Hierarchical nano ZnO-micro TiO2 composites: High UV protection yield lowering photodegradation in sunscreens

Abstract

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].

ZnO and quercetin encapsulated nanoparticles for sun protection obtained by miniemulsion polymerization using alternative co-stabilizers

“…Another drawback of inorganic compounds as ZnO and TiO 2 is the generation of free radicals when exposed to UV radiation [4]. In this sense, encapsulation of inorganic nanoparticles becomes a promising technique to reduce the formation of free radicals when exposed to UV radiation, beyond the contribution to the translucent appearance of the Sunscreens [4,5]. Also, the encapsulation of organic compounds may improve photostability, photo protection and safety of the compounds [6].…”

Implementation of Safe-by-Design for Nanomaterial Development and Safe Innovation: Why We Need a Comprehensive Approach

“…On the other hand, understanding of the functionality-material relationships is likewise necessary in order to develop functional materials [22]. Depending on the materials properties to be exploited for a distinct application, it might not be possible to maximise both functionality and safety at the same time, as highlighted by Reinosa et al [7]. …”

Influence of ZnO, SiO2 and TiO2 on the aging process of PLA fibers produced by electrospinning method

“…We hypothesized that modification of fibers with inorganic particles (SiO 2 , ZnO and TiO 2 ) can affect the stability of PLA. ZnO and TiO 2 are effective absorbers of UV [24,25] and are commonly used as UV-screen agents in sunblocks. Zhang reported that ZnO nanoparticles can stabilize poly(butylene succinate-co-butylene adipate) matrix and hinder the photodegradation of polymer [26].…”