Finding the Sweet Spot of Photocatalysis – A Case Study using Bipyridine-based CTFs

Covalent Triazine Frameworks (CTFs) are a class of Porous Organic Polymers which attracts continuously growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic frameworks’ structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far. Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows to tailor the physicochemical features of the CTF materials, including nitrogen content, apparent specific surface area and opto-electronic properties. Based on a comprehensive analytic investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as specific surface area, bandgap, charge separation and surface wettability with water. The entirety of those parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER). The material with the necessary balance between opto-electronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol·h-1·g-1 under visible light irradiation and in the presence of a platinum co-catalyst.