Research article

Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

CV Ramana^1,2 , U Becker¹ , V Shutthanandan³ and CM Julien⁴

¹Nanoscience and Surface Chemistry Laboratory, Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA

²Department of Metallurgical and Materials Engineering, University of Texas at El Paso, El Paso, Texas 79968, USA

³Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA

⁴Institut des Nano-Sciences de Paris, CNRS-UMR 7588, Université Pierre et Marie Curie Campus Boucicaut, 140 rue de Lourmel, 75015 Paris, France

author email corresponding author email

Geochemical Transactions 2008, 9:8doi:10.1186/1467-4866-9-8

Published:	5 June 2008

Abstract

Molybdenum disulfide (MoS₂), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS₂ is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.

The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA).

Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in size associated with a decrease in density with further annealing.