Improvement of Fe0.8Ni0.2S2 Peroxidase-like Activity through the Accelerated Conversion from Fe3+ to Fe2+

Nanoenzymes have been regarded as strong substitutes to natural enzymes in the last decades. However, high concentrations of substrates are always needed because of the low activity of nanozymes, which causes an increase of the cost and an increase in environmental pollution in practical applications. Thus, improved nanozymic activity is still urgent and vital to reduce the need for high concentrations of substrates. A series of binary metal sulfides (FexNi1–xS2), which exhibited intrinsic nanozymic activity, was first synthesized by a hydrothermal method. Among these samples, the nanosheet-shaped Fe0.8Ni0.2S2 showed the highest activity. Compared with those of FeS2, the catalytic constant (Kcat) and catalytic efficiency (Kcat/Km) of Fe0.8Ni0.2S2 increased about 1.9 and 3.6 times, respectively. The Michaelis–Menten constant (Km) of Fe0.8Ni0.2S2 is about 4.7-fold smaller than that of FeS2, and 193-fold smaller than that of natural enzyme horseradish peroxidase (HRP), indicating a stronger affinity to H2O2. The investigation on the mechanism indicated that Fe2+ and Fe3+ in Fe0.8Ni0.2S2 are the active sites. The synergistic effect between Ni2+ and Fe3+ accelerated the conversion from Fe3+ to Fe2+, which improved the nanozymic activity. In addition, Fe0.8Ni0.2S2 can be used as a nanozyme to detect H2O2 and ascorbic acid (AA) within 1 min at room temperature (25 °C). This work extends the development of binary metal sulfides as artificial enzymes.