Advanced degradation of organic substance in water using no-ferric Fenton reaction on Titania nanotube

Abstract

Highly reactive OH radicals facilitate advanced oxidation processes (AOPs) [1]. AOPs are irreplaceable in environmental remediation including but not limited to pollutant degradation [2]. H2O2 leading to OH radicals in iron based fenton systems are well known and few other oxides of alumina and ceria in non-ferrous fenton systems [1]. Majority of studied catalysts materials are in powder form, which limits the catalysts long term applicability in real systems due to separation and regeneration of the catalyst with required catalytic activity is costly. In this present work, we have studied anatase phased titania nanotube arrays (TNA) grown on Ti films prepared by an anodization approach for methyl orange (MO) dye degradation under photocatalytic conditions. Key findings reveal long stability of TNAs over fifty reaction cycles in batch process with higher degree of reproducible performance. Complete removal of MO was achieved after six hours of exposure in AM 1.5 G light (equivalent to 1 sun intensity), where hydrogen peroxide accounted for only 1/200th of the amount of initial dye concentration. This superior performance is ascribed to surface oxygen vacancies and Ti3+ sites promoting regeneration of peroxide in the ongoing reaction medium that is consequently transformed to OH radicals. This is further confirmed by the experiments conducted with formic acid, a known hydroxyl radical scavenger, where the dye degradation was observed to be minimal at a near zero rate even after six hours of reaction time, upon measurements with UV-visible spectroscopy. About 38% of the initial dye was oxidized after 1 h into the reaction under light irradiation in a typical system whereas activity was hugely promoted to over 55% when it was coupled with a Pt wire in an electroless process, without supply of additional power. In conclusion, TNA based this new material is highly regarded as environmentally sustainable, easily reusable, non-toxic and commercially viable candidate for real wastewater treatment plants where the treatments plants are usually large tanks constructed in the open space with access to freely available, energetically rich solar power.