What question did this study set out to answer?

The research aims to synthesize and characterize a magnetic biochar from avocado seed biomass for removing hexavalent chromium from water.

May 6, 2026Open Access

Avocado Seed-Derived Magnetic Biochar for Efficient Cr(VI) Removal: Influence of Magnetite Synthesis Route, Characterization and Kinetic Mechanism

Key Points

The research aims to synthesize and characterize a magnetic biochar from avocado seed biomass for removing hexavalent chromium from water.
Various magnetite synthesis routes including nitrogen-assisted and redox-controlled coprecipitation were evaluated.
Batch adsorption experiments were conducted at pH 2.0 to assess the effect of adsorbent dose and initial Cr(VI) concentration.
Equilibrium reached within 120 min, analyzed under the pseudo-second-order kinetic model.
Maximum adsorption capacity predicted at 42.49 mg g−1 at an initial Cr(VI) concentration of 100 mg L−1.
Kinetic studies indicated chemisorption governs the rate-controlling step (R2 ≥ 0.98).
The synthesis method succeeded in combining magnetite with biochar while maintaining structural integrity.

Abstract

This study investigates the synthesis and kinetic behavior of a magnetic biochar derived from avocado seed biomass for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Magnetite (Fe3O4) was synthesized through different routes, including nitrogen-assisted coprecipitation, redox-controlled coprecipitation, polyol, sol–gel, and sonochemical methods, to evaluate their structural properties and iron incorporation efficiency. Based on compositional and crystallographic analyses, the coprecipitation under an inert atmosphere exhibited improved phase purity and higher Fe3O4 content, which was selected for in situ incorporation onto biochar produced by pyrolysis at 450 °C. The resulting magnetic material and composite were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), confirming the suitability of the synthesis method and the successful deposition of magnetite onto the porous carbon matrix while preserving its structural integrity. Batch adsorption experiments were conducted at pH 2.0 to evaluate the effect of adsorbent dose and initial Cr(VI) concentration. The adsorption process reached equilibrium within 120 min and was better described by the pseudo-second-order kinetic model (R2 ≥ 0.98), suggesting that chemisorption governs the rate-controlling step, with diffusion phenomena contributing but not dominating the overall mechanism. The maximum adsorption capacity predicted by the kinetic model reached 42.49 mg g−1 at an initial concentration of 100 mg L−1. The results demonstrate that avocado-seed-derived magnetic biochar represents a sustainable and effective material for chromium-contaminated water treatment, integrating agro-industrial waste valorization with enhanced adsorption performance and magnetic separability.

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