Reduced graphene oxide supported C 3 N 4 nanoflakes and quantum dots as metal-free catalysts for visible light assisted CO 2 reduction

Abstract

The visible light photocatalytic reduction of CO 2 to fuel is crucial for the sustainable development of energy resources. In our present work, we report the synthesis of novel reduced graphene oxide (rGO)-supported C 3 N 4 nanoflake (NF) and quantum dot (QD) hybrid materials (GCN) for visible light induced reduction of CO 2 . The C 3 N 4 NFs and QDs are prepared by acid treatment of C 3 N 4 nanosheets followed by ultrasonication and hydrothermal heating at 130-190 °C for 5-20 h. It is observed that hydrothermal exposure of acid-treated graphitic carbon nitride (g-C 3 N 4 ) nanosheets at low temperature generated larger NFs, whereas QDs are formed at higher temperatures. The formation of GCN hybrid materials was confirmed by powder X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy (TEM), and UV-vis spectroscopy. High-resolution TEM images clearly show that C 3 N 4 QDs (average diameter of 2-3 nm) and NFs (≈20-45 nm) are distributed on the rGO surface within the GCN hybrid material. Among the as-prepared GCN hybrid materials, GCN-5 QDs exhibit excellent CO 2 reductive activity for the generation of formaldehyde, HCHO (10.3 mmol h -1 g -1 ). Therefore, utilization of metal-free carbon-based GCN hybrid materials could be very promising for CO 2 photoreduction because of their excellent activity and environmental sustainability.