Project Details
Projekt
Changes of nanoparticles along their life-cycle and of the local environment of nanoparticles
Applicant
Professor Dr. Thomas Baumann
Subject Area
Soil Sciences
Term
from 2011 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 172114680
Engineered inorganic nanoparticles (EINP) in the environment undergo changes which alter their mobility and toxicity, for instance, humic substances increase the stability of NPs while sulfidic coatings on Ag NP limit the release of Ag+. After release into the environment NOM seems to form a rather stable coating around Ag NP. This coating possibly replaces the original stabilizing agent (e.g. citrate), which can be deduced by the presence of the specific SERS signal of NOM. Current measurement technology offers limited access to the formation of coatings (e.g. EXAFS for inorganic coatings) but virtually no time resolution. The monitoring of the life cycle of NP-coatings, however, has not yet been addressed, due to analytical limitations.In the first phase Raman microspectroscopy (RM) was applied to gain information about coatings on Ag NP. Relevant coatings can be distinguished (i.e. different humic substances, soil extract) by RM or surface enhanced Raman scattering (SERS). Changes in the spectral features of NOM attached to Ag NPs suggest an aging of coatings, that is a change of the structure of NOM. Results obtained by subprojects MASK and PORESURFACE indicate that a coating with natural organic matter might be described by a closely bound first layer, which produces a SERS signal, and a weakly bound secondary layer where the fluorescence is of NOM is enhanced. At least the secondary coating seems to be reversible.The work program in the second phase is driven by the following assumptions: the formation of an initial coating and subsequent changes of the coating are on different time lines, depending on the sorption coefficients; higher concentrations of NPs are likely changing the local chemical environment; under spatially restricted conditions (biofilm, pore throats, gut) concentration gradients might develop. Finally, unless very high concentrations of EINP are present, reactions at EINP are likely limited to a local scale, thus hard to identify but nevertheless important to assess the stress imposed by NP. Based on the work in the first phase time resolved measurements of the stability and aging of coatings on Ag NP and Au NP (SERS effect) will be followed by time resolved 3D RM of model systems and real matrices, which provide data on the chemical environment of EINP in natural systems and possible changes within. Selected coating experiments will be conducted jointly with SOILMOBILE and MASK. Experiments will include measurement on SERS structured matrices, thus offering access to the coating and the chemical environment of TiO2 NP. Joint experiments will address the fate of EINP at the air-waterinterface, the detailed investigation of EINP incorporated in biofilms, the aging of coatings, and time-resolved measurements of EINP in Daphnia. Together this will provide a mechanistic understanding of the coatings of EINP in different media leading to an assessment of the fate of EINP.
DFG Programme
Research Units
Co-Investigator
Professor Dr. Reinhard Nießner
