Zongtao Zhang

Strongly Acidic and High-Temperature Hydrothermally Stable Mesoporous Aluminosilicates with Ordered Hexagonal Structure

Publisher Summary This chapter discusses strong acidic and high-temperature hydrothermally stable mesoporous aluminosilicates with well-ordered hexagonal structure. These mesoporous aluminosilicates have been successfully synthesized from the assembly of preformed aluminosilicate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The MAS-5 shows extraordinary stability both in boiling water and in steam. Temperature-programmed desorption of ammonia (NH3) shows that the acidic strength of MAS-5 is much higher than that of MCM-41.

Modelling for size-dependent and dimension-dependent melting of nanocrystals

A unified model, free of any adjustable parameters, for the size-dependence and dimension-dependence of melting point depression and superheating of nanocrystals is developed. In terms of the consideration of the surface/volume ratio of nanocrystals, the suppression of melting point of nanocrystals and superheating of embedded nanocrystals are predicted. The model predictions for the melting temperatures of nanocrystals are consistent with the experimental results and molecular dynamics simulations.

Superheating of nanocrystals embedded in matrix

In terms of a model for size-dependent melting and the Lindemann criterion, a model to interpret superheating of nanocrystals embedded in a matrix has been developed. When a ratio, α, between the mean square displacement of the surface atoms and that of interior ones for the nanocrystals, is smaller than 1, superheating arises when the nanocrystals have coherent or semi-coherent interfaces with the matrix which has a higher melting temperature than the nanocrystals. Moreover, the atomic diameter of the matrix should be smaller than that of the nanocrystals. The model prediction shows good agreement with the experimental evidence.

Melting thermodynamics of nanocrystals embedded in a matrix

A simple model, free of any adjustable parameter, is established for the melting temperature and melting entropy of nanocrystals embedded in a matrix where the interface between the nanocrystals and the matrix is coherent. The model is based on Lindemanns criterion for the melting, Motts equation for the melting entropy of bulk crystals and our model for the size-dependent melting temperature. It is shown that the melting temperature and the melting entropy of nanocrystals embedded in a matrix increase as the size of the nanocrystals decreases. The above predictions are supported by available experimental results on Pb and In nanocrystals embedded in an Al matrix. On the basis of the model, the melting mechanism of superheating is discussed.

Properties and application of Fe–6Si–14Mn–9Cr–5Ni shape memory alloy

Abstract Three iron based shape memory alloys were studied and Fe–6Si–14Mn–9Cr–5Ni alloy showed the best shape memory effect. By thermomechanical training, the shape memory effect was improved and an absolute recovery strain of 6·2% was obtained. To promote the ε→γ transformation, which is not complete even after heating the alloy to 1000 K, the As and Af temperatures are decreased and the transformation enthalpy is increased by thermal cycling and increasing prestrain. The alloy also shows good creep and stress relaxation resistance. In addition, under a tensile force of 20 kN and a sealing test pressure of 6 MPa pipe joints made using the alloy remain effective and can satisfy the requirements for possible industrial applications.

High activity in catalytic cracking over stable mesoporous aluminosilicates

Abstract A stable mesoporous aluminosilicate with hexagonal symmetry (MAS-5) has been synthesized by the co-templates of tetraethylammonium hydroxide (TEAOH) and cetyltrimethylammonium bromide (CTAB) cationic surfactant. The cracking of 1,3,5-triisopropylbenzene is used as probe reaction to test its catalytic properties. Catalytic data show that the conversion over the stable mesoporous aluminosilicate (HMAS-5) is higher than that over HA1-MCM-41, which is assigned to HMAS-5 which has stronger acidity than HAl-MCM-41. Furthermore, we observed that the catalytic conversion over HMAS-5 is much higher than that over HZSM-5, which is assigned to that the diffusion of large molecule of 1,3,5-triisopropylbenzene is strongly impeded by narrow channels of HZSM-5 zeolite.

Cadmium Sulfide and Nickel Synergetic Co-catalysts Supported on Graphitic Carbon Nitride for Visible-Light-Driven Photocatalytic Hydrogen Evolution

Design and preparation of noble-metal-free photocatalysts is of great importance for photocatalytic water splitting harvesting solar energy. Here, we report the high visible-light-driven hydrogen evolution upon the hybrid photocatalyst system consisting of CdS nanocrystals and Ni@NiO nanoparticles grown on the surface of g-C3N4. The hybrid system shows a high H2-production rate of 1258.7 μmol h−1 g−1 in the presence of triethanolamine as a sacrificial electron donor under visible light irradiation. The synergetic catalytic mechanism has been studied and the results of photovoltaic and photoluminescence properties show that efficient electron transfer could be achieved from g-C3N4 to CdS nanocrystals and subsequently to Ni@NiO hybrid.

Cobalt Phosphide Modified Titanium Oxide Nanophotocatalysts with Significantly Enhanced Photocatalytic Hydrogen Evolution from Water Splitting

Production of hydrogen from photocatalytic water splitting holds promise as an alternative energy source with superiority of cleanliness, environment friendliness, low price, and sustainability. Perfectly constructing the noble-metal-free and stable hybrid structure photocatalyst is quite essential; herein, for the first time the authors aim to use cobalt phosphide as the cocatalyst on titanium oxide to form a novel hybrid structure to enhance the utilization of the photoexcited electrons in redox reactions for improved photocatalytic H2 evolution activity. Thus, the achieved significantly increased photocatalytic H2 -evolution rate on the optimized CoP/TiO2 (8350 µmol h-1 g-1 ) is 11 times higher than that of the pristine TiO2 . Moreover, this work is expected to spur more insight into synthesizing such novel photofunctional systems, achieving high photocatalytic H2 evolution activity and sufficient stability for solar-to-chemical conversion and utilization.

Preparation, characterization, and optical properties of the host-guest nanocomposite material zeolite-silver iodide

Abstract Zeolites NaZSM-5 and NaY as hosts for producing nanoscale silver iodide guest were studied with the goal of investigating the optical properties of the prepared host-guest nanocomposite materials. The host-guest nanocomposite materials of NaY–AgI and (NaZSM-5)–AgI were prepared by a heat diffusion method. The nanocomposite materials prepared were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), X-ray photoelectric spectroscopy (XPS), and adsorption. The properties of the diffuse reflectance absorption spectra and the surface photovoltage spectra of the prepared nanocomposite materials were investigated. The quantum confinement effect of the channels of zeolites made the prepared host-guest nanocomposite materials show some interesting optical properties. This makes the investigated nanomaterials suitable for use as quantum electronic and optoelectric materials.

A novel and highly efficient earth-abundant Cu3P with TiO2 “P–N” heterojunction nanophotocatalyst for hydrogen evolution from water

Semiconductor-based photocatalytic hydrogen (H2) evolution from water is of great importance for solar-to-chemical conversion processes to boost and promote the future hydrogen economy. Here, for the first time, we demonstrate that p-Cu3P coupled with n-TiO2 forms a novel hybrid structure which accelerates electron-hole pair separation and transfer for improved photocatalytic H2-evolution activity. The rate of H2 evolution of the optimized Cu3P/TiO2 (7940 μmol h-1 g-1) is 11 times higher than that of bare TiO2, with an apparent quantum efficiency (AQE) of 4.6%. This work may provide more insight into the synthesis of novel phosphide-based hybrid materials with high photocatalytic H2-evolution activity and sufficient stability for solar-to-chemical conversion and utilization.