How do layered double hydroxides evolve? First in situ insights into their synthesis processes

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Layered double hydroxides (LDHs) are crucial materials with applications in catalysis, medicine, and water treatment.
• The crystallization process of LDHs remains under-investigated, hindering controlled synthesis and optimization.

Purpose of the Study:

• To investigate the formation dynamics of carbonate-intercalated Mg2+/Al3+ LDHs using in situ characterization.
• To explore the effects of temperature and reactant concentration on LDH crystallization kinetics and morphology.
• To provide experimental insights into the nucleation and growth phases of LDH formation.

Main Methods:

• Utilized a combinatorial multi-modal approach with in situ pH, ion conductivity, and light scattering measurements.
• Employed synchrotron-based in situ X-ray diffraction (XRD) for real-time structural analysis.
• Investigated co-precipitation methods under varying temperatures and reactant concentrations.

Main Results:

• Nuclei formation was indicated by a stable pH due to hydroxyl ion uptake.
• Crystal growth was detected by light scattering and confirmed by in situ XRD.
• Increased reactant concentration accelerated crystal growth onset by 70% with minimal impact on crystallite size.
• Elevated temperatures (up to 65 °C) had a minor effect on kinetics but doubled crystallite size.
• Reversing reactant addition order led to rapid saturation and formation of ~10 nm crystallites.

Conclusions:

• In situ characterization provides unprecedented access to LDH formation dynamics.
• Reactant concentration and temperature are key parameters influencing LDH crystallization kinetics and morphology.
• Understanding these dynamics enables tailored synthesis of LDHs for specific applications.