UV and Visible Light-Driven Production of Hydroxyl Radicals by Reduced Forms of N, F, and P Codoped Titanium Dioxide.

A M Abdullah,Suresh C Pillai,Kevin O'Shea,Miguel Á Garcia-Pinilla

doi:10.3390/molecules24112147

A M Abdullah, Suresh C Pillai + Show 2 more

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https://doi.org/10.3390/molecules24112147

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Abstract

The photocatalytic activities of reduced titanium dioxide (TiO2) materials have been investigated by measuring their ability to produce hydroxyl radicals under UV and visible light irradiation. Degussa P25 TiO2 was doped with nitrogen (N), fluorine (F), and/or phosphorus (P) and then subjected to surface modification employing a thermo-physicochemical process in the presence of reducing agent sodium borohydride (NaBH4). The reduced TiO2 materials were characterized by a number of X-ray, spectroscopic and imaging methods. Surface doping of TiO2 was employed to modulate the band gap energies into the visible wavelength region for better overlap with the solar spectrum. Hydroxyl radical generation, central to TiO2 photocatalytic water purification applications, was quantitated using coumarin as a trap under UV and visible light irradiation of the reduced TiO2 materials. At 350 nm irradiation, the yield of hydroxyl radicals generated by the reduced forms of TiO2 was nearly 90% of hydroxyl radicals generated by the Degussa P25 TiO2. Hydroxyl radical generation by these reduced forms of TiO2 was also observed under visible light irradiation (419 and 450 nm). These results demonstrated that simple surface modification of doped TiO2 can lead to visible light activity, which is important for more economical solar-driven applications of TiO2 photocatalysis.

Highlights

While titanium dioxide (TiO2 ) has attracted remarkable attention as a photocatalyst over the past few decades for the treatment of wastewater and the degradation of hazardous chemicals, significant industrial applications and commercial benefits have yet to be realized [1,2,3]
The visible light-activated reduced forms of TiO2 materials were prepared by a simple solid state thermo-physicochemical treatment using NaBH4
The materials were subsequently characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscope (HRTEM), energy dispersive X-ray fluorescence (EDXRF), UV-Visible, and Raman spectrometry

Summary

Introduction

While titanium dioxide (TiO2 ) has attracted remarkable attention as a photocatalyst over the past few decades for the treatment of wastewater and the degradation of hazardous chemicals, significant industrial applications and commercial benefits have yet to be realized [1,2,3]. TiO2 photocatalysis requires absorption of a photon, typically in the UV region (λ < 400 nm), to generate an electron (e− CB )/hole(h+ VB ) pair, Equation (1), which can initiate degradation through the production of reactive oxygen species (ROS) as outlined below in Equations (1)–(5). The recombination of the electron/hole pair is often a dominant process which eliminates the potential for the formation of ROS. The electron/hole pairs can migrate to the surface of TiO2 and form ROS in the presence of water and oxygen [4,5,6,7]. While direct oxidation and reduction of target substrates by electron/hole pair can be envisioned, such direct transformations are generally not competitive in aqueous solution. The primary processes leading to degradation of target pollutants usually involve

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