Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties

Accepted Manuscript Title: Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties Author: Wentao Gan Likun Gao Qingfeng Sun Chunde Jin Yun Lu Jian Li PII: DOI: Reference:

S0169-4332(15)00248-2 http://dx.doi.org/doi:10.1016/j.apsusc.2015.01.206 APSUSC 29643

To appear in:

APSUSC

Received date: Revised date: Accepted date:

17-9-2014 25-1-2015 27-1-2015

Please cite this article as: W. Gan, L. Gao, Q. Sun, C. Jin, Y. Lu, J. Li, Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.01.206 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties Wentao Gan1, Likun Gao1, Qingfeng Sun3*, Chunde Jin3, Yun Lu2* and Jian Li1* Material Science and Engineering College, Northeast Forestry University, Harbin

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1

Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing, 100091,

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2

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150040, China

China

School of Engineering, Zhejiang Agricultural and Forestry University, Lin'an 311300,

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3

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China

*Corresponding author. Tel: +86-451-82192399; fax: +86-451-82192399 addresses:

[email protected],

[email protected]

(Yun

Lu)

and

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E-mail

[email protected] (Jian Li).

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*To whom correspondence should be addressed.

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Corresponding author is Jian Li at the following postal address: Northeast Forestry University, No. 26 Hexing Road Xiangfang District, Harbin 150040, China. Tel: +86-451-82192399

Fax: +86-451-82192399

E-mail: [email protected]

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Abstract: Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties were obtained successfully by precipitated CoFe2O4 nanoparticles on

the

wood surface

and

then treated with

a layer of

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octadecyltrichlorosilane (OTS). The as-fabricated wood composites exhibited excellent magnetic property and the water contact angle of the OTS-modified

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magnetic wood surface reached as high as 150o, revealed the superhydrophobic

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property. Moreover, accelerated aging tests suggested that the treated wood composites also have an excellent anti-ultraviolet property.

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Keywords: CoFe2O4, magnetic property, hydrothermal method, superhydrophobicity,

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anti-ultraviolet property Introduction

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Magnetic wood would be a potential for electromagnetic shielding, indoor electromagnetic wave absorber and heavy metal adsorption, which achieved a good

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harmony of both woody and magnetic characteristics, it was firstly proposed and

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tested by the Oka group [1-7]. Although the magnetic wood materials have excellent magnetic property, some unfavorable end-product properties of wood materials such as hygroscopic property, dimensional instability and photodegradability have not been fully discussed.

When wood materials were exposed outdoors above ground, a complex combination of solar radiation and other environmental factors like water and temperature contributed to what was described as weathering. Ultraviolet (UV) light irradiation in sunlight was believed to be the most important factor resulted in wood

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components degradation, among which lignin was the most sensitive one. Under UV light irradiation, the structure of lignin would be destroyed and produced a great amount of free radicals, inducing a reaction with oxygen to produce chromophoric

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carbonyl and carboxyl groups, and leading to the color change [8-11]. Moreover, moisture, heat/cold environment were also contributed to the degradation process [12].

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In principle, natural wood materials with porous structure were hydrophilic, and water

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can be easily absorbed and penetrated into the deeper layers of wood by the capillary action of wood cell, which resulting in warping, cupping, face checking and new

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cracks on the wood surfaces, and accelerating the photodegradation process [13-15].

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Thus, there was a great significance to achieve a good harmony of both the superhydrophobicity and anti-ultraviolet property in the wood substrate.

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Hybrid wood/inorganic composites were the subject of the intense research activities. These hybrid materials not only exhibited the inherent properties of wood

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substrate, such as, the porosity, good strength to weight ratio and esthetic appearance

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[16], the inorganic properties, in particular anti-ultraviolet property [11] and magnetic properties [17], but also showed the potential synergistic properties, such as superhydrophobicity [18], fire-resistance [19] and biological resistance [20]. Many methods have been applied to the preparation of hybrid wood/inorganic composites [18, 21, 22]. Among these methods, hydrothermal process has been recently received much attention. Wang et al. [23] fabricated the superhydrophobic α-FeOOH film on the wood surface using the hydrothermal method, and the maximal contact angles of the superhydrophobic wood surface reached as high as 158o. In our previous reports

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[24-26], the superhydrophobic TiO2 film with water contact angle about 154o and the CeO2, ZnO nanoparticles film with excellent anti-ultraviolet property were fabricated on wood substrate via the facile hydrothermal process.

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Herein, the magnetic wood was produced successfully by precipitated CoFe2O4 nanoparticles on the wood surface. Then the surface should be subsequently modified

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with a layer of octadecyltrichlorosilane (OTS) to obtain superhydrophobicity and UV

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protection. The modified wood samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force

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microscopy (AFM), energy dispersive spectroscopy (EDXA), FTIR spectroscopy

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(FTIR) and X-ray diffraction (XRD). Moreover, the magnetic, hydrophobic and anti-ultraviolet properties of the modified wood composites were also evaluated.

Materials

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Materials and methods

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Poplar wood slices with the sizes of 15 mm (longitudinal) × 8 mm (tangential) × 1

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mm (radial) were ultrasonically washed in deionized water for 30 min and dried at 100 oC for 24 h in a vacuum. Cobalt chloride hexahydrate (CoCl2·6H2O), ferrous sulfate heptahydrate (FeSO4·7H2O), potassium nitrate (KNO3), sodium hydroxide (NaOH) and octadecyltrichlorosilane (OTS, 95%) used in this study were supplied by Shanghai Boyle Chemical Company Limited., and used without further purification. Synthesis The synthesis pathway of superhydrophobic and magnetic wood was described in Fig. 1. The untreated wood materials (step a) were suspended in the 20 mL of 0.2 mol/L of

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freshly prepared aqueous solution of FeSO4 and CoCl2 with a molar ration of [Fe2+]/[Co2+] = 2 via a vacuum process before transferred into a Teflon-lined stainless steel autoclave and heated the system to 90 °C for 3 h to thermally precipitate the

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non-magnetic metal hydroxides on the template (step b). Heating changed the color from transparent to translucent orange [27]. Until the end of the reaction, the

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supernatant was poured out and 15 mL of 1.32 mol/L NaOH solution with KNO3

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([Fe2+]/[NO3−] = 0.44) was added into the Teflon-lined stainless-steel autoclave. After an additional hydrothermal processing for 6 h at 90 °C, the precipitated precursors

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were converted into ferrite nanoparticles on the wood surfaces, resulting in high

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surface roughness with excellent magnetic property (step c). Finally, the prepared wood specimens were removed from the solution and washed by ultrasonically rinsed

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in deionized water for 30 min, and dried at 50 °C for over 24 h in the vacuum chamber. Using the above methods, the hydrophilic CoFe2O4 films were synthesized

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on the wood surfaces.

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The surface modification of the magnetic wood was carried out by a

self-assembly of OTS layer. The magnetic woods were immersed into the 20 mL of 5% (V/V) OTS ethanol solution at room temperatures under continuous mechanical stirring for 24 h and a layer of OTS molecular covered on magnetic wood surface (step d). Then the samples were dried at 50 °C for over 24 h in the vacuum. Finally, the superhydrophobic wood surface was obtained. Characterizations The surface morphology of the samples were characterized by the scanning electron

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microscopy (SEM, FEI, Quanta 200) and transmission electron microscope (TEM, FEI ,Tecnai G20). Atomic force microscopy (AFM) images were obtained using a Multimode Nanoscope
a controller (Veeco Inc., USA) with a silicon tip operated in

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a tapping mode to characterize the surface morphology and roughness. Crystalline structures of the samples were identified by the X-ray diffraction technique (XRD,

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Rigaku, D/MAX 2200) operating with Cu Kα radiation (λ = 1.5418Ao) at a scan rate

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(2θ) of 4o min-1 and the accelerating voltage of 40 kV and the applied current of 30 mA ranging from 5o to 80o. For FTIR analysis, thin sample disks were made by

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grinding small portion of the treated wood composites and pressing them with

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potassium bromide. The FTIR spectra for the wood samples were recorded using FTIR (Magna-IR 560, Nicolet). For magnetic characterization, wood specimens of 4

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mm (tangential) × 4 mm (radial) × 4 mm (longitudinal) were used. The magnetic properties of the composites were measured by a superconducting quantum

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interference device (MPMS XL-7, Quantum Design Corp.) at a room temperature

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(300 K). The contact angle analyzer (JC2000C, Beijing code tong technology co., LTD) at ambient temperatures with a droplet volume of 5 μL was employed to measure the WCA of the samples. An average of the five measurements taken at different positions on each sample was applied to calculate the final WCA angle. DR-UV/Visible spectra for the wood samples were obtained with the instrument TU-190, Beijing Purkinje, China, equipped with an integrating sphere attachment. BaSO4 was the reference. Accelerated aging test

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A QUV accelerated weathering tester (Accelerated Weathering Tester, Q-Panl, Cleveland, OH, USA) was used in this experiment, which allowed for water spray and condensation. The samples were fixed in stainless steel holders and then subjected to

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accelerated weathering through constant exposure to fluorescent UV-light radiation at a wavelength of 340 nm and a temperature of 50 °C for 8 h, followed by water spray

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for 4 h. The average irradiance was set to 0.77 W/m2, and the spray temperature was

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fixed at 25 °C. The exposure time ranged from 0 to 1200 h. The color change of the wood surface before and after the UV irradiation were measured using the portable

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spectrophotometer (NF-333, Nippon Denshoku Company, Japan) with CIELAB

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system in accordance with the ISO-2470 standard. CIELAB L*, a*, b*, parameters were measured at six locations on each specimen and average value was calculated. In

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the CIELAB system, L* axis represents the lightness, and varies from 100 (white) to 0 (black); a* and b* are the chromaticity indices; +a* is the red direction; -a* is green;

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Eqs. (1)-(3).

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+b*is yellow; and -b*is blue. The change of L*, a* and b* are calculated according to

Δa*=a2-a1

(1)

Δb*=b2-b1

(2)

ΔL*=L2-L1

(3)

Where ΔL*, Δa*and Δb* values were calculated from the difference of the final and initial values (i.e., after and before UV irradiation) of L*, a* and b*, respectively. a1, b1 and L1 are the initial color parameters; a2, b2 and L2 are the final parameters. These values were used to calculate the overall color change ΔE* as a function of the

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weathering time, according to the following equation:

(4)

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A lower ∆E* value corresponded to a smaller color difference and indicated

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strong resistance to UV radiation. Result and discussion

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The SEM images in Fig. 2 illustrate the surface morphologies of the untreated wood,

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magnetic wood and the wood treated by CoFe2O4 and OTS. In Fig. 2a, the pristine tracheids of poplar were smooth. However, the CoFe2O4 nanoparticles formed on

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wood masks the piths and other details (2b and 2c). The surface chemical elemental

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compositions of the magnetic wood were determined by EDXA spectrum, and the results were presented as an insert in Fig. 2b. Evidence of only carbon, oxygen, iron,

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cobalt and gold could be detected in the spectra. The gold originated from the coating

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layer used for scanning electron microscope observation, carbon element was from the wood substrate and no other elements were detected. Accordingly, CoFe2O4 nanoparticles were coated effectively on the wood surface. The TEM image shows the average size of the CoFe2O4 nanoparticles was 200 nm which peeled off from the magnetic wood samples by the ultrasonic treatment (Fig. 2c, Inset). The wood surface treated with CoFe2O4 and OTS was presented in Fig. 2d. Obviously, a thin layer of the wax crystalloids and nanoscale protuberances uniformly covered the wood surface. The presence of such a rough binary structure on the wood surface was the main requirement for superhydrophobicity [28-30].

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Fig. 3 shows the XRD patterns of the untreated wood and magnetic wood. In Fig. 3a, the diffraction peaks at 15o and 22o represent the characteristic diffraction peaks of the wood. In Fig. 3b, additional diffraction peaks represent the new crystal structures

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of the magnetic wood. The diffraction peaks at 18o, 30o, 35o, 43o, 53o, 56o and 62o

(440) planes of CoFe2O4 (PDF No. 22-1086), respectively.

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could be assigned to the diffractions of the (111), (220), (311), (400), (422), (511) and

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Fig. 4 illustrates the magnetic characterization of the untreated wood and the magnetic wood. The untreated wood shows non-magnetic characterizes, with

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maximum applied field up to 20 kOe (Fig. 4, Inset). Interestingly, the magnetic wood

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exhibits a polar property and shows a typical ferromagnetic behavior, the saturation magnetization (MS) and coercivity (HC) of the magnetic wood were 1.81 emu/g and

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451 Oe, respectively. The results reveal the wood after CoFe2O4 treated possessed excellent magnetic property compared with the untreated wood. An important

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question that still remains was whether a superhydrophobic wood surface can be

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created by coating with a rough CoFe2O4 nanoparticles film and self-assembly modification of OTS leading to a low surface energy. In Fig. 5 top view and three-dimensional surface plots (300 nm × 300 nm) AFM

representations were presented for the untreated wood, the magnetic wood and the wood treated by CoFe2O4 and OTS, respectively. Compared with the untreated wood surface (Fig. 5a), the magnetic wood surface (Fig. 5b) exhibited a fine microstructure and more complex surface texture which was consistent with a rough topography. The surface of the wood treated by CoFe2O4 and OTS (Fig. 5c) was composed of high

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“mountains” and deep “valleys”. The difference of the surface roughness can be reflected in the rms roughness values (rms = root mean square = the standard deviation of the Z value, Z being the total height range analyzed) of the three surface,

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which were 26.9 nm (the untreated wood), 49.9 nm (the magnetic wood) and 96.1 nm (the wood treated by CoFe2O4 and OTS), respectively. Therefore, it can be concluded

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that the modified surface topology was responsible for the film generated

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hydrophobic characteristics, due to a change in surface roughness.

Fig. 6 shows the FTIR spectra of the untreated wood, magnetic wood and the

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magnetic wood treated by OTS. For magnetic wood sample, the absorption band at

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3423 cm-1 assigned to the stretching vibration of OH groups became comparatively narrow after modification, probably due to interaction between the OH groups of

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wood surface and the deposited CoFe2O4 nanoparticles [14]. The bands at 425 cm-1 were attributed to Fe-O stretching vibrations at the octahedral site [31]. With the

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addition of OTS, the new adsorption bands at 2919 cm-1 (C-H asymmetric stretching

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vibrations) and 2850 cm-1 (C-H asymmetric stretching vibrations), were for the long-chain alkyl group of the coating surface. The bands around 1106 and 906 cm-1 were corresponded to Si-O-Si vibration bands. The characteristic band near 436 cm-1, which arises from the stretching vibration of Fe-O bonds, has a shifted to high wavenumbers. The phenomenon can be explained according to the formation of Fe-O-Si bonds where Fe-O-H groups on the surface of the CoFe2O4 nanoparticles were replaced by Fe-O-Si(O-)2-R as shown in Fig. 9 [32]. Superhydrophobic surface with a water contact angle (CA) higher than 150o, has

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a great potential for research and practical applications [28-30, 33]. Fig. 7 shows the wettability of the wood sample by static CA measurements. CA of the untreated wood and the magnetic wood were 40o and 7o, respectively, which demonstrated the

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hydrophilic property obviously. For the wood surface only treated with OTS can achieved a maximum water contact angle of about 100o and showed the hydrophobic

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property to a certain extent. However, after the combined treatment by CoFe2O4 and

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OTS, CA was found to be 150o, indicated an excellent hydrophobic property clearly. To further understand the superhydrophobic property of the treated wood surface,

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the Cassie’s equation, which was generally applicable to heterogeneous roughness and

(5)

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low-surface energy surfaces that exhibit superhydrophobicity, was employed [34]:

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where f was the fraction of the solid surface in contact with liquid, the fraction of

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air in contact with liquid at the surface was 1-f, θc and θ represented the water contact angle on rough and smooth surfaces, respectively. Here, the Cassie’s equation can be used to calculate the fraction of the air pockets at the surface. In this paper, the water contact angle θc on the magnetic wood surface treated with OTS was approximately 150o, and the water contact angle θ on the smooth surface modified with OTS was 100o. Therefore, by the use of Cassie equation, the fraction of air in contact with liquid at the surface was calculated as 0.84. In addition, the environmental stability and durability of the superhydrophobic wood surface have been investigated. The sample can be maintained at least for three

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months of storage in air, the water contact of wood surface has no negligible change, indicated its good stability in air. Fig. 8 shows the excellent magnetic and superhydrophobic properties of the wood

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samples. The superhydrophobic and magnetic wood was floating on the surface of the water, and could be easily attracted by using the external magnet (Fig. 8a). The

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magnetic wood samples were placed on the top of a desk, could be attracted and

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firmly adsorbed by the external magnet (Fig. 8b). The water droplet would drop down from the wood surface by driving the wooden platelet (Fig. 8c).

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Fig. 9 presents a schematic illustration of the superhydrophobic and magnetic

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wood. Since there were large surface-to-volume atomic ratio, high surface activity and amount of dangling bonds on nanoparticle surface, the atoms on the surface were apt

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to absorb ions or molecules in solution. For CoFe2O4 nanoparticles dispersed in aqueous solution, the bare atoms of Fe on the particle surface would adsorb OH-, so

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that there was OH-rich surface [32]. The untreated wood sample (Fig. 9a) was

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immersed into the precursor solution through a hydrothermal process and the plentiful OH groups between the CoFe2O4 nanoparticles and wood surface reacted with each other, and a CoFe2O4 layer arose on the surface, resulting in a increased surface roughness (Fig. 9b). When the OTS was introduced, the Si-Cl groups of the OTS molecule firstly hydrolyzed into Si-OH groups, the –OH on the surface of CoFe2O4 can react with Si-OH (Fig. 9c). With the continuous dehydration reaction, Si-O groups with the superhydrophobic long chain alkyl groups were formed onto the magnetic wood surface by chemical bond. Finally, under the combined effects of CoFe2O4

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nanoparticles and OTS, the surface became superhydrophobicity [33, 35]. The color changes before and after UV irradiations were measured in accelerated aging tests to evaluate the anti-ultraviolet property of the magnetic wood. The

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experimental results were presented in Fig. 10. In Fig. 10a, the change of Δa* value of the untreated wood sample under UV irradiation indicated that the surface color of the

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untreated wood sample became gradually redder with increasing UV irradiation time.

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The Δa* values of the magnetic wood showed the similar changing tendency compared with the untreated wood (only 1/10 of the untreated wood), which showed

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the stronger UV-resistant ability of the magnetic wood compared with that of the

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untreated wood. In Fig. 10b, the change of Δb* values indicated that the color of the untreated wood turned to dark yellow, while that of the magnetic wood turned to

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slight blue with increasing UV irradiation time. In Fig. 10c, ΔL*values of the untreated wood, magnetic wood became negative with the time, revealed the lightness

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turned to black. However, the tendency of ΔL* change of the magnetic wood had

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slight variation in comparison with the untreated wood, suggested a superior UV-resistant ability of the magnetic wood was obtained. In Fig. 10d, it could be seen that the total color change (ΔE*) of the magnetic wood had a slighter change compared with the untreated wood with increasing UV irradiation time, and the ΔE* values of the magnetic wood was only 1/4 of the untreated wood. This further confirmed that the magnetic wood have excellent UV-resistant ability. The UV/Vis diffuse reflection spectra of the untreated wood and magnetic wood were shown in Fig. 11. Zhu et al. [36] reported that the CoFe2O4 samples have the UV

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absorption at the region of 200-800 nm. This was consistent with our experimental results in Fig. 11. Magnetic wood clearly exhibited a much higher absorption at the 200-800 nm wavelength range compared with the untreated wood, indicated the

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magnetic wood has higher UV resistance than the untreated wood. Hence, better anti-ultraviolet property was achieved by modified with CoFe2O4 compared to the

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untreated wood samples. We attributed this to the CoFe2O4 nanoparticles film

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hindered the UV light from reaching the wood surface and thus prevented photodegradation of wood components [37].

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Conclusions

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Multifunctional wood materials with magnetic, superhydrophobic and anti-ultraviolet properties can be prepared through the combined effects of CoFe2O4 nanoparticles

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and octadecyltrichlorosilane (OTS). The saturation magnetization (MS) and coercivity

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(HC) of the magnetic wood were 1.8 emu/g and 450 Oe, respectively. The contact

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angel (CA) of the treated wood was around 150o. Moreover, the modified wood sample also showed a superior anti-ultraviolet performance. The presented approach may provide future direction for the multifunctional modification of wood. Acknowledgments

This work was financially supported by The National Natural Science Foundation of China (grant no. 31470584) and Doctoral Candidate Innovation Research Support Program of Science & Technology Review (kjdb2012006). References [1] H. Oka, H. Fujita, Experimental study on magnetic and heating characteristics of

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[35] P. Degen, A. Shukla, U. Boetcher, H. Rehage, Self-assembled ultra-thin coatings of octadecyltrichlorosilane (OTS) formed at the surface of iron oxide nanoparticles. Colloid. Polym. Sci. 286 (2008) 159-168.

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[36] Z. Zhu, X. Li, Q. Zhao, Y. Shi, H. Li, G. Chen, Surface photovoltage properties and photocatalytic activities of nanocrystalline CoFe2O4 particles with porous

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superstructure fabricated by a modified chemical coprecipitation method. J.

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Nanopart. Res. 13 (2011) 2147-2155.

[37] S. Donath, H. Militz, C. Mai, Weathering of silane treated wood. Holz. Roh.

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Werkst. 65 (2007) 35-42.

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Figure Captions Fig. 1. Preparing process of superhydrophobic and magnetic wood Fig. 2. SEM images of the surfaces of (a) untreated wood surface, and (b, c) magnetic

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wood at different magnifications; (d) the magnetic wood treated by OTS (Inset: EDXA spectrum of the magnetic wood and TEM image of magnetic nanoparticle)

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Fig. 3. XRD patterns of (a) the untreated wood, and (b) the magnetic wood

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Fig. 4. Magnetization curves at room temperatures of the untreated wood and the magnetic wood

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Fig. 5. AFM images of (a) the untreated wood, (b) the magnetic wood, and (c) the

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wood treated by CoFe2O4 and OTS

Fig. 6. FTIR spectra of (a) the untreated wood, (b) the magnetic wood, and (c) the

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magnetic wood and hydrolyzed octadecyltrichlorosilane (OTS) Fig. 7. Contact angels (CA) of 5-μl water droplet on the surface of (a) the untreated

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wood, (b) the wood sample only treated by CoFe2O4 nanoparticles, (c) the wood

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sample only treated with octadecyltrichlorosilane (OTS), and (d) the wood sample treated with CoFe2O4 nanoparticles and OTS Fig. 8. The superhydrophobic and magnetic wood samples, under the influence of an external magnet. (a1-a2) The floating specimen moved towards the magnet. (b1-b2) Actuation of magnetic wood platelet. (c1-c2) The water droplet would drop down from the wood surface by driving the magnetic wood. Fig. 9. Schematic illustration of the preparing process of superhydrophobic and magnetic wood surface

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Fig. 10. Change tendency of Δa*, Δb*, ΔL* and ΔE* of the untreated wood and the magnetic wood Fig. 11. UV-Vis diffuse reflection spectra of the untreated wood and the magnetic

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wood

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Fig. 1. Preparing process of superhydrophobic and magnetic wood

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Fig. 2. SEM images of the surfaces of (a) untreated wood surface, and (b, c) magnetic

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wood surface at different magnifications; (d) the magnetic wood treated by OTS

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(Inset: EDXA spectrum of the magnetic wood and TEM image of magnetic nanoparticle)

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Fig. 3. XRD patterns of (a) the untreated wood, and (b) magnetic wood

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Fig. 4. Magnetization curves at room temperatures of the untreated wood and the

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magnetic wood

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Fig. 5. AFM images of (a) the untreated wood, (b) the magnetic wood, and (c) the wood treated by CoFe2O4 and OTS

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Fig. 6. FTIR spectra of (a) the untreated wood, (b) the magnetic wood and (c) the

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magnetic wood and hydrolyzed octadecyltrichlorosilane (OTS)

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Fig. 7. Contact angels (CA) of 5-μl water droplet on the surface of (a) the untreated wood, (b) the wood sample only treated by CoFe2O4 nanoparticles, (c) the wood

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sample only treated with octadecyltrichlorosilane (OTS), and (d) the wood sample

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treated with CoFe2O4 nanoparticles and OTS

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Fig. 8. The superhydrophobic and magnetic wood samples, under the influence of an

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external magnet. (a1-a2) The floating specimen moved towards the magnet. (b1-b2) Actuation of magnetic wood platelet. (c1-c2) The water droplet would drop down from the wood surface by driving the magnetic wood

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Fig. 9. Schematic illustration of the preparing process of superhydrophobic and

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magnetic wood surface

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Fig. 10. Change tendency of Δa*, Δb*, ΔL* and ΔE* of the untreated wood and magnetic wood

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Fig. 11. UV-Vis diffuse reflection spectra of the untreated wood and the magnetic

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wood

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Research highlights ► Hybrid superhydrophobic magnetic wood materials with anti-ultraviolet property

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was prepared via precipitated CoFe2O4 nanoparticles on the wood surface

► The

prepared

wood/CoFe2O4

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followed by a treatment with a layer of Octadecyltrichlorosilane (OTS). composite showed

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strong

saturation

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magnetization, which can be attracted, oriented and actuated by an external

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magnet.

► The contact angel (CA) of the treated wood was around 150o.

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► The coated wood sample showed a superior anti-ultraviolet property.

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