Characterization of hydrous manganite (γ-MnOOH) surfaces -: an XPS study

Crystalline manganite (gamma-MnOOH) has been synthesized and characterized using x-ray diffraction and high-resolution transmission electron microscopy techniques. The surface composition was studied with XPS between pH 0.4 and 11. Special pre-cooling procedures were developed to keep the manganite/water interface intact before and during XPS measurements. The O/OH group ratio differs between pH 6 and 11, in agreement with the acid/base characteristics of the surface. Below pH 6, on the other hand, drastic changes can be seen in the 0 1s spectra due to dissolution of manganite. Possibly the interaction of OH groups with HI in acidic suspensions is a first step leading to dissolution. The surface charge arising at high and low pH is compensated by the counter-ions Na+ and Cl-, respectively. The XPS spectra are presented and discussed in terms of the mechanisms for surface complexation and dissolution processes. Copyright (C) 2002 John Wiley Sons, Ltd.