. A method for preparing a fully biomass-based fog water collector according to claim 6, characterized in that, The transition layer is oxalic acid-hydrolyzed chitin nanofibers. In step (2), negatively charged oxidized cellulose nanofibers and positively charged deacetylated chitin nanofibers are alternately spin-coated on the transition layer in sequence. Defining one alternate spin-coating as one layer, a total of 5-100 layers are spin-coated.

8. The method for preparing an all-biomass-based fog water collector according to claim 7, characterized in that, Among them, the pH of the oxalic acid-hydrolyzed chitin nanofiber dispersion is 3-5, and the zeta potential is 30-60 mV; the pH of the oxidized cellulose nanofiber dispersion is 6-8, and the zeta potential is -30~-80 mV; the pH of the deacetylated chitin nanofiber dispersion is 3-5, and the zeta potential is 30-80 mV. The concentration of the nanofibers is all 0.1 wt%-5.0 wt%.

9. A fully biomass-based fog water collector, characterized in that, Prepared by the preparation method of an all-biomass-based fog water collector according to any one of claims 1-8; the Young's modulus of the film is 1800-2300 MPa; the thickness of the nanofiber coating is 1.0-5.0 μm; The surface of the nanofiber coating tends to be smooth, with a roughness of 0.06 - 7.00 nm; the film has two-sided wettability, with a water contact angle of 35 - 60° on the hydrophilic side and 90 - 110° on the hydrophobic side; the fog water collection efficiency of the film is 55.9 - 90.9 mg·cm -2 ·h -1 .

10. Use of the all-biomass-based fog water collector prepared by the method for preparing an all-biomass-based fog water collector according to any one of claims 1-8, or the all-biomass-based fog water collector according to claim 9, in the fields of fog water collection, medicine, optics, electricity, environmental protection, packaging, adsorption or composite materials.

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