A new strategy to stabilize carbon nitride photocatalyst for nitrogen reduction

Researchers from the Institute of Solid State Physics, Hefei Institutes of Physical Science developed a boron doped carbon nitride nanosheets with B-N-C coordination to stabilize surface exposed active nitrogen atoms and dramatically enhance photocatalytic ammonia synthesis performance. Their findings were published in Small.

It is well known that nitrogen (N₂) accounts for ~78% in our atmospheric environment, which is essential element for almost all life forms including plants and animals on earth.

Up to now, the most mature technology of artificial synthetic ammonia (NH3) is the over century-old Haber-Bosch process, operated under drastic conditions due to the intrinsically inert characteristic of N₂ molecules.

Currently, photocatalytic N₂ reduction has been regarded as a promising means for sustainable NH₃ synthesis at ambient conditions. As a class of metal-free polymer semiconductor photocatalyst, graphitic carbon nitride (g-C₃N₄) possesses many advantages, such as low cost, abundance, superior visible-light activity and high chemical/photochemical stability, exhibiting great potential for photocatalytic nitrogen reduction reaction (NRR).

However, several issues are still existent associated with the NRR using the g-C₃N₄-based photocatalyst. It is an important issue that exposed active nitrogen atoms (e.g., edge or amino N atoms) in g-C₃N₄ could participate in NH3 synthesis during the photocatalytic NRR.

Moreover, the pristine bulk g-C₃N₄ generally possesses relatively low specific surface area, which is adverse to the N₂ adsorption and activation, as well as high recombination rate of photogenerated electrons and holes, resulting in its low photocatalytic efficiency.

Therefore, developing effective strategies to stabilize surface exposed active nitrogen atoms of g-C₃N₄, capable of improving the N₂ adsorption/activation and visible-light utilization, simultaneously effectively inhibiting the recombination of photogenerated carriers in g-C₃N₄, is critically important and highly needed to achieve high-efficiency g-C₃N₄ based photocatalysts.

Herein, the team synthesized the porous B-doped g-C₃N₄ nanosheets (BCN) by a facile thermal treatment approach using dicyandiamide (DICY) and boron oxide (B2O3) as reactants. The formed B-N-C coordination in BCN not only effectively enhanced the visible-light harvesting and suppressed the recombination of photogenerated carriers in g-C₃N₄, but also acted as the catalytic active site for N₂ adsorption, activation and hydrogenation.

The as-synthesized BCN exhibited high visible-light driven photocatalytic NRR activity, affording an NH₃ yield rate of 313.9 μmol g–1 h–1, nearly 10 times of that for pristine g-C₃N₄.