Pd Location–Dependent Confinement Effects in UiO‐66(Zr) Toward Catalytic Degradation of Carbamazepine

The practical application of the Fenton reaction is limited by the excessive generation of iron sludge, which results from the inefficient regeneration of ferrous ions during the Fe III /Fe II redox cycle. A hydrogen‐assisted strategy was introduced to address this issue. Pd was employed as a catalytic site to activate molecular H 2 , a green and sustainable reductant, thereby accelerating Fe III reduction and minimizing sludge formation. UiO‐66(Zr), a highly porous metal–organic framework, was utilized as the support to anchor Pd via two distinct configurations: Pd@UiO‐66(Zr), where Pd is confined within internal pores, and Pd/UiO‐66(Zr), where Pd is deposited on the external surface. The effect of the active center location on the reaction performance was systematically investigated. Mechanistic investigations revealed that singlet oxygen ( 1 O 2 ) dominated in the confined Pd@UiO‐66(Zr) system, whereas hydroxyl radicals (·OH) were prevalent in Pd/UiO‐66(Zr). Under optimal conditions (2 g·L −1 catalyst, 25 μM Fe II , 20 mM H 2 O 2 , 30 mL·min −1 H 2 , 20 mg·L −1 CBZ), the Pd@UiO‐66(Zr) system achieved complete CBZ removal within 30 s, while the Pd/UiO‐66(Zr) system required approximately 60 min. After six consecutive cycling tests, no obvious decline in removal efficiency was observed for Pd@UiO‐66(Zr), and Pd leaching was nearly undetectable. In contrast, a gradual decrease in removal efficiency was observed for Pd/UiO‐66(Zr), accompanied by noticeable Pd leaching. The superior performance of the Pd@UiO‐66(Zr) system was attributed to enhanced hydrogen activation, more efficient Fe II regeneration, and a distinct ROS pathway driven by spatial confinement.