Photocatalytic ozonation of aniline with TiO₂-carbon composite materials

The photocatalytic ozonation of aniline (ANL) aqueous solutions was carried out in the presence of neat titanium dioxide (TiO₂), multi-walled carbon nanotubes (MWCNT) and a composite of TiO₂ and MWCNT. Independent tests for catalytic ozonation and photocatalysis were also carried out in order to explore the potential occurrence of a synergetic effect. Photocatalytic and catalytic ozonation carried out with an ozone dose of 50 g m^-3 converted ANL in 15 min. Photocatalysis using P25, commercial TiO₂, and an 80:20 (w/w) composite of P25 and MWCNT also led to total ANL conversion, but at longer reaction times. Removal of TOC was higher than 70% for all photocatalytic ozonation systems at 1 h of reaction. With the exception of neat MWCNT, photocatalytic ozonation in the presence of the selected samples led to nearly complete mineralization after 3 h of reaction. Photocatalytic ozonation completely removed oxalic acid (OXA) formed during ANL degradation. The concentration of oxamic acid (OMA, other ANL degradation by-product more refractory than OXA) generally increased with time, and in the photocatalytic ozonation with P25 based materials its concentration decreased earlier. The presence of nitrates and ammonium was confirmed during ANL degradation by all tested treatments, with the exception of the cation in TiO₂ catalysed reactions.