Unraveling the Key Factors on Structure-Property-Activity Correlations for Photocatalytic Hydrogen Production of Covalent Organic Frameworks

It has been a challenging task to clearly elucidate various structural features and how their interactions affect the photocatalytic hydrogen production performance. In this work, various factors, including crystallinity, specific surface area associated with morphology, energy band gap and energy levels, surface charge, and hydrophilicity, were employed to investigate the structure-property-activity correlations of beta-ketoenamine-linked covalent organic framework (TpPa-1-COF) for photocatalytic H2 production, which could influence the light harvesting, charge separation and transfer, and surface catalytic active sites. By using different methods to prepare TpPa-1-COFs, we can regulate these influencing factors to investigate their relationship with activity. It is found that the TpPa-1-COF prepared by a molecular organization method (labeled as TpPa-1 (MO)) exhibits the highest photocatalytic H2 evolution activity compared with the TpPa-1-COF samples prepared by solvothermal methods using acetic acid (HOAc) as a catalyst (TpPa-1 (ST-HOAc)) and KOH solution as a catalyst (TpPa-1 (ST-KOH)), which is associated with the highest crystallinity, the optimal energy levels, the largest BET-specific surface area, and the best hydrophilicity for TpPa-1 (MO). Moreover, our findings suggest that the enhanced total photocatalytic H2 evolution efficiency (eta total) of TpPa-1 (MO) may be mainly attributed to the efficient separation and migration of photogenerated charges (eta 2) and the vibrant surface catalytic active sites (eta 3). Overall, this work provides some deep insights into the structure-property-activity relation of TpPa-1-COF photocatalysts, which offers valuable inspiration and guidance for the thoughtful design of COF-based photocatalysts for H2 evolution.