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

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.Sulfide minerals and the associated geological/physical/chemical processes are an active research topic for mineralogists, geochemists, and geotechnical/environmental engineers. Sulfide ores constitute a major source of metals, especially noble metals. In addition, the rich diversity in crystal chemistry, surface reactivity, phase transformations, stability, thermodynamics, and electronic properties makes the sulfide minerals attractive for a wide variety of industrial applications, such as lubricants and catalysts [1,2]. Molybdenite (MoS2) belongs to the family of the transition-metal dichalcogenide (TMD) minerals with the formula MX2 (where M = Cd, Ti, Mo, Sn and X = I, S, Se). Due to their layered