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 150 mg L−1 of nonylphenol (NP) by electrokinetic process with binary oxide electrodes (BMOEEK) under potential gradient of 2 V cm−1 and elapsed time of 8 h. Twenty experiments were conducted with four processing fluids of de-ionized water (DW), 0.06 M citric acid (CA), 0.2 M NaOH, and 0.1 M NaCl in a Pyrex glass cylindrical cell (4.2 cm in diameter × 12 cm 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 × 10−6 cm2 V−1 s−1) was found in citric acid, NaOH, and NaCl systems than in DI water system (0.6 × 10−6 to 2.5 × 10−6 cm2 V−1 s−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.

► Three binary metallic electrodes of MnO2/Ti, RuO2/Ti, and PbO2/Ti were investigated in EK systems. ► The oxidant of OCl− would be produced to enhanced degradation performance as using NaCl as processing fluid. ► The RuO2/Ti electrode was shown the best degradation efficiency of NP. ► The treatment efficiency was highly related to both processing fluid and binary metallic electrode, rather than only removed by conventional EK system.