Thermal stability of tetrabutyl-phosphonium and -ammonium exchanged montmorillonite: Influence of acid treatment

This study investigates the thermal stability of acid-treated organo-montmorillonites derived from the Na-form of SAz-1 montmorillonite modified with tetrabutylphosphonium (Bu4P+) and tetrabutylammonium (Bu4N+) salts. The objective was to assess the influence of acid treatment on the stability of these organoclays. A combination of thermogravimetric analysis (TGA) and infrared (IR) spectroscopic analysis was employed, alongside in-situ measurements of near-IR (NIR) spectra. Organoclays were treated with 6 M HCl at 80 °C for varying durations of 2 to 12 hours. Results indicated that both Bu4P-S and Bu4N-S exhibited higher resistance to decomposition compared to Na-S, with 44% and 52% of octahedral Mg/Al remaining in solid products after 12 hours, respectively. Notably, the decomposition temperature was higher for Bu4P-S than for Bu4N-S, indicating the type of cation influences stability. The mass loss associated with organic cation decomposition decreased significantly, and the temperature at which organic phases began to leach was elevated for Bu4P-S. NIR analysis further revealed that the onset of organic phase release occurred at lower temperatures for Bu4N-S than for Bu4P-S.