Abstract
The structural, vibrational, and magnetic properties of maghemite nanoparticles functionalized with zeolite type 5A and synthesized by coprecipitation were studied in detail. Crystallite and particle sizes were determined and discussed based on the polydispersity index. Its value of 0.4 has suggested the presence of a broad particle distribution with particle sizes between 3 and 20 nm. Three samples were successfully functionalized either before or after the formation of the maghemite nanoparticles. Infrared studies have shown that the functionalization has occurred by hydrated surface groups present in the zeolite type 5A surface, which have favored strong bindings and highly concentrated regions of maghemite nanoparticles. From the temperature dependence of the hyperfine magnetic field obtained by Mössbauer spectroscopy, the effective magnetocrystalline anisotropy constants of the three nanohybrids were determined. They are one order of magnitude higher than for the bulk counterpart, and there is evidence for strong interparticle interactions for the three studied nanohybrids. These strong magnetic interactions of the nanoparticles in the zeolite framework have favored a superspinglass-like behavior for all samples with transition temperatures located at 74 and 208 K, as confirmed by AC susceptibility measurements.
Highlights
Because of their similar x-ray diffraction (XRD) patterns, similar infra red (IR) vibration modes, and similar hyperfine parameters when experiments are done at room temperature (RT),15–18 the two iron-oxide phases cannot be differentiated using standard experimental procedures
From details of the Mössbauer spectral shape together with AC susceptibility data, we have concluded that the NPs are magnetically interacting and that a SSG state is established in the three samples, i.e., we have shown that the SSG state found in our γ-Fe2O3 NPs is a consequence of the functionalization with the zeolite type 5A since pure γ-Fe2O3 NPs synthetized by co-precipitation did not present such magnetic properties
For our Transmission Electron Microscopy (TEM) analysis, we got values higher than 0.4,19 which is representative of a broad particle size distribution, as typically expected of magnetic NPs synthesized by coprecipitation
Summary
Magnetic nanoparticles (NPs) are prominent materials, which can be used in many areas of current applied science. In biosensing, they are called nanozymes, where their catalytic properties enhance the electrochemical response of the sensor, for example, in the detection of viruses such as SARS-CoV-2 or Ebola. Their conjugation with zeolites, forming composite solid matrices with magnetic NPs (nanohybrids), is promising materials in the removal of heavy metals and nanoagriculture for improving crops’ and plants’ quality. magnetic interactions and the magnetic state of an ensemble of magnetic NPs are subjects that still need deeper investigations for a qualified application of the developed nanohybrids in different areas. A problem reported with the coprecipitation method is the fast oxidation that often occurs in Fe3O4 synthesis even in functionalized samples, precluding a reliable conclusive assignment of the oxide as Fe3O4 or γ-Fe2O3 Because of their similar x-ray diffraction (XRD) patterns, similar infra red (IR) vibration modes, and similar hyperfine parameters when experiments are done at room temperature (RT), the two iron-oxide phases cannot be differentiated using standard experimental procedures. This issue leads to frequent discussions concerning the proper assignment of a specimen assumed as Fe3O4 without deeper magnetic analysis. From details of the Mössbauer spectral shape together with AC susceptibility data, we have concluded that the NPs are magnetically interacting and that a SSG state is established in the three samples, i.e., we have shown that the SSG state found in our γ-Fe2O3 NPs is a consequence of the functionalization with the zeolite type 5A since pure γ-Fe2O3 NPs synthetized by co-precipitation did not present such magnetic properties.
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