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Title: Novel routes to asymmetric nanoparticles
Author: Foster, Katie
ISNI:       0000 0004 2746 9773
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2012
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Sick building syndrome, in which the victims feel dizzy, fatigued and nauseous is caused from the accumulation of indoor air contaminants such as volatile organic compounds (VOCs). Photocatalytic paints are an aesthetic approach for the reduction of such compounds via pollutant breakdown. The key constituent is titanium dioxide. Studies have shown, however, that incorporation of unmodified nanoparticulate TiO2 into paints causes film breakdown and VOC release. In this work the synthesis of asymmetric titanium dioxide particles whereby one half is coated with silica, via simple wet chemical techniques was investigated. Polystyrene micro- and nanospheres, and the novel use of carbon microspheres were used as sacrificial templates. The inner titania layer and outer silica layer were deposited onto the templates through hydrolysis and condensation of the relative precursors. The templates exhibiting the double coating were then removed via thermal degradation, leaving double shell hollow inorganic spheres with an inner layer comprising of crystalline titania and the outer shell composed from amorphous silica. To form asymmetric particles these hollow spheres were then ruptured using sonication and ball-milling. The polystyrene microspheres were successful at producing asymmetric platelets by simply crushing the hollow inorganic spheres after template removal. The majority of the double shell hollow inorganic spheres produced from polystyrene nanospheres remained intact and were too small to rupture using ball-milling. Platelets were therefore not produced. Carbon microspheres were not fully decomposed at the temperatures chosen and a mixture of asymmetric platelets and whole spheres were formed. Glass microsphcres were implemented as a non-sacrificial template to investigate greener routes into asymmetric platelet production. Three methods were investigated in terms of their ability to remove the silica-titania double coating producing asymmetric platelets, leaving the glass microspheres intact ready for reuse. Sonication produced colloidal dispersions of TiO2 and SiO2 nanoparticles but did however leave the surface of the spheres clean. Ball-milling not only removed the coating but also smashed the glass-spheres into smaller pieces rendering them obsolete. Heating the coated glass microspheres and then rapidly cooling them did not remove the coatings at all. The photocatalytic activity of the samples produced from each sacrificial template towards toluene breakdown was investigated using a glass-plate photoreactor with online residual gas analysis. The samples were deposited in both powdered form, and dispersed in polyvinyl acetate which acted as a mock paint film. The intact double-shell hollow inorganic microspheres showed no photocatalytic activity. However when these were crushed into asymmetric platelets the partial pressure of carbon dioxide rose and fell when the light was switched on and off respectively, indicating these asymmetric platelets exhibited photocatalytic activity due to exposure of the crystalline titania layer to toluene.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available