Tuning Carbon Material Modified Commercial Sponge Toward Pragmatic Oil Spill Cleanup

A practical approach to designing 3D porous materials with new functionalities for oil spill clean‐up attracts widespread attention. The carbonized seaweed‐coated melamine sponge (CMS) can selectively absorb oil immediately due to its countless pores using capillary‐driven force to absorb oil. The microstructure and behaviors of the CMS are thoroughly investigated in relation to the unique porous structure, mechanical stability, wetting response, and in‐depth processing of the high‐speed visualization experiment to determine its promising abilities. For the special CMS structure with a unit cell size of 1 × 1 × 1 cm, the total volume of oil inside the capillary tube is drawn inward after 56 ms, and the absorption rate is estimated to be ≈15 200 liters per spare metre hour without any external power inputs. According to the results, theoretical models are proposed to estimate the oil absorption rate as a function of time by continuity of the oil column in the capillary tube based on quantitative analysis of the optically analyzed oil interface phenomena. It is first shown to be a reliable approach for describing volumetric absorption rate and effective CMS thickness by visualizing the capillary spreading flow. It is expected that this research will hold tremendous potential strategies for environmental remediation.


Introduction
With the growth of the petroleum industries, the spillage of oil has resulted in instances of water resource pollution, which have severely harmed the ecological environment. [1]Despite clean-up efforts after the 1989 Exxon Valdez oil disaster, a study done in 2007 by the National Oceanic and Meteorological Agency revealed that 26 000 gallons of oil remained embedded in the sand DOI: 10.1002/admi.202300107along the Alaskan shore.In addition, scientists note that the amount of leftover oil is only diminished by less than 4% in a year. [2]The spillage of oil is a worldwide challenge, and for that reason, special attention is paid to oil spill cleaning techniques and approaches to treat oil spills.So, it is critically important to separate oil and water effectively.The most noticeable method is physical absorption, with many advantages over other methods in terms of high efficiency, reusability, simple approach, and prevention of secondary contamination.Previous studies have shown that there are many outstanding candidates for oil spill absorption materials.Many effective oil absorbent materials include sawdust, [3] membranes, [4,5,6] meshes, [7,8,9] and polymeric absorbents. [10,11]However, the limited absorption capacity and poor recyclability of these materials limit their industrial applicability.
[14][15][16] A promising way to combat spills and limit their effects is oil sorbents.They can absorb the oil, recover, and then reuse it.Designing 3D porous materials with new functionalities for oil spill clean-up has become a major challenge and has attracted widespread attention. [17,18,19,20,21]Sun and coworkers developed two different kinds of 3D melamine sponges (MSs), each of which was functionalized differently by reduced graphene oxide (RGO) sheets and Ag/RGO nanocomposite using a combination of chemical reduction and immersion techniques.A bifunctional MS for antibacterial and oil-water separation uses is embellished with Ag/RGO nanocomposites. [17]hu et al. utilized surface modification to create superhydrophobic and superoleophilic graphene-modified foam by adhering reduced graphene oxide on MS skeletons via thermal reduction of graphene oxide on the skeletons of MS and exhibiting high performance for oil/water separation. [18]The fabrication of a hydrophobic/oleophilic porous metal-organic framework (MOF)-derived carbon-coated sponge utilizing a simple and fast deposition approach that is also applicable to other porous solids, has been described by Bauza and co-workers.As a precursor material, a mildly formed mesoporous MOF MIL-100(Fe) was utilized to develop extremely porous carbon, which was then added using a facile technique to the 3D skeleton of the commercial MS. [19]Shuang Song et al. reported a simple ultrasonic-microwave synergistic approach for constructing superhydrophobic reduced graphene oxide-modified MS. [20] However, during most hydrophobic modifications of MS, expensive materials, complex processes, and even high energy consumption are required, limiting its industrialization.Furthermore, the in-depth investigation and absorption rate are frequently neglected.Thus, a possible mechanism for how capillary action could propagate oil, interface phenomena, and oil absorption rate as a function of time and effective material dimension should be created.
Modifying commercial MS, which has an inherently porous open-cell structure, combined with biomass-derived carbon, is a facile, scalable, and low-cost strategy for fabricating 3D porous materials.Due to its distinct features, MS was chosen for our study.As an amphiphilic material, though, it interacts with both water and oil.Therefore, using a surface modification strategy to separate or collect oil from water is practicable for MS.Furthermore, carbon-derived materials from biomass have been widely used as promising absorbents with the capability to remove oil pollution from water due to their natural abundance, low cost, and environmental sustainability. [22,23,24]Seaweed is a fantastic biomass precursor and has a wide range of applications. [25,26,27]he design of carbonized seaweed and the use of polyvinylidene fluoride (PVDF) as an adhesive agent, combined with the distinct porosity structure of MS, was considered to be the key component in the likely process of rapid oil absorption.We believe that the porous biomass selection and modification strategies would make this absorbent favorable for oil remediation.Hence, the MS coated with carbonized seaweed (CMS) was developed to deal with oil spills.Owing to their great oil absorption capabilities, strong recyclability, and eco-friendliness, the created MS-based would be a highly effective and reusable absorbent for spilled oil via facial approach.
Capillarity is a key performance indicator for industrial absorbent materials such as wipes, diapers, and commercial wicks.Capillarity has also received a lot of attention because of its importance in applications, particularly oil/water separation.In general, the wicking capability of porous materials is determined by direct visualization, infrared spectroscopy, and weighing techniques.Fluid flow in the porous medium is a critical process in a variety of applications, including oil clean-up, recovery, filtering, and oil/water separation.Thus, more work is needed to characterize the mechanism and to determine the absorption rate and effective material dimension.Particularly, the oil absorption behavior is analyzed by way of investigating the microstructure, mechanical strength, contact angles, and high-speed visualization experiment of the prepared CMS.In order to determine the theoretical approach, we created a simple experimental procedure during the oil penetration and determined the quantity of oil absorbed by the CMS.In addition, it was recognized that the capillary action between the oil and the surface morphology causes oil to penetrate the porous structure.In this work, CMS, 3D reticular architecture material was developed by coating carbonized seaweed/PVDF on the skeleton of MS via a facile approach.Besides, we describe a possible mechanism for how capillary action could propagate oil and estimate the amount of absorbed oil in the CMS.Based on our findings, we suggest theoretical models to quantify the optically examined oil-water interface phenom-ena and calculate the oil absorption rate as a function of time by continuity of the oil column in the capillary tube.The flow mechanism inside the porous microchannel is further examined by contrasting apparent and saturated wicking distances.In multilayer structure, the liquid spreads over the wide cross-sectional area as opposed to the interlayer microchannels, which are primarily where it spreads in MS-based structure.It is shown that a particular parameter in the radial flow model that incorporates the effects of surface tension and dynamic viscosity accurately depicts the influence of various fluids on the wicking behavior within MS-based structure.More importantly, this research not only offers an insightful perspective on how to address the critical issue of oily water waste or oil spills but also suggests a new approach to develop a highly effective CMS that is inspired by biomassderived materials and utilizes PVDF as an adhesive agent to modify MS surface.The outstanding performance of CMS along with its high absorption capacity, high mechanical strength, long lifetime, and cost-effective preparation point to its significant potential for employment in practical applications.

Surface Morphological Analysis
The scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) results of the carbonized seaweed are presented in the surface morphology in Figure 1.Apparently, carbonized seaweed powder is highly aggregated by microscale coarse and irregularly shaped particles in Figure 1a,b.During thermal treatment, dark-green dried seaweed flakes were pyrolyzed and turned black, which were apparently carbonderived material and were formed as shown in Figure S1, Supporting Information.This clearly demonstrates that pyrolysis in an argon environment could convert dried seaweed into carbon material.Based on the analysis of EDS in Figure 1c,d, the carbonized seaweed was primarily composed of C (82.52%), O (10.35%), N (2.13%), P (2.42%), S (2.07%), and Cl (0.51%), respectively.As there was no element addition during the carbonization process, carbon is one of the components that are most clearly identifiable, which shows that the dried seaweed was properly carbonized as demonstrated in Figure 1.
The 3D network porous structure of MS was clearly observed in Figure 2a,b, with an open-cell structure and pore size of ≈100 μm.Due to the chemical inertness of the MS skeleton, surface modification on CMS is difficult to perform.The pristine MS demonstrates a porous 3D network structure formed of numerous interconnected frameworks.Conversely, 0.5 wt% of carbonized seaweed and PVDF were used to assemble CMS, resulting in randomly arranged carbon particles on the MS scaffold and maintaining the shapes of the original MS.However, the crinkled and rough texture of the sponge skeleton covered with carbonized seaweed could be clearly noted.As shown in Figure 2c,d, MS/PVDF had adhered to the MS scaffold, and the carbonized seaweed particles were uniformly anchored to the skeleton surface structure, which was able to construct a microscale rough surface on the MS combined with biomass-derived material and PVDF as a binder.The binding mechanism of PVDF was generally based on its chemical and physical characteristics, which allowed it to create a strong bond with the carbon particles in the matrix.As the solvent evaporated, the PVDF molecules began to solidify and create a thin coating layer on the surface of the MS scaffold.The crystalline areas of PVDF had the tendency to align and form a network of interlocking chains when it was dissolved in a solvent, forming a robust, cohesive film.This film then worked as a binder, binding the carbon particles in place and generating a strong, cohesive layer.The binding force between those carbon particles became entirely robust owing to PVDF, which could function as an efficient adhesive agent for carbon particles.As a result, it is critical to fully comprehend the mechanism of binder/particle interaction that leads to the final sur- face form.The results show that CMS was effectively constructed using the dip coating method of carbonized seaweed on sponge skeletons.

Mechanical Behavior of CMS
For hydrophobic surfaces to be useful in practical applications, mechanical robustness is a crucial factor.Despite the fact that numerous research has been conducted on modified MS for oil/water separation, the majority of these studies have sought to critically investigate the long-term stability of modified MS.A rate of deformation was applied to the CMS, and the stress response was monitored, allowing for an accurate evaluation of the mechanical property.In Figure 3, the mechanical stability achieved by the compression process at the strain value of 60% after 1000 cycles of compression showed compressive strength, extending to practical applications, the reusability of CMS after absorption.There was barely a change in the compressive stress, indicating that the CMS had maintained its highly compressible feature.After 1000 cycles, the CMS still retained its original form without fracture or deformation.It is noteworthy that the CMS was achieved with long-term stability and that the coating layer was not peeled off or had any detachment from the MS scaffold.The carbonized samples subjected to a manual compressive force retained their apparent macroscopic morphology, demonstrating elastic behavior, despite the fact that the alveolar structure of the sponge skeleton had been maintained, as evidenced by the SEM images in Figure S2, Supporting Information.Followed by a series of absorption-squeezing cycles, the mass absorption capability of the CMS generally decreased slightly from 90.54 to 78.24 g g −1 , with over 86% of the oil absorption capacity still retained after 100 cycles, respectively.Furthermore, by simple squeezing, the recovered CMS could be reused for at least 100 cycles without any damage, which would be beneficial to prolong the lifetime of CMS.So, CMS was extremely durable in both mechanical and environmental tests.

The Wetting Response of CMS
In general, the wettability of a material surface is determined by two factors: geometrical microstructure and chemical composition. [28,29]To endow the MS with hydrophobicity, a carbon-derived surface coating strategy was utilized.The absorbent must have an affinity for oil and repellence toward the water in order to selectively absorb oil from water.Due to its hydrophobicity and 3D interconnected porous structure, CMS was able to selectively absorb stained oil instantly.Numerous pores in CMS facilitate the efficient separation of oil/water mixture by using capillary-driven force to quickly absorb oil as illustrated in Figure 4a.Accordingly, significant differences can be found between the MS and CMS behaviors via the wetting response with water contact angle measurement.Notably, MS interacts with both water and oils as an amphiphilic material.Therefore, using the wetting response strategy to compare the effect of differences in surface texture, both MS/PVDF and CMS were found to have water contact angles that were higher than 90°, showing both to be hydrophobic materials, as shown in Figure 4b.Through the use of a surface anchoring method developed from carbonized seaweed, CMS has a substantially greater water contact angle of ≈150°at the highest value, which can be considered as a hydrophobic surface.The results suggest that it has changed from a highly hydrophilic surface to a hydrophobic surface after successive treatments with carbonized seaweed and PVDF as an adhesive agent.

Absorption Capability of CMS
For the selective absorption of oil from an oil/water mixture, the CMS presence of contrasting water and oil wettability can be beneficial.The CMS was simply immersed in oil for 5 min to quantitatively measure its capacity to absorb oil.The CMS has a significant 90.54 g g −1 kerosene absorption capability.[32][33][34] In order to visually observe the phenomena, the CMS was purposefully put at the water/oil interface.As shown in Figure 5, CMS could selectively absorb stained oil immediately due to its hydrophobicity and 3D interconnected porous structure.It shows the oil movement path and absorption process of stained oil using CMS.Countless pores in CMS use capillary-driven force to rapidly absorb oil, acknowledging the effective separation of oil/water mixture.Due to the hydrophobic and oleophilic characteristics of CMS, oil floated on a water surface was selectively and completely absorbed into the pores channel when it was in contact with CMS.The CMS selectively absorbed oil, captured it, and stored it inside the CMS block by capillary action, and flowed into the MS skeleton as illustrated in Figure 5.Following that, a piece of CMS was put at the oil/water interface, and it was discovered that the CMS selectively absorbed the oil phase with virtually no evidence of water.Porous and easily modifiable surfaces are potentially appropriate for oil/water separation from a material aspect because of their characteristic 3D interconnected architectures.Pristine MS will sink to the bottom of the water because of its hydrophilicity and water-interacting characteristics.Meanwhile, CMS was submerged in water by the influence of an external force.The sur-face of CMS was surrounded by air bubbles and revealed a silver mirror-like surface, suggesting remarkable water repellency, which is given in Figure S3, Supporting Information.It may be attributed to the presence of a stable trapped air layer, suggesting that the substrate is in the non-wetting Cassie-Baxter state.The results indicate that CMS is a promising option in updating for oil/water remediation.

Visualization Experiment and Theoretical Approach
In order to verify the theoretical approach during the oil penetration and determine the quantity of oil absorbed by the CMS, we carried out a practical experiment.Figure 6 shows the configuration of the visualization test and the in-depth image processing to determine the absorption rate of the CMS.The PFA capillary tube has an inner diameter of 2.0 mm and was used for the high-speed visualization test.The capillary tube was placed perpendicular to the sample surface, which was positioned on a vertical transition stage.A side-view high-speed camera operating at 5000 frames per s was used to record the oil absorption process.To determine the height of the oil in the capillary tube at each instant, all photos were captured.The test surface was raised just enough with the support of a jack in order to make contact with the suspended pensile droplet from the capillary tube.To reduce external influences and provide a vibration-free environment, the experimental apparatus was mounted on an optical table workstation.
The liquid propagation acquired by the side high-speed camera may accurately depict the apparent meniscus movement in the capillary tube as can be clearly observed in Figure 7a.These figures were also interpreted as indicating the amount of oil absorbed in the pore channels of CMS.The total oil volume was calculated to be 23.58 μL using image processing based on the reference image with the pensile oil droplet, as shown in Figure 7a.The flow of the oil patterns through the open-cell porous structure of CMS and the rapid movement of flows between channels is illustrated in Figure 7b.The oil flow may penetrate through the gaps between the MS skeleton, a phenomenon known as a capillary invasion.Countless pores in CMS immediately sucked floating oil into their channel using capillary force.The wetting effects can have a considerable impact on the dynamics of displacement at the microscale, where capillary forces are dominant.Due to the interior space of the channels, capillary forces contribute to oil absorption into the network structure of CMS.When the oil droplets initially come into contact with the surface of CMS, the direction would be perpendicular, and the vertical capillary force would operate as the primary triggering factor for absorption.Regardless of the horizontal oil spreading driven by capillary forces between the complexly 3D interconnected structure, the vertical capillary force into the CMS would absorb the oil vertically.As the CMS surface contacts the pensile droplet, oil begins to penetrate through the interconnected 3D pore structure, and a capillary bridge forms.Subsequently, the bridge expands outwards with a rapid increment of absorbed volume; and then, recedes slightly and fluctuates until a steady meniscus forms.
The distinction between the classical method of a bundle of capillaries obtained from the Lucas-Washburn equation and competitive effects in a network of interconnected pores is described. [35]This relationship is only empirically valid if the imbibition rate maintains an identical √ t relationship over time.The widely used Lucas-Washburn equation correlates the volume rate of fluid absorption by a capillary to the pressure differential across a meniscus obtained from the wetting contact force of the fluid for the capillary wall with a resistive flow working concurrently to slow absorption.The oil flow spreading under the equilibrium relation of the capillary-driving pressure and the frictional forces was discovered and expressed in the simple  form, where  m is the effective thickness of CMS.
The force balance in the CMS may be used to explore the effects of capillary force on fluid spreading.Absorbed volume and oil height in the capillary tube as a function of time are shown in Figure 8.The oil droplet spreads quickly, leading to considerable increases in the diameters of the contact line and spreading area due to an actual force created by the difference between capillary and frictional forces (F capillary > F friction ).The entire absorption process exhibits the occurrence of an inertial regime stage I and a steady-wicking stage II, where capillary-driven flow is prominent.Particularly, in stage I, the capillary action is dominant; so that, the oil in the capillary tube is absorbed immediately at a constant absorption rate.Both forces are balanced in the transitional region between stages I and II (F capillary = F friction ).The frictional force in the capillary tube and the pore channels is dominant so that the volume of absorbed oil decreases gradually in stage II.The dispersed oil of the droplet with limited volume eventually causes the oil spreading to terminate (F capillary < F friction ).
As previously described, the total volume of the dispensed oil droplet is important in determining the oil absorption ability of CMS.In a previous study, authors not only successfully demonstrated capillary wicking and spreading of water on a nanotube surface but also estimated the volume of absorbed water in the nanotubes. [36]The radius of the capillary tube, R tube , determines the height and volume capillary tube in its initial states, which are expressed in Equation (3).More specifically, Equation (4), where H t is the height of the oil in the capillary tube, can be used to determine the amount of oil present in the tube at any given time.Using high-speed visualization of oil droplet propagating and oil absorption amount with a capillary tube on the CMS, the follow-ing Equation ( 5) is determined directly.
Relating the correlated differential volume to the differential height of the oil in the capillary tube may be expressed in Equation (6), The volumetric flow rate may also be calculated by the volume of liquid drawn into the porous structure of CMS per unit of time.The volume absorption rate dH/dtis a powerful factor in defining the capability and reusability of the absorbent material behavior as expressed in Equation ( 6).The absorption rate was recorded to be ≈15 200 L per square meter per h for the special CMS structure of a 1 × 1 × 1 cm unit cell after 56 ms when the total volume of oil inside the capillary tube was drawn inward.CMS characteristics may be used to calculate the absorption rate by considering geometrical parameter influence on absorbing capability.According to the results, we propose theoretical models to estimate the oil absorption rate as a function of time by continuity of the oil column in the capillary tube based on quantitative analysis of the optically analyzed oil-water interface phenomena.Regardless of the horizontal oil spreading caused by capillary forces, the complexly 3D interconnected microchannels provide a geometry that can generate capillary pressure and support the spreading oil.As the CMS surface contacts the pensile droplet, oil begins to permeate through the interconnected 3D pore structure, and a capillary bridge forms.Following that, the bridge spreads outwardly with a quick increment of absorbed volume; then, recedes slightly and fluctuates until a stable meniscus forms.The interface is formed between the CMS surface and capillary bridge during contact duration with kerosene as the test fluid.This height is calculated using the known capillary tube radius to determine the amount of absorbed oil over time.The effective cross-sectional contact area is 2R contactarea  m .Based on the correlation between the CMS surface and the oil bridge at the interface during the contact time, the effective contact area and thickness of the CMS are related through the expression: If R contactarea ≈ R tube , so m can be isolated as, Another noteworthy finding is that the specific condition for capillary penetration in 3D porous structure is revealed with proportionate thickness.A better understanding of the penetration mechanism is not only of experimental value but also closely related to environmental involvement.As the contact length remains generally constant, CMS maintains its high oil collection rate in stage I and progressively drops in stage II as the oil thins out in the actual collection of the spilled oil floating on the seawater surface.At the commencement of the spill, the oil is still relatively fluid and will spread quickly into a thin layer a few microns thick.The amount of floating oil does not change whether there are calm or wave sea conditions.After even a short period of floating on the ocean surface, the oil begins to change its physical properties owing to a variety of physical, biological, and chemical processes.Initially, the most volatile components of the oil evaporate, and to a lesser extent, part of the oil dissolves into the water column.This process will continue and may eventually account for the loss of a significant portion of the contaminant.Shorttime fluid uptake is important for processes such as oil recovery and phase separation.More importantly, this research suggests a novel strategy for creating a highly effective CMS that is inspired by biomass-derived materials and uses PVDF as an adhesive agent to modify MS surfaces, in addition to providing an insightful perspective on how to address the challenging issue of oily water waste or oil spills.Due to its distinct features, CMS is expected to be fabricated on an industrial scale and used for the treatment of industrial oily wastewater and oil spills in practical application.

Conclusion
Inspired by the biomass derived for modification of MS surface via PVDF as an adhesive agent, a highly efficient CMS was prepared by using a facile, eco-friendly, and cost-effective approach.The CMS maintained the shape of the original MS and had shown that it is an excellent candidate for oil absorption due to the fact that CMS exhibits both highly incorporating hydrophobic and oleophilic properties.Due to the 3D interconnected structure and unique properties, CMS has a significant absorption capacity, outstanding selectivity, and remarkable recyclability.Furthermore, the mass absorption capability of the CMS was then subjected to a series of absorption-squeezing cycles, and after 100 cycles without causing any deformation, it still retained more than 86% of its oil absorption capacity, which would be advantageous in extending the durability of CMS.It can be concluded that their distinctive architectures, abundance, and easy-to-modify surface are potentially suitable for oil/water separation from a material aspect.The microstructure and behaviors of the CMS were thoroughly investigated in relation to the unique porous structure, wetting response, and in-depth processing of high-speed visualization experiment to determine its promising abilities.Moreover, we proposed theoretical models to estimate the oil absorption rate as a function of time by continuity of the oil column in the capillary tube based on quantitative analysis of the optically analyzed oil-water interface.After 56 ms, when the total amount of oil inside the capillary tube was drawn inward, the absorption rate was measured to be ≈15 200 L per square meter per h for the CMS of a 1 × 1 × 1 cm unit cell.In the future, this material would be particularly beneficial for treating oil pollution because of its simple fabrication, high stability, absorption capacity, and recycling rate.Our approach may potentially lead the way for the development of extraordinarily responsive oil absorbent materials with pragmatic implications in the sectors of water remediation, oil spill clean-up, and oil recovery.

Experimental Section
Materials: A commercial MS was obtained from Basotect and used as raw material.Dimethyl sulfoxide (DMSO) was used as the solvent for the PVDF (Solef 1015) mixture preparation.The brown seaweed (Undaria pinnatifida) had been treated as a carbon precursor.To evaluate the absorption performance and material behaviors, kerosene was selected as the acting fluid and Oil Red O was utilized to stain the oil.For the capillary tube, a perfluoroalkoxy (PFA) tube with an inner diameter of 2 mm was chosen.These chemicals are analytic grades and were used as received without further purification.The general fabrication process of CMS is schematically illustrated in Figure S4, Supporting Information, where CMS was fabricated via a simple dip coating method on the framework of the MS.
Tuning Carbon Material by Direct Pyrolysis of Dried Seaweed: First, dried seaweed was roughly crushed into flakes.An alumina boat containing dried seaweed flakes was slightly placed in the center of the quartz tube furnace.It was operated at 800 °C under Argon condition with a flow rate of 0.5 sccm min −1 .The sample was heated for 1 h at the desired temperature at a rate of 5 °C min −1 .During thermal treatment, dark-green dried seaweed flakes were pyrolyzed and turned black which was apparently carbonderived material formed.Subsequently, the process of removing residues and purification of carbonized seaweed was carried out in turn by sifting and washing.The mixture was sifted with a fine test sieve (300 μm, ASTM E11) and alternatively washed with ethanol and deionized water.The carbonized seaweed powder was obtained and stored for further use.
Fabrication of CMS Via Facile Dip Coating Method: The optimized PVDF solution at 0.5 wt% in DMSO was vigorously stirred at 60 °C for 8 h.After that, carbonized seaweed powder was mixed with the above solution with a mass ratio of 0.5 wt% and followed by vigorous stirring for the next 1 h.Typically, MSs were cut into cubes of 1 × 1 × 1 cm for the standard sample unit.MS cubes were carefully washed with ethanol followed by sonication and dried in the air oven at 60 °C.Afterward, the MS cube was dipped in the as-prepared above mixture for ≈30 min.Last, the samples were allowed to dry in the air oven at 150 °C for 24 h.As a result, the desired CMS was obtained and stored for further use.
Oil Absorption Experiment: The CMS was simply submerged in oil for 5 min to determine its capability to absorb oil.The oil-saturated absorbent was then collected until all the free oil was drained.Before and after the absorption tests, the mass of CMS was measured by an electronic analytical balance.According to the following Equation ( 9), the absorption capacity was evaluated, where m 1 and m 0 were the weight (g) of CMS before and after oil absorption, respectively.
To assess the reusability of the CMS, the absorption-squeezing method was carried out by repeatedly immersing the CMS in the oil 100 times under the same circumstances.
Characterization: A scanning electron microscope (SEM, JSM-7800F/JEOL, Japan) was used to examine the structural behavior of the materials.X-ray energy-dispersive spectroscopy (EDS) mounted to the SEM was used to determine the elemental analyses.To assess the surface wetting of as-prepared materials, measurements of the water contact angle were performed using the Smart Drop system (Femtobiomed, Korea).Fully air-dried samples were placed out on the test base, and a 23-gauge blunt needle tip was used to drop 5 μL of distilled water over the surface of the samples.All contact angle values were confirmed by the goniometry method.The water contact angle was determined to be the average of the left and right angles.Two parallel flat surfaces were moved at a speed of 5 mm min −1 during the compressive mechanical tests,

Figure 1 .
Figure 1.a,b) SEM and transmission electron microscopy (TEM) images of the carbonized seaweed powder and c,d) EDS spectrum of dried and carbonized seaweed samples.

Figure 2 .
Figure 2. SEM images of a,b) the original structure of the MS skeleton, c) MS/PVDF have uniformly adhered to the MS scaffold, and d) CMS was modified with carbonized seaweed via a facile dip coating method.

Figure 3 .
Figure 3. a) Digital photos of the CMS during the compression process and b) the compression process at the strain value of 60% after 1000 cycles.

Figure 4 .
Figure 4. a) The oil is selectively collected by floating CMS with free oil/water mixture and b) the wetting response of MS/PVDF and CMS with water contact angle measurement.

Figure 5 .
Figure 5. Oil movement path and absorption process of CMS with stained oil.

Figure 7 .
Figure 7. a) The oil absorption by capillary action and b) flow of the oil patterns distributed inside the interconnected 3D structure of CMS.

Figure 8 .
Figure 8.The oil absorption rate in CMS as a function of time.