Artículos de revista INAMAT2 - INAMAT2 aldizkari artikuluak

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Open Access
UV-photoelectron spectroscopy and MS-CASPT2/CASSCF study of the thermolysis of azidoethyl-methyl sulfide: Characterization and mechanism of the formation of S-methyl-N-sulfenylethanimine
(American Institute of Physics (AIP), 2025-05-16) Algarra González, Manuel; Labat, Stephane; Rodríguez-Borges, José Enrique; Pino-González, María Soledad; Sotiropoulos, Jean Marc; Soto, Juan; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The thermal decomposition of azidoethyl methyl sulfide was studied by real-time UV-photoelectron spectroscopy (UV-PES) at temperatures ranging from 773 to 1023 K. Different ionization energies were obtained using density functional theory calculations to assign UV-PES spectra. The complete active space self-consistent field and multistate second-order perturbation methods were used to predict the formation of different species present in the thermal decomposition process. N2 and S-methyl-N-sulfenylethanimine are generated at 773 K. The first step of the reaction is the dissociation of the molecule into nitrene and nitrogen. The spin state (singlet or triplet) of nitrene formed in the first step of the reaction is temperature-dependent. At low temperatures (T ≤ 650 K), both states are formed with almost the same probability; in contrast, at high temperatures (T ≤ 1000 K), singlet nitrene is the majority intermediate. From this singlet nitrene, three stable reaction products were detected in the experiments: an imine derivative, a four-member cyclic derivative, and a sulfenyl derivative.
Open Access
Metal-free nanostructured-carbon inks for a sustainable fabrication of zinc/air batteries: from ORR activity to a simple prototype
(Wiley, 2024-08-14) Santos, Florencio; Lorca, Sebastián; González-Martínez, Juan F.; Urbina Yeregui, Antonio; Álvarez-Sánchez, Miguel A. ; González-Domínguez, José M.; García-Bordejé, Enrique; Ansón-Casaos, Alejandro; Benito, Ana M.; Maser, Wolfgang K.; Fernández Romero, Antonio J.; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Zinc/air batteries are convenient energy storage devices for both small and massive applications. While future perspectives indicate the need for low-cost components and sustainable fabrication processes, the battery performance is in part controlled by the kinetics of the oxygen reduction reaction (ORR), which typically involves transition metals as catalysts. In this context, we prepare a series of metal-free water-based carbon inks, which are tested for their catalytic performance, once deposited on a gas-diffusion substrate, in the air cathode of a simple battery prototype. The inks contain a variety of well-defined carbon nanomaterials and additives, exhibiting different physicochemical properties that critically influence the interaction with the gas diffusion hydrophobic substrate. The intrinsic ORR catalytic activity of the ink material is also analyzed on a glassy carbon electrode by the rotating ring-disc electrode (RRDE) method and specific capacitance measurements. The discharge capacity on our zinc/air battery prototype correlates well with the intrinsic catalytic activity in the RRDE. However, only the activity in the RRDE does not actually assure the performance on the commercial cathode of the prototype, since other chemical compatibility issues play a role. Thus, we highlight the importance of catalyst testing, not only on the RRDE but also under realistic device conditions.
Open Access
Compact wideband groove gap waveguide bandpass filters manufactured with 3D printing and CNC milling techniques
(MDPI, 2023-07-07) Máximo-Gutierrez, Clara; Hinojosa, Juan; Abad, José; Urbina Yeregui, Antonio; Álvarez-Melcon, Alejandro; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Zientziak
This paper presents for the first time a compact wideband bandpass filter in groove gap waveguide (GGW) technology. The structure is obtained by including metallic pins along the central part of the GGW bottom plate according to an n-order Chebyshev stepped impedance synthesis method. The bandpass response is achieved by combining the high-pass characteristic of the GGW and the low-pass behavior of the metallic pins, which act as impedance inverters. This simple structure together with the rigorous design technique allows for a reduction in the manufacturing complexity for the realization of high-performance filters. These capabilities are verified by designing a fifth-order GGW Chebyshev bandpass filter with a bandwidth BW = 3.7 GHz and return loss RL = 20 dB in the frequency range of the WR-75 standard, and by implementing it using computer numerical control (CNC) machining and three-dimensional (3D) printing techniques. Three prototypes have been manufactured: one using a computer numerical control (CNC) milling machine and two others by means of a stereolithography-based 3D printer and a photopolymer resin. One of the two resin-based prototypes has been metallized from a silver vacuum thermal evaporation deposition technique, while for the other a spray coating system has been used. The three prototypes have shown a good agreement between the measured and simulated S-parameters, with insertion losses better than IL = 1.2 dB. Reduced size and high-performance frequency responses with respect to other GGW bandpass filters were obtained. These wideband GGW filter prototypes could have a great potential for future emerging satellite communications systems.
Open Access
Optimization and modeling of ZrB2 ceramic processing by EDM for high-performance industrial applications
(Elsevier, 2025-04-11) Luis Pérez, Carmelo Javier; Torres Salcedo, Alexia; Puertas Arbizu, Ignacio; Ingeniería; Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2
This study investigates the Electrical Discharge Machining (EDM) of zirconium diboride (ZrB2), a novel conductive ceramic with exceptional properties, including high temperature resistance, excellent thermal conductivity, and remarkable hardness. These properties make ZrB2 highly suitable for extreme environments, such as aerospace and nuclear applications. To the best of our knowledge, no comprehensive studies have addressed the manufacturing of ZrB2 parts by EDM, positioning this research as a cutting-edge contribution. Two electrode materials, graphite (C) and copper-graphite (Cu–C), were used to analyze the material removal rate (MRR) and surface roughness (Ra) as functions of current intensity (I), pulse time (ti), and duty cycle (η). Multiple Linear Regression (MLR) and Artificial Neural Networks (ANN) were used to model the response variables. While MLR was effective for MRR (R2 > 0.9), ANN outperformed it in predicting Ra, especially for Cu–C electrodes (R2 = 0.9366 vs. 0.3847 for MLR). Current intensity was the most influential parameter for MRR, while pulse time significantly affected Ra. Residual analysis confirmed ANN superior accuracy for Ra, with residuals below ±1 vs. ±2 for MLR. The study culminated in the successful EDM manufacture of a ZrB2 hexagonal nut, employing optimized parameters (I = 6 A, ti = 50 μs, η = 0.3, for the C electrode) derived using ANN models and particle swarm optimization. This result demonstrates the EDM process ability to produce high-precision components with complex geometries, showcasing its versatility and industrial potential. Therefore, this study broadens the understanding of ZrB2 machinability and expands its applications in advanced technologies.
Open Access
Passive heating and cooling of photovoltaic greenhouses including thermochromic materials
(MDPI, 2021-01-15) Padilla, Javier; Toledo, Carlos; López-Vicente, Rodolfo; Montoya, Raquel; Navarro, José-Ramón; Abad, José; Urbina Yeregui, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The integration of photovoltaic technologies into greenhouse envelopes appears to be an innovative and environmentally-friendly way to supply their various energy demands. However, the effect on the inner growing conditions, especially on the temperature, must be assessed in order to effectively implement this solution. In this study, experimental temperature data were obtained over two years for four structures built with different photovoltaic technologies (mono-crystalline silicon, amorphous silicon, cadmium telluride, and an organic polymeric technology) and fitted to a thermal model in order to provide a comprehensive analysis of their potential utilization as a cover material in greenhouses. Additionally, the thermal effect of color in structures composed of several common construction materials (brick, wood, plasterboard and glass) was quantified and modelled, supplementing the thermal analysis of passive solutions for this application. In all cases, inner and ambient temperature differences of up to +20 °C, created by a passive heating effect during the day, and – 5 °C, created by a passive cooling effect during the night, have been observed, suggesting the use of the photovoltaic modules with different degrees of structure coverage, complemented with the color tuning of the modules themselves as passive methods to control the temperature and light spectrum of greenhouses.
Open Access
Short vs. long-distance avocado supply chains: life cycle assessment impact associated to transport and effect of fruit origin and supply conditions chain on primary and secondary metabolites
(MDPI, 2022-06-19) Pedreschi, Romina; Ponce, Excequel; Hernández, Ignacia; Fuentealba, Claudia; Urbina Yeregui, Antonio; González-Fernández, José J.; Hormaza, José I.; Campos, David; Chirinos, Rosana; Aguayo, Encarna; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Avocado consumption and trade are increasing worldwide, with North America and Europe being the main importing regions. Spain is the major European avocado producer (90% of the production), yet it only supplies 10% of the market. Consequently, more than 90% of the avocados consumed in Europe are imported from overseas, mainly from Chile and Peru. In this work, the Life Cycle Assessment (LCA) impact associated with the transport of two avocado supply chains (short (Spanish) and long (Chilean)) and the effect of the fruit origin and distance of both chains on primary and secondary metabolites from harvest to edible ripeness were evaluated using a gas chromatography-mass spectrometry (GC-MS) and liquid chromatography coupled to diode array detection (LC-DAD) based metabolite analysis. The LCA transport impact of the fresh supply chain from production centers in Chile (Quillota) and Spain (Malaga), and then the distribution to several cities in Europe, suggested road export from Spain to European capitals to have the lowest impact (0.14 to 0.22 kg CO2 eq/kg of avocado). When export from Chile was considered, the option of oceanic freight to European ports closer to final destinations was clearly a better option (0.21 to 0.26 kg CO2 eq/kg) than via the Algeciras port in Spain followed by road transport to final destinations in European capitals (0.34 to 0.43 kg CO2 eq/kg), although the situation could be somewhat different if the avocados are transported from the destination ports in northern Europe to long-distance capitals in other European countries. Fruit origin had a significant impact on avocado primary and secondary metabolites. The conditions of the supply chain itself (10 d in cold storage in regular conditions vs. 30 d cold storage + controlled atmosphere conditions) largely influence the fate of some metabolites that certainly affect the pool of metabolites at edible ripeness. The long-assumed hypothesis that the longer the supply chain the more negative impact on nutritional and functional compounds might not hold in this case, as long as transport conditions are adequate in terms of temperature, atmosphere conditions, and time considering distance from origin to destination.
Open Access
Fast calculation methods for the magnetic field of particle lattices
(AIP Publishing, 2025-02-14) Royo Silvestre, Isaac; Gandía Aguado, David; Beato López, Juan Jesús; Garayo Urabayen, Eneko; Gómez Polo, Cristina; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
With the rise of 3D printing and composite materials, components comprising dispersed magnetic particles have become more interesting due to the possibility to design magnetic elements of any shape with varying amounts of the actual magnetic material. However, quick and easy calculation methods are needed to design these components enabling the selection of the optimum required percentage of magnetic particles (millimeter parts contain billions of micro-sized particles). This work proposes a semi-analytical iterative method for the estimation of the magnetic field generated by magnetic composites formed by embedded magnetic particles. The model is compared in terms of accuracy and calculation speed with finite element analysis and the average magnetization model of the magnetic composite. The results are finally supported by the comparison with experimental measurements of the weak magnetic field generated by a magnetic particle lattice.
Open Access
How the pretreatment temperature of zeolitic catalysts can affect the reaction temperature of methanol to olefins and gasoline processes
(MDPI, 2025-03-20) Yunes, Simón; Rosas, Abel Gaspar; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The dehydration of methanol to produce light olefins and gasoline, known as MTO (methanol-to-olefins) process requires acidic catalysts that maintain their acidity at reaction temperatures. Zeolites, such as SAPOs and ZSM-5, are commonly used for this purpose due to their acidic centers. The initial step in these experiments involves the activation or pretreatment of these solids to remove physically adsorbed water from their pores. Inadequate pretreatment can lead to the destruction of the existing Brönsted sites through the dihydroxylation of surface -OH groups. Therefore, it is crucial to pretreat the zeolites properly to preserve the Brönsted sites. One method is to subject the fresh catalyst to programmed dehydration, which involves desorption at a controlled temperature while monitoring the appearance of water that results from Brönsted site dihydroxylation. The temperature at which the dehydration peak appears determines the optimal reaction temperature. The results presented in this work will demonstrate the progressive deactivation of the catalysts when the reaction temperature exceeds 400 °C.
Open Access
Quest for amorphous superconductors of Bi-Sb alloys by irradiation with swift heavy ions
(AIP Publishing, 2025-03-17) Andrino-Gómez, Alberto; Tabares, Gema; Moratalla, Manuel ; Redondo-Cubero, Andrés; Madurga Pérez, Vicente; Favieres Ruiz, Cristina; Vergara Platero, José; García-López, Gastón; Gordillo, Nuria; Ramos, Miguel Ángel ; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Crystalline Bi100−xSbx alloys are known as the first discovered topological insulators, as well as for their promising thermoelectric properties, while their amorphous counterparts exhibit superconductivity (Tc > 6 K). However, their strong tendency to crystallize has hindered both the study and practical applications of amorphous Bi and Bi–Sb alloys. To explore the possibility of obtaining amorphous superconducting phases and enhancing thermoelectric properties, we investigated ion-beam irradiation as a method to induce amorphization in Bi100−xSbx alloys. We report irradiation experiments on pure Bi and Bi100−xSbx using bismuth and iodine ions (tens of MeV), generating an estimated vacancy damage of 40%–80%. Structural characterization and electrical resistivity measurements (2–300 K) revealed that, while amorphization and superconductivity were not achieved, melt-spun samples exhibited an order of magnitude higher conductivity than thermally evaporated ones. Moreover, ion-induced disorder further improved electrical conductivity, particularly in Bi90Sb10, highlighting its potential for thermoelectric applications.
Open Access
Highly selective CO formation via CO2 hydrogenation over novel ceria-based high-entropy oxides (HEOs)
(Elsevier, 2025-03-01) Cortázar, María; Lafuente Adiego, Marta; Navarro Puyuelo, Andrea; García, Xènia; Llorca Piqué, Jordi; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the present study, new ceria-based high-entropy oxides (HEOs) were investigated as CO2 hydrogenation catalysts. The nominal composition was (Ce0.5Ni0.1Co0.1Cu0.1Zn0.1Mg0.1)Ox and the synthesis was accomplished through the citrate complexing sol-gel method. Characterization techniques utilized including ICP-AES, in situ XRD and in situ XPS, SEM-EDS, HR-TEM and HAADF-STEM, Raman spectroscopy, H2-TPR, CO2-TPD and N2 physical adsorption. The physicochemical characterization and the catalytic results revealed that the conditions of the thermal treatments at which the oxides were subjected critically determined the catalytic performance, especially the CO2 hydrogenation products selectivities. Calcination in air and/or reduction in hydrogen conducted at temperatures below 500 °C led to active but poorly selective catalysts that produced both methane and CO with significant yields. This was mainly attributed to the presence of metallic Cu, Ni and Co on the catalysts that appeared to be supported on ceria doped with the rest of the formulation elements. In contrast, thermal treatments at 750 °C favored the formation of a rocksalt entropy-stabilized (NiCoCuZnMg)Ox HEO supported on ceria that has stood out for showing an excellent selectivity towards the reverse water¿gas shift (RWGS) reaction. This catalyst led to CO selectivities of almost 100 % over a very wide range of reaction temperatures (300-700 °C). Long-term stability tests (100 h) showed only a slight decrease in CO2 conversion, while CO selectivity remained stable at nearly 100 % at 400 °C. XRD characterization of the used catalysts evidenced that, whereas the basic catalyst structure remained, some metallic copper exsolved during reduction and reaction period. These results are relevant and very promising, opening a door to the development of new catalysts for the valorization of CO2 through the RWGS reaction, thus expanding the low-temperature limit at which this process can be carried out selectively.
Embargo
Photodegradation of paracetamol on CaAlGa and ZnAlTi mixed metal oxides (MMO) synthesized via LDH from Al-saline slags
(Elsevier, 2025-03-27) Jiménez, Alejandro; Guerra, Miguel; Pascual, Dana; Trujillano, Raquel; Rives, Vicente; Vicente, Miguel Ángel; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Preparation of CaAlGa and ZnAlTi mixed metal oxides (MMO) synthesized via CaAlGa–hydrocalumites and ZnAl–hydrotalcite impregnated with TiO2 using saline slags as aluminum source, is reported for the first time. The solids obtained by calcination at 750 ºC are highly crystalline and the photocatalytically active crystalline phases Ca12Al14-xGaxO33, ZnO, ZnAl2O4 and Zn2TiO4 have been identified. The MMO were used for the catalytic degradation of paracetamol under UV irradiation, obtaining good results for the removal of this emerging pollutant, reaching a removal above 90 % for the sample containing 25 % Ga3 +, under the optimum photodegradation conditions ([Paracetamol]0 = 40 mg/L and catalyst dose = 1 g/L), showing better results than the commercial photocatalyst TiO2–P25 from Degussa and other more complex catalysts based on MMO. In addition, this photocatalyst was submitted to a cyclic process study, finding that it maintained its performance after at least two cycles.
Embargo
Modified rule of mixtures and Halpin-Tsai models applied to PCL/NiMnInCo 4D printed composites. Internal stresses study during the martensitic transformation.
(Elsevier, 2025-05-26) Lambri, Fernando Daniel; Bonifacich, Federico Guillermo; Lambri, Osvaldo Agustín; Weidenfeller, B.; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
4D printing enables the manufacturing of complex smart components in a wide variety of shapes. In devices based on 4D printed composite materials, the interaction between the active microparticles and the printable polymer matrix plays a critical role for the optimal functionality. Key parameters in these materials are the elastic misfit coefficient, which monitors internal stresses, and elastic energy transfer, which determines the ability to transfer strain from the microparticles to the surrounding matrix. In this work, the temperature-dependent shear modulus of PCL/Ni45Mn36.7In13.3Co5 4D printed composites is analysed using the modified rule of mixture (ROM) and Halpin-Tsai (HT) models. The molecular flow caused by the polymer chain movement under oscillatory mechanical stress at relatively elevated temperatures is examined and discussed using these models. Additionally, the effect of an external direct magnetic field on the shear modulus is also analysed. Finally, the internal stresses in the composite materials resulting from the martensitic transformation in the active microparticles are studied through a modified mean-field model based on the Eshelby's inclusion theory.
Open Access
Bio-oil fractionation according to polarity and molecular size: characterization and application as antioxidants
(American Chemical Society, 2024-12-21) Fonts, Isabel; Lázaro, Cristina; Cornejo Ibergallartu, Alfonso; Sánchez, José Luis; Afailal, Zainab; Gil-Lalaguna, Noemí; Arauzo, Jesús María; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Gobierno de Navarra / Nafarroako Gobernua
Bio-oil obtained from biomass pyrolysis has great potential for several applications after being upgraded and refined. This study established a method for separating bio-oil into different fractions based on polarity and molecular size to extract phenolic and polyphenolic compounds with antioxidant properties. The fractions were analyzed using various spectroscopic and chromatographic techniques, such as GC/MS, FTIR, UV-vis, SEC, DOSY-NMR, 13C-NMR, and 31P-NMR. The antioxidant properties of these fractions were tested by examining their ability to improve the oxidative stability of biodiesel. The results strongly connected the bio-oil's chemical functionalities and antioxidant power. During solvent fractionation, dichloromethane could extract phenolic structures, which were subsequently size-fractionated. The subfractions with lower molecular weight (in the order of monomers and dimers) outperformed the antioxidant potential of the crude bio-oil. Heavier subfractions from dichloromethane extraction did not show good antioxidant abilities, which was related to the low hydroxy group content. After solvent extraction, phenolic oligomers remained in the water-insoluble/dichloromethane-insoluble fraction, which showed good antioxidant potential despite its low solubility in biodiesel.
Open Access
Sintered glass filter as a membrane impregnated with g-C3N4 and AuAg/g-C3N4 to degrade rhodamine B with application in decentralized areas
(Elsevier, 2024-10-19) Sabogal-Paz, Lyda Patricia; Souza Freitas, Bárbara Luíza; Hoffmann, Maria Teresa; Royo-Pareja, David; López de Luzuriaga Fernández, José Manuel; Monge Oroz, Miguel; Santamaría Arana, Leticia; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Zientziak
This work shows a novel approach utilizing graphitic carbon nitride (g-C3N4) deposited on a sintered glass filter as a membrane enhanced with gold-silver nanoparticles for the removal of emerging pollutants. g-C3N4 was synthesized directly onto the membrane surface with a simple vapor deposition method. Membranes with two different porosities, g-C3N4 and the noble-metal nanoparticles were put to the test by exploring their photocatalytic capacity to degrade rhodamine B dye (RhB). FT-IR, PL, SEM, EDX and DRS characterization techniques were performed to analyse the catalysts. RhB degradation was tested in static (i.e. petri dish) and dynamic conditions (i.e. photocatalytic membrane setup). Filtered volumes, turbidity effect and stability were tested in dynamic conditions for the membrane that had the greatest potential for full-scale use. The results confirm the efficient RhB degradation capacity of the catalysts, highlighting the potential of this proposed setup; however, the cost of technology for decentralized areas is still an impediment. These findings not only contribute to advancing the understanding of pollutant removal technologies, but also, offer practical insights into the future deployment of such systems on a larger scale.
Open Access
The uniqueness of unconditional basis of the 2-convexified Tsirelson space, revisited
(Springer, 2024-10-13) Albiac Alesanco, Fernando José; Ansorena, José L.; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
One of the hallmarks in the study of the classification of Banach spaces with a unique (normalized) unconditional basis was the unexpected result by Bourgain, Casazza, Lindenstrauss, and Tzafriri from their 1985 Memoir that the 2-convexified Tsirelson space T(2) had that property (up to equivalence and permutation). Indeed, on one hand, finding a “pathological” space (i.e., not built out as a direct sum of the only three classical sequence spaces with a unique unconditional basis) shattered the hopeful optimism of attaining a satisfactory description of all Banach spaces which enjoy that important structural feature. On the other hand it encouraged furthering a research topic that had received relatively little attention until then. After forty years, the advances on the subject have shed light onto the underlying patterns shared by those spaces with a unique unconditional bases belonging to the same class, which has led to reproving the original theorems with fewer technicalities. Our motivation in this note is to revisit the aforementioned result on the uniqueness of unconditional basis of T(2) from the current state-of-art of the subject and to fill in some details that we missed from the original proof.
Embargo
Twenty-five years of greedy bases
(Elsevier, 2024-12-21) Albiac Alesanco, Fernando José; Ansorena, José L.; Temlyakov, Vladimir; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika; Institute for Advanced Materials and Mathematics - INAMAT2
Although the basic idea behind the concept of a greedy basis had been around for some time, the formal development of a theory of greedy bases was initiated in 1999 with the publication of the article [S.V. Konyagin and V.N. Temlyakov, A remark on greedy approximation in Banach spaces, East J. Approx. 5 (3) (1999), 365-379]. The theoretical simplicity of the thresholding greedy algorithm became a model for a procedure widely used in numerical applications and the subject of greedy bases evolved very rapidly from the point of view of approximation theory. The idea of studying greedy bases and related greedy algorithms attracted also the attention of researchers with a classical Banach space theory background. From the more abstract point of functional analysis, the theory of greedy bases and its derivates evolved very fast as many fundamental results were discovered and new ramifications branched out. Hundreds of papers on greedy-like bases and several monographs have been written since the appearance of the aforementioned foundational paper. After twenty-five years, the theory is very much alive and it continues to be a very active research topic both for functional analysts and for researchers interested in the applied nature of nonlinear approximation alike. This is why we believe it is a good moment to gather a selection of 25 open problems (one per year since 1999!) whose solution would contribute to advance the state of art of this beautiful topic.
Open Access
Visible-light-driven photocatalytic degradation of organic dyes using a TiO2 and waste-based carbon dots nanocomposite
(Elsevier, 2025-02-25) Sendão, Ricardo M.S.; Algarra González, Manuel; Lázaro-Martínez, Juan; Brandão, Ana T.S.C.; Gil Bravo, Antonio; Pereira, Carlos; Esteves da Silva, Joaquim C.G.; Pinto da Silva, Luís; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Herein we report a visible-light-active photocatalytic nanocomposite (NC50:50) prepared from carbon dots (CDs) and TiO2 nanoparticles, which was applied to the photodegradation of organic dyes in water. The CDs incorporated corn stover, a major agricultural waste, and were prepared via hydrothermal treatment. Using a visible-light irradiation source and the dye methylene blue as a representative of the organic dyes class, we observed that a 374% enhancement of the catalytic performance was achieved by adding CDs relative to bare TiO2. This was possible due to increased visible-light absorption and better photonic efficiency. Tests using reactive species scavengers indicated that three active species (superoxide anion, hydroxyl radicals, and electrons) were responsible for the photodegradation process, differing from bare TiO2 in which only the hydroxyl radical has a relevant role. Photocatalytic degradation was also observed toward Rhodamine B, Orange II and Methyl Orange. Finally, we performed a life cycle assessment (LCA) study to assess and analyse the associated environmental impacts of NC50:50 compared with other alternatives, which revealed that NC50:50 is the alternative resulting in the least environmental impacts. In summary, NC50:50 could, under visible-light irradiation, efficiently remove different organic dyes while incorporating organic waste materials and reducing the impacts associated with their use. We expect that this study provides a base for a more environmentally sustainable design of visible-light-active photocatalysts via waste upcycling.
Open Access
Comparative study of electrospun polydimethylsiloxane fibers as a substitute for fluorine-based polymeric coatings for hydrophobic and icephobic applications
(MDPI, 2024-11-30) Vicente Gómara, Adrián; Rivero Fuente, Pedro J.; Santos, Cleis; Rehfeld, Nadine; Rodríguez Trías, Rafael; Ingeniería; Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Univertsitate Publikoa, PJUPNA1929
The development of superhydrophobic, waterproof, and breathable membranes, as well as icephobic surfaces, has attracted growing interest. Fluorinated polymers like PTFE or PVDF are highly effective, and previous research by the authors has shown that combining these polymers with electrospinning-induced roughness enhances their hydro- and ice-phobicity. The infusion of these electrospun mats with lubricant oil further improves their icephobic properties, achieving a slippery liquid-infused porous surface (SLIPS). However, their environmental impact has motivated the search for fluorine-free alternatives. This study explores polydimethylsiloxane (PDMS) as an ideal candidate because of its intrinsic properties, such as low surface energy and high flexibility, even at very low temperatures. While some published results have considered this polymer for icephobic applications, in this work, the electrospinning technique has been used for the first time for the fabrication of 95% pure PDMS fibers to obtain hydrophobic porous coatings as well as breathable and waterproof membranes. Moreover, the properties of PDMS made it difficult to process, but these limitations were overcome by adding a very small amount of polyethylene oxide (PEO) followed by a heat treatment process that provides a mat of uniform fibers. The experimental results for the PDMS porous coating confirm a hydrophobic behavior with a water contact angle (WCA) ≈ 118° and roll-off angle (αroll-off) ≈ 55°. In addition, the permeability properties of the fibrous PDMS membrane show a high transmission rate (WVD) ≈ 51.58 g∙m−2∙d−1, providing breathability and waterproofing. Finally, an ice adhesion centrifuge test showed a low ice adhesion value of 46 kPa. These results highlight the potential of PDMS for effective icephobic and waterproof applications.
Embargo
Sustainable biomass-derived activated biochar/polyaniline/alginate composite beads for enhanced methylene blue adsorption: experimental and theoretical investigations
(Elsevier, 2025-02-25) Benamraoui, Faouzia; Kecir, Imene; Hechaichi, Chaima; Bourzami, Riahd; Boulahbal, Aziza Imene; Gil Bravo, Antonio; Boutahala, Mokhtar; Bounoukta, Charf Eddine; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
This study investigates biomass-derived adsorbents in powder and bead forms for the efficient removal of methylene blue MB from wastewater. Activated biochar powders (ABC and ABCZ) were synthesized using H3PO4 and ZnCl2 as activators for the chemical treatment of Crataegus azarolus CAS seed waste, while polyaniline (PA) and sodium alginate (SG) were integrated to form two bead-shaped composites. Compared to ZnCl2, H3PO4 activation produced similar acidic site concentrations but resulted in improved mesoporosity and larger pore diameters. Untreated lignin-like ABC and PA-functionalized ABC were successfully encapsulated into uniform composite beads (ABC-SG and ABC-PA-SG) with negatively charged surfaces at neutral pH of solution as confirmed by FTIR, TGA, and pHpzc analyses. Adsorption efficiency depended on material composition, form, and texture. Encapsulation significantly enhanced MB adsorption capacity, with ABC-PA-SG beads achieving 821 mg/g, compared to 261 mg/g for ABC powder. While greater surface area improved MB adsorption in powders, PA incorporation in composite beads contributed to higher adsorption performance. Kinetic modeling showed that MB adsorption on ABC powder was governed by chemisorption and pores filling, while composite beads followed a physical interaction-driven process. Thermodynamic analysis confirmed that adsorption was spontaneous and endothermic. Statistical modeling and DFT calculations provided deeper insights into the adsorption mechanisms. π-π interactions dominated MB adsorption, with a horizontal molecular arrangement. ABC powders exhibited multilayer pore filling on a heterogeneous surface, whereas adsorption on ABC-PA-SG beads followed a double-energy double-layer mechanism. This study provides integrated insights into biomass-derived composite beads adsorbents, highlighting their potential for sustainable wastewater treatment applications.
Open Access
Antibacterial performance of Co-Zn ferrite nanoparticles under visible light irradiation
(Wiley, 2024-11-20) Gubieda, Alicia G.; Abad-Díaz-de-Cerio, Ana; García-Prieto, Ana; Fernández-Gubieda, María Luisa; Cervera Gabalda, Laura María; Ordoqui Huesa, Eduardo; Cornejo Ibergallartu, Alfonso; Gómez Polo, Cristina; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
BACKGROUND: To address water scarcity and promote sustainable resource management, more efficient and cost-effective water treatment solutions are necessary. Particularly, pathogens in drinking water are a topic of growing concern. One promising technology is the use of photocatalytic nanoparticles activated by visible light as antibacterial agents. This study focuses on the characterization and antibacterial properties of Co-Zn ferrite nanocatalysts, tested against Escherichia coli. RESULTS: The CoxZn1¿xFe2O4 (x = 0, 0.1, 0.4 and 0.6) ferrites were synthesized by the co-precipitation method. Structural, morphological and optical analyses confirmed that these nanoparticles have a cubic spinel structure, with sizes of around 10 nm, and band gap energies suitable for visible light activation (1.4¿1.7 eV). The antibacterial efficacy of the nanoparticles against E. coli was tested and compared with their photocatalytic performance employing phenol as organic pollutant model (highest phenol degradation for x = 0.6). Specifically, the antibacterial capacity of these nanoparticles was evaluated by comparing the ability of bacteria to grow after being incubated with the nanoparticles under visible light and in the dark. It was found that nanoparticles with lower cobalt content (x = 0 and 0.1) significantly reduced bacterial culturability under visible light. Transmission Electron Microscopy analysis revealed that nanoparticles with cobalt content caused bacteria to secrete biofilm, potentially offering some protection against the nanoparticles. CONCLUSION: ZnFe2O4 nanoparticles show the highest antibacterial effect amongst those tested. This is attributed to the combined action of Zn2+ ion release and the photocatalytic effect under visible light. Furthermore, Zn might inhibit protective biofilm secretion, leading to higher antibacterial effects.