In-line monitoring of layered double hydroxide synthesis and insights on formation mechanism and kinetics

Anionic clays such as layered double hydroxides (LDH) are promising materials for pharmaceutical applications, electrochemistry, engineering, bioremediation, and agriculture. The understanding of the mechanisms involved in the formation of LDH is an important step for their safe application and reproducible production. In this study, we in-line monitored the synthesis of Zn2Al-Cl and Mg2Al-Cl LDH using near infrared spectroscopy to explain the formation mechanism and kinetics of these materials when employing the coprecipitation method in organic environments. The data were evaluated chemometrically and principal component analysis (PCA) was used to investigate existing components related to the reaction path. The zeta potential (ζ) values indicated that, initially, unstable particles formed (ζ < +30 mV), which nucleated fast, and this was followed by a second, slower reaction stage, owing to the crystallization of the LDH. These processes were confirmed using the multivariate curve resolution-alternating least squares method, which demonstrated that the synthesis reaction followed a second-order kinetics. These findings were corroborated using microscopic and diffraction analysis.