Tuning the C1 /C2 Selectivity of Electrochemical CO2 Reduction on Cu-CeO2 Nanorods by Oxidation State Control.

Ceria (CeO2 ) is one of the most extensively used rare earth oxides. Recently, it has been used as a support material for metal catalysts for electrochemical energy conversion. However, to date, the nature of metal/CeO2 interfaces and their impact on electrochemical processes remains unclear. Here, a Cu-CeO2 nanorod electrochemical CO2 reduction catalyst is presented. Using operando analysis and computational techniques, it is found that, on the application of a reductive electrochemical potential, Cu undergoes an abrupt change in solubility in the ceria matrix converting from less stable randomly dissolved single atomic Cu2+ ions to (Cu0 ,Cu1+ ) nanoclusters. Unlike single atomic Cu, which produces C1 products as the main product during electrochemical CO2 reduction, the coexistence of (Cu0 ,Cu1+ ) clusters lowers the energy barrier for C-C coupling and enables the selective production of C2+ hydrocarbons. As a result, the coexistence of (Cu0 ,Cu1+ ) in the clusters at the Cu-ceria interface results in a C2+ partial current density/unit Cu weight 27 times that of a corresponding Cu-carbon catalyst under the same conditions.

Heterojunction formation between copper(II) oxide nanoparticles and single-walled carbon nanotubes to enhance antibacterial performance.

We delineate the excellent bactericidal efficacy of stable heterojunction nanocomposites composed of single-walled carbon nanotubes (SWCNTs) and copper(II) oxide (CuO) synthesized via facile recrystallization and calcination. The bactericidal effectiveness of the fabricated nanocomposites was examined using the standard broth-dilution method and the growth-inhibition-zone analysis method, in which bacteria cultured in an incubator in tryptic soy broth medium were subjected to the prepared samples. The bactericidal activity of all of the as-synthesized samples is evident in both methods, displaying a substantial decrease in bacterial colonies and resulting in clear inhibition zones, respectively. Among the CuO-SWCNT nanocomposites, the sample subjected to calcination at 500 °C for 5 h was found to exhibit the best performance against Staphylococcus aureus and Escherichia coli, forming inhibition zones 182% and 162% larger than those formed by pure CuO, respectively.

Phase Evolution of Re1-xMoxSe2 Alloy Nanosheets and Their Enhanced Catalytic Activity toward Hydrogen Evolution Reaction.

Two-dimensional ReSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re1-xMoxSe2 alloy nanosheets with the whole range of x (0-100%) using a hydrothermal reaction. The phase evolved in the order of 1T″ (triclinic) → 1T' (monoclinic) → 2H (hexagonal) upon increasing x. In the nanosheets with x = 10%, the substitutional Mo atoms tended to aggregate in the 1T″ ReSe2 phase with Se vacancies. The incorporation of the 1T' phase makes the alloy nanosheets more metallic than the end compositions. The 10% Mo substitution significantly enhanced the electrocatalytic performance toward HER (in 0.5 M H2SO4), with a current of 10 mA cm-2 at an overpotential of 77 mV (vs RHE) and a Tafel slope of 42 mV dec-1. First-principles calculations of the three phases (1T″, 2H, and 1T') predicted a phase transition of 1T″-2H at x ≈ 65% as well as the production of a 1T' phase along the composition tuning, which are consistent with the experiments. At x = 12.5%, two Mo atoms prefer to form a pair along the Re4 chains. Gibbs free energy along the reaction path indicates that the best HER performance of nanosheets with 10% Mo originates from the Mo atoms that form Mo-H when there are adjacent Se vacancies.

Se-Rich MoSe2 Nanosheets and Their Superior Electrocatalytic Performance for Hydrogen Evolution Reaction.

Two-dimensional MoSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), although its catalytic activity needs to be further improved. Herein, we report Se-rich MoSe2 nanosheets synthesized using a hydrothermal reaction, displaying much enhanced HER performance at the Se/Mo ratio of 2.3. The transition from the 2H to the 1T' phase occurred as Se/Mo exceeded 2. Structural analysis revealed the presence of Se adatoms as well as the formation of Se-Se bonding. Based on first-principles calculations, we propose two equally stable Se-rich structures. In the first one, excess Se atoms bridge two MoSe2 layers via the interlayer Se-Se bonds. In the second one, the Se atoms substitute for the Mo atoms, and extra Se atoms are added closest to the Mo-substituted Se. Calculation of Gibbs free energy along the reaction path indicates that the Se adatoms of the second model are the most active sites for HER.

Orientation-specific switching of inelastic electron tunneling in an oxygen-pyridine complex adsorbed onto an Ag(110) surface.

Here, we report the development of a molecular rotary switch (a "stator-rotor" consisting of a single oxygen molecule as a stator and a single pyridine molecule as a rotor) on a silver surface. The pyridine molecule was bonded to the oxygen molecule and was found to rotate to enable "ON" or "OFF" vibrational conductance through the oxygen molecule. Four stable sites around the oxygen molecule were observed, and vibration conductance turned on and off depending on the site at which the pyridine molecule bonded. The spatially resolved mapping of the vibrational change revealed two locations of maximal vibration intensity, separated by ∼3 Å. These positions acted as two conducting channels. The two distinct vibrational energy levels were associated with the switching process. Adsorption-induced electron transfer between the silver layers and the molecules enhanced the local interactions between the molecules. The two vibration modes were excited by resonant tunneling despite substantial interactions between the molecules, which resulted in a decrease in tunneling conductance. An independent pathway exists for the vibrational excitation process by tunneling electrons and intermolecular interactions.

Two-dimensional MoS2/Fe-phthalocyanine hybrid nanostructures as excellent electrocatalysts for hydrogen evolution and oxygen reduction reactions.

Two-dimensional (2D) MoS2 nanostructures have been extensively investigated in recent years because of their fascinating electrocatalytic properties. Herein, we report 2D hybrid nanostructures consisting of 1T' phase MoS2 and Fe-phthalocyanine (FePc) molecules that exhibit excellent catalytic activity toward both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). X-ray absorption spectra revealed an increased Fe-N distance (2.04 Å) in the hybrid complex relative to the isolated FePc. Spin-polarized density functional theory calculations predicted that the Fe center moves toward the MoS2 layer and induces a non-planar structure with an increased Fe-N distance of 2.05 Å, which supports the experimental results. The experiments and calculations consistently show a significant charge transfer from FePc to stabilize the hybrid complex. The excellent HER catalytic performance of FePc-MoS2 is characterized by a low Tafel slope of 32 mV dec-1 at a current density of 10 mA cm-2 and an overpotential of 0.123 V. The ORR catalytic activity is superior to that of the commercial Pt/C catalyst in pH 13 electrolyte, with a more positive half-wave potential (0.89 vs. 0.84 V), a smaller Tafel slope (35 vs. 87 mV·dec-1), and a much better durability (9.3% vs. 40% degradation after 20 h). Such remarkable catalytic activity is ascribed to the HER-active 1T' phase MoS2 and the ORR-active nonplanar Fe-N4 site of FePc.

Two dimensional MoS2 meets porphyrins via intercalation to enhance the electrocatalytic activity toward hydrogen evolution.

Two-dimensional MoS2 meets porphyrin molecules to form unique 1T' phase intercalated complexes via a one-step procedure of hydrothermal reactions. The resultant Mn-porphyrin-MoS2 exhibits excellent electrocatalytic activity toward the hydrogen evolution reaction, with a Tafel slope of 35 mV dec-1 and 10 mA cm-2 at an overpotential of 0.125 V. Spin-polarized density functional theory calculations confirmed that the intercalation of Mn-porphyrin into 1T'-MoS2 is quite favourable due to strong charge transfer from Mn metals. Their outstanding catalytic performance could be ascribed to the high electron concentration as well as the low activation barrier of the Heyrovsky reaction.

Nitrogen-rich 1T'-MoS2 layered nanostructures using alkyl amines for high catalytic performance toward hydrogen evolution.

The imminent global energy crisis and current environmental issues have stimulated considerable research on high-performance catalysts for sustainable hydrogen energy generation. Two-dimensional layered MoS2 has recently drawn worldwide attention because of its excellent catalytic properties for the hydrogen evolution reaction (HER). In the present work, we prepared nitrogen (N)-rich 1T' (distorted 1T) phase MoS2 layered nanostructures using different alkyl amines with 1-4 nitrogen atoms (methylamine, ethylenediamine, diethylenetriamine, and triethylenetetramine) as intercalants. The amine molecules intercalate at 10 atomic%, and simultaneously supply the N atoms that substitute the S atoms to produce the N-doped MoS2, whose composition is MoS2(1-x)Nx, where x = 0.1-0.26. MoS2 prepared with amines having more N atoms has enhanced catalytic HER performance: a Tafel slope of 36 mV dec-1 and 10 mA cm-2 at -160 mV (vs. RHE). First-principles calculations showed that the amine intercalation and N doping increase the density of states near the Fermi level in a narrow range and bring about an effective overlap of the dz2(Mo), pz(S), and pz(N) states. These factors in turn increase the carrier (electron) concentration and mobility for improved HER. The calculation also predicted that the most active site is S vacancies. The present work illustrates how the HER catalytic performance of 1T' phase MoS2 can be effectively controlled by the amine molecules.

Intercalation of aromatic amine for the 2H-1T' phase transition of MoS2 by experiments and calculations.

The novel properties of two-dimensional materials have motivated extensive studies focused on transition metal dichalcogenides (TMDs), which led to many interesting findings in recent years. Further advances in this area would require the development of effective methods for producing nanostructured TMDs with a controlled structure. Herein, we report unique MoS2 layered nanostructures intercalated with dimethyl-p-phenylenediamine (DMPD) with various concentrations, synthesized by a one-step hydrothermal reaction. The MoS2 layers possess a significantly expanded interlayer spacing. Remarkably, as the concentration of DMPD increases, the MoS2 preferentially adopts a unique metallic 1T' (distorted 1T) phase. The intercalated MoS2 exhibits excellent catalytic performance in the hydrogen evolution reaction. First-principles calculations show that the phase transition from 2H to 1T' phase occurs with increasing concentrations of DMPD, which can be accelerated by the S vacancies. A significant charge transfer from the DMPD molecules to MoS2 stabilizes the 1T' over the 2H phase, driving the 2H-1T' phase conversion. The DMPD and the S vacancies increased the carrier concentration, which leads to the enhanced catalytic performance. The present work illustrates how the phase control of TMDs can be effectively achieved by the intercalation of electron-donating molecules.

Inorganic molecule (O2, NO) adsorption on nitrogen- and phosphorus-doped MoS2 monolayer using first principle calculations.

We performed a systematic study of the adsorption behaviors of O2 and NO gas molecules on pristine MoS2, N-doped, and P-doped MoS2 monolayers via first principle calculations. Our adsorption energy calculations and charge analysis showed that the interactions between the NO and O2 molecules and P-MoS2 system are stronger than that of pristine and N-MoS2. The spin of the absorbed molecule couples differently depending on the type of gas molecule adsorbed on the P- and N-substituted MoS2 monolayer. Meanwhile, the adsorption of O2 molecules leaves N- and P-MoS2 a magnetic semiconductor, whereas the adsorption of an NO molecule turns this system into a nonmagnetic semiconductor, which may provide some helpful information for designing new N- and P-substituted MoS2-based nanoelectronic devices. Therefore, P- and N-MoS2 can be used to distinguish O2 and NO gases using magnetic properties, and P-MoS2-based gas sensors are predicted to be more sensitive to detect NO molecules rather than pristine and N-MoS2 systems.

Reference intervals for free T3 and free T4 in Pakistani euthyroid patients: effect of age and gender on thyroid function.

OBJECTIVE: To establish reference intervals for Free Triiodothyronine (FT3) and Free Thyroxine (FT4) in euthyroid subjects and to assess the effect of age and gender on FT3 and FT4. STUDY DESIGN: Cross-sectional, analytical study. PLACE AND DURATION OF STUDY: Institute of Nuclear Medicine and Oncology (INMOL), Lahore, from January 2009 to April 2011. METHODOLOGY: FT3 and FT4 were measured in 852 euthyroid patients. Those with previous thyroid surgery, on thyroidrelated medication and severe non-thyroid illness were excluded. RESULTS: There were 215 males and 637 females with mean age of 46 years. The reference intervals, revealed by this study, for FT3 and FT4 were 2.80 - 5.39 pmol/L and 11.9 - 22.2 pmol/L respectively. The mean difference between gender groups and age groups was found statistically significant for FT3 (gender: p < 0.001; age: p < 0.001) but statistically insignificant for FT4 (gender: p=0.147; age: p=0.201). CONCLUSION: There was no effect of gender and age on FT3 and FT4. The age with serum FT3 and FT4 significantly negatively correlated but this correlation was stronger for FT3 as compared to FT4 levels. Reference intervals of FT3 and FT4 for male (2.99 - 5.63 pmol/L, 12.3 - 22.6 pmol/L) and female (2.77 - 5.29 pmol/L, 11.7 - 22.1 pmol/L) respectively are suggested.