Degradation of Polyvinylpyrrolidone by Photocatalytic Ozonation and Evaluation of the Influence of Some Operational Parameters

Photocatalytic degradation of polyvinylpyrrolidone (PVP) by titanium dioxide and ozone in an annular reactor was investigated using a 125-W mercury vapor lamp as the light source. It was observed that the TiO2/O-3/UV process presented a greater efficiency than the TiO2/UV process. In fact, around 90% of the mineralization was obtained in 1 h of reaction, reflecting the synergistic effect of the combination of O-3 and TiO2 under UV light, because the sum of the rate constants of the individual processes is less than the rate constant of the combined process. The effects of the initial PVP concentration, photocatalyst dosage, ozone input flow rate and pH on the PVP degradation rate were studied. In general, the results suggest that PVP can undergo a cross-linking process when the TiO2/O-3/UV treatment is applied. The reaction rate was increased when the photocatalyst dosage was increased up to 2.0 g L-1; however, increasing the initial PVP concentration led to a drop in the reaction rate. The efficiency also decreased at basic pH, because ozone is decomposed under alkaline conditions. In addition, it was noted that most of the nitrogen atoms of the macromolecules of PVP can be transformed into nitrate and ammonia during photocatalytic ozonation.