Investigation On Photocatalytic Hydrogen Evolution Performance Regulation Of Donor-acceptor Type Conjugated Polymers

Employing sunlight to realize photocatalytic water-splitting to generate hydrogen（H₂）is generally accepted to be a better way to alleviate and deal with the current energy shortage.Nevertheless,a significant amount of the existing photocatalysts are limited in practical applications because of their weakness in terms of poor visible-light absorption,unmatched energy band position,and inferior surface/interface reaction activity.Herein,it is critical to exploit novel photocatalysts that have excellent visible-light harvesting ability and admirable photocatalytic activity.By functionalizing the conjugated polymers to modulate the conduction/valence band positions of the composites to reduce the band gap,enhance the absorption of the composites in visible light,reduce the photogenerated electron-hole complex,and increase the electron transport efficiency.Based on this,more active photocatalysts will be constructed than the original photocatalytic materials,and some key existing scientific challenges will be solved.The main research elements are as follows.A donor-acceptor（D-A）structural CP of PyDTDO-3 was employed to host platinum（Pt）nanoparticles（NPs）using N,N′-dimethylformamide（DMF）as a protectant,stabilizer,and reducing agent,which not only promotes PtNPs to have excellent dispersion property on the surface of PyDTDO-3 but also endows Pt to maintain metallic Pt⁰ species（denoted as Pt/PyDTDO-3）.As a result,when exposed to visible light irradiation,the PyDTDO-3 loaded with PtNPs displays impressive hydrogen（H₂）production activity at a rate of 39.9mmol·g^-1·h^-1.Based on density functional theory（DFT）calculations,it has been demonstrated that PtNPs are selectively loaded onto the acceptor（A）unit of PyDTDO-3 that has the lowest adsorption energies(E_ads)and the number of electrons filling at the Fermi level（E_f）is also significantly higher,indicating the optimal 7%Pt/PyDTDO-3 with high electroconductivity timely captured and eliminated the photoinduced holes and recognized the effectiveness of electron-hole pairs in separating space.Overall,our findings offer a rational way to load metal cocatalysts onto CPs with good dispersion for efficient photocatalytic H₂ evolution.Moreover,the S-scheme heterojunction containing a donor-acceptor（D-A）type conjugated polymer of PyDTDO-3 and a two-dimensional（2D）-layered conjugated polymer of C₃N₄ nanosheets with conjugated heptazine units（denoted as PCNNS）was prepared for photocatalytic H₂ production.It is discovered that the photogenerated electron-hole pair recombination rate is significantly reduced by the construction of the S-scheme heterojunction structure through establishing an intimateπ-πconjugated heterointerface between PyDTDO-3and C₃N₄ NS.The density functional theory（DFT）calculations demonstrate that due to the difference in the work function,a Fermi level gap is formed between PyDTDO-3 and C₃N₄,which eventually leads to the band edge bent upward/downward and the presence of the built-in electric field causing the spontaneous interfacial charge transfer from C₃N₄ NS to PyDTDO-3 at theπ-πconjugated interface.Owing to its unique structure and optical properties,the optimal P₂CNNS heterojunction photocatalyst shows excellent photocatalytic H₂ generation performance,which reaches a maximum of 50.2 mmol·g^-1·h^-1 under visible illumination.