Journal of the Taiwan Institute of Chemical Engineers 89 (2018) 215–223 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Reduced graphene oxide supported raspberry-like SrWO 4 for sensitive detection of catechol in green tea and drinking water samples Shaktivel Manavalan a , Mani Govindasamy a , Shen-Ming Chen a,* , Umamaheswari Rajaji a , Tse-Wei Chen a , M. Ajmal Ali b , Fahad M.A. Al-Hemaid b , M.S. Elshikh b , M. Abul Farah c a Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, No.1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan b Department of Botany and Microbiology, College of Science, King Saud University, Riyadh - 11451, Saudi Arabia c Department of Zoology, College of Science, King Saud University, Riyadh - 11451, Saudi Arabia a r t i c l e i n f o Article history: Received 6 January 2018 Revised 21 April 2018 Accepted 3 May 2018 Available online 29 May 2018 Keywords: Food analysis Strontium tungstate Reduced graphene oxide Water safety Modified electrode Electroanalysis a b s t r a c t The raspberry-like strontium tungstate microspheres supported on reduced graphene oxide nanosheets (rGOSs@SrWO 4 ) were prepared by a hydrothermal method and it was applied to the electrocatalytic sensing of catechol. The as-prepared rGOSs@SrWO 4 composite was characterized by XRD, Raman, FESEM, EDX, EIS, and voltammetric techniques. Morphology studies reveal the uniform wrapping of raspberry- like SrWO 4 microstructure by thin sheets of rGOSs and the composite possesses large surface area and abundant catalytic active sites. The rGOSs@SrWO 4 composite modified screen-printed multi-conventional electrode (SPME) was fabricated which was found to exhibit extraordinary electrocatalytic activity and ex- cellent selectivity towards the detection of catechol. The rGOSs@SrWO 4 /SPME displayed a linear range of 0.034–672.64 μM and detection limit of 7.34 nM using differential pulse voltammetry as signal read-out. Furthermore, the electrode was durable, reproducible and repeatable. The practical utility of the method was demonstrated in green tea and drinking water samples. © 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Catechol (1, 2-hydroxybenzene) is a basic isomer of benzene- diol, which is naturally distributed ubiquitously in plants. It has primary role in biological and industrial production activities, such as fur dyes, lubricating oils, photographic rubbers, and pharma- ceuticals [1,2]. However, catechol is less degradable and toxic to the water and environmental resources [3]. As the human pop- ulation increases, the need for the production of more indus- trial products, such as pesticides, cosmetics, medicines, tanning re- movers, flavoring agents, photography chemicals is increases. As a result, industrial sewages are constantly released that contam- inates water resources such as, rivers, ponds, lakes, and oceans [4]. Because catechol is more attractive to the researchers to de- tect catechol even in low concentration and at the same time cate- chol to be detected in a reliable, simple and rapid manner [5,6]. Various methods are already in practice, such as capillary zone electrophoresis [7], synchronous fluorescence [8], chemilumines- cence [9], high-performance liquid chromatography [10], and elec- * Corresponding author. E-mail addresses: smchen1957@gmail.com (S.-M. Chen), majmalaliksu@gmail.com (M. Ajmal Ali). trochemical methods [6,11] . Compared with traditional analytical methods, electrochemical technique is cheap, robust, rapid, high sensitive, and selective [12–14]. Recently, increasing interest has been focused on the develop- ment of catechol sensors based on metal oxide electrode modi- fiers [15–17]. In recent years, metal tungstate (MWO 4 , M: Ca 2+ , Sr 2+ , Ba 2+ , Pb 2+ etc.) have attracted much attention due to their interesting structural and chemical properties. They have promis- ing applications in optics and photocatalysis. On the other hand, carbonaceous materials have high conductivity, unique mechani- cal, excellent flexibility, good corrosion resistance and high sur- face area and hence they are good support materials for metal tungstates [18–20]. Yet, mostly applied materials in electrochem- ical applications are graphite, porous carbon, n-doped graphene, and activated carbon [21–23]. In recent years, many of transition metal oxides/hydroxides/sulfides supported on carbonaceous mate- rials were developed for electrochemical sensing applications [24– 28]. Specially, graphene supported SrWO 4 attracted considerable attention in many fields because SrWO 4 materials are low-cost, highly stable, and holding excellent electrocatalytic property for several important reactions [29]. Here, we have synthesized strontium tungstate (SrWO 4 ) micro- spheres enveloped reduced graphene oxide nanosheets (rGOSs) via https://doi.org/10.1016/j.jtice.2018.05.001 1876-1070/© 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.