Synergistic effects of anions in iron salts on engineering hierarchical pores in activation of peach wood

Background Aromatization is an important reaction route to form stable carbon skeleton for reserving pores generated during activation of biomass. Salts with Lewis acidity are known to catalyze dehydration and condensation reactions to form aromatic skeletons, while anions of salts are generally not inert and could influence evolution of pore development. Elucidation of the potential synergistic effects anions on pore evolution of activated carbon (AC) is of importance in optimizing the process for activation. Methods This study investigated the activation of peach wood with FeCl 3 , FeCl 2 , Fe 2 (SO 4 ) 3 or Fe(NO 3 ) 3 ) at 700°C, combined with in-situ IR spectroscopy to capture real-time dynamic change of reaction intermediates during activation process. Significant findings The results showed that Cl - in the iron salts uniquely stabilizes Fe 3+ (a distinctive advantage over other anions) for achieving efficient aromatization, yielding AC with the highest S BET (816.8 m 2 /g) and superior capability for removal of basic fuchsin (87.4%). FeCl 2 (Fe 2+ ) had weakened activity for aromatization, forming AC with loosely porous aggregates (597.6 m 2 /g). The activation with Fe 2 (SO 4 ) 3 reduced the sulfates and led to sulfur deposit blocking pores (S BET : 23.5 m 2 /g), with in-situ IR identifying S-O species that directly interfered with aromatization process. Fe(NO 3 ) 3 generated oxidative radicals that disrupted aromatization and wrapped Fe 3 O 4 species in inner structure, clogging pores (S BET : 230.8 m 2 /g). Increasing temperatures from 700 to 900°C in activation with FeCl 3 reduced the S BET progressively to 642.7 m 2 /g, resulting from excessive gasification, which also decreased AC yield to 17.4% and induced irreversible micropore-to-mesopore conversion, a temperature-dependent pore evolution pattern rarely highlighted in iron-salt activation systems. Notably, In-situ IR analysis revealed accelerated dehydration and aromatization at 300-400°C for consolidating microporous frameworks by Cl - and oxidation of carbonaceous intermediates by NO 3 - as well as formation of S-O species from SO 4 2- and their interference on aromatization. This work fills the knowledge gap in decoupling the roles of anions and iron valence in biomass activation, providing a targeted strategy for designing high-performance ACs with unique pore characteristics.