Sustainable β-Cyclodextrin Modified Sawdust Biochar for Enhanced Organic Pollutant Removal in Circular Water Treatment

This study evaluates β-cyclodextrin (β-CD) and malonic acid functionalized pine sawdust biochar for organic pollutant removal, benchmarking efficacy against commercial Norit GSX activated carbon for sustainable water treatment. Characterization revealed that β-CD modification successfully developed porous structures, with Sawdust Activated Carbon (SDAC) and Norit GSX Activated Carbon (GSXAC) achieving Brunauer–Emmett–Teller (BET) surface areas of 438.36 m2/g and 1223.79 m2/g, respectively. Adsorption kinetics and isotherm studies demonstrated the superiority of β-CD-modified materials over traditional acid-functionalized variants. The adsorption kinetics were exceptionally well-described by the Pseudo-Second-Order model R2 > 0.99, indicating that the process is governed by chemical interactions rather than simple physical attachment. In contrast, the Pseudo-First-Order and Elovich models provided poor descriptions of the system (R2 = 0.54 and 0.11, respectively). An isotherm analysis further confirmed the heterogeneous nature of the SDAC surface, with the Freundlich model exhibiting an excellent fit (R2 > 0.99) and an n value of 0.79. For GSXAC, the Freundlich model also outperformed the Langmuir model, yielding a KF of 441.72 mg/g and n = 0.77, reflecting high adsorption intensity on a heterogeneous surface. The comparative advantage of β-CD is in line with its unique truncated cone structure, which is consistent with guest–host inclusion complex formation, multi-modal hydrogen bonding, and enhanced pH resilience. These findings validate β-CD-modified sawdust-derived adsorbents as potential, sustainable, high-capacity alternatives to industrial-grade carbons.