Green Synthesis of Highly Fluorescent Graphene Oxide/Carbon Quantum Dot Colloid from Rice

Carbon quantum dot-graphene oxide hybrids have been synthesized from rice precursor using a ball-milling-assisted hydrothermal method. The structure of the quantum dots and graphene oxide was studied using x-ray diffraction analysis, energy-dispersive x-ray spectroscopy, and elemental mapping. The size and morphology of the nanostructures were studied using field-emission scanning electron microscopy and transmission electron microscopy, revealing that the product was composed of spherical nanoparticles and nanosheets. We argue that the presence of some metals in the rice precursor can catalyze the synthesis of graphene oxide. The structure of the product was studied by Fourier-transform infrared spectroscopy. Investigation of the optical properties of the quantum dots and graphene oxide by ultraviolet-visible spectroscopy and photoluminescence (PL) spectroscopy revealed strong PL properties. The PL quantum yield could be improved by surface modification using polyethylene glycol, polyvinylpyrrolidone, ethylenediaminetetraacetic acid, and acetylacetone. The photocatalytic properties of the carbon nanomaterial (CNM) were investigated based on the decomposition of Eriochrome Black-T and Eosin Y dyes, revealing strong photocatalytic activity. The thermal stability of the product was examined by thermogravimetric analysis. Furthermore, atomic absorption spectroscopy showed that CNM could be used to eliminate cations of heavy metals such as lead and cadmium from toxic water.