Thermal Behavior of Synthesized Smectite-organic Complex and Formation of a Porous Material

Abstract

Thermal behavior of a synthesized hectorite-organic complex, which transforms to a porous material by heating the complex and removing the organic material from interlayers, were examined by thermal, specific surface area (SSA), infrared spectra (IR) and X-ray diffraction analyses. This complex was made from a hydrothermally synthesized hectorite and dialkyldimethylammonium ion having mainly octadecyl group as alkyl. The largest SSA was obtained in a sample heated at 600 °C. This temperature corresponds to that the IR absorption bands originated in alkyl chain of organic ion disappear. Pores of the porous material were, therefore, considered to be formed by eliminating the organic ion, which acted as a template, from hectorite interlayers. Products of heating the alkyl group depended on the atmosphere; under nitrogen flow, the alkyl group decomposed into hydrocarbon gases to volatilize at relatively low temperature, about 400 °C. Under air flow, on the other hand, oxides showing C=O IR absorption band were generated about 400 °C and remained in the interlayers up to over 700 °C. The dehydroxylation of the organic comple x shifted about 90 °C to higher temperature than the synthesized hectorite. As N-H bending vibration band was recognized in IR spectra of specimens heated between 400 and 700°C, ammonium ion balanced the charge with silicate negative charge and, consequently, contributed to the thermal stability of a produced porous material.