One pot selective synthesis of water and organic soluble carbon dots with green fluorescence emission

Abstract

In this work, two types of carbon dots (CDs), water soluble carbon dots (WCDs) and organic soluble carbon dots (OCDs), have been selectively synthesised via a simple, energy-saving process at room temperature. By using cetylpyridinium chloride monohydrate (CPC) as the carbon source, CDs with strong green fluorescence emission could be obtained only in the presence of NaOH, without the need for external heating or additional energy input such as microwave or ultrasound. By controlling the reaction conditions of concentration of NaOH and reaction time, WCDs and OCDs were synthesised and this is the first time for the controllable synthesis of WCDs and OCDs at ambient conditions. The as-prepared WCDs and OCDs were characterised by UV-vis absorption, photoluminescence (PL) spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and PL lifetime. The results show that both WCDs and OCDs have uniform particle distribution, better photostability and strong luminescence with a quantum yield of 7.2 and 16.7% for WCDs and OCDs, respectively. The formation mechanisms of WCDs and OCDs were postulated by detailed examining of the reaction process and characterisation of the WCDs and OCDs. Owing to the favourable properties of strong emission, good photostability and low toxicity, the WCDs have been successfully applied for bioimaging. This new bottom-up synthetic strategy results in harvesting high-quality CDs, exhibiting the potential of easy and inexpensive large-scale production of WCDs and OCDs.