Morphology and optical absorption of Bi2Fe4O9 crystals via mineralizer-assisted hydrothermal synthesis

► Rod-like Bi2Fe4O9 microcrystals were synthesized using KNO3 mineralizer in hydrothermal process. ► Ostwald ripening may be the likely formation mechanism for the Bi2Fe4O9 microrods. ► The prepared powder exhibits potential applications as a photocatalyst under visible light.