The fabrication of nanocomposite thin films with TiO2

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The fabrication of nanocomposite thin films with TiO2 nanoparticles by the layer-by-layer deposition method for multifunctional cotton fabrics To cite this article: ule S Ugur et al 2010 Nanotechnology 21 325603

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NANOTECHNOLOGY

Nanotechnology 21 (2010) 325603 (8pp)

doi:10.1088/0957-4484/21/32/325603

The fabrication of nanocomposite thin films with TiO2 nanoparticles by the layer-by-layer deposition method for multifunctional cotton fabrics S¸ule S Uˇgur1,4 , Merih Sarııs¸ık2 and A Hakan Aktas¸3 1 2 3

Department of Textile Engineering, Süleyman Demirel University, Isparta 32260, Turkey Department of Textile Engineering, Dokuz Eylül University, ˙Izmir 35160, Turkey Department of Chemistry, Süleyman Demirel University, Isparta 32260, Turkey

E-mail: [email protected]

Received 7 December 2009, in final form 7 June 2010 Published 21 July 2010 Online at stacks.iop.org/Nano/21/325603 Abstract A multilayer nanocomposite film composed of anatase TiO2 nanoparticles was fabricated on cationically modified woven cotton fabrics by the layer-by-layer molecular self-assembly technique. For cationic surface charge, cotton fabrics were pre-treated with 2,3-epoxypropyltrimethylammonium chloride (EP3MAC) by a pad-batch method. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to verify the presence of deposited nanolayers. Photocatalytic activities of the nanocomposite films were evaluated through the degradation of red wine pollutant. Nano-TiO2 deposition enhanced the protection of cotton fabrics against UV radiation in comparison with the untreated cotton fabrics. Air permeability and whiteness value analysis was performed on the fabrics before and after the treatment with TiO2 nanoparticles by the layer-by-layer deposition method. Tensile strength tests of the warp and weft yarns were performed to evaluate the effect of solution pH value changes during the alternate dipping procedures. For the first time the durability of the effect of the self-assembled multilayer films on the cotton fabric functional properties was analyzed after 10 and 20 washing cycles at 40 ◦ C for 30 min. (Some figures in this article are in colour only in the electronic version)

seemed to be suitable for deposition by the LbL method, but generally polyelectrolytes have been employed [2–13]. That any of these species in any order can be adsorbed layer by layer is the greatest advantage of self-assembly. The oppositely charged species are held together by strong ionic bonds and form long-lasting, uniform and stable films, which are often impervious to a solvent. Self-assembly is economical and readily amenable to scaling up for the fabrication of largearea defect-free devices on virtually any kind and shape of surfaces [1–4]. The process begins by charging a substrate appropriately. The charged substrate is then immersed in a dilute solution of oppositely charged polyelectrolyte, for a time optimized for the adsorption of a monolayer solution, then rinsed. Strong

1. Introduction The electrostatic attraction between oppositely charged molecules provides an excellent basis for the creation of nanolayer films. The sequential adsorption of oppositely charged colloids was reported in a seminar paper in 1966 by R Iler. Starting in the early 1990s, Decher’s group rediscovered layer-by-layer (LbL) processing to fabricate multilayer thin films from oppositely charged polyelectrolytes [1]. The LbL process is based on the alternating adsorption of charged cationic and anionic species. Most types of charged molecules, nanoparticles, dyes, proteins and other supramolecular species 4 Author to whom any correspondence should be addressed.

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Nanotechnology 21 (2010) 325603

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activity of anatase form TiO2 nanoparticles has been growing. In the literature anatase titania thin films were prepared by using relatively high temperature deposition methodologies, such as chemical vapor deposition, sputtering, the sol– gel process and dip-coating techniques. The formation of photocatalytic titanium films at low temperature is important for the fabrication of transparent films on textile substrates that cannot withstand high temperature treatment [21–30]. In the present study, an attempt was made to improve functional cotton fabrics by the deposition of anatase TiO2 nanoparticle multilayers. Cationic cotton was prepared by a cationization process. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR–ATR), scanning electron microscopy and x-ray photoelectron spectroscopy (XPS) measurements were used to verify the presence of the deposited nanolayers. The UV-protective and self-cleaning properties of the fabrics connected with the character of the deposited TiO2 nanolayers were also tested. Air permeability, whiteness values and tensile strength analyses were performed to examine the LbL process effect on the cotton textile fabric properties. The functional properties of multilayer films were analyzed after 10 and 20 washing cycles (40 ◦ C and 30 min).

electrostatic attraction occurs between a charged surface and an oppositely charged molecule in the solution. In principle, the adsorption of molecules carrying more than one equal charge allows for charge reversal on the surface. The next step is the immersion of the one layer covered substrate into a dilute dispersion of oppositely charged polyelectrolytes for a time optimized for the adsorption of a monolayer, followed by rinsing. In this way, an oppositely charged molecule is adsorbed in a second step on the top of the first one. Both adsorption steps can be repeated cyclically to form multilayer structures on the surface of a substrate [1–5]. Multilayers containing nanoparticles have been studied extensively for their potential use in various fields of science (anti-static coatings for plastics, sensors, light emitting diodes, fuel cells, polymer capsules etc), but only a few studies have shown that the LbL process can be used for textile materials. Hyde et al [12] examined the possibility of creating polyelectrolyte thin film coatings on textile materials by using the LbL deposition process. Ding et al [14] fabricated self-assembled LbL ultrathin hybrid TiO2 /PAA film coated CA nanofibrous mats by a combination of electrospinning and electrostatic LbL selfassembly techniques. Jantas and Polowinski [15] obtained very thin polyelectrolyte nanolayers on PET fabric to change its properties connected with the fiber surface. Dubas et al [16] have demonstrated and characterized the possible deposition of polyelectrolyte multilayer thin films assembled from cationic poly(diallyldimethylammonium chloride) and scarlet dye onto nylon fibers. Dubas et al [17] used the LbL process for coating silk fibers with polyelectrolyte multilayer thin films to improve their color fastness to washing. Polowinski [18] obtained polymeric complex layers on polypropylene and polyester non-woven fabrics via the LbL method. Chunder et al [19] fabricated ultrathin fibers comprising poly(acrylic acid) and poly(allylamine hydrochloride) by using the electrospinning technique with the LbL process. Dubas et al [20] have demonstrated coating of silk or nylon fibers with silver nanoparticles for antimicrobial properties by following the LbL method. According to the literature, nanoparticle multilayers can be formed on textile fiber surfaces using the LbL process. It is interesting to note that there is no report which investigates the durability of multilayer films after washing procedures on the textile materials. The LbL process has opened the way for the easy preparation of nanocomposite textile fibers, allowing the preparation of functional textiles for protective clothing. The LbL technique offers the possibility to tailor the surface properties of textile fibers by depositing nanolayers of polyelectrolytes, charged nanoparticles and non-reactive dyes in a controlled manner. The application of TiO2 nanoparticles to textile materials has been the object of several studies aimed at producing finished fabrics with different characteristics such as UVblocking, antibacterial and self-cleaning. The field of selfcleaning coatings is divided into two categories: hydrophobic and hydrophilic. Hydrophilic coatings chemically break down dirt when exposed to light, a process known as ‘photocatalysis’. In recent years, interest in the photocatalytic

2. Experimental details 2.1. Nanoparticle Anatase titanium oxide nanoparticles (particle size < 25 nm, specific surface area 200–220 m2 g−1 ) were purchased from Aldrich and used for multilayer film composition as received. The nanoparticle suspension was prepared at 40 W for 1 h by a Sonics Vibra-Cell ultrasonic homogenizer. The concentration of the suspension was adjusted to 0.1 wt%. The isoelectric point of anatase TiO2 was at pH 4.7–6.2 [31]. To make cationic and anionic TiO2 suspensions, the pH of the nanoparticle suspension was adjusted to 9.0 and 2.5 by using HCl and NaOH. 2.2. Substrate Mercerized and bleached cotton woven fabric was used as the substrate for the LbL process. The fabric properties were as follows: plain woven; 138.84 g m−2 ; 56 thread cm−1 warp and 31 thread cm−1 weft; yarn count 50/1. The fabric was cut into approximately 18 cm × 25 cm pieces before being chemically pretreated to impart the cationic charges. 2.3. Substrate preparation To impart cationic sites to the surface of the cotton fibers, we used a chemical modification technique named cationization [32]. Cationic cotton was prepared by using 2,3-epoxypropyltrimethylammonium chloride (EP3MAC). EP3MAC was prepared in aqueous solution by reacting 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHP3MAC) with NaOH. EP3MAC reacts with the hydroxyl groups of cellulose, creating cationic charges on the surface of the sample. CHP3MAC, 65%, and NaOH crystals were obtained from Aldrich. 100 g of CHP3MAC and 45.5 g of 2


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NaOH were mixed into 200 ml of deionized water. This solution was pad applied to the cotton specimens at 100% wet pick-up and the fabric samples were kept for 24 h at ambient conditions (20 ◦ C and 65% RH) in Ziploc bags. Cationized cotton fabrics were dried in a commercial dryer at 60 ◦ C. Random samples which were cut from the fabrics were dyed with anionic dyes to ensure that the cationization process had occurred.

The Australian–New Zealand standard indicates a system of classification of protective fabrics. UPF (ultraviolet protection factor) ratings indicate how much the material reduces UV exposure. For practical purposes UPF is used for rating the protection given by clothing. A UPF value of 15– 24 is classified as good protection, 25–39 as very good protection and above 40 as excellent protection against solar UV radiation.

2.4. Nanoparticle multilayer formation

2.5.5. Air permeability measurement. A TexTest Instruments FX 3300 Air Permeability Tester III instrument was used to obtain the air permeability values of the untreated and nanoTiO2 coated cotton fabrics at 100 Pa pressure according to the EN ISO 9237 standard.

For the multilayer deposition process, polypropylene transport trays (20 cm × 30 cm) were used. In the deposition process, the positively charged cotton fabrics were immersed into the following solutions alternately for 5 min periods: (a) the anionic TiO2 colloid solution; (b) the deionized water; (c) the cationic TiO2 colloid solution; (d) the deionized water. This deposition cycle was repeated until 10- and 16-layer TiO2 /TiO2 films were deposited on cotton fibers. Multilayer film coated cotton fabrics were dried at 60 ◦ C and cured at 130 ◦ C for 3 min.

2.5.6. Whiteness value measurement. A Minolta 3600d spectrophotometer was used to obtain the whiteness values of the untreated, cationized and nano-TiO2 coated cotton fabrics as the Stensby index using a D 65 light source to examine the LbL process effect on the yellowing properties of the fabrics. 2.5.7. Tensile strength measurement. The mechanical tests were performed on a Lloyd LR5K Plus electronic tensile strength machine according to the EN ISO 2062 Standard. The breaking strength and elongation of warp and weft yarns at fracture were tested in this work. Twenty samples were used for each test and the test results were evaluated with the SPSS 16.0 statistical analysis program.

2.5. Characterization of nano-TiO2 deposited cotton fabrics 2.5.1. Fourier transform infrared attenuated total reflectance (FTIR–ATR) measurements. A Bruker IFS 66/S FTIR spectrometer was used to obtain the infrared spectra of surfaces using an ATR sampler. The spectra were taken over a wavenumber range of 4000–400 cm−1 with a resolution of 2 cm−1 at room conditions.

2.5.8. Self-cleaning properties. The photocatalytic activity of the nano-TiO2 coated cotton fabrics was determined by a UV box with dimensions 45 cm × 45 cm × 60 cm. Cotton fabrics were cut into 5 cm × 5 cm samples and labeled. The red wine stains were introduced onto the cotton fabric using a micro-syringe with 50 μl of neat red wine (grape wine containing 10% alcohol). Fabric samples were placed in the box and kept for 72 h under specific UV irradiation (Philips TUW series UV-C lamp, 18 W, 254 nm wavelength, voltage 60 V, UVC radiation Wuv-c 5,0, lamp current 0.37 A) with air ventilation. The distance between the fabric samples and UV lamps in the box was 40 cm. The fabrics’ self-cleaning properties were determined according to the discoloration change of the treated and untreated fabrics [33].

2.5.2. X-ray photoelectron spectroscopy (XPS) measurements. XPS measurements were conducted using a SPECS spectrometer with an Mg source and a spherical mirror analyzer working in spectrum mode. The total pressure in the main vacuum chamber during analysis was typically 4 × 10−7 Torr. The chemical elements present on the samples were identified from survey spectra. Survey scans were of the spectrum type with an Mg Kα reference. The survey scans started at 1100 eV and ended at 0.80 eV, taking 0.40 eV steps with a dwell time of 0.30 ms. High resolution scans were performed around peaks of interest. 2.5.3. Scanning electron microscopy (SEM-EDS). A QUANTA 400F field emission high resolution scanning electron microscope (SEM) equipped with an energy dispersive spectroscopic (EDS) microanalysis system was used to examine the surfaces of woven cotton samples at an acceleration voltage of 10 kV. The cotton fabric samples were coated with 10 nm Au/Pd prior to SEM observation.

2.5.9. Washing procedure. Functional properties of nanoTiO2 coated cotton fabrics such as self-cleaning and UVprotective functions were analyzed after the LbL process. To determine the durability of these functional properties, cotton fabric samples were washed 10 and 20 times at 40 ◦ C for 30 min with a Gyrowash laboratory type washing machine. The Gyrowash washing speed was 40 rpm. The multilayered fabric samples were subjected to laundering according to the EN ISO 20105-C01 standard test method, and AATCC standard ECE detergent without optical brighteners was used throughout the laundering cycles. A solution of detergent was prepared with a concentration of 5 g l−1 . Then, the sample was introduced into the laundry solution bath with a volume of 125 ml. When a cycle was finished, samples were washing twice with deionized water for 1 min.

2.5.4. UV penetration and protection measurement. The ability of a fabric to block UV light is given by the ultraviolet protection factor (UPF) values. A UV Penetration and Protection Measurement Systems Camspec M350 UV– visible spectrophotometer (SDL/ATLAS) was used to obtain the UPF value of the multilayered cotton fabrics according to Australian–New Zealand Standard AS/NZS 4399:1996. 3


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Figure 1. XPS spectra for cationically charged woven cotton fabric.

Figure 2. XPS spectra for cationically charged woven cotton fabrics supporting 10 and 16 self-assembled layers of nano-TiO2 .

nanoparticle film supported cationized cotton fabric. TiO2 nanoparticles can be clearly seen on the fiber surfaces. Figure 4 shows SEM images of 16-layer TiO2 nanoparticle film supported cationized cotton fabric. The surface of the cotton fibers appears to be covered by TiO2 nanoparticles, and with the increase in the number of layers the nanoparticle density increases too. The crystalline phase of anatase TiO2 remained unchanged in the resultant TiO2 film coated cotton fibers, and nano-TiO2 film coated fibers showed rough surfaces with grains due to the deposition of aggregated TiO2 particles. SEM–EDS analysis was also performed to verify the elemental composition of the deposited TiO2 nanoparticles on the fiber surfaces. Figure 5 shows EDS survey spectra of 10- and 16-layer TiO2 nanoparticle film supported cationized cotton fabric substrates. The titanium amount is determined as 16.05% for 10-layer TiO2 nanoparticle film supported cationized cotton fabric and 18.68% for 16-layer TiO2 nanoparticle film supported cationized cotton fabric on the

3. Results and discussion X-ray photoelectron spectroscopy was used to examine the surfaces of the woven cotton samples. Figure 1 illustrates a survey spectrum of a cationized woven cotton fabric. As expected, distinctive peaks at 283.95 and 530.11 eV indicate the presence of carbon and oxygen, respectively. A trace amount of N, generated during the cationization process, was also detected at 399.6 eV. Figure 2 shows a survey spectrum of 10- and 16-layer TiO2 nanoparticle film supported cationized cotton fabric substrates. Distinctive peaks at 283.95, 461.7 and 530.11 eV indicate the presence of carbon, titanium and oxygen, respectively. With the LbL deposition process the titanium peak shows increase in intensity with increase in layer number. Scanning electron microscopy was used to verify the presence of the deposited nanolayers on cationized cotton fabrics. Figure 3 shows SEM images of 10-layer TiO2 4


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Figure 3. SEM images of cotton fabric coated with 10-layer nano-TiO2 .

Figure 4. SEM images of cotton fabric coated with 16-layer nano-TiO2 .

1.00

2.00

3.00

4.00

5.00

6.00

1.00

2.00

3.00

4.00

5.00

6.00

Figure 5. EDS spectra of (a) 10-layer TiO2 deposited cotton fabrics and (b) 16-layer TiO2 deposited cotton fabrics.

surface of the cotton fabrics. With the LbL deposition process the titanium peak shows an increase in intensity with an increase in layer number, similar to the XPS spectra. A trace amount of N and Cl generated during the cationization process was also detected in the EDS spectra of both multilayer TiO2 nanoparticle deposited fabrics. The FTIR–ATR spectra of untreated, 10-layer and 16layer nano-TiO2 deposited cotton fabrics are shown in figure 6. The untreated cotton fabric exhibited a number of FTIR spectra absorption features. It can be seen that nano-TiO2 deposited cotton fabrics maintained the FTIR features of untreated cotton fabric. For all samples a broad band between 3100 and 3700 cm−1 centered around 3360 cm−1 illustrated characteristics of OH functional groups in cellulose. With the LbL deposition process this band shows an increase in intensity as the number of layers deposited increases, suggesting that

the hydroxyl functional groups were occupied with TiO2 nanoparticles. A strong adsorption band with a maximum at 1030 cm−1 is a result of the overlapping bands attributed to functional groups of cellulose, namely the C–C, C–O and C– O–C stretching vibrations. The same intensity increase is seen in this band, too. A strong absorption peak around 450 cm−1 on the 10- and 16-layer nano-TiO2 deposited cotton fabrics’ FTIR spectra can be attributed to TiO2 nanoparticles. The presence of nano-TiO2 nanoparticles on the cotton fabric after the LbL process is verified with SEM, FTIR– ATR and XPS analysis. Table 1 shows the UPF factors of nano-TiO2 deposited cotton fabrics which were obtained from UV–visible spectroscopy. The durability of the treatment to repeated home laundering was evaluated by performing 10 and 20 washing cycles at 40 ◦ C for 30 min. For fabrics with 10- and 16-layer nano-TiO2 deposited cotton fabrics the 5


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Figure 6. FTIR spectra for a untreated cotton woven fabric and cotton fabrics coated with 10- and 16-layer nano-TiO2 .

Table 2. Air permeability and whiteness values of untreated cotton fabric and cotton fabrics coated with 10- and 16-layer nano-TiO2 .

Table 1. Rated UPF values of cotton fabrics coated with 10- and 16-layer nano-TiO2 . Rated UPF

TiO2 /TiO2 10 layers TiO2 /TiO2 16 layers

After coating

After 10 washing cycles

After 20 washing cycles

50+

50+

40

50+

50+

45

Untreated fabric TiO2 /TiO2 10 layers TiO2 /TiO2 16 layers

Air permeability (m−2 s)

Whiteness value (Stensby, D 65)

56.68 34.96 31.75

85.549 73.951 70.781

Table 3. Tensile strength of yarn from the untreated cotton fabric, cotton fabrics coated with 10- and 16-layer nano-TiO2 .

UPF value is obtained as 50+. According to the AS/NZS 4399:1996 standard test method the value of UPF > 40 shows excellent protection against UV. The UPF values were maintained after 10 washing cycles, but after 20 washing cycles the UPF values decreased to 40 and 45 for 10- and 16-layer nano-TiO2 deposited cotton fabrics, respectively. By the end of 20 washing cycles, the UPF values decreased, but still they showed excellent UV protection. These results showed that layers deposited by the LbL deposition process had a good durability after washing cycles. Table 2 shows air permeability values and whiteness values according to the Stensby index of untreated and multilayered fabrics. Air permeability tests showed that with the increase in the number of layers, the air permeability values of the fabric decreased. These results verified the presence of the deposited layers on the cotton fiber. The whiteness value of the fabrics is decreased as the number of layers increases, too. Since the fabric tensile properties can be greatly affected by solution pH value changes during the LbL process alternate dipping procedures, 20 weft and warp yarns from the fabrics were selected for tensile test. Table 3 shows the tensile strength of the untreated, cationized and 10- and 16-layer nano-TiO2 deposited fabrics’ weft and warp yarns. The tensile strengths

Tensile strength Weft yarn Untreated fabric Cationized fabric TiO2 /TiO2 10 layers TiO2 /TiO2 16 layers Warp yarn Untreated fabric Cationized fabric TiO2 /TiO2 10 layers TiO2 /TiO2 16 layers

Standard Mean deviation 4.12 4.22 4.39 3.69 5.05 4.58 4.11 4.97

0.87 0.62 0.79 0.38 0.69 0.66 0.78 0.48

Sig. 0.016a

0.000a

a

Mean values are statistically significantly different with significance < 0.05 in the tensile strength between the control and treated yarns.

decreased statistically with cationization and LbL deposition process. Figure 7 shows the aspect of a red wine stain on 10and 16-layer nano-TiO2 cotton fabrics before and after 72 h Suntest visible light irradiation. In both cases for all samples, a partial discoloration induced by light can be observed. This means that wine stains are partially degraded on the nanoTiO2 deposited surfaces and will be more inclined to react to detergents during household washing. 6


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Figure 7. Discoloration of red wine stains on the samples before irradiation and after 72 h Suntest irradiation.

them useful in applications such as multifunctional or technical textiles. The durability of the nanocomposite films after washing cycles validates the feasibility of using the LbL deposition process to develop potentially multifunctional textiles for protective clothing and technical textiles.

4. Conclusions In conclusion, we have demonstrated and characterized the possible deposition of an anatase TiO2 nanoparticle assembly onto woven cotton fabrics. Pre-treatment of the cotton samples with 2,3-epoxypropyltrimethylammonium chloride was proven to be an effective procedure to create cationic charges on the fibers to initiate the multilayer assembly of nanoparticles. FTIR–ATR, XPS and SEM–EDS verified the presence of the nanocomposite multilayer films on the cotton fibers. The crystalline phase of anatase TiO2 was retained in the resultant nanocomposite multilayer film coated fibers. The fabrics coated with the TiO2 nanoparticles exhibit attractive UVprotection and self-cleaning properties, which could render

Acknowledgments This research work has been supported by research grants from Süleyman Demirel University Scientific Research Project 1814-D-09. We would like to acknowledge Department of Textile Engineering and the Department of Metallurgy and Material Engineering of Dokuz Eylül University for their technical support. 7


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