APPLICATION OF SILVER NANOPARTICLES AS METAL MORDANT AND ANTIBACTERIAL AGENT IN WOOL NATURAL DYEING PROCESS Hossein Barani 1, Majid Nasiri Boroumand 2 1 Department of Carpet, Faculty of Art, University of Birjand, Birjand, Iran 2 Department of Carpet, Shahid Bahonar University of Kerman, Kerman, Iran Corresponding author: Hossein Barani;barani@birjand.ac.ir Extended Abstract Natural colorants are mainly mordant dyes and usually have weak dye fastness when applied on fabrics. It is common to improve their affinity to substrate or color fastness by applying metal salts as mordants [1]. Madder is mordant natural colorant, it produces brightly colored insoluble complexes or lakes with metal ions present on the mordanted fabric. Wool is a natural protein fiber and is a good medium for growing different microorganisms. Therefore, treating with efficient antibacterial agents is required by growing production of advanced medical, protective and hygiene textiles [2]. Silver both in ionic and nanoparticle form as well as compounds based on them are wellknown antibacterial agents and highly toxic to micro-organisms. Silver salt is generally used to induce antibacterial effect, but when silver nanoparticles are used, there is a huge increase in the surface area available for the microbe to be exposed to [3]. Silver nanoparticles compared to silver ions are increasingly used due to their slower dissolution rate, leading to a continuous release of silver ions [4]. Moreover, comparing the biological effects of ionic and nanoparticle form of silver, there is a high interest in use of silver nanoparticles in consumer products and medical products [5]. In the current study wool fabric was pretreated with silver in the form of ions or nanoparticles and dyed with madder as a natural colorant. The madder roots contain several polyphenolic compounds and these components are able to reduce silver ions to AgNPs[6]. The pretreated wool fabrics with silver and dyed with madder were examined by Scanning Electron Microscopy (SEM) and their colorimetric characteristics were evaluated. Moreover, the antibacterial property of samples was examined and reported as well. Optical absorption spectrum is one of the key techniques that can characterize the structure of metal nanoparticles. The presence of extinction peak around near 440 nm at AgNPs treated wool fabric samples (Fig.1) confirmed the synthesis of spherical shape AgNPs [7, 8].
0.16 441nm AgN400 Absorbance 0.12 0.08 444nm Ag400 0.04 0.00 350 400 450 500 550 Wavelength (nm) Figure 1. Uv_Vis Spectra of treated wool fabric with Ag ion and AgNPs and dyed with Madder Wool fibers able to bind with oppositely charged organic or inorganic molecules due to their polar and ionisable groups [9]. Carboxyl group (-COOH) on the amino acids and hydroxyl group (OH) on the dye molecule of madder are the most binding sites that can bind to positively charged molecules [10]. Silver ions (Ag + ) can be diffused or absorbed due to the electrostatic interaction and then are converted to silver atoms (Ag). Sodium borohydride is a strong reducing agent and silver ions of treated wool fibers were reduced to silver atoms when faced with this solution. Sodium borohydride resulted in a very quick reduction of silver ions which were free in treated solution of wool fabric or bonded to the wool fibers structure. The primary AgNPs coalesced with each other and formed large nanoparticles that are also known as secondary nanoparticles. The silver atoms clustered and created nanoparticles. Therefore, the color of wool fabric was altered to brown which can confirm the formation of silver nanoparticles in the wool fiber structure. The morphological features of the AgNPs treated wool fabric with two different methods at 400 ppm concentration was studied by SEM. Fig. 2a shows the SEM images of madder dyed wool fabric sample that was pretreated with Ag ions and the higher magnified inset image (Fig. 3a) exhibits synthesized AgNPs are in the average size of 375 nm. Madder roots contain several polyphenolic compounds able to reduce silver ions to AgNPs. Different reducing agents with different redox potentials could cause synthesis of AgNPs of different sizes [11]. Polyphenolic compounds are weak reducing agents and their reaction takes place slowly and therefore resulted in lager nanoparticles. Therefore, alizarin is the most important polyphenol acting as a reducing agent in AgNPs synthesis. Fig. 2b depicts the SEM images of madder dyed
wool fabric sample that was pretreated with AgNPs and the higher magnified inset image exhibits synthesized AgNPs are in the average size of 73nm. (a) (b) Figure 1. SEM images of dyed wool fabric with madder and mordanted with a) Ag ion and b) AgNPs The untreated wool fabric presented a lower color strength at all visible wavelengths compared to all the pretreated wool fabrics. Treating wool fabrics with Ag + or AgNPs resulted in the creation of more functional groups than in untreated wool fabric. Therefore, it can provide more reactive sites on pretreated wool fabrics that can attach to dye molecules, as well as an improved color strength [12]. The pretreated wool fabrics with AgNPs showed higher color strength compared to pretreated wool fabrics with Ag + at the same concentration. Moreover, it can be observed that the color strength values of dyed wool fabric increased with an increase of Ag + or AgNPs concentration. References 1. Barani, H., et al., Optimization of Dyeing Wool Fibers Procedure with Isatis tinctoria by Response Surface Methodology. Journal of Natural Fibers, 2012. 9(2): p. 73-86. 2. Gao, Y. and R. Cranston, Recent advances in antimicrobial treatments of textiles. Textile Research Journal, 2008. 78(1): p. 60-72. 3. Prabhu, S. and E. Poulose, Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects. International Nano Letters, 2012. 2(1): p. 1-10. 4. Beer, C., et al., Toxicity of silver nanoparticles Nanoparticle or silver ion? Toxicology Letters, 2012. 208(3): p. 286-292.
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