Abstract:

The generation of active hydrogen species (H*) is an essential step in the photocatalytic conversion of nitrogen molecules (N₂) to ammonia (NH₃). Metal-organic frameworks (MOFs) are versatile porous structures but they do not exhibit sufficient photocatalytic activities for nitrogen fixation. Adding appropriate amounts of noble metal species as a cocatalyst to MOFs can often improve their activities. This work uses a photoreduction strategy to reduce the right amount of Pt⁴⁺ to Pt clusters, and confines the remaining Pt⁴⁺ uniformly onto DUT-67(Zr). This is realized by taking advantage of a unique Pt-S electron channel, and the unsaturated Zr sites are concurrently in-situ generated under light exposure. The unsaturated Zr sites adsorb and activate N₂, while the Pt clusters are involved in the water splitting process on DUT-67(Zr) to generate more H*, leading to continuous H* supply that would speed up the catalytic hydrogenation of nitrogen intermediate NH_x. The Pt-S electronic channel formed between highly dispersed single atoms Pt and DUT-67(Zr) facilitates the separation and transfer of photo-generated charge carriers. Consequently, with the synergistic effect of unsaturated Zr sites, Pt clusters and Pt-S electron channels, a high photocatalytic nitrogen fixation performance of 78.8 μmol g^‒1 h^‒1 can be achieved. This is 10.4 times higher than that of the sample DUT-67-L with only unsaturated Zr sites and no Pt loading. This work provides an insight to rational design of uniform dispersed precious metal-based MOF photocatalyst for efficient photocatalytic ammonia synthesis.

Key words: Pt/DUT-67, Pt clusters, Pt single atoms, Synergistic effect, Photocatalytic nitrogen fixation