Abstract: Herein, thin-layer potentiometry combined with ion-exchange membranes as barriers for charged interferences is demonstrated for the analytical detection of creatinine (CRE) in undiluted human urine. Briefly, CRE diffuses through an anion-exchange membrane (AEM) from a sample contained in one fluidic compartment to a second reservoir, containing the enzyme CRE deiminase. There, CRE reacts with the enzyme, and the formation of ammonium is dynamically monitored by potentiometric ammonium-selective electrodes. This analytical concept is integrated into a lab-on-a-chip microfluidic cell that allows for a high sample throughput and the operation under stop-flow mode, which allows CRE to passively diffuse across the AEM. Conveniently, positively charged species (i.e., potassium, sodium, and ammonium, among others) are repelled by the AEM and never reach the ammonium-selective electrodes; thus, possible interference in the response can be avoided. As a result, the dynamic potential response of the electrodes is entirely ascribed to the stoichiometric formation of ammonium. The new CRE biosensor exhibits a Nernstian slope, within a linear range of response from 1 to 50 mM CRE concentration. As expected, the response time (15–60 min) primarily depends on the CRE diffusion across the AEM. CRE analysis in urine samples displayed excellent results, without requiring sample pretreatment (before the introduction of the sample in the microfluidic chip) and with high compatibility with development into a potential point-of-care clinical tool. In an attempt to decrease the analysis time, the presented analytical methodology for CRE detection is translated into an all-solid-state platform, in which the enzyme is immobilized on the surface of the ammonium-selective electrode and with the AEM on top. While more work is necessary in this direction, the CRE sensor appears to be promising for CRE analysis in both urine and blood.

Abstract: Understanding the fundamental dynamics in carbon nanotube (CNT) catalysts is of primary importance to understand CNT nucleation. This Letter reports on calculated bond switching (BS) rates in pure and carbon containing nickel nanoclusters. The rates are analyzed in terms of their temperature dependent spatial distribution and the mobility of the cluster atoms. The BS mechanism is found to change from vibrational to diffusional at around 900 K, with a corresponding strong increase in activation energy. Furthermore, the BS activation energy is observed to decrease as the carbon content in the cluster increases, resulting in an effective liquification of the cluster.

Abstract: A molecular dynamics (MD) study of MgxAlyOz thin films grown by magnetron sputtering is presented using an ionic model and comparing two potential sets with formal and partial charges. The applicability of the model and the reliability of the potential sets for the simulation of thin film growth are discussed. The formal charge potential set was found to reproduce the thin film structure in close agreement with the structure of the experimentally grown thin films. Graphical abstract A molecular dynamics study of growth of MgxAlyOz thin films is presented using an ionic model and comparing two potential sets with formal and partial charges. The simulation results with the formal charge potential set showed a transition in the film from a crystalline to an amorphous structure, when the Mg metal content decreases below 50% in very close agreement with the structure of the experimentally deposited films.

Abstract: Hydrogen-storage properties of complex hydrides depend of their form, such as a polymorphic form or an eutectic mixture. This Paper reports on an easy and reproducible way to synthesize a new stable form of magnesium borohydride by pressure-induced collapse of the porous gamma-Mg(BH4)(2). This amorphous complex hydride was investigated by temperature-programmed synchrotron X-ray diffraction (SXRD), transmission electron microscopy (TEM), thermogravimetric analysis, differential scanning calorimetry analysis, and Raman spectroscopy, and the dynamics of the BH4 reorientation was studied by spinlattice relaxation NMR spectroscopy. No long-range order is observed in the lattice region by Raman spectroscopy, while the internal vibration modes of the BH4 groups are the same as in the crystalline state. A hump at 4.9 angstrom in the SXRD pattern suggests the presence of nearly linear MgBH4 Mg fragments constituting all the known crystalline polymorphs of Mg(BH4)(2), which are essentially frameworks built of tetrahedral Mg nodes and linear BH4 linkers. TEM shows that the pressure-collapsed phase is amorphous down to the nanoscale, but surprisingly, SXRD reveals a transition at similar to 90 degrees C from the dense amorphous state (density of 0.98 g/cm(3)) back to the porous ? phase having only 0.55 g/cm(3) crystal density. The crystallization is slightly exothermic, with the enthalpy of -4.3 kJ/mol. The volumetric hydrogen density of the amorphous form is 145 g/L, one of the highest among hydrides. Remarkably, this form of Mg(BH4)2 has different reactivity compared to the crystalline forms. The parameters of the reorientational motion of BH4 groups in the amorphous Mg(BH4)(2) found from NMR measurements differ significantly from those in the known crystalline forms. The behavior of the nuclear spinlattice relaxation rates can be described in terms of a Gaussian distribution of the activation energies centered on 234 +/- 9 meV with the dispersion of 100 +/- 10 meV.

Abstract: IWW-type zeolite with Si/Ge of 4.9 is obtained using 5-azonia-spiro[4,4]nonane as template in fluoride-free medium under hydrothermal conditions at 175 °C. In an otherwise identical synthesis, using the related 5-azonia-spiro[4,5]decane as structure directing agent, a mixture of IWW and NON zeolite types was formed. In absence of GeO2 from the reactant mixture, pure NON formed. The IWW zeolite was characterized by XRD, SEM, and HRTEM. IWW zeolite displayed a unique morphology and could be calcined at 600 °C without loss of crystallinity. The Si/Ge ratio of the IWW zeolite was increased by postsynthesis modification. Part of the germanium could be eliminated from the as-synthesized IWW zeolite by acid leaching using 6 M HCl solution. Also the calcined material could be degermanated. Here the presence of a silicon source in the acidic leaching solution minimized structural damage. This way the Si/Ge ratio of the IWW zeolite was increased from 4.9 up to 10.

Abstract: 5,7-Substituted 1,4-diazepinoporphyrazine magnesium(II) complexes were synthesized via Mg(II)-alkoxide templated macrocyclization. A single crystal growth synchrotron diffraction analysis permitted what is to our knowledge the first structural characterization of a 1,4-diazepinoporphyrazine. It exists as a dimer in the solid state. In silico calculations supported by solution phase spectral studies involving a series of representative derivatives, provided insights into the factors governing dimerization of 1,4-diazepinoporphyrazines. The present 1,4-diazepinoporphyrazines serve as useful probes for understanding the determinants that guide dimermonomer equilibria and the self-assembly of phthalocyanine derivatives.

Abstract: Herein, we investigate the DDT (1-dodecanethiol) functionalization of exfoliated MoS2 by using experimental and theoretical tools. For the functionalization of MoS2, DDT treatment was incorporated into the conventional NMP (N-methyl pyrrolidone) exfoliation procedure. Afterward, it has been demonstrated that the functionalization process is successful through optical, morphological and theoretical analysis. The D, G and 2LA peaks seen in the Raman spectrum of exfoliated NMP-MoS2 particles, indicate the formation of graphitic species on MoS2 sheets. In addition, as the DDT ratio increases, the vacant sites on MoS2 sheets diminish. Moreover, at an optimized ratio of DDT-NMP, the maximum number of graphitic quantum dots (GQDs) is observed on MoS2 nanosheets. Specifically, the STEM and AFM data confirm that GQDs reside on the MoS2 nano-sheets and also that the particle size of the DDT-MoS2 is mostly fixed, while the NMP-MoS2 show many smaller and distributed sizes. The comparison of PL intensities of the NMP-MoS2 and DDT-MoS2 samples states a 10-fold increment is visible, and a 60-fold increment in NIR region photoluminescent properties. Moreover, our results lay out understanding and perceptions on the surface and edge chemistry of exfoliated MoS2 and open up more opportunities for MoS2 and GQD particles with broader applications.

Abstract: The exact structure and properties of the Si vertical bar SiO2 interface are very important in microelectronics and photovoltaic devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and solar cells. Whereas Si vertical bar SiO2 structures are traditionally produced by thermal oxidation, hyperthermal oxidation shows a number of promising advantages. However, the Si vertical bar SiO2 interface induced in hyperthermal Si oxidation has not been properly investigated yet. Therefore, in this work, the interface morphology and interfacial stresses during hyperthermal oxidation at room temperature are studied using reactive molecular dynamics simulations based on the ReaxFF potential. Interface thickness and roughness, as well as the bond length and bond angle distributions in the interface are discussed and compared with other models developed for the interfaces induced by traditional thermal oxidation. The formation of a compressive stress is observed. This compressive stress, which at the interface amounts about 2 GPa, significantly slows down the inward silica growth. This value is close to the experimental value in the Si vertical bar SiO2 interface obtained in traditional thermal oxidation.

Abstract: By means of chemical kinetics modeling, it is possible to elucidate the main dissociation mechanisms of CO2 in a gliding arc plasmatron (GAP). We obtain good agreement between the calculated and experimental conversions and energy efficiencies, indicating that the model can indeed be used to study the underlying mechanisms. The calculations predict that vibration-induced dissociation is the main dissociation mechanism of CO2, but it occurs mainly from the lowest vibrational levels because of fast thermalization of the vibrational distribution. Based on these findings, we propose ideas for improving the performance of the GAP, but testing of these ideas in the simulations reveals that they do not always lead to significant enhancement, because of other side effects, thus illustrating the complexity of the process. Nevertheless, the model allows more insight into the underlying mechanisms to be obtained and limitations to be identified.

Abstract: Polyester-grafted polyhedral oligomeric silsesquioxane (POSS) nanohybrids selectively produced by ring-opening polymerization of ε-caprolactone and L,L-lactide (A.-L. Goffin, E. Duquesne, S. Moins, M. Alexandre, Ph. Dubois, Eur. Polym. Journal, 2007, 43, 4103) were studied as masterbatches by melt-blending within their corresponding commercial polymeric matrices, i.e., poly(ε-caprolactone) (PCL) and poly(L,L-lactide) (PLA). For the sake of comparison, neat POSS nanoparticles were also dispersed in PCL and PLA. The objective was to prepare aliphatic polyester-based nanocomposites with enhanced crystallization behavior, and therefore, enhanced thermo-mechanical properties. Wide-angle X-ray scattering and transmission electron microscopy attested for the dispersion of individualized POSS nanoparticles in the resulting nanocomposite materials only when the polyester-grafted POSS nanohybrid was used as a masterbatch. The large impact of such finely dispersed (grafted) nanoparticles on the crystallization behavior for the corresponding polyester matrices was noticed, as evidenced by differential scanning calorimetry analysis. Indeed, well-dispersed POSS nanoparticles acted as efficient nucleating sites, significantly increasing the crystallinity degree of both PCL and PLA matrices. As a result, a positive impact on thermo-mechanical properties was highlighted by dynamic mechanical thermal analysis.

Abstract: Solid state compounds which exhibit non-centrosymmetric crystal structures are of great interest due to the physical properties they can exhibit. The 'hybrid improper' mechanism – in which two non-polar distortion modes couple to, and stabilize, a further polar distortion mode, yielding an acentric crystal structure – offers opportunities to prepare a range of novel non-centrosymmetric solids, but examples of compounds exhibiting acentric crystal structures stabilized by this mechanism are still relatively rare. Here we describe a series of bismuth-containing layered perovskite oxide phases, RbBiNb2O7, LiBiNb2O7 and NaBiNb2O7, which have structural frameworks compatible with hybrid-improper ferroelectricity, but also contain Bi3+ cations which are often observed to stabilize acentric crystal structures due to their 6s(2) electronic configurations. Neutron powder diffraction analysis reveals that RbBiNb2O7 and LiBiNb2O7 adopt polar crystal structures (space groups I2cm and B2cm respectively), compatible with stabilization by a trilinear coupling of non-polar and polar modes. The Bi3+ cations present are observed to enhance the magnitude of the polar distortions of these phases, but are not the primary driver for the acentric structure, as evidenced by the observation that replacing the Bi3+ cations with Nd3+ cations does not change the structural symmetry of the compounds. In contrast the non-centrosymmetric, but non-polar structure of NaBiNb2O7 (space group P2(1)2(1)2(1)) differs significantly from the centrosymmetric structure of NaNdNb2O7, which is attributed to a second-order Jahn-Teller distortion associated with the presence of the Bi3+ cations.

Abstract: Plasma-based dry reforming of methane (DRM) into
high-value-added oxygenates is an appealing approach to enable
otherwise thermodynamically unfavorable chemical reactions at
ambient pressure and near room temperature. However, it suffers
from coke deposition due to the deep decomposition of CH4. In this
work, we assess the DRM performance upon O2 addition, as well as
varying temperature, CO2/CH4 ratio, discharge power, and gas
residence time, for optimizing oxygenate production. By adding O2,
the main products can be shifted from syngas (CO + H2) toward
oxygenates. Chemical kinetics modeling shows that the improved
oxygenate production is due to the increased concentration of
oxygen-containing radicals, e.g., O, OH, and HO2, formed by electron
impact dissociation [e + O2 → e + O + O/O(1D)] and subsequent
reactions with H atoms. Our study reveals the crucial role of oxygen-coupling in DRM aimed at oxygenates, providing practical
solutions to suppress carbon deposition and at the same time enhance the oxygenates production in plasma-assisted DRM.

Abstract: The highly porous and desolvated (activated) coordination polymer [Zn4O(btb)2] (btb = benzene-1,3,5-tribenzoate; MOF-177) was loaded with the organometallic compounds [Cp2Fe], [Cp*2Zn], [Cu(OCHMeCH2NMe2)2], [CpCuL] (L = PMe3, CNtBu) and [CpPd(3-C3H5)] via solvent-free adsorption from the gas-phase. The inclusion compounds of the type [LnM]a@MOF-177, where [LnM] indicates the respective compound and the parameter a denotes the number of molecules per formula unit of the MOF-177, were characterised by elemental analysis, FT-IR, solid-state NMR spectroscopy and by powder X-ray diffraction (PXRD). Remarkably high effective loadings of up to 11 molecules [Cp2Fe] and 10 molecules [CpPd(3-C3H5)] per cavity were determined. The analytical data prove that the host lattice and the guest molecules interact only by weak van-der-Waals forces without any significant change of the framework or the chemical nature of the included molecules. Cu nanoparticles showing the typical surface plasmon resonance at 580 nm and Pd nanoparticles of about 2.6 nm in size were formed inside the cavities of MOF-177 by the thermally activated hydrogenolysis of the inclusion compounds [CpCuCNtBu]2@MOF-177 and by photolysis of [CpPd(3-C3H5)]10@MOF-177 in an inert atmosphere (Ar). PXRD, FT-IR and NMR studies revealed that the MOF-177 matrix remained unchanged during the decomposition process of the precursors. N2 adsorption studies of the obtained materials Cu@MOF-177 (e.g. 10.6 wt.% Cu, 2309 m2 g-1) and Pd@MOF-177 (e.g. 32.5 wt.%, 1063 m2 g-1) reveal high remaining specific surface areas (Langmuir model).