The microtopography of manganese dioxide formed in situ and its adsorptive properties for organic micropollutants

The microtopography of manganese dioxide formed in situ was captured by AFM. The adsorptive properties of manganese dioxide formed in situ were evaluated for trace organic pollutants' removal with four different organic pollutants as the model organics which have different functional groups on aromatic ring. Several factors, such as the structure of manganese dioxide formed in situ, the adsorption time, the adsorbent concentration, and the background constituents (Ca2+, Mg2+, fulvic acid, etc.) in natural water, were investigated to evaluate their effects on adsorption. Results showed that manganese dioxide formed in situ had smaller particle size and higher adsorption capacity than the coagulated one. Ca2+ and Mg2+ added to the aqueous solution decreased the organics' removal significantly by accelerating the coagulation of manganese dioxide formed in situ and competing the adsorption sites with organics. The presence of fulvic acid had little impact on organic removal though it competes for the surface sites of manganese dioxide with organics. The four organics adsorbed on manganese dioxide formed in situ are listed in the order of decreasing reactivity: aniline>phenol>nitrobenzene>benzoic acid. The relative reactivity of organics was discussed in terms of electrostatic interaction between organics and adsorbent.