Effects of Sonication and Hydrothermal Treatments on the Optical and Chemical Properties of Carbon Dots.

In our study, we have tested the effects of sonication and hydrothermal treatments on the properties of carbon dots synthesized from a microwave-assisted method (C-dotsMW). When the carbon dots are sonicated in an aerobic environment, the fluorescence quantum yield decreases drastically because the molecular fluorophores attached to the surface of the carbon dots are oxidized during the sonication process. Meanwhile, the sonicated C-dotsMW also lose their Hg2+ ion sensing and photoreduction activity due to the oxidization of surface functional groups. After the hydrothermal treatment, the fluorescence quantum yield of C-dotsMW increases due to the formation of new fluorophores; however, the Hg2+ ion sensitivity and photoreduction activity of C-dotsMW decrease significantly due to the oxidization of surface functional groups. By autoclaving the C-dotsMW at 100 °C, we have demonstrated that we can enhance the fluorescence quantum yield of C-dotsMW without losing their Hg2+ ion sensitivity. This finding can be used to improve the fluorescence quantum yield of the fluorescent ion sensor based on C-dots.

Intra- and intermolecular hydrogen bonds enhance the fluoride-responsiveness of functionalized glycolipid-based gelators.

We propose a facile approach toward enhancing the efficiency of fluoride-responsive gels through the positioning of functionalized receptor units, allowing tunable intra- and intermolecular hydrogen bonding, in the gelator molecules. We prepared the new glycolipid-based gelator 2 and its hydroxy and methoxy derivatives 2a and 2b, respectively, to study the effects of three types modes of supramolecular assembly: solely intermolecular hydrogen bonding in 2, solely intramolecular hydrogen bonding in 2b, and both inter- and intramolecular hydrogen bonding in 2a. 1H NMR spectra confirmed the self-assembly interactions of these glycolipid-based gelators. We measured the minimum gel concentrations and sol-gel transitions and recorded X-ray diffraction patterns and electron micrographs to characterize the gelation behavior and structural organization of each of these supramolecular gels. Among these three gelators, only 2 and 2a could form organogels in the test solvents, indicating that intermolecular hydrogen bonding plays a determinant role in the supramolecular assemblies leading to gelation. The self-assembly of 2 resulted in a bilayer-packed lamellar structure within ribbon-like fibers, whereas that of 2a resulted in hexagonally packed cylindrical micelles within tree-like fibers. A minimum amount of 0.3 equivalent of F- was required for complete disruption of the gel formed from 2a, which was approximately four times lower than that required for the gel formed from 2. Thus, the incorporation of a ß-hydroxy motif-the only difference in the chemical structures of 2 and 2a-led to interesting variations in the resulting gel morphologies and enhanced the gel's fluoride-responsiveness.