With a light absorption up to 740 nm, BaNbO 2 N is promising for solar water splitting but normally owns a low activity due to a high defect concentration. Here, Mg is adopted as a dopant to modify the BaNbO 2 N. The presence of Mg not only reduces the defect concentration and enhances surface hydrophilicity but also tunes the bandgap as well as the band edge positions. These modifications greatly promote the charge separation and transfer of BaNbO 2 N, boosting the photocatalytic activities for O 2 -evolution reactions. An apparent quantum efficiency of 1.65 % at 420 ± 20 nm has been attained for Mg modified BaNbO 2 N. Overall water splitting at a stable gas-evolution rate (∼ 2.0 μmol·h −1 for H 2 and ∼ 1.0 μmol·h −1 for O 2 ) has been realized by integrating Mg-modified BaNbO 2 N into a Z-scheme system. These findings justify Mg as an effective dopant to modulate the photocatalytic behavior of Nb-based perovskite oxynitrides.
Although BaNbO 2 N has visible light absorption as far as 740 nm, its photocatalytic activity is generally very poor under ordinary conditions, being incommensurate to its light absorption properties. In this work, we introduce Ca into the B site of BaNbO 2 N to form a complex perovskite BaNb 1− x /3 Ca x /3 O 2+ y N 1− y (0 ≤ x , y ≤ 1). The presence of Ca in BaNbO 2 N has great impact on a number of important properties such as band gap value, nitrogen content, surface hydrophilicity, and defects levels. In particular, defects such as Nb 4+ species are effectively suppressed in Ca-modified BaNbO 2 N. More importantly, photocatalytic activity of BaNbO 2 N for water oxidation reactions is substantially improved after Ca modifications. Compared with pristine BaNbO 2 N, more than twofold enhancement in photocatalytic oxygen evolution is observed for BaNb 0.8 Ca 0.2 O 2+ y N 1− y ( x = 0.6). Such improvements probably stem from the suppression of Nb 4+ species in the structure as well as enhanced surface hydrophilicity after Ca modification. The facile approach by incorporating alkaline earth cations into crystal structure can be well extended to other perovskite oxynitrides whose photocatalytic activity is subject to those defective species.
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