The Construction Of Efficient Heterojunction And Its Photocatalytic Performance For Hydrogen Evolution

The technology of photocatalytic decomposition of water to produce hydrogen has been widely used in energy and environment.The photocatalyst at the core of photocatalytic hydrogen production at present still exists problems that rapid recombination of photogenerated electrons and holes in semiconductor photocatalysts and insufficient active sites and reduced oxidation and reduction capacity.Hence,this article put forward the corresponding strategy for these problems.These strategies were construction of p-n and S-scheme heterojunction and use of co-catalyst.The main research content is as follows:（1）The construction of reasonable interface structure can directionally regulate carrier transference for photocatalyst and improve photocatalytic performance.In this work,the p-type and cube Cu₂O as electrons donor engaged with the n-type and laminated CoAl-LDH as electrons acceptor through a way of the electrostatic self-assembly.The formation of p-n heterojunction was accelerated by opposite surface electronegativity of CoAl-LDH and Cu₂O.The matching energy band of CoAl-LDH and Cu₂O was a viable thermodynamic path for the transference of electrons.More crucially,the strong internal electric field in p-n heterojunction great improved the charges separation and diversion,which enhanced the number of the electrons participating in reduction reactions.Furthermore,the more negative LUMO potential of eosin-Y（EY）can also provide electrons for conduction band（CB）of semiconductor photocatalyst.It’s optical and electrochemistry results demonstrated effective transference and separation of photo-induced charges.Ground on these prominent photo-catalytic advantages,the composite catalyst exhibited excellent hydrogen evolution activities achieved 1322μmol g^-1h^-1that was 5.2 and 9.3 times higher than the CoAl-LDH and Cu₂O.（2）The graphdiyne GDY coupled with Co₃O₄formed 0D/2D p-n heterojunction.The composite catalyst（GO-15）exhibited strong hydrogen evolution activity reached 2336.6μmol g^-1h^-1that is 8.6 and 3.8 times higher than the GDY and Co₃O₄.The strong catalytic activity of composite catalyst can ascribe that the coexistence of Co²⁺/Co³⁺and the strong internal electric field of p-n heterojunction in the GO-15 promoted the charges separation and diversion.Meanwhile,the 0D/2D structure brought more active sites and the more negative LUMO potential of EY can provide electrons for the GO-15.In addition,the effective charges transfer capability of GO-15 was demonstrated in both optical and electrochemical performance tests.To further reveal band structures of Co₃O₄,the density functional theory（DFT）calculation was adopted.（3）The regular octahedron Cu-MOFs and Mn_0.05Cd_0.95S nanoparticles were adopted to constitute a S-scheme heterojunction.The Cu-MOFs/Mn_0.05Cd_0.95S（5 wt%）composite exhibited powerful photocatalytic hydrogen evolution activity of 10950μmol g^-1h^-1after five hour under visible light irradiation,which was ascribed to structure a S-scheme heterojunction brought great redox capacity and efficient separation and transfer of electrons and holes.The PL,TRPL,and electrochemical properties further indicated that the composite photocatalysts had competent photocatalytic performance.The UV-vis DRS indicated that the composite catalyst had excellent light absorption capacity.It was confirmed that the composite photocatalysts owned excellent chemical stability by the XPS,FT-TR,and XRD.The S-scheme process can eliminate useless electrons and holes and provide more electrons to participate H₂evolution reduction.（4）The GDY was modified with Au nanoparticles（NPs）as co-catalyst.The CB of GDY was lower than the surface plasmon resonance（SPR）state of Au NPs.Hence,the excited energetic electrons in the SPR state can be injected in the CB of GDY and thus can participate in the hydrogen-evolution reaction on the surface of GDY.Meanwhile,the LUMO potential of EY was more negative than CB of the GDY,so the electrons can easy inject the CB of GDY.The dual electron injection（DEI）effect was that the EY and Au NPs can supply electrons for the GDY under illumination.Hence,the photocatalytic hydrogen evolution activity of the GDY obtained great improvement in the case of the DEI effect.The EY sensitized GDY located with Au nanoparticles（NPs）（EY-GA-40）had highest H₂evolution activities achieved 6382μmol g^-1h^-1after five hours under visible light irradiation that was 245.4 times higher than the unmodified GDY,due to the DEI effect.