Investigation On Preparation, Characterization And Adsorption Properties Of ACF/CNT Composites

Water pollution has become more and more serious with the development of industry and increase of population in recent years. The efficient treatment of dyes and heavy metals wastewater was proved to be one of the research hotspots and problems. The adsorption was selected to be preferred treatment technology in this study for its low cost, high efficiency, easy control and insensitive to toxic substance.In this paper, a new adsorption materials-ACF/CNT composites were firstly proposed and prepared with Ni(NO3)2·6H2O as catalyst precursor, C2H2as carbon source, H2as reduction gas and N2as carrier gas by growing carbon nanotubes(CNTs) on the surface of activated carbon fibers(ACFs) by chemical vapor deposition(CVD).The effects of preparation conditions and structure features were investigated for ascertaining the preparation mechanism of ACF/CNT composites and the growth mechanism of carbon nanotube. The results showed that CNTs were densely and well distributed on the surface of ACFs; C, Ni and O elements were found on the tip of CNTs; graphite CNTs and fcc nickel were found; the surface functional groups were changed after growing CNTs; micropores and mesopores dominated the ACF/CNT composites. The growth of CNTs followed VLS and top growth mechanism, and CNTs were found easy to grow on the pore sides.Aiming to rhodamine B, methyl orange, methylene blue and Cr(Ⅵ), controllability of performance and structure parameters including BET specific surface area, surface functional groups and pore size distribution was realized by adjusting pyrolysis temperature, pyrolysis time, catalyst precursor concentration, C2H2and H2flux.The adsorption abilities and mechanism of ACF/CNT composites for rhodamine B were showed that the adsorption capacity decreased from16.36to16.29mg/g with increasing pH from2to3, and then the adsorption capacity rised with increasing pH. The adsorption experimental data for rhodamine B were well fitted by Langmuir equation and pseudo-second-order kinetic model. The adsorption rate was not only controlled by intra-particle diffusion, but also by film diffusion. According to thermodynamic calculation, the adsorption process was a nonspontaneous and endothermic physisorption.The adsorption abilities and mechanism of ACF/CNT composites for methyl orange were investigated. The results showed that when pH rised from2to3, the adsorption capacity increased from96.88to114.81mg/g, then the increase rate droped. The adsorption experimental data of methyl orange were well described by Langmuir equation and pseudo-second-order kinetic model. The adsorption rate was controlled by intra-particle and film diffusion. The results from thermodynamic calculations suggested the the adsorption process was a spontaneous and exothermic physisorption.The adsorption abilities and adsorption mechanism of ACF/CNT composites for methylene blue were researched. The results declared that the adsorption capacity increased with increasing pH. The adsorption experimental data of ACF/CNT composites for methylene blue were well fitted by Freundlich equation and pseudo-second-order kinetic model. The adsorption rate was controlled by intra-particle diffusion and film diffusion. The results from thermodynamic calculations demonstrated that the adsorption process was a spontaneous and endothermic physisorption process.The adsorption abilities and adsorption mechanism of ACF/CNT composites for Cr(VI) were studied. The results indicated that when pH rised from2to3, the adsorption capacity decreased from4.992to4.987mg/g, then the decrease rate increased. The adsorption experimental data were well fitted by Freundlich equation. Furthermore, the kinetic data were well described by pseudo-second-order kinetic model. The adsorption rate was not only controlled by intra-particle diffusion, but also by film diffusion. The results from thermodynamic calculations indicated the adsorption process was a spontaneous and endothermic physisorption process.The adsorption mechanisms of rhodamine B and methylene blue are hydrogen bond, electrostatic attraction, n-n bond and micropore filling; the adsorption mechanisms of methyl orange are hydrogen bond, π-π bond and micropore filling. The adsorption mechanisms of Cr(VI) include electrostatic attraction and micropore filling.