A successful strategy to obtain self-supporting (100 microm), UV-absorbing, and, in the visible region, highly transparent TiO2-poly(methyl methacrylate) (PMMA) films was developed. The 15 nm large anatase TiO2 nanocrystals were prepared in a nonaqueous sol-gel approach involving the mixing of Ti(O(i)Pr)4 and benzyl alcohol. The surfaces of the resulting particles were modified with minute amounts of organic ligands in order to make the particles easily dispersible in nonpolar media like xylene and dichloromethane and compatible with PMMA, a polymer of high optical transparency and considerable technical importance. The empirical optimization process of composite fabrication was supplemented by fundamental studies of the crystallization and growth mechanism of anatase particles in a nonaqueous medium. After the preparation of corresponding nanocomposites, the materials were investigated with respect to their UV absorption capability, optical transparency in the visible-wavelength region, and photodegradation.

Defect engineering operated on metal oxides by chemical and structural modifications may strongly affect properties suitable for various applications such as photoelectrochemical behaviour, charge transport and luminescence. In this work we report the tuneable optical features observed in undoped monoclinic HfO 2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with decay time of few ns) overlaps with a slower emission (decay of several µs) due to extrinsic Ti -impurity centres. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modelled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at crystal boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO 2 under near-UV excitation.

Here, we show a simple approach to synthesize cobalt and cobalt oxide nanoparticles in an organic solvent. We find that the cubic Co 3 O 4 nanoparticles can be easily obtained, even at temperatures as low as 80 °C. Moreover, exactly the same reaction at 180 °C leads to metallic Co nanoparticles. Thus, in addition to the synthetic efforts, we study the mechanism of occurrence of oxidation and reduction of a Co 2+ precursor in benzyl alcohol. Remarkably, the in situ X-ray absorption and diffraction measurements of the synthesis at 140 °C reveal that oxidation of Co 2+ to Co 3+/2+ and reduction of Co 2+ to Co 0 reactions take place simultaneously. It is followed by a rapid formation of Co 3 O 4 nanoparticles and its consecutive solid-state reduction to CoO. In parallel, metallic Co nanoparticles begin to grow. In addition, Multicomponent Curve Resolution−Alternating Least Squares (MCR-ALS) analysis of X-ray absorption spectroscopy (XAS) data efficiently reveals the nontrivial interdependence between four different reactions. Our strategy to control reduction and oxidation of Co-based nanoparticles as they grow opens up an elegant pathway for the one-pot-synthesis of the hybrid materials for energy-related applications.

Closing the loop: initially, the reactivity of benzyl alcohol determines the nucleation of Cu nanoparticles, but as soon as they start to form they begin to catalyze the condensation of benzyl alcohol to dibenzylether.

We discuss fabrication techniques for porous metals with the focus on how to control the architecture over several length scales.