Optimization of heterogeneous photoelectrocatalysis on nanotubular TiO2 electrodes: Reactor configuration and kinetic modelling

Abstract

Photoelectrocatalytic degradation of target molecules on nanotubular titanium dioxide (TiO2) immobilized on meshed conductive substrate was assessed by measuring the photoelectrochemical response (i.e., generated photocurrent) as indicator of TiO2 performance. Furthermore, a simple and reliable methodology for degradation modelling and laboratory reactor optimization has been proposed and validated. Nanotubular TiO2 was grown by anodic oxidation of Ti wire meshes and characterized by ESEM and XRD. Immobilized TiO2 on Ti wire mesh was used as photo-anode under UV irradiation (254 nm) and subjected to electrical polarization. The photocurrent was monitored in a three-electrode cell, by varying polarization voltage, TiO2 electrode relative positioning to the UV source (distance), and concentration of a model azo dye compound (Reactive Red 243, RR243). Photoelectrochemical response was modelled as a function of operating parameters and guidelines for photoreactor configuration were identified. Optimized batch photoreactor configuration (1.8 L) was used for degrading a 25 mg L−1 RR243 aqueous solution, achieving 90% decolorization in 45 min and 60% mineralization in 100 min. Decolorization kinetics were effectively described by means of a modified Langmuir-Hinshelwood model based on experimentally measured photocurrents, accounting for the dynamic behaviour of the process due to the change in solution transmittance over time determined by the degradation of target compounds.