Collaborative strategy for elevated reduction of Cr(VI) through pyrolyzed graphite-based biosynthetic Schwertmannite composite catalyzed by oxalic acid

• Pyrolyzed graphite-based biosynthetic Schwertmannite (Sch@G) achieves 90.42% Cr(VI) removal within 60 min when combined with oxalic acid. • The composite exhibits exceptional performance across a wide pH range (2–10), with 97.9% removal at pH 10. • The synergistic mechanism involves enhanced electron transfer from oxalic acid to Cr(VI) and the release of low-valent Fe from Schwertmannite. • Sch@G shows robust adaptability in the presence of various anions, making it a promising candidate for real wastewater remediation.