Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece Photocatalytic reduction of Cr(VI) using star-shaped Bi 2 S 3 obtained from microwave irradiation of bismuth complex Damian C. Onwudiwe a,b, *, Opeyemi A. Oyewo c , Ufuk Atamtürk d , Olusola Ojelere d , Sanjay Mathur d, ** a Material Science Innovation and Modelling (MaSIM) Research Focus Area, Faculty of Agriculture, Science and Technology, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa b Department of Chemistry, School of Physical and Chemical Sciences, Faculty of Natural and Agricultural Science, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa c Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, 0001, South Africa d Institute of Inorganic Chemistry, University of Cologne Greinstraße 6, D-50939, Cologne, Germany ARTICLE INFO Keywords: Bi 2 S 3 Nanostructures Photoreduction Chromium(VI) Visible light ABSTRACT The reduction of hexavalent chromium specie, Cr(VI), to trivalent chromium, Cr(III), in aqueous solutions using star-shaped nanostructured Bi 2 S 3 , prepared via a facile microwave irradiation of bismuth dithiocarbamate complex is reported. The bismuth sulphide were characterized using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometer (EDX). The study showed that Cr(VI) reduction was dependent on its initial concentration, the pH value of the solution, and the Bi 2 S 3 dosage. Almost all the Cr(VI) in a concentration of 2 ppm and at pH 2 was reduced within 90 min by the addition of 100 mg L −1 of the Bi 2 S 3 . The reduction capacity of the nanostructure was attributed to photocatalytic-induced reduction process as well as the high specific surface area. Pseudo-first order kinetics model parameters well described the Cr(VI) reduction experimental data with high correlation factor of 0.998. This study demonstrates that microwave irradiation of precursor complex could offer a quick and facile route to nanostructured photocatalyst, which are good candidate material for the removal of trace chromium in surface water. 1. Introduction Chromium is one of the most dangerous heavy metals that find their way into the environment through different industrial activities. Due to its non-biodegradable nature, it contributes significantly towards en- vironmental pollution; thereby poses serious threats to the environment and human health even at trace level [1]. Among the different oxida- tion states of Cr, which includes II, III, and VI, the Cr(VI) species are very toxic agents because of their carcinogenic, mutagenic, and ter- atogenic nature which is dangerous to biological systems [2]. The toxicity of the hexavalent form has been reported to be about five hundred times greater than that of the trivalent form [3]. Consequently, Cr(VI) has been placed on the priority list of toxic pollutants by the US Environment Protection Agency (USEPA) and a maximum acceptable concentration of 50 μgL −1 in potable water and 2 mg L −1 for the total of all form of chromium has been mandated by both USEPA and World Health Organisation (WHO) [4]. Cr(VI) find its way into the ecosystem as content of effluents from different industrial, agricultural and mining processes [5,6]. The removal of Cr(VI) ion from wastewater is considered as one of the pressing environmental issues. Thus, different techniques such as chemical reduction [7], chemical precipitation [8], biological process [9], and adsorption [10] have been devised for the removal of Cr(VI) from aqueous systems. Among these, adsorption technology is one of the commonly used approaches for the general treatment of heavy metal pollution. This is due to reasons such as low cost, simple opera- tion, good removal effect, and recyclability [11,12]. Hence, the removal of toxic metals by adsorption techniques involving the use of metal oxides, metal sulphides or polymer/graphene immobilized metal su- phides such as polyacrylamide, graphene oxide and their composites https://doi.org/10.1016/j.jece.2020.103816 Received 4 January 2020; Received in revised form 16 February 2020; Accepted 29 February 2020 ⁎ Corresponding author at: Material Science Innovation and Modelling (MaSIM) Research Focus Area, Faculty of Agriculture, Science and Technology, North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho, South Africa. ⁎⁎ Corresponding author. E-mail addresses: Damian.Onwudiwe@nwu.ac.za (D.C. Onwudiwe), sanjay.mathur@uni-koenl.de (S. Mathur). Journal of Environmental Chemical Engineering 8 (2020) 103816 Available online 02 March 2020 2213-3437/ © 2020 Elsevier Ltd. All rights reserved. T