Plasma-Synthesized Combined Nitrogen and Cationic Species Doped-MnO2: Impact on Texture, Optical Properties, and Photocatalytic Activity

Boyom-Tatchemo, Franck W. Poupi, Albert Devred, François [UCL] Acayanka, Elie Kamgang-Youbi, Georges Aprile, Carmela [UNamur] Laminsi, Samuel Gaigneaux, Eric M. [UCL] et al.[show all]

This work explored the possibility of doping MnO2 structure simultaneously by cationic ( Na+, Mg2+ or K+) and nitrogen species during its synthesis through gliding arc plasma route. Therefore, NaMnO4, Mg(MnO4)2 or KMnO4 precursor has been precipitated via plasmachemical reduction thanks to NO⋅ and NO2 − respectively being short and long-lived species generated in plasma plume (gas phase) and plasma post-discharge (liquid phase). Physicochemical characterizations revealed nanostructured NaN–MnO2, MgN–MnO2 and KN–MnO2 respectively with specific surface areas of 36, 110 and 116 m2/ g, nitrogen atomic loading at surface of 0.6, 1.0 and 1.5%, and band gap values of 1.20, 1.30 and 1.45 eV. The three precursors with different cationic species allowed different nitrogen loading for their respective plasma-synthesized MnO2, which led to the different values of band gap energy. An increase of the N-loading induced an increase of band gap energy and enlarged the absorption capability of MnO2 from visible light to the UV region. Solar photocatalytic removal of TY revealed bleaching degrees of 53, 97 and 94% respectively for NaN–MnO2, MgN–MnO2 and KN–MnO2 materials. This enlargement, together with the increased specific surface area of the plasma-synthesized N–MnO2, led synergistically to an enhancement of its photocatalytic activity. This work highlights the usefulness of the synthesis via glidarc plasma, without any additional reagent, of MnO2, as allowing cationic species insertion in their structure, and simultaneously their doping with different N-loading, so leading to different crystalline structures, and photocatalytic activities.