Thiophene adsorption on phosphorus- and nitrogen-doped graphites: Control of desulfurization properties of carbon materials by heteroatom doping

The amounts of adsorbed thiophene were compared among phosphorus- and nitrogen-doped graphite and graphite damaged by Ar+ irradiation to clarify the influence of heteroatom doping on the adsorptive desulfurization properties of π-conjugated carbon materials. On the basis of thiophene coverages estimated from X-ray photoelectron spectroscopy, Phosphorus-doped graphite had an adsorption ability that was 10-20 times larger than that of Nitrogen-doped graphite, indicating that the adsorptive desulfurization property of carbon largely depends on dopant atoms. Polarization dependent analysis using near-edge X-ray absorption fine structure spectroscopy was used to distinguish the configurations at dopant sites, indicating that the curved structures of phosphorus sites exhibited approximately 10 times greater adsorption abilities when compared with the planar structures. Theoretical simulation using molecular orbital calculations indicated different dopant effects between phosphorus and nitrogen along with different thiophene adsorption behaviors between planar and curved structures. Finally, experimental thiophene desorption results obtained at different temperatures revealed an advantage of phosphorus doping for reactivation.