Sustainable upcycling iron scale waste into Fe2O3/Fe3O4/g-C3N4 photo-Fenton catalysts for wastewater remediation

Abstract

Iron mill scale (Fe(scale)), a by-product of steel manufacturing, is a largely underutilized secondary iron resource. In this work, iron mill scale waste was upcycled and combined with graphitic carbon nitride (g-C<inf>3</inf>N<inf>4</inf>) to fabricate Fe(scale)/g-C<inf>3</inf>N<inf>4</inf> composites as photo-Fenton catalysts for wastewater remediation. The materials were synthesized via a one-step thermal polymerization method and systematically characterized. The phase analysis confirmed the successful formation of Fe<inf>3</inf>O<inf>4</inf> and α-Fe<inf>2</inf>O<inf>3</inf> phases from Fe(scale), coupled with g-C<inf>3</inf>N<inf>4</inf>. The optimized composite (50% Fe(scale)) exhibited superior photo-Fenton performance, achieving complete degradation of Rhodamine B (RhB) within 60 min, approximately four times higher than that of pristine g-C<inf>3</inf>N<inf>4</inf>. This enhancement is attributed to improved light absorption and increased surface area, as confirmed by UV–Vis DRS and BET analyses. Furthermore, PL intensity and photocurrent density indicate that the composite exhibits approximately twofold lower photogenerated charge recombination than g-C<inf>3</inf>N<inf>4</inf>, resulting in enhanced electron generation efficiency. The catalyst demonstrated excellent stability, maintaining high activity over five cycles with negligible iron leaching. Radical scavenger and EPR analyses revealed that OH radicals are the dominant reactive species, supporting a S-scheme-like photo-Fenton mechanism. This work provides a sustainable and scalable strategy for converting industrial iron waste into value-added materials for environmental remediation.