Regeneration approaches for TiO2 immobilized photocatalyst used in the elimination of emerging contaminants in water

Abstract

The photocatalytic degradation in distilled water of 15 selected emerging contaminants (ECs) has been evaluated in a solar pilot compound parabolic collector (CPC) plant by using TiO2 photocatalysts immobilized on glass spheres. The durability of the photocatalysts has been evaluated by measuring its performance during 4 consecutive cycles. TiO2 was prepared by the sol–gel method using titanium isopropoxide as precursor, combined with commercial TiO2 Degussa P25 and polyethylene glycol (PEG) as the pore generating agent. The following microcontaminants in a concentration of 100μgL−1 have been studied: acetaminophen, antipyrine, atrazine, carbamazepine, diclofenac, flumequine, hydroxybiphenyl, ibuprofen, isoproturon, ketorolac, ofloxacin, progesterone, sulfamethoxazole and triclosan. The fluorine containing ECs, this is, flumequine and ofloxacin, are totally degraded under the studied reaction conditions. By contrary, a progressive decay of the photocatalytic activity is observed for the other contaminants. The contaminants with amine or amide groups but without halogen heteroatoms in the structure record the lowest degradation rates. In order to recover the photoactivity, different strategies using aqueous solutions containing H2O2 under UV irradiation, NaOH, NH4OH and direct heat treatment in air at 400°C, were adopted. For the sake of simplicity, these experiments have been performed in a solar simulator at 765Wm−2. In order to determinate the nature of the species adsorbed on the titania active sites, the used and the regenerated photocatalysts were analyzed by XPS. Chemical treatment with NaOH results in the removal of the TiO2 layer. The ECs containing sulphate, fluoride or chloride groups are easily adsorbed on the photocatalyst active sites as compared to the ECs containing amide or amine groups and are easily desorbed by the regeneration treatments. Amongst the different pretreatment studied, calcination and H2O2/UV irradiation are the most efficient methods to recover the photocatalytic activity.