Preparation and thermal analysis kinetics of the core–nanoshell composite materials doped with Sm

The core–nanoshell composite materials with magnetic fly-ash hollow cenosphere as core and nano SmFeO3 as shell were synthesized by high-energy ball milling method. The magnetic fly-ash hollow cenosphere, samarium nitrate, and iron nitrate were used as raw materials. The synthesis and growth kinetics of the composite materials were investigated using the thermogravimetry and differential thermal analysis (TG–DTA) at different heating rates. The results show that the precursor of the composite materials decomposes in three steps. The apparent activation energy of each stage was calculated using the Doyle–Ozawa and Kissinger methods. The reaction order, frequency factor, and rate equations were also determined. The activation energy of the nano crystallite growth is calculated to be 16.12 kJ mol−1 according to kinetics theory of nano crystallite growth. It can be inferred that the crystallite grows primarily by means of an interfacial reaction during the thermal treatment. The magnetic properties and microwave absorbing properties of samples were analyzed by the vibrating sample magnetometer analysis and vector network analyzer. The results indicated that the exchange coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating, which cause outstanding magnetic properties. In the frequency between 1 MHz and 1 GHz, the absorbing effectiveness of the composite absorbers can achieve −32 dB. The magnetic properties of the composite material are better than those of single phase. So it is consistent with requirements of the microwave absorbing material at the low-frequency absorption.National Natural Science Foundation (China) (No. 20976018)Liaoning Sheng (China) (Science Research Plan Project, Higher Education Department (No. L2013176))China. Ministry of Education (Key Laboratory of Industrial Ecology and Environmental Engineering, KLIEEE-12-03)China. Ministry of Education (National Project of China ‘‘Innovation and Entrepreneurship Training Program of Undergraduate students’’ (201310150002)

Achieving photocatalytic water oxidation on LaNbON2 under visible light irradiation

LaNbON2 has narrow bandgap and wide visible-light absorption band, yet no photocatalytic water oxidation on LaNbON2 has been reported. By a post-annealing treatment in Ar, anion vacancies were brought into LaNbON2 as shown by EPR spectroscopy. These could act as donors in the semiconductor. And consequently the oxidative power of holes was enhanced as indicated by the difference between fermi level and valence band maximum (EF-EVBM) evaluated from valence band XPS. The annealed LaNbON2 photocatalyst acquired water oxidation ability for the first time, which was improved by combining CoOx as cocatalyst. Annealed LaNbON2 derived from La3NbO7 had smaller particle size, higher concentration of anion vacancies, bigger EF-EVBM and better performance for photocatalytic oxygen evolution reaction than LaNbON2 derived from LaNbO4. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Chloride flux growth of crystalline strontium niobates and nitridation to perovskite SrNbO2N

Highly crystalline (110) layered perovskite Sr2Nb2O7, (111) layered perovskite Sr5Nb4O15 and complex perovskite Sr4Nb2O9 were prepared by NaCl-KCl flux growth method from SrCO3 and Nb2O5. This flux synthesis achieves single strontium niobate phase in contrast to mixed niobates from the solid state reaction with the same heating parameters. A little excess of Sr source was found to be required for the synthesis of Sr5Nb4O15 and Sr4Nb2O9 at elevated temperature due to slight evaporation. The three strontium niobates were converted to perovskite SrNbO2N via thermal ammonolysis under NH3 flow at 900 degrees C. Post-wash treatment was performed to remove the byproduct SrO. This makes additional nanopores in SrNbO2N in the cases of Sr5Nb4O15 and Sr4Nb2O9, and results in increasing surface areas of SrNbO2N with Sr:Nb ratios in the precursors (from 9.9 to 19.8 and 35.5 m(2)/g). On the other hand, the UV Vis diffusion reflectance spectra reveal decreasing light absorption by defects in SrNbO2N in this order. This suggests fewer low-valent Nb defects in SrNbO2N prepared from precursor with higher Sr:Nb ratio. SrNbO2N prepared from Sr4Nb2O9 would be advantageous for applications that require high surface area and low defect density of the material