Positron annihilation study of chitosan and its derived carbon/pillared montmorillonite clay stabilized Pd species nanocomposites

Abstract

To establish the structure-properties relations of an organic polymer-inorganic hybrid nanocomposite, insightful investigation of the molecules packing and interfacial interactions is essential. Positron annihilation lifetime spectroscopy (PALS) has been proven as one of the most suitable technique to characterize the free volume structure (molecular packing) of polymer matrices. However, most of the attentions were paid limitedly in organic polymer-based hybrid systems rather than inorganic-based hybrid systems. Classic spherical model was the most frequently used model in free volume holes size calculation of polymer matrix. In the present study, molecular level micro-defects within inorganic-based hybrid systems encaging polymers and carbon species, i.e. novel biological macromolecules of chitosan and its derived carbon/Al pillared montmorillonite clay (CS/PILC and CS-derived C/PILC) stabilized palladium species hybrid nanocomposites, have been investigated by PALS. Besides the classic spherical model, cuboidal and cylindrical models were used to evaluate the molecules packing behavior within the interlayer space of PILC matrices encaging of polymers of CS or CS-derived carbons. The layered porous structure of the nanocomposites was also characterized with other methods, such as X-ray diffraction, N2 adsorption/desorption, and high-resolution transmission electron microscopy, etc. The correlations of the microstructure and catalytic properties applied in Sonogashira coupling reactions of the nanocomposites were discussed.