Pore Structure And Properties Of Activated Liquefied Wood Carbon Fiber By Steam Activation

In the present work, phenol liquefied fir was used as raw material to fabricate liquefied wood activated carbon fiber (WACF) by steam activation. The evolution and formation mechanism of the micro/mesopore structure for WACF under different activation processes was investigated comprehensively. The effect and mechanism of the crystal structure of carbonized precursor fiber on the pore structure formation of WACF was studied by means of different carbonization’activation processes. By air pre-oxidation treatment on the precursor fiber, the influence and mechanism of the chemical structure of precursor fiber and the initial pore structure of carbonized precursor fiber on the pore structure formation of WACF was discussed. Furthermore, the electrochemistry performance and adsorption performance of methylene blue (MB) and Cu2+ for WACF were detected and the relationship between these properties and the porosity structure were also explored. The main conclusions were as follows:(1) As the increase of activation temperature or activation time, the BET specific surface area (SBET) and total pore volume (Kt) were increased. Under different activation temperatures, the formation and evolution of pore structure for WACF performed in various ways. When activated at 650-800℃, the micropores were formed; with the burn-off being more than 45%, the micropore volume and micropore specific surface area (Smi) kept constant. When activated at 850-950℃, the micro/mesopore size was enlarged; with the burn off being more than 75%, the Smi decreased sharply accompanied by the collapse of micropores smaller than 0.8 nm; when the burn-off was more than 90%, the maximum mesopores ratio was about 49.5% and mesopores at 2-5.8 nm were formed.(2) The "activation temperature-activation time" process plan for steam activation was constructed. According to this plan, WACFs with the same pore structure could be produced by combination of activation temperature and activation time.(3) In steam activation processes, the micropores were formed because of the erision of the axial microcrystalline by water steam. Meanwhile, the radial microcrystalline conflicted, resulting in the formation of a certain amount of pores, and rearranged. Highly ordered microcrystalline was in favor of the enhancement in the penetration rate of water steam into microcrystalline and the pore size enlargement.(4) With increasing pre-oxidation temperature, the SBET and Vt of WACF were remarkably increased. Pre-oxidation at 280℃ promoted the formation of mesopores, with the mesopore volume and ratio increased by 72.2% and 30.7% respectively. This was mainly caused by high content of phenolic ether bond and surface cracks which were formed from the evaporation of side chain radicals in the aromatic rings and reconnection among the aromatic rings in the pre-oxidized precursor fiber(5) The specific capacitance (Cs) of WACF reached 280 F g-1 in 1 M H2SO4 electrolyte, with 81.8% of Cs retention ratio at 10 A g-1. The Cs retention ratio after 2000 charging-discharging cycles at 10 A g-1 reached up to 99.3%. The good supercapacitor performance of WACF was due to large Smi (2300 m2 g-1) and mesopores at 3-4 nm connected reciprocally(6) With increasing the amount of WACF, the Cu2+ adsorption rate (Rcu2+) increased significantly. Under a certain amount of WACF, the RCu2+increased with the prolonged activation time, which was attributed to the improvement in the amount of adsorption site, which was caused by the increasing amount of surface acid oxygen-containing groups (C-O、C=O、COOH) and large SBET.(7) With pre-oxidation treatment, the methylene blue adsorption capacity of WACF was improved by 34%, mainly due to the increase in the amount of mesopores.