Exploring the use of dye-sensitisation by visible light and the lotus effect as new approaches to self-cleaning textiles
thesisposted on 28.02.2017, 03:18 by Afzal, Shabana
The primary motivation of the research work presented in this thesis is to develop dye-sensitised textiles capable of showing self-cleaning properties in daylight and indoor light environments. The photocatalytic degradation of organic contaminants by means of photoactive materials is one of the most effective and environmental-friendly methods for reducing the environmental pollution. Among the photoactive materials, anatase titanium dioxide is extensively investigated for a wide range of applications such as air purification, water treatment and self-cleaning surfaces. With high consumer demand for hygienic and contamination-free coatings, self-cleaning textiles based on anatase titanium dioxide photocatalysis have been of particular interest. However, the photocatalytic activity of anatase titanium dioxide is limited to ultraviolet region of the solar spectrum. To utilise the major portion of the solar spectrum, visible-light active photocatalytic systems are required in fabricating self-cleaning coatings. Chapter 1 introduces the topic by giving an account on the chemistry behind the photo-catalytic effect, dye-sensitisation, the use of porphyrins and examples of self-cleaning textiles that are state-of-the-art in the field. The chapter finishes by discussing the lotus effect and stating the thesis aims. By using meso-tetra(4-carboxyphenyl)porphyrin (TCPP) for sensitisation of TiO2, visible-light driven self-cleaning cotton has successfully been developed, that exhibited superior photocatalytic self-cleaning properties to that of titanium dioxide or the dye in isolation (Chapter 2). A complete degradation of methylene blue was achieved under visible-light irradiation for 110 min. In addition, decolourisation of coffee and red wine stains was observed under visible-light irradiation for 16 h. Chapter 3 and 4 investigate the use of metal complexes of TCPP (Fe, Co, Zn & Cu) as means of optimising the performance of our system on pristine cotton. In view of the practical applications of self-cleaning textiles, the stability of a photocatalyst is an important constraint. The results shown in this thesis indicate that meso-tetra(4-carboxyphenyl)-porphyrinato copper(II) (CuTCPP) showed enhanced photostability as compared to the high performing free-base porphyrin (TCPP). To enhance the performance of these new materials further, the concept of lotus effect has been combined within the visible-light photocatalysis to prepare better self-cleaning textiles (Chapter 5). The dual functional textiles exhibited a superhydrophobic effect, in addition to the photodegradation of organic contaminants by visible-light photocatalysis. Superhydrophobic and photocatalytic self-cleaning textiles offer great potential for indoor and outdoor self-cleaning applications. Chapter 6 briefly summarises the thesis and adds future perspectives to this research.