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<p>Rice husk, an abundant agricultural residue, was valorized into a nitrogen-doped activated biochar (N-ARHB) through a two-step strategy involving controlled pyrolysis followed by dual-alkali activation (K₂CO₃/Na₂CO₃) combined with in situ nitrogen incorporation using acrylamide. The resulting biochar exhibited a chemically heterogeneous carbon–silica framework with a hierarchical micro–mesoporous structure (BET surface area ≈ 78&#xa0;m² g⁻¹, total pore volume 0.0482&#xa0;cm³ g⁻¹, and a dominant pore radius of ≈ 1.92&#xa0;nm). Surface characterization revealed the coexistence of oxygen-, nitrogen-, and silica-derived functional groups together with a moderately negative surface charge (ζ ≈ −14.45 mV), highlighting the multifunctional nature of the biomass-derived sorbent. The adsorption performance of N-ARHB was systematically evaluated toward methylene blue (MB) and methyl orange (MO) under identical batch conditions, with particular emphasis on the effects of solution pH, contact time, sorbent dosage, initial dye concentration, and temperature. High removal efficiencies were achieved for both dyes over a wide pH range (2–10), demonstrating that adsorption is governed by a combination of electrostatic and non-electrostatic interactions rather than electrostatics alone. Kinetic data were well described by the pseudo-second-order model, while Weber–Morris analysis indicated a multi-stage uptake process in which intraparticle diffusion contributes as a secondary rate-modulating step. Equilibrium adsorption followed Langmuir/Sips behavior, yielding maximum monolayer capacities of 11.5&#xa0;mg g⁻¹ for MO and 12.6&#xa0;mg g⁻¹ for MB. Thermodynamic analysis confirmed that adsorption is spontaneous and exothermic, driven by cooperative pore filling, π–π interactions, hydrogen bonding, and Lewis acid–base interactions. Importantly, N-ARHB exhibited excellent regeneration capability, with desorption efficiencies exceeding 90% using acidic eluents, and demonstrated measurable decolorization when applied to a complex real aqueous matrix containing competing species. Collectively, these findings demonstrate a practical, biorefinery-compatible pathway for converting rice husk into regenerable biochars for the treatment of dye-laden wastewaters.</p>

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Nitrogen-functionalized rice husk biochar prepared by dual carbonate activation for adsorption of cationic and anionic dyes: kinetic, isotherm, and thermodynamic insights

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Walid M. Youssef,
  • Entsar H. Taha,
  • Adel A. El-Zahhar,
  • Majed M. Alghamdi,
  • Mohamed H. Taha

摘要

Rice husk, an abundant agricultural residue, was valorized into a nitrogen-doped activated biochar (N-ARHB) through a two-step strategy involving controlled pyrolysis followed by dual-alkali activation (K₂CO₃/Na₂CO₃) combined with in situ nitrogen incorporation using acrylamide. The resulting biochar exhibited a chemically heterogeneous carbon–silica framework with a hierarchical micro–mesoporous structure (BET surface area ≈ 78 m² g⁻¹, total pore volume 0.0482 cm³ g⁻¹, and a dominant pore radius of ≈ 1.92 nm). Surface characterization revealed the coexistence of oxygen-, nitrogen-, and silica-derived functional groups together with a moderately negative surface charge (ζ ≈ −14.45 mV), highlighting the multifunctional nature of the biomass-derived sorbent. The adsorption performance of N-ARHB was systematically evaluated toward methylene blue (MB) and methyl orange (MO) under identical batch conditions, with particular emphasis on the effects of solution pH, contact time, sorbent dosage, initial dye concentration, and temperature. High removal efficiencies were achieved for both dyes over a wide pH range (2–10), demonstrating that adsorption is governed by a combination of electrostatic and non-electrostatic interactions rather than electrostatics alone. Kinetic data were well described by the pseudo-second-order model, while Weber–Morris analysis indicated a multi-stage uptake process in which intraparticle diffusion contributes as a secondary rate-modulating step. Equilibrium adsorption followed Langmuir/Sips behavior, yielding maximum monolayer capacities of 11.5 mg g⁻¹ for MO and 12.6 mg g⁻¹ for MB. Thermodynamic analysis confirmed that adsorption is spontaneous and exothermic, driven by cooperative pore filling, π–π interactions, hydrogen bonding, and Lewis acid–base interactions. Importantly, N-ARHB exhibited excellent regeneration capability, with desorption efficiencies exceeding 90% using acidic eluents, and demonstrated measurable decolorization when applied to a complex real aqueous matrix containing competing species. Collectively, these findings demonstrate a practical, biorefinery-compatible pathway for converting rice husk into regenerable biochars for the treatment of dye-laden wastewaters.