Activated carbon fibers (ACFs) have been prepared from liquefied wood (W_liq) by chemical activation with KOH, with a particular focus on the effect of KOH/fiber ratio in term of porous texture and surface chemistry. ACFs based on steam activation served as a blank for comparison. The properties of the ACFs were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results show that the KOH-activated ACFs have rougher surfaces and more amorphous structure compared with the blank. The pore development was significant when the KOH/fiber ratio reached 3, and achieved a maximum Brunauer-Emmett-Teller (BET) surface area of 1371 m² g^-1 and total pore volume (V_tot) of 0.777 cm³ g^-1, of which 45.3% belong to mesopores with diameters of 2–4 nm, while the blank activated at the same temperature had a BET surface of 1250 m² g^-1 and V_tot of 0.644 cm³ g^-1, which are mainly micropores. The surface functional groups are closely associated with the KOH/fiber ratios. KOH-activated ACFs with KOH/fiber ratio of 3 have more oxygenated surface functional groups (C-O, C=O, -COOH) than the blank.

In this study, ZnCl₂ activation of phenol liquefied wood fibers at different temperatures was conducted to investigate the reaction mechanisms during the activation process. By combining Fourier transform infrared (FTIR) spectroscopy, thermogravimetric-FTIR-mass spectrometry (TG-FTIR-MS) and elemental analysis, the reaction mechanisms during the ZnCl₂ activation were deduced. Below 327 °C, dehydration of the hydroxyl groups and fracturing of molecular chains occurred inside the fiber. At 327–700 °C was the main stage of activation, where molecular structure was rearranged due to intramolecular condensation, crosslinking reactions and scission of molecular chains. A carbon net-like structure was preliminarily formed at 402 °C. Due to the removal of pyrolysis products such as H₂, H₂O, CO, CO₂, benzene and phenol, surface defects were filled in molten ZnCl₂. Pores would be left on the fiber surface after activation, cooling and cleaning. Above 700 °C, the aromatization degree and the degree of aromatic ring gradually improved.

Preparation and Characterization of Activated Carbon Fibers from Liquefied Wood by ZnCl2 Activation

Activated carbon fibers (ACFs) were successfully prepared from softwood lignin, which was isolated with polyethylene glycol 400 (PEG-400) as a solvolysis reagent, by water steam activation. The pore characterization and adsorption property of ACFs were investigated. The results showed that all the ACFs with more micropores exhibited high specific surface area and total pore volume which increased with the activation time prolonging; the highest ones were around 3100 m²/g and 1.5 mL/g, respectively. The specific surface area and total pore volume were much larger than those of other types of lignin-based ACFs and activated charcoal. Besides, with increasing activation time, the amount of graphitic carbon, which was the main compound on the surface of ACFs, decreased, while the amount of functional groups containing C–O slightly increased. In addition, the adsorption capacity of ACFs for methylene blue was highly increased as the activation time increased. Accordingly, lignin isolated with PEG is a promising precursor for ACF production.