Iron-Optimized Magnetic Biochar Modified with Polyethyleneimine: An Efficient Carrier for Laccase Immobilization and Nonylphenol Degradation

This study optimized corncob-derived magnetic biochar (MBC) with tailored iron content for laccase immobilization to boost nonylphenol (NP) degradation in water. Low-iron MBC (LMBC) and high-iron MBC (HMBC) from corncob were prepared via impregnation–pyrolysis at 700 °C, followed by modification with polyethyleneimine (PEI) and covalent immobilization of laccase using glutaraldehyde. Compared to HMBC, LMBC exhibited more mesopores, superior laccase activity recovery (60.5%) and Fe2+ release that was only 1/78 of HMBC’s. Furthermore, PEI modification and subsequent laccase immobilization on LMBC significantly reduced iron leaching (p < 0.05). X-ray diffraction and vibrating sample magnetometry analyses indicated that LMBC consists of crystalline Fe3O4, α-Fe, graphite, and carbon, with a saturation magnetization of 45.8 emu g−1. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy confirmed the microporous and mesoporous structure of LMBC, the successful PEI modification, and the effective immobilization of laccase on LMBC (L-LMBC). L-LMBC exhibited enhanced stability under acidic conditions (pH 3–7) and elevated temperatures (20–70 °C). After six repeated cycles, the NP removal efficiency by L-LMBC remained at 84.8%. Moreover, L-LMBC demonstrated effective NP removal in real environmental water samples. This study provides fundamental insights and demonstrates the potential application of MBC-immobilized laccase for degrading persistent pollutants in aqueous systems.