Removal of toxic tellurium (IV) compounds via bioreduction using flucloxacillin in aqueous acidic medium: A kinetic and mechanistic approach Ahmed Fawzy Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, Makkah, Saudi Arabia Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt abstract article info Article history: Received 1 June 2019 Received in revised form 20 July 2019 Accepted 23 July 2019 Available online 29 July 2019 This paper describes a novel method for the removal of potassium tellurite (Te IV ), a toxic tellurium (IV) com- pound, via its bioreduction using the drug flucloxacillin (Flx) in an aqueous sulfuric acid solution. The kinetics of the bioreduction process were monitored using UV–Vis absorption spectra at an ionic strength of 2.0 mol dm -3 and 298 K. The reaction between Te IV and Flx was set at a 1:1 stoichiometry. The reduction reaction followed first-order kinetics for [Flx] and fractional-first-order kinetics for [Te IV ] and [H + ]. The effects of ionic strength and relative permittivity of the reaction medium were also explored. Supplementation with divalent transition metal ions enhanced the reduction rate. The reaction products were identified, in order of their stoi- chiometric results, spot tests and FT-IR spectra as 3-(2-chloro-6-fluorophenyl)-5-methylisoxazol-4-carbocylic acid, 5,5-dimethyl-thiazolidine-2,4-dicarboxlic acid, ammonium ion, carbon dioxide and elemental tellurium (Te 0 ). The reaction rate dependence on temperature was studied, and the activation and thermodynamic param- eters were assessed and discussed. The derived rate-law expression was found to be in excellent accordance with the acquired investigational outcomes. A conceivable reaction mechanism has been provided, which includes a reaction between the protonated flucloxacillin (Flx + ) and tellurous acid (H 2 TeO 3 ) as the essential reactive spe- cies, resulting in the construction of an intermediate complex. Such complex decays in the rate-determining step to yield the final reaction products. © 2019 Elsevier B.V. All rights reserved. Keywords: Removal Tellurium (VI) Flucloxacillin Bioreduction Kinetics Mechanism 1. Introduction Tellurium is a harmful and essential rare metalloid present in a trace amounts in the earth's crust [1]. It exists in nature in several forms, in- cluding the nontoxic, elemental state (Te 0 ), telluride (Te 2- ), and as the oxyanions tellurite (TeO 3 2- ) and tellurate (TeO 4 2- ), which are toxic for a variety of life forms [2,3]. In humans, tellurium is one of the most abundant trace elements in bone. It is a critical element utilized in en- ergy and defence applications [4]. Tellurium compounds have several applications in the manufacture of ceramics, glass, semiconductors, and metals [3]. Tellurium oxyanions are strong oxidants that can be pro- duced by their reductive precipitation to form insoluble elemental tellu- rium (Te 0 )[5]. Tellurium oxyanions have also been investigated as potential antibacterial agents [6,7]. Tellurite (Te IV O 3 2- ) is highly toxic to a variety of microorganisms [4] and is an extremely stable compound, although it can be reduced to Te 0 by electrolysis, by using a powerful re- ducing agent [2,4,8], by living cells [9] or by some bacteria [10]. The re- duction of highly toxic soluble tellurite, which has detrimental impacts on the environment and human health, to the nontoxic insoluble Te 0 is important due to the increasing employment of tellurium in several in- dustries. Additionally, this process could be a treatment for the removal of toxic tellurite from polluted areas to address serious pollution prob- lems. Therefore, the development of a biochemical reduction method for toxic tellurite for environmental clean-up purposes is of interest. Antibiotics are a group of pharmaceutical drugs used to treat bacte- rial and fungal infections in both humans and animals. They are not only used in medicine but also in food industries and in scientific research ac- tivities [11]. However, antibiotics are chemical substances that are for- eign to the human body; hence, the body eliminates them through drug metabolism processes, which may result in pharmacologically ac- tive, inactive, or toxic metabolites. Antibiotics are introduced into the environment through many routes, including human or animal excreta, wastewater effluent and industrial wastes and processes [12,13]. The presence of such chemicals, which contain complex organic com- pounds, even at low environmental concentrations may negatively af- fect the ecosystem and human health and have toxic impacts on the soil, water resources and organisms. Therefore, they are designated as a dangerous environmental pollutant [13]. There has been increasing concern for the removal of these compounds to protect the human health and the environment [14]. Several well-known methods or Journal of Molecular Liquids 292 (2019) 111436 E-mail addresses: afsaad13@yahoo.com, afsayed@uqu.edu.sa. https://doi.org/10.1016/j.molliq.2019.111436 0167-7322/© 2019 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq