1,721,024 research outputs found
Carbon Dots for Hydrogen Production. How Do They Work?
No full textCarbon Dots (CDs) have gained significant attention for their fascinating optical properties, potential applications, and puzzling structural challenges. In the last decade, CDs have become the focal point in many photocatalysis studies, either as independent systems or combined with other established photocatalysts. CDs play a crucial role in enhancing the performance of heterostructures for overall water splitting, hydrogen (HER), and oxygen evolution reaction (OER). In these "Concepts," we briefly explore the structure of CDs, highlighting their critical aspects, including their role within heterostructures, composition, the presence of fluorophores, and the interaction between the graphitic core and surface functional groups. We will also examine how these factors impact their photocatalytic properties, particularly in the context of future research on H-2 production
From Defects to Photoluminescence in h-BN 2D and 0D Nanostructures
No full textIn the present Account, we report the recent progress of our research group on experimental and theoretical studies of defects in 2D and 0D hexagonal boron nitride. The studies of the effect of defects in boron-based structures have been also extended to boron oxide glasses. Engineering the different types of defects in h-BN is paramount because many functional properties of the material depend on them. This is particularly true for h-BN nanomaterials because of the main role played by surfaces. An important finding is that the formation of defects is directly dependent on the synthesis route; bottom-up or top-down syntheses generate different types of defects whose origins are generally connected to vacancies, dangling bonding, and substitutional oxygen impurities. We have focused our attention, in particular, on the correlation between defects and photoluminescence. The first part of this Account is dedicated to a general overview of defects that form in h-BN systems. In the second and third parts, we report on the rise of fluorescence in different types of h-BN nanostructures, in particular nanoflakes and BN dots. h-BN nanoflakes become fluorescent due to the presence of substitutional oxygen in the structure. The emission depends on the thermal processing of the material. A postsynthesis thermal treatment, because it induces the condensation of oxygen-related bonds that at the origin of fluorescence, changes the photoluminescence according to the degree of condensation of the structure. In the case of BN, the defects in dots and 0D nanostructures are discussed as a function of their preparation route. The analysis of defects in h-BN dots shows that not only vacancies and impurities can contribute to emission but also structural defects such as Stone-Wales. Understanding the origin of such defects and correlating them with specific optical properties is of the utmost importance because comprehending such phenomena could also guide the fabrication of new boron oxide emissive materials. In the last example, we show that the formation of defects, such as dangling bondings and vacancies, is the basis of a surprising phosphorescence at room temperature in boron oxide materials. We have observed, in particular, that the rise of boric acid phosphorescence after heat treatment is related to the presence of defects. The afterglow results from a trapping and detrapping process, which delays recombination at the active optical centers. The formation of near UV and blue optical transitions in absorption is revealed by a time-dependent density functional analysis of defective BOH molecules and clusters. In thermally processed boric acid samples, these defects cause photoluminescence
Fluorescent carbon dots in solid-state: From nanostructures to functional devices
Full text linkIn recent years, carbon dots (CDs) have attracted considerable attention for their potential application in photonics and optoelectronics. One of the main limitations in realizing efficient and reliable solid-state devices is the aggregation-caused quenching effect. At a short distance, the mutual interaction among nanoparticles enhances the non-radiative mechanisms, undermining the extraordinary optical properties of CDs. In this review, we have critically analyzed the main strategies for maintaining and empowering the optical properties of CDs from liquid to solid-state. These routes include the preparation of self-quenching-resistant fluorescent CDs and the embedding into different matrices. The material processing and the nature of the chemical environment surrounding the CDs are key parameters for selecting an optically transparent matrix. An optimized host material would preserve the fundamental properties of CDs, but also improve their performances extending the application field. Many types of matrices for CDs have been tested, such as polymers, organic-inorganic hybrid materials, mesoporous and layered materials. Besides, unconventional host materials have also used as a matrix, e.g. acid molecules condensates and inorganic salts. The successful use of CDs is highly relying on their incorporation into a solid-state matrix
Blocking viral infections with lysine-based polymeric nanostructures: a critical review
No full textThe outbreak of the Covid-19 pandemic due to the SARS-CoV-2 coronavirus has accelerated the search for innovative antivirals with possibly broad-spectrum efficacy. One of the possible strategies is to inhibit the replication of the virus by preventing or limiting its entry into the cells. Nanomaterials derived from lysine, an essential amino acid capable of forming homopeptides of different shapes and sizes through thermal polymerization, are an exciting antiviral option. In this review, we have critically compared the antiviral activities and mechanisms of action of lysine and its possible analogues in the form of linear, hyperbranched, dendrimer and nanoparticle polymers. The polycationic nature, as well as the structure of polylysine in its various forms, favours the electrostatic interaction with viruses by inhibiting their replication and endocytosis. In the case of lysine alone, the antiviral action is instead carried out inside the cell. The experimental results obtained so far show that the development of antivirals based on amino acids that inhibit the entry of viruses into cells represents a definite possibility for developing challenging solutions against present and future pandemics
Carbon dots as oxidant-antioxidant nanomaterials, understanding the structure-properties relationship. A critical review
Full text linkCarbon dots (C-dots) are a large family of nanomaterials characterized by an intense photoluminescence. The origin of the emission is multifaceted and is dependent on a number of factors, including structure, surface, and composition. The term "carbon dots" is quite broad and encompasses a wide range of carbon nanostructures. The multiple properties are a result of this variability, which also makes it difficult to es-tablish a clear structure-property relationship. Photoluminescence is the property of this class of nano-materials that has garnered the greatest attention due to the possibility of applications in various fields, including biotechnologies, electronics, and energy. Another property of C-dots that has only lately been recognized is their antioxidant activity, i.e., the ability to act as a free radical scavenger. Furthermore, it has been proven that certain types of C-dots function as oxidizing agents when exposed to visible and/or UV radiation. This dual oxidant-antioxidant nature is particularly intriguing and closely related to the C-dot properties. Although many articles have been published on the subject, it still needs to be understood what structure-property relationships regulate the responses to free radicals. This review aims to provide a general overview of the characteristics of C-dots as scavengers or radical emitters by a critical analysis of the relevant studies. Based on their intended application as oxidants or antioxidants, the findings of this review can be used to synthesize C-dots with precisely defined functional properties.(c) 2023 Published by Elsevier Ltd
Winou el shabab? Where are our youth? Arab Jacobins, State repression, Islamic radicalization and the continuous fight for a democratic turn
No full textThe idea of this volume is to bring into focus some “images of transformations” that
cross the space of the post-Arab-Spring Mediterranean. We begin with Fatima, promoter and leader of a network of Tunisian women who have lost their children and husbands in the migration. Her words, her question provided the title of this book: Winou el chabeb? Where are our youth
New phosphors with strongly reduced content of critical raw materials for lighting applications
No full textAluminium silicate crystal is proposed as new promising inert matrix as host of luminescent ions. In particular, we studied the luminescence properties of single doped and multi-doped Al2SiO5 samples (doping elements: Ce, Tb, Cr, Fe, Zr) to explore their suitability as phosphors in modern lighting systems. The Al2SiO5 host matrix, obtained in nano-sized crystals belonging to the high temperature phase known as sillimanite, allows to narrow down the presence of rare earth elements exclusively to the dopants, thus providing a promising solution to the critical raw material concern. The crystals doped with Fe, Ce and Zr are mainly excited in the UV range, and they are good candidate as phosphors in compact fluorescent lamp systems. Terbium single doped samples are efficient phosphors in the green region with direct excitation in the deep UV region, but their excitation spectrum can be down-shifted to near UV range in in co-doped Ce:Tb samples. Indeed, thanks to the efficient energy transfer from cerium ions, the green emission from Tb ions can be excited by commercial AlGaN light emitting diode, suggesting Ce:Tb doped Al2SiO5 crystals as promising phosphors for green LED system. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Strength and weakness of rare earths based phosphors: Strategies to replace critical raw materials
No full textRare earth based phosphors are largely the most applied luminescent materials in the present lightening devices. Their ubiquity in lighting system, like light emitting diodes or compact fluorescent lamps, is related to the optical high efficiency of the rare earth as luminescent ions but also to the relative easiness of growth technique as well high structural stability of rare earth based host matrices, like garnets, perovskites and oxyorthosilicatas. On the other hand, the need of new devices virtually free of any elements with high supply disruption, the ones classified by EU community and US government as critical raw materials, boosts the research for alternatives materials. In this paper, we focalize on the optical properties of the REE based phosphors with the intent to underline the performances the new materials should grant, thus addressing the possible direction for new material development. In particular the features related to the possibility of tuning the luminescence, the interaction among doping ions and with surface defects were analysed. Finally, a general model to predict the role of the REE in a host matrix is analysed. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Reversible aggregation of molecular-like fluorophores driven by extreme pH in carbon dots
No full textThe origin of carbon-dots (C-dots) fluorescence and its correlation with the dots structure still lack a comprehensive model. In particular, the core-shell model does not always fit with the experimental results, which, in some cases, suggest a molecular origin of the fluorescence. To gain a better insight, we have studied the response of molecular-like fluorophores contained in the C-dots at extreme pH conditions. Citric acid and urea have been employed to synthesize blue and green-emitting C-dots. They show a different emission as a function of the pH of the dispersing media. The photoluminescence has been attributed to molecular-like fluorophores: citrazinic acid and 4-hydroxy-1H-pyrrolo[3,4-c]-pyridine-1,3,6-(2H,5H)-trione. 3D and time-resolved photoluminescence, ultraviolet-visible (UV-vis) spectroscopy, and dynamic light scattering have been used to determine the aggregation state, quantum yield and emission properties of the C-dots. The dependence of the C-dots blue and green components on the chemical environment indicates that the origin of fluorescence is due to molecular-like fluorophores
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