pH-dependent mechanisms of methylene blue reacting with tunneled manganese oxide pyrolusite

► The mechanism of MB reacting with tunneled pyrolusite is significantly pH dependent. ► Pyrolusite being the oxidant at pH under the pHiep (4.70) while playing as catalyst at pH over pHiep. ► MB degradation followed N-demethylation; stepwise generated AB, AA, AC, and TH. ► TH is the alone compound adsorbed onto the pyrolusite surface.