Fluorine doping of nanostructured TiO2 using microwave irradiation and polyvinylidene fluoride

Fluorine doped metal oxides have shown great promise for use in many applications including Li-ion batteries (LiBs), photocatalysis and dye-sensitized solar cells. Both F-TiO2 and TiOF2 have been studied extensively for this purpose. However, fabrication of fluorine doped titanium oxide requires the use of dangerous fluorinated chemicals such as trifluoroacetic acid, hydrofluoric acid and fluorine gas which are both difficult to handle and create significant waste detrimental for the environment. Additionally, current procedures for fabrication of FTiO2 and TiOF2 require long heating times which are inefficient, wasting large amounts of energy. Because of these factors, fabrication of F-TiO2, TiOF2 and of other important fluorine doped metal oxides is expensive and dangerous to make. In this work, two new methods were used to greatly improve the safety and efficiency of synthesis. First, the fluorinated waste was eliminated by using the safe and inert polymer, polyvinylidene fluoride (PVDF), as the fluorine source. Second, microwave (MW) irradiation was used to reduce the time and energy required for synthesis by addition of the MW absorber, graphene, into the precursor material. The results show that when using the PVDF fluorine source with conventional oven heating it results in low levels of F-TiO2 which are dependent on heating temperatures. However, when using microwave irradiation high levels of doping were achieved creating both F-TiO2 and TiOF2 in as little as 6 min compared to several hours. This work has shown that by combining both PVDF and microwave irradiation fabrication of F-TiO2 and TiOF2 can now be done safely and efficiently with greatly reduced environmental impact.