Thermal evolution in air and argon of nanocrystalline MoS2 synthesized under hydrothermal conditions

Nanocrystalline molybdenum sulfide was synthesized between 150 degreesC and 225 degreesC under hydrothermal conditions starting from ammonium heptamol ybdate and thiourea. Samples were characterized with X-ray powder diffracti on. electron microscopy, nitrogen adsorption, thermoanalysis and infrared s pectroscopy. The hydroxyls involved in the synthesis and adsorbed on crysta ls surface hindered crystallization and samples still recrystallized after the final dehydroxylation step above 300 degreesC, just when hydroxyls were isolated from each other. This also promoted sulfur bond breaking that gav e rise to partial transformation of the MoS2 into MoO2 when the annealing a tmosphere was argon, and to the total transformation of the sulfide into Mo O3 when it was air. The initial MoS2 crystals were bend; many of them were isolated, and others associated in bundles that formed worm-like grains int eracting with each other to produce spherical grains aggregated in clusters . This morphology gave rise to samples with a low specific surface area. (C ) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.