Unveiling the structure, carrier separation and photocatalytic behavior in TiO2 nanomaterials for efficient metal ions photo-recovery

Copper contamination in industrial wastewater poses serious environmental and health risks, while the depletion of copper ores necessitates efficient recovery strategies. Photocatalytic reduction has emerged as a sustainable approach for both heavy-metal remediation and resource recycling, where the structure-dependent charge separation behavior of photocatalysts is the core determinant of their photocatalytic reactivity. In this work, TiO 2 nanomaterials with distinct morphologies were systematically studied to clarify the structure-carrier separation-photocatalytic performance relationship in metal ion reduction processes. Among the tested samples, thin-walled TiO 2 nanotubes stood out for their optimized structural features: transient photocurrent and open-circuit voltage decay analyses confirmed that the nanotubular architecture significantly enhances charge separation efficiency, accelerates electron transport dynamics, and extends photogenerated carrier lifetime. Specifically, the nanotubes achieved a Cu 2 + reduction rate of 0.3722 mmol/L·min (over three times higher than commercial P25 nanoparticles, 0.1149 mmol/L·min). Furthermore, the introduction of methanol as a hole scavenger further promotes charge utilization efficiency, ultimately enabling 66.7 % recovery of metallic copper. This work emphasizes that the rational design of TiO 2 nanostructures to enhance charge separation is critical for improving photocatalytic metal ion reduction performance. It not only establishes a clear structure-carrier separation-photoreactivity correlation for TiO 2 -based photocatalysts but also provides mechanistic insights and a sustainable strategy for advancing wastewater remediation and circular economy practices.