Layer-by-Layer-Stabilized Plasmonic Gold-Silver Nanoparticles on TiO2: Towards Stable Solar Active Photocatalysts

Abstract

To broaden the activity window of TiO2, a broadband plasmonic photocatalyst has been designed and optimized. This plasmonic ‘rainbow’ photocatalyst consists of TiO2 modified with gold–silver composite nanoparticles of various sizes and compositions, thus inducing a broadband interaction with polychromatic solar light. However, these nanoparticles are inherently unstable, especially due to the use of silver. Hence, in this study the application of the layer-by-layer technique is introduced to create a protective polymer shell around the metal cores with a very high degree of control. Various TiO2 species (pure anatase, PC500, and P25) were loaded with different plasmonic metal loadings (0–2 wt %) in order to identify the most solar active composite materials. The prepared plasmonic photocatalysts were tested towards stearic acid degradation under simulated sunlight. From all materials tested, P25 + 2 wt % of plasmonic ‘rainbow’ nanoparticles proved to be the most promising (56% more efficient compared to pristine P25) and was also identified as the most cost-effective. Further, 2 wt % of layer-by-layer-stabilized ‘rainbow’ nanoparticles were loaded on P25. These layer-by-layer-stabilized metals showed superior stability under a heated oxidative atmosphere, as well as in a salt solution. Finally, the activity of the composite was almost completely retained after 1 month of aging, while the nonstabilized equivalent lost 34% of its initial activity. This work shows for the first time the synergetic application of a plasmonic ‘rainbow’ concept and the layer-by-layer stabilization technique, resulting in a promising solar active, and long-term stable photocatalyst.

Gas phase deposition of well-defined bimetallic gold-silver clusters for photocatalytic applications

“…32–34 In that context, plasmonic ‘rainbow’ nanoparticles (gold–silver composite nanoparticles of various sizes and compositions) supported on TiO 2 P25 and coated by a protecting layer exhibited a 56% increase in efficiency compared to pristine P25 combined with a good stability under simulated solar light. 35 This corroborates numerous studies highlighting the higher visible light photoactivity of bimetallic Au–Ag/TiO 2 nanocomposites compared to their monometallic Ag/TiO 2 and Au/TiO 2 counterparts. 36,37 This demonstrates that Au–Ag nanoparticles are appropriate candidates for harvesting a large portion of the solar spectrum, in view of outdoor photocatalytic applications.…”

Probing oxygen activation on plasmonic photocatalysts

“…The rainbow photocatalyst synthesis is already described in previous work ( Verbruggen et al, 2016 ; Dingenen et al, 2021 ). In short, colloidal Au x Ag (1-x) nanoparticles of different sizes and compositions (x varying from 0.2 to 1) were prepared following a modified Turkevich synthesis ( Turkevich et al, 1951 ).…”

Sunlight-Powered Reverse Water Gas Shift Reaction Catalysed by Plasmonic Au/TiO2 Nanocatalysts: Effects of Au Particle Size on the Activity and Selectivity

“…Absorption over a broader visible light range is beneficial for maximising sunlight harvesting efficiency and to realise a high space-time-yield in sunlight-powered chemical processes. This can be achieved using plasmonic catalysts comprised of metal nanoparticles which absorb light over a broader range of the solar spectrum [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Plasmonic particles exhibit a localised surface plasmon resonance (LSPR) upon illumination.…”