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.