Characterization of hierarchical porosity in novel composite monoliths with adsorption studies

Two different and novel composite monolithic materials with multimodal hierarchical porosity were prepared. The composites were prepared by immobilizing porous clay hetrostructure (PCH) and aluminum pillared clay (PILC), individually, into highly porous framework of a foam like monolith zeolite (MZ). The MZ was prepared hydrothermally, by following a polyurethane foam (PUF) based induced-template procedure and, consists of ZSM-5 framework. The MZ was fabricated into different composite materials through a simple dip coating method. Characterization of these materials with X-ray, SEM, and low temperature nitrogen adsorption techniques shows that composites materials are the morphological mixture (hybrid) of constituting materials. It also show that PCH based composites are meso and microporous, where as PILC based composites are essentially microporous in nature. The materials were further characterized for their hierarchical porosities by adsorption of two VOCs, which were toluene and n-hexane, under ambient conditions. The difference in adsorption of various sized (small to large) molecules was considered to work out the hierarchy of pores in these materials. With help of adsorption data, the hierarchical porosity was established into three size ranges, based on pore volumes of certain pore size ranges (>0.36 nm–<0.49 nm, >0.49 nm–<0.66 nm, and ≥0.66 nm). Water adsorption studies on these materials confirm that the coating of zeolite monolith with clay based adsorbents can also modify the hydrophobicity of original zeolite structure.