On key factors for the fabrication of mesoporous tungsten oxide films from tungstic acid

Thermally stable mesoporous tungsten oxide films (TOFs) were prepared by surfactant templated sol-gel method using tungstic acid as tungsten oxide source. Influence of various experimental conditions on the obtained mesostructures was investigated, including the solvent compositions, addition of hydrogen peroxide, substrates, and aging time, heat treatment, etc. It has been found that the addition of hydrogen peroxide has a significant influence on the flexibility of formed meso-frameworks, and just a small amount can regenerate the degraded coating sol. TOFs were also found to crystallize on ITO coating easier than on bare glass, indicating that the different interactions with the substrates influence the crystallinity of obtained meso-structured TOFs. Film thickness can be adjusted by simply changing the solvent compositions while keeping mesostructures intact. This work clarified several key parameters in delivering well-defined mesostructured TOFs from cheap, moisture-insensitive tungstic acid precursor via the process developed.