Cyclic voltammetric and FTIR studies of powdered carbon electrodes in the electrosorption of 4-chlorophenols from aqueous electrolytes

Several types of carbon materials (activated carbon, carbon black, multiwalled carbon nanotubes) differing in porosity and surface chemistry were used to prepare powdered electrodes. Activated carbon (Norit R3-ex) was demineralized and modified by oxidation with conc. HNO3, heat treatment in NH3 at 900 °C or heat treatment in argon at 1800 °C. Carbon black (Vulcan XC72) was flushed with an organic solvent, while the MWCNTs were functionalized to the hydroxyl and carboxyl forms. Nitrogen adsorption isotherms were used to characterize the pore structure of these materials. Their surface chemistry was assessed using thermogravimetry (TG), elemental analysis, FTIR, EDS and XPS. The ability to adsorb (isotherms) 4-chlorophenol (4-CP) in aqueous solution was determined. Cyclovoltammetric (CV) measurements of powdered carbon electrodes were carried out for blank electrolyte solution (0.1 M Na2SO4) and with different concentrations of 4-CP. Changes in the electric double layer capacity and other electrochemical parameters were estimated from the CV curves. The dependence of the electrochemical behavior of a powdered carbon bed on porosity and surface chemistry is analyzed and discussed. The electrochemical properties were related to chlorophenol adsorption ability and FTIR spectral analysis of the adsorption layer.