Photocatalytic reduction of Cr ( <scp>VI</scp> ) via para‐toluene sulfonic acid doping on polypyrrole‐coupled g‐ <scp> C ₃ N ₄ </scp> nanosheet

Abstract The main goal of this study was to synthesize a two‐step composite of para‐toluene sulfonic acid‐doped polypyrrole‐coupled with g‐C 3 N 4 nanosheet (CNns/PPy). First, the g‐C 3 N 4 nanosheet was synthesized and then polymerized with para‐toluene sulfonic acid‐doped polypyrrole, and to utilize this photocatalyst for the reduction of chromium (VI) [Cr (VI)] to chromium (III) [Cr (III)] from an aqueous solution. To achieve this objective, the photocatalyst was examined using Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). The removal effectiveness of Cr (VI) reached 100% under optimal conditions, which included a pH of 3, a concentration of 10 mg/L (VI), and 1.0 g/L of CNns/PPy nanocomposite at ambient temperature for 60 min. The kinetic model was adjusted to the pseudo‐first‐order kinetics. In conclusion, the CNns/PPy photocatalyst, characterized by favorable physical and electrical conductivity attributes such as a high specific surface area and a reduced band gap energy, shows significant potential as an efficient photocatalyst for the reduction of Cr (VI) in water or wastewater.