Mesostructured lead dioxide grown on titania nanotubes for diclofenac water removal through electrocatalytic and photoelectrocatalytic processes

Abstract

Mesostructured PbO₂/TiO₂ materials were synthesized to perform electrocatalysis (as electrooxidation, EO) and photoelectrocatalysis for removing diclofenac (DCF), 15 ppm concentration in 0.1 M NaSO₄ solutions, at different pH conditions (3.0, 6.0 and 9.0) by applying 30 mA cm^-2. Titania nanotubes (TiO₂NTs)-based materials were prepared to synthetize with a massive PbO₂ deposit on this support to obtain TiO₂NTs/PbO₂ and a TiO₂NTs:PbO₂ material consisting in a dispersed PbO₂ deposit on TiO₂-NTs that allowed the formation of a heterostructured surface of combined composition (TiO₂ and PbO₂). Organics removal (DCF and byproducts) was monitored through UV-vis spectrophotometry and high-performance liquid chromatography (HPLC) during degradation tests. TiO₂NTs/PbO₂ electrode was tested in both processes, removing DCF at neutral and alkaline solution conditions in EO while an unimportant photoactivity was registered at this material. Conversely, TiO₂NTs:PbO₂ was used as electrocatalytic material in EO experiments, achieving more than 50% of DCF removal at pH 6.0 by applying 30 mA cm^-2. Also, for first time, the synergic effect was investigated when it was exposed to UV irradiation in photoelectrocatalytic experiments, enhancing its efficacy (⁓more than 20%) to remove DCF from a solution with 15 ppm over performance removals achieved (56%) when EO was applied under similar conditions. Chemical Oxygen Demand (COD) analyses showed that significantly higher DCF degradation is reached under photoelectrocatalysis, since COD values decrease a 76% against a 42% decrease achieved with electrocatalysis. Scavenging experiments showed a significant participation on the pharmaceutical oxidation process through the generation of photoholes (h⁺), hydroxyl radicals and sulfate-based oxidants.

Keywords: Diclofenac removal; Lead dioxide; Photoelectrocatalysis; Titania nanotubes.