Modified sol–gel synthesis greatly improves textural properties and photocatalytic performance of Cu-doped phase-pure ZnAl 2 O 4

conventional sol-gel synthesis. Elemental mapping confirmed uniform Cu incorporation, while ICP-MS confirmed the target stoichiometry. XPS confirmed an increase in oxygen vacancy concentrations with increasing Cu doping, and bandgap engineering (3.95 to 2.33 eV) enabled broad visible-light absorption at the higher Cu contents. Charge carrier dynamics were studied using time-resolved photoluminescence spectroscopy and revealed drastically suppressed radiative recombination and extended exciton lifetime from ~3 ns in undoped ZAO (or conventional ZAO Air) to >19 ns for Cu-doped variants. The evolution of these synergistic properties with Cu-loading improved the photocatalytic functionality of these materials: Cu-doped ZAO exhibited dramatically enhanced Congo Red photodegradation, while 5-20% Cu-loaded compositions achieved record hydrogen evolution rates among previously reported phase-pure aluminate spinels. The 20% Cu-ZAO photocatalyst showed the best performance under pure visible light (>400 nm) both with and without sacrificial agents, demonstrating excellent applicability for solar-driven water splitting. This work establishes a tunable platform for developing dual-function mesoporous photocatalysts with high surface area for advancing technology in sustainable energy and environmental remediation.