The nanomaterials in this thesis are developed to counteract harmful organic pollutants and bacteria in our environment. Titania-based nanomaterials are prepared and the properties are examined for photocatalytic purposes to decontaminate waters with organic pollutants. Silica-silver nanomaterials are developed for antibacterial purposes. Titania-based nanotubes and composites were developed for organic contaminants removal via photocatalysis. The nanotubes were prepared by chemical solution processing and rapid breakdown anodization (RBA) methods and further subjected to heat treatment. The chemical solution processing method yielded titanate-anatase mixed crystal structures, and anatase, rutile or brookite structures when using RBA. The heat treatment caused the tubular structure to collapse into rods and further into particles in both cases. The thermal stability of the tubular structure was higher for the titanate nanotubes compared to the nanotubes prepared by RBA. The surface area and amount of hydroxide functional groups reduced upon increasing heat treatment temperatures. The titania based composite consisted of four components, i.e., titania, graphene oxide, silver, and silver chloride. The photocatalytic efficiency was investigated using methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) under UV and/ or sunlight irradiation. The photocatalytic decolorization of MB under UV light was reduced upon increased heat treatment temperatures for the titanate nanotubes, due to the reduced hydroxyl groups and surface area. Almost complete photocatalytic decolorization of MO and RhB was achieved using titania nanotubes under sunlight irradiation. The graphene oxide/titania/silver/silver chloride composites showed a high adsorptive capability of MB, due to the abundance of hydroxyl functional groups. The photocatalytic decolorization reached 55 % under UV-light irradiation and increased by ca 80 % with the addition of graphene oxide to the titania/silver/silver chloride composites. The silica-silver composites were prepared by a modified Stöber method. The silica-silver composite powders were subjected to heat treatment to study the silver nanoparticle growth and to determine the activation energy for silver particle growth. The mean size of the silver particles grew with increasing heat treatment temperature. The activation energy for silver particle growth was determined as 0.14 eV, and the growth took place via diffusion and Ostwald ripening. The feasibility of a prolonged silver release from the composites was investigated via dissolution tests, which showed a prolonged release for at least 7 days' time. One silica-silver composite was chosen for antibacterial tests for wound dressing applications. The silica-silver composite hindered the growth of both methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli. The composite was also impregnated in a gauze to simulate a wound dressing and hindered the bacterial growth more efficiently than a commercial silver containing gauze. The antibacterial mechanism was elucidated for MRSA, where the silver ions eventually caused the loss of bacterial membranes.
|Translated title of the contribution||Titania and silica based nanomaterials for decontamination and antibacterial applications|
|Publication status||Published - 2018|
|MoE publication type||G5 Doctoral dissertation (article)|
- particle growth