Linker-length dependency of unsaturated Ni-oxo clusters in metal hydroxide-organic framework for photocatalytic CO2 reduction

Abstract

A series of two-dimensional (2D) Ni-based metal hydroxide-organic frameworks (Ni-MHOFs), where hydroxide sheets crosslinked using aromatic carboxylate linkers, were studied for photo-driven CO2 reduction to CO. The molar ratio of metal to ligand in Ni-MHOFs was analysed to estimate coordinatively unsaturated Ni-oxo sites based on inductively coupled plasma (ICP) of metal Ni and 1H NMR of ligands. Photoluminescence quenching of Ru-based photosensitizer (PS) was measured to understand photoelectron transfer mechanism. Ni-MHOF with the longest ligand afforded more accessible unsaturated Ni-oxo catalytic sites, which promoted the photoelectron transfer from PS to catalyst and then engendered better CO evolution performance. This work demonstrates the linker-length dependencies of metal-oxo clusters in 2D MOFs, which suggests a way to modulate the coordinative environment of catalytic sites to fulfill efficient photocatalysis.