Development of sustainable electrodes based on cobalt ferrite-decorated biochar for the voltammetric determination of paracetamol in biological fluids

Biochars (BC) obtained from biomass residues have been highlighted in electroanalytical applications for their distinct physicochemical properties and for making the devices cheaper and sustainable. In this work, we propose the use of BC derived from forest residues of eucalyptus, decorated with cobalt ferrite (CoFe₂O₄), as a modifying agent for carbon paste electrodes aimed at the voltammetric sensing of paracetamol (PAR) in biological fluids. BC was obtained by pyrolysis (450 °C, 72 h) and then decorated with CoFe₂O₄ synthesized <i>via</i> co-precipitation. The prepared materials were characterized by zeta potential, SEM, EDS, and N₂ adsorption (specific surface area). The electrochemical behavior of different modified electrodes in relation to the target analyte was explored through cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode prepared with 25% by mass of BC/CoFe₂O₄ (BC/CoFe₂O₄ 25) promoted more intense peak currents and lower charge transfer resistance for PAR compared to unmodified CPE, which can be attributed to the increase in active surface area. Differential pulse voltammetry (DPV) was applied for the determination of PAR, and under optimal conditions, a linear range of 0.416 to 31.5 μmol L^-1, with limits of detection and quantification of 0.028 and 0.083 μmol L^-1, respectively, was recorded. The proposed sensor was successfully applied in the determination of PAR in a synthetic urine sample, providing recoveries ranging from 103 to 108%. The results demonstrate the effectiveness of using biochar obtained from residual biomass sources as a support for cobalt ferrites in the development of more sustainable electrochemical sensors.