# Glassy Carbon Electrochemical Sensor for Gallic and Vanillic Acid Detection in Aqueous Solutions  
[PERSON]  
Department of Chemical Engineering, University of Patras, 26504 Patras, Greece; [EMAIL_ADDRESS] (C.I. ); [EMAIL_ADDRESS] (G.K.)  
C. K. K.  
to make a timely decision about their toxicity, before their discharge into inland surface waters. A typical electrochemical sensor consists of three electrodes, the working electrode (where redox reactions take place), the counter, and the reference electrodes [9]. The counter electrode serves as the electron collector, while the cell potential is recorded at the working reference circuit. The use of electrochemical sensors for the detection of pollutants in atmospheric, terrestrial, and aquatic environments is gaining increased research interest [13]. Among the known water pollutants, phenolic compounds exhibit substantial toxicity for both humans and the natural environment and are an impending threat to the food chain [14]. Electroanalytical methods using sensors fabricated from carbon and other materials are commonly utilized for the determination of phenolic compounds. Specifically, the electrochemical reaction (i.e., the electrooxidation of a phenolic compound) takes place on the surface of the sensor material upon potential application. In other words, there is a specific potential where each phenol can be electrooxidized resulting in a current peak. Due to its exceptional electrocatalytic behavior, pure Pt and various Pt alloys are commonly utilized as working electrodes for phenol electrooxidation [15; 16; 17]. Although noble metal-based electrodes are sufficiently active with high corrosion resistance, they are expensive and rare. Hence, alternative and more practical materials, such as carbon-based electrodes have become attractive in the research community for sensing phenolic compounds [18]. The electronic properties in combination with the high chemical stability of carbon materials appears to be suitable for these electrochemical systems. In addition, they display notable advantages such as commercial availability, minimization of phenol polymerization and electrode corrosion, and high overpotential for oxygen production [19]. However, modification of their surface is often reported in the literature, preventing electrode fouling and enhancing process efficiency and sensitivity [20]. [PERSON] et al. [21] studied the electrochemical oxidation of hydroxybenzene on glassy carbon (GC) electrodes using cyclic voltammetry and differential pulse voltammetry varying the pH of the solution from 7 to 12. According to the authors, a linear relationship between the oxidation peak and phenol concentration was observed, whereas a pH increase resulted in a shift of the oxidation peak potential to lower values. The deactivation of GC was also discussed due to electrode blocking by the polymeric byproducts formed after the second cycle. In a more recent study, [PERSON] et al. [22] designed a single-walled carbon nanotube (SWCNT) modified GC electrode for the electrocatalytic oxidation of various phenolic compounds (catechol, _para_-cresol, _ortho_-cresol, _meta_-aminophenol, _ortho_-chlorophenol, _meta_-nitropol, _ortho_-nitropol, etc.). The composite electrode exhibited high sensitivity and stability, suggesting that it can act as an ideal sensor for the simultaneous detection of multiple phenolic compounds. Along the same line, [PERSON] et al. [23] fabricated a GC electrode coated with a graphene/polymer film for rapid determination of phenols (such as hydroquinone and _para_-chlorophenol) in aqueous solutions. Activated carbon cloth (ACC) electrodes were investigated for the removal of phenolic compounds (i.e., hydroxybenzene) from aqueous solutions [24]. According to the authors, under acidic conditions the catalytic conversion of H\({}_{2}\)O\({}_{2}\) into hydroxyl radicals was enhanced thus increasing the phenol removal from 16% to 55% by its electrooxidation on the surface of ACC.