Synthesis and Optical Properties of Layered Inorganic-Imidazoline Monoliths

Abstract

Two types of layered inorganic-imidazoline monoliths (Mg-Imidazoline and Ni-Imidazoline) are synthesized, and optical properties (ultraviolet–visible (UV–vis) absorption and emission) arise from both inorganic and organic moieties that are covalently bonded with each other in the layered monoliths. Monoliths are synthesized under hydrothermal conditions at 170 °C and/or 150 °C using triethoxy-3-(2-imidazolin-1-yl)propylsilane (ITES) and magnesium and/or nickel acetates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirm the formation of layered compounds with interlayer distances of 1.8 nm in the Mg-Imidazoline and Ni-Imidazoline samples. Thermogravimetric and differential thermal analysis (TG-DTA) and elemental analyses show mole ratios of Mg/Si and Ni/Si and a considerable organic component. XRD and Fourier transform infrared spectroscopy (FT-IR) results show the inorganic moiety is similar to 2:1 phyllosilicates, and FT-IR spectra show several absorption peaks attributed to an imidazolyl group and Si–C. A model for Mg-Imidazoline and Ni-Imidazoline is then proposed, which has a layered structure, interlayer distance of 1.8 nm, and comprises inorganic layers with the imidazolyl group located between them. A cation (Mg2+ and/or Ni2+)-octahedral sheet is sandwiched between two siloxane sheets to form a 2:1 phyllosilicate-like layer, and each siloxane sheet bonds to the imidazolyl group via the S–C covalent bond. Mg-Imidazoline exhibits both absorption and emission in relation to the imidazolyl group, whereas Ni-Imidazoline exhibits scant emissions. The UV–Vis spectrum of Ni-Imidazoline shows absorption and weak absorption relating to the inorganic moiety and imidazolyl group, respectively.