Facile synthesis and selected characteristics of two-dimensional material composed of iron sulfide and magnesium-based hydroxide layers (tochilinite)

We report here a simple hydrothermal synthesis of 100-200 nm flakes of tochilinite m(Fe1 xS)n(Mg,Fe)(OH)2 constructed by interchanging atomic sheets of iron sulfide and magnesium hydroxide as a representative of a new platform of multifunctional two-dimensional materials. The formation and characteristics of the material was studied using X-ray and electron diffraction, TEM, EDS, X-ray photoelectron and 57Fe Mössbauer and UV-vis-NIR spectroscopies, measurements of magnetization, dielectric permittivity, and zeta potential of aqueous dispersions. The reliable formation of tochilinite was ensured by a large excess of sodium sulfide, which induced negative zeta potential (about -30 mV) of tochilinite dispersions, whereas the potential approached zero for nearly-stoichiometric S/Fe precursor ratios. The assembly of the metal sulfide and hydroxide sheets driven by their opposite electric charges starts immediately after mixing the reagents at room temperature. The hydroxide layers contain Fe3+, not Fe2+, cations, the quantity of which was reduced and increased in the range 10 to 40% of Mg2+ by addition of Al and Li, respectively. The Fe-deficient sulfide sheets contain comparable amounts of high-spin Fe3+ and Fe2+ centers, and minor S-S bonding. The room-temperature Mössbauer spectra were fitted with several doublets with the chemical shift of 0.35-0.4 mm/s and varying quadrupole splitting. Magnetic ordering at 4.2 K manifested by three six-line patterns with the hyperfine fields of ~290, 350 and 480 kOe attributed to overlapped Fe2+-S and Fe3+-OH signals, Fe3+-S centers and some Fe3+-O centers, respectively; a paramagnetic behavior was observed in SQUID experiments. The temperature and frequency dependences of permittivity revealed the activation energy of ~0.3 eV, probably, due to electron transitions involving Fe 3d states. A series of UV-vis absorption maxima were explained in terms of the high-index all-dielectric Mie resonance and the ligand-to-metal charge transfer alike Fe-S clusters in proteins. Prospective properties and applications of the materials are discussed.