Enhanced structural control of soft-templated mesoporous inorganic thin films by inert processing conditions

Abstract

Mesoporous thin films are widely used for applications in need of high surface area and good mass and charge transport properties. A well-established fabrication process involves the supramolecular assembly of organic molecules (e.g. block copolymers, and surfactants) with inorganic materials obtained by sol-gel chemistry. Typically, subsequent calcination in air serves to remove the organic template and reveal the pores. A major challenge for such coatings is the anisotropic shrinkage due to the volume contraction related to solvent evaporation, inorganic condensation, and template removal, affecting the final porosity as well as pore shape, size, arrangement and accessibility. Here, we show that a two-step calcination process, composed of high-temperature treatment in argon followed by air calcination, leads to reduced film contraction and enhanced structural control. Crucially, the formation of a transient carbonaceous scaffold enables the inorganic matrix to fully condense before template removal. The resulting mesoporous films retain a higher porosity as well as larger, more uniform pores with extended hexagonally closed-packed order. Such films present favorable characteristics for a variety of applications, such as improved mass transport of large biomolecules. This is demonstrated for the adsorption and desorption of lysozyme into the mesoporous thin films as an example of enzyme storage.