Direct Synthesis of Intermetallic Platinum-Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis.

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)3]2+ cation (bpy = 2,2'-bipyridine) and [PtCl6]2- anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.

Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst.

A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm-2, which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extended X-ray absorption fine structure analysis combined with electrochemical test shows that carbon shell coating prevents FeP nanoparticles from oxidation, making them highly stable under hydrogen evolution reaction operation conditions. Furthermore, we demonstrate that our synthetic method is suitable for mass production, which is highly desirable for large-scale hydrogen production.

Sulfur-Modified Graphitic Carbon Nitride Nanostructures as an Efficient Electrocatalyst for Water Oxidation.

There is an urgent need to develop metal-free, low cost, durable, and highly efficient catalysts for industrially important oxygen evolution reactions. Inspired by natural geodes, unique melamine nanogeodes are successfully synthesized using hydrothermal process. Sulfur-modified graphitic carbon nitride (S-modified g-CN x ) electrocatalysts are obtained by annealing these melamine nanogeodes in situ with sulfur. The sulfur modification in the g-CN x structure leads to excellent oxygen evolution reaction activity by lowering the overpotential. Compared with the previously reported nonmetallic systems and well-established metallic catalysts, the S-modified g-CN x nanostructures show superior performance, requiring a lower overpotential (290 mV) to achieve a current density of 10 mA cm-2 and a Tafel slope of 120 mV dec-1 with long-term durability of 91.2% retention for 18 h. These inexpensive, environmentally friendly, and easy-to-synthesize catalysts with extraordinary performance will have a high impact in the field of oxygen evolution reaction electrocatalysis.

Mn oxide-silver composite nanowires for improved thermal stability, SERS and electrical conductivity.

Redox transformation reaction between aqueous AgNO3 and Mn(CH3COO)2 at low temperature (∼80 °C) has been adopted for industrial-scale production of uniform Ag-MnOOH composite nanowires for the first time. Varying amounts of incorporated Ag in the composite retain the 1D morphology of the composite. Nanowires upon annealing evolve Ag-MnO2 nanocomposites, once again with the retention of the parental morphology. Just 4 % of silver incorporation in the composite demonstrates metal-like conducting performance from the corresponding semiconducting material. Transition of MnO2 to Mn2O3 to Mn3O4 takes place upon heat treatment in relation to successive increase in Ag concentrations in the nanowires. The composites offer resistance to the observed oxide transformation. This is evidenced from the progressive increase in transition temperature. In situ Raman, ex situ thermal and XRD analysis corroborate the fact. The composite with 12 % Ag offers resistance to the transformation of MnO2, which is also verified from laser heating. Importantly, Ag nanoparticle incorporation is proved to offer a thermally stable and better surface enhanced Raman scattering (SERS) platform than the individual components. Both the Ag-MnOOH and Ag-MnO2 nanocomposites with 8 atomic % Ag show the best SERS enhancement (enhancement factor ∼10(10)). The observed enhancement relates to charge transfer as well as electromagnetic effects.

PSO-XnB: a proposed model for predicting hospital stay of CAD patients.

Coronary artery disease poses a significant challenge in decision-making when predicting the length of stay for a hospitalized patient. This study presents a predictive model-a Particle Swarm Optimized-Enhanced NeuroBoost-that combines the deep autoencoder with an eXtreme gradient boosting model optimized using particle swarm optimization. The model uses a fuzzy set of rules to categorize the length of stay into four distinct classes, followed by data preparation and preprocessing. In this study, the dimensionality of the data is reduced using deep neural autoencoders. The reconstructed data obtained from autoencoders is given as input to an eXtreme gradient boosting model. Finally, the model is tuned with particle swarm optimization to obtain optimal hyperparameters. With the proposed technique, the model achieved superior performance with an overall accuracy of 98.8% compared to traditional ensemble models and past research works. The model also scored highest in other metrics such as precision, recall, and particularly F1 scores for all categories of hospital stay. These scores validate the suitability of our proposed model in medical healthcare applications.

Large-scale solid-state synthesis of Sn-SnO2 nanoparticles from layered SnO by sunlight: a material for dye degradation in water by photocatalytic reaction.

Phase pure spherical Sn-SnO2 nanoparticles (∼ 50 nm) in gram level have been synthesized from well-defined SnO microplates (∼ 2.0 µm) using focused solar irradiation. The first step of the reaction involves simple stirring of a strong NaOH solution with fine SnCl2·2H2O powder. Precipitated blue black microplates of SnO are finally transformed into high band gap Sn-SnO2 nanoparticles with sunlight. During the solid-state photodecomposition of microplates, spherical SnO2 nanoparticles along with tiny Sn(0) particles are evolved simultaneously. Tiny Sn(0) particles, improved surface area, stability toward adverse environmental conditions, and inherited negative surface charge electrostatically stabilize the Sn-SnO2 particle rendering it excellent water dispersible. The presence of Sn(0) nanoparticles in spherical SnO2 nanoparticles improves the charge (electrons and holes) separation efficiency. Then, the as-prepared particles selectively invite cationic dye molecules to the particle surface due to negative surface charge and degrade the dyes at a faster rate under UV light.

Optical photoresponse of CuS-n-Si radial heterojunction with Si nanocone arrays fabricated by chemical etching.

The paper deals with the fabrication of a p-CuS-n-Si nanocone heterojunction based highly sensitive broad band photodetector. Cone-like one dimensional Si nanostructures formed by metal assisted chemical etching, with superior antireflection characteristics have been used as templates for fabrication of the heterojunction. Covellite CuS material was synthesized by a simple chemical reaction for used as target material for the fabrication of p-CuS-n-Si nanocone heterojunctions via pulsed laser ablation. The effect of surface texturing of Si (cone like nanostructure vs. planar) on spectral photoresponse and detection is reported.

Selective and sensitive recognition of Cu2+ in an aqueous medium: a surface-enhanced Raman scattering (SERS)-based analysis with a low-cost Raman reporter.

In the present study, surface-enhanced Raman spectra of a bifunctional Raman reporter, 2-mercaptobenzimidazole, has been found to be responsive exclusively towards Cu(2+) ions while the reporter remains anchored on the Au nanoparticle surface. Thus a specific Cu(2+)-ion-detection protocol emerges. The simplicity, sensitivity, and reproducibility of the method allow routine and quantitative detection of Cu(2+) ions. An interference study involving a wide number of other metal ions shows the procedure to be uniquely selective and analytically rigorous. A theoretical study was carried out to corroborate the experimental results. Finally, the method is promising for real-time assessment of Cu(2+) ions in aqueous samples and also has the ability to discriminate Cu(I) and Cu(II) ions in solution.

Palladium-catalyzed dehydrative heck olefination of secondary aryl alcohols in ionic liquids: towards a waste-free strategy for tandem synthesis of stilbenoids.

All in one: a tandem strategy has been developed wherein secondary aryl alcohols are directly coupled with aryl halides to provide stilbenoids through a dehydrative Heck sequence in the ionic liquid [hmim]Br, and with water as a by-product under microwave irradiation. Classical methods do not permit this sequence to proceed in one pot, and some methods require multiple steps. hmim=1-n-hexyl-3-methylimidazolium.

Redox-switchable superhydrophobic silver composite.

Unique packaging of Ag(2)O on the surface of polycrystalline AgCl allows fabrication of a new useful, superhydrophobic composite material. This pure inorganic material with surface porosity of submicrometer aperture size fabricates air pockets, which make the composite material superhydrophobic. The new material behaves like lotus leaves, butterfly wings, or water strider's leg in relation to superhydrophobicity. Visible light induces photoreduction of solid Ag(2)O surface layer and generates Ag(0), making the composite surface superhydrophilic. Reoxidation of Ag(0) on the composite surface gives back the hydrophobicity that represents the redox-switchable wetting property of the material.