Removal of contaminants of emerging concern by photocatalysis with a highly ordered TiO2 nanotubular array catalyst

Abstract

In this work, the treatment of wastewater polluted with contaminants of emerging concern is evaluated by heterogeneous photocatalysis with TiO2. Titanium plates are anodized by different experimental conditions, and the influence of these conditions on the catalytic performance is evaluated by factorial design of experiments. The formation of TiO2 nanotubes in the anatase form is sought for photocatalysts with high active surface. Thus, electrolyte used in the anodization process (NH4F/H2O in ethylene glycol or H2SO4 in water), potential ramp (2 – 4 V min−1), maximal applied potential (20 – 60 V) and heat treatment are evaluated as influencing factors of the experimental design. The activity of these catalysts is tested by ofloxacin (pharmaceutical compound used as model of contaminant of emerging concern) degradation in wastewater treatment, obtaining the kinetic constant of the process, parameter chosen as response variable of the experimental design. Results show that NH4F/H2O as electrolyte, 2 V min−1, 40 V and a heat treatment are the optimum conditions for the formation of TiO2–anatase nanotubes with a good disposition and arrangement, observing the higher efficiency in the wastewater treatment process. In addition, wastewater treatment conditions are evaluated (UV wavelength, irradiance and initial concentration of ofloxacin), and it is found that UV-B, maximal irradiance and minimal initial concentration of the pollutant are the optimal factors for a higher process efficiency. This is a work that opens the door to the removal of contaminants of emerging concern from wastewater with a technology of low cost, with easy implantation and environmental compatibility, making possible to use only sunlight as a reagent.