In this study, thermally reduced graphene oxide (TRGO) was synthesized via thermal reduction of graphene oxide in air and used to construct a thermally reduced graphene oxide paste electrode (TRGOPE). The TRGO was characterized under a structural and morphological point of view. A wide range of complementary instrumental techniques, such as Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM), were applied. A novel electrochemical sensor based on TRGO in air was constructed, and an electrochemical characteristics of the TRGOPE were investigated using electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Compared to a conventional carbon paste electrode (CPE), a significantly improved electrochemical response of TRGOPE toward a ferrocyanide/ferricyanide redox couple was found due to the excellent conductivity of graphene. The TRGOPE was further successfully applied for the determination of an antiseptic and disinfectant agent, 4-chloro-3,5-dimethylphenol (PCMX). TRGOPE showed an excellent electrocatalytic oxidation activity toward PCMX with higher current response, improved sensitivity toward determination of PCMX as well as much lower limits of detection (LOD) than a CPE allowing highly sensitive voltammetric determination of PCMX. Under optimized experimental conditions, the square-wave voltammetric (SWV) signal of PCMX at a potential of ca. +0.7 V increased linearly with the increase of the PCMX concentration in the linear dynamic range (LDR) from 0.1 to 4.5 mu mol L-1 with an LOD of 20.8 nmol L-1, a sensitivity of 5.0 mu A L mu mol(-1), and a precision expressed as an intra-day and inter-day precision (n = 10) of 1.4% and 2.0%, respectively, with 0.1 mu mol L-1 of PCMX. Furthermore, the applicability of the TRGOPE for PCMX analysis in water samples (river and tap waters) was successfully demonstrated with satisfactory results. (C) 2018 Elsevier Ltd. All rights reserved.