Synergetic effect of photocatalysis and ozonation for enhanced tetracycline degradation using highly macroporous photocatalytic supports

Abstract

Photocatalysis and ozonation have limited efficiency for the degradation of persistent pollutants as well as the mineralization of byproducts. In this work, we intensify the degradation processes by using simultaneously both processes in macroporous catalytic supports under mild reaction conditions, for degradation of tetracycline. The total organic carbon removal reached up to 90% after 180 min of photocatalytic ozonation reaction, achieving this record value using mild conditions. A comparison among processes showed the synergetic effect of photocatalysis and ozonation carried out in the macroporous support, which presents a kinetics increase of ≈20% greater than the sum of the separated processes. About 100% of tetracycline degradation was achieved with a high total organic carbon removal. This effect is attributed to synergy with the porous structure, which promote better O3 and O2 species mass transfer, due to the tortuosity and turbulence developed within the structure channels, coupled with a augmented residence time of the reactants. The gas-liquid mixture moves slower inside the porous channels, the apparent relative viscosity of a bubble train can be orders of magnitude larger than the viscosity of the pure liquid within the channels. In this work conditions were estimated as 10 times greater per bubble. The better species distribution, the increased residence time, and e−/h + recombination hindering along an increase of free hydroxyl radicals improved the overall degradation of tetracycline, avoiding the use of free catalysts and allowing the direct reuse of the system.