Effect of fluorine doping on structure and CO2 adsorption in silicon carbide-derived carbon

We investigate the effect of fluorine-functionalisation of nanoporous silicon carbide-derived carbon (SiCDC), on its structural as well as adsorption properties, with the aim of assessing its suitability for CO2 capture. The morphology and structure of samples fluorinated to three different F/C ratios are characterized by several analysis techniques, as well as gas adsorption. Fluorination is seen to have a stabilising effect on SiCDC, and stronger C-F bonds are formed at high levels of fluorination. Further, increasing fluorination level leads to a decrease of specific surface area and total pore volume, consistent with recent simulation results from this laboratory. Fluorination has little effect on the ultra-microporosity at low levels of fluorination, but leads to significant decrease at high levels of fluorination. Sub-atmospheric pressure CO2 adsorption kinetics is interpreted using a bidisperse pore structure model, considering particle scale diffusion in large micropores and local grain scale diffusion with an interfacial barrier in ultra-micropores. The comparison of the CO2 uptake-time curves for the fluorinated and non-fluorinated samples shows slightly slower uptake with increasing fluorination level, largely due to decrease in pore volume and surface area. The isosteric heat of adsorption and activation energy barriers both decrease mildly with increased level of fluorination.