Shell-Thickness-Dependent Interfacial Charge-Carrier Dynamics and Photocatalytic CO₂Reduction over CdS/UiO-66-NH₂Core/Shell Nanorods

One-dimensional CdS/UiO-66-NH₂ core/shell nanorods (NRs) with tunable shell thickness were synthesized using dihydrolipoic acid as a bifunctional linker. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy confirmed strong electronic coupling and quasi-type-I band alignment at the CdS/UiO-66-NH₂ heterojunction. At an optimal shell thickness of 29 nm, the core/shell NRs exhibited a 7.6-fold enhancement in photocatalytic CO₂ reduction efficiency compared with pristine CdS NRs. The optimized system achieved apparent quantum efficiencies of ∼3% at 350 nm, 1% at 400 nm, and 0.6% at 500 nm, along with 85% selectivity toward CO₂-to-CH₄ conversion under solid–gas conditions. Ultrafast transient absorption spectroscopy revealed that increasing the UiO-66-NH₂ shell thickness suppresses defect-mediated recombination in the CdS core, while time-resolved photoluminescence demonstrated that the optimal structure exhibits a superior interfacial electron-transfer rate constant. This work establishes a direct correlation among the metal–organic framework (MOF) shell thickness, charge-carrier dynamics, and photocatalytic performance, providing valuable insights into the rational design of MOF-coated semiconductor photocatalysts for solar fuel production.