Tuning optical properties of graphene quantum dots using photoexcited TiO2 for catalytic application

Abstract

In this work, a simple strategy to tune the emission property of graphene quantum dots (GQDs) from green to blue color using a photochemical method is proposed. Further, the resultant materials are demonstrated to be an efficient and effective catalyst for the reduction of p-nitrophenol to p-aminophenol. Initially, green color emitting GQDs (g-GQDs) is prepared by using a chemical method involving acid reflux of graphene oxide obtained from a modified Hummer's method. Later these g-GQDs are exposed to photochemical excitation with titanium dioxide (TiO2) using UV light at a fixed wavelength of 365 nm and the resultant GQDs are observed to emit blue color (b-GQDs). Basically, the introduction of photochemically excited TiO2 nanoparticles provides excess electrons for g-GQDs to undergo further reduction to form b-GQDs leading to the formation of more sp2 hybridized domains within the carbon network than sp3 in the resultant b-GQDs. Consequently, the emission of GQDs is shifted from green to blue, and significantly ∼4 fold enhancement in the average quantum yield of GQDs is noted. These interesting research findings are analyzed by using zeta potential measurements, spectroscopic (FTIR, UV–visible, and Fluorescence) studies and microscopic investigation. Finally, TiO2 reduced GQDs are subsequently used for the reduction of p-nitrophenol to p-aminophenol, and the results obtained revealed that this material could potentially be employed as an effective catalyst.