Layered platforms of Ti4O7 as flow-through anodes for intensifying the electro-oxidation of bentazon.

In this study, we prepared Ti4O7 porous electrodes with continuous layered structures characterized by different layer-to-layer distance (from 2 to 10 µm) but the same total void fraction (88-90%), to modulate the electrodes' permeability and the volumetric electrochemical surface area (from 90 to 840 cm2 cm-3). These platforms were evaluated as anodes in the electro-oxidation (EO) of bentazon in a three-electrode cell under galvanostatic conditions, operated both in traditional batch (TB) or batch recycle flow-through (BRFT) modes. The performance was significantly enhanced when the liquid was recirculated through the lamellar structure of the electrodes. In BRFT mode, the electrode interlayer gap was found to be a key factor to control the bentazon and total organic carbon (TOC) conversions. For the best conditions evaluated (BRFT, 10 µm-interlayered Ti4O7 electrodes with a volumetric surface area of 90 cm2 cm-3), the effect of the applied current (1 or 3 mA) and liquid flow rate (10, 12 or 14 mL. min-1) was investigated. Specific energy consumption (SEC) values were estimated to reveal the performance of each of the EO treatments from an energetic point of view. The use of 10 µm-interlayered Ti4O7 electrodes at 1 mA in BRFT mode at a flow rate of 14 mL min-1 showed the best results, yielding 85% bentazon removal, 57% mineralization and SEC values of 0.006 kWh.gTOC-1 after 6 h of treatment. This contribution highlights the use of layered Ti4O7 electrodes as a promising strategy for intensifying EO processes, pointing to a trade-off between the accessibility to the internal electrode structure and the volumetric electrode surface area to enhance the contact between the target molecules and the hydroxyl radicals physisorbed on the electrode surface, while minimizing simultaneously the energy requirements.

Study of TiO2/Ti4O7 photo-anodes inserted in an activated carbon packed bed cathode: Towards the development of 3D-type photo-electro-Fenton reactors for water treatment.

In this work, commercially available Polymethyl-meta-acrylate (PMMA) spectroscopy cells were modified on the external walls with films of TiO2, Ti4O7 or TiO2/Ti4O7 mixtures. Film characterization was carried out using SEM and UV-vis spectroscopy. The results of photocatalytic (PC), electro-oxidation (EO), and photoelectrochemical (PEC) experiments on the decolorization of a methyl orange (MO) model dye solution showed that while anatase provides better photocatalytic properties and the partially reduced Ti4O7 larger electronic conductivity, the TiO2/Ti4O7 composite film behaves as a semiconductor substrate that combines the advantages of both materials (for PEC experiments for instance, decolorization values for the model dye solution using TiO2, Ti4O7 and a TiO2/Ti4O7 mixed film, corresponded to 35%, 46% and 53%, respectively). In order to test this film as an effective photoanode material in a 3-D type reactor for water treatment processes, a TiO2/Ti4O7 modified PMMA spectroscopy cell was inserted in an activated carbon (AC) bed so that the semiconductor material could be illuminated using an external UV source positioned inside the PMMA cell. The connected AC particles that were previously saturated with MO dye were used as cathode sites for the oxygen reduction reaction so that the photoelectrochemical reactions that take place in the anode could be complemented with coupled electro-Fenton processes in the cathode. As expected, the combination resulted in an effective decolorization of the dye solution that results from a complex combination of processes. The experimental decolorization data was successfully fitted to a pseudo-first order kinetic model so that a deeper understanding of the contribution of each process in the reactor could be obtained.