Preparation of porous solids composed of layered niobate walls from colloidal mixtures of niobate nanosheets and polystyrene spheres

Macroporous solids with crystalline layered walls were fabricated from colloidal mixtures of size-controlled niobate nanosheets and polystyrene spheres. The macroporous solids, obtained after burning off the spheres, were characterized by scanning electron microscopy and X-ray diffraction. The obtained structures strongly depended on the lateral dimension L of the nanosheets used. When small nanosheets (L = 100   nm) were used, partly ordered macroporous solids with interconnected pores were obtained, whereas sponge-like random macroporous structures were obtained with larger nanosheets (L = 190 and 270 nm). Peapod-like hollow structures were obtained when we used small (L = 190   nm) and very large (L = 3   μm) nanosheets at the same time. The microstructure of the pore walls was controllable by changing the calcination conditions. The walls were composed of propylammonium/K₄Nb₆O₁₇ intercalation compound which has a layered structure with exchangeable cations in the interlayer space, stable up to 350 °C for 6 h on calcination. The walls were converted to crystalline K₈Nb₁₈O₄₉ after calcination at 500 °C for 6 h.