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Sodium ion batteries (SIB) are among the most promising devices for large scale energy storage. Their stable and long-term performance depends on the formation of the solid electrolyte interphase (SEI), a nanosized, heterogeneous and disordered layer, formed due to degradation of the electrolyte at the anode surface. The chemical and structural properties of the SEI control the charge transfer process at the electrode-electrolyte interface, thus, there is great interest in determining these properties for understanding, and ultimately controlling, SEI functionality. However, the study of the SEI is notoriously challenging due to its heterogeneous nature and minute quantity. In this work, we present a powerful approach for probing the SEI based on solid state NMR spectroscopy with increased sensitivity from dynamic nuclear polarization (DNP). Utilizing exogenous (organic radicals) and endogenous (paramagnetic metal ion dopants) DNP sources, we obtain not only a detailed compositional map of the SEI but also, for the first time for the native SEI, determine the spatial distribution of its constituent phases. Using this approach, we perform a thorough investigation of the SEI formed on Li4Ti5O12 used as a SIB anode. We identify a compositional gradient, from organic phases at the electrolyte interface to inorganic phases toward the anode surface. We find that the use of fluoroethylene carbonate as an electrolyte additive leads to performance degradation which can be attributed to formation of a thicker SEI, rich in NaF and carbonates. We expect that this methodology can be extended to examine other titanate anodes and new electrolyte compositions, offering a unique tool for SEI investigations to enable the development of effective and long-lasting SIBs.
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Understanding adsorption processes at the molecular level has transformed the discovery of engineered materials for maximizing gas storage capacity and kinetics in adsorption-based carbon capture applications. In this work, we studied the molecular mechanism of gas (CO2, H2, methane, and ethane) adsorption inside an interconnected porous network of carbon. This was achieved by synthesizing novel macro-meso-microporous carbon (M3C) nanospheres with interconnected pore structures. The M3Cs showed a CO2 capture capacity of 5.3 mmol/g at atmospheric CO2 pressure, with excellent kinetics. This was due to fast CO2 adsorption within the interconnected hierarchical macro-meso-microporous M3C. In situ small-angle neutron scattering (SANS) under various CO2 pressures indicated that the macro- and mesopores of M3C enable fast diffusion of CO2 molecules inside the micropores, where adsorbed CO2 molecules densify into a liquid-like state. This strong densification of CO2 molecules causes fast CO2 diffusion in the macro- and mesopores of M3C, restarting the adsorption cycle for fresh CO2 molecules until all pores are completely filled. Notably, M3C also showed good capture capacities for hydrogen and various hydrocarbons, with excellent selectivity toward ethane over methane.
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The discovery of dendritic fibrous nanosilica (DFNS) has attracted great attention to the field of catalysis, CO2 capture, drug delivery due to its distinct morphology, and pore size distribution. Despite extensive research, the understanding of the DFNS formation process and its internal structure remains incomplete as microscopy and gas sorption techniques were not able to provide necessary in-depth structural information due to their inherent limitations. In the current work, we present a structural model of DFNS derived using small-angle X-ray scattering (SAXS) supported by 129Xe nuclear magnetic resonance (NMR), which provided intricate details of DFNS and its internal structure. Mechanistic understanding of the DFNS formation and growth process was achieved by performing time-resolved SAXS measurements during the synthesis of DFNS, which unveils the evolution of two levels of a bicontinuous microemulsion structure responsible for intricate DFNS morphology. The validity and the accuracy of the SAXS method and the model were successfully established through a direct correlation among the functionality of the DFNS scattering profile and its pore size distribution, as well as results obtained from the 129Xe NMR studies. It has been established that the DFNS structure originates from direct modulation of the bicontinuous structure controlled by a surfactant, a co-surfactant, and the silicate species formed during hydrolysis and the condensation reaction of the silica precursor.
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Efficient RNA extraction is critical for all downstream molecular applications and techniques. Despite the availability of several commercial kits, there is an enormous scope to develop novel materials that have high binding and elution capacities. Here, we show that RNA from the cells can be extracted by dendritic fibrous nanosilica (DFNS) with higher efficiency than commercially available silicas. This could be because of the unique fibrous morphology, high accessible surface area, and nanosize particles of DFNS. We studied various fundamental aspects, including the role of particle size, morphology, surface area, and charge on the silica surface in RNA extraction efficiency. Fourier transform infrared (FTIR) spectroscopy studies revealed the interaction of functional groups of RNA with the silica surface, causing selective binding. Due to the sustainable synthesis protocol of DFNS and the simplicity of various buffers and washing solutions used, this RNA extraction kit can be assembled in any lab. In addition to the fundamental aspects of DFNS-RNA interactions, this study has the potential to initiate the development of indigenous DFNS-based kits for RNA extraction.
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ARN , Dióxido de Silicio , Tamaño de la Partícula , ARN/genética , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
A colored hybrid based on a merocyanine adsorbed in a nanoporous-silica-composed dendritic fibrous silica was prepared by adsorption onto the nanoporous silica from a spiropyran solution during UV irradiation (photoinduced adsorption). The obtained red hybrid thus exhibited negative photochromism by visible-light irradiation. The hybrid was further combined with an organophilic clay by a solid-state mixing without using solvent to achieve excellent reversibility of the color change, which was thought to be achieved by molecular diffusion through the two materials, where nanoporous silica and organophilic clay accommodated the colored (merocyanine) and colorless (photogenerated spiropyran) isomers, respectively.
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This Review highlights stoichiometric reactions and elementary steps of catalytic reactions involving cooperative participation of transition-metal hydrides and main group Lewis acids. Included are reactions where the transition-metal hydride acts as a reactant as well as transformations that form the metal hydride as a product. This Review is divided by reaction type, illustrating the diverse roles that Lewis acids can play in mediating transformations involving transition-metal hydrides as either reactants or products. We begin with a discussion of reactions where metal hydrides form direct adducts with Lewis acids, elaborating the structure and dynamics of the products of these reactions. The bulk of this Review focuses on reactions where the transition metal and Lewis acid act in cooperation, and includes sections on carbonyl reduction, H2 activation, and hydride elimination reactions, all of which can be promoted by Lewis acids. Also included is a section on Lewis acid-base secondary coordination sphere interactions, which can influence the reactivity of hydrides. Work from the past 50 years is included, but the majority of this Review focuses on research from the past decade, with the intent of showcasing the rapid emergence of this field and the potential for further development into the future.
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We studied the formation mechanism of dendritic fibrous nanosilica (DFNS) that involves several intriguing dynamical steps. Through electron microscopy and real-time small-angle X-ray scattering studies, it has been demonstrated that the structural evolution of bicontinuous microemulsion droplets (BMDs) and their subsequent coalescence, yielding nanoreactor template, is responsible for to the formation of complex DFNS morphology. The role of cosurfactant has been found to be quite crucial, which allowed the understanding of this intricate mechanism involving the complex interplay of self-assembly, dynamics of BMDs formation, and coalescence. The role of BMDs in formation of DFNS has not been reported so far and the present work allows a deeper molecular-level understanding of DFNS formation.
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The photoinduced adsorption of a photochromic spiropyran (1-(2-hydroxyethyl)-3,3-dimethylindolino-6'-nitrobenzopyrylospiran) onto a dendritic fibrous nanosilica (DFNS) was investigated. By UV irradiation, the colorless suspension containing the spiropyran and DFNS changed to blue without stirring, while it turned to red by the irradiation under stirring. These two colors were attributed to the photogenerated merocyanine in a non polar environment (in toluene, blue) and on a protic environment (on DFNS, red). The long lifetime of the adsorbed merocyanine on DFNS (red) and the easy separation of DFNS from the suspension made it possible to follow the kinetics of the photoinduced adsorption as a pseudo-first order reaction with the rate constant of 0.0279 s-1. The rate limiting process was suggested to be the adsorption of the merocyanine onto DFNS.
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Nucleoside transport is an essential process that helps maintain the hyperproliferative state of most cancer cells. As such, it represents an important target for developing diagnostic and therapeutic agents that can effectively detect and treat cancer, respectively. This report describes the development of a metal-containing nucleoside designated Ir(III)-PPY nucleoside that displays both therapeutic and diagnostic properties against the human epidermal carcinoma cell line KB3-1. The cytotoxic effects of Ir(III)-PPY nucleoside are both time- and dose-dependent. Flow cytometry analyses validate that the nucleoside analog causes apoptosis by blocking cell cycle progression at G2/M. Fluorescent microscopy studies show rapid accumulation in the cytoplasm within 4 h. However, more significant accumulation is observed in the nucleus and mitochondria after 24 h. This localization is consistent with the ability of the metal-containing nucleoside to influence cell cycle progression at G2/M. Mitochondrial depletion is also observed after longer incubations (Δt â¼48 h), and this effect may produce additional cytotoxic effects. siRNA knockdown experiments demonstrate that the nucleoside transporter, hENT1, plays a key role in the cellular entry of Ir(III)-PPY nucleoside. Collectively, these data provide evidence for the development of a metal-containing nucleoside that functions as a combined therapeutic and diagnostic agent against cancer.
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Proliferación Celular/efectos de los fármacos , Metales/metabolismo , Nucleósidos/metabolismo , Nucleósidos/farmacología , Apoptosis/efectos de los fármacos , Línea Celular Tumoral , Núcleo Celular/metabolismo , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Citosol/metabolismo , Relación Dosis-Respuesta a Droga , Tranportador Equilibrativo 1 de Nucleósido/genética , Tranportador Equilibrativo 1 de Nucleósido/metabolismo , Puntos de Control de la Fase G2 del Ciclo Celular/efectos de los fármacos , Humanos , Iridio/metabolismo , Microscopía Fluorescente , Mitocondrias/metabolismo , Necrosis , Neoplasias/genética , Neoplasias/metabolismo , Neoplasias/patología , Interferencia de ARN , Factores de TiempoRESUMEN
Cyclometalated iridium complexes with efficient phosphorescence and good electrochemical stability are important candidates for optoelectronic devices. Isocyanide ligands are strong-field ligands: when attached to transition metals, they impart larger HOMO-LUMO energy gaps, engender higher oxidative stability at the metal center, and support rugged organometallic complexes. Aryl isocyanides offer more versatile steric and electronic control by selective substitution at the aryl ring periphery. Despite a few reports of alkyl isocyanide of cyclometalated iridium(III), detailed studies on analogous aryl isocyanide complexes are scant. We report the synthesis, photophysical properties, and electrochemical properties of 11 new luminescent cationic biscyclometalated bis(aryl isocyanide)iridium(III) complexes. Three different aryl isocyanides--2,6-dimethylphenyl isocyanide (CNAr(dmp)), 2,6-diisopropylphenyl isocyanide (CNAr(dipp)), and 2-naphthyl isocyanide (CNAr(nap))--were combined with four cyclometalating ligands with differential π-π* energies--2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (F2ppy), 2-benzothienylpyridine (btp), and 2-phenylbenzothiazole (bt). Five of them were crystallographically characterized. All new complexes show wide redox windows, with reduction potentials falling in a narrow range of -2.02 to -2.37 V and oxidation potentials spanning a wider range of 0.97-1.48 V. Efficient structured emission spans from the blue region for [(F2ppy)2Ir(CNAr)2]PF6 to the orange region for [(btp)2Ir(CNAr)2]PF6, demonstrating that isocyanide ligands can support redox-stable luminescent complexes with a range of emission colors. Emission quantum yields were generally high, reaching a maximum of 0.37 for two complexes, whereas btp-ligated complexes had quantum yields below 1%. The structure of the CNAr ligand has a minimal effect on the photophysical properties, which are shown to arise from ligand-centered excited states with very little contribution from metal-to-ligand charge transfer in most cases.
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A series of cyclometalated iridium complexes with ß-ketoiminate and ß-diketiminate ligands are described. Two different cyclometalating (C^N) ligands-2-phenylpridine (ppy) and 2-phenylbenzothiazole (bt)-are used in concert with three different ancillary (LX) ligands-a phenyl-substituted ß-ketoiminate (acNac(Me)), a phenyl-substituted ß-diketiminate (NacNac(Me)), and a fluorinated version of the ß-diketiminate (NacNac(CF3))-to furnish a suite of six complexes. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Ir(C^N)2(µ-Cl)]2 with potassium or lithium salts of the ancillary LX ligand. Four of the complexes are characterized by X-ray crystallography, and all six were subjected to in-depth optical and electrochemical interrogation. Cyclic voltammetry shows both reduction and oxidation waves, with the latter strongly dependent on the identity of the LX ligand. The complexes are all luminescent, with the nature of the emissive excited state and the quantum yield (Φ) dependent on the identity of both the C^N and LX ligands. Whereas the complexes Ir(ppy)2(NacNac(Me)) and Ir(ppy)2(acNac(Me)) are weakly luminescent (Φ ≈ 0.01), the complexes Ir(bt)2(NacNac(Me)) and Ir(bt)2(acNac(Me)) are strongly luminescent, with the latter's quantum efficiency (Φ = 0.82) among the highest ever observed for cyclometalated iridium complexes. Fluorination of the NacNac ligand gives rise to completely disparate emission behavior suggestive of a NacNac-centered emissive state. The results described here, in comparison with previous groups' studies on acetylacetonate (acac) analogues, suggest that the weaker-field NacNac and acNac ligands raise the energy of the metal-centered HOMO, with energy of the HOMO increasing in the order NacNac(CF3) < acNac(Me) < NacNac(Me).
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Fundamental study of enzymatic nucleoside transport suffers for lack of optical probes that can be tracked noninvasively. Nucleoside transporters are integral membrane glycoproteins that mediate the salvage of nucleosides and their passage across cell membranes. The substrate recognition site is the deoxyribose sugar, often with little distinction among nucleobases. Reported here are nucleoside analogues in which emissive, cyclometalated iridium(III) complexes are "clicked" to C-1 of deoxyribose in place of canonical nucleobases. The resulting complexes show visible luminescence at room temperature and 77 K with microsecond-length triplet lifetimes. A representative complex is crystallographically characterized. Transport and luminescence are demonstrated in cultured human carcinoma (KB3-1) cells.
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Complejos de Coordinación/química , Desoxirribosa/química , Iridio/química , Línea Celular Tumoral , Química Clic , Complejos de Coordinación/síntesis química , Complejos de Coordinación/metabolismo , Cristalografía por Rayos X , Ciclización , Humanos , Mediciones Luminiscentes , Microscopía Confocal , Conformación Molecular , Teoría Cuántica , TemperaturaRESUMEN
We report a hybrid material in which surface anchoring-induced enhanced luminescence of AuQC@BSA clusters on high surface area dendritic fibrous nanosilica of 800 nm diameter enabled their luminescence imaging at a single particle level. The photophysical and structural properties of the hybrid material were characterized by various spectroscopic and microscopic techniques. Concomitant imaging using scattering and luminescence of such mesostructures and their response to analytes have been used to develop a chemical sensor. The hybrid material was found to be catalytically active in silane to silanol conversion, and 100% conversion was observed in 4 h when the reaction was carried out at 30 °C in the presence of light. Such materials at submicron dimensions with enhanced surface area, emission in the solid state along with a high quantum yield of 12% in water along with enhanced scattering, and surface functionalities present numerous benefits for the creation of multifunctional materials.
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An excessive amount of CO2 is the leading cause of climate change, and hence, its reduction in the Earth's atmosphere is critical to stop further degradation of the environment. Although a large body of work has been carried out for post-combustion low-temperature CO2 capture, there are very few high temperature pre-combustion CO2 capture processes. Lithium silicate (Li4SiO4), one of the best known high-temperature CO2 capture sorbents, has two main challenges, moderate capture kinetics and poor sorbent stability. In this work, we have designed and synthesized lithium silicate nanosheets (LSNs), which showed high CO2 capture capacity (35.3 wt% CO2 capture using 60% CO2 feed gas, close to the theoretical value) with ultra-fast kinetics and enhanced stability at 650 °C. Due to the nanosheet morphology of the LSNs, they provided a good external surface for CO2 adsorption at every Li-site, yielding excellent CO2 capture capacity. The nanosheet morphology of the LSNs allowed efficient CO2 diffusion to ensure reaction with the entire sheet as well as providing extremely fast CO2 capture kinetics (0.22 g g-1 min-1). Conventional lithium silicates are known to rapidly lose their capture capacity and kinetics within the first few cycles due to thick carbonate shell formation and also due to the sintering of sorbent particles; however, the LSNs were stable for at least 200 cycles without any loss in their capture capacity or kinetics. The LSNs neither formed a carbonate shell nor underwent sintering, allowing efficient adsorption-desorption cycling. We also proposed a new mechanism, a mixed-phase model, to explain the unique CO2 capture behavior of the LSNs, using detailed (i) kinetics experiments for both adsorption and desorption steps, (ii) in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy measurements, (iii) depth-profiling X-ray photoelectron spectroscopy (XPS) of the sorbent after CO2 capture and (iv) theoretical investigation through systematic electronic structure calculations within the framework of density functional theory (DFT) formalism.
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Converting CO2 directly from the air to fuel under ambient conditions is a huge challenge. Thus, there is an urgent need for CO2 conversion protocols working at room temperature and atmospheric pressure, preferentially without any external energy input. Herein, we employ magnesium (nanoparticles and bulk), an inexpensive and the eighth-most abundant element, to convert CO2 to methane, methanol and formic acid, using water as the sole hydrogen source. The conversion of CO2 (pure, as well as directly from the air) took place within a few minutes at 300 K and 1 bar, and no external (thermal, photo, or electric) energy was required. Hydrogen was, however, the predominant product as the reaction of water with magnesium was favored over the reaction of CO2 and water with magnesium. A unique cooperative action of Mg, basic magnesium carbonate, CO2, and water enabled this CO2 transformation. If any of the four components was missing, no CO2 conversion took place. The reaction intermediates and the reaction pathway were identified by 13CO2 isotopic labeling, powder X-ray diffraction (PXRD), nuclear magnetic resonance (NMR) and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and rationalized by density-functional theory (DFT) calculations. During CO2 conversion, Mg was converted to magnesium hydroxide and carbonate, which may be regenerated. Our low-temperature experiments also indicate the future prospect of using this CO2-to-fuel conversion process on the surface of Mars, where CO2, water (ice), and magnesium are abundant. Thus, even though the overall process is non-catalytic, it could serve as a step towards a sustainable CO2 utilization strategy as well as potentially being a first step towards a magnesium-driven civilization on Mars.
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Nitrogen doped carbon spheres with wrinkled cages (NCSWCs), which were used for the first time as metal-free catalysts, exhibited high catalytic activity and selectivity in the oxidation of 5-hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) under base-free conditions using tert-butyl hydroperoxide (TBHP) as the oxidant. The mechanistic studies found that this reaction was catalyzed by the synergy between NCSWCs and TBHP. The density functional theory (DFT) calculations further suggested that the hydroperoxyl radicals from TBHP adsorbed on the carbon atoms adjacent to the graphitic N atoms are the active sites.
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The synthesis of solid acids with strong zeolite-like acidity and textural properties like amorphous aluminosilicates (ASAs) is still a challenge. In this work, we report the synthesis of amorphous "acidic aluminosilicates (AAS)", which possesses Brønsted acidic sites like in zeolites and textural properties like ASAs. AAS catalyzes different reactions (styrene oxide ring-opening, vesidryl synthesis, Friedel-Crafts alkylation, jasminaldehyde synthesis, m-xylene isomerization, and cumene cracking) with better performance than state-of-the-art zeolites and amorphous aluminosilicates. Notably, AAS efficiently converts a range of waste plastics to hydrocarbons at significantly lower temperatures. A Cu-Zn-Al/AAS hybrid shows excellent performance for CO2 to fuel conversion with 79% selectivity for dimethyl ether. Conventional and DNP-enhanced solid-state NMR provides a molecular-level understanding of the distinctive Brønsted acidic sites of these materials. Due to their unique combination of strong acidity and accessibility, AAS will be a potential alternative to zeolites.
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Morphology-controlled nanomaterials such as silica play a critical role in the development of technologies for use in the fields of energy, environment (water and air pollution) and health. Since the discovery of Stöber's silica, followed by the discovery of mesoporous silica materials (MSNs) such as MCM-41 and SBA-15, a surge in the design and synthesis of nanosilica with various sizes, shapes, morphologies and textural properties (surface area, pore size and pore volume) has occurred. Dendritic fibrous nanosilica (DFNS; also known as KCC-1) is one of the recent discoveries in morphology-controlled nanomaterials. DFNS shows exceptional performance in large numbers of fields, including catalysis, gas capture, solar energy harvest, energy storage, sensors and biomedical applications. This material possesses a unique fibrous morphology, unlike the tubular porous structure of various conventional silica materials. It has a high surface area to volume ratio, with improved accessibility to the internal surface, tunable pore size and pore volume, controllable particle size and, importantly, improved stability. However, synthesis of DFNS with controllable size, textural properties and fiber density is still tricky because of several of the steps involved. This protocol provides a comprehensive step-wise description of DFNS synthesis and advice regarding how to control size, surface area, pore size, pore volume and fiber density. We also provide details of how to apply DFNS in catalysis and CO2 capture. Detailed characterization protocols for these materials using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and thermal gravimetric analysis (TGA) studies are also provided.
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Dióxido de Carbono/química , Nanoestructuras/química , Nanotecnología/métodos , Dióxido de Silicio/química , Catálisis , Microscopía Electrónica de Rastreo , Microscopía Electrónica de Transmisión , Porosidad , Propiedades de Superficie , Termogravimetría/métodosRESUMEN
In this work, we showed the tuning of the catalytic behavior of dendritic plasmonic colloidosomes (DPCs) by plasmonic hotspots. A cycle-by-cycle solution-phase synthetic protocol yielded high-surface-area DPCs by controlled nucleation-growth of gold nanoparticles. These DPCs, which had varying interparticle distances and particle-size distribution, absorb light over the entire visible region as well as in the near-infrared region of the solar spectrum, transforming gold into black gold. They produced intense hotspots of localized electric fields as well as heat, which were quantified and visualized by Raman thermometry and electron energy loss spectroscopy plasmon mapping. These DPCs can be effectively utilized for the oxidation reaction of cinnamyl alcohol using pure oxygen as the oxidant, hydrosilylation of aldehydes, temperature jump assisted protein unfolding and purification of seawater to drinkable water via steam generation. Black gold DPCs also convert CO2 to methane (fuel) at atmospheric pressure and temperature, using solar energy.
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Photonic crystals are essentially a periodic ("crystalline") arrangement of dielectric nanoparticles that respond in unison to incident light. They can be used to harvest light in various applications such as photocatalysis, solar cells, and lasing. In this work, we prepared the photonic crystals of dendritic fibrous nanosilica (DFNS) by their self-assembly. Because of the narrow particle size distribution of the as-synthesized DFNS, they readily formed colored photonic crystals. The photonic band gap was found to be tunable by using DFNS of various sizes and fiber densities. Notably, even after having similar particle sizes (but with different fiber densities), they showed different photonic band gaps, indicating that the fiber density plays a role in the band gap of photonic crystals. Such observations have not been reported before. This could have arisen from the difference in their refractive indices because of the difference in their fiber densities and hence the variation in the silica content, leading to a different optical signature.