ABSTRACT
In this work, we used a one-step hydrothermal method to synthesize blue-emission sulfur-doped carbon dots (S-CDs) using jaggery as a carbon precursor. The synthesized carbon quantum dots showed low toxicity, good water solubility, anti-interference properties, and stable fluorescence. When excited at 310 nm, the S-CDs produced bright emission with a quantum yield of 7.15% at 397 nm. The S-CDs exhibited selective and sensitive quenching responses with limits of detection (LODs) of 4.25 µg mL-1 and 3.15 µg mL-1 for variable concentrations of Cr6+ and Fe3+, respectively, accompanied by a consistent linear relationship between fluorescence intensity and these concentrations. Fluorescence lifetime measurements were used to investigate the fluorescence quenching mechanism, which supports the static type of quenching. Outstanding benefits of the developed S-CD based fluorescence probe include its low cost, excellent sensitivity and selectivity, and ease of use for the detection of Cr6+ and Fe3+ ions. The developed carbon dot based fluorescent probe was successfully used to detect Cr6+ and Fe3+ ions in real water samples with an excellent recovery ratio.
ABSTRACT
The reaction between methionine and enneamolybdomanganate(IV) in perchloric acid was carried out under pseudo-first-order conditions keeping large excess of methionine. The orders in oxidant and substrate were found to be unity and 0.91, respectively. The reaction proceeds with rapid formation of complex between the reactants followed by its decomposition in a rate determining step. The accelerating effect of hydrogen ions on the reaction is due to the formation of active hexaprotonated oxidant species. The product of the reaction was found to be methionine sulfoxide. The reaction involves direct two-electron transfer step without any free radical intervention. The effect of ionic strength, solvent polarity and the activation parameters were also in support of the mechanism proposed.
