Mechanisms of Cu(II) Adsorption onto Biochars Derived from Fallen and Non-Fallen Maple Leaves

The ability of biochars derived from fallen (F-BC) and non-fallen (NF-BC) maple leaves to adsorb Cu 2+ ions from aqueous solutions was examined. Biochars were produced at pyrolysis temperatures of 350, 550, and 750 °C. Higher pyrolysis temperatures resulted in enhanced specific surface areas and promoted CaCO 3 crystallization while limiting MgCO 3 formation. The Cu 2+ adsorption capacity depended on the biochar type and pyrolysis conditions. Although the Cu 2+ adsorption efficiency of NF-BCs decreased with increasing pyrolysis temperature, F-BC550 exhibited a higher Cu 2+ adsorption capacity than F-BC750. Additionally, the Cu 2+ adsorption performance of both NF-BC350 and F-BC550 improved with increasing solution pH. Cu 2+ adsorption onto NF-BC350 and F-BC550 followed the two-compartment first-order (involving fast and slow adsorption compartments) and Langmuir (meaning homogeneous monolayer adsorption) models, respectively. The maximum Cu 2+ adsorption capacity of F-BC550 (147.3 mg Cu/g BC) was 7.8-fold higher than that of NF-BC350 (18.8 mg Cu/g BC), as determined by isotherm studies. The enhanced adsorption performance of F-BC550 may be attributable to physical adsorption facilitated by increased surface area and multiple mechanisms, including cationic attraction via functional groups, ion exchange (Ca and Mg), and van der Waals interaction facilitated by increased surface area. These findings suggest that F-BC550, derived from waste biomass, exhibits superior Cu 2+ adsorption performance compared to NF-BCs, making it a promising adsorbent for wastewater treatment applications.