A Simple Method for Synthesizing Nitrogen-Doped Carbon Quantum Dots for Fluorescent "Turn off" Mercury (II) Ion Sensing

Here, straightforward and environmentally friendly fluorescent nitrogen doped carbon quantum dots (N-CQDs) with a high blue fluorescence emission at 455 nm are used for ultrasensitive Hg2+ ion detection. Folic acid and urea are used as carbon sources in the carbonization process. Two broad absorption bands at around 280 and 370 nm from UV-Vis spectrum and characteristic absorption peaks from infrared spectrum confirms the successful synthesis of the N-CQDs. Energy dispersive X-Ray analysis confirmed the elemental composition of the N-CQDs. Transmission electron microscopy showed the homogeneous globular morphology of the N-CQDs with an average particle size of 65 nm. Zeta potential measurement established the stability and surface charge of N-CQDs. Dynamic light scattering measurement showed the average size of N-CQDs. With the addition of Hg2+ ion to N-CQDs, the blue fluorescence emission is quenched. Moreover, the N-CQDs can be applied to real water sample such as pond water, river water, and tap water. The detection limit is approximately calculated to be 12 nM and linear range is 0-30 parts per billion.

A Formyl Chromone Based Schiff Base Derivative: An Efficient Colorimetric and Fluorescence Chemosensor for the Selective Detection of Hg2+ Ions

A novel chromone-based Schiff base L was designed and synthesized by condensing an equimolar amount of 3-formyl chromone and 2,4-dinitro phenyl hydrazine. Schiff base L was developed as a potent colorimetric and fluorescent molecular probe to recognize Hg2+ ions over other competitive metal ions. In the presence of Hg2+, Schiff base L displays a naked-eye detectable color change under day and UV365 nm light. Various UV-Vis and fluorescence studies of L were performed in the absence and presence of Hg2+ to determine the sensitivity and the sensing mechanism. With high selectivity and specificity, the detection limit and association constant of L for Hg2+ were estimated at 1.87 µM and 1.234 × 107 M-1, respectively. The developed sensor L was applied to real soil samples for the detection of Hg2+.

Nanocomposites based on thermoplastic polyurethane, millable polyurethane, and organoclay: effect of organoclay content

Dynamically vulcanized thermoplastic polyurethane/millable polyurethane blend and its organoclay-based nanocomposites with co-agent assisted peroxide curative system were prepared by melt intercalation technique using batch mixer followed by compression molding to make sheets. Fourier transform infrared spectroscopy analysis revealed the presence of interfacial interactions due to hydrogen bonding of PUs with organoclays. X-ray diffraction and transmission electron microscopy analyses qualitatively established the uniform dispersion of organoclays within the PU matrix up to 5 phr Cloisite 30B (C30B) content and exhibited small aggregates at higher C30B loading. Mechanical testing reported significant improvement in tensile strength with addition of C30B up to 5 phr loading and then reduced a little but tensile modulus continuously increased with increase in C30B loading. Dynamic mechanical analysis (DMA) evaluated that the storage modulus ( E′) and glass transition temperature ( Tg) of both hard and soft segments of PU matrix substantially enhanced by incorporation of C30B. Thermogravimetric analysis revealed that the thermal stability of the PU matrix noticeably increased with C30B loading. Melt rheological characterization reported that all samples showed a strong shear thinning behavior within the scanned frequency range.