Description

Context:

Nanoparticles (NPs), emerging pollutants and tiny particles under 100 nanometres in size, represent a special threat due to the broad and efficient application within modern technologies[1]. They can enter the soil through industrial spills but they can also be used intentionally to clean the soil (e.g. they have been used to remove a range of pollutants from soil[2]). Models suggest that soil is a major receptor of NPs —more so than air or water but NPs can also infiltrate through the vadose zone to the water-table and the groundwater flow.

To improve environmental risk assessment of contaminants, it is recommended to perform experiments in soils. However, this is extremely complex and difficult to be studied in situ but also in the laboratory as soil constituents (minerals, organic matter, microbes …) can interact with contaminants. For instance, organic matter in soils is known for playing a critical role in the transport and fate of NPs in the environment[3] but also the mineral fraction[4]. The complexity of soils and the lack of powerful techniques capable to obtain detailed information of the phenomena occurring inside the soil hinder the complete understanding of processes controlling contaminant fate in soils.

Thus, in last decades NMR has emerged as invaluable tool to study the interactions of contaminants and the complex soil matrix at a molecular-level. It is composed on liquid (Dissolved Organic Matter or DOM) and solid inorganic components like sand and clay. In particular, we have recently developed an NMR relaxometry workflow using transverse relaxation times and also diffusion NMR to study the interactions of NPs and DOM at a molecular-level[5]. Based on this NMR relaxometry protocol, this PhD project will valorize it on different NPs with varying conditions (concentrations, pH, ionic strength) to better understand the interactions of NPs and DOM and it will develop/apply other NMR methods to better understand these interactions (e.g. kinetics, inorganic matter interactions).

Scientific methodology:

The experiments will be carried out on model soil samples from the International Humic Substances Society (IHSS). Humic acid samples will be used to study the interactions of NPs with DOM in solution-state NMR and whole soils will be used for solid-state NMR experiments for the interactions of organic and also inorganic fractions of soils. Liquid-state NMR experiments (both high- (700 MHz) and low-field (43 to 80 MHz)[6]) will be carried out at CEISAM (Nantes) and solid-state at ISCR (Rennes). As the presence of surface coatings affects the transport and the retention of NP in soils, we will study commercial NPs having different surface and coating properties (e.g. zeta potential values at around -40, 0, and +40 mV). The selected PhD candidate will have access to several equipment at the analytical chemistry platform of the GERS-EE laboratory, including ICP-MS/MS(QQQ), Zetasizer Ultra (DLS and ELS: particle/molecular size and zeta potential measurements respectively)[5,7].

 

This PhD project will focus on five main actions:

1)            Application of NMR relaxometry / diffusion spectroscopy to understand the interactions of NPs and DOM.

2)            Evaluation of compact NMR performance and comparison with high-field NMR.

3)            Development of fast / more sensitive / more resolved NMR methods to study kinetics.

4)            Application of solid-sate NMR to study the interactions of NPs with organic and inorganic matrices on whole                  soils.

5)            Integration of liquid and solid-state NMR data to better understand NPs / soil interactions.

 

References:

[1]           W. I. Hagens, A. G. Oomen, W. H. de Jong, F. R. Cassee, A. J. A. M. Sips, “What do we (need to) know about the kinetic properties of nanoparticles in the body?” Regulatory Toxicology and Pharmacology 2007, 49, 217–229.

[2]           R. Araújo, A. C. M. Castro, A. Fiúza, “The Use of Nanoparticles in Soil and Water Remediation Processes” Materials Today: Proceedings 2015, 2, 315–320.

[3]           N. Sani-Kast, J. Labille, P. Ollivier, D. Slomberg, K. Hungerbühler, M. Scheringer, “A network perspective reveals decreasing material diversity in studies on nanoparticle interactions with dissolved organic matter” Proceedings of the National Academy of Sciences 2017, 114, E1756–E1765.

[4]           R. Wang, F. Dang, C. Liu, D. Wang, P. Cui, H. Yan, D. Zhou, “Heteroaggregation and dissolution of silver nanoparticles by iron oxide colloids under environmentally relevant conditions” Environmental Science: Nano 2019, 6, 195–206.

[5]           M. Dia, J. Farjon, C. Raveleau, A. Simpson, P. Peyneau, B. Béchet, D. Courtier‐Murias, “Understanding the Interactions of Nanoparticles and Dissolved Organic Matter at the Molecular Level by1 H 2D Multi‐Exponential Transverse Relaxation NMR Spectroscopy” Magnetic Reson in Chemistry 2025, 63, 63–48.

[6]           J. Mandral, S. Roques, J.-N. Dumez, P. Giraudeau, J. Farjon, “Evaluation of pure shift NMR methods for the analysis of complex metabolite mixtures with a benchtop NMR spectrometer” Anal. Methods 2025, 17, 3171–3182.

[7]           M. Dia, P.-E. Peyneau, D. Courtier-Murias, B. Bechet, “Detection and quantification of nanoparticles in runoff from a highly trafficked urban motorway” Environ. Sci.: Nano 2025, 12, 1993–2007.