**Compact Integration of TiO 2 Nanoparticles into the Cross-Points of 3D Vertically Stacked Ag Nanowires for Plasmon-Enhanced Photocatalysis**

**Vo Thi Nhat Linh 1,2, Xiaofei Xiao 3, Ho Sang Jung 1, Vincenzo Giannini 3,4, Stefan A. Maier 3,5, Dong-Ho Kim 1,\*, Yong-Ill Lee 2,\* and Sung-Gyu Park 1,\***


Received: 27 February 2019; Accepted: 13 March 2019; Published: 20 March 2019

**Abstract:** The compact integration of semiconductor TiO2 nanoparticles (NPs) into the 3D crossed region of stacked plasmonic Ag nanowires (NWs) enhanced the photocatalytic activities through synergistic effects between the strong localized surface plasmon resonance (LSPR) excitation at the 3D cross-points of the Ag NWs and the efficient hot electron transfer at the interface between the Ag NWs and the TiO2 NPs. This paper explored new hybrid nanostructures based on the selective assembly of TiO2 NPs onto 3D cross-points of vertically stacked Ag NWs. The assembled TiO2 NPs directly contacted the 3D Ag NWs; therefore, charge separation occurred efficiently at the interface between the Ag NWs and the TiO2 NPs. The composite nanomaterials exhibited high extinction across the ultraviolet-visible range, rendering the nanomaterials high-performance photocatalysts across the full (ultraviolet-visible) and the visible spectral regions. Theoretical simulations clearly revealed that the local plasmonic field was highly enhanced at the 3D crossed regions of the vertically stacked Ag NWs. A Raman spectroscopic analysis of probe dye molecules under photodegradation conditions clearly revealed that the nanogap in the 3D crossed region was crucial for facilitating plasmon-enhanced photocatalysis and plasmon-enhanced spectroscopy.

**Keywords:** 3D hybrid nanostructures; localized surface plasmon resonance; hot electrons; environmental remedy; plasmon-enhanced photocatalysis
