IP: 185.14.195.214 On: Fri, 07 Dec 2018 07:32:31 Copyright: American Scientific Publishers Delivered by Ingenta Copyright © 2019 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 19, 383–388, 2019 www.aspbs.com/jnn Plasmonic Photocatalyst Design: Metal–Semiconductor Junction Affecting Photocatalytic Efficiency Tanujjal Bora 1 ∗ and Joydeep Dutta 2 1 Nanotechnology, Industrial System Engineering, School of Engineering and Technology, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani–12120, Thailand 2 Functional Materials, Applied Physics Department, School of Engineering Sciences School, Kungliga Tekniska Högskolan Royal Institute of Technology, Isafjordsgatan 22, SE-16440 Kista-Stockholm, Sweden Silver-zinc oxide nanorods (Ag–ZnO NRs) and gold-zinc oxide nanorods (Au–ZnO NRs) plasmonic photocatalysts were fabricated by the deposition of Ag and Au nanoparticles on ZnO NRs. The photocatalysts were studied with electron microscopy, energy dispersive spectroscopy (EDS), UV- vis optical absorption and photoluminescence spectroscopy. The effect of type of metals on the ZnO surface on its photocatalytic activity under ultra violet (UV) as well as visible light excitation are investigated and their contribution towards enhanced photo-generated charge separation in terms of the type of junction (Ohmic or Schottky) the metal forms with the semiconductor are explained. Keywords: Plasmonic Photocatalysis, Visible Light Photocatalysis, Metal-Semiconductor Catalyst, Ohmic Contact, Schottky Contact, Photocatalytic Treatment. 1. INTRODUCTION Study of metal–semiconductor (M–S) based plasmonic photocatalysts is becoming a popular choice due to the potential of such systems to efficiently utilize the visible light part of the solar spectrum for heterogeneous photo- catalytic degradation of contaminants in water or air. 1 Typ- ically, noble plasmonic metal nanoparticles are deposited on the surface of traditional nanostructured metal oxides, such as zinc oxide (ZnO) or titanium dioxide (TiO 2 , to fabricate the plasmonic photocatalyst. 2–4 These M–S systems provide several advantages over the traditional photocatalysts. The localized surface plasmon resonance (LSPR) absorption from the metal nanoparticles allow the overall absorption band of the photocatalyst to extend towards the visible region of the solar spectrum, and thus makes the photocatalyst active under visible light, unlike the traditional large bandgap semiconductors (such as, ZnO or TiO 2  which absorb light in the ultraviolet (UV) region. Depending on the electronic energy levels when combined with the metal nanoparticles, the M–S system could be tailored to enhance charge-separation of photo- generated carriers across the M–S junction which would lead to enhanced photocatalytic activities. 5 6 Since charge separation is dependent on the M–S interface and the ∗ Author to whom correspondence should be addressed. type of junction the two systems forms, it is thus cru- cial from the photocatalyst design viewpoint, to select the right combination of M–S system for enhanced plasmonic photocatalysis. 7 Two of the common metal systems used for the M–S plasmonic photocatalyst design are nanopar- ticles of gold (Au) and silver (Ag). 8 9 Gold nanoparticles, which have strong LSPR absorp- tion band around 530 nm, have been reported to show significant improvement in the visible light photocatalytic activity when incorporated over metal oxide surface. 10 11 Apart from its good chemical and thermal stability, gold nanoparticles typically form a Schottky type junction when deposited on the surface of traditional metal oxides (for example, ZnO or TiO 2  resulting in efficient charge sep- aration necessary for enhanced photocatalytic efficiency. 12 The ability of Au nanoparticles with controlled size to influence the energetics in Au–TiO 2 composite system by improving the photoinduced charge separation was reported by Subramanian et al. 13 The Schottky junction formation and its effect on visible light photocatalysis on Au–ZnO nanocomposite system was also investigated by our group previously, 12 where we have demonstrated that the Schottky barrier height is also influenced by the amount of surface defects present in ZnO. Similarly, sil- ver (Ag) nanoparticles are also investigated by our as well as many other groups as potential M–S plasmonic pho- tocatalyst for visible light photocatalytic applications. 14 15 J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 1 1533-4880/2019/19/383/006 doi:10.1166/jnn.2019.15785 383