Transport and fate of silver nanoparticles in the aquatic environment

• Main Author: Fernando, W. W. Busabaduge Prabhashini Madhushika
• Other Authors: Zhou Yan
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Environmental engineering; Engineering::Materials
• Online Access: https://hdl.handle.net/10356/136950
• Institution: Nanyang Technological University

The invention of new materials to enhance various product qualities has grabbed the consumer attention. Among them, engineered nanoparticles play a pivotal role due to their different physical and chemical characteristics. Silver nanoparticles (AgNPs), recorded as widely used in consumer products due to its unique antimicrobial properties undergo different transformations when present in the aquatic environment. The transformations of AgNPs will vary according to their physical properties and the chemical properties of the solution matrix they are present. The physical properties governing the transformations include size, shape, structure and the surface coatings. The chemical properties determining the transformation of AgNPs include pH, ionic strength, dissolved organic matter and extracellular polymeric substances. Understanding the transformations of AgNPs is important in predicting the transport and fate of the AgNPs in the environment and design adequate removal mechanisms. This thesis investigates the impact of different chemical properties of the matrix including solution pH, humic acid, protein, polysaccharides and extracellular polymeric substances on the transformations of AgNPs including aggregation, dissolution and colloidal stability. Freshly synthesized uncoated AgNPs were used during all the experiments to avoid the possible interferences resulting from the coatings and other chemicals. When assessing the impact of these factors the prominence was given to study the environmentally relevant conditions either in the natural environment or wastewater, which will provide important implications on the fate of AgNPs in the respective pathways. Furthermore, the long-term stability induced by the surfactants and polymers, which are used as coating agents in the transport and storage of AgNPs was also assessed. Commonly used surfactants and polymers representing the different categories were used in the experiments. Multitude of characterization and analytical techniques were used during the experiments including spectrometry, DLS, ICP-MS, TEM, EDX and FTIR. Finally, the suitability of a burgeoning technique, liquid cell transmission electron microscopy to track the time resolved changes in the transformations of the AgNPs was developed. The results obtained during the study provide an overview on the impact of the above-mentioned factors on the temporal changes in the transformations of the AgNPs in the aquatic matrices. The conclusions obtained during the study are important in predicting the transport and fate of AgNPs in the water, hence, the behavior of the engineered NPs in the aquatic environment. The insights obtained during the study can be utilized in assessing the life cycle of AgNPs and subsequently their overall impact on the nature.