Manganese oxide and graphite oxide/MnO2 composites as reactive adsorbents of ammonia at ambient conditions

Manganese oxide and manganese oxide/graphite oxide composites were synthesized and used as a new generation of adsorbents for efficient ammonia removal from air at ambient conditions. Two graphite oxides with different contents of oxygen were used. The initial and exposed to ammonia samples were characterized using adsorption of nitrogen, infrared spectroscopy, potentiometric titration, scanning electron microscopy and thermal analysis. The results indicated strong ammonia adsorption on manganese oxide. Composites with graphite oxides showed an enhanced adsorption capacity. The materials differ in their surface features depending on the degree of oxidation of graphite oxide used. A low degree of oxidation leads to the deposition of the manganese oxide component at lower oxidation state than that in the composite with a strongly oxidized graphene-type component. In the composites Mn(IV) acts as an oxidant for ammonia and graphite oxide functional groups contribute to oxygen activation and thus enhance oxidation process.

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► Manganese oxide composites with two graphite oxides (GO) were synthesized.
► Ammonia is strongly adsorbed on manganese oxide and the composites.
► The materials differ depending on the degree of oxidation of graphite oxide used.
► On less oxidized GO the manganese oxide component has lower oxidation state.
► Mn(IV) is ammonia oxidant while GO functional groups activate molecular oxygen.