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RobustFlower‐LikeTiO2@CottonFabricswithSpecialWettabilityforEffectiveSelf‐CleaningandVersatileOil/WaterSeparation

ARTICLEinADVANCEDMATERIALSINTERFACES·JUNE2015

DOI:10.1002/admi.201500220

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Robust Flower-Like TiO 2 @Cotton Fabrics with Special Wettability for Effective Self-Cleaning and Versatile Oil/Water Separation

Shuhui Li , Jiangying Huang , Mingzheng Ge , Chunyan Cao , Shu Deng , Songnan Zhang , Guoqiang Chen , Keqin Zhang , Salem S. Al-Deyab , and Yuekun Lai *

DOI: 10.1002/admi.201500220

Inspired by the hierarchical structure of the mastoid on the micrometer and nanometer scale and the waxy crystals of the mastoid on natural lotus sur-faces, a facile one-step hydrothermal strategy is developed to coat fl ower-like hierarchical TiO 2 micro/nanoparticles onto cotton fabric substrates (TiO 2 @Cotton). Furthermore, robust superhydrophobic TiO 2 @Cotton surfaces are constructed by the combination of hierarchical structure creation and low sur-face energy material modifi cation, which allows versatility for self-cleaning, laundering durability, and oil/water separation. Compared with hydrophobic cotton fabric, the TiO 2 @Cotton exhibits a superior antiwetting and self-cleaning property with a contact angle (CA) lager than 160° and a sliding angle lower than 5°. The superhydrophobic TiO 2 @Cotton shows excellent laundering durability against mechanical abrasion without an apparent reduc-tion of the water contact angle. Moreover, the micro/nanoscale hierarchical structured cotton fabrics with special wettability are demonstrated to selec-tively collect oil from oil/water mixtures effi ciently under various conditions (e.g., fl oating oil layer or underwater oil droplet or even oil/water mixtures). In addition, it is expected that this facile strategy can be widely used to construct multifunctional fabrics with excellent self-cleaning, laundering durability, and oil/water separation. The work would also be helpful to design and develop new underwater superoleophobic/superoleophilic materials and microfl uidic management devices.

S. Li, Dr. J. Huang, M. Ge, C. Cao, S. Deng, S. Zhang, Prof. G. Chen, Prof. K. Zhang, Prof. Y. Lai National Engineering Laboratory for Modern Silk College of Textile and Clothing Engineering Soochow University Suzhou 215123 , China E-mail: yklai@suda.edu.cn Dr. J. Huang, Prof. G. Chen, Prof. K. Zhang, Prof. Y. Lai Research Center of Cooperative Innovation for Functional Organic/Polymer Material Micro/Nanofabrication Soochow University Suzhou 215123 , China Prof. S. S. Al-Deyab Department of Chemistry College of Science King Saud University Riyadh 11451 , Saudi Arabia

1. Introduction Since the lotus phenomenon in nature has been revealed, scientists and researchers have endeavored various methods to fab-ricate or construct such special wetting surfaces in various potential application fi elds both in academic research and prac-tical application. [ 1–3 ] Superhydrophobicity is a special wettability with high water contact angle and low sliding angle. [ 4–6 ] As we all know that the surface roughness and surface energy are two signifi cant factors affecting the wettability. [ 7–9 ] Based on the principle, researchers were moti-vated to fabricate superhydrophobic sur-faces by constructing hierarchical micro/nanostructures and modifying low sur-face energy materials. [ 10–12 ] These special wetting materials with both superhydro-phobic and superhydrophilic properties have attracted a great deal of attention in the fi eld of friction reduction and oil/water separation. [ 13 ] However, the sur-face roughness would decrease due to the micro/nanostructure destroyed under mechanical forces such as friction, abra-sion, which result in the loss of long-lived

superhydrophobic surfaces. [ 14–16 ] Xue and Ma [ 17 ] generalized the approaches to improve the durability of superhydrophobic surfaces mostly focus on the mechanically durable, corrosion-resistance, self-healing, and easily repairable. Though great efforts have been made on retarding the loss of superhydro-phobicity, it was diffi cult to improve the mechanical stability on fabric surfaces. Zhao et al. [ 18 ] reported a durable superhydro-phobic coating on cotton fabrics by forming covalently bonds network among silica nanoparticles, polyelectrolyte chains, and the substrate. The as-prepared superhydrophobic cotton surfaces were durable against acids, bases, organic solvents, as well as repeated machine wash. A signifi cant improvement on the durability of superhydrophobic coating has realized, but the fabricate procedure is sophisticated.

TiO 2 nanoparticles have strong UV shielding capacity, good stability, safety, and nontoxic, which is regarded as multifunctional object and recently has been applied in

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textile fi elds. [ 19–21 ] Afzal et al. [ 22 ] prepared a superhydrophobic and photocatalytic self-cleaning cotton fabric under visible-light by step-wise deposition of anatase TiO 2 , meso-tetra(4-carboxyphenyl) porphyrin (TCPP) and trimethoxy(octadecyl) silane (OTMS). The as-prepared cotton fabrics exhibited excellent superhydrophobicity with a water contact angle (WCA) of 156° and superior photocatalytic activity by degradation of methyl blue (MB) under visible-light. Wet chemical method for one-step synthesis of TiO 2 nanostructures have become a focus of tremendous interests due to its conven-ient experimental condition to controllable synthesis rough TiO 2 structures on various substrates. [ 23 ] In this work, we developed a facile one-pot hydrothermal reaction strategy to construct micro/nanostructure fl ower-like TiO 2 particles on cotton fabric surface. The as-prepared TiO 2 @Cotton exhibited supe-rhydrophobicity with a high CA and a low SA after further modifying fl uoroalkylsilane. Considering to the application for fabrics, a good laundering durability is necessary. A laundering process is a combination of chemical interactions between fabric, the detergent and the mechanical interactions such as abrasion, friction, and shearing force. In addition to durable laundering, the as-prepared TiO 2 @Cotton surface also had a high effi ciency for oil/water separa-tion since the converse wetting properties between water and oil. Such a superhydrophobic surface with self-cleaning, laun-dering durability, and oil/water separation capacity by simple chemical reaction and had potential applications in repellent fabrics, self-cleaning materials, and oil/water separation. We expect that the facile approach to construct robust micro/nano-structure TiO 2 particles on cotton surface would be entered into industry and applied in various textile materials (e.g., polyester and spandex).

2. Results and Discussion

2.1. Characterization of Flower-Like TiO 2 @Cotton

The micro/nanostructure and low surface energy materials are indispensable to fabricate superhydrophobic surfaces. We applied a one-step hydrothermal reaction strategy to fi rst construct hierarchical micro/nanostructure rough structure on cotton fabric surface, subsequently modifi ed the TiO 2 @Cotton surfaces with low surface energy materials to achieve superhydrophobicity. Uniform fl ower-like hierarchical micro/nanostructure TiO 2 particles with an average diameter around 0.5–1.0 µm ( Figure 1 a) were dispersed on the surface of smooth cotton fi ber after hydrothermal reaction. The optical image of superhydrophobic fabric submerged in water with a mirror-like phenomenon was shown in Figure 1 a (inset). We can observed the superhydrophobic surface acts like a silver mirror but the

phenomenon would not be found on the cotton pristine or TiO 2 @Cotton without a mixed methanolic solution of hydrolyzed 1 vol% of 1H,1H,2H,2H-perfl uorooctyltriethoxysilane (POTS) modifi cation. This is due to an air layer trapped among micro/nanostructure particles and prevents the water from wetting the cotton fabric surface directly. The mirror-like phenomenon is caused by total refl ectance of light at the air layer trapped in the superhydrophobic cotton surface. The fl ower-like TiO 2 par-ticle was consisted of innumerable nanosheets or nanorods of 50–150 nm in length (Figure 1 b). The water droplet maintains a high contact angle of 157.2° on POTS modifi ed TiO 2 @Cotton surface (inset, Figure 1 b), indicating that the as-prepared TiO 2 @Cotton fabric modifi ed by POTS was superhydropho-bicity. However, water droplet will quickly spread and fi nally absorbed by fi bers on TiO 2 @Cotton fabric, displaying unmodi-fi ed TiO 2 @Cotton is superhydrophilic with a WCA less than 5° (Figure S1, Supporting Information). This was mostly due to the effect of TiO 2 particle intrinsic hydrophilic ability and the moisture regain caused by cotton fi ber. Besides, the capil-lary effect of cotton fi ber and hollow space between inter fabric induced water entirely infi ltration. The chemical composition of TiO 2 @Cotton was characterized by energy disperse spectros-copy (EDS) measurement. Figure 1 c showed the EDS spectra of TiO 2 @Cotton (150 °C, 20 h). The main elements were deter-mined to be C, O, Ti, and Ag. However, the pristine cotton is mostly consisted of C and O elements. The EDS elemental mapping picture of Ti element indicated that TiO 2 particles were distributed on cotton fi ber surface uniformly. It should be noted that the Ag element was caused by sputtering metallic silver on TiO 2 @Cotton sample for the scanning electron

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Figure 1. a,b) SEM image of the fl ower-like TiO 2 micro/nanoparticles decorated on cotton fabric surfaces fabricated at 150 °C for 20 h. Inset (a) is an optical photograph of superhydro-phobic sample submerged in water. Inset (b) is the picture of water droplet on corresponding superhydrophobic TiO 2 @Cotton fabrics. c) element mapping of C, O, Ti, Ag, and d) EDS spec-trum, the image inset in (d) is EDS scanning area and corresponding element percentages.

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microscopy (SEM) characterization. The relative atom ratio of C/O/Ti/Ag is about 32.85%/55.44%/11.12%/0.55%, respec-tively (Figure 1 d).

The surface chemical composition of cotton fabric before and after hydrothermal reaction and POTS modifi cation were further confi rmed by X-ray photoelectron spectroscopy (XPS). Figure 2 showed wide scan and C 1s, Ti 2p, and F 1s high-resolution spectra of cotton fabric before and after hydrothermal reac-tion and POTS modifi cation. Compared with pristine cotton, three additional char-acteristic peaks at binding energies (BEs) of 455.0, 689.0, and 832.0 eV for Ti 2p, F 1s, and F KLL species, respectively, are observed in wide scan spectra (Figure 2 a). A new peak at 455.0 eV for Ti 2p and a strong peak at 689.0 eV assigned for F 1s exhibited that TiO 2 particles and fl uorosilanes had been successfully deposited and self-assembled onto cotton fabric surface. The curved fi tted Ti 2p core level XPS spectrum componants of two distinct peaks at 458.9 and 464.6 eV assigned to Ti 2p3/2 and 2p1/2, respec-tively (Figure 2 b). The splitting energy of 5.7 eV between Ti 2p3/2 and 2p1/2 indi-cated the existence of normal state of Ti 4+ , which is consistent with the reported data for TiO 2 . The only peak appearing at a BE about 689.0 eV in the F 1s high-resolution spectrum indicated the immobilization of fl uoroalkylsiane monolayer onto TiO 2 @Cotton (Figure 2 c).

2.2. Effect of Reaction Temperature and Deposition Duration

To investigate the infl uence of hydrothermal reaction temperature and deposition dura-tion on the surface morphology, the results have been discussed by varying reaction temperature. Figure 3 showed SEM images of the as-prepared TiO 2 particle structures obtained with different reaction temperatures for 10 h. The results appeared that hydro-thermal reaction temperature and deposition duration had a signifi cant infl uence on the surface morphology. As shown in Figure 4 a, the surfaces of as-constructed TiO 2 @Cotton (120 °C) could be found numerous TiO 2 particles with a diameter range from 0.02 to 0.3 µm. In addition, TiO 2 particles were dis-tributed onto cotton surface uniformly. When the reaction temperature increased to 150 °C, numerous nanoscale particles with preferen-tial orientation were formed onto fi ber sur-face as hydrolysis and condensation reaction proceeded and became a shape of fl ower clusters (Figure 3 b). Continuing to raise reac-tion temperature, a clearly chrysanthemum fl ower-like hierarchical micro/nanostructure

TiO 2 particles was observed on as-prepared cotton surface and the amount as well as the size increased greatly (Figure 3 c). As the temperature reached to 200 °C, a thicker coating fi lm consist of fl ower-like TiO 2 particles was constructed on fi ber substrate (Figure 3 d). Compared with the TiO 2 microstructure particles deposited at lower reaction temperature, a thicker coating fi lm

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Figure 2. a) Survey XPS spectra of cotton fabric before and after hydrothermal reaction and POTS modifi cation. Corresponding high-resolution XPS spectra of b) Ti 2p, c) F 1s.

Figure 3. SEM images of TiO 2 particles onto cotton fabric surfaces when immersing the pris-tine cotton for 10 h at different temperatures: a) 120 °C, b) 150 °C, c) 180 °C, and d) 200 °C. Insets are the corresponding low magnifi ed images.

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could be constructed attributed to the second growth in situ of TiO 2 particles. However, the existence of accumulated internal stress in hydrothermal reaction made the cotton fi ber swelling, some cracks occurred on as-prepared cotton surface causing TiO 2 particles coated on cotton fabric surfaces unevenly, which is unfavorable to mechanical strength and usability. Except for the cotton substrate, we have successfully constructed TiO 2 particles on various textile substrates such as polyester and spandex (Figure S2, Supporting Information). We can observed that the surface of untreated polyester and spandex fabric were smooth, however, micro/nanostructure TiO 2 particles uniformly coated on fabrics at 150 °C for 10 h, indicating the applicability of such simple method. The static water contact angles for POTS modifi ed polyester and spandex are 152.3° and 152.4° (insets, Figure S2b,d, Supporting Information), respec-tively, while the pristine polyester has a contact angle of 93.5° (inset, Figure S2a, Supporting Information) due to the ultralow moisture regain itself and spandex blank is superhydrophilic with an almost 0° contact angle (inset, Figure S2c, Supporting Information).

Figure 4 showed the typical SEM images of TiO 2 particles on cotton surface after immersing the pristine cotton at 150 °C for different deposition time. The deposi-tion duration has a great effect on both the size and the density of the coated TiO 2 par-ticles. After depositing for 1 h, only some individual TiO 2 particles with a diameter of 0.05–0.25 µm were sparsely distributed over cotton fi ber (Figure 4 a). The morphology of TiO 2 particles made an interesting change with the increasing of deposition time. When the deposition time was 2 h, numerous micro/nanostructure TiO 2 particles reunited in a favorable area and formed large size of TiO 2 particles (Figure 4 b). It was confi rmed that fl ower-like hierarchical micro/nano-structure TiO 2 particles require suffi cient time to nucleate and crystallize together with

the hydrothermal reaction. Further to increase the deposition time, cotton fabric surfaces were covered with uniform and compact fl ower-like TiO 2 particles fi lm (Figure 4 c). The size of microscale particles increased to about 0.1–0.4 µm. With the increasing of deposition time, the fl ower-like microscale parti-cles began to aggregate sharply and the diameter and density of fl ower-like microparticles increased obviously. With the dep-osition time further increasing to 20 h (Figure 4 d), there are obvious changes in the size as well as mount of TiO 2 particles and the thickness of the fi lm decorated with TiO 2 @Cotton also increased. However, the fi lm appeared uneven to a certain extent when the reaction temperature keep increasing. This is due to continuous high temperature reaction, swelling occurred on cotton fi ber and resulted in the failure of nucleation and crystallization. The above discussion indicated that fl ower-like microparticles fi lm can be successfully prepared on the pristine cotton surfaces at a suitable reaction temperature (i.e., 150 °C) for suffi cient deposition duration (i.e., 10 h). Except for the reaction temperature and the deposition duration, the concen-tration of potassium titanium oxalate (PTO) also does great infl uence on the size and density of TiO 2 particles. As a result, a dense and uniform fi lm with fl ower-like hierarchical micro/nanostructure can be prepared under optimized parameters (temperature: 150–200 °C, deposition duration: 5–20 h).

Except the infl uence of surface morphology and size/den-sity of TiO 2 particles, the deposition duration and tempera-ture also had a great effect on the crystalline ( Figure 5 and Figure S3, Supporting Information) and wetting behavior and adhesion ( Figure 6 ). Figure 5 a shows the XRD pattern on sur-faces of TiO 2 @Cotton with various reaction temperature for depositing 5 h. When the hydrothermal reaction temperature was 120 °C, the crystalline phase of TiO 2 particles on surface of TiO 2 @Cotton had no difference with the pristine cotton. However, increasing the reaction temperature to 150 °C and even more, three characteristic peaks at 25.7°, 48.4°, 55.2° for anatase phase of TiO 2 appeared, which suggested the reaction temperature had a signifi cant effect on crystalline phase of TiO 2 particles. Besides, the higher reaction temperature, the sharper of the three characteristic peaks. Figure 5 b displayed the depo-sition time also affect crystalline phase of TiO 2 particles on as-prepared samples. When the deposition time was above 5 h, the crystalline phase of TiO 2 particles on TiO 2 @Cotton (150 °C) began to transform from amorphous to anatase. The similar

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Figure 4. SEM images of TiO 2 particles on cotton surfaces after immersing the pristine cotton at 150 °C for different deposition duration: a) 1 h, b) 2 h, c) 5 h, and d) 20 h. Insets are corresponding high magnifi ed images.

Figure 5. XRD patterns on surfaces of as-prepared TiO 2 @Cotton under various reaction tem-peratures with a deposition duration of a) 5 h and various deposition durations reacted at b) 150 °C.

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change rule occurred at the additional reaction temperature. Compared with the XRD pattern of TiO 2 @Cotton (150 °C), a longer deposition duration exceed 5 h was needed to the trans-formation of amorphous phase on TiO 2 @Cotton (120 °C) sur-faces. However, the anatase phase of TiO 2 particles occurred at the higher synthesis temperature (180 °C, 200 °C) for 2 h reac-tion (Figure S3, Supporting Information). The experimental results above illustrated both reaction temperature and depo-sition duration have great effect on phase transformation of TiO 2 particles. Raising the reaction temperature or increasing the reaction duration is effective to the phase transition of TiO 2 particles.

2.3. Wettability Measurement and Analysis

The wetting behavior of resultant surperhydrophobic surfaces is systematically characterized by static water contact angle and dynamic sliding angle. In addition, the adhesive force between water droplet and sample surface has a great effect on superhy-drophobicity. Generally, an excellent surperhydrophobic surface suggests it has a lower adhesion. Figure 6 a shows the change of water contact angle of modifi ed TiO 2 @Cotton surfaces with the various deposition times. The pristine cotton modifi ed with low surface energy (POTS) have an ≈138° static contact angle and an adhesion of 150 µN. Except for hydrothermal reaction temperature for 200 °C, an increasing trend on contact angle was observed easily. When the deposition time was less than 1 h, the reaction temperature had no extraordinary infl uence on contact angle and the static contact angle reached to 151.3° on the condition that the reaction temperature was 200 °C and the reaction time was 1 h. With the increasing of deposition duration, the contact angle appeared continual increasing. As a result, an increase of 11°–15° would happen along with the dep-osition time varies from 1 to 20 h. As shown in Figure 6 b, the change of adhesive force with deposition duration has an oppo-site trend to that of the contact angle. The deposition time and hydrothermal reaction temperature have great effect on adhe-sive force for superhydrophobic samples. When the deposition time was 1 h and the reaction temperature were 120 as well as 150 °C, no apparent changes were found on adhesion between modifi ed blank cotton and fl uoroalkylsianed TiO 2 @Cotton. This is due to no obvious microscale TiO 2 particles deposited on as-prepared cotton fabric surfaces. Once increasing the reac-tion temperature, the adhesion sharply decreased to ≈30–38 µN. Further to increase the deposition time, an apparent change occurred on such super-hydrophobic surfaces conducted at 120 °C hydrothermal reaction. After 20 h reaction, the superhydrophobic TiO 2 @Cotton surfaces have an adhesion of around 30 µN. This is ascribed to the roughness controlled by micro/nanostructure particles and low sur-face energy materials. The superhydrophobic structure was considered as Cassie–Baxter model, which has been widely recognized that the air trapped into the surface structure so that water droplet was hard to approach the fi ber surface. When increasing reaction

temperature to 180 or 200 °C, the adhesive force emerged a cer-tain decrease and reached a minimum limited of around 10 µN with a deposition duration of 10 h. However, the adhesion on modifi ed TiO 2 @Cotton surface structured at 200 °C for 20 h dramatically increased. This may attributed to the cracking of TiO 2 fi lm on cotton fi ber due to the swelling of fi ber at a contin-uous high temperature with a long time reaction, which caused the uneven of TiO 2 particles coated on cotton surface.

The topographical structure plays a signifi cant role in sliding angle and adhesive force. While the deposition time was less than 2 h, reaction temperature has a great effect on static contact angle and dynamic sliding angle. According to the Figure S4a, Supporting Information, although only a static con-tact angle contrast of 2.8° on superhydrophobic TiO 2 @Cotton fabrics constructed at 150 °C for 2 and 5 h, water droplets were not easily roll off the sample surface prepared for 2 h even when titling vertically the sample. When increasing the depo-sition duration, a superhydrophobic and self-cleaning surface with a low sliding angle less than 5° was obtained. The change of contact angle and adhesion (Figure S4b, Supporting Infor-mation) with the deposition time has a similar trend to that of shown in Figure S4a, Supporting Information. This is ascribed to TiO 2 hierarchical micro/nanostructures on as-prepared sam-ples. With short deposition duration, sparse TiO 2 microparticles coated on fi ber surface and the air layer trapped in the surface structure was thin, causing the formation of a large contact area between water droplet and fi ber surface. The drag force that compelled water droplet left from sample surface increasing naturally. The discussion above indicated that rough micro/nanostructure TiO 2 particles infl uenced the wetting capability of cotton surfaces.

The mechanism caused the adhesive force difference on as-prepared samples was discussed in detail. The surface adhesive force is infl uenced by both the surface chemical composition and the topographical structures. [ 24 ] Since the surfaces of as-prepared samples modifi ed with the same chemistry materials, the difference on adhesion was mainly affected by the surface microstructures. The surface adhesion (denoted as F) can be defi ned as a product of liquid/solid interfacial interaction (denoted as I) and the contact area (denoted as A) [ 25 ]

F = kIA (1)

F A∝ (2)

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Figure 6. The relationship between a) water contact angle, b) adhesive force of modifi ed TiO 2 @Cotton surfaces prepared at various reaction temperature with different deposition time.

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where k is a constant and I is related to the solid surface chem-istry and regarded to be the same for such samples modifi ed with fl uoroalkylsilane. Thus, the Equation ( 1) could be simpli-fi ed to Equation ( 2) and the liquid/solid contact area would be the primary factor that infl uences the adhesion. The surface microstructure of TiO 2 particles on fabric is decided by the reaction temperature and the deposition duration. For super-hydrophobic TiO 2 @Cotton (150 °C, 1 h), spare microparti-cles random dispersed on the surface (Figure 4 a) and A water droplet dyed with methyl blue was placed on such fabric sur-face ( Scheme 1 a), we can clearly observed the amplifi ed texture structure since the water droplet was acted as a convex lens. No obvious air layer between water and such superhydrophobic surface was found but an irregular shape of water trace marked by a red circle (Scheme 1 d) was left after absorbing the water with a fi lter paper. Therefore, the water droplet on such surface would exhibit the typical “area” contact model along with con-tinuous three-phase contact line (TCL), as shown in Scheme 1 g. In this state, water can intrude into most of the area of micro-particles and form a large liquid/solid contact area. According to Equation ( 2) , a high droplet adhesion (40–140 µN) would be produced and the droplet was diffi cult to roll off the surface even when the surface is turned upside down. Increasing the deposi-tion time to 5 h, the size and amount of micro/nanoparticles greatly changed. Numerous bigger TiO 2 microparticles with shorter distance were uniformly distributed on the fabric sur-face. We noticed an obvious air layer tapped between the sample and water droplet (Scheme 1 b) and the trace area left by water droplet decreased respectively (Scheme 1 e). This is due to water droplets contact with such “line” contact model (Scheme 1 h), a large amount of air trapped inside the liquid/solid contact area would prevent water from wetting the microstructure surface to some extent. According to the Equation ( 2) , a lower adhesion

and superhydrophobic surface would be expected. The static contact angle for TiO 2 @Cotton (150 °C, 5 h) is ≈157° and the cor-responding adhesive force is about 25 µN. Continuing to prolong the reaction time, the micro/nanostructure particles need enough time to nucleate and crystallize together to construct large-scale fl ower-like micro/nanoparticles (150 °C, 10–20 h). A distinct air layer appeared (Scheme 1 c) on the fl ower-like micro/nanoparticles superhydrophobic fabric surface. We can observed extremely weak blue trace as shown in Scheme 1 f. When water is placed on such surface, it cannot stay on surface and can easily roll away from the sample when the surface is tilted with a small angle. The situation of water droplet on such hierarchical surface with dual scale structures is similar to that on the lotus, and the water would reside in a special lotus-liked Cassie state with typical “point” contact model (Scheme 1 i). For this state, the water has less contact area with the top of fl ower-like micro/nanostructure, an air layer was trapped among micro/nanostructure parti-cles, which can prevent water from direct

intruding into the microstructure. Therefore, such surface has an extremely low adhesive force (<10 µN). These results indi-cated that the hierarchical surface with micro/nanostructure is important and effective for the construction of superhydro-phobic samples with lower droplet adhesion.

The change of adhesive force can be further confi rmed by the follow Cassie equation

cos (1 cos ) 1frθ θ= + − (3)

Here, θ and θ r are the contact angles for water droplet on fl at and micro/nanostructure TiO 2 @Cotton surfaces, f is the surface area coeffi cient and the value is the ratio of water droplet and the microstructure particles on solid sample surface in direct contact area with the geometric projection area. In the current experiment, θ refer to the intrinsic contact angle of the fl at cotton surface (ideally fl at) but it is hard to obtain. However, we could qualitative analysis the liquid/solid contact area among various samples. For example, superhydrophobic TiO 2 @Cotton (150 °C, 5 h) has a higher water CA than TiO 2 @Cotton (150 °C, 1 h) and the CAs of both samples are more than 90°, in other words, the value of cos θ r for TiO 2 @Cotton (150 °C, 5 h) is lower than the result of TiO 2 @Cotton (150 °C, 1 h) (it should be noted in here: cos θ r > −1). According to Equation ( 3) , the f for TiO 2 @Cotton (150 °C, 5 h) is smaller while cos θ is equivalent to the both superhydrophobic samples, which could be regarded as a constant. The results qualitative analyzed indicates that the sample deposited for 5 h has a smaller liquid/solid contact area and a relative lower adhesion. Based on the discussion above, it can be proved that the surface morphology and microstructure particles size as well as space distance among microstructure particles have a synergistic effect on adhesion of the as-prepared superhydrophobic surfaces.

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Scheme 1. Optical photographs of water droplets dyed with methyl blue on superhydrophobic TiO 2 @Cotton fabric surfaces with different adhesion a–c) and the surface traces after the water droplet left the cotton fabrics d–f). Schematic illustration of three types of solid/liquid/air three-phase contact models with adhesive forces ranging from high to low: g) “area” contact model with high adhesion; h) “line” contact model with medium adhesion; i) “point” contact model with low adhesion.

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2.4. Laundering Durability

Robust laundering durability is very important for reuse of textile fabrics, which represents the stability of superhydro-phobic fabric surfaces. Therefore, as an important performance index, it should be taken into account before water repellent fabrics entering into the market. Figure 7 showed the change of contact angle and adhesive force after laundering for fi ve cycles according to American Association of Textile Chemists and Colourists (AATCC 61–2006) standard method under 2A condition on superhydrophobic TiO 2 @Cotton constructed at 150 °C for 20 h by hydrothermal method. The specifi c evalu-ation method of laundering durability according to AATCC standard method under 2A condition was illustrated in sup-porting information. Before laundering, the superhydrophobic surface exhibited a static contact angle ≈159.0° and an adhesive force about 12 µN. After laundering for the fi rst cycle according to AATCC standard method, a slight decrease on contact angle and a notable increase (30 µN) on adhesion occurred. Although the decrease of contact angle for the second cycle was bigger than the fi rst one cycle, the surfaces still displayed superhydro-phobicity. In the next few laundering cycles, the contact angle and droplet adhesion on superhydrophobic fabric tended to be kept stable. Water droplets dyed with methyl blue on such superhydrophobic fabric surface remain spherical shape before and after laundering for fi ve accelerated cycles (Figure S5a,b, Supporting Information) and even could be roll away from the surface when raising up the side of sample. For the pris-tine cotton modifi ed with fl uoroalkylsilane, water droplet was shaped like a sphere (Figure S5c, Supporting Information) and no obvious change on water contact angle after laundering for one cycle (Table S1, Supporting Information), but the surface abruptly became highly hydrophilic combined with a high adhesion after the second laundering (Figure S5d, Supporting Information), indicating that the hierarchical TiO 2 particles decoration is vital for the superhydrophobicity stability. After fi ve accelerated laundering cycles under 2A condition, the supe-rhydrophobic sample surfaces was washed by deionized water and then dried on oven, the static CA and adhesive force tended to approach a plateau of about 151.2° and 55 µN, respectively,

demonstrating the superhydrophobic surface is stable. The roughness structure of cotton surface and the covalent bonding formed between fl uoroalkylsilane molecules and cotton sub-strate were considered for improving the stability of durable laundering. We have also conducted a multiple cycles washing test (14 accelerated laundering cycles) and the sample could still remained with highly hydrophobic (≈145°, see Figure S6, Supporting Information).

Figure 8 showed the SEM images after accelerated laundering for fi ve cycles on superhydrophobic cotton fabric surfaces pre-pared for 10 h at various temperatures. After laundering for fi ve cycles, the micro/nanostructure on cotton surfaces caused a subtle change. The fl ower-like structure decreased but micro-structure TiO 2 particles were coated on fi ber surface. This is due to the chemical interfaces and mechanical interfaces such as shearing force and friction during laundering process. The presence of steel balls caused amount of TiO 2 particles grinded down and even rubbed down. The destroyed section had a thin air layer between superhydrophobic surface and water droplet, causing the water CA decrease to a certain extent but always keep superhydrophobic. This demonstrated TiO 2 particles on cotton surfaces were robust and stable.

2.5. Self-Cleaning Property

To demonstrate the self-cleaning property of the superhydro-phobic TiO 2 @Cotton, saffron methyl orange (MO) powder was used as a contaminant. ( Figure 9 a–d and Video S1, Sup-porting Information). The superhydrophobic fabric was fi xed on a transparent glass slides that leans against a round dish with a small angle of inclination. A sparse layer of MO powder was distributed on the surface and subsequently cleaned by the directed movement of water droplets using a micropipette. The digital pictures were obtained at different moment. During the sliding process (Figure 9 b,c), the powder was immediately picked up, surrounded and carried away by the water droplets

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Figure 7. a) The effect of laundering cycles on contact angle and adhe-sive force of TiO 2 @Cotton (150 °C, 20 h) fabrics according to AATCC standard method under 2A condition. Insets are corresponding contact angle images with different laundering cycles. Figure 8. Typical SEM images after accelerated laundering on superhy-

drophobic cotton fabric surfaces prepared for 10 h with different tem-peratures: a) 120 °C, b) 150 °C, c) 180 °C, and d) 200 °C. Insets are the corresponding low magnifi ed images.

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and fi nally leaving behind a clean surface. Figure 9 e,g showed the high magnifi ed optical images of dusts on superhydro-phobic fabric surfaces before and after water cleaning, com-pared to the optical image before self-cleaning process, the MO powder was almost totally taken away by water. Several isolated MO particles embedded into the fi ber sur-face, this ascribed to the impact pressure of water droplets exerted on sample surface that removing particles from fi ber surface. If given a higher impact pressure of water droplet and proper injection direction, all particles can be removed and obtain a neatly cleaning surface. [ 26 ] The schematic illustration (Figure 9 f) was further demonstrate the self-cleaning process. Water droplets were easily roll away from the superhydrophobic fabric surface meanwhile take away the dusts staying on it when tilting the sample with a certain angle. It was observed that some water droplets maintained spherical shape even after they have taken up the contaminants (see Video S1, Supporting Information).

2.6. Oil/Water Separation Property

The properties of superhydrophobicity and underwater superoleophilicity are suitable for oil/water separation. The as-prepared samples with special wetting property can be used for selectively collecting oil from oil/water mixtures effi ciently under various conditions (e.g., fl oating oil layer or under-water oil droplet or even oil/water mixtures). We take the underwater superoleophobic TiO 2 @Cotton fabric for separating oil/water mixture. The proof-of-concept oil/

water separation experiment was performed as shown in Figure 10 a–d. The sample was prewetted by water prior to use and subsequently fi xed between two glass vessels. The mixture of petroleum ether and water (50% v/v) were poured into the upper glass vessel. The water was dyed with methyl blue (MB)

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Figure 9. a–d) The self-cleaning process of superhydrophobic surfaces with low surface energy. The high magnifi ed optical images of dusts on super-hydrophobic fabric surfaces e) before and g) after water droplets cleaning, and f) corresponding schematic illustration of the self-cleaning process.

Figure 10. a–d) Time sequence of the oil/water separation procedure with superhydrophilic TiO 2 @Cotton membrane for the selective permeation of methyl blue dyed water. Time sequence of e–g) capture oil layer (petroleum ether dyed red) on water surface, and h–j) underwater oil droplets (chloroform dyed red) with superhydrophobic fabrics.

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so as to clearly observe the phenomenon. During the separation process (Figure 10 b,c), water droplet permeated through prewetted TiO 2 @Cotton surface and dropped into con-ical fl ask without the requirement of external force. Finally, the methyl blue dyed water and petroleum ether were separated successfully. The contaminated cotton fabric was washed thoroughly by ethanol and water after oil/water separation experiment for reuse. For further visible observation, a whole proce-dure of oil/water separation was recorded in Video S2, Supporting Information. In addi-tion, the oil/water separation process and separation effi ciency of superhydrophobic TiO 2 @Cotton fabric were also charac-terized (Figure S7, Supporting Information). Meanwhile we have investigated the separation effi ciency of superhydrophilic TiO 2 @Cotton fabric (Figure S8, Supporting Information). After successive fi ve cycles of oil/water separation experiments, the separation effi ciencies of the reused superhydrophobic and superhydrophilic TiO 2 @Cotton fabrics without cleaning pre-treatment were 98.1% and 99.3%, respectively. However, a separation effi ciency as high as 99.8% would be achieved when the samples were rinsed with ethanol and water before the oil/water separation, indicating the excellent recycling ability.

For some specifi c oil/water mixture solution, such as a layer of oil on water surface or underwater, the as-prepared superhy-drophilic sample cannot realize effective oil/water separation. However, the POTS modifi ed TiO 2 @Cotton fabrics exhibiting excellent superhydrophobic and superoleophilic capacities would be promising to solve this separating problem under ambient environment or underwater conditions. Figure 10 e–j shows the process of capture petroleum ether from water sur-face and chloroform from underwater with superhydrophobic TiO 2 @Cotton fabrics, here the oil was dyed with Oil Red O for better experimental observation. When a piece of as-prepared sample entered into the water and near to a layer of oil which has a lower density than water (petroleum ether, e–g), the red dyed oils were instantaneously absorbed within a few seconds and leaving a clean water surface, meanwhile, the fabric turned red color since the presence of red oils. For the case of oils with a larger density than water (chloroform, h–j), the as-prepared sample was caught into water with a tweezer clamping, the fabric would quickly capture the oils as soon as it touched the oil surface. The detail processes of capture and absorb oils from water suface and underwater were recorded in Videos S3 and S4, Supporting Information. Therefore, these results suggest that such facile construction of TiO 2 @Cotton fabric with spe-cial wettability is promising for versatile separation of oil/water under various conditions (e.g., fl oating oil layer, underwater oil droplet or oil/water mixtures).

3. Conclusion

We have successfully constructed superhydrophobic TiO 2 @Cotton fabrics by one-step hydrothermal method and sub-sequently modifi ed with fl uoroalkylsilanes. The fl ower-like micro/nanostructure TiO 2 particles distributed on cotton

surface uniformly on reasonable condition (reaction tempera-ture: 150 °C, deposition time: 10 h). The as-prepared rough fl ower-like surfaces exhibited excellent superhydrophobicity, rolling-off, and self-cleaning properties. The resultant superhy-drophobic surface demonstrated remarkable antiwetting (CA above 163° and SA less than 5°) and excellent laundering dura-bility against chemical and mechanical interactions (abrasion, friction, and shearing force). In addition, the fl exible TiO 2 @Cotton fabrics with special wettability has been verifi ed for highly effi cient and recyclable for multiple oil/water separation processes due to its large contrast wetting ability for oil and water under various conditions. Finally, such facile wet chem-ical strategy to construct TiO 2 particles on cotton fabrics can be widely applied on various substrates with a scale-up production (polyester woven fabric and spandex knitted fabric). Therefore, these multi-functional TiO 2 @Cotton fabrics with special wetta-bility are anticipated to be effectively exploited in various fi elds including self-cleaning and oil/water separation.

4. Experimental Section Preparation of Hierarchical TiO 2 @Cotton Fabric : The fabrication of

hierarchical TiO 2 @Cotton fabric was produced by the following process ( Scheme 2 ): 0.75 g (2 × 10 −3 M ) of potassium titanium oxalate (PTO) was dissolved in deionized water (15 mL), then sonicated for 5 min in a ultrasonic cleaning machine (KQ100E, Kunshan Ultrasonic Instrument Co., Ltd) with a frequency of 40 kHz, followed by adding diethylene glycol (20 mL) under vigorous magnetic stirring. After stirring for 20 min, the mixed solution was transferred into a Tefl on-lined stainless steel vessel (100 mL). The cleaned cotton were immersed into the mixed solution and then reacted for a certain duration with the hydrothermal treatment temperature range from 120 to 200 °C, respectively. After the hydrothermal reaction was completed, the cotton pieces were thoroughly washed with deionized water to remove the residual reactants and dried at 70 °C in vacuum oven. It should be noted that TiO 2 @Cotton (R1, R2) represents the reaction temperature and reaction duration of as-prepared sample are R1 and R2, respectively. For example, TiO 2 @Cotton (150 °C, 10 h) represents the resultant sample is obtained at a reaction temperature of 150 °C for 10 h.

Fabrication of Superhydrophobic TiO 2 @Cotton Fabric Surfaces : The superhydrophobic surfaces were obtained by immersing the as-prepared TiO 2 @Cotton fabric in a mixed methanolic solution of hydrolyzed 1 vol% of POTS for 1 h and subsequently dried at 140 °C for 1 h.

Characterization : The surface structure and morphology of TiO 2 @Cotton fabrics were characterized by a fi eld-emission SEM (Hitachi-S4800). Energy disperse spectroscopy (EDS) spectrometer fi tted to TM3030 scanning electron microscope was applied for elemental analysis. All samples were coated by gold sputtering prior to SEM observations. XPS spectra were obtained by using a Kratos Axis

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Scheme 2. Schematic diagram of a facile one-pot hydrothermal process to construct TiO 2 particles coating on fabrics.

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Ultra HAS X-ray photoelectron spectroscopy with an Al Ka X-ray source at a reduced power of 100 W. The vacuum pressure in the analysis chamber was maintained at 4.0 × 10 −9 Pa. The binding energies were normalized to the signal for adventitious C 1s at 284.5 eV. The step size for high-resolution scan was 0.1 eV and the pass energy was 80 eV. The crystal phase analyses of samples were identifi ed by using an X-ray diffractometer (XRD, X’Pert-Pro MRD, Philips) with Cu Ka radiation (λ = 0.1542 nm) under a voltage of 40 kV and a current of 40 mA. The wettability of water droplets on sample surfaces were characterizated using an optical contact angle measurements instruments (Krüss DSA100, Germany). Deionized water was used for contact angle measurement. The volume of water droplets applied for static contact angle and dynamic sliding angle were 6 and 8 µL, respectively. The adhesive force was measured using a high-sensitivity micro-electromechanical balance system (Dataphysics DCAT11, Germany). A metal ring containing of 4 µL water droplets was placed above on sample and the sample table approach to metal ring at a constant speed of 0.1 mm s −1 at room temperature. The immerse depth between metal ring and sample was 0.1 mm. The maximum peak value (break point) was taken as the adhesive force, the values of adhesive force were average of fi ve results on different locations. The laundering durability of superhydrophobic TiO 2 @Cotton was conducted using a washing fastness tester (SW-12A, Wuxi textile machinery Co., Ltd) according to American Association of Textile Chemists and Colourists (AATCC 61–2006) standard method under 2A condition using a 0.15% standard reference detergent without optical brightener (WOB), and 50 stainless steel balls. One accelerated laundering durability test is equal to fi ve commercial or domestic laundering cycles.

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

Acknowledgements S. L. and J. H. contributed equally to this work. The authors thank the Natural Science Foundation of Jiangsu Province of China (BK20130313, BK20140400), National Natural Science Foundation of China (91027039, 51373110, 51203108, 51273134), Deanship of Scientifi c Research at King Saud University (PRG-1436-03), Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Qing Lan Project for Excellent Scientifi c and Technological Innovation Team of Jiangsu Province (2012), and Project for Jiangsu Scientifi c and Technological Innovation Team (2013) for fi nancial support of this work.

Received: May 1, 2015 Revised: June 12, 2015

Published online:

[1] a) Y. Lu , S. Sathasivam , J. L. Song , C. R. Crick , C. J. Carmalt , I. P. Parkin , Science 2015 , 347 , 1132 ; b) J. V. I. Timonen , M. Latikka , L. Leibler , R. H. A. Ras , O. Ikkaka , Science 2013 , 341 , 253 ; c) X. Deng , L. Mammen , H. J. Butt , D. Vollmer , Science 2012 , 335 , 67 .

[2] a) I. U. Vakarelski , N. A. Patankar , J. O. Marston , D. Y. C. Chan , S. T. Thoroddsen , Nature 2012 , 489 , 274 ; b) Y. M. Zheng , H. Bai , Z. B. Huang , X. L. Tian , F. Q. Nie , Y. Zhao , J. Zhai , L. Jiang , Nature 2010 , 463 , 640 ; c) T. S. Wong , S. H. Kang , S. K. Y. Tang , E. J. Smythe , B. D. Hatton , A. Grinthal , J. Aizenberg , Nature 2011 , 477 , 443 .

[3] a) K. S. Liu , M. Y. Cao , A. Fujishima , L. Jiang , Chem. Rev. 2014 , 114 , 10044 ; b) H. Bellanger , T. Darmanin , E. T. de Givenchy , F. Guittard , Chem. Rev. 2014 , 114 , 2694 ; c) X. M. Li , D. Reinhoudt , M. Crego-Calama , Chem. Soc. Rev. 2007 , 36 , 1350 .

[4] a) Y. T. Luo , J. Li , J. Zhu , Y. Zhao , X. F. Gao , Angew. Chem. Int. Ed. 2015 , 54 , 4876 ; b) Y. K. Lai , L. X. Lin , F. Pan , J. Y. Huang , R. Song , Y. X. Huang , C. J. Lin , H. Fuchs , L. F. Chi , Small 2013 , 9 , 2945 ; c) X. J. Liu , Y. M. Liang , F. Zhou , W. M. Liu , Soft Matter 2012 , 8 , 2070 .

[5] a) T. Jiang , Z. G. Guo , W. M. Liu , J. Mater. Chem. A 2015 , 3 , 1811 ; b) D. T. Ge , L. L. Yang , Y. F. Zhang , Y. D. Rahmawan , S. Yang , Part. Part. Syst. Charact. 2014 , 31 , 763 ; c) Y. K. Lai , F. Pan , C. Xu , H. Fuchs , L. F. Chi , Adv. Mater. 2013 , 25 , 1682 .

[6] a) J. Y. Huang , Y. K. Lai , L. N. Wang , S. H. Li , M. Z. Ge , K. Q. Zhang , H. Fuchs , L. F. Chi , J. Mater. Chem. A 2014 , 2 , 18531 ; b) T. Darmanin , E. T. de Givenchy , S. Amigoni , F. Guittard , Adv. Mater. 2013 , 25 , 1378 ; c) L. Y. Xu , X. M. Lu , M. Li , Q. H. Lu , Adv. Mater. Interfaces 2014 , 1 , 1400011 .

[7] a) L. Y. Xu , D. D. Zhu , X. M. Lu , Q. H. Lu , J. Mater. Chem. A 2015 , 3 , 3801 ; b) Z. J. Cheng , H. Lai , Y. Du , K. W. Fu , R. Hou , C. Li , N. Q. Zhang , K. N. Sun , ACS Appl. Mater. Interfaces 2014 , 6 , 636 ; c) Z. J. Cheng , R. Hou , Y. Du , H. Lai , K. W. Fu , N. Q. Zhang , K. N. Sun , ACS Appl. Mater. Interfaces 2013 , 5 , 8753 .

[8] a) J. L. Yong , F. Chen , Q. Yang , D. S. Zhang , U. Farooq , G. Q. Du , X. Hou , J. Mater. Chem. A 2014 , 2 , 8790 ; b) J. L. Yong , Q. Yang , F. Chen , H. Bian , G. Q. Du , U. Farooq , X. Hou , Adv. Mater. Inter-faces 2015 , 2 , 1400388 ; c) H. Zhou , H. X. Wang , H. T. Niu , T. Lin , Sci. Rep. 2013 , 3 , 2964 ; d) H. Zhou , H. X. Wang , H. T. Niu , J. Fang , Y. Zhao , T. Lin , Adv. Mater. Interfaces 2015 , 2 , 1400559 .

[9] a) Y. K. Lai , Y. X. Tang , J. Y. Huang , F. Pan , Z. Chen , K. Q. Zhang , H. Fuchs , L. F. Chi , Sci. Rep. 2013 , 3 , 3009 ; b) M. B. Oliveira , C. L. Salgado , W. L. Song , J. F. Mano , Small 2013 , 9 , 768 ; c) J. Y. Huang , Y. K. Lai , F. Pan , L. Yang , H. Wang , K. Q. Zhang , H. Fuchs , L. F. Chi , Small 2014 , 10 , 4865 .

[10] a) E. Ueda , P. A. Levkin , Adv. Mater. 2013 , 25 , 1234 ; b) W. Q. Feng , L. X. Li , E. Ueda , J. S. Li , S. Heissler , A. Welle , O. Trapp , P. A. Levkin , Adv. Mater. Interfaces 2014 , 1 , 1400269 ; c) H. Y. Erbil , A. Demirel , Y. Avci , O. Mert , Science 2003 , 299 , 1377 .

[11] a) Y. K. Lai , H. F. Zhou , Z. Zhang , Y. X. Tang , J. W. C. Ho , J. Y. Huang , Q. L. Tay , K. Q. Zhang , Z. Chen , B. P. Binks , Part. Part. Syst. Charact. 2015 , 32 , 355 ; b) X. T. Zhu , Z. Z. Zhang , G. N. Ren , J. Yang , K. Wang , X. H. Xu , X. H. Men , X. Y. Zhou , J. Mater. Chem. 2012 , 22 , 20146 ; c) Y. K. Lai , X. F. Gao , H. F. Zhuang , J. Y. Huang , C. J. Lin , L. Jiang , Adv. Mater. 2009 , 21 , 3799 .

[12] a) X. M. Tang , Y. Si , J. L. Ge , B. Ding , L. F. Liu , G. Zheng , W. J. Luo , J. Y. Yu , Nanoscale 2013 , 5 , 11657 ; b) X. M. Tang , Y. Si , J. L. Ge , B. Ding , L. F. Liu , G. Zheng , W. J. Luo , J. Y. Yu , J. Mater. Chem. A 2013 , 1 , 14071 ; c) S. Yang , Y. Si , Q. X. Fu , F. F. Hong , J. Y. Yu , S. S. Al-Deyab , M. El-Newehy , B. Ding , Nanoscale 2014 , 6 , 12445 .

[13] a) Q. An , Y. H. Zhang , K. K. Lv , X. L. Luan , Q. Zhang , F. Shi , Nanoscale 2015 , 7 , 4553 ; b) M. J. Cheng , G. N. Ju , C. Jiang , Y. J. Zhang , F. Shi , J. Mater. Chem. A 2013 , 1 , 14311 ; c) G. N. Ju , M. J. Cheng , F. Shi , NPG Asia Mater. 2014 , 6 , e111 .

[14] a) L. Wu , J. P. Zhang , B. C. Li , A. Q. Wang , J. Mater. Chem. B 2013 , 1 , 4756 ; b) J. P. Zhang , B. C. Li , L. Wu , A. Q. Wang , Chem. Commun. 2013 , 49 , 11509 ; c) X. Zhou , Z. Zhang , X. Xu , F. Guo , X. Zhu , X. Men , B. Ge , ACS Appl. Mater. Interfaces 2012 , 5 , 7208 ; d) M. J. Cheng , S. S. Zhang , H. Y. Dong , S. H. Han , H. Wei , F. Shi , ACS Appl. Mater. Interfaces 2015 , 7 , 4725 .

[15] a) C. H. Xue , Y. R. Li , P. Zhang , J. Z. Ma , S. T. Jia , ACS Appl. Mater. Interfaces 2014 , 6 , 10153 ; b) J. F. Ge , Y. Si , F. Fu , J. L. Wang , J. M. Yang , L. X. Cui , B. Ding , J. Y. Yu , G. Sun , RSC Adv. 2013 , 3 , 2248 ; c) J. Zimmermann , F. A. Reifl er , G. Fortunato , L. C. Gerhardt , S. Seeger , Adv. Funct. Mater. 2008 , 18 , 3662 .

[16] a) H. X. Wang , H. Zhou , A. Gestos , J. Fang , T. Lin , ACS Appl. Mater. Interfaces 2013 , 5 , 10221 ; b) H. Wang , H. Zhou , A. Gestos , J. Fang , H. Niu , J. Ding , T. Lin , Soft Matter 2013 , 9 , 277 ; c) H. L. Zou , S. D. Lin , Y. Y. Tu , G. J. Liu , J. W. Hu , F. Li , L. Miao , G. W. Zhang ,

FULL P

APER

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (11 of 11) 1500220wileyonlinelibrary.comAdv. Mater. Interfaces 2015, 1500220

www.MaterialsViews.com www.advmatinterfaces.de

H. S. Luo , F. Liu , C. M. Hou , M. L. Hu , J. Mater. Chem. A 2013 , 1 , 11246 .

[17] C. H. Xue , J. Z. Ma , J. Mater. Chem. A 2013 , 1 , 4146 . [18] Y. Zhao , Z. G. Xu , X. G. Wang , T. Lin , Langmuir 2012 , 28 , 6328 . [19] a) A. Fujishima , X. T. Zhang , D. A. Tryk , Surf. Sci. Rep. 2008 , 63 ,

515 ; b) Z. Y. Deng , W. Wang , L. H. Mao , C. F. Wang , S. Chen , J. Mater. Chem. A 2014 , 2 , 4178 ; c) Y. J. Yin , C. X. Wang , Q. K. Shen , G. F. Zhang , C. M. A. Galib , Ind. Eng. Chem. Res. 2013 , 52 , 10656 .

[20] a) M. Y. Wang , J. Ioccozia , L. Sun , C. J. Lin , Z. Q. Lin , Energy Environ. Sci. 2014 , 7 , 2182 ; b) X. K. Xin , M. Scheiner , M. D. Ye , Z. Q. Lin , Langmuir 2011 , 27 , 14594 ; c) M. Yu , Z. Q. Wang , H. Z. Liu , S. Y. Xie , J. X. Wu , H. Q. Jiang , J. Y. Zhang , L. F. Li , J. Y. Li , ACS Appl. Mater. Interfaces 2013 , 5 , 3697 .

[21] a) B. Deng , R. Cai , Y. Yu , H. Q. Jiang , C. L. Wang , J. Li , L. F. Li , M. Yu , J. Y. Li , L. D. Xie , Q. Huang , C. H. Fan , Adv. Mater. 2010 , 22 , 5473 ; b) J. Y. Huang , S. H. Li , M. Z. Ge , L. N. Wang , T. L. Xing ,

G. Q. Chen , X. F. Liu , S. S. Al-Deyab , K. Q. Zhang , T. Chen , Y. K. Lai , J. Mater. Chem. A 2015 , 3 , 2825 ; c) C. H. Xue , S. T. Jia , H. Z. Chen , M. Wang , Sci. Technol. Adv. Mater. 2008 , 9 , 035001 .

[22] a) S. Afzal , W. A. Daoud , S. J. Langford , J. Mater. Chem. A 2014 , 2 , 18005 ; b) S. Afzal , W. A. Daoud , S. J. Langford , ACS Appl. Mater. Interfaces 2013 , 5 , 4753 .

[23] a) W. Choi , A. Tuteja , S. Chhatre , J. M. Mabry , R. E. Cohen , G. H. McKinley , Adv. Mater. 2009 , 21 , 2190 ; b) S. H. Li , S. B. Zhang , X. H. Wang , Langmuir 2008 , 24 , 5585 ; c) M. A. Shirgholami , M. S. Khalil-Abad , R. Khajavi , M. E. Yazdanshenas , J. Colloid Inter-face Sci. 2011 , 359 , 530 .

[24] M. Liu , Y. Zheng , J. Zhai , L. Jiang , Acc. Chem. Res. 2010 , 43 , 368 .

[25] J. Ou , W. Hu , C. Li , Y. Wang , M. Xue , F. Wang , W. Li , ACS Appl. Mater. Interfaces 2012 , 4 , 5737 .

[26] B. Bhushan , Y. C. Jung , K. Koch , Langmuir 2009 , 25 , 3240 .