Coupled Nanoconfinement Effect and Host–Guest Interaction in the Fe(III)-Oxalate/LDH System for a Highly Efficient Photoassisted Fenton Reaction

Heterogeneous Fenton stands out as one of the most promising technologies for water decontamination, but its application is limited by the low reaction kinetics due to sluggish Fe(II) generation and mass transfer. Herein, we propose a novel photoassisted Fenton system employing Fe-oxalate confined into CuNi2Al-LDH (CNAL-0.8Fe(C2O4)x), aiming to accelerate reactive oxygen species (ROS)-involved reactions via the host–guest interaction. The photoactive Fe-oxalate complex system could improve photogenerated electron generation of the LDH host to drive the cycling of Cu(II)/Cu(I) and the self-cycling of Fe(III)/Fe(II). Moreover, the nanoconfinement effect could strengthen mass transfer at the interface, thus accelerating Fe(II)-catalyzed H2O2 decomposition to produce •OH and promoting Fe(III)-oxalate-involved photolysis to create •C2O4–/•CO2– with new Fe(II)-oxalate species. As a result, CNAL-0.8Fe(C2O4)x exhibits a 10-fold higher rate constant for phenol degradation compared to that in the system of its counterpart Fe-free catalyst, and the mineralization rate (91.1%) exhibits remarkable improvement compared to its analogue unconfined system (40.5%). DFT calculations confirm that introducing Fe(II)-oxalate can effectively decrease the energy barrier of H2O2 dissociation by 71%, boosting H2O2 utilization by 4.7-fold. This work provides an effective strategy to address the issue of Fe2+ regeneration difficulty and iron loss encountered in the traditional homogeneous Fenton process, enhancing the practical application of Fe-based AOPs in environmental remediation.