Showing papers in "Journal of Physical Chemistry Letters in 2012"
TL;DR: This study shows that these r-RuO2 and r-IrO2 NPs can serve as a benchmark in the development of active OER catalysts for electrolyzers, metal-air batteries, and photoelectrochemical water splitting applications.
Abstract: The activities of the oxygen evolution reaction (OER) on iridium-oxide- and ruthenium-oxide-based catalysts are among the highest known to date. However, the OER activities of thermodynamically stable rutile iridium oxide (r-IrO2) and rutile iridium oxide (r-RuO2), normalized to catalyst mass or true surface area are not well-defined. Here we report a synthesis of r-IrO2 and r-RuO2 nanoparticles (NPs) of ∼6 nm, and examine their OER activities in acid and alkaline solutions. Both r-IrO2 and r-RuO2 NPs were highly active for OER, with r-RuO2 exhibiting up to 10 A/goxide at 1.48 V versus reversible hydrogen electrode. When comparing the two, r-RuO2 NPs were found to have slightly higher intrinsic and mass OER activities than r-IrO2 in both acid and basic solutions. Interestingly, these oxide NPs showed higher stability under OER conditions than commercial Ru/C and Ir/C catalysts. Our study shows that these r-RuO2 and r-IrO2 NPs can serve as a benchmark in the development of active OER catalysts for electrol...
2,762 citations
TL;DR: In this paper, the authors compare trends in binding energies for the intermediates in CO2 electrochemical reduction and present an activity "volcano" based on this analysis, which describes the experimentally observed variations in transition-metal catalysts.
Abstract: The electrochemical reduction of CO2 into hydrocarbons and alcohols would allow renewable energy sources to be converted into fuels and chemicals. However, no electrode catalysts have been developed that can perform this transformation with a low overpotential at reasonable current densities. In this work, we compare trends in binding energies for the intermediates in CO2 electrochemical reduction and present an activity “volcano” based on this analysis. This analysis describes the experimentally observed variations in transition-metal catalysts, including why copper is the best-known metal electrocatalyst. The protonation of adsorbed CO is singled out as the most important step dictating the overpotential. New strategies are presented for the discovery of catalysts that can operate with a reduced overpotential.
1,168 citations
TL;DR: XPS and isotope labeling coupled with differential electrochemical mass spectrometry (DEMS) is used to show that small amounts of carbonates formed during discharge and charge of Li-O2 cells in ether electrolytes originate from reaction of Li2O2 both with the electrolyte and with the C cathode.
Abstract: We use XPS and isotope labeling coupled with differential electrochemical mass spectrometry (DEMS) to show that small amounts of carbonates formed during discharge and charge of Li–O2 cells in ether electrolytes originate from reaction of Li2O2 (or LiO2) both with the electrolyte and with the C cathode. Reaction with the cathode forms approximately a monolayer of Li2CO3 at the C–Li2O2 interface, while reaction with the electrolyte forms approximately a monolayer of carbonate at the Li2O2–electrolyte interface during charge. A simple electrochemical model suggests that the carbonate at the electrolyte–Li2O2 interface is responsible for the large potential increase during charging (and hence indirectly for the poor rechargeability). A theoretical charge-transport model suggests that the carbonate layer at the C–Li2O2 interface causes a 10–100 fold decrease in the exchange current density. These twin “interfacial carbonate problems” are likely general and will ultimately have to be overcome to produce a high...
998 citations
TL;DR: In this article, it was shown that many of the commonly studied two-dimensional monolayer transition metal dichalcogenide (TMDC) nanoscale materials are piezoelectric, unlike their bulk parent crystals.
Abstract: We discovered that many of the commonly studied two-dimensional monolayer transition metal dichalcogenide (TMDC) nanoscale materials are piezoelectric, unlike their bulk parent crystals. On the macroscopic scale, piezoelectricity is widely used to achieve robust electromechanical coupling in a rich variety of sensors and actuators. Remarkably, our density-functional theory calculations of the piezoelectric coefficients of monolayer BN, MoS2, MoSe2, MoTe2, WS2, WSe2, and WTe2 reveal that some of these materials exhibit stronger piezoelectric coupling than traditionally employed bulk wurtzite structures. We find that the piezoelectric coefficients span more than 1 order of magnitude, and exhibit monotonic periodic trends. The discovery of this property in many two-dimensional materials enables active sensing, actuating, and new electronic components for nanoscale devices based on the familiar piezoelectric effect.
834 citations
TL;DR: It is shown that r-GO sheets have ionizable groups with a single pK value (8.0) while GO sheets have groups that are more acidic (pK = 4.3), in addition to groups with pK values of 6.6 and 9.0.
Abstract: The chemistry underlying the aqueous dispersibility of graphene oxide (GO) and reduced graphene oxide (r-GO) is a key consideration in the design of solution processing techniques for the preparation of processable graphene sheets. Here, we use zeta potential measurements, pH titrations, and infrared spectroscopy to establish the chemistry underlying the aqueous dispersibility of GO and r-GO sheets at different values of pH. We show that r-GO sheets have ionizable groups with a single pK value (8.0) while GO sheets have groups that are more acidic (pK = 4.3), in addition to groups with pK values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r-GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pKa value by stabilizing the carboxylate anion, resulting in superior wate...
715 citations
539 citations
TL;DR: In this article, a meta-GGA exchange-correlation functional, called M11-L, was proposed to provide broad accuracy for both single-configurational and multiconfigurational molecules and for solid-state lattice constants.
Abstract: Local approximations to the exchange-correlation functional are of special interest because of their cost advantages and their useful accuracy for efficient calculations on systems (such as many transition metal catalysts) with significant multiconfigurational wave function character. We present a meta-GGA exchange-correlation functional, called M11-L, that employs dual-range local exchange to provide broad accuracy for both single-configurational and multiconfigurational molecules and for solid-state lattice constants. Also notable is the high accuracy (for a local functional) for chemical reaction barrier heights. The mean unsigned error on a broad chemistry database of 338 energetic data is lower than that for any other known functional, even hybrid functionals and range-separated hybrid functionals. This success shows that the dependence of the exchange energy density on interelectronic distance is quite different at short-range and long-range, and it establishes a new standard for the limit of what c...
537 citations
TL;DR: In this article, it was shown that BSCF82 can quickly undergo amorphization of its surface at OER potentials, which is accompanied by reduced surface concentrations of Ba2+ and Sr2+ ions as well as increased pseudocapacitive and OER currents.
Abstract: Perovskites such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF82) can be highly active for the oxygen evolution reaction (OER) upon water oxidation in alkaline solution. Here we report that BSCF82 can quickly undergo amorphization of its surface at OER potentials, which is accompanied by reduced surface concentrations of Ba2+ and Sr2+ ions as well as increased pseudocapacitive and OER currents. Such quick amorphization during OER was also observed for perovskite catalysts with similar OER activities such as Ba0.5Sr0.5Co0.4Fe0.6O3−δ and SrCo0.8Fe0.2O3−δ. In contrast, perovskite oxides with lower OER activities than BSCF82 did not undergo this transformation when subjected to identical electrochemical conditions. These findings demonstrate that the active chemistry and structure of oxide catalysts during OER can significantly differ from those of the as-synthesized material and that understanding how the oxide surface may change and impact the OER activity is critical to the design of highly active and stable OER catal...
525 citations
TL;DR: Some of the significant work performed with graphene and its derivatives for gas detection and a perspective on the challenges that need to be overcome to enable commercially viable graphene chemical sensor technologies are reviewed.
Abstract: Pioneering research in 2004 by Geim and Novoselov (2010 Nobel Prize winners in Physics) of the University of Manchester led to the isolation of a monolayer graphene sheet. Graphene is a single-atom-thick sheet of sp2 hybridized carbon atoms that are packed in a hexagonal honeycomb crystalline structure. Graphene is the fundamental building block of all sp2 carbon materials including single-walled carbon nanotubes, mutliwalled carbon nanotubes, and graphite and is therefore interesting from the fundamental standpoint as well as for practical applications. One of the most promising applications of graphene that has emerged so far is its utilization as an ultrasensitive chemical or gas sensor. In this article, we review some of the significant work performed with graphene and its derivatives for gas detection and provide a perspective on the challenges that need to be overcome to enable commercially viable graphene chemical sensor technologies.
514 citations
TL;DR: These unexpected molecular sieving properties of zeolitic imidazolate framework-8 (ZIF-8) open up new opportunities for ZIF materials for separations that cannot be economically achieved by traditional microporous adsorbents such as synthetic zeolites.
Abstract: We studied molecular sieving properties of zeolitic imidazolate framework-8 (ZIF-8) by estimating the thermodynamically corrected diffusivities of probe molecules at 35 °C. From helium (2.6 A) to iso-C4H10 (5.0 A), the corrected diffusivity drops 14 orders of magnitude. Our results further suggest that the effective aperture size of ZIF-8 for molecular sieving is in the range of 4.0 to 4.2 A, which is significantly larger than the XRD-derived value (3.4 A) and between the well-known aperture size of zeolite 4A (3.8 A) and 5A (4.3 A). Interestingly, because of aperture flexibility, the studied C4 hydrocarbon molecules that are larger than this effective aperture size still adsorb in the micropores of ZIF-8 with kinetic selectivities for iso-C4H8/iso-C4H10 of 180 and n-C4H10/iso-C4H10 of 2.5 × 10(6). These unexpected molecular sieving properties open up new opportunities for ZIF materials for separations that cannot be economically achieved by traditional microporous adsorbents such as synthetic zeolites.
500 citations
TL;DR: Compared to the native Si particles, the composite capsules have greatly improved performance as Li ion battery anodes in terms of capacity, cycling stability, and Coulombic efficiency.
Abstract: Submicrometer-sized capsules made of Si nanoparticles wrapped by crumpled graphene shells were made by a rapid, one-step capillary-driven assembly route in aerosol droplets Aqueous dispersion of micrometer-sized graphene oxide (GO) sheets and Si nanoparticles were nebulized to form aerosol droplets, which were passed through a preheated tube furnace Evaporation-induced capillary force wrapped graphene (aka, reduced GO) sheets around the Si particles, and heavily crumpled the shell The folds and wrinkles in the crumpled graphene coating can accommodate the volume expansion of Si upon lithiation without fracture, and thus help to protect Si nanoparticles from excessive deposition of the insulating solid electrolyte interphase Compared to the native Si particles, the composite capsules have greatly improved performance as Li ion battery anodes in terms of capacity, cycling stability, and Coulombic efficiency
TL;DR: S semiconductor and metal nanoparticles assembled on reduced graphene oxide sheets offer new ways to design multifunctional catalyst mat and the fundamental understanding of charge-transfer processes is important in the future design of light-harvesting assemblies.
Abstract: The Perspective focuses on photoinduced electron transfer between semiconductor–metal and semiconductor–semiconductor nanostructures and factors that influence the rate of electron transfer at the interface. The storage and discharge properties of metal nanoparticles play an important role in dictating the photocatalytic performance of semiconductor–metal composite assemblies. Both electron and hole transfer across the interface with comparable rates are important in maintaining high photocatalytic efficiency and stability of the semiconductor assemblies. Coupled semiconductors of well-matched band energies are convenient to improve charge separation. Furthermore, semiconductor and metal nanoparticles assembled on reduced graphene oxide sheets offer new ways to design multifunctional catalyst mat. The fundamental understanding of charge-transfer processes is important in the future design of light-harvesting assemblies.
TL;DR: This Perspective provides contemporary views on heterogeneous photochemical conversion, encompassing charge transport characteristics, radical chemistry and organic degradation mechanisms, photocatalyst design, and photoreactor engineering.
Abstract: The field of heterogeneous photocatalysis has expanded rapidly in the last four decades, having undergone various evolutionary phases related to energy and the environment. The two most significant applications of photocatalysis are geared toward solar water splitting and the purification of air and water. Notably, the interdisciplinary nature of the field has increased significantly, incorporating semiconductor physics, surface sciences, photo and physical chemistry, materials science, and chemical engineering. Whereas this forms the basis on which the field continues to grow, adequate bridging of multidisciplinary knowledge remains essential. By recalling some of the classical fundamentals of photocatalysis, this Perspective provides contemporary views on heterogeneous photochemical conversion, encompassing charge transport characteristics, radical chemistry and organic degradation mechanisms, photocatalyst design, and photoreactor engineering.
TL;DR: In this paper, the role of plasmonic nanostructures on fluorescence was reconsidered from the perspective of optical nanoantennas, which can dramatically enhance the performances of existing optical and optoelectronic devices such as solar cells, light-emitting devices, biosensors, and high-resolution fluorescence microscopes.
Abstract: Control over light absorption and emission using plasmonic nanostructures is an enabling technology, which can dramatically enhance the performances of existing optical and optoelectronic devices, such as solar cells, light-emitting devices, biosensors, and high-resolution fluorescence microscopes. This Perspective takes fluorescence as an example, illustrating how plasmonic nanostructures can control the light absorption and emission of nanoscale optical species. The origins of fluorescence intensity enhancements will be first discussed. Different parameters that can largely affect the interactions between plasmonic nanostructures and fluorophore molecules will be examined, including the distance between the fluorophore molecule and the metal nanostructure and the wavelengths of their respective optical responses. The role of plasmonic nanostructures on fluorescence will then be reconsidered from the perspective of optical nanoantennas. We expect that more functionalities of plasmonic nanostructures as o...
TL;DR: The chiral-induced spin selectivity (CISS) effect is reviewed and applications that can result from special properties of this effect, like the reduction of the elastic backscattering in electron transfer through chiral molecules are discussed.
Abstract: The chiral-induced spin selectivity (CISS) effect was recently established experimentally and theoretically. Here, we review some of the new findings and discuss applications that can result from special properties of this effect, like the reduction of the elastic backscattering in electron transfer through chiral molecules. The CISS effect opens the possibility of using chiral molecules in spintronics applications and for providing a deeper understanding of spin-selective processes in biology.
TL;DR: The current progress on tuning the luminescence properties of I-III-VI nanocrystals is highlighted, especially focusing on the advances in the synthesis, spectroscopic properties, as well as the primary applications in light-emitting devices and bioimaging techniques.
Abstract: In the past 5 years, colloidal I–III–VI nanocrystals such as CuInS2, CuInSe2, and AgInS2 have been intensively investigated for the potential to replace commonly available colloidal nanocrystals containing toxic elements in light-emitting and solar-harvesting applications. Many researchers from different disciplines are working on developing new synthetic protocols, performing spectroscopic studies to understand the luminescence mechanisms, and exploring various applications. To achieve enhanced performance, it is very desirable to obtain high-quality materials with tunable luminescence properties. In this Perspective, we highlight the current progress on tuning the luminescence properties of I–III–VI nanocrystals, especially focusing on the advances in the synthesis, spectroscopic properties, as well as the primary applications in light-emitting devices and bioimaging techniques. Finally, we outline the challenges concerning luminescent I–III–VI NCs and list a few important research tasks in this field.
TL;DR: It is shown that rechargeability in the various electrolytes is limited both by chemical reaction of Li2O2 with the solvent and by electrochemical oxidation reactions during charging at potentials below the onset of electrolyte oxidation on an inert electrode.
Abstract: Quantitative differential electrochemical mass spectrometry (DEMS) is used to measure the Coulombic efficiency of discharge and charge [(e–/O2)dis and (e–/O2)chg] and chemical rechargeability (characterized by the O2 recovery efficiency, OER/ORR) for Li-O2 electrochemistry in a variety of nonaqueous electrolytes. We find that none of the electrolytes studied are truly rechargeable, with OER/ORR <90% for all. Our findings emphasize that neither the overpotential for recharge nor capacity fade during cycling are adequate to assess rechargeability. Coulometry has to be coupled to quantitative measurements of the chemistry to measure the rechargeability truly. We show that rechargeability in the various electrolytes is limited both by chemical reaction of Li2O2 with the solvent and by electrochemical oxidation reactions during charging at potentials below the onset of electrolyte oxidation on an inert electrode. Possible mechanisms are suggested for electrolyte decomposition, which taken together, impose stri...
TL;DR: ZMoS2NRs have a remarkably enhanced binding interaction with Li without sacrificing the Li mobility, and thus are promising as cathode materials of Li-ion batteries with a high power density and fast charge/discharge rates.
Abstract: By means of density functional theory computations, we systematically investigated the adsorption and diffusion of Li on the 2-D MoS2 nanosheets and 1-D zigzag MoS2 nanoribbons (ZMoS2NRs), in comparison with MoS2 bulk. Although the Li mobility can be significantly facilitated in MoS2 nanosheets, their decreased Li binding energies make them less attractive for cathode applications. Because of the presence of unique edge states, ZMoS2NRs have a remarkably enhanced binding interaction with Li without sacrificing the Li mobility, and thus are promising as cathode materials of Li-ion batteries with a high power density and fast charge/discharge rates.
TL;DR: This study presents a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.
Abstract: Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.
TL;DR: In this article, the authors report on their current understanding on the nature of structural heterogeneities in ionic liquids, describing new experimental data supporting a microphase segregation structural model for these systems and proposing topics for further study.
Abstract: Ionic liquids represent an exciting novel class of materials with potentially enormous applicative impact; they are proposed as environmentally responsible replacements for the noxious volatile organic solvents, as smart separation and catalysis media, or to develop electrochemical devices, just to mention a few examples. Recently, compelling experimental as well as computational evidence highlighted the complexity of RTIL morphology at the mesoscopic spatial scale, as compared to traditional molecular liquids. In this Perspective, we report on our current understanding on the nature of structural heterogeneities in ionic liquids, describing new experimental data supporting a microphase segregation structural model for these systems and proposing topics for further study.
TL;DR: This work demonstrates a process that involves the physical separation of weakly bonded WS2 layers by use of a strong acid treatment at 2 mg/mL, followed by quenching in deionized water, and studied the electrochemical behavior of an acid-treated WS2 anode in a lithium half-cell configuration that showed a three-step charge-discharge behavior, characteristic of a conversion reaction.
Abstract: Separation of bulk tungsten disulfide (or WS2) into few-layer two-dimensional (2-D) crystals is of interest because of their high surface area for certain chemical processes and size-dependent optical and electronic characteristics. Herein, we demonstrate a process that involves the physical separation of weakly bonded WS2 layers by use of a strong acid treatment (chlorosulfonic acid) at 2 mg/mL, followed by quenching in deionized (DI) water. X-ray photoelectron spectroscopy of the superacid-treated WS2 suggests the formation of W–O type bonds, signifying oxidation of tungsten and reduction of the sulfur phase. Thermogravimetric analysis showed a three-phase weight-loss pattern, suggesting acid functionalization of WS2 surfaces. We also studied the electrochemical behavior of an acid-treated WS2 anode in a lithium half-cell configuration that showed a three-step charge–discharge behavior, characteristic of a conversion reaction. The electrochemical capacity was 118 mAh/g after 50 cycles.
TL;DR: A new optical antenna concept based on surface plasmon polariton (SPP) nanofocusing on conical noble metal tips to achieve efficient far- to near-field transformation of light from the micro- to the nanoscale is discussed.
Abstract: The efficiency of plasmonic nanostructures as optical antennas to concentrate optical fields to the nanoscale has been limited by intrinsically short dephasing times and small absorption cross sections. We discuss a new optical antenna concept based on surface plasmon polariton (SPP) nanofocusing on conical noble metal tips to achieve efficient far- to near-field transformation of light from the micro- to the nanoscale. The spatial separation of the launching of propagating SPPs from their subsequent apex confinement with high energy concentration enables background-free near-field imaging, tip-enhanced Raman scattering, and nonlinear nanospectroscopy. The broad bandwidth and spectral tunability of the nanofocusing mechanism in combination with frequency domain pulse shaping uniquely allow for the spatial confinement of ultrashort laser pulses and few-femtosecond spatiotemporal optical control on the nanoscale. This technique not only extends powerful nonlinear and ultrafast spectroscopies to the nanoscal...
TL;DR: Transport by hopping in semiconductor or weakly coupled metal nanocrystal solids dominates transport, as in disordered semiconductors, and such behavior at finite temperature is not proof of band-like conduction.
Abstract: In nanocrystal solids, the small density of states of quantum dots makes it difficult to achieve metallic conductivity without band-like transport. However, to achieve band-like transport, the energy scale of the disorder should be smaller than the coupling energy. This is unlikely with the present systems due to the size polydispersivity. Transport by hopping may nevertheless lead to an increased mobility with decreasing temperature for some temperature range, and such behavior at finite temperature is not proof of band-like conduction. To date, at low temperature, variable range hopping in semiconductor or weakly coupled metal nanocrystal solids dominates transport, as in disordered semiconductors.
TL;DR: A simple, cost-effective, and scalable approach to fabricate a piezoelectric nanogenerator (NG) with stretchable and flexible characteristics using BaTiO3 nanotubes, which were synthesized by the hydrothermal method.
Abstract: We have developed a simple, cost-effective, and scalable approach to fabricate a piezoelectric nanogenerator (NG) with stretchable and flexible characteristics using BaTiO3 nanotubes, which were synthesized by the hydrothermal method. The NG was fabricated by making a composite of the nanotubes with polymer poly(dimethylsiloxane) (PDMS). The peak open-circuit voltage and short-circuit current of the NG reached a high level of 5.5 V and 350 nA (current density of 350 nA/cm2), respectively. It was used to directly drive a commercial liquid crystal display. The BaTiO3 nanotubes/PDMS composite is highly transparent and useful for a large-scale (11 × 11 cm) fabrication of lead-free piezoelectric NG.
TL;DR: It is demonstrated that mixed MoS2/MoSe 2/MoTe2 compounds are thermodynamically stable at room temperature, so that such materials can be manufactured using chemical-vapor deposition technique or exfoliated from the bulk mixed materials.
Abstract: Using density-functional theory calculations, we study the stability and electronic properties of single layers of mixed transition metal dichalcogenides (TMDs), such as MoS2xSe2(1–x), which can be referred to as two-dimensional (2D) random alloys. We demonstrate that mixed MoS2/MoSe2/MoTe2 compounds are thermodynamically stable at room temperature, so that such materials can be manufactured using chemical-vapor deposition technique or exfoliated from the bulk mixed materials. By applying the effective band structure approach, we further study the electronic structure of the mixed 2D compounds and show that general features of the band structures are similar to those of their binary constituents. The direct gap in these materials can continuously be tuned, pointing toward possible applications of 2D TMD alloys in photonics.
TL;DR: PN-ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long-term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P or N only and even comparable to the commercially available Pt-C catalyst.
Abstract: Using a mixture of ferrocene, pyridine, and triphenylphosphine as precursors for injection-assisted chemical vapor deposition (CVD), we prepared the first vertically aligned multiwalled carbon nanotube array co-doped with phosphorus (P) and nitrogen (N) with a relatively high P-doping level (designated as PN-ACNT). We have also demonstrated the potential applications of the resultant PN-ACNTs as high-performance electrocatalysts for the oxygen reduction reaction (ORR). PN-ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long-term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P (P-ACNT) or N (N-ACNT) only and even comparable to the commercially available Pt-C catalyst (45 wt % Pt on Vulcan XC-72R; E-TEK) due to a demonstrated synergetic effect arising from the co-doping of CNTs with both P and N.
TL;DR: In this article, the effect of the size and shape of Pd nanoparticles on the catalytic activity, together with their stability, recycling ability, and the influence of different reaction parameters, are discussed.
Abstract: In this Perspective, we discuss some of the most significant aspects in the development of nanosized catalysts for Suzuki cross-coupling reactions. Thus, the effect of the size and shape of Pd nanoparticles on the catalytic activity, together with their stability, recycling ability, and the influence of different reaction parameters, will be brought up for consideration. Furthermore, a comprehensive discussion on the homogeneous or heterogeneous nature of the mechanism for Pd-catalyzed carbon–carbon bond-forming reactions will be conducted. Understanding where the active sites are and how the reaction takes place at those sites is the key for the design of new and more effective nanocatalysts.
TL;DR: This work fine-tuned van der Waals interaction parameters for specific ion pairs to reproduce experimental osmotic pressure of binary electrolyte solutions of biologically relevant ions in molecular dynamics simulations of an array of 64 parallel duplex DNA.
Abstract: Atomic-scale modeling of compacted nucleic acids has the ability to reveal the inner workings of spectacular biomolecular machines, yet the outcome of such modeling efforts sensitively depends on the accuracy of the underlying computational models. Our molecular dynamics simulations of an array of 64 parallel duplex DNA revealed considerable artifacts of cation–DNA phosphate interactions in CHARMM and AMBER parameter sets: both the DNA arrangement and the pressure inside the DNA arrays were found to be in considerable disagreement with experiment. To improve the models, we fine-tuned van der Waals interaction parameters for specific ion pairs to reproduce experimental osmotic pressure of binary electrolyte solutions of biologically relevant ions. Repeating the DNA array simulations using our parameters produced results consistent with experiment. Our improved parametrization can be directly applied to molecular dynamics simulations of various charged biomolecular systems, including nucleic acids, proteins...
TL;DR: In this article, a photochemical upconversion based on sensitized triplet-triplet annihilation can exhibit anti-Stokes emissions whose intensities with respect to the excitation power can vary between quadratic and linear using a non-coherent polychromatic light source.
Abstract: We present experimental data illustrating that photochemical upconversion based on sensitized triplet–triplet annihilation can exhibit anti-Stokes emissions whose intensities with respect to the excitation power can vary between quadratic and linear using a noncoherent polychromatic light source. The benchmark upconverting composition consisting of Pd(II) octaethylporphyrin (PdOEP) sensitizers and 9,10-diphenylanthracene (DPA) acceptors/annihilators in toluene was selected to generate quadratic, intermediate, and linear behavior under both coherent and noncoherent excitation conditions. Each of these power laws was traversed in a single sample in one contiguous experiment through selective pumping of the sensitizer using an Ar+ laser. Wavelength-dependent responses ranging from quadratic to pseudolinear were also recorded from the identical sample composition when excited by Xe lamp/monochromator output in a conventional fluorimeter, where the optical density at λex dictates the observed incident power de...
TL;DR: In this article, a delicate interplay exists between intrachain order and inter-chain coupling as revealed through the emission 0−0/0−1 vibronic intensity ratios of poly-3-hexylthiophene (P3HT) assembled in toluene.
Abstract: Nanofibers (NFs) of poly-3-hexylthiophene (P3HT) assembled in toluene exhibit single-chain J-aggregate character. Absorption, fluorescence emission, and Raman spectroscopy of dilute NF dispersions demonstrate that P3HT chains possess long-range intrachain order (planarity) that suppresses interchain exciton coupling. We demonstrate that a delicate interplay exists between intrachain order and interchain coupling as revealed through the emission 0–0/0–1 vibronic intensity ratios. Lowering temperature and application of pressure induces minor perturbations in the NF packing, which destroys J-aggregate character and partially restores predominant interchain interactions (i.e., H-aggregate behavior). The fact that π–π stacked P3HT chains can exhibit both H- and J-aggregate behavior opens up new possibilities for controlling electronic coupling through noncovalent stacking interactions.