Abstract

This study presents the first electrochemical sensor specifically designed to detect the Fe3+-EDDS complex, a widely used chelating agent in homogeneous photocatalysis for wastewater treatment at near-neutral pH. Measurements were performed off-line using a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs), thereby enhancing sensitivity and electron-transfer capability. Experimental parameters, including MWCNT concentration (0.5-2.0 mg/mL), accumulation time (0-4 min), and Fe3+-EDDS concentration (0.01-0.10 mM), were optimized to maximize performance. The sensor exhibited a strong linear response (R-2 = 0.992) with a sensitivity of 29.4 mu A/mM and a detection limit of 0.006 mM. In real wastewater effluents, signal attenuation led to a narrower effective linear range, with reduced proportionality above similar to 0.06 mM Fe3+-EDDS, highlighting both matrix effects and the need for matrix-specific calibration. Its long-term stability was confirmed for over 100 days using stored MWCNT dispersions. A robust correlation with UHPLC/DAD measurements (Pearson r > 0.91, R-2 > 0.95) validated the sensor's accuracy. The sensor was also tested in a pilot-scale UVA-LED photoreactor to monitor Fe3+-EDDS degradation under different Fe3+ and EDDS dosages. Results demonstrated the sensor's suitability for real-time monitoring of catalyst availability during advanced oxidation processes (AOPs). Additionally, a techno-economic analysis indicated a 78.3% reduction in per-sample cost relative to UHPLC/DAD, underscoring its potential for routine, cost-effective monitoring in wastewater treatment. This novel platform enables cost-effective, off-line monitoring of iron chelate availability in AOPs and provides a basis for future development toward real-time sensing in complex water matrices.