Abstract
The use of TiO2 nanoparticles in organic-based photocatalytic coatings imposes several challenges: poor activity under visible light, binder photo-degradation, need for UV activation and toxicity concerns. Here we present a scalable two-step synthesis route to prepare TiO2-based hollow microspheres (HoS) as alternative photocatalyst to commercial TiO2 nanoparticles. The hollow microspheres of TiO2 or WO3-doped TiO2 (3 mol% WO3) are synthesized via template-assisted spray-drying followed by calcination. The structure and composition of the powders are characterized and their photocatalytic performance is assessed using methylene blue photo-degradation under UV irradiation as model reaction. XRD analysis reveals the presence of anatase and TiO2(B) phases, indicating the heterostructured nature of the samples. The results of the dye photo-degradation tests confirm the photocatalytic functionality of the TiO2-based HoS. Moreover, the introduction of WO3 (TiO2/WO3 HoS) leads to an enhancement of the performance, approaching that of commercial (Aeroxide P25, ~21 nm) nanoparticles. The most active TiO2/WO3 HoS are incorporated into an acrylic formulation and the resulting coatings tested towards pollutant abatement under UV light. A coating containing P25 nanoparticles undergoes an activation process where binder degradation leads to increased TiO2 exposure and a rise in catalytic activity but possibly at the expense of coating stability. By contrast TiO2/WO3 HoS-acrylic coatings exhibit catalytic activity similar to the initial activity of P25 containing coatings, but does not cause the same partial binder photo-degradation.
Highlights
The rising concern about environmental pollution and its adverse effects on human health has encouraged the development of sustainable technologies for the removal of pollutants in e.g. urban environments [1]
A Keyence VHX-6000 digital microscope was used for the visual in spection of the dry films, as well as for performing sessile Water contact angle (WCA) mea surements on coatings subjected to UV exposure, as done in our previous publication [29]
In light of this finding, it is reasonable to assume that the photocatalytic degradation of the binder in the TiO2/WO3 HoS-acrylic coating is primarily limited to the imme diate environment of the hollow microspheres, enabling exposure of active sites to some extent without causing pore formation, in contrast to the nanoparticle-containing coating
Summary
The rising concern about environmental pollution and its adverse effects on human health has encouraged the development of sustainable technologies for the removal of pollutants in e.g. urban environments [1]. The film-forming agent (binder) and other components of the coating formulation hinder the access of light and reactants to the TiO2 surface resulting in an inefficient utilization of the photons and lead to lower performance compared to the photocatalyst powder on its own [24]. We present a simple, cost-effective, and scalable methodology for the production of TiO2-based hollow mi crospheres (HoS) using spray-drying technology, namely the calcination of spray-dried titanyl sulfate/citric acid composite spheres. This allows production of hollow particles with high surface area and a mesoporous structure. According to the solid content, coatings with ~40 μm dry film thickness (DFT) were obtained
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