Goethite–Carboxylate-Based Heterogeneous Photo-Fenton-Like Process Revisited: Competitive Adsorption versus Photodegradation

The heterogeneous photo-Fenton-like process, mediated by iron oxides and carboxylates, is recognized for its effectiveness in degrading organic pollutants. Despite its potential, the adverse effects of carboxylates on removing strongly adsorptive pollutants have not been thoroughly explored. Herein, based on a precomparison of three different micropollutants, p-arsanilic acid (ASA), a strong adsorbate, was used as a model pollutant to investigate its removal in goethite–carboxylate systems under UVA irradiation. The effects of oxalate, citrate, malate, and salicylate were assessed across varying carboxylate concentrations (0–2 mM) and goethite dosages (0.1–0.5 g·L–1). Key findings indicate that remarkable •OH contribution was only observed in oxalate and citrate systems following the generation of H2O2. Oxalate and citrate enhanced photodegradation but inhibited adsorption, with oxalate exhibiting a stronger promotional effect. In contrast, malate and salicylate suppressed adsorption without contributing to photodegradation. Without taking into account the suppression caused by competitive adsorption, one may overestimate the degradation of strongly adsorptive pollutants through a heterogeneous photo-Fenton-like process. These results contribute to a deeper understanding of the comprehensive effects of carboxylates in heterogeneous photo-Fenton-like systems, providing insights into the optimization of environmental remediation strategies.