Interfacial Charge-Transfer Engineering in Rare-Earth-Modified ZnO/Nanoporous Cu Heterostructures for Simulated-Solar-Light Methyl Orange Degradation

The development of simulated-solar-light photocatalysts for methyl orange (MO) removal is limited by insufficient light utilization, rapid photogenerated charge recombination, and restricted interfacial reaction sites. Here, vertically aligned ZnO nanorods on a conductive nanoporous Cu (NPCu) scaffold were modified with low-abundance RE-containing surface species (RE = Ce, Sm, Er, Tm, and Yb). The notation RE(OH)3@ZnO/NPCu is retained solely as an operational sample identifier and does not constitute a crystallographic or stoichiometric phase assignment. XRD resolves the ZnO/NPCu framework, EDS confirms the local presence of RE, and XPS identifies RE-dependent oxidation state and surface oxygen environments; collectively, these measurements do not uniquely establish RE(OH)3 or distinguish hydroxide from oxide, oxyhydroxide, and other hydroxylated/adsorbed surface configurations. The distinguishing feature is a controlled five-RE comparison on one common ZnO/NPCu architecture, together with separate evaluation of NPCu under H2O2-free and H2O2-assisted conditions. Across three independent H2O2-free runs, the Er-modified sample achieved 96.61 ± 0.30% MO degradation within 9 min with kobs = 0.3930 ± 0.0071 min−1. Dosage screening identified 20 μL of 40 wt% H2O2 in 20 mL MO solution (approximately 13.5 mM) as a practical plateau dosage. Photolysis, dark, NPCu/H2O2, and catalyst-removal controls support an additional solid-catalyst-dependent Cu-associated peroxide contribution while not excluding trace homogeneous reactions. Three independent cycling experiments and post-cycle SEM/XRD/EDS support operational durability, although quantitative metal leaching was not measured. Tauc, Mott–Schottky, EIS, temperature-dependent kinetic, and scavenger results are interpreted as comparative descriptors or indirect evidence rather than direct proof of intrinsic band gaps, atom-specific carrier densities, or a unique microscopic mechanism. The AI-assisted component is restricted to exploratory contextualization because reference-grouped validation shows poor out-of-reference generalization. The conclusions are confined to the tested MO system.