Harnessing Ti3C2-WS2 nanostructures as efficient energy scaffoldings for photocatalytic hydrogen generation

Two-dimensional (2D) Ti3C2 MXene have attracted a lot of attention as frontier materials for the development of effective photocatalysts that can transform solar energy into chemical energy, which is essential for water splitting to produce hydrogen. Here, we use first principle calculations to understand the structural, electronic, and vibrational features of a novel heterostructure comprising a monolayer of tungsten disulfide (WS2) and titanium carbide (Ti3C2) MXene. Our theoretical calculations revealed that the Ti3C2 maximizes the interfacial contact area with the WS2 monolayer creating a strong p–-d hybridization for the WS2/Ti3C2 heterostructure. As a result, a well-constructed Schottky junction is enabled, facilitating an interconnected electron pathway across the interface which is conducive for an efficient photocatalytic performance. Further, the experimentally designed WS2/Ti3C2 heterostructure and its photocatalytic activity based on the synergistic action between MXene and WS2 is investigated. Optical properties calculated are compared with experimental data derived from UV–Visible spectroscopy. The excellent conductivity and stability along with the light absorption in the visible region of WS2/Ti3C2 enhances the photocatalytic performance approaching photocurrent densities of ~33 and 120 μA/ cm2 in the HER and OER region, respectively. Overall, the present research not only improves our understanding of WS2/Ti3C2 heterostructure for an improved photocatalytic activity, but also provides an efficient method toward sustainable hydrogen productionUniversidade de Vigo/CISUGUniversidade de Vigo/CISU

Ferromagnetic elements in two‐dimensional materials: 2D magnets and beyond

Ferromagnetism in 2D materials has attracted tremendous interest from the scientific community thanks to its potential for the design of magnetic materials with unique properties. The presence of a ferromagnetic element in a 2D material can improve the existing properties and offer new ones, giving rise to the development of manifold applications. This review focuses on recent advances and perspectives of 2D materials that bear at least one ferromagnetic element (iron, cobalt, nickel) as i) structural constituent, ii) dopant atom, or iii) adjacent atom through proximity effect. By describing in detail the magnetic properties that have emerged so far, their potential to form next‐generation 2D magnets is discussed. Moreover, the contribution of such 2D materials is analyzed in various applications (electrochemical, photochemical, optical, and electronic), aiming to explore further functionalities and capabilities of ferromagnetic elements, apart from their magnetic nature. Special attention is given to gadolinium and other rare earth elements that display a ferromagnetic order even at ultra‐low temperatures and form part of 2D structured materials, with particularly appealing properties deriving from their 4f electrons.Agencia Estatal de Investigación | Ref. PID2020‐117371RA‐I00Agencia Estatal de Investigación | Ref. TED2021‐131628A‐I00Xunta de Galicia | Ref. ED431F2021/05Agencia Estatal de Investigación | Ref. RYC2018-026103-IUniversidade de Vigo/CISU

Impact of Coated Zinc Oxide Nanoparticles on Photosystem II of Tomato Plants

Zinc oxide nanoparticles (ZnO NPs) have emerged as a prominent tool in agriculture. Since photosynthetic function is a significant measurement of phytotoxicity and an assessment tool prior to large-scale agricultural applications, the impact of engineered irregular-shaped ZnO NPs coated with oleylamine (ZnO@OAm NPs) were tested. The ZnO@OAm NPs (crystalline size 19 nm) were solvothermally prepared in the sole presence of oleylamine (OAm) and evaluated on tomato (Lycopersicon esculentum Mill.) photosystem II (PSII) photochemistry. Foliar-sprayed 15 mg L−1 ZnO@OAm NPs on tomato leaflets increased chlorophyll content that initiated a higher amount of light energy capture, which resulted in about a 20% increased electron transport rate (ETR) and a quantum yield of PSII photochemistry (ΦPSII) at the growth light (GL, 600 μmol photons m−2 s−1). However, the ZnO@OAm NPs caused a malfunction in the oxygen-evolving complex (OEC) of PSII, which resulted in photoinhibition and increased ROS accumulation. The ROS accumulation was due to the decreased photoprotective mechanism of non-photochemical quenching (NPQ) and to the donor-side photoinhibition. Despite ROS accumulation, ZnO@OAm NPs decreased the excess excitation energy of the PSII, indicating improved PSII efficiency. Therefore, synthesized ZnO@OAm NPs can potentially be used as photosynthetic biostimulants for enhancing crop yields after being tested on other plant species

Nanocapsules of ZnO Nanorods and Geraniol as a Novel Mean for the Effective Control of Botrytis cinerea in Tomato and Cucumber Plants

Inorganic-based nanoparticle formulations of bioactive compounds are a promising nanoscale application that allow agrochemicals to be entrapped and/or encapsulated, enabling gradual and targeted delivery of their active ingredients. In this context, hydrophobic ZnO@OAm nanorods (NRs) were firstly synthesized and characterized via physicochemical techniques and then encapsulated within the biodegradable and biocompatible sodium dodecyl sulfate (SDS), either separately (ZnO NCs) or in combination with geraniol in the effective ratios of 1:1 (ZnOGer1 NCs), 1:2 (ZnOGer2 NCs), and 1:3 (ZnOGer2 NCs), respectively. The mean hydrodynamic size, polydispersity index (PDI), and ζ-potential of the nanocapsules were determined at different pH values. The efficiency of encapsulation (EE, %) and loading capacity (LC, %) of NCs were also determined. Pharmacokinetics of ZnOGer1 NCs and ZnOGer2 NCs showed a sustainable release profile of geraniol over 96 h and a higher stability at 25 ± 0.5 °C rather than at 35 ± 0.5 °C. ZnOGer1 NCs, ZnOGer2 NCs and ZnO NCs were evaluated in vitro against B. cinerea, and EC50 values were calculated at 176 μg/mL, 150 μg/mL, and > 500 μg/mL, respectively. Subsequently, ZnOGer1 NCs and ZnOGer2 NCs were tested by foliar application on B. cinerea-inoculated tomato and cucumber plants, showing a significant reduction of disease severity. The foliar application of both NCs resulted in more effective inhibition of the pathogen in the infected cucumber plants as compared to the treatment with the chemical fungicide Luna Sensation SC. In contrast, tomato plants treated with ZnOGer2 NCs demonstrated a better inhibition of the disease as compared to the treatment with ZnOGer1 NCs and Luna. None of the treatments caused phytotoxic effects. These results support the potential for the use of the specific NCs as plant protection agents against B. cinerea in agriculture as an effective alternative to synthetic fungicides

Synthesis and electrical characterization of monocrystalline nickel nanorods and Ni-CNT composites

Aerospace vessels require electrically conductive, light weight frames to minimize damage from electromagnetic radiation, electrostatic discharge and lightning strikes while economizing fuel. Nickel nanowires and hybrid nickel-carbon nanotube materials are suitable nanostructures to ensure high conductivity at low mass loading. Monocrystalline nickel structures have even better conduction properties than the polycrystalline equivalent due to possessing less particle-particle junctions. We have developed a solutionbased method that produces monocrystalline nickel nanowires via the decomposition of metalorganic precursors in the presence of self-assembled surfactants. The resulting wires are approximately 20 nm wide by 1.5 µm in length. These wires have a morphology consisting of semi-flattened rods with pyramidal ends. Despite the changing dimensions between the nanorod body and its head, there was no disruption in the crystallographic orientation, as observed with HRTEM and diffraction patterns. The nickel nanostructures were exposed to air for several weeks, but no oxidation was detectable by magnetic measurement, i.e. the saturation magnetization corresponds to Ni0 and no bias is observed in the hysteresis loops. It seems that the long alkyl chain amine surfactant, in addition to being a structuration agent, remains at the surface of the Ni wires after washing and acts as a protective layer. The magnetic field around Ni nanowires was imaged using electron holography. Each Ni wire is a magnetic monodomain. Routes to prepare hybrid nickel-CNT materials were explored using chemical vapor deposition in a fluidized bed, solution chemistry and dry preparation in a Fisher-Porter reactor. Different nickel compositions and material morphologies resulted, depending on the preparation technique. The nickel nanorods and hybrid materials were incorporated into carbon fiber-reinforced polymer composites. The electrical conductivity as a function of wt% loading was measured, showing promise for these materials in discharging electrostatic charges

Heat-Up Colloidal Synthesis of Shape-Controlled Cu-Se-S Nanostructures-Role of Precursor and Surfactant Reactivity and Performance in N Electroreduction

Copper selenide-sulfide nanostructures were synthesized using metal-organic chemical routes in the presence of Cu- and Se-precursors as well as S-containing compounds. Our goal was first to examine if the initial Cu/Se 1:1 molar proportion in the starting reagents would always lead to equiatomic composition in the final product, depending on other synthesis parameters which affect the reagents reactivity. Such reaction conditions were the types of precursors, surfactants and other reagents, as well as the synthesis temperature. The use of 'hot-injection' processes was avoided, focusing on 'non-injection' ones; that is, only heat-up protocols were employed, which have the advantage of simple operation and scalability. All reagents were mixed at room temperature followed by further heating to a selected high temperature. It was found that for samples with particles of bigger size and anisotropic shape the CuSe composition was favored, whereas particles with smaller size and spherical shape possessed a CuSe phase, especially when no sulfur was present. Apart from elemental Se, AlSe was used as an efficient selenium source for the first time for the acquisition of copper selenide nanostructures. The use of dodecanethiol in the presence of trioctylphosphine and elemental Se promoted the incorporation of sulfur in the materials crystal lattice, leading to Cu-Se-S compositions. A variety of techniques were used to characterize the formed nanomaterials such as XRD, TEM, HRTEM, STEM-EDX, AFM and UV-Vis-NIR. Promising results, especially for thin anisotropic nanoplates for use as electrocatalysts in nitrogen reduction reaction (NRR), were obtained

Enhanced detoxification of Cr6+ by Shewanella oneidensis via adsorption on spherical and flower-like manganese ferrite nanostructures

Maximizing the safe removal of hexavalent chromium (Cr6+) from waste streams is an increasing demand due to the environmental, economic and health benefits. The integrated adsorption and bio-reduction method can be applied for the elimination of the highly toxic Cr6+ and its detoxification. This work describes a synthetic method for achieving the best chemical composition of spherical and flower-like manganese ferrite (MnxFe3-xO4) nanostructures (NS) for Cr6+ adsorption. We selected NS with the highest adsorption performance to study its efficiency in the extracellular reduction of Cr6+ into a trivalent state (Cr3+) by Shewanella oneidensis (S. oneidensis) MR-1. MnxFe3-xO4 NS were prepared by a polyol solvothermal synthesis process. They were characterised by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), dynamic light scattering (DLS) and Fourier transform-infrared (FTIR) spectroscopy. The elemental composition of MnxFe3-xO4 was evaluated by inductively coupled plasma atomic emission spectroscopy. Our results reveal that the oxidation state of the manganese precursor significantly affects the Cr6+ adsorption efficiency of MnxFe3-xO4 NS. The best adsorption capacity for Cr6+ is 16.8 ± 1.6 mg Cr6+/g by the spherical Mn0.22+Fe2.83+O4 nanoparticles at pH 7, which is 1.4 times higher than that of Mn0.8Fe2.2O4 nanoflowers. This was attributed to the relative excess of divalent manganese in Mn0.22+Fe2.83+O4 based on our XPS analysis. The lethal concentration of Cr6+ for S. oneidensis MR-1 was 60 mg L-1 (determined by flow cytometry). The addition of Mn0.22+Fe2.83+O4 nanoparticles to S. oneidensis MR-1 enhanced the bio-reduction of Cr6+ 2.66 times compared to the presence of the bacteria alone. This work provides a cost-effective method for the removal of Cr6+ with a minimum amount of sludge production

Palladium nanoparticle-loaded cellulose paper: a highly efficient, robust, and recyclable self-assembled composite catalytic system

We present a novel strategy based on the immobilization of palladium nanoparticles (Pd NPs) on filter paper for development of a catalytic system with high efficiency and recyclability. Oleylamine-capped Pd nanoparticles, dispersed in an organic solvent, strongly adsorb on cellulose filter paper, which shows a great ability to wick fluids due to its microfiber structure. Strong van der Waals forces and hydrophobic interactions between the particles and the substrate lead to nanoparticle immobilization, with no desorption upon further immersion in any solvent. The prepared Pd NP-loaded paper substrates were tested for several model reactions such as the oxidative homocoupling of arylboronic acids, the Suzuki cross-coupling reaction, and nitro-to-amine reduction, and they display efficient catalytic activity and excellent recyclability and reusability. This approach of using NP-loaded paper substrates as reusable catalysts is expected to open doors for new types of catalytic support for practical applications

Self-assembly mechanisms for magnetic nanoparticles and formation of macroscopic two-dimensional arrays

A combined morphological, structural and magnetic investigation of several magnetic nanostructures, which are widely known as ‘nanoparticles’, was carried out in the framework of the current Doctorate Thesis. The main objective was to form arrays of magnetic nanoparticles with controllable size and shape and to understand the mechanisms for the correlation of the morphological and structural features with the magnetic behavior. Various monometallic and bimetallic nanoparticle systems were studied, each one of them composed of at least one transition metallic element. More specifically, arrays of monometallic nanoparticles (Ni, Co, CoO-Co₃O₄) and bimetallic alloy nanoparticles (FeCo, CoPt, MnPt) were prepared. Apart from the synthesis and characterization of the magnetic nanoparticles, we aimed at the creation of well-ordered 2D arrays consisted of nanoparticles with high size monodispersity. Several parameters were carefully adjusted in order to provide sufficient interparticle distances between the nanoparticles, avoiding the formation of large particle aggregates in a certain extent. Beside the big interest of the aforementioned nanostructures, due to the appearance of novel phenomena from the physics point of view, that arise mainly from the nanoscale size (1-100 nm), these materials are candidate building blocks for applications in fields such as magnetic recording, catalysis and biomedicine. The magnetic nanoparticles were synthesized by the so-called ‘wet-chemistry’ method, where properly selected organometallic compounds, diluted in organic solvents, are thermally decomposed in the presence of surfactants. The cautious choice of the reaction conditions as well as the careful handling of the nanoparticles in the post-preparation stage were prerequisites for the desired self-arrangement of the nanoparticles in 2D arrays. In particular, concerning the Co-based nanoparticles (Co, CoO, Co₃O₄), we were able to fabricate nanostructures with various morphologies (e.g. spherical particles, ‘polypod-like’ structures). Magnetic measurements showed a strong ferromagnetic character for the cobalt nanostructures (Ms ~ 182 emu/g), while the Co-oxide nanoparticles displayed very weak ferromagnetic features. The tuning of the size and shape of the nanoparticles was also feasible for the Ni system. By applying the appropriate synthesis parameters, Ni nanoparticles with tailored crystal structure were produced (either cubic (fcc) or hexagonal (hcp)). The magnetic properties of these two crystal phases were much different. The FeCo alloy nanoparticles presented a high size monodispersity (~ 15 nm), with a tendency for self-organization in extended arrays. In this system, the effect of air exposure was examined, which briefly led to the surface oxidation of the particles, thus resulting in a deterioration on the magnetic properties of the material. Regarding the bimetallic CoPt nanoparticles, the main observation is that they showed high coercivity values after annealing (~ 3.3 kOe at room temperature), which is an essential feature for the candidate materials to be employed in magnetic recording media. Moreover, concerning the MnPt alloy nanoparticles we were able to control the size in the range 2-9 nm, while the self-assembly in multiple layers was achieved in certain cases. The annealing resulted in considerably high coercivity values (~ 11 kOe), as revealed by magnetic measurements at low temperatures (10 K).Στα πλαίσια της παρούσας διατριβής πραγματοποιήθηκε μια συνδυασμένη μορφολογική, δομική και μαγνητική μελέτη ποικίλων μεταλλικών νανοδομών, που είναι γενικότερα γνωστές με τον όρο ‘νανοσωματίδια’. Ο κύριος στόχος ήταν η ανάπτυξη δικτύων μαγνητικών νανοσωματιδίων με ελεγχόμενη σύσταση, σχήμα και μέγεθος, καθώς και η μελέτη της συσχέτισης των μορφολογικών και δομικών τους χαρακτηριστικών με τη μαγνητική τους συμπεριφορά. Μελετήθηκαν διάφορες μονομεταλλικές και διμεταλλικές ενώσεις που είχαν σε κάθε περίπτωση ως κύριο συστατικό τουλάχιστον ένα μεταβατικό μεταλλικό στοιχείο. Πιο συγκεκριμένα, αναπτύχθηκαν δίκτυα μονομεταλλικών νανοσωματιδίων (Νi, Co, CoO-Co₃O₄) και διμεταλλικών κραμάτων νανοσωματιδίων (FeCo, CoPt, MnPt). Πέρα από τη σύνθεση και το χαρακτηρισμό των μαγνητικών νανοσωματιδίων, επιδιώχθηκε ο σχηματισμός διατεταγμένων δικτύων σε δύο διαστάσεις, αποτελούμενων από νανοσωματίδια με στενή κατανομή μεγέθους. Μελετήθηκαν προσεκτικά όλες οι παράμετροι με σκοπό τη διασπορά των νανοσωματιδίων σε ελεγχόμενες αποστάσεις, ώστε να αποφεύγεται, όσο είναι δυνατό, ο σχηματισμός ‘πυκνών’ επιστοιβάσεων νανοσωματιδίων (συσσωματώματα). Πέρα από τη μεγάλη σημασία που εμφανίζουν αυτές οι δομές εξαιτίας της εμφάνισης καινούργιων φαινομένων από άποψη βασικής φυσικής, τα οποία πηγάζουν κατά κύριο λόγο από το εξαιρετικά μικρό τους μέγεθος, που κυμαίνεται στη νανο-κλίμακα (1-100 nm), τα υλικά αυτά αποτελούν υποψήφιες δομικές μονάδες για εφαρμογές σε τομείς όπως η μαγνητική εγγραφή, η κατάλυση και η βιοϊατρική τεχνολογία. Η σύνθεση των μαγνητικών νανοσωματιδίων έγινε με τη μέθοδο της ‘υγρής χημείας’, όπου κατάλληλα επιλεγμένες οργανομεταλλικές ενώσεις, διαλυμένες σε οργανικούς διαλύτες, διασπώνται σε υψηλές θερμοκρασίες παρουσία επιφανειοδραστικών ενώσεων. Η προσεκτική ρύθμιση των συνθηκών της αντίδρασης καθώς και του χειρισμού των νανοσωματιδίων μετά την παρασκευή τους ήταν απαραίτητες προϋποθέσεις για τη στοχευμένη αυτοσυγκρότηση των σωματιδίων σε δισδιάστατα δίκτυα. Ειδικότερα, στο σύστημα Co-(CoO, Co₃O₄) κατέστη δυνατή η σύνθεση νανοδομών με διάφορες μορφολογίες (π.χ. σφαιρικά σωματίδια, δομές ‘polypod-like’ κλπ.) Μέσα από τις μαγνητικές μετρήσεις καταγράφηκε ο ισχυρός σιδηρομαγνητικός χαρακτήρας των νανοδομών κοβαλτίου (Ms ~ 182 emu/g), ενώ τα οξείδια του κοβαλτίου εμφάνισαν πολύ ασθενή σιδηρομαγνητική συμπεριφορά. O έλεγχος του σχήματος και του μεγέθους των νανοσωματιδίων ήταν εφικτός και για τα νανοσωματίδια Νi. Επιλέγοντας τις κατάλληλες παραμέτρους σύνθεσης, για το σύστημα αυτό παρασκευάστηκαν νανοδομές με εδροκεντρωμένη κυβική κρυσταλλική συμμετρία (fcc) και νανοδομές με εξαγωνική δομή (hcp). Oι παραπάνω κρυσταλλογραφικές φάσεις εμφάνισαν αρκετά διαφορετική μαγνητική συμπεριφορά μεταξύ τους. Τα νανοσωματίδια κράματος FeCo εμφάνισαν ικανοποιητική μονοδιασπορά μεγέθους (~ 15 nm) με τάσεις για αυτοοργάνωση σε μακροσκοπικά δίκτυα. Σε αυτό το σύστημα διερευνήθηκε η επίδραση της έκθεσης στον ατμοσφαιρικό αέρα, που οδήγησε στην επιφανειακή οξείδωση των νανοσωματιδίων, καθώς και οι συνέπειες του φαινομένου αυτού στις μαγνητικές ιδιότητες του υλικού. Για τα διμεταλλικά νανοσωματίδια CoPt, η σημαντικότερη παρατήρηση είναι ότι παρουσίασαν υψηλές τιμές συνεκτικού πεδίου μετά από ανόπτηση (~ 3.3 kOe σε θερμοκρασία δωματίου), μια ιδιότητα που είναι αναγκαία για τα υλικά που είναι υποψήφια για χρήση σε εφαρμογές μαγνητικής εγγραφής. Ακόμη, στα νανοσωματίδια κράματος ΜnPt ήταν δυνατός ο έλεγχος του μεγέθους τους στην περιοχή 2-9 nm καθώς και η αυτοοργάνωση σε πολλαπλά στρώματα σε ορισμένες περιπτώσεις, ενώ η ανόπτηση οδήγησε σε μεγάλες τιμές συνεκτικού πεδίου ( ~ 11 kOe), μετά από μαγνητικές μετρήσεις σε χαμηλές θερμοκρασίες (10 K)