Stability and Effects of Natural Coatings on Engineered Inorganic Nanoparticles (EINP) investigated by Surface Enhanced Raman Spectroscopy (SERS)

Melanie Kühn1, Natalia P. Ivleva1, Reinhard Nießner1, Thomas Baumann1
1 Institut für Wasserchemie, Technische Universität München

P 6.15 in Groundwater, soil and surface water interactions


Emissions of engineered inorganic nanoparticles into the environment are increasing sharply due to their growing applications in industry and consumer products. Simultaneously, there is an increasing number of reports regarding adverse impacts of EINP on aquatic ecosystems and possible health risks. EINP used in consumer products are often only weakly bound or even unbound to their substrate (e.g. silver nanoparticles in textiles, TiO2 nanoparticles in paints) and are therefore very likely to be released into the environment. Their transport in aquatic and terrestrial environments is controlled by the physical and chemical heterogeneity of the matrix along the flow path and the properties of the EINP themselves. While EINP are well characterized concerning their field of applications, there is still a lack of knowledge regarding their stability and transport behaviour when they are released into the environment. Additionally, EINP are likely to get coated with natural organic substances soon after release. Once the coating has formed, stability and transport behaviour of the nanoparticles will no longer be influenced by the core material, but mainly by the properties of the coating. Therefore, it is crucial to characterize the surface properties and stability of the EINP and their possible coating materials to predict their behaviour under environmental conditions. However, analytical methods to characterize organic coatings on nanoparticles are scarce. One suitable tool for the investiagtion of coatings on silver nanoparticles is surface enhanced Raman spectroscopy (SERS). Silver nanoparticles are known to enhance the Raman signal of adsorbed or nearby substances by a factor of 1e3 - 1e6. This leads to a considerably higher sensitivity of SERS compared to normal Raman micro-spectroscopy. Surface coatings on silver nanoparticles should therefore be accessible via the SERS effect. Citrate as well as hydroxylammoniumchloride stabilized silver nanoparticles were coated with humic acid for 24h, centrifuged and resuspended in deionised water. After this washing procedure, the samples were either dried on a silicon wafer or measured as liquid samples in a microtiter plate. Results indicate the formation of a stabilizing layer around the nanoparticles after contact with humic acid. Humic acid seems to form a quite stable coating around the nanoparticles that is even present after four steps of centrifugation and resuspension in deionized water. Interaction of EINP with physical and chemical heterogeneous model surfaces will be studied in microfluidic systems mimicking the flow paths in porous and fractured aquifers to quantify the transport properties of the nanoparticles as a function of different coating materials.

last modified 2013-10-31