Reduced graphene oxide-ZnO hybrid composites as photocatalysts: The role of nature of the molecular target in catalytic performance

Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water. Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach

Testing hydrostatic equilibrium in galaxy cluster MS 2137

We test the assumption of strict hydrostatic equilibrium in galaxy cluster MS2137.3-2353 (MS 2137) using the latest CHANDRA X-ray observations and results from a combined strong and weak lensing analysis based on optical observations. We deproject the two-dimensional X-ray surface brightness and mass surface density maps assuming spherical and spheroidal dark matter distributions. We find a significant, 40%-50%, contribution from non-thermal pressure in the core assuming a spherical model. This non-thermal pressure support is similar to what was found by Molnar et al. (2010) using a sample of massive relaxed clusters drawn from high resolution cosmological simulations. We have studied hydrostatic equilibrium in MS 2137 under the assumption of elliptical cluster geometry adopting prolate models for the dark matter density distribution with different axis ratios. Our results suggest that the main effect of ellipticity (compared to spherical models) is to decrease the non-thermal pressure support required for equilibrium at all radii without changing the distribution qualitatively. We find that a prolate model with an axis ratio of 1.25 (axis in the line of sight over perpendicular to it) provides a physically acceptable model implying that MS 2137 is close to hydrostatic equilibrium at about 0.04-0.15 Rvir and have an about 25% contribution from non-thermal pressure at the center. Our results provide further evidence that there is a significant contribution from non-thermal pressure in the core region of even relaxed clusters, i.e., the assumption of hydrostatic equilibrium is not valid in this region, independently of the assumed shape of the cluster.Comment: 11 pages, 4 figures, accepted for publication in Ap

Fermion Quasi-Spherical Harmonics

Spherical Harmonics, $Y_\ell^m(\theta,\phi)$, are derived and presented (in a Table) for half-odd-integer values of $\ell$ and $m$. These functions are eigenfunctions of $L^2$ and $L_z$ written as differential operators in the spherical-polar angles, $\theta$ and $\phi$. The Fermion Spherical Harmonics are a new, scalar and angular-coordinate-dependent representation of fermion spin angular momentum. They have $4\pi$ symmetry in the angle $\phi$, and hence are not single-valued functions on the Euclidean unit sphere; they are double-valued functions on the sphere, or alternatively are interpreted as having a double-sphere as their domain.Comment: 16 pages, 2 Tables. Submitted to J.Phys.

MoS2 Nanosheets Uniformly Anchored on NiMoO4 Nanorods, a Highly Active Hierarchical Nanostructure Catalyst for Oxygen Evolution Reaction and Pseudo-Capacitors

Hierarchical nanostructures have attracted considerable research attention due to their applications in the catalysis field. Herein, we design a versatile hierarchical nanostructure composed of NiMoO4 nanorods surrounded by active MoS2 nanosheets on an interconnected nickel foam substrate. The as-prepared nanostructure exhibits excellent oxygen evolution reaction per-formance, producing a current density of 10 mA cm−2 at an overpotential of 90 mV, in comparison with 220 mV necessary to reach a similar current den-sity for NiMoO4. This behavior originates from the structural/morphological properties of the MoS2 nanosheets, which present numerous surface-active sites and allow good contact with the electrolyte. Besides, the structures can effectively store charges, due to their unique branched network providing accessible active surface area, which facilitates intermediates adsorptions. Particularly, NiMoO4/MoS2 shows a charge capacity of 358 mAhg−1 at a current of 0.5 A g−1 (230 mAhg−1 for NiMoO4), thus suggesting promising applications for charge-storing devices

NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction

The sluggish kinetics of the oxygen evolution reaction (OER) is the bottleneck for the practical exploitation of water splitting. Here, the potential of a core–shell structure of hydrous NiMoO4 microrods conformally covered by Co3O4 nanoparticles via atomic layer depositions is demonstrated. In situ Raman and synchrotron-based photoemission spectroscopy analysis confirms the leaching out of Mo facilitates the catalyst reconstruction, and it is one of the centers of active sites responsible for higher catalytic activity. Post OER characterization indicates that the leaching of Mo from the crystal structure, induces the surface of the catalyst to become porous and rougher, hence facilitating the penetration of the electrolyte. The presence of Co3O4 improves the onset potential of the hydrated catalyst due to its higher conductivity, confirmed by the shift in the Fermi level of the heterostructure. In particular NiMoO4@Co3O4 shows a record low overpotential of 120 mV at a current density of 10 mA cm−2, sustaining a remarkable performance operating at a constant current density of 10, 50, and 100 mA cm−2 with negligible decay. Presented outcomes can significantly contribute to the practical use of the water-splitting process, by offering a clear and in-depth understanding of the preparation of a robust and efficient catalyst for water-splitting

Integer-spin Heisenberg Chains in a Staggered Magnetic Field. A Nonlinear σ\sigma-Model Approach

We present here a nonlinear sigma-model (NL$\sigma$M) study of a spin-1 antiferromagnetic Heisenberg chain in an external commensurate staggered magnetic field. We find, already at the mean-field level, excellent agreement with recent and very accurate Density Matrix Renormalization Group (DMRG) studies, and that up to the highest values of the field for which a comparison is possible, for the staggered magnetization and the transverse spin gap. Qualitative but not quantitative agreement is found between the NL$\sigma$M predictions for the longitudinal spin gap and the DMRG results. The origin of the discrepancies is traced and discussed. Our results allow for extensions to higher-spin chains that have not yet been studied numerically, and the predictions for a spin-2 chain are presented and discussed. Comparison is also made with previous theoretical approaches that led instead to predictions in disagreement with the DMRG results.Comment: RevTex, 5 pages + 3 postscript figure

Perceived coercion in psychiatric hospital admission: validation of the French-language version of the MacArthur Admission Experience Survey.

The MacArthur Admission Experience Survey (AES) is a widely used tool to evaluate the level of perceived coercion experienced at psychiatric hospital admission. The French-language AES was prepared using a translation/back-translation procedure. It consists of 16 items and 3 subscores (perceived coercion, negative pressures and voice). This study aimed to assess the psychometric properties of the French-language AES. 152 inpatients were evaluated. Reliability was estimated using internal consistency coefficients and a test-retest procedure. Internal validity was assessed using a two-parameter logistic item response model. Convergent validity was estimated using correlations between the AES scores and the Coercion Ladder (CL), the Coercion Experience Scale (CES) and the Global Assessment of Functioning (GAF) scale. Discriminatory power was evaluated by comparing the scores of patients undergoing voluntary or compulsory admission. The French-language AES showed good internal consistency and test-retest reliability. Internal validity of the three-factor model was excellent. Correlations between AES and CL, CES and GAF scores suggested good convergent validity. AES scores were significantly higher among patients subject to compulsory psychiatric hospital admission than among those admitted voluntarily. Overall, the French-language version of the AES demonstrated very good psychometric proprieties