Green conversion of potato-based starchy waste into photocatalyst coupled nanoparticles for efficient removal of reactive red 195 dye from textile effluents

• Catalyst retained ∼80 % efficiency after six cycles, confirming magnetic stability. • P-Char400@Fe₃O₄ enables circular agro-waste valorization for textile wastewater treatment. • Nearly 100 % Reactive Red 195 removed within 20 min at near-neutral pH. • Potato peel waste upcycled into biochar–magnetite photo-Fenton catalyst. • Oxidation followed pseudo-first-order reaction kinetics. A sustainable and low-cost route is presented for converting potato-based starchy waste into biochar–magnetite (P-Char@Fe₃O₄) composites that function as efficient heterogeneous photo-Fenton catalysts for the degradation of the azo dye Reactive Red 195 (RR195) in textile effluents. Potato peel biochars pyrolyzed at 200–600 °C were coupled with Fe₃O₄ nanoparticles that is prepared by co-precipitation to produce P-Char200@Fe₃O₄, P-Char400@Fe₃O₄, and P-Char600@Fe₃O₄. SEM/EDS and elemental mapping confirmed the successful anchoring of Fe₃O₄ and revealed temperature-dependent dispersion and crystallinity across the carbon matrix. Catalytic screening showed a performance trend of P-Char200@Fe₃O₄ > P -Char400@Fe₃O₄ > P -Char600@Fe₃O₄, attributed to the preservation of oxygenated surface functionalities and accessible pore structures at lower/intermediate pyrolysis temperatures. Optimized operation with the robust P-Char400@Fe₃O₄ (pH 6.5, catalyst 40 mg L⁻¹, H₂O₂ 400 mg L⁻¹, UV irradiation) achieved nearly 100% RR195 removal within 20 min. The system remained tolerant to realistic conditions, showing enhanced performance with increasing temperature (32–60 °C) but declining efficiency at high dye loads or excessive H₂O₂. Kinetic analysis confirmed pseudo-first-order behavior (R² > 0.98), while Arrhenius/Eyring evaluation yielded an activation energy of 30.98 kJ mol⁻¹, positive enthalpy of activation, and negative entropy that consistent with a surface-organized, radical-mediated mechanism. The catalyst preserved about 80% efficiency after six reuse cycles, demonstrating strong magnetic recoverability and structural stability. Compared with conventional Fenton and modified systems, the agro-waste-derived P-Char@Fe₃O₄ enables rapid decolorization at near-neutral pH, reduces sludge generation, and advances circular-economy valorization of food-processing residues, highlighting its potential for scalable textile wastewater treatment.