novel properties of pes fabrics modified by corona discharge and colloidal tio2 nanoparticles

Research Article

Received: 10 August 2009, Revised: 2 September 2009, Accepted: 8 September 2009, Published online in Wiley Online Library: 26 October 2009

(wileyonlinelibrary.com) DOI: 10.1002/pat.1568

Novel properties of PES fabrics modified bycorona discharge and colloidal TiO2

nanoparticles

Darka Mihailovica, Zoran Saponjicb, Marija Radoicicb, Ricardo Molinac,Tamara Radeticd, Petar Jovancica, Jovan Nedeljkovicb and Maja Radetica*

The objective of this study was to highlight the poten

Polym. Adv

tial application of the corona discharge at atmospheric pressurefor the surface activation of polyester (PES) fabrics in order to improve the binding efficiency of colloidal TiO2

nanoparticles. The obtained nanocomposite textile materials provide desirable level of UV protection, self-cleaningproperties, and photodegradation activity. The measured UV protection factor (UPF) of fabrics corresponds to UPFrating of 50R, designating the maximum UV protection. Additionally, the total photodegradation of methylene bluein aqueous solution was achieved after 24 hr of UV illumination and this capability was preserved and even improvedafter four repeated cycles. The results showed that the corona treated PES fabrics loaded with TiO2 nanoparticles hadconsiderably enhanced the overall efficiency compared to PES fabrics loaded only with TiO2 nanoparticles. Copyright� 2009 John Wiley & Sons, Ltd.

Keywords: PES fabric; TiO2 nanoparticles; corona discharge; UV protection; self-cleaning; photodegradation activity

* Correspondence to: M. Radetic, Textile Engineering Department, Faculty ofTechnology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120Belgrade, Serbia.E-mail: [email protected]

a D. Mihailovic, P. Jovancic, M. Radetic

Textile Engineering Department, Faculty of Technology and Metallurgy,

University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

b Z. Saponjic, M. Radoicic, J. Nedeljkovic

Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, Serbia

c R. Molina

Departamento de Nanotecnologıa Quımica y Biomolecular, IIQAB-CSIC,

08034 Barcelona, Spain

d T. Radetic

National Center for Electron Microscopy, Lawrence Berkeley Laboratory,

Berkeley, CA 94720, USA

Contract/grant sponsor: Ministry of Science of Republic of Serbia; contract/

grant numbers: TR 19007; 142066. 7

INTRODUCTION

Although often presented as a novel material, titania crossed along path from its early applications in chalking of titania-basedpaints to advanced applications in water and air remediation,manufacturing of sterile, self-cleaning, self-sterilizing, and anti-fogging surfaces, etc.[1] The development of simple routes forsynthesis of non-toxic, inexpensive, and highly photoactivetitania nanoparticles (TiO2 NPs) expanded the range of titaniacommercial applications.[1] Excellent technical and economicalresults experienced in different sectors of industry wereimmediately recognized by textile companies. Recently, stimulat-ing efforts to incorporate TiO2 NPs into the processing of highvalue added textile materials have been made.Recent studies indicated that UVprotection aswell as self-cleaning

effects can be tailored by depositing TiO2 NPs onto textile fibers,without changing the bulk properties of the fiber anddeteriorating of textile appearance.[2–14] However, the poorbinding of hydrophilic colloidal TiO2 NPs to hydrophobic fibers isa key issue, that can be overcome by plasma modification of thetextile surfaces.[15–16] A wide range of plasma chemical reactionscan be designed by selecting appropriate operating conditions(gas, gas rate, pressure, power, treatment time) to provide thedesirable effects on the textile surfaces.[17] Plasma oxidation andplasma etching induce the activation of the fiber surface, i.e.formation of new polar functional groups (C–O, C––O, –O–C––O,–COH, –COOH or –O–O–) facilitating the binding of TiO2

NPs.[15–16] Previous studies confirmed that treatment of polyester(PES) fabrics by radio-frequency (RF) or microwave (MW) oxygenplasma at low pressure ensures better interaction between thesurface of fibers and colloidal TiO2 NPs.[15–16] Although low-pressure plasma systems provide better stability, uniformity and

. Technol. 2011, 22 703–709 Copyright � 200

control of properties, these devices require expensive vacuumsystems and complex handling of textile materials. This can beavoided by using the systems operating at atmospheric pressure(corona discharge and dielectric barrier discharge).Plasma-induced functionalities on the PES fiber surface

provide enhanced interaction with highly reactive undercoordi-nated surface defect sites of TiO2 NPs. In fact, for the particles inthe nanocrystalline size range, a fraction of the surface atomswith significantly altered coordination environment and electro-chemical properties is large.[18] When diameter of nanocrystallineanatase TiO2 particles becomes smaller than 20 nm, the surface Tiatoms adjust their coordination environment from octahedral to

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D. MIHAILOVIC ET AL.

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pentacoordinated (square pyramidal).[19] Pentacoordinated sur-face Ti atoms are more reactive, contributing to better interactionwith PES fiber surface.This paper discusses the potential of using the industrial

corona discharge for the surface activation of PES fabrics in orderto enhance the binding efficiency of colloidal TiO2 NPs. Thesetextile nanocomposite materials were characterized by XPS andAAS. TiO2 NPs deposited onto PES fabrics provide desirable levelof UV protection, self-cleaning properties, and photodegradationactivity. The efficiency of UV blocking was evaluated bydetermining the UV protection factor (UPF) of PES fabrics. Thephotoactivity of TiO2 NPs deposited on PES fabrics was tested bydegradation of methylene blue as a model compound. Self-cleaning efficiency was examined with blueberry juice stains.

EXPERIMENTAL

Sample preparation

All the chemicals for the synthesis of TiO2 colloid were ofanalytical grade and used as received without further purification(Aldrich, Fluka). Milli-Q deionizedwater was used as a solvent. Thecolloidal solution of TiO2 NPs was prepared in a manner analo-gous to the procedure proposed by Rajh et al.[20] The solution ofTiCl4 cooled up to �208C was added drop-wise to cooled water(at 48C) under vigorous stirring and then kept at this temperaturefor 30min. The pH value of the solution was in a range 0–1,depending on TiCl4 concentration. Slow growth of the particleswas achieved by applying dialysis against water at 48C untilthe pH of the solution reached 3.5. The concentration of TiO2

colloidal solution was determined from the concentration of theperoxide complex obtained after dissolving the particles inconcentrated H2SO4.

[21]

Desized and bleached PES (115 gm�2) fabric was used as asubstrate in this study. To remove the surface impurities, fabricswere cleaned in the bath containing 0.5% nonionic washingagent Felosan RG-N (Bezema) at liquor-to-fabric ratio of 50:1.After 15min of washing at 508C, the fabrics were rinsed once withwarm water (508C) for 3min and three times (3min) with coldwater. Afterwards, the fabrics were dried at room temperature.Corona treatment of fabrics was accomplished at atmospheric

pressure using a commercial device Vetaphone CP-Lab MK II.Fabrics were put on the electrode roll covered with silicon coating,rotating at the minimum speed of 4mmin�1. The distancebetween electrodes was 2mm. The power was 900W and thenumber of passages was set to 30. The fabrics were always dippedinto the colloid of TiO2 NPs 2 hr after corona treatment.One gram of PES fabric was immersed in 20ml of TiO2 colloid

for 5min and dried at room temperature. After 30min long curingat 1008C, the fabrics were rinsed twice (5min) with deionizedwater and dried at room temperature.

Methods

Shape and size of TiO2 NPs were characterized by transmissionelectron microscopy (TEM, Phillips CM200, at 200 kV and JEOL100CX at 100 kV).The evaluation of surface chemical changes was conducted by

X-ray photoelectron spectroscopy (XPS) analysis. Samples wereanalyzed using a PHI Model 5500 Multitechnique System with anAl Ka monochromatic X-ray source operating at 350W. Themeasurements were conducted under a take-off angle of 458.

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Survey scans were in the range 0–1100 eV, with pass energy of187.85 eV. High resolution scans were obtained on the C 1s, O 1s,and Ti 2p photoelectron peaks, with pass energy of 23.5 eV.Binding energies were referenced to the C 1s photopeak positionfor C–C and C–H species at 285.0 eV. Surface composition hasbeen estimated after a linear background subtraction from thearea of the different photo-emission peaks modified by theircorresponding sensitivity factors.[22]

The total content of Ti in the PES fabrics was determined by aPerkin Elmer 403 atomic absorption spectrometer (AAS).The UV transmission spectra of the PES fabrics were obtained

by UV–Vis spectrophotometer Cary 100 Scan (Varian). The UPFvalue was automatically calculated on the basis of recorded dataaccording to Australia/New Zealand standard AS/NZS 4399:1996.For the examination of self-cleaning properties of the PES

fabrics, blueberry juice was used. Untreated PES fabric and fabricsloaded with TiO2 NPs were cut into 5 cm� 5 cm pieces. Thefabrics were stained with 100ml of blueberry juice. After drying atroom temperature, the fabrics were illuminated by ULTRA-VITALUX lamp, 300W (Osram) which provides sun-like irradiationwith a spectral radiation power distribution at wavelengthsbetween 300–1700 nm. To determine the color change after 2, 4,6, and 24 hr of irradiation, color coordinates of the stained fabrics(CIE L�, a�, b�) were determined with Datacolor SF300spectrophotometer under illuminant D65 using the 108 standardobserver. On the basis of measured CIE color coordinates, colordifference (DE�) was determined as:

DE� ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðDa�Þ2 þ ðDb�Þ2 þ ðDL�Þ2

q(1)

where DL� is the color lightness difference between treated(stained PES fabric loaded with TiO2 NPs) and control fabrics(stained PES fabric); Da� red/green difference between treatedand control fabrics; and Db� is yellow/blue difference betweentreated and control fabrics. Always the same position on thestained fabric (where the color intensity of the stain was thestrongest—the central part) was analyzed.Photodegradation activity of TiO2 NPs deposited on PES fabrics

was followed by decomposition of methylene blue (MB). 0.5 g ofPES fabric was immersed in 25ml of MB solution (10mg L�1, pH5.81) and illuminated by ULTRA-VITALUX lamp, 300W (Osram) for2, 4, 6, 8 and 24 hr. The MB concentration was determined bymeasuring absorption intensity at 664 nm using a UV–Visspectrophotometer Cary 100 Scan (Varian).

RESULTS AND DISCUSSION

Characterization of TiO2 NPs

The results of TEM characterization showed the presence of theagglomerates of Ti-based nanoparticles (Fig. 1). The individualparticles are in 5–10 nm size range. Neither diffraction pattern norHREM imaging revealed presence of the crystalline phaseindicating the amorphous structure of TiO2.

Elemental analysis of PES fabrics loaded with TiO2 NPs

In order to achieve stronger interaction between hydrophobicPES fibers and hydrophilic TiO2 NPs, corona treatment of PESfabrics was performed. The changes in chemical composition ofthe PES fibers surface, induced by corona discharge, wereanalyzed by XPS. The results of elemental composition analysis of

009 John Wiley & Sons, Ltd. Polym. Adv. Technol. 2011, 22 703–709

Figure 1. (a) Bright field TEM image of TiO2 NPs and (b) corresponding Ti

map: energy filtered TEM image formed using Ti L2,3 edge.

Figure 2. High-resolution C 1s spectra of the UPES and CPES fibers.

Table 2. Relative peak intensities of the deconvoluted C 1sspectra of UPES and CPES fibers

Sample

Atomic ratio (%)

C–C, C–H C–O C––O O–C––O285.0 eV 286.6 eV 288.3 eV 289.3 eV

UPES 72.4 16.3 0.0 11.3CPES 65.0 18.5 5.8 10.7

NOVEL PROPERTIES OF PES FABRICS

untreated (UPES) and corona treated (CPES) fibers are presentedin Table 1.It is evident that corona treatment resulted in an increase in O/

C atomic ratio by about 36%, indicating the formation of newoxygen-containing functionalities. The observed decrease in thecarbon content is characteristic for the plasma treatment ofpolymers. It occurs as a result of chain scission induced by theplasma active species.[23] The increase in the oxygen content canbe attributed to the presence of atomic oxygen in the dischargeduring the fabric processing and/or post-plasma reaction ofactivated fiber surface with environmental species.[23] Although itis well established that various active species (ozone, nitrogenoxides, radicals, etc.) are generated in corona discharge in air,atomic oxygen is considered to be responsible for the chemicalchanges on the fiber surface.[24,25] Atomic oxygen is formed in thedischarge as a product of electron impact induced dissociation ofoxygen molecules.[23,24] Excitation and dissociation of nitrogenmolecules may also initiate different plasma chemical reactionsthat can lead to a formation of atomic oxygen.[25,26]

In order to confirm the changes of functional groups on thePES fibers surface caused by corona treatment, the XPShigh-resolution C 1s spectra were examined (Fig. 2). The C 1sspectrum of UPES fabric was deconvoluted with three com-ponents (Table 2). The peak located at 285.0 eV is attributed toC–C and C–H groups. The peak at 286.6 eV corresponds to C–Ogroup, whereas the peak at 289.3 eV is assigned to O–C––Ogroups.

Table 1. Elemental composition of UPES and CPES fibers

Sample C (atom%) O (atom%) O/C (atom%)

UPES 76.3 23.7 31.0CPES 70.3 29.7 42.2

Polym. Adv. Technol. 2011, 22 703–709 Copyright � 2009 John Wiley

The results from Table 2 indicated that corona treatment of PESfabrics induced the decrease in content of C–C, C–H and O–C––Ogroups as well as the increase in C–O groups in comparison withUPES fiber. In the spectrum of CPES fibers, an additional peak at288.3 eV also emerged. It is related to free carbonyl groups (C––O).The generation of carbonyl groups as a consequence of CO2

plasma and corona treatments of PES fibers was also observed inprevious studies.[27,28]

Evident increase in oxygen-containing functionalities leads toan increase in hydrophilicity of PES fabrics, as was revealed bycontact angle measurements in our previous work.[29] Therefore,the hydrophylized surface of PES fibers becomes more accessiblefor TiO2 NPs.The results of XPS elemental analysis for the UPESþ TiO2 and

CPESþ TiO2 fibers are given in Table 3. The high resolution XPSspectra of Ti 2p photoelectron peaks for the UPESþ TiO2 and

Table 3. Elemental composition of UPESþ TiO2 andCPESþ TiO2 fibers

Sample C (atom%) O (atom%) Ti (atom%)

UPESþ TiO2 55.0 37.1 7.9CPESþ TiO2 52.5 37.9 9.6

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Figure 3. High-resolution spectra of Ti 2p photoelectron peaks for the

UPESþ TiO2 and CPESþ TiO2 fibers.

Table 4. Relative intensity data of the deconvoluted O 1sspectra of the UPESþ TiO2 and CPESþ TiO2 fibers

Sample

Atomic ratio (%)

TiO2 C–O C––O529.8 eV 532.9 eV 531.6 eV

UPESþ TiO2 52.7 27.0 20.3CPESþ TiO2 62.9 20.1 17.0


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CPESþ TiO2 fibers are presented in Fig. 3. The Ti 2p1/2 and Ti 2p3/2spin-orbital splitting electrons are located at binding energies of464.2 and 458.6 eV, respectively. As expected, corona treatmentpositively affected the binding efficiency of TiO2 NPs. Ti contenton PES fibers increased by approximately 22% after coronatreatment. For comparison, Qi et al. reported that oxygen RFplasma treatment of PES fabric increased the Ti content by10.2%.[16]

O 1s high-resolution spectra of UPES and CPES fibers loadedwith TiO2 NPs are shown in Fig. 4. The O 1s spectrum of thesefibers was deconvoluted with three components (Table 4). Thepeaks at binding energies of 529.8, 531.6, and 532.9 eVcorrespond to TiO2, C––O and C–O groups, respectively. Theexistence of the peak at 529.8 eV clearly proves the presence ofTiO2 NPs on the surface of both PES fibers.The total amount of Ti in the PES fabrics was determined by

AAS measurements. It was found that 1 g of UPES and CPES fabriccontains 10.1 and 12.2mg of Ti, respectively. It is worth noticingthat AAS results are in a quite good correlation with XPS resultssince corona treatment led to an increase in total Ti content by20.1%.

Figure 4. High-resolution O 1s spectra of the UPESþ TiO2 and CPESþTiO2 fibers.


UV protection of PES fabrics loaded with TiO2 NPs

The protection from excessive UV irradiation is becoming one ofthe key requirements for garments due to increasing damageof the ozone layer. Accurate evaluation of the UV protection levelprovided by PES fabrics requires measurements of the trans-mittance across the UVB (280–315 nm) and UVA (315–400 nm)spectral regions.[16] Figure 5 presents the UV transmission spectraof the UPES fabric and PES fabrics loaded with TiO2 NPs. It isevident that the deposition of TiO2 NPs onto PES fabrics led to anoverall decrease in UV transmission intensity and to a change ofthe shape of spectrum. The UV transmission of the PES fabrics isalmost completely cut off in the UVB region. The UV transmissionof the PES fabrics loaded with TiO2 NPs in the UVA region wasconsiderably lower with respect to UPES fabric. The transmittancecurves of the PES fabrics loaded with TiO2 NPs (UPESþ TiO2 andCPESþ TiO2 fabrics) significantly differ in the whole UVA region.This difference shows that the reduction in UV transmission ismore prominent on the CPESþ TiO2 fabric, implying its strongerabsorption ability.The efficient UV blocking of the PES fabrics loaded with TiO2

NPs was also confirmed by high UPF values. According toAustralia/New Zealand standard, it is suggested that UPF ofgarments should be at least 40 to 50þ.[3] The UPF value of 43 andcorresponding UPF rating of 40 categorize the UPES fabric tofabrics with an excellent UV protection. As expected, treatment ofthe PES fabrics with TiO2 NPs significantly enhanced the UVprotection of the PES fabrics. UPF value of the UPESþ TiO2 fabricwas 90 whereas of the CPESþ TiO2 fabric 113. Both values

Figure 5. Transmission spectra of the UPES fabric and PES fabrics loaded

with TiO2 NPs.



correspond to UPF rating of 50þ, which designates the maximumUV protection. The high UPF rating of the PES fabrics loaded withTiO2 NPs is due to strong absorption of UV light by TiO2 NPsdeposited on the PES fabrics surface. Higher UPF value of theCPESþ TiO2 fabric is attributed to higher amount of depositedTiO2 NPs confirmed by XPS and AAS measurements. After fivewashing cycles,[29] the UPF decreased to the value of 83 and 99for the UPESþ TiO2 and CPESþ TiO2 fabrics, respectively. In spiteof reduction of UPF value, the fabrics still provide maximum UVprotection, indicating the satisfactory laundering durability.

Self-cleaning efficiency of PES fabrics loaded with TiO2 NPs

Self-cleaning efficiency of the PES fabrics loaded with TiO2 NPswas examined by following the decoloration of blueberry juicestains. The decoloration effects on UPES fabric and PES fabricsloaded with TiO2 NPs were recorded after 0, 2, 4, 6, and 24 hr ofillumination. The images of samples recorded immediately afterblueberry juice staining (zero time of illumination) and after 24 hrof illumination are shown in Fig. 6.The color differences between stained UPES fabric and PES

fabrics loaded with TiO2 NPs (UPESþ TiO2 and CPESþ TiO2)expressed via DE�, DL�, Da�, and Db� values are given in Table 5. Itis noticeable that great color difference between these fabrics

Figure 6. Blueberry juice stains on the UPES fabric and PES fabrics

loaded with TiO2 NPs before and after 24 hr of illumination. This figure

is available in color online at wileyonlinelibrary.com/journal/pat


occurred immediately after staining (Fig. 6). Both, UPESþ TiO2

and CPESþ TiO2 fabrics became lighter, less red and less bluecompared to UPES fabric (Table 5). In addition to color change,the difference in the shape of stains can be observed (Fig. 6). Theshape of the stain on the UPES fabric was clearly defined.The stain on the UPESþ TiO2 fabric also exhibited quite a definiteshape unlike stain on the CPESþ TiO2 fabric, which seemed to bemore spread over. This is attributed to corona treatment andconsequently increased hydrophilicity of the PES fabrics.As could be predicted, longer illumination caused the higher

self-cleaning effects. The decoloration tendency of both stainedfabrics loaded with TiO2 NPs in the first 4 hr of illumination wasthe same: the stains were lighter, less red, and less blue comparedto those on the UPES fabric (Table 5). After the sixth hour ofillumination stains became lighter, less red and yellow and suchtrend continued in the next 18 hr of illumination. The DE�, DL�,Da�, andDb� values (Table 5) clearly indicate that the CPESþ TiO2

fabrics show better stain degradation activity than the UPESþ TiO2

fabrics in the whole range of examined UV illumination times. Asexpected, blueberry juice stain on the UPES fabric was almost notaltered even after 24hr of illumination. Mejıa et al.[30] recentlyreported similar discoloration effects on the RF plasma and TiO2

NPs treated cotton fabrics stained with red wine. The comparisonbetween the XPS spectra of red wine stained cotton fabrics beforeand after 24 hr of illumination indicated the slight shift of the Ti2p3/2 peak toward lower energies, suggesting that redox catalysisinvolving two oxidation states Ti4þ/Ti3þ is taking place during thedecoloration process.[30]

Obtained stain photodegradation provides practical appli-cation that relies on the possibility of daylight irradiation of stainsmaking the stained fabrics more prone to the action ofdetergents during household washing.[9,15] Consequently, costsaving in energy can be expected.

7

Photodegradation of methylene blue by TiO2 NPs depositedon the PES fabrics

Photodegradation activity of PES fabrics loaded with TiO2 NPsunder UV illumination was examined using the dye methyleneblue (MB) as a model compound. Absorption spectra of MBsolution were recorded after 2, 4, 6, 8, and 24 hr of UVillumination. To elucidate the trend of MB absorption and/orphotodegradation, the dependence of C/C0 versus time of UVillumination for the UPES, UPESþ TiO2 and CPESþ TiO2 fabricswas plotted (Fig. 7). Figure 7 reveals that the adsorption of MB onthe UPES fabric got saturated after 6 hr of UV illumination andthere was no further decrease in MB concentration withprolonged UV illumination time. Additionally, the fabric turnedfrom white to blue and this dye did not degrade under the UVillumination, demonstrating that the UPES fabric itself does notexhibit any photodegradation activity.[14]

After the rapid decoloration of MB solution in contact with theUPESþ TiO2 fabric in the first 4 hr of UV illumination, the processslowed down. The MB was completely removed from solutionafter 24 hr of UV illumination. The removal of MB from solution issuggested to be only partially due to photodegradation activityof TiO2 NPs. Namely, the fabric remained blue after 24 hr of UVillumination and after rinsing in water its color did not change.This implied that the MB dyed the fabric as well as that TiO2 NPson the UPES fabric did not provide the complete photodegrada-tion of MB on the fabric.


07

Table 5. Color difference between blueberry juice stained UPES fabric and CPES fabrics loaded with TiO2 NPs from colloid after 2, 4,6, and 24 of illumination

Time (hr) Sample DE� DL� Da� Db� Description

UPESþ TiO2 6.587 0.534 �6.443 1.263 Lighter, less red, less blue0 CPESþ TiO2 8.935 4.481 �7.531 1.742 Lighter, less red, less blue



UPESþ TiO2 12.083 3.635 �8.207 8.088 Lighter, less red, yellow6 CPESþ TiO2 13.053 5.404 �8.854 7.924 Lighter, less red, yellow

UPESþ TiO2 11.350 4.300 �8.152 6.624 Lighter, less red, yellow24 CPESþ TiO2 12.120 7.035 �9.036 3.967 Lighter, less red, yellow

Figure 7. The dependence of C/C0 versus time of UV illumination for the

UPES, UPESþ TiO2, and CPESþ TiO2 fabrics.

Figure 8. Changes in relative concentration of MB after repeated photo-

degradation processes under the UV illumination for the CPESþ TiO2

fabric.


708

CPESþ TiO2 fabric caused stronger decoloration of MB solutionafter 6 and 8 hr of UV illumination. The dye was completelyremoved after 24 hr of UV illumination. The fabric remained whiteand after rinsing in water the solution was colorless, indicatingthat the entire amount of MB photodegraded on the surface ofthe CPESþ TiO2 fabric. Qi et al. reported similar photodegrada-tion effects of Neolan Blue 2G with oxygen RF plasma treated PESfabric.[16] Higher content of TiO2 found on the CPES fabrics is oneof the reasons for higher photodegradation activity of theCPESþ TiO2 fabric in comparison with UPESþ TiO2 fabric.To evaluate the durability of photodegradation activity of the

CPESþ TiO2 fabric, the photodegradation process under the UVillumination was done four times (Fig. 8). The results showed thateven after four cycles of 24 hr long UV illumination, thephotoactivity of the CPESþ TiO2 fabric was not reduced.Repeated photodegradation cycles on the CPESþ TiO2 fabricswere considerably faster and around 96.5–99% of MB wasremoved already after 6 hr of UV illumination as shown in Fig. 8.Similar trend was reported by other researchers.[12] Higherphotocatalytic activity of TiO2 nanoparticles in repeated cyclesappears as a consequence of surface particles cleaning fromimpurity compounds during the first cycle.


The unique surface structure of the particles smaller than20 nm characterized by adjusted coordination environment ofsurface Ti atoms ensures better binding efficiency between theCPES fibers and TiO2 NPs.[18] Simultaneously, such surfacestructure provides better interaction with MB moleculesenhancing the overall photocatalytic activity.

CONCLUSIONS

Corona treatment of PES fabrics prior to loading of TiO2 NPspositively affected their UV protection, self-cleaning of blueberryjuice stains, and photodegradation abilities. High UPF valuescorresponding to UPF rating of 50þ, designate the maximum UVprotection. Deposition of colloidal TiO2 NPs onto coronapretreated PES fabrics provides excellent degradation of blue-berry juice stain under the UV illumination. Additionally, the totalphotodegradation of methylene blue was achieved after 24 hr ofUV illumination and this capability was preserved and evenimproved after four repeated cycles. Higher efficiency of coronaactivated PES fabrics loaded with TiO2 NPs can be attributed tohigher content of TiO2 NPs detected by XPS and AASmeasurements.



Acknowledgements

This work was performed in part at NCEM, which is supported bythe Office of Science, Office of Basic Energy Sciences of the U.S.Department of Energy under Contract No. DE-AC02-05CH11231.

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