The synthesis and excellent peroxidase-like activity for the colorimetric detection of H2O2 of core-shell Fe/FeS2@C nanoparticles

Enhancement of the peroxidase-like activity of hollow spherical FexNi1-xS2/SC nanozymes

Artificial nanozymes have been receiving considerable interest for their outstanding performance and wide application. However, their low activity results in a high concentration of substrates, costs, and environmental pollution. To enhance nanozymic activity, a composite, FexNi1-xS2/hollow carbon spheres (FexNi1-xS2/SC), was facilely synthesized by a solvothermal method. The response surface methodology (RSM) was used to optimize the Ni content in FexNi1-xS2/SC and the experimental conditions, where Fe0.75Ni0.25S2/SC exhibited the highest activity. The Km (Michaelis-Menten's constant) values of Fe0.75Ni0.25S2/SC are 0.025 and 0.021 mM with H2O2 and oxidized 3,3',5,5'-tetramethylbenzidine (TMB) as the substrates, respectively, which are 148 times and 20.5 times lower than those with HRP, 1.88 and 7.19 times lower than those of FeS2/SC, and 1.88 and 10.52 times lower than those of Fe0.8Ni0.2S2, meaning a strong affinity of Fe0.75Ni0.25S2/SC for the substrate. The catalytic efficiency (Kcat/Km) of Fe0.75Ni0.25S2/SC was 5.4 (H2O2) and 27.4 times (TMB), and 9.7 (H2O2) and 66.2 times (TMB) higher than those of FeS2/SC and Fe0.8Ni0.2S2, respectively. The effects of the synergistic interaction between Fe and Ni, the S-C bond formation, and the hollow carbon spheres on the activity were studied. A nanozymic mechanism was proposed. Fe0.75Ni0.25S2/SC could be used to detect cysteine (Cys) at room temperature in 1 min with a detection limit (LOD) of 0.049 μM.

Peroxidase-like activity of hollow sphere-like FeS2/SC boosted by synergistic action of defects and S-C bonding

Pyrite FeS₂ has been applied as a peroxidase due to its easy preparation and low cost. However, the low peroxidase-like (POD) activity limited its wide application. A hollow sphere-like composite (FeS₂/SC-5.3%) composed of pyrite FeS₂ and sulfur-doped hollow sphere-shaped carbon was synthesized by a facile solvothermal method, where the S-doped carbon was in situ formed during FeS₂ formation. The synergistic action such as the defects at the carbon surface and the formation of S-C bonding improved the nanozyme activity. The S-C bonding was a bridge between the carbon and the Fe atom in FeS₂, which enhanced the electron transfer between the Fe atom and the carbon and accelerated the conversion from Fe³⁺ to Fe²⁺. The optimum experimental conditions were obtained by the response surface methodology (RSM). The POD-like activity of FeS₂/SC-5.3% was significantly improved compared to that of FeS₂. The Michaelis-Menten constant (K_m) of FeS₂/SC-5.3% is 80 times lower than that of horseradish peroxidase (HRP, natural enzyme). FeS₂/SC-5.3% can be used to detect cysteine (Cys) with a limit of detection (LOD) as small as 0.061 μM at room temperature in only 1 min.

Double Z-Scheme ZnCo2O4/MnO2/FeS2 photocatalyst with enhanced photodegradation of organic compound: Insights into mechanisms, kinetics, pathway and toxicity studies

The present work highlights the preparation of double Z-scheme ZnCo2O4/MnO2/FeS2 nanocomposite (NCs) and investigated its photocatalytic activity against methyl orange (MO) dye degradation under visible light. An array of techniques was carried out to characterize the nanoparticles (NPs) in order to evaluate their morphological, structural, optical, and photocatalytic properties using FE-SEM, TEM, XRD, N2 adsorption and desorption studies, PL, UV-visible spectrophotometer, XPS, Raman, and UV-vis DRS analysis. The degradation efficiency of NCs was tested along with different parameter studies such as different pH, NCs concentration, dye concentration, reusability and structural stability. The NCs exhibited complete photodegradation of MO dye under visible light within 80 min at pH 4. The structural and compositional stability of the prepared NCs over 6 consecutive cycles was tested via XRD and XPS analysis. The results of active species trapping experiments showed that O2-• and OH• are responsible for the degradation of MO dye. The TOC analysis showed 95% of mineralization by the prepared NCs. The MO dye degradation pathway was determined using GC-MS/MS analysis and drafted all the intermediates involved. End product toxicity via seed germination and intermediate toxicity study using ECOSAR software results in less toxicity of end product compared to parent compound. Finally, the genotoxicity of the prepared NCs was evaluated using Allium cepa and showed its no causes of cytotoxicity & genotoxicity by the prepared NCs. ZnCo2O4/MnO2/FeS2 NCs exhibited its high photocatalytic activity and the toxicity studies confirms that there is no cause of any environmental impact.

Investigation on the Peroxidase-like Activity of Vitamin B6 and Its Applications in Colorimetric Detection of Hydrogen Peroxide and Total Antioxidant Capacity Evaluation

The peroxidase-like activity of vitamin B6 (VB6) was firstly demonstrated by catalyzing the peroxidase chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) at the existence of H2O2. The influence of different factors on the catalytic property of VB6, including pH, temperature, VB6 concentration, and incubation time, were investigated. The steady-state kinetic study results indicate that VB6 possesses higher affinity to H2O2 than natural horseradish peroxidase and some other peroxidase mimics. Besides, the radical quenching experiment results confirm that hydroxyl radical (•OH) accounts for the catalytic process. Based on the excellent peroxidase-like catalytic activity of VB6, the colorimetric methods for H2O2 and gallic acid (GA) detection were developed by measuring the absorbance variance of the catalytic system. Under the optimal conditions, the linear ranges of the methods for H2O2 and GA determination with good selectivity are 50.0–600.0 μM and 10.0–50.0 μM, respectively. In addition, the developed method was applied in the detection of H2O2 in milk samples and evaluation of total antioxidant capacity of different tea infusions. This study may broaden the application prospect of VB6 in environmental and biomedical analysis fields, contribute to profound insight of the physiological functions of VB6, as well as lay foundation for further excavation of small-molecule peroxidase mimics.