Macroporous Ceramic Monolith from Nanoparticle-Polyelectrolyte-Stabilized Pickering Emulsions.

In this work, we present a simple and scalable approach for fabricating porous ceramic from emulsions stabilized by a binary mixture of oppositely charged nanoparticles and a polyelectrolyte. The electrostatic heteroaggregation is exploited to form weakly charged particle-polyelectrolyte complexes (PPCs) that readily stabilize oil-in-water emulsions. The concentration of surface-active PPCs is varied to obtain Pickering emulsion gels that can be processed and converted into the macroporous ceramic structure. The polyelectrolyte in the binary mixture not only enables the adsorption of particles to the oil-water interface and renders processability of the emulsions but also acts as a binder. Nearly one-to-one correspondence between the microstructure of the green ceramic obtained after the evaporation of solvents from the gel-like emulsions and the parent emulsions is observed. The green ceramic is further sintered under controlled conditions to obtain a porous ceramic monolith. We demonstrate that the microstructure and the pore size distribution in the final ceramic can be altered by tuning the composition of the individual species used in the emulsion formulation, i.e., by optimization of the particle-polyelectrolyte ratio used in the processing route.