Chemical activation of willow with co-presence of FeCl3 tailors pore structure of activated carbon for enhanced adsorption of phenol and tetracycline

Abstract

FeCl₃ is a Lewis acid catalyzing condensation reaction, which might be beneficial for enhancing mass yield of activated carbon (AC) if used as a co-activator. Herein, this was verified by conducting activation of willow with various activators (ZnCl₂, K₂C₂O₄, H₃PO₄) in the presence/absence of FeCl₃. The results indicated that FeCl₃ competed with acid-catalyzed reactions induced by ZnCl₂ or H₃PO₄, interfering aromatization and diminishing AC yields (from 40.8 % to 37.0 % with ZnCl₂). In the activation with K₂C₂O₄ + FeCl₃, In-situ IR measurement showed that FeCl₃ catalyzed polymerization reactions, but polymeric products were not stable and were further cracked with K₂C₂O₄, reducing AC yield drastically from 27.6 % to 7.1 %. The co-presence of FeCl₃ in the activation reduced overall specific surface area (1201.6 versus 1127.2 m² g⁻¹ for K₂C₂O₄) by merging of micropores to form a higher percentage of mesopores (i.e. 2.0 % to 17.1 % for K₂C₂O₄, and 9.2 % to 41.4 % for H₃PO₄). This pore restructuring significantly enhanced tetracycline adsorption (99.9 % removal for AC- K₂C₂O₄ + FeCl₃ versus 61.1 % for AC-K₂C₂O₄ alone), while compromising phenol adsorption (48.7 % versus 96.1 %) due to reduced micropore availability. The reduced specific surface area was also attributed to the retention of inorganics by solid phase reactions between FeCl₃ and K₂C₂O₄ or H₃PO₄. Additionally, the presence of FeCl₃ resulted in more fragmented surface of ACs generated from all activators.