Regeneration performance of carbon nanotube by binary metallic oxide electrodes electrokinetic system

This study was aimed to investigate the regeneration performance of carbon nanotube saturated with 150 mg L−1 of nonylphenol (NP) by binary metallic oxide electrodes-electrokinetic (BMOEEK) system under potential gradient of 2 V cm−1 for 8 h of treatment. Twenty experiments were conducted with four processing fluids of de-ionized water (DW), citric acid (CA), NaOH, and NaCl in a Pyrex glass cylindrical cell. An inert electrode of carbon (C) and three binary metallic electrodes of PbO2/Ti (PT), PbO2–Co/Ti (PCT), and PbO2–SnO2 + Sb2O3/Ti (PSST) were investigated in this study. Results showed that higher electroosmotic permeability (6.2–26.3 × 10−6 cm2 V−1 s−1) was found in BMOEEK-CA, -NaOH, and -NaCl systems than in BMOEEK-DW system (0.8–1.4 × 10−6 cm2 V−1 s−1). A significant detached Pb2+ was found in BMOEEK systems with PT electrode. The best CNT regeneration efficiency of 71.4–80.0% was found in BMOEEK-NaCl system with PSST electrodes, which was 1.4–1.6 times greater than in BMOEEK-DW system. This might be resulted from both hypochlorite (OCl−) generation in anode reservoir by disassociation of NaCl and less Pb2+ detached from electrode with coating of Co and insulated layer of SnO2 + Sb2O3. For BMOEEK-NaOH and -NaCl systems, the degradation of NP is much more prominent than the combined removal by electroosmosis and electromigration and for the other two systems, the removal percentage is significant. It is concluded that both binary metallic electrode and processing fluid definitely played key roles in enhancing the regeneration performance of CNT. The electrode characteristics (progressive cyclic voltammogram, and SEM micrograph with EDS), electrokinetic behavior (specimen pH and current density), and regeneration mechanism in investigated systems would also be discussed in this study.

► Three binary metallic electrodes were investigated in the regeneration performance.
► We examined the effect of four processing fluid on regeneration performance.
► The insulated layers of either Co or SnO2 + SbO2 extend the life of PT electrode.
► Degradation by anode oxidation in reservoirs was dominant for the regeneration of CNT.