Facile synthesis and photophysics of graphene quantum dots

[Display omitted] •Well dispersed GQDs were synthesized using simple and low cost method.•The bi-exponential nature of decay is observed with time constants 53 and 762 ns.•The photoexcited GQDs relax to ground state via two parallel process.•GQDs show excellent photocatalytic activity by degrading the MB dye up to 80 % under sunlight. In this work, well controlled, high yield and mono-dispersed GQDs were synthesized using one pot hydrothermal method. The GQDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR) and ultraviolet-visible (UV–vis) spectroscopy techniques. The finger prints of carbon allotropes and presence of functional groups in the GQDs were investigated by Raman and FTIR spectroscopic measurements. The life time of defect states was measured with the help of transient absorption spectroscopy. A bi-exponential decay was observed with time constants of 53 and 762 ns and assigned to a parallel deactivation from both singlet and triplet states. The GQDs showed to be an efficient photocatalyst (80%) for the photodegradation of RhG dye under the sunlight.