Nanocomposites Based on Polyethylene and Nickel Ferrite: Preparation, Characterization, and Properties

Composite materials based on NiFe2O4 nanoparticles and polyethylene matrix have been synthesized by thermal decomposition to expand the application area of high-pressure polyethylene by filling it with nanoscale particles. The synthesized compositions were obtained in the form of a dark gray powder and compressed for further study According to TEM, the average particle size in composites was 2, 3, and 4 nm in samples with a filling of 10%, 20% and 30%. The concentration dependences of the specific electrical resistivity ρV, dielectric permittivity ε, saturation magnetization MS and the parameters of reflection and attenuation of microwave power of the obtained composites were investigated. The threshold for percolation in such materials is found to be within a concentration range of 20…30%. The electronic and atomic structure of composites was studied by methods of Mössbauer spectroscopy, X-ray diffraction and X-ray absorption spectroscopy. The closest atomic environment of nickel and iron in nanoparticles is close to that of crystalline NiFe2O4. The dependence of the nanoparticles size as well as the dependence of the number of tetrahedral or octahedral iron positions in nickel ferrite nanoparticles to their content in polyethylene matrix is established. It is shown that composite materials based on NiFe2O4 nanoparticles and polyethylene matrix can be used as components of electromagnetic compatibility systems.

Catalytic Decomposition of H2O2 in the Aqueous Dispersions of the Potassium Polytitanates Produced in Different Conditions of Molten Salt Synthesis

It is shown that the potassium polytitanate powder (PPT) synthesized at 500 °C via the treatment of powdered TiO₂ (rutile) in molten mixtures of KOH and KNO₃ is a cheap and effective catalyst of H₂O₂ chemical decomposition in aqueous solutions. At the same time, the PPT catalytic activity strongly depends on the [TiO₂]:[KOH]:[KNO₃] weight ratio in the mixture used for the synthesis, increasing with [KNO₃] in the order of PPT (30:30:40) < PPT (30:50:20) < PPT (30:70:0). The obtained results are explained by increased [Ti³⁺] in the PPT structure (XPS data), which is grown in this order from 0 to 4.0 and 21.9 at.%, respectively, due to the reduced oxidation activity of the melt used for PPT synthesis. The mechanism of the autocatalytic process taking place in the PPT-H₂O₂-H₂O system is analyzed. Taking into account the data of FT-IR spectroscopy, it is assumed that the increased catalytic activity of the investigated materials is related to the increased surface concentration of the Ti⁴⁺-O(H)-Ti⁴⁺ groups, formed from the Ti³⁺-O(H₃O⁺)-Ti⁴⁺ clusters and further transformed into Ti-O-O-H catalytic centers. Some possible applications of the PPT-H₂O₂-H₂O catalytic system, including the oxidation processes of green chemistry and photo-catalysis, are discussed.