Physicochemical mechanisms for gas adsorption on clay mineral interfaces and surfaces

Abstract

Increasing anthropogenic carbon emissions have a detrimental impact on our planet's ecosystems. If we want to keep our planet habitable for future generations, serious action is needed. We need to both reduce and mitigate our carbon emissions through utilization or storage. In this context, clay minerals are interesting. They are naturally abundant, provide large surface areas, are stable, have a low cost and are present in caprock formations for geological storage of carbon. Clay minerals are layered materials where the electrostatic forces hold together stacks of phyllosilicate layers. In this thesis, the adsorption of carbonaceous gases are investigated on pure and nano-functionalized clay mineral surfaces and interfaces to provide deeper insight into relevant physicochemical processes.

By employing a surface science approach, adsorption of CO, CO2 and CH4 by nickel nanostructures on muscovite mica are studied with photoemission spectroscopy, temperature-programmed desorption and atomic force microscopy. The thesis investigates how coverage and size of the nanostructures affects the adsorption of CO, how oxidation of the nanostructures increases the CO2 adsorption and how atomic hydrogen presumably results in the chemisorption of CH4 on Ni surfaces.

From a bulk and interface perspective, with X-ray and neutron diffraction, inelastic neutron spectroscopy, Raman spectroscopy and gravimetric adsorption, it is found that swelling and adsorption of CO2 in fluorohectorite is heavily dependent on the interlayer species. No adsorption of CO2 for dehydrated fluorohectorite with Na+, Cs+, Ca2+ and Ba2+ as the interlayer cations was observed, in partial disagreement with published literature. However, when fluorohectorite was exchanged for Li+ or Ni2+ swelling and uptake was observed in response to CO2. The thesis investigates the underlying mechanisms, showing a previously overlooked ordered interstratification of a nickel hydroxide species, how this species relates to CO2 adsorption, how the capacity for CO2 may be tuned by controlling the layer charge of each platelet and trying unravel how water present in the clay may affect the adsorption properties.

The results demonstrate new pathways for controlling the adsorption of carbonaceous gases in clay minerals, which ultimately may increase their technological relevance as gas adsorption materials.