เอกสารประชุมวิชาการระดับขาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 2561

927 งานวิจัยและนวัตกรรมเพื่อสังคมที่มั่นคง มั่งคั่ง และยั่งยืน (Research and Innovation for Social Stability, Prosperity and Sustainability) The MSA capped CdTe QDs provided the lowest sensitivity because its molecule is the biggest and hindered the accumulation of Pb 2+ at the core of the CdTe QDs. Therefore, TGA was selected for further experiment. Figure 3 Effect of stabilizer on the fluorescence quenching of CdTe QDs for the determination of Pb 2+ Reaction time The reaction between the TGA–capped CdTe QDs and Pb 2+ reached an equilibrium very quickly, within 1 min. Therefore, the reaction time of 1 min was selected as the optimum reaction time. Mechanism of quenching Several processes have been proposed to explain fluorescence quenching mechanisms including energy transfer, a non-radiative recombination pathway and collisional quenching. There are two types of fluorescence quenching: dynamic and static [11]. To explain the possible quenching mechanism between TGA–capped CdTe QDs and Pb 2+ , the Stern–Volmer relationship was studied from the equation: F 0 /F = 1  K sv [Q] (2) where F 0 and F are the fluorescence intensity in the absence and presence of Pb 2+ , respectively, K sv is the Stern–Volmer fluorescence quenching constant, which is related to the quenching efficiency of the quencher and [Q] is the concentration of the quencher (Pb 2+ ). If the Stern–Volmer description of the quenching mechanism of Pb 2+ and TGA–capped QDs involves dynamic quenching, the plot of F 0 /F as a function of [Q] should be linear. The obtained Stern–Volmer plot (Figure 4) indicates the involvement of the dynamic quenching process [12]. The quenching of the TGA-capped CdTe QDs was due to the competitive TGA binding of Pb 2+ with the QDs core (Figure 5). Figure 4 Stern–Volmer plot for the interaction of Pb 2+ and TGA-capped CdTe QDs (a), MPA-capped CdTe QDs (b), GSH-capped CdTe QDs (c) and MSA-capped CdTe QDs (d) by Pb 2+