OICC Press Iranian Journal of Catalysis 2345-4865 16 2 2026 06 30 Effect of Hematite Crystallinity on Catalytic Performance in the Heterogeneous Photo-Fenton Degradation of para-Nitrophenol 10.57647/ijc.2026.1602.14 EN Swastika Pitahaya Novianiti Department of Chemistry, Universitas Gadjah Mada, Faculty of Mathematics and Natural Sciences, Bulaksumur, Yogyakarta 55281, Indonesia https://orcid.org/0009-0002-6407-7229 Nurul Hidayat Aprilita Department of Chemistry, Universitas Gadjah Mada, Faculty of Mathematics and Natural Sciences, Bulaksumur, Yogyakarta 55281, Indonesia https://orcid.org/0000-0002-2132-6646 Endang Tri Wahyuni Department of Chemistry, Universitas Gadjah Mada, Faculty of Mathematics and Natural Sciences, Bulaksumur, Yogyakarta 55281, Indonesia https://orcid.org/0000-0002-0584-0549 Journal Article 2026 06 30 This study explores the effect of hematite (α-Fe₂O₃) crystallinity on the heterogeneous photo-Fenton degradation of para-nitrophenol (PNP). Hematite was synthesized by precipitating FeCl₃ with NaOH, followed by oven drying at 100°C and calcination at 250°C and 500°C to obtain catalysts with different crystallinity levels. The degradation was carried out under UV irradiation in the presence of H₂O₂ and hematite, with optimization of catalyst dosage, H₂O₂ concentration, initial pH, and irradiation time. The catalysts were characterized by XRF, XRD, BET, FTIR, and UV-Vis DRS. XRD and FTIR confirmed that higher calcination temperatures promoted crystallinity and phase purity, while BET analysis showed that elevated temperatures reduced surface area due to particle growth and sintering. UV-Vis DRS revealed band gap narrowing with increased crystallinity. Among the catalysts, hematite calcined at 250°C displayed moderate crystallinity, mesoporosity (2.9 nm), and the largest surface area (70.89 m²/g), achieving the highest PNP degradation (98.89%) at pH 6. In contrast, the oven-dried and highly crystalline (500°C) hematite exhibited lower catalytic performance. The 250°C catalyst also showed stability with minimal Fe leaching. These results highlight that moderate crystallinity optimizes catalytic activity and demonstrate the potential of engineered hematite as an efficient and reusable catalyst for sustainable water treatment. Highlights Hematite crystallinity controlled by calcination influences photo-Fenton activity Hematite calcined at 250 °C shows highest PNP degradation efficiency (98.89%) Moderate crystallinity balances surface area and band gap for optimal performance Catalyst stable with minimal Fe leaching, effective at near-neutral pH (3–6) Demonstrates potential of hematite as low-cost, reusable water treatment catalyst