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

FeCl 3 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 (ZnCl 2 , K 2 C 2 O 4 , H 3 PO 4 ) in the presence/absence of FeCl 3 . The results indicated that FeCl 3 competed with acid-catalyzed reactions induced by ZnCl 2 or H 3 PO 4 , interfering aromatization and diminishing AC yields (from 40.8 % to 37.0 % with ZnCl 2 ). In the activation with K 2 C 2 O 4  + FeCl 3 , In-situ IR measurement showed that FeCl 3 catalyzed polymerization reactions, but polymeric products were not stable and were further cracked with K 2 C 2 O 4 , reducing AC yield drastically from 27.6 % to 7.1 %. The co-presence of FeCl 3 in the activation reduced overall specific surface area (1201.6 versus 1127.2 m 2  g −1 for K 2 C 2 O 4 ) by merging of micropores to form a higher percentage of mesopores (i.e. 2.0 % to 17.1 % for K 2 C 2 O 4 , and 9.2 % to 41.4 % for H 3 PO 4 ). This pore restructuring significantly enhanced tetracycline adsorption (99.9 % removal for AC- K 2 C 2 O 4  + FeCl 3 versus 61.1 % for AC-K 2 C 2 O 4 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 FeCl 3 and K 2 C 2 O 4 or H 3 PO 4 . Additionally, the presence of FeCl 3 resulted in more fragmented surface of ACs generated from all activators.