Ionic liquid-enhanced rGO@Fe₂O₃ nanohybrid-based conducting paper for efficient phenolic pollutant detection in wastewater

We report the fabrication of a sensitive and selective electrochemical biosensor based on ionic liquid (IL)-modified reduced graphene oxide (rGO)-iron oxide (IL-rGO@Fe₂O₃) nanohybrid for the electrochemical detection of polyphenol compounds in the wastewater. The IL-rGO@Fe₂O₃ nanohybrid has been synthesised by grafting Fe₂O₃ nanoparticles onto the surface of rGO, followed by the functionalisation with 1-Allyl-3-methylimidazolium bromide and 1-Butyl-2-phenylimidazolium chloride ionic liquids (ILs). The synthesised IL-rGO@Fe₂O₃ nanohybrid has been used to fabricate the conducting paper (CP) electrode. Density functional theory and density of states analysis show that the functionalisation of ILs remarkably modifies rGO sheets’ electronic properties by enhancing conductivity. The effect of different solvents on the electrical conductivity of CP modified with IL-rGO@Fe₂O₃ was examined, and it has been observed that the electrical conductivity of the IL-rGO@Fe₂O₃/CP electrode enhanced to 4.42 × 10⁻² Scm⁻¹ after its treatment with DMSO. Further, the biosensing electrode has been fabricated by covalent immobilising the laccase (Lac) enzyme onto the IL-rGO@Fe₂O₃/CP electrode. The Lac/IL-rGO@Fe₂O₃/CP electrode showed high sensitivity (0.722 µA/µMcm²), a wide detection range (0.1–25 µM) and a low detection limit of 0.01 µM for hydroquinone (HQ) detection. The biosensor was able to detect HQ in river and tap water samples with an excellent recovery rate.