Intensified internal electrolysis for degradation of methylene blue as model compound induced by a novel hybrid material: Multi-walled carbon nanotubes immobilized on zero-valent iron plates (Fe0-CNTs)

This paper reported a novel iron–carbon hybrid material (Fe0-CNTs) as a technical improvement of internal electrolysis for water treatment. This material was fabricated by means of electrophoresis deposition (EPD) to immobilize carbon nanotubes on the surface of zero-valent iron plate and then stabilized by calcinations. The reactivity of Fe0-CNTs was examined by the degradation kinetics of methylene blue (MB) used as model compound. The presence of Fe0-CNTs material in water induced considerable enhancement in reaction rates, which was attributed to the numerous microscopic iron-carbon galvanic cells formed in situ. The oxidative pretreatment of carbon nano-tubes largely facilitated the electrochemical process due to the improvement in surface chemistry. The thickness of CNTs layer was optimized at about 10 μm (EPD time of 3 min) for a better performance of Fe0-CNTs. The Fenton-like oxidation chain reactions following Reactions (1)–(3) was verified to play the key role on the degradation of target organics. The direction of this pathway has been analyzed to depend on a complex stoichiometrical relation between hydrogen ion (H+) and dissolved oxygen (DO), since side reactions may also take place consuming both of them. This functionalized Fe0-CNTs material working through micro-electrolysis exhibited appreciable advantages in terms of reactivity, durability and operational simplicity. The knowledge gained from the effect of solution environments is of importance for process control.

► A Fe0-CNTs hybrid plate was produced as technical improvement for micro-electrolysis.
► The oxidative pretreatment of carbon nanotubes enhanced the reactivity of Fe0-CNTs.
► The Fenton-like oxidation pathway was verified to play the major role on degradation.
► The stoichiometrical relation between H+ and DO control the reaction pathway.