Second generation photocatalysts by metal and nitrogen codoping. The role of Ta and Nb.

Titanium dioxide is widely used as photocatalyst due to its features, e.g. chemical stability, low cost and non-toxicity. Its band gap (≥ 3.0 eV) makes it photoactive only in the UV light, which represents the 5% of the solar spectrum. Non-metal and metal dopings have been proposed as effective strategies to enhance TiO2 activity under visible and UV light. Especially, nitrogen is the most used species to promote absorption in the visible region. Nevertheless, niobium and tantalum have been strongly investigated as dopants for TiO2 thanks to the electronic disposition of their orbitals. Over the last few years, non-metal/metal codoping has attracted more and more attention. As a matter of fact, the charge compensation effect appears particularly useful for photocatalytic applications. Here, N/Nb/Ta doped and N,Nb/Ta codoped TiO2 nanomaterials were synthesized and deeply characterized under the structural, morphological, optical and spectroscopic point of view. Two different doping techniques were adopted to provide the guest species. All samples were photocatalytically tested in the gas phase degradation of ethanol under both UV and simulated solar light. Results were discussed in the light of DFT theoretical calculations, which enable to provide a comprehensive scenario about the electronic structure of the samples.