Boron-doped black titanium dioxide for visible-light and sacrificial-agent-free photocatalytic nitrate reduction

The photocatalytic conversion of nitrate (NO 3 − ) to ammonia (NH 3 ) represents a dual-benefit strategy for environmental remediation coupled with the recovery of a valuable chemical feedstock. In this work, we demonstrate that boron-doped black titanium dioxide materials (B x -TiO 2 ), synthesized using closo -dodecaborate dianion ([ closo -B 12 H 12 ] 2− ) as the boron (B) source, serve as efficient catalysts for photoreduction of NO 3 − to NH 3 in aqueous media under visible-light irradiation. B doping induces the formation of an amorphous phase in TiO 2 , which optimizes surface properties, narrows the band gap, and extends the optical absorption spectrum from the ultraviolet to the visible region—resulting in a significant enhancement in light utilization efficiency. Density functional theory (DFT) calculations reveal orbital hybridization between Ti and B, confirming their synergistic catalytic role. Among the series of synthesized materials, B 1 -TiO 2 exhibits the highest catalytic activity, achieving an ammonia production rate of 769.0 μmol g cat −1  h −1 , which compares favorably with previously reported systems. This work on heterogeneous B doping is expected to serve as a reference for the development of efficient catalysts in follow-up studies.