Matchstick-Like Cu2S@CuxO Nanowire Film: Transition of

Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article 2

x

A Matchstick-like CuS@CuO Nanowire Film: Transition of Superhydrophilicity to Superhydrophobicity Cailong Zhou, Huijing Li, Jing Lin, Kun Hou, Zhijie Yang, Pihui Pi, Shouping Xu, Xiufang Wen, and Jiang Cheng J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03645 • Publication Date (Web): 22 Aug 2017 Downloaded from http://pubs.acs.org on August 28, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

A Matchstick-like Cu2S@CuxO Nanowire Film: Transition of Superhydrophilicity to Superhydrophobicity

Cailong Zhou,

†

Huijing Li,

†

Jing Lin,

‡

Kun Hou,† Zhijie Yang,† Pihui Pi,† Shouping Xu,†

Xiufang Wen,† and Jiang Cheng †*

†

School of Chemistry and Chemical Engineering, South China University of Technology,

Guangzhou 510640, P.R. China ‡

School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006,

P.R. China

*

Corresponding author: J. Cheng; E-mail: [email protected]; Tel: +86-20-87112057

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 47

ABSTRACT. We fabricated a matchstick-like Cu2S@CuxO nanowire film on copper mesh by applying a Cu(OH)2 nanowires template-sacrificial method, which can transformed from superhydrophilic to superhydrophobic just after storage in air for a certain period without any further organic modification. The surface morphology, chemical composition and the wettability were investigated by Scanning Electron Microscopy (SEM), X-ray diffractometer (XRD), Raman, X-ray Photoelectron Microscopy (XPS) and contact angle measurement. Results showed that the change of surface chemical composition and the trapped air among the matchstick-like structures were the decisive factors for the wettability transition. Therefore, on-demand oil/water separation was achieved, which was performed by using the superhydrophilic-underwater superoleophobic mesh for separating light oil/water mixtures and the superhydrophobic one for separating heavy oil/water mixtures.


2

Page 3 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Wettability, as a macroscopic representation of the interaction between liquid and solid substrate, is a crucial property of solid surfaces from aspects of a theoretical viewpoint and practical applications.1 Inspired by nature, many anti-wetting or superwetting surfaces were prepared by controlling the surface free energy and surface micro/nanostructures. The typical applications of these surfaces include self-cleaning,2,3 oil/water separation,4-6 anti-icing and anti-fogging,7,8 atmospheric water collection,9 anti-corrosion,10 and antibacterial activities11 etc. Because of superior electrical and thermal conductivity, mechanical workability, malleability and relatively noble properties, copper becomes one of the most commonly used engineering materials.12 To obtain special wettability (such as superhydrophilicity and superhydrophobicity) on copper substrate, most efforts chose to create micro/nanostructures on the copper surface based on copper hydroxide or copper oxide, followed with chemical modification at times. For instance, Cheng et al. prepared ball-like structured Cu(OH)2 on copper foil and modified with alkyl thiol to obtain superhydrophobic surfaces with controlled adhesion.13 Zhang et al. fabricated a superhydrophilic Cu(OH)2 coated copper mesh and realized oil/water separation.14 Liu et al. achieved non-aqueous multiphase liquid separation using a robust Cu(OH)2 nanoneedles decorated copper mesh with tunable wettability.15 Li et al. obtained superhydrophobic CuO surfaces with different topographies on copper plate which could tune wettability between "Locus" state and "Gecko" state.16 Ansah et al. reported various morphologies on copper mesh, such as needle-like, hair-like, arch-like, and pine needle-like structures based on Cu(OH)2, CuO or their composite. The surfaces could turn to superhydrophobic after treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane.17


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 47

It is worth noticing that a two-step method is usually required to achieve superhydrophobicity, constructing micro/nanostructures and chemical modification by low surface free energy materials.18 Creating a superhydrophobic surface without any organic modification remains a great challenge in order to extend its durability, especially under harsh conditions in practical application.19 Some previous works have successfully prepared inorganic super-antiwetting surfaces on copper substrates by creating a uniform rough structure without further hydrophobization (details can be seen in Table 1). Electrodeposition, oxidation and displacement reaction are the main methods to fabricate superhydrophobic surface on copper substrates and CuO seems to be the material most presented in these works. However, CuO has poor resistance to acid which is similar to Cu(OH)2, giving this use a fatal limitation in industrial applications when exposed in acidic environment. Therefore, it is favorable to develop more chemically stable nanostructures to fabricate copper surfaces with special wettability. In order to solve the problem of poor acid-resistance of Cu(OH)2, we prepared previously a more stable CuC2O4 nanoribbons coated copper mesh and achieved oil/water separation.20 However, CuC2O4 is still not an optimal choice under the condition of high acid concentration. Copper sulfides (especially CuS and Cu2S) are known as important p-type semiconductors of versatility, availability, low-toxicity and stability over a wide range of pH,21 and widely studied in the fields of photocatalysis,22 photoelectrochemistry,23,24 solar cells,25,26 energy storage devices,27 and biomedical applications.28 Previously, we prepared a curled plate-like superhydrophilic-underwater

superoleophobic

Cu2S

coated

copper

mesh29

and

a

superhydrophobic poly(dimethylsiloxane) (PDMS) modified Cu2S@Cu2O micro/nanoparticles film on copper mesh30 to realize oil/water separation. In order to obtain ordered copper sulfides structures, we fabricated Cu2S@CuxO nanowires coated copper mesh (S-NWM) in the present


4

Page 5 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


work by immersing Cu(OH)2 nanowires coated copper mesh (H-NWM) into sodium sulfide solution. The freshly prepared S-NWM displayed superhydrophilicity and underwater superoleophobicity even under harsh environments. Interestingly, the matchstick-like Cu2S@CuxO nanowires film transformed from superhydrophilic to superhydrophobic after a period of storage in air without any organic modifier. According to the transformation of wettability, we could utilize the mesh to realize on-demand oil/water separation on the basis of the density of oil.

EXPERIMENTAL SECTION Materials. Ethanol, isopropanol, hydrochloric acid, n-hexane, dichloromethane, chloroform, Methylene Blue, Sudan II, sodium sulfide, sodium chloride, sodium hydroxide and ammonium persulfate were purchased from Damao Chemical Reagent Co., Ltd. (Tianjin, P.R. China) and used as purchased without further purification. Soybean oil was obtained from a local market. Kerosene was bought from SINOPEC (Beijing, P.R. China). Copper mesh with the average pore size of about 85 µm was produced by Xiancai Metallic Net Co., Ltd. (Anping, P.R. China). Fabrication of Cu2S@CuxO Film on Copper Mesh. Copper mesh was trimmed into pieces with the size of 3 cm × 3 cm and sequentially washed ultrasonically in ethanol, isopropanol and deionized water for 10 min. It was then immersed in 0.1 M of hydrochloric acid solution to remove surface oxide followed by deionized water rinsing. The preparation of S-NWM was realized via two room-temperature reactions including an alkali assisted oxidation process and a sulfurization process. Briefly, the mesh was firstly soaked into a mixture of 12.5 mL of 10 M NaOH, 5 mL of 1 M (NH4)2S2O8 and 32.5 mL of H2O for 10 min to form Cu(OH)2 nanowires on the mesh, resulting in a light-blue-color appearance. After being withdrawn from the solution,


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 47

cleaned with deionized water and dried in air, the light-blue mesh was further treated by soaking it into a 50 mL of 50 mM Na2S solution for certain durations. Finally, the resulting mesh was rinsed with an abundance of deionized water and dried in air. Characterization. The surface morphologies of the samples were observed with scanning electron microscopy (SEM, ZEISS Merlin). The crystalline structure of the nanowires was investigated by a transmission electron microscopy (TEM, FEI Tecnai G2 F20). X-ray diffraction data of samples were obtained using an X-ray diffractometer (XRD, Bruker D8 Advance) with Cu Kα radiation. Raman spectra were recorded on a Raman spectrometer (Renishaw inVia) using the laser wave number of 514 nm. The surface elements and composition of the film surface were investigated using an X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi) with Al Kα radiation. Three-dimensional surface imaging of the films was tested by an atomic force microscopy (AFM, Park Systems XE-100). The wetting properties of the mesh were conducted using a contact angle analyzer (Shanghai Zhongchen Powereach JC2000D1A) with the testing water or oil droplet of 5 µL.

RESULTS AND DISCUSSION Composition and Morphology of the H-NWM and S-NWM. As displayed in Scheme 1, copper mesh was first immersed into an aqueous solution containing of NaOH and (NH4)2S2O8 to form Cu(OH)2 nanowires on the surface. The as-prepared H-NWM was subsequently immersed into a Na2S solution to eventually obtain the S-NWM. Both steps were conducted at room temperature. The mesh turns light blue after alkali assisted oxidation (Figure S1 in Supporting Information). As shown in Figure 1a, XRD pattern confirms the formation of orthorhombic phase of Cu(OH)2 (JCPDS no. 72-0140) on the substrate surface. After immersion


6

Page 7 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of the H-NWM into Na2S solution for 5 min, the intensity of Cu(OH)2 peaks decreased and a slight peak at about 45.95 sprouted, which could be assigned to the (630) plane of monoclinic phase of Cu2S (JCPDS no. 83-1462). Prolonging the immersion time to 30 min, along with the clear disappearance of Cu(OH)2, the obviously presented characteristic peaks at 2θ equal to 37.60, 46.18 and 48.59 strongly associate with the (034), (630) and (-536) planes of Cu2S (JCPDS no. 83-1462), respectively. Meanwhile, characteristic peaks marked with rhombuses locate at about 36.48 and 42.55 are assignable to the (111) and (200) planes of the cubic phase of Cu2O (JCPDS no. 05-0667). When increasing the sulfurization time to 180 min, we could clearly observe that the film largely changed into Cu2S.

Scheme 1. Schematic of the preparation of the S-NWM. Besides XRD, Raman spectroscopy is also widely adopted to observe the microstructure of nanoscale materials because of its high sensitivity to explore the local atomic arrangements and vibrations of the materials, as well as to provide important information about the structure and bonds of materials.31 Especially for copper compounds, such as CuxO (x=1, 2), CuxS (x=1, 1.75, 1.8, 1.95, 2, etc.) and Cu(OH)2, Raman spectroscopy could help to investigate the much lower existence of the above phases compared with the limitation of detection by XRD.32-34 Figure 1b displays the Raman spectra of H-NWM and S-NWM. The peaks at the positions of 293 cm-1 and 492 cm-1 in the spectrum of H-NWM are well in agreement with the characteristic peaks of


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 47

Cu(OH)2.35 After the H-NWM was immersed in Na2S solution for 30 min, the peaks of Cu(OH)2 -

totally disappeared. The most intense peak at about 217 cm-1 was assigned to 2Γ12 in Cu2O, some sub-peaks such as 405 cm-1 and 625 cm-1 belong to 4Γ12-.36 Additionally, peaks at about 285 cm-1 and 331 cm-1 could be distributed to the Raman active modes of Ag and Bg(1) in CuO.37 It should be mentioned that CuO was not found in XRD, possibly due to its low crystallinity. Meanwhile, the Raman scattering possesses a better sensitivity to copper oxide than XRD.38 When the sulfurization time was increased to 60 min, peaks of Cu2O were weakened, indicating the decrease in content of Cu2O (the intensity of Raman scattering may relate directly to the content of products34). The characteristic peaks of CuO and Cu2O were largely suppressed in intensity when the sulfurization time was increased to 180 min. The strong peak at 471 cm-1 is the typical Raman scatting peak of Cu2S.33,39,40


8

Page 9 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. XRD patterns (a) and Raman spectra (b) of the H-NWM and S-NWM. XPS was further conducted to confirm the surface chemical state and composition of the freshly S-NWM which obtained by sulfurization for 60 min. As shown in Figure 2a, only Cu, O, S and C elements were found in the survey scan spectrum. The Cu 2p3/2 peaks split at 931.3 eV and 933.0 eV can be assigned to the Cu+/Cu and Cu2+ states, respectively. The two fitting peaks from Cu 2p1/2 at about 951.2 eV and 953.8 eV verify the existence of Cu+ and Cu2+, respectively. Satellite peaks at 942.7 eV, 940.2 eV and 961.5 eV confirm the presence of Cu2+ (Figure 2b).41 Apparently the results demonstrate the existence of CuO on the nanowires surface. The S 2p can be divided into two peaks of 2p3/2 and 2p3/1 at the position of 160.0 eV and 161.1 eV,


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 47

respectively (Figure 2c).23 The peaks located at 529.8 eV and 531.1 eV in the O 1s spectrum belonged to the lattice O of Cu-O and the adsorbed O of -OH, respectively (Figure 2d).42 There was no observation of peak assigning to Cu-O-Cu bond at the position of about 532.0 eV,43 indicating no Cu2O on the mostly outer surface of the nanowires.

Figure 2. XPS spectra of the S-NWM prepared by sulfurization for 60 min: (a) full spectrum, (b) Cu 2p, (c) S 2p and (d) O 1s.


10

Page 11 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. SEM images of: (a, f, k) H-NWM and S-NWM prepared by sulfurization for different durations: (b, g, l) 5 min, (c, h, m) 30 min, (d, i, n) 60 min, and (e, j, o) 180 min. Inset of (k) is the cross-section of the Cu(OH)2 nanowires film. Inset of (n) is a typical picture of a pile of matchsticks. Scale bars in (a, b, c, d, e), (f, g, h, i, j) and (k, l, m, n, o) are 20 µm, 1 µm and 200 nm, respectively. Figure 3 shows the SEM images of the H-NWM and S-NWM. The original copper mesh has an average pore size of about 85 µm (Figure S2). After alkali-assisted oxidation, an enormous amount of Cu(OH)2 nanowires grew on the mesh surface, with average diameter and length of the nanowires of 200 ~ 300 nm and about 20 µm, respectively (Figure 3a, f and k). When the as-prepared H-NWM was immersed into Na2S solution for just 5 min, the nanowires tend to be much rougher with a little increase in diameter because of some nanoscale particles appeared on the surface of the nanowires (Figure 3b, g and l). Increasing the sulfurization time to 30 min, the diameter of the nanowires grew to 400 ~ 500 nm (Figure 3c and h). A close-up view


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 47

of several nanowires shows that they look like the matchsticks with intumescent fronts (Figure 3m). Further increasing the sulfurization time to 60 min, no more obvious variation in the morphology and diameter of nanowires was observed (Figure 3d, i and n). When the sulfurization duration was prolonged to 180 min, intensive change has occurred on the morphology, some nano- and micro- particles aggregated on the top of the nanowires as shown in Fig. 3e, j and o, indicating combination in the fronts of matchsticks with each other along with the secondary growth of the clusters assembled on the nanowires. Formation Mechanism of the S-NWM. The Cu(OH)2 nanowires were prepared by immersing the Cu substrate into a mixture of NaOH and (NH4)2S2O8 solutions for 20 min (Step I in Scheme 1). The reaction process is mainly formulated as Eq. (1) shown.44 Cu + 4OH − + 2NH 4 + + S2 O8 2− → Cu(OH) 2 + 2SO 4 2 − + 2NH 3 ↑ + 2H 2 O

(1)

As a self-sacrificial template, the Cu(OH)2 nanowires were sequentially immersed in Na2S solution containing of S2- ions to convert to the matchstick-like nanostructures (Step II in Scheme 1). The surface content of Cu(OH)2 might be firstly reduced by S2- to generate Cu2O (Eq. (2)). However, the solubility constant of Cu2O (Ksp= 2.0 × 10-15) is much higher than that of Cu2S (Ksp= 2.5 × 10-48),24,45 the anion-exchange reaction could further occur between O2- and S2(Eq. (3)),46 making the Cu2O unstable in aqueous solution containing of S2-. 2Cu(OH)2 + S2 − → Cu 2 O + S ↓ + 2OH − + H 2 O H 2 O + Cu 2 O + S2− → Cu 2S + 2OH −

(2) (3)

These reactions resulted in an interfacial layer and separating the inner Cu(OH)2 from the outside sulfur sources. The core/shell structures were consequently formed, leading to a hindrance for the direct sulfurization reaction. Further reactions were contingent on the diffusion of Cu2+ or S2- ions through the interface till the Cu(OH)2 cores depleted.26 As an intermediate,


12

Page 13 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Cu2O might be presented until all converted to Cu2S if the duration of sulfurization incessantly increased according to the analysis of XRD and Raman. Most of the nanowire outer layer nanowires contacted relative higher concentration of S2- than the inner parts did, so more complete reaction of anion-exchange between O2- and S2- might occur on the outer surface, thus Cu2O was not observed from XPS. Another evidence for Eq.(2) is the simultaneous generation of S, which could be observed from the yellow sulfur sediments at the bottom of the Na2S solution after the sulfurization treatment (Figure S3). The Cu2S is monoclinic phase which prefers anisotropic growth, so the surface of the as-prepared nanowires was quite rough (also could be seen from TEM image in Figure S4). The top of the nanowires might provide a suitable platform for the growth of Cu2S, thus leading to an intumescent structure. The formation of CuO might be due to the dehydration of some Cu(OH)2 as shown in Eq. (4).47 Cu(OH)2 + 2OH − → Cu(OH) 4 2 −

CuO + 2OH − + H 2 O

(4)

This series of reactions occurred during the process of sulfurization, resulting in a composite of Cu2S and CuxO (x=1,2) in the matchstick-like nanowires. If the sulfurization was incessantly carried on, the CuO could further react with S2- to form Cu2S (Eq. (5)). This is because the solubility constant of Cu2S is also much lower than that of CuO (Ksp= 1.0 × 10-20),48 and the anion-exchange reaction could further occur between CuO and Cu2S.49 2CuO + 2S2− + 2H 2 O → Cu 2S + S ↓ + 4OH −

(5)

Wettability of the S-NWM. As is well known, the wetting property of a solid surface generally depends on the surface architecture induced roughness and the chemical composition.50 The pristine copper mesh has a water contact angle (WCA) of about 89o ± 1.5o (Figure S5a), displaying a typical Wenzel state. Meanwhile, the underwater oil contact angle (OCA) for dichloromethane on the pristine copper mesh was 136o ± 1.3o (Figure S5b). The freshly prepared


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 47

S-NWM was superhydrophilic with the WCA about 0o (Figure S5c). Figure 4 displays the subsequent underwater oil-repellency testing of the S-NWM prepared by 60 min of sulfurization. For a series of testing oils (including n-hexane, kerosene, soybean oil, dichloromethane and chloroform), the surface shows good superoleophobicity with the OCAs larger than 150o and the oil sliding angles (OSAs) lower than 10o (Figure 4a). The oil touching-detaching experiment also testifies the ultralow adhesion between oil and the S-NWM surface (Figure S6). The as-prepared S-NWM possesses an excellent anti-corrosive property. As displayed in Figure 4b, in some of the corrosive conditions such as 1 M HCl, 1 M NaOH and saturated NaCl aqueous solutions, the SNWM maintained the desirable underwater superoleophobicity. Especially for the acidic environment, the Cu2S@CuxO nanowires demonstrated much better acid-resistance than Cu(OH)2 or CuO nanowires. The Cu(OH)2 could be corroded when been immersed in 1 M HCl just for 1 s (Figure S7). The CuO nanowires coated copper mesh, prepared by annealing the HNWM at 190 °C for 3 h, was also inevitably corroded within 30 s when soaked it in 1 M HCl (Figure S8). As a comparison, the morphology of the Cu2S@CuxO nanowires remains almost unchanged after soaking in 1 M HCl for 48 h (Figure S9), exhibiting an outstanding acidresistance. It can be concluded that the presence of Cu2S could efficiently prevent the occurrence of acid corrosion.


14

Page 15 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Underwater OCA and OSA of various oils on the 60-min S-NWM sample surface. (b) Underwater OCA and OSA (the testing oil is dichloromethane) of the S-NWM in different corrosive solutions. It is intriguing that, after storage in air for about two weeks, all the S-NWM samples changed from superhydrophilic to (super) hydrophobic without any surface modifications (Figure 5a), while the H-NWM kept superhydrophilicity because of the inherent hydrophilicity of Cu(OH)2 (Figure S10). The WCA of S-NWM prepared by 30 min and 60 min of sulfurization treatment reached high up to 153o ± 2.4o and 157o ± 1.8o, respectively. In order to investigate the conversion progress of the wetting behavior, the wettability transition of the S-NWM with time was measured as shown in Figure 5b. When the freshly prepared S-NWM stored in air for 7 days, the WCA increased to 91.5o, that is, it has been switched to hydrophobic. After thirteen days of storage, the WCA increased to over 150o, enabling the complete transition from hydrophobicity to superhydrophobicity.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 47

Figure 5. (a) WCAs of the S-NWM prepared by sulfurization for different durations after storage in air for two weeks. (b) The WCA variation of the S-NWM prepared by sulfurization for 60 min when stored in air for diverse periods of time. Several tests have been performed to evaluate the superhydrophobicity of the as-stored SNWM. As displayed in Figure 6a, the water droplets could stand on the surface showing almost spheres. A jet of water can easily bounce off the mesh surface with no residues, indicating good water repellency (Figure 6b and Video S1). When the superhydrophobic mesh was submerged into water by an external force, it showed a clear silver mirror-like phenomenon (Figure 6c and Video S2). This is because an air layer may be trapped on the surface, consequently, a solidliquid-air interface would be established when submerging the mesh into water, which can prevent the water permeation effectively.51 Figure 6d shows a series of time-lapse photographs of


16

Page 17 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a water droplet (5 µL) impacting on the obtained superhydrophobic S-NWM surface employing a high speed camera. The water droplet could easily bounce for 4 times in 140 ms with no obvious decrease of height, indicating great superhydrophobicity. All the evidence demonstrates that, after stored in air for an adequate duration, the matchstick-like nanowires film has transformed from a superhydrophilic state to the lotus leaf-like state even no organic modifier was used.

Figure 6. Superhydrophobic behaviors of the S-NWM after stored in air: (a) Photographs of the deionized water droplets stay on the as-stored S-NWM surface. (b) A jet of water bouncing off the as-stored S-NWM surface. (c) The as-stored superhydrophobic S-NWM was immersed into water by an external force, showing a silver mirror phenomenon. (d) Time-lapse photographs of a water droplet bouncing on the as-stored S-NWM. To better understand the mechanism of wettability transition, the high resolution C 1s XPS spectra of freshly prepared S-NWM and the same sample after storage turning to superhydrophobic were conducted as shown in Figure 7. The C 1s peak resolved into three peaks with binding energies of 283.1 (283.3), 284.3 (284.4) and 287.4 (287.3) eV are corresponding to C-C/C=C, C–O and O-C=O, respectively.23,52 The presence of C-C/C=C reveals that there are


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 47

some airborne hydrocarbons generated during the reaction. In the surface of freshly prepared SNWM, the proportion of the hydrophobic hydrocarbons was 49.7%, and simultaneously, the proportion of C-O and O-C=O which are hydrophilic,53 was 32.9% and 17.4%, respectively. In contrast, the proportion of C-C/C=C in the as-stored S-NWM has a dominant position of 69.7%, and the proportion of C-O and O-C=O decreased to 18.3% and 12.0%, respectively. So one of the main reasons for the transition of superhydrophilicity to superhydrophobicity is the variation of the adsorbed organic hydrocarbons, which is in good agreement with the previous work by Li

et al.54 AFM further indicates a slight increase in average roughness (Ra) from 123 nm to 142 nm after stored to superhydrophobic state (Figure S11), suggesting the surface morphology changed little after storage, which is in agreement with the SEM result (Figure S12). Though the increase of hydrophobic hydrocarbons provided a significant probability for the increase of WCA, the storage-induced air-pockets in the hierarchical matchstick-like nanowires might be another important factor. Wang et al. demonstrated that the trapped air in the structures placed an important role in the transition of superhydrophobicity (underwater superoleophilicity) to underwater superoleophobicity.55 Barthlott et al. reported that the Salvinia surface which has eggbeater-shaped structure can effectively trap air thus caused the special water repellency performance.56 In this work, the surface of freshly prepared S-NWM had almost equal contents of hydrophobic groups and hydrophilic groups from C 1s peaks of XPS as shown in Figure 7, nevertheless, still displaying superhydrophilicity, which might be due to lack presence of air among the structures. After two weeks of storage, the percentage of C 1s peak increased slightly from 27.53% to 27.69%, while both the values of Cu 2p peak and S 2p peak decreased (Figure S13 and Table S1). Considering that the variation of the hydrophilic hydrocarbons (C-O and OC=O) to hydrophobic hydrocarbons (C-C/C=C) would result in reducing the amount of O, one


18

Page 19 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


can conclude that the additional O may come from the physically adsorbed oxygen molecules (O2) on the nanowire surface during air exposure. Notably, the matchstick-like nanowires structure, to some extent, likes the eggbeater-shaped structure, could provide enough space to store the air. Herein, the airborne hydrophobic hydrocarbons and the special structures cocontribute to the final superhydrophobicity even no further chemical modification was adopted.

Figure 7. C 1s core level XPS spectra of (a) the freshly prepared 60-min S-NWM and (b) the same sample stored in air for two weeks. The relationship between superhydrophilicity, underwater superoleophobicity and superhydrophobicity is illustrated in Figure 8a. In the water-oil-solid interface, the underwater OCA can be expressed as Eq. (6) according to Young’s equation:57

cos θ OW =

γ OA cos θOA − γ WA cos θ WA γ OW

(6)

where θOA, θWA and θOW, are the contact angles of oil in air, water in air, and oil in water, respectively. As well as, γOA, γWA, and γOW are the surface tensions of oil/air, water/air, and oil/water interfaces, respectively. When γOAcosθOA < γWAcosθWA, an oleophobic condition can be guaranteed. Meanwhile, oil surface tension is always much lower than that of water (γOA < γWA), so most of the hydrophilic surfaces (cosθWA > 0) are also underwater oleophobic. Especially for a


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 47

superhydrophilic surface, could possess underwater superoleophobicity simultaneously (Figure 8a). After storage in air, the water wettability transition can be understood theoretically by the Cassie-Baxter equation:58

cos θS = f1cosθ − f 2

(7)

where θ and θs are the CAs of the smooth surface and the S-NWM surface, respectively. f1 and f2 represent the fraction of the solid surface and air in contact with water, respecttively. So f1 + f2 = 1. We can easy to deduce that when the f2 increased and f1 decreased at the same time, θs would increase correspondingly. The trapped air pocket can prevent the penetration of water into the surface effectively (Figure 8a). Therefore, the WCA of the S-NWM would increase gradually with the prolongation of storage time, resulting in a finally superhydrophobic state. Among thousands of papers concerning the superhydrophobic surface, there is just a small quantity of inorganic superhydrophobic films without any organic modification. So, we have summarized some of this type of work, as listed in Table 1. Through an electrodeposition process or a displacement reaction to decorate metal on a substrate is the most popular approach to prepare inorganic superhydrophobic films without artificial modification. Copper oxides seem to be the most studied materials, they can easily form hierarchical structures on copper substrate and achieve superhydrophobicity. Rare earth oxides, in comparison, were relatively less studied. It's notable that, some of the materials need a storage procedure to form enough air pockets among the structure likewise.37,52,59,60 The reported morphologies are diverse, but most of them are 3D structures.


20

Page 21 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Summary of Some Inorganic Superhydrophobic Films without Organic Modifiers Methods

Chemical Composition WO3 Cu Cu Cu/Cu2O

Electrodeposition-based

Oxidation-based

Displacement reaction-based

Others

Sol-gel method followed by a growth process Chemical vapor deposition (CVD) A chemical reaction followed by an annealing process Atomic layer deposition (ALD) Anodic electrocrystallization

Substrates Indium tin oxide (ITO) glass Copper sheet Copper sheet Stainless steel mesh

Cu/ZnO/Zn/CuO/Z n(OH)2/Cu5Zn8

Copper sheet

Sn/SnOx

Tin, copper or iron disk

Bi/Bi2O3

Tin disk

Ni Ni/Co

Copper plate Copper disk

CuO

Copper plate

Morphology

151.3 ± 2.9o 162.1o 151o

62 63

Coral-like

163o

64

170o ± 2o

65

165o

66

164o

67

155.7o 163o

59 52

156o

60

Cu2O

Copper foil

ZnO, ZnO/Zn

Glass slide

Ag/Cu2O

Copper foil

Ag

Copper mesh

Sn

Zinc plate

ZnO

Glass wafer

Nanorod arrays

SnO2/SnO2/SiOx

Au-coated Al2O3 substrate

CuO/Cu3Pt/Cu

Copper sheet Copper plate

CuO/Cu(OH)2

Copper sheet

Ref.

o

Pebble beachlike Honeycomb-like Pyramid-like

Anomalous nanostructures Dendritic structures Dendritic structures Pine cone-like Flower-like Protuberances with nanowires Nanowires Sheet-like Microflowers on nanoneedles Porous film Clusters, clusters with nanorods Flower-like clusters “Sago cycas” branch-like Dendrite-like

CuO CuO

WCA#

61

o

~153 158o

68 69

159o

37

~152

o

70

158o, 155o

71

169.2o

72

159o

73 74

Nanowires with branches

156o 161.2o ± 1.3o 155.8o ± 1.1o

Copper plate

Coralline-like

170o

77

Y 2O 3

Si(100) with Si nanowires

50 nm-thick film

158o ± 4°

78

SnO

Tin disk

Pompon-like and flower-like Matchstick-like nanowires

153o

79

157o ± 1.8°

This work

A two-step reactions Cu2S/CuxO Copper mesh followed by storage # WCAs are the maximum values in the corresponding references.

75 76


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 47

Figure 8. (a) Schematic of the relationship between superhydrophilic, underwater superoleophobic and superhydrophobic surfaces. On-demand oil/water separation of: (b) "waterremoval" type and (c) "oil-removal" type. The oils (n-hexane (b) and dichloromethane (c)) and water were dyed with Sudan II and Methylene Blue, respectively. Separation efficiency of (d) underwater superoleophobic mesh for light oils (ρoil < ρwater) and (e) superhydrophobic mesh for heavy oils (ρoil > ρwater) versus the recycle numbers. Due to the special wettability of the S-NWM, we could use it to selectively separate water or oil from oil/water mixtures, especially for the oils with different densities. As is well known, the density of most oils is lower than that of water, so it is a better choice to use superhydrophilic/underwater superoleophobic filters (water-removal type) to separate these types of oil and water mixtures other than superhydrophobic/superoleophilic filters (oil-removal type).


22

Page 23 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


While

some

of

the

oils,

such

as

chloroform,

dichloromethane,

diiodomethane,

tetrachloromethane and 1, 2-dichloroethane, have a density greater than water, a superhydrophobic/superoleophilic filter is a relatively optimal choice under this condition.80 When selecting an inappropriate filter for separation of oil/water mixtures, a water (or oil) barrier layer would form on the mesh and prevent the separation from proceeding. For instance, if the density of oil is larger than water, the underwater superoleophobic mesh is not a good choice for separating heavy oil/water mixtures because the heavy oils will locate between the water and the filter to prevent water permeation (Figure S14). The previously common solution of this problem was to employ an acclivitous separation device which could make the filter-loving liquid touch the separation membrane.81 However, this approach is time-consuming and hard to control. Hence, we could use the S-NWM with alterable wettability to realize on-demand oil/water separation. Figure 8b and Video S3 show the separation process of n-hexane/water mixtures using the freshly prepared S-NWM. The n-hexane could remain stable on the water-prewetted SNWM while water quickly permeates through the S-NWM. Furthermore, we can use the superhydrophobic S-NWM to realize the separation of heavy oil/water mixtures, exhibiting the good flexibility (Figure 8c and Video S4). Figure 8d and e display the separation efficiency of the superhydrophilic/underwater superoleophobic and superhydrophobic S-NWMs for separating various oils with different densities. The separation efficiency was calculated using Eq. (8): 82 ES =

M filtrate × 100% M mixture

(8)

where Mfiltrate and Mmixture are the mass of water (or oil) in the filtrate and original oil/water mixture, respectively. For all the tested oils, the efficiency maintained above 96% after 5 cycles of separation, indicating the good stability.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 47

CONCLUSION In summary, we have demonstrated a facile two-step approach to preparing a matchstick-like Cu2S@CuxO nanowire film on copper mesh. A Cu(OH)2 nanowires film was adopted as a template because of its thermodynamic instability, which could further form Cu2S nanostructure through an anion-exchange reaction. The freshly prepared mesh displayed superhydrophilicity and underwater superoleophobicity even under severe acidic aqueous conditions. The matchstick-like Cu2S@CuxO nanowires coated mesh, nevertheless, can be transformed to superhydrophobic with a water contact angle high up to 157o ± 1.8o after about two-weeks of storage in air without any further modification by low surface energy materials. The transition may be attributed to the variation of surface chemical composition as well as the trapped air among the structure. Herein, we can utilize the special wetting behavior of the mesh to realize on-demand oil/water separation on the basis of the density of oil.

ASSOCIATED CONTENT

Supporting Information. Other information of the H-NWM and S-NWM. (PDF) A jet of water bouncing off the as-stored S-NWM surface. (AVI) The superhydrophobic S-NWM possesses silver mirror phenomenon. (AVI) Separation of n-hexane-water mixtures. (AVI) Separation of dichloromethane-water mixtures. (AVI)

AUTHOR INFORMATION

Corresponding Author [email protected]; Tel: +86-20-87112057. ORCID: Jiang Cheng: 0000-0002-9947-6193


24

Page 25 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


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.

ACKNOWLEDGMENT This work is supported by the National Natural Science Foundation of China (21776094), Science and Technology Planning Project of Guangdong Province (2014A010105052), Natural Science Foundation of Guangdong Province (2015A030313506) and One Hundred Steps Climbing Plan Program of SCUT (EC40617155). The authors gratefully thank Dr. Jingyu Wang for the AFM test.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 47

REFERENCES (1) Wang, Z. X.; Elimelech, M.; Lin, S. H. Environmental Applications of Interfacial Materials with Special Wettability. Environ. Sci. Technol. 2016, 50, 2132–2150. (2) Wang, Z. W.; Zhu, L. Q.; Li, W. P.; Liu, H. C. Bioinspired in Situ Growth of Conversion Films with Underwater Superoleophobicity and Excellent Self-Cleaning Performance. ACS Appl.

Mater. Interfaces 2013, 5, 10904–10911. (3) Kamegawa, T.; Shimizu, Y.; Yamashita, H. Superhydrophobic Surfaces with Photocatalytic Self-Cleaning Properties by Nanocomposite Coating of TiO2 and Polytetrafluoroethylene. Adv.

Mater. 2012, 24, 3697–3700. (4) Li, J.; Kang, R. M.; Tang, X. H.; She, H. D.; Yang, Y. X.; Zha, F. Superhydrophobic Meshes That Can Repel Hot Water and Strong Corrosive Liquids Used for Efficient Gravity-Driven Oil/Water Separation. Nanoscale 2016, 8, 7638–7645. (5) Zhou, C. L.; Cheng, J.; Hou, K.; Zhao, A.; Pi, P. H.; Wen, X. F.; Xu, S. P. Superhydrophilic and Underwater Superoleophobic Titania Nanowires Surface for Oil Repellency and Oil/Water Separation. Chem. Eng. J. 2016, 301, 249–256. (6) Song, S.; Yang, H.; Su, C. P.; Jiang, Z. B.; Lu, Z. Ultrasonic-Microwave Assisted Synthesis of Stable Reduced Graphene Oxide Modified Melamine Foam with Superhydrophobicity and High Oil Adsorption Capacities. Chem. Eng. J. 2016, 306, 504–511. (7) Wang, N.; Xiong, D. S.; Deng, Y. L.; Shi, Y.; Wang, K. Mechanically Robust Superhydrophobic Steel Surface with Anti-Icing, UV-Durability, and Corrosion Resistance Properties. ACS Appl. Mater. Interfaces 2015, 7, 6260–6272. (8) Yang, F. C.; Guo, Z. G. Bio-Inspired Design of a Transparent TiO2/SiO2 Composite Gel Coating with Adjustable Wettability. J. Mater. Sci. 2016, 51, 7545–7553.


26

Page 27 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(9) Ji, K. J.; Zhang, J.; Chen, J.; Meng, G. Y.; Ding, Y. F.; Dai, Z. D. Centrifugation-Assisted Fog-Collecting Abilities of Metal-Foam Structures with Different Surface Wettabilities. ACS

Appl. Mater. Interfaces 2016, 8, 10005–10013. (10) Zhang, X. F.; Chen, R. J.; Liu, Y. H.; Hu, J. M. Electrochemically Generated Sol-Gel Films as Inhibitor Containers of Superhydrophobic Surfaces for the Active Corrosion Protection of Metals. J. Mater. Chem. A 2016, 4, 649–656. (11) Manna, J.; Goswami, S.; Shilpa, N.; Sahu, N.; Rana, R. K. Biomimetic Method to Assemble Nanostructured Ag@ZnO on Cotton Fabrics: Application as Self-Cleaning Flexible Materials with Visible-Light Photocatalysis and Antibacterial Activities. ACS Appl. Mater. Interfaces 2015,

7, 8076–8082. (12) Xiao, F.; Yuan, S. J.; Liang, B.; Li, G. Q.; Pehkonen, S. O.; Zhang, T. J. Superhydrophobic CuO Nanoneedle-Covered Copper Surfaces for Anticorrosion. J. Mater. Chem. A 2015, 3, 4374– 4388. (13) Cheng, Z. J.; Du, M.; Lai, H.; Zhang, N. Q.; Sun, K. N. From Petal Effect to Lotus Effect: A Facile Solution Immersion Process for the Fabrication of Superhydrophobic Surfaces with Controlled Adhesion. Nanoscale 2013, 5, 2776–2783. (14) Zhang, F.; Zhang, W. B.; Shi, Z.; Wang, D.; Jin, J.; Jiang, L. Nanowire-Haired Inorganic Membranes with Superhydrophilicity and Underwater Ultralow Adhesive Superoleophobicity for High-Efficiency Oil/Water Separation. Adv. Mater. 2013, 25, 4192–4198. (15) Liu, J.; Wang, L.; Wang, N.; Guo, F. Y.; Hou, L. L.; Chen, Y. E.; Liu, J. C.; Zhao, Y.; Jiang, L. A Robust Cu(OH)2 Nanoneedles Mesh with Tunable Wettability for Nonaqueous Multiphase Liquid Separation. Small 2017, 13, 1600499.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 47

(16) Li, J.; Liu, X. H.; Ye, Y. P.; Zhou, H. D.; Chen, J. M. Fabrication of Superhydrophobic CuO Surfaces with Tunable Water Adhesion. J. Phys. Chem. C 2011, 115, 4726–4729. (17) Boakye-Ansah, S.; Lim, Y. T.; Lee, H. J.; Choi, W. S. Structure-Controllable Superhydrophobic Cu Meshes for Effective Separation of Oils with Different Viscosities and Aqueous Pollutant Purification. RSC Adv. 2016, 6, 17642–17650. (18) Si, Y. F.; Guo, Z. G. Superhydrophobic Nanocoatings: From Materials to Fabrications and to Applications. Nanoscale 2015, 7, 5922–5946. (19) Gu, C. D.; Tu, J. P. One-Step Fabrication of Nanostructured Ni Film with Lotus Effect from Deep Eutectic Solvent. Langmuir 2011, 27, 10132–10140. (20) Zhou, C. L.; Zhao, A.; Cheng, J.; Hou, K.; Pi, P. H.; Wen, X. F.; Xu, S. P. Xu, CuC2O4 Nanoribbons on Copper Mesh with Underwater Superoleophobicity for Oil/Water Separation.

Mater. Lett. 2016, 185, 403–406. (21) Roy, P.; Srivastava, S. K. Nanostructured Copper Sulfides: Synthesis, Properties and Applications. CrystEngComm 2015, 17, 7801–7815. (22) Li, S. C.; Yu, K.; Wang, Y.; Zhang, Z. L.; Song, C. Q.; Yin, H. H.; Ren, Q.; Zhu, Z. Q. Cu2S@ZnO Hetero-Nanostructures: Facile Synthesis, Morphology-Evolution and Enhanced Photocatalysis and Field Emission Properties. CrystEngComm 2013, 15, 1753–1761. (23) Li, M.; Zhao, R. J.; Su, Y. J.; Yang, Z.; Zhang, Y. F. Carbon Quantum Dots Decorated Cu2S Nanowire Arrays for Enhanced Photoelectrochemical Performance. Nanoscale 2016, 8, 8559– 8567. (24) Minguez-Bacho, I.; Courté, M.; Fan, H. J.; Fichou, D. Conformal Cu2S-Coated Cu2O Nanostructures Grown by Ion Exchange Reaction and Their Photoelectrochemical Properties.

Nanotechnology 2015, 26, 185401.


28

Page 29 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Jiang, Y.; Zhang, X.; Ge, Q. Q.; Yu, B. B.; Zou, Y. G.; Jiang, W. J.; Hu, J. S.; Song, W. G.; Wan, L. J. Engineering the Interfaces of ITO@Cu2S Nanowire Arrays toward Efficient and Stable Counter Electrodes for Quantum-Dot-Sensitized Solar Cells. ACS Appl. Mater. Interfaces

2014, 6, 15448−15455. (26) Wang, M.; Chen, W. L.; Zai, J. T.; Huang, S. S.; He, Q. Q.; Zhang, W.; Qiao, Q. Q.; Qian, X. F. Hierarchical Cu7S4 Nanotubes Assembled by Hexagonal Nanoplates with High Catalytic Performance for Quantum Dot-Sensitized Solar Cells. J. Power Sources 2015, 299, 212−220. (27) Lai, C. H.; Huang, K. W.; Cheng, J. H.; Lee, C. Y.; Hwang, B. J.; Chen, L. J. Direct Growth of High-Rate Capability and High Capacity Copper Sulfide Nanowire Array Cathodes Forlithium-Ion Batteries. J. Mater. Chem. 2010, 20, 6638–6645. (28) Goel, S.; Chen, F.; Cai, W. B. Synthesis and Biomedical Applications of Copper Sulfide Nanoparticles: From Sensors to Theranostics. Small 2014, 10, 631–645. (29) Pi, P. H.; Hou, K.; Zhou, C. L.; Wen, X. F.; Xu, S. P.; Cheng, J.; Wang, S. F. A Novel Superhydrophilic-Underwater Superoleophobic Cu2S Coated Copper Mesh for Efficient OilWater Separation. Mater. Lett. 2016, 182, 68–71. (30) Pi, P. H.; Hou, K.; Zhou, C. L.; Li, G. D.; Wen, X. F.; Xu, S. P.; Cheng, J.; Wang, S. F. Superhydrophobic Cu2S@Cu2O Film on Copper Surface Fabricated by a Facile Chemical Bath Deposition Method and Its Application in Oil-Water Separation. Appl. Surf. Sci. 2017, 396, 566– 573. (31) Tran, T. H.; Nguyen, V. T. Phase Transition of Cu2O to CuO Nanocrystals by Selective Laser Heating. Mater. Sci. Semicond. Process. 2016, 46, 6–9.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 47

(32) Kosec, T.; Qin, Z.; Chen, J.; Legat, A.; Shoesmith, D. W. Copper Corrosion in Bentonite/Saline Ground Water Solution: Effects of Solution and Bentonite Chemistry. Corros.

Sci. 2015, 90, 248–258. (33) Kumar, P.; Nagarajan, R. An Elegant Room Temperature Procedure for the Precise Control of Composition in the Cu-S System. Inorg. Chem. 2011, 50, 9204–9206. (34) Gan, Z. H.; Yu, G. Q.; Tay, B. K.; Tan, C. M.; Zhao Z. W.; Fu, Y. Q. Preparation and Characterization of Copper Oxide Thin Films Deposited by Filtered Cathodic Vacuum Arc. J.

Phys. D: Appl. Phys. 2004, 37, 81–85. (35) Hamilton, J. C.; Farmer, J. C.; Anderson, R. J. In Situ Raman Spectroscopy of Anodic Films Formed on Copper and Silver in Sodium Hydroxide Solution. J. Electrochem. Soc. 1986, 133, 739–745. (36) Wang, P.; Ng, Y. H.; Amal, R. Embedment of Anodized p-Type Cu2O Thin Films with CuO Nanowires for Improvement in Photoelectrochemical Stability. Nanoscale 2013, 5, 2952–2958. (37) Chaudhary,

A.;

Barshilia,

H.

C.

Nanometric Multiscale Rough

CuO/Cu(OH)2

Superhydrophobic Surfaces Prepared by a Facile One-Step Solution-Immersion Process: Transition to Superhydrophilicity with Oxygen Plasma Treatment. J. Phys. Chem. C 2011, 115, 18213–18220. (38) Gong, Y. S.; Lee, C.; Yang, C. K. Atomic Force Microscopy and Raman Spectroscopy Studies on the Oxidation of Cu Thin Films. J. Appl. Phys. 1995, 77, 5422–5425. (39) Bulakhe, R. N.; Sahoo, S.; Nguyen, T. T.; Lokhande, C. D.; Roh, C.; Lee, Y. R.; Shim, J. J. Chemical Synthesis of 3D Copper Sulfide with Different Morphologies for High Performance Supercapacitors Application. RSC Adv. 2016, 6, 14844–14851.


30

Page 31 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40) Li, L. Q.; Liu, Z. F.; Li, M.; Hong, L.; Shen, H.; Liang, C. L.; Huang, H.; Jiang, D.; Ren, S. Influence of Morphology on the Optical Properties of Self-Grown Nanowire Arrays. J. Phys.

Chem. C 2013, 117, 4253−4259. (41) Zhou, C. L.; Cheng, J.; Hou, K.; Zhu, Z. T.; Zheng, Y. F. Preparation of CuWO4@Cu2O Film on Copper Mesh by Anodization for Oil/Water Separation and Aqueous Pollutant Degradation. Chem. Eng. J. 2017, 307, 803–811. (42) Liu, L. J.; Liu, W. K.; Chen, R. F.; Li, X.; Xie, X. J. Hierarchical Growth of Cu Zigzag Microstrips on Cu Foil for Superhydrophobicity and Corrosion Resistance. Chem. Eng. J. 2015,

281, 804–812. (43) Hsu, Y. K.; Yu, C. H.; Chen, Y. C.; Lin, Y. G. Synthesis of Novel Cu2O Micro/Nanostructural Photocathode for Solar Water Splitting. Electrochim. Acta 2013, 105, 62– 68. (44) Zhang, W. X.; Wen, X. G.; Yang, S. H. Controlled Reactions on a Copper Surface: Synthesis and Characterization of Nanostructured Copper Compound Films. Inorg. Chem. 2003, 42, 5005– 5014. (45) Xiong, S. L.; Zeng, H. C. Serial Ionic Exchange for the Synthesis of Multishelled Copper Sulfide Hollow Spheres. Angew. Chem. Int. Ed. 2012, 51, 949–952. (46) Vedel, J.; Soubeyrand, M. Electrochemical Analysis of Copper Oxides Present in Cuprous Sulfide. J. Electrochem. Soc. 1980, 127, 1730–1733. (47) Cheng, N. Y.; Xue, Y. R.; Liu, Q.; Tian, J. Q.; Zhang, L. X.; Asiri, A. M.; Sun, X. P. Cu/(Cu(OH)2-CuO) Core/Shell Nanorods Array: In-Situ Growth and Application as an Efficient 3D Oxygen Evolution Anode. Electrochim. Acta 2015, 163, 102–106.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 47

(48) Lee, Y. I. Selective Transformation of Cu Nanowires to Cu2S or CuS Nanostructures and the Roles of the Kirkendall Effect and Anion Exchange Reaction. Mater. Chem. Phys. 2016, 180, 104–113. (49) Zhang, X.; Guo, Y. G.; Zhang, P. Y.; Wu, Z. S.; Zhang, Z. J. Superhydrophobic CuO@Cu2S Nanoplate Vertical Arrays on Copper Surfaces. Mater. Lett. 2010, 64, 1200–1203. (50) Su, B.; Tian, Y.; Jiang, L. Bioinspired Interfaces with Superwettability: From Materials to Chemistry. J. Am. Chem. Soc. 2016, 138, 1727−1748. (51) Zhou, C. L.; Chen, Z. D.; Yang, H.; Hou, K.; Zeng, X. J.; Zheng, Y. F.; Cheng, J. NatureInspired Strategy toward Superhydrophobic Fabrics for Versatile Oil/Water Separation. ACS

Appl. Mater. Interfaces 2017, 9, 9184−9194. (52) Khorsand, S.; Raeissi, K.; Ashrafizadeh, F.; Arenas, M. A. Super-Hydrophobic NickelCobalt Alloy Coating with Micro-Nano Flower-Like Structure. Chem. Eng. J. 2015, 273, 638– 646. (53) Aria, A. I.; Gharib, M. Reversible Tuning of the Wettability of Carbon Nanotube Arrays: The Effect of Ultraviolet/Ozone and Vacuum Pyrolysis Treatments. Langmuir 2011, 27, 9005– 9011. (54) Liu, P.; Cao, L.; Zhao, W.; Xia, Y.; Huang, W.; Li, Z. L. Insights into the Superhydrophobicity of Metallic Surfaces Preparedby Electrodeposition Involving Spontaneous Adsorption of Airborne Hydrocarbons. Appl. Surf. Sci. 2015, 324, 576–583. (55) Jin, M. H.; Li, S. S.; Wang, J.; Xue, Z. X.; Liao, M. Y.; Wang, S. T. Underwater Superoleophilicity to Superoleophobicity: Role of Trapped Air. Chem. Commun. 2012, 48, 11745–11747.


32

Page 33 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(56) Barthlott, W.; Schimmel, T.; Wiersch, S.; Koch, K.; Brede, M.; Barczewski, M.; Walheim, S.; Weis, A.; Kaltenmaier, A.; Leder, A.; et al. The Salvinia Paradox: Superhydrophobic Surfaces with Hydrophilic Pins for Air Retention Under Water. Adv. Mater. 2010, 22, 2325– 2328. (57) Liu, M. J.; Wang, S. T.; Wei, Z. X.; Song, Y. L.; Jiang, L. Bioinspired Design of a Superoleophobic and Low Adhesive Water/Solid Interface. Adv. Mater. 2009, 21, 665–669. (58) Cassie, A. B. D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546–551. (59) Khorsand, S.; Raeissi, K.; Ashrafizadeh, F. Corrosion Resistance and Long-Term Durability of Super-Hydrophobic Nickel Film Prepared by Electrodeposition Process. Appl. Surf. Sci. 2014,

305, 498–505. (60) Wang, G. Y.; Zhang, T. Y. Oxygen Adsorption Induced Superhydrophilic to Superhydrophobic Transition on Hierarchical Nanostructured CuO Surface. J. Colloid Interface

Sci. 2012, 377, 438–441. (61) Wang, S. T.; Feng, X. J.; Yao, J. N.; Jiang, L. Controlling Wettability and Photochromism in a Dual-Responsive Tungsten Oxide Film. Angew. Chem. Int. Ed. 2006, 45, 1264–1267. (62) Wang, H. B.; Wang, N.; Hang, T.; Li, M. Morphologies and Wetting Properties of Copper Film with 3D Porous Micro-Nano Hierarchical Structure Prepared by Electrochemical Deposition. Appl. Surf. Sci. 2016, 372, 7–12. (63) Meng, K. K.; Jiang, Y.; Jiang, Z. H.; Lian, J. S.; Jiang, Q. Cu Surfaces with Controlled Structures: From Intrinsically Hydrophilic to Apparently Superhydrophobic. Appl. Surf. Sci.

2014, 290, 320–326.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 47

(64) Hou, Y. P.; Feng, S. L.; Dai, L. M.; Zheng, Y. M. Droplet Manipulation on Wettable Gradient Surfaces with Micro-/Nano-Hierarchical Structure. Chem. Mater. 2016, 28, 3625−3629. (65) He, G.; Lu, S. X.; Xu, W. G.; Szunerits, S.; Boukherroub, R.; Zhang, H. F. Controllable Growth of Durable Superhydrophobic Coatings on a Copper Substrate via Electrodeposition.

Phys. Chem. Chem. Phys. 2015, 17, 10871−10880. (66) Cao, L.; Liu, J.; Xu, S. L.; Xia, Y.; Huang, W.; Li, Z. L. Inherent Superhydrophobicity of Sn/SnOx Films Prepared by Surface Self-Passivation of Electrodeposited Porous Dendritic Sn.

Mater. Res. Bull. 2013, 48, 4804−4810. (67) Cao, L.; Lu, X. Q.; Pu, F.; Yin, X. L.; Xia, Y.; Huang, W.; Li, Z. L. Facile Fabrication of Superhydrophobic Bi/Bi2O3 Surfaces with Hierarchical Micro-Nanostructures by Electroless Depositionor Electrodeposition. Appl. Surf. Sci. 2014, 288, 558–563. (68) Chang, F. M.; Cheng, S. L.; Hong, S. J.; Sheng, Y. J.; Tsao, H. K. Superhydrophilicity to Superhydrophobicity Transition of CuO Nanowire Films. Appl. Phys. Lett. 2010, 96, 114101. (69) Pei, M. D.; Wang, B.; Li, E.; Zhang, X. H.; Song, X. M.; Yan, H. The Fabrication of Superhydrophobic Copper Films by a Low-Pressure-Oxidation Method. Appl. Surf. Sci. 2010,

256, 5824–5827. (70) Shinde, S. L.; Nanda, K. K. Facile Synthesis of Large Area Porous Cu2O as Super Hydrophobic Yellow-Red Phosphors. RSC Adv. 2012, 2, 3647–3650. (71) Liu, Y.; Tan, T.; Wang, B.; Song, X. M.; Li, E.; Wang, H.; Yan, H. Superhydrophobic Behavior on Transparency and Conductivity Controllable ZnO/Zn Films. J. Appl. Phys. 2008,

103, 056104.


34

Page 35 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(72) Xu, P. H.; Wang, F. J.; Yang, C.; Ou, J. F.; Li, W.; Amirfazli, A. Reversible Transition between Superhydrophobicity and Superhydrophilicity of a Silver Surface. Surf. Coat. Technol.

2016, 294, 47–53. (73) Liu, L. Y.; Chen, C.; Yang, S. Y.; Xie, H.; Gong, M. G.; Xu, X. L. Fabrication of Superhydrophilic-Underwater Superoleophobic Inorganic Anti-Corrosive Membranes for HighEfficiency Oil/Water Separation. Phys. Chem. Chem. Phys. 2016, 18, 1317–1325. (74) Cao, L.; Liu, J.; Huang, W.; Li, Z. L. Facile Fabrication of Superhydrophobic Surfaces on Zinc Substrates by Displacement Deposition of Sn. Appl. Surf. Sci. 2013, 265, 597–602. (75) Feng, X. J.; Feng, L.; Jin, M. H.; Zhai, J.; Jiang, L.; Zhu, D. B. Reversible SuperHydrophobicity to Super-Hydrophilicity Transition of Aligned ZnO Nanorod Films. J. Am.

Chem. Soc. 2004, 126, 62–63. (76) Pan, J.; Song, X. F.; Zhang, J.; Shen, H.; Xiong, Q. H. Switchable Wettability in SnO2 Nanowires and SnO2@SnO2 Heterostructures. J. Phys. Chem. C 2011, 115, 22225–22231. (77) Zhang, N.; Lu, S. X.; Xu, W. G.; Zhang, Y. Controlled Growth of CuO-Cu3Pt/Cu MicroNano Binary Architectures on Copper Substrate and Its Superhydrophobic Behavior. New J.

Chem. 2014, 38, 4534–4540. (78) Oh, I. K.; Kim, K.; Lee, Z.; Ko, K. Y.; Lee, C. W.; Lee, S. J.; Myung, J. M.; LansalotMatras, C.; Noh, W.; Dussarrat, C.; et al. Hydrophobicity of Rare Earth Oxides Grown by Atomic Layer Deposition. Chem. Mater. 2015, 27, 148–156. (79) Yang, Y. C.; Liu, J.; Li, C.; Fu, L.; Huang, W.; Li, Z. L. Fabrication of Pompon-Like and Flower-Like

SnO

Microspheres

Comprised

of

Layered

Nanoflakes

by

Anodic

Electrocrystallization. Electrochim. Acta 2012, 72, 94–100.


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 47

(80) Raturi, P.; Yadav, K.; Singh, J. P. ZnO-Nanowires-Coated Smart Surface Mesh with Reversible Wettability for Efficient On-Demand Oil/Water Separation. ACS Appl. Mater.

Interfaces 2017, 9, 6007–6013. (81) Cao, Y. Z.; Zhang, X. Y.; Tao, L.; Li, K.; Xue, Z. X.; Feng, L.; Wei, Y. Mussel-Inspired Chemistry and Michael Addition Reaction for Efficient Oil/Water Separation. ACS Appl. Mater.

Interfaces 2013, 5, 4438−4442. (82) Joo, M.; Shin, J.; Kim, J.; You, J. B.; Yoo, Y.; Kwak, M. J.; Oh, M. S.; Im, S. G. One-Step Synthesis of Cross-Linked Ionic Polymer Thin Films in Vapor Phase and Its Application to an Oil/Water Separation Membrane. J. Am. Chem. Soc. 2017, 139, 2329–2337.


36

Page 37 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic


37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Schematic of the preparation of the S-NWM. 323x82mm (200 x 200 DPI)


Page 38 of 47

Page 39 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


XRD patterns (a) and Raman spectra (b) of the H-NWM and S-NWM. 253x389mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

XPS spectra of the S-NWM prepared by sulfurization for 60 min: (a) full spectrum, (b) Cu 2p, (c) S 2p and (d) O 1s. 347x356mm (150 x 150 DPI)


Page 40 of 47

Page 41 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SEM images of: (a, f, k) H-NWM and S-NWM prepared by sulfurization for different durations: (b, g, l) 5 min, (c, h, m) 30 min, (d, i, n) 60 min, and (e, j, o) 180 min. Inset of (k) is the cross-section of the Cu(OH)2 nanowires film. Inset of (n) is a typical picture of a pile of matchsticks. Scale bars in (a, b, c, d, e), (f, g, h, i, j) and (k, l, m, n, o) are 20 µm, 1 µm and 200 nm, respectively. 773x418mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) Underwater OCAs and OSAs of various oils on the 60-min S-NWM sample surface. (b) Underwater OCA and OSA (the testing oil is dichloromethane) of the S-NWM in different corrosive solutions. 262x269mm (150 x 150 DPI)


Page 42 of 47

Page 43 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) WCAs of the S-NWM prepared by sulfurization for different durations after storage in air for two weeks. (b) The WCA variation of the S-NWM prepared by sulfurization for 60 min when stored in air for diverse periods of time. 211x342mm (200 x 200 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Superhydrophobic behaviors of the S-NWM after stored in air: (a) Photographs of the deionized water droplets stay on the as-stored S-NWM surface. (b) A jet of water bouncing off the as-stored S-NWM surface. (c) The as-stored superhydrophobic S-NWM was immersed into water by an external force, showing a silver mirror phenomenon. (d) Time-lapse photographs of a water droplet bouncing on the as-stored S-NWM. 132x118mm (150 x 150 DPI)


Page 44 of 47

Page 45 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C 1s core level XPS spectra of (a) the freshly prepared 60-min S-NWM and (b) the same sample stored in air for two weeks. 343x176mm (150 x 150 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) Schematic of the relationship between superhydrophilic, underwater superoleophobic and superhydrophobic surfaces. On-demand oil/water separation of: (b) "water-removal" type and (c) "oilremoval" type. The oils (n-hexane (b) and dichloromethane (c)) and water were dyed with Sudan II and Methylene Blue, respectively. Separation efficiency of (d) underwater superoleophobic mesh for light oils (ρoil < ρwater) and (e) superhydrophobic mesh for heavy oils (ρoil > ρwater) versus the recycle numbers. 193x155mm (200 x 200 DPI)


Page 46 of 47

Page 47 of 47

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic 359x155mm (150 x 150 DPI)


Matchstick-Like Cu2S@CuxO Nanowire Film: Transition of

Recommend Documents