Titanium doped tin dioxide as potential UV filter with low photocatalytic activity for sunscreen products Alexander Morlando a , Dean Cardillo a , Thierry Devers b , Konstantin Konstantinov a,n a Institute for Superconducting and Electronic Materials, AIIM Facility, University of Wollongong Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia b Interface, Confinement, Matériaux et Nanostructures – ICMN UMR737, Site IUT de Chartres, France article info Article history: Received 28 September 2015 Received in revised form 4 February 2016 Accepted 21 February 2016 Available online 23 February 2016 Keywords: Optical materials and properties Particles Nanosize Powder technology X-ray techniques abstract Titanium doped tin dioxide nanopowders were produced using a simple precipitation method and displayed the same crystalline structure and decreasing particle size with increasing dopant con- centration. Optical absorption studies showed broad absorption in the UV region for each sample and enhanced absorption relative to commercial zinc oxide (ZnO) but significantly less absorption than the uncoated commercial titanium dioxide nanopowder (P-25). Photocatalytic studies showed that the 5%Ti doped sample had the lowest methylene blue (MB) degradation rate of (1.9 70.4) Â 10 À3 min À1 , fol- lowed by the undoped ((2.6 70.4) Â 10 À3 min À1 ) and 10% Ti-doped ((4.5 70.4) Â 10 À3 min À1 ) samples. All of the nanoparticle samples demonstrated substantially lowered photocatalytic activity compared to commercial ZnO and P-25 reference particles. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Exposure to solar UV radiation is a known cause of many types of skin cancer. In particular, UVA (320–400 nm) and UVB (290– 320 nm) radiation have been proven to cause DNA damage both directly and indirectly via the production of reactive oxygen spe- cies that bring about oxidative stress [1]. Application of sunscreens containing UV filtering additives (both organic and inorganic) to the skin is a common measure for protecting against UV radiation. Although there are a greater number of certified organic filters than inorganic, these materials typically have a lower photo- stability, are potential allergens and provide a relatively low level of protection when used on their own. Modern sunscreen for- mulations now contain a mixture of UV filters and the use of in- organic filters has become more extensive due to their lower po- tential of producing irritant reactions, high sun protection factor (SPF) and broad-spectrum absorption [2]. Titanium dioxide (TiO 2 ) and zinc oxide (ZnO) are the aforementioned inorganic filters currently used in sunscreens. Although both materials exhibit high photocatalytic properties which could lead to the production of harmful reactive oxygen species, their broadband absorption across the UVA and UVB range, have led to their extensive use in sunscreen products. Despite the apparent benefits of these nanomaterials, recent concern over the skin penetrating cap- abilities and potential toxicity has led to further investigation of the safety of these materials. As of 2013, in a review of the safety of TiO 2 and ZnO nanoparticles in sunscreens [3], the weight of evi- dence suggests that these materials remain on the skin surface and outer layer of the stratum corneum, which is composed only of non-viable cells. However, the review also highlighted the fact that there is conclusive in vitro evidence that, whilst in the presence of UV radiation, these materials bring about the production of re- active oxygen species, which can lead to the damaging of cells. As such, it is necessary to search for alternate materials that provide the same, if not improved, benefits provided by TiO 2 and ZnO as UV filters but without potential toxicological effects. Materials based on tin dioxide are most commonly used as transparent conducting oxides, oxidation catalysts and as solid state gas sen- sing materials [4 À 6]. With a wide band gap (3.60 eV) [7], tin di- oxide has a high optical transparency in the visible light range, making it a potentially cosmetically viable material. Additionally, tailoring of the band gap through induced defect sites and/or impurities could shift its absorption profile into the UVB or UVA range, allowing it to behave as a UV filter. Studies on tin oxide doping with a variety of materials [8 À 11] have shown that such bandgap tailoring is possible. In this study, the optical and pho- tocatalytic properties of titanium doped tin dioxide nanoparticles prepared via a chemical co-precipitation synthesis method are explored. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2016.02.094 0167-577X/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: konstan@uow.edu.au (K. Konstantinov). Materials Letters 171 (2016) 289–292