TiO2 nanotube catalysts for parabens mixture degradation by photocatalysis and ozone-based technologies

The evolution of the analytical techniques allowed the detection of pollutants so called contaminants of emerging concern (CEC). Water scarcity is a reality lived by some populations. Thus, water reuse is mandatory to minimize this problematic. This implies that wastewater treatments must be improved. The Advanced Oxidation Processes (AOP) such as photocatalysis and ozonation can be suitable solutions for CECs abatement. Also, TiO2 powder catalyst is an important material in this field. However, its powder form presents a huge obstacle for industrial application, and the solution may be to support this material. This work studies the degradation of a mixture of 3 parabens by photocatalysis, catalytic and photocatalytic ozonation using TiO2 nanotube arrays (NTs). The studied catalysts were produced using electrolyte solutions with different ages, so the nanotubes growth ocurred at 5 (NTs_5) and 20 (NTs_20) anodization cycles. The toxicological assessment for the initial mixture, final samples and along the reaction time was performed using the cress seeds Lepidium sativum and the bacteria Aliivibrio fischeri. The photocatalysis with UVA radiation led to 50 % and 35 % parabens removal for NTs_5 and NTs_20 catalysts. This can be related to the different dimensional characteristics of the nanotubes. Ozone technologies led to total parabens degradation with an improvement when catalytic ozonation was applied. The use of NTs as catalysts in ozonation also reduced the transferred ozone dose (TOD) required for total parabens abatement when compared to single ozonation. The main parabens degradation mechanism seems to be via direct pathway by molecular ozone. Regarding the toxicity assessment, the toxicity did not change significatively, which can be explained by the intermediate’s formation.