L-Cysteine/Silver Nitrate/Iodate Anions System: Peculiarities of Supramolecular Gel Formation with and Without Visible-Light Exposure

Abstract

In this study, novel anion photo-responsive supramolecular hydrogels based on cysteine–silver sol (CSS) and iodate anions (IO3−) were prepared. The peculiarities of the self-assembly process of gel formation in the dark and under visible-light exposure were studied using a complex of modern physico-chemical methods of analysis, including viscosimetry, UV spectroscopy, dynamic light scattering, electrophoretic light scattering, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. In the dark phase, the formation of weak snot-like gels takes place in a quite narrow IO3− ion concentration range. The visible-light exposure of these gels leads to an increase in their viscosity and dramatic change in their color. The morphology of gels alters after light irradiation that is reflected in the formation of a huge number of spherical/elliptical particles and the thickening of the fibers of the gel network. The interaction of CSS with IO3− anions has features of a redox process, which leads to the formation of silver iodide/silver oxide nanoparticles inside and on the surface of CSS particles. CSS possesses selectivity only to IO3− anions compared to many other inorganic ions relevant for humans and the environment. Thus, the CSS/IO3− system is non-trivial and can be considered as a novel low-molecular-weight gelator with photosensitive properties, as another way to produce silver iodide nanoparticles, and as a new approach for IO3− ion detection.