Cu-doped and S-scheme heterojunction binding modes for efficient photocatalytic nitrogen fixation by modulating energy band structure and built-in electric field

Currently, industrial ammonia synthesis still relies on the energy-intensive and environmentally detrimental Haber-Bosch process. Therefore, developing a green, energy-saving and sustainable method has become a crucial research objective. In this paper, an S-scheme heterojunction catalyst consisting of in situ copper ion-doped carbon nitride nanosheets (CN) and NH 2 -MIL-125 (NT) composite was constructed for photocatalytic nitrogen fixation. The copper was highly dispersed on CN with + 1 valence, and the three-dimensional lamellar morphology of NT was favorable for binding with CN to form a heterojunction structure. The nitrogen fixation efficiency of Cu-CN/NT reached 216.3 μmol/g/h, which was 27 and 18 times higher than that of the pristine CN and NT, respectively. Excellent photocatalytic activity was attributed to the synergistic effect of Cu doping and S-scheme heterojunction, where Cu doping altered the energy band structure of CN, increased the active sites, and promoted the nitrogen adsorption activation of the catalyst. Meanwhile, the construction of S-scheme heterojunction formed a built-in electric field, which promoted the separation and transfer of photogenerated electron-hole pairs and accelerated the photocatalytic nitrogen reduction reaction. This study emphasizes the key role of copper ions in the regulation of heterojunction and provides a new strategy for the construction of more efficient heterojunction catalysts in the field of photocatalytic nitrogen fixation.