Integration of Iron Phosphide with Schwertmannite to Enhance Heterogeneous Fenton Catalysis by Accelerating Fe(III) Reduction and Forming Acidic Environment

The widespread application of Fe-based heterogeneous Fenton in water treatment is hindered by two main challenges: the inefficiency of the Fe(III)/Fe(II) redox cycle and the requirement of acidic conditions. In this study, combining schwertmannite with iron phosphide (Sch/FeP) via pre-adding FeP in the formation process of Sch could enhance the Fe(II)/Fe(III) conversion and self-producing acidic environment by SO42– substitution. Specifically, the inclusion of FeP in the Sch/FeP composite markedly increased the content of ≡Fe(II) species, thereby improving the activation of H2O2 to produce substantial quantities of •OH and •O2– radicals. Sch/FeP-driven heterogeneous Fenton exhibited high total organic carbon (TOC) removal (∼60%) and utilization efficiency of H2O2 (100%) after 20 min. Furthermore, Sch/FeP exhibited excellent degradation performance across a broad pH range (2–10), which could be attributed to the SO42– substitution reaction. This study not only addresses critical challenges in heterogeneous Fenton processes but also provides a novel strategy for modifying sulfate minerals to enhance their environmental applicability.