Mechanosynthesis of a bismuth nanoparticle-decorated palm kernel mesocarp fiber (Bi-PKMF): adsorption of Pb(ii), kinetics and thermodynamics

Abstract

A new bismuth-decorated palm kernel mesocarp fiber (Bi-PKMF) adsorbent was prepared through green liquid-assisted mechano-chemical grinding, followed by thermal crystallization. Detailed characterization (SEM-EDX, TEM, BET, FTIR, and AFM) was performed to verify the uniform dispersion of bismuth oxide nanoparticles in the lignocellulosic matrix and the production of a high-surface-area mesoporous material (387 m² g⁻¹ and a pore size of 12.5 nm). Control experiments of the ball-milled PKMF indicated that bismuth functionalization provides chemical enhancement rather than mechanical enhancement. Bi-PKMF exhibited excellent Pb(II) adsorption capacity (112.3 mg g⁻¹), which was 231 times higher than that of pristine PKMF (48.5 mg g⁻¹) with more than 90% removal in 60 min at pH 6. The kinetics followed the pseudo-second-order model (R² = 0.999), and the obtained Dubinin–Radushkevich adsorption energy (12.6 kJ mol⁻¹) confirmed chemisorption. The mesoporous structure reduces the resistance to intraparticle diffusion, allowing access to the active sites (Bi–O, –OH, and –COO–). Spontaneous (ΔG° < 0), exothermic (ΔH° = −29.02 kJ mol⁻¹), and ordered adsorption were indicated by the thermodynamic parameters. The reusability of Bi-PKMF was good, retaining over 90% of its adsorption capacity after five regeneration cycles. The key to the increased Pb(II) uptake is surface chemistry, rather than physical structure, which makes Bi-PKMF a high-performance biosorbent for sustainable water purification.