Yong-Xin Qi

One step convenient synthesis of crystalline β-Si3N4

Well-crystallized β-Si3N4 was directly prepared at an initial reaction temperature of 150 °C through the reaction of SiCl4 and NaN3 in the presence of a small amount of CCl4. Characterization by X-ray diffraction, high-resolution electron microscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy indicates that the product synthesized is crystalline β-Si3N4. The yield of β-Si3N4 is about 86% based on the amount of precursor SiCl4 used at the initial reaction temperature of 150 °C, and is more than 90% at the reaction temperature of 200 °C with the product β-Si3N4 in high crystallinity. The dominant morphology of the product is short rods with the growth axis along the [001] direction. The formation mechanism of crystalline β-Si3N4 was discussed briefly, and the role of CCl4 in the formation process of β-Si3N4 was analyzed.

Facile synthesis of water-soluble and superparamagnetic Fe3O4 dots through a polyol-hydrolysis route

Monodisperse Fe3O4 dots with a mean size of about 2.3xa0nm were successfully synthesized via a polyol-hydrolysis route without adding any dispersant. Inorganic iron nitrate was used as the metal source and triethylene glycol (TEG) was used as the polyol solvent. The Fe3O4 dots were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selective area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, N2 adsorption–desorption, and magnetization measurements. The as-synthesized Fe3O4 dots can not only be coagulated from the polyol by ethanol and acetone, but also easily redispersed in water by ultrasonication, resulting in a clear Tyndall effect. The obtained Fe3O4 dots exhibited superparamagnetism at room temperature and the saturation magnetization is much lower than those reported in previous works. The formation mechanism of the Fe3O4 dots was proposed to be the hydrolysis of iron nitrates and subsequent dehydration and partial reduction of Fe3+ to Fe2+ at elevated temperatures in TEG.

The Potential of Cu‐SAPO‐44 in the Selective Catalytic Reduction of NOx with NH3

Nitrogen oxides (NOx) contribute much to acid rain, photochemical smog, and the depletion of tropospheric ozone. A novel, small‐pore Cu‐exchanged chabazite (Cu‐CHA) zeolite, Cu‐SAPO‐44, was first studied for the selective catalytic reduction of NOx with ammonia (NH3‐SCR), and exhibits excellent activity and N2 selectivity over the wide temperature window from 200–550u2009°C. The Cu content in Cu‐SAPO‐44 plays a significant role in the NH3‐SCR reactions. Two kinds of isolated Cu2+ species inside the large cages and in the six‐membered rings of the CHA structure were verified as the active sites, which are responsible for the low‐temperature and high‐temperature activity, respectively. Cu‐SAPO‐44 is shown to be a promising candidate as a SCR catalyst for deNOx with great potential in after‐treatment systems for either mobile or stationary sources.