Deep insight into the photocatalytic activity and electronic structure of amorphous earth-abundant MgAl2O4

Abstract

Developing inexpensive photocatalysts is of great value for industrial applications. In the work, magnesia–alumina spinel (MgAl₂O₄) made from earth-abundant elements is synthesized via a simple hydrothermal route and subsequent calcination. Theoretical calculation indicates that pure MgAl₂O₄ crystal has an energy band gap of 7.505 eV, and that the top of the valence band is mainly formed by hybridization between Mg-p and O-p states, while the bottom of the conduction band mainly originates from the Mg-s/p and O-s/p states. The UV-vis DRS results show that MgAl₂O₄ containing amorphous matter absorbs ultraviolet light with a band gap of 3.90 eV, which arises from the longer Mg–O bond length and presence of defects. This research also confirms that the visible-light photocatalytic activity reported in a previous paper is derived from the nitrogen element doping. The photocatalytic activity of MgAl₂O₄ is evaluated via the decomposition of methylene blue (MB) under UV-vis light illumination. The electron transfer route and the photocatalytic mechanism of MgAl₂O₄ for degrading MB are proposed. For the first time, the potentials of the energy bands of MgAl₂O₄ are obtained using Mott-Schottky electrochemical measurement.