Crystalline manganite (γ‐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 O 1s spectra due to dissolution of manganite. Possibly the interaction of OH groups with H + 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.
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Ramstedt et al. (2002) studied this question.
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