Open Access
Heatable magnetic nanocomposites with Fe3O4 nanocubes
(Elsevier, 2022-09-27) Larumbe Abuin, Silvia; Lecumberri, Cristina; Monteserín, María; Fernández, Lorea; Medrano Fernández, Ángel María; Garayo Urabayen, Eneko; Gómez Polo, Cristina; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The development of magnetic self-heating polymers is an area of great interest for many applications. The intrinsic magnetic properties of the magnetic fillers play a key role in the final heating capability of these nanocomposites. Thus, it has been already reported the improvement of the heating efficiency on Fe3O4 magnetic nanocubes with respect to spherical nanoparticles with the similar mean size1. This result is due to the contribution of the magnetic anisotropy giving rise to higher magnetic coercivity and as consequence, higher SAR (Specific Absorption Rate) values. In this work, well- defined Fe3O4 nanocubes were synthesized through thermal decomposition processes with a mean particle diameter around 70 nm (TEM) (Fig. 1). The SAR values were estimated through the measurement of the AC hysteresis loops, obtaining values of around 900 W/g for the dispersion of the nanocubes in water and values of 350 W/g for the nanocubes dispersed in agar (0.5% wt), with a frequency of 403 kHz and a field amplitude of 30kA/m . In this case, the decrease of the SAR values is due to the inmovilization of the particles in the medium and hence, the Brownian movement of the particles. The temperature increase was also characterized, where a clear enhancement of the heating properties was obtained for nanocubes comparing with spherical nanoparticles of similar mean diameter (Fig. 2). Finally, the heating capacity of the nanocomposites (30% weight of magnetic nanoparticles) was studied through the application of an external AC magnetic field with a Helmholtz coil (319 kHz, 400A, 200G approximately, induction equipment model EasyHeat Ambrell). The effect of the thickness of the polymeric discs on the final temperature achieved was studied (2 and 4 mm thickness and 30 mm diameter). Thus, temperatures of 100 °C or 250 °C were reached after 2 min for the nanocomposites with thicknesses of 2 and 4 mm respectively.
Open Access
Improved photocatalytic and antibacterial performance of Cr doped TiO2 nanoparticles
(Elsevier, 2021) Gómez Polo, Cristina; Larumbe Abuin, Silvia; Gil Bravo, Antonio; Muñoz Labiano, Delia; Rodríguez Fernández, L.; Fernández Barquín, Luis; García-Prieto, Ana; Fernández-Gubieda, María Luisa; Muela, Alicia; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The effect of Cr and N doping in the adsorption capacity, photocatalytic properties and antibacterial response of TiO2 anatase nanoparticles is analyzed. The nanoparticles (N-TiO2, Cr-TiO2 and Cr/N-TiO2) were prepared by the sol-gel method. The structural (X-ray diffraction and TEM) and magnetic (SQUID magnetometry) characterization confirms the nanosized nature of the anatase nanoparticles and the absence of secondary phases. The enhancement of the adsorption capacity of the dye (methyl orange) on the surface of the catalysts for the Cr and Cr/N doped samples, together with the redshift of the UV-Vis absorbance spectra promote a high photocatalytic performance under visible light in these nanocatalysts. The culturability and viability of the Escherichia coli DH5α in a medium supplemented with the nanoparticles was characterized and compared with the evolution under visible light (both without and with nanoparticles). The results show that Cr-TiO2 nanoparticles under visible light display antibacterial activity that cannot be accounted by the toxicity of the nanoparticles alone. However the antibacterial effect is not observed in N-TiO2 and Cr/N-TiO2. The differences in the electrostatic charge (isoelectric point) and the degree of nanoparticle dispersion are invoked as the main origins of the different antibacterial response in the Cr-TiO2 nanoparticles.
Open Access
Electromagnetic vibrational harvester based on U-shaped ferromagnetic cantilever: a novel two-magnet configuration
(Elsevier, 2024-09-07) Gandía Aguado, David; Garayo Urabayen, Eneko; Beato López, Juan Jesús; Royo Silvestre, Isaac; Cruz Blas, Carlos Aristóteles de la; Tainta Ausejo, Santiago; Gómez Polo, Cristina; Ciencias; Zientziak; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika; Institute for Advanced Materials and Mathematics - INAMAT2; Institute of Smart Cities - ISC
Electromagnetic vibrational harvesters are low-cost devices featuring high-power densities and robust structures, often used for capturing the energy of environmental vibrations (civil infrastructures, transportation, human motion, etc.,). Based on Faraday's law, energy generation relies on the modification of the magnetic field distribution within a magnetic element caused by mechanical vibrations inducing an electromotive force (EMF) in a pick-up coil. However, the practical implementation of this type of vibrational harvester is currently limited due to the reduced generated power under low-frequency vibrations. In this work, an electromagnetic vibrational harvester is experimentally characterized and analyzed employing magnetic circuit analysis. The harvester consists of a ferromagnetic U-shaped cantilever, a NdFeB magnet and a ferrite magnet used as ¿magnetic tip mass¿ to enhance the magnetic flux changes under vibrations of frequency < 100 Hz. For this configuration, an experimental voltage of ¿ 1.2 V peak-to-peak (open circuit) was obtained at a resonant frequency of 77 Hz, enabling the subsequent electronic rectification stage. Additionally, Finite Element Method (FEM) is used to explore different design possibilities including the modeling of complex geometries, mechanical properties and non-linear magnetic materials, enabling the tuning of the resonance frequency from 51 to 77 Hz, keeping constant the induced voltage.
Open Access
Modulating photocatalytic activity of nitrogen doped TiO2 nanoparticles via magnetic field
(Elsevier, 2024-07-30) Gómez Polo, Cristina; Cervera Gabalda, Laura María; Garayo Urabayen, Eneko; Beato López, Juan Jesús; Pérez de Landazábal Berganzo, José Ignacio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The effect of the magnetic field on the photocatalytic activity of TiO2-based nanoparticles is analyzed using a magnetically-assisted photoreactor with permanent magnets to generate a controlled uniform magnetic field, B (¿82 mT). Nitrogen doped TiO2 nanoparticles (sizes around 10 nm) were synthesized through a solvothermal method employing Ti(IV) butoxide and HNO3 (x = 0, 0.5, 1, 1.5 and 2 mL) as precursors and their structural, optical and magnetic properties were analyzed. Specifically, nitrogen doping is confirmed through Hard X-ray Photoelectron Spectroscopy (HAXPES) in those samples synthesized with low HNO3 concentrations (x = 0.5, 1). The correlation between spin polarization (magnetic susceptibility) and visible photocatalytic activity (methyl orange as a model organic pollutant) is particularly analyzed. Surprisingly, opposite effects of the magnetic field on the photocatalytic performance are found in the visible range (above 400 nm) or under UV-Vis irradiation (decrease and increase in the photocatalytic activity, respectively, under magnetic field). The Langmuir-Hinshelwood model allows us to conclude that the strong decrease in adsorption under the magnetic field (around 42 % for x = 0.5) masks the increase in the kinetic constant (close to 58 % for x = 0.5) related mainly to the effect of Lorentz forces on the reduction of the electron-hole recombination.
Open Access
Magnetic carbon Fe3O4 nanocomposites synthesized via magnetic induction heating
(Springer Nature, 2023) Cervera Gabalda, Laura María; Gómez Polo, Cristina; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra/Nafarroako Unibertsitate Publikoa
Magnetic Induction Heating (MIH) of magnetite nanoparticles is employed as a novel synthesis procedure of carbon based magnetic nanocomposites. Magnetic nanoparticles (Fe3O4) and fructose (1:2 weight ratio) were mechanically mixed and submitted to a RF magnetic field (305 kHz). The heat generated by the nanoparticles leads to the decomposition of the sugar and to the formation of an amorphous carbon matrix. Two sets of nanoparticles, with mean diameter sizes of 20 and 100 nm, are comparatively analysed. Structural (X-ray diffraction, Raman spectroscopy, Transmission Electron Microscopy (TEM)), electrical and magnetic (resistivity, SQUID magnetometry) characterizations confirm the nanoparticle carbon coating through the MIH procedure. The percentage of the carbonaceous fraction is suitably increased controlling the magnetic heating capacity of the magnetic nanoparticles. The procedure enables the synthesis of multifunctional nanocomposites with optimized properties to be applied in different technological fields. Particularly, Cr (VI) removal from aqueous media is presented employing the carbon nanocomposite with 20 nm Fe3O4 nanoparticles.
Open Access
U-shape magnetostrictive harvester: design and experimental validation
(IEEE, 2024-07-05) Gandía Aguado, David; Garayo Urabayen, Eneko; Beato López, Juan Jesús; Royo Silvestre, Isaac; Gómez Polo, Cristina; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Electromagnetic vibrational harvesters stand out due to their high-power density, long-life robust structure and low-cost design. Moreover, they can be designed using magnetostrictive materials. The mechanical vibrations cause stress on the magnetostrictive material, leading to variations in its magnetization. This, in turn, induces an electromotive force (EMF) in a well-designed pick-up coil system, thereby transforming mechanical energy into electrical energy. In spite of the potentiality of these electromagnetic harvesters, their practical implementation is limited due to the difficulties in the design optimization in terms of the device dimensions, effective stresses on the magnetostrive material, distribution and magnetic field strength of the permanent magnets and pick-up coil characteristics. Finite Element Methods (FEM) enable the estimation of the induced voltage and thus the output power as a function of harvester design parameters, allowing us to experiment with different configurations and identify optimal parameters.
Open Access
Giant stress-impedance (GSI) sensor for diameter evaluation incylindrical elements
(Elsevier, 2018-01-01) Beato López, Juan Jesús; Vargas Silva, Gustavo Adolfo; Pérez de Landazábal Berganzo, José Ignacio; Gómez Polo, Cristina; Ingeniería; Ingeniaritza; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Gobierno de Navarra / Nafarroako Gobernua
In this work, a magnetoelastic sensor to detect the micrometer diameter variations of cylindrical elements is analyzed. A nearly zero magnetostrictive amorphous ribbon with nominal composition (Co₀.₉₃Fe₀․₀₇)₇₅Si₁₂․₅B₁₂․₅ was selected as sensor nucleus. The sensor, based on Giant Stress-Impedance (GSI), is attached (glued) along the external perimeter of the cylindrical element. Changes in the cylindrical diameter, DM, induce effective tensile stresses, S, on the ribbon, giving rise to sensitive changes in the high frequency impedance, Z. The sensor response is analyzed in terms of the relationship between the induced strains and the diameter variations, where the effect of geometrical factors (cylinder diameter and sample length) is taken into account. The results indicate that although the maximum GSI ratio depends on the pre-induced bending stresses associated to the cylindrical configuration, the sample length plays the dominant role in the sensor sensitivity. The proposed device enables to monitor the micrometric diameter variation in cylindrical elements, with a maximum strain gauge factor (GF≈-80) for low induced strains.
Open Access
A survey on the mathematical foundations of axiomatic entropy: representability and orderings
(MDPI, 2018) Campión Arrastia, María Jesús; Gómez Polo, Cristina; Induráin Eraso, Esteban; Raventós Pujol, Armajac; Estatistika, Informatika eta Matematika; Zientziak; Institute for Advanced Research in Business and Economics - INARBE; Institute for Advanced Materials and Mathematics - INAMAT2; Estadística, Informática y Matemáticas; Ciencias
Different abstract versions of entropy, encountered in science, are interpreted in the light of numerical representations of several ordered structures, as total-preorders, interval-orders and semiorders. Intransitivities, other aspects of entropy as competitive systems, additivity, etc., are also viewed in terms of representability of algebraic structures endowed with some compatible ordering. A particular attention is paid to the problem of the construction of an entropy function or their mathematical equivalents. Multidisciplinary comparisons to other similar frameworks are also discussed, pointing out the mathematical foundations.
Open Access
Fe3O4-SiO2 mesoporous core/shell nanoparticles for magnetic field-induced ibuprofen-controlled release
(American Chemical Society, 2022-12-23) García Rodríguez, Lucía; Garayo Urabayen, Eneko; López Ortega, Alberto; Galarreta Rodríguez, Itziar; Cervera Gabalda, Laura María; Cruz Quesada, Guillermo; Cornejo Ibergallartu, Alfonso; Garrido Segovia, Julián José; Gómez Polo, Cristina; Pérez de Landazábal Berganzo, José Ignacio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PJUPNA2020; Gobierno de Navarra / Nafarroako Gobernua
Hybrid magnetic nanoparticles made up of an iron oxide, Fe3O4, core and a mesoporous SiO2 shell with high magnetization and a large surface area were proposed as an efficient drug delivery platform. The core/shell structure was synthesized by two seed-mediated growth steps combining solvothermal and sol—gel approaches and using organic molecules as a porous scaffolding template. The system presents a mean particle diameter of 30(5) nm (9 nm magnetic core diameter and 10 nm silica shell thickness) with superparamagnetic behavior, saturation magnetization of 32 emu/g, and a significant AC magnetic-field-induced heating response (SAR = 63 W/gFe3O4, measured at an amplitude of 400 Oe and a frequency of 307 kHz). Using ibuprofen as a model drug, the specific surface area (231 m2/g) of the porous structure exhibits a high molecule loading capacity (10 wt %), and controlled drug release efficiency (67%) can be achieved using the external AC magnetic field for short time periods (5 min), showing faster and higher drug desorption compared to that of similar stimulus-responsive iron oxide-based nanocarriers. In addition, it is demonstrated that the magnetic field-induced drug release shows higher efficiency compared to that of the sustained release at fixed temperatures (47 and 53% for 37 and 42 °C, respectively), considering that the maximum temperature reached during the exposure to the magnetic field is well below (31 °C). Therefore, it can be hypothesized that short periods of exposure to the oscillating field induce much greater heating within the nanoparticles than in the external solution.
Open Access
Magnetically recyclable TiO2/MXene/MnFe2O4 photocatalyst for enhanced peroxymonosulphate-assisted photocatalytic degradation of carbamazepine and ibuprofen under simulated solar light
(Elsevier, 2023) Grzegórska, Anna; Ofoegbu, Joseph Chibueze; Cervera Gabalda, Laura María; Gómez Polo, Cristina; Sannino, Diana; Zielinska-Jurek, Anna; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
In this study, a novel TiO2/Ti3C2/MnFe2O4 magnetic photocatalyst with dual properties, enabling (i) improved photocatalytic degradation with PMS activation under simulated solar light and (ii) magnetic separation after the degradation process in an external magnetic field was developed and applied for the efficient photodegradation pharmaceutically active compounds (PhACs) frequently present in wastewater and surface waters worldwide. MXene was used as a Ti precursor for anatase/rutile synthesis and as a co-catalyst in the photodegradation process. Manganese ferrite with ferrimagnetic properties was coupled with the TiO2/Ti3C2 composite to facilitate the magnetic separation after the purification process in an external magnetic field. Moreover, MnFe2O4 was used for PMS activation, producing •SO4- radicals with a strong oxidation ability and higher redox potential of 2.5–3.1 V (vs. NHE) than •OH radicals with a standard oxidation–reduction potential of 2.8 V. The effect of the manganese ferrite content in the composite structure (5 wt% and 20 wt%) on the physicochemical properties and photocatalytic activity of the magnetic photocatalyst was investigated. Furthermore, the most photocatalytic active composite of TiO2/MXene/5%MnFe2O4 was used for peroxymonosulphate-assisted photocatalytic degradation of ibuprofen and carbamazepine. The effect of peroxymonosulphate concentration (0.0625 mM, 0.125 mM, and 0.25 mM) and the synergistic effect of PMS activation on photocatalytic degradation was studied. Based on the obtained results, it was found that TiO2/MXene/5%MnFe2O4/PMS process is an efficient advanced treatment technology for the oxidation of emerging contaminants that are not susceptible to biodegradation. Carbamazepine and ibuprofen were completely degraded within 20 min and 10 min of the PMS-assisted photodegradation process under simulated solar light. The trapping experiments confirmed that •SO4- and •O2- are the main oxidising species involved in the CBZ degradation, while •SO4- and h+ in the IBP degradation. Furthermore, introducing interfering ions of Na+, Ca2+, Mg2+, Cl-, and SO42– in the model seawater did not affect the removal efficiency of both pharmaceuticals. In terms of reusability, the performance of the TiO2/MXene/5%MnFe2O4/PMS photocatalyst was stable after four subsequent cycles of carbamazepine and ibuprofen degradation.