Graphene oxide derived graphene quantum dots with different photoluminescence properties and peroxidase-like catalytic activity

Graphene quantum dots (GQDs), as a new kind of carbon nanomaterial, have been widely prepared with graphene oxide (GO) as precursor via various methods. However, little work has been done to detail the structural relationship between GQDs and pristine GO. Herein, we synthesized GQDs through acidic oxidation of GO and separated blue-photoluminescent GQDs (b-GQDs) and green-photoluminescent GQDs (g-GQDs) by a simple dialysis technique. Although the transmission electron microscopy (TEM) and atomic force microscopy (AFM) images reveal their similar morphology, the results of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy and zeta potential measurements reveal their distinct structures with different origins from the GO. The b-GQDs may originate from the intact sp(2) cluster of GO, while the g-GQDs are derived from the relaxed carbon backbone with numerous oxygen-containing functional groups. Besides photoluminescence (PL) properties, the peroxidase-like catalytic activity of the two GQDs was also compared. Interestingly, the g-GQDs exhibit higher peroxidase-like catalytic activity and can be used to detect H2O2 with a detection limit of 87 nM, which is lower than most other reported methods. We believe this work provides important insights into the structure, PL properties and potential applications of GO-derived GQDs.