CN110669249B - Preparation method of super-amphiphobic nano cellulose aerogel - Google Patents
Preparation method of super-amphiphobic nano cellulose aerogel Download PDFInfo
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Abstract
The invention discloses a preparation method of super-amphiphobic nano cellulose aerogel, and belongs to the technical field of high polymer materials. The invention relates to nano-cellulose prepared by a TEMPO oxidation method and
method for preparing nano SiO2Preparing a mixed suspension by taking the particles as a raw material, injecting the mixed suspension into a mold, freezing the mixed suspension in liquid nitrogen, and then freezing and drying the mixed suspension at a low temperature to obtain the nano-cellulose aerogel; through a chemical vapor deposition method, the THFOS is utilized to carry out lyophobic modification on the surface of the obtained nano-cellulose aerogel, and finally the super-amphiphobic nano-cellulose aerogel is obtained, wherein the average contact angle of water, castor oil and hexadecane of the obtained super-amphiphobic nano-cellulose aerogel reaches 166 degrees, 157 degrees and 150 degrees, and the super-amphiphobic nano-cellulose aerogel has the common characteristics of super-amphiphobic materials such as water resistance, oil resistance and the like, and has a good industrial application prospect.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation method of super-amphiphobic nano cellulose aerogel.
Background
The nano-cellulose aerogel is obtained by replacing water in gel on the premise of not changing a gel network and volume, is a known solid material with ultra-light weight and extremely high porosity, has unique performances such as high specific surface area, low thermal conductivity, high adsorbability and low dielectric constant, is considered as a third generation new aerogel following inorganic aerogel and synthetic polymer aerogel, and is widely applied to the fields of sound and heat insulation materials, adsorption materials, drug slow release, sensors, energy storage and the like.
A large amount of free hydroxyl exists at C2, C3 and C6 positions on the surface of the nano-cellulose, and the strong polarity of the hydroxyl enables the nano-cellulose to easily absorb water; on the other hand, a large number of hydrogen bonds exist in molecules and among molecules of the nano-cellulose, and the surface tension of the nano-cellulose is larger due to the existence of the hydrogen bonds, so that the nano-cellulose or the nano-cellulose-based material has strong hydrophilicity. The nano-cellulose material has a limited range of applications due to its own hydrophilicity. If the nano-cellulose aerogel is used in a humid environment, it absorbs water vapor in the air to cause collapse of the gel structure, which affects the final use effect.
In order to meet the requirements of practical application, the nano cellulose aerogel needs to be subjected to lyophobic modification treatment. Hydrophobic modification of nanocellulose aerogels has become a current focus of research. Mulyadi and the like use styrene-acrylic acid to hydrophobically modify Cellulose Nanofiber (CNF), and finally obtain hydrophobic aerogel for oil absorption material application, wherein the water contact angle of the hydrophobic aerogel can reach 149 degrees, the adsorption capacity of the hydrophobic aerogel on oil reaches 47 times of the self-mass, but the water absorption capacity is extremely low (less than 0.5g/g aerogel) (Mulyadi A, Zhang Z, Deng Y, Fluorine-free oil absorbents from cellulose nanofiber aerogels [ J].ACS applied materials&interfaces, 2016, 8 (4): 2732-2740.). Zhou et al use SiO2Adding nanoparticles into a suspension of NFC, stirring, adding methyltrimethoxysilane (MTMS) into the mixed solution as a low surface energy agent to prepare the NFC aerogel with the hydrophobic angle of 168.4 degrees for oil/water separation (J. Superhydrophilic cellular nanoparticle-assisted aerogels for high affinity water-in-oil emulsions separation)]ACS Applied Nano Materials, 2018, 1 (5): 2095-2103.). Gao et al prepared Superhydrophobic nanocellulose Aerogels by coating octadecylamine onto the NFC surface using polydopamine as a linking carrier between NFC and octadecylamine (Gao R, Xiao S, Gan W, et al, muscle additive-induced Design of Superhydrophobic Nanofibrated Cellulose Aerogels for Oil/Water Separation [ J]. ACS Sustainable Chemistry&Engineering，2018，6(7)：9047-9055.)。
However, superhydrophobic surfaces may still be contaminated with low surface energy oils in practical use. Therefore, the nano-cellulose aerogel is further endowed with super-oleophobic performance on the basis of super-hydrophobicity, and the prepared super-amphiphobic surface (the surface with contact angles of both water and oil reaching more than 150 degrees) can really realize self-cleaning effect and has the performances of water resistance, oil repellency, pollution resistance, corrosion resistance and the like. The research on the super-hydrophobic nano-cellulose aerogel has been reported in a large amount, and the research on the super-amphiphobic nano-cellulose aerogel has hardly been reported. Therefore, the research for developing the super-amphiphobic nano cellulose aerogel has important significance.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a preparation method of a super-amphiphobic nano cellulose aerogel so as to prepare the super-amphiphobic nano cellulose aerogel with high water resistance and oil resistance.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a preparation method of super-amphiphobic nano cellulose aerogel comprises the following steps: mixing nano cellulose solution and nano SiO2Mixing the solutions, injecting the solutions into a mold, freezing the solutions in liquid nitrogen, and then freezing and drying the solutions at a low temperature to obtain the nano-cellulose aerogel with the multistage micro-nano structure; and (3) carrying out lyophobic modification on the surface of the obtained nano-cellulose aerogel by using a fluorine-containing silane reagent through a Chemical Vapor Deposition (CVD) method to obtain the super-amphiphobic nano-cellulose aerogel.
Preferably, the concentration of the nanocellulose solution is 1.5 wt%.
Preferably, the nano SiO2The solids content of the solution was 7.0% by weight.
Preferably, the nano SiO2The solid content of the solution was 10% of the solid content of the nanocellulose solution.
Preferably, the fluorosilane reagent is Trichloro (1H, 1H, 2H, 2H-heptadecafluorodecyl) silane (Trichloro (1H, 1H, 2H, 2H-heptadecafluorodecyl) silane, THFOS).
Preferably, the mold consists of a polyethylene (Poly (ethylene, PE) plastic frame and stainless steel clamping plates, and the plastic frame is clamped by two stainless steel clamping plates from two sides to form a mold with the length of 4cm, the width of 2cm and the depth of 0.2 cm.
Preferably, the time for freezing in the liquid nitrogen is 3-10 min, and the specific conditions of freeze drying under the low-temperature condition are as follows: freeze-drying at-91 deg.C under 0.6Pa for 72 h.
Preferably, the chemical vapor deposition method is: putting a glass bottle containing THFOS into a small beaker, putting the nano-cellulose aerogel sample on the small beaker, and then inversely placing a large beaker to cover the small beaker; in a vacuum drying oven, under the condition of 100 ℃, as the vacuum degree is reduced, THFOS volatilizes and diffuses into a gap between a glass bottle and a beaker to react with the nano-cellulose aerogel for a period of time.
Preferably, the preparation method of the nano-cellulose solution comprises the following steps: soaking dried fiber pulp in deionized water, adding 2, 2, 6, 6-tetramethylpiperidine nitrogen oxide (2, 2, 6, 6-tetramethyll-1-piperidinyloxy, TEMPO) and NaBr, stirring and mixing uniformly, then adding NaClO solution for oxidation reaction, adjusting pH value by using NaOH solution in the reaction to maintain the pH value between 10 and 10.5 until the pH value is not reduced, and adding ethanol to stop the reaction; and (3) filtering the reacted slurry, soaking the slurry in HCl solution, acidifying and washing, quantifying, adjusting pH, and performing ultrasonic treatment to obtain the nano cellulose solution.
Preferably, the nano SiO2The preparation method of the solution comprises the following steps: adding ammonia water and ethanol into the reactor, stirring, adding Tetraethoxysilane (TEOS), stirring for reaction, and reacting to obtain white SiO2Adding water into the solution, centrifugally washing, and dispersing in water to obtain the nano SiO2And (3) solution.
Has the advantages that: compared with the prior art, the invention has the advantages that:
(1) the preparation method of the super-amphiphobic nano cellulose aerogel provided by the invention takes NFC as a raw material, and by adjusting the density of the aerogel and loading SiO2Nano particles, a multi-stage micro/nano coarse structure of the nano cellulose aerogel is constructed and optimized, and the nano cellulose base with the micro/nano coarse structure is preparedThe super-amphiphobic nano cellulose aerogel material with oil/water contact angles larger than 150 degrees is realized by combining vapor deposition fluorosilane reagent;
(2) according to the preparation method of the super-amphiphobic nano cellulose aerogel, the used fluorosilane reagent THFOS has extremely low surface energy, and is a good fluorosilane reagent for constructing a low-energy surface. Since the hydroxyl groups of NFC can react with THFOS to form covalent Si — O bonds, NFC aerogels can undergo fluorination reactions with THFOS by chemical vapor deposition. The use of the chemical vapor deposition method avoids the direct contact between the aerogel and the liquid fluorosilane, and the original shape and the inherent structure of the aerogel are reserved;
(3) the preparation method of the super-amphiphobic nano cellulose aerogel provided by the invention is characterized in that SiO is loaded in the aerogel2Nanoparticles optimize the micro/nano-roughness structure of NFC aerogels and SiO2The nano particles have higher reactivity with THFOS in the CVD process, so that the success and effective deposition of the THFOS on the NFC aerogel are enhanced, and the surface of the aerogel has high water-repellent and oil-repellent properties;
(4) according to the preparation method of the super-amphiphobic nano cellulose aerogel, liquid nitrogen is adopted for freezing, the rapid cooling of NFC in the liquid nitrogen is accompanied with the formation of amorphous ice crystals, so that the aerogel has a more uniform porous structure with a smaller pore diameter, and a stainless steel/polyethylene composite die (4cm multiplied by 2cm multiplied by 0.2 cm) adopted for preparing the aerogel has the advantages that the non-uniformity in the liquid nitrogen rapid freezing process is solved due to the good heat-conducting property of a stainless steel metal plate and the thickness of only 2mm, the ideal pore structure of the aerogel is ensured, and meanwhile, the flat surface of the metal plate endows the aerogel sample with good surface smoothness and uniformity;
(5) the super-amphiphobic nano cellulose aerogel obtained by the preparation method of the super-amphiphobic nano cellulose aerogel provided by the invention has average contact angles to water, ethylene glycol, castor oil and hexadecane respectively as high as 166 degrees, 162 degrees, 157 degrees and 150 degrees, so that the super-amphiphobic nano cellulose aerogel has the common characteristics of waterproof, oil-repellent and other super-amphiphobic materials, and has a simple preparation process and a good industrial application prospect.
Drawings
FIG. 1 is a schematic view of an aerogel mold structure and its use;
FIG. 2 is an infrared spectrum of NFC, FNA1.5 and FNSA 1.5;
FIG. 3 is an XPS spectrum of NFC, FNA0.5 and FNSA 1.5; panel (a) is an XPS spectrum of NA1.5, FNA1.5 and FNSA 1.5; graphs (b, c) correspond to high resolution XPS spectra for F1 s and Si 2p, respectively, for FNA 1.5; graphs (d, e, f) are C1 s high resolution XPS spectra for NA1.5, FNA1.5 and FNSA1.5, respectively;
FIG. 4 is an FE-SEM micrograph of different substrates: (a) FGS; (b) FNM; (c) FFP; (d) FNA 1.5;
FIG. 5 is a graph of density of aerogels made by NFC at different concentrations and contact angle data for various liquids;
FIG. 6 is an FE-SEM electron micrograph of aerogel with different densities: (a) FNA 0.5; (b) FNA 1; (c) FNA 1.5; (d) FNA 2;
FIG. 7 is a graph of the results of SEM analysis and contact angle measurements of FNA1.5 and FNSA 1.5; (a) FE-SEM photograph of FNA 1.5; (b) FE-SEM photograph of FNSA 1.5; (c) graph of contact angle data for five liquids at FNA1.5 and FNSA 1.5; (d) are photographs of the contact angles of water and castor oil on the surfaces of FNA1.5 and FNSA 1.5.
Detailed Description
The invention is further described with reference to specific examples.
Experimental materials: the pulp sheet is a bleached softwood pulp sheet purchased from Taisen Bo paper industry Co., Ltd, east Asia, and the remaining chemicals are either analytically pure or chemically pure.
Example 1: preparation of nanocellulose aerogel
(1) Preparation of Nanocellulose (NFC) by TEMPO oxidation: the nano-cellulose is prepared by a TEMPO oxidation method. Firstly, soaking a pulp board in water, obtaining pulp after defibering, taking 10g of absolutely dry fiber pulp, soaking the absolutely dry fiber pulp in 500mL of deionized water, sequentially adding TEMPO (0.16g) and NaBr (1.6g), and continuously and mechanically stirring at room temperature to uniformly mix the pulp. Then, 120mL of NaClO (6.6 wt%) solution was added to start the oxidation reaction. The pH value of the whole reaction system is maintained between 10 and 10.5 by adjusting the pH value by using 2mol/L NaOH during the reaction process until the pH value does not drop any more, and 50mL of ethanol is added to stop the reaction. And (3) filtering the reacted slurry, soaking the slurry in 0.1mol/L HCl solution, acidifying and washing, and repeating the steps of washing and filtering for three times. Quantifying the washed pulp to 1.0 wt%, adjusting the pH value of the quantified solution to 10 again, and finally carrying out ultrasonic treatment for 15min under ultrasonic waves to obtain a uniform and transparent nano cellulose solution. A portion of 1.0 wt% NFC raised the concentration to 2.0 wt% by means of rotary evaporation. 0.5 wt% of NFC was obtained by diluting 1.0 wt% and 1.5 wt% was obtained by diluting 2 wt% of NFC.
(2)
Method for preparing nano SiO2And (3) particle: SiO 22Nanoparticles through classical
The preparation method comprises the following specific steps: ammonia (4.5mL) and ethanol (50mL) were added to a 100mL three-necked flask, and after stirring mechanically, TEOS (4.5mL) was added to the mixture to start the reaction, and the whole reaction was stirred at room temperature for 2 hours until the reaction was complete. The obtained white SiO2The solution was washed centrifugally with water, the washing was repeated 3 times, and then SiO was added2Dispersed in water to a solids content of 7.0 wt.%.
(3) NFC aerogel and NFC/SiO2Preparing the composite aerogel: manufacture of NFC aerogel and NFC/SiO using mold2And (3) compounding the aerogel. The structure of the mold is shown in fig. 1, the mold is composed of a PE plastic frame and a stainless steel clamping plate, the PE plastic frame is used for adjusting the size of the mold (the internal dimension is 4cm multiplied by 2cm multiplied by 0.2 em), and the stainless steel clamping plate provides a flat surface and good heat conductivity, so that the flatness and uniformity of the surface of the aerogel are guaranteed. When the PE plastic frame is used, the upper surface and the lower surface of the PE plastic frame are clamped by stainless steel clamping plates to form a die with the length of 4cm, the width of 2cm and the depth of 0.2 cm.
Respectively injecting the prepared NFC suspension of 0.5 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt% into a mold, fixing the mold by using a metal clamp, and completely immersing in liquid nitrogen for freezing for 5 min. And transferring the frozen NFC sample to a freeze dryer, and freeze-drying for 72h at-91 ℃ and 0.6Pa to obtain NFC aerogels prepared in different concentrations, wherein the NFC aerogels are respectively named as NA0.5, NA1, NA1.5 and NA 2.
Mixing SiO2(7.0 wt%) was added to NFC (1.5 wt%) to form a mixed solution, SiO added2The oven dry mass is 10% of the oven dry mass of NFC. Stirring the mixed solution on a magnetic stirrer for 2h until the mixed solution is uniform, injecting the mixed solution into a mold, fixing the mold by using a metal clamp, and completely immersing the mold in liquid nitrogen for freezing for 5 min. Transferring the frozen sample to a freeze dryer, and freeze-drying for 72h at-91 ℃ and 0.6Pa to obtain NFC/SiO2Aerogel, named NSA 1.5.
(4) Chemical vapor deposition of aerogel substrate: and (3) carrying out lyophobic modification on the surface of the aerogel by adopting a chemical vapor deposition method. A5 mL glass bottle containing 200. mu.L of trichloro (1H, 1H, 2H, 2H-heptadecafluorodecyl) silane (THFOS) was placed in a 50mL beaker, the aerogel sample was placed on a small beaker, and a 250mL large beaker was inverted over the small beaker. The reaction is carried out for 3h in a vacuum drying oven, and under the condition of 100 ℃, THFOS volatilizes and diffuses into a gap between a glass bottle and a beaker along with the reduction of the vacuum degree, and reacts with the nano-cellulose aerogel. The reacted samples were stored in a dry dish and designated FNA0.5, FNA1, FNA1.5, FNA2 and FNSA1.5, respectively.
Example 2: characterization of the Nanocellulose aerogel
(1) FTIR analysis: the fully dried aerogel samples were compressed into thin sheets in a tablet press. Recording the FTIR spectrum of the aerogel by a total reflection infrared spectrometer FTIR-650, wherein the measuring wavelength range is 4000--1. Pure NFC was used as the control group for the experiment.
The FT-IR spectra of NFC, FNA1.5 and FNSA1.5 are shown in fig. 2. Aerogels prepared at different NFC concentrations had similar FTIR spectra, represented by FNA1.5 for analysis. Aerogel NFC samples differed significantly before and after CVD. At 3344cm-1And 1730cm-1The peaks at (a) can be attributed to the stretching vibrations of cellulose-OH and-COOH, respectively.The C-O stretching vibration peak value of NFC appears at 1056cm-1To (3). Typical absorption peaks of Si-O-Si bonds of FNA1.5 and FNSA1.5 and cellulose C-O bonds at 1130-1000 cm-1The absorption peaks within the range overlap. The FNA1.5 and FNSA1.5 samples are both 896cm-1A signal peak occurs due to the symmetric stretching vibration of the Si — O bond. 1235cm-1And 1200cm-1Respectively belong to CF2And CF3While these signal peaks were not present in the pure NFC aerogel, indicating successful loading of THFOS onto NFC aerogel after CVD.
(2) XPS analysis
And collecting the fully dried sample by X-ray photoelectron spectroscopy of AXIS UltraDLD of Shimadzu, and carrying out elemental composition identification and quantitative analysis on the sample to obtain an XPS spectrogram. Monochromatic Al K.alpha.is used with a power of 600W.
The surface chemical composition of three samples, NA1.5, FNA1.5 and FNSA1.5, was analyzed by X-ray photoelectron spectroscopy (XPS). As can be seen in fig. 3a, all three aerogel samples contained elemental carbon and elemental oxygen. FNA1.5 and FNSA1.5 showed peak positions around 688.2eV (F1 s) and 102.9eV (Si 2p), respectively (FIGS. 3b, c), indicating the presence of PFOTS on the surface of the aerogel. The C1 s spectrum of NA1.5 at 284.8eV, 286.5eV and 288.0eV is ascribed to C-C bonds or C-H bonds, C-O and O-C-O (FIG. 3 d). The C ls high resolution spectrum corresponding to FNA1.5 consists of 5 carbons of different environments (FIG. 3e), C-C/C-H (284.8 eV), C-O (286.5eV), O-C-O (288.3eV), CF, respectively2(291.4eV) and CF3(293.6 eV). Wherein the fluorocarbon chain is long and rich in CF2A bond, therefore CF2The peak of (a) is particularly strong. Similarly, the peaks of FNSA1.5 at 284.8eV, 286.2eV, 288.0eV, 291.2eV, and 293.3eV can be assigned to C-C/C-H, C-O, O-C-O, CF, respectively2And CF3(FIG. 3 f). For THFOS modified aerogels, there are no C-O and O-C-O bonds in the coating material and therefore should not be present at the surface. The appearance of the C-O signals of FNA1.5 and FNSA1.5 indicated that the coating thickness was less than the XPS sampling depth, and that the XPS detected cellulose material under the coating. Since XPS typically detects depths of up to 5nm, the thickness of CVD on aerogel should be less than 5 nm. Table 1 showsThe atomic compositions of NA1.5, FNA1.5, and FNSA are shown. The high oxygen content and low fluorocarbon ratio are inconsistent with the atomic composition of the coating THFOS, also indicating that the detection depth of XPS is greater than the coating thickness. The fluorine content of the FNA1.5 and FNSA1.5 surfaces is very high, close to the theoretical fluorine content of THFOS. The fluorine content by comparison of FNSA1.5 is higher than FNA1.5, which should be because SiO2The nano particles have higher reactivity with THFOS in the CVD process. Successful and efficient deposition of THFOS on NFC aerogels gives the aerogel surface a high probability of water and oil repellency.
TABLE 1 atomic concentration tables of individual elements of XPS for NA1.5, FNA1.5 and FNSA1.5
Example 3: factors influencing lyophobic performance of nano-cellulose aerogel
SEM analysis method: and (3) spraying gold on the surface of the completely dried aerogel sample, observing the surface morphology of the sample through a JSM-7600F field emission scanning electron microscope, taking a picture, wherein the working voltage of the electron microscope is 5kV, selecting five different positions for scanning and observing each sample, and selecting the picture with repeated characteristics for analysis.
Contact angle measurement method: the wettability of the samples was measured using a T200-Auto3 Plus optical contact angle tester. The software of the instrument automatically calculates the contact angle value according to the Young equation. In a static mode of room temperature conditions, 4 μ L of water droplets, glycerol, ethylene glycol, castor oil, and hexadecane were dropped onto the surface of the fluorinated aerogel samples, each sample having a contact angle measured at four different locations. The final value was determined after the contact angle had stabilized (10 seconds after droplet deposition). The Young's equation is, given that the uniform solid surface is perfectly smooth, γsv、γslAnd gammalvRespectively representing the tensions at three two-phase interfaces of solid-gas, solid-liquid and liquid-gas.
(1) Influence of base material and structure on lyophobic performance
Different materials have different surface appearances and different surface roughness, and the surface roughness can directly influence the lyophobic performance of the materials. This experiment has chooseed slide glass, nanometer cellulose membrane (NFC membrane) and filter paper for use and has made the control experiment with the NFC aerogel, compares different structural surface to the influence of lyophobic performance. The lyophobicity of the different substrates is given in table 2. The vapor deposited glass (FGS) only showed a water contact angle of 113.9 °; however, the water contact angles for FCN, FFP and FNA1.5 increased to 118.2 °, 150.8 ° and 155.1 °, respectively.
Table 2 contact angle data for different liquids on different substrates
Figure 4 shows FE-SEM micrographs of THFOS-modified slides, NFC membrane, filter paper, and NFC aerogel. Since the slide surface is smooth and flat with little roughness, the hydrophobicity of the slide is primarily due to the low surface energy reagents. From a comparison of fig. 4a, b, it can be seen that the NFC film is somewhat rougher than the glass slide and thus shows slightly better lyophobicity. From fig. 4c, d it is evident that the average size of the NFC beam in FNA1.5 is much smaller than the fiber size of the filter paper and that the coarse fibers on the surface of the filter paper form pores much larger than those of FNA 1.5. According to the theory of wetting model, the structure on the surface of the filter paper is not favorable for the rough structure formation of Cassie-Baxter model. NFC aerogels have a relatively uniform pore structure with many nano-and micro-scale fibrils on the surface. The protruding nanowires and the micron-scale NFC beams are combined together to construct a micro-nano multilevel structure. The reason why the value of the contact angle of FNA1.5 was the highest among the four samples was that NFC aerogel possessed the ideal microstructure and roughness. Because the NFC has small size, large specific surface area and more hydroxyl groups, strong hydrogen bonds are formed among molecules in the freeze drying process, and some NFC is agglomerated to form a sheet structure. In fig. 4d, it can be clearly seen that the substrate of the NFC aerogel is mainly a micron-scale sheet structure, and many nanofibrils are grown on the sheet structure. The micron sheet-like structure formed by NFC aggregation and the single nanofibril jointly form a complex nano microstructure.
(2) Influence of NFC aerogel density on lyophobic performance
The formula for density is defined as:
p and p hereina(1.63g/cm-3) The density of the aerogel and the density of the cellulose I crystal form, respectively. Different concentrations of NFC suspensions (0.5 wt% to 2.0 wt%) were used in this example to prepare NFC aerogels of different densities and compare them. Fig. 5 shows the porosity of aerogels at different NFC concentrations. An increase in NFC concentration results in an increase in aerogel density and a decrease in porosity. Fig. 5 also shows contact angle data for water, glycerin, ethylene glycol, castor oil, and hexadecane for different densities of NFC aerogel. Within the NFC concentration range of 0.5 wt% to 2.0 wt%, the average contact angle of each liquid increases with increasing NFC aerogel density. When the NFC concentration increased to 2.0 wt%, CAs of water, castor oil and hexadecane reached 163 °, 154 ° and 143 °, respectively. Since the surface tension of hexadecane is only 27.5mN/m, the contact angles of the four NFC samples exceed 130 degrees, and the NFC aerogel has good lyophobicity.
FIG. 6 shows FE-SEM micrographs of aerogels of different densities. Compared with the initial form of NFC, the NFC in the aerogel is significantly aggregated to form a three-dimensional porous structure during freeze-drying. The main structure of the aerogel mainly comprises micron-sized sheet structures formed by NFC self-aggregation, and forms a plurality of open network structures together with nano fibrils with the diameter of less than 1 mu m. As the aerogel density increases, both the number of pores and the average size decrease. The higher the NFC content is, the more obvious the nanowire structure is, the construction of a micro-nano structure is facilitated, and the lyophobic performance is improved.
(3) Nano SiO2Effect of load on lyophobic Properties
Preparation of SiO by classical Stober method2The average particle diameter of the nano-particles is 170nm (figure 7b), and Si-OH on the surface of the nano-particles can react with PFOTS to realize chemical gasAnd (4) phase deposition. Thus, loading SiO in NFC aerogel2The nano particles are a good choice, not only can construct a coarser micro-nano structure, but also can improve the efficiency of chemical vapor deposition.
FIGS. 7a and 7b present FE-SEM micrographs of FNA1.5 and FNSA 1.5. As shown in fig. 7a, FNA1.5 has a large number of micron-sized layered scaffolds and nanofibrils on the surface. It is noteworthy, however, that the protruding fibrils are typically in the submicron scale range and lack nanoscale structures. While in FIG. 7b the SiO is present in addition to the micrometer scale layered framework and protruding nanofibrils2Nanoparticles are also present on the micron-scale layered structures and fibrils. On the basis, the FNSA1.5 obtains an ideal micro-nano structure, and better super-hydrophobicity and oleophobicity are realized through chemical vapor deposition of THFOS. FIG. 7c is contact angle data for five liquids of FNA1.5 and FNSA 1.5. SiO 22The nano particles are loaded on an aerogel sample FNSA1.5, the average contact angles of the nano particles to water, ethylene glycol, castor oil and hexadecane are respectively as high as 166 degrees, 162 degrees, 157 degrees and 150 degrees, and the average contact angles are larger than the lyophobicity shown by FNA1.5, so that the super-amphiphobic performance is realized. FIG. 7d shows 4. mu.L castor oil and water drops on the surface of FNA1.5 and FNSA 1.5. SiO with the aid of THFOS2The introduction of the nano particles plays an important role in constructing a micro-nano structure, so that the nano particles have super-amphiphobicity.
Claims (9)
1. A preparation method of super-amphiphobic nano cellulose aerogel is characterized by comprising the following steps: mixing nano cellulose solution and nano SiO2Mixing the solutions, injecting the mixed solution into a mold, freezing the mixed solution in liquid nitrogen, and then freezing and drying the frozen solution at a low temperature to obtain the nano cellulose aerogel with the multistage micro-nano structure; carrying out lyophobic modification on the surface of the obtained nano-cellulose aerogel by using a fluorine-containing silane reagent through a chemical vapor deposition method to obtain the super-amphiphobic nano-cellulose aerogel; the nano SiO2The preparation method of the solution comprises the following steps: adding ammonia water and ethanol into a reactor, stirring uniformly, adding TEOS, stirring for reaction, and obtaining white SiO after the reaction is finished2Adding water into the solution, centrifuging, and dispersing in waterTo obtain nano SiO2And (3) solution.
2. The method for preparing super-amphiphobic nanocellulose aerogel according to claim 1, wherein the concentration of nanocellulose solution is 1.5 wt%.
3. The preparation method of the super-amphiphobic nano-cellulose aerogel according to claim 1, wherein the nano-SiO is2The solids content of the solution was 7.0% by weight.
4. The preparation method of the super-amphiphobic nano-cellulose aerogel according to claim 1, wherein the nano-SiO is2The solid content of the solution was 10% of the solid content of the nanocellulose solution.
5. The preparation method of the super-amphiphobic nanocellulose aerogel according to claim 1, wherein the fluorosilane reagent is THFOS.
6. The preparation method of the super-amphiphobic nanocellulose aerogel according to claim 1, wherein the mold is composed of a polyethylene plastic frame and stainless steel splints, and the plastic frame is clamped by the two stainless steel splints from two sides to form a mold with a length of 4cm, a width of 2cm and a depth of 0.2 cm.
7. The preparation method of the super-amphiphobic nanocellulose aerogel according to claim 1, wherein the freezing time in liquid nitrogen is 3-10 min, and the specific conditions of freeze drying under the low-temperature condition are as follows: freeze-drying at-91 deg.C under 0.6Pa for 72 h.
8. The preparation method of the super-amphiphobic nanocellulose aerogel according to claim 1, characterized in that said chemical vapour deposition method is: putting a glass bottle containing THFOS into a small beaker, putting the nano-cellulose aerogel sample on the small beaker, and then inversely placing a large beaker to cover the small beaker; in a vacuum drying oven, under the condition of 100 ℃, as the vacuum degree is reduced, THFOS volatilizes and diffuses into a gap between a glass bottle and a beaker to react with the nano-cellulose aerogel for a period of time.
9. The preparation method of the super-amphiphobic nanocellulose aerogel according to claim 1, characterized in that the preparation method of the nanocellulose solution is as follows: soaking completely dried fiber slurry in deionized water, adding TEMPO and NaBr, stirring and mixing uniformly, then adding NaClO solution for oxidation reaction, adjusting the pH value by using NaOH solution in the reaction to maintain the pH value between 10 and 10.5 until the pH value is not reduced, and adding ethanol to stop the reaction; and (3) filtering the reacted slurry, soaking the slurry in HCl solution, acidifying and washing, quantifying, adjusting pH, and performing ultrasonic treatment to obtain the nano cellulose solution.
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