Development of a graphite biodegradable composite based on NADES and soy wax association applied as a binder for carbon paste electrodes

Abstract Natural deep eutectic solvents (NADES) have emerged as promising alternatives to conventional organic solvents, offering advantages such as low melting points and biodegradability, aligned with green chemistry principles. In this work, a hydrophobic NADES (hNADES) composed of menthol and decanoic acid (1:1 molar ratio) was combined with soy wax to formulate a biodegradable binder for carbon paste electrodes (CPE), serving as a substitute for mineral oil. The binder and its precursors were characterized by thermal analyses (TGA/DTG and DSC) and FTIR spectroscopy, which evidenced chemical interactions between soy wax and hNADES through marked shifts in functional groups associated with hydrogen-bond formation. A hydrophilic ternary NADES based on glucose, tartaric acid, and glycerol (tNADES (gly) ) was also incorporated to enhance conductivity by improving paste cohesion and promoting proton-coupled electron transfer (PCET) mechanisms, attributed to the presence of free carboxylic acid groups. Electrochemical performance was assessed via cyclic voltammetry, enabling optimization of composition and identification of CPE (50) /hNADES:wax(3:1)/20%tNADES (gly) as the most suitable formulation. Electrochemical impedance spectroscopy further confirmed a pronounced decrease in charge-transfer resistance for the sustainable composite when compared with mineral-oil-based CPE (bare CPE). The resulting electrode, composed exclusively of non-toxic and biodegradable components, was evaluated to detect ascorbic acid, paracetamol, and sulfamethoxazole using differential pulse voltammetry, demonstrating its potential as an environmentally friendly electrochemical sensor which application could be further investigated to detect pollutants in hydric resources, for instance. The most significant analytical response was observed for paracetamol oxidation, presenting higher peak current values and better concentration-current correlation than the bare CPE (mineral oil composition).