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

Shu Kang Hsu, Zhao Jun Chang, Su-Min Chang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

In situ detection of Cu2+ 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 Cu2+ ions was well fitted by the Stern–Volmer equation, indicating a static quenching process. Interaction between the Cu2+ 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 Cu2+ ions in the field samples, even though those that contained Ca2+, Mg2 +, Na+, K+, and NH+ 4 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 Cu2+ ions are responsible for the benefits and the consequences of the TGA- and LC-capped QDs for Cu2+ sensing, respectively.

Original languageEnglish
Pages (from-to)547-563
Number of pages17
JournalAnalytical Letters
Volume51
Issue number4
DOIs
StatePublished - 4 Mar 2018

Keywords

  • Fourier transform infrared (FTIR) spectroscopy
  • inductively coupled plasma-optical emission spectrometry (ICP-OES)
  • L-cysteine (LC)
  • mercaptosuccinic acid (MSA)
  • quantum dots (QDs)
  • thin-film transistor-liquid crystal display (TFT-LCD)
  • thioglycolic acid (TGA)
  • transmission electron microscopy (TEM)

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