Tailoring Biomass‐Derived Organosolv Lignin Derivatives for High‐Capacity Adsorption of Rhodamine B

The valorization of biomass into renewable, high-performance, adsorbent materials offers a sustainable alternative to conventional synthetic sorbents. In this study, we investigate the potential of lignin derivatives as efficient adsorbents for removing the cationic dye Rhodamine B (RhB) from aqueous solutions. Five organosolv lignin derivatives were synthesized via a one-step process using phenol, catechol, resorcinol, pyrogallol, and hydroquinone as phenolic modifiers to introduce structural diversity. The influence of these modifications on the materials' physicochemical properties and adsorption behavior was examined. Comprehensive characterization included ³¹P NMR, Brunauer-Emmet-Teller surface area analysis, size exclusion chromatography, thermogravimetric analysis, and dynamic light scattering. Among the derivatives, resorcinol-modified lignin (ReL) showed the highest RhB adsorption capacity (101.2 mg g^-1), attributed to its favorable textural properties-high surface area and pore volume-together with increased availability of functional groups, which collectively enhanced adsorption efficiency. Adsorption kinetics for all materials followed the pseudo-second-order model, indicating chemisorption as the dominant mechanism. Isotherm analyses revealed Langmuir-type monolayer adsorption for ReL, pyrogallol-modified, and hydroquinone-modified lignins. Moreover, ReL demonstrated good recyclability, retaining 62% of its adsorption efficiency after five adsorption-desorption cycles. Collectively, these results highlight the promise of structurally engineered lignin-based adsorbents as cost-effective, efficient, and reusable materials for sustainable wastewater treatment.