Synthesis of kenyaite from synthetic silica glass scrap waste and organic modification using various quaternary alkylammonium salts

Abstract

Layered sodium polysilicate (kenyaite) was hydrothermally synthesized from synthetic silica glass scrap. In the hydrothermal process, a silica glass scrap block was first dissolved in a sodium hydroxide solution. Crystallization of the dissolved silica began after the silica concentration of the solution exceeded a threshold. Subsequently, the dissolution of silica glass and the crystallization of kenyaite progressed simultaneously, increasing the mass of kenyaite. Further hydrothermal treatment converts the kenyaite into quartz. Pure kenyaite could be produced from synthetic silica glass under a limited range of hydrothermal conditions. Then, kenyaite was organically modified with alkylammonium ions via ion exchange. This modification was systematically studied using various quaternary alkylammonium salts with different molecular structures. Tetradecyltrimethylammonium, hexadecyltrimethylammonium and octadecyltrimethylammonium ions were inserted into the interlayer spaces of the silicate sheets of kenyaite via host–guest intercalation, resulting in the formation of organo-kenyaite with an ordered structure. The molar content of the alkylammonium ions increased with increasing alkyl chain length. In addition, didodecyldimethylammonium, dioctadecyldimethylammonium, benzyldodecyldimethylammonium and benzyloctadecyldimethylammonium ions were successfully intercalated into kenyaite. Modification with decyltrimethylammonium ions yielded organo-kenyaite with a slightly ordered structure. In contrast, the use of decyltrimethylammonium salt, dodecylamine hydrochloride, and octadecylamine hydrochloride resulted in the formation of organo-kenyaite with a disordered structure. The structure and guest content of organo-kenyaite strongly depended on the molecular structure of the guest alkylammonium ion.