Theoretical and Experimental Studies on the Visible Light Activity of TiO2 Modified with Halide-Based Ionic Liquids

Marta Paszkiewicz-Gawron,Justyna Łuczak,Samanta Makurat,Adriana Zaleska-Medynska,Ewa Kowalska,Paweł Mazierski,Wojciech Lisowski,Janusz Rak,Magdalena Zdrowowicz

doi:10.3390/catal10040371

Abstract

Formation of a surface complex between organic molecules and TiO2 is one of the possible strategies for the development of visible light-induced TiO2 photoactivity. Herein, three ionic liquids (ILs) with the same cation and different anions (1-butylpirydynium chloride/bromide/iodide) have been applied for the surface modification of TiO2 and to understand the role of anions in visible light-induced activity of ILs-TiO2 systems. Photocatalytic screening tests (the measurements of phenol photodegradation reaction rate) revealed that anion type affected visible light activity (λ > 420 nm) of TiO2 obtained by the ILs-assisted solvothermal method. Density functional theory (DFT) calculations demonstrated that interactions between halogen anions and oxygen vacancies (OV) on the surface of the TiO2 particles could be responsible for the specific wavelength-induced excitation and finally for the observed photoactivity of titania under visible light. Finally, our theoretical calculations have been proven by experiments using monochromatic light (the apparent quantum efficiency was measured) and the properties of obtained samples were characterized using scanning electron microscopy (SEM), X-ray powder diffraction analysis (XRD), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS).

Highlights

Semiconductor photocatalysis, with a dominant role of TiO2 as a representative catalyst, was, up to date, applied to a variety of environmental and energy problems
More details about different ionic liquids (ILs) decomposition in the above mentioned conditions were described in our publication in which we developed computational methodology allowing for prediction properties of newly synthesized IL-TiO2 materials before their synthesis [25]
Based on our findings, we demonstrated that the improved, under visible irradiation, photoactivity of TiO2 modified with the selected ILs, originates from the interactions of the IL’s halogen anion (Cl− /Br− /I− ) and molecular oxygen with the TiO2 surface

Summary

Introduction

Semiconductor photocatalysis, with a dominant role of TiO2 as a representative catalyst, was, up to date, applied to a variety of environmental and energy problems. Since titania absorbs wavelengths shorter than 400 nm (due to the large band gap), its practical application requires usage of UV irradiation sources. In this regard, a lot of effort was made to design and tailor physical, chemical and optical properties of TiO2 to extend its absorption to the visible range. TiO2 photoactivity under visible irradiation out toAnother, be application of ionic liquids (ILs) preparation of TiO2 microparticles [6].

Methods

Results

Conclusion