A. Azenkeng, N.E. Stanislowski, J.D. Laumb
University of North Dakota Energy & Environmental Research Center,
United States
Keywords: graphene, optical properties, coal, photoluminescence
Summary:
The optical properties of coal-derived graphene quantum dots (GQDs) have been found to vary based on pretreatment of the starting coal material, including lignite, subbituminous coal, bituminous coal, and anthracite. GQDs produced from raw coal samples have lower ultraviolet–visible spectroscopy absorbances compared to those obtained from cleaned and partially deoxygenated coal samples. The photoluminescence (PL) intensities also varied with pretreatment conditions and with the concentration of GQDs in aqueous solutions. The PL emission maxima show an increasing redshift consistent with increasing coal maturity from lowest to highest coal rank, i.e., lignite, subbituminous, bituminous, and anthracite, respectively. The anthracite-derived GQDs showed a strong emission when excited with visible light as opposed to GQDs derived from the other coal ranks. These results highlight the importance of removing coal-borne impurities to improve the quality of the coal precursor for preparation of graphene products as well as assist in tailoring specific optical applications of GQDs derived from different coal ranks.