Tunable multicolour S/N co-doped carbon quantum dots synthesized from waste foam and application to detection of Cr3+ ions

Hydrothermal synthesis of B, S, and N-doped carbon quantum dots for colorimetric sensing of heavy metal ions

In this study, glucose was used as the carbon source to synthesize carbon quantum dots (CQDs) and also aimed to synthesize CQDs doped with heteroatoms such as sulphur, nitrogen, and boron to enhance their functionality. The obtained material has been characterized by several techniques. According to FL analysis, the highest peaks for CQD, N-CQD, B-CQD, and S-CQD were determined as 432 nm (ex 350), 425 (ex 350), 430 nm (ex 340 nm), and 436 nm (ex 340 nm), respectively. FTIR spectra showed different characteristic peaks for CQD, and the FTIR results show that CQDs have a unique structure. According to TEM analysis, the morphology of all CQDs was found to be spherical and monodisperse with average sizes in the range of 5-7 nm. The characterization results of CQDs show that the addition of heteroatoms changes the properties of CQDs. The synthesized CQDs were also tested as colorimetric sensors for the detection of heavy metals. It was observed that CQDs detected Fe3+ metal ions, B-CQD and S-CQD detected Fe3+ and Ag+ metal ions, and N-CQDs detected Ca2+ metal ions. Sensor studies were performed for all CQDs and linear plots were obtained against metal concentrations in the range of 0.06-1.23 μM. LOD values for CQD, N-CQD, S-CQD, and B-CQD were calculated as 0.187 μM (Fe3+), 0.391 μM (Ca2+), 0.224 μM (Fe3+)-0.442 μM (Ag+), and 0.182 μM (Fe3+)-0.174 μM (Ag+), respectively. The results show that the addition of B, N, and S atoms to CQDs plays a role in the improvement and modification of colorimetric sensor properties and has the potential to be used in sensor applications for the detection of heavy metals in areas such as the environment and health.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

Luminescence feature of new 3,6-di(thiazolidin-5-one-2-yl)-carbazole derivative: synthesis, photophysical properties, density functional theory studies, and crystal shape effect

A new carbazole chromophore conjugated with substituted thiazolidine-4-one (CzPT) was synthesized by applying the Knoevenagel reaction between 3,6-diformyl-N-hexylcarbazole and ethyl 2-aceto-2-(5-oxo-3-phenylthiazolidin-2-ylidene)acetate. The chemical structure of the new derivative (CzPT) was elucidated by spectral studies. The CzPT absorption spectra in different solvents exhibited a red shift for λ_max by increasing solvent polarity. Bands at 430-474 nm appeared and were attributed to intramolecular charge transfer with high π-π* characteristics. CzPT fluorescence spectra exhibited a red shift after increasing the solvent polarity. To understand the Stokes' shift ( ∆ ν ¯ ) behaviour of the CzPT derivative referring to the polarity of solvents, Lippert-Mataga and linear solvation-energy relationship (LSER) models were employed in which the LSER exhibited respectable results compared with Lippert-Mataga (r² = 0.9707). Moreover, time-dependent density functional theory absorption spectra in hexane and dimethylformamide showed that λ_max had a major contribution in the highest occupied molecular orbital to lowest unoccupied molecular orbital transition in both solvents. In addition, the reduced uniformity of crystal features may lead to dislocation or anomalous arrangement of crystals with irregular spacing, which automatically enhances the optical properties of such crystals.