In Situ Synthesis of SiO2 Nanoparticles by Sol-Gel Method on Cotton Fabrics and Investigation of Their Physical and Chemical Properties Sheila Shahidi 1,a , Hakimeh Mohammadbagherloo 2,b , Seyedmohammad Elahi 2,c , Sanaz Dalalsharifi 3,d , Rattanaphol Mongkholrattanasit 4,e * 1 Department of Textile, Arak Branch, Islamic Azad University, Arak, Iran 2 Depertment of Physics, Science and Research Branch, Islamic Azad University, Tehran, Iran 3 Department of Textile, Science and Research Branch, Islamic Azad University, Tehran, Iran 4 Department of Textile Chemistry Technology, Faculty of Industrial Textiles and Fashion Design, Rajamangala University of Technology Phra Nakhon, Bangkok, Thailand a sheila.shahidi@gmail.com, b mohammadbagherloo.hakimeh@gmail.com, c smohammad_elahi@yahoo.com, d ssana6470@yahoo.com, e rattanaphol.m@rmutp.ac.th Keywords: SiO2, Nanoparticle, Sol-Gel, Cotton, Fabric Abstract. In this paper, the sol-gel method was used for in-situ synthesis of SiO2 nanoparticles (NPs) on cotton fabrics with tetraethyl orthosilicate (TEOS) in the presence of acid and alkaline indicators. The samples were characterized using by (X-ray diffraction) XRD, (scanning electron Microscopy) SEM, (Inductively coupled plasma) ICP, water drop test and also the flame retardant properties were studied by char yield. The SEM images showed that the nanoparticles are spherical in shape and the acidity or alkalinity of the medium has an effect on the formation of particles. The XRD patterns showed the typical diffraction of amorphous SiO2 (Si-O short-order structure), also ICP analysis showed that by washing the fabrics, the nanoparticles are still present on the fabric, and this indicated the stability of the washing of the fabrics impregnated with the nanoparticles. By in-situ synthesis of SiO2 nanoparticles, the flame retardant properties have been improved significantly and the amount of residual char was increased and samples were observed to be hydrophilic. Introduction Nowadays inorganic nanoparticles (NPs) are used for various applications in the fields of engineering, textiles, cosmetics, food, and medicine. [1] In particular, SiO2 nanoparticles (NPs) an actively investigated topic due to their applications in many fields. [2] also they have attracted wide interest in view of their excellent optical, electrical and thermal properties. [3] These particles are used as catalysts [4], gas absorbers [5], heavy metal ion adsorbents [6], mineral delivery [7], drug delivery [8], semiconductors [9] and additives to polymers, including plastics and rubber [10]. In recent years, Nano-silica has been produced according to various applications in a variety of spherical Nano- powder forms [11], porous Nano-powder [2], Nano-tube [12] and thin layer [13]. On the other hand, different industries’ interests have increased in developing NPs on fabrics to their potential for use of human in various applications such as medical clothes, wound dressings, health-care (including disposable) appliances, protective garments, veterinary, and military [14]. Natural fibers particularly polysaccharides are available in large quantity, biodegradable and renewable resources in opposition to synthetic fibers. Among them, Cotton fiber is the purest cellulose and is the maximum rich polymer in the environment [15] for usage in many applications due to its availability, feel comfortable, fair mechanical strength, high durability, and cost -effectiveness. [14] SiO2 nanoparticles have been synthesized on cotton fabrics using various methods such as hydrothermal [16], chemical vapor condensation [17], direct oxidation [18], sol-gel technique and others. [16,19] In this work, In-Situ synthesis of SiO2 nanoparticles on cotton fabric was performed by a simple method namely sol-gel with tetraethyl orthosilicate (TEOS) as a precursor in the presence of acid and alkaline indicators. The main aim of this project is to improving the flame retardant properties of cotton fabric. Also, Key Engineering Materials Submitted: 2020-11-26 ISSN: 1662-9795, Vol. 891, pp 37-42 Accepted: 2020-12-01 © 2021 Trans Tech Publications Ltd, Switzerland Online: 2021-07-06 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (#557736002-15/04/21,17:45:09)