Synergistic Effect of Hydrochloric Acid and Phytic Acid Doping on Polyaniline-Coupled g‑C₃N₄ Nanosheets for Photocatalytic Cr(VI) Reduction and Dye Degradation

In this study, graphitic carbon nitride (g-C₃N₄) nanosheets (CNns) were modified using polyaniline (PANI) codoped with an inorganic (hydrochloric acid, HCl) and an organic (phytic acid, PA) acid. Our results revealed that these samples exhibited extended visible-light absorption and a three-dimensional (3D) hierarchical structure with a large specific surface area. They also inhibited photoluminescence emission, reduced electrical resistance, and provided abundant free radicals, resulting in high photocatalytic performance. The PANI/g-C₃N₄ sample demonstrated outstanding photocatalytic activity of a Cr­(VI) removal capacity of 4.76 mg·min^–1·g_c^–1, which is the best record for the reduction of a 100 ppm K₂Cr₂O₇ solution. Moreover, g-C₃N₄ coupled with PANI monotonically doped with HCl or PA did not demonstrate increased activity, suggesting that the codoping of HCl and PA plays a significant role in enhancing the performance. The improved photocatalytic activity of PANI/g-C₃N₄ can be attributed to the interchain and intrachain doping of PA and HCl over PANI, respectively, to create a 3D connected network and synergistically increase the electrical conductivity. Therefore, new insights into g-C₃N₄ coupled with PANI and codoped by HCl and PA may have excellent potential for the design of g-C₃N₄-based compounds for efficient photocatalytic reactions.