CO₂ Adsorption on Magnetite Fe₃O₄(111)

We monitored the adsorption of carbon dioxide (CO2) on well-ordered Fe3O4(111) films using infrared reflection-adsorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The results show that CO2 weakly interacts with the regular Fe3O4(111) surface and almost fully desorbs at temperatures above ∼140 K. Accordingly, IRA spectra show mainly physisorbed CO2 species. However, TPD and IRAS features corresponding to a more strongly bound, chemisorbed species were also observed. Their formation required relatively long CO2 exposure times, which we associated with adventitious coadsorption of residual water from the vacuum background. Since the Fe3O4(111) surface is known to be very sensitive toward water, we additionally investigated the correlation between water and CO2 adsorption process and found that the degree of surface hydroxylation plays a crucial role in CO2 binding to the Fe3O4(111) surface, ultimately leading to the formation of bicarbonate species