Kinetics and Optimization of Hexagonal Palladium Nanosheets: Unveiling Insights into CO-Mediated Synthesis Strategies and Mechanistic Understanding.

Nanoparticles with unique shapes and structures have attracted significant attention due to their distinctive properties and potential applications, but their growth mechanism is often overlooked. Hexagonal palladium nanosheets (HPNS) were synthesized through a CO-mediated reduction approach. Herein, we investigate the kinetics of the HPNS formation and modify the experimental conditions consistently by changing the carbon monoxide (CO) precursor, temperature, and stirring speed. The CO precursor plays a major role in HPNS formation with an emphasis on the kinetics of the release of CO in the solution. Slow-release and atmosphere CO precursors resulted in the highest shape yield of HPNS relative to tetrahedrons, while the fast-release CO precursor leads to the formation of a higher percentage of tetrahedrons. Additionally, an increase of the addition temperature of the CO precursor and a higher stirring rate were found to improve the shape yield of the HPNS, leading to an optimized synthetic strategy of the HPNS at high shape yield. Kinetics of the reaction with a slow-release CO precursor provided insights into the formation mechanism of the HPNS and suggested an aggregative model with an interplay between reduction kinetics and the thermodynamic stability of HPNS relative to the tetrahedrons.

Permselectivity and Ionic Conductivity Study of Na+ and Br- Ions in Graphene Oxide-Based Membranes for Redox Flow Batteries.

Permselectivity of a membrane is central for the development of electrochemical energy storage devices with two redox couples, such as redox flow batteries (RFBs). In RFBs, Br3-/Br- couple is often used as a catholyte which can cross over to the anolyte, limiting the battery's lifetime. Naturally, the development of permselective membranes is essential to the success of RFBs since state-of-the-art perfluorosulfonic acid (PFSA) is too costly. This study investigates membranes of graphene oxide (GO), polyvinylpyrrolidone (PVP), and imidazole (Im) as binder and linker, respectively. The GO membranes are compared to a standard PFSA membrane in terms of ionic conductivity (Na+) and permselectivity (exclusion of Br-). The ionic conduction is evaluated from electrochemical impedance spectroscopy and the permselectivity from two-compartment diffusion cells in a four-electrode system. Our findings suggest that the GO membranes reach conductivity and permselectivity comparable with standard PFSA membranes.

Cu2+-Induced self-assembly and amyloid formation of a cyclic D,L-α-peptide: structure and function.

In a wide spectrum of neurodegenerative diseases, self-assembly of pathogenic proteins to cytotoxic intermediates is accelerated by the presence of metal ions such as Cu2+. Only low concentrations of these early transient oligomeric intermediates are present in a mixture of species during fibril formation, and hence information on the extent of structuring of these oligomers is still largely unknown. Here, we investigate dimers as the first intermediates in the Cu2+-driven aggregation of a cyclic D,L-α-peptide architecture. The unique structural and functional properties of this model system recapitulate the self-assembling properties of amyloidogenic proteins including ß-sheet conformation and cross-interaction with pathogenic amyloids. We show that a histidine-rich cyclic D,L-α-octapeptide binds Cu2+ with high affinity and selectivity to generate amyloid-like cross-ß-sheet structures. By taking advantage of backbone amide methylation to arrest the self-assembly at the dimeric stage, we obtain structural information and characterize the degree of local order for the dimer. We found that, while catalytic amounts of Cu2+ promote aggregation of the peptide to fibrillar structures, higher concentrations dose-dependently reduce fibrillization and lead to formation of spherical particles, showing self-assembly to different polymorphs. For the initial self-assembly step to the dimers, we found that Cu2+ is coordinated on average by two histidines, similar to self-assembled peptides, indicating that a similar binding interface is perpetuated during Cu2+-driven oligomerization. The dimer itself is found in heterogeneous conformations that undergo dynamic exchange, leading to the formation of different polymorphs at the initial stage of the aggregation process.

An Engineered Nanocomplex with Photodynamic and Photothermal Synergistic Properties for Cancer Treatment.

Photodynamic therapy (PDT) and photothermal therapy (PTT) are promising therapeutic methods for cancer treatment; however, as single modality therapies, either PDT or PTT is still limited in its success rate. A dual application of both PDT and PTT, in a combined protocol, has gained immense interest. In this study, gold nanoparticles (AuNPs) were conjugated with a PDT agent, meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer, designed as nanotherapeutic agents that can activate a dual photodynamic/photothermal therapy in SH-SY5Y human neuroblastoma cells. The AuNP-mTHPC complex is biocompatible, soluble, and photostable. PDT efficiency is high because of immediate reactive oxygen species (ROS) production upon mTHPC activation by the 650-nm laser, which decreased mitochondrial membrane potential (∆ψm). Likewise, the AuNP-mTHPC complex is used as a photoabsorbing (PTA) agent for PTT, due to efficient plasmon absorption and excellent photothermal conversion characteristics of AuNPs under laser irradiation at 532 nm. Under the laser irradiation of a PDT/PTT combination, a twofold phototoxicity outcome follows, compared to PDT-only or PTT-only treatment. This indicates that PDT and PTT have synergistic effects together as a combined therapeutic method. Our study aimed at applying the AuNP-mTHPC approach as a potential treatment of cancer in the biomedical field.

Selective Catalyst Surface Access through Atomic Layer Deposition.

Catalyst poisoning is a prominent issue, reducing the lifetime of catalysts and increasing the costs of the processes that rely on them. The electrocatalysts that enable green energy conversion and storage, such as proton exchange membrane fuel cells and hydrogen bromine redox flow batteries, also suffer from this issue, hindering their utilization. Current solutions to protect electrocatalysts from harmful species fall short of effective selectivity without inhibiting the required reactions. This article describes the protection of a standard 50% Pt/C catalyst with a V2O5 coating through atomic layer deposition (ALD). The ALD selectively deposited V2O5 on the Pt, which enhanced hydrogen transport to the Pt surface and resulted in a higher mass activity in alkaline electrolytes. Cyclic voltammetry and X-ray photoelectron spectroscopy showed that the Pt was protected by the coating in the HBr/Br2 electrolyte which dissolved the uncoated 50% Pt/C in under 3 min.

Evaluation of Mg[B(HFIP)4]2-Based Electrolyte Solutions for Rechargeable Mg Batteries.

One of the greatest challenges toward rechargeable magnesium batteries is the development of noncorrosive electrolyte solutions with high anodic stability that can support reversible Mg deposition/dissolution. In the last few years, magnesium electrolyte solutions based on Cl-free fluorinated alkoxyborates were investigated for Mg batteries due to their high anodic stability and ionic conductivity and the possibility of reversible deposition/dissolution in ethereal solvents. Here, the electrochemical performance of Mg[B(hexafluoroisopropanol)4]2/dimethoxyethane (Mg[B(HFIP)4]2/DME) solutions was examined. These electrolyte solutions require a special "conditioning" pretreatment that removes undesirable active moieties. Such a process was developed and explored, and basic scientific issues related to the mechanism by which it affects Mg deposition/dissolution were addressed. The chemical changes that occur during the conditioning process were examined. Mg[B(HFIP)4]2/DME solutions were found to enable reversible Mg deposition, albeit with a relatively low Coulombic efficiency of 95% during the first cycles. Prolonged deposition/dissolution cycling tests demonstrate a stable behavior of magnesium electrodes. Overall, this system presents a reasonable electrolyte solution and can serve as a basis for future efforts to develop chlorine-free alternatives for secondary magnesium batteries. It is clear that such a conditioning process is mandatory, as it removes reactive contaminants that lead to unavoidable passivation and deactivation of Mg electrodes from the solution.

Investigations of Shape, Material and Excitation Wavelength Effects on Field Enhancement in SERS Advanced Tips.

This article, a part of the larger research project of Surface-Enhanced Raman Scattering (SERS), describes an advanced study focusing on the shapes and materials of Tip-Enhanced Raman Scattering (TERS) designated to serve as part of a novel imager device. The initial aim was to define the optimal shape of the "probe": tip or cavity, round or sharp. The investigations focused on the effect of shape (hemi-sphere, hemispheroid, ellipsoidal cavity, ellipsoidal rod, nano-cone), and the effect of material (Ag, Au, Al) on enhancement, as well as the effect of excitation wavelengths on the electric field. Complementary results were collected: numerical simulations consolidated with analytical models, based on solid assumptions. Preliminary experimental results of fabrication and structural characterization are also presented. Thorough analyses were performed around critical parameters, such as the plasmonic metal-Silver, Aluminium or Gold-using Rakic model, the tip geometry-sphere, spheroid, ellipsoid, nano-cone, nano-shell, rod, cavity-and the geometry of the plasmonic array: cross-talk in multiple nanostructures. These combined outcomes result in an optimized TERS design for a large number of applications.

Design of Surface Enhanced Raman Scattering (SERS) Nanosensor Array.

An advanced Surface-Enhanced Raman Scattering (SERS) Nanosensor Array, dedicated to serve in the future as a pH imager for the real-time detection of chemical reaction, is presented. The full flow of elementary steps-architecture, design, simulations, fabrication, and preliminary experimental results of structural characterization (Focused Ion Beam (FIB), TEM and SEM)-show an advanced SERS pixel array that is capable of providing spatially resolved measurements of chemical pH in a fluid target that became more than desirable in this period. Ultimately, the goal will be to provide real-time monitoring of a chemical reaction. The pixels consist of a nanostructured substrate composed of an array of projections or cavities. The shape of the nanostructures and the thickness of the metallic (Ag or Au) layer can be tuned to give maximal enhancement at the desired wavelength. The number and arrangement of nanostructures is optimized to obtain maximal responsivity.

A low-loading Ru-rich anode catalyst for high-power anion exchange membrane fuel cells.

Herein, we report a Ru-rich anode catalyst for alkaline exchange membrane fuel cells. The fuel cell with such a RuPdIr/C anode and Ag-based cathode attained a peak power density close to 1 W cm-2 with only 0.2 mg cm-2 anode precious group metal loading, reaching the highest mass activity reported for this technology.

First principles study of electrocatalytic behavior of olivine phosphates with mixed alkali and mixed transition metal atoms.

Lithium transition metal olivine phosphates are well known Li-ion battery cathode materials, but these materials can also be used as electrocatalyst. Recent experimental studies showed that olivine phosphates with mixed alkali metals (Li and Na) and mixed transition metals (Ni and Fe) provide better electrocatalytic activity compared to single alkali and transition metal alternatives. In the current work, we analyzed the role of alkali metals, transition metals and vacancies on the reactivity of a series of olivine phosphates with different stoichiometries using first principles calculations. To this end, we investigated the adsorption of water at the surface of these materials. We found that water binds preferably at Ni surface sites for materials devoid of alkali ion vacancies. We further found correlation between the calculated adsorption energy with experimentally measured overpotentials for a series of olivine phosphates. Additionally, we found correlation between the adsorption energy of the systems with the total charge polarization of surface and adsorbate. To explain the computed trends, we analyzed the occupancies of the partial density of states of the Ni and Fe 3d states and Bader atomic charges.

Self-faceting of emulsion droplets as a route to solid icosahedra and other polyhedra.

HYPOTHESIS: Temperature-controlled self-faceting of liquid droplets has been recently discovered in surfactant-stabilized alkane-in-water emulsions. We hypothesize that similar self-faceting may occur in emulsion droplets of UV-polymerizable linear hydrocarbons. We further hypothesize that the faceted droplet shapes can be fixed by UV-initiated polymerization, thus providing a new route towards the production of solid polyhedra. EXPERIMENTS: Temperature-induced shape variations were studied by optical microscopy in micron-size emulsion droplets of UV-polymerizable alkyl acrylate. When polymerized, the resultant solid particles' 3D shape and internal structure were determined by combined scanning electron microscopy (SEM) and focused ion beam (FIB) slicing. The SEM and FIB nanoscale resolution provided a far greater detail imaging than that achievable for the liquid droplets, which could only be studied by optical microscopy, severely limiting their 3D shape determination. FINDINGS: We demonstrate the formation of solid icosahedra, polyhedral platelets, and rods of hitherto-unreported sizes, well below the 3D-printing resolution (∼20µm). The presence of icosahedral shapes and the absence of any resolvable internal structure at sub-µm length scales, are in line with the surface-freezing-driven mechanism proposed for the faceting phenomenon. Further development of the method presented here may allow large-quantity production of shaped micron- to nano- sized colloidal building blocks for 3D metamaterials and other applications.

meso-Tetrahydroxyphenylchlorin-Conjugated Gold Nanoparticles as a Tool To Improve Photodynamic Therapy.

Photodynamic therapy (PDT) is a promising therapeutic modality for cancer. However, current protocols using bare drugs suffer from several limitations that impede its beneficial clinical effects. Here, we introduce a new approach for an efficient PDT treatment. It involves conjugating a PDT agent, meso-tetrahydroxyphenylchlorin (mTHPC) photosensitizer, to gold nanoparticles (AuNPs) that serve as carriers for the drug. AuNPs have a number of characteristics that make them highly suitable to function as drug carriers: they are biocompatible, serve as biomarkers, and function as contrast agents in vitro and in vivo. We synthesized AuNPs and covalently conjugated the mTHPC drug molecules through a linker. The resultant functional complex, AuNP-mTHPC, is a stable, soluble compound. SH-SY5Y human neuroblastoma cells were incubated with the complex, showing possible administration of higher doses of drug when conjugated to the AuNPs. Then cells were irradiated with a laser beam at 650 nm to mimic the PDT procedure. Our study shows higher rates of cell death in cells incubated with the AuNP-mTHPC complex compared to the incubation with the free drug. Using the new complex may form the basis for a better PDT strategy for a wide range of cancers.

On the impact of Vertical Alignment of MoS2 for Efficient Lithium Storage.

Herein, we report energy storage devices, which are based on densely packed, vertically aligned MoS2 (VA-MoS2) or planar oriented MoS2 (PO-MoS2) and compare their electrochemical performances. The VA-MoS2 films have been processed by chemical vapor deposition (CVD) to reach unprecedented micron-scale thick films while maintaining the vertical alignment for the whole thickness. The VA-MoS2 and the PO-MoS2 films form a high-performance Li-ion electrode, reaching the theoretical limits of reversible capacity for this material (800 mAh/g; twice the specific capacity of graphite). The vertical alignment allows faster charge-discharge rates while maintaining a high specific capacity (C-rate measurements). Noteworthy, the reversible cycling of the Li-ion electrode also benefits from the vertical alignment. In this article, we present the full synthesis, structural and electrochemical characterization of VA-MoS2 along with the properties of PO-MoS2 to deconvolute the intrinsic properties of MoS2 from the influence of the layers' orientation.

Photo-Crosslinkable Colloids: From Fluid Structure and Dynamics of Spheres to Suspensions of Ellipsoids.

Recently-developed photo-crosslinkable PMMA (polymethylmethacrylate) colloidal spheres are a highly promising system for fundamental studies in colloidal physics and may have a wide range of future technological applications. We synthesize these colloids and characterize their size distribution. Their swelling in a density- and index- matching organic solvent system is demonstrated and we employ dynamic light scattering (DLS), as also the recently-developed confocal differential dynamic microscopy (ConDDM), to characterize the structure and the dynamics of a fluid bulk suspension of such colloids at different particle densities, detecting significant particle charging effects. We stretch these photo-crosslinkable spheres into ellipsoids. The fact that the ellipsoids are cross-linked allows them to be fluorescently stained, permitting a dense suspension of ellipsoids, a simple model of fluid matter, to be imaged by direct confocal microscopy.

Magnetism in olivine-type LiCo(1-x)Fe(x)PO4 cathode materials: bridging theory and experiment.

In the current paper, we present a non-aqueous sol-gel synthesis of olivine type LiCo1-xFexPO4 compounds (x = 0.00, 0.25, 0.50, 0.75, 1.00). The magnetic properties of the olivines are measured experimentally and calculated using first-principles theory. Specifically, the electronic and magnetic properties are studied in detail with standard density functional theory (DFT), as well as by including spin-orbit coupling (SOC), which couples the spin to the crystal structure. We find that the Co(2+) ions exhibit strong orbital moment in the pure LiCoPO4 system, which is partially quenched upon substitution of Co(2+) by Fe(2+). Interestingly, we also observe a non-negligible orbital moment on the Fe(2+) ion. We underscore that the inclusion of SOC in the calculations is essential to obtain qualitative agreement with the observed effective magnetic moments. Additionally, Wannier functions were used to understand the experimentally observed rising trend in the Néel temperature, which is directly related to the magnetic exchange interaction paths in the materials. We suggest that out of layer M-O-P-O-M magnetic interactions (J⊥) are present in the studied materials. The current findings shed light on important differences observed in the electrochemistry of the cathode material LiCoPO4 compared to the already mature olivine material LiFePO4.

Hybrid Organic-Inorganic Perovskites (HOIPs): Opportunities and Challenges.

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

Hollow octahedral and cuboctahedral nanocrystals of ternary Pt-Ni-Au alloys.

Hollow particles of Pt-Ni-Au alloys have been prepared through a two-step reaction with the synthesis of NiPt octahedral and cuboctahedral templates followed by a galvanic replacement reaction by Au(iii). Metal etching presents an efficient method to yield hollow particles and investigate the Au diffusion in the metallic Pt-Ni framework through macroscopic (X-ray diffraction and SQUID magnetic measurement) and microscopic (HRTEM and STEM) measurements. The hollow particles retain the shape of the original nanocrystals. The nucleation of Au is found to be induced preferentially on the tip of the polyhedral nanocrystals while the etching of Ni starts from the facets leaving hollow octahedral particles consisting of 2 nm thick edges. In the presence of oleylamine, the Au tip grows and yields a heterogeneous dimer hollow-NiPt/Au. Without oleylamine, the Au nucleation is followed by Au diffusion in the Ni/Pt framework to yield a hollow single crystal Pt-Ni-Au alloy. The Pt-Ni-Au alloyed particles display a superparamagnetic behavior at room temperature.

Do we need covalent bonding of Si nanoparticles on graphene oxide for Li-ion batteries?

In this manuscript, we report our investigation of anode materials for Li-ion batteries based on silicon-graphene oxide composites. Previous reports in the literature on silicon-graphene oxide (GO) composites as anodes have shown a large discrepancy between the electrochemical properties, mainly capacity and coulombic efficiency. In our research, the surface chemistry of Si nanoparticles has been functionalized to yield a chemical bond between the Si and GO, a further annealing step yields a Si-reduced GO (Si-rGO) composite while controlled experiments have been carried on mechanical mixing of GO and Si. For all samples, including a simple mixing of Si nanoparticles and GO, a high specific capacity of 2000 mA h g(Si)(-1) can be achieved for 50 cycles. The main difference between the samples can be observed in terms of coulombic efficiency, which will determine the future of these composites in full Li-ion cells. The Si-rGO composite shows a very low capacity fading and a coulombic efficiency above 99%. Furthermore, the Si-rGO composite can be cycled at very high rate to 20 C (charge in 3 minutes).