The Preparation And Adsorption Kinetics Of Composite Nano Activated Carbon Fibers

In this paper, the polyacrylonitrile (PAN)/cellulose acetate (CA) composite fibers and polyacrylonitrile (PAN)/cellulose acetate (CA)-silver nitrate (AgNO3) composite fibers were prepared by electrostatic spinning. The PAN/CA activated carbon fibers (PAN/CA-ACF) and PAN/CA-Ag activated carbon fibers (PAN/CA-Ag-ACF) were prepared after pre-oxidation, carbonization and activation. The changes of the silver nitrate, the surface mophology and structure of the two composite fibers in the process of pre-oxidation, carbonization and activation were analysised by many characterization methods. We investigated the two composite activated carbon nano fibers’effect on adsorption of sulfur dioxide under different conditions by the adsorption device which was made by ourselves. At last, the absorption rate curves of sulfur dioxide were fitted with absorption kinetics of Quasi-one adsorption equation, Quasi-two adsorption equation and Ben Graham equation.Through analysis of the viscosity and conductivity of precursor solution and surface morphology of the fibers, the best spinning conditions for the PAN/CA composite fibers were obtained. The mass ratio of PAN and CA is8:2, the spinning solution concentration is14wt%, the spinning voltage is lOkV and the receiving distance is24cm. The addition of AgNO3results in the increase of the conductivity of the solution and the decrease of the average diameter of PAN/CA composite fiber. Through analysis of Thermogravimetry and Differential Scanning Calorimetry (TG-DSC), we determined the pre-oxidation conditions of PAN/CA composite fibers:the composite fibers were treated from room temperature to300℃with1℃/min heating rate and keeping the temperature lasting90min under air atmosphere. After impregnate in H3PO4(1mol/L) for18h, the two pre-oxidated composite fibers were treated from the temperature to300℃with1℃/min heating rate and keeping the temperature lasting30min under N2atmosphere:The results of Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR) and Transmission Electron Microscopy (TEM) indicate that the surface morphology of pre-oxidated fiber happened collapses, contraction and cross-linking among the fibers obviously. The linear macromolecular chains of PAN and CA are broken, cyclized and a trapezoidal structure gradually formed. After carbonation and activation, the-C=N bond and-C-O bond in the two ACF have turned into the structure of the carbon skeleton with-C=C bond. The AgNO3turned into Ag nanoparticles with the size of the lattice is68.86(106pm3). The Ag nanoparticles tend to agglomerated in the surface of the fibers with the size being8～10nm. BET characterization gave the results that the specific surface area of PAN/CA-ACF and PAN/CA-Ag-ACF were1038.5m2/g and1176.5m2/g. The microspore volume proportion was more than95%in both of the ACF.Through adsorption experiment of SO2we conclude that the best adsorption time is150min and the adsorption rate of SO2increased with the increasing of SO2concentration in both of the two kinds of ACF. Because of the AgNO3thermal decomposition, the specific surface area and pore volume of PAN/CA-Ag-ACF is higher than that of PAN/CA-ACF. So the effect of SO2adsorption by the PAN/CA-Ag-ACF is better than that by the PAN/CA-ACF. The adsorption kinetics of SO2by PAN/CA-ACF and PAN/CA-Ag-ACF is better fitted the Ban Graham dynamics equation.