Investigation of photocatalytic properties of shape and size controlled with Co AND Fe doped zinc oxide

Zinc oxide (ZnO) is one of the mineral-based ingredient used in sunscreens. ZnO is non-toxic and exhibits high UV absorption; however, it exhibits high photocatalytic activity which increases when the particle size approaches nano scale. Therefore, it is crucial to reduce free radical formation during interaction of photocatalytic materials with UV rays in sunscreens. In this study, Fe- and Co-doped micron sized MicNo® ZnO hexagonal platelets composed of nano-primary particles with shape and dimension control are synthesized using a solvotermal technique developed by our group. The structural and functional properties of doped powders are also investigated. The scientific goal is to investigate the effects on Co- and Fe-doping on the structure of MicNo® ZnO with Zn1-xMxO stoichiometry using 1%, 2%, 3%, and 4% Co and 0.5%, 1%, 1.5% and 2% Fe-doping content by mass. Special emphasis is given for investigating photocatalytic activity of such powders from their optical characteristics. On the other hand, the technological goal is to reduce photocatalytic activity of MicNo® ZnO UV filters showing advantages of both nano and micron dimension. More specifically, the optical properties of MicNo® ZnO are tailored via doping to reduce the photocatalytic activity of primary nanoparticles. XRD analyses indicated that ZnO powders with doping levels up to 2% Fe or 4% Co did not exhibit any additional phase. Rietveld analysis and WD-XRF suggested that Fe and Co elements were successfully doped into ZnO lattice. SEM and particle size analysis confirmed that shape and size of MicNo®ZnO did not change considerably after doping. ~85% reduction in photocatalytic activity with respect to reference MicNo®ZnO powder was achieved by 3% Co doping which was attributed to reduced OH and O2 free radical concentration.