Covalent Triazine-based Frameworks with Covalently Anchored Ru-tda based Catalyst for Photoinduced Water Oxidation

Light-induced water splitting (hv-WS) for the production of hydrogen as a solar fuel is considered a promising sustainable strategy for the replacement of fossil fuels. An efficient system for hv-WS involves a photoactive material that, upon shining light, is capable of separating and transferring charges to catalysts for the hydrogen and oxygen evolution processes. Covalent triazine-based frameworks (CTFs) represent an interesting class of 2D organic light-absorbing materials that have recently emerged thanks to their tunable structural, optical and morphological properties. Typically, catalysts (Cat) are metallic nanoparticles generated in situ after photoelectroreduction of metal precursors or directly drop-casted on top of the CTF material to generate Cat-CTF assemblies. In this work, we report the synthesis, characterization and photocatalytic performance of a novel hybrid material, Ru-CTF, based on a CTF structure featuring dangling pyridyl groups that allow to covalently bond to a Ru-tda (tda is [2,2':6',2''-terpyridine]-6,6''-dicarboxylic acid) water oxidation catalyst (WOC) unit. The Ru-CTF molecular hybrid material can carry out the light-induced water oxidation reaction very efficiently at neutral pH, reaching values of maximum TOF of 17 h-1 and TONs in the range of 220 using sodium persulfate as a sacrificial electron acceptor and in the absence of Ag. The present molecular hybrid system based on organic light-absorbers, constitutes a low cost and sustainable alternative to metal-based inorganic semiconductors generally containing expensive and/or critical metals.