Controlled formation of multi-scale porosity in ionosilica templated by ionic liquid

TL;DR

This study introduces a new hydrolytic synthesis method for ionosilica films with tunable mesopores templated by ionic liquids, comparing it to traditional methods and analyzing pore structures using multiple techniques.

Contribution

It presents a novel hydrolytic synthesis pathway for ionosilica films with mesopores, providing a detailed geometrical model and insights into pore formation and optimization.

Findings

Both synthesis pathways produce similar pore geometries.

Hydrolytic films show higher mesoporosity due to better IL incorporation.

The study offers a pathway to optimize porous ionic membranes for energy applications.

Abstract

Mesoporous systems are ubiquitous in membrane science and applications due to their high internal surface area and tunable pore size. A new synthesis pathway of hydrolytic ionosilica films with mesopores formed by ionic liquid (IL) templating is proposed and compared to the traditional non-hydrolytic strategy. For both pathways, the multi-scale formation of pores has been studied as a function of IL content, combining results of thermogravimetric analysis (TGA), nitrogen sorption, and small-angle X-ray scattering (SAXS). The combination of TGA and nitrogen sorption provides access to ionosilica and pore volume fractions, with contributions of meso- and macropores. We then elaborate an original and quantitative geometrical model to analyze the SAXS data based on small spheres (Rs = 1 -- 2 nm) and cylinders (Lcyl = 10 -- 20 nm) with radial polydispersity provided by the nitrogen sorption isotherms. As a main result, we found that for a given incorporation of templating IL, both synthesis pathways produce very similar pore geometries, but the better incorporation efficacy of the new hydrolytic films provides a higher mesoporosity. Our combined study provides a coherent view of mesopore geometry, and thereby an optimization pathway of porous ionic membranes in terms of accessible mesoporosity contributing to the specific surface. Possible applications include electrolyte membranes of improved ionic properties, e.g., in fuel cells and batteries, as well as molecular storage.