Structural and Functional Behaviour of Ce-Doped Wide-Bandgap Semiconductors for Photo-Catalytic Applications

Giulia Forghieri,Michela Signoretto,Danny Zanardo,Federica Menegazzo,Elena Ghedini,Alessia Giordana,Giuseppe Cruciani,Giuseppina Cerrato,Alessandro Di Michele

doi:10.3390/catal11101209

Abstract

Increasing the photocatalytic efficiency of earth-abundant wide-bandgap semiconductors is of high interest for the development of cheap but effective light-driven chemical conversion processes. In this study, the coupling of ZnO and TiO2 with low contents of the rare-earth Ce species aimed to assess the photo-catalytic performance of the two semiconductors (SC). Structural and optical characterizations were performed to estimate the effect of the different interactions between Zn2+, Ti4+ and Ce4+ ions, and how the photo-responsive behaviour of Ce-Ti and Ce-Zn composites was affected. Therefore, photo-catalytic tests were performed for all Ce-modified SC to assess both their photo-oxidative and photo-reductive properties. Amongst all the tested materials, only Zn-based samples resulted in being suitable for the photo-oxidation of the methylene blue (MB) organic pollutant in a synthetic-dependent fashion.

Highlights

Since it was first introduced, the light-mediated catalytic conversion of many organic and inorganic molecules— referred as photocatalysis—has become increasingly attractive, especially in the context of energy transition [1]
The diffused reflectance spectroscopy (DRS) analysis of both CZ20 and CCZ20 showed a red shift of the absorption, increased affinity for CO, owing to the increased basicity of the material, as expected by indicated by the small tail2 in the visible region and attributed to the presence of CeO2, as introducing CeO and, as suggested, by attenuated total reflectance (ATR) spectroscopy
DRS analysis of CT20 displayed a broader visible abThe optical behaviour of the synthesized materials was further elucidated by diffused sorption band than bare TiO2 (P25, Evonik), which was related to the achievement of TiO2 reflectance spectroscopy (DRS) and photo-luminescence (PL) analysis

Summary

Introduction

Since it was first introduced, the light-mediated catalytic conversion of many organic and inorganic molecules— referred as photocatalysis—has become increasingly attractive, especially in the context of energy transition [1]. Therein, photocatalysis was widely employed for both photo-oxidation, such as photo-degradation of water pollutants, and photo-reductive reactions, such as the CO2 reduction or H2 production from water splitting [2], which were extensively studied mainly in wide-bandgap semiconductors [1,3]. In this context, photocatalysis refers to the ability of a semiconductor (SC) to employ the energy of incident photons to form new chemical bonds in a chemical redox reaction via electrons or holes transfer. When dealing with heterogeneous catalysis, either in gaseous or liquid media, other parameters become relevant for the catalytic performance, including the mass, the surface area and presence of active sites of the catalyst, the wavelength employed, the initial concentration of the contaminant, the temperature and the pressure of oxygen, if present [5]

Objectives

Methods

Results

Conclusion