Improvement of Fe_0.8Ni_0.2S₂ Peroxidase-like Activity through the Accelerated Conversion from Fe³⁺ to Fe²⁺

Abstract

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 (Fe x Ni1–x S2), 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 (K cat) and catalytic efficiency (K cat/K m ) of Fe0.8Ni0.2S2 increased about 1.9 and 3.6 times, respectively. The Michaelis–Menten constant (K m ) 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.

2D/3D-Shaped Fe0.8Ni0.2S2/ZIF-67 as a Nanozyme for Rapid Measurement of H2O2 and Ascorbic Acid with a Low Limit of Detection

“…Compared with Fe 0.8 Ni 0.2 S 2 , the molar ratios of Fe 2+ /Fe 3+ and Ni 2+ /Ni 3+ increased for Fe 0.8 Ni 0.2 S 2 /ZIF-67. The molar ratio of Fe 2+ /Fe 3+ improved and induced high nanozymic activity …”

“…The peaks at 712.7 and 727.2 eV correspond to Fe–O and Fe 3+ , respectively. , In Figure C, the peaks belong to Ni 2+ , Ni 3+ , and Ni–O and the satellite oscillation at 856.4, 874.2, 878.3, and 863.2 eV, respectively. − Figure D shows the S 2p spectrum with three peaks at 162.9, 164.1, and 168.8 eV corresponding to the S 2 2– in pyrite FeS 2 , sulfur atoms of the intermediate oxidation state, and the SO x group, respectively. , Figure E shows the Co 2p spectrum, in which Co 2+ and a satellite oscillation were found. − Figure F shows the C 1s spectra, in which the C–C, the C–N, and the O–CO bonds are at 284.8, 286.5, and 289.2 eV, respectively. − The bonding energy represents the change in the electronic density of the element. The higher the binding energy means the lower the electronic density . The effect of ZIF-67 addition on the electronic density of metal elements was studied by comparing with XPS spectra of Fe 0.8 Ni 0.2 S 2 and ZIF-67 in Table , where the results of Fe 0.8 Ni 0.2 S 2 and ZIF-67 were cited from refs and .…”

“…The higher the binding energy means the lower the electronic density . The effect of ZIF-67 addition on the electronic density of metal elements was studied by comparing with XPS spectra of Fe 0.8 Ni 0.2 S 2 and ZIF-67 in Table , where the results of Fe 0.8 Ni 0.2 S 2 and ZIF-67 were cited from refs and . The results indicate that ZIF-67 affects the binding energy and electronic densities of the metal elements in Fe 0.8 Ni 0.2 S 2 /ZIF-67.…”

“…TMB and H 2 O 2 were used as substrates to study the activity of the composite. The experimental conditions were similar as those in ref . The experimental results were obtained after being three times repeated under the same conditions.…”

“…High H 2 O 2 concentration was always needed to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB because of the low sensitivity of this method . To enhance the nanozymic activity can improve the sensitivity. , Binary metal sulfides show higher nanozymic activity than single metal sulfides through electron movement and conversion of Fe 3+ to Fe 2+ accelerated …”