Elsevier

Catalysis Communications

Volume 34, 5 April 2013, Pages 35-40
Catalysis Communications

Short Communication
Antibacterial activity of photocatalytic electrospun titania nanofiber mats and solution-blown soy protein nanofiber mats decorated with silver nanoparticles

https://doi.org/10.1016/j.catcom.2013.01.002Get rights and content

Abstract

Highly porous photocatalytic titania nanoparticle decorated nanofibers were fabricated by electrospinning nylon 6 nanofibers onto flexible substrates and electrospraying TiO2 nanoparticles onto them. Film morphology and crystalline phase were measured by SEM and XRD. The titania films showed excellent photokilling capabilities against E. coli colonies and photodegradation of methylene blue under moderately weak UV exposure (≤ 0.6 mW/cm2 on a 15-cm illumination distance). In addition, solution blowing was used to form soy protein-containing nanofibers which were decorated with silver nanoparticles. These nanofibers demonstrated significant antibacterial activity against E. coli colonies without exposure to UV light. The nano-textured materials developed in this work can find economically viable applications in water purification technology and in biotechnology. The two methods of nanofiber production employed in this work differ in their rate with electrospinning being much slower than the solution blowing. The electrospun nanofiber mats are denser than the solution-blown ones due to a smaller inter-fiber pore size. The antibacterial activity of the two materials produced (electrospun titania nanoparticle decorated nanofibers and silver-nanoparticle-decorated solution-blown nanofibers) are complimentary, as the materials can be effective with and without UV light, respectively.

Highlights

► TiO2 decorated nanofibers inhibit growth of E. coli and kill them under UV light ► Silver nanoparticles decorated soy protein nanofibers inhibit E. coli inherently ► Our antibacterial nanofiber mats can be combined in water purification industry ► Our nanofibers are biocompatible, allowing applications in wound healing bandages

Introduction

Water pollution and shortage pose serious environmental problems worldwide, and interests in water purification or antibacterial treatments are growing substantially. Antimicrobial functionalities in water filtration are required in multiple applications, starting from membranes used in construction industry to bandages used for wound healing. For this reason, fabrication of antibacterial materials has become one of the most challenging global research issues [1], [2], [3]. Nanoparticles have recently gained significant attention due to their high surface to volume ratio which leads to specific characteristics that differ from bulk material. Both semiconducting ceramic and metal nanoparticles are of interest due to their potential to act as antibacterial. In previous studies [4], [5], it was shown that such metals as silver, titanium, zinc, and calcium act as antimicrobial agents, while titanic oxide, tin oxide, and silver oxide have also been proven to be potential antibacterial ceramic materials [6], [7]. In particular, these metals and ceramics are sources of cations that react with hydroxyl and anionic groups of enzymes in bacteria which results in change of functionalization in bacterial cells. Of all metal particles, silver has shown the strongest antibacterial effect which has been investigated vastly [4], [5]. As a result, silver nanoparticle-coated surfaces made their way into cosmetics, textile, and pharmaceutical products. Growing interest in functionalizing silver nanoparticles for different applications brought about toxicity issue of these particles, yet it has been documented that moderate usage of silver in human's body would not have a major reverse impact [8]. As for the ceramic nanoparticles, TiO2 has been proven to be the most promising photokilling material because of its ability to generate hydroxyl radicals upon receiving UV-light [9]. Antibacterial activity of TiO2 must be activated by UV while UV is not necessary for antibacterial activity of silver. The combination of the superior hydrophilicity and photokilling effect of TiO2 led to its usage in water purification, medical applications [7], odor elimination, decoloring wastewater [10], [11], mineralization of both hazardous organic and inorganic materials [12], [13], soil decontamination [14], destruction of cancer cells and viruses [15], and medical sterilization.

The use of nanoparticles for antibacterial application is often difficult, e.g. for water purification, nanoparticles should be dispersed in a polluted aqueous medium to make best usage of their high surface to volume. However, the subsequent separation of nanoparticles from purified water is difficult as they remain in a colloidal state and do not sufficiently settle. As a result, an additional equipment is required [16]. In lieu of this, an immobilized mode, or fabrication of films is often proposed as an alternative. However, this immobilized mode prevents the effective usage of nanoparticles by compacting them into a two-dimensional film which dramatically reduces the interfacial contact between nanoparticles the polluted medium. Antibacterial treatments imply a significant area of contact of an active material with polluted medium. Nano-textured materials with open porosity, such as electrospun or solution-blown nanofiber mats possess specific surface area in the range 10–100 m2/g, which makes them attractive candidates for nanoparticle supports in water purification processes [4], [5], [17]. In addition, nanofibers can be used as filters as pores with sizes in the range ~ 1–10 μm can catch pollutants more efficiently than standard filters [18]. In addition to filtration, nanofibers are also shown to be effective for wound dressing [19], [20]. Nanofibers with antimicrobial functionalities can facilitate development of very efficient membranes. In this respect, TiO2 and silver nanoparticles represent themselves as two best possible candidates because TiO2 can perform in the presence of UV light, whereas silver is active without UC light due to its intrinsic antimicrobial capability.

In this work, we form and test two model types of the antibacterial materials. The first one is solution-blown soybean-nylon nanofiber mats decorated with silver nanoparticles. Their antibacterial effect does not require UV illumination. We also form and test the antibacterial effect of electrospun nylon nanofiber mat decorated with TiO2 nanoparticles. Such nanofiber mats become bioactive upon UV illumination. This allows us to introduce such novel biocatalyst supports which can be active with or without UV light, or both with and without UV light when silver and TiO2-coated nanofibers are used simultaneously.

Section snippets

Electrospinning of titania nanoparticle decorated nanofiber

Fig. 1 shows the process of titania-decorated nanofiber mat fabrication. Agglomerated TiO2 nano-particles (P25-Daegusa, Germany) are a mixture of 80% anatase and 20% rutile, whose actual size was in the range of micro-scale because of severe agglomeration, and are dispersed in ethanol solution to facilitate electrospray deposition onto flexible glass substrates attached to the cylinder rotating at 300 RPM. Polymer solution (15 wt.% nylon 6 dissolved in formic acid, Sigma Aldrich) was

Titania-decorated nanofibers

SEM images of the titania decorated nanofibers are shown in Fig. 1. It can be seen that titania nanoparticle formed agglomerate on the nanofiber mat. Porosity of the electrospun nanofiber mat was estimated to be approximately 38%, which was obtained by counting the void pixels from the 2D SEM image. It should be mentioned that the composite fiber mat was collected on a flexible substrate. It could be bent as shown in Fig. 1 without causing any delamination of nanoparticles from the fiber mat,

Conclusions

In this work two different system of antimicrobial substrates based on polymer nanofibers were studied: (a) electrospun nylon 6 nanofibers decorated with TiO2 nanoparticles, and (b) solution-blown soy protein-based nanofibers coated with silver nanoparticles. The rate of electrospinning is much lower than that of the solution blowing and the inter-fiber pore size in electrospun mats is smaller than that in the solution-blown mats, which are fluffier. It was found that TiO2 decorated

Acknowledgements

This work was supported by a research contract with the United Soybean Board, Chesterfield, Missouri (research contract no. 0491). Help of Dr. Wonhwa Cho and Marian Fernando (UIC) is greatly appreciated. This work was also supported by National Research Foundation of Korea (2012-0001169, 2011-0030433, and 2010-0010217), and the Converging Research Center Program (2010K000969). This study was also supported by a grant from the cooperative R&D Program (B551179-08-03-00) funded by the Korea

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