Carbon-based antiviral nanomaterials: graphene, C-dots, and fullerenes. A perspective

The appearance of new and lethal viruses and their potential threat urgently requires innovative antiviral systems

Optical and structural characterization of metal oxides and carbon nitride compounds for the development of organic/inorganic hybrid systems

Metal oxides (MOs) play a key role in many areas of chemistry, physics and materials science. They are characterized by a wide variety of high technological interest compounds (e.g. TiO2, Fe3O4, Fe2O3, Y2O3, ZnO). The still increasing interest for this class of materials is mainly due to the ability to take advantage of their diversity to find new important applications in several research field. Their applicability, strengthened by the low cost, safety, ease of synthesis, ranges from (photo)catalysis to microelectronics and in vivo biological studies. Most of the MOs-based devices present outstanding performance derived from their reduced dimensions. To date, the research on nanostructured MOs is highly active in order to deeper gain knowledge about surface states and their influence on chemical and physical properties, motivating an always more multidisciplinary approach. However, some characteristics of oxides can limit their use, e.g. high band gap with almost negligible absorption in the visible, lack of optical response (luminescence) or conduction band edge not sufficiently negative to promote proton reduction (limited photocatalytic activity). The introduction of doping elements in the MO matrix to reduce these limitations can have the drawbacks of the new defects generation at the surface and/or in the bulk. Other limitations can be overcome by creating hybrid materials, such as organic and inorganic systems. In such scenario, it is necessary a detailed study aimed to characterize the properties of organic material and the means of implementation of the hybrid system. In the first part of the present thesis, we examine the stability of some exemplar metal oxides systems. The aim of this work is to extend the comprehension of nanostructured MOs phase transformation and to analyse the conditions for which the transformation takes place. The second part presents a study on carbon nitride (CN) based molecular materials performed with spectroscopy and X-ray diffraction experiments. Our characterizations reveal that CN materials present high chemical and physical stability and good control of the optical properties. Finally, we propose a structural and optical characterization of some carbon-nitride/ metal oxides hybrids. Firstly, we focus on Tb3+ doped Y2O3 system, a good candidate for nanosized phosphors, where organic passivation of the surfaces by melamine (C3H6N6) has the dual role of replacing species for hydroxides quenchers and activators of Tb by energy transfer mechanism. Then, we conclude with TiO2/CN hybrids for photocatalysis applications, realized by chemical methods and atomic layer deposition, stressing the importance of functional and terminating groups of molecular systems

Hydroxylated boron nitride materials: from structures to functional applications

Abstract Functionalization of boron nitride (BN) materials with hydroxyls has attracted great attention to accomplish better performances at micro- and nanoscale. BN surface hydroxylation, in fact, induces a change in properties and allows expanding the fields of application. In this review, we have summarized the state-of-the-art in developing hydroxylated bulk and nanoscale BN materials. The different synthesis routes to develop hydroxyl BN have been critically discussed. What emerges is the great variety of possible strategies to achieve BN hydroxylation, which, in turn, represents one of the most suitable methods to improve the solubility of BN nanomaterials. The improved stability of BN solutions creates conditions for producing high-quality nanocomposites. Furthermore, new interesting optical and electronic properties may arise from the functionalization by OH groups as displayed by a wide range of both theoretical and experimental studies. After the presentation of the most significant systems and methodologies, we question of future perspective and important trends of the next generation BN materials as well as the possible areas of advanced research. Graphical abstract Hydroxyl functionalization of boron nitride materials is a key method to control and enhance the properties and design new functional applications

Thermal Induced Polymerization of l-Lysine forms Branched Particles with Blue Fluorescence

AbstractThe polycondensation of amino acids can originate complex polymers that display fascinating structural and optical properties. Thermally induced amidation of l‐lysine allows forming a branched polymer without the support of any catalyst. The polycondensation is completed at 240–250 °C; at higher temperatures, the amino acid degrades. The obtained polylysine particles have been studied by transmission electron microscopy (TEM), nuclear magnetic resonance, and infrared spectroscopy that allow for investigating the different steps of the synthesis. The resulting structure is characterized by peculiar optical properties, e.g., excitation‐dependent blue fluorescence and good quantum efficiency. Hydrogen bonds and the interactions of the amino acids are considered responsible for the optical properties of both l‐lysine monomer solutions at high concentrations and the branched nanopolymers

Structure Solution of NaYO2 Compound Prepared by Soft Chemistry from X-Ray Diffraction Powder Data

In this work we reveal the structure of a NaYO2 compound solved from the X-ray diffraction powder pattern using the “ab-initio” structure solution approach. The compound turned out to be of trigonal structure, S. G. R-3m isomorphous with α-NaFeO2 layered compound. The lattice parameters are a = 3.404 and c = 16.602 Å, respectively, the atoms being located in Wickoff sites (cba) for O, Na and Y, respectively, leading to a calculated density of 4.31 g/cm3. The ordering of sodium and yttrium atoms into alternate (111) planes of the cubic close-packed oxygen lattice of NaYO2 is very regular. The octahedra are slightly distorted, the positive deviation of the Oz parameter from 0.25 elongates the NaO6 octahedra while compressing the YO6 octahedra. Actually the Na-O and Y-O bond distances are 2.58 (1) and 2.25 (1) Å, respectively, as it is expected from their ionic radii values reported (1.16 vs 1.04 radii for both ion-species octahedral coordination). Finally, the Na-Y, Y-Y, and Na-Na next neighbor distances are close to 3.40 Å.JRC.F.2-Energy Conversion and Storage Technologie

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications

Selecting molecular or surface centers in carbon dots-silica hybrids to tune the optical emission: A photo-physics study down to the atomistic level

In this work, we unveil the fluorescence features of citric acid and urea-based Carbon Dots (CDs) through a photo-physical characterization of nanoparticles synthesized, under solvent-free and open-air condi-tions, within silica-ordered mesoporous silica, as a potential host for solid-state emitting hybrids. Compared to CDs synthesized without silica matrices and dispersed in water, silica-CD hybrids display a broader emission in the green range whose contribution can be increased by UV and blue laser irradi-ation. The analysis of hybrids synthesized within different silica (MCM-48 and SBA-15) calls for an active role of the matrix in directing the synthesis toward the formation of CDs with a larger content of graphitic N and imidic groups at the expense of N-pyridinic molecules. As a result, CDs tuned in size and with a larger green emission are obtained in the hybrids and are retained once extracted from the silica matrix and dispersed in water. The kinetics of the photo-physics under UV and blue irradiation of hybrid samples show a photo-assisted formation process leading to a further increase of the relative contribution of the green emission, not observed in the water-dispersed reference samples, suggesting that the porous matrix is involved also in the photo-activated process. Finally, we carried out DFT and TD-DFT calcula-tions on the interaction of silica with selected models of CD emitting centers, like surface functional groups (OH and COOH), dopants (graphitic N), and citric acid-based molecules. The combined experimen-tal and theoretical results clearly indicate the presence of molecular species and surface centers both emitting in the blue and green spectral range, whose relative contribution is tuned by the interaction with the surrounding media

Defect-assisted photoluminescence in hexagonal boron nitride nanosheets

The development of functional optoelectronic applications based on hexagonal boron nitride nanosheets (h-BNNs) relies on controlling the structural defects. The fluorescent emission, in particular, has been observed to depend on vacancies and substitutional defects. In the present work, few-layerh-BNNs have been obtained by sonication-assisted liquid-phase exfoliation of their bulk counterpart. The as-prepared samples exhibit a weak fluorescent emission in the visible range, centred around 400 nm. Tailored defects have been introduced by oxidation in air at different temperatures. A significant increase in the fluorescent emission of the oxidatedh-BNNs has been observed with maximum emissive intensity for the samples treated at 300 degrees C. A further increase in temperatures (>300 degrees C) determines a quenching of the fluorescence. We investigated, by means of detailed microscopic and spectroscopic analysis, the relationship between the optical properties and defects ofh-BNNs. The investigation of the optical properties as a function of treatment temperature highlights the critical role of hydroxyl groups created by the oxidation process. Onlyh-BN exfoliated in water allows introducing OH groups with consequent enhancement of fluorescence emission. Quantum chemical calculations support the experimental findings

From 2-D to 0-D Boron Nitride Materials, The Next Challenge

The discovery of graphene has paved the way for intense research into 2D materials which is expected to have a tremendous impact on our knowledge of material properties in small dimensions. Among other materials, boron nitride (BN) nanomaterials have shown remarkable features with the possibility of being used in a large variety of devices. Photonics, aerospace, and medicine are just some of the possible fields where BN has been successfully employed. Poor scalability represents, however, a primary limit of boron nitride. Techniques to limit the number of defects, obtaining large area sheets and the production of significant amounts of homogenous 2D materials are still at an early stage. In most cases, the synthesis process governs defect formation. It is of utmost importance, therefore, to achieve a deep understanding of the mechanism behind the creation of these defects. We reviewed some of the most recent studies on 2D and 0D boron nitride materials. Starting with the theoretical works which describe the correlations between structure and defects, we critically described the main BN synthesis routes and the properties of the final materials. The main results are summarized to present a general outlook on the current state of the art in this field