Hypergolic Synthesis of Inorganic Materials by the Reaction of Metallocene Dichlorides with Fuming Nitric Acid at Ambient Conditions: The Case of Photocatalytic Titania

Abstract

Hypergolic materials synthesis is a new preparative technique in materials science that allows a wide range of carbon or inorganic solids with useful properties to be obtained. Previously we have demonstrated that metallocenes are versatile reagents in the hypergolic synthesis of inorganic materials, such as γ-Fe2O3, Cr2O3, Co, Ni and alloy CoNi. Here, we go one step further by using metallocene dichlorides as precursors for the hypergolic synthesis of additional inorganic phases, such as photocatalytic titania. Metallocene dichlorides are closely related to metallocenes, thus expanding the arsenal of organometallic compounds that can be used in hypergolic materials synthesis. In the present case, we show that hypergolic ignition of the titanocene dichloride–fuming nitric acid pair results in the fast and spontaneous formation of titania nanoparticles at ambient conditions in the form of anatase–rutile mixed phases. The obtained titania shows good photocatalytic activity towards Cr(VI) removal (100% within 9 h), with the latter being dramatically enhanced after calcination of the powder at 500 °C (100% within 3 h). Notably, this performance was found to be comparable to that of commercially available P25 TiO2 under identical conditions. The cases of zirconocene, hafnocene and molybdocene dichlorides are discussed in this work, which aims to show the wider applicability of metallocene dichlorides in the hypergolic synthesis of inorganic materials (ZrO2, HfO2, MoO2).