Effect of graphene quantum dot concentration on p-toluenesulfonic acid-doped polyaniline–graphene quantum dot nanocomposites: chemical, optical, and electrical characterization for benzo[def]phenanthrene detection

Abstract

Monitoring of benzo[def]phenanthrene as a toxic component is essential for environmental assessment because of its adverse impact on human health and ecological systems. P-Toluenesulfonic acid-doped polyaniline (PANI) and PANI-graphene quantum dot (PANI-GQD) nanocomposites were fabricated by incorporating graphene quantum dot (GQD) concentrations between 100 and 500 ppm through oxidative chemical polymerization of aniline under acidic conditions at ambient temperature. The materials were analysed using Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetry analysis (TGA), UV–visible and photoluminescence (PL) spectroscopy, and electrical conductivity measurements. Key findings included significant shifts in FT-IR peaks (C=N stretching from 1651 to 1694 cm⁻¹) and an increase in the AB/AP ratio from 0.27 to 0.333, indicating enhanced sp² hybridization and improved electrical conductivity. XRD analysis showed improved molecular ordering in PANI-GQD nanocomposites. FE-SEM revealed changes in morphology from flat layers to spherical and flaky mixtures with increasing GQD concentrations. Film thickness increased from 13.52 μm (PANI-GQD-1) to 30.07 μm (PANI-GQD-5). The PANI-GQD-3 nanocomposite exhibited the lowest bandgap (2.39 eV) and the highest PL intensity because of enhanced energy transfer between PANI and GQD. Electrical conductivity decreased with increasing GQD concentration, with PANI-GQD-5 showing 2.17 (Ω cm)^–1. PANI-GQD-3 successfully detected benzo[def]phenanthrene at concentrations ranging from 0.001 mol L⁻¹ to 10 × 10⁻⁹ mol L⁻¹ with a limit of detection of 1.5 × 10⁻⁹ mol L⁻¹ through gas chromatography. Results demonstrated the potential of PANI-GQD nanocomposites for sensor and biosensor applications.