Abstract
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•NP loading effect of plasmonic-metal@semiconductor microsphere is investigated.•FEM is adopted to compute the broadband absorption in the visible light region.•Broadband absorption exhibits universal logarithmic increment at moderate loading.•Analytical expression is derived to estimate the loading at coupling-onset.•Keep actual loading less than that at coupling-onset achieves better cost-efficiency.
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plasmonic-coupling effect which causes red-shift on the absorption spectrum and rendering the logarithmic increment no longer valid.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 10.92wt% for 30nm-Au@0.6μm-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.