Tuning surface interactions with bentonite-graphite composite material for fouling-resistant electrochemical sensing of phenol in olive mill wastewater

Abstract

A bentonite-modified carbon paste electrode (CPEB) was developed and evaluated as an efficient electrochemical sensor for phenol detection in aqueous systems, with a particular focus on enhancing sensitivity, selectivity, and fouling resistance through interfacial material design. The bentonite modifier was comprehensively characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption-desorption isotherms (BET), and scanning electron microscopy (SEM), revealing a high surface area and layered structure conducive to molecular-level interactions in liquid-phase sensing. A series of CPEBs with 10–50 wt% bentonite were fabricated, with the 40 wt% composition (CPEB-40 %) exhibiting the optimal electroactive surface area (0.162 cm²), as determined via ferri/ferrocyanide redox probing. Electrochemical assessments identified linear scan voltammetry (LSV) as the most effective technique for phenol detection, delivering a sharp response (250 μA) and a linear dynamic range from 5 to 1000 μM. The sensor achieved a low limit of detection (LOD) of 0.015 μM and a quantification limit (LOQ) of 0.052 μM. The molecular recognition behavior of the electrode surface, facilitated by bentonite’s layered silicate structure and charge distribution, endowed the sensor with excellent selectivity toward phenol over potential interferents, including Cu²⁺ ( ± 2 %), Fe³ ⁺ ( ± 6.2 %), Zn²⁺ ( ± 7.1 %), 4-nitrophenol ( ± 5.1 %), and 2-nitrophenol ( ± 10.8 %). In real-sample analysis, the CPEB-40 % reliably quantified phenol in olive mill wastewater (OMW), detecting 4.30 µM (∼0.40 ppm), a value close to environmental regulatory thresholds. The electrode displayed a low fouling rate (k = 0.94 s⁻¹), high initial peak current (Iₚₒ = 190 μA), and robust reproducibility (R² = 0.983), underscoring its durability under complex matrix conditions. These findings highlight the utility of clay-based modifications in tuning physicochemical properties at the electrode–solution interface, offering a promising molecular-level strategy for the selective detection of hazardous organic compounds in aqueous environments. • Bentonite-modified CPE enhances phenol detection in aqueous Olive Mill Wastewater. • CPEB-40 % shows the highest electrochemical area of 0.162 cm² among all tested. • Sensor achieves ultra-low LOD (0.015 µM) and LOQ (0.052 µM) for phenol detection. • Exhibits strong selectivity with minimal interference from ions and phenol derivatives. • Fast kinetics (k = 0.94 s⁻¹) and low fouling ensure stable and reliable sensor response.