Titanium Phosphonate Based Metal-Organic Frameworks with Hierarchical Porosity for Enhanced Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) are porous crystalline materials constructed from metal ions or clusters and multidentate organic ligands. Recently, the use of MOFs or MOF composites as catalysts for synergistic catalysis and tandem reactions has attracted increasing attention due to their tunable open metal centres, functional organic linkers, and active guest species in their pores. In this review, the applications of MOFs with multiple active sites in synergistic organic catalysis, photocatalysis and tandem reactions are discussed. These multifunctional MOFs can be categorized by the type of active centre as follows: (i) open metal centres and functional organic linkers in the MOF structure, (ii) active guest sites in the pores and active sites in the MOF structure, and (iii) bimetallic nanoparticles (NPs) on MOF supports. The types of synergistic catalysis and tandem reactions promoted by multifunctional MOFs and their proposed mechanisms are presented in detail. Here, catalytic MOFs with a single type of active site and MOFs that only serve as supports to enhance substrate adsorption are not discussed.

Porous P-doped g-C3N4 nanosheets prepared by combining P doping and thermal exfoliation exhibit a high visible-light photocatalytic H2-production activity of 1596 μmol h−1 g−1 and a quantum efficiency of 3.56% at 420 nm.

An optimized and general synthetic strategy based on in-situ iodine modifying of polymeric graphitic carbon nitride is discussed. The as-prepared iodine functionalized g-CN shows enhanced electronic and optical properties, as well as increased photocatalytic activities in an assay of hydrogen evolution.