Generation And Evolution Of Pore Structure Of Activated Carbon Fiber Prepared From Phenol Liquefied Wood And Its Regulation Mechanism

In order to adjust the pore structure of wood based-activated carbon fiber(WACF)flexibly to meet the application requirements in different fields,in the present work,Chinese fir liquefied by phenol was used as a raw material to prepare WACF by KOH activation in the specific activation conditions.The reaction path of pore structure of WACF and its evolvement mechanism were investigated during the KOH activation process.Based on it,microporous and mesoporous WACFs with high specific surface area(SSA)were prepared via combing KOH activation and steam activation and changing the activation order.The regulation mechanism of pore structure during the reactivation was also investigated.Furthuremore,The adsorption properties and electrochemical performance of WACF with different pore structure were studied to reveal the effect of pore structure on the performance of WACF.The main conclusions were as follows:(1)Activation temperature and alkali carbon ratio had significant effect on the pore structure of WACF during the KOH activation process.In the initial stage of KOH activation,ultramicropores of 0.5 nm were mainly generated.Rasing activation temperature would promote the generation of more micropores.When the temperature was above 800?,mesopores were developed to a certain extent due to the intercalation effect of metal potassium vapor.When the alkali carbon ratio was relatively low,KOH would be used up in the early stage of activation process.During the subsequent activaton process,most micropores collapsed,so the prepared WACF was mainly mesoporous.The increasing alkali carbon ration could make the KOH fully react with carbon to from more micropores.The as-prepared WACF was mainly microporous.The activation time did not change the region of pore size distribution but changed the pore amounts in the different region.(2)When the precursor fibers were carbonized at 500? to transform into CFs,the main involved reactions were substitution and scission reactions of methylene,oxidation of methylene and phenolic hydroxyl by hydroxyl radical,decomposition of macromolecule substances from incomplete liquefaction and preliminary cyclization reactions.A preliminary graphite-like microcrystalite structure was formed.Reactions during the activation process where KOH impregnated CFs were carbonized at 850?primarily refer to polycyclic reactions,reactions between KOH and carbon,and reactions of the resulting potassium compounds with carbon.The graphite-like microcrystalite structure was well developed.(3)KOH-steam reactivation was an effect method to develop the porosity of WACF,especially the microporosity.The pores generated by the single KOH activation mainly distributed around 0.5 nm.Steam reactivation enlarged those micropores and new micropores were generated aound 0.7-2.0 nm,which led to the decrease of micropores at 0.5 nm.Meanwhile,the amount of mesopores distributed at 2.0-4.0 nm increased slightly.Steam-KOH reactivation was also an effect method to deveop the porosity of WACF,especially the mesoporosity.The reactivation temperature has a significant effect on the generation and development of mesopores.Based on this,prolonging the activation time could further develop the mesoporosity.The ratio of mesopore volume to total pore volume was as high as 66.8%.(4)The micropore volume of WACF had significant effect on its iodine adsorption capacity,while the adsorption capacity for methylene blue was closely related with the mesopore volume.Langmuir model was favorable for adsorption of MB onto the liqufied wood-based ACFs,implying the homogeneous nature of ACF surface and the adsorption of MB onto liquefied wood-based ACFs was monolayer adsorption.The kinetic adsorption behavior of methylene blue onto liquefied wood-based ACFs can be favorably described by pseudo-second-order model.(5)The ultramicropores(<0.6 nm)of WACF had a great contribution to the electric double layer capacitance.The mesopores distributed at 2.0-4.0 nm were available for rapid chage transmission.The specific capacitance of the WACF-based supercapacitor was 242 F g-1 using KOH as electrolyte at a current density of 0.5 A g-1.After 10000 charging/discharging cycles,the supercapacitor could retain 91.8%of its initial capacitance.When the WACF was used to fabricate yarn based supercapacitor,the length capacitance was 43 mF cm-1 at the scan rate of 2 mV s-1.It also showed a good mechanical flexibility with high capacitance retention(97%)when crumpled.