A new approach for the synthesis of layered niobium sulfide and restacking route of NbS₂ nanosheet

We have developed a new process for the synthesis of a layered niobium sulfide that involves heating K₄Nb₆O₁₇·3H₂O with a H₂S/N₂ gas mixture. It was confirmed that heating the starting layered oxide at 750 °C for 10 h under the gas flow yielded a highly crystalline, single-phase K_0.34(H₂O)_0.7NbS₂. The layered sulfide slabs had a large plate-like shape. Potassium ions in the interlayer of K_0.34(H₂O)_0.7NbS₂ could be exchanged with protons by stirring in 2 M H₂SO₄. It was found that the proton in the proton-exchanged form can be easily exchanged with other cations. The proton-exchanged form was exfoliated into NbS₂ nanosheets by ultrasonication in water. According to the atomic force microscopy (AFM) images, NbS₂ nanosheets had a thickness of around 4 Å, which roughly corresponded to the thickness of a single NbS₂ host layer. NbS₂ nanosheets could be restacked with the intercalation of Eu³⁺ or tetrabutylammonium ions by an electrostatic self-assembly deposition (ESD) technique.