Controlled Metal Oxide and Porous Carbon Templation Using Metal-Organic Frameworks

Abstract

Templated porous carbons are promising due to their robust chemical and thermal properties. However, investigations into the formation mechanisms and structure–property relationships are limited. We report a systematic study of the carbonization of two metal-organic frameworks (MOFs) with varying connectivities and metal centers to determine how the resulting porous carbon structure is affected by temperature and gas environment. Surface area analysis reveals that the porosity depends on the number of residual carbon species, while diffraction analysis shows the strong effect of carbonization temperature on the resulting metal oxide phase. A higher connectivity parent MOF also indicates a more controllable and typically higher-surface-area porous carbon. This effect is especially noticeable when coordinating gases are used as the calcination environment, suggesting that a kinetically controlled decoordination event is responsible for reducing the carbon surface area. Neutron total scattering and pair distribution function (PDF) analysis showed that larger carbon domain sizes also cause higher surface areas, which indicates that the formation of domains within the materials promotes rigid backbones and aids in the production of high surface areas. PDF analysis showed that the MOF template could also be used to maintain the symmetry of the parent cluster in the resulting carbon, with the Zr6O4(OH)4 of UiO-66 forming the cubic phase of the metal oxide.