Assessing the performance of novel and sustainable electrochemical sensor based on cobalt sulfide/upcycled reduced graphene oxide from plastic waste

Developing electrochemical sensors that are both highly sensitive and environmentally sustainable is a pressing need in modern healthcare and environmental analysis. In this study, a cobalt sulfide/reduced graphene oxide (CoS/rGO) nanocomposite was synthesized via a straightforward, low-cost method that integrates thiourea and cobalt acetate to form CoS, with rGO derived from recycled plastic waste. The structural and electrochemical properties of the composites were systematically investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The addition of rGO, varied from 0 to 50 wt%, notably enhanced the electrical conductivity and surface activity of the sensing interface. Among the tested formulations, the composite containing 40 wt% rGO exhibited the highest performance, achieving a sensitivity of 12.4 μA mM⁻¹ cm⁻² and a detection limit of 0.2 μM, which is approximately 7.5 times lower than that of pristine CoS. Kinetic analysis confirmed that the sensing mechanism follows a pseudo-second-order model, indicative of a chemisorption-driven interaction between paracetamol molecules and the sensor surface. The sensor displayed excellent operational stability over 100 consecutive cycles and high repeatability with a relative standard deviation below 2.5 %. This work demonstrates a novel, green strategy for sensor fabrication that effectively combines electronic functionality with environmental sustainability, making the CoS/rGO nanocomposite a viable platform for next-generation sensing technologies.