Enhancing the understanding of surfactant influence in LTA crystallization through microwave-assisted methods at different temperatures

Achieving specific framework structures and morphologies in zeolite synthesis is crucial for broad applications. This study addresses the limited understanding of surfactant effects on crystal imperfections and phase purity in LTA zeolite synthesis, particularly under microwave-assisted conditions. We hypothesized that anionic, cationic, and non-ionic surfactants would significantly affect phase purity, morphology, crystallite size, and imperfections in LTA zeolites synthesized at varying microwave temperatures. Synthesized materials were characterized using powder X-ray diffraction, scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Findings revealed that within the 100–150 °C microwave temperature range, all surfactants primarily yielded the LTA-type zeolite structure. However, a metastable phase was observed in materials synthesized at 130 °C with Sodium Dodecyl Sulfate (SDS), as indicated by reduced crystallinity and an additional Raman peak at 471 cm⁻¹. This suggests that while the LTA framework remained predominant, symmetry disturbances at this temperature impacted TO₄ stretching vibrations, possibly leading to a partial deviation from phase purity. Surfactants significantly influenced phase purity, morphology, crystallite size, and crystal imperfections, with optimal phase purity achieved at lower temperatures (100–110 °C) for anionic and non-ionic surfactants and at higher temperatures (130–150 °C) for cationic surfactants. Crystallite sizes varied in a complex, temperature-dependent manner, suggesting further investigation into crystallization mechanisms. An inverse correlation between microstrain and crystallite size was observed across samples, except at 130 °C, likely due to added stress and supplementary crystal phases. This study establishes foundational knowledge for selecting surfactants to modify pore structures in hierarchical LTA zeolites and offers insights for designing LTA zeolites with tailored properties, addressing knowledge gaps, and advancing zeolite synthesis techniques.

Graphical abstract