A general ligand-assisted self-assembly approach to crystalline mesoporous metal oxides

Mesoporous transition metal oxides with high crystallinity and large pore volumes were successfully synthesized by a widely applicable ligand-assisted self-assembly approach. In this approach, a carboxyl-containing ligand is employed as a coordination agent to retard the hydrolysis and condensation rates of the precursors. The ligands interact with the PEO chains of P123 via hydrogen bonds, which cooperatively ensures the controllable co-assembly of template micelles and the metal source during solvent evaporation. The X-ray diffraction, transmission electron microscopy, and nitrogen sorption results show that the obtained mesoporous metal oxides are constructed from numerous highly crystalline nanoparticles and possess close-packed mesostructures with uniform pore size distributions. A series of mesoporous transition metal oxides (Co3O4, Mn2O3, Fe3O4, NiO, CuO, ZnO, and Cr2O3) and multi-metal oxide composite materials (Co3O4/Fe3O4, Co3O4/NiO, and Fe3O4/NiO) were successfully synthesized. By employing the crystalline Co3O4/Fe3O4 composites as electrocatalysts, high catalytic activity can be achieved during the oxygen evolution reaction. A low overpotential of 322 mV at a current density of 10 mA cm−2 is exhibited, which shows that this approach has great significance not only in synthesis but also in electrocatalysis. Self-assembled polymer templates for creating porous catalysts have been synthesized by scientists in China. Mesoporous materials contain voids of between two and fifty nanometers in diameter. These materials are useful for energy storage, catalysis and gas sensors. One strategy for creating mesoporous materials is to shape the oxide of a transition metal such as iron, nickel, copper or cobalt using a template. Zhen-An Qiao and colleagues from Jilin University, Changchun, have developed a simple soft polymer template for this purpose that self-assembles into the required structure with the help of carboxyl-based ligands in a solution. Using this template, they were able to create stable mesoporous transition metal oxides with large pore volumes, including cobalt oxide and iron oxide, and demonstrate their use as efficient catalysts for oxygen evolution reactions. A general ligand-assisted self-assembly approach allows the synthesis of thermally stable and highly crystalline mesoporous transition-metal oxide. Carboxyl contained ligands and metal precursors are linked by coordination bonds, and the ligand molecules attach to the PEO chains through hydrogen bonds, which cooperatively ensure the controllable co-assembly and the formation of well-defined mesostructure. The mesoporous structures provide abundant reaction sites in electrolyte, which makes them have the possibility to be used as remarkable electrochemical materials.