"Nanoparticles and light - Characterization of dynamic changes to nanoparticle surfaces"
Due to novel properties such as optical properties and high specific surface area, noble metal and semiconductor nanoparticles have been implemented in a wide rangeof products in different fields. Semiconductor NPs like TiO2and ZnO have been used as efficient photocatalytic materials in water purification for degradation of toxic organic pollutantsin the presence of light. Noble metal and semiconductor NPs also show antibacterial characteristics,and therefore they have been implemented in a wide varietyof products.However, NPs can be released into the environment during their production, application and disposal,which can adversely result inunknown risks to human health and the environment.Nanoparticles are stabilized with different coating agentsto enhance their efficiency by avoiding their aggregation and dissolution,which mayalso alter the environmental fate of NPs after their release into the environment.Among different methods implemented to characterize the coating of NPs, surface-enhanced Raman spectroscopy is an emerging technology which benefits from optical properties of NPs and has a great potential for detection of different coatings especially on noble metal NPs.In this thesis by profitingfrom the optical properties of noble metal and semiconductor NPs, we try to develop the knowledge and application of nanotechnology in environmental fields.In the first part of this thesis, we synthesized Au@Ag nanoparticles to study the exchange and competition of different coating agents with different binding abilities to simulate the release of NPs into a water body with severalpotential coating agents. Suwannee River Natural Organic Matter (SRNOM), 4-mercaptobenzoic acid (4-MBA) and 4-Mercaptopyridine (4-MPy) were selected molecules for the experiments. It was shown, 4-MPyhas a higher binding affinity than SRNOM and 4-MBA through the presence of simultaneous sulfur and nitrogen atoms which leads to dominating the coating process when two coating agents are present in the media at the same time. Furthermore, 4-MBA and 4-MPymake bonds to the SRNOM coated nanoparticle despite that SRNOM coating has been previously formed.In the second part, the synthesized Au@Ag NPs were successfully coated on silicon wafer to produce SERS substrates to detect different molecules. 4-MBA and 4-MPy were selected as sample molecules,and a detection limit of 5 x 10-9M was obtained.Also, the substrate was implemented to characterize the 4-MPy coating on P25 Degussa TiO2NPs.n the third part, the P25 Degussa TiO2NPs were thermally modified at different temperaturesto achieve NPswith different characteristics. The modified NPs were used tocharacterize the formation and stability of coatings by SERS and also as photocatalytic material for deactivation of sample bacteria. It was observed that the crystal structure of TiO2NPs plays an essentialrole in their application. It was also observed that SERS Spectra of the coating show some changes if heavy metal ions are present in the media during the coating process.In the last section, ZnO NPs with different morphologies were successfully synthesized via aneasysolvothermal method with different solvents. The ZnO NPs were employed for degradation of a sample azo dye. SEM imagingrevealed that the particles synthesized in 1-hexanol, ethylene glycol and waterhaverod, sphere andflowershape, respectively.The photocatalytic efficiencies of the ZnO NPs were affected by theirdifferent morphologies and crystal growth habits, particle size and optical properties. Results indicate that flower-like ZnO NPs showed significantly higher photocatalytic efficiency than rod-and sphere-like ZnO NPs.