How Sn and Zn species affect both the physicochemical properties and the photocatalytic power of N-doped nano titania

Semiconductor photocatalysis is one of the most proficient methods in the field of Advanced Oxidation Processes (AOPs) for environmental remediation, especially for the removal of emerging pollutants in aqueous environment. Titanium dioxide (TiO2), despite its high efficiency, is characterized by high electron/hole recombination rates which strongly decrease its performance as a photocatalyst. Recently, mixed composites attracted much attention as advanced systems able to promote the photocatalytic efficiency. Actually, the creation of semiconductor heterojunctions or doped photocatalysts with superior activity under visible light may significantly affect the pollutant degradation pathway, thus influencing the capability to obtain non-hazardous reaction intermediates and/or high mineralization degrees. In the present work, the photocatalytic degradation of an emerging pollutant, tetracycline hydrochloride, belonging to the class of pharmaceuticals and personal care products (PPCPs) was performed by sol-gel synthesized TiO2, N:TiO2 and (Sn/Zn, N):TiO2 doped and codoped systems (Fig. 1). Samples were tested under both UV and simulated solar light. Moreover, different Sn/Ti and/or Zn/Ti ratios (0, 5 and 20 %) were used in order to obtain different proportions among the guest and host species. Moreover, the effect of different thermal treatments (a calcination at 400°C or a hydrothermal procedure in autoclave) on the photocatalytic performance and the heterojunction features were investigated. All synthesized samples were characterized by structural, morphological and optical point of view exploiting HR-TEM, XRPD, DRS and BET analyses revealing strong modifications of the physicochemical features upon guest species introduction. Further, in order to comprehend the effect of the different composites on the tetracycline degradation pathway, GC-MS analyses were performed; different reaction intermediates will be identified and the results will be interpreted in the light of the electronic structure and the physicochemical properties of the mixed systems.