Electrosorption Behavior of Carbon Nanotube and Carbon Nanofiber Film Electrodes

Abstract

In this review work, the synthesis of cost-effective, large area carbon nanotube and nanofiber (CNT-CNF) film by low pressure and low temperature thermal chemical vapor deposition and its electrosorption properties in salt solutions are studied. Successful purification of water with good reproducibility by electrosorption of CNT-CNF films is achieved because of optimal pore size distribution that results in lower electrical double-layer overlapping effect. It is found that electrosorption of CNT-CNF film electrodes is mainly due to Coulombic interaction on the electrical double-layer and the ion sorption followed a Langmuir isotherm, indicating monolayer adsorption. The kinetics and thermodynamics analyses indicate that the electrosorption of NaCl onto CNT-CNF electrodes follows first order kinetics model and is driven by a physisorption process. Several experiments are conducted to study the ion removal capacity and selectivity of CNT-CNF film electrodes, showing that multivalent cations are preferentially adsorbed from the aqueous solution. For cations with same charge, the one with smaller hydrated radius will be more effectively removed. Keywords: Electrosorption, Carbon nanotubes, Capacitive deionization, Langmuir isotherm, Hydrated radius, Carbon Nanofiber, CNT-CNF, electrical double-layer overlapping effect, monolayer adsorption, physisorption process, deionization technologies, evaporation, reverse osmosis, electrodialysis, water purification technology, distillation columns, thermal heaters, pore microstructure, pore size distribution, arbon aerogel material, carbon aerogels, mass-transfer resistance, activated carbon cloth, chemical vapor deposition (CVD), Conductive plates, surface morphology, JEOL JSM-6700F, scanning electron microscopy (SEM), JEOL JEM-1200EX transmission electron microscopy (TEM), Raman spectroscopy, pore size distribution and Brunauer-Emmet-Teller (BET), counter electrode, reference electrode, polymethyl methacrylate plate, rectangular nylon spacer, rubber spacer, Batch-mode Electrosorption, CNT-CNF electrode, low mass-transfer, adsorption process, adsorption, –, desorption curves, mesoporous material, oxidation/reduction peaks, interaction, electrochemical reaction, double-layer capacitance (DLC), electrode surface inhomogeneity, Electrosorption Capacity, Freundlich isotherms, Electrosorption Kinetics, first-order, second-order, parabolic diffusion, Electrosorption Thermodynamics, Free energy of adsorption (DG0), enthalpy (DH0), van't Hoff plots