Possible pathway of zeolite formation through alkali activation chemistry of metakaolin for geopolymer–zeolite composite materials: ATR-FTIR study

Abstract

Geopolymer–zeolite composite materials are hybrid materials that combine the advantageous properties of both constituents. This study reports the effect of alkali concentration on the production of zeolite in geopolymer materials for synthesizing geopolymer–zeolite composite materials. The effects of the concentrations of activators on organic aluminosilicate raw materials based on metakaolin were studied. The phase changes were characterized by X-ray diffraction with qualitative phase amounts. Scanning electron microscopy was used to confirm the zeolite crystal and geopolymer. In situ and ex situ attenuated total reflectance–Fourier transform infrared (ATR-FTIR) were used to study the changes in the aluminosilicate structure with different curing times from 5 ​min until 112 days. The sodium hydroxide concentration played an important role in controlling the reaction mechanism of the metakaolin-based geopolymer. The Si/Al ratio was fixed at 1.01 with different Na/Al ratios from 1.18 to 3.05. The templating function of sodium hydroxide activators was responsible for the suppression of crystallization. The results show that sodalite zeolite, zeolite-A, and zeolite-X were produced in geopolymer composite materials with different concentrations of sodium hydroxide. Moreover, the increase in sodium hydroxide concentration promoted the higher dissolution and ordering structure that can be seen from the ATR-FTIR results.