Horseradish Peroxidase Immobilized on Modified Fe3O4-Geopolymer Composite Material for Phenolic Compounds Removal from Wastewater

Magnetite–geopolymer composites have primarily been investigated as adsorbents, whereas their use as enzyme carriers offers a catalytic route for phenol removal. Here, a magnetic allophane–kaolin geopolymer biofunctionalized with tangerine peel extract was developed as a support for covalent horseradish peroxidase (HRP) immobilization. This study combines this material platform with an integrated assessment of phenol and halogenated phenol removal, operational stability, water matrix effects, and post-treatment phytotoxicity. This study evaluates the obtained T-M-AK-G-HRP as a recoverable biocatalyst and assesses the contribution of biofunctionalization by comparing it with pristine and non-biofunctionalized magnetic geopolymer supports. At an initial phenol concentration of 10 mg/L, immobilized HRP (0.7 U/mL, n(H2O2)/n(phenol) = 1:1) achieved complete removal within 1 h, whereas the support showed no measurable phenol adsorption under the tested conditions. Removal efficiencies of 72–95% were obtained in spiked real-water matrices after 2 h. At 25 mg/L, removal efficiencies for phenol and derivatives ranged from 80.2% to 96.6% after 1 h. The biocatalyst was magnetically recovered for repeated use, achieving 56.6% phenol removal in the fourth treatment cycle. Treatment also reduced phytotoxicity in the Allium cepa assay. These findings extend magnetic geopolymer applications from pollutant adsorption to enzyme-mediated treatment and identify biofunctionalization as a strategy for improving biocatalyst reusability.