Valorization of pineapple leaf waste into Fe-Modified biochar for efficient H₂S adsorption

Thailand generates large amounts of agricultural residues, particularly pineapple leaves (PAL), which are often underutilized. In this study, pineapple leaf-derived biochar (PALC) was developed as an efficient hydrogen sulfide (H₂S) adsorbent via FeCl₃ pretreatment and pyrolysis under oxygen-free conditions at 400-800°C, with PAL-to-Fe mass ratios of 0.5-3. The adsorption performance was governed by pore structure and iron species, both influenced by pyrolysis temperature and Fe loading. The optimal material, 2Fe/PALC600, dominated by Fe₃O₄, achieved the highest adsorption capacity of 380.1 ± 15.4 mg H₂S g^-1 under 40%RH conditions. While humidity enhanced H₂S removal, the presence of 40%v/v CO₂ significantly suppressed performance due to competitive surface physisorption. X-ray photoelectron spectroscopy (XPS) analysis revealed transformations of Fe species on the biochar surface before and after H₂S exposure, and density functional theory (DFT) calculations provided further insights into the adsorption mechanism. These findings highlight the strong potential of Fe-modified PAL-derived biochar as a sustainable and cost-effective material for gas purification, while also valorizing agricultural waste.