| This study was devoted to improving the adsoption capacity and antibacterial activity of carbon fibers derived from liquefied wood (WCF), extending their applications. WCF were modified by silver nitrate after steam activation. The effect of activation parameters on the property and microstructure of activated carbon fibers (WACF) was investigated, including their adsorption capactity, mechanical property, surface morphology, crystal structure, surface chemical structure, and pore structure. According to these variations of microstructure, the formation process of pore structure was concluded. Moreover, the microstructure and antibacterial property of silver-containing WACF (WACF/Ag) were discussed to illustrate their pore filling and antibacterial mechanism.The main results of this study as follows:1. The tensile strength (>0.13 Gpa) of WACF was comparable to commercial ACF. The iodine adsorption capacity increased with an increase in activation temperature (700-900 ℃), activation time (10-90 min), or steam flow (1.0-2.5 ml/min/g), finally reaching to 1800 mg/g.2. The crystallite size of WACF increased initially and then decreased with the increase in activation temperature and time, whereas it always kept the decreasing trend with the increase of steam flow. The samples, activated at 800 ℃ for periods of 60 min with steam flow of 1.0 ml/min/g, had the largest crystallite size. The specific surface area and volume of micropores and mesopores were directly related to the activation temperature, activation time, and steam flow. With these paramenters raising, more element carbon and oxygen-containing functions were found on WACF, while less element oxygen and graphitic carbon groups existed in WACF.3. Formation of pore structure in WACF:some tiny micropores were produced in the carbonization, because of the developed defects in or between micrographene layers. Activation rendered steam molecules to react with unsaturated cabon atoms, enlarging interlayer spacing of crystallites, decreasing crystal size. Meanwhile, some new defects were developed, forming more micropores.4. Characteristics and distribution of silver particles:both silver atoms and ions existed in silver particles. The content of silver atoms (about 85%) was much higher than that of silver ions. As the soaking concentration of silver nitrate solution increased, the percentage of micropores filled by silver particles varied from 4% to 17%, whereas the percentage of filled mesopores decreased from 36% to 8%.5. Pore filling mechanism of silver particels:silver ions were adsorbed to pores of WACF and were reduced into silver atoms. The increasing silver atoms migrated and aggregated together to form silver particels with various number of silver atoms (0.35 nm per atom). The micropores were firmly filled by 2-20 silver atoms, and the silver particels composed of more atoms filled the mesopores or were distributed on the surface of WACF.6. Antibacterial mechanism:after seven cycles of antibacterial tests on the same group of WACF/Ag, their antibacterial ratios were still 91.89-99.95%, indicating that WACF/Ag had the excellent antibacterial activity and durability. The increase in activation time and soking concentration of silver nitrate solution could strengthen their antibacterial activity. At the soking concentration of 0.2 mol/L, less silver ions were released, and WACF/Ag showed the higher antibacterial activity. The reason for WACF/Ag possessing the excellent antibacterial activity and durability can be arrtibuted to numerous nanosilver particles in micropores. |
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