The Development of ZnO Nanoparticle Coated Cotton Fabrics for Antifungal and Antibacterial Applications

In the textile industry, cotton is the most popular choice among all the natural fibers due to its unique properties such as softness, affinity to skin, biodegradability, absorbency, and moisture being comfortable to wear. Zinc Oxide Nanoparticles (ZnO NPs) were produced and coated on cotton fabrics. The concentration of Zinc acetate was varied. 2-methoxy-ethanol has been used as a solvent. Using the dip coating technique, ZnO NPs have been coated on the cotton fabric in different mole concentrations. Scanning Electron Microscopy (SEM), Ultraviolet Visible (UV-VIS) spectroscopy, the antifungal and antibacterial activity of the ZnO NPs was performed on the coated fabrics. The SEM images depicted that the nanoparticles are well dispersed on the fabric at 3M concentration of ZnO solution. It was found that the UV absorbance increases with the increase of concentration up to 2M concentration and after that it decreases. It was also found that maximum antibacterial and antifungal activity is at 2M concentration.


Introduction
Due to the surface effect and quantum size effect, nanoparticles exhibit exceptional physical, chemical, optical properties from bulk materials [1] [2]. This UV radiation from the sun provide vitamin D that can contribute to bone development, the intense UV radiation can cause skin cancer, Alzheimer's diseases, inflammatory disorders, etc. which is harmful to our outdoor workers [15] [16].
Therefore, NPs are used to protect the UV rays from the sun by coating on fabrics.
Among the total fibers used in the textile industry, about 48% of cotton fibers are used around the world due to its excellent properties such as hygroscopicity, air permeability, softness, breathability, bio-degradation, regeneration, no static electricity, etc. [17] [18] [19]. It is an abundant natural renewable fiber that consists of about 88% -96% of pure cellulose [20] [21]. As cotton fabrics have a high specific surface area and have the ability to retain moisture, microorganisms can grow easily into the cotton fabric [22] [23]. To get rid of microorganisms, numerous chemical agents have been coated on the fabrics. Among these chemical agents, ZnO NPs shows strong inhibitory and antibacterial effects against Staphylococcus aureus and Escherichia coli, etc. [24]. In 2016, Shaban M et al. synthesized ZnO NPs by using the sol-gel method and coated ZnO NPs on cotton fabric via a spin coating technique. They found that ZnO NPs showed high photocatalytic activity and self-cleaning property against methyl orange dye under the sunlight and lamp illumination [25]. Becheri Alessio et al. synthesized and characterized ZnO NPs and coated on cotton and wool fabrics for UV shielding. They claimed that a significant increment of the UV absorbing activity due to coating ZnO NPs on the cotton and wool fabrics can protect our body from solar radiation [26]. Rajendra R. et al. prepared ZnO NPs and coated on cotton fabric by wet chemical method and investigated the antimicrobial property. They clearly confirmed that the ZnO NPs treated fabrics showed a better antibacterial effect than the bulk ZnO against S. aureus and E. coli [24].
In this study, the ZnO solution has been prepared by using a chemical method. Different mole concentrations (1M, 1.5M, 2M, 2.5M, and 3M) have been prepared and dip-coated on the cotton fabric for enhancing the UV-VIS spectroscopy, antifungal, and antibacterial properties. We have investigated the change of properties with varying mole concentrations. The morphological characteristic, UV-VIS spectroscopy, antifungal and antibacterial properties of ZnO Distilled water was utilized throughout the whole research work.

Washing of the Cotton Fabric
To remove the impurities such as wax and fat, the cotton fabric was washed first with water and detergent at 80˚C for 30 min.  for 2 h at 500 rpm stirring rate. Then the solutions were aged for 24 hours at room temperature before the coating process on the cotton fabric. Figure 1 shows the flowchart of the preparation of ZnO NPs.

Coating Process
In this study, dip coating has been carried out for coating ZnO solution on the cotton fabric. In this process, fabric was dipped at room temperature for 60 sec into the ZnO solution. Then it was dried at 80˚C for 30 min in a drier to get rid of the excess 2-methoxyethanol and monoethanolamine residuals in vacuum oven at 150 mbar pressure. The process was done by dip coater (TL0.01 Dip Coater, MTI Corporation, USA). The process is composed manually dipping and withdrawing at speed of 30 cm/min [26]. The dipping is a manual operation.
These coating steps were repeated for ten times and finally the dried fabrics were annealed in a furnace at 150˚C in air for 2 h [25].

Samples Characterization
The surface morphology of ZnO nanoparticle coated cotton fabrics was meas-    with the previously reported ZnO samples [27]. With the increasing concentra-  cotton fabric has absorbed the lowest UV-VIS rays. So, it can be concluded that 2.5M concentration of ZnO nanoparticle is the optimum concentration for the ZnO nano particle coated cotton fabrics to absorb UV-VIS rays.

Antifungal and Antibacterial Activity Analysis
Zone of inhibition indicates a circular area where bacteria or fungal do not grow.
In our study, we have taken one fungal (Aspergillus niger) and two bacteria (Staphylococcus aureus and Escherichia coli) to test antifungal and antibacterial effect by "Disk Diffusion Method".     [30]. Therefore, it is expected that the ZnO nano particle coated cotton fabric can be used in medical applications such as disposable bedding linen, antibacterial bandage and uniforms for health worker etc. since it exhibits bacterial effect [29] [30].

Conclusion
This work describes the methods and results obtained in the development of