K-g-C3N4@PDA nanozyme for the colorimetric detection of ferric ammonium citrate in edible salt

A K-doped carboxylated polydopamine (PDA) modification of the g-C₃N₄ (K-g-C₃N₄@PDA) nanozyme was effectively performed by one-step potassium salt-assisted thermal copolymerization and hydrothermal strategies. K-g-C₃N₄@PDA showed excellent peroxidase (POD)-like activity, and ferric ammonium citrate (FAC) efficiently promoted the generation of hydroxyl radicals (˙OH). Furthermore, K-g-C₃N₄@PDA oxidized 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in the presence of H₂O₂ to produce a blue-green product, and FAC boosted the POD-like activity with an exceptional linear relationship and low detection limit (0.018 μg mL⁻¹). Importantly, a recovery rate of 94.09–105.17% was attained when the developed method was effectively used to assess FAC in culinary salt samples using a spiking procedure.