Templated synthesis of multi-hierarchical layered double hydroxide microspheres

Abstract

Herein, we report a green, scalable and cost-effective synthesis of microspherical Mg/Al–CO₃ LDHs with an average particle size and size distribution of 34 ± 6 μm with a multi-hierarchical morphology. The microspheres are composed of crystalline 300 nm thick Mg_2.25±0.025Al–CO₃ LDH platelets that are radially oriented into a hierarchical spherical motif. The LDH microspheres were synthesised via a hydrothermal reaction of NaAlO₂ with flower-like MgO microspheres which serve as both a structural template and a magnesium source. Our optimised synthesis conditions allow a uniformly dispersed phase pure LDH formation within 2 h at 80 °C. Comprehensive characterisation, including XRD, FT-IR, TGA, FIB-SEM, N₂ adsorption–desorption measurement, and CO₂-TPD, revealed that the obtained LDH microspheres exhibit a high specific surface area, total pore volume and basicity number. Our time-resolved studies provided further insights into the kinetics, structure evolution and crystallinity changes during the transformation process. These multi-hierarchical LDH microspheres can be calcined to produce multi-hierarchical layered double oxide (LDO) microspheres that demonstrate an exceptional CO₂ capture performance of 0.95 mmol g⁻¹ (1 atm, 40 °C) and an adsorption capacity 2.8 times higher than that of flower-like MgO and 32 times higher than that of commercial MgO. This study highlights the potential for an atom-efficient templated synthesis of multi-hierarchical, porous LDH microspheres and their application in catalysis and sorption.