Synthesis, characterization, and challenges faced during the preparation of zirconium pillared clays

In this study, Zr-pillared montmorillonite clays (Zr-PILCs) were synthesized using two different precursor materials: raw montmorillonite (CM) and sodium ion-saturated montmorillonite (Na-CM) at different Zr/clay ratios (2.5, 5 and 10 mmol/g). To study the effect of Zr concentration and clay pre-treatment with NaCl on pillaring, the modified clay samples were characterized in detail using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (STEM-EDX). The XRD analysis showed the increase of basal spacing of Zr-PILCs prepared from both precursor materials: from 1.26 to 1.74 nm in the case of CM, and from 1.13 to 1.93 nm for Na-CM. Results from FT-IR revealed new bands ascribed to Zr-O bonds in the range of 400–500 cm−1 in Zr-pillared samples obtained from Na-CM at Zr/clay ratios of 2.5 and 5 mmol/g. The distribution and nature of Zr species in between the silicate layers were studied using STEM-EDX and HAADF imaging. They were found to be separated by a distance of 1.5–3 nm and their thickness lies in the range of 1–2 nm. Pillared clays prepared from pre-treatment with NaCl were more thermally stable at higher temperatures.