Photocatalysis: Past achievements and future trends

Photocatalysis holds great promise to enable sustainable chemical processes related to, for example, the production of renewable fuels or prevention of pollution through advanced oxidation. However, despite significant progress and continuing interest from academia, industry and policy makers, key challenges have to be overcome. First, ideal photocatalytic materials should obey stringent requirements related to stability, cost, bandgap compatibility, availability of raw materials, and photon efficiency. In spite of certain limitations, such as an undesirable band gap, titania remains the frontrunner in terms of research and commercial applications. This chapter briefly discusses strategies to expand the allowable bandgap of photocatalytic materials. A key focus is on the use of metal-organic frameworks (MOFs). MOFs have an organic-inorganic structure, exhibit a high surface area and can be tuned with tremendous flexibility, which makes them promising candidates to advance photocatalysis. Second, the development of photocatalytic reactors is discussed. The design and operation of photocatalytic reactors is not trivial due to requirements for efficient contact of reactants with the catalyst and efficient utilization of photons. The former requirement is common for any heterogeneous catalytic reactor whereas the latter is unique for photocatalysis. Consequently, numerous reactor configurations have been designed specifically for photocatalysis of which a selection is reviewed in this chapter. Recent advances in simulation and optimization of mathematical models of photocatalytic reactors offer an important support for design. Furthermore, novel solid-state light sources provide opportunities for increased robustness, reduced costs and improved flexibility for the design and operation of future photocatalytic reactors.