The student will be based in the School of Engineering at Newcastle University (supervised by A. Neumann), where laboratory-based experiments will be carried out to answer questions 1 and 2. The student will visit Durham University to learn and apply specific experiments, as well as computational chemistry tools (molecular dynamics: supervised by C. Greenwell; density functional theory (DFT): supervised by S. Clark), to complement experimental observations with a fundamental understanding of the governing molecular level processes and mechanisms.
Laboratory experiments (Question 1) will be carried out with well-characterised clay minerals differing in total Fe content, extent and location of excess charge, and including kaolinite-type and smectite-type minerals. Additionally, Fe-containing clay minerals will be redox-altered, i.e. Fe(III)-bearing clay minerals will be reduced and Fe(II)-bearing clay minerals will be oxidised to study the effect of redox changes on chlorinated solvent sorption. Sorption kinetics, swelling capacity and extent will be quantified for a large range of relevant contaminants, including hexachloroethane (HCA), tetrachloroethene (PCE), trichloroethene (TCE), isomers of dichloroethene (DCE), and vinylchloride (VC). In a second step and to answer Question 2, a subset of the same clay mineral will be assessed for the effect of interlayer cations (Na+ vs K+ vs Ca2+), anions (Cl- vs SO42- vs CO32-), ionic strength, and pH value on the chlorinated compound sorption. Bulk sorption experiments will be combined with measurements of mineral charge (zeta-potential) and, where needed, with studies of surface wettability and bulk swelling. Question 3 will be addressed by implementing classical atomistic molecular dynamics simulations and DFT calculations for selected reaction conditions tested in laboratory experiments, where significant effects are noted.
Key equipment and methods to be used in the Environmental Engineering laboratories at Newcastle University include an anaerobic glovebox, enabling experiments under controlled environmental conditions; analytical instruments for organic contaminant analysis (GC-MS, GC-ECD) and ion quantification (ICP-OES for cations, IC for anions); and techniques for mineral characterization (XRD, FT-IR, MÃƒÂ¶ssbauer spectroscopy, zeta-potential measurements). Equipment for studying surface wettability (including contact angle apparatus/goniometer, chemical force microscopy and fluorescence microscopy) is available in the Greenwell Group chemistry labs at Durham University, as are bespoke instruments for measuring compacted bulk clay mineral swelling and in situ X-ray diffraction of crystalline swelling, (supervisor: C. Greenwell). Durham University also hosts the equipment/access to software needed for the molecular dynamics (GROMACS or LAMMPS) and DFT calculations (with Clark a developer of the CASTEP code) as well as the Hamilton high performance computing service.