Iron sulfide nanoparticles Fe3S4 and Fe1-xS were synthesized via solvothermal decomposition of piperidine iron(III) dithiocarbamate complex in oleylamine. At a reaction temperature of 230 degrees C, the cubic Fe3S4 phase (greigite) was obtained whereas at 300 degrees C, monoclinic Fe1-xS (pyrrhotite) was obtained. In both cases, hexagonal sheet like structures with sizes ranging from 50 to 200 nm were obtained. Powder X-ray diffraction studies reveal that the temperature plays a significant role in determining the crystalline structure and chemical composition of the as-synthesized nanoparticles (NPs). Gas sensing applications further reveal activities which are phase-dependent. The greigite has a higher response to humidity but saturates faster than the pyrrhotite. The pyrrhotite phase however outwits the greigite on response to H-2, NO2, NH3 and CH4. In these gases, the greigite displays early saturation as well as noisy and uncoordinated signals. (C) 2017 Elsevier B.V. All rights reserved.