Synthesis of sulfur-chlorine-doped fluorescent carbon quantum dots from leachate membrane concentrate as a selective probe for Pd2+ detection

Abstract

In this work, humic acid-based sulfur-chlorine-doped carbon quantum dots (L-CQDs) were synthesized by using a polyethylene glycol (PEG)-assisted hydrothermal technique using landfill leachate concentrate (LLC) as a carbon source. The prepared L-CQDs contain many oxygen-containing functional groups on the surface with a small average particle size of 4–6 nm, resulting in excellent hydrophilicity and dispensability. The three-dimensional fluorescence spectrum shows that the characteristic peak for humic acid for LLC is redshifted after adding PEG as an inactivator, indicating that L-CQDs are synthesized by PEG encapsulation and linkage. The optimum condition for preparing L-CQDs involves the addition of 0.5 g PEG (MW = 2000) into 20 mL LLC and reaction at 200 °C for 5 h, with the optimal L-CQD quantum yield reaching 5.32%. L-CQDs were used to prepare fluorescent nanoprobes for the detection of palladium ions (Pd2+). The obtained nanoprobe shows admirable performance in detecting Pd2+, with high selectivity, excellent water solubility and stability. The fluorescence intensity of the nanoprobe is selectively quenched through static quenching by Pd2+ in the concentration range of 5–40 μmol L−1. This work provides a simple, easy, and fast detection method for Pd2+ and opens up a way for the resource utilization of LLC.