Novel Eu³⁺ and transition metal (Zn/Al) co-doped CuO photocatalysts: physical properties and enhanced visible-light-driven environmental remediation

Visible-light photocatalysis is pivotal for the sustainable degradation of organic pollutants in wastewater. We designed, in this research, novel europium (Eu) and transition metal (Zn/Al) co-doped CuO nanocatalysts, Cu_0.94Eu_0.03Zn_0.03O (6CEZ) and Cu_0.97Eu_0.015Al_0.015O (3CEA), synthesized via low-cost coprecipitation. Structural analysis confirmed a pure monoclinic phase for all samples, with 6CEZ exhibiting lattice expansion and 3CEA showing contraction due to dopant-induced strain. Optical characterization revealed a significant bandgap reduction from 1.5 eV (pure CuO) to 1.41 eV (6CEZ) and 1.47 eV (3CEA), enhancing visible-light absorption. The 6CEZ catalyst achieved 94% methylene blue (MB) degradation in 40 min, surpassing 3CEA (77%) and pure CuO (61%), with a kinetic rate constant of 0.06 min⁻¹. 6CEZ retained > 90% degradation efficiency over five reuse cycles. This superior performance is attributed to the synergistic effect of Eu³⁺/Zn²⁺ co-doping, which optimally narrows the bandgap and generates a high density of oxygen vacancies, thereby enhancing visible-light absorption and suppressing charge carrier recombination.