Electrochemically reduced graphene oxide films from Zn-C battery waste for the electrochemical determination of paracetamol and hydroquinone.

Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO) films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer's method. The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k0) were observed for all redox systems studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 µmol L-1 and 0.65 µmol L-1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determination of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources.

Carbon Nanomaterials-Based Screen-Printed Electrodes for Sensing Applications.

Electrochemical sensors consisting of screen-printed electrodes (SPEs) are recurrent devices in the recent literature for applications in different fields of interest and contribute to the expanding electroanalytical chemistry field. This is due to inherent characteristics that can be better (or only) achieved with the use of SPEs, including miniaturization, cost reduction, lower sample consumption, compatibility with portable equipment, and disposability. SPEs are also quite versatile; they can be manufactured using different formulations of conductive inks and substrates, and are of varied designs. Naturally, the analytical performance of SPEs is directly affected by the quality of the material used for printing and modifying the electrodes. In this sense, the most varied carbon nanomaterials have been explored for the preparation and modification of SPEs, providing devices with an enhanced electrochemical response and greater sensitivity, in addition to functionalized surfaces that can immobilize biological agents for the manufacture of biosensors. Considering the relevance and timeliness of the topic, this review aimed to provide an overview of the current scenario of the use of carbonaceous nanomaterials in the context of making electrochemical SPE sensors, from which different approaches will be presented, exploring materials traditionally investigated in electrochemistry, such as graphene, carbon nanotubes, carbon black, and those more recently investigated for this (carbon quantum dots, graphitic carbon nitride, and biochar). Perspectives on the use and expansion of these devices are also considered.