Microwave Irradiation Synthesis Of CdTe Quantum Dots At Expected Temperature And Their Application In The Detection Of Heavy Metal Ions (Hg²⁺,Ag⁺)

Quantum dots, also referred to as colloidal semiconductor nanocrystals, have unique optical and electrical properties. In comparison with dyes, Quantum dots have high fluorescence quantum yields, good photostability and negligible photobleaching. The synthesis and application of IIB-VIA group QDs are the topic of the scientific research, and CdTe QDs is one of the most important QDs among the IIB-VIA QDs. To date, two rudimentary approaches have been reported for the synthesis of QDs. One is the organometallic route. The as-prepared QDs are generally capped with hydrophobic ligands, and hence cannot be directly employed in bioapplications. The other is the aqueous synthesis route, producing QDs with excellent water solubility, biological compatibility, and stability. Due to the photoluminescence (PL) property of QDs is closely related to the nature of the surface, the PL efficiency changes with the interactions between the surface of QDs and given chemical species. On this basis, QD-based optical sensor is constructed. Recently, the effect of ionic species on the luminescence of QDs has attracted much attention. Especially important in this regard is sensors that detect heavy metal ions which have severe effects on the human health and environment. In this paper, highly luminescent water-soluble CdTe QDs are synthesized in an aqueous environment and they are used as ion probes to detect heavy metal ions. The main contents can be summarized as follows:1. A facile one-pot microwave irradiation reduction route has been developed for the synthesis of highly luminescent CdTe quantum dots using Na₂TeO₃ as the Te source in an aqueous environment. The photoluminescence quantum yield of CdTe quantum dots prepared using relatively short reaction times (10-40min) reached 40-60% (emission peaks at 550-640nm). The obtained CdTe QDs were characterized by X-ray diffraction spectrometry (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV-vis and fluorescence spectrometry. The experiment results show that the diameter is homogeneous and the size distribution is narrow. CdTe QDs with high QY are stable and their fluorescence is negligible even after aging for 63 days. The synthesis parameters of this simple and rapid approach, including the reaction temperature and time, the pH of the reaction solution and the molar ratio of the 3-mercaptopropionic acid (MPA) stabilizer to Cd²⁺, have considerable influence on the particle size and photoluminescence quantum yield of the CdTe quantum dots. Furthermore, The as-obtained water-soluble CdTe QDs with high QY can be used to develop highly sensitive and selective probes for the detection of mercury (II) ions. The response was linearly proportional to the concentration of Hg²⁺ ion in the range 8.0×10^-9 mol/L to 2.0×10^-6 mol/L with a detection limit of 2.7×10^-9 mol/L.2. A facile one-pot microwave irradiation reduction route is developed for the synthesis of highly luminescent CdTe quantum dots using gelatin as stabilizer in an aqueous environment. The obtained CdTe QDs are characterized by X-ray diffiaction spectrometry (XRD), IR spectrum, UV-vis and fluorescence spectrometry. Based on the fluorescence quenching of CdTe QDs by Ag⁺ ions, a simple, rapid, sensitive and selective detection method for silver ion is proposed. The mechanism between Ag⁺ and gelatin-capped CdTe QDs is also discussed by fluorescent spectrum and absorbance spectrum. The interaction between Ag⁺ and the QDs surface should be of the ion-binding type.