Photochemical processes in molecules and semiconductor nanocomposites: photoacid/photobase generators and TiO2/Graphene photocatalysts

In the last years, the use of light as a reagent has launched a huge variety of new reaction pathways, leading to the development of many new applications. During my PhD, I studied photochemical processes in molecules and semiconductors, working respectively with photoinitiators such as photoacid and photobase generators and with photocatalysis of semiconductors, such as TiO2. In the first part of this work, photoacid and photobase generators have been treated with the aim of controlling and localizing pH variations with light. This potentiality was exploited to obtain controlled precipitation and dissolution of calcium carbonate. We first focused on the development of a photoprecipitation/photodissolution method for application as a new technique for artwork restoration. Photoinduced precipitation of CaCO3 was also implemented in a gel matrix to fix CaCO3 crystals generated by the light stimulus. The possibility to embed CaCO3 crystals in a support can allow to write CaCO3 structures by light with high precision and apply this process to lithography and patterning systems. In the second part of this work photocatalytic behaviour of TiO2 in environmental remediation has been treated. TiO2 colloidal nanoparticles were synthesized by an easy surfactant-assisted method, for water decontamination. Photocatalytic properties were investigated for water remediation by organic pollutants, using Rhodamine B as a model; a great enhancement of photocatalytic performances has been achieved with respect to commercial TiO2 aqueous dispersions and further improvement was obtained by modifying TiO2 nanoparticles with graphene, MoS2 and polydopamine (PDA). Finally, TiO2 photocatalytic coatings modified by Graphene and embedded in cement matrix were studied for air remediation (using NOx gases as model). We also studied photocatalytic response to aging effects in which the system showed a great resistance that made it suitable for the real application in self-cleaning cementitious surfaces.