Atomic Interfacial N-Bridging Locks Z-Scheme Charge Transfer in CsPbBr₃@UiO-66-NH₂ Heterojunctions

Precise control over interfacial charge-transfer pathways is pivotal for the rational design of high-efficiency heterojunction photocatalysts yet remains a formidable challenge, primarily owing to the scarcity of atomic-level modulation strategies. Here, we demonstrate that the pendant amino groups (-NH₂) of the metal-organic framework UiO-66-NH₂ spontaneously form dative coordination bonds (N-bridges) with surface Pb atoms of CsPbBr₃ perovskite, thereby engendering a well-defined heterojunction interface. By combining X-ray photoelectron spectroscopy binding-energy shift analysis with density functional theory (DFT) calculations, we reveal that this interfacial N-bridge fulfills a dual function: it templates the preferential exposure of the catalytically active (040) facet of CsPbBr₃ and concurrently serves as a directional conduit for interfacial electron transfer. DFT calculations further predict a ground-state charge redistribution of approximately 0.80 e^- from the metal-organic framework (MOF) to the perovskite. Critically, this atomic-scale bridge preferentially channels the charge flow into a direct Z-scheme pathway, a mechanism strongly corroborated by the transition of the dominant reactive species from superoxide radicals (·O₂^-) in pristine CsPbBr₃ to hydroxyl radicals (·OH) in the heterojunction. This N bridge-mediated Z scheme configuration affords exceptional spatial charge separation while preserving robust redox potentials, yielding a net photocurrent response approximately 3.5-4.0-fold and 2.8-3.3-fold higher than those of pristine CsPbBr₃ and UiO-66-NH₂, respectively, under identical measurement conditions. The functional efficacy of this interface design is substantiated by photoelectrochemical measurements and the efficient degradation of model organic pollutants─tetracycline and ciprofloxacin, employed as mechanistic probes─with the composite retaining high activity upon immobilization on porous substrates in real water matrices. This work establishes interfacial N-bridging as a generalizable atomic-scale design paradigm for governing charge-transfer kinetics in heterojunction systems, thereby transcending empirical optimization toward the rational engineering of interfaces.