<p>A novel magnetically separable nano-heterogeneous Fenton-like catalyst (Fe₃O₄/CEWSB) was successfully fabricated via a one-pot oxidation precipitation approach, in which Fe₃O₄ nanoparticles were uniformly anchored on cerium-modified walnut shell biochar (CEWSB) to form a stable composite structure. Systematic characterizations including SEM, BET, Raman, FTIR, XRD, XPS and VSM confirmed that Fe₃O₄/CEWSB possesses rich surface oxygen-containing functional groups (−OH, −COOH), well-developed mesoporous structures, and abundant oxygen vacancies as well as carbon defects. The Fe₃O₄/CEWSB significantly enhances methylene blue (MB) removal efficiency through abundant carbon defects and oxygen vacancies, synergistic Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ redox cycles, and oxygen-containing functional groups. At the condition of pH 3.0, H₂O₂ 30 mM, catalyst 1.0 g/L, Fe₃O₄/CEWSB exhibits the highest degradation capacity (&gt;99%), the degradation process followed pseudo-first-order reaction kinetics with a high rate constant of 0.0440 min⁻¹. Scavenger experiments identified ·OH and ·O₂⁻/·O₂H as the dominant reactive species participating in MB decomposition. Possible degradation intermediates and reaction pathways were elucidated through GC-MS characterization. The Fe₃O₄/CEWSB catalyst maintained excellent reusability and outstanding stability with 89.37% removal rate of MB and low Fe leaching (1.085%) in 5 cycles. This study develops a sustainable and efficient catalyst for textile wastewater degradation.</p>