An effective porous biochar adsorbent derived from Platanus orientalis leaves for the removal of rhodamine B: adsorption performance and mechanism insight.

Abstract

In this study, a series of porous biochar material (PoLC-600, PoLC-700, PoLC-800) adsorbents were fabricated from waste Platanus orientalis leaves via pre-carbonization combined with KOH activation. The optimized PoLC-800 exhibited a large specific surface area of 1384 m2 g-1 and displayed an ultrahigh maximum adsorption capacity of 2761 mg g-1 toward rhodamine B (RhB), outperforming PoLC-600, PoLC-700 and most reported biomass-derived adsorbents. Adsorption isotherms fit well with the Langmuir model, and kinetic results reveal that the adsorption follows the pseudo-second-order model dominated by chemisorption. After five consecutive adsorption-desorption cycles, PoLC-800 maintained over 80% of its original adsorption efficiency. It exhibited favorable tolerance toward pH variation and coexisting cations, and showed broad adsorption capacity for both cationic and anionic dyes. FT-IR, XPS and DFT calculations demonstrated that plentiful O-/N-containing functional groups triggered synergistic interactions of hydrogen-bonding, electrostatic attraction, n-π and π-π stacking. Combining experimental characterization with theoretical simulations, the adsorption of RhB onto PoLC-800 is comprehensively determined to be a multi-mechanism synergistic process involving external mass transfer, intra-particle diffusion, and interfacial chemical interactions. This study provides molecular-level insights into dye removal by low-cost biomass-derived porous biochar and offers technical support for resource utilization of urban fallen-leaf waste.