|Title:||Preparation and characterization of novel photoactive compounds for self-cleaning textile finishes|
|Advisors:||Kan, Chi-wai (ITC)|
Yao, Zhongping (ABCT)
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Textile finishing agents
|Department:||Institute of Textiles and Clothing|
|Pages:||xiii, 125 pages : color illustrations|
|Abstract:||Cotton fabrics have been used for about last 7000 years. Although, the synthetic fibers such as polyesters, polyamides, acrylics and polypropylenes have been used in many applications for 50 years, the use of cotton textiles is still more than half of the worldwide textile market due to its excellent inherent properties such as softness, comfort, warmth, biodegradability and breathability. Due to these appealing characteristics, cotton fabrics have been used in wide variety of applications. The cotton fabric is composed of natural cellulose polymeric chains having hydroxyl groups (-OH) on its surface. In the past few decades, the surface treatment of the cotton fabrics to impart multiple functionalities has been the major focus of the researchers. Coating the cotton fabrics with photocatalytic materials can extend its usage as self-cleaning textiles. Due to strong oxidizing power, chemical and photostability, cost-effective and environmentally friendly nature of TiO₂, coating of the cotton fabric with TiO₂ extends its versatile applications such as self-cleaning, antimicrobial, deodorization, anti-fogging and wastewater treatments. TiO₂ coated cotton fabrics help breakdown of carbon-based stains in the presence of sunlight. However, it has been seen that commercial applications of TiO₂ coated textile fabrics are limited due to two major reasons. First major factor that limits the practical applications of TiO₂ is its UV light absorption. Solar spectrum comprises of only 3-5% UV region thus TiO₂ coated textile fabrics are only active under UV light. Second factor is the fast recombination rate of electron-hole pair in the excited state of TiO₂. This short life time of electron-hole pair reduces its practical photocatalytic applications. Therefore, the development of stable, efficient and visible light active coatings on cotton fabric surface is an emerging field of research. Several strategies have been adopted to overcome the limitations of TiO₂ either by doping with metals and non-metal elements such as Au, Ag, N and SiO2 or using some photosensitizer for TiO₂. These strategies enhance the photocatalytic properties of TiO₂; however, the coatings of these materials are either unstable or very complex and costly process.|
In this study, we report the preparation and photocatalytic characterization of novel photoactive compounds for self-cleaning textile finishes. Phthalocyanine based reactive dyes, C.I. Reactive Blue 25 (RB-25) and C.I. Reactive Blue-21 (RB-21) were used as photosensitizers for TiO₂ to enhance its photocatalytic efficiency. This study consists of three parts. In the first part, cotton fabric was coated in two steps. In step 1, the cotton fabric was coated by TiO₂ nano-sol via dip-pad-dry-cure method. In step 2, the TiO₂ coated cotton fabric was dyed with the RB-25. In the second part of this study, RB-25 was first mixed with TiO₂ nano-sol and then RB-25/TiO₂ sol was coated on the cotton fabric via dip-pad-dry-cure method. In third part, RB-21 was mixed with the TiO₂ nano-sol and the RB-21/TiO₂ sol was coated on the cotton fabrics. The surface structural properties of the cotton fabric coated with TiO₂ sensitized by RB-25 (the first part), RB-25/TiO₂ coated cotton fabric (the second part) and RB-21/TiO₂ coated cotton fabric were studied using FTIR, UV-visible absorption spectrophotometric and color yield measurements. The photocatalytic efficiency of all coated cotton fabrics was evaluated by the degradation of rhodamine B (RhB) dye in the presence of coated cotton fabric photocatalysts. Surface morphologies of all coated fabrics were studied by using high power X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM). UV blocking properties of the RB-25/TiO₂ and RB-21/TiO₂ coated cotton fabrics were analyzed by measuring the UV-protection factor. FTIR and UV-visible absorption studies confirmed the attachment of all the coated photoactive compounds on the cotton fabric surface. A bathochromic shift (red shift) of 13nm and 14nm in the Q band of RB-25 and RB-21 respectively was observed when these dyes were coated on the cotton fabrics along with TiO₂. This red shift confirms the attachment of RB-25 and RB-21 on the cotton fabrics. In addition, the XRD and SEM studies also confirmed the attachment of the photoactive compounds on the cotton fabric surface. The degradation of RhB in the presence of these coated cotton fabric show remarkable photocatalytic results. The photocatalytic and self-cleaning efficiency of these coated cotton fabrics was in the following order; RB-21/TiO₂ coated cotton fabric > RB-25/TiO₂ coated cotton fabric > cotton fabric coated with TiO₂ sensitized by RB-25. Moreover, these coated cotton fabrics showed excellent UV blocking characteristics. The coated cotton fabrics showed good laundering stability, however, little self-degradation of RB-25 and RB-21 was observed when exposed to light source for long time (30 h).
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