Parasitic Light Absorption, Rate Laws and Heterojunctions in the Photocatalytic Oxidation of Arsenic(III) Using Composite TiO 2 /Fe 2 O 3

• Published in: Chemistry : a European journal 2022-03, Vol.28 (16), p.e202104181
• Main Authors: Bullen, Jay C, Heiba, Hany F, Kafizas, Andreas, Weiss, Dominik J
• Format: Article
• Language: English
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202104181

Composite photocatalyst-adsorbents such as TiO /Fe O are promising materials for the one-step treatment of arsenite contaminated water. However, no previous study has investigated how coupling TiO with Fe O influences the photocatalytic oxidation of arsenic(III). Herein, we develop new hybrid experiment/modelling approaches to study light absorption, charge carrier behaviour and changes in the rate law of the TiO /Fe O system, using UV-Vis spectroscopy, transient absorption spectroscopy (TAS), and kinetic analysis. Whilst coupling TiO with Fe O improves total arsenic removal by adsorption, oxidation rates significantly decrease (up to a factor of 60), primarily due to the parasitic absorption of light by Fe O (88 % of photons at 368 nm) and secondly due to changes in the rate law from disguised zero-order kinetics to first-order kinetics. Charge transfer across this TiO -Fe O heterojunction is not observed. Our study demonstrates the first application of a multi-adsorbate surface complexation model (SCM) towards describing As(III) oxidation kinetics which, unlike Langmuir-Hinshelwood kinetics, includes the competitive adsorption of As(V). We further highlight the importance of parasitic light absorption and catalyst fouling when designing heterogeneous photocatalysts for As(III) remediation.