Synthesis and characterization of various transition metals doped SnO 2 @MoS 2 composites for supercapacitor and photocatalytic applications S. Asaithambi a , P. Sakthivel a , M. Karuppaiah a , K. Balamurugan a , R. Yuvakkumar a , M. Thambidurai b , G. Ravi a, * a Department of Physics, Alagappa University, Karaikudi, 630003, Tamil Nadu, India b Centre for Opto Electronics and Biophotonics (COEB), School Electrical and Electronic Engineering, The Photonics Institute (TPI), Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore article info Article history: Received 20 August 2020 Accepted 4 September 2020 Available online 8 September 2020 Keywords: SnO 2 @MoS 2 Supercapacitor Photocatalytic Methylene blue abstract In this article, we synthesize the bifunctional materials of various transition metals (TM) (Co, Ni and Mn) doped SnO 2 @MoS 2 composites for enhanced energy storage and improved photocatalytic activity for removing organic pollutants. Herein, we use a facile hydrothermal method for sample synthesis and the physico chemical properties of the synthesized samples were investigated in detail using various analytical tools. The energy dispersive X-ray spectra and elemental mapping confirmed the presence of species in the synthesized samples. X-ray photoelectron spectroscopy analysis revealed the corre- sponding energy state of various TM doped SnO 2 @MoS 2 samples. The Mn doped SnO 2 @MoS 2 composite exhibited a higher specific capacitance of 242 F/g at a current density 0.5 A/g. The capacitance retention of 83.95% was observed after 5000 continuous charge/discharge cycles. Further, the Mn doped SnO 2 @- MoS 2 composite had higher degradation efficiency (97%) compared to all other samples using methylene blue as an organic dye under visible light irradiation. Henceforth, this study demonstrates the optimum concentration of Mn doped SnO 2 @MoS 2 composite is the outstanding bifunctional materials for super- capacitor and photocatalytic applications. © 2020 Elsevier B.V. All rights reserved. 1. Introduction The energy crisis and environmental pollution have emerged as two main worldwide problems recently due to rapid growth of industrialization. Our major energy demand in industries is dependent on non-renewable energy sources like coal, oil and natural gas etc [1 ,2]. While burning the fossil fuels, huge amount of carbon dioxide (CO 2 ) is released which causing the environmental pollution and global warming [3,4]. Therefore, an alternate renewable, sustainable and green energy is urgently required. On the other hand, the industries like textiles, leather, plastics and pharmaceuticals are releasing very harmful nitrogen-containing organic pollutants (dyes) that are resistant to biodegradation and its an anaerobic degradation yields dangerous and carcinogenic byproducts which affects the environment and human severely. In this regard, researchers and scientists are seeking an efficient technology and making an effort to develop bifuctional, smart materials to resolve these current issues in energy and environ- ment [5e9]. So far, the various eco-friendly energy conversion and storage technologies such as solar cells, Li-ion batteries, supercapacitors and hydrogen evolution reaction have been employed to resolve the energy shortage problems without affecting the environment [10e12]. Among them, supercapacitors have got great attention for the energy storage devices because of its high power density, long life cycle, fast charge-discharge timings than batteries and tradi- tional capacitors. Based on the mechanism of charge storage, the supercapacitors are classified into two types: (i) Electric double- layer capacitors (EDLCs) and (ii) pseudocapacitors [13, 14]. EDLCs (carbon-based materials) store the charges at the interface between the electrode and electrolyte, whereas, the pseudocapacitors (metal oxides, sulfides, hybrids, and polymers) store the charges by the way of fast and reversible faradaic reaction on the surface of the electrodes [15, 16]. On the other hand, several physical and * Corresponding author. E-mail address: gravicrc@gmail.com (G. Ravi). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2020.157060 0925-8388/© 2020 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 853 (2021) 157060