TiO 2 is a commonly used semiconductor photocatalyst but, as a paradox, it is also widely used as UV filter in sunscreens. Moreover, its capacity to form free radicals under UV irradiation generates reactive free radicals that provoke sunscreens degradation. In this work a hierarchical composite made of ZnO nanoparticles anchored onto TiO 2 microparticles is developed in a safe-by-design way by using the sol-gel method. The aim of this composite is to gain the advantages of inorganic nanoparticles avoiding their potential drawbacks. The hierarchical composite presents higher UV absorption than the pure TiO 2 or ZnO counterparts.The functional stability study on standard sunscreen reveals a 50% high Solar ProtectionFactor (SPF) values over time for the hierarchical composite lowering the photodegradation of the formulation. Under authors´ knowledge, it is the first time that the combination of these oxides increases the UV attenuation as inhibits the negative effects of free radicals. The high UV absorption without degradation opens a new orientation for the effective use of UVabsorbers without the photocatalyst adverse effects. The results in sunscreens generate a proposed mechanism of functionality that explains the observed differences on the efficiency of photocatalytic activity of these materials for other application fields.Both oxides act as inorganic UV blockers, so they are used into sunscreens in order to protect the skin, but the effective degradation of organic substances by the photocatalyst effect is contrary to applications in which the matrix must be preserved as paints, paper, plastics or cosmetics. In these cases, a proposed solution consists of doping trap centers into TiO 2 and ZnO, resulting in the elimination of free radicals generation and ROS [4]. Also, the aggregation of metal oxide nanoparticles has been found to decrease the photocatalytic properties in the generation of the mentioned species [5,10].

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2D particles forming a nanostructured shell: a step forward cool NIR reflectivity for CoAl2O4 pigments.

We are studying the formation of a nanostructured spinel CoAl2O4 layer on α-Al2O3 giving rise to a core-shell composite. In the final product, two mechanisms of CoAl2O4 crystallization onto a α-Al2O3 microparticle surface are observed, depending on the dispersion grade of Co3O4: a 3D nanostructure from the arrangement of Co3O4 agglomerated nanoparticles; 2D nanoparticles from the diffusion mechanism of isolated Co3O4 nanoparticles. As a consequence, two different crystallization pathways may occur during the thermal treatment. In order to understand the formation mechanisms a Raman Confocal Study is performed. The features of the Raman spectra of the samples depend strongly on the morphology of the nanoparticles located in the shell of the microparticle.Average spectra of the samples show a variation in the Raman shift between the different samples. The differences between 3D or 2D structures is associated with the transmission of phonons among the nanoparticles. The high results clearly indicate that extrinsic parameters such as the size of the crystals and their aggregation state affects their Raman properties.

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