Conjugated Polymer Modification To Construct Chemically Bonded Heterostructures For Photocatalytic Hydrogen Production

Conjugated microporous polymers have more development potential in the field of photocatalytic hydrogen production due to the diversity of synthesis methods,the wide selection of monomers,and the tunability of structure and properties.At the same time,there are also some shortcomings such as poor thermal stability and high binding energy Frenkel excitons are easy to quickly recombination.In order to design catalysts with higher photocatalytic performance and visible light utilization,polymer modification strategies were proposed.The modification strategies are mainly from the following aspects:1)enhancing visible light absorption;2)suppressing recombination of electron-hole pairs;3)boosting surface catalytic reaction.The three strategies mainly include these methods,that is,copolymerization,modifying cross-linker,constructing donor-acceptor structures,functionalization,fabricating organic heterojunction,and surface modification.This paper concerns mainly with copolymerization,modifying cross-linker,and fabricating organic heterojunction to modify polymer.The main research contents are as follows:（1）Conjugated polymer with tetrabromopyrene-bis（2-thiophene）ketone as backbone was synthesized by C–H/C–Br cross coupling reaction,and four kinds of CPs,Py-BKh0,Py-BKh1,Py-BKh2 and Py-BKh3 of tetrabromopyrene（D₁）-bis（2-thiophene）ketone（A）-bithiophene（D₂）type electron transfer system were constructed by adding different proportions of secondary donor unit.The results show that controlling the proportion of secondary donor can not only expand the range of light absorption,but also promote the separation of photogenic charge.Py-BKh1 shows the best hydrogen production performance of 10.2 mmol h^-1 g^-1 and the maximum apparent quantum yield at 500 nm is 9.5%under visible light irradiation（λ>420nm）in the absence of a co-catalyst.In addition,the D₂-D₁-A electron transfer system was constructed by introducing secondary donor with different connection modes as the control group.The structure,properties,and hydrogen production performance were compared to confirm the positive influence of different connection modes on the photocatalytic performance and the superiority of the D₁-A-D₂ electron transfer system.（2）The star unit dibenzothiophene sulfone（BSO₂）and 3,4-vinyl dioxythiophene（EDOT）were introduced by C–H/C–Br cross coupling reaction,Suzuki coupling reaction,and Schiff base reaction using a sequential polymerization strategy,the precursor polymers PPD-BSO₂,TPA-EDOT,TPA-BSO₂,and TPA-Ph were synthesized.Then the bonded heterostructures structure of the polymer/polymer was successfully constructed by modifying the substituted groups based on the Schiff base reaction.The combination of two different organic polymer semiconductors can promote the separation and migration of photogenerated carriers in the bonded heterostructures,effectively reduce the fluorescence intensity and charge transfer resistance,and thus have good photocatalytic activity.The photocatalytic hydrogen production test shows that the hydrogen production performance of TPA-Ph@PPD-BSO₂ can reach 16.5mmol h^-1 g^-1and the maximum AQY at 500 nm is 10.4%under visible light irradiation in the absence of a co-catalyst.Therefore,the Schiff base reaction based on the bonded heterostructures strategy can be applied to the post-modification of organic conjugated polymers.Through this strategy,the structure and band location of a single organic semiconductor can be optimized,and the rapid recombination of photogenerated electrons and holes can be reduced.