1,721,103 research outputs found
Sol-gel processing for advanced ceramics, a perspective
No full textSol-gel chemistry and the process that peculiarly defines the derived materials, represent an essential tool for the chemical synthesis of materials. Since the intensive research activity that began in the late 1980s, whole new families of advanced ceramic materials obtained via chemical synthesis combined with low-temperature heat treatment have been developed. These materials include, among others, aerogels, organic-inorganic hybrid materials, and mesoporous materials. The success of the process has thus opened up new possibilities for obtaining nanomaterials through a highly refined design of the structure and, thus, of the properties. Despite the intervening time, the sol-gel process is still the focus of intense research, and more and more new applications are successfully entering the market. This article is devoted to a brief review of the future prospects of the process and materials obtained through sol-gel chemistry
Hydrophobic thin films from Sol–Gel processing: A critical review
No full textFabrication of hydrophobic thin films from a liquid phase is a hot topic with critical technological issues. Interest in the production of hydrophobic surfaces is growing steadily due to their wide applications in several industrial fields. Thin films from liquid phases can be deposited on different types of surfaces using a wide variety of techniques, while the design of the precursor solution offers the possibility of fine-tuning the properties of the hydrophobic coating layers. A general trend is the design of multifunctional films, which have different properties besides being hydrophobic. In the present review, we have described the synthesis through sol–gel processing of hydrophobic films enlightening the main achievements obtained in the field
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
Mechanical properties of 3-glycidoxypropylmethoxysilane based hybrid organic-inorganic materials
No full textAbstract
Hybrid organic-inorganic materials were synthesized from acid catalysed sols of tetraethyl orthosilicate, 3-glycidoxypropyltrimethoxysilane and titanium or zirconium alkoxides. The mechanical properties of these materials were measured in different conditions of preparation. The elastic modulus E was determined by a resonance method and by Knoop microindentation. After a thermal treatment at 125°C for 120 h, E was around 3–5 and 1–2 GPa for the samples synthesized with titanium butoxide or zirconium butoxide, respectively. An increase in E in the samples cured for longer times was observed. Knoop microhardness also increased with the heating time and was larger in samples synthesized from titanium alkoxides than zirconium alkoxides. The two methods gave results in good agreement when applied to samples treated for shorter times. In the other samples Knoop microindentation gave a larger value of E compared to the resonance vibration method. Hardness to elastic modulus ratio, H/E, was evaluated by Knoop microindentation. The elastic recovery at the longest heat treatment time was similar to that of soda-lime glasses. Fracture toughness was measured by three points flexural test, a KIc in the range of 0.4–0.5 MPa m1/2 was evaluated for samples treated during 168 h
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
Low temperature synthesis of MgxAl2(1−x)Ti(1+x)O5 films by sol-gel processing
No full textAluminium titanate films thicker than 0.5 microns have been synthesized by sol–gel methods. The films have been deposited via repetitive dip-coating on silicon wafers and their thermal stability has been tested as a function of the annealing time and temperature. The sol–gel approach has allowed the formation of the aluminium titanate phase at temperatures (∼700 °C) much lower than those necessary for solid-state reactions (∼1450 °C). Magnesium oxide has been used to improve the thermal stability of the films at high temperatures. The behavior of
samples prepared with two different Mg content, i.e. Mg0.2Al1.6Ti0.8O5 and Mg0.6Al0.8Ti1.6O5, has been studied. The films have proven to be stable at 1150 °C, for up to 90 h. X-ray photoelectron spectroscopy has shown that after firing at 500 °C the surface chemical composition of
the films is in accordance with the nominal one, whilst at higher annealing temperatures some differences, attributed to diffusion effects, have been observed
Water Droplets to Nanotechnology. A journey through self-assembly
No full textThe ability of nanostructures to organize into complex arrangements leads to unique materials with valuable applications. Self-assembly is therefore a key concept for
nanotechnology, but it can be quite a complex and difficult
subject to approach. Water Droplets to Nanotechnology gives a simple and general overview of the different self-assembly processes which are at the basis of recent developments in nanotechnology.
The book shows how simple phenomenon from everyday
examples can become sophisticated tools for self-assembly and the fabrication of nanomaterials. By exploring the coffee stain and tears of wine phenomena, the first part looks at how
the evaporation of a droplet of colloidal solution can be used in designing organized structures. This leads onto more complex systems such as templated porous materials, photonic crystals, colloidal nanocrystals and quasi-crystals through to bottom-up
systems for designing hierarchal materials.
By taking the reader on a journey from everyday life to the secrets of nanotechnology, the book is suitable for a nonspecialist
audience interested in self-assembly as well as the wider perspectives and latest developments of nanoscience
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
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