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Bio-Inspired Underwater Super Oil-Repellent Coatings for Anti-Oil Pollution Yupeng Chen, Jingxin Meng, Zhongpeng Zhu, Feilong Zhang, Luying Wang, Zhen Gu, and Shutao Wang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b01061 • Publication Date (Web): 08 May 2018 Downloaded from http://pubs.acs.org on May 8, 2018

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Bio-Inspired Underwater Super Oil-Repellent Coatings for Anti-Oil Pollution Yupeng Chen†,§, Jingxin Meng†*, Zhongpeng Zhu†,§, Feilong Zhang,§, Luying Wang§, Zhen Gu†, Shutao Wang†,§* †

CAS Key Laboratory of Bio-inspired Materials and Interfacial Science, CAS Center for

Excellence in Nanoscience, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China. §

University of Chinese Academy of Sciences, Beijing, 100049, P. R. China.

ABSTRACT: Underwater superoleophobic surfaces have attracted great attention due to their broad applications such as anti-oil adhesion, oil capture and transportation, and oil/water separation. However, it is often fairly complex and time-consuming, involving in the construction of micro/nanostructures and the regulation of chemical compositions, there is an urgent need to develop new strategies to conquer these problems. Inspired by the strong anchoring capability and easy accessibility of plant polyphenols, we can readily and rapidly fabricate tannic acid (TA) coated copper surfaces with the excellent underwater super oil-repellent property. To achieve the optimal condition for TA modification, the influence of immersing time, TA concentration and pH value on underwater oil wettability and adhesion has been systematically explored. Furthermore, the underwater super oil-repellent feature can be widely achieved for different oils and on various metal sheets, suggesting the potential applications for plenty of fields such as anti-oil pollution. KEYWORDS: tannic acid, superoleophobic, oil-repellent, dip-coating, microstructure 1 ACS Paragon Plus Environment

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1. INTRODUCTION Underwater superoleophobic surfaces have attracted much attention due to their broad applications,1-5 such as anti-oil adhesion of oil pipeline, marine equipments and industrial metals,6 oil transportation,7-8 and oil/water separation.9-13 To fabricate these surfaces, the main approaches consist of template method depending on the construction of bio-inspired micro/nanostructures,14-17 surface coating process relying on the regulation of chemical compositions,10, 18-19 and their combination.20-23 For example, inspired by the specific wetting behavior of fish scales, anisotropic underwater oleophobicity have also been obtained by mimicking the oriented hook-like spines on the fish skin.15, 17 In addition, switchable oiladhesion have been achieved on underwater superoleophobic surfaces grafted from poly(acrylic acid) and poly(2-vinylpyridine)-b-polydimethylsiloxane, showing their promising applications in controllable oil/water separation and oil transportation.18-19 In recent years, robust underwater superoleophobic materials composed of polyacrylic acid/polyvinylidene fluoride–graphene nanosheet composites have also been fabricated by integrating hierarchical structures with hydrophilic surfaces.20,

22

Although they exhibit excellent function and

potential application, most of these reported methods seem complex and time-consuming, urgently requiring new methods to conquer these problems. In our daily life, we sometimes observe the stain adhered on the wall of cups after the serving of tea or grape wine. It is the plant polyphenols in tea and grape wine that are responsible for the strong staining.24-25 As an important member of the large family of polyphenols, tannic acid (TA) (Figure S1a), can be considered as one of the ideal molecules for surface modification due to its strong anchoring capability.26-39 For instance, polyphenols inspired multifunctional coatings have been prepared on various substrates by immersing in aqueous solutions containing polyphenols, showing strong antibacterial property and no observable cytotoxicity.24 By utilizing coordination bonding between TA and the trivalent iron cation, metal-polyphenol capsules have also been prepared for promising applications in 2 ACS Paragon Plus Environment

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the fields of drug delivery, biosensing and bioimaging.40-41 Recently various functional metalphenolic networks from TA and metal ions can be used as supports in catalysis or nanofiltration membranes for wastewater remediation.42-43 Regarding the strong anchoring ability and the easy availability of plant polyphenols (e.g., TA), we wonder if the superior oilrepellent coatings can be fabricated by utilizing the anchoring interaction between TA molecules and metal surfaces. Herein, we report a general strategy to prepare underwater super oil-repellent coatings. Taking advantage of the strong anchoring capability of TA molecules, we can readily and rapidly prepare TA-coated copper surfaces with the excellent underwater superoleophobic property and ultra-low oil adhesion. To obtain the optimal condition for TA modification, the influence of immersing time, TA concentration and pH value has been systematically explored. Furthermore, the underwater superoleophobic property can be widely achieved on various metal sheets and for different oils. Therefore, the good processability and low cost of this strategy for the fabrication of super oil-repellent coatings, suggest its promising applications such as anti-oil pollution. 2. EXPERIMENTAL SECTION 2.1. Materials. Tannic acid (TA, ACS reagent, Mw = 1701.23 Da) was purchased from J&K and used as received. Copper (II) chloride dehydrate (CuCl2·2H2O), various oils (i.e., ndecane, n-hexane, petroleum ether, 1, 2-dichloroethane, vegetable oil) and commercial metal sheets (i.e., copper, titanium, nickel, iron, and zinc) were purchased from Sinopharm Chemical Reagent Co., Ltd.. Quartz crystal microbalance (QCM) resonators were purchased from Biolin Scientific. Deionized water (>1.82 MΩ cm, Milli-Q system) was used. 2.2. Fabrication of Flat Copper Surfaces. High-impurity (99.9%) source materials of copper powders (φ 3 mm × 5 mm) were used to deposit the Cu layer on cleaned Si wafers in a high vacuum chamber (~10-6 torr) at room temperature by an e-beam evaporator (Ohmiker50B, Cello Technology, Taiwan). In detail, a 10 nm layer of Cr and 100 nm layer of Cu were 3 ACS Paragon Plus Environment

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sequentially deposited on Si wafers. After that, the flat copper surfaces were stored in dry and clean containers. 2.3. Preparation of Super Oil-Repellent Coatings. The commercial metal sheets were cut into square shapes with the size of 2 cm × 2 cm. The metal sheets were put into 0.1 - 3.0 mg mL-1 TA solutions for different immersing time and pH value. The pH of TA solutions was precisely changed from 3 to 10 by adding 0.01 M NaOH or HCl solution. For instance, the copper sheets were firstly immersed in 0.01 M HCl solution for 30 s to remove surface oxide, followed by sonication in acetone, ethanol, and water for 10 min each and dried with nitrogen gas. Then, the cleaned copper sheets were put into 0.1 mg mL-1 solutions of TA at pH 10. Finally, these TA modified copper sheets were thoroughly rinsed with water and dried with nitrogen gas. 2.4. Preparation of CuII-TA Solutions. The CuII-TA solutions were achieved by mixing the individual additions of CuCl2·2H2O and TA molecules with the final concentrations of 0.04 mg mL-1 CuCl2 and 0.1 mg mL-1 TA, respectively. Then, the pH value of CuII-TA solutions was readily adjusted by adding 0.01 M NaOH or HCl solution. 2.5. Quartz Crystal Microbalance (QCM) Measurements. The CuII-TA coatings were prepared on QCM resonators using Q-Sense E1 system (Q-Sense E1, Biolin Scientific, Sweden). For copper-coated resonators: Initially, the QCM channel was washed with deionized water for ca.10 min. Then, TA solution at the concentration of 0.1 mg mL-1 and pH 10 was injected into the channel at a flow rate of 150 µL min-1. For gold-coated resonators: Initially, the QCM channel was washed with water for 10 min. Then, TA solution at the concentration of 0.1 mg mL-1 and pH 10 was injected into the channel at a flow rate of 150 µL min-1 for 1 min. Following, the TA was adsorbed for 10 min and then rinsed by water at the same pH value for 1 min to remove the unabsorbed TA molecules. Next, 0.04 mg mL-1 CuCl2 solution at pH 5 was injected into the channel for 1 min and remained adsorbed for another 10 min. The same operation was repeated for multi-step assembly of CuII-TA coatings. 4 ACS Paragon Plus Environment

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2.6. Characterization. Surface morphologies of bare and TA-coated copper sheets were observed with a field-emission scanning electron microscope (SEM) (JSM-6700F, JEOL, Japan). X-ray photoelectron spectroscopy (XPS) was performed on the Thermo Scientific ESCALab

250Xi

(ESCALab250Xi,

Thermo

Scientific,

America)

using

200

W

monochromated Al Kα radiation. The 500 µm X-ray spot was used for XPS analysis. The base pressure in the analysis chamber was about 3×10-10 mbar. Typically the hydrocarbon C1s line at 284.8 eV from adventitious carbon is used for energy referencing. The surface topography images were obtained using a nano-search microscope (OLS-4500, Olympus, Japan). Atomic force microscope (AFM) tip (OMCL-AC240TS-C3, Olympus, Japan) with spring constant 1.7 (N/m) and resonant frequency 70 (kHz) were used. The scan rate is 1 Hz and the scan size is 5 µm × 5 µm. The underwater oil contact angles (OCAs) were measured using an OCA25 machine (OCA25, Dataphysics, Germany) UV-vis absorption spectra of the TA and CuII-TA solution were recorded on a UV-vis absorption spectrophotometry (UV 2550, Shimadzu, Japan). Fourier transform infrared spectroscopy (FT-IR) spectra of the TA and CuII-TA solution (air-dried) were carried out on a Bruker EQUINOX55 instrument (EQUINOX 55, Bruker, Germany) with 20 scans per sample. The adhesive force measurement of oil droplet on metal sheets were conducted by using a high-sensitivity microelectromechanical balance system (DCAT21, Dataphysics, Germany). Firstly, an oil droplet (ca. 10 µL) was hung on a copper cap connected to the microbalance, and then the metal sheets were controlled to move upward towards the oil droplet at a constant speed of 0.05 mm s−1 until it contacted with the oil droplet. The metal sheets were then moved down and left the oil droplet. The shape change of the oil droplet, as well as the force change during the whole measuring process were recorded. During the measurement process, an optical microscope lens and a charge-coupled device (CCD) camera system were used to record the related images. 3. RESULTS AND DISCUSSION 5 ACS Paragon Plus Environment

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3.1. Fabrication of Underwater Super Oil-Repellent Coatings By modifying TA through a dip-coating method (Figure S1b), we can readily and rapidly fabricate underwater super oil-repellent coatings on metal sheets. Taking the flat copper surface as an example, we explore the influence of TA modification on surface morphology, the wettability and oil adhesion properties. Compared with bare flat copper surface (Figure 1a), TA-coated one show no obvious generation of microstructures, demonstrated by the scanning electron microscopy (SEM) images in Figure 1b. On the contrary, oleophobic properties were remarkably varied with underwater oil contact angles (OCAs) increasing from 141.4 ± 3.2° to 161.9 ± 1.1° (Figure S2), due to the introduction of TA molecules rather than microstructures (Figure 1b). We measured the water and oil (1, 2-dichloroethane) contact angles of bare and TA-coated flat copper surfaces in air after immersing for 30 min in 0.1 mg/mL TA solutions. As shown in Figure S3, after TA modification, the water and oil contact angles in air decreased from 69.5 ± 4.2° to 27.6. ± 3.1° and from 13.3 ± 1.7° to 8.2 ± 0.9°, respectively. The decrease of water contact angles in air indicates the increase of hydrophilicity after TA modification corresponding to the better underwater oleophobicity. In addition, their corresponding oil adhesion performance could be revealed by comparing the sliding behavior of oil droplets and oil adhesive force underwater. In detail, the oil droplet did not move at all even when the bare copper surface was tilted vertically (inset in Figure 1a), whereas the oil droplet rapidly rolled off when the oil sliding angle (OSA) of the TA-coated copper sheet was very low (ca. 2°, inset in Figure 1b). Furthermore, the underwater oil adhesive force was dynamically measured by contacting an oil droplet (10 µL, 1, 2dichloroethane) with the copper surfaces then allowing to leave. By utilizing a high-sensitivity micro-electromechanical balance system, the adhesion force between the oil droplet and the surface can be recorded accurately. Bare flat copper surface was highly adhesive to oil (45.3 ± 4.4 µN), exhibiting a large shape distortion of the oil droplet (Figure 1c). In contrast, the oil adhesive force on TA-coated flat copper surface was declined to ca. 0 µN, revealed by 6 ACS Paragon Plus Environment

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negligible deformation and loss of the oil droplet (Figure 1d). These results confirm that underwater super oil-repellent coatings can be prepared by coating TA molecules on flat copper surfaces without introducing microstructures. In addition, X-ray photoelectron spectroscopy (XPS) data reveal surface chemical compositions of bare and TA-coated copper surfaces. As shown in Figure 1e-f, the amounts of Cu 2p signal decreased, with a concurrent increase in the amounts of C 1s signal and O 1s signal, indicating the successful modification of TA molecules. Using a nano-search microscope, we compared the surface topography images of bare and TA-coated flat copper surfaces after immersing in 0.1 mg/mL TA solutions. As shown in Figure S4, the surface roughness increased slightly after immersing in TA solutions, indicating the homogeneity of underwater super oil-repellent coatings. Furthermore, the binding energy for C 1s core-level spectrum is observed to be 284.9 eV, which can be attributed to the presence of hydrocarbons in TA (Figure S5a). For the Cu 2p core-level spectrum, the peak at 933.2 eV is consistent with the presence of CuII species (Figure S5b). As shown in Figure S6, the C 1s spectra of bare and TA-coated copper surfaces were fitted. The corresponding ratio of different carbon species was assessed by peak fitting of experimental data (Table S1), indicating that C-C, C-O and C=O increase from 31.12% to 48.57%, 5.57% to 13.57%, 2.77% to 4.15%, respectively. These results also show that TA molecules were successfully modified on the copper surfaces. Furthermore, there is a major peak at 531.7 eV and a relatively small peak at 533.4 eV, which can be assigned to the Cu-OH and Cu-O species, respectively (Figure S7).40 Therefore, these results show that plenty of TA and CuII ion on the TA-coated copper surfaces may lead to the generation of underwater super oil-repellent coatings.

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Figure 1. Comparisons of surface morphology, underwater oil adhesion and chemical composition between bare and TA-coated flat copper surfaces. a, b) Scanning electron microscopy (SEM) images of the bare and TA-coated flat copper surfaces. Images inseted in a, b) exhibit the oil droplet still adheres on the vertically tilted surface or readily rolls off the slightly tilted surface when the oil sliding angle (OSA) was ca. 2°. c, d) The underwater oil adhesion performance on these two surfaces. ∆F in c) is the adhesive force measured between the oil droplet and the copper surface. In contrast, there is no force drop in the receding curve of d). e, f) The corresponding X-ray photoelectron spectroscopy (XPS) of these two surfaces.

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3.2. The Influence of Different Factors on Underwater Super Oil-Repellent Property We further explored the influence of different factors on preparing underwater super oilrepellent coatings, including TA concentration, immersing time, and pH value. With the gradual increase of TA concentration and immersing time (Figure 2), the introduction of TA endows the copper surfaces with underwater super oil-repellent property, leading to the higher OCAs (ca. 162°) and ultra-low oil adhesion (less than 2.5 µN), even at a very low TA concentration (i.e., 0.1 mg/mL) and a short immersing time (i.e., 5 min). We further immersed flat copper surfaces in TA solutions with a much lower concentration of 0.01 mg/mL. After TA modification, the OCAs of TA-coated flat copper surfaces is 148.6 ± 5.0° for 30 min (Figure S8), whereas the TA-coated flat copper surfaces have higher OCAs (ca. 162°) in 0.1 mg/mL (Figure 2a), revealing that 0.1 mg/mL is the minimum concentration of TA to obtain the super oil repellent surfaces. Therefore, these results show that underwater super oilrepellent coatings could be achieved under a universal condition.

Figure 2. The wettability and underwater oil adhesion of the TA-coated flat copper surfaces in various concentration of TA aqueous solutions and at different immersing time. a) The underwater superoleophobicity and ultra-low oil adhesion of the TA-coated copper surfaces alter slightly as the concentration of TA solutions increases. b) The underwater superoleophobicity and ultra-low oil adhesion of the TA-coated copper surfaces could be obtained at a short immersing time. 9 ACS Paragon Plus Environment

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To investigate the influence of pH value on underwater super oil-repellent coatings, we firstly explore the UV-vis absorption spectra of TA and CuII-TA solutions at different pH values (Figure S9). For TA solutions (pH 3-4), they exhibit two typical peaks at 224 nm and 275 nm, suggesting the neutral form of TA. With the further increase of pH value (pH > 4), a broad absorption band between 330 nm and 350 nm was gradually observed and its intensity was slightly enhanced for TA solutions. A clear peak at 330 nm appeared at pH 9 and peaks at 250 nm and 350 nm emerged at pH 10, respectively. These new peaks indicated the phenolate form of TA, resulting from ionization of phenolic hydroxyl groups in alkaline solution.44-45 Comparing to those of TA solutions, the peaks of CuII-TA solutions at 224 nm and 275 nm shifted to longer wavelengths when the pH value increased. The change of absorption peak was assigned to charge-transfer transition induced by the coordination reaction between CuII ion and TA.40 At pH 8, a new peak at 330 nm appeared clearly, and its intensity increased to the maximum value at pH 10, indicating the transition of CuII-TA state from mono-complex to bis-complex.46-47 These results reveal the transition of dominant CuII-TA state under different pH values. Although the coordination states between TA and CuII ion were pHdependent, underwater super oil-repellent sheets could still be obtained under pH 3-10. Figure S10 shows that the OCAs were always greater than 150° and the oil adhesive forces were less than 4 µN, suggesting the promising application under a relatively wide pH range. 3.3. The Formation Mechanism of Underwater Super Oil-Repellent Coatings As shown in Figure 3a, we propose a possible growth mechanism of underwater super oilrepellent coatings, including anchoring, dissolving and coordinating processes. In the initial stage, the catechol groups of TA incline to anchor on the oxidized surfaces of the copper sheets, forming a monolayer of TA. Then, the partial copper on the surfaces are dissolved into the TA solutions. Finally, the free TA in solutions would coordinate with the dissolved CuII ion, forming the crosslinked CuII-TA coatings. To demonstrate this above-mentioned mechanism, the modification process of TA molecules on the metal surfaces was firstly in situ 10 ACS Paragon Plus Environment

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monitored by quartz crystal microbalance (QCM). Due to the anchoring behavior of catechol groups of TA, the resonance frequency of copper-coated resonator in Figure 3b decreased after injecting TA solution (e.g., pH 10). The average thickness of CuII-TA coatings is estimated to be ca. 20 nm after the initial anchoring stage by QSence Dfind using equation ∆δ =

∆F × 17.7 100

nm (∆δ and ∆F represent the thickness and the frequency, respectively.). As

shown in Figure S4, the surface roughness of the TA-coated copper surfaces increased slightly with the increase of immersing time. After a short time (ca. 160 s), the resonance frequency sharply increased, suggesting the dissolving process of copper from the resonator surface. We measured the underwater oil wettability of TA-coated flat copper surfaces after immersing for 1 min in 0.1 mg/mL TA solutions. After TA modification, the copper surfaces show a rather higher underwater oil adhesion (ca. 29.9 ± 8.4 µN) and a lower OCAs (ca. 148.1 ± 3.3°) (Figure S11). Through the analysis of the modification process of TA, the immersing time (1 min) is shorter than the anchoring time of TA (ca. 160 s) in the initial stage of modification process which is obtained from the QCM results. Thus, the copper surface is not sufficiently modified by TA molecules after immersing for 1 min, which is not good enough for underwater oil-repellent performance. Then, the copper-coated resonator is replaced by the gold one to reveal the coordinating process (Figure 3c). Because of the anchoring of catechol groups, the resonance frequency also decreased after adding the TA solution at pH 10. Later, the injection of the CuCl2 solution (pH 5) would lead to the further decrease of the resonance frequency, resulting from the coordination interaction between TA and CuII ion. Ultimately, the CuII-TA coatings were successfully performed on the gold-coated resonator via the multistep assembly of TA and CuII ion, demonstrated by the gradual decrease of the resonance frequency (Figure S12). Compared with pure TA, Fourier transform infrared spectroscopy (FT-IR) spectra of the TA solutions immersed with copper sheets indicated the coordination interaction between the phenolic hydroxyl groups and CuII ion, revealed by the reduced 11 ACS Paragon Plus Environment

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intensity of HO-C stretching peak at 1202 cm-1 (Figure 3d).39 Thus, these results suggest that the generation of underwater super oil-repellent coatings may result from complicated modification process of TA on the copper surfaces.

Figure 3. a) Schematic illustration of the in situ growth mechanism of the CuII-TA coatings. R represents the remainder of the TA molecule. b) Growth of the CuII-TA coatings on the copper-coated resonator by injecting TA solution at pH 10, in situ monitored using a quartz crystal microbalance (QCM). c) Growth of the CuII-TA coatings on the gold-coated resonator via two-step assembly. Firstly, TA solution at pH 10 was injected, then the CuCl2 solution at pH 5 was injected. d) Fourier transformed infrared (FT-IR) spectra of TA and TA solution immersed with copper sheets. The dotted line indicates the HO-C stretching peak at 1202 cm-1.

3.4. The Universalities and Applications of Underwater Super Oil-Repellent Coatings To verify the universality of this surface coating strategy inspired by plant polyphenols, we employed various oils and different metal sheets. As shown in Figure 4a, the TA-coated 12 ACS Paragon Plus Environment

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commercial copper sheets also showed the outstanding underwater super oil-repellent properties for various oils, including n-decane, n-hexane, petroleum ether, 1, 2-dichloroethane, dichloromethane, and vegetable oil. Although there are no obvious changes for the rough morphologies of copper sheets after TA modification (Figure S13), the underwater super oilrepellent features can always be obtained, showing that the OCAs are all greater than 160° and the adhesive forces are less than 4 µN. When we extended to different metal sheets (i.e., Cu, Ti, Ni, Fe and Zn), similar underwater super oil-repellent results can be observed in Figure 4b. For active metals (e.g. Zn and Ni), there are also no obvious changes on the surface morphologies after immersing for 30 min in 0.1 mg/mL TA solutions at pH 10 (Figure S14). To further reveal the anti-oil pollution capability, we dipped these bare and TA-coated metal sheets into silicon oil dyed by oil red O, respectively. After washing by water, no residual oil can be stained on the TA-coated metal sheet compared with the heavily stained bare one (Figure 4c), revealing their excellent anti-oil adhesion property. Taking the TA-coated copper sheet as an example, the corresponding anti-oil pollution performance is further shown in Movie S1. In addition, we observed the process of oil droplet contacting the surface (Figure S15). The neglected deformation and residue of oil droplet indicates the underwater super oilrepellent property of the TA-coated copper surfaces. Therefore, these experimental results reveal that it is a universal strategy to fabricate underwater super oil-repellent coatings for various oils and on different metal sheets.

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Figure 4. A general strategy to fabricate underwater superoleophobic surfaces with ultra-low oil adhesion for different oils and metal sheets. The underwater superoleophobicity and ultralow oil adhesion of a) different oils and b) various TA-coated metal sheets. c) Digital images show that there is no residual oil (silicon oil dyed by oil red O, viscosity = 14000 cst) stained on the TA-coated sheets after washing by water comparing with the bare sheets, revealing the excellent anti-oil adhesion property.

4. CONCLUSIONS In conclusion, we have prepared underwater super oil-repellent coatings on the metal sheets, showing underwater superoleophobic property with ultra-low oil adhesion. This kind of underwater super oil-repellent coatings could be rapidly achieved under universal conditions. Furthermore, it is a general strategy to fabricate underwater superoleophobic coatings for different oils and on various metal sheets without constructing microstructures. Therefore, this strategy exhibits the good processability and low cost for preparing underwater super oilrepellent coatings, showing great application in the crucial area of anti-oil pollution.

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ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This research is supported by National Natural Science Foundation of China (21425314, 21501184, 21434009, 21421061 and 21504098), National Program for Special Support of Eminent

Professionals,

Beijing

Municipal

Science

&

Technology

Commission

(Z161100000116037), and Youth Innovation Promotion Association CAS (2017036). ABBREVIATIONS TA, tannic acid; QCM, quartz crystal microbalance; SEM, scanning electron microscope; OCAs, oil contact angles; OSA, oil sliding angle; XPS, X-ray photoelectron spectroscopy; AFM, atomic force microscope; FT-IR, Fourier transform infrared spectroscopy. REFERENCES (1)

Chu,

Z.;

Feng,

Y.;

Seeger,

S.

Oil/Water

Separation

with

Selective

Superantiwetting/Superwetting Surface Materials. Angew. Chem. Int. Ed. 2015, 54, 15 ACS Paragon Plus Environment

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