NiO/Ni nanocomposite (micro)structure evolution induced by thermal annealing and milling

Abstract

Poster Sessions C323 subjects with various parameters of their microstructure (sizes of microparticles, specific surface) and substructure (sizes of nanoparticles and crystallites) governing their working properties.The purpose of the work is to find correlations between synthesis conditions of samples with nanosized η-TiO 2 , their characteristics and structural, sorption, catalytic and photocatalytic properties.The determination of η-TiO 2 cell parameters (a~3.8Å, c~19Å) has been made using sources of electrons, X-rays and synchrotron scattering. These parameters are associated with ones of anatase modification (a 0~3 .8Å, c 0~9 .5Å) by the relationship a~a 0 , c~2c 0 . Optimization of the sulfate method allowed increasing the yield of η-TiO 2 up to 95%. The samples were characterized by a set of methods showing variations in sizes of microparticles/ agglomerates (200/3000 nm; SEM, BET), nanoparticles (8÷24 nm, rarely 28÷55 nm; small angle X-ray scattering), crystallites, or coherent scattering regions (L=3÷6 nm; large angle X-ray scattering), as well as in sizes (~17 nm; BET) and capacities (0.02 cm 3 /g; BET) of pores and specific surface (4.5÷16 m 2 /g; BET). Dependence of some parameters (in particular, value L) on synthetic conditions (the initial concentration of TiOSO 4 • xH 2 SO 4 •yH 2 O reagent, the temperature and duration of hydrolysis, the heating speed of reaction mixture and so on) was found.Photocatalitic activity (in model reactions of decomposing methyl-orange, methylene-blue and xylenol-orange indicators under UV radiation), sorption properties (extraction of various ions from aqueous media) and catalytic properties (oxidation of CO to CO 2 in air at room temperature) depend on sample characteristics. Efficiency of CO conversion to CO 2 correlates with specific surface. For bismuth, arsenic and vanadium ions, degree of sorption equal to maximal permissible concentration was achieved. A relation between the degree of metal-ion sorption and the coherent scattering regions (value L) has been established. Degree of metal-ion sorption and rate constant for photocatalytic reactions are maximal for L ~ 4.5 nm. Photocatalytic activity (pH < 3) for the samples with η-TiO 2 is considerably higher than for commercial photocatalysts Degussa P25 (anatase-rutile mixture) tested in comparable conditions. The photocatalytic and catalytic activities obtained confirm unique surface properties of η-TiO 2 .From the X-ray diffraction study data by means of crystallochemical approach, the structure of η-TiO 2 was proposed. The quasi-layered structure model provides a very fit to the experimental data (in particular, the sorption properties). Details of structure and microstructure changes of ferrite nanoparticles are assessed using synchrotron X-ray and TOF neutron diffraction data by combining Rietveld method in reciprocal space with the atomic pair distribution function (PDF) method in direct space. Such obtained (micro)structural parameters were correlated with physical properties revealed by HRTEM, Mössbauer ...