Face or Edge? Control of Molybdenite Surface Interactions with Divalent Cations

• Published in: Journal of physical chemistry. C Vol. 124; no. 1; pp. 372 - 381
• Main Authors: Lu, Zhenzhen, Ralston, John, Liu, Qingxia
• Format: Journal Article
• Language: English
• Published: American Chemical Society 09.01.2020
• Subjects: adsorption; anisotropy; atomic force microscopy; calcium chloride; cations; dielectric properties; graphene; hydrolysis; magnesium chloride; mass spectrometry; minerals; molybdenum disulfide; saline water; surface interactions
• ISSN: 1932-7447; 1932-7455; 1932-7455
• DOI: 10.1021/acs.jpcc.9b07632

Molybdenite, MoS2, a 2-D transition metal dichalcogenide, is a potential substitute for graphene. Molybdenite mineral particles are separated from gangue minerals by flotation, a process often performed in saline waters, where the presence of divalent cations can cause serious selectivity issues. A fundamental question is posed: how do divalent cations, which are subject to hydrolysis as a function of pH, interact with anisotropic molybdenite surfaces? By use of a combination of atomic force microscopy (AFM) surface force measurements with time-of-flight secondary ion mass spectrometry (ToF-SIMS) surface spectroscopy, the surface potentials and surface ion species of MoS2 immersed in aqueous MgCl2 and CaCl2 solutions were distinguished for the face and the edge surfaces, respectively, for the first time. The adsorption mechanisms of MgII and CaII on anisotropic MoS2 surfaces are revealed as a function of pH, ion species in solution, and solid characteristics (dielectric constant and surface chemical groups). As a consequence of these fundamental insights, improved particle flotation pathways are available.