Development of titanium dioxide based photocatalytic systems for CO2 photoreduction

In this thesis, different aspects related to carbon dioxide photoreduction with water, focusing are discussed, focusing in particular on the two most important issues: catalyst design and reaction conditions investigation. On one side, catalyst formulation was considered and several titanium dioxide based materials were synthesised by different techniques to tune physicochemical properties. Considering reaction mechanism, modifications on this material were performed aimed at improving carbon dioxide adsorption introducing alkali-earth oxides on catalytic surface, reaching total selectivity to methane avoiding water splitting side reaction. Furthermore, to lengthen electron-hole life on titania surface, metal promotion was investigated introducing, in one case, copper oxide as a co-catalyst and, in the other, gold nanoparticles for their plasmon resonance properties. In this way, it was possible to obtain an increase in photoactivity and a modification in products distribution, which was explained by an in-depth characterisation by a wide range of analytical techniques. On the other side, reaction conditions effect was investigated. Titanium dioxide effectiveness in CO2 photoreduction in gas phase was increased by three orders of magnitude developing a thin film reactor which maximised light harvesting providing promising results even in mild conditions. Furthermore, developed materials were tested in different photocatalytic systems to investigate the effect of experimental conditions. Reaction medium proved to be an important feature: in fact, performing CO2 photoreduction in liquid phase using the same catalysts provided a much wider products distribution, indicating a strong effect on reaction mechanism and products distribution as a consequence. Finally, reaction was performed in high irradiance conditions and, by a design of experiments approach, the effect of irradiance and reaction time differs according to experimental regime was assessed.