Aging of photocatalytic coatings under a water flow: Long run performance and TiO2 nanoparticles release

Although photocatalytic coatings may experience severe wearing in most of their application, little work has been done to investigate their aging in a comprehensive way. In this article, we present an original experimental protocol to simulate an accelerated aging of photocatalytic coatings under a water flow, and test it on two materials: a well-known commercial product, Pilkington Activ™, and an experimental coating. The influence of intrinsic properties of the coatings (chemical nature, thickness) as well as environmental parameters (water matrix, UV-light) is investigated while the consequences of aging are evaluated under three different endpoints, related either to the long run performance of photocatalytic coatings or their environmental impact: (i) loss of the photocatalytic activity, (ii) degradation of mechanical properties, and (iii) release of TiO2 nanoparticles. It is observed that both photocatalytic coatings experienced a deactivation of their active sites upon prolonged immersion. The extent of deactivation varies depending on the coating, being around 20% for experimental coatings and 65% for Pilkington Activ™ but shows little dependency on water matrix or illumination. An alteration of mechanical properties is seen on experimental coatings, which was accompanied by TiO2 emissions as high as 150.5 μg L−1. Although no reduction in film hardness or adhesion could be evidenced for Pilkington Activ™, TiO2 concentrations up to 30.8 μg L−1 was detected in the aging water showing that some release of TiO2 nanoparticles also took place on this material. Interestingly, a common mechanism of release, triggered by an interaction between TiO2, NaCl and UVA could be identified. Most severe damages were observed in presence of sodium chloride. These results suggest that the use of photocatalytic coatings with surface-bound nanoparticles in environmental applications may entail new entries of nanomaterials into the aqueous medium. They also prove that aging assays are an effective way of assessing the emissions.

Figure optionsDownload as PowerPoint slideHighlights▸ Accelerated aging of two photocatalytic coatings under a water flow. ▸ Deactivation of photocatalytic active sites upon prolonged immersion. ▸ Release of TiO2 nanoparticles even in absence of mechanical deterioration. ▸ Common pattern of aging for the two coatings. ▸ Strongest damages in presence sodium chloride.