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

Abstract

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.