Preparation of biopolymer-supported spinel cobalt ferrite with controlled composition as a peroxydisulfate activator for glyphosate-contaminated wastewater treatment

Abstract

This study optimized the extraction of biopolymers from waste banana skins (BiP) and developed spinel cobalt ferrite nanoparticles with tunable compositions (CoFe_2+xO₄; x = 0.0, 0.3, and 0.5), which were subsequently supported on the extracted biopolymer at various loadings (0–25 wt%) to form CoFe_2+xO₄@BiP-y catalysts. These catalysts were employed to activate peroxydisulfate (PS) for glyphosate (GPS) mineralization in aqueous media. Structural characterization confirmed the retention of the spinel structure and Co²⁺ incorporation into the crystal lattice, despite Fe content variation. As the Co : Fe ratio decreased from 1 : 2.0 to 1 : 2.3, GPS mineralization, evaluated via COD removal, improved significantly from 51.9% to 67.7% in the CoFe_2+xO₄/PS system. Among the various compositions, CoFe_2.3O₄@BiP-15 exhibited the highest performance in activating PS, achieving 95.7% GPS removal and a reaction rate of 0.025 min⁻¹ under optimal conditions of pH 5.0, 0.4 g L⁻¹ CoFe_2.3O₄@BiP-15, and 300 mg L⁻¹ PS. The proposed mechanism involves both radical and non-radical pathways, including the generation of reactive oxygen species (ROS) such as ¹O₂, *SO₄⁻, *OH, and *O₂⁻, which participate in GPS mineralization. Notably, the promoted GPS removal efficiency was primarily attributed to the iron enrichment in CoFe_2.3O₄, which not only accelerated the regeneration of Co²⁺—the main catalytic active species responsible for PS activation—but also enabled Fe²⁺ to directly activate PS via electron transfer, generating more ROS. Additionally, the high dispersion of CoFe_2.3O₄ on the BiP, with enriched oxygen-containing functional groups (OCFGs), acted as active sites, donating electrons for PS to form ROS. Reusability tests showed stable GPS removal over four consecutive cycles. The findings provide principle for the rational design of biopolymer-supported bimetallic catalysts with controlled compositions, enabling more effective advanced oxidation processes for mineralizing persistent organic pollutants.