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

Abstract

We report here a simple hydrothermal synthesis of 100–200 nm flakes of tochilinite (Fe_1−xS)·n(Mg,Fe)(OH)₂ constructed by interchanging atomic sulfide and hydroxide sheets as a representative of a new platform of multifunctional two-dimensional materials. The reliable formation of tochilinites was ensured by an excess of sodium sulfide, with the assembly of the metal sulfide and hydroxide sheets driven by their opposite electric charges. X-ray photoelectron spectroscopy found that the hydroxide layers involved Fe³⁺ cations from 10 to 40% of total iron tuned by addition of Al and Li entering the layers; the Fe_1−xS sheets comprised comparable amounts of high-spin Fe³⁺ and Fe²⁺ centers, and minor S–S bonding. The room-temperature Mössbauer spectra fitted with several doublets (chemical shift of 0.35–0.4 mm s⁻¹ and varying quadrupole splitting) transformed to three six-line patterns (hyperfine fields of ∼290, 350 and 480 kOe) due to magnetic ordering at 4.2 K, albeit the paramagnetic behavior observed in SQUID experiments. A series of UV-vis absorption maxima were explained in terms of both the high-index all-dielectric Mie resonance, in line with the permittivity measurement data, and the ligand-metal charge transfer resembling that in Fe–S clusters in proteins. Prospective properties and applications of the materials are discussed.