Highly selective photocatalytic CO₂ reduction to ethane enabled by a tandem Au/UiO-68-NH₂@MoS₂ composite

Solar-driven CO₂ reduction to energy-dense C₂ fuels remains challenging due to limited catalytic surfaces capable of sustaining both C-C coupling and full hydrogenation of intermediates in water. In this work, we report a tandem composite, Au/U68N(X)@MS, assembled from 3 wt% Au-preloaded UiO-68-NH₂ (denoted as U68N) microcrystals and few-layer MoS₂ nanosheets engineered with sulfur vacancies and dense Mo-edge ensembles. Under visible-light irradiation, Au/U68N motif serves as the photo-induced electron and CO-supply module, whereas vacancy-rich Mo sites on the edges of MoS₂ chemisorb adjacent ∗CO intermediates, stabilize CO-CO-type dimers, and sustain subsequent multi-electron, proton-accessible hydrogenation steps that favor C₂H₆ formation over C₁ product. Systematic modulation of the Au/U68N loading on MoS₂ reveals that increasing the modification level progressively enhances interfacial conductivity and CO₂ uptake capacity. In situ spectroscopic analyses further reveal a plasmon-enhanced Z-scheme charge-transfer pathway that preserves strong redox potentials across the heterointerface. Among the composites, Au/U68N(50)@MS delivers optimal tandem synergy, achieving a C₂H₆ productivity of 48.3 μmol h^-1 g^-1 with 72% selectivity. This outstanding performance positions Au/U68N(50)@MS among the most efficient photocatalytic CO₂-reduction composites reported to date, highlighting that precise engineering of heterojunctioned composites is a decisive design parameter for steering aqueous CO₂-to-C₂ conversion.