Study On Preparation Of Nano-TIO₂and Composite Hydrosol And Application In Functional Textiles

Titanium dioxide, as an excellent semi-conductor which can absorb sunlight and beexcited to decompose organic pollutions, has become very popular in science research inrecent years. It can be used in air purification, sewage treatment, self-cleaning glass andcosmetics. Especially nano-TiO₂photocatalyst has been given more attention in the fieldsof textile, as it can endow the fabrics with self-cleaning, UV-blocking and antibacterialdeodorant properties. But there are still some disadvantages for the application ofnano-TiO₂, including low utilization ratio of solar energy, high sintering temperature morethan300℃during the wet chemical preparation of nano-TiO₂, and the poor durability ofthe treated fabrics, restricting its scope of application. Therefore, low temperature synthesisand visible absorption of nano-TiO₂and its application in textiles, were studied in thispaper to solve these problems above.Firstly, nano-TiO₂hydrosol was prepared by sol-gel method with Ti（OC4H9）4, H2Oand CH3COOH system under low temperature. The effects of water amount, pH value andthermal crystallization treatment on low temperature crystallization of nano-TiO₂wereinvestigated. The results showed that TiO₂sol was prepared when the molar ratio ofTi（OC4H9）4and H2O was1:200, and pH value was1². And then after TiO₂sol wassteamed at100¹30℃, anatase TiO₂obtained in this condition had complete crystal shape,uniform dispersion, high crystallinity and the particle size of8¹0nm, which had theexcellent degradation rate of methylene blue more than97.1%after UV irraditation for1.5h. The nano-TiO₂powder or nano-TiO₂film prepared by thermal crystallization treatmentin low temperature can be applied to coat on the materials with poor temperatureresistance.Secondly, by mixing and fractional precipitation, TiO₂/ZnO composite powders weresuccessfully prepared with the doping molar ratio of10:1and then were characterized byXRD, DRS, SEM and EDS. The composite powders had the improved visible lightresponse. The photocatalytic degradation of methylene blue （MB） of TiO₂/ZnO composite powders prepared by two methods were compared. Under UV light, UV-VIS light andvisible light, the results revealed the MB degradation activity sequence of nano-TiO₂/ZnOprepared by the above two methods, TiO₂/ZnO-1（mixing method）>TiO₂/ZnO-2（fractional precipitation method）> TiO₂. The composite powders prepared bythe above two methods had greater photocatalytic activity than a single semiconductor.Because of the ZnO doping, surface electron-hole pairs combination of the compositepowders was reduced, and the bandgap became narrower, leading to the increase of lightabsorption efficiency of composite powder.Thirdly, nano-TiO₂sol could be applied to functional finishing of cotton fabrics,endowing the fabrics with UV-blocking and self-cleaning properties. The cotton fabricscoated by different finishing processes were characterized by XRD and SEM. Theself-cleaning effects of cottons coated by TiO₂also were evaluated by the degradationactivities of MB and red wine stain. The results showed that a uniform layer ofnanocrystalline titania had been formed on cotton textiles treated by the dip-pad-dry-steamfinishing process, which had higher crystalline intensity than cotton textiles treated by thedip-pad-dry and dip-pad-dry-hydrothermal finishing process. Besides, these cotton fabricstreated by dip-pad-dry-steam finishing process had excellent photocatalytic self-cleaningproperties. As for the coated cotton fabrics, the degradation rate of MB reached more than88%after UV irradiation for5h, and the obvious discoloration of both a red wine stain anda coffee stain was observed after48h of UV irradiation. The self-cleaning effect and otherproperties of cottons coated by both TiO₂and TiO₂/ZnO under sunlight irradiation werestudied.Finally, in order to improve the adhesion between nano-TiO₂and cotton fabrics, inthis paper the low temperature plasma technology was used for cotton fiber surface etchingand activation. A variety of functional groups like C=O,-O-C=O,-COH,-COOH, CH2-OHcould be produced on the cotton fiber surface. These groups could chemically react withnano-TiO₂in the presence of active groups such as O and O＊2, leading to the greatimprovement of the durability of treated fabrics. The results showed that cotton pretreatedby plasma were firmly bonded with nano-TiO₂particle. The cotton pretreated by plasmaafter10times of washing still had good self-cleaning effect for red wine stain.