Photocatalytic improvement of Mn-adsorbed g-C3N4

•The photocatalytic efficiency of Mn-adsorbed g-C3N4 is three times higher that of pristine g-C3N4.•The Mn atoms adsorbed on g-C3N4 stably form ionic bond with N atoms, as confirmed by DFT calculation and experiment.•The photocatalytic efficiency enhancement of Mn-adsorbed g-C3N4 is attributed to the decrease of band gap, the half-filled Mn 3d states in the forbidden gap, and the up-shifting of band edges.

This study employed experimental results and theoretical calculations to investigate Mn-adsorbed g-C3N4 as a potential photocatalyst with high efficiency. Mn was chosen as the incorporating element, because among the 3d transition metals it exhibits the highest binding energy and most suitable band edge positions. The photocatalytic efficiency of Mn-adsorbed g-C3N4 is 3 times higher that of pristine g-C3N4. Although small variations in the phase and surface morphology were observed, which were confirmed to not be the determining factors to improve efficiency. The factors that affect the high photocatalytic efficiency are therefore the electronic structure, optical absorption, and band edge variations after Mn-adsorption. The Mn atoms stably are bonded with N atoms, due to the strong absorption energy and ionic bond. Moreover, reduction of the g-C3N4 band gap after Mn-adsorption results in a red shift of the absorption band edge. The half-filled Mn 3d state introduces impurity states into the forbidden band gap, which will increase the life time of charge carriers. In addition, the up-shifting of band edges of Mn-adsorbed g-C3N4 leads to inhibition of the electron-hole recombination. As a consequence, the photocatalytic efficiency of Mn-adsorbed g-C3N4 is enhanced due to the combination of the aforementioned effects.

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