Simple Growth of Faceted Au-ZnO Hetero-nanostructures on Silicon Substrates (Nanowires and Triangular Nanoflakes): A Shape and Defect Driven Enhanced Photocatalytic Performance under Visible Light Arnab Ghosh, † Puspendu Guha, † Aneeya K. Samantara, ‡ Bikash Kumar Jena, ‡ Rajshekhar Bar, § Samit Ray, § and Parlapalli V. Satyam* ,† † Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005, India ‡ CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751013, India § School of Nano Science & Technology, Indian Institute of Technology, Kharagpur 721302, India * S Supporting Information ABSTRACT: A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au-ZnO hetero- nanostructures (HNs) either with nanowires (NWs) or with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. This work reports on the use of these nanostructures on substrates for photodegradation of rhodamine B (RhB) dyes and phenol under the visible light illumination. The photoluminescence measurements showed a substantial enhancement in the ratio of defect emission to band-edge emission for TNF (ratio ≈ 7) compared to NW structures (ratio ≤ 0.4), attributed to the presence of more oxygen defects in TNF sample. The TNF structures showed 1 order of magnitude enhancement in photocurrent density and an order of magnitude less charge-transfer resistance (R ct ) compared to NWs resulting high-performance photocatalytic activity. The TNFs show enhanced photocatalytic performance compared to NWs. The observed rate constant for RhB degradation with TNF samples is 0.0305 min -1 , which is ≈5.3 times higher compared to NWs case with 0.0058 min -1 .A comparison has been made with bulk ZnO powders and ZnO nanostructures without Au to deduce the effect of plasmonic nanoparticles (Au) and the shape of ZnO in photocatalytic performance. The results reveal the enhanced photocatalytic capability for the triangular nanoflakes of ZnO toward RhB degradation with good reusability that can be attracted for practical applications. KEYWORDS: hetero-nanostructures, triangular nanoflakes, oxygen defects, photoelectrochemistry, photocatalyst, dye degradation 1. INTRODUCTION Highly ordered and oriented nanoscale metal oxides structures (NSs) in conjunction with plasmonic noble-metal nanoparticles (NPs) have great potential in micro-/nanodevices for electronic, optical, and photocatalytic applications. 1-5 In the past few decades, environmental problems such as air and water pollution have become a major issue for economic develop- ment and human health. Semiconductor based photocatalytic reactions have attracted intense interest as an effective candidate for environmental treatments. 6,7 Among several oxide semiconductor photocatalysts, TiO 2 and ZnO have been most exciting materials for detoxification/purification of water/air and degradation of persistent organic pollutants (such as various dyes) present in wastewater through photocatalytic processes. 8-17 In comparison with TiO 2 , ZnO has been actively worked upon from a variety of research communities due to their high photosensitivity, large direct bandgap (3.37 eV), relatively high exciton binding energy (60 meV), nontoxic character, abundance in reserve, and low-cost large-scale synthesis viability. 12-15,17-19 Besides the photocatalytic appli- cations of ZnO NSs, they have been extensively used in several functional devices. 20-24 As the size and shape of the NSs have key importance on their applications, various one-dimensional (1-D) ZnO NSs with different morphologies, such as nanowires (NWs), nanorods (NRs), nanotubes (NTs), nanobelts, nano- nails, nanoflakes (NFs), nanowalls, nanotetrapods, and nano- sheets, have been synthesized. 25-27 To get such variations, several growth/synthesis protocols have been established, such as solution based synthesis, pulsed laser deposition, and vapor phase depositions (such as CVD, MOCVD, and thermal evaporation etc.) with and without catalyst and so forth. 25,27-30 The pure ZnO NSs show the absorption capabilities only in UV light (λ ≤ 370 nm) due to its high bandgap (3.37 eV). This limits the use of ZnO in facile visible light driven photocatalytic Received: January 21, 2015 Accepted: April 21, 2015 Published: April 21, 2015 Research Article www.acsami.org © 2015 American Chemical Society 9486 DOI: 10.1021/acsami.5b00634 ACS Appl. Mater. Interfaces 2015, 7, 9486-9496