Understanding materials with dimensions down to few nanometers is of major importance for fundamental science as well as prospective applications. Structural transformation and phononconfinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm size. Here we investigate the effect of size on the surface chemistry, microscopic structure, and Raman scattering of high-pressure high-temperature (HPHT) and detonation nanodiamonds (DNDs) down to 2-3 nm. The surface and size of NDs are controlled by annealing in air and ultracentrifugation resulting in three ND fractions. Particle size distribution (PSD) of the fractions is analyzed by combining dynamic light scattering (DLS), analytical ultracentrifugation (AUC), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) as complementary techniques. Based on the obtained PSD we identify size-dependent and synthesis-dependent differences of NDs properties. In particular, interpretation of Raman scattering on NDs is revisited. Comprehensive comparison of detonation 3 and pure monocrystalline HPHT NDs reveals effects of diamond core size and defects, chemical and temperature (in)stability as well as limitations of current phonon confinement models. In addition, low-frequency Raman scattering in the 20 -200 cm -1 range is experimentally observed.The size dependence of this signal for both HPHT NDs and DNDs suggests that it may correspond to confined acoustic vibrational, "breathing-like" modes of NDs.

Five different water-based precipitation methods have been used to prepare nanoceria with significantly different redox and acid/base properties, which have been described in detail by a number of analytical methods....

A series of mesoporous cerium−iron binary oxides was prepared by a hydrothermal technique using CTAB as a template. The influence of the Fe/Ce ratio and the variations in the preparation techniques such as the type of solvent and the precipitation agent, the approach of the template release, and the temperature of calcination on the phase composition, textural, structural, surface, and redox properties of the obtained materials was studied in details by XRD, nitrogen physisorption, TPR, FTIR, UV−vis, XPS, Raman, and Moessbauer spectroscopies. The materials were tested as catalysts in methanol decomposition and total oxidation of ethyl acetate. It was assumed that the binary materials represented a complex mixture of differently substituted ceria-and hematite-like phases. Critical assessment of their formation on the base of a common mechanism scheme was proposed. This scheme declares the key role of the formation of shared Ce−O−Fe structures by insertion of Fe 3+ in the ceria lattice and further competitive compensation of the lattice charge balance by the existing in the system ions, which could be controlled by the Fe/Ce ratio and the hydrothermal synthesis procedure used. This mechanism provides proper understanding and regulation of the catalytic behavior of cerium−iron oxide composites in methanol decomposition with a potential for hydrogen production and total oxidation of ethyl acetate as a model of VOCs.

Ag nanoparticles decorated-TiO2 P25 are a viable alternative for the degradation, through a rutile-mediated mechanism, of fluoroquinolone-based antibiotics under visible light irradiation and, at the same time, for bacteria inactivation in water.