Nanostructure retention to 1100 °C in soft-templated niobium tungstates using dual-carbon strategy

Abstract

Mesoporous metal oxides (MMOs) have diverse applications including energy storage, catalysis, and separation membranes. Block polymer structure directing agents enable the control of morphology and pore size, however preservation of the nanostructure is often limited to a narrow range of heat treatment temperatures which constrains the tailoring of defect chemistries. High temperature treatments typically lead to collapse of the porous structure as surface area is reduced during crystal growth. Here, using a mesoporous niobium tungstate it is shown that neither in situ carbon generation nor ex situ carbon infiltration alone enable preservation of the ordered mesostructure at temperatures high enough to effectively modify defect chemistry (1100 °C). In contrast, it is shown that a combination of these methods enables preservation of the ordered structure as evidenced by SAXS analysis and electron microscopy. X-ray photoelectron spectroscopy confirmed reduced metal states in the resulting mesoporous materials. This work extends the thermal stability of soft templated niobium tungstates by 500 °C as compared to conventional annealing to enable improved structure preservation after high temperature heat treatment.