Photocatalytic hydrogen production over Aurivillius compound Bi3TiNbO9 and its modifications by Cr/Nb co-doping

In this work, we have applied Cr/Nb co-doping strategy to the wide band gap semiconductor Bi 3 TiNbO 9 and have performed a detailed investigation on the structure, optical and photocatalytic properties of these modified Aurivillius compounds Bi 3 Ti 1-2x Cr x Nb 1+x O 9 (x   =   0, 0.1, 0.2, 0.3). Our results suggest that Cr/Nb doping slightly expand the unit cell of Bi 3 TiNbO 9 with a doping limit around 20%. The involvement of Cr/Nb dopants in the crystal structure significantly reduces the band gap of Bi 3 TiNbO 9 by nearly 1   eV. Photocatalytic experiments and photoelectrochemical measurements confirms the critical role of Cr/Nb dopants in improving photocatalytic hydrogen production and anodic photocurrent. More than two-fold enhancement in hydrogen production has been noticed for merely 10% Cr/Nb co-doping. The highest photocatalytic activity belongs to Bi 3 Ti 0.8 Cr 0.1 Nb 1.1 O 9 (x   =   0.1) for full range illumination and to Bi 3 Ti 0.6 Cr 0.2 Nb 1.2 O 9 (x   =   0.2) for visible light illumination, with apparent quantum efficiency (AQE) approaching 0.52% and 0.27%, respectively. DFT calculation discloses the role of Cr in forming a new valence band inside the band gap of Bi 3 TiNbO 9 . In addition, strong anisotropic phenomenon in charge transportation of Bi 3 TiNbO 9 is also verified by DFT, as both conduction band minimum (CBM) and valence band maximum (VBM) are buried in the [BiTiNbO 7 ] 2− perovskite slabs and charges are only allowed to migrate within the slabs.