Nanoparticle loading effects on the broadband absorption for plasmonic-metal@semiconductor-microsphere photocatalyst

摘要

Encapsulating a single plasmonic-nanoparticle inside a large semiconductor-microsphere could substantially enhance its broadband absorption [Sun et al., ACS Catal. 4 (2014) 4269-4276]. However, the multi-nanoparticle loading effect is unclear and hinders the practical catalyst design. Herein, we study the nanoparticle loading effect of plasmonic-metal@semiconductor-microsphere photocatalyst on its broadband absorption in the visible light spectrum. Finite-element-study suggests that the broadband absorption holds a universal logarithmic relation with the number of nanoparticles at moderate loading range. Higher loading brings the nanoparticles in proximity, inducing plasmonic-coupling effect which causes red-shift on the absorption spectrum and rendering the logarithmic increment no longer valid. Based on the universal scaling of plasmonic-coupling, an analytical expression to estimate the loading rate at coupling-onset (below which no plasmonic-coupling presents) is derived for arbitrary plasmonic-metal@semiconductor-microsphere (for instance, the loading rate is 10.92 wt% for 30 nm-Au@0.6 mu m-TiO2 microsphere with 399 broadband absorption enhancement at coupling-onset). Further considering the diminishing increment nature of the logarithmic relation, the actual loading is recommended to be lower than that at coupling-onset to achieve better cost-efficiency (with loading 30% lower than that at coupling-onset, the broadband absorption reduces only 10%). These findings could provide the experimentalists useful guidelines in the development of the plasmonic-metal@semiconductor-microsphere photocatalyst. (C) 2016 Elsevier B.V. All rights reserved.