What question did this study set out to answer?

This work aims to evaluate gamma irradiation's effect on rice husk's ability to adsorb heavy metals from water.

January 6, 2026Open Access

Valorizing Rice Husk Waste as a Biosorbent with Gamma-Induced Surface Modification for Enhanced Heavy-Metal Adsorption

Key Points

This work aims to evaluate gamma irradiation's effect on rice husk's ability to adsorb heavy metals from water.
Rice husk samples were gamma-irradiated at doses up to 40 kGy.
Characterization techniques included SEM-EDS, FTIR, XRF, XRD, and BET analyses.
Batch adsorption experiments were conducted to measure removal efficiencies of metal ions.
40-kGy irradiated rice husk showed the highest removal efficiencies: 415% for Cu2+, 502% for Cr3+, 663% for Zn2+.
Kinetic studies indicated rapid adsorption dominated by boundary-layer diffusion and later shifted to chemisorption.
The pseudo-second-order model fit well with R2 = 0.999, showing high adsorption capacities for each metal.

Abstract

This work investigated the effects of gamma irradiation on the adsorption capacities of rice husk (RH) for the removal of Cu2+, Cr3+, and Zn2+ ions from aqueous solutions, with potential applications in wastewater remediation. RH samples were gamma-irradiated at doses up to 40 kGy and characterized using SEM-EDS, XRF, FTIR, XRD, and BET analyses. While morphological and textural changes remained subtle, FTIR and SEM-EDS confirmed the formation and intensification of oxygen-containing functional groups, including –OH, –COOH, and C=O, as well as increased exposure of silica (Si–O) on the surfaces, which substantially enhanced surface reactivity of RH toward metal ions. Batch adsorption experiments revealed that 40-kGy irradiated RH samples (RH-40) exhibited the highest removal efficiencies compared to non-irradiated and lower-dose samples (RH-0, RH-10, RH-20, and RH-30), specifically with improvements of 415% for Cu2+, 502% for Cr3+, and 663% for Zn2+ compared to RH-0, determined at the initial concentration of 10 mg/L. Kinetic studies also showed rapid adsorption within the first 10–15 min, dominated initially by boundary-layer diffusion, followed by chemisorption-driven equilibrium behavior. The pseudo-second-order (PSO) model provided an excellent fit for all metals (R2 = 0.999), indicating maximum model-predicted kinetic capacities of 555.56 mg/g (Cu2+), 769.23 mg/g (Cr3+), and 434.78 mg/g (Zn2+). Langmuir isotherms also fitted well (R2 = 0.941–0.995), with predicted monolayer capacities of 535.33 mg/g (Cu2+), 491.64 mg/g (Cr3+), and 318.88 mg/g (Zn2+). Freundlich modeling further indicated favorable heterogeneous adsorption, with KF values of 42.614 (Zn2+), 20.443 (Cr3+), and 16.524 (Cu2+) and heterogeneity factors (n) greater than 1 for all metals. These overall results suggested that gamma irradiation substantially enhanced RH functionality that enabled fast and high-capacity heavy-metal adsorption through surface oxidation and carbon valorization. Gamma-irradiated RH, therefore, represented a promising, low-cost, and environmentally friendly biosorbent for wastewater treatment applications.

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