Time-Resolved MIR Reflection–Absorption Spectroscopy of N2O, CO, and CH4 Adsorption on Graphene

The time- and temperature-dependent adsorption of N2O, CO, and CH4 on CVD-grown graphene has been investigated by MIR reflection–absorption spectroscopy to gain information about the adsorption kinetics, notably the rate constants k and activation energies Ea of the adsorption step. The gas adsorption is followed by determining the change of the reflected beam intensity with time by taking difference spectra, i.e., subtracting the baseline signal (reflectivity of graphene at the respective gas excitation line) from the measurement with added gas. The experiments yield adsorption activation energies Ea of −19.6 ± 1.1 (N2O), −12.1 ± 0.2 (CO), and −9.5 ± 1.7 kJ/mol (CH4). The obtained Ea values are in excellent agreement with the literature results from theory, thereby confirming these studies. The Ea values indicate physisorption, i.e., no strong bonding of the gas molecules to graphene. The analyzed adsorption rate constants k are reported for the first time and are on the order of 1011 to 1012 molecules·s–1·cm–2 with N2O showing the highest value and CH4 the lowest value. The adsorption rate constants follow the series N2O > CO > CH4, in line with the charge transfer abilities of the molecules. This work can be easily extended to kinetic studies of other gases hazardous to the environment and adsorption studies with other 2D materials using versatile MIR reflection–absorption spectroscopy.