Fluorescence Sensing of Some Important Nitroaromatic Compounds by Using Polyaniline Ag Composite

Abstract

Conducting polymers (CPs) have contributed significantly to the field of sensing. The sensing of nitroaromatic compounds by fluorescence has recently gained more attention due to its sensitivity and selectivity. In this study, polyaniline (PANI) was functionalized by forming a polyaniline-Ag (PANI-Ag) composite and used as a fluorophore for sensing. The nitro groups present in nitroaromatic compounds (NACs) such as 2,4,6-trinitrophenol (picric acid-TNP) and Dinitrobenzene (DNB) act as electron-accepting molecules and quench the fluorescence of polymer chains by showing an amplified quenching effect in which trace amounts of electron-accepting NACs quench emissions of several fluorophore units. The PANI-Ag composite synthesized by interfacial polymerization was analyzed using UV-vis spectroscopy and Fourier-transform infrared (FTIR) spectroscopy for determination of molecular structure; X-ray powder diffraction (XRD) and scanning electron microscopy (SEM/EDAX) for its morphology, which is cubic crystalline silver; and thermogravimetric analysis (TGA) for the thermal stability. The fluorescence quenching mechanism was deduced from the Stern–Volmer plot. The quenching constant value (Ksv) obtained from the Stern–Volmer (S–V) plot was found to be Ksv = 0.1037 × 106 M−1 (TNP) and Ksv = 0.161 × 104 M−1 (DNB). The plot shows a single mechanism with formation of an exciplex complex for TNP with a photoinduced electron transfer (PET) mechanism. The limit of detection (LOD) is found to be TNP = 5.58 × 10−7 M, whereas DNB = 23.30 × 10−6 M shows that the PANI-Ag composite is a potential fluorophore for sensing of nitroaromatic compounds in trace levels.

Keywords

• conducting polymers
• fluorescence quenching
• nitroaromatic compounds
• spectroscopic method