Control of the oxidizing and hydrophilicizing properties of photocatalytic TiO₂ thin films coated on a polyethylene-terephthalate substrate

Abstract

Polyethylene-terephthalate (PET) films coated with photocatalytic TiO 2 and silicone as a binder were fabricated and attached to a window pane. A white substance was observed on the surface after exposure for several months in an area with air pollution. The white substance was analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy, ion chromatograph and capillary electrophoresis, and was identified as CaSO 4 . Although the oxidizing properties of the films were affected by the particle size and the amount of TiO 2 in the photocatalytic layer, the hydrophilicizing properties of the films were hardly changed by them. In this study, we found that it was possible to decrease the oxidizing properties of photocatalytic PET films while maintaining the hydrophilicizing properties constant by using small TiO 2 particles and controlling the ratio of TiO 2 /binder.

Heterogeneous photocatalysis and its potential applications in water and wastewater treatment: a review

“…This depends mainly on the photocatalytic reactor configuration and its build-material. For example, TiO 2 and g-C 3 N 4 are more suitable for fixed-bed type reactors because they can easily be immobilized by coating on substrates such as quartz [196], concrete [197], glass [198], Al 2 O 3 [50],limestone [199] and polymers such as polyacrylonitrile [200], polyethyleneterephthalate [201] and pulysulfone [194]. On the other hand, Fe 3 O 4 -based nanomaterials aid with the magnetic separation, and reduce the cost associated with the additional separation unit.…”

Photo-induced hydrophilicity of brookite TiO₂ prepared by hydrothermal conversion from Mg₂TiO₄

“…Despite the excellent hydrophilicity of the anatase TiO 2 /SiO 2 composite film, the strong oxidizing ability of anatase TiO 2 also accelerated the formation of CaSO 4 from Ca 2+ ions and SO x gas in air, resulting in undesirable white precipitates on the PET-film-coated window glass. 19) Here, we propose that TiO 2 with somewhat milder oxidizing ability maintaining hydrophilicity, perhaps brookite, is more suitable for the self-cleaning applications on plastic films. Brookite TiO 2 has a band-gap of ³3.0 eV, which is comparable to that of rutile TiO 2 .…”

“…14) 17) In 19981999, Machida et al focused on the selfcleaning functions of anatase TiO 2 and developed an anatase TiO 2 /SiO 2 composite system with excellent hydrophilicity, even under dark conditions. 18) More recently, Machida et al 19) have also reported on a long-term field testing of self-cleaning functions using anatase TiO 2 /SiO 2 composite film; silicone resin with the hardening temperature of ³120°C was used as the SiO 2 precursor since a polyethylene-terephthalate (PET) film covering on a window-glass panel was used as the substrate. Despite the excellent hydrophilicity of the anatase TiO 2 /SiO 2 composite film, the strong oxidizing ability of anatase TiO 2 also accelerated the formation of CaSO 4 from Ca 2+ ions and SO x gas in air, resulting in undesirable white precipitates on the PET-film-coated window glass.…”

Facile synthesis of > 99% phase-pure brookite TiO2 by hydrothermal conversion from Mg2TiO4

“…Rutile and anatase are widely used for practical applications since they are easily synthesized and cost-effective. In our previous study [8], we reported that the excessive oxidizing ability of anatase TiO 2 caused some problems in the self-cleaning; it formed CaSO 4 white precipitates on a window from atmospheric pollutants. Hence, in our recent study [9], we have focused on brookite TiO 2 with a mild oxidizing ability, which is suitable for the self-cleaning.…”