Assembly of molten transition metal salt-surfactant in a confined space for the synthesis of mesoporous metal oxide-rich metal oxide-silica thin films

Uniform and homogeneous coating of mesoporous materials with an active (catalytically, photonic, electrical) nanostructure can be very useful for a number of applications. Understanding chemical reactions in a confined space is important in order to design new advanced materials. In this work, we demonstrate that an extensive amount (as high as 53 mol percent) of transition metal salts can be confined between silica walls and two surfactant domains (cetyltrimethylammonium bromide, CTAB, and lauryl ether, C₁₂H ₂₅(OCH₂CH₂)₁₀OH, C ₁₂EO₁₀) as molten salts and then converted into sponge-like mesoporous silica-metal oxides by thermal annealing. This investigation has been carried out using two different salts, namely, zinc nitrate hexahydrate, [Zn(H₂O)₆](NO₃) ₂, and cadmium nitrate tetrahydrate, [Cd(H₂O) ₄](NO₃)₂, in a broad range of salt concentrations. The ZnO (or CdO) layers are as thin as about ∼1.6 nm and are homogenously coated as crystalline nano-islands over the silica pore walls.