No abstract

In order to enhance the hydrogen storage properties of Mg, flowerlike NiS particles have been successfully prepared by solvothermal reaction method, and are subsequently ball milled with Mg nanoparticles (NPs) to fabricate Mg-5 wt % NiS nanocomposite. The nanocomposite displays Mg/NiS core/shell structure. The NiS shell decomposes into Ni, MgS and MgNi multiple-phases, decorating on the surface of the Mg NPs after the first hydrogen absorption and desorption cycle at 673 K. The Mg-MgS-MgNi-Ni nanocomposite shows enhanced hydrogenation and dehydrogenation rates: it can quickly uptake 3.5 wt % H within 10 min at 423 K and release 3.1 wt % H within 10 min at 573 K. The apparent hydrogen absorption and desorption activation energies are decreased to 45.45 and 64.71 kJ mol. The enhanced sorption kinetics of the nanocomposite is attributed to the synergistic catalytic effects of the in situ formed MgS, Ni and MgNi multiple-phase catalysts during the hydrogenation/dehydrogenation process, the porthole effects for the volume expansion and microstrain of the phase transformation of MgNi and MgNiH and the reduced hydrogen diffusion distance caused by nanosized Mg. This novel method of in situ producing multiple-phase catalysts gives a new horizon for designing high performance hydrogen storage material.

With the intention of improving the hydrogenation/dehydrogenation kinetics of Mg, Mg-7.5 wt % Nb nanocomposite has been prepared by hydrogen plasma-metal reaction (HPMR) approach. The spherical Nb nanoparticles (NPs) of 12 nm are uniformly decorated on the surface of Mg NPs. The Mg-Nb nanocomposite can quickly uptake 4.0 wt % H 2 in 10 min and reach a saturation value of 5.7 wt % H 2 in 60 min at 473 K. Furthermore, it can also release 4.0 wt % H 2 in 60 min at 573 K. The reversible hydrogen storage capacity is as high as 7.0 wt % at 673 K. Nb NPs transform into NbH during hydrogenation and recover after dehydrogenation process. They restrain the growth of Mg and work as catalysts to accelerate the hydrogen transportation in the Mg-based nanocomposite by decreasing the activation energies of hydrogenation/dehydrogenation to 70.9 and 86.4 kJmol -1 , respectively. The catalytic mechanism of Nb NPs is explained in terms of spillover, d-electrons and electronegativity effects. The nanosizing effects of both Mg and Nb and the catalytic effect of Nb NPs give rise to the improved hydrogen storage properties of the Mg-Nb nanocomposite at moderate temperatures.

Composite biological and inorganic fouling occurs in plate heat exchangers (PHEs) using treated sewage as heat transfer medium, which lowers the heat transfer coefficient and increases the frictional resistance. In order to optimize the heat exchange process and improve the anti-fouling strategies, the dynamic behavior of composite fouling at a vertical surface of stainless steel (ANSI 316L) was investigated under typical conditions of PHEs. The growth curves of composite fouling were obtained. The evolution of composite fouling was characterized by means of environmental scanning electron microscopy (ESEM). Backscattered Electron Image (BEI) and energy dispersive X-ray spectrometry (EDS) were used as aids in interpreting the results. The experimental results show that a preliminary stage of a 6-day period with a low fouling growth rate exists during the composite fouling development. A significant change of the fouling growth rate happens after the preliminary stage during which the bacterial behaviors at the surface could be recorded clearly. After the preliminary stage, a space netshape, mainly consisting of bacteria, extracellular products (EPS) and inorganic particles, could be established on the surface of the fouling layer. The change of fouling growth rate occurs synchronously with the evolution.

Herein, two Wells -Dawson-type arsenomolybdates, formulated as [Cu(pyr)][AsMoO] (1) and [Ag(pyr)][AsMoO] (2) (pyr = pyrazole), were hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction, elemental analysis, IR and UV-vis-NIR spectroscopies, XPS, XRD, and TG analysis. The structural analysis indicated that compounds 1 and 2 were isomorphic. They are the first reported 3D honeycomb structures of Wells-Dawson-type arsenomolybdates. The [M(pyr)] (M = Cu and Ag) connected with [AsMoO] polyoxoanions to form the {8·12}{8} topological structure. The contributions of organic ligands, pH value, reaction temperature, and transition-metal (TM) to the construction of 3D networks were elucidated. Furthermore, compounds 1 and 2 exhibited fluorescence properties in the solid state at room temperature, highly efficient catalytic ability for the degradation of five organic dyes (MB, RhB, MO, AP, and CR) under UV irradiation, and obvious electrocatalytic activities for the reduction of HO. The mechanisms of photocatalysis and electrocatalysis have also been discussed in detail.