Facile Photopolymerization of High-Molecular-Weight Polyaniline Composites Induced by g-C3N4 at Room Temperature for Trace Fe Ion Sensors

Polyaniline (PANI) has attracted more and more attention due to its excellent sensing performance, conductivity, and corrosion resistance. However, the synthesis conditions of PANI are extremely harsh, requiring not only traditional oxidants but also a low-temperature environment. In this study, graphitic carbon nitride (g-C3N4) was prepared into a g-C3N4 nanosheet (CN) solution by ultrasonic-assisted liquid-phase exfoliation, and CN and NO3– were induced at room temperature (R.T.) to polymerize metal-free PANI composites (CNPANI). Capture experiments showed that the photogenerated hole (h+) and hydroxyl radical (•OH) play a synergistic role in the photopolymerization of CNPANI. The results of the four-point probe, solid-state 13C NMR, and ultraviolet–visible (UV–vis) spectra show that CNPANI is the emeraldine salt (ES state, blue-green). Gel permeation chromatography (GPC) and intrinsic viscosity [η] show a high molecular weight (Mw = 222,405 Da) and a narrow molecular weight distribution (PD = 1.62) of CNPANI. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) show that the impedance of CNPANI with Fe(III) intercalation (CNPANI-Fe) under visible light is smaller than that of CNPANI, and the photocurrent is obviously enhanced. CNPANI has a detection range of 0.1–1000 nM for Fe ions with a limit of detection (LOD) of 1.103 pM and has no obvious response to other ions. This work not only provides a novel and facile method for the synthesis of high-molecular-weight conductive PANI but also provides an intelligent method for PANI as a sensor for trace Fe(III).