The electrosorptive response of a carbon nanotube flow-through electrode in aqueous systems

Abstract

The capture and recovery of valuable products from wastewater and/or bio-broths is one of today’s industrial challenges. Potential-controlled chromatography is a versatile solution to separate charged or polarized target species from aqueous systems. This capacitive flow-through technique combines the advantages of capacitive desalination and ion-exchange chromatography. The separation principle is controlled by system-dependent solid–liquid interaction mechanisms at the potential-controlled interface and characterized by the electrochemical double layer (EDL) formation. We conducted new experiments on the process- and environment-dependent surface effects in aqueous systems to better understand electrically driven processes inside a macroporous multi-walled carbon nanotube electrode. Here, the column and current response are investigated as a function of flow rate, as well as mobile phase pH-value, composition and concentration. Due to the strong water affinity of the material, water ions significantly co-define the EDL. The current response depends particularly on the ion properties and concentration. The use of electrolytes promotes capacitive and faradaic current and diminishes pH-deviation occurring at a negative potential. The effective range of the EDL decreases with increasing shear forces. Finally, a better performance for electrosorbing maleic acid is guaranteed at higher electrolyte concentration and low flow rate. This paper successfully addresses research gaps in potential-dependent effects that occur in multi-walled carbon nanotube electrodes.