Hexagonal boron nitride with functional groups for efficient photocatalytic reduction of nitrate without additional hole scavengers

Hole scavengers must be added into the photocatalytic nitrate reduction system to achieve the efficient NO₃⁻ conversion in water. Herein, for the first time, high NO₃⁻ conversion of 97.94% and N₂ selectivity of 97.31% are obtained without additional hole scavengers, using a catalyst of treated hexagonal boron nitride (h-BN) with modified −OH and −NH₂ groups on its edges. The functionalized h-BN presents excellent reuse stability. Moreover, the functions of various groups are explored during photocatalytic nitrate reduction. −NH₂ groups and OH⁻ (accompanied product of −NH₂ protonation) behave as hole stabilizers and hole scavengers, respectively. They considerably improve the separation of electron-hole pairs, ensuring a remarkable capability to generate electrons for direct nitrate reduction without hole scavengers incorporation. New active sites of −OH groups and NH₃⁺ (product of −NH₂ protonation) are much more conducive to the reduction of nitrate than boron-terminated edges. More importantly, −OH groups play a major role in producing N₂. This study provides a reference for efficient photocatalytic reduction of NO₃⁻ in water without additional hole scavengers by the functionalized catalysts.