Antibacterial Activities and UV Protection of the in Situ Synthesized

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Antibacterial activities and UV-protection of the in-situ synthesized titanium oxide nanoparticles on cotton fabrics Mehrez El-naggar, Tharwat I. Shaheen, Saad Zaghloul, Mohamed Hussein El-Rafie, and Ali Ali Hebeish Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04315 • Publication Date (Web): 22 Feb 2016 Downloaded from http://pubs.acs.org on February 24, 2016

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Industrial & Engineering Chemistry Research

Antibacterial activities and UV-protection of the in-situ synthesized titanium oxide nanoparticles on cotton fabrics Mehrez E. El-Naggar, Tharwat I. Shaheen*, Saad Zaghloul, Mohamed H. Elrafie, Ali Hebeish National Research Centre, Textile Research Division, Dokki, Cairo, Egypt *Corresponding Author: Dr. Tharwat Shaheen; Email: [email protected]

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Abstract In situ synthesis of titanium oxide nanoparticles (TiO2NPs) on cotton fabrics was innovatively studied. The synthesis involved the use of titanium isopropoxide (TIP) as a source of titanium hydroxide and urea nitrate as a peptizing agent responsible for conversion of titanium hydroxide to TiO2NPs. Characterization of TiO2NPs was performed using SEM-EDX, XRD, FTIR, TEM, particle size analyzer and zeta potential. Results obtained signify the following features. TiO2NPs are deposited in the form of coating on the surface of cotton fibres. They are composed of aggregated nanoparticles with an average size dimension that does not exceed 50 nm. On the other hand, TiO2NPs - loaded cotton fabrics exhibits bacterial reduction of more than 95% which is sustainable even after 20 washing cycles; the bacterial reduction increases by increasing urea nitrate concentration used in the synthesis of TiO2NPs. Cotton fabrics coated with TiO2NPs displays excellent UV protection before and after washing.

Key words: In situ; durable; UV- protection; antibacterial, TiO2 nanoparticles; cotton.


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1. Introduction Improved qualities and functionalities of cotton fabrics are necessary for children's clothing, and medical bandage cloths 1. It is, therefore, a must to protect such clothes from harmful UV and to reduce the transmission of harmful microorganisms 2 and to diminish the spread of the secondary infections within a curative environment3. During the last few years high-performance textile materials have been prepared using nanotechnology in textile finishing and, in so doing, new properties were imparted which enhanced the added value of the finished products compared to the finishing with the traditional finishing agent 4. The structurally modified cellulose fabrics with metal

2, 5

and metal oxide

nanoparticles have some interesting properties such as antibacterial 2, UV protection6, antistatic and self-cleaning which withdrawn scientific attention . Currently, Surface coating of textiles with nano-sized particles of metal oxides has gained more importance by virtue of their specific advantages. For instance, TiO2NPs have been used to induce antibacterial 7, self-cleaning 7a, 8, UV protection 9, and flame retardant to fabrics as well as dye degradation in textile effluent

10

. Substantial deal of research has been reported for

preparation of TiO2 NPs, e.g., thermolysis 11, sol-gel 12, ultrasonic 13, solvothermal 14 and hydrothermal technique

15

in which chemical reactions can take place in aqueous or

organo-aqueous media such as isopropanol/H2O. Upon heating, the simultaneous generation of pressure has been used to prepare TiO2NPs whereby the resulted particles were annealed at suitable temperature to obtain crystalline TiO2. The annealing process at relatively high temperature would inevitably lead to particles agglomeration and hence reduction of their specific surface area 16. Daoud et al worked on the deposition of anatase TiO2NPs on the cotton fabrics at low temperature. They reported that the so coated cotton fabrics have UV protection, antibacterial performances, and self-cleaning properties17. Also, Uddin et al.



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deposited and grafted TiO2NPs on the cotton fabric by using the sol–gel method at low

temperature. They have succeeded to create self-cleaning and UV protection properties to the treated cotton fabric. Obviously, these methods involved two- successive step processes: synthesis of TiO2NPs process and coating process 17-18. During the past years, many efforts have been made to in situ deposit TiO2NPs onto cotton fabrics whose advantage is to reduce time of the finishing processes and to improving washing durability19. But using nitric acid in peptization during the preparation of TiO2NPs and finishing in one-stage process leads to textile fabric degradation. This stimulates our innovative work to use urea nitrate (UN) as a source of gradual release of HNO3 to avoid the harmful effect of the latter on the mechanical strength properties of the treated cotton fabrics. The crystal

structure of the white powder urea nitrate (UN) was demonstrated that the acidic proton is located on the carbonyl oxygen atom, revealing the basic character of the oxygen atom and the electrostatic stability of the crystal form. However UN dissociates to form a mixture of urea and nitric acid when dissolved in polar organic solvents such as dimethylsulphoxide (DMSO), acetone or iso-propanol.

Dissociation of the crystal

structure to urea and nitric acid was also a part of the degradation process. To the best of our knowledge, the only research in this field involved using urea nitrate for peptization of titanium hydroxide. The latter is formed from the hydrolysis of titanium isoppropoxide (TIP), which, in turn, converted to nanoparticles of titanium oxide. The so formed TiO2NPs are found inside as well as deposited on the surface of the cotton fabrics without any effect on the tensile strength and elongation of cotton fabrics. The current research is undertaken with a view to devise a plausible route for in situ synthesis of TiO2NPs coating onto cotton fabrics without seriously damaging the fabrics. The route comprises: 1) preparation of urea nitrate for nitric acid release; 2) hydrolysis of TIP to yield titanium hydroxide and; 3) peptization of titanium hydroxide using the nitric 4 ACS Paragon Plus Environment

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acid released from urea nitrate. Optimal conditions for the in situ synthesis of TiO2NPs coating on cotton fabric are to be established. Characterization and properties of the TiO2NPs and TiO2NPs loaded cotton fabric will be done using TEM, DLS, zeta potential, EDX-SEM, FT-IR and XRD. It is anticipated that the output of the present work will be useful in terms of cotton fabrics with well-defined TiO2NPs. Moreover, the coated fabrics display antibacterial activity and UV protection with marginal decrement in its tensile strength.

2. Materials and methods 2.1. Materials Titanium isopropoxide (TIP) was purchased from Sigma Co, USA. Urea and nitric acid were obtained from fischer Co. USA. Isopropyl alcohol was purchased from across Co, Germany. Bleached cotton fabrics was kindly supplied by EL-Nasr Company for Spinning, Weaving, and Dyeing, El-Mehalla Elkubra, Egypt. The bleached fabrics were washed with Egyptol diluated with tap water and then dried at room temperature. All chemicals are of analytical grade. For all experiments, distilled water was used.

2.2. Methods A- Preparation of urea nitrate The synthesized urea nitrate (UN) from urea was used as initiator for the gradual release of nitric acid used for hydrolysis of titanium isopropoxide (TIP) and subsequently titanium oxide nanoparticles (TiO2NPs) was formed. Before preparation and utilization of UN, safety considerations should be taken due to its explosive nature. UN was prepared as described in previous works

20

with minor modifications as follows. Nitric acid (15.9

M, 5.75 ml) was added drop-wise to a cold (15°C) urea solution (10.86 g, 0.083 mol) 5 ACS Paragon Plus Environment


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under gentle stirring. The mixed solutions were kept under magnetic stirring for 15 min. The addition of nitric acid to urea solution leads to raising the temperature to approximately 25oC and hence precipitation of white crystals powder occurs. The solution was stirred for stir 30 min. at room temperature. Finally the UN was vacuum filtered, washed with distilled water at 0 °C. The filter cake was dried under vacuum in a desiccator to yield urea nitrate (UN). B- In situ preparation of TiO2 nanoparticles loaded cotton fabrics Dissolve 4 ml of titanium isopropoxide (TIP) in 100 ml isopropanol in shaking water bath at room temperature for 30 min (bath 1). Various concentrations of urea nitrate (0.2, 0.4, 0.6 g/100) were dissolved in 100 ml of 95/5 ml of isopropanol/ distilled water mixture kept under stirring for 15 min at room temperature to insure the complete solubility of UN (bath 2). The bleached Cotton fabric samples were first immersed in the aqueous solution of TIP (bath 1) accompanied by padding to a pick up of 100% followed by drying at 80 oC for 5 min. The dried samples were then immersed in UN solution (bath 2). The treated cotton samples were rinsed with distilled water to remove any residual unreacted chemicals, dried at 80 oC /5 min then cured at 130 oC for 3min for thermo-fixation. The treated and untreated cotton fabric samples were kept at room temperature for further characterization. In addition, the washing water of the treated samples was centrifuged at 4500 rpm for 1 h. and the precipitated powder was kept for characterization.

2.3. Characterization The surface morphology of untreated and TiO2NPs coated cotton fabrics were characterized by scanning electron microscopy (SEM, JEOL 840 A). The elemental analysis of TiO2 NPs deposited on the surface of cotton fibres was characterized using 6 ACS Paragon Plus Environment

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Energy dispersive X-ray (EDX), which is an attachment to the scanning electron

microscopy (SEM). The creation of new bands for the nano-sized TiO2 deposited on the cotton fabrics sample

were

analyzed

using

FT-IR

spectra

(Perkin-Elmer

spectrum

1000

pecrophotometer). The FT-IR spectra were scanned over the wave number range of 4000–400 cm−1. The crystallinity phase of TiO2NPs loaded fabric samples was characterized by Xray diffraction (XRD, Philips PW3040 X-Ray diffractometer system). The scanning for each sample was recorded from 5° to 80° (2ɵ) at 40 keV. The morphological structure and size distribution of the TiO2NPs extracted from washing water of the treated cotton fabrics was observed throughout TEM (JEOL, JEM2010, Japan). The determination of the average particle size distribution as well as the zeta potential of the TiO2 NPs after extraction from TiO2Nps-cotton fabrics sample followed by solution extraction using centrifuge were analyzed by using Zetasizer Nano ZS (Malvern Instruments, UK). The measurement was repeated three times f or each sample. The mechanical properties was evaluated by strip method according to ASTM D 5035:2006 using universal testing machine (INSTRON 4201) at room temperature with crosshead speed of 20 mm/min. The tensile strength and elongation at auto break were measured for both untreated cotton fabrics and those treated at different concentrations of UN and TIP. The samples were cut into strips of 5 cm width and 20 cm length and every data point is the average of three measurements. The antibacterial properties of the treated cotton fabrics were evaluated according to an American Association of Textile Chemist and Colorists (AATCC) test method 100– 2004. Two bacteria, gram-positive bacteria, Staphylococcus aurous, abbreviated as (S. 7 ACS Paragon Plus Environment


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aurous) and gram-negative bacteria, Escherichia coli abbreviated as (E. coli), as were used. 10 µg of cotton fabrics treated with TiO2 NPs was added to a tube containing 5 ml of freshly prepared brain heart infusion broth BHIB, (HiMedia, India) which is inoculated with the nominated bacteria (1.6 x 105/ mL). The tubes were incubated at 37oC for 24 h in the presence of light source. The turbidity of the test tubes was compared visually to control, BHIB tube. Each tube was diluted and fractions were plated on Nutrient Agar plates and incubated at 37oC for 24 h. Colony forming units/ml was calculated by multiplying the number of colonies by the dilution factor. Antibacterial activities was expressed in terms of the percentage reduction of the microorganisms and calculated by (Equation 1).

Bacterial Reduction R% =

− × 100 .

Where A and B are the number of microorganisms colonies on untreated and treated cotton fabrics, respectively.

The UV transmission spectra of TiO2NPs coated cotton fabrics sample were measured by making use of UV/Vis spectrophotometer (Perkin, Elmer Lambda 3B UV-Vis spectrometer). UPF values were automatically calculated on the basis of the recorded using a Startek UV fabric protection application software version 3.0 (Startek Technology).


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3. Results and discussion Urea nitrate (UN) is crystalline compound of carbon, hydrogen, oxygen and nitrogen with the chemical formula (NH2) 2 CO-HNO3. UN is synthesized by the reaction of urea with nitric acid (Equation 2) which is soluble in water. OH+ O

O NH2 C NH2 HNO3 (aq. sol.)

Low temperature

-

NH2 C NH2

O+

N

Eq. 2

(aq. sol.)

O Urea

Urea Nitrate

On the other hand, the decomposition of urea nitrate at high temperature below its melting point produces urea and nitric acid as illustrated in Equation 3.

OH+ O NH2 C NH2

-

O-

O NH2 C NH2 HNO3

Heat

+

N

Eq. 3

O

The in situTiO2NPs-coated cotton fabrics was obtained by in situ deposition of the synthesized TiO2 NPs onto the cotton fabrics via (1) the hydrolysis of titanium isopropoxide (TIP) using iso-propanol was displayed in Equation 4. (2) Peptization using gradual release of nitric acid which is formed by the reaction of titanium hydroxide and UN (Equation 5). The oxolation bonds between ≡Ti–O–Ti≡ breaks easily due to the pepization effect of the released HNO3 and promote the formation of TiO2NPs with different shape (rutile/anatase/mixture of both) after structural rearrangements. Ti (OC3H7)4 Ti (OH)4

4

H2O

Hydrolysis

Peptization

2Ti

TiO2 nH2O

(OH)4

4

(C3H7OH)

drying curing

TiO2 NPs

Eq. 4 Eq. 5



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According to the above equations, controlled release of nitric acid has the ability to peptize TIP molecules to TiO2NPs.

The large surface area and a number of hydrophilic groups of the cotton macromolecules provide more active sites for the deposition of TiO2 than generally supporting materials. The challenge here is to control the release of nitric acid from urea nitrate, which can act as peptizing agent. The peptizing agent can accelerate the degradation of cellulose chains beside peptization of TIP while it is directly in contact with the fabrics.

3.1. XRD of TiO2 NPs coated cotton fabrics The crystalline phases of TiO2NPs with different concentrations (based on the concentration of UN) on the surface of cotton fabrics have been characterized by making use of X-ray diffraction (XRD) using Cu radiation as presented in Figure 1. As shown in Figure 1, the outlined peaks at 14.8°, 16.6°,

22.7° as well as peak at 34.4 ° are

consistent with the diffraction pattern of the reference cotton cellulose I 5a.


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Figure 1: XRD of untreated and treated cotton fabrics with TiO2 NPs based on different concentration of UN, A) untreated, T1) treated cotton fabric with 0.2 g, T2) treated cotton fabric with 0.4 g and T3) treated cotton fabric with 0.6 g of UN.

More importantly, a relatively strong reflection peaks at 27.56° and 40.44°, 43.33°, 65.88 ° and 87.42 are corresponding to TiO2NPs as shown in figure 1(T1). It was observed that there is minor shift for the as said peak with increasing the concentration of TiO2 NPs as shown in figure 1 (T2 and T3). The observed TiO2 NPs Peaks are in good agreement with that of literature elsewhere

21

. The prepared TiO2NPs could be well indexed to rutile phase (JCPDS no.

65-0191), the intense diffraction peaks appearing for TiO2NPs are corresponding with those from (110), (101), (111), (211), and (220) orientation respectively.

3.2. FT-IR studies of untreated and TiO2NPs treated cotton fabrics



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The FT-IR spectra of the cotton fibres before and after treatment with TiO2 were monitored using FT-IR spectroscopy as shown in figure 2. This was done to ascertain whether IR spectroscopy could be a good tool for tracing the presence of TiO2NPs located on the external surface of the cotton fibres along with any degradation of the cotton fibres caused by the presence of the TiO2 photoactive phase. It is observed from figure 2 that the presence of a broad peak centered at 3300 cm-1 is due to O–H stretching. Also the broad peak at 2900 cm-1 region is attributed to C–H stretching. Although cellulose has – CH2 – groups in their structure, the peaks corresponding to the symmetric and asymmetric stretching modes have never been separated as sharp peaks. A peak around 1640 cm-1 is due to the adsorbed water molecules.

Figure 2: FT-IR of (B) untreated and treated cotton fabrics with TiO2 NPs using different conc. of UN; T1 (0.2 g UN), T2 (0.4 g UN) and T3 (0.6 g UN).

FTIR of The cotton fabrics treated with different concentrations of UN nominated (T1, T2 and T3) are shown in figure 2. It was Known that the peaks at range from 436 to 465 cm-1 are assigned for Titanium. Typically, there are distinct peaks at 436, 447 and 465 for T1, T2 and T3 respectively, and a peak around 960 cm-1 observed in TiO2 sample corresponds to O-Ti-O bonding. 12 ACS Paragon Plus Environment

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Ti-O and O-Ti-O- flexion vibration give rise to the broad absorption bands at 400 cm1

and 800 cm-1 and peaks at 1450 cm-1 show stretching vibrations of Ti-O-Ti. The band

centered at 1610 cm-1 is characteristic of δH2O bending. The vibration bands between 1300 cm-1 and 4000 cm-1 can be attributed to the chemisorption and/or physisorption of H2O and CO2 molecules on the surface of the compound. So from the obtained data, it is concluded that FT-IR of untreated cotton fabrics did not show any peaks at 436 to 465 cm-1, which confirms the presence of TiO2NPs in the treated samples.

3.3. Scanning electron Microscopy (SEM) and Energy dispersive-X-Ray

(EDX) of TiO2 NPs coated cotton fabrics Typical SEM images of the cotton samples before and after treatment with TiO2NPs are shown in figure 3. It is clearly seen that the surface of the untreated cotton fiber is very smooth to the touch as shown in figure 3 A. The treated cotton fibers provide a change in their morphological structure as shown in figure 3(T1, T2 and T3). Hereby, the cotton fiber surface becomes somewhat rough and uneven indicating that TiO2NPs, are successfully deposited on the fiber surface. This, indeed, proves that the TiO2NPs are loaded on the cotton fiber.



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Figure 3: SEM of (A) Untreated cotton fabric , TiO2 NPs Treated cotton fabrics using (T1) 0.2 g of UN, (T2) 0.4 g of UN and (T3) 0.6 g of UN, (e) EDX and (f) elemental contents of TIO2NPs treated cotton fabrics for figure 1 d.

As is evident from figure 3, the surface coating exhibits a compact coating with a number of small TiO2 clusters. The number of particle increases with increasing the concentration of TiO2NPs due to increasing the concentration of UN, which has the ability to make hydrolysis of TIP. Energy dispersive X-ray spectrometer (EDX) was employed to examine the crucial information regarding the chemical composition of the TiO2NPs coated cotton fabrics. The EDX of nanoparticles deposited onto cotton fabrics when UN concentration of 0.6 is shown in figure 3e. The elemental analysis of C, O, and Ti were found in the EDX spectrum confirming that, there is a Ti layer coating onto the surface of cotton fabrics. As shown previously in fig. 1, XRD patterns confirm that the source of Ti 14 ACS Paragon Plus Environment

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isTiO2NPs. The element of gold (Au) is coming from the coating layer used for the EDX measurement and C element is from the cotton substrate. The weight percentages of C, O and Ti of TiO2NPs loaded cotton fabric (T3) a particular region are 35.55, 30.56 and 4.35, respectively (Table, in inset figure 3f). In addition, the resulting spectrum indicates that the nanoparticles are essentially TiO2 with no indication of contamination. In addition there is no nitrogen element, which confirmed that the released HNO3 is consumed in the hydrolysis of TIP onto cotton fabrics and the rest is removed by washing with distilled water.

3.4. Surface shape, particle size and zeta potential of TiO2NPs extracted from treated cotton fabrics For more details about the morphological structure of TiO2NPs, the cotton fabric samples coated with TiO2NPs were washed with distilled water several times to remove the weakly adsorbed TiO2NPs on the surface of fabrics. The obtained solutions were centrifuged for 1 h. at 4500 rpm in order to precipitate the unreactedTiO2NPs powder. The resultant white powder was then washed with distilled water and dried at 160 °C for 120 min. The obtained washing water that contains the residual TiO2NPs was centrifuged at 4500 rpm for 1 h. The dried powder was diluted with distilled water and characterized using TEM, particle size analyzer as well as zeta potential to confirm the successful formation of TiO2NPs on the surface of fabrics. Figure 4 shows typical TEM image, particle size analyzer and zeta potential of TiO2NPs extracted from the washing water for TiO2NPs coated cotton fabrics (T3). The titania nanoparticles are shown to have a spherical shape and uniform size distribution.



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TEM image also reveals the presence of TiO2 NPs with a few aggregations. However the aggregated particle is very small and does not exceed 50 nm in its cluster form.

Figure 4: (a) TEM, (b) Particle size analyzer and (c) zeta potential of the extracted TiO2NPs from the washed TiO2NPs coated cotton fabrics Figure 4b illustrated the particle size distribution of TiO2NPs. It is seen that the majority of particle size is around 100 nm. The difference in size between TEM and DLS may be due to the aggregation of TiO2NPs in the aqueous solution in the case of DLS technique while no aggregation can be occurred in the case of TEM (the samples are measured in dry state). Particle size obtained from DLS occurs in a solution form, so the nanoparticles may be swelled with time while measuring.

Zeta potential of the 16

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precipitated TiO2NPs after dilution is depicted in figure 4c. The value of zeta potential for TiO2NPs is -31.2 mv. The resulted value illustrated the good stability of TiO2NPs without noticeable aggregation.

3.5. Mechanical properties of TiO2 NPs loaded cotton fabrics The conventional treatments of cotton fabrics with TiO2NPs lead to damage of the structure of cotton due to the cleavage of cellulosic chains. That is why the mechanical properties of untreated and treated cotton fabric samples were measured in order to clarify the effect of nitric acid released from UN during the peptization of TIP. Measured properties were the elongation at auto break and tensile strength for the fabrics before and after treatments. Table 1 shows the mechanical properties of untreated and treated samples with different concentrations of UN. It is observed that the untreated sample has elongation around 11 mm and tensile strength of 82.328 kgF. After treatment with UN and TIP followed by drying and curing, the elongation and tensile strength marginally decreases and reaches 10.5 mm and 74.761 kgF respectively. That is, the treatment causes a loss in the elongation at break by 4% and tensile strength by about 9%. Both losses are practically acceptable. Increasing the concentration of UN leads to further decrease in the elongation at break and tensile strength of the material but such a decrement is still acceptable from practical point of view. By and large in situ synthesis of TiO2NPs within the structure of cotton - as verified by current results - does not significantly damage the strength properties of cotton.



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Table 1: Mechanical Properties of TiO2NPs treated cotton fabrics at different concentrations of UN

Sample

Elongation at Auto Break Tensile Strength (KgF) (mm)

Blank

11± 4

82.328± 7

T1

10.5± 3

74.761 ± 5

T2

9.5± 2

73.597± 7

T3

9.25± 2

71.249± 6

1.1. Antibacterial Activities of Nano-TiO2 Loaded Cotton Fabric

The antibacterial activity was determined by colony forming units (CFU) with time intervals. Table 1 shows the antibacterial activity of gram-positive bacteria (S.

aureus) and gram-negative bacteria (E. coli) for untreated and treated TiO2NPs cotton fabrics. The zero reduction of untreated cotton fabric against bacteria is attributed to the absence of any antibacterial agent in the structure or on the surface of the untreated cotton. But cotton fabrics treated with TiO2NPs nominated T1, T2 and T3 have excellent bacterial reduction. The treated fabrics (T1) showed 95.5% and 95.42% for S. aurous and

E. coli respectively. While the activity of the treated cotton fabrics against S. aurous and E. coli when the concentration of UN was 0.4 g (T2) showed 97.2 and 96.77 respectively. The bacterial reduction of treated fabrics with 0.6 g UN have the maximum and showed 99.4 and 99.37 for S. aurous and E. coli. It is clear from the data (table 2) that the effect of antibacterial activity of fabrics increases with TiO2NPs coatings and follow the order T3 >T2>T1. 18 ACS Paragon Plus Environment

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Table 2: Bacterial reduction percent of TiO2NPs treated cotton fabrics at different concentrations of UN

Sample

Reduction %

Reduction %

S. aurous

E. coli

Blank

0

0

T1

95.5

95.42

T2

97.2

96.77

T3

99.4

99.37

The great antibacterial of TiO2NPs coated cotton fabrics is could be associated with the photocatalytic effect to that the TiO2NPs. When exposed to light, photons with energy equal to or greater than the band gap of the titanium dioxide excite electrons up to the conduction band. The excited electrons within the crystal structure react with oxygen atoms in the air, creating free-radical oxygen. These oxygen atoms are powerful oxidizing agents, which can break down the cell wall of microorganisms through oxidationreduction reactions [42].



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1.2.Durability of Nano-TiO2 Loaded Cotton Fabric against Washing Cycles

Cotton fabrics treated with TiO2 NPs prepared using UN at a concentration of 0.6 g / 100 ml was selected for further characterization against bacteria before and after washing cycles. To examine the durability to wash, and as the textile items are washed many times during the life, the treated fabric samples were subjected to, 1, 10, and 20 wash cycles in home laundering machine and subjected to UPF and antibacterial activity tests according to the above mentioned testing methods. The washing durability of antibacterial activity of the fabrics loaded with TiO2NPs were investigated according to standard method for different washing times. Typically, samples were cut into 5 cm × 10 cm swatches and put into a stainless cup at 50 0C for various washing time to simulate 5,10, 15 and 20 wash cycles of home/commercial launderings.

Table 3 clarifies that the bacterial reduction % highly correlates with the number of repeated washing cycles. It is also certain that, the bacterial reduction % of the samples exhibits marginal decrease upon increasing the washing cycles. The bacterial reduction % after twenty washing cycles reaches above 92 and 89 % for S. aurous and E. coli respectively, which is still bearing a good antibacterial activity toward two pathogenic bacteria.

Table 3: Bacterial reduction of TiO2 NPs loaded cotton fabrics at different concentrations of UN after repeated washing

Sample

Reduction %

Reduction %

S. aurous

E. coli


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T3 (5 washing)

97.6

96.05

T3 (10 washing)

95.5

94.23

T3 (20 washing)

92.87

89.4

Based on the above, it is suggested that TiO2NPs have great affinity toward hydroxyl and carboxyl groups. The physical linkages between the hydroxyl groups of cotton and TiO2 NPs systems play the main role in producing a durable loading of TiO2NPs on the fabric surfaces.

1.3. UV-Protection of TiO2NPs treated Cotton fabrics

The UV-protection effect of cotton fabrics treated with TiO2NPs using different concentrations of UN and constant concentration of TIP was measured and results obtained are shown in table 4. The results obtained in terms of the absorption characteristics, which expressed as UPF values are summarized along with the effect of washing cycles of cotton fabrics coated with TiO2NPs on the UPF values. All samples were exposed to 5 and 15 washing cycles (40 °C, 20 min, washing agent 1 g/l) before the UV absorption was investigated. The results shown in table 4 are the average of measured triplicate for each sample.

Table 4: UPF of cotton fabrics treated with different concentrations of UN and constant concentration of TIP

SampleUPF protection Value T1

27.7

Very good

UPF after 5 washes UPF after 15 washes 25.8

Good

22.68

good



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T2

38.19

Excellent

32.5

Very good

25.48

good

T3

42.11

Excellent

35.2

Very good

29.69

Very good

It is seen from the table 4 that, by increasing the concentration of UN /TIP ratio which gradually increases from T1 then T2 and Then T3, the UPF values increase indicating an excellent UV protection property of the treated fabrics. Furthermore, the UPF value recorded from T3 is significantly greater than that of T2 and T1, which could be attributed to magnitude peptization occurred on using high concentration of UN (T3). Consequently, increasing the amount of TiO2NPs deposited on the surface of cotton fibers. Reasonable decrease in UPF values is observed gradually along with washing cycles of the treated cotton fabrics up to 15 cycles. However, by, decreasing the UPF values of the washed samples, the UV protection is still very good at concentration T3 after 15 washing cycles. This together with the results discussed above would imply that our discovery presents an effective route to prepare TiO2 nanoparticles in situ on cotton fabrics in order to impart to cotton fabric anti-bacterial and UV protection properties with high durability. It is as well to note that the ability of TiO2NPs to provide protection against UV is a manifestation of TiO2NPs large surface area per unit mass and volume and leading to effective UV blocking radiation; so the cotton fabric treated with TiO2NPs provide excellent UV protection beside imparting antibacterial activity.

4. Conclusions


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Titanium oxide nanoparticles (TiO2NPs) was synthesized in situ on cotton fabrics using titanium isopropoxide (TIP) as precursor and urea nitrate (UN) as peptizing agent for the first time. The release nitric of acid from urea nitrate has the ability to produce TiO2NPs deposited on the surface of the cotton fabrics. Increasing UN concentration increases the amount of nanoparticles deposited on the surface. Surface morphology and elemental contents of TiO2NPs coated cotton fabrics using SEM-EDX confirmed the presence of TiO2NPs on the cotton fiber. XRD proved the formation of TiO2NPs in crystal phase. TiO2NPs loaded cotton fibers were composed of the aggregated particles with an average dimension, which does not exceed 50 nm. FT-IR indicates that new peaks are created for TiO2NPs. TEM, particle size analyzer and zeta potential of the extracted TiO2NPs from the coated cotton fabrics demonstrated the presence of these nanoparticles in spherical shape with small size as well as good stabilization. The treated fabrics give excellent bacterial reduction with values exceed 95 %. The bacterial reduction increased with increasing UN concentration. Furthermore the bacterial reduction is excellent for TiO2NPs deposited cotton fabrics even after 20 washing cycles. In addition, this treatment imparted an excellent UV protection to the cotton fabric before and after washing which could render them useful in applications such as multifunctional textiles. Finally, the method of synthesis had no much influence on the strength properties of the treated fabric. This together with the other results would call for the appropriateness of the devised method.



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