Accepted Manuscript

Title: Novel Superhydrophobic and Superoleophilic Sawdustas a Selective Oil Sorbent for Oil Spill Cleanup

Author: Deli Zang Feng Liu Ming Zhang Zhengxin GaoChengyu Wang

PII: S0263-8762(15)00219-1DOI: http://dx.doi.org/doi:10.1016/j.cherd.2015.06.014Reference: CHERD 1924

To appear in:

Received date: 31-3-2015Revised date: 21-5-2015Accepted date: 8-6-2015

Please cite this article as: Zang, D., Liu, F., Zhang, M., Gao, Z., Wang,C.,Novel Superhydrophobic and Superoleophilic Sawdust as a Selective Oil Sorbentfor Oil Spill Cleanup, Chemical Engineering Research and Design (2015),http://dx.doi.org/10.1016/j.cherd.2015.06.014

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 proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

Page 1 of 23

Accep

ted

Man

uscr

ipt

1

Novel Superhydrophobic and Superoleophilic Sawdust as a Selective

Oil Sorbent for Oil Spill Cleanup

Deli Zang, Feng Liu, Ming Zhang, Zhengxin Gao, Chengyu Wang*

Key Laboratory of Bio-based Material Science and Technology, Ministry of

Education, Northeast Forestry University, Harbin 150040, China

*Corresponding Author. E-mail: wangcy@nefu.edu.cn, Tel (Fax): +86-451-82191889

Highlights

Synthetic route for superhydrophobic/superoleophilic sawdust is facile and cheap.

The wettability of sawdust transforms from superhydrophilic to superhydrophobic.

The product can continuously absorb oil while completely repelling water.

This sorbent possesses excellent chemical stability and environmental durability.

The product can be used as a selective oil sorbent for the removal of oil from water.

Abstract: Oil spill pollution has been aggravating current situation of water shortages,

thus people pay more attention to collecting oil from water by using efficient oil

adsorption materials which are of necessity for water protection. In the present study,

sawdust was triumphantly endowed with simultaneous performances of

superhydrophobicity and superoleophilicity. Analytical results disclosed that

superhydrophobic and superoleophilic properties of sawdust product were resulted

from the deposition of silica (SiO2) particles on polystyrene-coated fiber surface and

Page 2 of 23

Accep

ted

Man

uscr

ipt

2

chemical modification by self-assembled octadecyltrichlorosilane (OTS) monomers.

Notably, the proposed superhydrophobic/superoleophilic sawdust with water contact

angle of 153° and oil contact angle of 0° was employed as an oil sorbent to separate

oil from water, it continuously absorbed oil while completely repelling water,

providing strong evidences for its highly promising for the application in the field of

spilled oil disposal.

Keywords: Superhydrophobic; Superoleophilic; Sawdust; Oil sorbent

1. Introduction

Oil contaminants have become one of the main pollutants in waterbody and have

posed a serious threat to river, marine environment and human life [1-4]. With the

continued strengthening of people's awareness of global environmental protection，

there is increasing concern about the development of effective adsorbent material for

oil spillage absorption treatment [5]. Plenty of tactics yet have been put forward to

tackle oil spill pollution including the application of adsorbing materials [6, 7], in-situ

burning [8], dispersing agents [9], enhanced bioremediation [10] and so on. Thereinto,

various oil adsorbents are considered to be a common technique for the collection of

oil spill and natural fibers are the most widely used raw material [11, 12]. In practice,

polymer oil absorbent normally encounters some drawbacks of high-priced, secondary

pollution, low adsorption capacity and environmental damage. For this reason and at

the moment, biodegradable natural material becomes the focus of current attention as

raw material for the fabrication of new types of oil sorbents to take place of traditional

industrialized synthetic polymer materials.

Page 3 of 23

Accep

ted

Man

uscr

ipt

3

In recent years, researchers are committed to studying superhydrophobic plants

in nature and have discovered that superhydrophobic surface with water contact angle

larger than 150° is controlled by not only the geometric microstructure but also

surface chemical composition [13-16]. The common technologies to fabricate

superhydrophobic materials include chemical etching [13, 17], template method [18],

self-assembly treatment [19, 20], sol-gel process [21], electrostatic spinning [22-24],

etc. As a matter of fact, superhydrophobic and superoleophilic absorbent can totally

repel water and absorb oil, which greatly improves its separation efficiency [25-27].

In an attempt to resolve negative influences of oily wastewater on surroundings, a

variety of materials based on both superhydrophobic and superoleophilic characters

have been proposed to remove oil from the mixture of oil and water. For instance, Lee

and co-workers [28] reported a thermal chemical vapor deposition procedure to

fabricate superhydrophobic and superoleophilic carbon porous structured nanotube

mesh by growing vertically-aligned multi-walled carbon nanotube onto a commercial

stainless steel mesh and evaluated its competence for water-oil separation. Wang et al.

[29] adopted a facile and inexpensive dip-coating method for the preparation of a

robust superhydrophobic/superoleophilic sponge which could selectivity expulse oil

from oil-water mixture.

On the one hand, sawdust is a sort of agriculture, forestry and solid waste. As a

natural cellulosic material, sawdust is a renewable resource in nature and is an easily

available by-product in timber and paper industry. Therefore, sawdust is relatively

abundant and low-cost which can be advantageous over conventional adsorbents. The

Page 4 of 23

Accep

ted

Man

uscr

ipt

4

exploitation of sawdust as oil sorbent is an effective way to comprehensively utilize

waste sawdust resource. On the other hand, the high surface area and low buoyancy

allow sawdust to efficiently adsorb oil content from oil-water mixture. Thus, sawdust

is being investigated as a promising adsorbent for removing oil contaminate from

water and exhibits outstanding sorbent performance. Comprehensively considering

the factors of expense, functionality and output, sawdust is regarded as a relatively

dominant material among all kinds of adsorbents thanks to its advantages of low-cost,

eco-friendly, low-density and natural biodegradable material. Therefore, in this study,

we chose sawdust as crude material to accomplish successful preparation of

superhydrophobic and superoleophilic oil sorbent by the combination of SiO2 grains

on sawdust fiber surface and self-assembly of OTS monomer. Concretely, a large

number of SiO2 particles deposited on individual polystyrene-coated fiber surface to

create hierarchical rough structure, meanwhile, OTS reagent was responsible for low

surface energy during the actual synthesis procedure of

superhydrophobic/superoleophilic sawdust. In addition, as-prepared sawdust

possessed excellent chemical stability and environmental durability because of the

viscidity of polystyrene fixed on sawdust fiber surface. The superhydrophobic and

superoleophilic properties determined oil-absorption and waterproof of as-obtained

sawdust, indicating the usefulness of resulting sawdust product for oil-water

separation. More important, sawdust is selected as the carriers for OTS-SiO2 to form

a superhydrophobic and superoleophilic oil sorbent which will benefit both the

environment and wood agriculture.

Page 5 of 23

Accep

ted

Man

uscr

ipt

5

2. Experimental

2.1 Materials

Hydrogen peroxide, sodium hydroxide, hydrochloric acid, anhydrous ethanol,

tetraethoxysilane (TEOS), ammonia and glacial acetic acid were provided by Tianjin

Kaitong Chemical Reagent Co., Ltd. OTS used to decorated SiO2 particles was

purchased from New Jersey. Polystyrene (Mw=101,900) was purchased from

Shanghai XiBao Biological Technology Co., Ltd. Tetrahydrofuran was obtained from

Xilong Chemical Co., Ltd. All chemical reagents were of analytical reagent grade and

were used as received without further purification. Ultrapure water used throughout

this work to prepare solution was self-made. Diesel oil, gasoline, kerosene used for oil

contact angle measurement and oil-adsorption capacity test and mesh screens were

purchased from Harbin. Sawdust was collected from Carpenter's laboratory of

Northeast Forestry University.

2.2. Pretreatment of the sawdust

Sawdust was initially sifted through 40 and 60 mesh screens to receive a uniform

grading of smaller than 425 μm and greater than 250 μm. Then, sawdust was

thoroughly rinsed with ultrapure water, anhydrous ethanol and ultrapure water before

usage. After that, sawdust was dumped into the mixture containing 200 mL of

0.5wt.% sodium hydroxide aqueous solution and 7 mL of 30% hydrogen peroxide at

ambient temperature for 13 h. Next, 6 mol/L hydrochloric acid was dropwise added to

adjust pH 6.5-7.5. In the end, after washing with ultrapure water several times, the

pretreated sawdust was placed in an oven at 50 oC until its weigh got steady.

Page 6 of 23

Accep

ted

Man

uscr

ipt

6

2.3. Preparation of SiO2 particles

In detail, 5 mL ammonia was dropwise added under vigorous stirring into a

mixture of 5 mL TEOS, 100 mL anhydrous ethanol and 10 mL ultrapure water at

ambient temperature for 1 h. Afterwards, the mixture was aged for 8 h to obtain white

emulsion, purified by centrifugation in anhydrous ethanol, dried at 60 oC for 6 h to get

homogeneous SiO2 particles powder.

2.4. Preparation of modified SiO2 particles

The as-prepared SiO2 particles were modified by OTS reagent. To be brief, 1.5

mL OTS was mixed with 0.02 mL glacial acetic acid, 0.1 mL ultrapure water and 50

mL anhydrous ethanol to form OTS ethanol solution. Subsequently, SiO2 was added

into OTS ethanol solution under stirring at 40 oC for 1 h, dried under vacuum at 50 oC

for 4 h to acquire OTS-modified SiO2 particles.

2.5. Preparation of superhydrophobic and superoleophilic sawdust

In this step, sawdust was blended with 10 mL polystyrene tetrahydrofuran

solution (1%, m/v) containing 0.1 g modified SiO2 particles under vigorous stirring at

room temperature for 30 min. Finally, after drying at 50 oC for 2 h,

superhydrophobic/superoleophilic sawdust was successfully obtained.

2.6. Characterization

The surface morphologies of pristine sawdust and the as-prepared

superhydrophobic/superoleophilic sawdust were examined by a scanning electron

microscopy (SEM, FEI QUANTA200) on condition that all samples were precoated

with a conductive layer of sputtered gold. The chemical composition of resulting

Page 7 of 23

Accep

ted

Man

uscr

ipt

7

sawdust was characterized by using Fourier transform infrared spectroscopy (FT-IR,

Magna-IR 560, Nicolet). The water contact angle (WCA) and oil contact angle (OCA)

measurements were carried out on a contact angle instrument (Hitachi, CA-A) by

dropping 5 μL ultrapure water or oil droplet onto at least five different positions of

sawdust specimens. The ultima values of WCA and OCA were determined as

averages of those of five measurements.

2.7 Evaluation of sorption capability

Sorption capability test was performed in pure oil system by dipping nylon net

bag filled with 0.5 g sawdust into a breaker containing 150 mL measured oil at room

temperature. After 5 h, the nylon net bag was taken out from the oil and stood for 10

min. Sorption capability was defined as:

2 1 1( ) /q m m m

where q is sorption capability (g/g); m1 is the initial weight of sawdust before the

absorption; m2 is the weight of sawdust after the absorption. The final value of

maximal oil absorption capacity was determined as average value of five experiments.

3. Results and discussion

3.1. Fabrication and microscopies of superhydrophobic/superoleophilic sawdust

surface

In the first place, we prepared silica particles according to the Stöber method

using TEOS as a precursor and ammonia as a catalyst. The entire chemical reaction

process could be divided into two steps consisting of the hydrolysis of TEOS and

condensation polymerization of hydrolyzed intermediate [30-32]. The concrete

Page 8 of 23

Accep

ted

Man

uscr

ipt

8

forming procedure of SiO2 particles was presented as follows:

The hydrolysis reaction of TEOS:

OH-2 3Si OR) xH O Si OH) OR) ROH 4( ( (

OH-x 2 x 4-xSi OR) xH O Si OH) OR) ROH (x=2, 3, 4) ( ( (

The condensation polymerization of hydrolyzed intermediate:

=Si-OR HO-Si= =Si-O-Si ROH

=Si-OH HO-Si= =Si-O-Si HOH

In fact, abundant of hydroxyl groups which formed on silica particles surface are

critical to the synthesis of superhydrophobic and superoleophilic sawdust product.

In our work, OTS chemical agent served as a hydrophobic modifier and its

modification mechanism was as follows: silicon hydroxyl groups generated from

hydrolysis reaction of OTS reagent reacted with hydroxyl groups on the surfaces of

SiO2 particles and pristine sawdust fibers, thereby the hydrophobic long-chain alkyl of

OTS was introduced onto sawdust fiber surface to induce low surface energy of

superhydrophobic/superoleophilic sawdust.

As is well-known, surface morphology primarily accounts for the establishment

of superhydrophobic surface, similar to the lotus leaf’s self-cleaning property,

resulting from its micro/nano structure. So, it is necessary to investigate surface

geometric construction so that as-prepared sawdust product can be explored to take

over properties of superhydrophobicity and superoleophilicity which enabled itself the

capacity for an oil sorbent. Fig. 1 presented corresponding SEM images of crude

sawdust and superhydrophobic/superoleophilic sawdust at different magnifications.

Page 9 of 23

Accep

ted

Man

uscr

ipt

9

According to Fig. 1a-e, it could be seen that before and after the treatment of

OTS-modified SiO2, there was no marked difference in surface morphology between

samples, in other words, a series of treatments had not changed the arrangement of

sawdust fibers and the shape of sawdust fibers was identical. Apparently, sawdust

fiber cross section was always “♊” shape which was analogous to special chemical

fiber (Fig. 1a and c). This special section structure would greatly extend surface area

of sawdust fibers, leading to the increase of total contact area with oil, and then

sawdust fiber could capture more oil content. In the high magnification of

longitudinal section of crude sawdust (Fig. 1b), we could observe that individual fiber

was relatively neat with average width diameter of 20 μm and there were pit cavities

on fiber surface. Besides, these three-dimensional microfibers closely connected with

protruding portions along longitudinal edge of fibers, it made high frames among

fibers. Plus with abundant hydroxyl groups on fiber surface, hence pristine sawdust

possessed good hygroscopicity and breathability with water contact angle of 0° (Fig.

2a). Nevertheless, in contrast with the crude one, resulting sawdust fiber was rough

rather than glossy which indicated the successful deposition of insoluble layer of

uniform particles onto sawdust surface as shown in Fig. 1c-d. Under this circumstance,

glutinous polystyrene did duty for a binder to firmly attach SiO2 grains onto sawdust

fiber surface during the fabrication of superhydrophobic/superoleophilic product,

creating a steady bond between certain scale particles and sawdust fiber. Fig. 1e

clearly showed that a large amount of spherical grains were randomly distributed with

average diameter of 300 nm that completely covered on microfiber surface. Therefore,

Page 10 of 23

Accep

ted

Man

uscr

ipt

10

as-prepared sawdust exhibited hierarchical structure composed of micron grade fiber

and plentiful particles overspread every fiber surface, which provided necessary

roughness for the acquisition of superhydrophobic and superoleophilic features.

Among these particles on stratified surface, abundant cavities and interspaces could

capture a large amount of air. When a water droplet was dripped onto the surface of

as-prepared sample, it would contact with capturing air. On this basis, combined with

hydrophobic modification of OTS, surface free energy of sawdust specimen had been

greatly reduced. Consequently, water droplet could not wet the surface of resulting

sawdust. As soon as water was sloped on sample surface, it would bounce off without

leaving residues, demonstrating excellent water-repelling performance of as-obtained

sawdust product. In this way, the wettability of sawdust transformed from

superhydrophilicity to superhydrophobicity.

Fig. 1. SEM images of (a) cross section and (b) longitudinal section of crude sawdust

fiber, (c) cross section and (d-e) longitudinal section of as-prepared

Page 11 of 23

Accep

ted

Man

uscr

ipt

11

superhydrophobic/superoleophilic sawdust fiber at different magnifications.

3.2. Surface wettability of superhydrophobic/superoleophilic sawdust

In reality, surface wettability of a material is determined by contact angle value.

We further surveyed actual water contact angle and oil contact angle of sawdust

surface with the aim to verify superhydrophobic and superoleophilic properties of

resulting sawdust product. As presented in Fig. 2a, the measured water contact angle

on crude sawdust surface was 0°, which was mainly because of abundant hydroxyl

groups and pit cavities existed on crude fiber surface. However, in Fig. 2b, a brightly

spherical water droplet was visible on as-prepared sawdust surface and sample’s water

contact angle reached 153°, demonstrating the well-produced water repellent

performance of superhydrophobic/superoleophilic sawdust sample. In addition, oil

droplet could quickly diffused into resulting sawdust in less than 1s to display perfect

oil wettability and oil contact water approached 0° as shown in Fig. 2c. Hence, it was

obvious that as-prepared sawdust product rendered exceedingly superhydrophobic and

superoleophilic performances.

Generally, we could deeply understand theoretical principle of surface wettability

in terms of fundamental equations of interface chemistry. Firstly, wettability is

defined by Young equation,

cos sv sl

lv

where γsv, γsl, γlv are the interfacial free energy of solid/vapor, solid/liquid, and

liquid/vapor, respectively; θ is the contact angle. This equation is applicable to a

homogeneous and smooth surface at equilibrium state without any special effect

Page 12 of 23

Accep

ted

Man

uscr

ipt

12

between solid and liquid.

Based on a homogeneous interface without any air pockets, Wenzel [33]

proposed a model to overcome Young equation’s drawback of inadaptable for rough

surfaces. Wenzel equation answered the relationship between surface roughness and

contact angle of a liquid droplet. The relevant mathematical equation is:

cos cosr r

where θr and θ are the apparent contact angle on a rough surface and Young's contact

angle on a smooth surface, respectively; r is the surface roughness factor. Considering

about lyophobic material with a contact angle θ greater than 90°, the actual value of

contact angle θr will increase with the increasement of surface roughness.

In the experiment of hydrophobic fabric performance, Cassie [34] proposed a

new surface roughness model—air cushion model and its expression is:

1 2cos cosc f f

where f1 and f2 are the fractions of liquid/solid and liquid/vapor contact, θc and θ are

observed water contact angle on a rough surface and that on a flat surface. As a matter

of fact, improving air cushion part proportion will enhance superhydrophobic

property.

In light of the above discussion, we could draw a conclusion that surface

wettability of an object is dominated by surface chemical composition and

morphology structure. In this work, the combination of numerous aggregations of

SiO2 particles and surface modification by OTS could lead to preventing water from

wetting the treated sample surface. Water droplet on obtained sawdust would roll off

Page 13 of 23

Accep

ted

Man

uscr

ipt

13

without any residues, which was manifested as non-wetting by water, determining that

as-prepared sawdust only absorbed oil while completely repelling water.

Fig. 2. Photographs of (a) water droplet on pristine sawdust, (b) water droplet and (c)

oil droplet on as-prepared superhydrophobic/superoleophilic sawdust.

3.3. Chemical Component Analysis

The surface chemical component of superhydrophobic/superoleophilic sawdust

was characterized by Fourier transform infrared spectroscopy (FT-IR). The correlative

FT-IR spectra of OTS-modified SiO2 particles and superhydrophobic/superoleophilic

sawdust were presented in Fig. 3. In the high frequency region, the broad peaks

appeared at 3278 cm-1 in both Fig. 3a and Fig. 3b were for the bonded –OH stretching

vibrations. The absorption peak at 3660 cm-1 was attributed to free -OH stretching

vibrations, however, it almost entirely disappeared in Fig. 3b, from which we inferred

that the total quantity of -OH groups was reduced. The absorption peaks at 792 cm-1

and 1044 cm-1 in both spectrums were ascribed to Si-O-Si asymmetric stretching and

symmetric stretching vibrations, which confirmed the existence of SiO2 particles. In

addition, corresponding to -CH3 and -CH2 from longchain alkyl groups of OTS

reagent, two typical peaks recorded at 2851 cm-1 and 2919 cm-1 were observed (Fig.

3a-b), proving the generation of OTS that was utilized to modify SiO2 particles. By

Page 14 of 23

Accep

ted

Man

uscr

ipt

14

comparison, as shown in Fig. 3b, new absorption bands at 696 cm-1 due to C-H

bending vibrations of benzene ring and 1452 cm-1 due to characteristic adsorption of

benzene ring were introduced by polystyrene. To conclude, by virtue of these

absorption bands in Fig. 3 which revealed the presence of SiO2, OTS, and polystyrene,

it could be confirmed that SiO2 particles were successfully decorated by OTS and

polystyrene was authentically subsistent as a binder to robustly tack modified SiO2

granules onto as-prepared sawdust surface.

Fig. 3. FTIR spectra of (a) OTS modified-SiO2 particles and (b) as-prepared

superhydrophobic/superoleophilic sawdust.

3.4. Stability analysis and application in water-oil separation

The chemical stability as well as environmental durability of as-obtained

superhydrophobic/superoleophilic sawdust was investigated allowing for their

significant influence on industrial and practical application so that we could ascertain

product’s access to extensive use. Thereamong, chemical stability was assessed by the

Page 15 of 23

Accep

ted

Man

uscr

ipt

15

changes of water and oil contact angle after sample was immersed into aqueous

solution with various pH values range from 0 to 14 for 24 h. Fig. 4 revealed the

variation of water and oil contact angle of superhydrophobic/superoleophilic sawdust

with pH value of aqueous solution. As can be seen, water contact angle on as-prepared

sawdust surface varied slightly between 153° and 151°, while oil contact angle

maintained 0° all the same, showing that resulting sample owned noteworthy stability

against erosion of acid and alkali. Apart from chemical stability, we evaluated

product’s environmental durability under the condition of room temperature and

humidity (24.5 oC, 37%) in order to determine long-time stability of obtained

superhydrophobic/superoleophilic sawdust. After 150 days of air explosion, the

measured water and oil contact angle had no apparent change as detailed in Fig. 5,

demonstrating excellent environmental durability of obtained sawdust in atmospheric

condition. Accordingly, it could be deduced that the properties of superhydrophobicity

and superoleophilicity of as-prepared sawdust product still remained unchanged no

matter in corrosion solution or long-time storage in air. That is to say, as-prepared

sawdust possessed distinguished corrosion resistance, chemical stability and

environmental durability, which was likely due to good stickness of polystyrene as a

caking agent that robustly adhering particles to sawdust fiber surface, thus enhancing

the stability of resulting superhydrophobic/superoleophilic product.

Page 16 of 23

Accep

ted

Man

uscr

ipt

16

Fig. 4. Variation of water contact angle and oil contact angle of as-prepared sawdust

with different pH of aqueous solution.

Fig. 5. The relationship between water contact angle of resulting sawdust with days of

storage in air environment.

On the one hand, due to the fact that superhydrophobic property of as-prepared

sawdust could give rise to intrinsic water-repellence and superoleophilic nature of

sample resulted in oil-absorbing. On the other hand, in view of outstanding chemical

stability and environmental durability of superhydrophobic/superoleophilic sawdust,

we employed as-obtained sawdust as an oil sorbent for water-oil separation to explore

Page 17 of 23

Accep

ted

Man

uscr

ipt

17

its real application in the field of oily wastewater treatment. Fig. 6 illustrated the

process of resulting sawdust product as a selective oil sorbent for the separation of

water and gasoil mixture. For the adsorption experiment, the composition of water/oil

mixture was 25 mL water and 3 mL gasoil, the operating temperature was 24.5 oC and

the sorption time was 1.5 h. As expected, as soon as

superhydrophobic/superoleophilic sawdust was thrown into the mixture, it would

continuously absorb oil from water surface and all red oil was quickly absorbed by

sawdust, leaving a transparent region on water surface. Furthermore, the sawdust

filled with red liquid could be separated from the surface of the water. Ulteriorly, the

maximal oil absorption capacity of raw sawdust and

superhydrophobic/superoleophilic sawdust for n-hexane, gasoline, diesel oil, crude oil

and engine oil under ambient temperature were listed in Fig. 7. The maximum oil

absorption capacities of superhydrophobic/superoleophilic sawdust was almost triple

that of raw sawdust for the same oil, revealing the significant improvement of the oil

sorption capacity of the as-prepared superhydrophobic/superoleophilic product.

Through the comparison of the sorption uptake of various adsorbents (table 1), it is

observed that this sorbent had advantages of higher sorption uptake in contrast with

other oil sorbents. Previous reported oil sorbents were hydrophilic or hydrophobic

rather than superhydrophobic. Our study was the first reported technique for sawdust

to receive superhydrophobic and superoleophilic property which resulted in high

sorption uptake and separation efficiency. As a consequence, this sort of

superhydrophobic/superoleophilic sawdust was suitable of the cleanup of oil spills.

Page 18 of 23

Accep

ted

Man

uscr

ipt

18

Fig. 6. The process of resulting sawdust product as an oil sorbent for the separation of

water and gasoil mixture. (a) as-prepared superhydrophobic/superoleophilic sawdust

(b) water and gasoil mixture (gasoil was colored with SudanⅢ for clear observation).

(c) all given red gasoil was absorbed and red sawdust floated on the water (d) after

adsorption, the sawdust filled with red liquid was separated.

Fig. 7. Maximum absorption capacities of raw sawdust and the as-prepared

superhydrophobic/superoleophilic sawdust for different types of oils under ambient

temperature.

Page 19 of 23

Accep

ted

Man

uscr

ipt

19

Table 1. Comparison of the sorption uptake of various adsorbents

Sorbent Sorption uptake

(g crude oil/g fiber)

Reference

Superhydrophobic/superoleophilic sawdust 17.50 This study

Lauric acid treated oil palm leaves 1.18 [12]

Hydrophobic aerogel 2.80 [35]

Horn shell residues treated by ionic liquid 0.55 [36]

Acetylated peat moss 8.00 [5]

Black rice husk ash via pyrolysis method 6.22 [11]

Oleic acid-grafted sawdust 6.00 [37]

4. Conclusions

In conclusion, we have reported a novel, convenient and low-cost process for the

design of environmentally friendly sawdust in possession of the performances of

superhydrophobicity and simultaneous superoleophilicity via the deposition of

homogeneous OTS-modified SiO2 grains on sticky polystyrene-coated sawdust fiber

surface. Specifically, the appropriate conclusions distinctly revealed that as-prepared

sawdust surface formed sufficient roughness because of its hierarchical surface

morphology made up of SiO2 grains attached to individual sawdust fiber surface,

meanwhile, self-assembly of OTS monomer had brought about the decline of surface

energy. The contact angles tests reflected that superhydrophobicity/superoleophilicity

sawdust with water contact angles of 153° and oil contact angle of approximate 0°

had remarkable chemical stability and environmental durability which was attributed

Page 20 of 23

Accep

ted

Man

uscr

ipt

20

to the glutinous polystyrene employed to adhere abundant particles to sawdust fiber

surface. In addition, the products exhibited excellent oil absorptive capacity of 14.4

g/g for diesel oil in water-oil separation experiment, demonstrating its remarkable

potency as an oil absorbent material for removing spilled oil from water.

Acknowledgements:

This research was supported by the National Natural Science Foundation of

China (31470584).

References：

[1] A.A. Al-Majed, A.R. Adebayo, M.E. Hossain, A sustainable approach to controlling oil spills, Journal of environmental management 113 (2012) 213-227.[2] E.R. Oliveira, B. Silveira, F.L. Alves, Support mechanisms for oil spill accident response in costal lagoon areas (Ria de Aveiro, Portugal), Journal of Sea Research 93 (2014) 112-117.[3] P.W. Sammarco, S.R. Kolian, R.A.F. Warby, J.L. Bouldin, W.A. Subra, S.A. Porter, Distribution and concentrations of petroleum hydrocarbons associated with the BP/Deepwater Horizon Oil Spill, Gulf of Mexico, Marine Pollution Bulletin 73 (2013) 129-143.[4] D. Zhang, A. Ding, S. Cui, C. Hu, S.F. Thornton, J. Dou, Y. Sun, W.E. Huang, Whole cell bioreporter application for rapid detection and evaluation of crude oil spill in seawater caused by Dalian oil tank explosion, Water Research 47 (2013) 1191-1200.[5] C. Cojocaru, M. Macoveanu, I. Cretescu, Peat-based sorbents for the removal of oil spills from water surface: Application of artificial neural network modeling, Colloids and Surfaces A: Physicochemical and Engineering Aspects 384 (2011) 675-684.[6] D. Zadaka-Amir, N. Bleiman, Y.G. Mishael, Sepiolite as an effective natural porous adsorbent for surface oil-spill, Microporous and Mesoporous Materials 169 (2013) 153-159.[7] S.A. Sayed, A.M. Zayed, Investigation of the effectiveness of some adsorbent materials in oil spill clean-ups, Desalination 194 (2006) 90-100.[8] J. Fritt-Rasmussen, P.J. Brandvik, Measuring ignitability for in situ burning of oil spills weathered under Arctic conditions: From laboratory studies to large-scale field experiments, Marine Pollution Bulletin 62 (2011) 1780-1785.[9] S. Inouye, K. Yamagami, Y. Yamazaki, S. Ichino, Y. Kume, S. Yamada, S. Abe, Effect of dispersing agents and stirring mode on the adsorption of major components of lavender, tea tree and grapefruit oils to a rubber glove in an aromatic bath,

Page 21 of 23

Accep

ted

Man

uscr

ipt

21

International Journal of Aromatherapy 15 (2005) 199-204.[10] E.Z. Ron, E. Rosenberg, Enhanced bioremediation of oil spills in the sea, Current Opinion in Biotechnology 27 (2014) 191-194.[11] L. Vlaev, P. Petkov, A. Dimitrov, S. Genieva, Cleanup of water polluted with crude oil or diesel fuel using rice husks ash, Journal of the Taiwan Institute of Chemical Engineers 42 (2011) 957-964.[12] S.M. Sidik, A.A. Jalil, S. Triwahyono, S.H. Adam, M.A.H. Satar, B.H. Hameed, Modified oil palm leaves adsorbent with enhanced hydrophobicity for crude oil removal, Chemical Engineering Journal 203 (2012) 9-18.[13] R. Liao, Z. Zuo, C. Guo, Y. Yuan, A. Zhuang, Fabrication of superhydrophobic surface on aluminum by continuous chemical etching and its anti-icing property, Applied Surface Science 317 (2014) 701-709.[14] D.Y. Cui, W. Li, T.H. Li, H.Y. Zhang, Development of a simple method for the fabrication of superhydrophobic surfaces with NH4VO3 and SiO2, Materials Letters 70 (2012) 105-108.[15] D. Zang, F. Liu, M. Zhang, X. Niu, Z. Gao, C. Wang, Superhydrophobic coating on fiberglass cloth for selective removal of oil from water, Chemical Engineering Journal 262 (2015) 210-216.[16] C.G. Obeso, M.P. Sousa, W. Song, M.A. Rodriguez-Pérez, B. Bhushan, J.F. Mano, Modification of paper using polyhydroxybutyrate to obtain biomimetic superhydrophobic substrates, Colloids and Surfaces A: Physicochemical and Engineering Aspects 416 (2013) 51-55.[17] H. Li, S. Yu, X. Han, E. Liu, Y. Zhao, Fabrication of superhydrophobic and oleophobic surface on zinc substrate by a simple method, Colloids and Surfaces A: Physicochemical and Engineering Aspects 469 (2015) 271-278.[18] W. Zhong, Y. Li, Y. Wang, X. Chen, Y. Wang, W. Yang, Superhydrophobic polyaniline hollow bars: Constructed with nanorod-arrays based on self-removing metal-monomeric template, Journal of Colloid and Interface Science 365 (2012) 28-32.[19] J. Jia, J. Fan, B. Xu, H. Dong, Microstructure and properties of the super-hydrophobic films fabricated on magnesium alloys, Journal of Alloys and Compounds 554 (2013) 142-146.[20] C. Zhang, S. Zhang, P. Gao, H. Ma, Q. Wei, Superhydrophobic hybrid films prepared from silica nanoparticles and ionic liquids via layer-by-layer self-assembly, Thin Solid Films 570, Part A (2014) 27-32.[21] C. Holtzinger, B. Niparte, S. Wächter, G. Berthomé, D. Riassetto, M. Langlet, Superhydrophobic TiO2 coatings formed through a non-fluorinated wet chemistry route, Surface Science 617 (2013) 141-148.[22] M. Obaid, N.A.M. Barakat, O.A. Fadali, M. Motlak, A.A. Almajid, K.A. Khalil, Effective and reusable oil/water separation membranes based on modified polysulfone electrospun nanofiber mats, Chemical Engineering Journal 259 (2015) 449-456.[23] N. Zhan, Y. Li, C. Zhang, Y. Song, H. Wang, L. Sun, Q. Yang, X. Hong, A novel multinozzle electrospinning process for preparing superhydrophobic PS films with controllable bead-on-string/microfiber morphology, Journal of Colloid and Interface

Page 22 of 23

Accep

ted

Man

uscr

ipt

22

Science 345 (2010) 491-495.[24] L. Wang, S. Yang, J. Wang, C. Wang, L. Chen, Fabrication of superhydrophobic TPU film for oi-water separation based on electrospinning route, Materials Letters 65 (2011) 869-872.[25] C. Du, J. Wang, Z. Chen, D. Chen, Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Applied Surface Science 313 (2014) 304-310.[26] F. Liu, M. Ma, D. Zang, Z. Gao, C. Wang, Fabrication of superhydrophobic/superoleophilic cotton for application in the field of water/oil separation, Carbohydrate Polymers 103 (2014) 480-487.[27] X. Huang, X. Wen, J. Cheng, Z. Yang, Sticky superhydrophobic filter paper developed by dip-coating of fluorinated waterborne epoxy emulsion, Applied Surface Science 258 (2012) 8739-8746.[28] C.H. Lee, N. Johnson, J. Drelich, Y.K. Yap, The performance of superhydrophobic and superoleophilic carbon nanotube meshes in water-oil filtration, Carbon 49 (2011) 669-676.[29] B. Ge, Z. Zhang, X. Zhu, X. Men, X. Zhou, A superhydrophobic/superoleophilic sponge for the selective absorption oil pollutants from water, Colloids and Surfaces A: Physicochemical and Engineering Aspects 457 (2014) 397-401.[30] S.S. Latthe, H. Imai, V. Ganesan, A.V. Rao, Superhydrophobic silica films by sol-gel co-precursor method, Applied Surface Science 256 (2009) 217-222.[31] N.D. Hegde, A.V. Rao, Organic modification of TEOS based silica aerogels using hexadecyltrimethoxysilane as a hydrophobic reagent, Applied Surface Science 253 (2006) 1566-1572.[32] G.Y. Bae, B.G. Min, Y.G. Jeong, S.C. Lee, J.H. Jang, G.H. Koo, Superhydrophobicity of cotton fabrics treated with silica nanoparticles and water-repellent agent, Journal of Colloid and Interface Science 337 (2009) 170-175.[33] R.N. Wenzel, Resistance of solid surfaces to wetting by water, Industrial & Engineering Chemistry 28 (1936) 988-994.[34] A. Cassie, S. Baxter, Wettability of porous surfaces, Transactions of the Faraday Society 40 (1944) 546-551.[35] D. Wang, T. Silbaugh, R. Pfeffer, Y. Lin, Removal of emulsified oil from water by inverse fluidization of hydrophobic aerogels, Powder Technology 203 (2010) 298-309.[36] J. Li, M. Luo, C.-J. Zhao, C.-Y. Li, W. Wang, Y.-G. Zu, Y.-J. Fu, Oil removal from water with yellow horn shell residues treated by ionic liquid, Bioresource technology 128 (2013) 673-678.[37] S.S. Banerjee, M.V. Joshi, R.V. Jayaram, Treatment of oil spill by sorption technique using fatty acid grafted sawdust, Chemosphere 64 (2006) 1026-1031.

Page 23 of 23

Accep

ted

Man

uscr

ipt

23

The superhydrophobic/superoleophilic sawdust fiber with water contact angle of 153°

and oil contact angle of 0° was successfully prepared by the deposition of

OTS-modified SiO2 granules onto polystyrene-coated fiber surface to achieve enough

surface roughness and low surface free energy.

SEM images of (a) cross section and (b) longitudinal section of crude sawdust fiber,

(c) cross section and (d-e) longitudinal section of as-prepared

superhydrophobic/superoleophilic sawdust fiber at different magnifications.