Nano-structured zinc oxide–cotton fibers: synthesis, characterization and applications
Zinc oxide nanoparticles were prepared and subsequently deposited onto the surface of the cotton fiber by ultrasonic irradiation. The optical, structure and morphology of the coated and un-coated cotton were examined by UV, fourier transform infrared spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscope (SEM)/Energy Dispersive X-ray analysis. XRD analysis revealed the presence of the crystalline metal oxide of hexagonal phase with an average crystallite size of 12 nm. These nanoparticles are probably physically adsorbed onto the cotton fiber surface. SEM analysis showed a distribution of ZnO nanorod assemblies of various diameters and lengths physically adsorbed onto the cotton fiber surface may take place. The ZnO-cotton fiber nano-composite were tested against Escherichia coli (gram negative) and Staphylococcus aureus (gram positive) cultures, and showed a significant antimicrobial activity.
KeywordsCotton Material Cotton Fiber Ultrasonic Irradiation Coated Cotton Coated Cotton Material
Zinc oxide (ZnO), with a wide band gap of 3.4 eV and a large exciton binding energy of 60 meV, has attracted considerable attentions and is recognized as one of the most promising semiconductor materials in electronic and photonic applications . Preparation and applications of nano metal oxide coatings onto cotton and glass substrates have received much attention in recent years due to its promising applications [2, 3, 4, 5, 6, 7, 8, 9]. There is a growing awareness of the use of antibacterial fabrics in the form of medical clothes, protective garments, and bed spreads to minimize the chance of the nosocomial infections . Nanoparticles are much more active than larger one because of their higher surface area and they display unique physical and chemical properties . Textiles coated with silver nanoparticles have become quite common . ZnO nanoparticles is very efficient in impart of antibacterial effect to fabric [13, 14], they are currently being tested as antibacterial agent against Escherichia coli (gram negative) and Staphylococcus aureus (gram positive) cultures. An important aspect of the use of ZnO as antibacterial agent is the requirement that the particles are not toxic to human cell [15, 16]. Although the exact mechanism has not yet been clearly elucidated, the suggested mechanisms include: the role of reactive oxygen species (ROS) generated on the surface of the particles  zinc ion release  and formation of H2O2  remain possibilities.
There were two general routes to impregnated ZnO nano particles onto the cotton fiber, the first route in which the prepared ZnO nano crystals, were coated onto cotton fibers simply by cure process . The second route was to use the ultrasonic irradiation as an effective method for the deposition of nano materials onto the surface of cotton fibers and other substrates [5, 18, 19, 20, 21, 22, 23, 24]. Perelshtein and others have previously used the second route to impregnated some metal oxides ricated nanoparticles onto fabricated cotton materials . In this research the ZnO nanoparticles were impregnated and deposited on/into the natural cotton fibers by irradiation of ultrasound vibrations, so many multi–applications could be addressed. In our previous article we reported the preparation of nanopartiles CuO-coated cotton composite and its application . The aim of the present research was to produce ZnO nanoparticles coated onto nature cotton fibers and to estimate its antibacterial properties against E. coli and S. aureus. ZnO nanoparticles act as antibacterial agent, while cotton act as a substrate which can be used to fabricat medical clothes. Scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) were used to reveal information about the sample, including external morphology, chemical composition, and crystalline structure and orientation of materials making up the sample. Energy dispersive X-ray (EDX) was applied to identify the atomic percentage contents of the main formulation’s elements, that has been applied in coating using EDX unit connected to the SEM microscope. Fourier transform infrared spectroscopy (FTIR) and UV–Visible spectra were used to confirm the formation of ZnO nanoparticles onto the cotton fibers.
2.1 Materials and instrumentals
Zinc sulfate, sodium hydroxide and ethanol were purchased from MERCK and used without further purification. Cotton was purchased from local market as an Egyptian cotton product. The UV spectra of ZnO were recorded on a SHIMADZU-1601 UV–VIS spectrophotometer in the range 200–800 nm. The infrared spectra for the ZnO coated materials were recorded on a SHIMADZU-1802 FTIR spectrophotometer, using KBr disk in the range 4,000–400 cm−1. Chemical analysis of the ZnO-coated cotton fibers was obtained by Energy Dispersive X-ray spectroscopy (EDX) using an Oxford on X-Max (area:20 mm2) detector installed on a Hitachi S3400N Scanning Electron Microscope (SEM). Calibration of the instrument was performed on Ti Ka at 4.509 keV. Powder X-ray diffraction (XRD) study was performed on a Bruker D8 Advance Diffractometer using Cu-Kα radiation (λ = 0.15418 nm at 45 kV and 40 mA, 0.05 step size and 60 s step time over arrange of 0° to 80°.
2.2 Coating procedure
Cotton fibers were first washed in a water bath containing 5 % of sodium dodecyl sulfate (SDS) at 40 °C for an hour. After rinsing with distilled water, the fibers were dried in vacuum at 60 °C for 24 h. The ZnO-coated cotton material were prepared as follows: 0.05 g dry cotton was first soaked into 10 ml of distilled water containing 0.12 g of ZnSO4·5H2O solution in a sonicated flask and irradiated for 10 min with Ultrasonic Senerator Model US-150 Ti-horn (20 kHz, output 10 Turning 7). 0.06 g of NaOH was added to the mixture under stirring. The mixture was then resonicated at 35–40 °C for one hour. The bath temperature was kept at a constant temperature around 40 °C. The product was then washed thoroughly several times with distilled water to remove any excess of hydroxide and dried in vacuum at 60 °C overnight. The Zinc concentration in the fiber was determined by titration method (3–4 wt%).
2.3 Antibacterial activity screening
The antimicrobial activity of cotton coated with ZnO nanoparticles was tested against gram negative and gram positive bacteria. A small piece of cotton coated with ZnO nanoparticles was added to a tube containing 5 ml of freshly prepared brain heart infusion broth BHIB, (HiMedia, India) that is inoculated with E. coli and S. aureus (these are clinical isolates were kindly provided by the Microbiology laboratory of Al-Shifa hospital). The tubes were incubated at 37 °C for 24 h. The turbidity of the test tubes was compared visually to an uninoculated (control) BHIB tube. 100 μl of each tube was diluted and fractions were plated on Nutrient Agar plates and incubated at 37 °C for 24 h. Colony forming units/ml was calculated by multiplying the number of colonies by the dilution factor.
3 Results and discussion
3.2 XRD results
Crystallite sizes calculated from the peaks
3.3 SEM and EDX results
3.4 UV–VIS and FTIR spectra
3.5 Antibacterial activity
Antibacterial activity of ZnO coated cotton against E. coli and S. aureus
ZnO coated cotton
Negative at 10−1
Negative at 10−1
ZnO nanoparticles were deposited onto cotton fibers by ultrasonic irradiation. The morphology and structure of the ZnO coated cotton fibers were examined by XRD, SEM/EDX, FTIR and UV visible spectra. XRD analysis revealed the presence of the crystalline metal oxide of hexagonal phase on the cotton fibers. SEM analysis showed that different forms of ZnO nanoparticles were developed which may be dependent on the chemical conditions; and physical environment during the growing. These materials can be used as antibacterial fabrics in the form of medical cloths, protective garments and bed spreads and other many purposes to minimize the chance of nosocomial infections. Since ZnO is used in the form of nanoparticle, it will have a very good absorption, penetration and availability. It showed a great reduction in the bacteria activity.
The authors would like to thank the French Government for the Al-maqdisi grant jointly with the Palestinian Ministry of Higher Education.
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