Regeneration of spent carbon nanotube by electrokinetic process with binary metallic oxide electrodes of MnO₂/Ti RuO₂/Ti, and PbO₂/Ti

This study was aimed to investigate the regeneration performance of carbon nanotube saturated with 150mgL⁻¹ of nonylphenol (NP) by electrokinetic process with binary oxide electrodes (BMOEEK) under potential gradient of 2Vcm⁻¹ and elapsed time of 8h. Twenty experiments were conducted with four processing fluids of de-ionized water (DW), 0.06M citric acid (CA), 0.2M NaOH, and 0.1M NaCl in a Pyrex glass cylindrical cell (4.2cm in diameter×12cm in length). Two inert electrodes of carbon (C) and titanium (Ti) and three binary metallic electrodes of MnO₂/Ti, RuO₂/Ti, and PbO₂/Ti were investigated in this study. Results were shown that higher EO permeability (3.8×10⁻⁶ to 10.0×10⁻⁶cm²V⁻¹s⁻¹) was found in citric acid, NaOH, and NaCl systems than in DI water system (0.6×10⁻⁶ to 2.5×10⁻⁶cm²V⁻¹s⁻¹). The regeneration efficiency of CNT was 16.5–29.5%, 27.3–49.2%, 30.8–54.8% and 38.4–69.0% in BMOEEK–DW, –CA, –NaOH, and –NaCl systems, respectively. This might largely be because both OCl- and OH-radical were contributing for NP degradation in BMOEEK–NaCl system and, however, OH radical was the only contributor in other systems. Among the investigated electrodes, the RuO₂/Ti electrode has shown the best degradation performance of NP. Results of this study concluded that NP was degraded by BMOEEK system, which was highly related to both processing fluid and binary metallic electrode, rather than removal only by conventional EK system. The innovative BMOEEK technology was promoted to be a sustainable technology.