Fluorescent Determination of Copper(II) in Industrial Wastewater Using Thiol-Capped Cadmium Sulfide-Zinc Sulfide Quantum Dots as the Probe

• Published in: Analytical letters 2018-03, Vol.51 (4), p.547-563
• Main Authors: Hsu, Shu-Kang, Chang, Zhao-Jun, Chang, Sue-Min
• Format: Article
• Language: English
• Subjects: Bonding agents; Cadmium sulfide; Capping; Chemical bonds; Copper; Copper compounds; Early warning systems; Fluorescence; Fourier transform infrared (FTIR) spectroscopy; inductively coupled plasma-optical emission spectrometry (ICP-OES); Industrial wastes; L-cysteine (LC); LCDs; Ligands; Liquid crystal displays; Manufacturing; mercaptosuccinic acid (MSA); Quantum dots; quantum dots (QDs); Quenching; Semiconductor devices; Thin film transistors; thin-film transistor-liquid crystal display (TFT-LCD); thioglycolic acid (TGA); transmission electron microscopy (TEM); Wastewater; Zinc sulfide
• ISSN: 0003-2719; 1532-236X
• DOI: 10.1080/00032719.2017.1338715

In situ detection of Cu 2+ ions in the effluent from thin-film transistor-liquid crystal display (TFT-LCD) manufacturing facility has been successfully achieved using thiol-capped CdS/ZnS quantum dots (QDs) as the fluorescence probes. Three types of ligands, including L-cysteine (LC), mercaptosuccinic acid (MSA), and thioglycolic acid (TGA), were used as capping agents for stabilizing and functionalizing the QDs. Fluorescence quenching of the QDs by Cu 2+ ions was well fitted by the Stern-Volmer equation, indicating a static quenching process. Interaction between the Cu 2+ ions and the thiol-based capping agents to form Cu-S bonding was responsible for the nonradiative decay. The thiol-capped probes exhibited low detection limits (0.016-0.063 mg L −1 ), high recovery (81.7-114.5%), good precision (relative standard deviation = 0.36-4.56%), and suitable accuracy for the detection of Cu 2+ ions in the field samples, even though those that contained Ca 2+ , Mg 2 + , Na + , K + , and ions, which were 300-16,600 times higher in concentration than the target. These results clearly verify the feasibility of using the QDs as an early warning system for assisting TFT-LCD manufacturing facilities in compliance with strict effluent standards (0.15 mg L −1 ). Among the three types of thiol-capped QDs, the TGA-capped probes were the most sensitive and the LC-capped probes exhibited the highest errors. Substantial loading of the small TGA ligands on the surface and competitive complexation of the amino groups with Cu 2+ ions are responsible for the benefits and the consequences of the TGA- and LC-capped QDs for Cu 2+ sensing, respectively.