Iron-foam as a heterogeneous catalyst in the presence of tripolyphosphate electrolyte for improving electro-Fenton oxidation capability

Fe-Foam (Fe-F) was used as a catalyst in the presence of tripolyphosphate (TPP) electrolyte for electro-Fenton (EF) at circum-neutral pH. Characteristics of Fe-F catalyst were studied by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) and x-ray photoelectron spectroscopy (XPS). Operational conditions (pH and current) influencing H₂O₂ electrogeneration in TPP electrolyte at a three-dimensional printed gas diffusion electrode (GDE) were systematically investigated. Moreover, linear sweep voltammetry was used to evaluate the system. Results showed that Fe-F, a three-dimensional porous structure catalyst, was covered with Fe²⁺, Fe³⁺ and Fe⁰. The Fe-F/TPP/EF process allowed an 8.55-fold increase in the rate of phenol degradation (used as a model pollutant), higher pseudo-first-order rate constants (6.22 × 10⁻² min⁻¹ against 7.30 × 10⁻³ min⁻¹), a significantly higher mineralization yield (88.69%% against 30% after 8 h electrolysis) and lower energy consumption (0.10 kWhg⁻¹ against 0.98 kWhg⁻¹), as compared to conventional EF process. The high efficiency in Fe-F/TPP/EF was attributed to the following benefits: i) Fe-F was capable of providing Fe²⁺ ions by chemical corrosion to form Fe²⁺-TPP complex, which induced the one-electron transfer activation of O₂ leading to formation of ^[rad]OH, ii) chemical Fe²⁺ regeneration combined with Fe⁰ corrosion provided an additional source of Fe²⁺ and compensated the low capacity of Fe³⁺ reduction at GDE, and iii) both surface-mediated and homogeneous reactions contributed to pollutant degradation. The new proposed Fe-F/TPP/EF process displayed promising properties for wastewater treatment applications.