Inspired　by　biological　nitrogen　fixation　(BNF)　via　nitrogenase,　researchers　develop　novel　metal-organic　frameworks　(MOFs)-based　photocatalytic　nitrogen　fixation　(PNF)　systems　to　address　the　challenge　of　activating　N2.　However,　the　inherent　low　mobility　of　charge　carriers　in　MOFs　results　in　insufficient　migration　of　photogenerated　electrons　to　active　sites　for　N2　reduction.　In　this　work,　a　series　of　CdS/MIL-68(Fe)　heterojunctions　(x%CdS/MF)　were　successfully　developed　by　in-situ　growth　of　various　mass　fractions　of　ultrafine　CdS　nanoparticles　(about　5.0　nm)　for　biomimetic　photocatalytic　N2　fixation.　A　tightly　combined　interface　between　MIL-68(Fe)　and　CdS　via　a　Fe–S　bond　induces　interfacial　electric　field,　promoting　the　charge　mobility.　CdS　functions　as　an　electron　donor　(the　role　of　the　Fe　protein　in　nitrogenase)　to　transfer　additional　electrons　to　the　active　sites　(the　role　of　the　FeMo-cofactor　in　nitrogenase),　i.e.　the　coordinatively　unsaturated　Fe　sites　in　MIL-68(Fe).　Consequently,　CdS/MIL-68(Fe)　heterojunctions　effectively　mimic　the　behavior　of　the　two　fundamental　components　in　nitrogenase.　10　%CdS/MF　exhibits　the　highest　NH4+　production　rate　(51.6　µmol·h–1·g–1),　which　is　15.6　and　5.1　times　higher　than　those　of　unmodified　MIL-68(Fe)　and　pristine　CdS,　respectively.　This　work　sheds　new　light　on　the　rational　design　of　MOF-based　photocatalysts　for　biomimetic　N2　fixation.　©　2025　Elsevier　B.V.