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

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.

Graphene-Silver Based Passive Q-Switcher

Pulsed fiber laser has gain massive attention among researchers. As one of the recognized methods in generating pulsed lasers, passive Q-switching technique in 1.5 micrometer region was used in this work. A graphene-silver composite (Gr-Ag) was integrated as the saturable absorber (SA) in this work. For ease of integration, a free-standing SA film was fabricated by using chitin as the host polymer. The pulsed fiber laser was generated within the input pump power of 135.7 mW to 181.5 mW. Distinct trends of repetition rate and pulse width was observed where the former shows an increasing trend and vice versa for the latter. At 181.5 mW, pulsed laser with repetition rate and pulse width at 59.97 kHz and 2.74 µs, respectively were recorded while the pulse energy and instantaneous peak power were at 5.64 nJ and 1.93 mW, respectively. The findings from this work have shown Gr-Ag SA as a suitable candidate in Q-switched pulsed laser generation.