Nanotechniques let us “see” at the nanometre scale, where all the action is. We use them to learn nature’s secrets, to understand the fundamental physical and chemical processes that take place at the interface between natural materials and fluids (water, oil, CO2, O2, anything that flows). Then we use our new knowledge to find solutions to society’s challenges.
The challenges we tackle include finding ways i) to ensure safe drinking water, ii) to store waste responsibly, iii) to convert CO2 back to rock form where it will be stable for thousands of years, iv) to understand how organisms make biominerals, such as bones, teeth and shells and v) to squeeze a bit more oil from reservoirs that are reaching the end of their lifetime. Our research on how organic compounds interact with mineral surfaces also provides better insight into how to remediate contaminated drinking water aquifers, and offers clues for how fluids flow in other porous media such as catalysts, filtration systems, soils and sediments. Our approach is well suited for characterising natural nanoparticles in general, such as the volcanic ash that closed Europe’s airspace. Occasionally we contribute information and data interpretation for the Mars mission.
The NanoGeoScience group works closely with X-ray physics in the Nano-Science Center and has tight partnerships with the Danish Technical University and universities in Toulouse, F; Leeds, Warwick, University College London, York, Sheffield and Cambridge, UK; Oslo, N; Reykjavik, I; Karlsruhe, Münster, Potsdam and Max Planck Göttingen, D; Twente, NL; Waterloo, Canada; Berkeley and PNNL, USA as well as with several companies, including Maersk Oil, BP, DONG, Reykjavik Energy, Rockwool, Haldor Topsøe, Níras, COWI, GEO as well as AMPHOS21, a consulting engineering firm in Spain.
We have collected expertise and instrument facilities that are unique in the world for characterising natural materials at nanometre scale, for example, X-ray photoelectron spectroscopy (XPS), focused ion beam scanning electron microscopy (FIB-SEM) and atomic force microscopy (AFM) with chemical force mapping (CFM). We are frequent users of a range of techniques at synchrotron radiation (SR) facilities around the world, such as X-ray tomography (XCT) and we make good use of computational approaches, including molecular dynamics (MD) and density functional theory (DFT).
This year, we commissioned a new instrument, a NanoIR2. It is based on atomic force microscopy (AFM), which maps topography on surfaces with nanometre resolution laterally and sub-nanometre resolution perpendicular to the surface. Coupled to the AFM is a pulsed, tuneable infrared (IR) laser. Material on the surface can be detected by the tip when the wavelength of the laser matches its absorption energy. We can record IR spectra at chosen surface sites, for fingerprinting, or we can select a wavelength and map material that absorbs at that specific wavelength, e.g. 1,400 cm-1, representing C-O stretching and O-H bending (see figure below). We are excited about the possibilities for applying this capability in several current and future projects.
X-ray tomography (XCT) provides 3D images of the micro and nanostructure of materials without destroying the sample. This is useful for time-dependent studies, when the material is fragile or when analysis with several techniques is required. One of our large projects, Predicting Petrophysical Parameters (P3), funded by Maersk Oil and the Danish Innovation Foundation, aims to derive information from drill cuttings, about pore networks and flow of oil and water, to optimise production strategies. Microstructural characterisation of soil and aquifer material can contribute to groundwater protection or remediation of contaminated sites. There are also other interesting applications. For example, we worked with the Smithsonian Institute, USA to study biodegradation of handmade paper from the 17th century. XCT had not previously been applied on cultural heritage materials suffering fungal deterioration. This was a challenge because both paper fibres and fungal cells are made of organic compounds so X-ray attenuation for these materials is quite similar.
We developed a method to screen for shape, size and texture of the subspherical fungi to differentiate them from the cellulose fibres, which were larger and mostly linear. The 3D images showed that fungus permeated the paper, meaning that surface fungicide treatment can never be effective.
Some organisms use minerals for protection or support. They engineer organic molecules to enhance crystal growth with a form that fits their purpose. Understanding how CaCO3 transforms from the precursor, amorphous calcium carbonate ,ACC, to calcite or aragonite, in the presence of biomolecules, provides clues about the controls that organisms exert on their environment. Citrate is thought to modify local atomic structure in ACC, directing its transformation. Our analyses with microscopy, spectroscopy and advanced synchrotron X-ray scattering demonstrated that citrate dramatically enhanced ACC lifetime, thermal stability and changed calcite morphology but regardless of the concentration, the interatomic distances were minimally affected.