Direct Z-Scheme Heterojunction Catalysts Constructed by Graphitic-C3N4 and Photosensitive Metal-Organic Cages for Efficient Photocatalytic Hydrogen Evolution

Abstract

The demand for improving the activity, durability, and recyclability of metal-organic cages (MOCs) that work as photocatalytic molecular devices in a homogeneous system has promoted research to combine them with other solid materials. An M2L4 type photosensitive metal-organic cage MOC-Q2 with light-harvesting ligands and catalytic Pd2+ centers has been synthesized and further heterogenized with graphitic carbon nitride to prepare a robust direct Z-scheme heterojunction photocatalyst for visible-light-driven hydrogen generation. The optimized g-C3N4/MOC-Q2 (0.7 wt%) sample exhibits a high H2 evolution activity of 6423 μmol g−1 h−1 in 5 h, and a total turnover number of 39,695 after 10 h, significantly superior to the bare MOC-Q2 used in the homogeneous solution and the comparison sample Pd/g-C3N4/L-4. The enhanced performances of g-C3N4/MOC-Q2 can be ascribed to its direct Z-scheme heterostructure, which effectively improves the charge separation and transfer efficiency. This work presents a rational approach of designing a binary photocatalytic system through combing micromolecular MOCs with heterogeneous semiconductors for water splitting.

A Direct Z‐Scheme Quasi‐2D/2D Heterojunction Constructed by Loading Photosensitive Metal–Organic Nanorings with Pd Single Atoms on Graphitic–C3N4for Superior Visible Light‐Driven H2Production

“…[ 3,41,42 ] Compared with the type II heterojunction, a Z‐scheme system has also been recognized as achieving enhanced light‐collecting ability coupled with high charge transfer efficiency and strengthened redox property. [ 3,43,44 ] Our group synthesized three photosensitive metal–organic cages (MOCs), denoted as MOC‐Q1, [ 45 ] MOC‐Q2, [ 46 ] and MOC‐Py‐Zn, [ 47 ] which were assembled by versatile organic sensitizers and catalytically Pd metal sites. Under visible light irradiation, excited electrons from chromophores can be rapidly transferred to catalytic centers within these nanocages, so MOCs can act as photochemical molecular devices (PMDs).…”

Anion–Cation Co-Doped g-C3N4 Porous Nanotubes with Efficient Photocatalytic H2 Evolution Performance

“…However, the photocatalytic activity of pristine bulk g-C 3 N 4 is greatly restricted by its intrinsically low specific surface area and inadequate visible-light response range, and the rapid recombination of photogeneration electron–hole pairs originates from its organic π conjugated structure [ 4 , 5 , 6 , 7 ]. Therefore, a variety of g-C 3 N 4 -based photocatalysts with superior photocatalytic activity have been synthesized through multiple strategies, such as element doping [ 8 , 9 ], heterojunction construction [ 10 , 11 , 12 , 13 ] and morphology regulation [ 14 , 15 , 16 ].…”