The aim of this project is to gain a mechanistic understanding of diffusion and diffusive isotope fractionation in aqueous systems. The findings will contribute to advance the basic science of solute diffusion in aqueous systems and will also have important practical applications since compound specific isotope analysis is a technique that is increasingly used in practical applications in a wide variety of scientific fields including environmental sciences, physiology, chemical and biochemical engineering as well as food and nutrition science.
Stable isotope data allow improving the understanding of both physical and transformation processes as well as their interaction in complex environmental systems. In the last decade compound-specific isotope analysis developed at a fast pace and today it has a very wide spectrum of practical applications. In particular, stable isotope techniques are frequently used to track the fate and transport of organic contaminants in environmental systems. Most of the research in this field has focused on the study of isotope fractionation during transformation processes and little is known about the isotopic shifts due to physical transport processes of organic contaminants. The focus of this project is to investigate diffusion in aqueous solution and isotopic fractionation during diffusive processes that are salient transport processes in subsurface environments such as soils and groundwater. The study will address the diffusive and fractionating behavior of key groundwater organic contaminants such as chlorinated solvents and petroleum hydrocarbons. The work will be conducted by combining laboratory experiments and molecular dynamic simulations:
- Laboratory experiments will be performed to investigate and quantify the extent of diffusive isotope fractionation of the organic contaminants using gel diffusion tubes (Jin et al., Environmental Science & Technology, 2014). The experiments allow quantifying the diffusivity of organic chemicals and to resolve spatial isotopic gradients during diffusive transport. Such gradients originate by the isotopic substitutions in the chemicals and are determined by measuring stable isotope ratios by compound-specific isotope analysis.
- Molecular dynamic simulations will be instrumental to gain a mechanistic understanding of the impact of isotopic substitution on the diffusive behavior of organic chemicals. They will allow us to quantitatively investigate the role of different properties such as molecular structure of the organic chemicals, polarity, solute-solvent interactions and temperature on diffusion and diffusive isotope fractionation.
The project is suitable for a wide variety of candidates from different disciplines including environmental engineering, chemistry, chemical engineering, physics and computational sciences. Depending on the specific interests and skills of the candidate he/she could focus in more detail either on the experimental or on the modeling tasks. The main requisite of an ideal candidate for this project is that he/she should be curious and interested in the basic understanding of diffusion processes and in the interpretation of isotopic signatures of organic contaminants in the environment and/or in engineering systems. The project is a cooperation between DTU Environment and DTU Chemistry.