Coal tar pitch (CTP), a by-product of coking industry, has a unique molecule structure comprising an aromatic nucleus and several side chains bonding on this graphene-like nucleus, which is very similar to the structure of graphene quantum dots (GQDs). Based on this perception, we develop a facile approach to convert CTP to GQDs only by oxidation with hydrogen peroxide under mild conditions. One to three graphene layers, monodisperse GQDs with a narrow size distribution of 1.7 ± 0.4 nm, are obtained at high yield (more than 80 wt. %) from CTP. The as-produced GQDs are highly soluble and strongly fluorescent in aqueous solution. This simple strategy provides a feasible route towards the commercial synthesis of GQDs for its cheap material source, green reagent, mild condition, and high yield.

Humic acid (HA) was extracted by a hydrothermal method from Huolinhe lignite from Inner Mongolia. The effects of the alkali-to-carbon mass ratio, water-to-coal mass ratio, reaction temperature, and reaction time on the HA yield were investigated. The physicochemical characterization of the products was performed, and the reaction mechanism was explored. Raw coal, HA, and residual coal were characterized using Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–VIS), elemental composition, and X-ray diffraction (XRD) analyses and compared to each other. The maximum HA yield (90.2%) was obtained from the 0.250–0.180 mm size fraction of the coal sample at a reaction temperature and time of 190 °C and 7 h. Proximate analysis proved that the ash and sulfur of lignite can be removed by hydrothermal treatment. Elemental analysis showed that the O/C and H/C ratios were highest for HA, followed by those for residual coal and raw coal, indicating an increase in the oxygen and hydrogen content of HA. FTIR and UV–VIS analyses showed that hydrothermal extraction destroyed the macromolecular structure of lignite. Moreover, the organics were degraded and hydrolyzed during the reaction process.