Higher-Order Nanostructures of Two-Dimensional Palladium Nanosheets for Fast Hydrogen Sensing

Two-dimensional (2D) materials often show a range of intriguing electronic, catalytic, and optical properties that differ greatly from conventional nanoparticles. While planar configuration is often desirable, a range of applications such as catalysis and sensing benefit greatly from the accessibility to large surface areas. The 2D materials generally tend to form stacks in order to reduce the overall surface energy. Such densely packed structures however are detrimental when access to high surface area is required. Herewith we demonstrate a chemical strategy to generate Pd three-dimensional (3D) structures from its flexible 2D nanosheets. Solvent polarity is shown to play an important role to control the final morphology of these nanosheets. Our data indicate when these Pd 3D materials were integrated into hydrogen sensing devices, response time was found to be an order of magnitude faster than their 2D-constrained counterparts. The easy accessibility to the surfaces by hydrogen gas is considered to be an important factor for the observed fast response time based on the sensing model

Hanoi Tower-like Multilayered Ultrathin Palladium Nanosheets

This paper describes the synthesis, formation mechanism, and mechanical property of multilayered ultrathin Pd nanosheets. An anisotropic, Hanoi Tower-like assembly of Pd nanosheets was identified by transmission electron microscopy and atomic force microscopy (AFM). These nanosheets may contain ultrathin Pd layers, down to single unit cell thickness. Selected area electron diffraction and scanning transmission electron microscopy data show the interconnected atomically thick layers stacking vertically with rotational mismatches, resulting in unique diffractions and Moiré patterns. Density functional theory (DFT) calculation with van der Waals correction (DFT+vdW) shows the adsorption of Pd₄(CO)₄(OAc)₄ on Pd(110) surface (<i>E</i>_ad = −5.68 eV) is much stronger than that on Pd(100) (<i>E</i>_ad = −4.72 eV) or on Pd(111) (<i>E</i>_ad = −3.80 eV). The adsorption strength of this Pd complex is significantly stronger than that of CO on the same Pd surfaces. The DFT+vdW calculation results suggest a new mechanism for the observed anisotropic growth of nanosheets with unusually high aspect ratio, in which the competitive adsorptions between Pd₄(CO)₄(OAc)₄ complex and CO on various surfaces result in a favored growth along the ⟨110⟩ directions and inhibition along ⟨111⟩ directions. The mechanical property of these multilayered Pd nanosheets was studied using AFM and nanoindentation techniques, which indicate multilayered nanosheets show more plastic deformation than the bulk in response to an applied force

Ca₂Mn₂O₅ as Oxygen-Deficient Perovskite Electrocatalyst for Oxygen Evolution Reaction

This paper presents the use of Ca₂Mn₂O₅ as an oxygen-deficient perovskite electrocatalyst for oxygen evolution reaction (OER) in alkaline media. Phase-pure Ca₂Mn₂O₅ was made under mild reaction temperatures through a reductive annealing method. This oxygen deficient perovskite can catalyze the generation of oxygen at ∼1.50 V versus (vs) reversible hydrogen electrode (RHE) electrochemically, and reach an OER mass activity of 30.1 A/g at 1.70 V (vs RHE). In comparison to the perovskite CaMnO₃, Ca₂Mn₂O₅ shows higher OER activities. The molecular level oxygen vacancies and high spin electron configuration on manganese in the crystal structures are likely the contributing factors for the enhanced performance. This work demonstrates that oxygen-deficient perovskite, A₂B₂O₅, is a new class of high performance electrocatalyst for those reactions that involve active oxygen intermediates, such as reduction of oxygen and OER in water splitting

Logistic regression results of injection use.

<p>Logistic regression results of injection use.</p

Comparison of intervention effect in each month after intervention.

<p>Note: The value of OR is for the variable after × group.</p><p>*P<0.05.</p><p>Comparison of intervention effect in each month after intervention.</p

Change in injection prescribing rate by month.

<p>Change in injection prescribing rate by month.</p

Basic characteristics of the sample.

<p>Note: BI means before intervention, and AI means after intervention.</p><p>Basic characteristics of the sample.</p

Quantitative Analysis of Different Formation Modes of Platinum Nanocrystals Controlled by Ligand Chemistry

Well-defined metal nanocrystals play important roles in various fields, such as catalysis, medicine, and nanotechnology. They are often synthesized through kinetically controlled process in colloidal systems that contain metal precursors and surfactant molecules. The chemical functionality of surfactants as coordinating ligands to metal ions however remains a largely unsolved problem in this process. Understanding the metal–ligand complexation and its effect on formation kinetics at the molecular level is challenging but essential to the synthesis design of colloidal nanocrystals. Herein we report that spontaneous ligand replacement and anion exchange control the form of coordinated Pt–ligand intermediates in the system of platinum acetylacetonate [Pt­(acac)₂], primary aliphatic amine, and carboxylic acid ligands. The formed intermediates govern the formation mode of Pt nanocrystals, leading to either a pseudo two-step or a one-step mechanism by switching on or off an autocatalytic surface growth. This finding shows the importance of metal–ligand complexation at the prenucleation stage and represents a critical step forward for the designed synthesis of nanocrystal-based materials

Additional file 1 of Physical activity and sleep pattern in relation to incident Parkinson’s disease: a cohort study

Supplementary Material