ADVANCED OXIDATION/REDUCTION TECHNOLOGIES: AN PERSPECTIVE FROM IBEROAMERICAN COUNTRIES Photoelectro-Fenton treatment of pesticide triclopyr at neutral pH using Fe(III)–EDDS under UVA light or sunlight Izabelle C. Da Costa Soares 1,2 & Roger Oriol 1 & Zhihong Ye 1,3 & Carlos A. Martínez-Huitle 2 & Pere L. Cabot 1 & Enric Brillas 1 & Ignasi Sirés 1 Received: 20 July 2020 /Accepted: 26 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract One of the main challenges of electrochemical Fenton-based processes is the treatment of organic pollutants at near-neutral pH. As a potential approach to this problem, this work addresses the use of a low content of soluble chelated metal catalyst, formed between Fe(III) and ethylenediamine-N,N'-disuccinic (EDDS) acid (1:1), to degrade the herbicide triclopyr in 0.050 M Na 2 SO 4 solutions at pH 7.0 by photoelectro-Fenton with UVA light or sunlight (PEF and SPEF, respectively). Comparison with electro- Fenton treatments revealed the crucial role of the photo-Fenton-like reaction, since this promoted the production of soluble Fe(II) that enhanced the pesticide removal. Hydroxyl radicals formed at the anode surface and in the bulk were the main oxidants. A boron-doped diamond (BDD) anode yielded a greater mineralization than an IrO 2 -based one, at the expense of reduced cost- effectiveness. The effect of catalyst concentration and current density on the performance of PEF with BDD was examined. The PEF trials in 0.25 mM Na 2 SO 4 + 0.35 mM NaCl medium showed a large influence of generated active chlorine as oxidant, being IrO 2 more suitable than RuO 2 and BDD. In SPEF with BDD, the higher light intensity from solar photons accelerated the removal of the catalyst and triclopyr, with small effect on mineralization. A plausible route for the herbicide degradation by Fe(III)– EDDS-catalyzed PEF and SPEF is finally proposed based on detected byproducts: three heteroaromatic and four linear N- aliphatic compounds, formamide, and tartronic and oxamic acids. Keywords Ethylenediamine-N,N'-disuccinic (EDDS) acid . Hydroxyl radical . Pesticide . Photoelectro-Fenton . Sunlight . Triclopyr . Water treatment Introduction In recent years, the treatment of biorecalcitrant organic pollut- ants dissolved in water by electrochemical advanced oxidation processes (EAOPs) such as electrochemical oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) has re- ceived substantial attention (Brillas and Martínez-Huitle 2015; Ganiyu et al. 2018; Martínez-Huitle and Panizza 2018). PEF is the most complex process, since it combines the oxidation ability of EO and EF with the photolytic action of UVA photons (Martínez-Huitle et al. 2015). Artificial UVA light can be replaced by natural sunlight to increase the sus- tainability of the technology, giving rise to the so-called solar PEF (SPEF) process (Brillas 2014; Pérez et al. 2017). The common feature of EF, PEF, and SPEF processes is the con- tinuous electrochemical generation of Fenton’s reagent (Fe 2+ Roger Oriol and Zhihong Ye contributed equally to this work. Responsible Editor: Vítor Pais Vilar * Ignasi Sirés i.sires@ub.edu 1 Laboratori d’Electroquímica dels Materials i del Medi Ambient, Departament de Química Física, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain 2 Laboratório de Eletroquímica Ambiental e Aplicada, Instituto de Química, Universidade Federal do Rio Grande do Norte, Lagoa Nova, Natal, RN 59072-900, Brazil 3 Environmental Engineering Research Centre, Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China Environmental Science and Pollution Research https://doi.org/10.1007/s11356-020-11421-8