In this time period, metal-organic framework (MOF)-based and MOF-derived materials saw increased interest in heterogeneous catalysis. The application of semiconductor engineering to photocatalysis saw compounds of classes General Inorganic and Oxide increasingly applied to green hydrogen production throughout the decade alongside their use as catalyst supports. Finally, polymers began to be studied as components in heterojunction catalysts , as tunable stand-alone porous photocatalysts (in the case of covalent organic frameworks), and as precursors to engineered carbonaceous catalyst materials. The top-studied materials from these classes in 2021 are shown below in Table alongside their respective important research focuses.