Wrapping AgCl Nanostructures with Trimetallic Nanomeshes for Plasmon-Enhanced Catalysis and in Situ SERS Monitoring of Chemical Reactions Han-Jung Ryu, †,∥ Hyunku Shin, ‡,∥ Seunghyun Oh, § Jang Ho Joo, † Yeonho Choi,* ,‡,§ and Jae-Seung Lee* ,† † Department of Materials Science and Engineering, ‡ Department of Bio-convergence Engineering, and § School of Biomedical Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea * S Supporting Information ABSTRACT: Selective chemical control of multiple reactions is incredibly important for the fabrication of sophisticated nanostruc- tures for functional applications. A representative example is the synthesis of plasmonic nanomaterial −silver chloride (AgCl) conjugates, where metal ions should be selectively reduced into metallic nanostructures for plasmon-enhanced catalytic activity, while the reducible AgCl nanomaterials remain intact despite the presence of a chemical reductant. In addition to the selectively controlled reduction, the plasmonic nanostructures should be appropriately designed for the high stability and photoefficiency of catalysts. In this study, we demonstrate how AgCl nanocubes and nanospheres could be comprehensively wrapped by plasmonic three-dimensional nanomesh structures consisting of gold, silver, and palladium by the selective reduction of their ionic precursors while the AgCl nanostructures remain intact. Complete trimetallic wrapping provided the absorption of visible light, while the porosity of the nanomesh structures exposed the photocatalytic AgCl surface to catalyze desired reactions. Platinum in place of palladium was examined to demonstrate the versatility of the wrapping scheme, resulting in an extraordinary catalytic activity. Importantly, the detailed chemical mechanism behind the trimetallic wrapping of the AgCl nanostructures was systematically investigated to understand the roles of each reaction component in controlling the chemical selectivity. The synthesized AgCl−trimetal nanoconjugates excellently exhibit both metal-based and plasmon-enhanced catalytic properties for the removal of environmentally harmful Cr 6+ . Moreover, their applications as surface-enhanced Raman-scattering (SERS) probes for the in situ monitoring of catalytic reduction in real-time and as single-nanoparticle SERS probes for molecular detection are thoroughly demonstrated. KEYWORDS: AgCl, trimetallic wrapping, photocatalysis, SERS, plasmonic enhancement ■ INTRODUCTION Silver halide (AgX) nanomaterials have emerged as versatile building blocks and templates for advanced functional nanostructures. Depending on the type of halide, however, their utilization is often limited because of the very high solubility (AgF) in aqueous media 1 or the crucial failure in controlling sizes and shapes in their chemically pure forms (AgBr and AgI) often in organic media. 2−6 Free from such troubles, silver chloride (AgCl) has been frequently employed in nanoscience owing to its facile preparation with controlled shapes and sizes for the synthesis of various metallic and metal/ceramic composite nanostructures. 7−13 One concern with AgCl is the fairly high standard reduction potential (E° = 0.222 V) in comparison with those of AgBr and AgI (E° = 0.071 and −0.152 V, respectively). This potentially poses a significant problem of undesired reduction and consequent deformation of AgCl during the chemical reduction of metal- ion precursors for the synthesis of noble metal nanostructures on AgCl. 14,15 Although several reports have demonstrated that AgCl nanomaterials can maintain their shapes when used to synthesize metallic nanostructures, their reactions required mild reductants such as methyl orange, ethylene glycol, and hydroquinone, often under light irradiation, or had to be conducted with rather large, and thus, chemically stable AgCl materials (>500 nm). 8−10,16−18 In addition to their roles as templates, AgCl nanomaterials have sometimes been used merely as a source of metallic Ag by being either completely or partly reduced. 9, 12, 14, 19−22 These observations raise an important question: how can we determine and control the roles of AgCl nanomaterials while they are involved in the synthesis of metallic nanomaterials under reductive conditions? It is our general understanding that the potential reductive deformation of AgCl templates during the synthesis of metallic structures needs to be slowed down or preferably hindered by Received: October 10, 2019 Accepted: December 13, 2019 Research Article www.acsami.org Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acsami.9b18364 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX Downloaded via BIU SANTE on December 31, 2019 at 11:13:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.