We report here a molten salt (MS) process for the synthesis of nanoporous carbon structures and carbon sheets. Using glucose as the model carbon precursor, the process yields different porous carbon ...structures with specific surface area up to near 2000m2/g in molten LiCl/KCl containing different dissolved oxysalts KNmOx, where Nm are nonmetal elements of H, B, C, N, P, S, and Cl. These oxysalts dissolved in LiCl/KCl exert a dominating influence on the pore formation as well as two-dimensional growth of the carbons in MS. Based on the energetics of the redox reaction between carbon and the above oxysalts, a general mechanistic explanation for the pore formation and the activation process in MS is presented. The process reported here not only provides an easy route to convert biomass molecules to carbon-based functional nanomaterials, but also opens up a new direction towards carbonization and two-dimensional growth in high temperature ionic solvent systems.
Transfer of energy occurs endlessly in our universe by means of radiation. Compared to energy transfer (ET) in free space, in solid state materials the transfer of energy occurs in a rather confined ...manner, which is usually mediated by real or virtual particles, including not only photons, but also electrons, phonons, and excitons. In the present review, we discuss the recent advances in optical ET by resonance mediated with photons in solid materials as well as their nanoscale counterparts, with focus on the photoluminescence behavior pertaining to ET between optically active centers, such as rare earth (RE) ions. This review begins with a brief discussion on the classification of optical ET together with an overview of the theoretical formulations and experimental method for the examination of ET. We will then present a comprehensive discussion on the ET in practical systems in which normal photoluminescence, upconversion and quantum cutting resulted from ET involving metal ions, QDs, organic species, 2D materials and plasmonic nanostructures. Diverse ET systems are therefore simply categorized into cases of ion-ion interactions and non-ion interactions. Special attention has been paid to the progress in the manipulation of spatially confined ET in nanostructured systems including core-shell structures, as well as the ET in multiple exciton generation found in QDs and organic molecules, which behave quite similarly to resonance ET between metal ion centers. Afterwards, we will discuss the broad spectrum of applications of ET in the aforementioned systems, including solid state lighting, solar energy utilization, bio-imaging and diagnosis, and sensing. In the closing part, along with a short summary, we discuss further research focus regarding the problems and possible future directions of optical ET in solids.
Low‐dimensional (LD) materials demonstrate intriguing optical properties, which lead to applications in diverse fields, such as photonics, biomedicine and energy. Due to modulation of electronic ...structure by the reduced structural dimensionality, LD versions of metal, semiconductor and topological insulators (TIs) at the same time bear distinct nonlinear optical (NLO) properties as compared with their bulk counterparts. Their interaction with short pulse laser excitation exhibits a strong nonlinear character manifested by NLO absorption, giving rise to optical limiting or saturated absorption associated with excited state absorption and Pauli blocking in different materials. In particular, the saturable absorption of these emerging LD materials including two‐dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q‐switching and mode‐locking ultra‐short pulse generation across the visible, near infrared and middle infrared wavelength regions. Beside the large operation bandwidth, these ultrafast photonics applications are especially benefit from the high recovery rate as well as the facile processibility of these LD materials. The prominent NLO response of these LD materials have also provided new avenues for the development of novel NLO and photonics devices for all‐optical control as well as optical circuits beyond ultrafast lasers.
Two‐dimensional materials, topological insulators, and plasmonic nanomaterials exhibit distinct and intriguing electrical and optical properties, making them the focus of intensive research in the past decade. Their interactions with intense pulse lasers are strongly nonlinear, and, surprisingly, all of them can serve as efficient saturable absorbers to enable ultrafast pulse generation in a wide spectral range.
Materials synthesis in the liquid phase, or wet-chemical synthesis, utilizes a solution medium in which the target materials are generated from a series of chemical and physical transformations. ...Although this route is central in organic chemistry, for materials synthesis the low operational temperature range of the solvent (usually below 200 °C, in extreme 350 °C) is a serious restriction. Here, salt melt synthesis (SMS) which employs a molten inorganic salt as the medium emerges as an important complementary route to conventional liquid phase synthesis. Depending on the nature of the salt, the operational temperature ranges from near 100 °C to over 1000 °C, thus allowing the access to a broad range of inorganic crystalline materials and carbons. The recent progress in SMS of inorganic materials, including oxide ceramic powders, semiconductors and carbon nanostructures, is reviewed here. We will introduce in general the range of accessible materials by SMS from oxides to non-oxides, and discuss in detail based on selected examples the mechanisms of structural evolution and the influence of synthetic conditions for certain materials. In the later sections we also present the recent developments in SMS for the synthesis of organic solids: covalent frameworks and polymeric semiconductors. Throughout this review, special emphasis is placed on materials with nanostructures generated by SMS, and the possible modulation of materials structures at the nanoscale in the salt melt. The review is finalized with the summary of the current achievements and problems, and suggestions for potential future directions in SMS.
Salt melt synthesis provides alternative access to various oxide and non-oxide ceramics, semiconductors, covalent frameworks, and carbon nanostructures.
The flow structure and turbulence in an open cavity shear layer has been investigated experimentally at a Reynolds number of
$4. 0\times 1{0}^{4} $
, with an emphasis on interactions of the unsteady ...pressure field with the cavity corners. A large database of time-resolved two-dimensional PIV measurements has been used to obtain the velocity distributions and calculate the pressure by spatially integrating the material acceleration at a series of sample areas covering the entire shear layer and the flow surrounding the corners. Conditional sampling, low-pass filtering and time correlations among variables enable us to elucidate several processes, which have distinctly different frequency ranges, that dominate the shear layer interactions with the corners. Kelvin–Helmholtz shear layer eddies have the expected Strouhal number range of 0.5–3.2. Their interactions with the trailing corner introduce two sources of vorticity fluctuations above the corner. The first is caused by the expected advection of remnants of the shear layer eddies. The second source involves fluctuations in local viscous vorticity flux away from the wall caused by periodic variations in the streamwise pressure gradients. This local production peaks when the shear layer vortices are located away from the corner, creating a lingering region with peak vorticity just above the corner. The associated periodic pressure minima there are lower than any other point in the entire flow field, making the region above the corner most prone to cavitation inception. Flapping of the shear layer and boundary layer upstream of the leading corner occurs at very low Strouhal numbers of ∼0.05, affecting all the flow and turbulence quantities around both corners. Time-dependent correlations of the shear layer elevation show that the flapping starts in the boundary layer upstream of the leading corner and propagates downstream at the free stream speed. Near the trailing corner, when the shear layer elevation is low, the stagnation pressure in front of the wall, the downward jetting flow along this wall, the fraction of shear layer vorticity entrained back into the cavity, and the magnitude of the pressure minimum above the corner are higher than those measured when the shear layer is high. However, the variations in downward jetting decay rapidly with increasing distance from the trailing corner, indicating that it does not play a direct role in a feedback mechanism that sustains the flapping. There is also low correlation between the boundary/shear layer elevation and the returning flow along the upstream vertical wall, providing little evidence that this returning flow affects the flapping directly. However, the characteristic period of flapping, ∼0.6 s, is consistent with recirculation time of the fluid within the cavity away from boundaries. The high negative correlations of shear/boundary layer elevation with the streamwise pressure gradient above the leading corner introduce a plausible mechanism that sustains the flapping: when the shear layer is low, the boundary layer is subjected to high adverse streamwise pressure gradients that force it to widen, and when the shear layer is high, the pressure gradients decrease, allowing the boundary layer to thin down. Flow mechanisms that would cause the flapping-induced pressure changes, and their relations to the flow within the cavity are discussed.
A Facile Molten-Salt Route to Graphene Synthesis Liu, Xiaofeng; Giordano, Cristina; Antonietti, Markus
Small (Weinheim an der Bergstrasse, Germany),
January 15, 2014, Letnik:
10, Številka:
1
Journal Article
Recenzirano
Efficient synthetic routes are continuously pursued for graphene in order to implement its applications in different areas. However, direct conversion of simple monomers to graphene through ...polymerization in a scalable manner remains a major challenge for chemists. Herein, a molten‐salt (MS) route for the synthesis of carbon nanostructures and graphene by controlled carbonization of glucose in molten metal chloride is reported. In this process, carbohydrate undergoes polymerization in the presence of strongly interacting ionic species, which leads to nanoporous carbon with amorphous nature and adjustable pore size. At a low precursor concentration, the process converts the sugar molecules (glucose) to rather pure few‐layer graphenes. The MS‐derived graphenes are strongly hydrophobic and exhibit remarkable selectivity and capacity for absorption of organics. The methodology described may open up a new avenue towards the synthesis and manipulation of carbon materials in liquid media.
Carbonization of sugar in molten metal chlorides leads to polymerization and formation of disordered carbonaceous materials. Under sufficiently low concentration, sugar molecules are carbonized in a two‐dimensional manner, to yield rather pure few‐layer graphenes in the salt melt. The molten‐salt‐derived graphenes are hydrophobic and show high capacity for the absorption of organics.
PharmMapper is a web server for drug target identification by reversed pharmacophore matching the query compound against an annotated pharmacophore model database, which provides a computational ...polypharmacology prediction approach for drug repurposing and side effect risk evaluation. But due to the inherent nondiscriminative feature of the simple fit scores used for prediction results ranking, the signal/noise ratio of the prediction results is high, posing a challenge for predictive reliability. In this paper, we improved the predictive accuracy of PharmMapper by generating a ligand–target pairwise fit score matrix from profiling all the annotated pharmacophore models against corresponding ligands in the original complex structures that were used to extract these pharmacophore models. The matrix reflects the noise baseline of fit score distribution of the background database, thus enabling estimation of the probability of finding a given target randomly with the calculated ligand–pharmacophore fit score. Two retrospective tests were performed which confirmed that the probability-based ranking score outperformed the simple fit score in terms of identification of both known drug targets and adverse drug reaction related off-targets.
The development of high-power white light-emitting diodes demands highly efficient and stable all-inorganic color converters. In this respect, phosphor-glass/ceramic composites show great promise as ...they could combine the merits of high quantum efficiency of phosphors and high chemical and thermal stabilities of glass/ceramic matrices. However, strong interfacial reaction between phosphors and matrices at high temperature results in quantum efficiency loss of the embedded phosphors, and traditional solutions rely on high-pressure consolidation techniques. Here we report the intrinsic inhibition of interfacial reaction by using silica glass rather than multicomponent glasses as the matrix. The embedment of phosphors is achieved via a pressureless sintering method, rendering these color-tunable phosphor-glass composites not only accessible to three-dimensional printing technique, but also highly efficient (internal quantum efficiency >90.0%), thermally stable at 1200 °C and hydrothermally stable at 200 °C. Our results provide a facile and general strategy for developing all-inorganic functional composites.
Solvents and catalysts played important roles on the selective dissolution and conversion of hemicellulose in actual biomass to produce furfural with high yield and selectivity.
Display omitted
•The ...production of furfural directly from raw biomass is reviewed.•The effective utilization of raw biomass materials to its fullest is discussed.•Selective dissolution of hemicellulose keeping cellulose and lignin intact.•Effective conversion of hemicellulose to furfural with high yield and selectivity.•The important roles of solvents and catalysts in hemicellulose upgrading process.
As one main component of lignocellulosic biomass, hemicellulose is a promising alternative for the replacement of limited fossil resources to produce furfural, thus preserving a high atom efficiency. However, the complex structure of hemicellulose and the interaction between the other two components in lignocellulosic biomass (cellulose and lignin) make the effective utilization of naturally formed structure of hemicellulose challenging. This review presents an overview of the production of furfural directly from hemicellulose in lignocellulosic biomass with special emphasis on achieving the effective utilization of hemicellulose, which includes the selective dissolution of hemicellulose from lignocellulosic biomass and the selective formation of furfural from hemicellulose derivatives. Whereas the cellulose and lignin structures are retained, which can be utilized separately. Solvents and catalysts are considered as two main factors in this valorization process of hemicellulose.
Light-matter interactions are greatly enhanced and spatially well-confined in plasmonic nanostructures in the spectral resonance range. In colloidal plasmonic nanoparticle (NP), this effect is ...manifested by the strong absorption caused by the collective oscillation of conduction electrons in NPs, known as the localized surface plasmon resonance (LSPR). The strong spectral resonance due to LSPR also contributes to the large enhancement in optical nonlinearity, such as nonlinear absorption and optical Kerr effect, and the ultrafast transient photo-bleaching in those materials making them ideal platforms for exploring optical switching behavior that is needed in all optical devices. Here, we review the recent advances in the use of colloidal processed noble metal, metalloid, chalcogenide and oxide plasmonic NPs for ultrafast optical switches to drive pulse laser generation in both solid state and fiber lasers. The broadband and ultrafast response of these plasmonic NPs offers a significant advantage in devices performance and allows the pulse generation from near infrared (NIR) to middle infrared (MIR) spectral range with pulse duration down to 100-femtosecond level. Compared with commercial products and other optical switches based on 2D materials, these plasmonic NPs are expected to provide a competitive and cost-efficient material solution to compact ultrafast pulse lasers and relevant devices.
PDF
