1D ZnO Nanostructures in Analytical Systems for Cu(II) and Fe(III) Ion Sensing

Heavy metal ion contamination requires sensitive and selective detection methods for environmental and health monitoring. This study demonstrates that one-dimensional (1D) zinc oxide (ZnO) nanostructures with a controlled morphology enable highly sensitive photoluminescence-based detection of Cu2+ and Fe3+ ions. Three distinct ZnO morphologies─nanotetrapods, nanorods, and nanofibers─were synthesized and comprehensively characterized. ZnO nanotetrapods exhibited promising sensing performance, with detection limits of 0.92 μM for Cu2+ and 1.4 μM for Fe3+, response times of 10.6–10.9 ± 2 min, and adequate selectivity over 12 interfering metal cations. The enhanced performance correlates with nanotetrapods’ structure properties, defect chemistry, and highly negative surface charge (−42.3 mV at pH 7). We propose a sensing mechanism based on electrostatic ion adsorption followed by charge transfer that reduces Cu2+ to Cu+ and Fe3+ to Fe2+ on the ZnO surface, causing photoluminescence quenching. These findings establish the structure–property relationships for ZnO-based sensors with detection capabilities well below the WHO drinking water guidelines, demonstrating their strong potential for environmental monitoring applications.