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

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.