Morphology-Controlled Synthesis of Three-Dimensional Hierarchical Flowerlike Mg-Al Layered Double Hydroxides with Enhanced Catalytic Activity for Transesterification

With the aim of simultaneously achieving synthesis and morphology control of three-dimensional (3D) hierarchical layered double hydroxide (LDH) by more efficient and environmentally friendly methods, a facile and cost-efficient double-drop coprecipitation method was creatively applied to fabricate 3D flowerlike microstructures (Al2O3-MgAl-LDHs) using gamma-Al2O3 as a sacrificial template. The morphology evolution process and growth characteristics of Al2O3-MgAl-LDHs were investigated in detail, revealing that gamma-Al2O3 not only provides an effective support for the crystal growth of LDH but also is involved in the LDH layer formation process through self-decomposition. More importantly, LDH morphologies can be regulated by varying the reaction conditions, such as the gamma-Al2O3 concentration, Mg2+/Al3+ molar ratio, and pH. Additionally, a possible formation mechanism for 3D hierarchical flowerlike Al2O3-MgAl-LDHs was illustrated. Remarkably, owing to the high specific surface area and low/medium/high-strength basic sites, the as obtained LDH after calcination exhibited excellent catalytic activity and reusability in the transesterification of glycerol with dimethyl carbonate.