Structure and surface states of Cu-O based nanocrystalline powders

Abstract

An investigation of physical and chemical properties of nanopowders as a result of substantial specific surface contribution the detailed information about surface states and their variations due to the different chemical transformations is required. This is particularly important for catalysis and adsorbent applications. Both bulk structural properties and surface states (existence of hydroxide, carbonate groups and different oxygen states) of the gas-condensation nanocrystalline Cu-O powders were studied by X-ray, TEM, Rutherford Backscattering (RBS), XPS, TGM, FTIR-spectroscopy and other methods. As-prepared oxide samples synthesized by gas condensation contained only Cu 2O phase. In the same samples the excess of the oxygen concentration more than 30 at.% as compared with stoichiometric composition Cu2O was revealed using RBS method. At further exposure of Cu2O nanopowders in argon atmosphere the captured oxygen reacts with Cu2O and partially oxidizes Cu2O nanopowder to CuO. It was experimentally shown that on the surface of nanoparticles at relatively short exposure of samples in air hydroxide and carbonate groups were formed. The existence of Cu(OH)2 and CuCO3 compounds was confirmed under investigation of nanocrystalline powders of different granulometric and chemical composition by XPS. The influence of heat treatment in vacuum (up to 300°C) on the stability of hydroxide and carbonate groups was studied. It was demonstrated that at degassing of samples in vacuum and their contact with air for several minutes over 2 wt% of different gaseous impurities are adsorbed again on sample surface.