Formation of 3D interconnectively macro/mesoporous TiO2 sponges through gelation of lotus root starch toward CO2 photoreduction into hydrocarbon fuels

A particular TiO2 sponge, consisting of macroporous framework with interconnected mesoporous channels, was fabricated through a co-gelation of lotus root starch (LRS) with TiO2 precursor, followed by lyophilization and subsequent calcination. This strategy advantageously inherits both the traditional hard-templating technique for well-defined 3D predesigned macroporous architecture and soft-templating techniques for interpore connectivity. The resulting TiO2 sponge exhibits about a 2.60 fold improvement in CO2 photoconversion rate (CH4: 5.13 ppm h(-1)) compared to the referred TiO2 (1.97 ppm h(-1)) formed in the absence of the LRS. The generation rate of CH4 over macro/mesoporous TiO2 sponge could be further significantly enhanced to 11.95 ppm h(-1) by co-loading Pt (0.9 wt%) and Cu (1.7 wt%) as co-catalysts by improvement of the separations of the photogenerated electron-hole pairs. The higher photocatalytic activity of the macro/mesoporous TiO2 sponge can be attributed to the following three reasons: (1) macroporous architecture favors gas diffusion of the reactants and the products; (2) macroporous architecture also promotes the multiple-reflection effect occurring inside the interior macrocavities, which enables trapping (or harvest) the incident light in the photocatalyst for a longer duration and bring forth more opportunities for light absorption; and (3) the mesoporous structure enhances gas capture/adsorption of the reactants and provides more reaction sites.