Study On Electrosorption Of F-and Cu2+from Water By Activated Carbon Fiber With TiO2-coating

Water pollution has been increasingly serious recently. The pollution of inorganic ions like F-and Cu2+has attracted intensive attention. Generally, electrosorption is one kind of effective method for removing inorganic ions from water because of its high adsorption capacity, no-secondary pollution and convenience for regenerating. In this work, activated carbon fiber coated with TiO2(TiO2/ACF) was employed as electrodes. The removal effects of F-and Cu+by electrosorption were investigated. The kinetics and adsorption isotherms, the effects of impact factors (voltage, pH, initial ion concentration and coexistence ions) on the removal of F-and Cu+and regeneration properties of the electrodes were analyzed as well. Moreover, the machanism of electrosorption processes was preliminarily discussed. The main conclusions were as follows:After coated with TiO2, ACF had a rough surface and its specific surface area (BET) and total pore volume decreased, while both the mesopore volume and the average pore diameter showed contradictory variation trend. The PSD of TiO2/ACF mainly concentrated in mesopore range. The XRD patterns indicated that the content of TiO2were anatase crystal. Based on the FT-IR study, the vibrating peaks of Ti-O-C and Ti-O appeared in the surface of TiO2/ACF. In addition, the locations of all peaks were shifted to lower wavelengths. Isoelectric point values of ACF and TiO2/ACF were2.94and4.45, respectively. Moreover, cyclic voltammetry, constant current charge-discharge and AC impedance were further demonstrated that the modified electrode had larger capacitance, better charge and discharge properties, but had larger charge transfer resistance.The results of electrosorptive defluorination indicated that adsorption capacity of TiO2/ACF electrode could be enhanced under external electric field. The electrosorption equilibrium time was12hours. Kinetics data for the adsorption of F-were in good agreement with the pseudo-second equations. The electrosorption isotherms of F-fitted well with the Langmuir equations. The electrosorption capacity was1.32mg·g-1at initial fluoride ions concentration of4mg·L-1, voltage of2V, neutral pH and adsorption time of12h. Adsorption capacity could also increase with the increase of the voltage and initial fluoride ion concentration, but the removal rate of fluoride ions displayed an opposite trend under the effect of initial fluoride ion concentration. Complex changes of electrosorption capacity occurred with the change of pH values and coexistence ions. Electrode corrosion phenomena didn’t appear on the surface of ACF electrode and TiO2/ACF electrode after electrosorption. The structure characteristics of electrode surface had slight changes. Specific surface area and pore volume of TiO2/ACF electrode slightly reduced, while the average pore diameter increased. Electrosorption effect of Cu2+was very good. The electrosorption equilibrium time was6hours and fitting equations of electrosorption kinetics and isotherms for Cu2+were the same as those for F-Voltage, pH, initial ion concentration, and coexistence ions had great influence on electrosorption effect. The electrosorption capacity of TiO2/ACF electrode was8.75mg·g-1in Cu(NO3)2solutions with copper ions concentration of50mg·L-1at voltage of2V, pH6and duration of8h. After adsorption of Cu2+, corrosion phenomenon on the electrode surface didn’t occur. The pore structure characteristics of electrode surfaces were much same as before.The materials could be renewable through electrode reverse connection, and regeneration efficiency was high. This indicates that ACF is an excellent electro-adsorbent.