Editor’s Choice – Catalytic and Photothermo-catalytic Applications of TiO2-CoOx Composites

Author(s):Roberto FiorenzaMarcello CondorelliLuisa D’UrsoGiuseppe CompagniniMarianna BellarditaLeonardo Palmisano and Salvatore Scirè*

Volume 1, Issue 1, 2020

Page: [3 – 15]

Pages: 13

DOI: 10.2174/2665976X01666200219113505

Abstract

Background: The necessity to have green and sustainable industrial processes has promoted new technologies for air and water purification together with the research of new energy sources. In this contest, the TiO2-based photocatalysis can be considered a promising route for both environmental applications and hydrogen production through water splitting.

Objective: In this work, we have investigated the photocatalytic performance of TiO2-CoOx composites on both photooxidation and photoreduction reactions. Specifically, we have compared the performance of the composites in the thermo-catalytic, photo-catalytic and photothermal-catalytic oxidation of ethanol chosen as model volatile organic compound (VOC) and in the photocatalytic hydrogen production by simulated solar light from aqueous solution of ethanol.

Methods: The samples were prepared with a simple impregnation method, and were characterized by Scanning Electron (SEM) and Transmission Electron (TEM) microscopies, X-ray powder diffraction (XRD), N2 adsorption-desorption measurements, Temperature Programmed Reduction in hydrogen (H2- TPR) and X-ray Photoelectron (XPS), Raman, UV-Vis Diffuse Reflectance (UV-Vis DRS) and Photoluminescence (PL) spectroscopies. The catalytic and photocatalytic activity were carried out on pyrex reactors irradiated with a solar lamp and analyzing the reactions products through gas chromatography.

Results: The presence and the amount of cobalt oxide were found crucial in determining the performance of the TiO2-based composites for both the catalytic and photocatalytic processes. In particular, the addition of 1 weight percent of CoOx led to the best performance in the photocatalytic processes, whereas a higher amount was beneficial in the thermo-catalytic tests. The multi-catalytic approach based on the synergistic effect of photocatalysis and thermocatalysis in the presence of the TiO2-1%CoOx sample allowed the temperature necessary to obtain 50% ethanol conversion and 50% yield in CO2 to be reduced by 40°C and 50°C, respectively. The same sample was also the best catalyst for photocatalytic solar H2 production.

Conclusion: The presence of small amounts of cobalt oxide leads to an efficient composite with TiO2 facilitating the space charge separation and increasing the lifetime of the generated photoholes and electrons. The wide versatility of TiO2-CoOx catalysts both for photooxidation and photoreduction reactions motivates to further exploit the use of these systems in real solar-driven photocatalysis. Read now: https://bit.ly/3dGdsJ5

Editor’s Choice – Simultaneous Photocatalytic Abatement of NO and SO2: Influence of the TiO2 Nature and Mechanistic Insights

Author(s):María D. Hernández-AlonsoSilvia Suárez Fernando FresnoJuan M. Coronado* and Benigno Sánchez*

Volume 2, Issue 2, 2021

Published on: 03 March, 2021

Page: [130 – 139]

Pages: 10

DOI: 10.2174/2665976X02666210303124330

Abstract

Background: TiO2 is currently being incorporated into several construction materials, such as cement and asphalt because this photocatalyst can act as a passive system to reduce the concentration of typical urban pollutants like NOx and SO2 under solar illumination.

Objective: In order to get further insights on the possible influence of the interaction between common pollutants, the present work investigates the mechanism of NOx photo-oxidation in the presence of SO2 traces over TiO2 samples of different textural and morphological characteristics.

Methods: The performance for the photo-oxidation of NOx and SO2 in a dry air stream over TiO2 samples, both commercial and lab-prepared by hydrothermal and thermal methods, was evaluated by means of FTIR analyses of the gas phase. These materials were characterized by XRD, N2 adsorption isotherms, and DR UV-vis spectroscopy. Mechanistic studies were performed by in situ DRIFT under UV irradiation.

Results: Photocatalytic tests showed a very efficient removal of the two selected pollutants using most of the TiO2 samples. In the case of SO2, elimination of these molecules is due not only to photocatalytic oxidation but also to a significant extent, to adsorption. Although in shorter periods, no byproducts are generated, following irradiation for several hours, the production of NO2 progressively increases and reaches 100 % selectivity over some photocatalyst. In situ DRIFTS analyses show the evolution of the surface composition and reveal the formation of the different types of surface nitrates with different symmetry. Under these operating conditions, a minor amount of sulfates are also formed.

Conclusion: The presence of a low concentration of SO2 does not appear to be detrimental for NO removal. NO2 formation is delayed on the TiO2 samples with high specific surface area, which also tend to be more active. The spectroscopic results confirm the involvement of surface hydroxyls in the formation of adsorbed nitrate species. Read now: https://bit.ly/3QwTpep

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