A Safe by Design Approach for the Synthesis of a TiO2-based Paint for the Photocatalytic Degradation of Pollutants under Visible Light

TiO₂ is considered as one of the most efficient photocatalysts for the degradation of air and liquid indoor pollutants. However, pristine TiO₂ can mainly absorb the UV fraction of solar light [1]. In addition, TiO₂ nanoparticles (NPs) were recently classified as a suspected carcinogen [2]. To address these challenges, Creative Nano is currently developing waterborne paints containing sulfur doped TiO₂ NPs that are photocatalytically active under visible light irradiation [3]. Moreover, the S-doped TiO₂ NPs were combined with silica to produce S-TiO₂/SiO₂ nanocomposites, following a “safe by design” approach, because the presence of a silica layer surrounding TiO₂ NPs has been shown to restrict release of NPs into the environment [4].

In this work, a series of S-doped TiO₂/SiO₂ samples with different SiO₂ content were prepared via sol-gel synthesis. The samples were characterized by InfraRed (IR) and Diffuse Reflectance spectroscopy (DRS) in the solid-state whereby their particle size was measured by Dynamic Light Scattering (DLS) in water. The samples were evaluated versus the photocatalytic degradation of methyl orange (MO) in water under visible-light irradiation. Our results showed that the introduction of a SiO₂ layer had a beneficial effect on photocatalytic activity compared to pristine S-TiO₂. The highest MO degradation was observed for S-TiO₂/SiO₂ NPs with ~4 wt % SiO₂.

The best performing nanopowder was incorporated in a waterborne paint formulation. The photocatalytic properties of the paint were evaluated at lab-scale by monitoring MO degradation in solution . 45±3 % MO removal was observed after 5 h of visible light irradiation over five cycles.