Determination of the point-of-zero charge of manganese oxides with different methods including an improved salt titration method

Abstract

Manganese (Mn) oxides are important components in soils and sediments. Points-of-zero charge (PZC) of three synthetic Mn oxides (birnessite, cryptomelane, and todorokite) were determined by using three classical techniques (potentiometric titration or PT, rapid PT or RPT, and salt titration or ST) and a modified salt titration method with a prolonged equilibration time (ST method with a prolonged equilibration time [PST]). The same methods have been applied to goethite, which was used as a reference material. The PZC values of goethite obtained by PT and RPT methods were both 7.95, and those by the ST and PST method were 8.16 and 8.30, respectively, for birnessite cryptomelane, and todorokit..