Original Article Facile synthesis of MnWO 4 /BiOI nanocomposites and their efficient photocatalytic and photoelectrochemical activity under the visible- light irradiation V. Ramasamy Raja a, b , A. Karthika a , A. Suganthi a, c, * , M. Rajarajan d, ** a P.G & Research Department of Chemistry, Thiagarajar College, Madurai 625 009, Tamil Nadu, India b K.P. National College of Arts and Science, Batlagundu 624 202, Tamil Nadu, India c Mother Teresa Women's University, Kodaikanal 624102, Tamil Nadu, India d Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India article info Article history: Received 8 April 2018 Received in revised form 17 June 2018 Accepted 8 July 2018 Available online xxx Keywords: MnWO 4 -BiOI Nanocomposite Visible light Celestin blue Photocatalytic activity abstract The novel MnWO 4 /BiOI nanocomposite materials were successfully synthesized by a precipitation deposition method. The as-prepared photocatalyst was characterized by XRD, SEM, EDAX, UV-DRS, FT-IR, TEM and BET techniques. The as-prepared MnWO 4 /BiOI nanocomposites were further utilized to study the degradation of the Celestin blue aqueous solution under visible-light irradiation. Absorption range and band gap energy, which are responsible for the observed photocatalyst behavior, were investigated by the DRS spectroscopy. The photocatalytic test suggested that MnWO 4 /BiOI nanocomposites posses a higher activity for the degradation of these pollutants than the pure BiOI and MnWO 4 under the visible- light irradiation. Among the as-prepared nanocomposites, the one of 3% MnWO 4 /BiOI displays the best photocatalytic activity of the degradation. Factors, such as the effect of the catalyst dosage, the solution pH and the initial dye concentration affecting the photocatalytic activity were investigated. The in- vestigations of the adsorption kinetics and isotherm demonstrate that the adsorption process follows the pseudo-first-order kinetic model and the Langmuir adsorption isotherm, respectively. © 2018 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction With the rapid development of economy and society, water contamination has been an increasing environmental problem for humans [1,2]. To solve this trouble, abundance of efforts have been devoted to develop efficient methods for decomposing environ- mental pollutants, such as filtration, solvent extraction, chemical oxidation, adsorption, floatation and photocatalytic degradation. Photocatalytic approaches have been devoted to extensive studies on the environmental purification [3e7]. Transition metal tungstates belong to an important family of inorganic materials which have potential application in versatile fields and have been studied for many years [8]. MnWO 4 is a narrow band gap semiconductor (E g ~ 2.8 eV), which is expected to be a novel excellent photocatalyst [9]. MnWO 4 has nailed its extensive research interests due to its novel electrochromic, multiferroic, ionic properties and its significance in gas sensor, electrochemical and catalytic etc. applications [10,11]. However, the issues regarding the control of shape and size are considered as the negative effect on their applications. As reported in lit- eratures, semiconductor photocatalysts, such as MnWO 4 /Poly- aniline [12], MnWO 4 /Reduced Graphene oxides [13], exhibit efficient photocatalytic degradation. In addition to that MnWO 4 when added to BiOI the degradation property seems to be enhancing. Amongst the materials, BiOI exhibits as the most attractive semiconductor the most promising visible-light e harvesting photocatalytic properties, because of its narrow band gap and efficient sunlight-harvesting nature [14e16]. BiOI has been recog- nized as one of the most promising photocatalytic materials also because of its strong oxidation ability and high stability, etc. [17]. Owing to its open and layered crystalline and electronic structure, * Corresponding author. Mother Teresa Women's University, Kodaikanal 624102, Tamil Nadu, India. Fax: þ91 4542 241121. ** Corresponding author. Fax: þ91 4542 241121. E-mail addresses: suganthiphd09@gmail.com (A. Suganthi), rajarajan_1962@ yahoo.com (M. Rajarajan). Peer review under responsibility of Vietnam National University, Hanoi. Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd https://doi.org/10.1016/j.jsamd.2018.07.003 2468-2179/© 2018 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/). Journal of Science: Advanced Materials and Devices xxx (2018) 1e11 Please cite this article in press as: V. Ramasamy Raja, et al., Facile synthesis of MnWO 4 /BiOI nanocomposites and their efficient photocatalytic and photoelectrochemical activity under the visible-light irradiation, Journal of Science: Advanced Materials and Devices (2018), https:// doi.org/10.1016/j.jsamd.2018.07.003