Preparation and spectroscopic characteristics of coal⁃based graphene quantum dots from demineralized anthracite in Jiangoushan，Ningxia

The feasibility of preparing graphene quantum dots(GQDs)from demineralized anthracite was studied by one⁃step chemical oxidation using the Jiaogoushan anthracite in Ningxia as carbon source. The chemical structure and composition of demineralized anthracite and graphene quantum dots were characterized by X⁃ray diffraction， Raman spectroscopy，high⁃resolution transmission electron microscopy，X⁃ray photoelectron spectroscopy and fluores⁃ cence spectroscopy. The carbon content of the Jiangoushan anthracite and its demineralized samples is high，94.19% and 94.43% respectively，and the H / C atomic ratio is very low，0.14 and 0.15 respectively. The macerals of raw coal are mainly vitrinite，accounting for 81.4%. The results of X⁃ray diffraction analysis show that the aromatic layer diame⁃ ter(La)，stacking height(Lc)and average stacking layer number(Nave)of demineralized anthracite are all good，with La being more than 6.0 nm，Lc being 2.02 nm，Nave being more than 6 and fa being 0.89. The Raman spectroscopy analysis shows that the C—C vibration of the demineralized anthracite polycyclic aromatic compounds is strong，the ID / IG value is 0.85，and the G—D value is 157.88 cm-1，which is conducive to the preparation of graphene quantum dots. It is found that the graphene quantum dots with uniform size，good crystal form and stable fluorescence properties can be prepared by one⁃step chemical oxidation from the Jiangoushan anthracite. The overall size of aromatic clusters of GQDs is large(8-9 nm)，the maximum diameter is 12 nm，and the number of aromatic clusters with sizes between 6-10 nm reaches 92%. Compared with precursor coal samples，the graphene quantum dots prepared from the demineralized coal samples have smaller defects，with ID / IG values of 0.81 and G-D values of 264.25 cm-1. Under the high⁃resolu⁃ tion transmission electron microscope， the aromatic rings of coal⁃based graphene quantum dots are arranged regularly，the hexagonal crystal structure is visible，and the crystallinity is good. The X⁃ray photoelectron spectroscopy shows that the oxygen containing functional groups of the demineralized anthracite and graphene quantum dots prepared are relatively simple，mainly C