Repurposing waste sugarcane bagasse as a green and sustainable adsorbent for efficient and reversible capture of low-concentration ammonia

Abstract

Green and sustainable chemistry principles advocate for the conversion of waste streams (e.g., sugarcane bagasse) into functional materials to mitigate pollution and enable resource circularity. In this work, we report the demethylation of lignin from waste sugarcane bagasse to obtain hydroxyl-functionalized lignin (OH-lignin), which is effectively used for the adsorption and separation of low-concentration NH₃. The results show that OH-lignin has an NH₃ adsorption capacity of 11.89 mmol g⁻¹ at 298.2 K and 1 bar, which is 159.27% higher than that of unmodified lignin. Furthermore, OH-lignin has ultrafast adsorption kinetics for NH₃, which can quickly capture more than half of its total NH₃ capacity within 1 min (7.86 mmol g⁻¹ at 58 seconds), and has notable selective adsorption for NH₃/N₂ (2163) and NH₃/H₂ (1345). The density functional theory (DFT) calculations indicate that the modified OH-lignin adsorbent significantly enhances its adsorption interaction with NH₃, while effectively reducing the binding energy with competitive gases (H₂ and N₂). Breakthrough experiments with a dynamic gas mixture (NH₃/H₂/N₂, 3%/72.75%/24.25%) further reveal that the breakthrough time of OH-lignin was up to 51 min g⁻¹ and reaches saturation adsorption at 117 min g⁻¹. Additionally, cyclic adsorption–desorption tests show that OH-lignin eliminates the NH₃ residue typically found in conventional NH₃ adsorbents and retains over 96% of its NH₃ adsorption capacity after eight cycles. Therefore, this work presents a sustainable strategy for upgrading waste sugarcane bagasse into a high-performance adsorbent for the treatment of low-concentration NH₃ emissions.