A value product after the hydrothermal treatment of sludge: Carbon quantum dots and its application

Abstract

Carbon quantum dots (CQDs) are highly promising fluorescent nanomaterials with a wide range of applications. This study presented a novel, clean, hydrothermal carbonization (HTC) method for synthesizing fluorescent CQDs from sludge. A response surface design method was employed to optimize synthesis conditions, resulting in CQDs with excellent fluorescence properties. They were excited at 320 nm and emitted blue fluorescence at 450 nm under UV light. A mechanism for the formation of CQDs from sludge during HTC was proposed and revealed that the CQDs had an aromatic polymer structure with abundant oxygen-containing groups. X-ray photoelectron spectroscopy confirmed N and Fe doping of CQDs, which significantly improved their fluorescence properties. Additionally, a fluorescence quenching analysis showed that the CQDs selectively detected Pb2+ in the aqueous phase, indicating their potential application in Pb2+ detection. The photoinduced electron transfer (PET) arising from amino groups and other reductive functional groups has been shown to align with the quenching mechanism during the detection of Pb2+ by CQDs. This study provided a cost-effective and scalable approach that could be used to produce CQDs for the in situ detection of Pb2+ in wastewater.