Metal-organic aerogels based on titanium(IV) for visible-light conducted CO2 photoreduction to alcohols

Abstract

Metal-organic frameworks (MOFs) imply an appealing source of photocatalysts as they combine porosity with tailorable electronic properties and surface chemistry. Herein, we report a series of unprecedented metal-organic aerogels (MOAs) comprised by Ti(IV) oxo-clusters and aromatic dicarboxylic linkers as an alternative to microporous MIL-125 and MIL-125-NH2 MOFs. Discrete titanium oxo-clusters polymerized upon the addition of the dicarboxylic linkers to give rise to a metal-organic gel. Their supercritical drying led to aerogels comprised by nanoscopic particles (ca. 5-10 nm) cross-linked into a meso/macroporous microstructure with surface area ranging from 453 to 617 m2·g-1, which are comparatively lower than the surface area of the microporous counterparts (1336 and 1145 m2·g-1, respectively). However, the meso/macroporous microstructure of MOAs can provide a more fluent diffusion of reagents and products than the intrinsic porosity of MOFs, whose narrower channels are expected to imply a more sluggish mass transport. In fact, the assessment of the continuous visible-light-driven photocatalytic CO2 reduction into methanol shows that MOAs (221-786 [M] mol·g-1·h-1) far exceed not only the performance of their microporous counterparts (49-65 [M]mol·g-1·h-1) but also surpass the production rates provided by up-to-date reported photocatalysts.