Abstract
Photocatalysts for water purification typically lack efficiency for practical applications. Here we present a multi-component (Pt:SiO2:TiO2(P25)) material that was designed using knowledge of reaction mechanisms of mono-modified catalysts (SiO2:TiO2, and Pt:TiO2) combined with the potential of atomic layer deposition (ALD). The deposition of ultrathin SiO2 layers on TiO2 nanoparticles, applying ALD in a fluidized bed reactor, demonstrated in earlier studies their beneficial effects for the photocatalytic degradation of organic pollutants due to more acidic surface Si–OH groups which benefit the generation of hydroxyl radicals. Furthermore, our investigation on the role of Pt on TiO2(P25), as an improved photocatalyst, demonstrated that suppression of charge recombination by oxygen adsorbed on the Pt particles, reacting with the separated electrons to superoxide radicals, acts as an important factor for the catalytic improvement. Combining both materials into the resulting Pt:SiO2:TiO2(P25) nanopowder exceeded the dye degradation performance of both the individual SiO2:TiO2(P25) (1.5 fold) and Pt:TiO2(P25) (4-fold) catalysts by 6-fold as compared to TiO2(P25). This approach thus shows that by understanding the individual materials’ behavior and using ALD as an appropriate deposition technique enabling control on the nano-scale, new materials can be designed and developed, further improving the photocatalytic activity. Our research demonstrates that ALD is an attractive technology to synthesize multicomponent catalysts in a precise and scalable way.
Highlights
Titania (TiO2) was first discovered as an active photocatalyst almost half a century ago [1] and still serves as a widely used benchmark for the development of new photocatalytic materials or as a substrate material to improve their photocatalytic properties [2,3,4]
We have reported on the mechanisms of SiO2:TiO2(P25) [16] and present a multi-component (Pt):TiO2(P25) [35] for the photocatalytic degradation of organic pollutants
For Pt:TiO2(P25), the role of dissolved O2 in combination with the enhanced charge separation turned out to be crucial for the enhancement of the photocatalytic activity
Summary
Titania (TiO2) was first discovered as an active photocatalyst almost half a century ago [1] and still serves as a widely used benchmark for the development of new photocatalytic materials or as a substrate material to improve their photocatalytic properties [2,3,4]. Pt enhances the photocatalytic activity of TiO2(P25) for dye degradation by acting as an adsorption surface for O2 suppressing charge carrier recombination by facilitating improved radical generation via the conduction pathway in the Nanomaterials 2020, 10, 1496 presence of dissolved O2 [15,35]. Our previous findings for the role of an ultrathin SiO2 coating on TiO2(P25) nanoparticles demonstrated an improved photocatalytic activity due to the improved generation of OH radicals at the SiO2 surface from the more efficiently separated holes on the SiO2 surface by the more acidic Si-OH surface groups [14,16], which is different from TiO2(P25) as well as Pt:TiO2(P25) From this detailed analysis of the photocatalytic mechanisms, the question arises whether the advantages of these bi-material composites, Pt:TiO2(P25) and SiO2:TiO2(P25), can be combined in a tri-material composite resulting in a further improved photocatalyst for dye degradation.
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