Sequential Vapor Infiltration of Metal Oxides into Sacrificial Polyester Fibers: Shape Replication and Controlled Porosity of Microporous/Mesoporous Oxide Monoliths

The preparation of microporous and mesoporous metal oxide materials continues to attract considerable attention, because of their possible use in chemical separations, catalyst support, chemical sensors, optical and electronic devices, energy storage, and solar cells. While many methods are known for the synthesis of porous materials, researchers continue to seek new methods to control pore size distribution and macroscale morphology. In this work, we show that sequential vapor infiltration (SW) can yield shape-controlled micro/mesoporous materials with tunable pore size, using polyesters as a sacrificial template. The reaction proceeds by exposing polymer fiber templates to a controlled sequence of metal organic and co-reactant vapor exposure cycles in an atomic layer deposition (ALD) reactor. The precursors infuse sequentially and thereby distribute and react uniformly within the polymer, to yield an organic inorganic hybrid material that retains the physical dimensions of the original polymer template. Subsequent calcination in air results in an inorganic microporous/mesoporous material that again retains the macroscopic physical shape of the starting polymer matrix. The microporous/mesoporous structure is confirmed by microscopy and nitrogen adsorption/desorption analysis, and the resulting pore size is controlled by the size of the starting polymer repeat unit and by the kinetics of the infiltration/annealing process steps. In situ infrared transmission and quartz crystal microbalance results confirm the chemical reaction mechanisms. The chemical transformation that occurs during SVI could be important for a range of applications that utilize well-defined porous nanostructures.