Determinant factors of photocatalytic hydrogen evolution activity for Schiff-base conjugated polymers

Conjugated polymers are promising catalysts for photocatalytic hydrogen evolution (PHE) from water. Here, a series of imine-linked conjugated polymers were synthesized via Schiff-base condensation using an easy and low-temperature protocol with cheap raw materials and green solvent. Several readily available diaminobenzene with different amino substitution positions on the phenyl ring were used to react with terephthalaldehyde, leading to formation of polymers varying from one dimensional (1D) nanorods to two dimensional (2D) and three-dimensional (3D) networks. The obtained polymer with 1D crystalline structure was found to show the highest hydrogen production rate at similar to 24.3 mu mol/h under visible light irradiation (lambda > 420 nm) without adding any additional metal co-catalysts. Detailed analysis of the structure, morphology and photoelectron-chemical properties of these as-synthesized polymers leads to the conclusion that 1D nanorods and high LUMO (the lowest unoccupied molecular orbital) play more important roles than large conjugation and surface area in improving the PHE capacity of polymer. This study illustrated a protocol for the production of metal-free photocatalyst synthesized using cheap and green solvent at low-temperature.