Sustainable Fabrication of Silver Nanoparticles on Functionalized Cotton Fibers

The synthesis of silver nanoparticles in natural fibers has become a promising green field. The antimicrobial properties of silver nanoparticles make them suitable for potential usage in wearable medical devices designed to monitor various human body conditions. For another thing, the high demand for cotton cloth results in excess of them, making the field of cotton cloth recycling important. This study researched a series of functional group modifications of cellulose aiming to make the whole process of silver nanoparticle synthesis green, safe, and effective.<br/>In this study, cotton cloths were first treated with different chemicals for deweaving and modification of functional groups. Then the treated cotton fibers were soaked in a type of mild reducing agent made up of urea and lecithin. After that, the fibers were submerged in silver nitrate solution for silver nanoparticle synthesis.<br/> 25 pieces of 0.5cm×0.5cm square cotton cloths were treated separately with 40ml of 0.5M citric acid solution^[1], 1M sodium hydroxide solution, 1M urea solution, and 1M urea, 1M sodium hydroxide mixed solution for 0.5 hours at 50 degrees Celsius with magnetic stir for 1000rpm to chemically deweave cotton cloths down to fibers. After filtration, the samples were dried in a vacuum overnight. Next, the samples were soaked in a 50ml solution with 0.25g lecithin and 0.5g urea at room temperature for 24 hours as the reduction process for nanoparticle synthesis. Then, the solutions were switched to 0.1M silver nitrate solution, and samples were fully submerged in the solution at room temperature for 18 to 24 hours to synthesize silver nanoparticles. Last, the samples were dried under a small fan at room temperature for two days, additional drying was performed in a vacuum for X-ray Photoelectron Spectroscopy (XPS). All the solutions used were made of high-purity deionized water (18mΩ/cm).<br/>Various methods of characterization and analysis were conducted on the samples and cotton cloth, including Optical and Digital Microscopy, Elemental Analysis, Fourier Transform Infrared Spectroscopy in DRIFT mode (DRIFT-FTIR), X-ray Photoelectron Spectroscopy (XPS), X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS).<br/>X-ray Fluorescence was used to check contaminants in cotton cloth, finding a relatively large amount of calcium and potassium which may come from the process of cotton cloth manufacturing. The figure obtained through the microscope indicates the most thorough deweaving process occurred in the sample treated by both sodium hydroxide and urea, which may indicate an interaction of urea and sodium hydroxide in changing the structure of cellulose. Comparing the differences of peaks in the Fourier Transform Infrared Spectroscopy, the modifications of the functional groups on cellulose were found. To be specific, the peak at 1663cm^-1 indicates the amine group attributed to urea and the peak at 1730cm^-1 indicates C=O attributed to citric acid. It was discovered by scanning electron microscopy that silver particles scaled from nano to micro sizes, forming clusters of particles coated on the fibers and distributed uniformly. Besides, the particles were all pure silver but not compounds, tested by energy dispersive spectroscopy, suggesting a promising usage for acute care.<br/>Future works could focus on testing the functional properties of silver nanoparticle coated cotton fibers, including conductivity, thermal stability, cell toxicity, and encapsulation of silver nanoparticle coating.<br/>The research was carried out based on former research of Environmentally Benign Low Temperature Degradation of Muslin Cloth with patent application number 050-9046.<br/>[1] Cuiffo, Michael; Jung, Hye Jung; Skocir, Asta; Schiros, Theanne; Evans, Emily, Orlando, Elizabeth; Lin, Yu-Chung; Rafailovich, Miriam; Kim, Taejin; Halada, Gary, Thermochemical Degradation of Cotton Fabric Under Mild Conditions, <i>Fashion & Textiles</i>, 8:25, <b>2021</b>.