Superhydrophobic wood sponge with intelligent pH responsiveness for efficient and continuous oil-water separation

In recent years, the leakage of crude oil and the discharge of oily wastewater in industrial production have seriously endangered the water environment and ecological safety. Adsorbent materials with excellent oil-water separation performance play an important role in water purification. In this work, we employed a simple yet effective strategy to prepare highly compressible wood sponges. And with the prepared wood sponge as the substrate, the prepared pH-responsive copolymer was coated on the surface of the wood sponge by spraying method, and the pH-responsive superhydrophobic wood sponge was successfully prepared. The experimental results show that the wood sponge has excellent pH-responsive properties and can complete the transition of surface wettability between superhydrophobicity and hydrophilicity according to the change of pH value. The wood sponge has good oil adsorption capacity (12.72 g g−1), and reusability. Continuous oil-water separation can be carried out under the vacuum pump, and the oil-water separation efficiency in one separation cycle is above 92%. It has great application potential in the treatment of oily wastewater.


Introduction
Crude oil is a natural resource that can bring great convenience to people's lives, but while crude oil provides convenience, it also brings corresponding negative effects. Frequent oil spill accidents and increasing discharge of oily wastewater have brought a serious impacts on the ecological environment [1][2][3]. As countries around the world have successively formulated strict laws and regulations and increased awareness of environmental protection, a variety of methods have been developed for the separation of oil/water mixtures to solve the problem of oil spill pollution, mainly including in situ combustion, biodegradation, gravity drive , adsorption, in which the use of adsorption to collect oil phase from oily wastewater is the most economical, simplest and most effective method [4][5][6][7][8]. Materials with special wetting surfaces are widely used in oil-water separation. Researchers build superhydrophobic surfaces by increasing surface roughness and reducing surface energy to achieve selective oil/water separation [9][10][11][12][13]. In recent years, a lot of research has been done on superhydrophobic materials for oil-water separation, including two-dimensional superhydrophobic materials, mainly superhydrophobic paper, superhydrophobic films, etc, and superhydrophobic materials with threedimensional network structure, including aerogels, sponge etc. [14][15][16][17][18]. Two-dimensional superhydrophobic materials have the problems of poor selective separation and non-reusability in oil-water separation, making it difficult for large-scale applications. Biomass aerogels based on nanocellulose are one of the current research hotspots. However, pure nanocellulose aerogels have poor mechanical properties and need to be compounded with other materials to prepare composite aerogels, which increases the cost and complexity of the preparation process [19][20][21][22]. Therefore, biomass sponges that are environmentally friendly, low-cost, and have good mechanical properties have gradually entered the public's field of vision [23][24][25][26].
Balsa is a low density, naturally renewable, environmentally friendly material. It has a 3D layered and porous structure, and the cell wall of balsa is composed of cellulose, lignin, and hemicellulose [27][28][29]. In recent years, researchers have used balsa wood as raw material to prepare balsa wood sponges by chemical treatment and prepared various functional materials based on balsa wood sponges. Fabrication of mechanically compressible, anisotropic balsa wood sponges using a simple, low-cost top-down approach, and through the LPD modification strategy, it was immersed in an ethanol solution of methyltrimethoxysilane for superhydrophobic modification for multiple behaviors and reusable oil-water separation [30]. Some researchers explored the optimal concentration and pH value conditions required for the preparation of wood sponge and prepared a wood sponge with excellent performance under the optimal conditions and successfully modified the wood sponge with super hydrophobicity, which has excellent oil-water separation performance and reusability [31]. Balsa wood retains fibrous structure after delignification and hemicellulose treatment with excellent mechanical compressibility, larger comparative area, and higher porosity [32], it has good application prospects in the fields of adsorption [33], electromagnetic shielding [34], sensors [35], etc.
Smart-responsive superhydrophobic materials with switchable surface wettability that can adapt to complex environmental changes have attracted great interest from researchers. The surface wettability of this smart responsive superhydrophobic material can be switched between hydrophilicity and hydrophobicity when subjected to external stimuli such as Ph [36][37][38][39][40], temperature [41][42][43], light [44][45][46], and magnetic field [47]. pH response has the advantages of fast response and simple operation and is favored by more researchers. In general, pH-responsive superhydrophobic materials can be prepared by synthesizing pH-responsive copolymers. In a previous study, researchers synthesized a triblock fluorine-free copolymer from a fluorine-free monomer solution, and combined it with silica nanoparticles/polydimethylsiloxane through a dip coating process, and successfully prepared a pH-responsive paper and cotton fabrics [48]. Researchers successfully synthesized solution-processable Ph-responsive copolymers via dodecyl methacrylate, 3-trimethoxysilylpropyl methacrylate, and 2-dimethylaminoethyl methacrylate , and then prepared smart coatings for controllable separation of oil/water [49]. So far, the research on intelligently responsive superhydrophobic materials (single response to a single stimulus, multiple responses to multiple stimuli [50][51][52]) has mainly focused on the twodimensional field, using simple methods to prepare three-dimensional superhydrophobic materials with excellent performance still challenging.
In this work, a pH-responsive superhydrophobic wood sponge was developed through a simple spraying process. First, a two-step chemical treatment was used to selectively remove lignin and hemicellulose from natural balsa wood, and then freeze-drying was used to produce a wood sponge with high compressibility. Next, using lauryl methacrylate (LMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) as raw materials, a pHresponsive polymer were obtained by free radical polymerization , and a simple spraying process was carried out. A pH-responsive wood sponge whose surface wettability varies with pH has been developed. The results showed that the as-prepared wood sponge exhibited superhydrophobicity in neutral and alkaline environments, and hydrophilicity in acidic environments. The product has good oil absorption performance. It only needs a simple mechanical extrusion to recover the absorbed oil, and after multiple extrusions, its oil-absorbing performance is also very good, and it can be used repeatedly. This method can realize the continuous separation of oil and water.

Preparation of wood sponge
The pH value of the NaClO 2 solution with a mass fraction of 3 wt% was adjusted to 4.0 with glacial acetic acid, and then the dried natural balsa wood was immersed in it, and delignified at 95°C for 6 h to remove most of the lignin. The treated samples were transferred to a 7 wt% NaOH solution and heated at 100°C for 5 h to remove hemicellulose and residual lignin. The samples were first soaked in ethanol for 12 h and then washed with hot water to remove unreacted residues. The washed samples were frozen at −20°C for 8 h and then freeze-dried at −56°C for 36 h to obtain balsa sponge.

Preparation of the pH-responsive copolymer
We used a typical free radical polymerization method to prepare the pH-responsive copolymer (PLMA-co-PDMAEMA). Dissolve LMA (2.54 g) and DMAEMA (6.28 g) in 30 g of anhydrous toluene, add 0.16 g of initiator AIBN, and stir magnetically for 1 h until the mixture is completely dissolved. The mixture was then transferred to a closed three-necked flask, and the air was replaced with nitrogen to allow polymerization. Then, the sealed three-necked flask was placed in an oil bath, and the mixture was stirred with a magnetic force at 70°C for 6 h to perform polymerization. The mixture was then cooled to room temperature and fed into a beaker, where most of the solvent was evaporated in a water bath at 70°C, Then the rest of the mixture was dissolved in acetone, and n-hexane was added to the acetone solution of the mixture to precipitate the copolymer. Finally, the pH response copolymer was put into a vacuum drying oven and dried at 50°C for 12 h, ground into powder, and stored for later use.

Preparation of pH-responsive superhydrophobic wood sponge
First, 2 g of pH-responsive copolymer (PLMA-co-PDMAEMA) was weighed and ultrasonically treated in 20 g of anhydrous toluene for 30 min to obtain a superhydrophobic coating with good pH reponsiveness. On this basis, the pH-responsive superhydrophobic coating was coated on the sponge wood with a spray gun and dried at 70°C for 1 h to obtain the pH-responsive superhydrophobic wood sponge. The flow of the preparation process is shown in figure 1.

Characterization
The surface morphology of balsa wood and balsa wood sponge was analyzed by scanning electron microscope (SEM, SU-8010, Japan). The group structure of the samples was determined by Fourier transform infrared spectroscopy (SHIMADZU, Japan, 8400 S). X-ray photoelectron spectroscopy (XPS, Axis Ultra, Kratos Analysis, Kratos Analysis) was used to analyze the sample composition. The mechanical compressive properties of wood sponge were tested by a universal compressive testing machine (Instron5500). A contact angle meter (JY-PHb, Jinhe, China) was used to measure the wettability of the sample surface. The contact angle (CA) was measured at 5 random points on the sample surface, and the average value was taken as the contact angle (CA) of the sample surface. And a pH-responsive performance test was carried out. After immersing the samples in an alkaline solution of NaOH and an acidic solution of HCl for a period of time, respectively, the contact angles (CAs) were measured.
Calculate the porosity of the sample using the following formula [31]: Where ρ b is the bulk density of the sample, which is calculated by dividing the mass of the sample by the volume. ρ s represents the skeleton density of the sample. According to previous research results [53], the ρ s of wood is 1.49 g cm −3 ,and the ρ s of microfiber cellulose is 1.48 g cm −3 , respectively.

Adsorption capacity and reusability testing
Using the organic solvent, toluene, n-hexane, 1,2-dichloroethane, vegetable oil, and mineral oil as oil phase, the adsorption properties of various oils were studied. Adsorption capacity (M) is the mass of oil absorbed per unit mass of sorbent. First, soak the samples in different oil phases for 10 min to make the samples reach adsorption equilibrium in different oil phases, and weigh them to determine the adsorption capacity of the samples. The calculation method of M is as follows: The weight of the sample after adsorption was denoted as m t , and the weight of the sample before adsorption was denoted as m 0 . We evaluated the reusability of the sample through a simple adsorption-extrusion cycle. Immerse the sample in vegetable oil, calculate the oil absorption M by the method described above, recover it by a simple mechanical extrusion method, and reweigh it to determine the residual oil content in the sample. A total of 10 adsorption extrusion cycles were performed.

Oil-water separation testing
Toluene, vegetable oil, mineral oil, 1.2, dichloroethane, and n-hexane were selected as experimental oil and deionized water to construct the oil-water mixture. The oil phase is stained with oil red, and the deionized water is stained with methylene blue. Then, through the oil-water separation device, the oil-water separation test was completed under the action of the vacuum pump, and the oil-water separation effect was observed. After the oilwater separation is complete, the oil-water separation efficiency can be calculated according to the following formula [54].
On this basis, V 1 represents the amount of oil collected after completing one oil-water separation, and V 0 represents the initial oil amount.

Results and discussion
3.1. Surface morphology analysis of wood sponge As one of the lightest woods in the world, the pore structure of balsa wood is distributed in the transverse section, with almost no pore structure in the tangential plane and radial section [55]. The cross-section scanning electron microscope (SEM) of different wood samples is shown in figure 2. Natural wood (a) contains dark lignin that appears as yellow blocks. From the SEM of the cross-section, the surface contains a large number of honeycomblike porous structures. with low density and high porosity (table 1) and thinner cell walls. Sodium chlorite (NaClO 2 ) solution generates chlorine dioxide (ClO 2 ) under acidic conditions, which can decompose lignin. The delignified wood(b) changed from yellow to white, indicating that the natural wood was treated with an acidic sodium chlorite (NaClO 2 ) solution, which removed the dark lignin and left colorless polysaccharides [56]. After being treated with sodium chlorite (NaClO 2 ) solution, the density of wood was also reduced, the porosity was increased (table 1), and the originally closely arranged honeycomb structure became regional. Although a large amount of honeycomb structure was still retained, it became no longer intact with partial cell wall disruption. The honeycomb structure in the wood sponge(c) disappears completely, replaced by a wavy hierarchy. Compared with natural wood, the thin cell walls of wood sponges were ruptured, exposing cellulose, indicating that further treatment with sodium hydroxide (NaOH) removed the hemicellulose, leaving the fibrous backbone.

Chemical analysis of wood sponge
Fourier infrared spectrum tests were conducted on natural wood, delignified wood, and wood sponge, and their Fourier infrared spectrum curves were shown in figure 3(a). The characteristic peaks of lignin (1593, 1505 and 1462 cm −1 ) are mainly attributed to the vibration of aromatic skeleton in lignin and the stretching of C-H on methyl and methylene [57]. The peaks from 1736 to 1235 cm −1 are mainly caused by the stretching vibration of C=O on the acetyl group of hemicellulose and the contraction vibration of O=C-O [58]. The characteristic peak (2898 cm −1 ) of cellulose is mainly the stretching vibration of −OH and C-H [30], and the characteristic peak of cellulose at 899 cm −1 is mainly the stretching vibration of C-C [59]. Compared with natural wood, the characteristic peak of lignin in delignification wood disappeared, but the characteristic peak of hemicellulose and cellulose was retained.This indicated that the acidic sodium chlorite solution selectively removed most of the lignin in the natural wood, leaving hemicellulose and cellulose. The characteristic peaks of cellulose and hemicellulose were not observed in the Fourier infrared spectral curves of wood sponge, but only the characteristic peaks of cellulose were observed, indicating that the two-step chemical treatment selectively removed lignin and hemicellulose. As shown in figures 3(b) and (c), X-ray photoelectron spectroscopy (XPS) analysis was performed on natural wood and wood sponges. C and O elements can be seen in both natural wood and wood sponges. From the C 1 s fine spectrum of natural wood, it can be seen that it contains three types of C, C1 (284.6 eV), C2 (286.2 eV), and C3 (287.8 eV). Similarly, wood sponge also contains three types of carbon, C1 (284.5 eV) , C2 (286.0 eV), C3 (287.5 eV). According to table 2, the content of C and the ratio of O/C changed, the content of C decreased from 71.65% of natural wood to 63.3% of wood sponge, and the O/C increased from 0.38 of natural wood to 0.56 of wood sponge. The higher carbon content in wood is mainly due to the large amount of lignin and extractives on the surface of the wood, while the reduction in carbon and the increase in O/C means a large loss of extractives and lignin [60]. O content increased from 27.14% of natural wood to 35.39% of wood sponge. Increased O content largely due to extraction and removal of hemicellulose [58]. C1 mainly comes from lignin and extracts [31], C2 mainly comes from cellulose in wood [58], and C3 is mainly supplied by cellulose and hemicellulose [61]. The results showed that the content of C1 in sponge wood was lower than that in natural wood. The contents of C2 and C3 increased; FT-IR and XPS analysis results showed that most of the lignin and hemicellulose were removed in the production of natural wood to sponge, leaving only the fiber skeleton. Figure 4 shows the weight loss rate TG (a) and weight loss speed DTG (b) curves of natural wood and wood sponge in the temperature range of 30°C-700°C. The pyrolysis process of wood is actually the pyrolysis of lignin, hemicellulose, and cellulose in wood. At 210°C to 340°C, compared with natural wood, wood sponge needs higher temperature when the mass loss rate is the same. And the pyrolysis of wood sponge is slower in this temperature range. This is mainly because wood sponge contains less hemicellulose which is less thermally stable. The coke produced by wood thermal decomposition is the result of lignin thermal decomposition. As shown in figure 4(a), wood sponge has lower residual carbon (14.06%) than natural wood (22.78%), indicating that wood sponge contains more lignin than natural wood. The results showed that in natural wood, most of the  lignin and hemicellulose had been removed. At 700°C, its quality residue rate shows the reduction of the main chemical components in natural wood, resulting in a decrease in its heat resistance.

Mechanical properties of wood sponge
Compression resilience tests were performed on wood sponges. As shown in figure 5 (a), the wood sponge is compressed and can basically return to the original height after releasing the stress. Figure 5(b) shows the stressstrain curves for one compression cycle at 20%, 35%, and 50% of the maximum deformation. During the loading process, due to the deformation of elasticity of the wood sponge fiber skeleton and the overlap of layered structures, a linear area with slowly increasing stress and a dense area with rapidly increasing stress are formed [28]. As the stress is released, the strain gradually decreases to zero. At the maximum strain of 50%, the height  retention rate (as a percentage of initial height) reaches 95%, and slight plastic deformation occurs, which can be ignored, indicating that the wood sponge has excellent compressibility and resilience. As shown in figure 5(c), five compression cycles were performed at a steady state strain of 35%. Compared with the first compression cycle, the second compression cycle produces a tiny plastic deformation, and the stress-strain curves from the second compression cycle to the fifth compression cycle basically coincide, which is consistent with the previous reports [62]. We explored the height retention of wood sponge during 120 compression cycles at a maximum deformation of 35%, as shown in figure 5(d). After 120 compression cycles, its height retention was approximately 94%, illustrating the stability of the wood sponge structure.
3.5. FT-IR analysis of pH-responsive superhydrophobic wood sponge FT-IR detection was performed on LMA, DMAEMA, pH-responsive copolymer, wood sponge, and pHresponsive copolymer-coated wood sponge, as shown in figure 6. The C-H group in LMA provides the characteristic peak of 2926 cm −1 . The peak at 1720 cm −1 is attributed to the tensile shock of C=O in LMA and DMAEMA. The peak at 1166 cm −1 is attributed to the tensile shock of C-N in DMAEMA. The above peaks can be found in the Fourier infrared spectra of pH-responsive copolymers. This indicates the successful preparation of pH-responsive copolymers. Compared with wood sponge, the characteristic peak of C=O appeared at 1720 cm −1 in the fourier infrared spectrum curve of wood sponge coated with pH-responsive copolymer. This was provided by DMAEMA in the pH-responsive copolymer, indicating that the pH-responsive copolymer was successfully coated on the wood sponge.  3.6. Wettability and pH response As shown in figure 7(a). Under neutral and alkaline conditions, the water droplets did not penetrate the surface of the pH-responsive wood sponge, maintained a good spherical morphology, and exhibited hydrophobic properties. When the pH-responsive wood sponge was treated with acid, water droplets penetrated its surface, exhibiting hydrophilic properties. It can be known from the water contact angle (b) of the pH-responsive wood sponge at different pH values, the water contact angle of the pH-responsive wood sponge without acid-base treatment can reach 155.8°, the water contact angle is 151.5°after being treated with an alkaline solution with a pH value of 12, all have excellent superhydrophobic properties. The surface water contact angles of the pHresponsive wood sponges were both 0°after being treated with acidic solutions with pH values of 3 and 1, showing hydrophilic properties. From the dynamic contact angle photographs (c) of the acidic droplets with  pH values of 3 and 1, it can be seen that the acidic droplets gradually wet the surface of the pH-responsive wood sponge from the initial spherical shape. The droplet with a pH value of 3 completed wetting in 240 s, while the droplet with a pH value of 1 only needed 40 s, indicating that the pH-responsive wood sponge can complete the transition from hydrophobicity to hydrophilicity under acidic conditions, and the lower the pH value, the more responsive faster. As shown in figure 7(d). The water droplets on the surface of the pH-responsive wood sponge without acid-base treatment roll off rapidly with the tilt of the wood sponge. In the process of measuring the contact angle, after the water droplet comes into contact with the surface of the pH-responsive wood sponge, the water droplet will leave its surface along with the needle tube. These results again illustrate the excellent superhydrophobicity of pH-responsive wood sponges under neutral conditions.

Mechanical durability of pH-responsive superhydrophobic wood sponge
Mechanical durability is an important property of superhydrophobic materials. To evaluate the mechanical durability of pH-responsive superhydrophobic wood sponge, we used the same test method [63][64][65] (tape peeling) as in the literature. As shown in figure 8(a), 3M600 test tape was selected in this experiment, and 100 times of tape stripping cycles were conducted on the samples. It can be seen from the relationship between the contact angle and the number of stripping cycles in figure 8(b) that the contact angle decreased from 155.8°to 151.3°during the 100 times of tape stripping experiment, which only slightly reduced, and showed superhydrophobicity after 100 times of stripping cycles. The experimental results show that the pH-responsive superhydrophobic wood sponge has excellent mechanical durability.

Analysis of pH response mechanism
The pH-response mechanism was analyzed by XPS detection of neutral, acid-treated and alkali-treated pHresponse wood sponges. It can be seen from figure 9 that Cl and Na elements appeared in the pH-responsive wood sponges treated with acid (b) and alkali (c), respectively, because the prepared acid-base solutions were hydrochloric acid solution (HCl) and sodium hydroxide solution, respectively (NaOH), indicating that the surface of wood sponge is already acidic and alkaline. There is only one peak at 399 eV in the N 1 S fine spectrum (a) of the pH-responsive wood sponge under neutral conditions, which is attributed to the tertiary amine group in the pH-responsive monomer DMAEMA. A new peak at 401 eV appeared in the fine spectrum of N 1 S after acid treatment(b), which was attributed to the quaternary ammonium group, indicating that DMAEMA was protonated. No quaternary ammonium group at 401 eV was observed in the N 1 S spectrum after alkali treatment(c), only a tertiary amine group at 399 eV was observed, indicating that DMAEMA was deprotonated.

Analysis of pH-responsive wood sponge adsorption and reusability
In this work, we selected toluene, n-hexane, vegetable oil, mineral oil, and 1,2-dichloroethane as the experimental oils to explore the oil adsorption properties and reusability of pH-responsive wood sponges. As shown in figure 10(a), the upper layer is vegetable oil dyed with oil red, and the lower layer is colorless deionized water. The pH-responsive wood sponge was placed in a mixture of vegetable oil and water, and the wood sponge gradually absorbed the red vegetable oil, leaving a colorless deionized water at the end. After the pH-responsive wood sponge completes the adsorption, it still floats on the water surface, which is convenient for collection and recycling. The oil adsorption capacity of the pH-responsive wood sponge refers to the mass of oil adsorbed per unit mass of the sample. As shown in figure 10(b), the pH-responsive wood sponge has a maximum adsorption capacity of 12.72 g g −1 for various oils, which is better than that of carbonaceous aerogels [66] and Poly (vinylidene fluoride) aerogels with the highest adsorption capacity of 6.78 g g −1 [67]. pH-responsive wood sponge can recover the adsorbed oil by simple mechanical extrusion, and the extruded pH-responsive wood sponge can return to its original shape after releasing the stress, which is due to the excellent compressibility and resilience of the wood sponge, As shown in figure 10(c). As shown in figure 10(d), the adsorption capacity decreased slightly from 10.22 g g −1 to 9.24 g g −1 after ten adsorption-extrusion cycles. The above results show that pH-responsive wood sponge has good adsorption capacity and good reusability for various oils and is an ideal adsorbent for various oil spill water pollution.

Continuous oil-water separation
To explore the oil-water separation performance of pH-responsive wood sponges, we constructed an oil-water separation device consisting of a vacuum pump, suction filter bottle, rubber tube, glass tube, and pH-responsive wood sponge. One end of the glass tube is connected to a pH-responsive wood sponge that acts as a filter, and the other end is connected to a suction filter bottle connected to a vacuum pump through a rubber tube. Oil-water separation of pH-responsive wood sponges without acid-base treatment as shown in figure 11(a). pH-responsive wood sponges that have not been treated with acid and alkali are immersed in a mixture of vegetable oil and water dyed with oil red, and the vegetable oil on the upper layer is continuously pumped through the wood sponge and piped under vacuum into a suction filter bottle, and the water in the lower layer remains in the beaker. Oil-water separation of pH-responsive wood sponges after acid treatment as shown in figure 11(b). The acid-treated pH-responsive wood sponge was immersed in a mixture of water (methylene blue stained) and 1,2dichloroethane, and the upper blue water was continuously pumped into a suction filter bottle, and the lower layer of colorless 1,2-dichloroethane remains in the beaker. Illustrating that pH-responsive wood sponges can be used for continuous oil-water selective separation. Figure 11(c) shows the oil-water separation efficiency in one separation cycle. Including the separation efficiency of pH-responsive wood sponges without acid-base treatment for various oils and the separation efficiency of pH-responsive wood sponges treated with acid in water. The separation efficiency of pH-responsive wood sponge for toluene, n-hexane, vegetable oil, and mineral oil without acid-base treatment is above 92%, and the separation efficiency of toluene reaches 98.9%. The pHresponsive wood sponge treated with acid had a water separation efficiency of 95.7%. This indicates that pHresponsive wood sponge has excellent oil-water separation performance. In order to evaluate the oil-water separation durability of pH-responsive superhydrophobic wood sponge, we explored the oil-water separation efficiency of wood sponge placed for different times. As shown in figure 11(d), after 40 days, the oil-water separation efficiency still reached 93.2%, which indicates that pH-responsive superhydrophobic wood sponge has excellent oil-water separation durability.

Conclusion
In this paper, a low-density, high-porosity wood sponge was prepared by a top-down approach. And the pHresponsive copolymer was prepared by free radical polymerization and used as a coating to prepare pHresponsive superhydrophobic wood sponge. The prepared pH-responsive wood sponge is superhydrophobic under both neutral and alkaline conditions, and hydrophilic under acidic conditions, with excellent pHresponsive properties. The removal of lignin and hemicellulose, the successful synthesis of copolymers, and the pH-responsive mechanism were verified using FT-IR and XPS. Through adsorption and oil-water separation tests, it was determined that the pH-responsive wood sponge has excellent adsorption capacity, reusability, and oil-water separation performance. In conclusion, a novel oil-water separation material with excellent pH performance has been prepared, which has great application potential in the field of water pollution purification.