Glycothermal synthesis of fluorinated Fe3O4 microspheres with distinct peroxidase-like activity

Fe3O4@iron-based metal-organic framework nanocomposite [Fe3O4@MOF (Fe) NC] as a recyclable magnetic nano-organocatalyst for the environment-friendly synthesis of pyrano[2,3-d]pyrimidine derivatives

Various pyrano[2,3-d]pyrimidines were synthesized by the multicomponent reaction of aldehydes, malononitrile, and acidic C-H compounds such as barbituric acid through the tandem Knoevenagel-Michael cyclocondensation pathway in an environmentally friendly reactive medium in the presence of a recoverable nanocomposite. This nanocomposite includes Fe₃O₄ nanoparticles placed on an organometallic framework. The synthesized Fe₃O₄@iron-based metal-organic framework nanocomposite was characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, a vibrating sample magnetometer, and thermogravimetric analysis.

Catalytic Wet Peroxide Oxidation of Anionic Pollutants over Fluorinated Fe3O4 Microspheres at Circumneutral pH Values

Fluorinated Fe3O4 microspheres with 7.1 ± 1.4 wt% of fluoride (F-Fe3O4-1) were prepared via glycothermal synthesis. Fluorination significantly enhanced the activity of F-Fe3O4-1 in catalytic wet peroxide oxidation of anionic dyes (including orange G (OG) and congo red) at pH ~7. However, the promotional effect of fluorination became less obvious for amphoteric rhodamine B and was not observed for cationic methylene blue. After reacting with H2O2 (40 mM) for 2 h at pH 6.5 and 40 °C, the decolorization rates of OG (0.1 mM) and the pseudo-first-order rate constant were 96.8% and 0.0284 min−1 over F-Fe3O4-1 versus 17.6% and 0.0011 min−1 over unmodified Fe3O4. The effects of reaction parameters (initial H2O2 concentration and pH value and reaction temperature) on OG decolorization with H2O2 over F-Fe3O4-1 were investigated. The reusability of F-Fe3O4-1 was demonstrated by OG decolorization in eight consecutive runs. Fluorination increased the isoelectric point of F-Fe3O4-1 to 8.7 and facilitated the adsorption and degradation of anionic dyes on the surface of F-Fe3O4-1 at pH ~7. Scavenging tests and EPR spectra supported that hydroxyl radicals were the main reactive species for the OG decolorization over F-Fe3O4-1.

Fabrication of FeS2/SiO2 Double Mesoporous Hollow Spheres as an Artificial Peroxidase and Rapid Determination of H2O2 and Glutathione

Nanozymes as one of artificial enzymes show many advantages than natural enzymes. The high Michaelis-Menten constant (K_m) to H₂O₂ is the drawback for nanozymes, which means a high H₂O₂ concentration to oxidize 3,3',5,5'-tetramethylbenzidine (TMB). For this problem, FeS₂/SiO₂ double mesoporous hollow spheres (DMHSs) were first synthesized as an artificial peroxidase through a solid reaction. The experimental results demonstrate that Fe₃O₄ vulcanization and DMHS formation were effective strategies to enhance affinity to H₂O₂ for the nanozyme. The K_m of FeS₂/SiO₂ DMHSs (H₂O₂ as the substrate) is 18-fold smaller than that of FeS₂ nanoparticles (NPs). The catalytic efficiency (K_cat/K_m) of FeS₂/SiO₂ DMHSs is about 16 times higher than that of FeS₂ NPs. FeS₂/SiO₂ DMHSs can be used as a nanozyme to sensitively and rapidly detect H₂O₂ and glutathione within 1 min at room temperature.