Three-dimensional porous boron nitride with enriched defects and free radicals enables high photocatalytic activity for hydrogen evolution.

• 3D porous BN microbeads are assembled by 2D BN nanosheets by solvent-free strategy. • Porous BN microbeads with defects result in narrowed band gaps and OB 3 structure. • Porous BN as a semiconductor enhances light absorption and electron delocalization. • The change of BN from a photocatalytic inert to highly active material comes true. Due to large band gap and low charge delocalization, hexagonal boron nitride (h-BN) is usually used as catalytic support rather than catalyst, particularly photocatalyst for hydrogen evolution. Herein, three-dimensional porous BN microbeads assembled by 2D BN nanosheets with enriched defects and high specific surface area have been synthesized by solvent-free strategy, leading to multiply narrow band gaps and radical-contained OB 3 structure. Mott-Schottky test indicates that the as-fabricated porous BN is a n-type semiconductor. The narrowed band gaps together with radicals enhance the light absorption and electron delocalization which is further confirmed by Density Functional Theory (DFT) calculation, resulting in the change of BN from a photocatalytic inert to highly active material. This work not only provides a stable and effective BN-based photocatalyst but also benefits to design and develop more highly efficient two-dimensional photocatalysts for hydrogen evolution. [ABSTRACT FROM AUTHOR]