Electrochemical Degradation of Toluene Using TiO₂ Nanotubes

Toluene is a solvent widely used to produce paints, thinners, varnishes, and adhesives, as well as an octane rating improvement additive in gasoline. This compound can, unfortunately, be released into the environment in car exhaust fumes or when products containing toluene are used. Continuous exposure at high levels can cause permanent brain damage in animals. TiO2 nanotubes (TiO2,nt) increase the surface/volume ratio, as well as efficient electron transport, in the metallic substrate of Ti, enhancing the electrochemical degradation of organic compounds such as toluene. An anodizing procedure has been performed to synthesize TiO2 in the present work. The team varied two anodizing operating conditions: potential (10, 20, 30, 40, and 50 V) and cathode material (titanium, Ti, and stainless-steel, SS) to achieve desirable results. The synthesized electrodes were characterized by Raman spectroscopy to identify the different crystallographic phases. We identified the presence of the three typical phases of TiO2 (anatase, rutile, and brookite), mainly in the synthesized electrodes at 30 V (using Ti and SS as the cathode). More significant intensity signals were observed than those corresponding to the anatase and rutile phases. Additionally, the different electrodes were analyzed by scanning electron microscopy with microanalysis (SEM-EDX) to identify the external morphology and validate their chemical composition. The toluene was hydrolyzed in ethanol with the different synthesized electrodes (Ci = 1.0 ppm, E = 2.0 V, t = 180 min, n = 150 rpm, cathode = Ti or SS). Toluene removal was monitored by gas chromatography with detector BID (CG-BID). Results indicate that the electrodes synthesized at 30 V show the highest removal efficiencies in a minimal time. The TiO2,nt|Ti synthesized using the TiO2,nt|Ti ||Ti configuration showed a toluene removal of 94.53 % in 12 min. In contrast, for the TiO2,nt|Ti synthesized using the TiO2,nt|Ti||SS configuration showed a 100 % toluene removal achieved in 6 min. In conclusion, the best result for synthesizing the TiO2,nt|Ti reactive nanotube-rich surface was the configuration using stainless steel as the cathode (TiO2,nt|Ti||SS), applying a potential of 30 V during the 15 min anodizing treatment. This modified surface showed the highest toluene removal efficiency, 100 %, at 6 min when this VOC was dissolved in ethanol with 0.1 M KCl as the supporting electrolyte. This result is due to the anatase and rutile phases of TiO2, as verified with Raman spectroscopy. The corresponding stoichiometric relationship of two atoms of oxygen and one atom of titanium in the TiO2 nano-tubes when analyzed using SEM-EDX. After the electrolysis of toluene, the anatase phase was lost.