Chromium‐substituted GdFeO ₃ perovskites for efficient visible‐light photo‐Fenton degradation of rhodamine B

Chromium‐doped (1‐х)GdFeO 3 – хGdCrO 3 ( x = 0.2, 0.4, 0.5, 0.6, 0.8) perovskites were synthesized by high‐temperature solid‐state reaction and quantitatively correlated structure with photocatalytic performance. X‐ray diffraction confirmed single‐phase orthorhombic Pbnm solid solutions with lattice contraction upon Cr substitution and a deviation from Vegard's law at x = 0.6; octahedral distortion (d) and in‐plane strain (s) further showed an anomaly at x = 0.4. Under visible light (λ > 400 nm) with H 2 O 2 (photo‐Fenton conditions), Rhodamine B (RhB) degradation after 240 min spanned 32%–77% across the series, with the x = 0.6 composition giving the highest apparent rate constant k = (4.96 ± 0.09) × 10 −3 min −1 (vs (2.38 ± 0.09) × 10 −3 min −1 at x = 0.5 and (1.09 ± 0.05) × 10 −3 min −1 for the blank). Control tests showed negligible conversion without either light or H 2 O 2 , whereas combining both with GFCO ( x = 0.6) yielded 77% conversion in 240 min. Radical‐quenching identified the active species: AgNO 3 (e − ) and EDTA‐2Na (h + ) reduced degradation to 34% and 24%, while trapping •OH, •O 2 − and 1 O 2 by IPA, TEMPOL, and NaN 3 lowered it to 11%, 4%, and 9%, respectively, evidencing a •OH/•O 2 − / 1 O 2 ‐dominated pathway. The activity maximum at x = 0.6 correlates with the structural anomalies, indicating a defect‐assisted visible‐light photo‐Fenton mechanism and defining the optimal Cr loading for pollutant decomposition.