1,721,029 research outputs found
Structure and hydrogen sorption properties of Mg-Mg2Ni nanoparticles prepared by gas phase condensation
Full text linkThe aim of this work is to investigate the hydrogen sorption kinetics and thermodynamics of Mg-Ni nanoparticles at relatively low temperature in relation to their microstructure. To this purpose, Mg-Ni nanoparticles (20 at% Ni) were prepared by gas phase condensation employing two thermal vapour sources. In the as-prepared state, Mg and Ni are mixed within individual nanoparticles, but the intermetallic Mg2Ni compound is not fully formed. After keeping the nanoparticles at 150 °C for two hours under high vacuum or at a mild hydrogen pressure of 0.15 bar, the formation of a Mg-Mg2Ni or MgH2-Mg2NiH0.3 nanocomposite is observed. Subsequently, fast kinetics of hydrogen sorption are recorded at 150 °C with activation energy of 80±8 kJ/mol (absorption) and 60±6 kJ/mol (desorption). However, the maximum hydrogen storage capacity is limited to 2.5 wt% because the transformation from Mg2NiH0.3 to Mg2NiH4 does not take place at 150 °C even at pressures well above the expected thermodynamic equilibrium. Therefore, only the transformation Mg↔MgH2 contributes to the reversible storage capacity. The corresponding equilibrium pressure determined by pressure-composition isotherms of absorption and desorption at 150 °C is 7.5 mbar, very close to the extrapolated value for bulk Mg. The partial replacement of Ni with Fe does not significantly alter the thermodynamics and kinetics of hydrogen sorption. The structure and hydrogen sorption properties of Mg-Ni nanoparticles are compared to those of Mg-Ti nanoparticles prepared by a similar procedure
The Renaissance of Luminescent Solar Concentrators: The Role of Inorganic Nanomaterials
No full textWhile luminescent solar concentrators (LSCs) have a simple architecture—a transparent matrix embedding a luminescent fluorophore coupled with solar cells at the lateral side of the LSC slab—multiple paths for possible light losses exist. These are inherently interconnected, and in the past, limited the interest in this device, due to the gap between the theoretical possibilities and experimental achievements. This gap was a result, primarily, of the optical features of the luminescent dyes, since conventional organic luminophores are affected by limited performance in LSC devices. The rise of a wide portfolio of optically active inorganic nanomaterials in the last decade provides an alternative to organic dyes and has lead to a renaissance in the role of LSCs among the unconventional solar energy conversion devices. This paper reviews the latest results in the development of LSCs based on different classes of nanomaterials, focusing on the specific features and critically analyzing the pros and cons of the proposed structures. Particular attention is devoted to the role of the luminescence properties, e.g., the Stokes shift and the photoluminescence quantum yield, with respect to the performance of the LSC device. Future challenges to the successful employment of these devices for building integrated photovoltaics are also discussed
Reduced graphene oxide-ZnO hybrid composites as photocatalysts: The role of nature of the molecular target in catalytic performance
Full text linkSpurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water. Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach
Microwave-assisted vs. Conventional hydrothermal synthesis of mos2 nanosheets: Application towards hydrogen evolution reaction
Full text linkMolybdenum sulfide (MoS2 ) has emerged as a promising catalyst for hydrogen evolution applications. The synthesis method mainly employed is a conventional hydrothermal method. This method requires a longer time compared to other methods such as microwave synthesis methods. There is a lack of comparison of the two synthesis methods in terms of crystal morphology and its electrochemical activities. In this work, MoS2 nanosheets are synthesized using both hydrothermal (HT-MoS2 ) and advanced microwave methods (MW-MoS2 ), their crystal morphology, and catalytical efficiency towards hydrogen evolution reaction (HER) were compared. MoS2 nanosheet is obtained using microwave-assisted synthesis in a very short time (30 min) compared to the 24 h hydrothermal synthesis method. Both methods produce thin and aggregated nanosheets. However, the nanosheets synthesized by the microwave method have a less crumpled structure and smoother edges compared to the hydrothermal method. The as-prepared nanosheets are tested and used as a catalyst for hydrogen evolution results in nearly similar electrocatalytic performance. Experimental results showed that: HT-MoS2 displays a current density of 10 mA/cm2 at overpotential (−280 mV) compared to MW-MoS2 which requires −320 mV to produce a similar current density, suggesting that the HT-MoS2 more active towards hydrogen evolutions reaction
Colloidally stable silicon quantum dots as temperature biosensors
No full textAmong semiconductor quantum dots, silicon nanocrystals (SiNCs) are gaining interest due to their high biocompatibility and natural abundance of silicon. The optical properties make SiNCs optimal candidates for luminescent bioprobes: (i) emission energy tuneable to the red and NIR spectral region, compatible with the biological window; (ii) high photoluminescence quantum yield; (iii) no sensitivity to molecular oxygen despite the long lifetime of emission; (iv) long-lived luminescence that enables time-gated detection in the hundreds of μs timescale, which allows removal of scattered excitation light and autofluorescence of the biological sample with a low-cost equipment (gating times of the order of hundreds of μs). SiNCs can be passivated through covalent bond formation between Si and C atoms giving extremely robust systems. The two major issues for SiNCs are the poor absorption outside the UV spectral region and the difficulty to obtain water suspendable SiNCs that maintain their photo physical properties. Our group addressed the first problem by introducing light absorbing units on the SiNCs surface; these dyes can be excited and transfer the energy to the silicon core behaving like a light-harvesting antenna. Regarding the second issue, several attempts are reported in literature to make SiNCs water dispersible, but these approaches often suffer of scarce stability in aqueous environment, and loss of SiNCs photophysical properties. Our approach is based on covalent functionalization of SiNCs via two-step synthesis involving a first coating step in organic solvent and a post-functionalization through thiol-ene click chemistry in order to introduce poly(ethyleneglycol) (PEG) as a water soluble group. SiNCs obtained with this approach are colloidally stable and retain NIR emission with long emission lifetimes (tens of microsecond)
High efficiency sandwich structure luminescent solar concentrators based on colloidal quantum dots
No full textLuminescent solar concentrators (LSCs) have received significant attention because of their low cost, large-area and high efficiency sunlight energy harvesting. Colloidal core/shell quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs. However, due to the limitation of QDs properties and device architectures, LSCs fabricated using QDs still face the challenges of low optical efficiency and limited long-term stability for the large-area LSCs. In this work, we synthesized CdSe/CdS QDs, and found that higher CdS shell growth temperature results in improved uniformity in structure and morphology and more suitable optical properties. Based on the CdSe/CdS QDs, a large-area (∼100 cm 2 ) sandwich structure luminescent solar concentrator (LSC) was fabricated. By laminating the QDs layer between two sheets of optical clear glass, the reabsorption losses of the device can be reduced due to the decrease of photon escape. The as-fabricated sandwich structure device exhibits an external optical efficiency of ∼ 2.95% under natural sunlight illumination, which represents a 78% enhancement in efficiency over the single layer film LSCs based on CdSe/CdS QDs. More importantly, the sandwich structure can protect the QDs interlayer from the impact of the ambient environment (e.g. oxygen, moisture and alkalinity) and enhance the long-term stability of LSCs. Our work shows that the use of suitably tuned core-shell QDs and the sandwich structure in LSC architecture can dramatically enhance the external optical efficiency of LSC devices based on CdSe/CdS QDs
Bioinspired Design of Graphene‐Based Materials
No full textIt can be difficult to know where to begin when considering the research opportunities of a material with such outstanding potential as graphene. When searching for a “killer application,” the researcher often neglects to query the world around them, forgetting that nature has been evolving for billions of years to elegantly solve every day problems. Bioinspiration is an intelligent strategy to nucleate new ideas and speed up the innovation process by providing ready-made prototypes. Graphene is uniquely placed to take advantage of this approach thanks to its superlative properties and versatile nature. In this review, the state-of-the-art in the bioinspired design of graphene-based materials has been analyzed, and three distinct sources of inspiration have been identified: natural functions, such as adhesion and actuation; natural structures, such as layers and pores; and natural processes, such as surface functionalization and biomineralization. Implementing this philosophy into further graphene research will provide new ways to solve problems and suggest novel applications that may not otherwise be considered
Distribution of Relaxation Times Based on Lasso Regression: A Tool for High-Resolution Analysis of IMPS Data in Photoelectrochemical Systems
Full text linkIntensity-modulated photocurrent spectroscopy (IMPS) has been largely employed in semiconductor characterization for solar energy conversion devices to probe the operando behavior with widely available facilities. However, the implementation of IMPS data analysis to complex structures, whether based on the physical rate constant model (RCM) or the assumption-free distribution of relaxation times (DRT), is generally limited to a semi-quantitative description of the charge carrier kinetics of the system. In this study, a new algorithm for the analysis of IMPS data is developed, providing unprecedented time resolution to the investigation of μs to s charge carrier dynamics in semiconductor-based systems used in photoelectrochemistry and photovoltaics. The algorithm, based on the previously developed DRT analysis, is herein modified with a Lasso regression method and available to the reader free of charge. A validation of this new algorithm is performed on a α-Fe2O3 photoanode for photoelectrochemical water splitting, identified as a standard platform in the field, highlighting multiple potential-dependent charge transfer paths, otherwise hidden in the conventional IMPS data analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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