A Robust Photocatalytic Hybrid Material Composed of Metal-Organic Cages and TiO2 for Efficient Visible-Light-Driven Hydrogen Evolution.

The design of photochemical molecular devices (PMDs) for photocatalytic H2 production from water is a meaningful but challenging subject currently. Herein, a Pd2 L4 type metal-organic cage (denoted as MOC-Q2) is designed as a PMD, which consists of two catalytic centers (Pd2+ ) and four photosensitive ligands (L-2) with four pyridine anchoring groups. Subsequently, the MOC-Q2 is combined with TiO2 to form TiO2 -MOC-Q2 hybrid materials with different MOC-Q2 contents by a facile sol-gel method, which have micro/mesoporous structures and large surface areas. The optimized TiO2 -MOC-Q2 (6.5 wt%) exhibits high H2 production activity (7.9 mmol g-1  h-1 within 5 h) and excellent durability, giving a TON value of 23477 or 11739 (based on MOC-Q2 or Pd moles) after recycling for 7 rounds. By contrast, the pure MOC-Q2 only shows an ordinary photocatalytic H2 production rate (0.84 mmol g-1  h-1 within 5 h) in the homogeneous system. It can be deduced that TiO2 drives the photocatalysis and simultaneously acts as the structure promoter. This study presents a meaningful and distinctive attempt of a new approach for the design and development of MOC-based heterogeneous photocatalysts.