Shape-selective formation of MnWO 4 nanomaterials on a DNA scaffold: magnetic, catalytic and supercapacitor studies† U. Nithiyanantham, a Sivasankara Rao Ede, a T. Kesavan, b P. Ragupathy, b M. D. Mukadam, c S. M. Yusuf c and Subrata Kundu * a A new route for the aqueous phase synthesis of single crystalline, shape-selective, magnetic MnWO 4 nanomaterials on a DNA scaffold has been reported. The synthesis was done by the reaction of MnCl 2 $4H 2 O with Na 2 WO 4 in DNA within five minutes of microwave heating. The process exclusively generates wire-like, flake-like and rice-like morphology just by tuning the DNA to Mn(II) salt and WO 4 2 ion concentration and changing other reaction parameters. The field-cooled (FC) and zero-field-cooled (ZFC) magnetization study reveals that the flake-like structure shows the highest magnetization at 5 K compared to that of the wire-like and rice-like structures. The potential of the shape-selective MnWO 4 nanomaterials has been tested in two different applications, firstly in a catalysis study for the decomposition of toxic KMnO 4 and secondly in electrochemical supercapacitor applications. It was found that the MnWO 4 nanomaterials showed different specific capacitance (SC) values for the various shapes and the order of the SC values is: wire-like > flake-like > rice-like. The highest SC of 34 F g 1 was observed for MnWO 4 having wire-like shape. The yields of the products with uniform shapes have been found to be significantly high and the synthesized materials are stable for more than six months under ambient conditions. The present work will find a new platform for the generation of other mixed oxides using bio-molecules as scaffolds at low temperature and in short time scales. Moreover, the synthesized material might be useful for other potential applications in the fields of catalysis, sensors, energy storage materials and so on. Introduction Over the last few years considerable interest has been focused on the fabrication of nano/microstructured materials, mainly due to their unique electronic, optical, magnetic and catalytic properties and various applications. 1–4 Among the different materials, the shape-selective synthesis of mixed metal oxide nanoparticles (NPs) has become one of the essential topics in nanoscience as their unique properties are generally not avail- able in single metal oxide NPs. The shape-selective formation of mixed metal oxide NPs has gained much attention in the elds of electronics, optics, sensors, biology, magnetism, catalysis and luminescence studies. 5,6 Moreover, they show fascinating color change in the UV-Vis region due to their close lying conduction and valence bands in which electrons can move freely. The specic shape of nanomaterials dictates their phys- icochemical properties because the number of active atom located at the edges/corners and exposed facets of the crystal. 7 The fascinating properties of mixed metal oxide NPs depend not only on the complex morphology but also on the crystallinity of the particles in microarchitectures. 8 As an examples, individual spherical superparticles of CdSe/CdS showed strong linear polarized emission but single disk spherical superlattices nano rods does not show any signicant polarization. 9 Therefore, shape-selective formation of single-crystalline mixed metal oxide NPs are highly desirable for tailoring their unique prop- erties and for high performance in many potential applications. Among the different mixed metal oxide studied so far, manganese tungstate (MnWO 4 ) is one of the most promising material which shows high sensitivity in humidity change and have unique magnetic property. 10,11 MnWO 4 has a Wolframite type of structure having space group P2/C (no. 13) in which each Mn and W atom have an approximately octahedral coordination a Electrochemical Materials Science (ECMS) Division, CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630006, Tamil Nadu, India. E-mail: skundu@ cecri.res.in; kundu.subrata@gmail.com; Fax: +91-4565-227651; Tel: +91-4565- 241487 b Fuel Cell Division, CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630006, Tamil Nadu, India c Solid State Physics Division, Bhabha Atomic Research Centre (BARC), Trombay, Mumbai 400085, India † Electronic supplementary information (ESI) available: The detailed discussions and the related Fig. (S-1 to S-5) for UV-Vis study, TEM analysis, energy dispersive X-ray spectroscopy (EDS), LASER Raman and study with other reaction parameters (TEM images) are given. The datas related to FT-IR analysis are provided in Table T-1. See DOI: 10.1039/c4ra04839c Cite this: RSC Adv. , 2014, 4, 38169 Received 22nd May 2014 Accepted 14th August 2014 DOI: 10.1039/c4ra04839c www.rsc.org/advances This journal is © The Royal Society of Chemistry 2014 RSC Adv. , 2014, 4, 38169–38181 | 38169 RSC Advances PAPER Published on 15 August 2014. 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