▎ 摘　　要

The effective use of solar energy in sewage disposal has been extensively investigated. This work focuses on the photocatalytic property of graphene quantum dots (GQDs) and polymer-modified GQDs under visible light. A hydrothermal synthesis route to GQDs was developed by using citric acid as a carbon precursor. The GQDs were modified with polyethylenimine (PEI) and polyethylene glycol (PEG). The obtained GQDs, GQDs-PEls, and GQDs-PEGS were characterized and their structural information was determined through Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), photoluminescence spectroscopy, and UV-Vis absorption spectroscopy. Results revealed that the GQDs were uniform in size (2-5 nm) and rich in oxygen-containing groups. The GQDs exhibited a strong blue and excitation-independent photoluminescent behavior under excitation wavelengths of 320-420 nm. The photocatalytic performance of these samples was demonstrated on the basis of methylene blue (MB) degradation. The photocatalytic rates of GQDs, GQDs-PEIs, and GQDs-PEGS decreased successively. The polymer-modified GQDs could qualitatively control the degradation rate of MB. Free radical species were generated to oxidize MB under light irradiation. Thus, photocatalytic organic matter degradation, sustained drug release, and tracking can be combined to implement proper sewage disposal. Prime novelty: The main object of this work is to find out a novel property of graphene quantum dots (GQDs) as efficient nanomaterials for degradation of organic pollutant dyes under visible light irradiation. And, the GQDs exhibited a strong blue and excitation-independent,photoluminescent behavior under excitation wavelengths of 320-420 nm. Moreover, the degradation rate could be qualitatively controlled by using different polymer modified GQDs. Thus, photocatalytic organic matter degradation, sustained drug release, and tracking can be combined to implement proper sewage disposal. Also, the degradation mechanism is discussed. (C) 2016 Elsevier B.V. All rights reserved.