Tale of Two Layered Semiconductor Catalysts toward Artificial Photosynthesis.

The ever-increasing reliance on nonrenewable fossil fuels due to massive urbanization and industrialization created problems such as depletion of the primary feedstock and raised the atmospheric CO levels causing global warming. A smart and promising approach is artificial photosynthesis that photocatalytically valorizes CO into high-value chemicals. The inexpensive layered semiconductors like g-CN and rGO or GO have the potential to make the process practically feasible for real applications. The suitable band positions with respect to the reduction potentials coupled with the typical surface properties of these layered semiconductors play a beneficial role in photoreduction of CO. Additionally, the creation of heterojunction interfaces to achieve the Z-scheme by anchoring g-CN and rGO with another semiconductor with proper band alignment and dispersing plasmonic nano metals to obtain Schottky barriers on the layered surfaces also help retarding the electron-hole recombination and boost up the catalytic efficacy. Extensive exploration happened in recent years toward artificial photosynthesis over these materials, which needs a critical compendium. Surprisingly, in spite of the recent explosion of studies on photocatalytic reduction of CO over metal-free semiconductors, there is not a single review on comparing the mechanistic aspects of photoreduction of CO over the layered semiconductors g-CN and rGO. This review stands out as a unique documentation, where the mechanism of photocatalytic reduction of CO over this set of materials is critically examined in the context of band and surface modifications. An overall conclusion and outlook at the end indicates the need to develop prototypes for artificial photosynthesis with these well-studied semiconducting layered materials to yield solar fuels.