Titanium dioxide nanoparticle was synthesized by the reduction of titanium tetrachloride using borohydride, water as solvent, and polyvinyl-pyrrolidone as stabilizer. The average size of nano-TiO
2 is estimated to be 5 - 10 nm using a transmission electron microscope (TEM); this was confirmed by X-ray diffraction and UV-Vis spectroscopy. Nano-TiO
2 was impregnated into cotton fabric to impart multifunctional properties and this was confirmed by scanning electron microscope and scanning electron microscope coupled with high energy distribution X-Ray (SEM-EDX). The TiO
2 nanoparticles loaded cotton fabrics showed excellent antibacterial activity against two representative bacteria, Staphylococcus aureus (Gram positive) 96.6% and Klebsiella pneumonia (Gram negative) 95.2%. Also, TiO
2 nanoparticles enhanced the self-cleaning and the protection of cotton fabrics against UV radiation in comparison with the untreated cotton fabrics. The TiO
2 nanoparticles were durable in-situ cotton fabrics even after 20 laundering wash cycles.
Nanotechnology has gained increasing worldwide consideration because of offering huge benefits in a wide range of end utilities. The distinctive and new properties of nanomaterials have attracted not only scientists and researchers but also businesses community, due to their vast economical prospective. Utilization of nanotechnology in the textile industry has enormously increased due to its exclusive and important properties.
The first work on nanotechnology in textiles was carried out by Nano-Tex, a supplementary of the US-based Burlington Industries [1]. One of the common techniques used to apply nano-particles onto textiles is coating. The coating material applied to the surface of textiles is mostly composed of nano-particles, a surfactant, ingredients and a carrier medium [2]. Numerous methods can be used for coating onto fabrics, including spraying, transfer printing, washing, rinsing and padding. Of these methods, padding is the most generally used [3,4]. The nano-particles are attached to the fabrics by using a padder adjusted to an appropriate pressure and speed, followed by drying and curing. The properties imparted to textiles using nanotechnology include water repellence, soil resistance, wrinkle resistance, anti-bacterial, antistatic and UV-protection, flame retardation, enhancement of dye ability and many others. Nanotechnology also improves the water-repellent property of the fabric by creating nano-whiskers, which are hydrocarbons and 1/1000 of the size of a typical cotton fibre, that are added to the fabric to generate a peach fuzz effect without lowering the strength of cotton. The spaces between the whiskers on the fabric are smaller than the typical drop of water, but still larger than water molecules; water thus remains on the top of the whiskers and above the surface of the fabric [1,5,6]. However, liquid can still pass through the fabric, if pressure is applied. The application is permanent while maintaining breathability [1]. On the other hand, a hydrophobic property can be imparted to a cotton fabric by coating it with a thin nanoparticulate plasma film [7]. Furthermore, inorganic UV blockers are more preferable than the organic UV blockers as they are non-toxic and chemically stable under exposure to both high temperatures and UV. Inorganic UV blockers such as TiO2, SiO2 and Al2O3 [3,8-12] are frequently used. Various research activities for the UV-blocking treatment to fabric using nanotechnology have been conducted [3,13]. UV-blocking treatment for cotton fabrics was developed using the sol-gel method. A thin layer of titanium dioxide is formed on the surface of the treated cotton fabric which provides excellent UV-protection; the effect can be maintained after 50 home launderings [14]. In addition, the widespread applications of nano-TiO2
has two key advantages, (a) TiO2 is essential functional oxides, exhibiting excellent photo-catalytic activity [3, 8-10]. (b) TiO2 is bio-safe and biocompatible [15], and can be used for biomedical applications [16]. With these unique characteristics, TiO2 could be one of the most important nanomaterials in future applications. Titanium dioxide is a photocatalyst [10], during the reaction, the photocatalyst is able to decompose common organic matters in the air such as odour molecules, bacteria and viruses [17-25]. Titania (TiO2) has three main polymorphs viz. anatase, rutile and brookite. Among these three kinds of crystal structure of TiO2, anatase TiO2 fine particles are the most active for photo-catalysis [26]. Titanium dioxide is widely used in different areas because of their unique photo-catalytic, electrical, electronic, optical, dermatological, and antibacterial properties [12,27- 33]. For these applications, the nanoparticles need to be dispersed homogeneously in the different matrices, and a number of new synthetic strategies have been developed in order to prevent particles agglomeration, and increase the stability of TiO2 nanoparticles dispersions [34-38].
The main objective of this paper is to prepare and characterize the titanium dioxide nanoparticles and its application on woven cotton fabrics to impart multifunctional properties.
2. Experimental Methods2.1. Materials
Full bleached and scoured 100% woven cotton fabric 130 g/m2, sodium borohydride (Aldrich CO), and polyvinylpyrrolidone (PVP) (Mwt = 10.000) as stabilizer (Sigma CO), titanium tetrachloride (Aldrich CO) and acrylic binder (Texacryl binder SLN). All laboratory chemicals used were of analytical grade.
2.2. TiO<sub>2</sub> Nanoparticles Preparation
Titanium nanoparticle was synthesized by the reduction of titanium tetrachloride using borohydride, water as solvent, and polyvinyl-pyrrolidone as stabilizer according to the reported method [39] as follow; 50 ml of TiCl4 was gradually added to the 200 ml distilled water in an ice cool bath containing 4.5 wt% of polyvinylpyrrolidone. The beaker was removed from the ice bath and was kept in magnetic stirrer to make a homogeneous solution for 30 min at room temperature. 50 ml of sodium borohydrate (5 gm in 100 ml distilled water) was added to the beaker drop by drop touching the walls of the beaker under constant stirring for 1 h. The solution turned into white colloid without any precipitation. After the complete reaction the solution was allowed to settle and was washed with distilled water for 5 times.
2.3. Characterization of TiO<sub>2</sub> Nanoparticles2.3.1. Transmission Electron Microscopy (TEM)
The shape and size of the particles were obtained through TEM, using a Philips EM201C apparatus operating at 80 kV. The samples for TEM measurements were placed on carbon-coated copper grids. The samples for TEM measurements were prepared from much diluted dispersions of the particles in 2-propanol.
2.3.2. X-Ray Diffraction (XRD)
The crystalline phase on prepared nano-TiO2 was determined using XRD diffraction with D/max-IV diffractometer with Cu Kα radiation (l = 1.5418 Å). The sample was scanned from 10˚ to 80˚ (2q). The crystallite domain size (D) was examined from the XRD peak based on the Scherrer equation [40].
2.3.3. UV-Visible Spectroscopy
UV-visible absorbance spectra of prepared TiO2 nanoparticles were obtained on UV-visible spectrophotometer using a UV-2200 (Shimadzu, Tokyo, Japan) in the range of 200 - 700 nm.
2.4. Cotton Fabric Sample Treatment
Nano-TiO2 was applied to cotton fabric sample using pad-dry-cure method. Padding solution was prepared as following; 1 g of nanoparticles was sonicated for 30 min with 98 g water and 1 g of acrylic binder. The mixture was then stirred at 4000 rpm for 1 h. The cotton fabric sample was padded in the prepared solution and then passed through a padding mangle to remove the excess solution. A 100% wet pick-up was maintained for the fabric sample. Padded fabric sample was dried for 5 min at 80˚C and then cured for 3 min at 140˚C. In order to evaluate the nanoparticles adhesion to the textile fibers, the treated fabrics were washed five times. For this purpose, laundry machine was used and the washing cycles were performed at 40˚C, using detergent without optical brighteners. Treated cotton fabric samples were characterized using scanning electron microscopy coupled with an energy dispersive X-ray and evaluated for antibacterial activity, self-cleaning as well as UV-protection.
Metal Content
The metal content expressed as mmol/100 g fabric sample was quantitatively determined by using atomic absorption spectrophotometer, Varian SpectrAA (220) with graphite furnace accessory and equipped with deuterium as background corrector. The procedure is as follows: 0.5 g of dried fabric sample was dissolved in 10 mL of cold 72% H2SO4. Taking 0.5 mL of this solution and diluting up to 25 mL using phosphate buffer solution (pH 7.6) before analysis.
2.5. Characterization of Treated Cotton Fabric Sample Using Scanning Electron Microscopy (SEM-EDX)
High resolution scanning electron microscope (SEM) equipped with an energy dispersive spectroscopic (EDX) microanalysis (type JXA-840 an electron probe microanalyzer-JOEL), 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.
The measured quantity of 3 g coffee powder was suspended in 100 distilled and heated for 5 min at 90˚C. Few drops of prepared coffee solution were introduced onto the cotton fabric sample and allowed to spread. One half of each stain on the fabric was exposed to sunlight for 12 - 48 hours while the other half was enclosed with a black paper to avoid its irradiation from sunlight. The exposed part of the stain was compared with that of the covered part for self-cleaning action. The self-cleaning action was quantified by comparing the K/S values of the exposed and the unexposed portion of the same stain. The values were calculated using UltraScan Color Measurement Spectrophotometer. The K/S value of the unexposed part of the stain was taken and the relative decrease percent in the K/S value of the exposed part was calculated using the following relation:
Self-cleaning properties were determined according to the discoloration change of the treated and untreated fabrics
2.7. 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 cotton fabric samples according to Australian-New Zealand Standard AS/NZS 4399:1996. 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.
2.8. Antibacterial Activity Measurement
Antibacterial tests for treated fabric samples were carried out with Staphylococcus aureus (ATCC No. 6538) (gram positive bacteria) and Klebsiella Pneumonia, (ATCC No. 4352) (gram negative bacteria). The Quantitative measurement was determined according to AATCC Test Method 100 - 2004. The reduction rate of bacteria by the treated fabrics is reported as R,. where R = % reduction A = the number of bacteria recovered from the inoculated treated test sample swatches in the jar incubated over 24 hours and B = the number of bacteria recovered from the inoculated treated test example swatches in the jar immediately after inoculation (at “0” contact time).
2.9. Washing Procedure
To determine the durability of nano-TiO2 treated cotton fabrics, the fabric samples were washed 10 and 30 times at 40˚C 30 min with a Gyro wash laboratory type washing machine at the speed of 40 rpm. The treated 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. Then, the samples were introduced into the laundry solution bath with a volume of 125 ml. When a cycle was finished, samples were washed twice with deionized water for 1 min.
3. Results and Discussion3.1. Characterization of TiO<sub>2</sub> Nanoparticles Using X-Ray Diffraction (XRD)
The formation of titanium dioxide nanoparticles synthesized was supported by X-ray diffraction measurements. Figure 1 shows that, XRD analysis showed seven distinct diffraction peaks at 25.3˚, 37.8˚, 47.9˚, 54.5˚, 62.8˚, 69.5˚ and 75.1˚ which indexed the planes 101, 004, 200, 105, 204, 116 and 215 respectively of the cubic face
centered titanium dioxide (JCPDS No. 21-1272). The sharp peaks and absence of unidentified peaks confirmed the crystallinity and higher purity of the prepared nanoparticles
3.2. Characterization of TiO<sub>2</sub> Nanoparticles Using TEM
In order to investigate the size of the nanoparticles, the dispersion of the nanoparticles was sonicated at 30˚C for 2 hours and the morphology of the dispersed samples was observed by TEM. As shown in Figure 2, the particle size of TiO2 was found to range between 5 - 10 nm. TEM micrographs in Figure 2 shows that, the nanoparticles analysed are very stable and no aggregation could be observed.
3.3. Characterization of Prepared Nanoparticles Loaded Fabric Sample Using UV-Visible Spectroscopy
Figure 3 shows UV-Vis absorption spectra from 220 nm to 450 nm of TiO2 nanoparticles suspension solution. Strong absorption was observed at the wavelengths lower than 270 nm. This fact indicates that the TiO2 nanoparticles suspension possesses a high ability to absorb ultraviolet light.
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. where R = % reduction A = the number of bacteria recovered from the inoculated treated test sample swatches in the jar incubated over 24 hours and B = the number of bacteria recovered from the inoculated treated test example swatches in the jar immediately after inoculation (at “0” contact time).