Preparation of peanut shell cellulose nanofibrils and their superhydrophobic aerogels and their application on cotton fabrics

Nowadays, the application range of biomass materials is more and more extensive. In this work, peanut shell powder was used as the raw material. The cellulose nanofibrils was extracted from it by chemical mechanical method. Then, using the sol-gel method, methyltrimethoxysilane (MTMS) was added to the peanut shell cellulose nanofibrils suspension to modify it. Finally, the nano-cellulose superhydrophobic aerogel was prepared by freeze-drying method. The nano-cellulose aerogel and polydimethylsiloxane (PDMS) were coated on the cotton fabric by spraying method, and the superhydrophobic aerogel and superhydrophobic cotton fabric were analyzed and characterized respectively. The results shown that the prepared nanocellulose aerogel had a three-dimensional sheet-like structure with superhydrophobicity. The hydrophobic property and water contact angle (WCA) of cotton fabrics were significantly improved after superhydrophobic finishing. The WCA can reached 160°, the finished fabric has good antifouling performance and self-cleaning performance, and the oil-water separation efficiency can reach 82.2%.


Introduction
With the continuous increase of human consumption of oil and natural gas resources and the decline of the reserves of non-renewable resources, the utilization of renewable resources has become the trend of social development. Cellulose was a natural polymer with abundant reserves, cheap and renewable. Nanocellulose was extracted from biomass raw materials, which was one of the effective ways for its high-value utilization [1]. Nanocellulose is roughly classified into cellulose nanocrystals, cellulose nanofibrils, and cellulose nanoparticles. The resulting cellulose nanofibrils were prepared herein. China is a country that produces a lot of peanuts, and the annual output can reach tens of millions of tons. Peanut shells were the residues of peeling peanuts. That were excepting for being rarely used as feed action, reduce energy consumption, and finally get the final purified cellulose we need.
As the most widely used selective oxidation system, TEMPO/NaClO/NaBr can be oxidized by NaClO and catalyzed by TEMPO or NaBr. At the same time, it can also achieve selective oxidation with polysaccharide polymers. The specific oxidation mechanism is shown in the following fig. 1: As a large number of hydroxyl groups exist on the surface of cellulose, cellulose has hydrophilic characteristics, which also greatly limits the application range of cellulose. However, it is precisely because of the large number of hydroxyl groups on the surface of cellulose that various functional groups can be introduced for modification through esterification, alkylation [8], amidation and other reactions to produce cellulose materials with different properties. Therefore, in order to prepare cellulose aerogels and combine them with fabrics to improve the hydrophobic properties of fabrics, the cellulose aerogels can be modified to have superhydrophobic properties. It has been found that in order to improve the hydrophobicity of nanocellulose, various treatment methods can be used, including physical adsorption modification [9], esterification/acetylation modification [10], graft copolymerization modification [11], and silane coupling agent modification [12].
Because of its soft texture and affordable price, cotton fabrics are very common on the market and widely used in our daily life. However, due to the good hydrophilicity of cotton fabrics, it is easy to be polluted, so it is difficult to popularize and apply in many fields. According to the research, the surface of lotus leaf and gecko is hydrophobic [8][9][10][11][12]. Therefore, in the application of cotton fabrics, the surface of the cotton fabric is treated to meet the requirements of increasing the surface roughness, and at the same time combine low surface energy substances to give cotton fabrics super-hydrophobic properties. Cellulose aerogel is a new type of composite material. Compared with traditional silicon aerogel and polymer aerogel, its biocompatibility and degradability are significantly improved, and it has green and renewable characteristics [13][14][15]. There is no pollution to the environment and no stimulation and harm to the human body, in line with the requirements of sustainable social development. At present, there are relatively few studies on the rough structure of cellulose aerogels on the surface of fabrics. Combined with the advantages of cellulose aerogels, it is worthwhile to apply cellulose aerogels to fabrics.
In this paper, peanut shell cellulose nanofibrils was prepared by chemical-mechanical method using peanut shell as a raw material. Using the prepared peanut shell cellulose nanofibrils as raw material and methyltrimethoxysilane (MTMS) as silane hydrophobic modifier, the MTMS-modified cellulose nanofibrils was prepared by sol-gel method, and then freeze-dried. Polymethylsiloxane-modified superhydrophobic cellulose nanofibrils aerogels were prepared, and then the aerogels were pulverized and treated with low surface energy substances on cotton fabrics by spraying to obtain cellulose nanofibrils superhydrophobic cotton fabrics.

Preparation of peanut shell cellulose nanofibrils
First, benzene-ethanol solution in a volume ratio of 2:1 was prepared. Then 8 g 200-mesh peanut shell powder that wrap with filter paper were put into a Soxhlet extractor and treated with benzene-ethanol solution at a constant temperature of 90 °C for 6 h following with air dry. Lastly, the air-dried samples were stirred with 8% hydrogen peroxide solution at 50 °C for 8 h and then washed with deionized water constantly until reached a neutral state. Then adjusted the acidic conditions according to the ratio of pH = 4 ~ 5 glacial acetic acid, and then added NaClO 2 with a concentration of 2% to carry out secondary treatment for 4 h at a constant temperature of 75 °C. The powder was then rinsed off again with deionized water to remove most of the LI. Treated again with hydrogen peroxide as in the previous step. Prepared a 2% sodium hydroxide solution (solid-to-liquid ratio of 1 g:20 mL) to soak the sample at room temperature for 24 h to completely remove the hemicellulose in the powder, and rinsed with deionized water. In order to ensure that the LI can be completely removed, the purified cellulose from peanut shells was obtained by treating with hydrogen peroxide and washing to neutrality.
Weighed a certain mass of NaHCO 3 and Na 2 CO 3 and dissolved them in 300 mL of deionized water to form a buffer solution with a molar ratio of Na 2 CO 3 /NaHCO 3 of 7:3. Then weighed a certain amount of NaBr and TEMPO, dissolved them into the above solution, dispersed by ultrasonic for 15 min, then added the purified cellulose obtained in the above step, and kept the state of magnetic stirring. Then used a graduated cylinder to slowly drop it into the mixed solution, and then adjusted the pH of the solution to 10.4-10.8 with NaOH solution. The prepared solution was then placed in a water bath at 30 °C, and stirring was continued for 4 h. When the experiment was about to be completed, added anhydrous C 2 H 5 OH to end the reaction. After that, it was taken out from the water bath, left standing for 2 h, the supernatant was sucked out with a dropper, and the precipitate was repeatedly washed with deionized water. The pH valued of the final product was maintained at neutral. The peanut shell purified cellulose was put into an ultrasonic cell pulverizer for 1 h (20 min once), and finally peanut shell cellulose nanofibrils (CNF) were prepared.

Preparation of Superhydrophobic Aerogels from Peanut Shell Cellulose Nanofibrils
The CNF prepared above was dissolved in deionized water at a concentration of 1 wt%. After ultrasonic treatment for 30 min, the pH of the solution was adjusted to 4 with 0.1 mol/L hydrochloric acid to prepare a CNF suspension for use. The preparation process of the aqueous solution of MTMS is as follows: take a certain amount of deionized water, adjust the pH of the solution to 4 with hydrochloric acid, then dropwise add MTMS and stir mechanically. Different volumes of MTMS acid solutions were added dropwise to 100 mL of CNF suspension, stirred at room temperature for 3 h, and then ultrasonically dispersed for 5 min to obtain silanized cellulose (M-CNF) suspension, which was finally placed for 1 h. After the solution was stable, after aspirating the supernatant, the M-CNF suspension was poured into the mold, placed in the refrigerator for 20 h, and then placed in a freeze dryer at -60 °C for freeze-drying to obtain peanut shell cellulose nanofibrils superhydrophobicity (M-CNF) aerogel.

Preparation of superhydrophobic cotton fabrics
The M-CNF aerogel with the largest contact angle was pulverized into powder, and then the M-CNF aerogel powder was ultrasonically dispersed in deionized water for 30 min (solution A). A 10:1 mass ratio of PDMS and curing agent with solvent tetrahydrofuran solution was stirred for 10 min (solution B). First, the solution A was sprayed on the cotton fabric with a spray gun, dried for 5 min, then the solution B was sprayed on the fabric, and finally placed in an oven at 120 °C for 60 min to obtain a superhydrophobic cotton fabric. (2) Measurement of aerogel density: Cut a piece of cakeshaped aerogel sample, weigh its mass m, and calculate DSA100 contact angle meter from KRUSS, Germany, and the water droplet was 10 µL. (9) Anti-fouling and self-cleaning properties of the fabric:

Material characterization
(a) Fix the super-hydrophobic cotton fabric on a glass slide, put the slide glass into the methylene blue solution at an inclination angle of 30°, and then take it out to observe whether the surface of the fabric changes; (b) Adhere the fabric to the glass slide, drop 20 µL of water, milk, beverage and tea on the surface of the fabric respectively, and observe the surface of the fabric; (c) Fix the superhydrophobic cotton fabric on the glass slide and sprinkle it on the surface of the fabric apply methylene blue powder and tilt it at 15°. Use a dropper to release water droplets through the fabric surface to observe the final fabric surface condition.
Oil-water separation measurement: Use a rubber band to wrap the super-hydrophobic cotton fabric around the mouth of the beaker to form a separator, then immerse the separator in the water-oil (water and oil are dyed separately in advance) mixture, the oil will penetrate the cotton fabric into the beaker, and the water will be excluded from the beaker, so as to achieve the purpose of oil-water separation. The oil-water mixture separation efficiency is calculated by formula (4).
Where: η is the oil-water separation efficiency. V a is the volume of oil before separation. V b is the volume of oil entering the separator.

Contents of chemical components in peanut shells after chemical treatment
The chemical components of the peanut shell raw powder and the products at each stage during the chemical treatment process are shown in Table 1, and the changes in each stage of the peanut shell chemical treatment are shown in Fig. 2. According to Table 1, it can be seen that the content of LI in the raw peanut shell powder is 30.3%, the content of hemicellulose is 8.84%, and the content of lignin is higher than that of hemicellulose. The original powder color was the volume V of the aerogel sample. In the density calculation, formula (1) can be used: (3) Determination of porosity: ignoring the density of the air inside the aerogel, the porosity can be calculated from the aerogel density ρ b and the skeleton density ρ s of the fiber itself (ρ s = 1.528 g/cm 3 ) [16] according to formula (2) .
(4) The samples were treated with a SCD-005 gold sprayer for 40 s with a gold spray current of 10 mA. S-4800 N scanning electron microscope (SEM) was used to observe the micro-morphological structure of peanut shell fibers and samples at various stages, as well as the micro-morphological structure of M-CNF aerogel and composite cotton fabric, and the scanning voltage was 3.0 kV. (5) The infrared spectra of peanut shell cellulose nanofibrils and M-CNF aerogels and composite cotton fabrics at various stages were measured by Avatar 380 Fourier transform infrared spectrometer, with a scanning range of 450-4000 cm − 1 . (6) The crystallinity and crystal structure of cellulose nanofibrils were determined by X-ray diffractometer (Ultima IV) with a wavelength of 0.154 nm, a scanning speed of 5°/min, a scanning range of 10°-80°, and a step size of 0.02°.The relative crystallinity was calculated according to the Segal method [5], Where: Cr is the relative crystallinity (%). I 002 is the diffraction intensity of the (002) crystal plane, that is, the maximum intensity.
I am is the scattering intensity of amorphous background diffraction when 2θ is close to 18°. into discontinuous tiles, because the content of LI in peanut shells is high, even more than 30%, and the proportion of hemicellulose is less than 10%, which is low. After the removal of LI by the treatment of H 2 O 2 and a small amount of NaClO 2 , the round rod-like structure of peanut shell fibers was changed, and the shape became elongated and hollow rod-like. As shown in Fig. 3c, a larger increase in fiber diameter can be seen. This was because after a large amount of LI was removed by oxidation, some cellulose nanofibrils aggregated through hydrogen bonds [5] during drying, so the width increased, but a small amount of LI could still be seen on the surface of the fibrils.
The samples were then treated with NaOH, which was used to get inside the cell wall to remove most of the hemicellulose in CNFs. Finally, the H 2 O 2 treatment was repeated again, which can further remove the remaining LI and finally obtain purified cellulose. Its structure was shown in Fig. 3-d, the shape of the fiber was still an elongated rod, and it can be observed that its surface attachments had been completely removed. In this way, the cellulose was clearly exposed, and the large amount of -OH was due to the aggregation of the fibers into bundles under the action of hydrogen bonds.
Under the reaction conditions of the TEMPO system, the final oxidized CNF obtained after the reaction was shown in Fig. 3-e. It can be found that the fibers were tightly bonded together, and the surface of the cellulose exhibits a peeling phenomenon. Not only that, but some parts can also see continuous film formation. The reason for these phenomena was that some hydrophilic groups in CNF macromolecules, such as -OH and -COOH, appear under oxidative conditions. CNF will swell due to water absorption [5], and then more hydrogen bonds will be formed after drying conditions, so that the structure of CNF will be more compact. In addition, the skeleton of CNFs will also be damaged after TEMPO oxidation, and the damaged CNFs can be more closely combined with each other after drying. In the last Fig. 3f, it can be seen that after ultrasonic cell crushing, the diameter of peanut shell nanocellulose was in the range of 10 to 30 nm, reaching the nanometer level through TEM image testing.

Infrared analysis of peanut shell cellulose nanofibrils (FTIR)
The characteristic peak intensity of peanut shell CNF changed slightly during the processing stage. As shown in Fig. 4, the absorption peak near 3333 cm − 1 belongs to the stretching vibration of OH in cellulose-OH [17], which is affected by the -OH bond in LI. The above absorption peaks are superimposed on each other, so that the characteristic peaks at this place become wider. The absorption peak located near 2908 cm − 1 corresponds to the still turmeric (bottle a in Fig. 2). After H 2 O 2 and a small amount of NaClO 2 treatment, the proportion of LI decreased to 4.2%, indicating that there was still residual LI, but the cellulose content increased significantly, reaching 79.7%, and the color of the sample weakened to light yellow (bottle b in Fig. 2). After that, the samples were soaked in NaOH for 24 h, and then a small amount of hemicellulose and part of lignin were removed by alkali treatment, so that the cellulose content of the obtained samples was higher. After the H 2 O 2 treatment was repeated for the last time, the lignin content in the sample was reduced to 0.3 wt%, and the cellulose content had been increased to 95.2%, and finally pure white cellulose nanofibrils could be obtained (bottle c in Fig. 2).

Scanning Electron Microscopy Analysis of peanut shell cellulose nanofibrils (SEM)
From the naked eye observation, the peanut shell is a porous network structure. Figure 3 shows the SEM images of the peanut shell powder sample at different stages. It can be seen from Fig. <link rid="fig3">3</link>-a and 3-b that the natural fibers of peanut shells were surrounded by LI and hemicellulose, and the fibers showed a round rod shape. The fibers and matrix in peanut shells are piled up   Fig. 4, a strong absorption peak can be observed around 1054 cm − 1 , which corresponds to the CO stretching stretching vibration of C-H in cellulose-CH 2 [18]. The characteristic peak shape of curve a located at 2908 cm − 1 in Fig. 4 is also slightly wider due to the existence of -CH 2 and -OCH 3 bonds in LI. In curves a and b of Fig. 4, the characteristic peaks located at 1736 cm − 1 and 1649 cm − 1 was selectively oxidized, but the hydroxyl group at the C 2 and C 3 positions had no effect. In addition, no new chemical functional groups were found during the preparation of peanut shell CNF, indicating that during the preparation of peanut shell CNF [19], the chemical structure of cellulose was not destroyed or changed, and the basic structure was preserved.

X-ray diffraction analysis of Peanut Shell Nanocellulose (XRD)
As shown in Fig. 5, the strong diffraction peaks located at 15.9° and 22.1° correspond to the (110) and (200) crystal planes of peanut shell CNF, respectively. Although the intensity and position of the diffraction peaks change slightly, the structures are basically consistent. The XRD patterns showed that the internal crystal structure of peanut shell CNF cellulose was not damaged at various stages of chemical treatment, especially after the matrix was removed during the cross-treatment with H 2 O 2 and a small amount of NaCl and NaOH, which further confirmed that the chemical structure of cellulose was not destroyed or changed during the preparation of peanut shell CNF. The relative crystallinity of the samples was calculated from the intensities of the XRD diffraction peaks using Eq. (3). According to the calculation results, the crystallinity of peanut shell raw powder was only 39.1%. It may be because peanut shell CNF was mostly hidden in hemicellulose and LI, and peanut shell raw powder contained a lot of amorphous substances, resulting in a large amorphous area. After cross treatment of H 2 O 2 and a small amount of NaClO 2 , after NaOH removal of the matrix, the crystallinity of the obtained purified cellulose increased to 67%, which was 27.9% higher than that of raw peanut shell powder. It can be seen that, due to the removal of LI and hemicellulose, the cellulose is completely exposed, especially part of the amorphous region is also removed. During this process, the area of the crystallized region thus increases, so the calculated value increases relatively, and the cellulose crystallinity increases. The crystallinity of nanocellulose after TEMPO oxidation was 61.2%, which was lower than that of purified cellulose. During this process, the hydrogen bonds in the crystalline region of cellulose were destroyed, and some crystalline regions still exist. The fiber bundles were divided into filaments one by one, resulting in a decrease in the crystallinity of CNFs and an increase in the amorphous region. More -OH and -COOH are displayed because the crystallinity of CNF decreases, thus increasing the scope of application of CNF, which can make CNF easier to be modified and combined with other substances, and finally become a new performance material [20]. vibration peak of the alcoholic hydroxyl group (R-OH) in cellulose. The characteristic peak at 3333 cm − 1 corresponds to the -OH stretching vibration peak in cellulose-OH, indicating that there were still a large number of -OH groups in the molecule after the cellulose was oxidized, and only part of the -OH groups were oxidized to -COOH groups. In the TEMPO-NaBr-NaClO catalytic oxidation system, the hydroxyl group at the C 6 position of the cellulose molecule chain. Then the exposed methyl groups outside the macromolecules will endow CNF aerogels with hydrophobic properties, thus meeting the requirements for hydrophobic modification of CNF aerogels [21].

Scanning Electron Microscopy Analysis of Peanut Shell Cellulose Nanofibrils Superhydrophobic Aerogels (SEM)
It can be seen from Fig. 7 that the skeleton of peanut shell cellulose nanofibrils aerogel is a three-dimensional sheetlike structure, which is formed by the aggregation of adjacent rod-shaped cellulose nanofibrils through hydrogen bonding during the drying process. This phenomenon is often seen in freeze-dried cellulose aerogel samples [22]. The surface of the two aerogels is a honeycomb-like random pore structure, and the two have a certain similarity. The main reason is that the moisture present in the vacuum

Formation mechanism of peanut shell cellulose nanofibrils superhydrophobic aerogels
The peanut shell cellulose nanofibrils superhydrophobic aerogel was prepared by sol-gel method and freeze-drying. The schematic diagram of the preparation process of the sample is shown in Fig. 6.
The sol-gel method was used to silanize and modify cellulose in the water phase, and then freeze-dried, and the gas replaced the water, and finally a very light cellulose nanofibrils superhydrophobic aerogel was prepared. Since methyltrimethoxysilane (MTMS) has silyl hydroxyl groups (Si-OH) after hydrolysis, condensation reaction or hydrogen bonding can occur, which is due to the occurrence of Si-OH and -OH on the cellulose nanofibrils macromolecular Preparation process and mechanism diagram of superhydrophobic aerogel peak of cellulose hydroxyl appeared near 3330 cm [− 1 [23]] , and the stretching vibration peak of saturated -CH appeared near 2902 cm [− 1 [24]] . The bending vibration peaks of -OCH and -CH 2 appeared near 1416 cm [− 1 [25]] , and the stretching vibration peaks of -C ═ C-appeared near 1603 cm − 1 . Through detection and analysis, it can be seen that the chemical functional groups in the original aerogel did not change after the cellulose nanofibrils were treated with MTMS modified element. In addition, new characteristic peaks appeared after the aerogel modification. It can be seen that the hydroxyl groups of cellulose nanofibrils have been modified by silane. The characteristic peaks modified by MTMS appeared on the surface of the treated cellulose nanofibrils.

Effect of MTMS concentration on the properties of aerogels
It can be seen from Fig. 9 above that the prepared peanut shell cellulose nanofibrils superhydrophobic aerogel conforms to the high porosity and light weight (diameter d = 6 cm, height h = 0.8 cm) of aerogels. The phenomenon shows that during the silanization of cellulose, the properties of the aerogel are not changed. It can be seen from the figure that the changes of the density and porosity of the aerogel were relatively stable when the addition amount of MTMS was within 3 mL, indicating that the cellulose was modified by silane and the silane compound was fully reacted. However, when the addition amount exceeded 3 mL, relatively large changes in density and porosity occur, because the presence of unreacted MTMS in the solution led to a gradual decrease in porosity. But in general, the silane modification did not destroy the properties of aerogels.
freeze-dried aerogel is directly replaced by gas, and the cellulose nanofibrils is squeezed by ice crystals. On the basis of the same magnification, the aerogel and the modified aerogel were observed, and it was found that the pore size of the former was larger, while the pore size of the modified aerogel was smaller and denser, which was due to the substitution reaction of the hydroxyl group of MTMS.

Infrared spectroscopy analysis of peanut shell cellulose nanofibrils superhydrophobic aerogels (FTIR)
By infrared analysis of the superhydrophobic aerogel, its spectrum is shown in Fig. 8. By comparing it with the unmodified cellulose nanofibrils aerogel, the stretching vibration Fig. 9 The density, porosity and contact angle of aerogels change with the increase of MTMS  [25]] . In addition, the bending vibration peaks of -OCH and -CH 2 appeared near 1436 cm − 1 . The spectra of cotton fabrics treated with M-CNF aerogel and PDMS showed enhanced peaks at 1023 cm − 1 and 3333 cm − 1 because the substrate of the aerogel was also cellulose nanofibrils. In the infrared spectrum of M-CNF aerogel superhydrophobic cotton fabric, the symmetrical stretching vibration peak of Si-O-Si appeared at 792 cm − 1 , and the peak corresponding to the methyl group of Si-CH 3 in PDMS also appeared at 1260 cm [− 1 [27]] . The appearance of these two emerging new peaks indicated that the M-CNF aerogel and PDMS were successfully processed onto the fabric.

X-ray photoelectron spectroscopy analysis of peanut shell cellulose nanofibrils aerogel superhydrophobic cotton textiles (XPS)
According to the full spectrum of Fig. 12-a, it can be seen that the raw cotton fabric was composed of carbon and oxygen. After completing the M-CNF superhydrophobic aerogel and PDMS treatment on the fabric, two new peaks It can be seen from Fig. 9 that the silanol groups released by MTMS after hydrolysis can undergo condensation reactions or form hydrogen bonds with the hydroxyl groups on the surface of cellulose macromolecules. The exposed methyl groups make the cellulose aerogel hydrophobic, thereby achieving the hydrophobic effect of the cellulose aerogel [26]. When the amount of MTMS added was 3 mL, the maximum contact angle was 152°, indicating that the superhydrophobic aerogel was successfully prepared.

Scanning electron microscopy (SEM) analysis of peanut shell cellulose nanofibrils aerogel superhydrophobic cotton textiles
It can be seen from Fig. 10-a that the fiber surface of the untreated raw cotton fabric is relatively smooth and has no rough structure. It can be clearly seen from Fig. 10-b that the M-CNF aerogel particles are stacked on the fiber surface to form a rough structure, and the PDMS and gel particles are firmly attached to the cotton fiber surface. The particles and cotton fibers were connected and fixed under the action of PDMS. In addition, it can be seen from Fig. 10-c that the fibers in the cotton fabric are also filled with aerogel and fixed on the fabric surface by PDMS. This phenomenon is sufficient to indicate that the PDMS and M-CNF aerogels are successfully attached to the surface of cotton fabrics to form superhydrophobic cotton fabrics.

Infrared spectroscopy analysis of peanut shell cellulose nanofibrils aerogel superhydrophobic cotton textiles (FTIR)
By analyzing the structural composition of cotton fabrics, cellulose is the main component, and cellulose is mainly composed of elements such as C, H and O. Through the analysis of Fig. 11, the absorption band of raw cotton fabric around 3333 cm − 1 is strong and broad, which is the characteristic peak of stretching vibration of the hydroxyl group (-OH) of cellulose macromolecules [23]. The stretching vibration of -CH 2 was found at 2890 cm [− 1 [24]] and the  and PDMS film covering the surface of the cotton fabric. It can be seen from the narrow spectrum of Si element in Fig. 12-b that there is no Si element on the raw cotton fabric, and only solution A is sprayed onto the cotton fabric and then dried. A new peak appeared in the test, which proved that the aerogel was successfully processed onto the cotton fabric. Since solution B was also sprayed onto the fabric, the peak intensity in Fig. 12-b became stronger, and a Si-C sub-peak appeared in Fig. 12-c, indicating that PDMS was successfully deposited on the fabric. Furthermore, it can be seen from Fig. 12-a that the characteristic peak intensities of C and O elements increase, which is due to the large amount of O element in cellulose aerogel and the large amount of C element in PDMS. This further confirms that the aerogel and PDMS were successfully finished onto cotton fabrics.

Self-cleaning and antifouling test of superhydrophobic cotton textiles
It can be seen from Fig. 13-a that water has no contact angle on the raw cotton textile, and it is in a wet state. This is because the surface of cotton fibers is hydrophilic and has many hydrophilic groups, such as hydroxyl groups. It can be seen from Fig. 13-b that 122.1° is the water contact angle of the PDMS composite cotton fabric. Observing Fig. 13-c, it can be seen that the contact angle of the M-CNF aerogel composite cotton fabric is 138.7°, which cannot meet the superhydrophobicity requirement. However, when the aerogel and PDMS were treated together on the fabric, the contact angle increased significantly, reaching 160.4°, showing superhydrophobicity. This was attributed to the rough surface composed of aerogel sheet-like particles on the surface of cotton textiles, which are combined with low surface energy substances to perfectly present a superhydrophobic effect. appeared at 102.5 eV and 151.3 eV, which indicated the existence of the superhydrophobic cellulose nanofibrils aerogel  shell cellulose nanofibrils. Aerogels were successfully prepared by sol-gel method, modified by silanization with MTMS, and finally freeze-dried. By discussing the amount of MTMS added, combined with porosity and density, it was finally determined that when 3 mL of MTMS was added, the contact angle could reach 151.4°. On the basis of cotton fabrics, M-CNF/PDMS composite cotton fabrics can be prepared by spraying M-CNF aerogel particles and PDMS. The measured contact angle of the fabric surface is 160.4°. The treated M-CNF aerogel/PDMS composite cotton fabric had excellent anti-fouling and self-cleaning properties, and the oil-water separation efficiency can reach 82.2%, and the fabric after oil-water separation still had superhydrophobic properties.
The super-hydrophobic fabric in Fig. 14 above also had excellent self-cleaning function. Methylene blue powder was sprinkled on the surface of the fabric and water drops were dropped through the dropper to make the powder slide into the fabric. Finally, it can be seen that there was no powder residue on the surface of the finished fabric. The fabric surface was as clean as ever. And it can also be observed that when the treated fabric was put into the methylene blue solution and taken out again, the surface of the fabric did not change and remains dry without being contaminated by dyes. And dripping cola, Fanta, tea, water and milk on the surface of the fabric will not be wetted. Experiments show that the superhydrophobic cotton fabric had excellent antifouling properties.

Oil-water separation test of superhydrophobic cotton textiles
It can be observed from Fig. 15 that the separator was composed of fixing the superhydrophobic cotton fabric to the mouth of a small beaker with a tie, and putting it into 218 mL of oil-water mixture (V water = 200 mL, V oil = 18 mL). The oil (yellow) was quickly absorbed and gravitated through the surface of the cotton fabric into the small beaker. Due to the super-hydrophobicity of the cotton fabric, water (light blue) was repelled on the surface of the fabric and cannot pass through, thereby achieving the purpose of oil-water separation. According to formula (3), the oilwater separation efficiency was 82.2%, and the measured water contact angle after separation was about 151°, which still had superhydrophobic performance and good oil-water separation ability.

Conclusion
In this paper, the biomass material peanut shell was used, and the LI and hemicellulose in the peanut shell powder were gradually removed by chemical treatment to obtain the purified peanut shell cellulose, which was then oxidized and modified in the TEMPO-NaBr-NaClO system. Finally, ultrasonic pulverization was performed to obtain peanut Fig. 15 The process of separating oil and water mixing superhydrophobic cotton fabric