ZIF-8/Zn₂GeO₄ nanorods with an enhanced CO₂ adsorption property in an aqueous medium for photocatalytic synthesis of liquid fuel

The photoreduction of CO2 on inorganic semiconductors has been researched for several decades, but the conversion efficiency is still low due to the recombination of photo-generated electron–hole pairs, low utilization efficiency of solar energy and weak adsorption of CO2. Here we for the first time demonstrate that metal–organic frameworks such as ZIF-8 can effectively adsorb CO2 dissolved in water, and promote photocatalytic activity of a semiconductor catalyst in CO2 reduction into liquid fuels in an aqueous medium. In particular, Zn2GeO4/ZIF-8 hybrid nanorods were successfully synthesized by growing ZIF-8 nanoparticles on Zn2GeO4 nanorods. The Zn2GeO4/ZIF-8 nanocomposite inherits both high CO2 adsorption capacity of ZIF-8 nanoparticles and high crystallinity of Zn2GeO4 nanorods. The Zn2GeO4/ZIF-8 hybrid nanorods containing 25 wt% ZIF-8 exhibit 3.8 times higher dissolved CO2 adsorption capacity than the bare Zn2GeO4 nanorods, resulting in a 62% enhancement in photocatalytic conversion of CO2 into liquid CH3OH fuel. The strategy reported here is promising for developing more active photocatalysts for improving CO2 conversion efficiency by taking advantage of excellent adsorption property of metal–organic frameworks in aqueous media.