This article was published in the above mentioned Springer issue.The material, including all portions thereof, is protected by copyright;all rights are held exclusively by Springer Science + Business Media.

The material is for personal use only;commercial use is not permitted.

Unauthorized reproduction, transfer and/or usemay be a violation of criminal as well as civil law.

ISSN 1388-0764, Volume 12, Number 7

RESEARCH PAPER

Titanium dioxide-coated nanofibers for advanced filters

Byung-Yong Lee • Kris Behler • Murat Erdem Kurtoglu • Meghan Ann Wynosky-Dolfi •

Richard F. Rest • Yury Gogotsi

Received: 29 January 2009 / Accepted: 23 November 2009 / Published online: 10 December 2009

� Springer Science+Business Media B.V. 2009

Abstract This article reports on titanium dioxide

(TiO2)-coated nanofibers deposited on a filter surface

by the electrospinning process. After depositing a

micrometer-thick film of polyamide 11 nanofibers on

polypropylene fabric, TiO2 nanoparticles can be

directly electrosprayed onto the nanofibers. X-ray

diffraction and Raman spectroscopy showed minimal

change in the phase composition (anatase and rutile)

and no change in the particle size of nanocrystalline

TiO2 after coating. Scanning electron microscopy

demonstrated that nanofibers were uniformly coated

by titanium dioxide nanoparticles without agglomer-

ation. TiO2-coated filters showed excellent photo-

catalytic-bactericidal activity and photo-induced

hydrophilicity.

Keywords Electrospinning � Titanium dioxide �Photocatalyst � Filter � Fibers � Electrospraying �Nanomanufacturing

Introduction

The electrospinning technique has been widely used

for manufacturing nanofibers with different function-

alities required in drug delivery systems, nanosen-

sors, micro/nano electronic devices, scaffolds for

tissue engineering and filtration media (Li and Xia

2004; Burger et al. 2006). In particular, electrospun

nanofibers have high specific surface areas with a

distinctive nanoscale surface texture, for which they

have been extensively studied in applications ranging

from high-performance filters to chemical and bio-

logical sensors, and protective clothing because their

small mesh allows trapping of very small (submi-

crometer) particles (Ko 2006). As a result of this

increased interest, the electrospinning method has

been applied not only to polymeric materials but also

to ceramics, particularly to metal oxides (Li et al.

2003). Among the metal oxides, titanium dioxide has

attracted a great deal of interest for electrospinning

applications because of its unique photoinduced

catalytic activity and superhydrophilicity coupled

with low cost, chemical stability and biological

inertness (Im et al. 2008; Li and Xia 2003). In

general, electrospun hybrid organic–inorganic fibers

have been prepared either by co-electrospinning (Ko

et al. 2003; Ko et al. 2006; Ye et al. 2004) or by

impregnating inorganic precursors into a polymeric

solution followed by the nucleation and growth of

functional inorganic particles on the electrospun

polymer fibers. However, co-electrospinning is not

B.-Y. Lee � K. Behler � M. E. Kurtoglu � Y. Gogotsi (&)

Department of Materials Science and Engineering,

A.J. Drexel Nanotechnology Institute, Drexel University,

Philadelphia, PA 19104, USA

e-mail: gogotsi@drexel.edu

M. A. Wynosky-Dolfi � R. F. Rest

Department of Microbiology and Immunology,

Drexel University College of Medicine,

Philadelphia, PA 19129, USA

123

J Nanopart Res (2010) 12:2511–2519

DOI 10.1007/s11051-009-9820-x

Author's personal copy

the method of choice when nanoparticles require

access to the surface, because they will be wrapped

by polymer. Nucleation and growth of inorganic

materials, particularly metal oxides, usually require

post-treatment at elevated temperatures, which pre-

vents their applicability to temperature-sensitive

substances like polymers. Therefore, pre-crystalline

precursors that do not need a high temperature post-

treatment would be more suitable for this purpose.

To place TiO2 on fabric surfaces, dip coating has

been used (Horikoshi et al. 2002). However, TiO2

particles within the fabric are not exposed to

sufficient UV light to produce a significant photo-

catalytic effect, and they can be carried by air flow,

due to the loosely bound particle-like structure of

the coating, potentially affecting people who breathe

the filtered air.

In this work, titanium dioxide-coated filters were

prepared by electrospraying polyamide 11 (PA 11)

nanofibers onto the surface of a conventional filter

followed by electrospraying a suspension of nano-

crystalline titanium dioxide onto the electrospun

nanofibers. This potentially allows producing a filter

capable of both trapping small particles such as

viruses and destroying them on the filter surface.

Experimental

Materials

Non-woven polypropylene fabric obtained from

Amerinova LLC, USA, was used as the filter

substrate for consecutive nanofiber and TiO2 deposi-

tions. Polyamide 11 (Rilsan�, Arkema, Inc), which is

a green polymer produced from renewable resources,

was used for nanofiber electrospinning. Formic acid

(99%, Acros) and dichloromethane (99.5?%, Alfa

Aesar) were used without further purification. Col-

loidal silica binder was prepared using TEOS (tetra-

ethyl orthosilicate, 98%, Acros), anhydrous ethanol,

nitric acid (70%, Sigma-Aldrich) and distilled water.

Degussa P25 TiO2 (composed of 70% anatase and

30% rutile) was used to prepare the aqueous TiO2

dispersion. Methylene blue (Sigma-Aldrich) was

selected as a model pollutant for the photocatalytic

activity tests.

Preparation of TiO2-coated electrospun nanofiber

Non-woven fabric was thoroughly cleaned by dipping

into a deionized water–ethanol mixture and subse-

quently dried at room temperature. Before electros-

pinning of the PA 11 nanofibers, the polypropylene

fabric substrate was dip-coated with a sol–gel silica

solution to improve the adhesion of the electrospun

nanofibers onto the hydrophobic fabric by forming

silanol groups. Silica-impregnated polypropylene

substrate was sonicated for 5 min to remove loosely

attached residual particles and dried in an oven at

60 �C. Silica solution was prepared by sol–gel

technique as follows; 104 g of TEOS was mixed

with 500 g of anhydrous ethanol and stirred for 1 h.

Then a 184 g of distilled water, ethanol, and HNO3

mixture was drop-wise added to this solution fol-

lowed by 6 h of vigorous stirring. Before coating, the

solution was aged at room temperature for 12 h.

For polymeric solution, 2 g of PA 11 powder was

dissolved in 60 ml formic acid–dichloromethane (1:1

v/v) mixture followed by heating to 70 �C on a hot

plate with vigorous stirring. This solution was then

drawn into a syringe with a 30 G needle. Non-woven

fabrics were attached to the surface of aluminum foil

which was placed on an electrically grounded,

rotating collection drum. Prepared polymeric solu-

tions were electrospun (Nanofiber Electrospinning

Unit, Kato Tech Co., Japan) onto silica-coated fabric

to produce PA 11 nanofibers with the following

parameters: two different voltages of 10 and 20 kV,

syringe pump speed from 1.2 to 3 cm/h, tip-to

collector distance (TCD) 15 cm, coating time

1–3 min (Behler et al. 2007).

TiO2 particle suspensions were prepared by son-

icating 5 g TiO2 powder in a 95 g water: ethanol (1:1

w/w) mixture. 3-Aminopropylmethoxysilane was

added to the mixture to functionalize the TiO2

surfaces. One gram of NaCl was added to increase

the electrical conductivity of the suspension. After

stirring the final suspension on a magnetic stirrer for

4 h, it was electrosprayed onto the electrospun PA 11

nanofibers using the following parameters: 15 kV,

7.5 cm TCD, 18 G syringe needle. After electrospin-

ning for 3 h, the prepared TiO2-electrosprayed

nanofibers on the filters were kept in air for 1 h,

and dried at 70 �C for 30 min. In addition to

polypropylene fabric filters, a set of electrospun

2512 J Nanopart Res (2010) 12:2511–2519

123

Author's personal copy

TiO2–PA 11-coated aluminum foils was also pre-

pared, using the same parameters.

Characterization

The SEM images of the electrospun nanofibers coated

with TiO2 were collected by a Zeiss Supra 50VP from

5 to 10 spots. To confirm TiO2 presence on the filter,

EDX analysis was conducted using an Oxford Energy

Dispersive X-ray Microanalyser. The crystal structure

of the electrosprayed TiO2 was analyzed by X-ray

diffraction (XRD) using Siemens D500 with nickel

filtered Cu Ka radiation (40 kV, 30 mA) between

2h = 20� and 80�. The diffraction peaks of the

anatase (101) and rutile (110) planes were selected to

analyze the crystallinity and the anatase-to-rutile ratio

of the electrosprayed TiO2. Raman spectra were

measured at room temperature using a 514.5 nm Ar-

ion laser as the excitation source (Renishaw

RM1000). Optical spectra of the samples were

collected by Thermo Scientific, Evolution 600 UV–

Vis Spectrophotometer equipped with a reflectance

sphere.

Photocatalytic activity testing

Methylene blue degradation tests were carried out on

the TiO2 electrosprayed PA 11 nanofibers on both

filters and aluminum foils in order to evaluate the

photocatalytic activity. The samples were covered by

800 ll, 1.4 9 10-6 M methylene blue solution and

irradiated with two 15 W UV-A lamps (1 mW/cm2,

Philips F15T8) for 4 h. Methylene blue concentration

on the samples was monitored by visually observing

the change in color and by measuring absorbance at

664 nm with a spectral colorimeter (Spectra UV-

4000). Contact angle measurements were performed

by the sessile drop method at room temperature using

a home-made apparatus, equipped with a CCD solid

state color video camera (HITACHI VK-C360,

camera: Nikon) (Mattia et al. 2006).

Antibacterial test

Escherichia coli (E. coli) was grown in Luria Bertani

(LB) broth, a standard and widely used growth media

for E. coli, overnight at 37 �C with shaking at

250 rpm. Bacteria were pelleted and resuspended to

desired concentrations. One centimeter squares of

TiO2-electrosprayed filters or aluminum foil were

placed in wells of a 24 well tissue culture plate and

50 ll drops of bacteria were carefully placed in the

center of the filter or foil squares. Remaining wells of

24 wells of plate were filled with water and a 2 mm

thick, 10 cm 9 15 cm Pyrex glass plate was placed

on top of the tissue culture plate to maintain a humid

environment and to avoid evaporation. This set-up

was repeated in duplicate—one placed under UV

light and the other not. Samples were irradiated with

2 UV-A bulbs suspended 8 cm above the 24 well

plate at room temperature. At 0, 30, 60, and 120 min,

bacteria were recovered from the filter or foil squares,

diluted, and plated on LB agar plates. LB agar plates

were incubated at 37 �C overnight, at which time

colonies were counted. Data are represented as three

independent experiments.

Results and discussion

The surface morphology of the polypropylene fabric

before and after PA 11 electrospinning is shown in

Fig. 1. Finely distributed PA 11 nanofibers on the

polypropylene fabric can be seen after electrospin-

ning. The average diameters of PA 11 nanofibers

electrospun at 20 and 10 kV were about 250 and

400 nm, respectively, which are consistent with

previously reported results (Behler et al. 2007).

Although it was possible to create nanofibers with

smaller diameters by increasing the applied voltage

(Havel et al. 2008), there was an increased chance of

bead formation, a common problem of electrospin-

ning, due to the difficulty of obtaining a stable

conical drop with increased voltage (Li and Xia

2004).

Morphology of the electrospun TiO2 particles on

PA 11 nanofibers and particle size distribution (PSD)

of TiO2 nanoparticles is shown in Fig. 2a and b,

respectively. Calculated PSD of the electrosprayed

TiO2 was 15 to 30 nm with a mode of 23 nm. This is

consistent with the average primary particle size of

Degussa P25 (Degussa 2005), and shows that TiO2

particles were electrosprayed onto the target surface

without any agglomeration. Also, as shown in

Fig. 2c, electrosprayed TiO2 on electrospun PA 11

nanofibers shows a uniform coating pattern without

any TiO2 beads or large agglomerates. In comparison,

TiO2 coatings prepared by dip coating polypropylene

J Nanopart Res (2010) 12:2511–2519 2513

123

Author's personal copy

were not homogeneous (Fig. 2d). Large agglomerates

of TiO2 particles were easily detectable even under

low magnification. The presence of TiO2 particles

and colloidal silica for all of the samples were

confirmed by EDX analysis (data not shown).

The X-ray diffraction diagram of the TiO2-coated

fabric via electrospinning is shown in Fig. 3. The

main peak positions and their relative intensities of

the anatase and rutile phases on nanofibers are

consistent with the diffraction patterns of the as-

received TiO2 powder, albeit with much more noise

in the nanofibers’ spectra due to the limited thickness

of titania. No broadening of the peaks was observed

on the XRD pattern of the electrospun TiO2 samples

compared to the original TiO2 powder. On the other

hand, the rutile to anatase volume ratio, calculated by

the Spurr equation (Spurr and Myers 1957), was

slightly increased from 0.16 in the original powder to

0.19 on the electrospun substrate. This behavior was

attributed to the slightly higher charge accumulated

on the rutile particles inside the solution due to the

lower point of zero charge (PZC) of rutile compared

to that of anatase (Kosmulski 2002), which possibly

resulted in better functionalization of the rutile

surfaces. Since the change in composition is very

small, a significant change of the photocatalytic

activity was not expected.

Raman spectra of the TiO2-electrosprayed nanof-

ibers and Degussa P25 are shown in Fig. 4. On

Degussa P25 TiO2 powder spectra, we identified the

main Raman peaks of anatase at 147 cm-1 (Eg),

198 cm-1 (Eg), 398 cm-1 (B1g), 519 cm-1 (A1g and

B1g), and 640 cm-1 (Eg), 801 cm-1 (B1g), and of

rutile at 448 cm-1 (Eg). Positions and the intensities

of the Raman active peaks were in agreement with

previously reported results (Ocana et al. 1992; Zhao

et al. 2008; Nuansing et al. 2006). The reported

144 cm-1 (B1g) peak of rutile was likely an overtone

with the anatase assigned peak (147 cm-1) and was

not observed (Arabatzis et al. 2002; Miao et al. 2004).

The intensities of the peaks at 235, 448, and

612 cm-1, which were attributed to the rutile phases

with TiO2-electrosprayed nanofiber, somewhat

increased compared to the original TiO2 powder.

This was consistent with our XRD results, which also

showed that there was more rutile in the coatings than

in the powders, though anatase was still the dominant

phase in the titania coating. Although the reason for

this is unclear, it may be due to a better response of

the rutile phase to the applied potential during

electrospraying, causing more rutile particles to be

deposited on the fibers. This assumption is reasonable

if the reported point of zero charge (PZC) values of

anatase (pH 6.2) and rutile (pH 5.3) are considered

(Malati 1999). As the prepared dispersion was around

pH 4.6, the anatase phase particles were expected to

be more positively charged than the rutile ones,

which in turn, increase the chances of attraction of

rutile particles to the negatively charged substrate.

Raman peaks of PA 11 were also observed. As

shown in Fig. 4, TiO2-electrosprayed nanofibers

exhibit peaks at 1108 and 1122 cm-1 corresponding

to the trans-C–C symmetric stretching in the PA 11

chain (Behler et al. 2007). Raman peaks of PA 11

Fig. 1 a SEM images of as-received base non-woven poly-

propylene fabric. b PA 11-electrosprayed nanofiber with 10 kV

electronic voltage

2514 J Nanopart Res (2010) 12:2511–2519

123

Author's personal copy

(c) (d)

(a)

15 20 25 30 350

5

10

15

20

25

30

Diameter of particles (nm)

Dis

trib

uti

on

(re

lati

ve n

um

ber

%) (b)

Fig. 2 a SEM image and b calculated particle size distribution (PSD) of electrosprayed TiO2 particles. c SEM images of TiO2-

electrosprayed PA 11 nanofiber. d TiO2 dip-coated polypropylene substrate

Fig. 3 X-ray diffraction patterns of the TiO2-electrosprayed

nanofiber and the as-received TiO2 powder

200 400 600 800 1000 1200

Inte

nsi

ty (

a.u

.)

Raman Shift (cm-1)

801

Electrosprayed TiO2 on PA 11

Electrospun PA 11

TiO2 powder (P25)

147

198 235

398448 519

612

640

801

1122

11081062

11081062 1122

147

198

398

448

519

640

Fig. 4 Raman spectra of TiO2-deposited electrospun nanofi-

ber, electrospun PA 11, and TiO2 (P25) powder

J Nanopart Res (2010) 12:2511–2519 2515

123

Author's personal copy

were not observed below 800 cm-1, as previously

observed (Hernandez et al. 1995; Cui and Yan 2005).

There were no peaks attributable to colloidal silica in

the Raman spectra, which usually shows a broad peak

at 440 cm-1 and weaker peaks at 492, 605, 800, and

1,060 cm-1 (Bosc et al. 2006). We assume that the

film was too thin and silica peaks were suppressed by

closely positioned TiO2 peaks.

Since the optical spectra of the TiO2-coated fabric

samples could be difficult to be interpreted accurately

caused by the unusual scattering of the substrate, an

aluminum foil which was prepared by the same

procedure was used instead. As shown in Fig. 5, the

spectra of as-received aluminum foil do not have any

band edges within the 200–800 nm wavelength

range, whereas electrosprayed TiO2 had a clear band

edge near 350 nm, which corresponds to the anatase.

Methylene blue decomposition by TiO2-electro-

sprayed fabric and aluminum foil was performed

under UVA light to investigate their photocatalytic

properties. Non-treated fabric and aluminum foil

were used as controls. Figure 6 shows the dye

concentration versus time measured in 20 min inter-

vals. No detectable dye degradation was seen on the

control samples after 3 h of illumination. For TiO2-

coated aluminum foil, total decomposition of the dye

occurred after 75 min (Fig. 7). This shows excellent

photocatalytic performance for electrosprayed TiO2.

For TiO2-electrosprayed nanofibers on polypropylene

fabric, partial decomposition of the dye was observed

after about 40 min, but no further decomposition of

the dye was observed after that. On the other hand,

90% decomposition was observed on the TiO2-

deposited aluminum foil after 40 min. The discrep-

ancy between the fabric and foil may have been

300 400 500 600 700 8000

10

20

30

40

50

60

70

80

90

100

TiO2 electrosprayed nanofiber

on aluminum foil

As-received aluminum foil

Ref

lect

ance

(%

)

Wavelength (nm)

Fig. 5 Diffuse-Reflectance (DR) UV-visible spectra of as-

received aluminum foil and TiO2-electrosprayed aluminum foil

0 20 40 60 80 100 120 140 160 1800.0

0.2

0.4

0.6

0.8

1.0

non-treated aluminum foil

non-treated polypropylene fiber

electrosprayed aluminum foil

electrosprayed PA 11 nanofiber

Co

nce

ntr

atio

n c

han

ge,

C /

C0

(a.u

.)

UV illumination time (min)

Fig. 6 Photo-decomposition of methylene blue under UVA

illumination by TiO2-electrosprayed substrates and non-treated

controls for 3 h (light intensity: 1 mW/cm2)

Before UVA illumination, t = 0

(1) (2) (3)

t = 75 minutes

Fig. 7 Methylene blue dye degradation on TiO2-electro-

sprayed samples for 75 min; (1) TiO2-electrosprayed fabric,

(2) TiO2-electrosprayed aluminum foil, (3) control (non-treated

fabric and aluminum foil)

2516 J Nanopart Res (2010) 12:2511–2519

123

Author's personal copy

caused by the absorption of the dye inside the fabric

where TiO2 particles were not available or did not

receive the required UVA irradiation that was

blocked by the surface layer of fibers. The nanofi-

ber-supported TiO2 would destroy particles and

aerosols coming into contact with the filter surface,

but liquid that penetrated through the film would not

have direct contact with TiO2, which could explain

incomplete decomposition of methylene blue on the

filter. Although some of the dye would desorb to the

surface in the presence of a liquid (i.e., water), quick

drying of the dye should have prevented the complete

desorption in a reasonable time scale.

This has been confirmed by E. coli killing on

untreated and TiO2-coated fabric and foil (Fig. 8).

Similar to dye degradation tests, a significant bacte-

ricidal effect of TiO2 was observed after 30 min;

however, while complete killing was achieved when

TiO2 was deposited on foil, only partial killing of

bacteria occurred on fibers, regardless of coating.

Apparently, uncoated foils were able to kill more

bacteria than that of uncoated fabrics, which is due to

the higher amount of UV exposure resulting from the

higher reflectivity of the aluminum foils. These

results support the proposed concept, but suggest

that further optimization of TiO2 coverage will be

required to increase the bactericidal properties of the

filter (Kau et al. 2009).

Figure 9 shows the contact angle measurement

results. As-spun PA 11 nanofibers were hydrophobic

with a contact angle of 65�. After modifying the

surface with TiO2 particles, surfaces became more

hydrophilic with a contact angle of 30�. TiO2-coated

fabric showed photo-induced super-hydrophilicity, as

expected. After an hour of illumination with UVA

light, the contact angle decreased below 5� showing

increased hydrophilicity and excellent wetting.

Results of this study show that it is possible to

combine both nanofiber protection and photocatalytic

properties of TiO2 leading to bactericidal properties

in filter manufacturing. The proposed technique is

simple and can be applied to any filter surface.

Moreover, by using the electrospraying technique,

TiO2 was placed exactly where it is needed—on the

very surface of the filter. This serves two functions—

to decrease the consumption of TiO2, thus decreasing

filter cost, and to eliminate TiO2 from the inner layers

of the filter.

Conclusions

Electrosprayed-TiO2 nanoparticles maintained their

primary particle size after spraying onto electrospun

PA 11 nanofibers with a uniform distribution. Meth-

ylene blue degradation showed a high photocatalytic

activity of TiO2-coated nanofibers. Contact angle

measurements demonstrated super-hydrophilic

behavior of electrosprayed TiO2 under UVA radia-

tion. We showed that it is possible to electrospray

TiO2 particles directly onto nanofibers to add photo-

catalytic properties to masks and filters. The use of a

2

4

6

8

10

12 Uncoated fabric TiO

2-coated electrospun fabric

1209060300

UVA illumination time (min)

Nu

mb

er o

f E

. co

li(x1

05 ce

ll /m

l)

Nu

mb

er o

f E

. co

li(x1

05 ce

ll /m

l)

0

2

4

6

8

10

12

1209060300

UVA illumination time (min)

Uncoated foil TiO

2-coated electrospun foil

(a)

(b)

Fig. 8 Photocatalytic E. coli inactivation on TiO2-electro-

sprayed samples in comparison with controls under UVA light

illumination. a Number of E. coli colonies on fabric and b on

foil with and without TiO2 coating

J Nanopart Res (2010) 12:2511–2519 2517

123

Author's personal copy

thin nanofiber coating on the surface of polypropyl-

ene fabric decreases the mesh, enabling the filter to

catch smaller particles and increase the active surface

area improving the contact between TiO2 and

biological or organic contaminants. Electrospraying

decreases the amount of TiO2 used and places TiO2

particles on the outer surface of the filter, where they

are most required.

Acknowledgments This work was supported in part by

Amerinova LLC, USA, and Drexel University College of

Medicine. The authors are grateful to Lou Schiliro

(Amerinova) for helpful discussions and to Arkema, Inc. for

providing PA 11. M.E.K. was supported by ArtCraft Glass,

Inc., Kutahya, Turkey. K. B. was supported by the NSF

Graduate Student Research Fellowship.

References

Arabatzis I, Antonaraki S, Stergiopoulos T, Hiskia A, Papa-

constantinou E, Bernard M, Falaras P (2002) Preparation,

characterization and photocatalytic activity of nanocrys-

talline thin film TiO2 catalysts towards 3,5-dichlorophe-

nol degradation. J Photochem Photobiol A 149:237–245

Behler K, Havel M, Gogotsi Y (2007) New solvent for

polyamides and its application to the electrospinning of

polyamides 11 and 12. Polymer 48:6617–6621

Bosc F, Ayral A, Guizard C (2006) Mixed TiO2-SiO2 meso-

structured thin films. Thin Solid Films 495:252–256

Burger C, Hsiao B, Chu B (2006) Nanofibrous materials and

their applications. Annu Rev Mater Res 36:333–368

Cui X, Yan D (2005) Preparation, characterization and crys-

talline transitions of odd-even polyamides 11, 12 and 11,

10. Eur Polym J 41:863–870

Degussa (2005) Technical information Aeroxide and Aeroperl

titanium dioxide as photocatalyst. TI No 1243

Havel M, Behler K, Korneva G, Gogotsi Y (2008) Transparent

thin films of multiwalled carbon nanotubes self-assembled

on polyamide 11 nanofibers. Adv Funct Mater 18:2322–

2327

Hernandez M, Servant L, Grondin J, Lassegues J (1995)

Spectroscopic characterization of metal chloride/polyam-

ide complexes. Ionics 5–6:454–468

Horikoshi S, Watanabe N, Onishi H, Hidaka H, Serpone N

(2002) Photodecomposition of a nonylphenol polyeth-

oxylate surfactant in a cylindrical photoreactor with TiO2

immobilized fiberglass cloth. Appl Catal B 37:117–129

Im J, Kim M, Lee Y (2008) Preparation of PAN-based elec-

trospun nanofiber webs containing TiO2 for photocatalytic

degradation. Mater Lett 62:3652–3655

Kau J, Sun D, Huang H, Wong M, Lin H, Chang H (2009) Role

of visible light-activated photocatalyst on the reduction of

anthrax spore-induced morality in mice. PLoS ONE

4:e4167

Ko F (2006) Nanofiber technology. In: Gogotsi Y (ed)

Nanomaterials handbook. CRC Press, Boca Raton, pp

553–564

Ko F, Gogotsi Y, Ali A, Naguib N, Ye H, Yang G, Li C, Willis

P (2003) Electrospinning of continuous carbon nanotube-

filled nanofiber yarns. Adv Mater 15:1161–1165

Ko F, Lam H, Titchenal N, Ye H, Gogotsi Y (2006) Coelec-

trospinning of carbon nanotube reinforced nanocomposite

fibrils. Polym Nanofibers 918:231–245

0 20 40 60 80 100 120

0

5

10

15

20

25

30

Co

nta

ct a

ng

le o

f w

ater

dro

p (

°)

UV illumination time (min)

As-spun PA 11

Fig. 9 The water contact

angle dependence on the

UVA illumination time for

the TiO2-electrosprayed

nanofiber (light intensity:

1 mW/cm2)

2518 J Nanopart Res (2010) 12:2511–2519

123

Author's personal copy

Kosmulski M (2002) The significance of the difference in the

point of zero charge between rutile and anatase. Adv

Colloid Interface Sci 99(3):255–264

Li D, Xia Y (2003) Fabrication of titania nanofibers by elec-

trospinning. Nano Lett 3:555–560

Li D, Xia Y (2004) Electrospinning of nanofibers: reinventing

the wheel? Adv Mater 16:1151–1170

Li D, Wang Y, Xia Y (2003) Electrospinning of polymeric and

ceramic nanofibers as uniaxially aligned arrays. Nano Lett

3:1167–1171

Malati M (1999) Experimental inorganic/physical chemistry:

an investigate, integrated approach to practical project

work. Horwood Publishing, West Sussex

Mattia D, Bau H, Gogotsi Y (2006) Wetting of CVD carbon

films by polar and nonpolar liquids and implications for

carbon nanopipes. Langmuir 22:1789–1794

Miao L, Tanemura S, Toh S, Kaneko K, Tanemura M (2004)

Fabrication, characterization and Raman study of anatase-

TiO2 nanorods by a heating-sol-gel template process. J

Cryst Growth 264:246–252

Nuansing W, Ninmuang S, Jarernboon W, Maensiri S, Sera-

phin S (2006) Structural characterization and morphology

of electrospun TiO2 nanofibers. Mater Sci Eng B

131:147–155

Ocana M, Garcia-Ramos J, Serna C (1992) Low-temperature

nucleation of rutile observed by Raman spectroscopy dur-

ing crystallization of TiO2. J Am Ceram Soc 75:2010–2012

Spurr R, Myers H (1957) Quantitative analysis of anatase-rutile

mixtures with an X-ray diffractometer. Anal Chem

29:760–762

Ye H, Lam H, Titchenal N, Gogotsi Y, Ko F (2004) Rein-

forcement and rupture behavior of carbon nanotubes-

polymer nanofibers. Appl Phys Lett 85:1775–1777

Zhao J, Jia C, Duan H, Li H, Xie E (2008) Structural properties

and photoluminescence of TiO2 nanofibers were fabri-

cated by electrospinning. J Alloys Compd 461:447–450

J Nanopart Res (2010) 12:2511–2519 2519

123

Author's personal copy