Insights into γ-valerolactone-mediated lignin recovery and its adsorption performance for methylene blue

The recovery of lignin from sweet potato vines via γ-valerolactone (GVL)-mediated processes with different GVL addition sequences during pretreatment and acid precipitation sequences was systematically investigated. The GVL dosing sequence was identified as the core factor determining lignin recovery efficiency and purity. For Process I (GVL added during the pretreatment stage, denoted as GVL/NaOH-LP), the maximum lignin recovery yield of 0.38 ± 0.02 g was achieved, albeit with the lowest purity of 47.79% ± 1.44%. By comparison, Process III (GVL added prior to acid precipitation, denoted as NaOH/GVL-LP) produced lignin with a significantly improved purity of 82.48% ± 0.001%, but the recovered mass was only 0.19 ± 0.002 g, indicating that process optimization requires a balance between recovery yield and product purity. The adsorption behavior of methylene blue (MB) on GVL/NaOH-LP was fitted well by the Langmuir isotherm model and pseudo-second-order kinetic model (R ² = 0.8616), with a maximum adsorption capacity of 38.75 mg g^-1. Characterization confirmed that MB adsorption on lignin particles was driven by a synergistic mechanism involving π-π stacking interactions, functional groups, and a mesopore-facilitated adsorption process.