The controllable synthesis of substitutional and interstitial nitrogen-doped manganese dioxide: the effects of doping sites on enhancing the catalytic activity

Doping with nitrogen atoms is an effective approach to alter the electronic structures of metal oxides. However, the further identification of doping sites and their effects on catalytic activity has not been clearly addressed. Herein, N atoms were selectively doped at substitutional or interstitial sites in the MnO2 lattice for the first time by controlling the N2 plasma treatment time. The effects of N-doping sites on atomic structures, valence states and electronic structures were investigated. The results indicate that both substitutional and interstitial N-doping can significantly reduce the oxygen vacancy formation energy. Furthermore, doping with N atoms can introduce new singly ionized oxygen vacancies. But in comparison with substitutional N-doping, interstitial N-doping can effectively narrow the band gap and enhance electron transport, which is conducive to the formation of oxygen vacancies. Due to its greater number of oxygen vacancies and stronger oxygen activation ability, the interstitial N-doped MnO2 exhibited improved catalytic activity for decomposing carcinogenic HCHO compared with substitutional N-doped MnO2. This research provides a site-selective N-doping method and a deep insight into the different effects of doping sites.