Magnetochemistry, Volume 9, Issue 8 (August 2023) – 14 articles

Traditional printed products have to some extent affected the development of smart structures and their application in multiple fields, especially in harsh environments, due to their complex mechanisms and control principles. The 4D printing technology based on magnetically controlled smart materials exploits the advantages of magnetically controlled smart materials with good operability and security, and its printed smart structures can be obtained under magnetic field drive for unfettered remote manipulation and wireless motion control, which expands the application of printed products in complex environments, such as sealed and narrow, and has broad development prospects. At present, magnetically controlled smart material 4D printing technology is still in its infancy, and its theory and application need further in–depth study. To this end, this paper introduces the current status of research on magnetically controlled smart material 4D printing, discusses the printing process, and provides an outlook on its application prospects. Full article

As an abundant potentially dangerous waste, red mud (RM) requires a straightforward method of resource management. In this paper, an RM catalyst loaded with cobalt (Co-RM) was prepared by the coprecipitation method for the efficient activation of persulfate (PS). Its degradation performance and mechanism of ofloxacin (OFL) were investigated. The characterization results of scanning electron microscopy, X-ray diffractometer, and energy dispersive spectrometer showed cobalt was successfully loaded onto the surface of RM, and the catalyst produced could effectively activate PS. Under the conditions of 15 mg/L OFL, 0.4 g/L Co-RM, 4 g/L PDS, 3.0 pH, and 40 °C temperature, the maximum removal rate of OFL by the Co-RM/PDS system was 80.06%. Free radical scavenging experiments confirmed sulfate radicals were the main active substances in the reaction system. The intermediates in OFL degradation were further identified by gas chromatography-mass spectrometry, and a possible degradation pathway was proposed. Finally, the relationship between defluorination rate and time in the Co-RM/PDS degradation OFL system was described by the first-order kinetic equation. This work reports an economical, environmental solution to the use of waste RM and provides a research basis for the further exploration of RM-based catalysts. Full article

Magnetite/gold core-shell nanoparticles (magnetite/gold NPs) have important optical and magnetic properties that provide potential for applications, especially biomedical ones. However, their preparation is not exempt from difficulties that might lead to unexpected or undesired structures. This work reports the synthesis and characterization of magnetite/gold NPs using tetramethylammonium hydroxide (TMAH) to promote the formation of a continuous interface between the magnetite core and the thin gold shell. The synthesized magnetite/gold NPs were characterized using transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), field emission scanning electron microscope (FE-SEM), ζ-potential, vibrating sample magnetometer (VSM), selected area electron diffraction (SAED), UV-Visible spectroscopy, and dynamic light scattering (DLS), confirming the core-shell structure of the NPs with narrow size distribution while evidencing its plasmonic and superparamagnetic properties as well. Further, the magnetite/gold NPs were associated and stabilized with a β-cyclodextrin nanosponge (β-CDNSs), obtaining a versatile magneto-plasmonic system for potential applications in the encapsulation and controlled release of drugs. Full article

In this study, Ni-Fe alloy nanoparticles were prepared using the proteic sol–gel method, followed by a reduction in H₂ at 500 and 700 °C, namely hereafter as NiFe-500 and NiFe-700, respectively. The morphological, structural, and magnetic properties were tuned via the thermal treatment in H₂. The samples were studied using XPS, TEM, Mössbauer spectroscopy, DC magnetic measurements, and electrochemical measurements. Ritveld refinements showed that the sample NiFe-500 has FCC (face-centered cubic) and BCC (body-centered cubic) NiFe alloys, while the sample NiFe-700 has only FCC NiFe alloy. For both samples, magnetization measurements in the range of 300–900 K showed the presence of the Griffiths phase, indicating the formation of clusters of either Fe or Ni-Fe alloys rich in Fe. The sample NiFe-500 presented ferromagnetic (FM) transitions at 533, 700, and 834 K, assigned to the alloys Ni₃₇Fe₆₃-FCC, Ni₄₆Fe₅₄-FCC, and Ni₅₅Fe₄₅-FCC, respectively. In contrast, we could not observe the FM transition of the BCC Ni-Fe alloy because of limitations in our experimental setup (T ≤ 900 K). Meanwhile, three FM transitions were observed for the sample NiFe-700 at 480, 655, and 825 K, attributed to the alloys Ni₃₄Fe₆₆-FCC, Ni₄₃Fe₅₇-FCC, and Ni₅₄Fe₄₆-FCC, respectively. At 5 K, the samples NiFe-500 and NiFe-700 have saturation magnetizations of 164.2 and 173.6 emu g⁻¹, respectively. For application in Oxygen Evolution Reaction catalysis, the samples NiFe-500 and NiFe-700 showed different overpotentials of 319 and 307 mV at 10 mA cm⁻². These low overpotential values indicate a higher electrochemical activity of the FCC Ni-Fe alloy and, for both samples, a superior electrocatalytic activity in comparison to RuO₂ e IrO₂ conventional catalysts. Furthermore, the samples showed high electrochemical stability in chrono potentiometric studies for up to 15 h. This current work highlights that the Ni-Fe alloys produced via the proteic sol–gel and with a reduction in H₂ methods can be promising for OER systems due to their good performance and low costs. Full article

This study describes the synthesis of an innovative nanomaterial (patent application number BR 1020210000317) composed of cobalt ferrite functionalized in niobium pentoxide CoFe₂O₄@Nb₅O₂ (CFNb), synthesized via green synthesis using tangerine peel extract. The material emphasizes the combination of a magnetic material (which allows for easy recovery after application) with niobium pentoxide (a metal which is abundant in Brazil). CFNb was applied as a catalyst for the paracetamol (PCT) degradation by photocatalysis. The new materials were characterized through surface and pore analysis (S_BET, S_EXT, S_mic, V_mic, and V_TOTAL), photoacoustic spectroscopy (PAS), zero charge point (pH_PZC, scanning electron microscopy (SEM/EDS), and X-ray diffraction (XRD). The reaction parameters studied included pH and catalyst concentration. The results indicated that the CFNb nanocatalysts were efficient in the paracetamol degradation, presenting better results in conditions of low pH (close to 2) and low catalyst concentration under irradiation of the 250 W mercury vapor lamp (greater than 28 mW·cm⁻²) at 60 min of reaction. Full article

We propose an experimental method for the unidirectional excitation of spin waves. By structuring Au nanowire arrays within a coplanar waveguide onto a thin yttrium iron garnet (YIG) film, we observe a chiral coupling between the excitation field geometry of the nanowire grating and several well-resolved propagating magnon modes. We report a propagating spin wave spectroscopy study with unprecedented spectral definition, wavelengths down to 130 nm and attenuation lengths well above 100 μm over the 20 GHz frequency band. The proposed experiment paves the way for future non-reciprocal magnonic devices. Full article

In this paper, the electron and magnetic state of iron placed either on the surface or in the core of TiO₂ nanoparticles were investigated using magnetometric methods, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. It was demonstrated that the EPR spectra of TiO₂ samples with iron atoms localized both on the surface and in the core of specific features depending on the composition and size of the nanoparticles. Theoretical calculations using the density functional theory (DFT) method demonstrated that the localization of Fe atoms on the surface is characterized by a considerably larger set of atomic configurations as compared to that in the core of TiO₂ nanoparticles. Mössbauer spectra of the samples doped with Fe atoms both on the surface and in the core can be described quite satisfactorily using two and three doublets with different quadrupole splitting, respectively. This probably demonstrates that the Fe atoms on particle surface and in the bulk are in different unlike local surroundings. All iron ions, both on the surface and in the core, were found to be in the Fe³⁺ high-spin state. Full article

The microfluidics of magnetic fluids is gaining popularity due to the possibility of the non-contact control of liquid composite systems using a magnetic field. The dynamics of non-magnetic droplets and gas bubbles in magnetic fluids were investigated for various configurations of magnetic fields, coatings, and channel geometries, as well as the rate of component supply and their physical properties. Optimal regimes for forming droplet and bubble flows were determined. The mechanism for non-contact control of the size of droplets and bubbles using a magnetic field is proposed in this article. The dependences of the sizes of non-magnetic inclusions in magnetic liquids on the continuous phase flow rate and the displacement of magnets were obtained. The obtained dependences of the volume of non-magnetic inclusions on the flow rate of the continuous phase follow the classic dependences. Changing the size of air bubbles can be achieved by shifting the magnet from −5 mm to +2 mm. The ratio of the maximum and minimum breakaway inclusion varies from 5 to 2 depending on the flow rates of the continuous phase. The range of changing the size of oil droplets with the displacement of magnets is from 1.1 to 1.51. These studies show how, with the help of various mechanisms of influence on microfluidic flows, it is possible to control the size of bubbles and droplets forming in microchannels. The obtained data can be applied for controlled microfluidic dosing and counting devices. Full article

Hybrid magnetic molecularly imprinted polymers (MMIPs) have the advantages of the technology of molecularly imprinted material and magnetic nanoparticles. The magnetic properties of MMIPs allow easy magnetic separation of various pollutants and analytes. A convenient and simple approach has been developed for the preparation of MMIPs based on polyamide (nylon-6) and magnetic nanoparticles. The polymer matrix was formed during the transition of nylon-6 from a dissolved state to a solid state in the presence of template molecules and Fe₃O₄ nanoparticles in the initial solution. Methylene blue (MB) was used as a model imprinted template molecule. The MMIPs exhibited a maximum adsorption amount of MB reached 110 µmol/g. The selectivity coefficients toward MB structural analogs were estimated to be 6.1 ± 0.6 and 2.1 ± 0.3 for 15 μM hydroxyethylphenazine and toluidine blue, which shows high MMIP selectivity. To prove the MMIPs’ specificity in MB recognition, magnetic nonimprinted polymers (MNIPs) were synthesized without the presence of a template molecule. MMIPs exhibited much higher specificity in comparison to MNIPs. To show the remarkable reusability of the MMIP sorbent, more than four MB absorption and release cycles were carried out, demonstrating almost the same extraction capacity step by step. We believe that the proposed molecular imprinting technology, shown in the MB magnetic separation example, will bring new advances in the area of MMIPs for various applications. Full article

Nanocomposites of polyaniline (PANI)/Fe_2.85Ni_0.15O₄ (PFN) were successfully prepared using the co-precipitation method combined with an in-situ polymerization process. The FN and PFN nanocatalysts were characterized using various methods for the photocatalytic degradation of Rhodamine B (RhB). The XRD, Raman, TEM, and DTA-DTG analyses suggest that the FN nanoparticles (NPs) were effectively coated by PANI and that there were interactions between FN and PANI. Magnetic measurements indicated that PFN nanocomposites exhibited good superparamagnetic behavior and high saturation magnetization (39.5–57.6 emu/g), which are suitable for separating photocatalysts from solution for reuse. Adsorption-desorption analysis showed that the specific surface area of PFN was higher than that of FN. The UV-vis absorption spectra of FN and PFN nanocomposites exhibited strong absorption of visible light, attributed to the doping of Ni, which resulted in the reduction of the band-gap energy (E_g) of Fe₃O₄ to 2.4 eV. PFN nanocomposites with different mass ratios of PANI demonstrated superior photocatalytic activity compared to FN NPs. Furthermore, it was observed that PFN with a 10% mass ratio of PANI exhibited the highest RhB degradation efficiency, achieving a rate of approximately 98% after 300 min of irradiation. Finally, the possible photocatalytic degradation mechanisms of the PFN nanocomposites on RhB were discussed. PFN photocatalysts with good photocatalytic activity, inexpensive materials, and easy preparation could be potential candidates for wastewater purification applications. Full article

SrLnCuSe₃ (Ln = Dy, Ho, Er, Tm) compounds crystallize in the Pnma and Cmcm orthorhombic space group and belong to the Eu₂CuS₃ and KCuZrS₃ structural type, respectively. According to a single-crystal XRD study, the SrTmCuSe₃ unit cell parameters are a = 4.0631 (4), b = 13.4544 (14), c = 10.4430 (10) Å, and V = 570.88 (10) ų. All the studied SrLnCuSe₃ samples in the temperature range of 1.77–300 K demonstrate paramagnetic behavior without any features pointing to magnetic ordering. The measured Curie constants coincide with the values expected for Ln³⁺ ions with good accuracy, which confirms the stoichiometric composition of the samples and the non-magnetic state of the copper ions, Cu¹⁺ (S = 0). The conducted optical absorption study showed that the polycrystalline SrLnCuSe₃ (Ln = Dy, Ho, Er, Tm) samples are semiconductors with a direct bandgap ranging from 2.14 eV to 2.31 eV. Two indirect bandgaps were revealed and explained by the presence of optical transitions to highly dispersive subbands in the conduction band. The compounds demonstrate two reversible phase transitions α⇆β, β⇆γ and an incongruent melting at 1606 K (Dy), 1584 K (Ho), 1634 K (Er), and 1620 K (Tm) associated with the formation of solid solutions of SrSe, Cu_2-XSe, and Ln₂Se₃ binary compounds. Full article

In this study, we grew pristine and Ni-doped vertically aligned zinc oxide nanowires (NWs) on a glass substrate. Both the doped and pristine NWs displayed dominant 002 peaks, confirming their vertical alignment. The Ni-doped NWs exhibited a leftward shift compared to the pristine NWs. TEM measurements confirmed the high crystallinity of individual NWs, with a d-spacing of ~0.267 nm along the c-axis. Ni-doped NWs had a higher density, indicating increased nucleation sites due to nickel doping. Doped NW films on glass showed enhanced absorbance in the visible region, suggesting the creation of sub-gap defect levels from nickel doping. Magnetization vs. magnetic field measurements revealed a small hysteresis loop, indicative of soft ferromagnetic behavior. Current transient plots demonstrated an increase in current with an applied magnetic field. Two-terminal devices exhibited a photo response that intensified with magnetic field application. This increase was attributed to parallel grain alignment, resulting in enhanced carrier concentration and photo response. In the dark, transport properties displayed negative magnetoresistance behavior. This magneto-transport effect and enhanced photo response (under an LED at ~395 nm) were attributed to giant magnetoresistance (GMR) in the aligned NWs. The observed behavior arose from reduced carrier scattering, improved transport properties, and parallel spin alignment in the magnetic field. Full article

In this work we present a systematic, theoretical investigation of the ¹³C NMR chemical shifts for several mono-, di- and trisaccharides in the solid state. The chemical shifts have been calculated using density functional theory (DFT) together with the gauge including the projector augmented wave (GIPAW) method as implemented in the CASTEP program. We studied the changes in the ¹³C NMR chemical shifts in particular due to the formation of one or two glycosidic linkages and due to crystal water. The largest changes, up to 14 ppm, are observed between the mono- and disaccharides and typically for the glycosidic linkage atoms, but not in all cases. An analysis of the bond angles at the glycosidic linkage and the observed changes in chemical shifts displays no direct correlation between them. Somewhat smaller changes in the range of 2 to 5 ppm are observed when single crystal water molecules are close to some of the atoms. Relating the changes in the chemical shifts of the carbon atoms closest to the crystal water to the distance between them does, however, not lead to a simple relation between them. Full article

This review article aims to provide a comprehensive overview of recent FMR studies on magnetic oxide nanoparticles and their potential applications. The use of the FMR technique is a powerful tool to study the magnetic properties of magnetic nanoparticles and can provide valuable information on their behavior. For this, we will start by discussing the purpose of these magnetic nanoparticles and their application in various fields, including biomedical applications, energy storage, and environmental remediation. We will then discuss the methods used to prepare magnetic nanoparticles and the theory behind FMR including the superparamagnetic effect. Additionally, we will present the most recent studies on FMR for magnetic oxide nanoparticles by highlighting the effect of temperature and doping on the magnetic properties of these nanoparticles. Full article